2024-03-28T18:12:35Z
https://eartharxiv.org/api/oai/
oai:EA:id:1679
2018-07-02T13:17:47Z
The Effect Of Clay Type On The Properties Of Cohesive Sediment Gravity Flows And Their Deposits
Baker. Megan L.
Baas. Jaco H
Malarkey, Jonathan
Jacinto. Ricardo Silva
Craig. Melissa J.
Kane, Ian
Baker, Simon
The present knowledge of cohesive clay-laden sediment gravity flows (SGFs) and their deposits is limited, despite clay being one of the most abundant sediment types on earth and subaqueous SGFs transporting large volumes of sediment into the ocean. Lock-exchange experiments were conducted to contrast SGFs laden with noncohesive silica flour, weakly cohesive kaolinite, and strongly cohesive bentonite in terms of flow behavior, head velocity, runout distance, and deposit geometry across a wide range of suspended-sediment concentrations.
The three sediment types shared similar trends in the types of flows they developed, the maximum head velocity of these flows, and the deposit shape. As suspended sediment concentration was increased, the flow type changed from low-density turbidity current (LDTC) via high-density turbidity current (HDTC) and mud flow to slide. As a function of increasing flow density, the maximum head velocity of LDTCs and relatively dilute HDTCs increased, whereas the maximum head velocity of the mud flows, slides, and relatively dense HDTCs decreased. The increase in maximum head velocity was driven by turbulent support of the suspended sediment and the density difference between the flow and the ambient fluid. The decrease in maximum head velocity comprised attenuation of turbulence by frictional interaction between grains in the silica-flour flows and by pervasive cohesive forces in the kaolinite and bentonite flows. The silica-flour flows changed from turbulence-driven to friction-driven at a volumetric concentration of 47% and a maximum head velocity of 0.75 m s−1; the thresholds between turbulence-driven to cohesion-driven flow for kaolinite and bentonite were 22% and 0.50 m s−1, and 16% and 0.37 m s−1, respectively. The HDTCs produced deposits that were wedge-shaped with a block-shaped downflow extension, the mud flows produced wedge-shaped deposits with partly or fully detached outrunner blocks, and the slides produced wedge-shaped deposits without extension. For the mud flows, slides, and most HDTCs, an increasingly higher concentration was needed to produce similar maximum head velocities and runout distances for flows carrying bentonite, kaolinite, and silica flour, respectively. The strongly cohesive bentonite flows were able to create a stronger network of particle bonds than the weakly cohesive kaolinite flows of similar concentration. The silica-flour flows remained mobile up to an extremely high concentration of 52%, and frictional forces were able to counteract the excess density of the flows and attenuate the turbulence in these flows only at concentrations above 47%.
Dimensional analysis of the experimental data shows that the yield stress of the pre-failure suspension can be used to predict the runout distance and the dimensionless head velocity of the SGFs, independent of clay type. Extrapolation to the natural environment suggests that high-density SGFs laden with weakly cohesive clay reach a greater distance from their origin than flows that carry strongly cohesive clay at a similar suspended-sediment concentration, whilst equivalent fine-grained, noncohesive SGFs travel the farthest. The contrasting behavior of fine-grained SGFs laden with different clay minerals may extend to differences in the architecture of large-scale sediment bodies in deep marine systems.
2017-10-23T16:36:42Z
2017-10-23T16:25:03Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/x6h4e
https://eartharxiv.org/repository/manager/1679/download/3570/
1679
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Physical Sciences and Mathematics
Sedimentology
clay
Yield stress
sediment gravity flow
turbidity current
flume
Cohesion
Mud Flow
Submarine slide
oai:EA:id:1678
2018-07-02T13:17:47Z
Metrology and Traceability of U-Pb Isotope Dilution Geochronology (EARTHTIME Tracer Calibration Part I)
Condon, Daniel
Schoene, Blair
McLean, Noah
Bowring, Samuel
Parrish, Randall
Mixed 235U–233U–205Pb(–202Pb) tracers for U–Pb isotope-dilution isotope ratio mass spectrometry have been prepared under the auspices of the EARTHTIME Initiative. The methods and results for the preparation and calibration of the U/Pb ratio and isotopic abundances are given, and the various sources of uncertainty are discussed and quantified. The accuracy of the EARTHTIME U–Pb tracer isotopic composition can be traced back to SI units via a series of assay and isotopic composition reference materials combined with the experiments described herein. The parameters used in calculating U/Pb ratios (and inferentially U–Pb dates) have correlated uncertainties that result in a total uncertainty contribution to 206Pb/238U dates of ± < 0.03% (95% confidence). For suitable terrestrial materials such as zircon, when other sources of uncertainty have been minimised (e.g., open-system behaviour, 238U/235U variation, intermediate daughter product disequilibrium, common Pb, etc.) the U–Pb tracer calibration uncertainty is a limiting factor in the accuracy of U–Pb geochronology – but less so than the uncertainty in the 238U and 235U decay constants (±0.11 and 0.14% 2σ). The calibration approach of the mixed EARTHTIME 235U–233U–205Pb(–202Pb) tracers, in addition to updated values for reference materials (e.g., mixed gravimetric reference solutions), and parameters (e.g., Pb reference material assay), can be applied to other laboratory-specific U–Pb tracers and will facilitate the generation of accurate and directly inter-comparable U–Pb data.
2017-10-23T17:24:01Z
2017-10-23T17:14:38Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.gca.2015.05.026
10.31223/osf.io/kr3ge
https://eartharxiv.org/repository/manager/1678/download/3569/
1678
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geochemistry
Geology
Physical Sciences and Mathematics
Geochronology
EARTHTIME
oai:EA:id:1677
2018-07-02T13:17:47Z
Lake Baikal isotope records of Holocene Central Asian precipitation
Swann, George
Mackay. Anson W.
Vologina, Elena
Jones, Matthew
Panizzo, Virginia
Leng, Melanie
Sloane, Hilary
Snelling, Andrea
Sturm, Michael
Climate models currently provide conflicting predictions of future climate change across Central Asia. With concern over the potential for a change in water availability to impact communities and ecosystems across the region, an understanding of historical trends in precipitation is required to aid model development and assess the vulnerability of the region to future changes in the hydroclimate. Here we present a record from Lake Baikal, located in the southern Siberian region of central Asia close to the Mongolian border, which demonstrates a relationship between the oxygen isotope composition of diatom silica (δ18Odiatom) and precipitation to the region over the 20th and 21st Century. From this, we suggest that annual rates of precipitation in recent times are at their lowest for the past 10,000 years and identify significant long-term variations in precipitation throughout the early to late Holocene interval. Based on comparisons to other regional records, these trends are suggested to reflect conditions across the wider Central Asian region around Lake Baikal and highlight the potential for further changes in precipitation with future climate change.
2017-10-23T19:41:35Z
2018-04-27T14:28:20Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.quascirev.2018.04.013
10.31223/osf.io/7g4kq
https://eartharxiv.org/repository/manager/1677/download/3565/
1677
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geochemistry
Geology
Physical Sciences and Mathematics
paleoclimatology
Precipitation
isotope
paleolimnology
Russia
Diatom
Mongolia
Lake Baikal
oai:EA:id:1676
2018-07-02T13:17:48Z
An alternative review of facts, coincidences and past and future studies of the Lusi eruption
Tingay, Mark
Manga, Michael
Rudolph, Maxwell
Davies, Richard
The cause of the Lusi mud eruption remains controversial. The review by Miller and Mazzini (2017) firmly dismisses a role of drilling operations at the adjacent Banjarpanji-1 well and argues that the eruption was triggered by the Mw6.3 Yogyakarta earthquake 254 km away. We disagree with both of these conclusions. We review drilling data, and specifically the daily drilling reports, which clearly confirm that the wellbore was not intact and that there was a subsurface blowout. Downhole pressure data from Lusi directly witness the birth of Lusi at the surface on the 29th of May 2006, indicating a direct connection between the well and the eruption. Furthermore, the daily drilling reports specifically state that Lusi activity was visibly altered on three separate occasions by attempts to kill the eruption by pumping dense fluid down the BJP-1 well, providing further evidence of a connection between the wellbore and Lusi. By comparison with the other examples of newly initiated eruptions, the Yogyakarta earthquake was far away given its magnitude. We show that other shallow earthquakes with similar frequencies produced stronger ground shaking and did not trigger an eruption. Finally, the data from the BJP-1 well indicates that there was no prior hydrodynamic connection between deep overpressured hydrothermal fluids and the shallow Kalibeng clays, and that there was no evidence of any liquefaction or remobilization of the Kalibeng clays induced by the earthquake. We thus strongly favor initiation by drilling and not an earthquake.
NOTE: This is a comment on a paper (Miller and Mazzini, 2017), which is available from JMPG. Please contact us if you need help finding it.
2017-10-24T03:25:51Z
2017-10-24T02:23:44Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.marpetgeo.2017.12.031
10.31223/osf.io/qt7dz
https://eartharxiv.org/repository/manager/1676/download/3564/
1676
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geology
Physical Sciences and Mathematics
Drilling
Lusi
Mud Volcano
oai:EA:id:1675
2019-05-10T21:00:28Z
The stratigraphic record and processes of turbidity current transformation across deep-marine lobes
Kane, Ian
Pontén, Anna
Vangdal, Brita
Eggenhuisen. Joris T.
Hodgson, David
Spychala. Yvonne T.
Sedimentary facies in the distal parts of deep-marine lobes can diverge significantly from those predicted by classical turbidite models, and sedimentological processes in these environments are poorly understood. This gap may be bridged using outcrop studies and theoretical models. In the Skoorsteenberg Fm., a downstream transition from thickly-bedded turbidite sandstones to argillaceous, internally layered hybrid beds is observed. The hybrid beds have a characteristic stratigraphic and spatial distribution, being associated with bed successions which generally coarsen- and thicken-upwards reflecting deposition on the fringes of lobes in a dominantly progradational system. Using a detailed characterisation of bed types, including grain size, grain fabric and mineralogical analyses, a process-model for flow evolution is developed. This is explored using a numerical suspension capacity model for radially spreading and decelerating turbidity currents. The new model shows how decelerating sediment suspensions can reach a critical suspension capacity threshold beyond which grains are not supported by fluid turbulence. Sand and silt particles, settling together with flocculated clay, may form low yield-strength cohesive flows; development of these higher concentration lower boundary layer flows inhibits transfer of turbulent kinetic energy into the upper parts of the flow ultimately resulting in catastrophic loss of turbulence and collapse of the upper part of the flow. Advection distances of the now transitional to laminar flow are relatively long (several km) suggesting relatively slow dewatering (several hours) of the low yield strength flows. The catastrophic loss of turbulence accounts for the presence of such beds in other fine-grained systems without invoking external controls or large-scale flow partitioning, and also explains the abrupt pinch-out of all divisions of these sandstones. Estimation of the point of flow transformation is a useful tool in the prediction of heterogeneity distribution in subsurface systems.
2017-10-24T09:54:31Z
2017-10-24T09:46:55Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1111/sed.12346
10.31223/osf.io/xmj2w
https://eartharxiv.org/repository/manager/1675/download/3563/
1675
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Physical Sciences and Mathematics
Sedimentology
sedimentology
turbidite
transitional flow
hybrid event bed
karoo
tanqua
oai:EA:id:1674
2018-07-02T13:17:49Z
Modelling silicon supply during the Last Interglacial (MIS 5e) at Lake Baikal
Panizzo, Virginia
Swann, George
Mackay. Anson W.
Pashley, Vanessa
Horstwood. Matthew S. A
Throughout the Quaternary, lake productivity has been shown to be sensitive to drivers such as climate change, landscape evolution and lake ontogeny. In particular, sediments from Lake Baikal, Siberia, provide a valuable uninterrupted and continuous sequence of palaeoproductivity, which document orbital and sub-orbital frequencies of regional climate change. Here we augment these records through the application of silicon stable isotope analyses of diatom opal (δ30Sidiatom), from sediments spanning the Last Interglacial cycle (approximately equivalent to Marine Isotope Stage [MIS] 5e; c. 130 to 115 ka BP) as a means to test the hypothesis that diatom nutrient utilisation was greater, than during the
Holocene. Results show that diatom dissolved silicon (DSi) utilisation, was significantly greater (p=0.001) during MIS 5e than the current interglacial, which reflects increased diatom productivity over this time (concomitant with higher biogenic silica and warmer pollen-inferred vegetation reconstructions). Diatom biovolume accumulation rates (BVAR) are used, in tandem with δ30Sidiatom data, to model DSi supply to Lake Baikal surface waters. When constrained by sedimentary mineralogical archives of catchment weathering indices (e.g. the Hydrolysis Index), data highlight the small degree of weathering intensity and therefore representation that catchment-weathering DSi sources had, over the duration of MIS 5e. Changes to DSi supply during the Last Interglacial are attributed to variations in within-lake conditions (e.g. turbulent mixing) over the period, where periods of both high productivity and modeled-DSi supply (e.g. strong convective mixing) account for the decreasing trend in δ30Sidiatom compositions (after c. 124 ka BP).
2017-10-24T11:18:30Z
2017-10-24T11:10:05Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/wvs9r
https://eartharxiv.org/repository/manager/1674/download/3562/
1674
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Biogeochemistry
Earth Sciences
Environmental Sciences
Life Sciences
Physical Sciences and Mathematics
isotope
Palaeoclimate
Diatom
Lake Baikal
MIS 5e
Silicon
oai:EA:id:1673
2019-03-15T20:36:29Z
Cenozoic contourites in the eastern Great Australian Bight, offshore southern Australia: implications for the onset of the Leeuwin Current
Jackson. Christopher Aiden-Lee
Magee, Craig
Hunt-Stewart, Esther
Thermohaline oceanic currents influence global heat transfer, controlling local and global variations in climate, biodiversity, and the terrestrial biosphere. Paleoceanographic studies typically use biostratigraphic and geochemical proxies to reconstruct the dynamics of these currents in Earth’s ancient oceans, although seismic reflection data have also been successfully employed, most commonly in the North Atlantic Ocean. Here we use 2D seismic reflection data from the Ceduna Sub-basin, Great Australian Bight, offshore southern Australia to describe middle Eocene-to-Recent contourites deposited within an overall carbonate-dominated succession. These deposits comprise large (100 m wavelength by up to 50 m tall) bedforms and deep (10–90 m), wide (up to 3 km) erosional scours. The scours are particularly well-developed at one specific stratigraphic level, defining moats that encircle Middle Eocene shield volcanoes, which formed syn-depositional bathymetric highs. We suggest that sediment erosion, transport, and deposition record middle Eocene initiation of the Leeuwin Current, one of the most important ocean currents in the southern hemisphere. Deepest seabed scouring occurs within the middle of the middle Eocene-to-Recent sequence, and may reflect middle Miocene waxing of the so-called ‘proto-Leeuwin Current’, possibly driven by changes in ocean circulation patterns caused by the Miocene Global Optimum. The results of this seismic reflection-based study are consistent with results derived from other paleoceanographic proxies, thereby highlighting the continued key role seismic reflection data have in understanding the occurrence, geographical distribution, and significance of ancient ocean currents.
2017-10-24T11:35:45Z
2018-12-12T14:30:48Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.2110/jsr.2019.16
10.31223/osf.io/adw6s
https://eartharxiv.org/repository/manager/1673/download/3557/
1673
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geology
Geophysics and Seismology
Physical Sciences and Mathematics
Sedimentology
Stratigraphy
Volcanology
oceanography; geology; Bight Basin; volcanology; stratigraphy; Leeuwin Current
oai:EA:id:1672
2018-07-02T13:17:49Z
Turbulence, displacement, death and worms: a day in the life of a fluvial Carboniferous bivalve
Kane, Ian
In the Pennsylvanian Rough Rock Flags and Rough Rock of northern England, trace fossils attributed to the non-marine bivalve Carbonicola are found. Carbonicola, recorded by Lockeia and associated trace fossils, lived a semi-infaunal lifestyle and thus were influenced by both the sediment in which they were hosted, and the currents which supplied their nutrients and oxygen. A number of palaeocurrent indictors are commonly associated with Lockeia and are confirmed by this study: (a) downstream inclination of vertical burrows; (b) palaeoflow-parallel orientation of long axes. Additional palaeocurrent indicators include: (c) steeper scouring and higher sediment surface on the upstream side; (d) diffuse lamination downstream of the trace, or, more widespread downstream erosion. These semi-infaunal bivalves were partly exposed to the prevailing flow and acted as bed defects, disturbing flow over an otherwise relatively smooth surface; flow separation and acceleration enhanced flow turbulence around the bivalve leading to erosion and the development of a variably developed fan shaped zone of scour immediately downstream. Disturbance and destabilisation of sediment in this way may affect bivalves immediately downstream, plausibly explaining the relatively regular spacing pattern of individual Lockeia, or clusters of Lockeia, exposed on bedding planes and revealed by nearest neighbour analyses. Bivalves that did not survive high energy flow events were either trapped within the sediment, or transported downstream and deposited in lower-energy environments within the otherwise high-energy deposits of the Rough Rock. These are often associated with Planolites and Cochlichnus, trace fossils of scavenging worms which radiate around the imprints of dead bivalves. This assemblage of trace fossil s indicates that areas suitable for bivalve colonisation occurred in upstream areas.
2017-10-24T12:18:25Z
2017-10-24T12:16:05Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1111/j.1502-3931.2009.00202.x
10.31223/osf.io/hb2r4
https://eartharxiv.org/repository/manager/1672/download/3556/
1672
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Paleontology
Physical Sciences and Mathematics
Sedimentology
fluvial
bivalve
Braided
Burrow
Carboniferous
Cracken Edge
Ichnofacies
Ichnology
Lockeia
Pennslyvanian
Rough Rock
oai:EA:id:1671
2018-07-02T13:17:49Z
Seismicity Induced by Longwall Coal Mining at the Thoresby Colliery, Nottinghamshire, U.K.
Verdon, James
Kendall, John-Michael
Butcher, Antony
Luckett, Richard
Baptie, Brian
The U.K. has a long history of deep coal mining, and numerous cases of mining-induced seismicity have been recorded over the past 50 years. In this study we examine seismicity induced by longwall mining at one of the U.K.’s last deep coal mines, the Thoresby Colliery, Nottinghamshire. After public reports of felt seismicity in late 2013 a local seismic monitoring network was installed at this site, which provided monitoring from February to October 2014. This array recorded 305 seismic events, which form the basis of our analysis.
Event locations were found to closely track the position of the mining face within the Deep Soft Seam, with most events occurring up to 300 m ahead of the face position. This indicates that the seismicity is being directly induced by the mining, as opposed to being caused by activation of pre-existing tectonic features by stress transfer. However, we do not observe correlation between the rate of excavation and the rate of seismicity, and only a small portion of the overall deformation is being released as seismic energy.
Event magnitudes do not follow the expected Gutenberg-Richter distribution. Instead, the observed magnitude distributions can be reproduced if a Truncated Power Law distribution is used to simulate the rupture areas. The best-fit maximum rupture areas correspond to the distances between the Deep Soft Seam and the seams that over- and underlie it, which have both previously been excavated. Our inference is that the presence of a rubble-filled void (or goaf) where these seams have been removed is preventing the growth of larger rupture areas.
Source mechanism analysis reveals that most events consist of dip-slip motion along near-vertical planes that strike parallel to the orientation of the mining face. These mechanisms are consistent with the expected deformation that would occur as a longwall panel advances, with the under- and over-burdens moving upwards and downwards respectively to fill the void created by mining. This further reinforces our conclusion that the events are directly induced by the mining process. Similar mechanisms have been observed during longwall mining at other sites.
2017-10-24T14:56:24Z
2017-10-24T14:51:07Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/5k3er
https://eartharxiv.org/repository/manager/1671/download/3555/
1671
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geophysics and Seismology
Physical Sciences and Mathematics
geomechanics
induced seismicity
coal mining
Source mechanisms
oai:EA:id:1670
2018-07-02T13:17:51Z
Tempo of magma degassing and the genesis of porphyry copper deposits
Chelle-Michou, Cyril
Rottier, Bertrand
Caricchi, Luca
Simpson, Guy
Porphyry deposits are copper-rich orebodies formed by precipitation of metal sulphides from hydrothermal fluids released from magmatic intrusions that cooled at depth within the Earth’s crust. Finding new porphyry deposits is essential because they are our largest source of copper and they also contain other strategic metals including gold and molybdenum. However, the discovery of giant porphyry deposits is hindered by a lack of understanding of the factors governing their size. Here, we use thermal modelling and statistical simulations to quantify the tempo and the chemistry of fluids released from cooling magmatic systems. We confirm that typical arc magmas produce fluids similar in composition to those that form porphyry deposits and conclude that the volume and duration of magmatic activity exert a first order control on the endowment (total mass of deposited copper) of economic porphyry copper deposits. Therefore, initial magma enrichment in copper and sulphur, although adding to the metallogenic potential, is not necessary to form a giant deposit. Our results link the respective durations of magmatic and hydrothermal activity from well-known large to supergiant deposits to their metal endowment. This novel approach can readily be implemented as an additional exploration tool that can help assess the economic potential of magmatic-hydrothermal systems.
2017-10-25T10:51:48Z
2017-10-25T10:46:08Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1038/srep40566
10.31223/osf.io/xhe5r
https://eartharxiv.org/repository/manager/1670/download/3554/
1670
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geochemistry
Physical Sciences and Mathematics
Volcanology
oai:EA:id:1669
2018-07-02T13:17:51Z
Pre-Cadomian to late-Variscan odyssey of the eastern Massif Central, France: Formation of the West European crust in a nutshell
Chelle-Michou, Cyril
The East Massif Central (EMC), France, is part of the internal zone of the Variscan belt where late Carboniferous crustal melting and orogenic collapse have largely obliterated the pre- to early-Variscan geological record. Nevertheless, parts of this history can be reconstructed by using in-situ U-Th-Pb-Lu-Hf isotopic data of texturally well-defined zircon grains from different lithological units. All the main rock units commonly described in the EMC are present in the area of Tournon and include meta-sedimentary and meta-igneous rocks of the Upper Gneiss Unit (UGU) and of the Lower Gneiss Unit (LGU), as well as cross-cutting Variscan granitoid dikes and a heterogeneous granite coring the major Velay dome. Herein we demonstrate that the UGU and the LGU have markedly distinct zircon records. The results of this study are consistent with deposition of the protoliths of the paragneisses within a back-arc basin that was located adjacent to the Arabian-Nubian shield and/or the Saharan Metacraton during the late Ediacaran and collected detritus from the Gondwana continent. At ~ 545 Ma some of these sedimentary rocks were affected by a first melting event that formed the protoliths of the LGU orthogneisses, those of which subsequently remelted at ca. 308 Ma to form the Velay granite-migmatite dome. Protoliths of the UGU result mainly from a bimodal rift-related magmatism at ~ 480 Ma, corresponding to melting of the Ediacaran sediments and depleted mantle. Zircon rims from the UGU additionally provide evidence for a metamorphic/migmatitic overprint during the Lower Carboniferous (~ 350–340 Ma). Finally, several generations of granite dikes of which inherited zircons display characteristics of both the UGU and the LGU were protractedly emplaced from ~ 322 Ma to ~ 308 Ma, the youngest of which being coeval with the formation of the Velay dome. Our data further show that the vast majority of crustal material ultimately involved in the Variscan orogeny, which forms the present-day basement in the EMC, was derived from a sedimentary mixture of various components from the Gondwana continent deposited in Ediacaran times, with no evidence for the involvement of an older autochthonous crust.
2017-10-25T11:04:23Z
2017-10-25T10:57:54Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.gr.2017.02.010
10.31223/osf.io/w6qvx
https://eartharxiv.org/repository/manager/1669/download/3553/
1669
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geochemistry
Geology
Physical Sciences and Mathematics
Variscan orogeny
Zircon
Cadomian Orogeny
Massif Central
North Gondwana Margin
Pan-African orogeny
oai:EA:id:1668
2018-07-02T13:17:51Z
Multidisciplinary Investigations at P.O.W. Camp 198, Bridgend, Wales: Site of a Mass Escape in March 1945.
Rees-Hughes, Luis
Pringle. Jamie K
Russill, Nick
Wisniewski. Kristopher D
Doyle, Peter
The largest escape of German Prisoner of War (PoW) in WW2 was in March 1945 from Camp 198, situated in Bridgend, South Wales, UK. Since camp closure the site has become derelict, and has not been scientifically investigated. This paper reports on the search to locate the PoW escape tunnel that was dug from Hut 9. This hut remains in remarkable condition, with numerous PoW graffiti still present. Also preserved is a prisoner-constructed false wall in a shower room behind which excavated material was hidden, though the tunnel entrance itself has been concreted over. Near-surface geophysics and ground-based LiDAR were used to locate the tunnel. Mid-frequency GPR surveys were judged optimal, with magnetometry least useful due to the above-ground metal objects. Archaeological excavations discovered the intact tunnel and bed-board shoring. With Allied PoW escape camp attempts well documented, this investigation provides valuable insight into German escape efforts.
2017-10-25T12:30:15Z
2017-10-25T12:20:05Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1080/15740773.2017.1357900
10.31223/osf.io/6pk4y
https://eartharxiv.org/repository/manager/1668/download/3552/
1668
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geology
Geophysics and Seismology
Other Earth Sciences
Physical Sciences and Mathematics
Geology
Geophysics
earth science
Archaeology
Military Geoscience
oai:EA:id:1667
2018-07-02T13:17:52Z
Rift zone-parallel extension during segmented fault growth: application to the evolution of the NE Atlantic
Bubeck, Alodie
Walker, Richard
Imber, Jonathan
Holdsworth, Bob
MacLeod, Chris
Holwell, David
The mechanical interaction of propagating normal faults is known to influence the linkage geometry of first-order faults, and the development of second-order faults and fractures, which transfer displacement within relay zones. Here we use natural examples of growth faults from two active volcanic rift zones (Koaʻe, Island of Hawaiʻi and Krafla, northern Iceland) to illustrate the importance of horizontal-plane extension (heave) gradients, and associated vertical axis rotations, in evolving continental rift systems. Second order extension and extensional-shear faults within the relay zones variably resolve components of regional extension, and components of extension and/or shortening parallel to the rift zone, to accommodate the inherently three-dimensional (3D) strains associated with relay zone development and rotation. Such a configuration involves volume increase, which is accommodated at the surface by open fractures; in the subsurface this may be accommodated by veins or dikes oriented oblique- and normal to the rift axis. To consider the scalability of the effects of relay zone rotations, we compare the geometry and kinematics of fault and fracture sets in the Koaʻe and Krafla rift zones with data from exhumed contemporaneous fault and dike systems developed within a >5x10e4 km2 relay system that developed during formation of the NE Atlantic Margins. Based on the findings presented here we propose a new conceptual model for the evolution of segmented continental rift basins on the NE Atlantic margins.
2017-10-25T20:17:56Z
2017-10-25T19:53:55Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/k6g2e
https://eartharxiv.org/repository/manager/1667/download/3551/
1667
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Physical Sciences and Mathematics
Tectonics and Structure
rifting
normal fault
relay zone
Heave gradient
Non co-axial deformation
Vertical axis rotation
oai:EA:id:1666
2018-07-02T13:17:53Z
Distal turbidites reveal a common distribution for large (>0.1 km3) submarine landslide recurrence
Clare. Michael Andrew
Talling, Peter
Hunt. James E.
Challenor, Peter
Malgesini, Giusseppe
Submarine landslides can be far larger than those on land, and are one of the most important processes for moving sediment across our planet. Landslides that are fast enough to disintegrate can generate potentially very hazardous tsunamis, and produce long run-out turbidity currents that break strategically important cable networks. It is important to understand their frequency and triggers. We document the distribution of recurrence intervals for large landslide-triggered turbidity currents (>0.1 km3) in three basin-plains. A common distribution of recurrence intervals is observed, despite variable ages and disparate locations, suggesting similar underlying controls on slide triggers and frequency. This common distribution closely approximates a temporally-random Poisson distribution, such that the probability of a large disintegrating slide occurring along the basin margin is independent of the time since the last slide. This distribution suggests that non-random processes such as sea level are not a dominant control on frequency of these slides. Recurrence intervals of major (>M 7.3) earthquakes have an approximately Poissonian distribution, suggesting they could be implicated as triggers. However, not all major earthquakes appear to generate widespread turbidites, and other as yet unknown triggers or sequential combinations of processes could produce the same distribution. This is the first study to show that large slide-triggered turbidites have a common frequency distribution in distal basin plains, and that this distribution is temporally random. This result has important implications for assessing hazards from landslide-tsunamis and seafloor cable breaks, and the long-term tempo of global sediment fluxes.
2017-10-26T10:18:11Z
2017-10-26T10:14:34Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1130/G35160.1
10.31223/osf.io/ge27p
https://eartharxiv.org/repository/manager/1666/download/3550/
1666
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geology
Physical Sciences and Mathematics
Probability
Sedimentology
Statistics and Probability
geohazard
submarine landslide
Landslide
turbidity current
Geohazards
oai:EA:id:1665
2018-07-02T13:17:53Z
Direct monitoring of active geohazards: emerging geophysical tools for deep-water assessments
Clare. Michael Andrew
Talling, Peter
Cartigny, Matthieu
Dix, Justin
Belal, Mohammad
Himsworth, Matt
Harris, John
Whitehouse, Richard
Seafloor networks of cables, pipelines, and other infrastructure underpin our daily lives, providing communication links, information, and energy supplies. Despite their global importance, these networks are vulnerable to damage by a number of natural seafloor hazards, including landslides, turbidity currents, fluid flow, and scour. Conventional geophysical techniques, such as high-resolution reflection seismic and side-scan sonar, are commonly employed in geohazard assessments. These conventional tools provide essential information for route planning and design; however, such surveys provide only indirect evidence of past processes and do not observe or measure the geohazard itself. As such, many numerical-based impact models lack field-scale calibration, and much uncertainty exists about the triggers, nature, and frequency of deep-water geohazards. Recent advances in technology now enable a step change in their understanding through direct monitoring. We outline some emerging monitoring tools and how they can quantify key parameters for deepwater geohazard assessment. Repeat seafloor surveys in dynamic areas show that solely relying on evidence from past deposits can lead to an under-representation of the geohazard events. Acoustic Doppler current profiling provides new insights into the structure of turbidity currents, whereas instrumented mobile sensors record the nature of movement at the base of those flows for the first time. Existing and bespoke cabled networks enable high bandwidth, low power, and distributed measurements of parameters such as strain across large areas of seafloor. These techniques provide valuable new measurements that will improve geohazard assessments and should be deployed in a complementary manner alongside conventional geophysical tools.
2017-10-26T10:30:11Z
2017-10-26T10:32:31Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.3997/1873-0604.2017033
10.31223/osf.io/m3gkj
https://eartharxiv.org/repository/manager/1665/download/3548/
1665
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geology
Oceanography
Oceanography and Atmospheric Sciences and Meteorology
Physical Sciences and Mathematics
Sedimentology
oai:EA:id:1664
2018-07-02T13:17:53Z
2-D numerical study of hydrated wedge dynamics from subduction to post-collisional phases
Regorda, Alessandro
Roda, Manuel
Marotta. Anna Maria
Spalla. Maria Iole
We developed a 2-D finite element model to investigate the effect of shear heating and mantle hydration on the dynamics of the mantle wedge area. The model considers an initial phase of active oceanic subduction, which is followed by a post-collisional phase characterized by pure gravitational evolution. To investigate the impact of the subduction velocity on the thermomechanics of the system, three models with different velocities prescribed during the initial subduction phase were implemented. Shear heating and mantle hydration were then systematically added into the models. We then analysed the evolution of the hydrated area during both the subduction and post-collisional phases, and examined the difference in Pmax–T (maximum pressure–temperature) and P–Tmax (pressure–maximum temperature) conditions for the models with mantle hydration. The dynamics that allow for the recycling and exhumation of subducted material in the wedge area are strictly correlated with the thermal state at the external boundaries of the mantle wedge, and the size of the hydrated area depends on the subduction velocity when mantle hydration and shear heating are considered simultaneously. During the post-collisional phase, the hydrated portion of the mantle wedge increases in models with high subduction velocities. The predicted P–T configuration indicates that contrasting P–T conditions, such as Barrovian- to Franciscan-type metamorphic gradients, can contemporaneously characterize different portions of the subduction system during both the active oceanic subduction and post-collisional phases and are not indicative of collisional or subduction phases.
2017-10-26T12:29:29Z
2017-10-26T12:21:31Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1093/gji/ggx336
10.31223/osf.io/uztng
https://eartharxiv.org/repository/manager/1664/download/3547/
1664
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geology
Geophysics and Seismology
Physical Sciences and Mathematics
Tectonics and Structure
numerical modelling
Continental margins: convergent
Heat generation and transport
Subduction zone processes
oai:EA:id:1663
2018-07-02T13:17:53Z
Morphological expressions of crater infill collapse: model simulations of Chaotic Terrains on Mars
Roda, Manuel
Govers, Rob
Westerweel, Jan
Marketos, George
Martian chaotic terrains are characterized by deeply depressed intensively fractured areas that contain a large number of low-strain tilted blocks. Stronger deformation (e.g. higher number of fractures) is generally observed in the rims when compared to the middle regions of the terrains. The distribution and number of fractures and tilted blocks are correlated with the size of the chaotic terrains. Smaller chaotic terrains are characterized by few fractures between undeformed blocks. Larger terrains show an elevated number of fractures uniformly distributed with single blocks. We investigate whether this surface morphology may be a consequence of the collapse of the infill of a crater. We perform numerical simulations with the Discrete Element Method and we evaluate the distribution of fractures within the crater and the influence of the crater size, infill thickness and collapsing depth on the final morphology. The comparison between model predictions and the morphology of the Martian chaotic terrains shows strong statistical similarities in terms of both number of fractures and correlation between fractures and crater diameters. No or very weak correlation is observed between fractures and the infill thickness or collapsing depth. The strong correspondence between model results and observations suggests that the collapse of an infill layer within a crater is a viable mechanism for the peculiar morphology of the martian chaotic terrains.
2017-10-26T12:38:03Z
2017-10-26T12:30:50Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1002/2017GC006933
10.31223/osf.io/t59c7
https://eartharxiv.org/repository/manager/1663/download/3546/
1663
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geology
Geomorphology
Other Earth Sciences
Physical Sciences and Mathematics
Tectonics and Structure
oai:EA:id:1662
2018-07-02T13:17:53Z
Thermo-mechanical numerical model of the transition from continental rifting to oceanic spreading: the case study of the Alpine Tethys
Roda, Manuel
Marotta. Anna Maria
Conte, Katya
Spalla. Maria Iole
We develop a two-dimensional thermo-mechanical numerical model in which the formation of oceanic crust and serpentinite due to the hydration of the uprising mantle peridotite has been implemented, with the aim of discussing the behavior of the lithosphere of the Alps and Northern Apennines during the transition from continental rifting to ocean spreading of the Alpine Tethys. The predictions of the model are compared with natural data related to the Permian–Triassic high- temperature – low-pressure (HT-LP) metamorphism affecting the continental lithosphere and data from the Jurassic P–T evolution of the oceanic lithosphere from the Alps and the Northern Apennines. Our analysis indicates that a thinned continental crust, an ocean–continent transition zone and an oceanic lithosphere characterize the final structure of the system in a poor magma rift pre-Alpine configuration. We also find that mantle serpentinization starts before crustal break-up and that denudation occurs before ocean spreading. The mantle denudation starts several million years before the gabbros/basalt formation, generating an ocean–continent transition zone from the passive continental margin to the oceanic lithosphere of size 160–280 km. The comparative analysis shows that the extension of a hot and weak lithosphere, which promotes the development of hyperextended Alpine margins, better agrees with the natural data. Finally, our comparative analysis supports the hypothesis that the lithospheric extension preceding the opening of the Alpine Tethys did not start in a stable continental lithosphere, but developed by recycling part of the old Variscan collisional suture.
2017-10-26T13:13:52Z
2017-10-26T13:09:50Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1017/S0016756816000856
10.31223/osf.io/sp2uz
https://eartharxiv.org/repository/manager/1662/download/3545/
1662
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geology
Geophysics and Seismology
Physical Sciences and Mathematics
Tectonics and Structure
oai:EA:id:1661
2018-07-02T13:17:53Z
Preconditioning and triggering of offshore slope failures and turbidity currents revealed by most detailed monitoring yet at a fjord-head delta
Clare. Michael Andrew
Talling, Peter
Cartigny, Matthieu
Pratomo, Danar
Clarke. John Hughes
Rivers and turbidity currents are the two most important sediment transport processes by volume on Earth. Various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths, including direct plunging of river discharge, delta mouth bar flushing or slope failure caused by low tides and gas expansion, earthquakes and rapid sedimentation. During 2011, 106 turbidity currents were monitored at Squamish Delta, British Columbia. This enables statistical analysis of timing, frequency and triggers. The largest peaks in river discharge did not create hyperpycnal flows. Instead, delayed delta-lip failures occurred 8–11 h after flood peaks, due to cumulative delta top sedimentation and tidally-induced pore pressure changes. Elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water. Elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta-lip, which is the most significant of all controls on flow timing in this setting.
2017-10-26T13:28:35Z
2017-10-26T13:25:34Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.epsl.2016.06.021
10.31223/osf.io/uvqs6
https://eartharxiv.org/repository/manager/1661/download/3544/
1661
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geology
Oceanography
Oceanography and Atmospheric Sciences and Meteorology
Physical Sciences and Mathematics
Sedimentology
geohazard
submarine landslide
turbidity current
mass failure
river delta;
sediment flow
oai:EA:id:1660
2018-07-02T13:19:41Z
A type D breakdown of the Navier Stokes equation in d=3 spatial dimensions
Geurdes, Han
In this paper a type D breakdown of the Navier Stokes equation in d=3 spatial dimensions is demonstrated. The element of breakdown also occurs in the Euler equation.
2017-10-26T15:43:55Z
2017-10-26T15:38:13Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1080/2331835.2017.1284293
10.31223/osf.io/7mcnx
https://eartharxiv.org/repository/manager/1660/download/3543/
1660
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Applied Mathematics
Partial Differential Equations
Physical Sciences and Mathematics
Navier Stokes equation Clay Millenium Problem solved
oai:EA:id:1659
2018-07-02T13:19:41Z
The prognostic equation for biogeochemical tracers has no unique solution.
Geurdes, Han
In this paper, a tracer prognostic differential equation related to the marine chemistry HAMOCC model is studied. Recently the present 5 6 7 8 author found that the Navier -Stokes equation has no unique general solution [Geurdes, 2017]. The following question can therefore be justified. Do numerical solutions, found from prognostic equations akin to the Navier Stokes equation, provide unique nutrient distribution information.
2017-10-26T16:09:27Z
2017-10-26T16:06:37Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/3cqfn
https://eartharxiv.org/repository/manager/1659/download/3542/
1659
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Biochemistry, Biophysics, and Structural Biology
Life Sciences
Mathematics
Physical Sciences and Mathematics
biogeochemistry
Nutrient distribution in the ocean
Partial differential equations
oai:EA:id:1658
2018-08-14T16:53:32Z
Continuous separation of land use and climate effects on the past and future water balance
Zipper, Sam
Motew, Melissa
Booth. Eric G
Chen, Xi
Qiu, Jiangxiao
Kucharik. Christopher J
Carpenter, Stephen
Loheide. Steven P
Understanding the combined and separate effects of climate and land use change on the water cycle is necessary to mitigate negative impacts. However, existing methodologies typically divide data into discrete (before and after) periods, implicitly representing climate and land use as step changes when in reality these changes are often gradual. Here, we introduce a new regression-based methodological framework designed to separate climate and land use effects on any hydrological flux of interest continuously through time, and estimate uncertainty in the contribution of these two drivers. We present two applications in the Yahara River watershed (Wisconsin, USA) demonstrating how our approach can be used to understand synergistic or antagonistic relationships between land use and climate in either the past or the future: (1) historical streamflow, baseflow, and quickflow in an urbanizing subwatershed; and (2) simulated future evapotranspiration, drainage, and direct runoff from a suite of contrasting climate and land use scenarios for the entire watershed. In the historical analysis, we show that ~60% of recent streamflow changes can be attributed to climate, with approximately equal contributions from quickflow and baseflow. However, our continuous method reveals that baseflow is significantly increasing through time, primarily due to land use change and potentially influenced by long-term increases in groundwater storage. In the simulation of future changes, we show that all components of the future water balance will respond more strongly to changes in climate than land use, with the largest potential land use effects on drainage. These results indicate that diverse land use change trajectories may counteract each other while the effects of climate are more homogeneous at watershed scales. Therefore, management opportunities to counteract climate change effects will likely be more effective at smaller spatial scales, where land use trajectories are unidirectional.
2017-10-26T17:05:06Z
2018-05-25T02:32:25Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.jhydrol.2018.08.022
10.31223/osf.io/atqxg
https://eartharxiv.org/repository/manager/1658/download/3540/
1658
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Hydrology
Physical Sciences and Mathematics
climate change
evapotranspiration
runoff
urbanization
baseflow
land use change
streamflow
oai:EA:id:1657
2018-07-02T13:19:41Z
Preprint: Tremor migration patterns and the collective behavior of deep asperities mediated by creep
LUO, Yingdi
Ampuero, Jean Paul
Slow-slip events (SSE) and non-volcanic tremors have revealed a broad spectrum of earthquake behavior, involving entangled seismic and aseismic slip, and offer a unique window into fault mechanics at the bottom of seismogenic zones. A hierarchy of migration patterns of tremors has been observed in the Cascadia subduction zone, including large-scale along-strike tremor propagation and Rapid Tremor Reversals (RTR) migrating in opposite directions with much higher propagation speeds. Here we show that these tremor migration patterns can be reproduced by two end-member models of a fault with heterogeneous mechanical properties, composed of competent asperities embedded in a more frictionally stable, incompetent matrix. In the SSE-driven-tremor model, SSEs are spontaneously generated by the matrix, even in absence of seismic asperities, and drive tremor. In the tremor-driven-SSE model the matrix is stable, it slips steadily in absence of asperities, and SSEs result from the collective behavior of tremor asperities interacting via transient creep in the form of local afterslip fronts. We study these two end-member models through 2D quasi-dynamic multi-cycle simulations of faults governed by rate-and-state friction with heterogeneous frictional properties and effective normal stress, using the earthquake simulation software QDYN . In both models, tremor migration patterns emerge from interactions between asperities mediated by creep transients. The models successfully reproduce forward tremor propagation and RTRs, as well as various other observed tremor migration patterns, without the need to finely tune model parameters. Our modeling results suggest that, in contrast to a common view, SSE could be a result of tremor activity. Also, the hierarchical pattern of tremor migrations provides general constraints on fault zone rheology, and the location of RTRs and other tremor patterns might shed light on the finer scale spatial variability of fault properties. We also find that, despite important interactions between asperities, tremor activity rates are proportional to the underlying aseismic slip rate, supporting an approach to estimate SSE properties with high spatial-temporal resolutions via tremor activity.
2017-10-26T22:51:02Z
2017-10-26T22:46:46Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/mbcav
https://eartharxiv.org/repository/manager/1657/download/3539/
1657
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geophysics and Seismology
Physical Sciences and Mathematics
rate-and-state friction
tremor
heterogeneous fault
slow slip event
oai:EA:id:1656
2018-07-02T13:19:41Z
The role of microbes in snowmelt and radiative forcing on an Alaskan icefield
Ganey, Gerard
Loso, Michael
Burgess. Annie Bryant
Dial. Roman J.
A lack of liquid water limits life on glaciers worldwide but specialized microbes still colonize these environments. These microbes reduce surface albedo, which, in turn, could lead to warming and enhanced glacier melt. Here we present results from a replicated, controlled field experiment to quantify the impact of microbes on snowmelt in red-snow communities. Addition of nitrogen–phosphorous–potassium fertilizer increased alga cell counts nearly fourfold, to levels similar to nitrogen–phosphorus-enriched lakes; water alone increased counts by half. The manipulated alga abundance explained a third of the observed variability in snowmelt. Using a normalized-difference spectral index we estimated alga abundance from satellite imagery and calculated microbial contribution to snowmelt on an icefield of 1,900 km2. The red-snow area extended over about 700 km2, and in this area we determined that microbial communities were responsible for 17% of the total snowmelt there. Our results support hypotheses that snow-dwelling microbes increase glacier melt directly in a bio-geophysical feedback by lowering albedo and indirectly by exposing low-albedo glacier ice. Radiative forcing due to perennial populations of microbes may match that of non-living particulates at high latitudes. Their contribution to climate warming is likely to grow with increased melt and nutrient input.
2017-10-27T00:31:36Z
2017-10-27T00:22:13Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1038/NGEO3027
10.31223/osf.io/c58a3
https://eartharxiv.org/repository/manager/1656/download/3538/
1656
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Biogeochemistry
Earth Sciences
Glaciology
Physical Sciences and Mathematics
snow
Glacier
abledo
alaska
alga
oai:EA:id:1655
2018-07-02T13:19:42Z
Balancing sub- and supra-salt strain in salt-influenced rifts: Implications for extension estimates
Coleman. Alexander James
Jackson. Christopher Aiden-Lee
Duffy. Oliver B.
The structural style of salt-influenced rifts may differ from those formed in predominantly brittle crust. Salt can decouple sub- and supra-salt strain, causing sub-salt faults to be geometrically decoupled from, but kinematically coupled to and responsible for, supra-salt forced folding. Salt-influenced rifts thus contain more folds than their brittle counterparts, an observation often ignored in extension estimates. Fundamental to determining whether sub- and supra-salt structures are kinematically coherent, and the relative contributions of thin- (i.e. gravity-driven) and thick-skinned (i.e. whole-plate stretching) deformation to accommodating rift-related strain, is our ability to measure extension at both structural levels. We here use published physical models of salt-influenced extension to show that line-length estimates yield more accurate values of sub- and supra-salt extension compared to fault-heave, before applying these methods to seismic data from the Halten Terrace, offshore Norway. We show that, given the abundance of ductile deformation in salt-influenced rifts, significant amounts of extension may be ignored, leading to the erroneous interpretations of thin-skinned, gravity-gliding. If a system is kinematically coherent, supra-salt structures can help predict the occurrence and kinematics of sub-salt faults that may be poorly imaged and otherwise poorly constrained.
2017-10-28T11:15:24Z
2017-10-28T11:08:47Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.jsg.2017.08.006
10.31223/osf.io/rhcws
https://eartharxiv.org/repository/manager/1655/download/3537/
1655
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geology
Physical Sciences and Mathematics
Tectonics and Structure
seismic reflection
structural geology
seismic
normal faulting
Norway
salt
kinematics
folding
Halten Terrace
oai:EA:id:1654
2018-07-02T13:19:42Z
Pre-existing normal faults have limited control on the rift geometry of the northern North Sea
Claringbould. Johan S
Bell. Rebecca E.
Jackson. Christopher Aiden-Lee
Gawthorpe. Robert Leslie
Odinsen, Tore
Many rifts develop in response to multiphase extension with numerical and physical models suggesting that reactivation of first-phase normal faults and rift-related variations in bulk crustal rheology control the evolution and final geometry of subsequent rifts. However, many natural multiphase rifts are deeply buried and thus poorly exposed in the field and poorly imaged in seismic reflection data, making it difficult to test these models. Here we integrate recent 3D seismic reflection and borehole data across the entire East Shetland Basin, northern North Sea, to constrain the long-term, regional development of this multiphase rift. We document the following key stages of basin development: (i) pre-Triassic to earliest Triassic development of multiple sub-basins controlled by widely distributed, NNW- to NE-trending, east- and west-dipping faults; (ii) Triassic activity on a single major, NE-trending, west-dipping fault located near the basins western margin, and formation a large half-graben; and (iii) Jurassic development of a large, E-dipping, N- to NE-trending half-graben near the eastern margin of the basin, which was associated with rift narrowing and strain focusing in the Viking Graben. In contrast to previous studies, which argue for two discrete periods of rifting during the Permian-Triassic and Late Jurassic-Early Cretaceous, we find that rifting in the East Shetland Basin was protracted from pre-Triassic to Cretaceous. We find that, during the Jurassic, most pre-Jurassic normal faults were buried and in some cases cross-cut by newly formed faults, with only a few being reactivated. Previously developed faults thus had only a limited control on the evolution and geometry of the later rift. We instead argue that strain migration and rift narrowing was linked to the evolving thermal state of the lithosphere, an interpretation supporting the predictions of lithosphere scale numerical models. Our study indicates that additional regional studies of natural rifts are required to test and refine the predictions of physical and numerical models, more specifically, our study suggests models not explicitly recognising or including thermal or rheological effects might over emphasise the role of discrete pre-existing rift structures such as normal faults.
2017-10-28T11:28:37Z
2017-10-28T11:20:37Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.epsl.2017.07.014
10.31223/osf.io/56r73
https://eartharxiv.org/repository/manager/1654/download/3536/
1654
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geology
Physical Sciences and Mathematics
Tectonics and Structure
structural geology
rifting
normal faulting
3D seismic reflection data
extension
North Sea
East Shetland Basin
Strain
Viking Graben
oai:EA:id:1652
2018-07-02T13:19:42Z
Influence of fault reactivation during multiphase rifting: the Oseberg area, Northern North Sea rift
Deng, Chao
Fossen, Haakon
Gawthorpe. Robert Leslie
Rotevatn, Atle
Jackson. Christopher Aiden-Lee
Fazlikhani, Hamed
Multiphase rifts tend to produce fault populations that evolve by the formation of new faults and reactivation of earlier faults. The resulting fault patterns tend to be complex and difficult to decipher. In this work we use seismic reflection data to examine the evolution of a normal fault network in the Oseberg Fault Block in the northern North Sea Rift System – a rift system that experienced Permian – Early Triassic and Middle Jurassic – Early Cretaceous rifting and exhibits N-S, NW-SE and NE-SW oriented faults. Both N-S- and NW-SE-striking faults were established during the Permian – Early Triassic rifting, as indicated by Triassic growth packages in their hanging walls. In contrast, the NE-SW-striking faults are younger, as they show no evidence of Permian – Early Triassic growth, and offset several N-S- and NW-SE-striking faults. Structural analysis show that a new population of NW-SE-striking faults formed in the Lower – Middle Jurassic (inter-rift period) together with reactivation of N-S-striking Permian – Early Triassic faults, indicating a NE-SW inter-rift extension direction. During the Middle Jurassic – Early Cretaceous rifting, faults of all orientations (N-S, NW-SE and NE-SW) were active. However, faults initiated during the Middle Jurassic – Early Cretaceous rifting show mainly N-S orientation, indicating E-W extension during this phase. These observations suggest a reorientation of the stress field from E-W during the Permian – Early Triassic rift phase to NE-SW during inter-rift fault growth and back to E-W during the Middle Jurassic – Early Cretaceous rift phase in the Oseberg area. Hence, the current study demonstrates that rift activity between established rift phases can locally develop faults with new orientations that add to the geometric and kinematic complexity of the final fault population.
2017-10-28T12:00:49Z
2017-10-28T11:55:19Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.marpetgeo.2017.07.025
10.31223/osf.io/d6yvx
https://eartharxiv.org/repository/manager/1652/download/3534/
1652
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geology
Physical Sciences and Mathematics
Tectonics and Structure
structural geology
rifting
normal faulting
North Sea
Norway
crustal extension
oai:EA:id:1653
2018-07-02T13:19:42Z
Igneous sills record far-field and near-field stress interactions during volcano construction: Isle of Mull, Scotland
Stephens. Tara Louise
Walker, Richard
Healy, David
Bubeck, Alodie
England. Richard W
McCaffrey, Ken
Sill emplacement is typically associated with horizontally mechanically layered host rocks in a near-hydrostatic far-field stress state, where contrasting mechanical properties across the layers promote transitions from dykes, or inclined sheets, to sills. We used detailed field observations from the Loch Scridain Sill Complex (Isle of Mull, UK), and mechanical models to show that layering is not always the dominant control on sill emplacement. The studied sills have consistently shallow dips (1◦–25◦) and cut vertically bedded and foliated metamorphic basement rocks, and horizontally bedded cover sedimentary rocks and lavas. Horizontal and shallowly-dipping fractures in the host rock were intruded with vertical opening in all cases, whilst steeply-dipping discontinuities within the sequence (i.e. vertical fractures and foliation in the basement, and vertical polygonal joints in the lavas) were not intruded during sill emplacement. Mechanical models of slip tendency, dilation tendency, and fracture susceptibility for local and overall sill geometry data, support a radial horizontal compression during sill emplacement. Our models show that dykes and sills across Mull were emplaced during NW–SE horizontal shortening, related to a far-field tectonic stress state. The dykes generally accommodated phases of NE–SW horizontal tectonic extension, whereas the sills record the superposition of the far-field stress with a near-field stress state, imposed by emplacement of the Mull Central Volcano. We show that through detailed geometric characterisation coupled with mechanical modelling, sills may be used as an indication of fluctuations in the paleostress state.
2017-10-28T12:12:54Z
2017-10-28T11:44:41Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.epsl.2017.09.003
10.31223/osf.io/f2ehc
https://eartharxiv.org/repository/manager/1653/download/3535/
1653
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Physical Sciences and Mathematics
Tectonics and Structure
Volcanology
Sills
horizontal shortening
intrusions
mechanical stratigraphy
oai:EA:id:1651
2018-07-02T13:19:42Z
A Bayesian Method to Quantify Azimuthal Anisotropy Model Uncertainties: Application to Global Azimuthal Anisotropy in the Upper Mantle and Transition Zone
Yuan, Kaiqing
Beghein, Caroline
Seismic anisotropy is a powerful tool to constrain mantle deformation, but its existence in the deep upper mantle and topmost lower mantle is still uncertain. Recent results from higher mode Rayleigh waves have, however, revealed the presence of 1% azimuthal anisotropy between 300 km and 800 km depth, and changes in azimuthal anisotropy across the mantle transition zone boundaries. This has important consequences for our understanding of mantle convection patterns and deformation of deep mantle material. Here, we propose a Bayesian method to model depth variations in azimuthal anisotropy and to obtain quantitative uncertainties on the fast seismic direction and anisotropy amplitude from phase velocity dispersion maps. We applied this new method to existing global fundamental and higher mode Rayleigh wave phase velocity maps to assess the likelihood of azimuthal anisotropy in the deep upper mantle and to determine whether previously detected changes in anisotropy at the transition zone boundaries are robustly constrained by those data. Our results confirm that deep upper mantle azimuthal anisotropy is favored and well-constrained by the higher mode data employed. The fast seismic directions are in agreement with our previously published model. The data favor a model characterized, on average, by changes in azimuthal anisotropy at the top and bottom of the transition zone. However, this change in fast axes is not a global feature as there are regions of the model where the azimuthal anisotropy direction is unlikely to change across depths in the deep upper mantle. We were, however, unable to detect any clear pattern or connection with surface tectonics. Future studies will be needed to further improve the lateral resolution of this type of model at transition zone depths
2017-10-28T17:15:22Z
2017-12-20T16:12:53Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/vfzcb
https://eartharxiv.org/repository/manager/1651/download/3532/
1651
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geophysics and Seismology
Physical Sciences and Mathematics
Surface waves
Seismic tomography
Seismic anisotropy
Inverse theory
Probability distributions
statistical seismology
higher modes
upper mantle
mantle transition zone
oai:EA:id:1650
2018-08-24T13:48:08Z
On the scales of dynamic topography in whole-mantle convection models - preprint version
ARNOULD, Maëlis
Coltice, Nicolas
Flament, Nicolas
Seigneur, Valentin
Müller. R. Dietmar
Mantle convection shapes Earths surface by generating dynamic topography. Observational constraints and regional convection models suggest that surface topography could be sensitive to mantle flow for wavelengths as short as 1,000 km and 250 km, respectively. At these spatial scales, surface processes including sedimentation and relative sea-level change occur on million year timescales. However, time dependent global mantle flow models do not predict small-scale dynamic topography yet. Here, we present 2D-spherical annulus numerical models of mantle convection with large radial and lateral viscosity contrasts. We first identify the range of Rayleigh number, internal heat production rate and yield stress for which models generate plate-like behaviour, surface heat flow, surface velocities and topography distribution comparable to Earths. These models produce both whole mantle convection and small-scale convection in the upper mantle, which results in small- (< 500 km) to large-scale (> 10^4 km) dynamic topography, with a spectral power for intermediate scales (500 to 10^4 km) comparable
to estimates of present-day residual topography. Timescales of convection and the associated dynamic topography vary from five to several hundreds of millions of years. For a Rayleigh number of 10^7, we investigate how lithosphere
yield stress variations (10-50 MPa) and the presence of deep thermochemical heterogeneities favour small-scale (200-500 km) and intermediate scale (500-10^4 km) dynamic topography by controlling the formation of small scale convection and the number and distribution of subduction zones, respectively. The interplay between mantle convection and lithosphere dynamics generates a complex spatial and temporal pattern of dynamic topography consistent with constraints for Earth.
2017-10-30T00:34:22Z
2017-10-30T00:25:53Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1029/2018GC007516
10.31223/osf.io/sx6th
https://eartharxiv.org/repository/manager/1650/download/3531/
1650
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geophysics and Seismology
Physical Sciences and Mathematics
mantle convection
Dynamic topography
Geodynamics
subduction
lateral viscosity variations
small-scale convection
oai:EA:id:1649
2018-07-02T13:19:44Z
Seismic Interpretation of Sill-Complexes in Sedimentary Basins: The ‘Sub-Sill Imaging Problem’
Eide. Christian Haug
Schofield, Nick
Lecomte, Isabelle
Buckley, Simon
Howell, John
Application of 3D-seismic reflection-data to igneous systems in sedimentary basins has led to a revolution in the understanding of mafic sill-complexes. However, there is considerable uncertainty on how geometries and architecture of sill complexes within the subsurface relates those imaged in seismic reflection-data. To provide constraints on how sill complexes in seismic data should be interpreted, we present synthetic seismograms generated from a seismic-scale (22x0.25 km) outcrop in East Greenland constrained by abundant field-data.
This study highlights how overlying igneous rocks adversely affect imaging of underlying intrusions and rocks by decreasing seismic amplitude, frequency and making steeply dipping features near-impossible to image. Furthermore, seismic modelling shows that because of the high impedance contrast between siliciclastic host rock and dolerites, thin (< 5m) intrusions should in principle be imaged at relatively high amplitudes. This is contrary to many published ‘rules of thumb’ for seismic detectability of sill intrusions. However, actual seismic data combined with well-data shows significant amounts of un-imaged sill intrusions, and this is likely due to limited resolution, overburden complexity, poor velocity-models, and interference between closely spaced sill-splays. Significant improvements could be made by better predicting occurrence and geometry of sill intrusions and including these in velocity models.
2017-10-30T09:26:18Z
2017-10-30T09:18:40Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1144/jgs2017-096
10.31223/osf.io/jfs9x
https://eartharxiv.org/repository/manager/1649/download/3530/
1649
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geology
Geophysics and Seismology
Physical Sciences and Mathematics
Volcanology
North Atlantic
Sills
seismic interpretation
igneous sill complexes
Jameson Land Suite
mafic sills
seismic modelling
oai:EA:id:1648
2018-07-27T12:40:43Z
Normal fault growth in layered basaltic rocks: the role of strain rate in fault evolution
Bubeck, Alodie
Walker, Richard
Imber, Jonathan
MacLeod, Chris
Conceptual models for the evolution of dilatant faults in volcanic rift settings involve a step-wise growth pattern, involving upward propagation of subsurface faults, surface monocline formation, which are breached by subvertical, open faults. Immature, discontinuous normal faults are considered representative of the early stages of mature, linked faults that accommodate extensional strains. We consider the evolution of surface-breaching normal faults using a comparison of the distribution and geometry of normal faults from two volcanic rift zones: the Koaʻe fault system, Hawaiʻi, and the Krafla fissure swarm, NE Iceland. Field mapping highlights similarities to current predicted geometries, but also prominent differences that are not reconciled by current models. Variable deformation styles record magma supply changes within the rift zones, which drive local strain rate gradients. Building on existing studies, we present a conceptual model of fault growth that accounts for spatial and temporal changes in strain rate within the deforming regions. We propose that faults in separate rift systems may not advance through the same stages of evolution and that faults within individual rift systems can show differing growth patterns. Variations in surface strains may be indicative of subsurface magmatic system changes, with important implications for our understanding of volcano-tectonic coupling.
2017-10-30T12:56:58Z
2018-07-27T12:49:20Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.jsg.2018.07.017
10.31223/osf.io/zmt54
https://eartharxiv.org/repository/manager/1648/download/3528/
1648
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Physical Sciences and Mathematics
Tectonics and Structure
Volcanology
normal fault
extension
monocline
Basalt
dilatant fault
volcanic rift
oai:EA:id:1647
2018-07-02T13:19:46Z
Morphometric analysis in Geographic Information Systems: applications of free software GRASS and R
Grohmann. Carlos Henrique
Development and interpretation of morphometric maps are important tools in studies related to neotectonics and geomorphology; Geographic Information Systems (GIS) allows speed and precision to this process, but applied methodology will vary according to available tools and degree of knowledge of each researcher about involved software.
A methodology to integrate GIS and statistics in morphometric analysis is presented for the most usual morphometric parameters - hypsometry, slope, aspect, swath profiles, lineaments and drainage density, surface roughness, isobase and hydraulic gradient.
The GIS used was the Geographic Resources Analysis Support System (GRASS-GIS), an open- source project that offers an integrated environment for raster and vector analysis, image processing and maps/graphics creation. Statistical analysis of parameters can be carried out on R, a system for statistical computation and graphics, through an interface with GRASS that allows raster maps and points files to be treated as variables for analysis.
The basic element for deriving morphometric maps is the digital elevation model (DEM). It can be interpolated from scattered points or contours, either in raster or vector format; it is also possible to use DEMs from NASAs Shuttle Radar Topographic Mission, with 30m of ground resolution for the USA and 90m for other countries.
Proposed methodology can be adapted according to necessities and available tools. The use of free and open-source tools guarantees access to everyone, and its increasing popularization opens new development perspectives in this research field.
2017-10-30T19:27:02Z
2017-10-30T19:23:55Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.cageo.2004.08.002
10.31223/osf.io/6vx7c
https://eartharxiv.org/repository/manager/1647/download/3527/
1647
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Other Earth Sciences
Physical Sciences and Mathematics
Social and Behavioral Sciences
Spatial Science
Tectonics and Structure
geographic information systems
open source software
Morphometric analysis
GRASS-GIS
neotectonics
oai:EA:id:1646
2018-07-02T13:19:46Z
Trend-surfaces analysis of morphometric parameters: A case-study in southearstern Brazil
Grohmann. Carlos Henrique
Trend-surface analysis was carried out on data from morphometric parameters isobase and hydraulic gradient. The study area, located in the eastern border of Quadrilátero Ferrífero, southeastern Brazil, presents four main geomorphological units, one characterized by fluvial dissection, two of mountainous relief, with a scarp of hundreds of meters of fall between them, and a flat plateau in the central portion of the fluvially-dissected terrains. Morphometric maps were evaluated in GRASS-GIS and statistics were made on R statistical language, using the spatial package. Analysis of Variance (ANOVA) was made to test the significance of each surface and the significance of increasing polynomial
degree. The best results were achieved with 6th-order surface for isobase and 2nd-order surface for hydraulic gradient. Shape and orientation of residuals maps contours for selected trends were compared with structures inferred from several morphometric maps, and a good correlation is present.
2017-10-30T23:42:17Z
2017-10-30T23:39:06Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.cageo.2005.02.011
10.31223/osf.io/9vu72
https://eartharxiv.org/repository/manager/1646/download/3526/
1646
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Other Earth Sciences
Physical Sciences and Mathematics
Social and Behavioral Sciences
Spatial Science
Tectonics and Structure
geographic information systems
Morphometric analysis
GRASS-GIS
Analysis of Variance
R statistical language
Trend-surface analysis
oai:EA:id:1645
2018-07-02T13:19:46Z
r.roughness – a new tool for morphometric analysis in GRASS
Grohmann. Carlos Henrique
This article briefly describes r.roughness, a shell script written to calculate the surface roughness of raster surfaces. The method is based on Hobson (1972), where roughness is defined as the ratio be- tween surface and plan area of square cells.
2017-10-31T00:05:32Z
2017-10-31T00:03:27Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/fsvmw
https://eartharxiv.org/repository/manager/1645/download/3525/
1645
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Computer Sciences
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Physical Sciences and Mathematics
Social and Behavioral Sciences
Spatial Science
Theory and Algorithms
Morphometric analysis
Surface Roughness
GRASS-GIS
oai:EA:id:1644
2018-07-02T13:19:46Z
Resampling SRTM 03”-data with kriging
Grohmann. Carlos Henrique
The purpose of this article is to present the steps necessary to improve the resolution of a DEM us- ing variogram modelling and kriging, as well as a brief comparison of the results with those obtained with interpolation by Regularised Splines with Ten- sion (RST).
2017-10-31T00:09:36Z
2017-10-31T00:07:47Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/dbx3j
https://eartharxiv.org/repository/manager/1644/download/3524/
1644
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Computer Sciences
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Physical Sciences and Mathematics
Social and Behavioral Sciences
Spatial Science
Kriging
GRASS-GIS
Resampling
SRTM
Interpolation
oai:EA:id:1643
2018-07-02T13:19:46Z
SRTM-based morphotectonic analysis of the Poços de Caldas Alkaline Massif, southeastern Brazil
Grohmann. Carlos Henrique
An evaluation of SRTM 03” data applicability in geomorphology and morphotectonics analysis is proposed, considering the morphometric parameters slope, aspect, surface roughness and isobase surface. The study area, in southeastern Brazil, comprises the Poços de Caldas Alkaline Massif, a 33km-diameter Late Cretaceous collapsed volcanic caldera. Morphometric indices evaluated showed the correlation of landscape within the massif with NE-SW and NW-SE structures, as well as landforms related with recent tectonic influence. DEM-derived drainage presented satisfactory results when compared to a 1:50 000 topographic map.SRTM 03” proved to be a good resource for geomorphological analysis, up to the semi-detail scale.
2017-10-31T00:45:48Z
2017-10-31T00:42:17Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.cageo.2006.05.002
10.31223/osf.io/hz4ct
https://eartharxiv.org/repository/manager/1643/download/3523/
1643
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Physical Sciences and Mathematics
Social and Behavioral Sciences
Spatial Science
Tectonics and Structure
geomorphology
Morphometric analysis
DEM
SRTM
Alkaline massif
Poços de Caldas
oai:EA:id:1642
2018-07-02T13:19:46Z
Development of cutoff-related knickpoints during early evolution of submarine channels
Sylvester, Zoltan
Covault, Jacob
Submarine channels are often thought of as having relatively simple geometries, with significant along-channel morphologic and stratigraphic continuity. Using high-resolution seismic reflection data from offshore Angola and a kinematic model of channel evolution, we present evidence that channels on the seafloor can develop slope variability as a result of meander cutoff events. When cutoffs develop, the shortened flow paths produce locally steep gradients, thus initiating knickpoints. Waves of knickpoint retreat and the related channel incision explain the occurrence of terraces and associated remnant channel deposits above the youngest channel thalweg. The simple processes of meander cutoff followed by knickpoint retreat are intrinsic to submarine channels and result in significant morphologic variability, erosion, and stratigraphic complexity, without any external forcing. These insights highlight the early evolution of submarine channels, a phase with a record that is commonly fragmented or completely absent as a result of subsequent erosion, and allow a better understanding of the autogenic controls on deep-marine stratigraphy.
2017-10-31T01:14:55Z
2017-10-31T01:10:33Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1130/G38397.1
10.31223/osf.io/gxh3f
https://eartharxiv.org/repository/manager/1642/download/3522/
1642
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Earth Sciences
Geology
Geomorphology
Physical Sciences and Mathematics
stratigraphic architecture
Submarine channels
meandering
cutoffs
incision
sinuosity
oai:EA:id:1641
2018-07-02T13:19:46Z
Shallow water benthic imaging and substrate characterization using recreational-grade sidescan-sonar
Buscombe. Daniel David
In recent years, lightweight, inexpensive, vessel-mounted ‘recreational grade’ sonar systems have rapidly grown in popularity among aquatic scientists, for swath imaging of benthic substrates. To promote an ongoing ‘democratization’ of acoustical imaging of shallow water environments, methods to carry out geometric and radiometric correction and georectification of sonar echograms are presented, based on simplified models for sonar-target geometry and acoustic backscattering and attenuation in shallow water. Procedures are described for automated removal of the acoustic shadows, identification of bed-water interface for situations when the water is too turbid or turbulent for reliable depth echosounding, and for automated bed substrate classification based on singlebeam full-waveform analysis. These methods are encoded in an open-source and freely-available software package, which should further facilitate use of recreational-grade sidescan sonar, in a fully automated and objective manner. The sequential correction, mapping, and analysis steps are demonstrated using a data set from a shallow freshwater environment.
2017-10-31T02:57:27Z
2017-10-31T02:54:05Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.envsoft.2016.12.003
10.31223/osf.io/gfxa6
https://eartharxiv.org/repository/manager/1641/download/3521/
1641
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Civil and Environmental Engineering
Earth Sciences
Engineering
Geomorphology
Hydraulic Engineering
Physical Sciences and Mathematics
Sedimentology
Acoustical remote sensing
Benthic habitat
Habitat mapping
Sidescan sonar
oai:EA:id:1640
2018-07-02T13:19:47Z
Spatially explicit spectral analysis of point clouds and geospatial data
Buscombe. Daniel David
The increasing use of spatially explicit analyses of high-resolution spatially distributed data (imagery and point clouds) for the purposes of characterising spatial heterogeneity in geophysical phenomena necessitates the development of custom analytical and computational tools. In recent years, such analyses have become the basis of, for example, automated texture characterisation and segmentation, roughness and grain size calculation, and feature detection and classification, from a variety of data types. In this work, much use has been made of statistical descriptors of localised spatial variations in amplitude variance (roughness), however the horizontal scale (wavelength) and spacing of roughness elements is rarely considered. This is despite the fact that the ratio of characteristic vertical to horizontal scales is not constant and can yield important information about physical scaling relationships. Spectral analysis is a hitherto under-utilised but powerful means to acquire statistical information about relevant amplitude and wavelength scales, simultaneously and with computational efficiency. Further, quantifying spatially distributed data in the frequency domain lends itself to the development of stochastic models for probing the underlying mechanisms which govern the spatial distribution of geological and geophysical phenomena. The software package PySESA (Python program for Spatially Explicit Spectral Analysis) has been developed for generic analyses of spatially distributed data in both the spatial and frequency domains. Developed predominantly in Python, it accesses libraries written in Cython and C++ for efficiency. It is open source and modular, therefore readily incorporated into, and combined with, other data analysis tools and frameworks with particular utility for supporting research in the fields of geomorphology, geophysics, hydrography, photogrammetry and remote sensing. The analytical and computational structure of the toolbox is described, and its functionality illustrated with an example of a high-resolution bathymetric point cloud data collected with multibeam echosounder.
2017-10-31T03:02:57Z
2017-10-31T03:00:36Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.cageo.2015.10.004
10.31223/osf.io/wr2pf
https://eartharxiv.org/repository/manager/1640/download/3520/
1640
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Civil and Environmental Engineering
Civil Engineering
Computer Sciences
Earth Sciences
Engineering
Geomorphology
Geophysics and Seismology
Numerical Analysis and Scientific Computing
Physical Sciences and Mathematics
Sedimentology
remote sensing
Geospatial Analysis
texture
spectral analysis
roughness
point clouds
oai:EA:id:1639
2018-07-02T13:19:47Z
Bacterial Fe(II)-oxidation Distinguished by Long-Range Correlation in Redox Potential
Enright, Allison
Ferris, Grant
The kinetics of bacterial Fe(II) oxidation was investigated 297m underground at the Äspö Hard Rock Laboratory (near Oskarshamn, Sweden) under steady state groundwater flow conditions in a flow-through cell containing well-developed flocculent mats of bacteriogenic iron oxides (BIOS). Pseudo first-order rate constants of 0.004 min^-1 and 0.009 min^-1 were obtained for chemical and bacterial Fe(II) oxidation, respectively, based on the 104 min retention time of groundwater in the flow cell, inlet Fe(II) concentration of 21.0± 0.5μm, outlet Fe(II) concentration of 8.5 ± 0.7 μm, as well as constant pH = 7.42 ± 0.01, dissolved O2 concentration of 0.11 ± 0.01mg/L, and groundwater temperature of 12.4± 0.1°C. Redox potential was lower at the BIOS-free inlet (-135.4± 1.16mV) compared to inside BIOS within the flow cell (-112.6± 1.91mV), consistent with the Nernst relationship and oxidation of Fe(II) to Fe(III). Further evaluation of the redox potential time series data using detrended fluctuation analysis (DFA) revealed power law scaling in the amplitude of fluctuations over increasing intervals of time with significantly different (p<0.01) DFA α scaling exponents of 1.89 ± 0.03 for BIOS and 1.67 ± 0.06 at the inlet. These α values not only signal the presence of long-range correlation in the redox potential time series measurements but also distinguish between the slower rate of chemical Fe(II) oxidation at the inlet and faster rate accelerated by FeOB in BIOS.
2017-10-31T04:04:38Z
2017-10-31T03:59:18Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1002/2015JG003306
10.31223/osf.io/e5m3v
https://eartharxiv.org/repository/manager/1639/download/3519/
1639
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Biogeochemistry
Earth Sciences
Geochemistry
Physical Sciences and Mathematics
fluctuation analysis
Fe(II)-oxidizing microbial mats
oai:EA:id:1638
2018-07-02T13:19:47Z
Fluctuation Analysis of Redox Potential to Distinguish Microbial Fe(II) Oxidation
Enright, Allison
Ferris, Grant
We developed a novel method for distinguishing abiotic and biological iron oxidation in liquid media using oxidation-reduction (redox) potential time series data. The instrument and processing algorithm were tested by immersing the tip of a Pt electrode with an Ag-AgCl reference electrode, into an active iron-oxidizing biofilm in a groundwater discharge zone, as well as in two abiotic systems: a killed sample and a chemical control from the same site. We used detrended fluctuation analysis to characterize average root-mean-square fluctuation behaviour, which was distinct in the live system. The calculated α value scaling exponents determined by detrended fluctuation analysis were significantly different at p < 0.001. This indicates that time series of electrode response data may be used to distinguish live and abiotic chemical reaction pathways. Due to the simplicity, portability, and small size, it may be suitable for characterization of extraterrestrial environments where water has been observed, such as Mars and Europa.
2017-10-31T04:50:40Z
2017-10-31T04:48:33Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1089/ast.2016.1509
10.31223/osf.io/dsphg
https://eartharxiv.org/repository/manager/1638/download/3518/
1638
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Biogeochemistry
Earth Sciences
Geochemistry
Physical Sciences and Mathematics
Biosignatures
fluctuation analysis
oai:EA:id:1637
2018-07-02T13:19:47Z
Nature, origin and evolution of a Late Pleistocene incised valley-fill, Sunda Shelf, Southeast Asia
Alqahtani, Faisal
Johnson. Howard D.
Jackson. Christopher Aiden-Lee
Som. Rapi B.
Understanding the stratigraphic fill and reconstructing the palaeo-hydrology
of incised valleys can help to constrain those factors that controlled their origin,
evolution and regional significance. This condition is addressed through
the analysis of a large (up to 18 km wide by 80 m deep) and exceptionally
well-imaged Late Pleistocene incised valley from the Sunda Shelf (South
China Sea) based on shallow three-dimensional seismic data from a large
(11 500 km2), ‘merge’ survey, supplemented with site survey data (boreholes
and seismic). This approach has enabled the characterization of the planform
geometry, cross-sectional area and internal stratigraphic architecture, which
together allow reconstruction of the palaeo-hydrology. The valley-fill displays
five notable stratigraphic features: (i) it is considerably larger than
other seismically resolvable channel forms and can be traced for at least
180 km along its length; (ii) it is located in the axial part of the Malay Basin;
(iii) the youngest part of the valley-fill is dominated by a large (600 m wide
and 23 m deep), high-sinuosity channel, with well-developed lateral accretion
surfaces; (iv) the immediately adjacent interfluves contain much smaller,
dendritic channel systems, which resemble tributaries that drained into
the larger incised valley system; and (v) a ca 16 m thick, shell-bearing, Holocene
clay caps the valley-fill. The dimension, basin location and palaeohydrology
of this incised valley leads to the conclusion that it represents the
trunk river, which flowed along the length of the Malay Basin; it connected
the Gulf of Thailand in the north with the South China Sea in the south-east.
The length of the river system (>1200 km long) enables examination of the
upstream to downstream controls on the evolution of the incised valley,
including sea-level, climate and tectonics. The valley size, orientation and
palaeo-hydrology suggest close interaction between the regional tectonic
framework, low-angle shelf physiography and a humid-tropical climatic setting.
2017-10-31T10:30:58Z
2017-10-31T10:26:29Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1111/sed.12185
10.31223/osf.io/w6p5c
https://eartharxiv.org/repository/manager/1637/download/3517/
1637
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geology
Geomorphology
Physical Sciences and Mathematics
Sedimentology
Stratigraphy
seismic reflection
Pleistocene
fluvial
River
South China Sea
Incised valley
Sea-level
Late Pleistocene
Sunda Shelf
oai:EA:id:1636
2018-07-02T13:19:47Z
Aplicações dos modelos de elevação SRTM em geomorfologia
Grohmann. Carlos Henrique
A missão Shuttle Radar Topography Mission (SRTM) foi realizada para mapear o relevo da área continental da Terra com interferometria de radar entre 60º de latitude norte e 54º de latitude sul. A utilização de Modelos Digitais de Elevação (MDEs) em geomorfologia permite o cálculo de variáveis associadas ao relevo com rapidez e precisão. Neste artigo, apresenta-se uma visão geral de aplicações dos modelos de elevação SRTM em análises geomorfológicas realizadas em território brasileiro, bem como uma apreciação das limitações existentes e de perspectivas futuras.
2017-10-31T11:42:02Z
2017-10-31T11:28:47Z
PREPRINTS
eScholarship Publishing
10.31223/osf.io/amn2t
https://eartharxiv.org/repository/manager/1636/download/3516/
1636
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Other Earth Sciences
Physical Sciences and Mathematics
Remote Sensing
Social and Behavioral Sciences
Spatial Science
geomorphology
morphotectonics
SRTM
neotectonics
oai:EA:id:1635
2018-07-02T13:19:47Z
SRTM resample with short distance-low nugget kriging
Grohmann. Carlos Henrique
The Shuttle Radar Topography Mission (SRTM), was flow on Space Shuttle Endeavour in February 2000, with the objective of acquire a digital elevation model of all land between 60º north latitude and 56º south latitude, using Interferometric Synthetic Aperture Radar (InSAR) techniques. SRTM data is distributed at horizontal resolution of 1 arc-second (aprox. 30m) for areas within the USA and at 3 arc-second (aprox. 90m) resolution for the rest of the world. A resolution of 90m can be considered suitable for small or medium-scale analysis, but it is too coarse for more detailed purposes. One alternative is to interpolate the SRTM data at a finer resolution; it wont increase the level of detail of the original DEM, but it will lead to a surface where there is coherence of angular properties (i.e., slope, aspect) between neighbouring pixels, an important characteristic when dealing with terrain analysis.
This work intents to show how the proper adjustment of variogram and kriging parameters, namely the nugget effect and the maximum distance within which values are used in interpolation, can be set to achieve quality results on resampling SRTM data from 3 to 1. We present for a test area in western USA, which include different adjustment schemes (changes in nugget effect value and in the interpolation radius) as well as comparisons with the original 1 model of the area, with the National Elevation Dataset DEMs, and with other interpolation methods (splines and IDW).
The basic concepts for using kriging to resample terrain data are: 1) to work only with the immediate neighbourhood of the predicted point, due the high spatial correlation of the topographic surface and omnidirectional behaviour of variogram in short distances; 2) add a very small random variation to the coordinates of the points prior to interpolation, to avoid punctual artifacts generated by predicted points with the same location than original data points and 3) use a small value of nugget effect, to avoid smoothing that can obliterate terrain features.
Drainages derived from the surfaces interpolated by kriging and by splines have good agreement with streams derived from the 1 NED, with correct identification of watersheds, even though a few differences occur in the positions of some rivers in flat areas. Although the 1 surfaces resampled by kriging and splines are very similar, we consider the results produced by kriging as superior, since the spline-interpolated surface still presented some noise and linear artifacts, which were removed by kriging.
2017-10-31T11:58:09Z
2017-10-31T11:54:28Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1080/13658810701730152
10.31223/osf.io/bg8a7
https://eartharxiv.org/repository/manager/1635/download/3515/
1635
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Other Earth Sciences
Physical Sciences and Mathematics
Social and Behavioral Sciences
Spatial Science
Tectonics and Structure
geostatistics
Kriging
SRTM
Interpolation
Nugget value
Variogram
oai:EA:id:1634
2018-07-02T13:19:48Z
Comparison of roving-window and search-window techniques for characterising landscape morphometry
Grohmann. Carlos Henrique
Neighbourhood analysis in a Geographical Information System (GIS) calculates the value of a given raster cell from the values of its neighboring cells. Common operations include filtering (high-pass, low-pass, etc) and smoothing (mean, mode) of data, operations that can be done by means of roving-windows or search-windows. Digital terrain analysis (or geomorphometry) relies on neighbourhood operations to calculate morphometric variables such as slope, aspect, local relief or surface roughness (among many others) at scales ranging from local (i.e., single landforms) to regional (entire mountain chains).
The intent of this paper is to compare both techniques in a multi-scale study of geomorphometry, in central-eastern Brazil.
2017-10-31T12:38:14Z
2017-10-31T12:36:14Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1016/j.cageo.2008.12.014
10.31223/osf.io/x6brz
https://eartharxiv.org/repository/manager/1634/download/3514/
1634
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Computer Sciences
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Physical Sciences and Mathematics
Social and Behavioral Sciences
Spatial Science
Theory and Algorithms
Morphometric analysis
GRASS-GIS
Moving-window
Roving-window
oai:EA:id:1632
2018-07-02T13:19:48Z
Quantificação da Deformação Finita nos Metagranitoides Cariris Velhos na Região de Alagoa Grande (PB)
Grohmann. Carlos Henrique
The Cariris Velhos Metagranitoids are considered an important geological unit of the Transversal Zone (Borborema Province – NE Brazil). We evaluated the use of raw and processed digital images to obtain the deformation ellipsoid for the Cariris Velhos Metagranitoids using the Inertia Tensor and Intercepts methods. The ellipsoid symmetry of the deformed fabric was very similar for both methods, the Inertia Tensor and Intercepts, although with different anisotropy values. The orientations of the ellipsoid axes are similar to the orientation of geological structures observed in the eld (principal foliations and mineral lineations). When analyzing the characteristics of the deformation ellipsoids obtained in this study, it is worth pointing out the strong orientation of the C-axis (foliation pole) and the predominance of ellipsoids associated with planar to planar- linear fabrics ( attening eld). The deformation observed in the Cariris Velhos Metagranitoids is associated with the development under transpressive stress of regional Brasiliano shear zones.
2017-10-31T13:03:46Z
2017-10-31T13:00:46Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.5327/Z1519-874X2010000300005
10.31223/osf.io/bpf62
https://eartharxiv.org/repository/manager/1632/download/3512/
1632
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Physical Sciences and Mathematics
Tectonics and Structure
Deformation ellipsoid
Inertia tensor
Intercepts method
Strain Analysis
oai:EA:id:1631
2018-07-02T13:19:48Z
Análise digital de terreno e evolução de longo-termo de relevo do centro-leste brasileiro
Grohmann. Carlos Henrique
Geomorphological theories for long-term relief evolution postulate the existence of planation surfaces, created by the con- tinuous work of erosion/deposition during periods of tectonic quiescence and recognized as extensive areas of very gentle relief disturbed only locally by residual elevations, or by the apparent leveling of summit heights in a given region. After decades since the publication of the main theories on landform evolution, the validity of these models is still an open dis- cussion. In this paper, we present studies about the compartmentalization of landform elements, on a regional-scale basis, of central-eastern Brazil. The methods involved Digital Terrain Analysis in Geographic Information Systems, aiming the extraction and characterization of topographic variables and the compilation and mathematical analysis of geophysical and thermochronological data. Results were interpreted according to the geological context and the theories for long-term relief evolution. The integration of morphometric, thermochronological and geophysical data does not support the validity of us- ing planation surfaces in regional stratigraphic correlations.
2017-10-31T13:09:50Z
2017-10-31T13:08:44Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.5327/Z1519-874X2012000200009
10.31223/osf.io/ekb4n
https://eartharxiv.org/repository/manager/1631/download/3511/
1631
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geographic Information Sciences
Geography
Geomorphology
Physical Sciences and Mathematics
Social and Behavioral Sciences
Spatial Science
Tectonics and Structure
geographic information systems
geomorphology
Digital Terrain Analysis
Planation surface
South American planation surface
oai:EA:id:1633
2018-07-02T13:19:48Z
A general model for the helical structure of geophysical flows in channel bends
Azpiroz-Zabala, Maria
Cartigny, Matthieu
Sumner. Esther J.
Clare. Michael Andrew
Talling. Peter J.
Parsons, Dan
Cooper, Cortis
Meandering channels host geophysical flows that form the most extensive sediment transport systems on Earth (i.e. rivers and submarine channels). Measurements of helical flow structures in bends have been key to understanding sediment transport in rivers. Turbidity currents differ from rivers in both density and velocity profiles. These differences, and the lack of field measurements of turbidity currents, have led to multiple models for their helical flow. Here we present the first measurements of helical flows from turbidity currents in the ocean. These ten flows lasted between one and ten days, had up to ~80-metre thickness, and all displayed the same helical structure. This structure comprised two vertically-stacked cells, with the bottom cell rotating with the opposite direction to helical flow in rivers. Furthermore, we propose a general model that predicts the range of helical flow structures observed in rivers, estuaries and turbidity currents based on their density stratification.
2017-10-31T13:21:51Z
2017-10-31T12:42:47Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1002/2017GL075721
10.31223/osf.io/pfb7u
https://eartharxiv.org/repository/manager/1633/download/3513/
1633
EarthArXiv
http://opensource.org/licenses/AFL-3.0
Civil and Environmental Engineering
Earth Sciences
Engineering
Environmental Engineering
Environmental Sciences
Fluid Dynamics
Geology
Geomorphology
Geophysics and Seismology
Hydrology
Life Sciences
Natural Resources and Conservation
Oceanography
Oceanography and Atmospheric Sciences and Meteorology
Oil, Gas, and Energy
Other Physical Sciences and Mathematics
Physical Sciences and Mathematics
Physics
Risk Analysis
Sedimentology
ADCP
Turbidity currents
helical flow
Direct observations
Meandering channels
Secondary circulation
Submarine channel systems
Submarine density flows
oai:EA:id:1630
2018-07-02T13:19:48Z
Electromagnetic torques in the core and resonant excitation of decadal polar motion
Mound, Jonathan
Motion of the rotation axis of the Earth contains decadal variations with amplitudes on the order of 10 mas. The origin of these decadal polar motions is unknown. A class of rotational normal modes of the core–mantle system termed torsional oscillations are known to affect the length of day (LOD) at decadal periods and have also been suggested as a possible excitation source for the observed decadal polar motion. Torsional oscillations involve relative motion between the outer core and the surrounding solid bodies, producing electromagnetic torques at the inner-core boundary (ICB) and core–mantle boundary (CMB). It has been proposed that the ICB torque can explain the excitation of the approximately 30-yr-period polar motion termed the Markowitz wobble. This paper uses the results of a torsional oscillation model to calculate the torques generated at Markowitz and other decadal periods and finds, in contrast to previous results, that electromagnetic torques at the ICB can not explain the observed polar motion.
This article has been accepted for publication in Geophysical Journal International ©: 2004 RAS Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
2017-10-31T14:27:12Z
2017-10-31T14:19:31Z
PREPRINTS
eScholarship Publishing
https://doi.org/10.1111/j.1365-246X.2004.02495.x
10.31223/osf.io/5zadf
https://eartharxiv.org/repository/manager/1630/download/3510/
1630
EarthArXiv
https://creativecommons.org/licenses/by/4.0/legalcode
Earth Sciences
Geophysics and Seismology
Physical Sciences and Mathematics
core dynamics
Earth rotation
Markowitz wobble
torsional oscillations
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