Preprints
Filtering by Subject: Geology
Unravelling intrusion-induced forced fold kinematics and ground deformation using 3D seismic reflection data
Published: 2017-11-17
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics
Sills emplaced at shallow-levels are commonly accommodated by overburden uplift, producing forced folds. We examine ancient forced folds developed above saucer-shaped sills using 3D seismic reflection data from the Canterbury Basin, offshore SE New Zealand. Seismic-stratigraphic relationships indicate sill emplacement occurred incrementally over ~31 Myr between the Oligocene (~35–32 Ma) and Early [...]
Fault growth and interactions in a multiphase rift fault network: Horda Platform, Norwegian North Sea
Published: 2017-11-15
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Tectonics and Structure
Physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non-colinear normal fault sets. Furthermore, multiphase rifts will display a greater frequency and range of styles of fault interactions than single-phase rifts. Although these physical models have yielded useful information on the evolution of fault [...]
Distribution of discontinuous mudstone beds within wave-dominated shallow-marine deposits: Star Point Sandstone and Blackhawk Formation, Eastern Utah, USA
Published: 2017-11-08
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Sedimentology, Stratigraphy
Deposits of wave-dominated shorelines are typically considered to act as relatively simple hydrocarbon reservoirs and are commonly modeled as “tanks of sand”. However, important heterogeneities that can act as barriers to fluid flow occur at the parasequence, bedset and bed scales, especially in viscous oil or low permeability oil fields. Heterogeneities at the parasequence and bedset scale have [...]
Environmental signal propagation in sedimentary systems across timescales
Published: 2017-11-07
Subjects: Earth Sciences, Geology, Geomorphology, Physical Sciences and Mathematics, Sedimentology, Stratigraphy
Review of concepts of environmental signal (climate, tectonics, anthropogenic, etc.) propagation in sedimentary systems from source to sink.
Sequential growth of deformation bands in carbonate grainstones in the hangingwall of an active growth fault: Implications for deformation mechanisms in different tectonic regimes
Published: 2017-11-06
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Tectonics and Structure
Deformation bands in porous sandstones have been extensively studied for four decades, whereas comparatively less is known about deformation bands in porous carbonate rocks, particularly in extensional settings. Here, we investigate porous grainstones of the Globigerina Limestone Formation in Malta, which contain several types of deformation bands in the hangingwall of the Maghlaq Fault: (i) [...]
Pastoralism may have delayed the end of the green Sahara
Published: 2017-11-06
Subjects: Earth Sciences, Environmental Studies, Geology, Physical Sciences and Mathematics, Social and Behavioral Sciences
The benefits of pastoralism for marginal, arid environments are often not appreciated. One notable past example of the human response to encroaching desertification comes from the regional climate deterioration after the most recent African Humid Period, which ended around 5,500 years ago. Recent evidence points to a population expansion in northern Africa prior to this, associated with the [...]
Rifts and Rifted Margins: A Review of Geodynamic Processes and Natural Hazards
Published: 2017-11-06
Subjects: Earth Sciences, Geology, Other Earth Sciences, Physical Sciences and Mathematics, Tectonics and Structure
This review provides an introduction to the geodynamic processes that influence tectonic rift evolution and rifted margin architecture. With a strong focus on numerical modeling, I summarize classical and recent insights on rift evolution with differentiation between 2D and 3D concepts and models. One of the key processes during rift evolution is crust-mantle coupling, which controls not only the [...]
Controls of inherited lithospheric heterogeneity on rift linkage: Numerical and analog models of interaction between the Kenyan and Ethiopian rifts across the Turkana depression
Published: 2017-11-06
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Tectonics and Structure
Inherited rheological structures in the lithosphere are expected to have large impact on the architecture of continental rifts. The Turkana depression in the East African Rift connects the Main Ethiopian Rift to the north with the Kenya rift in the south. This region is characterized by a NW-SE trending band of thinned crust inherited from a Mesozoic rifting event, which is cutting the [...]
Constraints on the numerical age of the Paleocene‐Eocene boundary
Published: 2017-11-05
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Stratigraphy
Here we present combined radioisotopic dating (U-Pb zircon) and cyclostratigraphic analysis of the carbon isotope excursion at the Paleocene-Eocene (P-E) boundary in Spitsbergen to determine the numerical age of the boundary. Incorporating the total uncertainty from both radioisotopic and cyclostratigraphic data sets gives an age ranging from 55.728 to 55.964 Ma, within error of a recently [...]
Multiple Palaeoproterozoic carbon burial episodes and excursions
Published: 2017-11-05
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Stratigraphy
Organic-rich rocks (averaging 2–5% total organic carbon) and positive carbonate-carbon isotope excursions ( ‰ δC13>+5‰ and locally much higher, i.e. the Lomagundi-Jatuli Event) are hallmark features of Palaeoproterozoic successions and are assumed to archive a global event of unique environmental conditions following the c. 2.3 Ga Great Oxidation Event. Here we combine new and published [...]
Dating the termination of the Palaeoproterozoic Lomagundi-Jatuli carbon isotopic event in the North Transfennoscandian Greenstone Belt
Published: 2017-11-05
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Stratigraphy
Existing radio-isotopic age constraints indicate that the global Palaeoproterozoic Lomagundi-Jatuli large, positive carbonate carbon isotopic excursion, with δ13C values >+5‰, occurred between 2.2 and 2.06 Ga. In the North Transfennoscandian Greenstone Belt of the Kola Peninsula, NW Russia, northern Norway and Finland, the Lomagundi-Jatuli Event is recorded in the carbonate rocks of the Umba [...]
A users guide to Neoproterozoic geochronology
Published: 2017-11-05
Subjects: Earth Sciences, Geochemistry, Geology, Paleontology, Physical Sciences and Mathematics, Stratigraphy
Geochronology is essential for understanding Neoproterozoic Earth history. Here we review the types of rocks and minerals that are used to date geologic events and the analytical protocols for the different radio-isotopic decay systems employed. We discuss the limitations and potential of these methodologies for dating Neoproterozoic stratigraphy, highlighting the major sources and magnitudes of [...]
U-Pb geochronology and global context of the Charnian Supergroup, UK: Constraints on the age of key Ediacaran fossil assemblages
Published: 2017-11-05
Subjects: Earth Sciences, Geology, Paleontology, Physical Sciences and Mathematics, Stratigraphy
U-Pb (zircon) ages for key stratigraphic volcanic horizons within the ~3200-m-thick Ediacaran-age Charnian Supergroup provide an improved age model for the included Avalonian assemblage macrofossils and, hence, temporal constraints essential for intercomparisons of the Charnian fossils with other Ediacaran fossil assemblages globally. The Ives Head Formation (Blackbrook Group), the oldest exposed [...]
Duration and nature of the end-Cryogenian (Marinoan) glaciation
Published: 2017-11-05
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Stratigraphy
The end-Cryogenian glaciation (Marinoan) is portrayed commonly as the archetype of snowball Earth, yet its duration and character remain uncertain. Here we report U-Pb zircon ages for two ash beds from widely separated localities of the Marinoan-equivalent Ghaub Formation in Namibia: 639.29 ± 0.26 Ma and 635.21 ± 0.59 Ma. These findings verify, for the first time, the key prediction of the [...]
Precision and Accuracy in Geochronology
Published: 2017-11-05
Subjects: Earth Sciences, Geochemistry, Geology, Paleontology, Physical Sciences and Mathematics, Stratigraphy, Tectonics and Structure, Volcanology
Geochronology in Earth and Solar System science is increasingly in demand, and this demand is not only for more results, but for more precise, more accurate, and more easily interpreted temporal constraints. Because modern research often requires multiple dating methods, scrupulous inter- and intramethod calibration in absolute time is required. However, improved precision has highlighted [...]