Preprints
Filtering by Subject: Geochemistry
Metabolite cycling indicated by long-range correlation in a sediment bioreactor mixed microbial community
Published: 2018-05-16
Subjects: Biogeochemistry, Earth Sciences, Environmental Sciences, Geochemistry, Physical Sciences and Mathematics
Geophysical surveys add value to biogeochemical studies because of their ability to characterize systems remotely, and their precise time resolution. One limitation, however, is their lack of biogeochemical process specificity. Here, electrochemical time series from an oxic-anoxic cyclical bioreactor experiment were reanalyzed with detrended fluctuation analysis (DFA) to distinguish dominant [...]
The Mesozoic and Palaeozoic granitoids of north-western New Guinea
Published: 2018-05-09
Subjects: Earth Sciences, Geochemistry, Geology, Other Earth Sciences, Physical Sciences and Mathematics, Tectonics and Structure, Volcanology
A large portion of the Birds Head Peninsula of NW New Guinea is an inlier that reveals the pre-Cenozoic geological history of the northern margin of eastern Gondwana. The peninsula is dominated by a regional basement high exposing Gondwanan (Australian) Palaeozoic metasediments intruded by Palaeozoic and Mesozoic granitoids. Here, we present the first comprehensive study of these granitoids, [...]
Late Pliocene marine pCO2 reconstructions from the Subarctic Pacific Ocean
Published: 2018-04-30
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics
The development of large ice-sheets across the Northern Hemisphere during the late Pliocene and the emergence of the glacial-interglacial cycles that punctuate the Quaternary mark a significant threshold in Earths climate history. Although a number of different mechanisms have been proposed to initiate this cooling and the onset of major Northern Hemisphere glaciation, reductions in atmospheric [...]
Geochemistry and origin of the Neoproterozoic Natkusiak Flood Basalts and related Franklin Sills, Victoria Island, Arctic Canada
Published: 2018-04-19
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
The Natkusiak continental flood basalts and Franklin sills of Victoria Island preserve an exceptional record of the ca. 716–723 Ma Franklin large igneous province and are synchronous with major climatic variations and breakup of the supercontinent Rodinia. The Natkusiak Formation basalts record an early phase of discontinuous rubbly flows (<100 m, low-Ti Type 1 magmas) overlain by a thicker [...]
Numerical models of P-T, time and grain-size controls on Ar diffusion in biotite: an aide to interpreting 40Ar/39Ar ages
Published: 2018-04-06
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
40Ar/39Ar dating of biotite is used extensively to determine the timing of cooling and exhumation in metamorphic terranes. 40Ar/39Ar age interpretations commonly assume that 40Ar diffuses out of biotite through temperature-dependent volume diffusion, and therefore that the age represents the time at which biotite cooled through the nominal closure temperature. Several processes or scenarios [...]
Climatic influences on the offset between d18O of cave drip waters and precipitation inferred from global monitoring data
Published: 2018-03-08
Subjects: Earth Sciences, Engineering, Environmental Monitoring, Environmental Sciences, Geochemistry, Hydrology, Physical Sciences and Mathematics, Speleology
We present a meta-analysis of data from 22 caves and 96 drip sites from 4 continents where both the cave drip water d18O and the weighted mean d18O of precipitation have been measured. Drip water d18O is similar to the weighted mean d18O of precipitation (within ± 0.3 ‰) for sites where mean annual temperature (MAT) is less than 15 °C (85% of drips where MAT < 15 °C) and an aridity index [...]
The new CLOCIT irradiation facility for 40Ar/39Ar geochronology: Characterization, comparison with CLICIT, and implications for high-precision geochronology
Published: 2018-02-20
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
The Cadmium-Lined Outer-Core Irradiation Tube (CLOCIT) is a new irradiation facility for 40Ar/39Ar geochronology at the Oregon State University TRIGA® reactor. We report fluence parameters from the first four CLOCIT irradiations and compare them to the existing Cadmium-Lined Inner-Core Irradiation Tube (CLICIT). CLOCIT provides an average neutron flux equivalent of 1.45–1.53 ×10-4 J/h; about 55% [...]
Distributions of geohopanoids in peat: implications for the use of hopanoid-based proxies in natural archives
Published: 2018-02-04
Subjects: Biogeochemistry, Chemistry, Earth Sciences, Environmental Sciences, Geochemistry, Other Physical Sciences and Mathematics, Physical Sciences and Mathematics
Hopanoids are pentacyclic triterpenoids produced by a wide range of bacteria. Within modern settings, hopanoids mostly occur in the biological 17β,21β(H) configuration. However, in some modern peatlands, the C31 hopane is present as the thermally-mature 17α,21β(H) stereoisomer. This has traditionally been ascribed to isomerisation at the C-17 position catalysed by the acidic environment. However, [...]
Detecting orogenic wedge state and the rise of the External Alps by detrital thermochronology
Published: 2018-01-26
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Tectonics and Structure
Critical taper theory permits the modelling of an orogenic wedge as a single mechanical entity. However, although shallow-crustal orogens dominated by brittle failure have been successfully modelled using critical taper, this remains controversial for major, ductile-failure-dominated orogens. In critical taper models, the steepness of the basal and upper orogenic surfaces defines the critical [...]
Relict topography within the Hangay Mountains in central Mongolia: Quantifying long-term exhumation and relief change in an old landscape
Published: 2018-01-14
Subjects: Earth Sciences, Geochemistry, Geology, Geomorphology, Physical Sciences and Mathematics, Tectonics and Structure
The Hangay Mountains are a high-elevation, low-relief landscape within the greater Mongolian Plateau of central Asia. New bedrock apatite (U-Th)/He single-grain ages from the Hangay span ~70 to 200 Ma, with a mean of 122.7 ± 24.0 Ma (2σ). Detrital apatite samples from the Selenga and Orkhon Rivers, north of the mountains, yield dominant (U-Th)/He age populations of ~115 to 130 Ma, as well as an [...]
Climate-driven unsteady denudation and sediment flux in a high-relief unglaciated catchment-fan using 26Al and 10Be: Panamint Valley, California
Published: 2018-01-13
Subjects: Earth Sciences, Geochemistry, Geology, Geomorphology, Physical Sciences and Mathematics, Sedimentology
Environmental changes within erosional catchments of sediment routing systems are predicted to modulate sediment transfer dynamics. However, empirical and numerical models that predict such phenomena are difficult to test in natural systems over multi-millennial timescales. Tectonic boundary conditions and climate history in the Panamint Range, California, are relatively well-constrained by [...]
Introduction to Geochronology
Published: 2017-12-29
Subjects: Cosmochemistry, Earth Sciences, Geochemistry, Physical Sciences and Mathematics
These lecture notes cover the first half of an Isotope Geology module at University College London that deals with the geochronological aspects of the subject. The notes introduce the basic principles of radioactive decay, mass spectrometry and isotope dilution before discussing the most common geochronometers in use today, including radiocarbon, Rb-Sr, Sm-Nd, U-Pb, Pb-Pb, K-Ar, Ar-Ar, U-Th-He, [...]
Temperatures recorded by cosmogenic noble gases since the last glacial maximum in the Maritime Alps
Published: 2017-11-24
Subjects: Earth Sciences, Geochemistry, Geomorphology, Glaciology, Other Earth Sciences, Physical Sciences and Mathematics
While proxy records have been used to reconstruct late Quaternary climate parameters throughout the European Alps, our knowledge of deglacial climate conditions in the Maritime Alps is limited. Here, we report temperatures recorded by a new and independent geochemical technique—cosmogenic noble gas paleothermometry—in the Maritime Alps since the last glacial maximum. We measured cosmogenic 3He in [...]
The INTAV intercomparison of electron-beam microanalysis of glass by tephrochronology laboratories, results and recommendation
Published: 2017-11-23
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
The INternational focus group on Tephrochronology And Volcanism (INTAV) of the International Union for Quaternary Research (INQUA) has conducted an intercomparison of tephrochronology laboratories with electron-beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries. This assessment includes most active tephrochronology laboratories and [...]
Quantifying closed-basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records
Published: 2017-11-08
Subjects: Biogeochemistry, Earth Sciences, Geochemistry, Physical Sciences and Mathematics
Lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in Earth history, such as carbon cycle perturbations and glacial-interglacial cycles. Geochemical measurements of biogenic carbonate (for example, δ18O, δ13C, 87Sr/86Sr, [Li], [U], [Sr], and [Mg]) are indicators of hydrologic variability in lake systems throughout the geologic [...]