Preprints
Filtering by Subject: Geochemistry
Geodynamic, geodetic, and seismic constraints favour deflated and dense-cored LLVPs
Published: 2021-06-18
Subjects: Cosmochemistry, Earth Sciences, Geochemistry, Geophysics and Seismology, Mineral Physics, Physical Sciences and Mathematics
Two continent-sized features in the deep mantle, the large low-velocity provinces (LLVPs), influence Earth's supercontinent cycles, mantle plume generation, and its geochemical budget. Seismological advances have steadily improved LLVP imaging, but several fundamental questions remain unanswered, including: What is their vertical extent? And, are they purely thermal anomalies, or are they also [...]
Independent constraints on deep-sea temperatures across two early Eocene hyperthermals from clumped isotope thermometry
Published: 2021-06-08
Subjects: Earth Sciences, Geochemistry
The early Eocene hothouse experienced the occurrence of transient global warming events, so-called hyperthermals. The deep ocean constitutes a stable and vast heat reservoir, and hence arguably provides a good estimate of the global mean climate state. However, available proxy deep-sea temperature reconstructions rely on uncertain assumptions of non-thermal influences associated with seawater [...]
Timing of Martian Core Formation from Models of Hf–W Evolution Coupled with N-body Simulations
Published: 2021-06-04
Subjects: Geochemistry, Mineral Physics, Planetary Sciences
Determining how and when Mars formed has been a long-standing challenge for planetary scientists. The size and orbit of Mars are difficult to reproduce in classical simulations of planetary accretion, and this has inspired models of inner solar system evolution that are tuned to produce Mars-like planets. However, such models are not always coupled to geochemical constraints. Analyses of Martian [...]
Exhuming the Canadian Shield: preliminary interpretations from low-temperature thermochronology and significance for the sedimentary succession of the Hudson Bay Basin
Published: 2021-05-20
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Stratigraphy, Tectonics and Structure
The geological history of the Canadian Shield is difficult to constrain because the sedimentary record is missing in those areas where Precambrian basement is exposed at the surface. This study presents preliminary results and interpretations of new apatite fission-track (AFT) analyses to elucidate the low-temperature (< 120 °C) history across Canada. The AFT modelling of samples from Southampton [...]
Chromium evidence for protracted oxygenation during the Paleoproterozoic
Published: 2021-05-18
Subjects: Earth Sciences, Geochemistry, Paleobiology
It has commonly been proposed that the development of complex life—e.g., aerobic eukaryotes—coincided with atmospheric oxygenation. To test this hypothesis, we measured chromium-based oxygen proxies in a >2400-m core from the Onega Basin (NW-Russia), deposited ~2.1–2.0 billion years ago—closely preceding the first eukaryote fossils. Fractionated chromium isotopes are documented throughout the [...]
Nature and timing of anatectic event of the Hida Belt (Japan): Constraints from titanite geochemistry and U-Pb age of clinopyroxene-bearing leucogranite
Published: 2021-05-17
Subjects: Geochemistry, Geology
The Hida Belt, central Japan, is a continental fragment, which was once a part of the crustal basement of the East Asian continental margin. It consists mainly of Permo-Triassic granite-gneiss complexes with both syn-to-late-metamorphic migmatite or granite bodies. Clinopyroxene-bearing leucogranite, locally called as 'Inishi'-type migmatite, occurs characteristically in the migmatite zone [...]
Geochemical signatures of rare earth elements and yttrium in the vicinity of an ion-adsorption type deposit: roles of source sediment control
Published: 2021-05-13
Subjects: Biogeochemistry, Geochemistry, Geology, Hydrology
The elevated concentrations of rare earth elements (REE) and yttrium (REE+Y) in acid mine drainage (AMD) constitute an opportunity for REE+Y recovery. However, the source and control of REE+Y signatures in AMD remains uncertain. Water, rock, sediment and sludge samples were collected from an ion-adsorption rare earth mining area to investigate REE+Y concentration and fractionation patterns in [...]
Primordial and recycled sulfur sampled by the Iceland mantle plume
Published: 2021-05-13
Subjects: Earth Sciences, Geochemistry
Stable sulfur isotope ratios of mid-ocean ridge and ocean island basalts (MORBs and OIBs) preserve unique information about early Earth processes and the long-term volatile cycles between Earth’s mantle and the surface. Icelandic basalts present ideal material to examine the oldest known terrestrial mantle reservoir, accessed through a deep-rooted mantle plume, but their multiple sulfur [...]
A re-examination of the mechanism of whiting events: A new role for diatoms in Fayetteville Green Lake (New York, USA)
Published: 2021-05-08
Subjects: Biogeochemistry, Environmental Microbiology and Microbial Ecology Life Sciences, Geochemistry, Life Sciences, Sedimentology
Whiting events – the episodic precipitation of fine-grained suspended calcium cabonates in the water column – have been documented across a variety of marine and lacustrine environments. Whitings likely are a major source of carbonate muds, a constituent of limestones, and important archives for geochemical proxies of Earth history. While several biological and physical mechanisms have been [...]
SOLUBILITY PRODUCT CONSTANTS FOR NATURAL DOLOMITE (0-200°C) THROUGH A GROUNDWATER-BASED APPROACH USING THE USGS PRODUCED WATER DATABASE
Published: 2021-05-02
Subjects: Earth Sciences, Geochemistry
The calculation of a reliable temperature dependent dolomite solubility product constant (Ksp°−dol) has been the subject of much research over the last 70 years. This study evaluates log10(aCa2+/aMg2+) using PHREEQC (Pitzer approach) for a screened subset (n=11,480) of formation waters in the U.S. Geological Survey National Produced Waters Geochemical Database V2 (PWGD), an extensive inventory of [...]
Late Paleozoic–Early Mesozoic granitoids in the Khangay–Khentey basin, Central Mongolia: Implication for the tectonic evolution of the Mongol–Okhotsk Ocean margin
Published: 2021-04-26
Subjects: Geochemistry, Geology
The Mongol–Okhotsk Belt is the youngest segment of the Central Asian Orogenic Belt, which is the venue of the massive juvenile crust emplacement, and it is formation and evolutions are still pending problems. This paper presents the first up-to-date U-Pb zircon ages, Hf-in-zircon isotope, geochemical and whole-rock Nd isotope data from igneous rocks of the Khangay–Khentey basin, Central Mongolia. [...]
Source region geochemistry from unmixing downstream sedimentary elemental compositions
Published: 2021-04-15
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
The geochemistry of river sediments is routinely used to obtain information about geologic and environmental processes occurring upstream. For example, downstream samples are used to constrain chemical weathering and physical erosion rates upstream, as well as the locations of mineral deposits or contaminant sources. Previous work has shown that, by assuming conservative mixing, the geochemistry [...]
A global hydrothermal reactor triggered prebiotic synthesis on Earth
Published: 2021-04-15
Subjects: Biogeochemistry, Earth Sciences, Geochemistry, Geology, Planetary Geology
Biosignatures in the rock record limit the time available for life to start on Earth to 600-800 million years1 (4.5-3.7 Ga; Hadean-Archean). Whether the conditions for the synthesis of complex organic molecules were unique to this time or remain present today is unclear, but understanding these conditions is essential for the search of life on other planets. The outer portion of the Hadean Earth [...]
Paleoclimate Changes in the Pacific Northwest Over the Past 36,000 Years from Clumped Isotope Measurements and Isotope-Enabled Model Analysis
Published: 2021-04-07
Subjects: Climate, Geochemistry, Geology, Physical Sciences and Mathematics, Soil Science
Since the last glacial period, North America has experienced dramatic changes in regional climate, including the collapse of ice sheets and changes in effective precipitation. We use clumped isotopes and analysis of transient climate simulations to provide constraints on hydroclimate changes in the Pacific Northwest. The coldest soil temperatures (~10.5 ±1.°C to 14.9 ±1.2°C) occurred [...]
Silurian carbonate high-energy deposits of potential tsunami origin: distinguishing lateral redeposition and time averaging using carbon isotope chemostratigraphy
Published: 2021-03-17
Subjects: Earth Sciences, Geochemistry, Geology, Sedimentology, Stratigraphy
Stable carbon isotope curves are used as a precise stratigraphic tool in the Paleozoic, even though they are commonly based on shallow-water carbonate record, characterized by low stratigraphic completeness. Identification of episodes of large-scale redeposition and erosion may improve δ13Ccarb-based correlations. Here, a series of at least three episodes of high-energy onshore redeposition are [...]