查看更多>>摘要：The source area of the Yellow River (SAYR) in the northeastern Tibetan Plateau (TP) has a series of lakes with an outflowing stream that crosses an active left-lateral strike-slip fault. How and when these lakes began to flow into the Yellow River remains an open question. Here, using geologic maps and a digital elevation model (DEM), we map the drainage network and relate it to tectonically active structural features to explore the role of tectonic processes in drainage integration. We also date paleo-shorelines and other geomorphological features around the modern Gyaring Lake and Ngoring Lake using optically stimulated luminescence (OSL) to illuminate the climate-driven processes leading to lake overspill. Our results show that: (1) drainage reversal in Duoshi Gorge was driven by subsidence in a pull-apart basin, likely during Marine Isotope Stage (MIS) 3; (2) Gyaring Lake and Ngoring Lake experienced two simultaneous overspill highstand periods: one during the last deglaciation (similar to 14-12 ka) and a second during the early Holocene (similar to 9 ka), similar to records from closed-basin lakes in the northeastern TP; (3) alluvial fan aggradation was likely enhanced during cold-to-warm transitions, including MIS 5b-a, MIS 4-3, and the last deglaciation; (4) aeolian sediments blanketing the landscape accumulated since the middle Holocene (similar to 6 ka), consistent with the interpretation of improved trapping efficiency due to increasing moisture availability and denser vegetation. Based on the geomorphic features and dating results, we propose a lake overspill model to explain the land surface processes, reconciling our new observations with previous data on the SAYR. Together, our results indicate a complex history of drainage integration, initiated by a tectonic-driven capture event likely during MIS 3 and punctuated by episodic climate-driven lake overspill and river incision. The lake overspill model may be widely applicable across the Tibetan Plateau, and potentially to Mars in the high plateau of its southern hemisphere. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Thermal conductivity is a crucial parameter for the thermal evolution of Earth's core. In this paper, the thermal conductivity of Fe-Ni-O fluid was calculated by ab initio simulations, and then age of inner core and thickness of thermal stratification were derived. The results indicate that the thermal conductivity of Fe-Ni-O fluid along the core adiabatic curve ranges from 111.68 to 182.33 W/m/K. The thermal conductivity at the core-mantle boundary increases monotonically with temperature as expected. The thermal conductivity of Fe-Ni-O fluid is lower than that of pure Fe and Fe-Ni fluids. The age of the inner core is determined to be 0.868 Ga in our fiducial model by calculating the energy budget in the core and time evolution of thermal conductivity of Fe-Ni-O fluid. The thickness of thermal stratification is 454 km when dT(c)/dt=100 K/Ga by calculating the temperature gradient. (C) 2022 Published by Elsevier B.V.
查看更多>>摘要：Fluids such as He-4, H-2, CO2 and hydrocarbons accumulate within Earth's crust. Crustal reservoirs also have potential to store anthropogenic waste (e.g., CO2, spent nuclear fuel). Understanding fluid migration and how this is impacted by basin stratigraphy and evolution is key to exploiting fluid accumulations and identifying viable storage sites. Noble gases are powerful tracers of fluid migration and chemical evolution, as they are inert and only fractionate by physical processes. The distribution of He-4, in particular, is an important tool for understanding diffusion within basins and for groundwater dating. Here, we report noble gas isotope and abundance data from 36 wells across the Paradox Basin, Colorado Plateau, USA, which has abundant hydrocarbon, He-4 and CO2 accumulations. Both groundwater and hydrocarbon samples were collected from 7 stratigraphic units, including within, above and below the Paradox Formation (P.Fm) evaporites. Air-corrected helium isotope ratios (0.0046 - 0.127 R-A) are consistent with radiogenic overprinting of predominantly groundwater-derived noble gases. The highest radiogenic noble gas concentrations are found in formations below the P.Fm. Atmosphere-derived noble gas signatures are consistent with meteoric recharge and multi-phase interactions both above and below the P.Fm, with greater groundwater-gas interactions in the shallower formations. Vertical diffusion models, used to reconstruct observed groundwater helium concentrations, show the P.Fm evaporite layer to be effectively impermeable to helium diffusion and a regional barrier for mobile elements but, similar to other basins, a basement He-4 flux is required to accumulate the He-4 concentrations observed beneath the P.Fm. The verification that evaporites are regionally impermeable to diffusion, of even the most diffusive elements, is important for sub-salt helium and hydrogen exploration and storage, and a critical parameter in determining He-4-derived mean groundwater ages. This is critical to understanding the role of basin stratigraphy and deformation on fluid flow and gas accumulation. (C) 2022 The Author(s). Published by Elsevier B.V.
Schaefer, BettinaSchwark, LorenzBottcher, Michael E.Smith, Vann...
15页
查看更多>>摘要：The Early Eocene represents the warmest climate during the Cenozoic Era punctuated by transient warming events. Here, we apply for the first time biomarker and stable isotope data to describe the depositional and environmental changes at the actual Chicxulub impact crater [International Ocean Discovery Program (IODP) Site M0077A] during the Early Eocene (similar to 56-48 Ma) including the Early Eocene Climate Optimum (EECO; similar to 53-49 Ma). TEX 86 -based reconstructions indicate elevated sea surface temperature around 37 degrees C for the entire succession, punctuated by warmer and cooler periods (37.8 degrees C, 35.7 degrees C, respectively). Biomarker and delta C-13-org data of the core sediments reveal a shift from an organic-lean lower to an organic-rich upper section of the Early Eocene interval. Embedded in the lower section is a prominent organic-rich black shale layer. The lower section, directly overlying strata deposited upon the Paleocene-Eocene Thermal Maximum (PETM), is organically lean with low biomarker concentrations indicating low primary productivity. In the upper section, higher concentrations of algal and bacterial biomarkers are ascribed to high primary productivity and nitrogen fixation in an epipelagic zone, potentially supported by upwelling. The organic-rich black shale layer exhibits a negative delta C-13-org isotope excursion ascribed to recycling of C-13-depleted organic matter via upwelling attributed to a transient hyperthermal event. (C) 2022 Elsevier B.V. All rights reserved.
Toner, J. D.Sletten, R. S.Liu, L.Catling, D. C....
11页
查看更多>>摘要：Recurring Slope Lineae (RSL) are dark streaks that seasonally propagate and fade on Martian slopes. The morphology and dynamics of RSL suggest that they might be brine flows; however, more recent hypotheses propose that they are dry, granular flows. To determine if RSL are consistent with brine flows, we investigated Mars analog wet streaks in Wright Valley Antarctica using new chemical analyses of soils and waters, time-lapse photography, and satellite images. Results show that the source of water to wet streaks is primarily local snowmelt, which seasonally percolates downslope. Meltwater leaches hygroscopic CaCl2-rich salts from soils and underlying Ferrar dolerite bedrock. These salts accumulate at soil surfaces via evapoconcentration and deliquesce/effloresce in response to daily relative humidity changes, causing the surface brightness to fluctuate. Over several years, the active CaCl2 salt component leaches back into the subsurface and the streaks dry, leaving a residue of less hygroscopic salts at the surface. Applied to Mars, wet streaks are inconsistent with the surface expression and dynamics of RSL. Wet streaks propagate and fade over multiple years, drain onto low angled slopes, and have a characteristic pattern of dark downhill and lateral edges. In contrast, RSL are seasonal features, terminate on angle-of-repose slopes, and typically appear monochromatic. These inconsistencies provide evidence against brine flow hypotheses of RSL formation. (C) 2022 Elsevier B.V. All rights reserved.
Young, Edward D.Macris, Catherine A.Tang, HaolanHogan, Arielle A....
15页
查看更多>>摘要：We use new experiments and a theoretical analysis of the results to show that the isotopic fractionation associated with laser-heating aerodynamic levitation experiments is consistent with the velocity of flowing gas as the primary control on the fractionation. The new Fe and Mg isotope data are well explained where the gas is treated as a low-viscosity fluid that flows around the molten spheres with high Reynolds numbers and minimal drag. A relationship between the ratio of headwind velocity to thermal velocity and saturation is obtained on the basis of this analysis. The recognition that it is the ratio of flow velocity to thermal velocity that controls fractionation allows for extrapolation to other environments in which molten rock encounters gas with appreciable headwinds. In this way, in some circumstances, the degree of isotope fractionation attending evaporation is as much a velocimeter as it is a barometer. (C) 2022 The Author(s). Published by Elsevier B.V.
查看更多>>摘要：Unique deposits that formed in the Precambrian oceans are the Banded Iron-Formations (BIFs) which are chemical sediments comprised of alternating layers of iron- and silica-dominated precipitates. The origin of this enigmatic banding is still debated, with most favoring a primary sedimentary and a few others arguing for a secondary diagenetic origin. We here use a high-resolution integrated multi-proxy approach and report on the Ge-Si-Fe and Th-U systematics and on the isotopic composition of Cr in exceptionally pure adjacent magnetite and metachert bands from the similar to 2.7 billion years old Temagami BIF, Ontario, Canada.While each of the geochemical proxies alone may be controversial, our multi-proxy approach sheds new light on their applicability, as the two types of adjacent BIF bands are each characterised by a distinct geochemical signature. The magnetite bands show super-crustal (i.e. fractionated) Ge/Si ratios approaching those of modern marine high-temperature hydrothermal fluids, unfractionated Th/U ratios similar to those of crustal rocks, and unfractionated Cr isotope ratios similar to "Bulk Silicate Earth". Adjacent metachert bands, however, show lower (i.e. unfractionated) Ge/Si ratios close to those of modern seawater, sub-crustal (i.e. fractionated) Th/U ratios, and fractionated Cr isotope ratios above those of Bulk Silicate Earth. The composition of the magnetite bands suggests that the original iron-oxyhydroxide precipitated during periods when the dissolved Ge, Th, U, and Cr inventory of ambient seawater was dominated by input from mafic crust via anoxic high-temperature hydrothermal fluids. In contrast, the composition of the metachert bands indicates that these formed during times when ambient seawater was dominated by low-temperature riverine input from an evolved landmass that despite its Neoarchean age had provided environments for oxidative Cr and U mobilization during terrestrial weathering. This suggests that habitats with oxygenic photosynthesis existed on land at least 200 million years before the Great Oxidation Event. The systematic and internally consistent difference between the geochemical signatures shown by the two types of adjacent BIF bands also demonstrates that the prominent banding of BIFs is a primary depositional feature reflecting precipitation from different watermasses and is not the result of post-depositional separation of an initially homogeneous chemical sediment. (c) 2022 Published by Elsevier B.V.
查看更多>>摘要：The most abundant group of meteorites currently falling to Earth, ordinary chondrites, originate from S-type (Si-rich) asteroids and are thought to have originated in the inner Solar System. These asteroids typically underwent only minor aqueous alteration but experienced varying degrees of thermal metamorphism that altered their primary compositions and textures. However, some rare members remain unaltered and retain the pristine compositions they obtained in the protoplanetary disk prior to accretion of their parent asteroids. In contrast, comets formed in the icy reaches of the outer Solar System. Here we report on silicate minerals in pristine ordinary chondrites that are compositionally distinct from those in all other known chondrites but show similarities to those found in comet samples returned from Comet Wild 2 by NASA's Stardust mission and those sourced from an unknown number of comets represented by interplanetary dusty particles. The identification of this material suggests that comets may have formed from diverse far-flung Solar System materials, including grains that migrated from the inner Solar System to the comet-forming region between similar to 1 Myr and potentially greater than or similar to 3 Myr after the first Solar System solids formed. This finding suggests that migration from the inner to the outer Solar System lasted for millions of years and that comets are composed of residual materials from the entire early Solar System. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Many factors, both natural and anthropogenic, can influence the seismogenic pattern of injection-induced earthquakes (IIE). With an enhanced earthquake catalog and a comprehensive fluid injection database compiled for the southern Montney play in northeast British Columbia, we explore the relative significance of the potential controlling factors of IIE. We first show that hydraulic fracturing (HF) operations are most likely responsible for the increased seismicity in the region. For areas with comparable HF activities, the regional structural geology could be one primary factor correlating with the distribution of IIE. Our investigations further reveal that the stratigraphic formation for HF is the next important factor deciding the level of IIE. Specifically, the number of HF stages targeting the Upper Montney is about five times of that targeting the Lower-Middle Montney (LMM), yet the latter ones are responsible for the majority of IIE. The elevated seismic response with LMM may be attributed to two possible mechanisms, 1) the proximity to deeper permeable formations and subvertical graben faults that facilitates the downward migration of injected fluid and stress perturbation to reactivate pre-existing faults in the basement, and 2) the geomechanical heterogeneity of the two newly recognized geological units (Altares Member and Pocketknife Member) along the upper and lower boundaries of the LMM that enhances the seismogenesis of IIE. Our results provide an important framework of constructively mitigating the injection-related seismic hazard. Crown Copyright (C) 2022 Published by Elsevier B.V. All rights reserved.
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