Terrestrial microbialites provide constraints on the mesoproterozoic atmosphere

Palaeoclimate data indicate that Earth surface temperatures have remained largely temperate for the past 3.5 Byr despite significantly lower solar luminosity over this time relative to the present day. There is evidence for episodic early and late Proterozoic glaciation, but little evidence of glaciation in the intervening billion years. A prolonged equable Mesoproterozoic Earth requires elevated greenhouse gas concentrations. Two endmember scenarios have been proposed for maintaining global warmth. These include extremely high pCO2 or more modest pCO2 with higher methane concentrations. This paper reports on the δ13C of organic matter in 1.1 Ga stromatolites from the Copper Harbor Conglomerate (CHC) of the Mesoproterozoic Midcontinent Rift (North America) and δ18O and Δ47 temperatures of inorganic stromatolite carbonate to constrain formation and burial conditions and the magnitude of ancient carbon isotope discrimination. CHC sediments have never been heated above ~125–155°C, providing a novel geochemical archive of the ancient environment. Stromatolite Δ47 data record moderate alteration, and therefore, the occluded organic matter was unlikely to have experienced significant thermal alteration after deposition. The δ13C values of ancient mat organic matter and inorganic carbonate show isotope discrimination (εp) values ~15.5–18.5‰, similar to modern microbial mats formed in equilibrium with low concentrations of dissolved inorganic carbon. In combination, these data are consistent with a temperate climate Mesoproterozoic biosphere supported by relatively modest pCO2. This result agrees with Atmosphere‐Ocean Global Circulation Model reconstructions for Mesoproterozoic climate using 5–10 times present atmospheric levels pCO2 and pCH4 of >28 ppmv. However, given marine modelling constraints of CH4 production that suggest pCH4 was below 10 ppm, this creates a methane paradox. Either an additional source of CH4 (e.g. from terrestrial ecosystems) or another greenhouse gas, such as N2O, would have been necessary to maintain equable conditions in the Mesoproterozoic.This paper, entitled ‘Terrestrial Microbialites Provide Constraints on the Mesoproterozoic Atmosphere’ offers a new look at 1.1 billion‐year‐old stromatolites in the Mesoproterozoic Midcontinent Rift in Michigan to provide new constraints on pCO2 during the long period of earth’s history that is colloquially known as the ‘boring billion’. New clumped isotope temperature measurements are provided to constrain upper temperature bounds for microbial carbonate formation temperature and post‐depositional thermal alteration, as well as organic and inorganic carbon isotope data that are used to constrain carbon isotope discrimination that is regulated by atmospheric carbon dioxide concentrations.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154283/1/dep279_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154283/2/dep279.pd

Organic molecular and inorganic isotope records of Cenozoic topography, ecosystem and climate evolution of the Southern Central Andes

The Andes are part of the longest mountain range on earthand their evolution has influenced global climate,weathering, and ecosystems since the Cretaceous. Weanalyzed the distribution and δ2H and δ13C of plant-derivedorganic biomarkers, the δ2H of volcanic glass, and thedistribution of soil-derived glycerol dialkyl glyceroltetraethers from Cenozoic sediments in the Malargüe Basinof Argentina (~35°S). Organic molecular and inorganic datawere measured to reconstruct Cenozoic changes inprecipitation isotopes, temperature, moisture deficit, andecosystems on the eastern flank of the Southern CentralAndes. Two variables (precipitation isotopes andtemperature) are strongly related to the topography of anorogen through isotopic distillation of precipitation duringrainout and changes in temperature with elevation.However, molecular biomarkers also provide keyinformation about climate and aridity through time. Weshow that organic biomarker and volcanic glass δ2H datafrom the Malargüe basin record late Cenozoic reduction oforographic lifting of airmasses associated with localdowndrop of the basin. In addition, molecular data reflectlong-term shifts in moisture deficit and plant water stressthat are consistent with regional patterns of changingclimate and aridity due to late Cenozoic cooling. Soilderivedtetraether lipid records mirror the patterns observedin organic molecular and inorganic isotope data, yet recordtemperatures that are unrealistic. These data highlight thecomplexity of universally applying the soil GDGT proxy toall terrestrial systems. In total, combined organic andinorganic data highlight the importance of multi-proxyrecords to produce a coherent representation of long-termecosystem and climate change in a region impacted byevolving climatic and tectonic boundary conditions.Fil: Hren, Michael. University of Connecticut; Estados UnidosFil: Brandon, Mark Thomas. University of Yale; Estados UnidosFil: Fennell, Lucas Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Smolen, Jonathan. University of Connecticut; Estados UnidosFil: Super, James. University of Yale; Estados UnidosGoldschmidt MeetingEstados UnidosGeochemical SocietyEuropean Association of Geochemistr

Paleoelevation estimates for the northern and central proto–Basin and Range from carbonate clumped isotope thermometry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99057/1/tect20016.pd

Eocene to modern topographic evolution of an Andean retroarc foreland basin (35°S) from stable isotope paleoaltimetry: implications for tectonic and geodynamic models

Andean basins contain a unique sedimentary record reflecting mountain building processes along thewestern margin of South America throughout its entire Meso-Cenozoic evolution (Horton, 2018). Inparticular, the retroarc foreland basins in west-central Argentina contain an archive of sedimentaccumulation rates, provenance, paleodrainage and deformation timings related to the growth of theSouthern Central Andes (27°-46°30?S; Ramos, 1999). However, this dataset has non-unique tectonicinterpretations, resulting in contrasting geodynamic scenarios. During the last decade, paleoaltimetrystudies using proxies to obtain the stable isotopic composition of paleoprecipitation have proved to be apowerful tool when assessing such contrasting scenarios, not only by reconstructing topography, butalso by adding a key element towards understanding changes in regional climate and biologicaldiversification (Mulch, 2016).The stable isotopic composition of precipitation reflects the degree of isotopic distillation during rainoutas an airmass moves across a landscape. Thus, materials that record this geochemical variable canprovide an indication of the present or past elevations along a moisture transport pathway. As volcanicashes are deposited on a landscape, they readily hydrate, providing a record of the isotopic compositionof ambient water over a timescale of 1-10 thousand years. Following hydration, water uptake ceasesand this initial signature is preserved, providing a long-term record of stable hydrogen isotopes (ID) ofpaleo-precipitation. Therefore, given that the activity of the Andean magmatic arc has resulted in anear-continuous production of felsic ashes for more than 65 million years, the stable isotope content ofhydrated volcanic glass from the Malargüe foreland basin (35°S) was extracted to analyze itstopographic evolution and compare it to the geological record.The ID of volcanic glasses preserved within strata of the Malargüe basin suggest high-standingtopography since at least 55 Ma, along with an increase in orographic fractionation during middleEocene to Oligocene times, followed by a decrease between the middle Miocene and the Pliocene.While the first event coincides with low accumulation rates during lacustrine and distal fluvial depositionin the basin, the second episode overlaps with high accumulation rates and proximal fluvial and alluvialsedimentation. These results support the hypothesis of a pre-Neogene orographic barrier and could bereflecting topographic changes associated with deep mantle processes that have been affecting theSouth American continent throughout most of the Cenozoic (Flament et al., 2015).Flament, N., Gurnis, M., Müller, R.D., Bower, D.J., and Husson, L., 2015. Influence of subduction history on South American topography. Earth andPlanetary Science Letters, 430, 9-18.Horton, B.K., 2018. Sedimentary record of Andean mountain building. Earth-Science Reviews, 178, 279-309.Mulch, A., 2016. Stable isotope paleoaltimetry and the evolution of landscapes and life. Earth and Planetary Science Letters, 433, 180-191.Ramos, V.A., 1999. Plate tectonic setting of the Andean Cordillera. Episodes, 22(3), 183-190.Fil: Fennell, Lucas Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Hren, Michael. University of Connecticut; Estados UnidosFil: Brandon, Mark. University of Yale; Estados UnidosFil: Colwyn, David. State University of Colorado at Boulder; Estados UnidosFil: Martos, Federico Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Lewis, Amelia. Oberlin College; Estados UnidosFil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina8th International Symposium on Andean GeodynamicsQuitoEcuadorEscuela Politécnica NacionalInstitut de Recherche pour le Développemen

The Cenozoic Climatic and Topographic Evolution of the Western North American Cordillera

Herein we present oxygen isotope records from Cretaceous to Recent terrestrial sediments in the western North American Cordillera. The purpose of this analysis is to use oxygen isotope records to understand the coupled surface elevation and climate histories of this region through the Cenozoic. To do this we constructed δ¹⁸(O) maps of surface waters for time intervals that trace the development of topography of western North America. These maps are based on 4861 oxygen isotope analyses from both published (4478) and new (383) data. We determined the δ¹⁸(O) values of surface waters using paleotemperatures derived previously from floral assemblages and the appropriate isotope fractionation factors. These data suggest that in the late Cretaceous to early Eocene the Sevier hinterland formed a plateau of unknown height. Around 50 Ma, a topographic wave developed in British Columbia and eastern Washington that swept southward reaching northeastern Nevada at ~40 to 38 Ma, and southern Nevada ~23 Ma. This southward encroachment of an Eocene Plateau (SWEEP) caused reorganization of drainage patterns such that the intraforeland basins of Wyoming and Utah drainages extended deep within the Sevier hinterland as the wave swept southward. The landscape within the Sevier hinterland developed into a rugged and high mountain range with the hypsometric mean elevation of ~4 km and relief of ~1.5 km. This Eocene highland was bordered on the west by a high Sierra Nevada ramp and on the east by the intraforeland basins that captured water draining these growing highlands. The spatial and temporal evolution of this highland correlates with the timing of volcanism and extension. These observations support tectonic models that call for north to south removal of the Farallon slab or piecemeal removal of mantle lithosphere. The isotopic data show that prior to growth of this highland the North American Monsoon (NAM) penetrated much farther north in the Paleocene/Eocene than today. The combined effects of global cooling, increasing latitudinal temperature gradients, and the generation of the orographic barrier created by the growing north to south highland produced a southward migration of the NAM front. By the Oligocene the hydrologic regime that we observe today was in place. It has been modified since then as a result of Basin and Range extension and collapse of the highlands in the mid-Miocene. This collapse allowed the NAM to penetrate farther north into the Great Basin of Nevada and Utah

A Multidisciplinary Approach to Resolving the End-Guadalupian Extinction

The transition from the middle to late Permian (Guadalupian–Lopingian) is claimed to record one or more extinction events that rival the ‘Big Five’ in terms of depletion of biological diversity and reorganization of ecosystem structure. Yet many questions remain as to whether the events recorded in separate regions were synchronous, causally related, or were of a magnitude rivaling other major crises in Earth\u27s history. In this paper, we survey some major unresolved issues related to the Guadalupian–Lopingian transition and offer a multidisciplinary approach to advance understanding of this under-appreciated biotic crisis by utilizing records in Southern Hemisphere high-palaeolatitude settings. We focus on the Bowen-Gunnedah-Sydney Basin System (BGSBS) as a prime site for analyses of biotic and physical environmental change at high palaeolatitudes in the middle and terminal Capitanian. Preliminary data suggest the likely position of the mid-Capitanian event is recorded in regressive deposits at the base of the Tomago Coal Measures (northern Sydney Basin) and around the contact between the Broughton Formation and the disconformably overlying Pheasants Nest Formation (southern Sydney Basin). Initial data suggest that the end-Capitanian event roughly correlates to the transgressive “Kulnura Marine Tongue” in the middle of the Tomago Coal Measures (northern Sydney Basin) and strata bearing dispersed, ice-rafted gravel in the Erins Vale Formation (southern Sydney Basin). Preliminary observations suggest that few plant genera or species disappeared in the transition from the Guadalupian to Lopingian, and the latter interval saw an increase in floristic diversity

Barozh 12: formation processes of a late Middle Paleolithic open-air site in western Armenia

© 2020 Elsevier Ltd Barozh 12 is a Middle Paleolithic (MP) open-air site located near the Mt Arteni volcanic complex at the margins of the Ararat Depression, an intermontane basin that contains the Araxes River. Sedimentology, micromorphology, geochronology, biomarker evidence, together with an assessment of artifact taphonomy permits the modelling of site formation processes and paleoenvironment at a level of detail not previously achieved in this area. Obsidian MP artifacts were recovered in high densities at Barozh 12 from four stratigraphic units deposited during marine oxygen isotope stage 3 (MIS 3) (60.2 ± 5.7–31.3 ± 3 ka). The MIS 3 sequence commences with low energy alluvial deposits that have been altered by incipient soil formation, while artifact assemblages in these strata were only minimally reworked. After a depositional hiatus, further low energy alluvial sedimentation and weak soil formation occurred, followed by higher energy colluvial (re)deposition and then deflation. Artifacts in these last stratigraphic units were more significantly reworked than those below. Analysis of plant leaf wax (n-alkane) biomarkers shows fluctuating humidity throughout the sequence. Collectively the evidence suggests that hunter-gatherers equipped with MP lithic technology repeatedly occupied this site during variable aridity regimes, demonstrating their successful adaptation to the changing environments of MIS 3

Integrative Imaging Informatics for Cancer Research: Workflow Automation for Neuro-oncology (I3CR-WANO)

Efforts to utilize growing volumes of clinical imaging data to generate tumor evaluations continue to require significant manual data wrangling owing to the data heterogeneity. Here, we propose an artificial intelligence-based solution for the aggregation and processing of multisequence neuro-oncology MRI data to extract quantitative tumor measurements. Our end-to-end framework i) classifies MRI sequences using an ensemble classifier, ii) preprocesses the data in a reproducible manner, iii) delineates tumor tissue subtypes using convolutional neural networks, and iv) extracts diverse radiomic features. Moreover, it is robust to missing sequences and adopts an expert-in-the-loop approach, where the segmentation results may be manually refined by radiologists. Following the implementation of the framework in Docker containers, it was applied to two retrospective glioma datasets collected from the Washington University School of Medicine (WUSM; n = 384) and the M.D. Anderson Cancer Center (MDA; n = 30) comprising preoperative MRI scans from patients with pathologically confirmed gliomas. The scan-type classifier yielded an accuracy of over 99%, correctly identifying sequences from 380/384 and 30/30 sessions from the WUSM and MDA datasets, respectively. Segmentation performance was quantified using the Dice Similarity Coefficient between the predicted and expert-refined tumor masks. Mean Dice scores were 0.882 ($\pm$0.244) and 0.977 ($\pm$0.04) for whole tumor segmentation for WUSM and MDA, respectively. This streamlined framework automatically curated, processed, and segmented raw MRI data of patients with varying grades of gliomas, enabling the curation of large-scale neuro-oncology datasets and demonstrating a high potential for integration as an assistive tool in clinical practice

Short-term occupations at high elevation during the Middle Paleolithic at Kalavan 2 (Republic of Armenia)

The Armenian highlands encompasses rugged and environmentally diverse landscapes and is characterized by a mosaic of distinct ecological niches and large temperature gradients. Strong seasonal fluctuations in resource availability along topographic gradients likely prompted Pleistocene hominin groups to adapt by adjusting their mobility strategies. However, the role that elevated landscapes played in hunter-gatherer settlement systems during the Late Pleistocene (Middle Palaeolithic [MP]) remains poorly understood. At 1640 m above sea level, the MP site of Kalavan 2 (Armenia) is ideally positioned for testing hypotheses involving elevation-dependent seasonal mobility and subsistence strategies. Renewed excavations at Kalavan 2 exposed three main occupation horizons and ten additional low densities lithic and faunal assemblages. The results provide a new chronological, stratigraphical, and paleoenvironmental framework for hominin behaviors between ca. 60 to 45 ka. The evidence presented suggests that the stratified occupations at Kalavan 2 locale were repeated ephemerally most likely related to hunting in a high-elevation within the mountainous steppe landscape.info:eu-repo/semantics/publishedVersio

Stable isotope food-web analysis and mercury biomagnification in polar bears ( Ursus maritimus )

Mercury (Hg) biomagnification occurs in many ecosystems, resulting in a greater potential for toxicological effects in higher-level trophic feeders. However, Hg transport pathways through different food-web channels are not well known, particularly in high-latitude systems affected by the atmospheric Hg deposition associated with snow and ice. Here, we report on stable carbon and nitrogen isotope ratios, and Hg concentrations, determined for 26, late 19th and early 20th century, polar bear ( Ursus maritimus ) hair specimens, collected from catalogued museum collections. These data elucidate relationships between the high-latitude marine food-web structure and Hg concentrations in polar bears. The carbon isotope compositions of polar bear hairs suggest that polar bears derive nutrition from coupled food-web channels, based in pelagic and sympagic primary producers, whereas the nitrogen isotope compositions indicate that polar bears occupy > fourth-level trophic positions. Our results show a positive correlation between polar bear hair Hg concentrations and δ 15 N. Interpretation of the stable isotope data in combination with Hg concentrations tentatively suggests that polar bears participating in predominantly pelagic food webs exhibit higher mercury concentrations than polar bears participating in predominantly sympagic food webs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73930/1/j.1751-8369.2009.00114.x.pd