Assessing orbital vs. volcanic control on carbon cycle during the Early Cretaceous

The interval from the Valanginian to the Barremian stages (137?121 Ma; Early Cretaceous) ispunctuated by several episodes of environmental changes, accompanied by shifts in weatheringintensity on the continents and changes in the Tethyan neritic carbonate production. Wesynthetize here the astrochronology of two recent studies performed in the Neuquén basin,Vocontian Basin and Subbetic Domain (Aguirre-Urreta et al., 2019; Martinez et al., 2020), anchoredto CA-ID-TIMS U-Pb ages, which conclusions have been included in the Geologic Time Scale 2020(Gale et al, in press). We applied this time scale to a compilation of carbon-isotope ratio frombelemnites and proxies of detrital supply in the Tethyan area (Vocontian Basin and SubbeticDomain). From this compilation, we show that the episodes of environmental changes are pacedby a 2.4-Myr cycle and, with a lower amplitude, a 1.2-Myr cycle. In addition, the new time scaleshows the synchronicity between the Weissert Event and the Parana-Etendeka Large IgneousProvince. In the series of carbon-isotope ratios measured on belemnite rostra, the amplitude ofthe 2.4-Myr cycle is twice higher during the Valanginian than in the Late Barremian and threetimes higher than in the Hauterivian and Early Barremian, suggesting that the activity of theParana-Etendeka Large Igneous Province amplified the initial orbital forcing to trigger theenvironmental changes observed during the Mid-Valanginian.Fil: Martinez, M.. Géosciences Rennes; FranciaFil: Aguirre Urreta, María Beatriz. 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: Lescano, Marina Aurora. 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: Dera, G.. Université Paul Sabatier; FranciaFil: Omarini, Julieta. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; ArgentinaFil: Tunik, Maisa Andrea. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Frederichs, Tomas. Universitat Bremen; AlemaniaFil: Palike, Heiko. Université Paul Sabatier; FranciaFil: O'Dogherty, Luis. Universidad de Cádiz; EspañaFil: Aguado, Roque. Universidad de Jaén; EspañaFil: Company, Miguel. Universidad de Granada; EspañaFil: Sandoval, Jose. Universidad de Granada; EspañaEGU General Assembly 2021AlemaniaEuropean Geosciences Unio

Ice sheet–free West Antarctica during peak early Oligocene glaciation

One of Earth’s most fundamental climate shifts – the greenhouse-icehouse transition 34 Ma ago – initiated Antarctic ice-sheet build-up, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma) that immediately followed this transition, a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization, is uncertain. Here, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin – a key region for understanding Antarctic ice sheet-evolution. These data indicate a cool-temperate environment, with mild ocean and air temperatures preventing West Antarctic Ice Sheet formation. Climate-ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change

New details about the LGM extent and subsequent retreat of the West Antarctic Ice Sheet from the easternmost Amundsen Sea Embayment shelf

In recent years several previously undiscovered grounding-zone wedges (GZWs) have been described within the Abbot-Cosgrove palaeo-ice stream trough on the easternmost Amundsen Sea Embayment shelf. These GZWs document both the Last Glacial Maximum (LGM; 26.5-19 cal. ka BP) grounding-line extent and the subsequent episodic retreat within this trough that neighbors the larger Pine Island-Thwaites trough to the west. Here we combine bathymetric, seismic, and geologic data showing that 1) the grounding line in Abbot Trough did not reach the continental shelf break at any time during the last glacial period, and 2) a prominent stacked GZW constructed from six individual wedges lying upon another was deposited 100 km upstream from the LGM grounding-line position. The available data allow for calculating volumes for most of these individual GZWs and for the entire stack. Sediment cores were recovered seawards from the outermost GZW in the trough, and from the individual wedges of the stacked GZW in order to define the LGM grounding-line extent, and provide minimum grounding-line retreat ages for the respective positions on the stacked GZW. We present implications of a grounded-ice free outer shelf throughout the last glacial period. Furthermore, we assess the significance of the grounding-line stillstand period recorded by the stacked GZW in Abbot Trough for the timing of post-LGM retreat of the West Antarctic Ice Sheet from the Amundsen Sea Embayment shelf

Ice sheet–free West Antarctica during peak early Oligocene glaciation

One of Earth’s most fundamental climate shifts – the greenhouse-icehouse transition 34 Ma ago – initiated Antarctic ice-sheet build-up, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma) that immediately followed this transition, a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization, is uncertain. Here, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin – a key region for understanding Antarctic ice sheet-evolution. These data indicate a cool-temperate environment, with mild ocean and air temperatures preventing West Antarctic Ice Sheet formation. Climate-ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change