Quantified sea level history for the middle Jurassic (Bajocian) through Cretaceous (Santonian) based on Russian platform and Siberian stratigraphic data

Quantified Eustatic Curve (QEC) for Bajocian (Mid Jurassic) through Santonian (Upper Cretaceous) was constructed on the basis of the stratigraphy of the Russian Platform. The Mesozoic tectonic stability of the central part of the Russian Platform provided a valid frame of reference upon which to base the eustatic curve. As such, this curve can be considered a reliable representation of eustasy. The stratigraphic hiatuses left by unconformities in the central part of the Russian Platform were filled with stratigraphic information from the more continuous stratigraphy of the subsiding regions such as Ryazan Saratov Trough and Northern Siberia. The curve makes it possible to filter the eustatic signal from basin stratigraphic data (in any basin) and thereby quantify basin subsidence and sedimentation history more accurately than previously possible. In order to test its validity the QEC was compared to the existing eustatic reconstructions for Jurassic-Cretaceous of the European and U.S. mid-continent sections. Good correlation (within limits of biostratigraphic resolution) of sea-level events interpreted from the regions with different tectonic histories made it possible to prove eustatic nature of several sea-level events. These include transgressive/highstand episodes: (1) late Bathonian; (2) late Callovian; (3) middle Oxfordian; (4) late Oxfordian; (5) late Albian; (6) Cenomanian/Turonian boundary; (7) mid-Volgian, and regressive events such as: (1) latest early Oxfordian; (2) middle late Oxfordian. Good agreement with some discrepancies was found for: early-mid Callovian, Kimmeridgian, Hauterivian, Aptian, Late Albian-Turonian intervals of the QEC. Additional testing is needed to prove their eustatic origin. West Siberian basin served as a first site for an application of the QEC. Sequence stratigraphic analysis of the Jurassic and Neocomian sections of the selected regions in West Siberia led to identification of depositional sequences and an improved understanding of their depositional histories. Good correlation (100% correspondence for Oxfordian) was found between the QEC and sea-level change patterns inferred from Late Bathonian-Kimmeridgian and Valanginian-Hauterivian stratigraphic intervals of West Siberia. This result demonstrates the main role of eustasy as a factor controlling the deposition of the Mid-Upper Jurassic and Clinoform Neocomian sections

Intra‐clinothem variability in sedimentary texture and process regime recorded down slope profiles

Shelf‐margin clinothem successions can archive process interactions at the shelf to slope transition, and their architecture provides constraints on the interplay of factors that control basin‐margin evolution. However, detailed textural analysis and facies distributions from shelf to slope transitions remain poorly documented. This study uses quantitative grain‐size and sorting data from coeval shelf and slope deposits of a single clinothem that crops out along a 5 km long, dip‐parallel transect of the Eocene Sobrarbe Deltaic Complex (Ainsa Basin, south‐central Pyrenees, Spain). Systematic sampling of sandstone beds tied to measured sections has captured vertical and basinward changes in sedimentary texture and facies distributions at an intra‐clinothem scale. Two types of hyperpycnal flow‐related slope deposits, both rich in mica and terrestrial organic matter, are differentiated according to grain size, sorting and bed geometry: (i) sustained hyperpycnal flow deposits, which are physically linked to coarse channelized sediments in the shelf setting and which deposit sand down the complete slope profile; (ii) episodic hyperpycnal flow deposits, which are disconnected from, and incise into, shelf sands and which are associated with sediment bypass of the proximal slope and coarse‐grained sand deposition on the medial and distal slope. Both types of hyperpycnites are interbedded with relatively homogenous, organic‐free and mica‐free, well‐sorted, very fine‐grained sandstones, which are interpreted to be remobilized from wave‐dominated shelf environments; these wave‐dominated deposits are found only on the proximal and medial slope. Coarse‐grained sediment bypass into the deeper‐water slope settings is therefore dominated by episodic hyperpycnal flows, whilst sustained hyperpycnal flows and turbidity currents remobilizing wave‐dominated shelf deposits are responsible for the full range of grain sizes in the proximal and medial slope, thus facilitating clinoform progradation. This novel dataset highlights previously undocumented intra‐clinothem variability related to updip changes in the shelf process‐regime, which is therefore a key factor controlling downdip architecture and resulting sedimentary texture

Mesozoic and Cenozoic Sequence Chronostratigraphic Framework of European Basins, P. C. De Graciansky

Mutualisms are key components of biodiversity and ecosystem function, yet the forces maintaining them are poorly understood. We investigated the effects of removing large mammals on an antAcacia mutualism in an African savanna. Ten years of large-herbivore exclusion reduced the nectar and housing provided by plants to ants, increasing antagonistic behavior by a mutualistic ant associate and shifting competitive dominance within the plant-ant community from this nectardependent mutualist to an antagonistic species that does not depend on plant rewards. Trees occupied by this antagonist suffered increased attack by stem-boring beetles, grew more slowly, and experienced doubled mortality relative to trees occupied by the mutualistic ant. These results show that large mammals maintain cooperation within a widespread symbiosis and suggest complex cascading effects of megafaunal extinction