Ben Creisler
New papers:
Susannah C.R. Maidment & Adrian Muxworthy (2019)
A chronostratigraphic framework for the Upper Jurassic Morrison Formation, western U.S.A.
Journal of Sedimentary Research 89 (10): 1017-1038.
doi: https://doi.org/10.2110/jsr.2019.54
https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/89/10/1017/574611/A-chronostratigraphic-framework-for-the-Upper?redirectedFrom=fulltext
A chronostratigraphic framework for the Upper Jurassic Morrison Formation, western U.S.A.
Journal of Sedimentary Research 89 (10): 1017-1038.
doi: https://doi.org/10.2110/jsr.2019.54
https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/89/10/1017/574611/A-chronostratigraphic-framework-for-the-Upper?redirectedFrom=fulltext
The fluvial, overbank, and lacustrine deposits of the Upper Jurassic Morrison Formation of the Western Interior, U.S.A. have been intensively studied due to their diverse and well-preserved dinosaurian fauna, and the presence of economic quantities of uranium and vanadium ores. The formation crops out over 12 degrees of latitude and 1.2 million km2, and is an excellent case study for the examination of paleoecology, community structure, and evolutionary dynamics at a time in Earth's history when the climate was significantly warmer than today. However, paleoecological studies have been hampered by lack of correlation across the formation. Assuming a primarily tectonic control on fluvial architecture, we propose the first chronostratigraphic framework of the formation, which is based on sequence stratigraphy, magnetostratigraphy, and radiometric dating. The formation can be divided into three sequences each represented by a period of degradation followed by aggradation. This chronostratigraphic framework indicates that the formation youngs to the north, and was deposited over about 7 million years during the late Kimmeridgian and Tithonian. This framework provides a foundation for future sedimentological, stratigraphic, and paleobiological studies of the iconic dinosaurian fauna known from the Morrison.
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Free pdf:
Benjamin J. Linzmeier, Andrew D. Jacobson, Bradley B. Sageman, Matthew T. Hurtgen, Meagan E. Ankney, Sierra V. Petersen, Thomas S. Tobin, Gabriella D. Kitch & Jiuyuan Wang (2019)
Calcium isotope evidence for environmental variability before and across the Cretaceous-Paleogene mass extinction.
Geology (advance online publication)
doi: https://doi.org/10.1130/G46431.1
https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G46431.1/574630/Calcium-isotope-evidence-for-environmental
Carbon dioxide release during Deccan Traps volcanism and the Chicxulub impact likely contributed to the Cretaceous-Paleogene (K-Pg) mass extinction; however, the intensity and duration of CO2 input differed between the two events. Large and rapid addition of CO2 to seawater causes transient decreases in pH, [CO32â], and carbonate mineral saturation states. Compensating mechanisms, such as dissolution of seafloor sediment, reduced biomineralization, and silicate weathering, mitigate these effects by increasing the same parameters. The calcium isotope ratios (Î44/40Ca) of seawater and marine carbonates are hypothesized to respond to these perturbations through weathering/carbonate deposition flux imbalances and/or changes in fractionation between carbonate minerals and seawater. We used a high-precision thermal ionization mass spectrometry method to measure Î44/40Ca values of aragonitic bivalve and gastropod mollusk shells from the K-Pg interval of the LÃpez de Bertodano Formation on Seymour Island, Antarctica. Well-preserved shells spanning the late Maastrichtian (ca. 67 Ma) to early Danian (ca. 65.5 Ma) have Î44/40Ca values ranging from â1.89â to â1.57â (seawater [sw]). Shifts in Î44/40Ca inversely correlate with sedimentological indicators of saturation state. A negative excursion begins before and continues across the K-Pg boundary. According to a simple mass-balance model, neither input/output flux imbalances nor change in the globally integrated bulk carbonate fractionation factor can produce variations in seawater Î44/40Ca sufficient to explain the measured trends. The data are consistent with a dynamic molluscan Ca isotope fractionation factor sensitive to the carbonate geochemistry of seawater. The K-Pg extinction appears to have occurred during a period of carbonate saturation state variability caused by Deccan volcanism.
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