Matthew Jarrell Jeffrey

Bio: Matthew Jarrell Jeffrey is an academic researcher from University of Missouri. The author has contributed to research in topics: Paleozoic & Facies. The author has an hindex of 2, co-authored 3 publications receiving 40 citations. Previous affiliations of Matthew Jarrell Jeffrey include University of Louisville.

Decoupling biogeochemical records, extinction, and environmental change during the Cambrian SPICE event

Abstract: Several positive carbon isotope excursions in Lower Paleozoic rocks, including the prominent Upper Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE), are thought to reflect intermittent perturbations in the hydrosphere-biosphere system. Models explaining these secular changes are abundant, but the synchronicity and regional variation of the isotope signals are not well understood. Examination of cores across a paleodepth gradient in the Upper Cambrian central Missouri intrashelf basin (United States) reveals a time-transgressive, facies-dependent nature of the SPICE. Although the SPICE event may be a global signal, the manner in which it is recorded in rocks should and does vary as a function of facies and carbonate platform geometry. We call for a paradigm shift to better constrain facies, stratigraphic, and biostratigraphic architecture and to apply these observations to the variability in magnitude, stratigraphic extent, and timing of the SPICE signal, as well as other biogeochemical perturbations, to elucidate the complex processes driving the ocean-carbonate system.

Marine anoxia and sedimentary mercury enrichments during the Late Cambrian SPICE event in northern Scotland

Abstract: Elevated mercury concentrations in ancient sedimentary rocks are used as a fingerprint for large igneous province (LIP) volcanism because there is a tight association between known LIPs and coeval sedimentary Hg anomalies. While nonvolcanic processes of sedimentary Hg enrichment, including redox variations, have been demonstrated in modern settings, interpretations of ancient sedimentary Hg records have focused on LIP volcanism. Here, we document a link between sedimentary Hg enrichment and marine redox changes during the late Cambrian Steptoean positive isotopic carbon excursion (SPICE) event, a time with no known LIP. We report a new occurrence of the SPICE event from the Eilean Dubh Formation of northern Scotland, which preserves a series of coeval Hg enrichments. Abundant glauconite, a redox-sensitive iron-bearing mineral, co-occurs stratigraphically with the SPICE and Hg enrichments but is rare to absent from the rest of the section, and bioturbation is low in strata spanning the SPICE. We suggest that local Hg enrichments were driven by changing marine redox conditions during the SPICE event, rather than emplacement of a LIP. Redox oscillations should be considered as an additional control on Hg enrichments in the geologic record.

Evidence for the development of local anoxia during the Cambrian SPICE event in eastern North America.

Abstract: The later Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE) event was an episode marked by pronounced changes to the global biogeochemical cycles of carbon and sulfur and significant extinctions on several paleocontinents including Laurentia (North America). While the exact cause(s) of these events remains debated, various lines of evidence suggest an increase in the areal extent of anoxia at the seafloor was a likely feature. Here, we explore whether changes in local oxygenation accompanied the onset of the SPICE in southern Laurentia using cores of the Nolichucky and Eau Claire Formations from Ohio and Kentucky, USA, that represent a transect into the Rome Trough/Conasauga intrashelf basin. At our study locations, the initial positive δ13 C shift of the SPICE occurs in conjunction with increases in the abundance and δ34 S of sedimentary pyrite. Further local redox conditions, tracked using iron speciation analysis, indicate anoxic conditions developed at the two proximal locations after the start of the paired isotopic excursions. However, the location near the basin center shows no indication for anoxia before or during the onset of the SPICE. While this signal may reflect the structure of local redox conditions within the basin, with the development of anoxia limited to the basin margins, we argue that authigenic iron enrichments were muted by sedimentary dilution and/or the enhanced authigenesis of iron-bearing sheet silicates near the basin center, masking the signal for anoxia there. Regardless of the areal extent of anoxia within the basin, in either scenario the timing of the development of anoxic bottom waters was concurrent with local faunal turnover, features broadly consistent with a global expansion of anoxia playing a role in driving the isotopic trends and extinctions observed during the event.