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August 2012 - April 2016
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Publications (31)
The major glaciation at the end of the Ordovician is associated with the 2nd largest mass extinction event of the Phanerozoic. Growth of Late Ordovician ice sheets requires a dramatic cooling from the ‘greenhouse’ conditions that prevailed for most of the Ordovician, but when and how fast this cooling occurred is controversial. The controversy is d...
The Guttenberg Isotope Carbon Excursion (GICE), a positive carbon isotope excursion that occurs near the base of the Katian Stage, is thought to be a global event possibly related to Late Ordovician cooling. Documenting how much regional and global variability exists in carbon isotopic trends prior to and during the GICE is a critical aspect in und...
The Permian-Triassic (P-T) mass extinction is the largest extinction event of the Phanerozoic and has been causally related to eruption of the Siberian Traps (Siberia, Russia) through climatic and ecological effects of volcanically forced greenhouse gas emissions. Given anthropogenic changes to the atmosphere, documenting details of links between g...
A presumed link between carbon isotopic trends and sea level change features prominently in many studies of epicontinental carbonates. In these shallow marine environments, a combination of basin restriction, burial/oxidation of organic carbon, proximity to terrestrial carbon sources, carbonate mineralogy, and/or meteoric influence can result in δ1...
The oxygen isotopic compositions (δ18O) of minimally altered phosphate minerals and fossils, such as conodont elements, are used as a proxy for past ocean temperature. Phosphate is thermally stable under low to moderate burial conditions and is ideal for reconstructing seawater temperatures because the P-O bonds are highly resistant to isotopic exc...
Sea-level change influences carbon isotopic trends in both modern and ancient carbonate depositional environments. Generally, this relationship is manifested as a positive carbon isotopic excursion where the rising limb of the excursion is associated with transgression. These excursions exist because sea level can influence 1) local/regional/global...
The Maritimes Basin of Atlantic Canada contains a rich record of Pennsylvanian cyclothems. Previous studies have focused on rapidly subsiding depocenters in the central part of the basin where Carboniferous successions feature cyclic alternations between terrestrial and marginal marine strata. In contrast, the Pennsylvanian Clifton Formation was de...
Global cooling and the establishment of a moderate climate in the Middle Ordovician has been invoked as the primary driver of the tenfold increase in marine biodiversity that characterized the Great Ordovician Biodiversification Event (GOBE). Arguments suggesting that climate change played a significant role in biodiversification purport that the E...
Warming after the big one
The Chicxulub impact 65 million years ago, which caused the mass extinction at the Cretaceous-Paleogene boundary, also initiated a long period of strong global warming. Using data from phosphatic microfossils, including fish teeth, scales, and bone, MacLeod et al. estimated global average temperature. Immediately after the...
The GICE (Guttenberg Carbon Isotope Excursion) is a positive δ13C excursion and a prominent feature of the Late Ordovician chemostratigraphic record. The GICE has been identified on different paleocontinents, and its cause is still unresolved. One explanation suggests that the GICE is the carbon isotopic expression of changes that occurred during t...
Latest Sandbian to early Katian sequences across Laurentia's epicontinental sea exhibit a transition from lithologies characterized as ‘warm-water’ carbonates to those characterized as ‘cool-water'carbonates. This shift occurs across the regionally recognized M4/M5 sequence stratigraphic boundary and has been attributed to climatic cooling and glac...
Oxygen isotopic measurements of conodont elements can provide important paleoclimatic, paleoecological, and paleoenvironmental information. However, preparation techniques are often cited as a potential, albeit poorly constrained, source of error. Prior to isotopic measurements, conodont elements are typically liberated from a calcium carbonate mat...
Oxygen isotopic ratios of conodont apatite can be a robust proxy for sea surface temperatures and provide important constraints on global climate. The oxygen isotopic composition of seawater is a function of local, regional, and global processes. To determine the relative importance of regional and local influences (and therefore make global infere...
The argument that temperature change and biological change during the Ordovician are correlated and, perhaps, causally related has been advanced by measurements of δ18Ophos values on conodont apatite, a phase more resistant to diagenetic alteration than carbonates. However, the available conodont δ18Ophos records are discontinuous and are biased to...
Oxygen isotopic ratios of conodont apatite can be a robust proxy for sea surface temperatures and provide important constraints on global climate. The oxygen isotopic composition of seawater is a function of local, regional, and global processes. To determine the relative importance of regional and local influences (and therefore make global infere...
The sedimentological, paleontological, and geochemical record of the Late Ordovician Laurentian epicontinental seaway shows a number of shifts that have been variously interpreted as indicating progressive cooling, episodes of upwelling, intervals of enhanced weathering, and times of organic carbon burial with seafloor anoxia, among other hypothese...
