Past warm climate intervals - Paleocene-Eocene Thermal Maximum (PETM) event - Origin of Cretaceous black shales - Evolutionary dynamics of nannofossils - The Cretaceous/Tertiary boundary - Mesozoic and Paleogene time scales

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The major focus of my work has been the use of calcareous nannofossil stratigraphy and paleoecology in addressing a diverse set of paleoceanographic, stratigraphic and tectonic problems ranging from the Triassic to the Pleistocene.   A routine part of my work includes the synthesis of geochemical data, including organic carbon, stable isotopes, and trace elements with floral and faunal assemblage and biostratigraphic data in interpreting the environments of times in the geologic past, especially times of extreme warmth.   

Paleocene-Eocene Thermal Maximum event

The Paleogene is a significant climatic transition from a warm, "greenhouse" Earth to one in which sizeable glaciers advanced on Antarctica.    My research in this area has focused on the long-term climatic change, but more recently on transient warming events that occurred within this transition. The Paleocene-Eocene Thermal Maximum (PETM) event is among the most rapid and transient (~150 kyr) warming events known from the geologic record.   Thus this is one of the best intervals for geologists to contribute to the continuing debate over the consequences of present global warming. I have been involved in the study of the micropaleontology and geochemistry of the PETM based on the recovery of unique records during Ocean Drilling Program legs.   Ongoing work focuses on the PETM sections at five different sites recovered during ODP Leg 198.   In addition, data from Leg 198 suggest that the PETM may not be unique.   An event in the mid-Paleocene at ~58.4 Ma associated with marked evolutionary changes in nannoplankton and foraminifera corresponds to a prominent lithologic horizon and an increase in deep-sea dissolution.

Studies of Cretaceous black shales  

My research addresses determining oceanic primary productivity levels during time periods of black shale accumulation, assessing the spatial and temporal factors that caused organic-rich sediments to accumulate in so-called Oceanic Anoxic Events (OAEs), and providing a time framework for study of some of these OAE intervals. My students and I are involved in studies of organic-rich sections in Northern Mexico, Venezuela, the US Western Interior and at Ocean Drilling Program sites.

Evolutionary Dynamics of Nannofossils

The calcareous nannoplankton have a rich evolutionary record. We are interested in the forces that drive evolution and changes in evolutionary rates. In current investigations we are using astrochronology to determine whether speciation and extinction events are geologically instantaneous on an ocean-wide basis and, if not, what factors control the extent of the diachroneity.

The Cretaceous/Tertiary Boundary

In the past I have worked on high-energy K/T deposits from the Caribbean region including DSDP sites on the Campeche margin and outcrops in Cuba. I am currently involved in two studies of the K/T boundary. The first concerns interpretation of the boundary interval in the YAX-1 drill site in the Chicxulub crater. We are in the process of investigating nannofossils in the immediate boundary succession. The second concerns the dynamics of the recovery of nannoplankton in the earliest Paleocene.

Mesozoic and Paleogene time scales

A major focus of my research has been to improve several aspects of the Mesozoic and Cenozoic time scale.   Early studies focused on improving the correlation between biostratigraphy and magnetostratigraphy, and increasing the resolution of nannofossil biostratigraphy by identifying additional non-zonal biohorizons to add to traditional zonal markers.   More recently we have just completed an investigation of mid-Cretaceous strontium isotope stratigraphy. I am currently in the midst of a study to improve the Cretaceous and Paleogene time scales based on nannofossil biostratigraphy of datable-ash-bearing sections in California, revision of biostratigraphy of DSDP and ODP sites, and calibration of bio- and magnetostratigraphy with astrochronology.