Paleobiology Seminar: "Diastem Didactic: Some Recent Advances in Late Cretaceous Geochronology, Chronostratigraphy, and OAE Studies"


Thursday, December 4, 2014, 1:30pm to 2:30pm


Haller Hall (Geology Museum 1020

Speaker: Dr. Brad Sageman (Northwestern University)

Abstract: In 1917, Joseph Barrell published a paper titled "Rhythms and the Measurements of Geologic Time" in which he proposed that the sedimentary record was made up of more surfaces representing missing time than rock representing recorded time.  This insight has been appreciated for generations since, and eventually led to the development of an entire brach of stratigraphy based on the subdivision of strata by major unconformities.  But we have largely ignored the ubiquitous small gaps that pervade the stratigraphic record because they are commonly difficult to identify in many facies types and, at a certain level of resolution, effectively averaged into geologic time scales.  In recent years, however, advances in geochronologic and chronostratigraphic methods have led to increased recognition of these gaps - the diastems of Barrell - and their impact on higher resolution reconstructions of geologic time that we are now seeking to establish.   In this talk, I will present the results of some recent collaborative studies of Late Cretaceous strata in which a combination of new geochronologic and astrochronologic methods has allowed significant refinement of the geologic time scale.  Better time scales, and improved recognition and understanding of hiatuses, provide a much improved framework for the analysis of critical events, such as Ocean Anoxic Event 2 (OAE2) in the Late Cenomanian.  By carefully placing key geochemical proxy records within this refined chronostratigraphic framework, new insights concerning the initiation and progression of OAE's are possible.