Abstract

Resolving the eustatic and tectonic signals of sedimentary successions has long been a central goal of stratigraphers. Marine retroarc basins such as the Cretaceous western interior basin are ideal sites in which
to develop this art. They contain the record of global sea level change, and, as regions of continuous subsidence adjacent to the earth's major mountain chains, they also contain the only real geologic data with which the geodynamic histories of these chains can be deduced. Recently, models have been presented for stratigraphy in retroarc settings where tectonism as well as eustasy must be taken into account, leading to distinctive stratigraphic patterns. The study described in this talk is testing these models. The study is focused on the problem of third-order cyclicity; depositional cycles of 1-10 my duration ("clastic wedges"). It is designed to corroborate insights developed to the north, in the Alberta basin, and to the south, in the Book Cliffs, and to extract additional generalizations that can used to separate eustatic and tectonic signals elsewhere in time and space.

Recent studies suggest that late Cretaceous sea levels peaked simultaneously in the USA and Northwest Europe, but thrust-loading, erosion and isostatic response generated a tectonic overprint on the eustatic record, which became intensified with the advent of thick-skinned tectonics during the Campanian. This hypothesis will be tested on high-resolution regional correlations of the Santonian-Campanian interval in the central Rocky Mountains, supported
by numerical experiments. The study area is a "central Wyoming corridor" that crosses the Powder River, Bighorn and Green river basins of Central Wyoming, and extends to the tectonic front. Here optimal biostratigraphic control exists, Recent lithostratigraphic studies in the corridor permit the transformation of the classic stratigraphic
succession to an allostratigraphic format that is amenable to numerical experiments.

Biographical Sketch

Dr. Swift holds a Slover Chair of Oceanography and has been designated Eminent Professor. He has been awarded the F. P. Shepard Medal for excellence in Marine Geology. His research interests include shallow marine sediments and sedimentary dynamics, and shallow marine stratigraphy at the event, facies and sequence stratigraphic scales.

Light refreshments are served in the Interaction Area (4th floor of the Oceanography/Physics Building) at 4:00 p.m.

All seminars begin at 3:00 p.m. and are held in room 200 of the Oceanography/Physics building.