Shell Offshore Time Stratigraphic Chart

Michael J. Styzen

The northern Gulf of Mexico basin has the highest density of Cenozoic biostratigraphic data of any basin in the world Shell's Gulf of Mexico biostratigraphic database contains information from over four thousand wells. Each well may have biostratigraphic information based on planktonic and benthic forams, calcareous nannofossils, and palynomorphs. This chart presents the biostratigraphic zonations used by Shell Offshore in the Gulf of Mexico, commonly used "Industry" zones along with standard worldwide zonations. Historically the vast majority of the regional geologic time markers in the Gulf have been based on benthic foraminifera. In the past attempts to use this data to tie into published time stratigraphic schemes has been hampered by the inability to accurately match these benthic markers to an absolute time scale. Recently the incorporation of correlations based on planktonic foraminifera and especially calcareous nannofossils into the Gulf of Mexico biostratigraphic scheme has allowed a more accurate match to be made to the worldwide system. On the chart the Shell biostratigraphic markers have been related to the time scale of Harland et al. (1990). This time scale was chosen because it is the best documented scheme published at this time. By comparing the age assignments presented here to paleomagnetic datums they can be adapted to any other published time scale. The chart has columns presenting the coastal onlap and tectono-eustatic curves of Haq (1988) reformatted to this time scale. The age assignments for the benthic foraminiferal markers were made by bracketing them between published planktonic events with good paleomagnetic control and combining Shell biostratigraphic and paleobathymetric data with geological and geophysical evidence from the Gulf of Mexico and the Haq curve. Calibration of the exceptionally high density, high resolution Gulf of Mexico biostratigraphy to a worldwide time frame allows effective application of published glacio-eustatic frameworks to model deposition in exploratory settings.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995