Oxygen Isotope and Sequence Stratigraphy of a Late Pleistocene Outer Shelf/Upper Slope Delta Complex in the Northeastern Gulf of Mexico

R. H. Fillon, V. Kolla, B. Long

Late Pleistocene sediments afford sequence stratigraphers an opportunity to critically assess relationships between sea level (independently documented for the period from studies of raised coral terraces) and the fundamental properties of system tracts.

A multidisciplinary study of a Late Pleistocene shelf margin delta complex located southeast of the modern Mississippi Delta identified six sequence boundaries and maximum flooding surfaces associated with oxygen isotope stages 1 through 13. This study utilizied oxygen isotope stratigraphy (obtained from planktonic and benthic foraminiferal tests); biostratigraphy (microfossil age markers, abundances, and paleobathymmetry); sedimentology (depositional systems, stacking patterns, sedimentary structures, grain size and composition); wire line gamma logs (from four continuously cored boreholes); and, high resolution reflection seismic data. Analysis of these multiple data sets determined that the dominant progradational facies of middle shelf o upper slope sequences comprising the delta complex (including important reservoir analogs) were deposited mainly during the fall and early rise of sea levels within glacial (even numbered) isotope stages. The longest continuous isotopic record of a single progradational event was encountered in an outer shelf/upper slope setting in Viosca Knoll block 774 where 60+ meters of prodeltaic silts and clays span glacial isotope stage 10 and the 10-9 transition, clearly indicating deposition during a deglacial sea level rise. Superimposed on the effects of sea level change, there is evidence that frequent autocyclic delta switching contributed significantly to the complex erosional and depositional patterns within sequences.

Cores and reflection seismics used in this study were obtained by the Gulf of Mexico Shelf/Slope Research Consortium.

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