Gulf of Mexico Outer Shelf/Slope Research Consortium Corehole in Main Pass 303, Louisiana Continental Shelf: Integrated Biostratigraphic, Lithostratigraphic, Isotopic Investigation of Highstand and Transgressive System Tracts
FILLON, RICHARD H., Texaco, Inc., New Orleans, LA, BARRY KOHL, Chevron, U.S.A., Inc., New Orleans, LA, and HARRY H. ROBERTS, Louisiana State University, Baton Rouge, LA
Investigation of a 300 ft continuously cored section through an outer shelf delta, including coarse fraction analysis, X-radiography, and a gamma ray log reveal an upward succession consisting of shale greater than carbonate-rich shale, which is greater than silty shale with fine sandy laminae, which is greater than bedded, cross laminated fine to medium sand, which is greater than shale with terrigenous organic matter, which is greater than massive, medium to coarse sand, which is greater than carbonate-rich shale.
Paleo sea-level estimates based on benthic foraminifera indicate an upward inner shelf which is greater than outer neritic, which is greater than marginal marine, which is greater than outer neritic transition. Planktonic biostratigraphy and isotope data are consistent with a last interglacial age for the lower, and a Holocene age for the upper, high sea-level stands. Multiple data sets define a maximum flooding surface (MFS) near the base of the high interglacial sea-level interval, and another MFS within the upper carbonate-rich shale.
The interval extending upward from the interglacial MFS encompasses condensed, limestone/nodular section that may represent a significant portion of interglacial time. The fine to medium sand overlying the interglacial contains a record of declining sea levels, declining planktonic foraminiferal abundance, and increasing terrigenous sand content documenting a progradational high-stand system tract bounded above by a ravinement surface or type 1 (para) sequence boundary which is evident in X-radiographs.
Concentrated terrigenous organic matter immediately above the ravinement surface suggests nonmarine relief-fill deposition during the minimum to earliest rising phase of the sea-level cycle. The fining upward character of the sand unit above the relief fill is consistent with transgressive system tract deposition during the early Holocene postglacial marine transgression.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)