Paleocene benthic foraminiferal biostratigraphy, paleoecology, and paleoceanography of the eastern Gulf Coastal Plain.

摘要

A stratigraphic and paleontological analysis of 303 samples of Paleocene sediments of the eastern Gulf Coastal Plain of Mississippi, Alabama, and Georgia provided the basis for a geochronologic, quantitative paleoecologic, and paleoceanographic model.; One hundred fifty four samples bearing benthonic and planktonic foraminifera were studied; 166 benthonic foraminiferal species were identified and their biostratigraphic distribution yielded 4 biozones which were integrated into the global time framework. This was achieved by correlating the benthonic foraminifera with the planktonic foraminifera in a few selected samples.; The 4 biozones are: the Eponides elevatus Zone (= Zone plb), the Alabamina midwavana Zone (= Zone Plc through lower P4), the Discorbis washburni Zone (= middle Zone P4) and the Alabamina westraliensis Zone (= upper Zone P4 through P6a). The use of benthic foraminifera in short distance correlation is an effective tool, particularly in the case of surface and subsurface sections which have a paucity of planktonic foraminifera.; Principal Component Analysis of the benthic foraminiferal fauna yielded six assemblages which when combined with two other qualitatively derived assemblages provide the basis for a paleoceanographic model of the Eastern Gulf Coastal Plain.; The presence of Subbotina trinidadensis and Planorotalites pseudomenardii as well as a paleolatitude ranging from 15{dollar}spcirc{dollar}N (for the Campeche Shelf) to 25{dollar}spcirc{dollar}N (for the coastal plain) emphasizes a paleoclimatic regime which is dominantly tropical. Thus it is inferred that normal marine waters were brought into the Gulf of Mexico by two major currents: (1) The easterly flowing Pacific counter current which when deflected by the southern most Gulf margin generated a minor cyclonic flow around the Campeche Shelf and (2) the west flowing equatorial current generated by the southern margin of the North Atlantic anticyclonic gyre which fed the central and northern Gulf.; Patterns of distribution in the benthic foraminiferal assemblages strongly suggest a distribution which is controlled by (1) the character of the circulation, (2) water mass properties, (3) climate, and (4) subtle oscillations in sea level during the Paleocene.; Strandline displacements are thought to be directly related to subtle transgressive and regressive sea level movements. A well delineated quasi-cyclicity strongly suggestive of the 400,000 year cycles is identified along the refined sea level curve.