Upper Cretaceous (Cenomanian to Maastrichtian) stratigraphic breaks in Alabama coastal plain: criteria for recognition and relationship to eustatic sea level change
- Auburn Univ., AL (USA)
In Alabama, the Upper Cretaceous section (450 m thick) rests on pre-Mesozoic basement and consists mainly of clastic shoreline and nearshore facies and hemipelagic shelf facies. The section contains several distinctive stratigraphic breaks, most of which are ascribed to third-order eustatic sea level drops on the current world sea level curve. However, a few distinctive breaks in the section are not related to eustatic sea level changes and cannot be attributed to changes in shelf subsidence rate. The eustatic-related stratigraphic breaks are delineated on correlations by erosional relief up to 25 m, lateral continuity (in dip section) over 200 km, and biostratigraphic discontinuity. On outcrop, a sharp facies discontinuity and a conglomeratic zone bearing teeth, bones, and phosphatic clasts mark these breaks. The most notable breaks correlate biostratigraphically with eustatic sea level drops at 90 Ma (125-m drop at the Tuscaloosa-Eutaw Formations contact), 80 Ma (65-m drop at the Blufftown-Mooreville and Cusseta-Demopolis lithosome contact), and 68 Ma (95-m drop at the Ripley Formation and Prairie Bluff-Providence lithosome contact). Other eustatic breaks indicated only by outcrop-scale evidence occur within the Ripley Formation (71 Ma, a 55-m drop) at the Cusseta-Demopolis and Ripley Formations contact (75 ma, a 50-m drop), and at the Eutaw Formation and Blufftown-Mooreville contact (84 Ma, a 45-m drop). In addition, marine facies discontinuities (traceable over 200 km in dip section) are correlated with all minor (< 45 m) eustatic sea level drops. Some facies discontinuities which cannot be matched with coeval eustatic sea level change are uniquely characterized by sandy shelf-bar development and are attributable only to a briefly elevated clastic sedimentation rate.
- OSTI ID:
- 5698302
- Report Number(s):
- CONF-890404-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 73:3; Conference: AAPG annual convention with DPA/EMD Divisions and SEPM, San Antonio, TX (USA), 23-26 Apr 1989; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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