--> Abstract: Albian Sea Level and Reservoirs in Gulf Coast Carbonate/Siliciclastic Sequences, by Robert W. Scott, Ernest A. Mancini, and William C. Ward; #90078 (2008)

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Albian Sea Level and Reservoirs in Gulf Coast Carbonate/Siliciclastic Sequences

Robert W. Scott1, Ernest A. Mancini2, and William C. Ward3
1Geosciences, University of Tulsa, Cleveland, OK
2Department of Geological Sciences, University of Alabama, Tuscaloosa, AL
3Consultant, Boerne, TX

Albian depositional sequences on the Texas Comanche shelf record at least eleven deepening-shallowing cycles. Transgressive facies in the nearshore parts of the cycles are siliciclastics and offshore are deeper water marls reflecting rapid drowning. Maximum flooding and cycle turnaround are indicated by marl with ammonites and diverse mollusks and echinoids. Shoaling facies are rudist buildups, carbonate grainstone, mixed evaporite-mudstone, and shelf wackestone. The top surfaces of some cycles are iron-stained, bored hardgrounds. The contact at the top of the Edwards Formation has a subaerial isotope signature. Foraminifera and mollusca biofacies suggest drowning to depths of at least 50 m. Sea-level change was in pulses of rapid flooding followed by slow filling of accomodation and final fall exposing the shelf.

The ages of cycles in six key Texas sections are interpolated by graphic correlation with a chronostratigraphic database composed of more than 100 global sections and over 2000 taxa. Durations of Lower Albian cycles range from 0.62 to 1.2 myr. Middle Albian comprises one 4.5 myr transgressive-regressive cycle with three short-term retrogradational transgressive cycles in the lower part. Early Late Albian continent-wide flooding began at 103.0 Ma during the Hysteroceras orbignyi Zone. Five Upper Albian cycles are from 0.76 to 1.65 myr duration. Cycle frequencies suggest that relative sea level fluctuated more rapidly during the Early and Late Albian than during the Middle. The timing of Albian cycles is similar to those in European basins and on the Oman Shelf suggesting that these sea-level changes may indeed be eustatic. The amplitude of sea level change is estimated by different authors to vary from 50 m to 100 m. Hydrocarbon reservoirs tend to be in the highstand facies set.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas