Biostratigraphic, chronostratigraphic, and stratigraphic sequence analysis of Lower Tertiary marine sediments of Alabama for indicators of sea-level change

Conference · Fri Mar 01 00:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:7259570

Thompson, P R ^[1]; Baum, G R ^[2]

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1. ARCO Oil and Gas Co., Plano, TX (United States)
2. ARCO Alaska, Inc., Anchorage (United States)

Early Eocene to late Oligocene marine sedimentary units in southwestern Alabama were sampled at closely spaced intervals to derive a precise time-stratigraphic framework and to determine the paleoecological and mineralogical responses to fluctuations in sea level. Paleontologic control consisted of planktonic, smaller and larger benthonic foraminifera, calcareous nannofossils, dinoflagellates, and megafossils. Paleomagnetic reversals were delineated in two boreholes which, when supplemented by strontium isotope dates and the biostratigraphic control, provided a robust in situ chronostratigraphy for the Gulf Coast lower Tertiary. Paleoecologic trends in regression and transgression can be clearly correlated across major regional facies changes. Using the chronostratigraphy developed here, the second-, third-, and fourth-orders of Vail's global sea-level cycles can be recognized and demonstrate the influence of sea-level change on sedimentation. Stratigraphic systems tracts (SSTs) and bounding surfaces in outcrop were determined by lithologic variations and paleoecologic trends, and additionally by gamma logs in the cores. The lower sequence boundary occurs at a contact where an older, relatively fine-grained, deep-water, fossiliferous unit was abruptly succeeded by a coarse-grained, shallow-water, poorly fossiliferous unit. The transgressive surface occurs at the base of a fining- and deepening-upwards unit that was commonly glauconitic and very fossiliferous. Transgression culminated with a pulse of planktonic microfossils in a bed having reduced clastic sedimentation; on the log the surface of maximum starvation was marked by a gamma spike.

• OSTI ID: 7259570
• Report Number(s): CONF-910403-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ALABAMA
GEOLOGIC DEPOSITS
SEDIMENTARY ROCKS
AGE ESTIMATION
GEOCHEMISTRY
STRATIGRAPHY
BENTHOS
FORAMINIFERA
GAMMA LOGGING
GEOLOGIC HISTORY
PALEOMAGNETISM
PALEONTOLOGY
PLANKTON
SEA LEVEL
TERTIARY PERIOD
ANIMALS
AQUATIC ORGANISMS
CENOZOIC ERA
CHEMISTRY
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGY
INVERTEBRATES
LEVELS
MAGNETISM
MICROORGANISMS
NORTH AMERICA
PROTOZOA
RADIOACTIVITY LOGGING
ROCKS
SARCODINA
USA
WELL LOGGING
580000* - Geosciences