ABSTRACT: Origin of Regressive-Transgressive Sequences in the Claiborne Group
HULL, ROBERT A., Maxus Energy Corp., Dallas, TX
Origin of regressive-transgressive sequences within the Claiborne Group along the Texas and Louisiana coast have been variably attributed to eustatic sea level changes, autocyclic delta lobe switching, and changes in sediment sources. By using seismic, well logs, core data, and sedimentological and stratigraphic principles, this project determines the sequence stratigraphic relationships within this Eocene group. System tracts, defined by flooding surfaces and sequence boundaries, are examined as defined by various sedimentary models. By understanding the sequence stratigraphic relationships within these formations, it is possible to advance our understanding of the regional changes in sea level along the Texas Gulf Coast as well as to highlight sedimentary relationships and models fo this group. The Claiborne Group in the Victoria, Jackson, Wharton, Colorado and Fort Bend counties area exhibits apparent features predicted by the Vail model for a changing sea level. At least four major unconformity surfaces are recognized in seismic data acquired over this region of the Texas Gulf Coast from the San Marcos arch to the Houston embayment. Sequences beneath these unconformities have upwards of hundreds of meters of missing section. Seismic dip lines demonstrate that these surfaces have numerous onlapping and downlapping marine strata onto them. The surfaces can best be seen where the effects of salt or major growth faulting is not as significant as that encountered farther east.
Seismic data used includes 1990-vintage data, 36 to 60 fold with offsets over 3000 m. Seismic vertical resolution is around 25 to 30 m. Preliminary dating of the unconformities shows they occur within the Yegua, Cook Mountain, Sparta and Queen City Formations. Maximum flooding surfaces appear to onlap these surfaces. Three maximum flooding surfaces are recognized. Using the chronology of Haq et al., these maximum flooding surfaces occur at base of Supercycle TA4 and the top of TA3. They appear to correlate to the third order cycles 4.1 at 38.8 m.y., 3.6 at 40.0 m.y., and 3.5 at 41.2 m.y.
Apparently there may be a relationship between a change in climate and the timing of one of these unconformity surfaces. The relation between worldwide oxygen isotope data is shown. Although these sequence bounding surfaces may continue updip to the outcrop, seismic resolution prohibits tracing the thinning sequences updip. These unconformities apparently are not evident on all seismic sections in the region. Whether this is due to variations in sediment supply and deposition, or seismic resolution is uncertain. These unconformity surfaces are most easily observed where the Claiborne Group expands over the rapidly subsiding Wilcox Group.
AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)