VINCENT, FRANK S., Upstart Exploration, Inc., Lafayette, LA; and THOMAS E. EWING, Venus Exploration, Inc., San Antonio, TX
The lower Claiborne units, of Lutetian age-middle Eocene, are recognized as a series of marine shelf, marginal marine, and deltaic-strandline deposits. Regional closely-spaced well-log cross-sections extending for almost 500 miles from south Texas to eastern Louisiana updip of the Claiborne shelf margins clearly show the regional stratigraphic architecture from southeast Texas through east-central Louisiana. The obvious internal forms when viewing the lower Claiborne at such great scale are large, very-low-angle, sigmoidal clinoform sets delineated by regional flooding surfaces. These large downlaps are roughly oriented from NW to SE across coastal Texas and into central Louisiana demonstrating the time-transgressive nature of the entire lower Claibornethe downlaps proceed from oldest to youngest coming from west to east.
The Reklaw, Queen City, and Weches depositional episodes in south and central Texas have prograded across the narrower shelf there and are recognized out into slope environments. However, because of distance from sediment supply and a widening shelf in south Louisiana, these formations thin, downlap, and condense as they are traced into western Louisiana. The Queen City and Weches units are readily correlatable as thin but distinctive resistive bedsets that account for about the lowermost third-to-half of the Cane River Marl in western Louisiana. The Reklaw is questionably traceable into Louisiana but is likely very thin and at the base of the Marl.
The distinctive Cane River Marl of southwest and central Louisiana is a greatly condensed section (less than 30 feet total thickness in parts of south-central Louisiana) being composed of very thin, downdip, time-equivalents of the Reklaw(?), Queen City, Weches, and in its upper portions some of the oldest down-dip Sparta prograding units. The Cane River Marl sits, by regional disconformity, on top of the Wilcox Formation.
At least ten cycles (probably 4th5th Order) of silty-sandy zones within the Sparta genetic stratigraphic unit progradedownlap gulfward and eastward in Louisiana. These stacked silty-sandy sections pass down-dip into deeper-water, finer-grained sediments transitional to what is called lithostratigraphically the Cane River Shale. Older units of the latter themselves pass into, even further down-dip, the much condensed upper beds of the Cane River Marl.
The lower Claiborne section is apparently bounded regionally by major Transgressive Surfaces of Erosion (ravinement surfaces, or regional disconformities): one at the base of the Reklaw-Cane River Marl/top Wilcox, and the other at the base of the Cook Mountain/top Sparta. Thus, the lower Claiborne section (the Lutetian spanned approximately 810 m.y.) described here represents a complete 2nd Order Cycle.
VINCENT, FRANK S., and THOMAS E. EWING
AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas