ABSTRACT: Correlation of Yegua/Cockfield Genetic Cycles, Texas and Louisiana

EWING, THOMAS E. and FRANK VINCENT

Regional sections extending from west of Houston to north of Lafayette allow the correlation of marginal-marine Yegua sand-bearing cycles updip of the shelf margin eastward into the Cockfield Formation of Louisiana. Important observations include:

1. The uppermost Texas cycle below the Moodys Branch MFS (Yegua 10-15, called "Cockfield" in Texas) condenses and disappears into the Moodys Branch as picked in Louisiana. The easternmost sand in this interval occurs in eastern Beauregard parish (documented by Lock 1988).

2. The five documented sand-bearing intervals in Allen Parish and eastward are equivalent to the Yegua 20-50 of Central Texas. The Yegua 20 interval is condensed onto the Yegua 30 over a substantial region.

3. The lower Yegua cycles (Yegua 50-90) of central Texas lose sandstone eastward and condense into a limestone unit usually called the "Sparta Lime" in central Louisiana. There is a marked downlap geometry.

4. Several of the lower and middle Yegua flooding surfaces are marked by limestone stringers in Louisiana. These stringers, usually called "Cook Mountain Lime" are shingled and not correlative.

5. In general, the thick shale sequences of Texas become thinner limestones to the east in Louisiana. The Jackson downlaps entirely and is very thin on the shelf north of Lafayette.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana