Morphology and Evolution of Shale-Filled Paleochannel in Wilcox Group (Paleocene-Eocene), Southeast Texas

Peter J. Hutchinson

Local extensive paleochannels exist within the upper to lower Wilcox Group (Paleocene-Eocene) of the Gulf Coast of North America. Recent reports document the following paleochannels of the Wilcox Group: Bejuco-Lalaja, Chicontepec, DeSoto, Nautla, Ovejas, St. Landry, and Yoakum. An eighth, the Tyler (Hardin) channel, suggests that passive submarine erosional forces shaped the channels prior to any active erosional forces, such as those related to turbidity currents.

The north-south-trending Tyler (Hardin) channel is 24 mi (40 km) long, 12 mi (20 km) wide, and displays over 1,000 ft (300 m) of shale fill. The channel thalweg bifurcates updip into two meandering steep-walled channels that display numerous side gullies.

The channel grew from the youthful to the mature stage through passive erosive mechanisms. During the mature stage, it may have been further enlarged by more active erosional agents, such as turbidity currents. Old age began with increased paralic sedimentation and infilling of the channel with deep-marine shale. Eventually, progradation and eustatic drop in sea level buried the channel, its younger fill, and older adjacent deposits.

Paleochannels are salient economic features. The deep-marine shale infill of the channel acts as a source of oil and gas and a seal for adjacent reservoir rock. Upward migration of oil through fractures, faults, and sediments fills reservoirs in overlying structures formed in nearshore deposits of the upper Wilcox. Most of the major oil and gas fields of the Wilcox Group in Tyler and Hardin Counties are localized in structures overlying the channel fill.

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.