ABSTRACT: High-Resolution Correlation of Mid-Cretaceous Sequences in the Gulf Coast and Western Interior

SCOTT, R. W., Amoco Production Co., Tulsa, OK

Four scales of depositional cycles are developed within the mid-Cretaceous section: about 8.1, 4.1, 2.0, and 0.81 Ma. Major transgressions marked by significant onlap and regional unconformities, such as the Washita Group, are approximately 8.1 Ma in duration. Within these cycles are packages of limestone-shale and sandstone-shale, such as the Pearsall Formation, about 4.1 Ma in duration. These units can be divided further into complex shale-limestone bed sets of about 2.0 Ma duration. The thinnest conformable shale-limestone cycles are parasequence sets about 0.81 Ma long, such as several pairs of formations in the upper Washita Group in north Texas.

Graphic correlation techniques applied to the mid-Cretaceous section in north Texas and the southern Western Interior show that the same scale of cycles is developed. The basal Washita drowning unconformity correlates with the unconformity/transgressive surface at the base of the Cheyenne/Kiowa formations in Kansas. Other regional erosional unconformities in one basin correlate with drownings of the shallow shelf in the other basin. The Western Interior erosional unconformity between the Purgatoire-Kiowa and Dakota formations correlates with the drowning event between the Fort Worth and Denton formations in north Texas. The regional erosional contact within the Dakota in the Denver basin correlates with the drowning of the Mainstreet Formation shelf by the shelf-basin facies of the Gr yson Formation. The major Gulf Coast erosional unconformity at the base of the Woodbine Formation correlates with the flooding of the Dakota by the Graneros Formation.

Regional lowstand unconformities in one basin may correlate with transgressive surfaces in another basin. High-precision correlation provides a tool to test the relative interactions of eustasy, differential basin subsidence, and sediment supply.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)