Correlation of Red Beds and Evaporite Units between Surface and Subsurface: Addressing Challenges for Petroleum Geology

Benison, Kathleen C.; Zambito, James

Rock units consisting of both evaporites and siliciclastics, such as those of the Permian-Triassic of the midcontinental U.S., are of interest to the petroleum industry because they typically serve as seals, act as marker beds as seen in well logs, and pose drilling hazards. However, distinct differences in mixed evaporite-siliciclastic units between surface and subsurface have been overlooked. These differences present challenges in resolving stratigraphic nomenclature, lithologic correlation, and age determinations. Here we use observations of cores and outcrops from the Nippewalla Group of the southern midcontinent and the Opeche/Goose Egg/Spearfish Formations of the northern midcontinent to compare and contrast the sedimentology and stratigraphy at different depths and various spatial scales. We recognize multiple petrographic textures of rocks composed of both evaporites and siliciclastics and, from them, interpret a variety of depositional and diagenetic processes. Supplemental dissolution experiments add a semi-quantitative framework, allowing for estimation of loss of rock thickness and volume to late-stage, shallow diagenesis. Our observations lead to refinements in facies interpretations and diagenetic history as well as relation of seemingly different lithological units present in core and outcrop. This new knowledge yields solutions to the stratigraphic challenges of extrapolating outcrop data to the subsurface, and vice versa.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013