Framework and Sedimentation Patterns of Tullock Member of Fort Union Formation, East-Central Powder River Basin, Montana and Wyoming: ABSTRACT

Abstract

Regional subsurface and outcrop studies of the fluvial Tullock Member of the Paleocene Fort Union Formation, in the east-central Powder River basin, Montana and Wyoming, indicate basin filling from the east and southeast by low-energy fluvial systems grading upward to high-energy stacked channel systems. Maps of sand-body geometry, lithofacies variations, and paleogeographic reconstructions were prepared from the analysis of approximately 200 well logs. Emphasis on subsurface data was necessary because of poor, inaccessible, or nonexistent outcrops in the study area. Where possible, subsurface models were field tested by matching paleocurrent data with inferred sandbody axes, as well as by comparing vertical and lateral grain-size variations with nearby well-log signatures.