Abstract: Interaction of Upper Pennsylvanian and Wolfcampian Systems with Paleotectonic Elements of the Northern DJ basin, Nebraska and Colorado

John C. Webb

Deposition of Upper Pennsylvanian (Missourian and Virgilian) and Lower Permian (Wolfcampian) strata occurred in subsiding trough (Denver Embayment) that formed East of the Ancestral Rocky Mountains during Early Pennsylvanian time. The Trans-continental Arch an Wattenberg High are identified by isopach data. These large-scale elements range from six to twenty miles in width, and extend in a northeasterly direction for more than 100 miles. Smaller features include uplifted basement blocks and neighboring grabens. These features generally cover less than two square miles.

Paleotectonic features significantly influenced environments of deposition, diagenesis and porosity development. Large-scale features were the loci for deposition of algal mound and grain-rich carbonates during sea level high-stands and subsequent regressions. During low stands, these large scale features were subaerially exposed, resulting in soil formation, dissolution of allochems, recrystallization of lime and dolomite mud, and local to sub-regional erosion. Intervening lows were loci for deposition of mud-rich carbonate and shaly lithofacies during sea level high stands. During low stands, paleo-lows were also exposed, but experienced different styles of diagenetic alteration due to local or persistent ponding.

Lithofacies mapping suggests that in spite of greater subsidence in the western portion of the Denver Embayment, relative to the area of the Transcontinental Arch, sedimentation rates in the Denver Embayment exceeded subsid-ence, resulting in a predominance of continental and shoreward lithofacies to the west.

AAPG Search and Discovery Article #90952©1996 AAPG Rocky Mountain Section Meeting, Billings, Montana