UNDERSTANDING THE TRIASSIC DOCKUM GROUP OF WEST TEXAS AND NORTHEAST NEW MEXICO IN CONTEXT WITH THE MEGAMONSOON HYPOTHESIS: A PALEOGEOGRAPHIC AND HYDROLOGIC ANALYSIS

The Dockum Group of the west Texas panhandle and eastern New Mexico is a dryland fluvial-lacustrine system that was deposited during the Triassic Period. Despite being identified in the late 1800’s a definitive depositional model has yet to be established. Most of the research on these strata focuses on the rich abundance of large vertebrate fossils of the Upper Triassic section, and these studies have aided in drawing time equivalency between the Dockum Group and the Chinle Formation directly to the west.

The Chinle Formation has been extensively studied and generalizations of the Dockum climate are largely based on the assumption of similarity. However, recent work in the Dockum Group has uncovered a dominance of upper flow regime storm sheets and channels in outcrop. These structures and bedforms have yet to be interpreted in the Chinle, yet they play an integral part in understanding the climate within the larger Triassic system. Due to both the paleolatitude and the landward positioning of the Dockum Group at the time of deposition, a megamonsoon hypothesis is proposed to explain the occurrence of these upper flow regime structures. The megamonsoon hypothesis states that the pressure differentials generated by the heating of a landmass the size of Pangea could generate monsoonal storms magnitudes larger than any modern storms.

Calculating a paleodischarge from the upper flow regime channels and storm sheets aids in confirming the megamonsoon hypothesis. These hydrologic calculations within the context of stacking relationships between upper and lower flow regime lithofacies assemblages tells a more complete story of how this weather phenomenon affected the deposition of the Dockum Group.

The strata of the Dockum Group are dominated by upper flow regime channels whereas the lower flow regime channels are the exception. The lower flow regime channels are primarily secondary channels located on the floodplain, and they represent low-stage channels from the floodout events. The key to unlocking the Dockum Group relies on understanding the hydrologic setting of the upper flow regime channels and sheets and putting that knowledge into a larger scale paleogeographic reconstruction. With further knowledge on how the Dockum system functioned, new light is shed on the Triassic climate system as a whole.