SUBSIDENCE ANALYSIS AND SEDIMENTOLOGY INDICATES A WRENCH BASIN FOR THE WESTERN PORTION OF THE TAOS TROUGH (Invited Presentation)

The Taos trough is a late Paleozoic basin that accumulated sediments derived from uplifted Precambrian-cored blocks during the ancestral Rocky Mountain orogenic event. Proposed models of the basin evolution are conflicting. One model suggests that basin subsidence was driven by thrust-loading of the western margin of the basin. Whereas, the other model proposes a wrench basin where the western margin is a strike-slip fault. In the wrench model, basin subsidence is assumed to be driven by block rotation during intrabasinal thrusting coupled with a dip-slip component along the Picuris-Pecos fault.

A composite stratigraphic column, compiled from localities in the axis of the Taos trough, was subjected to backstripping to assess the magnitude and duration of subsidence. Using a combination of existing biostratigraphic control and new conodont biostratigraphy, subsidence began in the Early Pennsylvanian, reached the highest rate and magnitude in the Desmoinesian, and then greatly diminished by Late Pennsylvanian. An uptick in subsidence rate and magnitude occurred in the early Permian before essentially ceasing by the end of the Leonardian. Magnitude and duration of subsidence most closely compare to geohistory curves of basins located in strike-slip settings.

Sediment transport indicators in shallow marine facies demonstrate transport directions that range from southwest to northwest. Nonmarine directional transport indicators predominantly align in a southwest direction. This data signals an eastern provenance for the study area. Pennsylvanian strata form a growth syncline adjacent to Laramide-aged thrusts in the Taos trough indicating these thrusts were also active in the Pennsylvanian. Thus, intrabasinal Precambrian-cored thrust blocks are the preferred provenance region rather than the far-field Sierra Grande uplift.

This analysis demonstrates that structural models for the Taos trough must be compatible with strain partitioning that allows north-south dextral strike-slip motion and east-verging thrusts. For the western Taos trough, subsidence analysis and sediment transport indicators are most consistent with the proposed wrench model. However, subsidence for the eastern portion of the Taos trough region may largely have been through thrust loading.