Depositional Setting of the Triassic Dockum Group, Texas Panhandle Eastern New Mexico

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McGowen, J. H.
Granata, G.
Seni, Steven J.

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The upper Triassic Dockum Group accumulated in relict Paleozoic basins defined in Texas by the Amarillo Uplift on the north and the Glass Mountains on the south. These basins were reactivated during the late Paleozoic or early Mesozoic by tectonic activity that was probably related to the opening of the Gulf of Mexico. As basins subsided and some relict positive elements were uplifted, sedimentation rates increased.

More than 2,000 ft (610 m) of terrigenous elastics, derived chiefly from Paleozoic sedimentary rocks, accumulated within the basin. Source areas were in Texas, Oklahoma, and New Mexico; sediment transport was from the south, east, north, and west. The Dockum Group accumulated in a variety of depositional environments including: (1) braided and meandering streams; (2) alluvial fans and fan deltas; (3) distributary-type lacustrine deltas (high-constructive elongate deltas); (4) ephemeral and relatively long-lived lakes; and (5) mud flats.

Alternation of wet and dry climate caused cyclic sedimentation in the Dockum. The main control on climate was most likely tectonism. During wet periods, lake level was relatively stable. Meandering streams supplied sediment to high-constructive elongate deltas in the central basin area of Texas and New Mexico, whereas braided streams and fan deltas were dominant depositional elements along southern and northern basin margins. Lake area and depth decreased when dry conditions prevailed. Under these conditions, base level was lowered, valleys were cut into older Dockum deposits, and small fan deltas were built into ephemeral lakes; evaporites, calcretes, silcretes, and soils developed upon emergent surfaces ranging from floors of ephemeral lakes to delta platforms.


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