Sedimentology and stratigraphy of Upper Triassic carbonate and clastic strata of the Chulitna terrane, Alaska Range, south-central Alaska

The Chulitna terrane of the southern Alaska Range is one of the more enigmatic tectonic terranes in the North American Cordillera and is defined in part by the occurrence of Upper Triassic red bed and carbonate units that occur in association with basalt and serpentinite in the Alaska Range suture zone. New geologic mapping and measured stratigraphic sections of Upper Triassic strata from the Chulitna terrane reveal a continuous record of siliciclastic, volcaniclastic, and carbonate sedimentation. Red bed units consist largely of interbedded successions of poorly-sorted and matrix-supported sandstone, siltstone, and conglomerate. Individual beds are typically 0.25--2 m thick and exhibit tabular geometries. Upper Triassic units in the Chulitna terrane were originally thought to represent three distinct successions that were stratigraphically unrelated. However, measured sections revel that carbonate and red bed units are interbedded throughout the Chulitna terrane. Clastic and carbonate strata are interpreted to represent deposition in a marginal marine fan-delta complex characterized largely by debris flow processes, fluvial-deltaic and beach-barrier island sedimentation, as well as lagoon and carbonate reef/bank sedimentation. Upper Triassic carbonate and clastic strata of the Chulitna terrane are interpreted to represent sedimentation associated with an isolated period of exhumation and clastic sedimentation, bimodal volcanism, and carbonate precipitation during at the end of the Triassic.