STRATIGRAPHIC FACIES DEVELOPMENT IN A LOWER JURASSIC FOREARC BASIN, TALKEETNA FORMATION, SOUTH-CENTRAL ALASKA

The Lower Jurassic Talkeetna Formation of south-central Alaska represents the most complete exposure of accreted arc volcanic and volcaniclastic rocks yet documented. Detailed interpretation of facies development within this sequence is essential to an understanding of the tectonic processes that operated during the evolution of this arc. We present the most complete stratigraphic analysis available of the Talkeetna volcanic and volcaniclastic sequence, and compare the Talkeetna facies array with modern intra-oceanic arc analogs. The dominance of reworked primary volcanic material and proximal mass-flow deposits within the Talkeetna Formation implies proximal forearc deposition rather than more distal trench-slope sedimentation. Forearc and backarc facies are inferred on the basis of stratigraphic evolution in combination with geochemical characteristics. The sedimentary history of the Talkeetna Arc is consistent with its evolution above a north-dipping subduction zone, prior to the collision of this terrane with North America.