Abstract
Four diamicton facies occur in end moraines located in the Animas River valley of the San Juan Mountains, southwestern Colorado. Pebble fabric, grain size, sedimentary structures, and stratigraphic relationships with associated fluvial sediment are used to interpret diamicton origin. (1) A massive, matrix-dominated diamicton with abundant silt is ubiquitous in the Animas City II and III end moraines. This facies has a weak fabric (Si eigenvalues of 0.4 to 0.7), and is interbedded with sandy and pebbly fluvial sediment. This facies is interpreted to be sediment-gravity-flow deposit. (2) A matrix-dominated diamicton with color bands and strong fabric (Si = 0.7 to 0.9) occurs at one site in the Animas City III end moraine, and is interpreted to be meltout till. (3) A clast-dominated diamicton with weak fabric (Si = 0.4 to 0.6) and interbedded silty to pebbly fluvial sediment occurs in places in the Animas City II and III moraines and is interpreted to be either a sediment-gravity-flow deposit or fluvial sediment. (4) A compact, matrix-dominated diamicton with weak fabric (Si = 0.5 to 0.7) occurs in the Baker's Bridge moraine. Bedrock striations at the base of the diamicton, lodgedboulder striations within the diamicton, and a prominent pebble-fabric mode reveal a strong N 30? W trend. This sediment is interpreted to be lodgement till.
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