In this lecture we return to the Late Devonian/ Early Mississippian to discuss the Antler Orogeny. In this image we see the sheared and folded deep water sediments of the distal Antler marine basin thrust over and emplaced on top of the shallow water deposits of the continental margin. It is uncertain how and why these deep water sediments were thrust up and over the continental edge extending from southern California to Alaska. We have a good idea that they were not transported much more than a few hundred kilometers as the sediments contain fossils of North American affinity but lack and volcanic or Arc materials. As we will discuss in a few slides, some believe that the edge or North America began to collapse and sink. This allowed the oceanic materials to overlap the continental edge. To understand the story of what happened when, we rely on the sediments deposited at the time that the events were occurring. The Antler foredeep (introduced in a previous lecture) records the sediments derived from the mountain building event that occurred as the deep-water sediment overrode the shallow sediments. In the foredeep, we see both sediments derived locally off the topographically high Antler thrust sheet and those from the long traveling continental rivers. The Antler sediments, transported from the west are composed of conglomeratic deposits composed of cherts, shales and other low-grade metamorphic rocks. Transported from the east, we find finer-grained, quartz-rich sediments that have traveled great distances (during transport, other minerals are eroded away, weathered or deposited, leaving quartz grains preferentially carried over large distances).
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