ELL Rx Paleogeography 2011 - EAS 1700, The Rock Cycle,...

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EAS 1700, The Rock Cycle, Sediment, and Paleogeography Page 1 of 8 9 February 2011 T HE R OCK C YCLE , S EDIMENT , AND P ALEOGEOGRAPHY I NTRODUCTION All parts of the earth system are involved in one great geochemical cycle. The mainly solar- powered parts are known as the exogenic cycle ; and the mostly fission-powered parts, featured in the first laboratory exercise, are known as the endogenic cycle . The rock cycle exists at the interface between the two, as accompanying diagrams explain. The sedimentary rock featured in the exercise on stratigraphic correlation and the time scale represents material that was caught at one stage in the rock cycle sometime between the Cambrian and Devonian, and has stayed there ever since. Uplift and erosion begin the recycling of one generation of rock into another, most often by way of sediment. Uplift and erosion are concentrated in episodes of mountain building like the one that left the Taconic unconformity as a big bite out of the Cambrian-Silurian correlation chart: the Taconic Orogeny. Typically, the route to the next generation of sedimentary rocks begins in eroding uplands along the boundary of a tectonic plate, and runs downhill from there along a course something like this: Weathering 1 : weathering to “immature” sediment (generally close to source): CO 2 + H 2 O + igneous rock (feldspar, mica, quartz) rock fragments + ions in solution weathering to “mature” sediment (generally far downstream from source): CO 2 + H 2 O + rock fragments quartz + clays + ions in solution Deposition of siliciclastics (mostly in sedimentary basins downstream from the mountains): deposition of “immature” sediment (generally in basins along the plate boundary): rock fragments redbeds (on continents) or graywacke (along volcanic arcs) deposition of “mature” sediment (farther downstream and commonly far from plate boundaries): quartz + clay quartz sandstone + clay shale Deposition of carbonates
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ELL Rx Paleogeography 2011 - EAS 1700, The Rock Cycle,...

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