EPSC 201 Lecture Notes - Lecture 17: Metamorphic Reaction, Clastic Rock, Dune
26 Jan 2017
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Document Summary
Ripple marks are frequently preserved in sandy sediments. Found on bedding surfaces of ancient sedimentary rocks: dunes are similar to ripples except they are much larger (tens of cm to hundreds of m). They occur in streams and in desert or beach regions from water- or wind- transported sand: cross beds created by ripple and dune migration. Sediment moves up the gentle side of a ripple or dune. Sediment piles up, then slips down the steep face. Added sediment forms sloping cross beds: bed-surface markings occur after deposition while sediment is still soft. They indicate alternate wet and dry terrestrial conditions. Fossil footprints evidence of past life: depositional environments are locations where sediment accumulates. In glacial environments, sediments are created, transported, and deposited by the actions of moving glacial ice. A common feature of this environment is glacial till, a poorly sorted mixture of all grain sizes, gravel, sand, silt, and clay.
