kimerajamm
Joined: 28 Nov 2010
Posts: 785
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 Posted: Sat May 07, 2011 4:16 pm Post subject: filling sediment |
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On these basement rocks was deposited the sedimentary formation of the Pahrump Group. This occurred after uplift-associated erosion removed whatever rocks covered the Proterozoic-aged rocks. The Pahrump is composed of arkose conglomerate (quartz clasts in a concrete-like matrix) and mud stone in its lower part, followed by dolomite from carbonate banks topped by algal mats in stromatolites, and finished with basin-filling sediment derived from the above, including possible glacial till from the hypothesized Snowball Earth glaciation.[27] The very youngest rocks in the Pahrump Group are from basaltic lava flows.
The Noonday Dolomite was formed from a carbonate shelf after the break-up of Rodinia.
[edit] Rifting and deposition
A rift opened and subsequently flooded the region as part of the breakup of the supercontinent Rodinia in the Neoproterozoic (by about 755 million years ago) and the creation of the Pacific Ocean. A shoreline similar to the present Atlantic Ocean margin of the United States lay to the east. An algal mat-covered carbonate bank was deposited, forming the Noonday Dolomite.[28] Subsidence of the region occurred as the continental crust thinned and the newly formed Pacific widened, forming the Ibex Formation. An angular unconformity (an uneven gap in the geologic record) followed.
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