What type of depositional environment must have existed in Death Valley from lat

Question

What type of depositional environment must have existed in Death Valley from late Paleozoic to early Mesozoic time, when a 20,000-ft thick section of limestone and dolomite rocks was deposited?

No sedimentary rocks of Jurassic through Eocene age have been found in the park. What geologic process(es) was/were operating along western N. America during this period?

What are the main sources of fresh water today in Death Valley? What geologic features would the water come out of?

What animal would you find in some of these water bodies?

Explanation / Answer

By about 550 million years ago the Death Valley area had switched marine depositional environments from sandy mudflats to a shallow sea of warm, clear water in which the main types of rock being deposited were carbonates, forming thick Paleozoic limestone and dolomite formations. These deposits were evidence of thrust-faulting and mountain-building processes that were happening north of the Death Valley area and would eventually be arriving in the area.Total thickness uncertain because of faulting; estimated 2,000 feet (600 m).

Not represented, area was being eroded.Erosion over many millions of years created a relatively featureless plain. Thirty-five million years ago, sluggish streams migrated laterally over its surface. Several other similar formations were also laid down.

Several of the larger Death Valley springs derive their water from a regional aquifer, which extends as far east as southern Nevada and Utah. Much of the water in this aquifer has been there for many thousands of years, since the Pleistocene ice ages, when the climate was cooler and wetter. Today's drier climate does not provide enough precipitation to recharge the aquifer at the rate at which water is being withdrawn.his ecoregion contains some of the most extreme conditions inhabited by freshwater life and its biota has been extensively studied. Ash Meadows, covering an area of about 756 km2, is of particular interest, as its more than 30 springs and seeps create an oasis in the middle of the desert (Williams et al. 1985). Devils Hole is the highest in elevation of these springs, at 732 m. With increasing elevation, springs have been isolated from each other for a longer time, and springs only a kilometer apart may have been isolated for thousands of years (Williams et al. 1985). In this arid area groundwater recharge is so slow that the aquifers supplying springs such as Devils Hole contain fossil water .

Despite its bone-dry landscape, Death Valley is home to thousands of pupfish. The colorful, sardine-like fish live in isolated waterholes only a few feet wide.With the exception of the fish in the Owens River and Mojave River basins, all of the endemic freshwater species in this ecoregion are associated with springs or spring margins. Given the minute amount of freshwater available in this ecoregion, this biodiversity is truly impressive.The endemic fish come from four families, with subspecies of two minnows (Rhinichthys osculus and Gila bicolor), one sucker species (Catostomus fumeiventris), the extinct Ash Meadows killifish (Empetrichthys merriami), and four pupfish (Cyprinodon radiosus, C. diabolis, C. nevadensis, and C. salinus). Of these, five subspecies of C. nevadensis and two of C. salinus are recognized, as are three subspecies of speckled dace (R. osculus) (Sada et al. 1995). The Devil’s Hole pupfish (C. diabolis) is distinguished by having the smallest range of any vertebrate species—23 square yards in a spring-fed, limestone cavern in Ash Meadows.

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