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Geology of the National Parks - Death Valley

 

click for timescale Death Valley National Park through time

Illustration on the way
Striped Butte in Butte Valley. Steeply tilted limestone beds of the Permian Anvil Spring Formation. A major fault behind the butte separates it from Precambrian Noonday and Johnnie Formation rocks, about 1/2-billion years older.

Death Valley- Caribbean-style: Middle Cambrian to Permian time

The sandy mudflats gave way about 550 million years ago to a carbonate platform which lasted for the next 300 million years of Paleozoic time. Erosion had so subdued nearby parts of the continent that rivers ran clear, no longer supplying abundant sand and silt to the continental shelf. Since, in addition, Death Valley's position was then within ten or twenty degrees of the Paleozoic equator, the combination of a warm sunlit climate and clear mud-free waters promoted prolific organic carbonate production. Just as in the bays, lagoons, banks, and channels of the Bahamas and Florida today, the skeletal disintegration of countless generations of flourishing corals, shellfish, and algae created a wealth of lime mud and sand. When buried by yet more sediment, this consolidated into the limestone and dolomite formations, more than two miles thick, which today comprise Death Valley's craggiest terrain. Such rocks are especially prominent in the Grapevine and Cottonwood Mountains, along the rugged northeast wall of Furnace Creek Wash, and on the lower slopes of the Panamint Range from Death Valley Canyon to Tucki Mountain. Thickest of these units is the dolomitic Bonanza King Formation which forms the dark-and- Iight-banded lower slopes of Pyramid Peak and the gorges of Titus and Grotto Canyons.

Although details of geography varied during this immense interval of time, a north-northeasterly trending coastline generally ran from Arizona up through Utah. A marine carbonate platform only tens of feet deep but more than 100 miles wide stretched westward to a fringing rim of offshore reefs. (One such reef is still identifiable in rocks of Ordovician age twenty miles east of Death Valley on Meiklejohn Peak above the town of Beatty.) Down gentle slopes to the west of such rims of reefs, limy mud and sand eroded by storm waves from the reefs and platform collected on the quieter ocean floor at depths of 100 feet or so. Death Valley's carbonates appear to represent all three environments (down-slope basin, reef, and back-reef platform) owing to fluctuating geographic position of the reef-line itself.

The extent and stability of this great shallow carbonate-rich sea are not matched in today's restless world. Caribbean analogs are tiny by comparison. The low-lying Paleozoic continent had far less freeboard than does rugged North America today, so inland encroachment of shallow shelf-seas was much more extensive.

The carbonate uniformity was seriously interrupted only twice. (1) About 450 million years ago, an immense sheet of pure quartz sand swept across the platform to produce the 400-foot thick Eureka Quartzite. This great white band of Ordovician rock stands out on the summit of Pyramid Peak, widely near the Racetrack, and high on the east shoulder of Tucki Mountain. No American source is known for the Eureka sand, which once blanketed a 150,000 square-mile belt from California to Alberta. It may have been swept southward by longshore currents from an eroding sandstone terrain in Canada, but the origin of both the Eureka and contemporaneous sands blanketing much of the Midwest remains shrouded in mystery. (2) Between 350 and 250 million years ago sporadic pulses of mud swept southward into the Death Valley region during the erosion of highlands in north-central Nevada. These occasional brief interruptions of carbonate formation were warnings of momentous events, thrust-faulting and mountain-building, already in progress well to the north and eventually to overwhelm the Death Valley area as well. For the brachiopods, ostracods, corals, and clams the days were numbered. The billion- year-old marine shelf was soon to dry up, the coastline to shift far to the west.

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