Monday, April 11, 2016

A Single "Moment" in Geologic Time: A Finder of Lost Worlds in Death Valley

Red Pass in the Grapevine Mountains, Titus Canyon Road
Death Valley is one of the premier paleontology parks in the entire National Park system. There is a stunningly complete record of fossil-bearing strata extending over nearly a billion years, including rocks from every period of the Paleozoic era (543-251 million years ago). The Paleozoic era was a critical period of Earth's history, having seen the first appearance of most of the most important (i.e., diverse and common) animals and plants. There were the marine invertebrates like the brachiopods, corals, bryozoans, gastropods, cephalopods, pelycypods, and graptolites. There were the first fish, the first amphibians, and the first reptiles. There was the first invasion of the land by plants and animals. In fact, the only major groups that didn't evolve in Paleozoic time were dinosaurs, birds and mammals. 
Outcrop of the Titus Canyon Formation along Titus Canyon Road
Even the Grand Canyon is missing vast swaths of geologic time from the Paleozoic, including the entire Ordovician and Silurian periods.  Death Valley is truly unique, but when we start a discussion of the next two geologic eras, Death Valley is lacking in some respects. The thing is, if we are going to see exposures of the oldest rocks, rocks that are usually buried deep in the crust, than something has to happen to bring them to the surface. At Death Valley, only one layer can be found from the Mesozoic era (251-65 million years), and it's from the earliest period, the Triassic. There are Jurassic and Cretaceous rocks, but they are intrusive in nature, having formed deep in the crust from molten magma (granite and related rocks). Although dinosaurs and early mammals no doubt roamed the landscape many miles above, no record remains of their existence at Death Valley, as the rocks were uplifted and eroded away long ago.
Exposures of the Titus Canyon formation
The situation is the same for the Cenozoic era (65 million years to the present). In most parts of the park, Cenozoic rocks can be found, but none are more than 14 million years old. In other words, there is a gap of well over two hundred million years at Death Valley for which no fossil records can be found. Except for a single moment in time 34 million years ago...
Titus Canyon Road above Titanothere Canyon
Death Valley was proclaimed as a national monument in 1933 by the only U.S. president who had a career as a geologist, Herbert Hoover. A newly graduated geologist named H. Donald Curry was appointed as the first ranger/naturalist at the park. In his role, he provided evening programs for park visitors and did research during the day. He mapped large areas of the park, and was the first to describe the enigmatic turtleback surfaces that led to the discovery of an entirely new kind of fault, the detachment fault.
Upper Titus Canyon at Red Pass
Some blasting was being done to clear a road to Leadfield and down Titus Canyon. Curry noticed the rocks in the upper canyon were sedimentary, and that a skull was exposed in one of the roadcuts. It turned out to be the first discovery of a Titanothere west of the Rocky Mountains, and an entirely new species to boot (it's now called Protitanops curryi, after Curry). Further work revealed numerous other fossils as well, including Mesohippus (one of the earliest of horses), Colodon (a species of tapir), Teletaceras (a primitive Rhinoceros), Protoreodon (extinct species of artiodactyl, distantly related to modern cows, deer, pigs, and camel), and Leptomeryx (a small deer-like ruminant). Other fossils included early species of rodent, fish, and turtles.
Titanothere (Source: Wikipedia)
In other words, Curry had stumbled across a snapshot of a single moment in time that provides us a look at the world that existed after the dinosaurs had been extirpated. Mammals were working themselves into dominance of the rapidly changing terrestrial environments of the early Cenozoic era (they were in a rather intense competition for a time with the birds). That these sediments were preserved at all is lucky, as rocks of similar age are found nowhere else in the region. Somehow the so-called Titus Canyon formation was not eroded even though all the rocks dating from the time of the dinosaurs had disappeared, as well as those from the first thirty million years of the Cenozoic era. It would be another twenty million years before other sedimentary rocks would be preserved in the Death Valley region (the Artist Drive formation, 14 million years ago).
Mesohippus, an early horse species found in the Titus Canyon formation of Death Valley (from Wikipedia)

The Titus Canyon formation is composed of conglomerate, sandstone, calcareous mudstone, algal limestone, and tuffaceous sandstone, preserving what once was a savanna environment with adjacent forests. Although rocks like the Titus Canyon aren't found elsewhere in Death Valley, rocks of similar age are found in southern California (the Sespe formation), and west of the Sierra Nevada in the Great Valley (Ione formation).
Figure 147: The holotype skull and mandible of Protitanops curryi (LACM/CIT 1854). (A) Left view, (B) lateral view of right external auditory pseudomeatus, (C) dorsal view slightly rotated to the left, (D) anterior view, (E) posterior view.
The type specimen of the Protitanops curryi. A replica was on display for many years in the Death Valley National Park visitor center Source: Researchgate
This has been part of an off and on series about our February visit to Death Valley National Park. We were following the gravel road that crosses the Grapevine Mountains and descends through Titus Canyon. The road is accessible by most cars, though high clearance is recommended, and travel is definitely not recommended in bad weather (the road passes through a narrow canyon in the lower reaches). From here, we were about to pass through an upside-down mountain range!

1 comment:

Anonymous said...

Great post on Death Valley. Always enjoy your NPS posts and insights to the geology.

If you've not seen this post over at Running from Moose, she too hits on one of the more fascinating paleontology aspects there

Her 1950s era picture of the camelid and felid tracks is backwards.

-an anonymous NPS person.