Death Valley National Park geology, Part IV: Neogene and Quaternary

Very low-level photo across the salt flats of Badwater

...And finally we reach the top of the stratigraphic column at Death Valley National Park (DEVA). For convenience, here are the links to Parts I, II, and III. A lot of geologists just love the most recent 23 or so million years of Death Valley geology. For one thing, it gives people fantastic fodder for arguments about when various events happened, their extent, and even the basic mechanisms. DEVA features not only the pull-apart tectonics of the Basin and Range, but also lateral movements on strike-slip faults. As a result, there are depositional basins of a wide range of sizes. Terminology is a bit of a nightmare. The Wiki page on Death Valley geology isn't bad, but its strat column isn't a patch on the glorious Cenozoic complexity lurking in the park.

Death Valley National Park geology, Part III: Mesozoic through Paleogene

We made it out of the Precambrian. We made it out of the Paleozoic. We aren't nearly out of Death Valley, though. There's still about 250 million years to go, during which the valley was converted from marine property to land, became gently toasted by massive subterranean plutons, and was eventually pulled apart into the modern topography over about 15-20 million years of nonstop faulting, with volcanic eruptions and inland lakes thrown in for variety.

And the state fossil of Minnesota is...

...nothing. Despite the map on "List of U.S. state fossils" [note, 2018/2/22: this has since been fixed], Minnesota does not have an official state fossil. There was a push to draft the giant beaver into this position, but the rodent fell short. The immediate political reason for its failure can be grasped from its scientific name: Castoroides ohioensis. Should the state fossil of Minnesota refer to another state? Certainly not!

Death Valley National Park geology, Part II: Cambrian through Permian

When we left Death Valley National Park (DEVA) last week, we'd gotten partway through the Cambrian, into the early stages of a passive continental margin with shallow marine deposition. We return to find that predictable shallow marine deposition held sway until fairly late in the Paleozoic, when things got complicated in a hurry.

Death Valley National Park geology, Part I: Proterozoic to Cambrian

As I mentioned a few months ago, one of the main components of my day job over the past few years has been preparing paleontological resource summaries for National Park Service Inventory and Monitoring networks. Between new and updated summaries, I've completed ten (Greater Yellowstone, Mediterranean Coast, Northern Colorado Plateau, Northern Great Plains, Northeast Coastal and Barrier, Northeast Temperate, Sonoran Desert, Southeast Coast, Southern Colorado Plateau, and Southern Plains). Each network has its own foibles and presents different challenges. Some are much more easily tackled than others; smaller parks generally have less to worry about than larger parks, with small urban cultural or historical units usually being the simplest. After finishing the Southern Plains Network last spring, I knew that the Mojave Desert Network (MOJN) would be one of the obvious candidates for the next project. It was completed under a superseded format, so it was already in the hopper, and we were already working with Death Valley National Park and Lake Mead National Recreation Area, so the iron was hot. The attraction for me was the challenge. The MOJN parks have superb geological records exposed by the combination of Basin and Range faulting and restricted plant cover, and they cover vast areas.

Mostly bryos and burrows

It's still a little early to be out and about in the metro rocks and expect good luck (for one thing, the Decorah is still in winter-spring-transition mud mode) or consistent weather, but we're getting close, and sooner than usual. Here's one seasonal photo and then a few interesting pieces I hadn't featured before. These are all photos of Decorah Shale fossils from the St. Paul side of the river.

Lower Decorah a couple of weeks ago, after having been relatively warm and dry for several days. These two fragments were covered with half-burrows (imagine a tubular burrow split along its long axis), and several other pieces from the same area and probably a similar stratigraphic level had the same kind of abundant half-burrows.

Meroktenos thabanensis: not Early Jurassic, just ahead of its time

It's been about a month since Meroktenos thabanensis made its (re)appearance, but I'm just now getting around to it. A bunch of other topics muscled ahead of it, which is fitting, I suppose. Prosauropods (by which the reader should understand "sauropodomorphs what ain't sauropods"; if you should want me to write "basal sauropodomorph" over and over again instead, I accept large cash bribes) are among those dinosaurs which never seem to get much respect. They have been fertile subjects for arm-waving, though, one result of which being that a survey of popular-audience dinosaur books will turn up wildly differing depictions over the years. Bipedal or quadrupedal? Herbivorous, omnivorous, predatory, or scavenging? A stem leading into sauropods, a bunch of rungs, or a distinct empire of prosauropods? Gleefully extreme lumping or splitting? What about herrerasaurids? What about Teratosaurus? (if that last one means anything to you, congratulations, you're in your mid-30s or older, or you study rauisuchids.) Prosauropods have also not been helped by a certain vague uniformity of body shape, nor have they been done any favors by geography. North America has an unimpressive record for these dinosaurs, so far including Anchisaurus (let's not kid ourselves about Ammosaurus being distinct), Sarahsaurus, Seitaad, the unnamed Nova Scotia form, and odds and ends. For a group that did not have horns, frills, spikes, bony armor, crests, ridge-backs, spectacular size, or big pointy teeth, and had the poor sense to go extinct before the appearance of tyrannosaurs or dromies to prey upon them, not being well-represented in North America has not helped their exposure. But I digress.