And now we come to the last part, and the reason I started this in the first place: National Park Service Cenozoic nonmarine sedimentary rocks and deposits. I had advance knowledge that the theme for this year's National Fossil Day features would be the Cenozoic, so I thought I'd tag along.
Sunday, January 25, 2015
Sunday, January 18, 2015
Quite a number of NPS units record some form of Cenozoic igneous activity, from the obvious (active volcanoes) to the subtle (rock formations that are composed of volcanic debris, or ancient lake deposits that were laid down after a lava flow blocked a river). Restricting the category to just those with Cenozoic igneous rocks still nets quite a few. I decided to go with just those where the igneous rocks are responsible for a headline attraction, or make up a significant part of the bedrock. I've got both a map and a spreadsheet of igneous activity in geologic time, and as you go through you may notice a few patterns. First, a lot of the featured parks have fairly recent activity, roughly Miocene to the present, a span of about 23 million years. Part of this is a natural bias of erosion (younger, less-eroded igneous features are more impressive than old, worn-down features), and part of this is due to the timing of the eruptions themselves. Volcanism on the Rio Grande Rift of New Mexico began shortly before 23 Ma, Great Basin volcanism began around the same time, the Yellowstone Hotspot trail has only been traced back around 16 million years, and the volcanoes of the Hawaii parks only poked out from the ocean during the Pleistocene. Another feature is location. There is a nice arc through southern Alaska, and clusters in northern California–southern Oregon, around the Great Basin–Mojave Desert, in New Mexico, and eastern Idaho–northwestern Wyoming, which correspond to centers of igneous activity.
Sunday, January 11, 2015
I thought it might be interesting to briefly highlight some National Park Service units in terms of geology, and started working in the Cenozoic Era (66 million years ago to the present; you can get a fresh new geologic time scale here). The draft became quite long, so I chopped out the igneous and terrestrial sedimentary parts for later and collected the smaller headings. Many of the following parks have been detailed in NPS Geologic Resource Division publications and maps, which can be found here.
Sunday, January 4, 2015
Winter in the U.S. is not the best time for looking for fossils. It's cold, the days are short, and a significant portion of the ground is covered with snow and ice. There are, however, other places to see fossils than in the field, some of which you may pass every day. Many buildings include fossil-bearing stone, representing sites around the world.