Now that I've seen a fair amount of the Cambrian rocks of St. Croix National Scenic Riverway and the St. Croix Valley, it seems like a good time to set them out as was done for the MNRRA formations. This time around, we'll go to the base of the Cambrian sequence in Minnesota/Wisconsin and work our way up to where the sequence overlaps with the MNRRA rocks. One day I'll have to get into southeastern Minnesota and complete the Paleozoic sequence with the rest of the Ordovician and the Devonian.
As with the MNRRA formations, we're covering a fairly narrow span of time. The Cambrian formations were all deposited between about 500 to 491 million years ago based on biostratigraphic correlations. This includes some unconformities. One other note: I'm working from the Minnesota side of the St. Croix River, and I'm most familiar with the Minnesota names. Mossler (2008) harmonized the stratigraphic nomenclature of Minnesota's Paleozoic rocks with the schemes used in neighboring states, but there is still one difference: the Minnesota Geological Survey uses lithological terms in formation names, while the Wisconsin Geological & Natural History Survey doesn't. The upshot is slightly different names. For example, the units called the Jordan Sandstone and Oneota Dolomite on the Minnesota side of the river are called the Jordan Formation and Oneota Formation on the Wisconsin side. There isn't really a practical difference; the names just look different. In ascending order, the rock units we're most concerned with are the Mount Simon Sandstone, Eau Claire Formation, Wonewoc Sandstone, Tunnel City Group, St. Lawrence Formation, and Jordan Sandstone.
Sunday, January 28, 2018
Sunday, January 14, 2018
Pride of priority for the first new nonavian dinosaur of 2018 (not counting any of those "available online before 2018 but not in print" guys) goes to Diluvicursor pickeringi, a small ornithopod from Australia. It's the kind of dinosaur that would have been called a hypsilophodont 20 years ago, which means today there's always a chance it ends up outside of Ornithopoda or within Iguanodontia. (Honestly, if your phylogenetic analysis puts all of the old-time hypsilophodonts outside of Ornithopoda, you might as well just abandon the name "Ornithopoda" and go with Iguanodontia for the remainder.)
Sunday, January 7, 2018
For 2018's first post, I once again peer into the mists of futurity and offer dinosaur-centric predictions on the year to come.
|Will I once again be called upon to fight a mammoth inside a building? Well, that's always the dream.