Changes in rocks, changes in wheeling: Pride Mtn. Formation

As noted in the previous post, the Pride Mtn formation was dark shales and sandstones at the type locality I visited. The previous post discussed the younger (on top…Upper Mississippian…~330 mya) Harstelle Formation. This post shows some photos of the Pride Mtn Formation. After meeting Big Hill from Mountainside, I stopped and collected a hand sample, which is limestone (HCl fizzes in contact), and took a photo of the exposure. Here is the exposure, after hundreds of drive-overs by four-wheelers. 2015-04-09 11.05.26

Even after so much punishment, this bivalve (unknown to me at this time) survived! 2015-04-09 11.11.38

After driving around a while, I found this great exposure behind the barn near the bottom of Thompson’s Draw. The gray massive rock above is what I showed in the previous photo. The lower unit is more interesting… …2015-04-09 13.05.02

This exposure was accessible from the truck (the dogs were happy) and it showed this remarkable fossile bed, which includes Spiniferid brachiopods, bryozoan calyxes (kinda like spinal disks), and other fossils. I couldn’t get a hand sample of this, however… 2015-04-09 13.06.33

This kind of fossil assemblage is used to know were these rocks fit into geological time. The exposure photo above shows how different these layers appear but the following hand sample photos show how similar they are internally..first, the more massive layer from Big Hill: 2015-04-19 18.29.28

and then the fossiliferous layer from the barn…

2015-04-20 18.51.15

Weathering sometimes causes slight differences in limestone mineralogy (calcite) to accentuate fossils against their containing rock, as seen in the photo above with the fossil bed, even though the rock looks the same when broken apart. These limestones are described in the formal description of the Pride Mtn Formation, but what about the shales (i.e. mud)? I didn’t document the change from redder mud (from the overlying Hartselle FM) as I drove down Mountainside, but the mud (i.e. weathered shale) a Big Hill was darker. I will discuss this in the final post from Hawk Pride


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