Wheeling in Eocene Delta Sediments
As noted in the prologue post, we moved back in time as we travel northeast, just as in driving to NE Alabama. The difference between these two drives is the time-interval covered by our 8-hour drive; we time-traveled 330 my (million years) to go to AL whereas the trip to TX only covered about 60 my.
The ancestral Appalachian Mtns. were located all along the eastern seaboard as they still are today. All of those rocks and the titanic collision with Africa pushed the earth’s crust downward as well as upward, as vast quantities of sediment were eroded from the rapidly rising mountains. Thus, the Mississippian Era (~330 mya) rocks deposited in NE AL were buried deep (and produced oil and coal because of it), but the crust has rebounded over the last several HUNDRED million years and these old, previously deeply buried sediments from a delta are now exposed at Hawk Pride ORV park.
When I drove to Gilmer, instead of seeing a regular, albeit incomplete (due to erosion) stack of sediments, I drove over Pleistocene (<2 mya) terraces produced by changes in sea level on a relatively stable coastline. There were also missing rocks as in Mississippi, especially the gap between the Pleistocene terraces (~2 mya) and the Miocene rocks we encountered near Natchitoches (~20 mya), and the even longer diastem (missing rocks) between the Miocene and Eocene sediments we will see in Gilmer (~40 mya). As we get into older sediments, they become more uniform (i.e. the smooth transition from Eocene to Paleocene near the TX-LA border on I-20.
This post is intended to remind me of the similarity of the rocks and history on the east and west sides of the MS embayment, which has little to do with the ancestral Appalachians but it does overprint its impacts on the older ones…We must always think 4-dimensionally with geology…LOL