Lonestar Jamboree 2015: Prologue

The next series of posts discuss the geologic time travel across the Mississippi Embayment into Texas. My destination is Barnwell Mtn Recreational Area, which is run by the state, unlike Hawk Pride, a private park. Before I can get to Texas, however, I must cross the down-warped Cenozoic (<65 mya) rocks of the MS embayment. I am going to try and take pictures of the contacts seen in the below image as I drive up, because I have installed the WordPress Ap on my phone (good luck with that!). Thus, I won't say much here…

la geologic map

These rocks are time-synchronous with the rocks I briefly described as I drove to Hawk Pride last month, but they are different because the sediments that formed them were further from a source of erosion (i.e. Ancestral Southern Appalachian Mountains). This trip, as I drive northwest, the rocks get progressively older because of the down-warping beneath the MS river (note that erosion removed any rocks that were exposed to the wind and rain…etc).

This photo shows the geologic map of NE TX, with the park indicated by a black circle. The oldest rocks I will encounter are Eocene Claiborne Group sedimentary rocks, which were deposited in an environment just like the mouth of the MS River today!

tx geologic map

The dominant rock type in the park (Gilmer, TX, Ushur County) is a sandstone, but anyone who has been wheeling there will tell you about the sticky! mud. The name of the primary stratigraphic unit (aka formation) is the Queen City Sandstone (a group comprises several formations), but I bet there is some mud in there if the sediments were deposited in a delta front environment!

This topographic map, with the very rough outline of the park, shows the topographic relief to be about 200 feet, but the park encompasses the entire mountain. I hope to see if I can identify changes in the sedimentary facies within this small area.

park topography

Looking forward to a great time-travel trip…see you then!

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