Fossils Found And Not Found In Western Louisiana

[Oxytropidoceras]

For all of the week of May 27^th, I was out in the field geological mapping with other geologists as a part of an ongoing compilation of a new geological map for the Natchitoches 30 by 60 degree quadrangle in western Louisiana. The purpose of this trip was to ground truth the linework for the geological mapping that is being compiled and resolve questions about conflicts in the various interpretations of the regional geology made by previous geologists. Although fossil collecting was not the objective of this trip, a number of fossil-bearing type locations and other outcrops of specific stratigraphic units were visited along any outcrop that could be found. As a result, a number of reported fossil locations were visited as a part of obtaining information about the geology of the area and general characteristics of the different stratigraphic units. Also, we looked out for fossils as a part of the geologic mapping.

The mapping went well from a logistical standpoint. The weather was sunny with some clouds. It rained a few times. However, the rain occurred during our lunch stops and was not enough to get the roads muddy to any degree. As happens in the field, we spent the usual 10 hours a day. But that is life as a field geologist and we got lots of ground covered. Besides, it is always nice to get out of the office with other geologists and actually deal with real dirt and rock instead of dealing with rather abstract material such as well logs and LiDAR DEMs.

What was found was that the vast majority of previously published outcrops, including all of the published fossil-bearing outcrops, that we visited were either very, very badly degraded or simply gone. The outcrops and associated fossil locations that were reported from roadcuts along highways had all been cut back, graded, and sodded. The only exposures that we found in these roadcuts where because of the acidic, solid rock, or other adverse nature of sediments, the establishment of grass cover failed and bald spots formed. As a result, some of the underlying sediments have been exposed by gullying and sheet erosion. For example, in one large and long bald spot in a roadcut along Highway 171 near Many, Louisiana, a 0.5 m thick lignite bed is exposed and a large, partially carbonize log was observed in it. Selenite crystals occur about 1 to 2 m above the lignite bed. Presumably, the selenite is related to the decay of pyrite in the lignite bed and associated carbonaceous, laminate silts and clays. I looked for fossil leaves, but found nothing but unidentifiable fragments.

Along parish roads, the exposures in roadcuts and ditches that were visited have naturally been largely covered by colluvium and slumping and overgrown by grass and trees. For example, the reported outcrops of the Ostrea thirsae zone in the Marthaville, Louisiana, area were found to be gone. They have either been naturally or artificially covered and grown over. Similarly, previously reported outcrops of the Logansport Formation were found to be either completely overgrown or in such poor conditions that no fossils were observed. At best, they only provided a minimum and basic information about the general lithology of this stratigraphic unit.

The bluffs along the Red River in this area also are in a very sad state of affairs. The “channelization” of the Red River and addition of locks and dams to it has largely stopped the meandering of its channel. As a result, the bluffs along it are no longer being kept clean by ongoing bank erosion. As a result, they have slumped and are now grown over. For example, during previous geological mapping, the well-known fossiliferous Montgomery Landing (Creole Bluff) was visited and found to be completely slumped and overgrown with dense vegetation. The large bluff at Grand Ecore, Louisiana, is still relatively intact. However, only one point of land access, involving lots of poison ivy and steep slopes, was found. No fossils were observed. Only some rather interesting concretions were found and examined.

However, the USACE Grand Ecore Visitor Center is worth visiting. It has some really nice exhibits about local fossils, archaeology, history, and natural history. There, a person can see Civil War earthworks and full-size replica of the Basilosaurus cetoides (Owen) skull found at Montgomery Landing (Creole Bluff).

In case of the Sabine River, the condition of localities is worst. The type localities and fossil locations associated with Sabine River cutbanks and shoals have been for decades submerged beneath Toledo Bend Reservoir. These important outcrops and fossil locations are simply gone forever.

We did find a number of small outcrops of various formations in borrow and dirt pits. Although these were useful for purposes of our geological mapping, none of them yielded any fossils.

The extensive destruction and severe degradation of many of the outcrops described in the published literature is quite discouraging. Although the general lithology and paleontology of them has been documented on a basic level, detailed sedimentological and taphonomy studies have not been made on the vast majority of them. The primary exception is the former bluff at Montgomery Landing. It will be extremely difficult for anyone to examine in greater detail the depositional environments and taphonomy of regional fossil-bearing strata, i.e. the “crab zone” in the Crockett Formation and Ostrea thirsae zone of the Marthaville Formation, unless new outcrops of them can be found.

There will be one more trip to look at outcrops in the Natchitoches 30 by 60 degree quadrangle in western Louisiana. I am working getting permission to visit some dirt pits and mines that we lacked permission to visit during this last trip. At this point, I am gathering any information that I can find about outcrops, which can be visited. Any suggestions that members of this list might have about outcrops to visit, even if they do not contains fossils, would be very greatly appreciated via personal messenger or my work email. Since the ongoing work involves a regional geologic map, there are no plans to publish any of the information collected for this research about outcrops and fossil locations.

The location of the Natchitoches 30 by 60 degree quadrangle can be seen in http://www.academia.edu/3676946/Index_Map_of_Current_Louisiana_Geological_Mapping_as_of_Jaunary_2013

Finally, I might note, that any questions about Louisiana geology and fossils are welcome via private messenger or offlist email.

Some online material:

USACE Grand Ecore Visitor Center - http://www.mvk.usace.army.mil/Missions/Recreation/GrandEcoreVisitorCenter.aspx

Index of Current Louisiana Geological Mapping http://www.scribd.com/doc/83277046/Geologic-Map-Index-of-Louisiana-January-2013

Hunting for Fossils in Louisiana - http://appl027.lsu.edu/MNSEducation/VirtualMuseum/3-Fossils%20in%20LA%20Gravels/Sophie%20-%20Hunting%20for%20fossils%20in%20gravels.ppt

Fossil Hunting in Louisiana Gravels - http://appl027.lsu.edu/MNSEducation/Saturday/Hunting%20for%20Fossils%203.pdf

Yours,

Paul H.

Fossil log found in roadcut near Many, Louisiana. In it, the pick handle is 40 cm

long.

Grand Encore Bluff at Grand Encore, Louisiana, http://en.wikipedia.org/wiki/Grand_Ecore,_Louisiana

Edited June 9, 2013 by Oxytropidoceras

[Plantguy]

Hi Paul, thanks for the interesting read! I wish I had something but I have nothing to offer with Louisiana geology unfortunately--been only thru the state in passing!

Just a quick post though to follow on your observations. I haven't been in some parts of the country in years but have been using Google earth to look at and retrace some of my road cut/highway field outings from 30-40 years ago. Its been remarkable for me and sometimes gut wrenching to see the changes and sites that no longer exist thru development, vegetative growth and erosion. If I had only known I would have done some more serious collecting back then....uggh!

Thanks for your post! Regards, Chris

Edited June 10, 2013 by Plantguy