CTU - BLACKLAND PRAIRIE is TAYLOR MADE!
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Midas treasure
Blackland Prairie
Awaits Earthcache pleasure.
Come see where Bullhide Creek exposes how the Blackland Prairie is "Taylor" made.
Cache is on Crunk Road right-of-way, Falls County TX
CONGRATULATIONS TO CPRH FOR FTF!!!!
INTRODUCTION======================================
This is another in my series of earthcaches describing CTU or "Central Texas Underfoot."
Here we have a magnificent cutaway view of a stretch of Blackland Prairie; from its rocky roots to the rich, dark soil that gives the Prairie its name.
The coordinates bring you to a bridge crossing Bullhide Creek. The water has exposed the underlying "bedrock" (unweathered marls and mudstones) as well as some interesting cobbles and boulders.
Now why does that golden matrix turn so BLACK?
THE TEST ==========================================
(Paperless cachers have requested that the questions be placed to the front of the cache page -- so here they are. PLEASE read to the end -- you may find the answers to the questions in there. Besides, this is an earthcache -- you're supposed to learn something. =smile= Now.... let us begin.)
To log this Earthcache, please *email* (or message) me the answers to the following questions:
1> Is the Taylor Marl a strong or weak ‘rock’? What features (or lack thereof) in the streambed make you say so?
2> Observe the riparian habitat. Do you consider it rich (biodiverse) or poor? Why?
Now look at the plant life immediately at the edge of the water and in the streambed itself. Think of other streams you've visited (like Brushy Creek or San Marcos Springs). Is the stream itself a rich or poor plant habitat? Why do you think this might be? (The answer to question 1 is a strong hint.)
3> Given that younger geologic deposits tend to come out on top, why do you suppose these late Cretaceous formations (Austin Chalk & Taylor) dominate much lower elevations than the earlier Cretaceous formations of, say, the Glen Rose and Edwards to the West of Balcones Fault Zone; or, for that matter, the seriously ancient granites of Enchanted Rock?
4> The Taylor Group can be differentiated, after a manner, into two general formations. What are they called? [You don't have to Google, just read below. =wink=]
5> Why is it called the BLACK Prairie, and what behavior of the Taylor group contributes to that naming?
Logs without verification email will be regretfully deleted, though not without forewarning. If you visit as a group, a single representative email for the group is acceptable – but I expect good logs in exchange. [This is an Earthcache, you need to EARN your icon. Bwahahaha.]
If feasible, when you log, please include a picture taken at/from ground zero – with or without yourself and your party. [GPS not required in picture.]
LOGS WITH ACTUAL CONTENT ENCOURAGED!!!!
TEXAS GEOLOGY====================================
The geologic history of Texas is recorded in its rocks. Mountains, seas, rivers, volcanoes, and earthquakes, all add their chapters to this unfolding story, and the keen observer can read the ground like a history book, as the various strata document origins in billions of years of changing geography.
CENTRAL TEXAS UNDERFOOT==========================
The ground and underground of Central Texas is comprised of several geologic units. These include (in order of youngest to oldest): a top-dusting of alluvium, then, after a 70-million year (plus) gap, the Taylor Group, layered over the Austin Group (also called Austin Chalk), the Eagle Ford Formation, Buda Formation, Del Rio Claystone, Georgetown Formation, Edwards Limestone (which comprises the important aquifer and karst formations), Comanche Peak Limestone, Walnut Formation, and Glen Rose Formation.
The Balcones Fault Zone divides the limestones of the Texas Hill Country from the mudstones, marls, and "chalks" of the Blackland Prairie. Short of the igneous volcanism of the Pilot Knob area, nearly all of these rocks are estimated to be marine in origin, laid down in the advances and retreats of the Prehistoric Gulf of Mexico over the eons.
We are standing on the comparatively young Taylor Group, just downstream from Austin Chalk exposures. (No, sorry can't see them from here, I'll have to place another earthcache.)
TAYLOR GROUP ====================================
The youngest of the Cretaceous strata, deposited above the Austin Chalk in the Black Prairie region of Texas, is the Taylor Group -- also called "Taylor Marl." Firm rock strata here is rare enough to be exceptional: the Taylor Group being composed almost entirely of unindurated (e.g. neither compacted nor particularly cemented) layers. The beds are principally calcareous clays, marls, and mudstones, which weather so rapidly into a mantle of thick black soil that continuous sections of them cannot be seen or measured with accuracy. Therefore their thickness, sequence, and general character has been judged largely from well holes. In places, as at Corsicana, the Taylor Group is estimated to be fully 2,000 feet thick.
The Taylor Group can be differentiated, after a manner, into two general formations: the lower of which may be termed the Taylor (also called Ozan Formation) and the upper the Navarro. [Further reading: Geography and geology of the Black and Grand prairies, Texas, with detailed descriptions of the Cretaceous formations and special reference to artesian waters Publication 4171875. http://lib.utexas.edu/books/landscapes/publications/txu-oclc-4171875/txu-oclc-4171875-a-336.html]
While yellow in fresh exposures, Taylor and Austin Chalk ‘rock’ weather to a black waxy soil. In its lower portion, the Taylor Group is comparatively free from sand, but higher in the section the sand increases and quantities of glauconite occur. Glauconite is an iron potassium phyllosilicate (mica group) mineral of characteristic green color with very low weathering resistance and very friable [en.wikipedia.org/wiki/Glauconite and www.webmineral.com/data/Glauconite.shtml]. Not surprisingly, flora and fauna also change with the appearance of the glauconite, and to this portion of the beds the name Navarro is applied. [The geology of East Texas, Issue 1869 By Edwin Theodore Dumble, Southern Pacific Company, University of Texas. Division of Economic Geology http://books.google.com/books?id=SZ_PAAAAMAAJ&pg=PA23&lpg=PA23&dq=Taylor+Marl+geology&source=bl&ots=Se6frRAXGO&sig=K8h2FomGeso4wUqZvN142kIbZf0&hl=en&ei=8S69S5f-EIT48Abv--HpCA&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCUQ6AEwBw#v=onepage&q&f=false]
BULLHIDE CREEK ===================================
Where you stand, you can tell that Bullhide Creek is not a gravel-bed stream. The gravel/cobble substrates are highly imbedded with finer material and the channel is very active, with the sediments scouring the limestone bedrock . The wetted channel is much narrower, than, say, upstream reaches in the Austin Chalk (which tend to be much more ‘sculptural’ with stairsteps and multiple scoured channels), and meanders only slightly among the irregular gravel bars and vegetated terraces contained within the larger channel.
“Bullhide Creek is quite different from a typical Hill Country stream. The channel morphology and substrate composition are different, the riparian corridor is composed of different vegetation, and the surrounding landscape, particularly with respect to topography, soils and land use, differs substantially from that of the Hill Country. The water quality of Bullhide is entirely characteristic of the Blackland Prairie.” [Application of WMARSS for TPDES Permit No. WQ0014782001 Location of Change in Channel Substrate on Bullhide Creek; James Miertschin & Associates, Inc. Environmental Engineering http://www.wmarss.com/Forms/BullhideBed2.pdf]
BLACKLAND PRAIRIE =================================
“The Blackland Prairie is a special mixture of soil and mineral deposits that distinguishes the blackland ecosystem from other prairie and woodland types and supports its diverse array of plant and animal species. Described as ‘black velvet’ when freshly plowed and moistened from a good rain, true blackland soils are deep, dark, calcareous deposits renowned for their high productivity. Scientists believe the richness of the prairie soils is derived from the abundant invertebrate fauna and fungal flora found in the soils themselves. Dominant native grasses of the original prairie included Big Bluestem (Andropogon gerardii gerardii), Switch Grass (Panicum virgatum), Little Bluestem (Schizachyrium scoparium), and Indian Grass (Sorghastrum nutans). Several rare plant species are found on some of the prairies, including purple beard tongue (Penstemon cobea), and eared false foxglove (Tomanthera auriculata) in the Blackland Prairie of Arkansas. Steigman's crayfish (Procambarus sub geiardiella steigmani) is found on some larger prairies in North Central Texas. R.C. Anderson writes that the eastern prairies and grasslands ‘would mostly have disappeared if it had not been for the nearly annual burning of these grasslands by the North American Indians.’ In the West, as well, Indian burning also greatly extended the area of grasslands and reduced the area of forest.” [Preservation Society for Spring Creek Forest “The Blackland Prairie in NC Texas” http://www.springcreekforest.org/Blackland%20Prairie.htm]
The Blackland Prairie gets its name from its exceedingly dark soil, called the Houston Black clay (approximately 289 million acres in extent!). Dominating the Blackland Prairie region, as noted, it has developed from soft calcareous sediments, mostly marine (Cretaceous Austin Chalk and Taylor Marl), but in some extents is theorized to be partly of terrestrial origin (the Miocene age Lagarto clay is thought to be a terrestrial deposit). [The Clay Mineral Composition of Representative Soils from Five Geological Regions Of Texas * G. W. Kunze, E. H. Templin, and J, B. Page http://www.clays.org/journal/archive/volume%203/3-1-373.pdf
ENDNOTES=========================================
Excellent further reading on the various strata formations can be found in the documents at The University of Texas at Austin: Virtual Landscapes of Texas http://www.lib.utexas.edu/books/landscapes/ , particularly in the Fourth annual report of the Geological Survey of Texas Publication 5235917-4 http://www.lib.utexas.edu/books/landscapes/publications/txu-oclc-5235917-4/txu-oclc-5235917-4-a001a.html (their search function is very good)
Encyclopedia > Geology of Texas; http://www.statemaster.com/encyclopedia/Geology-of-Texas
Geologic maps of Texas: http://www.aeg-tx.org/geo.asp
Texas Geology - Map of Texas http://geology.com/states/texas.shtml
Fossils of Texas A Journey - http://fossilsoftexas.webs.com/formations.htm
Ozan Formation: “lower Taylor Marl” USGS “Mineral Resources On-Line Spatial Data “ http://tin.er.usgs.gov/geology/state/sgmc-unit.php?unit=TXKo%3B0
Texas blackland prairies (NA0814) http://www.worldwildlife.org/wildworld/profiles/terrestrial/na/na0814_full.html Texas blackland prairies (NA0814)
Native Prairies Association of Texas http://texasprairie.org/index.php/npat_prairies/region_info/blackland_prairies/
Blackland Prairie Ecological Region http://www.tpwd.state.tx.us/landwater/land/habitats/cross_timbers/ecoregions/blackland.phtml
And for something completely different: Geology at the University of Texas Coloring Book http://www.lib.utexas.edu/books/landscapes/publications/txu-oclc-244294995/txu-oclc-244294995.pdf
CONCLUSION ==========================================
I hope you enjoyed seeing this exposed classroom of Blackland Prairie dynamics. Geology is in action all around us, and the savvy cacher can read the land like a scout of yore could track quarry through the wilderness.
Again -- Logs without verification email will be regretfully deleted, though not without forewarning. If you visit as a group, a single representative email for the group is acceptable – but I expect good logs in exchange. [This is an Earthcache, you need to EARN your icon. Bwahahaha.]
If feasible, when you log, please include a picture taken at/from ground zero – with or without yourself and your party. [GPS not required in picture.]
LOGS WITH ACTUAL CONTENT ENCOURAGED!!!!
Thanks again! Cache on!
Additional Hints
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