KARST REGIONS OF TEXAS
by A. Richard Smith and George Veni
(with minor additions by William R. Elliott)
INTRODUCTION
Why divide Texas into karst regions? It aids in understanding
the histories of karst areas. It helps us compare and contrast different
karst styles and their relationships to regional geology and geomorphology.
And it provides insight to the types and extents of caves to be found in
each region.
The karst regions described here are delimited on several
criteria: geomorphology and geomorphic history, stratigraphy, structure,
cave density and types. Obviously, karst requires soluble rocks. Are these
thin limestone beds interbedded with sandstone and shale (North Texas)
or are they massive gypsum beds (Gypsum Plain)? Are they highly fractured
with many joints and faults guiding cave orientations (Balcones Fault Zone)
or are fractures less important to cave development (Maverick Basin)? Does
the area consist of isolated, high-relief mountains (Block-faulted Ranges)
or flat, low-relief plains (Northwest Texas)? Are the caves principally
horizontal stream conduits (Lampasas Cut Plain) or vertical shafts which
transmit water to humanly inaccessible conduits (Devils River Trend)? Clearly,
distinct karst regions in Texas can be defined, as we have done below.
We also describe a few areas of pseudokarst deserving notice. The regions
and subregions are shown in a linked
map of Texas
karst and pseudokarst.
Texas karst regions are divided into three main categories
based on rock type. The carbonate regions include those areas where caves
are almost entirely formed in limestone or dolomite, although a few are
in interbedded gypsum. Gypsum area caves are mostly in gypsum, although
some caves are in interbedded dolomite. Pseudokarst regions contain caves
in rocks that are much less soluble than limestone or that formed by means
other than solution. Although isolated pseudo-karst caves occur throughout
Texas, only those areas with several caves of similar origin are presented.
SUMMARY
Texas caves have developed from a highly diverse range of geologic conditions. Some areas stand out as exceptionally good cave-formers while others are cave-poor. Preliminary attempts to compare the density of caves within the regions outlined in this report demonstrates that this scale does not yield meaningful results. A more detailed analysis is needed. About 9,000 caves, sinkholes, and rock shelters are known in Texas. Surveys for new caves continue in many karst areas. Nearly 2,000 caves have been added to the Texas Speleological Survey's database during the past ten years-a trend that seems certain to continue for many more years. This work should prove invaluable to better defining and delimiting the karst regions of Texas, and to advancing the conceptual basis of cave development.
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