Soil Survey of Karnes County, Texas - Soil Data Mart - US ...

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(15). The Fleming Formation has a higher proportion
of overbank clayey sediments than the Oakville
Sandstone.
The formations are topped mainly by the Coy-
Monteola and the Weesatche-Pernitas general soil
map units. The Oakville Sandstone corresponds to
the Coy-Monteola general soil map unit. The Fleming
Formation corresponds to the Weesatche-Pernitas
general soil map unit. Soils of the Coy-Monteola unit
have clayey substrates and were probably formed
in overbank, flood basin muds. Soils of the
Weesatche-Pernitas unit have loamy substrates
and were probably formed on crevasse splays and
levee materials. The minor Shiner soils, which have
sandstone substrates, are on coarser channel and
point bar deposits.
Goliad Formation
The Goliad Formation overlies the Fleming
Formation and is Miocene (8) or Pliocene (15) in age.
The Goliad Formation is fluvial in origin with probable
paleo-Blanco and paleo-San Antonio River sources
(15). The outstanding feature of the Goliad Formation
is the thick surface deposits of caliche that indicate its
presence in most places in south Texas. Below the
caliche cap, the formation contains clays and sands,
some cross-bedded, and conglomerates of siliceous
gravels, most of which in near-surface, shallow
exposures and quarries have calcium carbonate
matrices or cements. The Goliad Formation in Karnes
County crops out in isolated outliers in the
southeastern part of the county. To the southeast in
Goliad and Bee counties, it is exposed in continuous
tracts.
The origin of the caliche in the Goliad Formation, as
well as in other parts of Texas and the southwestern
United States, has generated considerable literature
(10). The dominant viewpoint is that the caliche
accumulates from the top down, mostly from
atmospheric additions as dry dust falls, or from
precipitation (9). Several stages are recognized as
the pore space in the soil is filled by precipitated
calcium carbonate carried by percolating rain water.
The final stages include the formation of a “plugged
horizon” in which the grain-to-grain contacts of the
soil or sediment are lost and the grains are “floating”
in a matrix of calcium carbonate. Downward
percolation is reduced, resulting in a final impervious
“laminar horizon” (petrocalcic horizon) stage. This
horizon, with continued impeded drainage and
increments of calcium carbonate, accumulates in an
upward direction.
Pleistocene Terraces, Eolian Deposits, and
Holocene Alluvium
The Geologic Atlas of Texas shows Pleistocene
deposits along the San Antonio River, Ecleto Creek,
and Cibolo Creek (4).
No single general soil map unit seems to be
dedicated to the “fluviatile terrace deposits.” This
is probably because the soils are a mixture of upland
soils and soils that have been influenced by, or added
to, by eolian activity. The closest approximation for
features with a fluvial terrace morphology is the
Papalote-Nusil general soil map unit. The obviously
eolian-influenced soils, especially the Nusil and the
Rhymes soils, are not all on terraces. Some of these
materials may be the remnants of obscure unmapped
terraces and some may be wind-transported from
areas of well-defined terraces.
The Holocene alluvium is in the major stream
valleys, including the San Antonio River. The alluvium
consists of clays, silts, and fine sands. The Holocene
alluvium is well defined by the Sinton-Buchel-Zunker
general soil map unit. The Buchel soils are clayey and
are on flood basin deposits. The loamy Sinton soils
and the sandy Zunker soils are on the point bar and
levee deposits.