Abstract

Within a 100-mile radius of Junction, Kimble County, Texas, secondary calcium carbonate, commonly called caliche, occurs (1) as soft pulverulent material at small folds and collapse structures in limestone and at certain outcrops of calcareous shales and spongy dolomites, (2) as adherent coatings on limestone boulders lying on poorly drained surfaces, and (3) as the well-known duricrust deposits cementing limestone gravel and colluvial rubble.

Field observations of the lateral gradation of limestone strata into soft caliche and petrographic evidence of the replacement of coarse calcite by microcrystalline calcium carbonate in coated boulders indicate that in the first two types of occurrence the caliche has not been brought in from overlying soil or rocks by migrating water but has formed in place by solution and reprecipitation of calcium carbonate as a result of alternate wetting and drying of the limestone. The senior author tried unsuccessfully to duplicate this process in the laboratory.

Small anticlines having arches filled with caliche, southeast of Junction, resemble the “pseudo-anticlines” in Mexico described by Price, but evidence of the in situ formation of the caliche suggests that the folding may have been caused by the expansion accompanying hydration of anhydrite associated with the Kirschberg Evaporite of Barnes, and that the caliche is the result rather than the cause of the distortion and folding of the limestone.

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