Origin, Classification, and Geologic History of Caliche on the Southern High Plains, Texas and Eastern New Mexico

Abstract

The caliche profiles on the southern High Plains, Texas and eastern New Mexico, are of Pliocene, Pleistocene, and Holocene age. The Pliocene caliche is colloquially known as the "caprock." Differences in age, physical factors, and chemistry allow classification of the caliche into young, mature, and old types. Young caliche is incompetent and powdery except when formed as a laminated zone over an underlying plugged profile. Mature caliche is characteristically nodular, grading downward into old caliche which contains diagenetic quartz. Massive caliches form on semiarid, rapidly aggrading, flat surfaces of desert loess (regional eolian sand ergs), on thick calcareous sands providing local climate fluctuates between humid and semiarid, and on near-surface carbonate rocks. The base and sequential development of the caliche, regardless of parent material, are determined by extent and amount of infiltration of water during humid periods following accumulation of calcareous loess, permeability of the parent material, and rapidity of plugging in the caliche profile. Caliche anticlines, or expansion structures, form only in mature caliche or preexisting carbonates due to expansion of the entire zone caused by filling of horizontal and vertical desiccation cracks by vadose silt and calcareous dripstone. The horizontal desiccation cracks are termed "buckle cracks." The most intense expansion structures form on interbedded lacustrine clays and sands; however, isolated structures due to other causes, such as solution and collapse, injection of lacustrine clays, or structures which antedate the caliche, also exist. Induration of the upper part of a thick caliche results mainly from exposure, induration of the lower part of the profile resulting from deposition of diagenetic quartz and carbonate.