Geohydrologic significance of lithofacies of the Carrizo Sand of Arkansas, Louisiana, and Texas and the Meridian Sand of Mississippi

Abstract

The study of the Carrizo and Meridian Sands is the fourth part of an investigation of the geohydrology of the Claiborne Group. The regional dip of the Carrizo and Meridian Sands is into the Desha basin, Mississippi embayment, and gulf coast geosyncline. Some movement of major structural features took place during Carrizo and Meridian time. Normal faulting is rather extensive in southern Arkansas and in Texas. The thickness of the Carrizo and Meridian Sands varies from 0 in areas of nondeposition to a maximum of 700-750 feet in De Witt and Karnes Counties, Tex. The Carrizo and Meridian Sands are lithologically almost uniform, being composed of more than 80 percent sand in about three-fourths of the area of study. In Arkansas, Louisiana, Mississippi, and part of eastern Texas, the formations were deposited as valley and channel fills and as beach sands over an irregular erosional surface. The Carrizo Sand over most of Texas was deposited as alongshore and nearshore bar and beach sands. Aquifer tests indicate that the coefficient of permeability increases with increase in sand-unit thickness, but the range in values in the Carrizo and Meridian Sands is not as great as the range in values found in the other Claiborne aquifer formations. The areas of highest transmissivity of the formations are in west-central Mississippi and in southern Texas. Recharge to the Carrizo and Meridian Sands takes place by infiltration of precipitation in the outcrop area and by infiltration'of water from streams. Natural discharge from the Carrizo and Meridian Sands occurs primarily by leakage through the overlying confining beds. Regional flow of water in the formations is generally down the dip of the formations except where modified by long-term heavy withdrawals and in southern Texas where thick sand in the overlying Reklaw and Queen City Formations facilitates the escape of water from the Carrizo because of increased vertical permeability. In Mississippi and Texas the dominant anion is bicarbonate in water from the Carrizo and Meridian Sands from depths of 1,700 to more than 2,500 feet. In Arkansas and Louisiana, chloride is the dominant anion below depths of 500-1,000 feet. Appreciable amounts of sulfate have been found in water from the Carrizo Sand in Texas to depths of more than 2,000 feet. Sodium is the dominant cation in water from the Carrizo and Meridian Sands of Arkansas, Louisiana, and eastern Texas. Calcium and magnesium occur in significant amounts in water from the Carrizo Sand in southern Texas to depths greater than 2,900 feet below land surface. The distribution of the dissolved-solids content of water from the Carrizo and Meridian Sands reflects the influence of geologic and hydrologic factors on water movement and the extent of flushing of the formations by fresh water. INTRODUCTION