A large part of the Gulf Coast of the United States and the Gulf of Mexico is underlain at depth with deposits of bedded salt. In the Gulf Coast geosyncline the salt probably reaches a depth of 30,000–40,000 feet, as indicated by geophysical profiles. At such depths, the temperature of the connate salt is calculated to be about 450°–500° F. Because the plasticity of salt increases rapidly with rise in temperature, movement of salt upward through the overlying sediments would be greatly facilitated at the high connate temperature; and the formation of salt structures, such as domes and stocks, can be more easily explained. In certain exploratory wells drilled in southwest Texas on or near salt structures, the temperatures within or adjacent to the salt are much higher than those that would be expected to be present according to the normal geothermal gradient. These abnormally high temperatures may be caused by the salt in these structures having retained much of its connate temperature as it moved upward toward the surface.

The rate and depth of pedogenic carbonate accumulation in soils formed in Quaternary alluvium may be viewed as a theoretical problem that involves the mutual interaction of several independent and dependent soil-forming variables. We propose a model for carbonate accumulation in which the soil column is defined by a vertical sequence of 1-cm 2 -area compartments, each with a specified texture, bulk density, water-holding content, lithologic and mineralogic composition, soil-air pCO 2 , ionic strength, and temperature. On the basis of these data, rates of carbonate solubility and dissolution within a given compartment are determined. In arkosic to lithic arkosic sandy parent materials, high carbonate solubility (0.137 to 0.212 mg/ml) and the large reactive surface area of eolian calcareous dust result in rapid carbonate dissolution (0.79 to 9.92 × 10 −10 g/cm 2 /sec) that promotes rapid translocation of carbonate by infiltrating water. We derive a group of equations and use them to calculate net carbonate depletion or accumulation in a soil compartment over an interval of time as a function of the independent variables temperature and precipitation. These two variables largely determine or strongly influence soil-water balance, the external carbonate influx rate, and carbonate solubility. The carbonate distribution that our model predicts closely resembles the observed carbonate distribution in soils associated with Holocene deposits forming in arid, hyperthermic to xeric, thermic moisture-temperature regimes in southern California. This modeling indicates that with a mean carbonate influx rate of 1 × 10 −4 g/cm 2 /yr and in a semiarid, thermic climate, the maximum depression of the top of the Cca horizon is attained within only a few thousand years. In contrast, given the same influx rate, our model predicts that a noncalcareous B horizon cannot form in an arid, hyperthermic climate, a conclusion supported by field and laboratory studies of calcic soils in this climate. The influence of glacial-to-interglacial climatic changes on carbonate accumulation can be modeled by calculating latest Pleistocene soil-water balance with the aid of published estimates of full-glacial temperature and precipitation. On the basis of these modeling results, we propose that either of two types of glacial-to-interglacial climatic changes may account for the strongly bimodal, apparently polygenetic carbonate distribution that is observed in late Pleistocene soils of the eastern Mojave Desert of southern California. Such results of compartment-strategy modeling are encouraging and indicate the great potential of combined theoretical and empirical methods for considering pedological problems of interest to Quaternary geologists.

Abstract The paleosol–carbonate CO 2 barometer is widely accepted to be the most reliable method for reconstructing Earth’s atmospheric CO 2 concentrations in deep time. Currently, the largest source of error in atmospheric CO 2 calculated using the paleosol barometer originates from uncertainty in soil CO 2 concentrations during soil carbonate formation. Many of the paleosols used for CO 2 reconstruction were formed in clay-rich alluvium and have vertic properties, which may influence soil CO 2 .We hypothesized that the cracking during drying of shrink–swell clays results in rapid CO 2 escape and low soil CO 2 concentrations. We tested our hypothesis by monitoring soil cracking and the concentration of CO 2 in the pore spaces of surface Vertisols (the Houston Black and Heiden series fine, smectitic, thermic Udic Haplusterts). Crack porosity of soils was estimated by measuring soil subsidence, and CO 2 was measured in syringe samples collected from soil gas wells. During the period of study, pore-space CO 2 concentrations at ~1-m soil depth varied by two orders of magnitude, from 10% during water-saturated conditions to <0.1% during hot, dry episodes. These large seasonal variations likely result in significant calcite dissolution and reprecipitation during pedogenesis. Soil CO 2 concentrations decreased as soil-crack porosity increased. Moreover a compilation of published records of soil CO 2 variability indicates that the variability of CO 2 concentrations in Vertisols is significantly larger than the variability in other soil orders, regardless of climate or vegetation. These results suggest that soil cracking is a primary control on soil CO 2 in Vertisols and that a soil-order-specific calibration of the paleosol barometer should be developed for application to clay-rich paleosols with soil cracks and/or pedogenic slickensides.