Paleo-Environmental Interpretation of Basalt-Derived Paleosols.

Clayey or earthy red layers intercalated in basalt flows are known from several parts of the world. Though described in detail in several studies, their origin has remained somewhat obscure. For some, they represent meteoric weathering products, such as soils (paleosols); for others they are the result of the hydrothermal alteration of basalt. In some cases the differentiation is difficult. Among the major reasons for these difficulties is the "fritting" or "baking" that affects many of these layers.

The reported ages of these layers extend from subrecent to Precambrian. The study of paleosols is of interest because of their value as paleo-environmental indicators. Features of the paleosols, and particularly their mineral composition, chemical composition and weathering pattern, can be used for paleoclimatic interpretation. In the case of basalt-derived paleosols, the interpretative value is increased because of the fairly homogeneous nature of the basaltic parent-material and the possibility of relating the paleosol characteristics to those of modern soils formed on similar basalt. If the ages of the associated basalt-flows can be determined, valuable information on past climatic conditions can be derived. Thus, paleosols preserved in basalt sequences  South Africa, Western Australia, the Deccan Traps, and Columbia River basalt provided high resolution paleoclimatic recording of terrestrial environment during times of mass extinction (Permian-Triassic, Cretateous-Tertiary) or climatic change (middle Miocene). Equilibrium models to simulate formation of the paleosol, mineral assemblages and mass balance characteristics serve to reconstruct paleoclimate parameters such as paleoprecipitation and paleotemperature. Element mobility patterns of Fe give clues as to composition of paleoatmosphere. Structural elements (wedge-shaped aggregates, cutans, slickensides) suggest type of paleosol and, by proxy, paleoclimate. Some Cretaceous and Tertiary basalt-derived paleosols in Europe and Israel have a clay mineralogy that distinctly indicates warm and moist climates, sharply differentiating them from modern pedological clay formation