Paleoclimate deduced from some early Jurassic basalt-derived paleosols from northern Israel

Earthy red layers, intercalated amid basalt flows from an early Jurassic, 2500 m thick volcanic sequence in northern Israel were examined mineralogically, micromorphologically and chemically. Distinct pedological features, such as wavy illuviation argillans and iron oxide nodules, observed by micromorphological examinations, identified the clayrich layers as basalt-derived paleosols. The clay (<2 μm) fraction was low in bases (compared to normative basalt) and relatively enriched in Fe and Al. The dominant clay mineral was smectite, accompanied in one paleosol by appreciable kaolinite. Crystalline iron oxides, particularly hematite, were present in all paleosols. DCB extractable Fe was high, and was concentrated in the non-clay fractions. Chemistry and mineralogy of the paleosols, suggested possible identification with Vertisols. Though buried at great depth (3000 m), the clay minerals had not been affected by diagenesis, i.e. the swelling properties of smectite had been preserved. This was attributed to low K contents in the basalt, and high density of the paleosolic material. By comparison with the mineralogy and micromorphology of modern basalt-derived Vertisols, a moderately wet, mediterranean-type climate with pronounced seasonality was inferred for the formation time of the paleosols. A similar Lower Jurassic paleoclimate had previously been inferred from a paleosol in the Negev.