The Apennine Front Core 15007/8: Irradiational and depositional history

Abstract

Ferromagnetic resonance (FMR), magnetic, and noble gas measurements were made on soils from the Apennine Front core 15007/8 as part of a multidisciplinary study. Values of the Is/FeO surface exposure (maturity) index and FeO concentrations are reported for 0.5 cm depth intervals; noble gas and FMR data are reported for 13 soils and 2 clasts selected from various depths in the ∼57‐cm‐long core. These data, along with mineralogical and stratigraphic data reported by others, indicate four major core units whose contacts are at ∼18, 49, and 55 cm. An in situ reworking zone at the top of the core is not indicated by the Is/FeO data, and the cosmogenic gas data show that the core soils have experienced multistage exposure to cosmic rays. The 0–18 cm unit has values of cosmogenic 131Xe/ 126Xe that are higher than underlying soil and are indicative of irradiation at average depths >50 cm; thus this unit cannot have a simple irradiational relationship to soil beneath it. This unit is probably the ejecta from the crater on whose rim the core was collected. The 18–49 cm unit is characterized by relatively constant values of Is/FeO and abundances of cosmogenic gases and most likely represents a soil zone well mixed, possibly by downslope movement during the precrater era. Is/FeO drops by about 30 units at the 49‐cm contact. The two units below it are correspondingly more immature than overlying soil and, in addition, contain soils with either high concentrations of green glass or relatively low FeO contents. The significant heterogenetics in these two units indicate they have not been involved in the mixing layer which is presumed to occur due to downslope soil movement. Comparison of the 15007/8 core to other cores suggests that soils on slopes tend to be mixed and not contain units with long in situ irradiation profiles. Such cores are less likely to contain old or exotic soil layers.