Metamorphosed palaeosols associated with Cretaceous fossil forests, Alexander Island, Antarctica

Abstract

Fossil soils are present within mid-Cretaceous fluvial sediments of the Fossil Bluff Group, Alexander Island, Antarctica. The palaeosols contain in situ fossil trees and rooted plants. These palaeosols are typically composed of two dominant horizons: an upper organic-rich horizon with identifiable plant remains, and a lower horizon with well-developed blocky ped structures, clay cutans and mottling. These features are typical of modern soils in seasonally dry climates. Although evidence of flooding is apparent from interbedded fluvial sandstones and mudstones, the palaeosols indicate that this high-latitude mid-Cretaceous environment was predominantly seasonally dry. The presence of the zeolites laumontite, prehnite and pumpellyite indicates a later metamorphic overprint on the palaeosols, resulting from burial diagenesis of this region at depths of about 3.8–5.2 km and temperatures of 150–170 °C.