Paleoclimate of Antarctica reconstructed from clast weathering rind analysis

Previous analysis of extractable Fe/Al in paleosols near New Mountain, Antarctica, suggests a pre-Middle Miocene, possibly Late Oligocene-Early Miocene age for paleosol 831 emplaced during the alpine event prior to the growth of the Inland Ice Sheet. Recent analysis of weathering zones in clasts with encrusted Fe/salts from the pebble pavement overlying the 831 paleosol reveals a succession of three weathering zones in a sandstone clast that record a paleoclimate transitioning from warm/wet (temperate) to cold/dry (polar). The first zone corresponds to an association of quartz cemented with berthierine (smectite-serpentine) and illite clay minerals. The second zone transitional from weathered clast to Na-encrusted rind contains smaller amounts of berthierine and illite formed in grains of partially dissolved quartz with minor salt content. Zone three corresponds to an ~ 3 mm (3 × 106 nm) thick mass of porous nitrate and gypsum. The contact between zones 2 and 3 appears to be correlative with the transition from temperate to polar ice which is considered to have occurred prior to or coincident with the Middle Miocene Climatic Optimum.