Pedological Iron/Al Extracts, Clast Analysis, and Coleoptera from Antarctic Paleosol 831: Evidence of a Middle Miocene or Earlier Climatic Optimum

摘要

An unusual and remarkable find of fossilized Coleoptera exoskeletons, soil organics/plant roots, and microbes-recovered from an alpine-age paleosol in moraine at New Mountain near the Taylor Glacier in the Antarctic Dry Valleys-provides evidence for an ameliorative Early to middle Miocene Climatic Optimum (MMCO). Compared with the microbial analysis of other nearby and somewhat younger paleosols (sites 827-829) in nearby moraine deposits at both New Mountain and Aztec Mountain (sites that are known to contain bacteria and fungi), paleosol horizons at the alpine-age site (831) contain prolific fossil evidence of either an expanded MMCO or an earlier Early Miocene/Oligocene age. Together with fossil filamentous forms of either algae or fungi and bacteria, these Coleoptera exoskeletons make up part of a higher-altitude tundra ecosystem distantly related to a many-fold increase in terrestrial pollen and woody plants that inhabited the Dry Valley Coast similar to 15 Ma or earlier. While the age of the 831 paleosol as discussed elsewhere is impossible to assess with precision, the presence of a mix of subround/subangular sands-a high percentage carrying V-shaped percussion cracks-signals significant aqueous transport, with the sediment believed to have been deposited before the transition from warm/wet to cold/dry ice. In addition, fossilized organics including salt-encrusted earth, roots, and clay/mineral coatings on both sands and biogenic specimens-suggest at least an early cold/semihumid environment conducive to weathering, probably mediated by microbe activity. Other chemical indices reported previously are here analyzed with extractable Fe/Al, which suggests greater antiquity, possibly Early Miocene or Oligocene.