Retallack 2007 Proserpina principle - University of Oregon

Record of Past Soil and Global Change 15Figure 10Deep clastic dike in a coal of the Weller Coal Measures of the Allan Hills, Antarctica, interpretedas infill of periglacial polygonal patterned ground (E. S. Krull for scale).sedimentary rocks near Lochinvar in southeasternAustralia (Retallack, 1999a). Taiga(polar forest) paleosols with discontinuous permafrostdeformation are found in Early Permianred beds near Kiama, also in southeasternAustralia (Retallack, 1999b).Milankovitch-scale temporal variation in climateand sea level has long been recognized incyclothemic sedimentation in North Americanpaleotropical Carboniferous marginal marinesequences, and this in turn has been relatedto ice-volume fluctuations on the south polarGondwana supercontinent (Rasbury et al.,1998; Miller and West, 1998). Full glacial coalseams (Histosols) alternating with interglacialmarine rocks are a clear indication of thesechanges. Environmental alternations of fullglacial,dry, calcareous, swelling-clay soils(Vertisols), and interglacial, wet, decalcified,forest soils (Alfisols) indicate a terrestrialcontribution to multimillenial-scale change inatmospheric greenhouse gases and paleoclimate(Retallack, 1995).By Middle Devonian time, the evolution ofincreasingly larger plants culminated in treeswith trunks up to 1.5 m in diameter, whichleave obvious large root traces in paleosols(Driese et al., 1997), as well as abundant permineralizedstumps and logs (Meyer-Berthaudet al., 1999). Middle Devonian paleosols arealso the oldest known with clay-enriched subsurfacehorizons (argillic horizons of SoilSurvey Staff, 1999). The clay in modern forestsoils is partly formed by weathering in place,and is partly washed down root holes, whichtaper strongly downward in forest trees. Evidenceof both neoformation and illuviation ofclay can be seen in thin sections of Devonianforested paleosols (Retallack, 1997b).Latest Devonian paleosols also include coalsfrom the oldest woody peats. Thin peats ofherbaceous plant remains such as the RhynieChert of Scotland (Rice et al., 1995) and theBarzass coal of Siberia (Krassilov, 1981) arefound in Early Devonian rocks, but by the latestDevonian (Algeo and Scheckler, 1998) andinto the Carboniferous, woody coals becamewidespread and thick (Figure 9d). Carbon consumptionby accelerated weathering in forestsoils and carbon burial in coals are widely acknowledgedas the likely cause for mass balanceestimates of Late Paleozoic highatmospheric oxygen levels (perhaps 35 vol.%)and near-modern CO 2 levels (Berner et al.,2000). Low Permian atmospheric CO 2 levelsare also confirmed by stomatal index studies(Retallack, 2001b). These atmospheric trendsand coeval changes in oceanic Mg/Ca ratiocould be attributed to changes in volcanic andhydrothermal activity, particularly at midoceanridges (Stanley and Hardie, 1999).However, the abundance of Early Paleozoicpedogenic dolomite, but Late Paleozoic andNeogene pedogenic calcite (Retallack, 1985,1993), suggests a role for soils in these changesin oceanic ionic chemistry, as well as inchanging atmospheric CO 2 levels.5.18.3.8 Triassic–Jurassic GreenhousePaleosolsGreenhouse paleoclimates right from thevery beginning of the Mesozoic have beenrevealed by discovery of deeply weatheredpaleosols in earliest Triassic rocks of Antarctica(Figure 11), which even at that time was at