DEEP-CALCIC PALEOSOLS AT TIMES OF OCEANIC ANOXIC EVENTS IN LATE DEVONIAN ROCKS OF PENNSYLVANIA

Depth to calcic horizon in paleosols of the Catskill Formation in central Pennsylvania is mostly 40-70 cm, but some paleosols have depth to calcic horizon as deep as 80-100 cm. A 12-m-thick zone of 3 deep-calcic paleosols is traceable for 100 km through Pennsylvania from the Hyner tetrapod locality south to Newport. Deep-calcic paleosols represent subhumid paleoclimatic episodes distinct from long-term semi-arid paleoclimate, judging from the relationship between mean annual precipitation and depth to calcic horizon in modern soils. A long sequence of Catskill Formation paleosols along state highway 11/15 south of Selinsgrove reveals 494 successive paleosols, including 4 separate groups of 1-4 deep-calcic paleosols, which represent 4 transient (<1 m. yr) pluvial episodes interrupting generally semi-arid conditions. Taking the upper Trimmers Rock Formation as early Frasnian and lower Spechty Kopf Formation conglomerates as basal Mississippian, these pluvial episodes are distributed through the formation at stratigraphic intervals with highly significant graphic correlation with Nehden, Condroz-Enkeberg, Annulata and Hangenberg marine black shales and oceanic anoxic events. This pedostratigraphic approach correlates the Hyner tetrapod locality with the Annulata marine event, which is 366 Ma in the Gradstein et al. (2005) time scale. This is close to the 363-365 Ma age estimated for the Hyner locality from spores of zone Fa2c. The projected level of the Frasnian-Famennian boundary and marine upper and lower Kellwasser black shale events has only non-calcareous paleosols in the Selinsgrove section, so cannot yet be identified in the field, but chemical analyses in progress may reveal Frasnian-Famennian paleoclimatic and other changes on land. Temporal coincidence of deep-calcic paleosols and black shales also is found at the end-Permian, when high terrestrial precipitation and oceanic stagnation were consequences of a transient carbon dioxide greenhouse. Thin Late Devonian black shales may also be consequences of short-lived ocean-atmospheric redox crises, rather than due to long-term events such as oceanic eutrophication following the evolution and spread of forest ecosystems.