MICROSTRATIGRAPHY OF THE LOWER MISSISSIPPIAN SUNBURY SHALE - A RECORDOF SOLAR-MODULATED CLIMATIC CYCLICITY

Microstratigraphic analysis of the Sunbury Shale has yielded a high-re solution record of probable short-term climatic changes in the Early M ississippian central Appalachian basin. The formation is a laminated b lack shale that contains pervasive millimetre-thick couplets composed of alternating thin black and thick dark gray laminae, and decimetre-t hick bands that are alternately dark and light. Total organic carbon c ontent varies at length scales corresponding to both orders of cyclici ty, and correlation of total organic carbon values to X-radiograph gra y-scale densities permitted rapid stratigraphic analysis of millimetre -scale lithologic variation in the 5.0-m-thick formation. Spectral ana lysis of gray-scale density time series revealed strong power concentr ations at intervals of 23 +/- 2 and 70 +/- 5 couplets. These results a re interpreted to represent varved deposition of the Sunbury Shale mod ulated by the approximately 22 yr Hale and approximately 70-90 yr Glei ssberg solar activity cycles. These cycles were probably recorded beca use of deposition in a stratified anoxic environment that was sensitiv e to short-term climatic fluctuations and subject to high sedimentatio n rates (4.5 mm/yr).