AN OCEANIC MODEL FOR LITHOLOGICAL AND FAUNAL CHANGES TESTED ON THE SILURIAN RECORD

A model for oceanic cycles is presented. The cycles are expressed as changes between more humid low latitude and cooler high latitude climates (P episodes), and dryer low latitude and warmer high latitude climates (S episodes). The cyclicity may be self-regulating through changes in the CO2 storage capacity of the deep ocean due to temperature changes and through changes in the oceanic input and output of dissolved carbonate. The model permits over 30 predictions regarding observable changes in both deep water and shelf lithologies and variations in the abundance, diversity and extinction rate of planktic and benthic faunas. Sedimentary changes involve fluctuations in the rate of clay deposition and carbonate production, the advance and retreat of carbonate deposition on the shelf edge, the timing of oolite, reef, and black shale formation, and changes between oxic and anoxic deep water. Faunal effects include both iterative evolution and intermittently widespread taxa ('Lazarus taxa'). These predictions agree well with changes observed in well known sequence of Wenlock and Ludlow age, as well as changes seen in selected older and younger sequences.