A 30-MILLION YEAR RELATIVE SEA LEVEL HISTORY FOR THE LATE CARBONIFEROUS ARCHIVED IN THE DONETS BASIN CYCLOTHEMIC SUCCESSION

The sedimentary succession of the Donets Basin, eastern Ukraine, archives a continuous, long-lived relative sea-level history for the Carboniferous reflecting high rates of accommodation and a hierarchy of cyclicity preserved in the mixed carbonate-siliciclastic succession. Here we present a relative sea-level history, calibrated using 11 high precision (±0.1%) U-Pb ages, for a 30 myr interval (Visean to Ghzelian) of the Carboniferous based on the stratigraphic and across-basin patterns of paralic facies assemblages and their cyclicity recorded in 200 core logs and 20+ outcrop sections. Facies belts group into widely correlatable, regularly repeating sequences (n = 240). These cyclothems constitute composite sequences that in turn bundle into larger-scale stratigraphic packages delineating longer-term progradational, retrogradational and aggradational trends. The resulting relative sea-level history defines multiple major regressive-transgressive packages with two periods of maximum sea-level lowstand and inferred ice sheet growth across the mid-Carboniferous boundary (323.5-322 Ma) and in the mid-Moscovian (314-311 Ma). These lowstands correspond within <± 0.3 myr with the U-Pb constrained ages of two glacial periods in southwestern Gondwana (Gulbranson et al., 2010). The ensuing ~9 myr period of long-term sea-level rise is punctuated by at least four episodes of glaciation (<0.5 to 1.5 myr duration) that become increasingly shorter-lived and less extensive culminating with an ~ 1 myr period of maximum sea-level rise in the earliest Gzhelian (~303-302 Ma). The latter is interpreted to record a glacial minimum or possibly ice-free conditions in the late Pennsylvanian. Each of the mid-to-late Pennsylvanian short-term sea-level falls can be correlated to sea level lows and glaciations inferred from the mid-continent cyclothemic record (Heckel, 2008). Relative sea level fell gradually through the remainder of the Gzhelian reaching long-term lowstand by 300 Ma coincident with the onset of the earliest Permian glacial apex. Periods of regional aridity indicated by bedded evaporates and loss of coals are coincident with high-latitude glacial minima while increased coal deposits and paleosol indicators of regional humidity define periods of high-latitude Southern Hemisphere glacial maxima.