NEW INSIGHTS INTO FAR-FIELD RESPONSE TO THE ONSET OF LATE PALEOZOIC GLACIATION: DATA FROM THE UPPER MISSISSIPPIAN SUCCESSION OF EAST FIFE, SCOTLAND

Several recent studies of Carboniferous stratigraphy worldwide converge upon a late Mississippian (Visean, Asbian, basal Chesterian, c. 333-332 Ma) age for the earliest, large-scale, relative sea-level fluctuations attributed to growth of Gondwanan ice centers and the onset of the late Paleozoic Ice Age (LPIA). In this study, we document a well-exposed succession of Asbian-Brigantian age in eastern Scotland, and suggest that a major change in stratigraphic stacking patterns within sediments of coastal plain to shallow marine origin can be attributed to the onset of large-magnitude relative sea-level fluctuation in the late Asbian. The section of interest spans the upper part of the Strathclyde Group (Asbian) and the overlying Lower Limestone Group (Brigantian), and is continuously exposed in intertidal platforms between the villages of Pittenweem and St Monans on the Fife coast. The succession can be divided broadly into two facies assemblages with overlapping elements. The first assemblage, which characterizes the upper Strathclyde Group up to about 140 m from the top of the unit, comprises erosionally-based, cross-bedded sandstones (coastal fluvial channel belt deposits), heterolithic sandstone-mudrock intervals in many cases organized into coarsening-upward cycles a few meters thick (estuarine and coastal plain lakes/bays), and thin carbonaceous intervals (coastal plain mires). The second assemblage, which accounts for the uppermost 140 m of the Strathclyde Group and the overlying Lower Limestone Group, contains the facies noted above, but in addition preserves thick monotonous mudrock intervals and limestones (both offshore marine shelf deposits), and thicker (<30 m) coarsening-upward intervals (delta front). The upper assemblage denotes a regime in which large-magnitude relative sea-level fluctuations were common, in contrast to the lower assemblage where such fluctuations are not recorded. The change in regime occurs at a horizon corresponding to the late Asbian, suggesting that far-field growth of Gondwanan ice sheets was first felt at this time in paleotropical eastern Scotland. This interpretation is consistent with a variety of recently-published estimates of LPIA onset, and somewhat earlier than the onset interpreted from near-field stratigraphic records of eastern Australia.