A sequence stratigraphic model for the Lower Coal Measures (Upper Carboniferous) of the Ruhr district, north‐west Germany

Abstract

Upper Carboniferous Coal Measures strata have been interpreted traditionally in terms of cyclothems bounded by marine¯ooding surfaces (marine bands) and coal seams. Correlation of such cyclothems in an extensive grid of closely spaced coal exploration boreholes provides a robust stratigraphic framework in which to study the Lower Coal Measures (Namurian C±Westphalian A) of the Ruhr district, north-west Germany. Three distinct types of cyclothem are recognized, based on their bounding surfaces and internal facies architecture.(1) Type 1 cyclothems are bounded by marine bands. Each cyclothem comprises a thick (30±80 m), regionally extensive, coarsening-upward delta front succession of interbedded shales, siltstones and sandstones, which may be deeply incised by a major¯uvial sandstone complex. The delta front succession is capped by a thin (<1 m), regionally extensive coal seam and an overlying marine band de®ning the top of the cyclothem. (2) Type 2 cyclothems are bounded by thick (»1 m), regionally extensive coal seams with few splits. The basal part of a typical cyclothem comprises a thick (15±50 m), widespread, coarsening-upward delta front or lake in®ll succession consisting of interbedded shales, siltstones and sandstones. Networks of major (>5 km wide, 20±40 m thick), steep-sided, multistorey¯uvial sandstone complexes erode deeply into and, in some cases, through these successions and are overlain by the coal seam de®ning the cyclothem top. (3) Type 3 cyclothems are bounded by regionally extensive coal seam groups, characterized by numerous seam splits on a local (0á1±10 km) scale. Intervening strata vary in thickness (15±60 m) and are characterized by strong local facies variability. Rootpenetrated, aggradational¯oodplain heteroliths pass laterally into single-storeȳ uvial channel-®ll sandstones and coarsening-upward, shallow lake in®ll successions of interbedded shales, siltstones and sandstones over distances of several hundred metres to a few kilometres. Narrow (<2 km) but thick (20± 50 m) multistorey¯uvial sandstone complexes are rare, but occur in a few type 3 cyclothems. Several cyclothems are observed to change character from type 1 to type 2 and from type 2 to type 3 up the regional palaeoslope. Consequently, we envisage a model in which each cyclothem type represents a different palaeogeographic belt within the same, idealized delta system, subject to the same allogenic and autogenic controls on facies architecture. Type 1 cyclothems are dominated by deltaic shorelines deposited during a falling stage and lowstand of sea level. Type 2 cyclothems represent the coeval lower delta

Sequence stratigraphy and onlap history of the Donets Basin, Ukraine: Insight into Carboniferous icehouse dynamics

“…Pebble conglomerates mantle erosional channel bases. Where stratigraphically positioned above finer-grained delta-top facies, they are interpreted as channels that incised delta-plain deposits during sustained falls in base level (Shanley and McCabe, 1994;Hampson et al, 1999). Multi-story channelized deposits are interpreted to record the onset of relative sea-level rise and consequent reworking of older lowstand deposits (Strong and Paola, 2008).…”

What Happened to the Coal Forests During Pennsylvanian Glacial Phases?

“…On the other hand, overlying economic coal seams suggest a shift to ever-wet climate (Cecil et al, 2003). In addition, brackish-marine sediments of the Transgressive and Highstand System Tracts (TST and HST) suggest sea-level rise during deglaciaton (e.g., Hampson et al, 1999;Heckel, 2008;Fischbein et al, 2009;Falcon-Fang et al, 2009). This glacial-interglacial signature is, of course, complicated by local tectonics and sediment supply.…”

Sequence stratigraphy of the upper Millstone Grit (Yeadonian, Namurian), North Wales

“…Mineralogical compositions are estimated from point counting of 100 points in a thin section from each sample, and errors are given for 50% confidence level (Galehouse 1971). boundary is also identified in the Culm Basin of southwest England at the base of the Raleigh Sandstone multistorey fluvial sandbody (Hampson 1998;Davies et al 1999). Further examples occur at the base of a 'sharp-based mouth bar' sandbody in the Ruhr Basin of Germany (Hampson et al 1999b) and at the bases of multistorey fluvial sandbodies in the Campine Basin of Belgium, East Silesian Basin of the Czech Republic, Lublin Basin of Poland and Central Appalachian Basin of the USA (Davies et al 1999). The candidate sequence boundary below the Cumbriense Marine Band has a correlative in the western Central Province Basin, at a well-developed palaeosol capping the Lower Haslingden Flags (Maynard 1992;Hampson et al 1996), and in the Leinster Coalfield of Ireland, at the base of a multistorey fluvial sandbody (Davies et al 1999).…”