Lithostratigraphical framework for Carboniferous successions of ...

limestones as minor, but important components. These reflect
the development of lakes characterised by the accumulation of
abundant algal remains. during the late visean, the succession
in the east was still dominated by fluviodeltaic and lacustrine
deposits, but with periodic marine incursions (Figure 2c)
during the asbian and the Brigantian. marine incursions,
associated with the formation of thin limestones, were at their
most frequent during the late Brigantian, when shelf seas
intermittently covered the whole of the midland valley of
scotland.
The early visean depositional environment of the
Northumberland Trough was dominated by lacustrine and
fluviodeltaic clastic sedimentation. The main deltaic deposits
were derived from the north–east and prograded gradually
along the axis of the trough (Figure 2b). meanwhile, south
of the Northumberland Trough, a period of marine
transgression resulted in the establishment of platform
carbonates, which gradually onlapped raised horst and tiltblock
highs. during late visean, a cyclic succession of
fluviodeltaic clastic sediments, marine-reworked sandstones
and shallow shelf marine carbonates (Yoredale facies † )
dominated across northern england, terminating deposition
of the platform carbonates.
Rifting during the early visean led to the initiation of
basinal marine conditions in the Craven Basin, which
expanded with time into a series of linked embayments
extending from the east midlands to Republic of ireland
(Figure 2c).
Throughout the visean the wales–Brabant High was
probably emerged, flanked to both the north and south by
shelf carbonates (waters and Lawrence, 1987; davies et al.,
2004). in south-west england these carbonates pass
southward into the deep marine Culm Basin, which is
associated predominantly with pelagic deposits. By the end
of the visean, thin siliciclastic turbidites were deposited,
sourced in part from a highland area that developed to the
south in response to closure, uplift and erosion of the more
southerly basins (Figure 2c).
1.2.3 Namurian
The midland valley of scotland is characterised by cyclic
(Yoredale facies) sequences with interbedded fluviodeltaic
sediments, coals and marine shelf limestones, the last
marking highstands of sea level. Fluvial sediment input
continued from the north-east (Figure 2d). during pendleian
times coal-forming environments with Lingula and
† see Chapter 2 for use of terms
5
nonmarine bivalves were common, but with intermittent
marine incursions. The mid to late Namurian succession is
characterised by alluvial deposits (Browne and monro,
1989), with palaeosols rather than coals.
during pendleian times, a fluviodeltaic system (Millstone
Grit facies) transported siliciclastic sediment into the northern
margin of the Central pennine sub-basin. initial deposition
into the basinal areas is marked by the formation of thick
turbidite-fronted delta successions. By marsdenian times the
deltas had prograded across, and largely infilled, the Central
pennine sub-basin, resulting in a predominance of relatively
thin, sheet-like deltaic sandstones and well-developed deltatop
deposits. meanwhile, erosion of the emergent
wales–Brabant High provided a source for more localised
fluviodeltaic successions, which prograded short distances
both to the north and south of the high (Figure 2d).
in the North devon and Culm basins, the early Namurian
succession was dominated by a continuation of the deposition
of pelagic shales. during the mid Namurian, following the
first major compressional deformation event to affect the
Culm Basin, siliciclastic turbidites, mainly sourced from the
north, spread diachronously across the region.
1.2.4 Westphalian to Stephanian
From early in the westphalian, a coal-forming delta-top
environment became established across the midland valley
of scotland, the pennine Basin and between south wales
and the Culm Basin and eastwards to Kent (Figure 2e).
although the ‘Coal measures’ cyclic successions are
lithologically similar, the three basinal areas were, at least in
part, isolated by the upland areas of the southern uplands
and wales–Brabant highs. marine incursions, represented
by the widespread marine bands, were relatively rare during
deposition of these successions. in the Culm Basin, relatively
shallow water deltaic deposits accumulated, with coalbearing
strata deposited in the north of the basin
By Bolsovian times fluvial sediments (‘pennant measures’)
derived from the northward propagating thrust sheets of the
Hercynian Highlands encroached northward across much of
southern england and south wales (Figure 2f). meanwhile,
on the flanks of the wales–Brabant High, reddened alluvial
deposits accumulated. during westphalian d and stephanian
times, the ‘pennant measures’ accumulated within the south
wales Basin. The ‘pennant measures’ breached the wales–
Brabant High and for a short period during the westphalian d
strata were deposited within the pennine Basin.