Page 51 - An Atlas of Carboniferous Basin Evolution in Northern England

30 Chapter 4

the northwestern side of the Askrigg Block. Sequence EC3: syn-rift II (late Chadian-Holkerian) Sequence EC4: post-rift II (late Holkerian-mid Asbian)
Cementstone-type fades were established during the early Dinantian in the
Scottish Borders in fluvio-lacustrine and hypersaline lake environments. The late Chadian-Holkerian EC3 sequence comprises a series of carbonate Considerably more data are available to constrain the EC4 palaeogeography
Widespread drainage from the Southern Upland Massif provided coarse ramps with associated basinal mudstones south of the Manx-Cumbrian Ridge compared to the older syn-rift tectono-stratigraphic sequences. Over 200
siliciclastic sediments to the Northumberland Trough, e.g. Rerrick, Annan and and Alston Block, with fluvio-deltaic deposition dominant in the Northumber- boreholes penetrate late Holkerian to mid Asbian strata and outcrops of shelf,
Whita alluvial systems (Leeder 1974; Johnson 1984). In Kirkudbrightshire, the land Trough (Fig. 27). Locally, the base of EC3 is a pronounced angular shelf margin and basinal facies are present in the Derbyshire Dome, Bowland
northern Solway Fault was active and the Criffel Granite unroofed, leading to unconformity in the footwall of fault blocks. Basin, North Wales, Cumbria and across the Alston and Askrigg Blocks.
localized alluvial fan and fan delta deposition along the fault-controlled The palaeofacies map for the early part of EC3 (late Chadian-Arundian) The Holkerian-Asbian (EC3/EC4) boundary is poorly defined biostrati-
northern margin of the Solway Basin. By the end of the Courceyan, marine shows clear evidence of a major transgression from the west, although delta top graphically (Ebdon et al. 1990), but can be observed seismically as strong
facies and faunas were prevalent in the Northumberland Trough-Solway siliciclastics persist in the eastern Northumberland Trough and northern downlap of the prograding shelf margins (e.g. Fig. 12). In the East Midlands
Basin. Cleveland Basin (Seal Sands-1 borehole) (see Figs 2 and 27). Both the Alston rimmed shelf margins are resolved on regional seismic lines, and in basinal
The subsidence of the Northumberland Trough was accompanied by and Askrigg Blocks were increasingly subject to marine incursions. The settings high-amplitude reflectors represent an increase in carbonate within an
extensive alkaline fissure basalts (Birrenswark/Kelso/Cockermouth Lavas) conodont fossils recorded from Ravenstonedale (Higgins & Varker 1982) otherwise mudstone-dominated succession (e.g. Fig. 12). The progradational
along its northern bounding fault (Leeder et al. 1989). Igneous activity is also indicate increasing water depths during the Arundian, consistent with regional and aggradational clinoforms identified on the basin margins are believed to
recorded in the East Midlands by tuffaceous sediments of Courceyan age transgression. During this transgressive phase, extensive carbonate shelf areas represent the development of carbonate ramp to rimmed shelf facies, although
encountered in Welton-Al and Grove-3 (see Figs. 2 and 25). developed and onlapped upland areas. The Manx-Cumbrian Ridge was none of the clinoforms have been penetrated by wells. Shelfward of these
apparently separated by shallow shelf seas from the Alston and Askrigg features, and confirmed by borehole data, shallow marine shelf carbonate
'islands'. In the central Pennines, around the Pendle, Rossendale and Holme grainstones and packstones accumulated (Fig. 28).
Sequence EC2: post-rift I (Chadian) Highs, Arundian shelf margins backstepped towards footwall crests compared By EC4 times, the extensive Arundian-Holkerian shelf and ramp systems
to the older Chadian margins (Evans & Kirby 1999). had evolved into a series of land-attached (e.g. North Wales) and isolated (e.g.
During Chadian times, low-angle carbonate ramps developed peripheral to the Renewed extensional tectonic activity at the end of the Chadian is indicated Derbyshire Dome, Pendle and Holme highs) carbonate platforms with well
Mercian Massif and along the southern margin of the Manx-Cumbrian- by boulder beds and slumping (olistostromes) observed in outcrops in the developed shelf-slope breaks (Fig. 28). In the Pendle and Holme areas,
Alston Ridge, Askrigg Block and around the Pendle and Holme Highs (Fig. Bowland Basin (e.g. Gawthorpe 1987a; Riley 1990) (Fig. 27). Here EC3 is carbonate platforms were drowned and backstepped so that they are less
26). In contrast, north of the Manx-Cumbrian-Alston Ridge, the Chadian represented by the Worston Shale, a mudstone-dominated succession with aerially extensive than their Arundian counterparts (Evans & Kirby 1999). In
succession is dominated by siliciclastics. thinly bedded hemipelagics and calciturbidites. During the rifting, seismic areas of shallow water, starved of clastic sediment, shoaling-upward cyclic shelf
In the East Midlands, EC2 has been penetrated in Hathern-1 on the footwall shocks associated with slip events on the major normal faults triggered syn- carbonates were deposited; for example the Great Scar Limestone and
of the Hoton Fault (see Figs 2 and 26). Here the sequence is developed as sedimentary slumps and slides in sediments of EC3 age (Gawthorpe & equivalents in western Stainmore and on the Alston and Askrigg Blocks.
shallow-water limestones (Llewellyn & Stabbins 1968, 1970) which are dated as Clemmey 1985). A similar mechanism has been suggested for major dewatering Typically these shelf cycles are 5-30 m thick and are interpreted to reflect high
no older than the CF4 Zone of Conil et al. (1979). Restricted basinal facies are horizons within fluvial sediments of the Solway and Northumberland basins frequency glacio-eustatic sea-level fluctuations (e.g. Walkden 1987; Horbury
interpreted for the Widmerpool Gulf and Gainsborough Trough half graben. (Leeder 1987b; Leeder et al. 1989). The tectonism was also accompanied by 1989). Where the platforms are land-attached, pronounced fluvial lowstand
On the adjacent East Midlands Platform EC2 is the oldest of the Dinantian some alkali volcanism, e.g. the Cockermouth Lavas in west and north Cumbria incised valley fills are developed (e.g. North Wales, Walkden & Davies 1983),
sequences preserved, and is developed as shelf limestones (Strank 1987), with (Johnson 1984) (Fig. 27). otherwise these high-frequency sequences are dominated by shoaling upward
the topographic highs of Sproxton, Stixwold, Nocton, Foston and Woo Dale Alluvial and nearshore facies of Arundian age crop out in the Mold district deposits of the highstand systems tract capped by palaeosols marking
preserving no Chadian sediments. Nearshore siliciclastics and dolomitic of North Wales (Somerville & Strank 1984). Arundian limestones onlap earlier interfluve sequence boundaries (e.g. Horbury 1989).
carbonates are recorded from boreholes in the East Midlands area (e.g. Carboniferous sequences and, in places, overstep onto Lower Palaeozoic rocks In the East Midlands and Bowland Basin, shelf carbonates pass basinwards
Bardney-1, NCB Bassingham, Hathern-1, Eakring-146, Ironville-5, Strelley-1, along the northern margin of the Wales-Brabant High. Non-depositional highs through platform margin facies into hemipelagic lime mudstones and
Grove-3 and the Eyam borehole) (see Figs 2 and 26). persisted to some extent in the East Midlands, but the Woo Dale high in calciturbidites of the foreslope. This carbonate slope facies association shows
The Chadian was a time of major carbonate production in the Bowland Derbyshire was finally submerged (Woo Dale borehole; Cope 1973) (Fig. 27). a coarsening upward trend, reflecting overall progradation of the rimmed shelf.
Basin (Gawthorpe 1986, 1987a; Riley 1990). The Clitheroe Limestone There was no major tectono-stratigraphic break between the Arundian and Shelf margin complexes are exposed in the Derbyshire Dome, Bowland Basin
Formation and equivalents, exposed in the Bowland Basin, reflect deposition Holkerian with continued deepening and progressive onlap. This interval and North Wales. There was a general absence of framework building
on a southwest dipping carbonate ramp. Carbonate grainstone shoals were marked the maximum extent of the Dinantian transgression, with shelf organisms during the Dinantian and boundstone reefs were not usually
developed above wave base on the shallower parts of the ramp and these grade limestones more extensive during the Holkerian than at any other time in the formed. Instead, the platform margins commonly comprise bioclastic shoals
basinwards into interbedded argillaceous limestones and mudstones. To the Dinantian (Strank 1987). Carbonates with minor siliciclastics accumulated with abundant fauna including crinoids, productids and other brachiopods and
southeast of the Bowland Basin, the lowermost Dinantian in Holme Chapel-1, across the East Midlands, and the Nocton, Foston, Stixwold and Askern- solitary corals.
Boulsworth-1, Roddlesworth-1 and Wessenden-1 comprises carbonates of Spital highs were all submerged (Strank 1987). Shelf-ramp carbonates extended Along the exposed section of the northern margin of the Derbyshire
probable Chadian age that form ramp/shelf carbonates with poorly defined northward beyond the Alport-1 borehole in the Edale Gulf (Fig. 27). platform, the depositional talus slope attained angles of up to 30° (Broadhurst
shelf margins that fringe developing fault controlled highs (see Figs 2 and 26) In places, on the Derbyshire Dome, the Holkerian is thin or absent, & Simpson 1973). These steep angles would have been maintained by early
(Evans & Kirby 1999). representing local emergence or non-deposition (e.g. Dovedale). Highly porous cementation. This footwall margin was weakly progradational, but did not
Waulsortian buildups are also characteristic of EC2 in the in the southern dolomitised shelf limestones (Woo Dale Limestone) have been described by extend significantly beyond the controlling fault (see Edale Gulf seismic line,
half of the northern England rift province. Miller & Grayson (1982), Grayson Schofield & Adams (1985) who interpreted the environment of deposition as a Fig. 17). The form and location of the rimmed shelf margins were largely
& Oldham (1987) and Riley (1990) report Waulsortian facies of Chadian age shallow subtidal carbonate shelf which experienced varying degrees of controlled by faulting and the margins can be extrapolated around the fault-
from the central part of the Bowland Basin, and in Dovedale, on the restriction from open marine conditions. Carbonate shelf environments controlled East Midlands basins (Widmerpool Gulf, Edale Gulf and
Derbyshire Dome, an elongate Waulsortian complex is reported by Bridges & persisted around the islands and uplands to the north (Fig. 27). Gainsborough Trough) (Fig. 28). The angle of slope and amount of
Chapman (1988) (Fig. 26). In contrast to the carbonate-dominated environ- Despite the retreat of the Fell delta system due to the Holkerian progradation were greatly affected by the amount of throw on the fault and
ments to the south, marine pro-delta mudstones accumulated in the North- transgression, it still covered most of the Northumberland and Cleveland whether the shelf margin developed on the footwall or hanging-wall dip slope.
umberland and Cleveland basins (Fig. 26). However, in the northeastern part basins. Coal swamps developed on the upper delta plain and provided The marginal facies were also controlled by their leeward or windward position
of the area, delta-front and alluvial deposition was already established, for structured woody plant material to the pro-delta organic-rich mudstone facies as recognised in the Derbyshire Dome (Schofield 1982), with grainstone facies
example the Fell Sandstone delta system. deposited in the southern Cleveland and Solway basins (Fig. 27). apparently developed on the north-facing windward margins. Slope facies