Page 43 - An Atlas of Carboniferous Basin Evolution in Northern England

24 Chapter 3

Leeds Basin offshore domain. The major basin-bounding faults in the north are the en margin, and these reflectors have been interpreted to represent a prograding
echelon Lunedale, Wigglesworth and Butterknowle Faults (Figs 1, 10 and 21). carbonate platform (Collier 1991). However, elsewhere in the rift system
The Leeds Basin forms a relatively minor, NE-SW-trending half graben which The southern margin of the basin, which is not represented on the regional carbonate margins are associated with high-angle clinoforms (e.g. Widmerpool
links the Edale Gulf and Cleveland Basin (Figs 10 and 19). Regional seismic seismic data, is fault bounded, probably along the line of the Stockdale Gulf, Fig. 12). Thus the low-angle clinoforms observed in the hanging-wall of
data (Fig. 19) suggests up to 3 km of ?Upper Devonian and Dinantian disturbance (Collier 1991). the Wigglesworth Fault are more likely to represent a clastic depositional
sediments preserved in the basin. There is also evidence for a major intra- Previously published interpretations of the Stainmore Trough (George et al. system, an Ashfell Sandstone equivalent, that infilled topographic lows within
Dinantian unconformity in the area of the Aldfield borehole which may be 1976; Burgess & Holliday 1979) have been based largely on outcrop and the Stainmore Trough.
related to either inversion or footwall erosion in late Chadian Holkerian (EC3) shallow borehole data, with the thickness of Dinantian strata estimated by The EC3-EC4 sequence boundary is marked in the Stainmore Trough by an
times. There is little borehole control on facies as the Aldfield borehole only Johnson (1982) at 1.5 km and by Bott et al. (1984) at 2.5 km. Seismic reflection angular unconformity in the hanging-wall of the main basin-bounding fault
penetrated the uppermost part of the late Dinantian (EC6) carbonates. Facies data tied to surface outcrop and the deep Seal Sands-1 borehole (Fig. 2) have and early Asbian (early EC4) strata are absent on the Alston Block (Burgess &
and stratigraphy have been interpreted by regional analogy and from seismic greatly improved our ability to interpret the scale and style of Dinantian Holliday 1979) (Fig. 21). However, the early Asbian succession in the
facies analysis, therefore a degree of uncertainty exists with the geological sedimentation within the Stainmore Trough. Stainmore Trough reaches 300 m in thickness and pinches out by onlap onto
interpretation presented in Figure 19. In the immediate hanging-wall of the Lunedale-Wigglesworth-Butterknowle the EC3/EC4 boundary along the northern margin of the basin (Fig. 21). This
fault zone, along the northern basin margin, up to about 6 km of Dinantian are unconformity may be indicative of a previously unrecognised late Holkerian
imaged on regional seismic sections (Fig. 21). There are no well penetrations basin inversion event, coinciding with the cessation of EC3 rifting.
Cleveland Basin beneath the Chadian/Arundian (EC3) and the timing of rift initiation can The late Holkerian-mid Asbian (EC4) sequence is marked by the continuous
therefore be estimated only from regional considerations. By analogy with and widespread Melmerby Scar/Great Scar Limestone and its southerly
Further north within the northern England rift system, seismo-stratigraphic neighbouring rift basins such as the Northumberland Trough (Leeder 1974) equivalents (Burgess & Mitchell 1976; Wilson & Cornwell 1982) (Fig. 9). This
interpretation becomes more problematic as, unlike the East Midlands, the and the Bowland Basin (Gawthorpe 1986), the age of the earliest basin-fill limestone marks a regional transgression over both the basin and surrounding
Dinantian basins were not sediment starved and consequently had a sediments is interpreted to be late Devonian-Courceyan. The nearest outcrops footwall blocks. There is a variation in seismic facies of the Melmerby/Great
dominantly clastic fill. In the Cleveland Basin, biostratigraphically calibrated of early Dinantian strata occur around Ravenstonedale to the west, with rapid Scar reflector across the Alston Block margin into the basin (Fig. 21). The
borehole data have been crucial to interpretation of the stratigraphy and facies local thickness changes and facies variations related to local valley-fill limestone is 35-50 m thick over the Alston Block, (Woolacott 1923; Dunham et
(Figs 1, 10 and 20). processes and to movements on growth faults such as the Swindale Beck al. 1965) and thins across the Butterknowle and Wigglesworth Faults into the
The Cleveland Basin trends east-west (Fig. 1) and is overlain for the most Fault (Burgess & Harrison 1967, Burgess & Holliday 1979, Kimber & Johnston basin, where it is represented by a single high-amplitude event.
part by a thick Permian and Mesozoic cover which represents the onshore 1986). At Ravenstonedale the Pinskey Gill Formation (Courceyan), which was The late Asbian-Brigantian Alston Group (sequence EC5), which overlies
extension of the Sole Pit Trough (Kent 1975, Glennie & Boegner 1981; Van deposited in a nearshore environment, rests directly upon Lower Palaeozoic the Great Scar Limestone, increases in thickness into the basin from 450 m to
Hoorn 1987). The basin takes the form of two half graben offset by a major basement and is overlain by coarse siliciclastics of alluvial fan origin 700 m across the Wigglesworth Fault, suggesting renewed tectonic subsidence.
intra-basinal transfer system (Fig. 20). These transfer faults were reactivated to (Gawthorpe et al. 1989). These deposits are widely exposed in the western parts of Stainmore and form
form the loci for later Mesozoic listric extensional faults that sole out within Early Courceyan-Arundian (EC1-EC3) rift sequences are picked from 0.75 high frequency Yoredale shallow marine to fluvio-deltaic cycles (Burgess &
Permian Zechstein evaporites and laterally equivalent shales. to 2.5 s TWTT, which converts to a sedimentary thickness of about 4 km. The Mitchell 1976; Leeder & Strudwick 1987). The Yoredale cycles (Fig. 9) include
Up to 4 km of Dinantian strata are preserved in the basin but the early syn- ECl seismic sequence includes downlapping clinoforms located against the a variety of fluvio-deltaic and shallow marine sandstones and shallow marine
rift fill (ECl) has not been penetrated by boreholes. Wedge-shaped geometries northern basin-bounding faults and interpreted as footwall-derived alluvial carbonates, but are too thin to be resolved as separate reflections or packets of
are observed on seismic and deposition is interpreted as alluvial fan and fan- fans or fan deltas up to 4 km in diameter. Active rifting is inferred to have reflections on the regional seismic data.
delta by analogy with contemporaneous rift systems elsewhere in northern taken place during late Devonian-Courceyan (ECl) times in order to generate
England. In the deeper parts of the basin a major angular unconformity is the fault scarp and basin topography necessary to accommodate the fan
observed, overlying the wedge-shaped ECl sequence, which may represent geometries. Within the basinal sediments of this suspected early rift sequence a
either the EC1/EC2 or EC2/EC3 sequence boundary (Fig. 20). The oldest number of continuous high-amplitude reflectors are observed (Fig. 21). Data Northumberland Trough-Solway Basin
Dinantian strata penetrated in two deep boreholes in the basin, High Hutton from outcrop at Ravenstonedale, where shallow-water carbonates such as the
and Kirby Misperton-1, are of Holkerian age (EC3) and represent the deposits Scandal Beck Limestones are encountered, suggest that the reflectors most The Northumberland Trough-Solway Basin forms a major NE-SW-trending
of deep water clastic delta systems which progressively infilled the basin from likely represent the basinal equivalent of these carbonates. An alternative half graben bounded to the north by the Southern Uplands and to the south by
the north throughout the later part of the Dinantian (Fig. 9). interpretation, based on analogy with the Northumberland Basin, is that the the Alston Block and Lake District Massif (Fig. 1). Geological relationships
Intense inversion and erosion in the late Carboniferous removed most of the reflectors represent a limited input of early, syn-rift volcanics to the basin. (Johnson 1984) and gravity data suggest a basement high, across which there is
Namurian and Westphalian sediments from the central part of the basin north Shallow-water carbonates dominate the Arundian to early Asbian (EC3 and a change in dip polarity, partly separating the western end of the North-
of the Barton Fault, forming a marked base Permian unconformity (Fig. 20). EC4 sequences) on the Ravenstonedale and Askrigg highs to the west and umberland Trough from the Solway Basin.
Where preserved on the footwall of the Barton Fault, these deposits are up to south. These carbonates are interbedded with fluvio-deltaic and shallow- Although the simple view of the Northumberland Trough as a half graben
2500 m thick and are typical Yoredale, Millstone Grit and Coal Measures marine sandstones. Within the Stainmore Trough, the seismic character of the (Leeder 1974, 1982) has been confirmed by seismic reflection data (Kimbell et
facies characteristic of the shallow-water clastic delta systems encountered basinal equivalents of the Ashfell Sandstone and the upper parts of the al. 1989; Figs 10 and 22), it should be noted that the southern bounding
throughout the Pennine Basin. The 2500 m of Silesian strata on the footwall Ravenstonedale Limestone show reflectors of varying continuity and extensional faults mapped at surface are Permian or younger in origin (Leeder
represents a lower limit for the original thickness of the post-rift which must amplitude (EC3 seismic sequence). Up to 2.5 km of mudstones and sandstones et al. 1989). They are believed to overlie, or nucleate upon buried syn-
have been deposited over the Cleveland Basin. with occasional thin carbonates are ascribed to this stratigraphic interval in the depositional structures present at depth below the post-rift thermal subsidence
basin, similar to the succession penetrated between 2000 m and TD (4170 m) in fill, similar to structures noted in the Cleveland Basin to the south.
the Seal Sands-1 borehole. There appears to have been only minor onlap of the The Northumberland Trough is controlled by a major boundary fault in the
Stainmore Trough Ashfell Sandstones onto the Askrigg Block and the Ravenstonedale Shelf south defined by the Stublick-Ninety Fathom Fault (Fig. 1). The Solway Basin
suggesting that fault-controlled differential subsidence between the basin and is controlled in the north by the major fault separating it from the Southern
The Stainmore Trough is a major east-west-trending half graben lying to the surrounding footwall blocks was active throughout the late Chadian Uplands (Tarras Fault and equivalents, Johnson 1984). Comparison of the
north of the Cleveland Basin (Fig. 1). In the west it is separated from the Holkerian (EC3). successions in the Northumberland and Solway basins suggests that subsidence
Cleveland Basin by the eastwards extension of the Askrigg Block, but probably Locally low angle shingled to sigmoidal clinoforms can be resolved within and sedimentation were largely synchronous, at least during the Dinantian
merges with the Cleveland Basin towards the east to form a single basin in the the EC3 seismic sequence that prograde southwards from the northern basin (Johnson 1984). The exposed sequences are very similar in the two basins,