Page 48 - An Atlas of Carboniferous Basin Evolution in Northern England

Chapter 4

Palaeogeography and fades evolution

Overview sediment derived from areas of Larentia-Baltica affected by Caledonian In the East Midlands area approximately 275 m of coarse breccias,
orogeny dominates Namurian depositional systems. During the latest consisting of pebbles of quartzite, metasediments and igneous rocks, rest on
Having discussed the broad-scale tectono-stratigraphic subdivision of the Namurian, westerly sources become more important (e.g. Collinson & Banks Lower Palaeozoic phyllites in Eakring-146. These are interpreted to reflect
north of England Carboniferous in the previous section, we now use the 1975; McLean & Chisholm 1996) and dominate the mid Westphalian A to mid deposition in close proximity to an active fault-scarp. Other boreholes
megasequences and tectono-stratigraphic sequences to determine the spatial Westphalian B of the Yorkshire Coalfield (e.g. Hallsworth & Chislom 2000; penetrating siliciclastic rocks of probable late Devonian age are Caldon Low
and temporal evolution of depositional systems using sequence palaeogeo- Hallsworth et al. 2000). The location of this westerly source is still problematic (c. 170 m red-brown pebbly sandstone) situated on the footwall of the
graphies. as zircon ages cannot be reconciled with derivation from the Appalachians- Widmerpool Gulf, and Whittington Heath (c. 1 m pebbly sandstone) in the
By late Devonian times, rifting had begun in northern England with Newfoundland-Labrador area (Hallsworth et al. 2000). Southerly sources, hanging-wall of the Birmingham Fault (see Figs 2 and 24).
sedimentation occurring in incipient half graben under an arid climate. The probably derived from the uplift and erosion in the Variscan orogenic belt to Further evidence for early syn-rift sedimentation in the East Midlands area
remnant Caledonian mountain belt to the north acted as a major sediment the south and SE became important from mid/late Westphalian B times comes from gravity and seismic data. Late Devonian sedimentary basins are
source (e.g. Gilligan 1920; Leeder 1988; Gawthorpe et al 1989) and, in the onwards (Glover et al. 1996; Leng et al. 1999; Hallsworth & Chisholm 2000; generally localized around gravity lows e.g. the Eakring-Foston and
study area, Caledonian structures were reactivated and also acted as local Hallsworth et al. 2000; Evans et al. 2001). Local uplift and erosion, presumably Gainsborough troughs (Fig. 24).
sediment sources. related to inversion, in the Westphalian D-?Stephanian, is suggested by clasts
The northward drift of European Pangaea during the Dinantian led to a of Dinantian carbonates and chert (Glover & Powell 1996).
change to humid climatic conditions by the late Dinantian (Duff, 1980). This, During late Westphalian C times, the thermal subsidence regime was
together with regional transgression, caused a change from red-bed style modified by inversion tectonics related to the progressive northwards move- Sequence EC 1: late syn-rift I (Courceyan)
deposition to fluvio-deltaic deposition in the north of the area, close to the ment of the Variscan deformation front. In addition, continued northwards
major sediment source, and predominantly carbonate depositional systems in drift of Pangea led to a return to arid conditions by late Westphalian times. A marine transgression occurred across much of northern England during the
the south of the area, particularly on footwall highs starved of clastic sediment. Sedimentation was initially confined to internally drained molasse basins which Courceyan. Basinal areas such as Northumberland, Cleveland-Stainmore and
The development of high-frequency cyclicity in late Dinantian times (e.g. were eventually swamped by increasing amounts of sediment shed northwards Bowland-Craven, were already subsiding and receiving siliciclastic sediment
Walkden 1987; Leeder & Strudwick 1987) signifies the growing importance of from the evolving Variscan orogen lying to the south, although east to west (Fig. 25). The main topographic highs, e.g. Southern Uplands, Manx-
glacio-eustasy as a control on stratigraphic development; a control which axial transport of sediment from the central European Variscides has been Cumbria-Alston-Askrigg ridge and Mercian Massif, remained emergent and
became dominant in the Silesian. suggested for SW England (Sherlock et al. 2000). in some cases persisted as highs throughout the Dinantian.
There is general agreement that northern Britain occupied an equatorial Coastal sabkhas developed around the northern margin of the Mercian
position during the Namurian (Scotese et al. 1979; Smith et al. 1981), and the Massif, with approximately 100 m of anhydrite and dolomite proven in
occurrence of coal and bauxitic soil horizons in Scotland indicates a humid, Syn-rift megasequence Hathern-1 (Falcon & Kent 1960; Llewellyn & Stabbins 1968, 1970), suggesting
tropical climate (Cope et al. 1992). The increasing rainfall, and associated restricted marine influence on the Hathern Shelf at this time (Fig. 25).
increase in sediment supply, may in part have been responsible for the The syn-rift meagasequence can be divided into six tectono-stratigraphic Palynological analysis (Llewellyn et al. 1969) indicates a Courceyan age
southward progradation of a delta system of Brahmaputra scale in earliest sequences on the basis of three phases of rifting (EC1, EC3 and EC5). Figure equivalent to the CM Zone of Clayton et al. (1977). Thicker evaporitic deposits
Namurian times. However, Morton & Whitham (2002) have suggested uplift in 23 presents a summary isopach map for the EC2-EC6. The lack of well control are inferred for the Widmerpool Gulf. Thin (c. 80 m) transgressive siliciclastics
the Norwegian-Greenland Sea region created widespread erosion and diverted and poor seismic definition of the top basement reflector mean that EC1 could were proven in the Eyam borehole in Derbyshire (Dunham 1973; Strank 1985).
a major northerly flowing fluvial systems southward into the UK. On a more not be mapped regionally with confidence. The thickest syn-rift sections occur Other wells such as Caldon Low (Institute of Geological Sciences 1978, Welsh
local scale, an additional factor influencing the marked southerly progradation in discrete depocentres located in the immediate hanging-wall of the major & Owens 1983) and Eakring-146 encountered nearshore or alluvial plain
in early Namurian times on is likely to have been the change in tectonic regime basin-bounding normal fault zones. Over 3 km of syn-rift stratigraphy is siliciclastics (see Figs 2 and 25). Dolomitic carbonates with subordinate
from rapid, local fault-controlled subsidence of the syn-rift megasequence to preserved in these structural locations (e.g. Cleveland and Bowland Basins), siltstones and mudstones in Grove-3, Caldon Low, Welton-Al and Gun Hill-1
slower, regional subsidence of the post-rift megasequence. The mineralogy of which contrasts with < 500 m of stratigraphy preserved on the footwall highs boreholes represent the initial stage of a widespread carbonate ramp
the delta system suggests a provenance in the Scottish/Scandinavian (e.g. Alston and Askrigg blocks) (Fig. 1). development in northern England (see Figs 2 and 25).
Caledonides (Gilligan 1920; Leeder 1988) and transportation is thought to Sabkha evaporites accumulated along the northern flank of the Bowland
have been via braided river systems flowing generally southward. Namurian Basin (Gawthorpe 1986, 1987a, Arthurton et al. 1988) and in the North-
sedimentation was initially controlled by the inherited Dinantian rift Sequence EC I: early syn-rift I (late Devonian-earliest umberland Trough (Johnson 1984) (Fig. 25). Elsewhere, evaporites and
topography and caused local diversion of regional sediment transport Dinantian) restricted-shelf carbonates are proposed for nearshore environments around
pathways with axial flow along the Dinantian rift basins. With continued the margins of developing half graben, such as the Rossendale, Huddersfield
infilling of the sediment-starved Dinantian basins and broad thermal There are very few data to constrain the palaeogeography of northern England and Edale Basins and the Stainmore Trough (e.g. Evans & Kirby 1999).
subsidence, more widespread deposition occurred over most of northern during the late Devonian. By this time, the mountainous topography of the Old Courceyan strata tentatively identified at the base of the Seal Sands-1 borehole
England through to Westphalian C times. Red Sandstone continent, particularly over northern Britain, was much in the eastern Stainmore Trough comprise siliciclastics, possibly derived from
Recent provenance studies (e.g. Hallsworth & Chisholm 2000; Hallsworth et subdued. Conglomerate deposition developed along newly active fault-scarps, the emergent Alston Block to the north.
al. 2000), whole-rock Sm-Nd isotopic data (Glover et al. 1996; Leng et al. such as the Gamblesby-Melmerby-Ousby fans along the Deep Slack, Fellside Alluvial fans developed in fault-bounded lows within the Manx-Cumbria-
1999) and U-Pb dating of detrital zircon and monazite (Drewery et al. 1987; and Swindle Beck Faults and the Mell Fell Conglomerate, along the Eden- Alston-Askrigg Ridge (Fig. 25), for example the Shap Red Beds (Kimber &
Cliff et al. 1991; Evans et al. 2001) have helped to determine the characteristics Pennine Fault in east Cumbria (Fig. 24). The Whita and Annan Sandstones in Johnson 1986). These include conglomerates derived from the Silurian
of the northern source and have highlighted the importance of other sediment the Northumberland Trough (Leeder 1974) are interpreted as examples of greywackes to the south and SW, grading up into cross-bedded sandstones.
sources to the Namurian and Westphalian of northern England. Overall more sheet-like hanging-wall derived fan systems. Similar conglomerates at Sedbergh to the south were probably derived from