Craven Basin and southern Pennines

Carboniferous rocks within this area occupy the region contiguous with the northern Pennines to the north (Chapter 12) and the Peak District to the south (Chapter 10). All of the stages of the Carboniferous are present at outcrop, with the exception of Stephanian strata, which are absent. The oldest Tournaisian strata crop out within the Craven Basin, and are represented by ramp carbonate rocks (Bowland High Group) deposited on the Bowland High and adjacent Lancaster Fells and Bowland sub-basins. These carbonate rocks are overlain by mainly Visean hemipelagic mudstone and carbonate turbidites (lower part of Craven Group). To the south of the Pendle Fault System (Fig. 11.1), further platform carbonate rocks are proved in the subsurface above the Central Lancashire High (Trawden Limestone Group) and the Holme High and Heywood High (Holme High Limestone Group). These carbonate rocks, which developed during the Tournaisian to late Visean, are known only from well records and geophysical information and are not divided into formations. During the Visean, the platform carbonate rocks pass laterally into more basinal successions in the Harrogate, Rossendale and Huddersfield sub-basins (Craven Group). The lithostratigraphical nomenclature for the Tournaisian and Visean strata is that of Waters et al. (2009), adapted from Riley (1990)

South Wales

Carboniferous rocks in this region occur in a broadly east-west trending syncline, the core of which includes the South Wales and Pembrokeshire coalfields (Fig. 5.1). Tournaisian and Visean strata (Avon and Pembroke Limestone groups) represent deposition on a southward prograding carbonate ramp evolving into a carbonate shelf (Wright 1987), in a succession which shows similarities to that of the Bristol and Mendips areas (Chapter 6). The main outcrops, in south Pembrokeshire, Gower and the Vale of Glamorgan, occur along the southern periphery of the coalfields and are commonly affected by Variscan thrusting and folding. Thinner successions occur along what is termed the East Crop and North Crop of the South Wales Coalfield, where much of the Visean succession is absent due to sub-Namurian and intra-Visean unconformities. Namurian fluvio-deltaic deposits (Marros Group) flank the South Wales and Pembrokeshire coalfields. Much of the lower and middle Namurian succession is absent across the region, except in the west of the South Wales Coalfield where only small parts are absent beneath an intra-Namurian unconformity. Westphalian fluvio-lacustrine deposits (South Wales Coal Measures Group) form the South Wales and Pembrokeshire coalfields, located to the east and west of Carmarthen Bay, respectively. Westphalian to Stephanian Pennant alluvial facies (Warwickshire Group) occur in the core of the South Wales Coalfield syncline. Deposition of the South Wales Coal Measures and Warwickshire groups was probably laterally contiguous with those in the Bristol and Somerset coalfields (Chapter 6), but the Usk-Cowbridge High controlled and restricted sedimentation for much of the Carboniferous, with pre-Namurian uplift and erosion removing the Tournaisian and Visean succession. Later uplift is also believed to have caused attenuation of the Warwickshire Group in the east of the South Wales Coalfield. The lithostratigraphical nomenclature for the region is that of Waters et al. (2007; 2009)

A factor analysis approach to modelling the early diversification of terrestrial vegetation

peer reviewedData from a new comprehensive macrofossil-based compilation of early plant genera are analyzed via a Q-mode factor analysis. This compilation ranges from the Silurian to the earliest Carboniferous and illustrates the key vegetation changes that took place during the configuration of early terrestrial ecosystems. Results reveal that four factors can be used to explain more than 90% of the variance in the data. These factors are interpreted as the major phases of the early land plant evolution: a first Eotracheophytic flora (Silurian-Lochkovian) dominated by basal eutracheophytes and rhyniophytoids, an early Eophytic Flora (Early Devonian) dominated by zosterophylls, a transitional late Eophytic Flora (Middle Devonian-earliest Carboniferous) dominated by lycopsids and cladoxylopsids, and finally, the earliest phase of the Palaeophytic Flora (Late Devonian-earliest Carboniferous) dominated by the first seed plants. These floras present different but complementary diversity patterns, which help us to understand the overall trajectory of changes in plant diversity. Results further show how the maximum peaks of diversity appear linked to the rise of each new flora but, interestingly, these diversifications are not associated with any exponential declines of the previously dominant one. This new four-phase diversification model reflects the early steps of Earth's greening

Bristol, Mendips and Forest of Dean

Carboniferous rocks within this region occur in a series of inliers, many occurring in the cores of periclines and anticlines. The Tournaisian and Visean strata comprise ramp carbonate successions (Avon and Pembroke Limestone groups), which show similarities with equivalent strata to the west in South Wales (Chapter 5). The main outcrops, broadly from south to north, are the Cannington Park inlier and Mendips and at Weston-super-Mare, Broadfield Down, Bristol and Avon, Cromhall and Chepstow to Monmouth (Fig. 6.1). Namurian strata are present only in the south of the region, in the Bristol and Somerset coalfields. Little information is available on the nature of these strata, though they show some similarities to the fluvial and deltaic successions of the Marros Group of South Wales (Chapter 5). Westphalian strata are present in all the coalfields, broadly from south to north, the Somerset, Bristol, Severn, Forest of Dean and Newent coalfields (Fig. 6.1). Fluvio-lacustrine deposits (South Wales Coal Measures Group) are present only in the Somerset, Bristol and the south-eastern part of the Nailsea coalfields. These coalfields are laterally contiguous beneath Mesozoic strata. Deposition was also probably laterally contiguous with the concealed Berkshire Coalfield (Chapter 7). Lateral continuity with the South Wales Coalfield (Chapter 5) is not possible to demonstrate. Strata of this facies are absent from the Newent, Forest of Dean and Severn coalfields and the Cannington Park inlier along the axis of the syn-Westphalian Usk Anticline. It is not clear if the Coal Measures were deposited and subsequently removed by erosion during late Bolsovian to early Asturian deformation or were never deposited at all. Although thinning of the succession can be demonstrated in the Nailsea Coalfield, there is no facies change to indicate passage towards a growth anticline. A Westphalian to Stephanian alluvial succession of Pennant facies (Warwickshire Group) occurs within all six coalfields, though proved Stephanian strata are restricted to the Somerset and Forest of Dean coalfields. Deposition was probably laterally contiguous with the South Wales Coalfield (Chapter 5) and the concealed Oxfordshire and Berkshire coalfields (Chapter 7)

Biostratigraphy

The Tournaisian and Visean platform carbonate successions of the UK and Ireland initially relied upon development of coral and brachiopod zonations to aid correlation. However, such zones are strongly facies-controlled and are only of local to regional significance. Over recent years, emphasis has been placed upon the use of foraminifers, and notably conodonts, to define international stages. They have been studied increasingly within the Tournaisian and Visean successions of the UK and Ireland, but are of limited stratigraphical value in younger Carboniferous strata. Ammonoids (goniatites) provide the greatest biostratigraphical resolution for the late Visean, Namurian and early Westphalian Stages. Some ammonoid biozones can be recognised across Western Europe and some biozones are applicable globally. However, the marine bands that contain these ammonoids may be absent towards basin margins and marine influence is lost entirely throughout late Westphalian and Stephanian times. Within strata lacking ammonoids, biostratigraphical correlation initially relied upon recognition of non-marine bivalve zonation, but over recent decades palynomorphs (miospores) and plant macrofloras have assumed greater importance

Lower Jurassic floras from Hope Bay and Botany Bay, Antarctica

Hope Bay and Botany Bay, Graham Land, Antarctica have yielded two of the most diverse floras known from the Jurassic. Because of its high diversity, as well as its early discovery and description (by T. G. Halle in 1913), the Hope Bay flora has served as a taxonomic standard for studies of other Mesozoic floras from Gondwana. This paper presents a major revision of the Hope Bay flora, based on extensive subsequent collections. A nearby flora from Botany Bay is described for the first time. Thirty-seven species are now recognised in the Hope Bay flora and 32 from Botany Bay. The floras are closely similar; 80 per cent of the Botany Bay species also occur at Hope Bay. They are shown here to be Early Jurassic, which contradicts the results of previous studies that suggested a Late Jurassic or earliest Cretaceous age. The revision of their age has special significance for our understanding of the Mesozoic geological history of the Antarctic Peninsula. It also highlights the need for reappraisal of a number of other Mesozoic Gondwanan floras that had been dated mainly on their close similarity to the Hope Bay flora. The taxonomic work has resulted in establishment of a new combination, Taeniopteris taeniopteroides, and emendation of the diagnoses of Coniopteris oblonga, Sphenopteris nordenskjoeldii, Sphenopteris pecten and Komlopteris indica