The Experts below are selected from a list of 132 Experts worldwide ranked by ideXlab platform
Charles H. Wellman - One of the best experts on this subject based on the ideXlab platform.
-
spore assemblages from the lower devonian lower Old Red Sandstone deposits of the northern highlands of scotland the berriedale outlier
Earth and Environmental Science Transactions of The Royal Society of Edinburgh, 2014Co-Authors: Charles H. WellmanAbstract:Assemblages of well-preserved dispersed spores have been recoveRed from the ‘Lower Old Red Sandstone’ deposits of the Berriedale Outlier in the Northern Highlands of Scotland. They belong to the annulatus–sextantii Spore Assemblage Biozone (AS SAB), in the spore zonation of Richardson & McGregor (1986), indicating an Early Devonian Emsian (but not earliest Emsian or latest Emsian) age. Comparison with the spore zonation of Streel et al . (1987) suggests they may be confined to the annulatus–bellatulus Oppel Zone (AB OZ), further constraining the age to early Emsian. This new biostratigraphical datum provides an age constraint for the onset of ‘Lower Old Red Sandstone’ sedimentation in the Orcadian Basin and, in particular, northwest of the Great Glen Fault System on the Northern Highlands. In the Orcadian Basin, there is a gap between ‘Lower Old Red Sandstone’ and ‘Middle Old Red Sandstone’ sedimentation, represented by either unconformity or disconformity, which appears to be variable in duration. In the Berriedale Outlier, it is estimated to represent up to 16 million years, but with an unknown thickness of ‘Lower Old Red Sandstone’ sequence removed at the unconformity. However, this basin-wide unconformity/disconformity is likely due to minor, local rather than large-scale, regional tectonism, and the evidence suggests little, if any, syn-depositional strike-slip movement along the Great Glen Fault System during Devonian ‘Old Red Sandstone’ deposition. The described spore assemblage is the most diverse AS SAB/AB OZ assemblage described from the British Isles. However, compaRed to contemporary spore assemblages from elsewhere on the Old Red Sandstone continent, the Scottish material is rather depauperate, with certain key taxa absent. This probably reflects subtle ecological effects, with the Scottish material representing restricted floras of the inland intermontaine basins.
-
spore assemblages from the lower devonian lower Old Red Sandstone deposits of arran scotland
Earth and Environmental Science Transactions of The Royal Society of Edinburgh, 2009Co-Authors: Charles H. WellmanAbstract:Dispersed spore assemblages have been recoveRed from the Am Binnein Sandstones from the upper part of the ‘Lower Old Red Sandstone’ sequence on the island of Arran, Scotland. The spore assemblages belong with the Emphanisporites annulatus – Camarozonotriletes sextantii (AS) Spore Assemblage Biozone (SAB), indicating an Early Devonian, Emsian (but not earliest Emsian or latest Emsian) age. This is the first reliable age constraint for the ‘Lower Old Red Sandstone’ of Arran, and enables correlation with the more extensive sequence developed on the mainland in the Midland Valley of Scotland. The Am Binnein Sandstones are confirmed as correlatives of the Strathmore Group.
-
the cosheston group lower Old Red Sandstone in southwest wales age correlation and palaeobotanical significance
Geological Magazine, 1998Co-Authors: Charles H. Wellman, Dianne Edwards, R G Thomas, Paul KenrickAbstract:Upper Silurian–Lower Devonian ‘Lower Old Red Sandstone’ facies deposits cropping out in southwest Wales are poorly age-constrained and difficult to correlate. Spore assemblages have been recoveRed from sequences of these deposits belonging to the lower part of the Cosheston Group. The spore assemblages are equated with the breconensis–zavallatus and polygonalis–emsiensis Spore Assemblage Biozones and indicate an early Devonian age (late Gedinnian (late Lochkovian)–Siegenian (Pragian)). The new biostratigraphical data enable correlation of the lower part of the Cosheston Group with the Senni Beds from the main outcrop of the Lower Devonian in South Wales and the Welsh Borderland. In addition, the new age data and stratigraphical correlation place important plant megafossil assemblages from the Cosheston Group and Senni Beds in a more secure stratigraphical framework, thus facilitating comparisons with other Lower Devonian plant megafossil assemblages and enhancing palaeobotanical understanding. Evidence from palynofacies analysis supports sedimentological interpretations which suggest that the ‘Lower Old Red Sandstone’ facies deposits belonging to the Cosheston Group accumulated in a continental fluviatile environment.
-
Palynology of the ‘Lower Old Red Sandstone’ at Glen Coe, Scotland
Geological Magazine, 1994Co-Authors: Charles H. WellmanAbstract:Abstract‘Lower Old Red Sandstone’ deposits preserved by cauldron subsidence at Glen Coe, Scotland have hitherto lacked secure biostratigraphical age constraint. A sporomorph assemblage recoveRed from basal sediments of these deposits permits age determination, despite being highly carbonized. The sporomorph assemblage is correlated with the micrornatus-newportensis Sporomorph Assemblage Biozone, indicating a late early-early late Lochkovian age (early Devonian). Sporomorph assemblages from basal sediments of the ‘Lower Old Red Sandstone’ sequence at nearby Lorne, a suggested correlative of the Glen Coe deposits, are Older (latest Pridoli-earliest Lochkovian age). However, the new biostratigraphical data do not preclude the possibility that the Glen Coe and Lorne deposits are lithological correlatives and the basal sediments are diachronous.
Paul V Wright - One of the best experts on this subject based on the ideXlab platform.
-
the dangers of taking mud for granted lessons from lower Old Red Sandstone dryland river systems of south wales
Sedimentary Geology, 2007Co-Authors: Paul V Wright, Susan B MarriottAbstract:Abstract Mudrocks are a prominent feature of many ancient dryland successions but they are not always a product of the settling out of suspension load. From studies of the late Silurian–early Devonian Old Red Sandstone mudrocks of South Wales it has been shown that many were not overbank sediments deposited from suspension on floodplains, but were emplaced as sand- and silt-sized aggregates transported as bed load and deposited in sinuous channels and as braid-bar complexes on multi-stage floodplains in dryland river systems. Using the Old Red Sandstone examples criteria are provided for the recognition of similar deposits in the sedimentary record. One important aspect of these mudrocks is that they can represent multiple recycling events and can constitute condensed deposits that may be characteristic of closed alluvial basins with periodically limited sediment supply.
Paul Kenrick - One of the best experts on this subject based on the ideXlab platform.
-
the cosheston group lower Old Red Sandstone in southwest wales age correlation and palaeobotanical significance
Geological Magazine, 1998Co-Authors: Charles H. Wellman, Dianne Edwards, R G Thomas, Paul KenrickAbstract:Upper Silurian–Lower Devonian ‘Lower Old Red Sandstone’ facies deposits cropping out in southwest Wales are poorly age-constrained and difficult to correlate. Spore assemblages have been recoveRed from sequences of these deposits belonging to the lower part of the Cosheston Group. The spore assemblages are equated with the breconensis–zavallatus and polygonalis–emsiensis Spore Assemblage Biozones and indicate an early Devonian age (late Gedinnian (late Lochkovian)–Siegenian (Pragian)). The new biostratigraphical data enable correlation of the lower part of the Cosheston Group with the Senni Beds from the main outcrop of the Lower Devonian in South Wales and the Welsh Borderland. In addition, the new age data and stratigraphical correlation place important plant megafossil assemblages from the Cosheston Group and Senni Beds in a more secure stratigraphical framework, thus facilitating comparisons with other Lower Devonian plant megafossil assemblages and enhancing palaeobotanical understanding. Evidence from palynofacies analysis supports sedimentological interpretations which suggest that the ‘Lower Old Red Sandstone’ facies deposits belonging to the Cosheston Group accumulated in a continental fluviatile environment.
J R L Allen - One of the best experts on this subject based on the ideXlab platform.
-
Source rocks of the Lower Old Red Sandstone: Exotic Pebbles from the Brownstones, Ross-on-Wye, Hereford and Worcester
Proceedings of the Geologists' Association, 2009Co-Authors: J R L AllenAbstract:The pebble suite, preserved in Sandstones and conglomerates, comprises various igneous, sedimentary, and metamorphic rocks. The igneous rocks are acid lavas and tuffs, some of the latter with Ordovician graptolites. The sediments include gray-wackes and a variety of well sorted Sandstones, some preserving Silurian shelf-facies faunas, and others Old Red Sandstone faunas together with an Old Red petrography. There are also cataclasites, a metamorphic quartzite, and jaspers that invite comparisons with Precambrian rocks of the type now known in Anglesey. It is concluded on the grounds of fauna, petrographic comparisons, and the facies and cross-bedding orientation of the preserving deposit, that the assemblage originated in the Welsh region from Ordovician, Silurian, early Lower Old Red Sandstone and, perhaps, Precambrian rocks. Its character amplifies the earlier view that by late Lower Devonian times denudation in the Welsh region had already led to the partial removal of early Devonian and Silurian rocks.
-
intraformational conglomerates and scouRed surfaces in the lower Old Red Sandstone of the anglo welsh cuvette
Geological Journal, 2007Co-Authors: J R L AllenAbstract:ScouRed surfaces occur in the upper part of the Lower Old Red Sandstone of the Anglo-Welsh cuvette between cyclothems consisting of intraformational conglomerate→Sandstone→siltstone. The conglomerates are formed chiefly of rocks which can be matched in the deposits of the cuvette, and contain little or no gravel from more distant sources. The scouRed surfaces persist laterally and are preserved typically as casts. They discordantly cut earlier beds, and show a variety of discordantly-filled minor structures (sole marks) due to current scour: flute-like and lobate forms, current crescents, sack-like bulges, terraces and small flat-bottomed channels. Large channels are also known. ScouRed surfaces occur also in the Lower Old Red Sandstone amongst Sandstones, within which they may delineate major groups of sedimentation units as well as individual units in trough cross-stratified compilations. The basal features of the cyclothems (scouRed surfaces, intraformational conglomerates) record periods when sediments of the cuvette were reworked. This probably took place as the rivers instrumental in deposition of the Lower Old Red Sandstone underwent major changes in their courses, perhaps as the result of crevassing directly onto their floodplains. By reference to modern river sands, the trough cross-stratified Sandstones appear to have accumulated on sandbanks in the stream channels of the cuvette through the action of megaripples.
-
Intraformational conglomerates and scouRed surfaces in the lower Old Red Sandstone of the Anglo‐Welsh cuvette
Geological Journal, 2007Co-Authors: J R L AllenAbstract:ScouRed surfaces occur in the upper part of the Lower Old Red Sandstone of the Anglo-Welsh cuvette between cyclothems consisting of intraformational conglomerate→Sandstone→siltstone. The conglomerates are formed chiefly of rocks which can be matched in the deposits of the cuvette, and contain little or no gravel from more distant sources. The scouRed surfaces persist laterally and are preserved typically as casts. They discordantly cut earlier beds, and show a variety of discordantly-filled minor structures (sole marks) due to current scour: flute-like and lobate forms, current crescents, sack-like bulges, terraces and small flat-bottomed channels. Large channels are also known. ScouRed surfaces occur also in the Lower Old Red Sandstone amongst Sandstones, within which they may delineate major groups of sedimentation units as well as individual units in trough cross-stratified compilations. The basal features of the cyclothems (scouRed surfaces, intraformational conglomerates) record periods when sediments of the cuvette were reworked. This probably took place as the rivers instrumental in deposition of the Lower Old Red Sandstone underwent major changes in their courses, perhaps as the result of crevassing directly onto their floodplains. By reference to modern river sands, the trough cross-stratified Sandstones appear to have accumulated on sandbanks in the stream channels of the cuvette through the action of megaripples.
-
studies in fluviatile sedimentation implications of pedogenic carbonate units lower Old Red Sandstone anglo welsh outcrop
Geological Journal, 2007Co-Authors: J R L AllenAbstract:Carbonate units occur in varying numbers in the fine-grade members of the alluvial fining-upwards cyclothems present in the Lower Old Red Sandstone of the Anglo-Welsh outcrop. They closely resemble contemporary soil-carbonates (calcretes) and hence show that the local Siluro-Devonian climate was relatively hot with a comparatively low seasonal rainfall. CompaRed with contemporary calcretes, the units suggest that sites on the alluvial plains were denied river-borne sediments for periods each in the general order of 104 years. The pedogenic interpretation of the carbonate units, developed in the light of the behaviour of rivers today, leads to alternative models for the geomorphology of the Siluro-Devonian alluvial plains and for their gross subsurface structure. Geomorphologically, the plains at any instant presented depositionally active and inactive areas in juxtaposition. Under some circumstances the relief was provided only by alluvial ridges. Under others, relief was afforded by valley sides and perhaps river terraces, in addition to ridges. Knowledge of the character of the Lower Old Red Sandstone in vertical sequence leaves as plausible three alternative gross structures for the alluvial pile beneath the plains. They differ chiefly in the lateral variability and connectedness of the palaeosols and place hitherto unavailable limits on the three-dimensional character of the cyclothems.
Susan B Marriott - One of the best experts on this subject based on the ideXlab platform.
-
the dangers of taking mud for granted lessons from lower Old Red Sandstone dryland river systems of south wales
Sedimentary Geology, 2007Co-Authors: Paul V Wright, Susan B MarriottAbstract:Abstract Mudrocks are a prominent feature of many ancient dryland successions but they are not always a product of the settling out of suspension load. From studies of the late Silurian–early Devonian Old Red Sandstone mudrocks of South Wales it has been shown that many were not overbank sediments deposited from suspension on floodplains, but were emplaced as sand- and silt-sized aggregates transported as bed load and deposited in sinuous channels and as braid-bar complexes on multi-stage floodplains in dryland river systems. Using the Old Red Sandstone examples criteria are provided for the recognition of similar deposits in the sedimentary record. One important aspect of these mudrocks is that they can represent multiple recycling events and can constitute condensed deposits that may be characteristic of closed alluvial basins with periodically limited sediment supply.
