scholarly journals The Cosheston Group (Lower Old Red Sandstone) in southwest Wales: age, correlation and palaeobotanical significance

1998 ◽  
Vol 135 (3) ◽  
pp. 397-412 ◽  
Author(s):  
C. H. WELLMAN ◽  
R. G. THOMAS ◽  
D. EDWARDS ◽  
P. KENRICK
Keyword(s):  
Lower Devonian ◽  
New Age ◽  
Early Devonian ◽  
Red Sandstone ◽  
South Wales ◽  
Upper Silurian ◽  
Devonian Age ◽  
Sandstone Facies

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.

Vertebrate remains from Upper Silurian – Lower Devonian beds of Hall Land, North Greenland

1999 ◽  
pp. 1-80 ◽  
Author(s):  
Henning Blom
Keyword(s):  
Lower Devonian ◽  
Age Determination ◽  
Early Devonian ◽  
Marine Strata ◽  
South Of Siberia ◽  
Minor Part ◽  
Upper Silurian ◽  
A Minor ◽  
Devonian Age ◽  
North Greenland

NOTE: This monograph was published in a former series of GEUS Bulletin. Please use the original series name when citing this monograph, for example: Blom, H. (1999). Vertebrate remains from Upper Silurian – Lower Devonian beds of Hall Land, North Greenland. Geology of Greenland Survey Bulletin, 182, 1-80. https://doi.org/10.34194/ggub.v182.5126 _______________ Vertebrate microscopic remains of twenty-six taxa of thelodonts, heterostracans, osteostracans, anaspids, acanthodians and chondrichthyans are described from limestone beds in two localities of Late Silurian - Early Devonian age of the Chester Bjerg Formation, Hall Land, North Greenland. The limestone beds form a minor part of a monotonous calcareous sandstone-siltstone-mudstone sequence at the top of the Franklinian Basin succession.Stratigraphical recognition using several thelodont and acanthodian taxa, supported by regional geological and structural trends, suggests a Silurian-Devonian boundary interval between beds of the Halls Grav and Monument localities. This possible resolution of the previous problematic correlation between the two distant sections of monotonous nature demonstrates the potential biostratigraphic utility of thelodonts in Silurian -Devonian marine successions.The Chester Bjerg Formation thelodont assemblage is unique with several new endemic taxa, but Loganellia cf. L. tuvaensis is very similar to the type material of the Tuva region south of Siberia, Russia and indicates a Late Silurian age for the beds of the Halls Grav locality. Canonia cf. C. grossi suggests an Early Devonian age for the Monument locality, since Canonia is so far only found in Lower Devonian marine strata of Arctic Canada and Russia. Fragments of cosmopolitan acanthodian genera such as Poracanthodes, Gomphonchus and Nostolepis are found together with heterostracans, osteostracans, anaspids and chondrichthyans at both localities but do not give a more exact age determination than Late Silurian - Early Devonian. New thelodont taxa are Loganellia almgreeni sp. nov., Paralogania foliala sp. nov., Praetrilogania grabion gen. et sp. nov. and Thulolepis striaspina gen. et sp. nov. Nostolepis halli sp. nov. is a new acanthodian species.

scholarly journals II - The Acanthodian fishes

1937 ◽  
Vol 228 (549) ◽  
pp. 49-146 ◽  
Keyword(s):  
Lower Devonian ◽  
Good Evidence ◽  
Caudal Fin ◽  
Red Sandstone ◽  
The World ◽  
Upper Silurian ◽  
Devonian Age ◽  
Fin Spines

The Acanthodian fishes form one of the most sharply demarcated and recognizable groups of vertebrate fossils. Their characteristic squamation of square, exceedingly minute ganoid scales, and the fact that all the fins except the caudal fin are supported by large anterior spines, distinguish them sharply from all other fishes, and enable even fragmentary specimens to be recognized without doubt. They are worldwide in distribution, and their range in tim e is thus known with considerable certainty. The first fragments, attributed on very good evidence to the group, are isolated fin spines, found in Upper Silurian rocks perhaps not earlier than the Downtonian, which seem to be identical with those found in complete fishes of Lower Devonian age. The group was more varied in structure and played a larger part in the world in Lower Devonian times than at any other period. Even in the Middle Old Red Sandstone the range in structure had been reduced, and by Carboniferous times very few forms remained.

Lower Devonian plant and spore assemblages from Lower Old Red Sandstone strata of Tredomen Quarry, South Wales

2011 ◽  
Vol 165 (3-4) ◽  
pp. 183-208 ◽  
Author(s):  
Jennifer L. Morris ◽  
John B. Richardson ◽  
Dianne Edwards
Keyword(s):  
Lower Devonian ◽  
Red Sandstone ◽  
South Wales

Chronometric calibration of mid-Ordovician to Tournaisian conodont zones: a compilation from recent graphic-correlation and isotope studies

1992 ◽  
Vol 129 (6) ◽  
pp. 709-721 ◽  
Author(s):  
Barry G. Fordham
Keyword(s):  
High Resolution ◽  
High Precision ◽  
Time Scale ◽  
Lower Devonian ◽  
New South ◽  
Upper Ordovician ◽  
South Wales ◽  
Isotope Studies ◽  
Stratotype Section ◽  
Upper Silurian

AbstractThree available graphic-correlation analyses are used to calibrate mid-Palaeozoic conodont zonations: Sweet's scheme for the mid- to Upper Ordovician; Kleffner's for the mid- to Upper Silurian; and Murphy & Berry's for the lower and middle Lower Devonian. The scheme of Sweet is scaled by applying the high-precision U-Pb zircon date of Tucker and others for the Rocklandian and linked with that of Kleffner by scaling the graptolite sequence of the Ordovician-Silurian global stratotype section to fit two similarly derived dates from this sequence. The top of Kleffner's scheme, all of Murphy & Berry's, as well as standard zones to the Frasnian are calibrated by using tie-points of the latest Cambridge-BP time-scale (GTS 89). However, the recent microbeam zircon date by Claoué-Long and others for the Hasselbachtal Devonian-Carboniferous auxiliary stratotype is used to calibrate the standard Famennian zones. Also the similarly derived but preliminary determination reported by Roberts and others from the Isismurra Formation of New South Wales is tentatively taken as the top of the Tournaisian and so used to calibrate Tournaisian zones. Despite the considerable extrapolation required to compile these schemes and their inherent errors, the resultant time-scale closely agrees with other dates of Tucker and others from the Llanvirn as well as the GTS 89 Homerian-Gorstian tie-point. This suggests that stratigraphic methods can be usefully applied to geochronometry. The Llandovery appears to have lasted longer (16 m. y.) than usually envisaged and the Ordovician-Silurian boundary may need to be lowered to approximately 443.5 Ma. Certainly, chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high-resolution dating for their calibration will be crucial to more accurate biochronometries.

Synchronology

1985 ◽  
Vol 309 (1138) ◽  
pp. 11-27 ◽  
Keyword(s):  
Sea Level ◽  
Quantitative Methods ◽  
Lower Devonian ◽  
Practical Interest ◽  
Radiometric Dating ◽  
Vertebrate Evolution ◽  
Significant Evidence ◽  
Red Sandstone ◽  
Level Curves ◽  
Upper Silurian

Radiometric dating cannot as yet approach the resolution obtainable in Silurian and Devonian biostratigraphy. Progress towards achievement of a global standard for the Wenlock and Emsian interval (against which evolution and environment must be seen) is reviewed. In biostratigraphical correlation with this standard certain groups are especially useful. Correlation between marine Upper Silurian and Lower Devonian rocks and their equivalents in the Old Red Sandstone magnafacies presents particular problems and yet the latter provides significant evidence of plant and vertebrate evolution at this time. The recognition of widespread physical events such as volcanic episodes may sometimes prove useful. Sea level curves seldom provide a precise synchronology not achievable through biostratigraphy. Quantitative methods of correlation are so far of theoretical rather than practical interest.

scholarly journals A Lower Devonian age for the Corvock Granite and its significance for the structural history of South Mayo and the Laurentian margin of western Ireland

2021 ◽  
Author(s):  
John Graham ◽  
Nancy Riggs
Keyword(s):  
Lower Devonian ◽  
Early Devonian ◽  
North East ◽  
The North ◽  
Granite Emplacement ◽  
History Of ◽  
Western Ireland ◽  
Laurentian Margin ◽  
Devonian Age ◽  
Restraining Bend

The Silurian Croagh Patrick succession, which crops out just south of a fundamental Caledonian structural zone near Clew Bay, western Ireland, is a series of psammites and pelites with a strong penetrative cleavage. These rocks are intruded by the Corvock granite. A suite of minor intrusions associated with the granite contains the regional cleavage whereas the Corvock granite is undeformed. New U-Pb dates are 413 + 7 / -4 Ma for a strongly cleaved sill and 410 ± 4 Ma for the main granite and closely constrain the age of crystallization of the granite and coeval cleavage formation as Lower Devonian (Lochkovian or Pragian), implying syn- to late-kinematic granite emplacement. These data are consistent with evidence for strong sinistral shear shown by the Ox Mountains granodiorite just to the north-east dated at 412.3 ± 0.8 Ma. This Devonian cleavage is superimposed on Ordovician rocks of the South Mayo Trough. The localisation of the strong deformation is interpreted as being due to its position at a restraining bend during regional sinistral motion on a segment of the Fair Head-Clew Bay Line to the north. Contemporaneous deformation in the syn-kinematic Donegal batholith suggests a transfer of sinistral motion to this intra-Grampian structure rather than simple along-strike linkage to the Highland Boundary Fault in Scotland. Our new data indicate diachronous deformation during the late Silurian and early Devonian history of the Irish and Scottish Caledonides and also support previous interpretations of diachronous deformation between these areas and the Appalachian orogens.

Spore assemblages from the Lower Devonian ‘Lower Old Red Sandstone’ deposits of Arran, Scotland

2009 ◽  
Vol 100 (04) ◽  
pp. 391-397 ◽  
Author(s):  
Charles H. Wellman
Keyword(s):  
Lower Devonian ◽  
Early Devonian ◽  
Red Sandstone ◽  
Extensive Sequence

ABSTRACTDispersed 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 theEmphanisporites 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.

Lower Devonian conodonts from Port St. Nicholas, southeastern Alaska

1977 ◽  
Vol 14 (12) ◽  
pp. 2928-2936 ◽  
Author(s):  
Norman M. Savage ◽  
Michael Churkin Jr. ◽  
G. Donald Eberlein
Keyword(s):  
Lower Devonian ◽  
Early Devonian ◽  
Devonian Age

Conodonts from a limestone interval exposed above Port St. Nicholas, Prince of Wales Island, southeastern Alaska, include Pandorinellina exigua philipi (Klapper), Eognathodus sulcatus Philip, and Pelekysgnathus serratus Jentzsch. These conodonts indicate an early to middle Pragian age (informal faunal units 5 or 6 of Klapper et al). This middle Early Devonian age is supported by the presence of the graptolites Monograptus yukonensis, M. craigensis, and M. pacificus in shales above the limestone and by some shelly fossils from within the limestone.

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