Page 1. A CORALLINE-LIKE RED ALGA FROM THE LOWER ORDOVICIAN OF WALES by ROBERT RIDING, JOHN С W. ... more Page 1. A CORALLINE-LIKE RED ALGA FROM THE LOWER ORDOVICIAN OF WALES by ROBERT RIDING, JOHN С W. COPE and PAUL D. TAYLOR Abstract. A new alga, Arenigiphyllum crustosum gen. et sp. nov., from the ...
Volcanic rocks of Neoproterozoic age form several fault-related inliers in Wales and the Welsh Bo... more Volcanic rocks of Neoproterozoic age form several fault-related inliers in Wales and the Welsh Borderland. Those in North Wales and the Borderland have been investigated recently, while those in southwest Wales remain little studied. In southwest Wales, basic to intermediate lavas and related volcaniclastic rocks and silicic tuffs in the St David’s area comprise the Pebidian Supergroup, which is intruded by minor basic intrusions, while the Coomb Volcanic Formation, exposed farther east around Llangynog, is composed of basic and silicic lavas and silicic tuffs, intruded by a single dacite sill and numerous dolerite sills. New geochemical data show that both the Pebidian and Coomb basalts have subduction-related characteristics. The Coomb basalts are geochemically similar to those of the Uriconian Group of the Welsh Borderland, while the Pebidian basalts bear a similarity to volcanic rocks recovered from the Bryn-teg Borehole, in the Harlech Dome. Uriconian-type volcanic rocks may un...
Detailed mapping of the Precambrian rocks of the Llangynog Inlier, made possible by a series of n... more Detailed mapping of the Precambrian rocks of the Llangynog Inlier, made possible by a series of new exposures, has allowed the establishment for the first time of the 1100 m thick succession within the Precambrian rocks of the area. All boundaries of the Precambrian rocks with younger strata in the area are either faults or unconformities. Some 350–400 m of rhyolitic lavas form the oldest rocks seen in the area; they are extensively silicified and devitrified and show little of their original texture, although flow-banding is visible in some outcrops and the presence of perlitic and snowflake textures imply that originally they were glassy in part. These lavas are succeeded by a varied succession dominated by volcaniclastic siltstones showing evidence of shallow water deposition and containing medusoids and trace fossils of Ediacaran age. Interbedded in the sediments are basaltic lavas, autobreccias and rare hyaloclastites displaying textural features characteristic of submarine eru...
... REFERENCES bates. D. е. в. 1968. ... 155pp., 99 text-figs., 30plates. Price £16 (US $24). 21.... more ... REFERENCES bates. D. е. в. 1968. ... 155pp., 99 text-figs., 30plates. Price £16 (US $24). 21. (for 1978): Devonian Ammonoids from the Appalachians and their bearing on International Zonation and Correlation, by MR house. 10pp., 12 text-figs., 10plates. Price £12 (US $18). 22. ...
ABSTRACT: Considerable confusion exists in the interpretat ion of the te rm Kimmeridgian. As the ... more ABSTRACT: Considerable confusion exists in the interpretat ion of the te rm Kimmeridgian. As the Kimmeridge Clay Formation is the principal source rock in the nor thern North Sea, this confusion has important implications for geoscientists working there. The source of the confusion is historical, but the introduct ion of the Bolonian Stage as a local secondary standard stage would result in a Kimmeridgian Stage of uniform length, no mat ter w h e t h e r a company preferred to use Volgian or Portlandian as the terminal Jurassic Stage. The resolution of this ambiguity will be we lcomed by all.
A low diversity Sinuitesdominated gastropod community is described from the Floian, Arenig Serie... more A low diversity Sinuitesdominated gastropod community is described from the Floian, Arenig Series, of the Llangynog Inlier, southwest of Carmarthen, South Wales. The abundant material comes from shallowwater siltstone and mudstone beds of the Bolahaul Member of the Ogof Hên Formation. The locality has an exceptionally diverse molluscdominated fauna (63.5% of the fauna), with gastropods constituting 6% and tergomyans 1% and echinoderms, arthropods and other fauna making up the rest. Except for one rare tergomyan mollusc, identified as Carcassonnella cf. vizcainoi, other tergo myans are described elsewhere. Nearly half of all gastropod specimens are represented by Sinuites ramseyensis. Three of the five taxa described are new: Mimospira llangynogensis sp. nov., Catalanispira prima sp. nov., and Ceratopea? moridunensis sp. nov. The assemblage compares best with those of contemporaneous highlatitude periGondwana areas. Early Ordovician species of Carcassonnella are typically found...
Page 1. A CORALLINE-LIKE RED ALGA FROM THE LOWER ORDOVICIAN OF WALES by ROBERT RIDING, JOHN С W. ... more Page 1. A CORALLINE-LIKE RED ALGA FROM THE LOWER ORDOVICIAN OF WALES by ROBERT RIDING, JOHN С W. COPE and PAUL D. TAYLOR Abstract. A new alga, Arenigiphyllum crustosum gen. et sp. nov., from the ...
Volcanic rocks of Neoproterozoic age form several fault-related inliers in Wales and the Welsh Bo... more Volcanic rocks of Neoproterozoic age form several fault-related inliers in Wales and the Welsh Borderland. Those in North Wales and the Borderland have been investigated recently, while those in southwest Wales remain little studied. In southwest Wales, basic to intermediate lavas and related volcaniclastic rocks and silicic tuffs in the St David’s area comprise the Pebidian Supergroup, which is intruded by minor basic intrusions, while the Coomb Volcanic Formation, exposed farther east around Llangynog, is composed of basic and silicic lavas and silicic tuffs, intruded by a single dacite sill and numerous dolerite sills. New geochemical data show that both the Pebidian and Coomb basalts have subduction-related characteristics. The Coomb basalts are geochemically similar to those of the Uriconian Group of the Welsh Borderland, while the Pebidian basalts bear a similarity to volcanic rocks recovered from the Bryn-teg Borehole, in the Harlech Dome. Uriconian-type volcanic rocks may un...
Detailed mapping of the Precambrian rocks of the Llangynog Inlier, made possible by a series of n... more Detailed mapping of the Precambrian rocks of the Llangynog Inlier, made possible by a series of new exposures, has allowed the establishment for the first time of the 1100 m thick succession within the Precambrian rocks of the area. All boundaries of the Precambrian rocks with younger strata in the area are either faults or unconformities. Some 350–400 m of rhyolitic lavas form the oldest rocks seen in the area; they are extensively silicified and devitrified and show little of their original texture, although flow-banding is visible in some outcrops and the presence of perlitic and snowflake textures imply that originally they were glassy in part. These lavas are succeeded by a varied succession dominated by volcaniclastic siltstones showing evidence of shallow water deposition and containing medusoids and trace fossils of Ediacaran age. Interbedded in the sediments are basaltic lavas, autobreccias and rare hyaloclastites displaying textural features characteristic of submarine eru...
... REFERENCES bates. D. е. в. 1968. ... 155pp., 99 text-figs., 30plates. Price £16 (US $24). 21.... more ... REFERENCES bates. D. е. в. 1968. ... 155pp., 99 text-figs., 30plates. Price £16 (US $24). 21. (for 1978): Devonian Ammonoids from the Appalachians and their bearing on International Zonation and Correlation, by MR house. 10pp., 12 text-figs., 10plates. Price £12 (US $18). 22. ...
ABSTRACT: Considerable confusion exists in the interpretat ion of the te rm Kimmeridgian. As the ... more ABSTRACT: Considerable confusion exists in the interpretat ion of the te rm Kimmeridgian. As the Kimmeridge Clay Formation is the principal source rock in the nor thern North Sea, this confusion has important implications for geoscientists working there. The source of the confusion is historical, but the introduct ion of the Bolonian Stage as a local secondary standard stage would result in a Kimmeridgian Stage of uniform length, no mat ter w h e t h e r a company preferred to use Volgian or Portlandian as the terminal Jurassic Stage. The resolution of this ambiguity will be we lcomed by all.
A low diversity Sinuitesdominated gastropod community is described from the Floian, Arenig Serie... more A low diversity Sinuitesdominated gastropod community is described from the Floian, Arenig Series, of the Llangynog Inlier, southwest of Carmarthen, South Wales. The abundant material comes from shallowwater siltstone and mudstone beds of the Bolahaul Member of the Ogof Hên Formation. The locality has an exceptionally diverse molluscdominated fauna (63.5% of the fauna), with gastropods constituting 6% and tergomyans 1% and echinoderms, arthropods and other fauna making up the rest. Except for one rare tergomyan mollusc, identified as Carcassonnella cf. vizcainoi, other tergo myans are described elsewhere. Nearly half of all gastropod specimens are represented by Sinuites ramseyensis. Three of the five taxa described are new: Mimospira llangynogensis sp. nov., Catalanispira prima sp. nov., and Ceratopea? moridunensis sp. nov. The assemblage compares best with those of contemporaneous highlatitude periGondwana areas. Early Ordovician species of Carcassonnella are typically found...
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