Ludlow Age Research Articles

Silurian Pinnacle Reefs of the Canadian Arctic

Pinnacle reefs are commonly an attractive target for oil exploration because they are usually porous carbonate bodies entombed in impervious, deep-water shales that provide both the source and the seal for hydrocarbons. Silurian pinnacle reefs, the first described in the Canadian Arctic Archipelago, are exposed on Ellesmere and Devon Islands. Two main reef trends occur, one of early middle Llandovery to middle Ludlow age and a second of middle Ludlow to Late Silurian or Early Devonian age. Reefs of both phases contain lime mudstone cores: some are stromatactoid-rich and others consist predominantly of microbialite-rich lime mudstone or microbial boundstone. Facies sequences of both reef phases show evidence of upward-shallowing overall, but, in the older reefs, isochronous capping facies are dominated either by coral-mirian or by stromatoporoid boundstone and floatstone. This difference perhaps reflects variation in wave stress and apparent ability of a few corals,thickly encrusted by or associated with microbial boundstone and skeletal algae, to withstand greater wave energy than a stromatoporoid-coral-rich reef community. These reefs constitute one of the bright prospects of hydrocarbon exploration in rocks of the Franklinian succession. 43 refs., 9 figs.

Upper Silurian Trilobitesof Bohemian affinities from the West Asturian-Leonese zone (NW Spain)

Fossiliferous localities within chloritoid slates of Upper Ludlow age from the West Asturian-Leonese Zone (N.W. Spain) in the Peñalba and Sil synclines are here reviewed. On a regional scale, the occurrence of similar facies and faunas within both synclines indicates that the limit between the West Asturian-Leonese Zone and the Central-Iberian Zone most probably runs within the Sil syncline. Trilobite faunas with representatives of the genera Crotalocephalus, Cerauroides, Cromus, Denckmannites? and Lioharpes (Fritchaspis) have clear affinities with the Prionopeltis archiaci Assemblage of the Upper Ludlow in Bohemia. From a palaeogeographical point of view, the occurrence of Silurian trilobites with Bohemian affinities in N.W. Spain as well as in Pyrenees and Catalonia may suggest the possible existence of a North-Iberian. Domain including these regions and southern France (Aquitaine, Montagne Noire).

Some late Wenlock and Ludlow monograptid graptolites, Cornwallis Island, Arctic Canada

Seven species of uncompressed latest Wenlock and Ludlow monograptid graptolites, isolated from calcareous concretions, are described and illustrated. The biostratigraphically important species "Pristiograptus" ludensis, of latest Wenlock age, and Saetograptus fritschi linearis and Monograptus ceratus, of mid-Ludlow age, are illustrated in uncompressed form for the first time. The remaining species described include Bohemograptus bohemicus tenuis, Colonograptus colonus, Saetograptus ex gr. chimaera, and Pristiograptus dalejensis, all of Ludlow age. The last-named species is the most common but is biostratigraphically long ranging.

Palynology of the Stonehaven Group, Scotland: evidence for a Mid Silurian age and its geological implications

AbstractPalynomorphs from the Stonehaven Group indicate a late Wenlock to early Ludlow age. This is older than the currently accepted Pridoli age based on fish and arthropods. Reasons for this discrepancy are discussed. A previous correlative of the Stonehaven Group has been the Old Red Sandstone of Kerrera, Argyll. However, palynological assemblages from both Kerrera and the adjacent succession at Oban are in fact younger than that from Stonehaven in being of latest Silurian to earliest Devonian age. The palynomorphs from Kerra and Oban lie beneath the important geochronological tie-point of the Lorne Lavas and suggest that the Silurian-Devonian boundary is older than currently accepted.

Ludlow and Pridoli (Upper Silurian) graptolite biostratigraphy of the central Arctic Islands: a preliminary report

A fauna, comprising slightly more than 30 species of Upper Silurian graptolites, has been recognized from the Arctic Islands. The following preliminary biostratigraphic biozones are recognizable: Lobograptus progenitor, Saetograptus fritschi linearis, and Bohemograptus bohemicus tenuis zones of Ludlow age; and the Pseudomonoclimacis parultinus, Pseudomonoclimacis ultimus, Monograptus bouceki, "Pristiogratpus" transgrediens, and Monograptus cf. birchensis zones of Pridoli age. The last-named zone may range into the Devonian. The faunal composition and zones are relatively close to coeval faunas of northern Yukon. They are, however, distinctly depauperate in comparison with the faunas of Poland, Czechoslovakia, or Kazakhstan.

An oceanic model for lithological and faunal changes tested on the Silurian record

A model for oceanic cycles is presented. The cycles are expressed as changes between more humid low latitude and cooler high latitude climates (P episodes), and dryer low latitude and warmer high latitude climates (S episodes). The cyclicity may be self-regulating through changes in the CO 2 storage capacity of the deep ocean due to temperature changes and through changes in the oceanic input and output of dissolved carbonate. The model permits over 30 predictions regarding observable changes in both deep water and shelf lithologies and variations in the abundance, diversity and extinction rate of planktic and benthic faunas. Sedimentary changes involve fluctuations in the rate of clay deposition and carbonate production, the advance and retreat of carbonate deposition on the shelf edge, the timing of oolite, reef, and black shale formation, and changes between oxic and anoxic deep water. Faunal effects include both iterative evolution and intermittently widespread taxa (‘Lazarus taxa’). These predictions agree well with changes observed in well known sequence of Wenlock and Ludlow age, as well as changes seen in selected older and younger sequences.

Silurian ostracoderms from Washington Land (North Greenland), with comments on cyathaspid structure, systematics and phyletic position

The few detached dermal elements recorded here document a new ostracoderm fauna comprising undeterminable species of one anaspid, two cyathaspids and a heterostracan which might have its closest relatives among the pteraspids. This fauna is derived from marine deposits of ultimate Wenlock or possibly Early Ludlow age at the top of the Lafayette Bugt Formation in its type section, in Washington Land, western North Greenland. It is probably equivalent to one of the undescribed faunas known from the Monograptus testis - M. nilssoni sequence of the Cape Phillips Formation in the Canadian Arctic Archipelago. Comparative material from Norway and Spitsbergen is considered in this study which prompted general comments on cyathaspid squamation, vestigial fin structure, cyathaspid systematics, their phyletic position relative to the pteraspids, system of stability control in swimming, their habitats and diets.

Silurian palynomorphs from the Chester Bjerg Formation, Hall Land, western North Greenland

Silurian palynomorphs from a single sample from the Chester Bjerg Formation, near Halls Grav, Hall Land, western North Greenland are of Wenlock or possibly early Ludlow age. Graptolites from the same sequence indicate a Pridoli (latest Silurian) age. The strata in question are the youngest known pre-Innuitian orogeny deposits in North Greenland. Possibie reworking of the palynomorphs in the turbidite sequence is discussed.

Silurian trilobites from arctic Canada

SummaryTrilobites of upper Ludlow age are described from Member A of the Read Bay Formation on Cornwallis Island. Four new species are represented: Helokybe spio gen. et sp.nov. (Dechenellinae), Encrinurus hyperboreus sp. nov., Kailia? capra sp.nov. (Encrinurinae) and Hemiarges echinatus sp.nov. Other taxa present are: an effaced scutelluid; Cyphaspis sp.; a warburgelline; two more encrinurids; two other forms of Hemiarges. The trilobites occur in sediments indicative of a shallow subtidal environment, with the exception of the warburgelline which occurs in sediments deposited under deeper subtidal conditions below storm wave-base.

Ordovician Graptolites from the Kashmir Himalayas

THE discovery of graptolites near the village of Harpatnar in the Anantnag District of Kashmir1 was of considerable interest to geologists studying the history of the Himalayas, because the apparent absence of graptolites from the Himalayas had long been the subject of considerable debate and speculation. The graptolites (described in ref. 2) indicate a Ludlow (Late Silurian) age for the Harpatnar Beds from which they were collected2.

SILURIAN STROMATOPOROIDS OF THE MATAPEDIA–TEMISCOUATA AREA, QUEBEC

Stromatoporoids are abundant in parts of the Sayabec, St. Leon, and Mont Wissick formations of Wenlock and Ludlow age in eastern Quebec, Canada. The fauna is a mixture of species from Wenlock strata of northern Europe, the Wenlock and Ludlow beds of Baie des Chaleurs, Quebec, and Niagaran rocks of the Great Lakes region. Clathrodictyon crickmayi and Stromatopora prima show the affinity of the fauna to that described by Parka from Baie des Chaleurs. Densastroma astroites indicates a close connection of the fauna with the rocks of Wenlock age in England and the Baltic area. Stromatopora antiqua shows the affinity of the fauna to that of central North America. Ecclimadictyon fastigiatum is a widespread species in all these regions. A new species of Actinodictyon (A. quebecense) is described. Two unnamed species of Stromatopora and Clathrodictyon cf. podolica make up the rest of the fauna.

Discovery of a Diplochone (Rugosa) in the Silurian of the Subpolar Urals

Diplochone kozhimica n. sp. is described from deposits of Ludlow age in the northern Urals. One of the described specimens grew on the surface of a colony of Squameofavosites sp. The morphologic effects on the rugose coral include basal processes that extend into the tabulate corallites, a broad, enlarged base, and stereoplasmic thickening of skeletal elements. — W. A. Oliver, Jr..

Origin and distribution of rocks of Ludlow age (Late Silurian) in the northern Appalachians

Origin and distribution of rocks of Ludlow age (Late Silurian) in the northern Appalachians

Graptolites from the Kashmir Himalayas, also a Note on the Discovery of Fossils in the Muth Quartzite

IN continuation of our note1 “Graptolites in the Indian sub-continent”, field work was recommenced by one of us (V. J. G.) earlier in 1964 and resulted in further graptolite discoveries. The doubt conveyed in our previous note in referring the graptolites we illustrated to Didymograptus (?) was well founded because examination of these by Dr. C. J. Stubblefield revealed sicular structures of Monograptid type and he refers the figured specimens to Monograptus cf. vulgaris Wood and to M. cf. colonus (Barrande) of Lower Ludlow (Silurian) age. Additional graptolites collected this year from 3 ft. higher in the succession he refers to Monograptus cf. dubius (Suess), a species which, in Europe, ranges from Wenlock to Lower Ludlow in age. Further Monograptids were found associated with an internal mould of Cardiola cf. interrupta Broderip 30 ft. below M. cf. dubius; in Europe this lamellibranch species ranges from Wenlock to Ludlow. Thus we surmise that these 30 ft. of mudstones are of Lower Ludlow age, but possibly include some Wenlock.

REVISION OF THE GENUS PLASMOPORA

In a study based on published descriptions and illustrations of Silurian heliolitid corals and on new collections of Ludlow age from Kzakhstan, the author assigns species whichhave been or which might have been assigned to Plasmopora, to six genera in two families and orders of heliolitids. The genera are based on coenenchyme character (tubular, vacuolar, mixed) and septal structures (plates, spines, squamulae). In the following classification the type species of new genera are in parentheses: Order Heliolitida, Family Heliolitidae, Subfamily Pseudoplasrnorinae (new), Visbylites gen. nov. (Plasmopora stella Lindstrom, 1899), Pseudoplasmopora gen. nov. (P. conspecta sp. nov.). Order Proporida, Family Plasmoporidae, Laminoplasma gen. nov. (Plasmopora calyculata Lindstrom, 1899), Plasmopora F and H, 1849, Eolaminoplasma gen. nov. (Plasmopora osa Lindstrom, 1899), Squameolites gen. nov. (S. squamiger sp. nov.). William A. Oliver, Jr.

Metamorphosed Silurian Brachiopods from New Hampshire

Generically identifiable Silurian brachiopods from rocks of the staurolite and sillimanite zones of regional metamorphism have been found at a number of localities in the Clough Formation of west-central New Hampshire. They include representatives of 19 brachiopod genera, 1 gastropod, 1 trilobite, and 1 pelmatozoan. The fossils occur as two faunas. The first, characterized by Stricklandia lens cf. S. lens ultima, is probably of C4 to C5 or C6 age; the second, characterized by Eocoelia hemisphaerica, is of C3 to C5 age. Paleogeographically these New Hampshire fossils demonstrate that during late Llandovery time Appalachia was quite narrow, even if allowance is made for subsequent deformation. The present distance from Utica, New York (where marine beds of Clinton age occur to the west and nonmarine beds to the east), to the Connecticut River valley (where the widely distributed Clough Formation contains marine fossils of late Llandovery age) is about 140 miles. The northern and southern bounds of Appalachia are not well delimited for this time interval. The northern limit may have been an area east of Lake Temiscouata, Quebec, and the southern limit an area in northwestern Georgia. Thus Appalachia during this time is reconstructed as a narrow, elongate island or archipelago extending from Quebec to Georgia. A brachiopod (Howellella sp.) from the Shaw Mountain Formation of eastern Vermont indicates an age of C3 to early Gedinnian for that unit. The brachiopods of Ludlow age from the type Fitch Formation of northern New Hampshire are redescribed.

The silurian succession at cwm graig DDU (breconshire)

AbstractThe Silurian rocks of Cwm Graig Ddu consist mostly of blue and grey shales and mudstones, all of Ludlow age, the succession extending from the nilssoni Zone of the Lower Ludlow to the Holopella Grits and Shales at the top of the Upper Ludlow. They are overlain by the Tilestones of the Lower Downtonian. The rocks are exposed along the side of the Brecon road on the western side of the valley, in the cliffs at its head, and in the roadside quarries beyond its head. The succession, generally, closely resembles that of the Builth district, but differs in detail. The Lower Ludlow rocks contain many slumped bands which vary in thickness from several inches to many feet.

The Highest Silurian Hooks of the Clun-Forest District (Shropshire)

I. Introduction. In the counties of Radnorshire, Montgomeryshire, Shropshire, and Herefordshire, rocks of Ludlow age have been indicated over considerable areas on the Geological Survey maps. 1 There are also several large outliers of Old Red Sandstone strata in this region, and both sets of rocks are crossed from Church Stretton on the north to beyond Presteign on the south by the great Church-Stretton Fault (see fig. 1, p. 222). This fault marks approximately the boundary between the shelly calcareous type of Silurian sediment in Shropshire and the argillaceous type in Wales. The Shropshire succession of Ludlow rocks has been studied in detail (most recently by Miss G. L. Elles & Miss I. L. Slater 2 ), and the ground has been well known to geologists since the original work of Murchison. 3 On the other hand, the country immediately to the west of the great fault is little known, and no detailed account of the uppermost Silurian and Old Red Sandstone rocks has been published. Scattered references certainly exist, but they deal with the general characters of the district rather than with special features and definite localities. It was, therefore, suggested by Dr. A. H. Cox that I should undertake an examination of the area, with the view of determining the sequence and distribution of the uppermost Silurian strata. These rocks are here of especial interest, since the district occupies an intermediate position between the Shropshire (Ludlow) district with its calcareous type of sediment, on the one side, and the Welsh area, where

The Zonal Classification of the Salopian Rocks of Cautley and Ravenstonedale

I. I ntroduction and L iterature . W e were induced by Dr. Marr to undertake the examination of the Salopian rocks of the area under consideration. He had failed in former years to obtain any zonal succession of the rocks of Wenlock age in the Lake District, owing to the cleaved nature of the rocks of that age above the lowest beds containing Cyrtograptus murchisoni . An examination of the less cleaved representatives of the Wenlock Beds near Cautley had convinced him that a succession might be established there, similar to that described in Scania by Tullberg, and in Wales and the Welsh borderland by Mrs. Shakespear and Miss Elles. Our study of the Wenlock and Ludlow rocks of the Cautley and Ravenstonedale area has convinced us that these beds are capable, of a division into zones, although some of the zones recognized farther south apparently do not persist when traced northwards to this district. The Cautley and Ravenstonedale area is situated north of Sedbergh; its northern and eastern limits are defined by Carboniferous rocks, but on the west it is continuous with the Salopian of the Lake District. The physiography of the district and the features due to ice-action have recently been described by Dr. Marr & Mr. Fearnsides: it will suffice, therefore, to mention here that the area is a very hilly one, the fells often rising steeply from the 600- to the 1750-foot contour-line. North-west of the Rawthey the hilltops are everywhere formed of hard grits of Ludlow age, while on

II. Carboniferous Rocks of the Solway, Scotland

On the Solway, fringes of Lower Carboniferous rocks occur in six districts. 1. From White Port to Abbey Burnfoot. 2. From Abbey Burnfoot to Airds Point. 3. From the Urr Water to Gutchers Isle. 4. From Portowarren to Portling. 5. Near mouth of Southwick Water. 6. From Southerness Point to Hogus Point. Inland they rest unconformably either on Silurian strata or on granite of the Criffel-Dalbeattie mass, and probably at places on remnants of Old Red Sandstone, and at parts are faulted against the older rocks. 1. White Port to Abbey Burnfoot. At White Port, a small bay, with neither houses, harbour, nor road, Silurian strata (probably of Ludlow age, and closely resembling the thin-bedded strata of that formation on the Greenock Water, near Muirkirk) are seen in the tideway, with a steep dip to the N.W. On the high bank above, the Carboniferous strata dip to the S.E., but the junction between the two formations is obscured by debris and vegetation. The junction is probably an unconformity—not a fault—as there is a basal conglomerate with abundance of bits of Silurian rocks. Here the “Survey” got the Carboniferous fossil Syringopora ramulosa . Parts of this conglomerate are cemented by limestone. The next conglomerate higher up, and separated from the last by a band of red shale, is 10 feet thick, and conspicuous from the large quantity of white quartz pebbles it contains, there being a few pebbles of metamorphosed Arenig chert in it. No other conglomerate on the Solway This 250-word extract was created in the absence of an abstract