Lower Ordovician Conodonts in North America

1970 ◽  
pp. 63-82 ◽  
Author(s):  
Raymond L. Ethington ◽  
David L. Clark
Keyword(s):  
North America ◽  
Lower Ordovician

New echinoderms from the Early Ordovician of west Texas

1994 ◽  
Vol 68 (2) ◽  
pp. 324-338 ◽  
Author(s):  
James Sprinkle ◽  
Gregory P. Wahlman
Keyword(s):  
North America ◽  
El Paso ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
West Texas ◽  
Lower Ordovician ◽  
Single Well ◽  
Thecal Plate ◽  
Stem Segments

Four specimens of blastozoan and crinozoan echinoderms are described from the Lower Ordovician El Paso Group in the southern Franklin Mountains just north of El Paso, west Texas.Cuniculocystis flowerin. gen. and sp., based on two partial specimens, appears to be a typical rhombiferan in most of its morphologic features except that it lacks pectinirhombs and instead has covered epispires (otherwise known only from Middle Ordovician eocrinoids) opening on most of the thecal plate sutures. The covered epispires inCuniculocystisindicate that some early rhombiferans had alternate respiratory structures and had not yet standardized on pectinirhombs, a feature previously used as diagnostic for the class Rhombifera.Bockia?elpasoensisn. sp. is a new eocrinoid based on one poorly preserved specimen that has a small ellipsoidal theca and unbranched brachioles attached to a flat-topped spoutlike summit. It is the earliest known questionable representative of this genus and the only one that has been described from North America.Elpasocrinus radiatusn. gen. and sp. is an early cladid inadunate crinoid based on a single well-preserved calyx. It fits into a lineage of early cladids leading to the dendrocrinids and toCarabocrinus.Several additional separate plates, stem segments, and a holdfast of these and other echinoderms are also described.

Arenig (Lower Ordovician) conodonts and biozonation in the eastern Siljan district, central Sweden

1994 ◽  
Vol 68 (6) ◽  
pp. 1350-1368 ◽  
Author(s):  
Anita M. Löfgren
Keyword(s):  
North America ◽  
The Other ◽  
South Central ◽  
Lower Ordovician ◽  
Conodont Zone ◽  
Local Base ◽  
Reference Section ◽  
Zones And Subzones

Based on biostratigraphic investigations in the eastern Siljan district, central Sweden, and combined with earlier studies at Hunneberg, south-central Sweden, it is shown that the early post-Tremadoc-age Paroistodus proteus conodont Zone can be divided into four successive subzones. These are, in ascending order: the Drepanoistodus aff. D. amoenus Subzone; the Tripodus Subzone; the Paracordylodus gracilis Subzone; and the Oelandodus elongatus-Acodus deltatus deltatus Subzone. The lowermost of the subzones is a concurrent range zone, with its reference section at Storeklev, Hunneberg, and the other three interval zones with the reference section at Sjurberg in the eastern Siljan district. Correlations between these two areas, as well as with the Flåsjö area, Jämtland, the Finngrundet core, and some other areas, are discussed, and it is concluded that the Drepanoistodus aff. D. amoenus Subzone and the Tripodus Subzone together correspond to the Megistaspis (Ekeraspis) armata trilobite Zone, and occur below the Hunnegraptus copiosus graptolite Zone. The Paracordylodus gracilis Subzone is equivalent with the lower part of the Megistaspis (Varvaspis) planilimbata trilobite Zone, and may correspond to the Hunnegraptus copiosus Zone. The uppermost subzone, the Oelandodus elongatus-Acodus deltatus deltatus Subzone, equals the upper part of the M. (V.) planilimbata Zone, and the local base of the Tetragraptus phyllograptoides graptolite Zone is close to the base of this conodont subzone. The last occurrences of T. phyllograptoides are close to the top of this conodont subzone. Also included in the investigation are the uppermost part of the uppermost Tremadoc Paltodus deltifer Zone and the conodont zones overlying the P. proteus Zone in the eastern Siljan district, the Prioniodus elegans Zone and the Oepikodus evae Zone; the latter zone corresponds to the trilobite zones of Megalaspides (M.) dalecarlicus and Megistaspis (Varvaspis) estonica. A few samples from the superimposed Baltoniodus triangularis, B. navis, and Paroistodus originalis Zones have been investigated and are described as well. The correlation of these conodont zones and subzones with those of areas outside Baltoscandia, particularly North America, is also discussed.

ALLOGRAPTUS CANADENSIS N. SP.; ITS SIGNIFICANCE TO LOWER ORDOVICIAN CORRELATION

1967 ◽  
Vol 4 (4) ◽  
pp. 609-617 ◽  
Author(s):  
Bernd-Dietrich Erdtmann
Keyword(s):  
New Species ◽  
North America ◽  
Stratigraphic Correlation ◽  
Lower Ordovician ◽  
The Family ◽  
A New Species

A declined four-branched graptoloid is referred to a new species of Allograptus, a genus of the family Sinograptidae described from the uppermost Lower Ordovician of China. This new Canadian species has been discovered from the upper Lévis Formation at Lévis, Québec, and is the first representative of Allograptus in North America. A description of A. canadensis n. sp. is presented with a discussion on its possible significance for international stratigraphic correlation.

Revision of certain Lower Ordovician Faunas from Ireland

1945 ◽  
Vol 82 (2) ◽  
pp. 55-66 ◽  
Author(s):  
F. R. C. Reed
Keyword(s):  
North America ◽  
Present Author ◽  
Western North America ◽  
General Aspect ◽  
The West ◽  
Upper Cambrian ◽  
Lower Ordovician ◽  
West Of Ireland

Since the publication of the papers by Messrs. Gardiner and Reynolds on the Tourmakeady and Glensaul districts in the west of Ireland, with palaeontological appendices by the present author, Raymond (1925, p. 167) has compared the faunas with those of Newfoundland and pointed out some striking resemblances. Other Lower Ordovician faunas have since then been described from various foreign regions, and in the light of this increased knowledge the specimens in the collections from Ireland have been re-examined; this has resulted in revised generic identifications, though confirming the reference of the beds to the Lower Ordovician as the author originally maintained (1910, p. 271). The trilobites, several of which are now put in other genera, are mostly allied to or comparable with species of the Canadian and Ozarkian of North America, Newfoundland, and Greenland which Poulsen (1937, p. 72) correlates with the Arenig and Tremadoc, and they also show resemblances to some of those of the Ceratopyge fauna (Brögger, 1896) of Europe and Western North America (Raymond, 1922) as well as with those of Newfoundland. The brachiopods, the determination of which had been found a matter of much difficulty owing to their poor preservation, possess affinities with many of the American Upper Ozarkian and Canadian species recently named by Ulrich and Cooper (1938), especially with those from Canada, rather than with any of the European forms with which they were previously compared or identified. The admixture of Upper Cambrian fossils with those of the Ceratopyge zone, especially in Nevada and the Mount Robson district, was noted by Raymond (1922, p. 20); and similar interrelations of the two faunas are also traceable in the present case. From the general aspect of the faunas from the Irish localities, Ulrich (1930, p. 19) was inclined to put the beds “about the middle or upper Chazyan”; Grabau (1935, p. 101), relying on the lists of brachiopods and trilobites in the present author’s original papers, would refer them to the Middle rather than the Lower Ordovician, but this view can no longer be held.

Strike-slip terranes and a model for the evolution of the British and Irish Caledonides

1987 ◽  
Vol 124 (5) ◽  
pp. 405-425 ◽  
Author(s):  
Donald H. W. Hutton
Keyword(s):  
North America ◽  
Continental Margin ◽  
Strike Slip ◽  
Slip Zone ◽  
Lake District ◽  
Early Ordovician ◽  
Boundary Fault ◽  
Lower Ordovician ◽  
Major Strike ◽  
Back Arc

AbstractEvidence is presented that many of the major strike faults in the British and Irish Caledonides were active as sinistral strike-slip zones in the end-Silurian to pre-mid-Devonian period. Some, such as the Highland Boundary Fault, moved in this way at an earlier stage in the Ordovician. These data allow the Caledonian rocks lying between the Laurentian miogeocline (whose basement is represented by the Lewisian, Moine and possibly the Dalradian) and the Gondwanaland miogeocline (Midland Platform and Welsh Basin) to be re-analysed as a group of disorganized terranes which originated to the southwest in North America and southwest Europe/Africa prior to the Silurian. The Highland Border Terrane and Northern Belt Terrane are interpreted as duplicated pieces of a mid-Ordovician sequence which was a back are to northwest subduction. The Midland Valley Terrane is interpreted as a slice of Laurentian foreland onto which ophiolites were obducted in the lower Ordovician but which became the basement of a continental margin arc to northwest subduction in the mid-Ordovician. The Cockburnland Terrane is inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip. The Connemara Terrane is regarded as an allochthonous piece of the Dalradian miogeocline and the South Mayo Terrane as a remnant of an early Ordovician arc and fore arc which in mid-Ordovician times became a back arc/marginal basin to northwest subduction. The Lake District-Wexford Terrane is part of an arc to southeast subduction under Gondwanaland whose activity climaxed in the mid-Ordovician. The Central Terrane is interpreted as a Silurian overstep assemblage which blankets the junction between Laurentian- and Gondwanaland-derived oceanic terranes, and therefore Iapetus is regarded as an Ordovician ocean which closed prior to the Silurian. The model suggests that at the end of the Silurian, a clockwise-rotating Gondwanaland, having carried Laurentia into collision with Baltica, broke free and created a major sinistral strike-slip zone which disrupted the Ordovician palaeogeography in the British Isles/North American sector of Iapetus.

Age and origin of the Boil Mountain ophiolite and Chain Lakes massif, Maine: implications for the Penobscottian orogeny

1997 ◽  
Vol 34 (5) ◽  
pp. 646-654 ◽  
Author(s):  
T. M. Kusky ◽  
J. S. Chow ◽  
S. A. Bowring
Keyword(s):  
North America ◽  
Late Ordovician ◽  
Ophiolite Complex ◽  
Middle Ordovician ◽  
Iapetus Ocean ◽  
Lower Ordovician ◽  
Mid Ocean Ridge ◽  
Back Arc ◽  
Ocean Ridge ◽  
Age Constraints

The Boil Mountain ophiolite complex of west-central Maine is widely interpreted to mark the Lower Ordovician Penobscottian suture between the Dunnage, Chain Lakes, and Gander terranes. The ophiolite consists of two distinct volcanic groups, including a lower island-arc tholeiite sequence and an upper mid-ocean-ridge basalt sequence. A new Middle Ordovician 477 ± 1 Ma U–Pb age on a tonalite sill that intrudes the lower volcanic–gabbroic sequence is younger than other ca. 500 Ma age constraints for the ophiolite and represents a maximum age for the ophiolite prior to final emplacement over gneissic rocks of the Chain Lakes massif. A comparison of ages and paleogeography of the Boil Mountain ophiolite with ophiolitic sequences in Quebec and Newfoundland indicates that the Taconian and Penobscottian orogenies and ophiolite obduction occurred simultaneously, although on different margins of the Iapetus Ocean. The Taconian ophiolite sequences were obducted onto the Appalachian margin of Laurentia during its collision with the Notre Dame – Bronson Hill belt in the Middle Ordovician, whereas the Boil Mountain ophiolite was obducted onto the Gander margin of Gondwana during its collision with the Exploits subzone – Penobscot arc of the Dunnage terrane in the Lower – Middle Ordovician. We suggest that the lower volcanic–gabbroic sequence of the Boil Mountain ophiolite represents the fore-arc ophiolitic basement to the Penobscot arc. Middle Ordovician rifting of the Penobscottian orogenic collage on the Gander margin formed a new volcanic sequence (Popelogan arc) in front of a growing back-arc basin, and erupted the upper tholeiitic sequence of the Boil Mountain ophiolite in a back-arc-basin setting. The tonalité sill formed during this event by partial melting of the lower volcanic–gabbroic sequence. Spreading in this back-arc basin (Tetagouche basin) brought a fragment of the Gander margin (Chain Lakes massif), along with an allochthonous ophiolitic cover (Boil Mountain complex) across Iapetus, where it collided with the Taconic modified margin of North America in the Late Ordovician and was then intruded by the Ashgillian Attean pluton.

A new Lower Ordovician (Arenig) faunule from the Coy Pond Complex, central Newfoundland, and a refined understanding of the closure of the Iapetus Ocean

1992 ◽  
Vol 29 (9) ◽  
pp. 2046-2057 ◽  
Author(s):  
S. Henry Williams ◽  
W. Douglas Boyce ◽  
Stephen P. Colman-Sadd
Keyword(s):  
North America ◽  
First Record ◽  
Ophiolite Complex ◽  
Early Ordovician ◽  
South Central ◽  
Iapetus Ocean ◽  
Lower Ordovician ◽  
Age Limit ◽  
Southern Upland

A newly discovered fossiliferous horizon within sediments belonging to the Coy Pond Complex of the Exploits Subzone in central Newfoundland yields the graptolite Undulograptus austrodentatus s.l. and cyclopygid trilobite Cyclopyge grandis brevirhachis. This late Arenig faunule constrains the upper age limit of the ophiolite complex and is the first record of an Early Ordovician cyclopygid trilobite in North America. This is consistent with a paleogeographic affinity for south-central Newfoundland with the northern oceanic margin of Avalonia in a peri-Gondwanan position during the Early Ordovician and contrasts with coeval shelly and graptolitic faunas from the Notre Dame Subzone of central Newfoundland, which show marked Laurentian affinities. The Exploits Subzone is generally considered equivalent to the region of Scotland lying south of the Southern Upland Fault. The Newfoundland discovery, which is supported by faunal data from elsewhere in Newfoundland and in Ireland, suggests that the region around the Southern Upland Fault, rather than the Solway Firth, represents the location of the "Iapetus suture" in Britain in Lower Ordovician rocks.

First occurrence of Helicotoma Salter (Gastropoda) from the Ordovician of Alaska

1988 ◽  
Vol 62 (2) ◽  
pp. 304-306 ◽  
Author(s):  
David M. Rohr ◽  
Robert B. Blodgett
Keyword(s):  
North America ◽  
Single Specimen ◽  
Lower Paleozoic ◽  
Lower Ordovician ◽  
First Occurrence ◽  
Lack Of Knowledge

Middle and lower Ordovician gastropods have not previously been described from Alaska, and the genus Helicotoma Salter has not been reported from western and arctic North America with the exception of one locality in California (Rohr, 1980). Like many other Paleozoic gastropod genera, Helicotoma has several species assigned to it, but the species are often based on poor material and, in some cases, on a single specimen. This lack of knowledge of variation within the species as well as the detailed features of the shell make further interpretations of the gastropods difficult. The occurrence of relatively abundant, well-preserved Helicotoma specimens in Alaska is important for biogeographic and biostratigraphic studies of lower Paleozoic mollusks.

Jujuyaspis and associated trilobites from the Mungok Formation (Lower Ordovician), Yongwol, Korea

2000 ◽  
Vol 74 (6) ◽  
pp. 1031-1042 ◽  
Author(s):  
Dong Hee Kim ◽  
Duck K. Choi
Keyword(s):  
North America ◽  
South America ◽  
North China ◽  
Lower Ordovician ◽  
America South ◽  
Mungok Formation ◽  
First Time

The trilobite genus Jujuyaspis Kobayashi, 1936, an index fossil of earliest Ordovician age, is recorded from the Yosimuraspis Zone of the Mungok Formation (Lower Ordovician) for the first time in Korea. The Yosimuraspis Zone comprises Yosimuraspis vulgaris Kobayashi, 1960; Jujuyaspis sinensis Zhou in Chen et al., 1980; Elkanaspis jilinensis Qian in Chen et al 1985; and pilekid genus and species indeterminate. Closely comparable faunas to the Yosimuraspis Zone are well represented in North China. The occurrence of Jujuyaspis allows the correlation of the Yosimuraspis Zone with the earliest Ordovician faunas of North America, South America, and Scandinavia, and suggests that the Cambrian-Ordovician boundary in Korea be placed at the base of the Yosimuraspis Zone.

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