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.

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.

Paleomagnetic reexamination of the Lower Ordovician Wabana and Bell Island Groups of the Avalon Peninsula of Newfoundland

1982 ◽  
Vol 19 (5) ◽  
pp. 1055-1069 ◽  
Author(s):  
K. L. Buchan ◽  
J. P. Hodych
Keyword(s):  
North America ◽  
Early Paleozoic ◽  
Magnetization Direction ◽  
Early Ordovician ◽  
End Point ◽  
Iapetus Ocean ◽  
Lower Ordovician ◽  
Avalon Peninsula

The Wabana and Bell Island Groups of the Avalon Peninsula of Newfoundland contain oolitic hematite beds of Early Ordovician age, dipping ~11° north-northwest. Twenty-one oolitic hematite samples from nine sites were thermally demagnetized in 10 or 11 steps to 660 or 680 °C. At 450 °C, 15 samples from six sites define a stable magnetization direction (D = 21.2°, I = −12.5°, k = 137, α95 = 5.7°) with respect to bedding. The remaining six samples failed to attain the stable end-point, five of them because of growth of much "magnetite," which probably resulted from breakdown of siderite during thermal demagnetization.The paleopole for the Wabana – Bell Island Groups lies at 33°N 102°E (dm = 5.8°, dp = 3.0°). It is compared with other early Paleozoic paleopoles from cratonic North America and the Avalon zone, and its significance for the Iapetus Ocean is discussed.

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.

The brachiopod Ptychopleurella lapworthi (Davidson) from the Ordovician of Girvan, S.W. Scotland

1986 ◽  
Vol 60 (4) ◽  
pp. 845-850 ◽  
Author(s):  
D. A. T. Harper
Keyword(s):  
North America ◽  
Sedimentary Facies ◽  
Upper Ordovician ◽  
Middle Ordovician ◽  
Identity Recognition ◽  
Early Ordovician ◽  
Iapetus Ocean ◽  
Northwestern Margin

The small, distinctive, glyptorthinine brachiopod Ptychopleurella Schuchert and Cooper is widely distributed in rocks of early Ordovician to late Silurian age. Several species are known from the Barr and Ardmillan successions (middle-upper Ordovician) of the Girvan district, S.W. Scotland, one of which, ‘Orthis Lapworthi’ Davidson, has not been described in modern terms as there has been some confusion concerning its true identity. Recognition of this species of Ptychopleurella permits comparison with congeners elsewhere, strengthens the correlation of this part of the Girvan Succession with the middle Ordovician of North America, and provides a more complete record of this genus in the slope sedimentary facies of the northwestern margin of the Iapetus Ocean.

Ordovician rhipidognathid conodonts from Australia and Iran

2001 ◽  
Vol 75 (1) ◽  
pp. 186-207 ◽  
Author(s):  
Yong Y. Zhen ◽  
Robert S. Nicoll ◽  
Ian G. Percival ◽  
Mir Alireza Hamedi ◽  
Ian Stewart
Keyword(s):  
North America ◽  
New South ◽  
First Record ◽  
Bedding Plane ◽  
Upper Ordovician ◽  
East Central ◽  
Canning Basin ◽  
Early Ordovician ◽  
South Wales ◽  
Water Depths

Based on specimens from Australia and Iran, five species of rhipidognathid conodonts, Appalachignathus delicatulus Bergström, Carnes, Ethington, Votaw, and Wigley, 1974, Bergstroemognathus extensus (Graves and Ellison, 1941), B. hubeiensis An (MS) in An, Chen, and Li, 1981, B. kirki Stait and Druce, 1993, and Rhipidognathus? yichangensis (Ni, 1981), are described and revised in terms of multielement morphology. All three genera comprising the Rhipidognathidae are interpreted as having a septimembrate apparatus, partially confirmed by bedding plane assemblages of B. extensus from Victoria. Occurrence of A. delicatulus in allochthonous limestones (about the Middle-Upper Ordovician boundary) of central New South Wales is the first record of the species outside North America. Recognition of Rhipidognathus? yichangensis in Early Ordovician strata of the Canning Basin, reinforces biogeographic affinities of Australia and South China. The three described species of Bergstroemognathus are mainly restricted to late Early Ordovician strata. Bergstroemognathus extensus is widely distributed in North America, western Argentina (Precordillera), China, and Australia. Bergstroemognathus hubeiensis, described from east-central Iran, has been previously recorded only from China, while the slightly younger B. kirki seems endemic to central and northern Australia, where it was restricted to shallow, warm water environments. In contrast, B. extensus and B. hubeiensis inhabited a spectrum of water depths from shallow to deep.

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.

The palaeogeographic position of the Lake District in the early Ordovician

1989 ◽  
Vol 126 (1) ◽  
pp. 9-17 ◽  
Author(s):  
R. A. Fortey ◽  
R. M. Owens ◽  
A. W. A. Rushton
Keyword(s):  
North America ◽  
Lake District ◽  
The South ◽  
Early Ordovician ◽  
Iapetus Ocean ◽  
First Time

AbstractThe early Ordovician was a time of maximum continental separation and hence a time when faunal evidence can be used to assess palaeogeography in a critical way. We summarize the known trilobite occurrences (18 genera) from the Arenig–Llanvirn of the Lake District, and record some genera for the first time. Maps of the distribution of some of these forms are given. All genera except Cyclopyge were confined to the Gondwana continent at the time, and some are known from many localities; and two species are widespread in England, Wales, France, Iberia and Bohemia. The fauna is entirely distinct from those of Scandinavia and North America. All the palaeontological evidence points to the Lake District being adjacent to Ordovician Gondwana. In the earlier Ordovician it is not reasonable to suggest that the Iapetus Ocean lay to the south of the Lake District as did Allen (1987).

Early Ordovician (Skullrockian) Trilobites of the Antiklinalbugt Formation, Northeast Greenland, and their Biostratigraphic Significance

2014 ◽  
Vol 88 (5) ◽  
pp. 982-1018
Author(s):  
Lucy M. E. McCobb ◽  
W. Douglas Boyce ◽  
Ian Knight ◽  
Svend Stouge
Keyword(s):  
North America ◽  
Field Studies ◽  
Carbonate Sediments ◽  
Lower Upper ◽  
Early Ordovician ◽  
Lower Ordovician

The Antiklinalbugt Formation of northeast Greenland comprises peritidal to subtidal carbonate sediments, deposited in shallow shelf settings during an early Tremadocian transgressive-regressive megacycle. The succession of shales and microbial, muddy and grainy limestone, with minor dolostone at the base and top, terminates at the cryptic Fimbulfjeld disconformity. The formation has yielded trilobites collected on Ella Ø, Albert Heim Bjerge, and Kap Weber by C. Poulsen (1920s and 1930s), J. W. Cowie and P. J. Adams (1950s), and during recent field studies in 2000 and 2001. The fauna includes dimeropygidsTulepyge cowieiandT. tesellan. spp., hystricuridsMillardicurusandHystricurus, and several species ofSymphysurina. Micragnostus chiushuensis(Kobayashi, 1931) is rare, as areChasbellussp.,Clelandiasp., andLunacrania?. The presence of severalSymphysurinaspecies places the Antiklinalbugt Formation within theSymphysurinaZone.Chasbellusindicates the upper (lower Ordovician) part of theSymphysurinaZone for the lower upper Antiklinalbugt Formation. Conodonts place the middle lower formation in theCordylodus intermediusconodont Biozone, the lower upper part in theCordylodus angulatusconodont Biozone and the uppermost part in theRossodus manitouensisconodont Biozone. This combined fauna is characteristic of the upper Skullrockian Stage of the Ibexian Series, with the lower part of the Antiklinalbugt Formation lying within the uppermost Cambrian of North America, and the upper part within the lower Ordovician. The entire formation lies within the global Tremadocian Stage of the early Ordovician.

The first Early Ordovician graptolites and marine incursions in eastern Alborz, Iran

2021 ◽  
pp. 1-14
Author(s):  
Adrian W. A. Rushton ◽  
Mansoureh Ghobadi Pour ◽  
Leonid E. Popov ◽  
Hadi Jahangir ◽  
Arash Amini
Keyword(s):  
Northern Iran ◽  
Early Ordovician ◽  
Lower Ordovician ◽  
Shale Formation ◽  
Kopet Dagh ◽  
Semnan Province

Abstract Graptolites have been collected from sections through Lower Ordovician strata in northern Iran. At the Saluk Mountains, in the Kopet–Dagh region, mudrocks yielded fragmentary tubaria of Rhabdinopora sp. cf. R. flabelliformis, indicating the presence of lower Tremadocian strata there; stratigraphically, they lie between two limestone beds with the euconodont Cordylodus lindstromi. At Simeh–Kuh in the eastern Alborz Mountains (Semnan Province), upper Tremadocian – lower Floian strata include laminated dark mudstones that contain restricted graptolite faunas, mainly of small declined didymograptids; these are thought to represent incursions of plankton during periods of marine highstands. The lower major flooding surface in Simeh–Kuh coincides with an invasion of the graptolite biofacies and an incursion of Hunnegraptus? sp.; the second major flooding surface is associated with an incursion of Baltograptus geometricus. They were most probably synchronous with those in the lower part of the Hunnegraptus copiosus Biozone and at the base of the Cymatograptus protobalticus Biozone in the of the Tøyen Shale Formation succession of Västergötland, Scandinavia, suggesting that observed characters of sedimentation were eustatically controlled.

Sign in / Sign up

Export Citation Format

Share Document