Early Ordovician Age Research Articles

Paleozoic basin development in northern Chile (21°–27°S)

The oldest non-metamorphic sediments of northern Chile (21‡–27‡S) are of Early Ordovician age. The partly strong volcanic influence in the clastic series of the Pre-Cordillera and the Puna might be connected with the extensive Ordovician magmatism on the eastern side of the Argentinian Puna. The geochemical character of the tholeiitic intercalations in the pelites and turbidites of the »Complejo Igneo-Sedimentario del Cordon de Lila« (C.I.S.L.) in the Pre-Andean Depression indicates a ?Lower Ordovician extensional regime in this area.

The Cambrian and Ordovician Systems around the Pacific Basin, Part III

The tenth chapter is dealt with the history of research in older rocks and Cambro-Ordovician of eastern North America. In last century Pre-Cambrian stratigraphy was started in Canada, while the New York System was instituted around Albany, N. Y. and later it was correlated to the European sequence. Subsequently the Cambrian and Ordovician Systems were classified in detail. Starting with the ventral anatomy of trilobites Walcott made invaluable contributions on the Cambrian geology and palaeontology, i.e. the Olenellus fauna, unique fauna the Burgess shale and so forth. His “Cambrian Fauna of China” 1913 provided a firm basis for the Cambrian of Eastern Asia.The relation of the Cambro-Ordovician faunas of the continent to the European ones in the northern part of the Appalachian geosyncline and their distribution in the Appalachian mountains and further westerly beyond the lower Mississipy river and also in the interior lowland are briefly outlined.These systems in the Cordilleran geosyncline is described in the eleventh chapeter. Stratigraphy in the western sites is followed by notes on the Alaskan faunas in the north which were allied to the Siberian ones at the beginning, but later to the Eastern Asiatic ones also. In the south it is a remarkable fact that the Mexicoan faunas are more related to the Andean ones than those of the United States, particularly in the early Ordovician age.The Circum-Pacific Cambro-Ordovician belt is taken up in the final chapter. The history of this belt's history started in the Sinian period. In the early Cambrian age the eastern side belonged to the Olenellian province, but the other side constitued the Redlichia province. Subsequently, however, trilobites of the two sides became closer related to each other, although the early Upper Cambrian Kushan fauna was quite isolated. Trilobites were intimate between the two sides of the Northern Pacific and also on the southern Pacific side in the early Ordovician age. The aspect of the provinciality in the middle and late Ordovician ages is still obscure, sofar as trilobites are concerned.

The age of the Danmarks Fjord Member, eastern North Greenland

Conodonts of late Early Ordovician age (late Canadian, early-middle Arenigian) are identified from the Danmarks Fjord Member of the Wandel Valley Formation at its type locality near the head of Danmark Fjord, eastern North Greenland. The identifications confirm recent suggestions of an Early Ordovician age for the member made on lithostratigraphic grounds, and refute earlier opinions that the dolomite was probably of Early Cambrian age.

The Sjælland Fjelde Formation: a new Ordovician formation from eastern North Greenland

The name Sjælland Fjelde Formation is introduced for a varied sequence of shallow-water platform dolomites and dolomitic limestones, about 105 m in thickness, in Kronprins Christian Land, eastern North Greenland. The new formation lies between the previously described Wandel Valley and Børglum River Formations. Conodont faunas indicate that the Sjælland Fjelde Formation is of Middle to earliest Late Whiterockian (early Middle Ordovician) age and that it can be eorrelated with the upper part of the Wandel Valley Formation of Peary Land to the north-west.

Early Ordovician trilobites from the Wandel Valley Formation, eastern North Greenland

A small trilobite fauna is described from the Wandel Valley Formation of Kronprins Christian land, eastern North Greenland. It has a specific composition identical to the fauna from the Catoche Formation, western Newfoundland, which is typical of the shallow water bathyurid biofacies of the eastern part of the Ordovician Laurentian palaeocontinent. The fauna is of early Ordovician age, trilobite Zone H, equivalent to the early Arenig.

Geology of the Mt Windsor subprovince—a lower Palaeozoic volcano‐sedimentary terrane in the northern Tasman orogenic zone

The Mt Windsor Subprovince encompasses the dismembered remnants of a thick volcanic and sedimentary succession predominantly of Late Cambrian and Early Ordovician age located within the northern part of the Tasman Orogenic Zone. The succession is divided into four formations which together comprise the Seventy Mile Range Group. Its lower part, Puddler Creek Formation, comprises immature terrigenous clastic strata lacking in volcanics but hosting numerous penecontemporaneous dolerite sills and dykes. Its upper part, Mt Windsor Volcanics, Trooper Creek Formation and Rollston Range Formation, is dominated by acid and intermediate volcanics and volcaniclastics. The group has been dismembered, deformed and in part metamorphosed by emplacement of the Middle Ordovician Ravenswood Granodiorite Complex which is regarded as having been diapirically emplaced. Stratigraphic relationships and reconnaisance geochemistry suggest that the volcanics comprise a consanguineous series ranging from basaltic andesite to rhyoli...

Possible significance of Early Paleozoic fluctuations in bottom current intensity, northwest Iapetus Ocean

Sedimentologic and geochemical characteristics of red and green deep water mudstone exposed in the central Appalachian orogen define climatically‐induced fluctuations in bottom current intensity along the northwest flank of the Iapetus Ocean in Early and Middle Ordovician time. Red mudstone accumulated under the influence of moderate to vigorous bottom current velocities in oxygenated bottom water produced during climatically cool periods. Interbedded green mudstone accumulated at greater sedimentation rates, probably from turbidity currents, under the influence of reduced thermohaline circulation during global warming periods. The close association of green mudstone and carbonate turbidites of Early Ordovician (late Tremadocian to early Arenigian) age suggests that a major warming phase occurred at this time. Increasing temperatures reduced bottom current velocities and resulted in increased production of carbonate sediment and organic carbon on the carbonate platform of eastern North America. Much of the excess carbonate sediment and organic carbon was transported into deep water by turbidity currents. Although conclusive evidence is lacking, this eustatic event may reflect a climatic warming phase that followed the postulated glacio‐eustatic Black Mountain event. Subsequent Middle Ordovician fluctuations in bottom current intensity recorded by thin red‐green mudstone couplets probably reflect periodic growth and shrinkage of an ice cap rather than major glacial episodes.

Cambrian platform stratigraphy in the Warming Land – Freuchen Land region, North Greenland

Cambrian platform strata in the Warming Land - Freuchen Land region are briefly described and correlated with sequences in more easterly and westerly areas of North Greenland. The name Ryder Gletscher Group is proposed for a mainly carbonate sequence (thickness about 640 m) in the Warming Land - Wulff Land area of Early Cambrian - Early Ordovician age. Dominant lithologies are dark burrow-mottled dolomites and paIe, cryptaIgaI laminites, but micrites, thin shales and thin sandstones are common in higher beds. Six formations are recognised but not formally described.

A Paleozoic suture in eastern Gondwanaland

A new tectonic interpretation of southeastern Australia, Tasmania, and north Victoria Land, Antarctica, is given, in which a major N‐S trending lineament, representing a suture zone, is recognized separating essentially shallow water shelf and continental deposits of latest Cambrian or Early Ordovician age from deeper water Ordovician flysch deposits. Lateral offset of this lineament, which is interpreted as a suture along which thrust telescoping and major strike‐slip faulting occurred, could adequately explain the present distribution of major rock types in the three areas and also removes a number of problems previously encountered in correlation.

Lower Ordovician conodonts from Washington Land, western North Greenland

Early Canadian (Lower Ordovician) conodonts have been recorded from loose slabs which were collected by J. C. Troelsen in 1941 at Kap Clay, Washington Land, western North Greenland. The samples probably derived from the Cape Clay Formation which is exposed in the steep coastal cliff. The macrofauna of the samples includes Symphysurina sp. of Early Ordovician age. The conodont fauna comprises "Paltodus" bassleri Furnish, Utahconus oneotensis (Furnish}, "Oistodus" triangularis Furnish, and species of Cordylo­dus Pander and "Acontiodus" Pander. The fauna correlates with Fauna C of the North American Mid­continental Faunal succession and with the Cordylodus angulatus Zone of the Baltic-Scania succession. Locally, it correlates with the conodont fauna recorded from the Cape Clay formation of Southern Devon Island, Canadian Arctic Archipelago. The conodont fauna is described applying multielement taxonomy. In all 314 specimens, representing 20 multielement species, were recorded. Some species are new, but they are referred to only in open no­menclature because of the unsettled stratigraphical status of the loose blocks.

Exploration in Ordovician of Central Michigan Basin

Deep wells in the central Michigan basin have provided sufficient data to define two new mappable formations--the Foster Formation and the Bruggers Formation. Recent conodont studies have corrected the age assignments of the strata containing these formations. Previously, the lower section (Foster) was classified as mostly Cambrian, and the upper unit (Bruggers) was identified as Early Ordovician. Conodont identifications indicate an Early and Middle Ordovician age for the Foster Formation and a Middle Ordovician age for the Bruggers Formation. The Michigan basin existed in embryonic form in the Late Cambrian, but the full outline of the present-day basin did not develop until Early Ordovician. Gas and condensate are produced from the Bruggers Formation as deep as 11,252 ft (3,429 m). Geothermal investigations suggest that gas production is possible to the base of the Paleozoic section in the central basin (17,000 ft or 5,181 m). Paleotemperatures were higher during the Paleozoic owing to 3,000-4,000 ft (914-1,291 m) of additional sedimentary cover. Five wells are producing from the Bruggers Formation. All are deeper tests in anticlines producing from Devonian reservoirs discovered earlier. The structures are the result of vertical movements of basement fault blocks activated by regional stresses.

Early Ordovician Dounans Limestone fauna, Highland Border Complex, Scotland

ABSTRACTA diverse, but sparsely distributed silicified fauna of over 30 taxa has been recovered from 7·5 tonnes of acid-etched Lower Ordovician Dounans Limestone from the Highland Border Complex, near Aberfoyle. The 13 trilobite taxa obtained include 3 new formally named species:Distazeris adoceta, Punka aetholiciocorusandIschyrotoma stubblefieldi.Other elements, representingCarolinites, Illaenus, Goniotelina, Sycophantia, Kawina, Heliomeroides, Strotactinus, Ectenonotus, Ceratocephalaand an indeterminate bathyurelline are described under open nomenclature although at least 4 are also probably new and 2 more may be conspecific with previously described species. The brachiopods include representatives ofArchaeorthis, Nothorthis, Orthidium, ?Camerella, Idiostrophia, Orthambonitesand 4 other indeterminate stocks. Gastropods tentatively assigned toMurchisonia, Subulites, Straparollina, MacluritesandCyrtodiscusare described, as are bryozoans, an orthocone, crinoids, andIncertae sedis.This profoundly North American fauna is Late Canadian ( = mid Arenig) in age and equates with the Cassinian Stage: it is key evidence in showing that the Highland Border rocks are not part of the Dalradian Supergroup whose earliest deformations and metamorphism predate the Ordovician. The field relationships of the limestone, together with evidence from derived clasts in Middle Ordovician and Devonian sequences near Girvan in SW Scotland and at Stonehaven in eastern Scotland suggest that it forms part of a widespread sub-Old Red Sandstone carbonate sequence of Early Ordovician age beneath the northern Midland Valley.

A palaeomagnetic reconnaissance of Kashmir, northwestern Himalaya, India

Thermal demagnetization studies of 800 Palaeozoic and Lower Mesozoic samples, mainly carbonates, from 14 localities in Kashmir, showed four magnetic components: (A)A recent field component of normal polarity and large intensity. (B)A Middle to Late Tertiary secondary component of large intensity and of reversed and normal polarity, which indicates clockwise rotation of central and eastern Kashmir over approximately 45° with respect to peninsular Indo-Pakistan. (C)Primary magnetic components of Triassic, Late Permian, Early Carboniferous, Siluro-Ordovician and Middle to Early Ordovician age. The Triassic and Late Permian components show a 20–30° cumulative counterclockwise offset with respect to the Indo-Pakistan apparent polar wander path (APWP). This indicates a post-Middle to -Late Triassic counterclockwise rotational movement of Kashmir over 65–75° with respect to peninsular Indo-Pakistan. (D)A component of low inclination and predominantly east-west declination, which is observed only in rocks of pre-Panjal Traps age. A secondary origin associated with extrusion of the Panjal Traps flows is surmised, but could not be established beyond doubt. Alternatively, this component may be related to the regional foliation. The Triassic and Late Permian primary component directions are predominantly of normal polarity. This suggests a pre-Punjabian (Late Permian) upper age limit for the Permo-Carboniferous (Kiaman) reversed polarity interval, which is earlier than the Early to Late Tatarian limit observed in the U.S.S.R.

Ordovician conodonts from metamorphosed carbonates of the Salton Trough, California

Research Article| July 01, 1983 Ordovician conodonts from metamorphosed carbonates of the Salton Trough, California Richard H. Miller; Richard H. Miller 1Allison Center, Department of Geological Sciences, San Diego State University, San Diego, California 92182 Search for other works by this author on: GSW Google Scholar Mark S. Dockum Mark S. Dockum 2Conoco Inc., Ventura, California 93003 Search for other works by this author on: GSW Google Scholar Author and Article Information Richard H. Miller 1Allison Center, Department of Geological Sciences, San Diego State University, San Diego, California 92182 Mark S. Dockum 2Conoco Inc., Ventura, California 93003 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1983) 11 (7): 410–412. https://doi.org/10.1130/0091-7613(1983)11<410:OCFMCO>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Richard H. Miller, Mark S. Dockum; Ordovician conodonts from metamorphosed carbonates of the Salton Trough, California. Geology 1983;; 11 (7): 410–412. doi: https://doi.org/10.1130/0091-7613(1983)11<410:OCFMCO>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract About 70 poorly preserved conodonts were recovered from a sample of marble from the Coyote Mountains, southern California. The specimens are all highly altered coniform elements of Early Ordovician age and indicate that lower Paleozoic marble, schist, and quartzite occurs in the Salton Trough, west of the San Andreas–Gulf of California plate boundary. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Fossils from the Poulsen Cliff Formation, Washington Land, western North Greenland

The Poulsen Cliff Formation of Washington Land, western North Greenland, is a recessive, pale weathering unit, 100-125 m in thickness, of thinly-bedded dolomite, shale and sandstone witll conspicuous evaporites. The formation represents the continuation into Greenland of the lower part (member a) of the Baumann Fiord Formation evaporite sequence of the Canadian Arctic Islands, which outcrops over a distance of about 1000 km from Cornwallis Island to Ellesmere Island (Mossop, 1979; Peel &amp; Christie, 1982; Peel, in press). The Poulsen Cliff Formation was first described by Troelsen (1950). It did not yield fossils to Troelsen but could with certainty be ascribed an Early Ordovician age on account of its stratigraphic position between fossiliferous units (Poulsen, 1927; Peel &amp; Christie, 1982).

Remagnetization and tectonic rotation of Upper Precambrian and Lower Paleozoic strata from the Desert Range, southern Nevada

In the Desert Range of southern Nevada, miogeoclinal sedimentary rocks, mostly shallow‐water limestones of latest Precambrian through Early Ordovician age, yield three components of magnetization having different blocking temperature spectra: (1) a low blocking temperature component near the direction of the present axial‐dipole field; (2) an intermediate blocking temperature component with northerly declination and inclination ∼+60°; and (3) a characteristic component with southeasterly declination and inclination ∼−20°. Combinations of alternating field and thermal demagnetization indicate that the intermediate and characteristic components reside in magnetite. The intermediate magnetization probably reflects a viscous partial thermoremanent magnetization (VPTRM) imposed between the Late Cretaceous and mid‐Cenozoic; it was probably acquired when the strata were dipping slightly eastward. The characteristic magnetization is probably a VPTRM imposed during regional uplift in the Late Permian. The degree of heating required to have destroyed any primary magnetization is consistent with the conodont color alteration index observed in the Ordovician rocks; additionally, the characteristic magnetization in those rocks is younger than bedding disruption caused by major, late stylolitization. Red‐purple mudstones from the middle member of the Wood Canyon Formation, in which a directionally similar characteristic magnetization resides in fine‐grained hematite, also appear to have been remagnetized; in these rocks, the remagnetization probably reflects partial recrystallization, as the blocking temperatures are too high to have been reset by burial heating. The sampled sections have undergone relative tectonic rotation about a vertical axis, consistent with late Tertiary oroflexural bending that had been proposed on independent geologic evidence. The characteristic magnetization probably provides a reliable estimate of the magnitudes of the vertical axis rotations, as the regional geology suggests the Desert Range strata were essentially horizontal throughout the Paleozoic. The total observed relative rotation is 44°±5°, representing absolute counterclockwise rotation (27°±4°) of the northern part of the Desert Range, and absolute clockwise rotation (17°±5°( of the southern part. The only unit in the Desert Range sequence that may retain a primary magnetization is the late Precambrian Rainstorm Member of the Johnnie Formation. The characteristic magnetization of this unit exhibits two polarities and probably resides in specular hematite; after correction for 18° of counterclockwise rotation, the resulting pole (5°N, 151°E) is near other late Hadrynian poles from North America.

Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland

ABSTRACTBioherms are common in the St George Group, a sequence of shallow‐water carbonate rocks deposited on the western continental shelf of Iapetus Ocean. They range from small heads and metre‐sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent. The cores of these bioherms are principally composed of thrombolites (unlaminated, branching, columnar stromatolites), structures quite distinct from laminated stromatolites which are common in intertidal beds. Associated with thrombolites is a diverse fauna of burrowing invertebrates, trilobites, nautiloids, pelmatozoans, brachiopods, gastropods, rostroconchs and archaeoscyphiid sponges.On the basis of framework‐building components, three main bioherm types are distinguished: (1) thrombolite mounds, (2) thrombolite‐Lichenariaor ‐sponge mounds and (3) thrombolite‐Lichenaria‐Renalcisreef complexes. The framework of the last is the most complex, with abundant cavities and a demonstrably uneven growth surface of thrombolites, corals and free‐standingRenalcisheads, walls and roofs. Some cavities were active sediment conduits while others were protected, their roofs draped withRenalcisand their walls coated by cryptalgal laminites.These bioherms possess the attributes of shallow‐water ecologic reefs. They span a critical time gap in the development of reefs, the transition period from algal‐dominated bioherms of the Precambrian and Cambrian to the metazoan‐dominated bioherms of the Middle Ordovician and remaining Phanerozoic.

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

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.

Reconnaissance Paleomagnetic Investigation in the Spider Lake-Woburn Area

The paleomagnetic research presented is concerned with geological formations outcropping in the Spider Lake-Woburn area in the southern Appalachians of Quebec. The age of these formations ranges from Precambrian to Late Devonian. Experiments combining AF and thermal cleaning and analytical techniques such as end-points, vector subtraction and the method of great circles indicate different components of magnetization. Fold test and baked contact test on the hornfels are also included. In some rock types, up to five components may be distinguished and isolated. AF demagnetization is particularly effective for the serpentinites, hornfels and metasediments and only thermal cleaning is effective on the other formations. Many of the components are secondary and the baked contact test is still equivocal. A tentative explanation of the time and mode of emplacement of the Precambrian granite gneiss is proposed. This study shows that at the Early Ordovician age, the paleopole position was located at 163°E, 29°N (mixed polarities) and at the Late Devonian age in the vicinity of 138°E, 37°N (mixed polarities).

Geology of Central Lake Michigan

The geology beneath Lake Michigan between 43°00^prime and 44°00^primeN and between 86°30^prime and 87°40^primeW is interpreted from a synthesis of 1,700 km of continuous seismic reflection profile data, bathymetry, grab samples, and onshore surface and subsurface information. The continuous seismic reflection profiles and bathymetry provided information for maps of unconsolidated sediment thickness and Paleozoic bedrock topography. The map of unconsolidated sediment (primarily Pleistocene) shows thicknesses ranging from 180 m in a steep-walled, northeast-trending valley to less than 10 m over a mid-lake topographic high. This valley and the mid-lake high are the dominant topographic features developed on the gently eastward-dipping Paleozoic rocks along this part of the western flank of the Michigan basin. Two structural-stratigraphic cross sections of the study area were constructed by utilizing a composite subsurface-surface section for eastern Wisconsin and two control wells in western Michigan. The cross sections, grab samples previously described in the literature, the bedrock topographic map, and published maps were used to construct a Paleozoic geologic map for central Lake Michigan. Rocks from Middle Silurian through Early Mississippian age form subcrops beneath the study area, whereas rocks of Early Silurian, Ordovician, and Late Cambrian age are present at greater depth. The Upper Cambrian rocks unconformably overlie Precambrian igneous and metamorphic rocks. The structural-stratigraphic cross sections also allow us to speculate about the petroleum potential beneath Lake Michigan. The possibility of oil occurrences within the Silurian is enhanced by major east-west facies changes, and other horizons with promise are present in Devonian and Ordovician rocks. Although Michigan and Wisconsin laws currently prohibit petroleum exploration in Lake Michigan, it is an area with future potential.