Early Paleozoic Paleogeography Research Articles

Detrital zircon and rutile of southern Mexico Cambrian–Ordovician sandstone: Their significance for sediment provenance and Rheic Ocean evolution

The Cambrian–Ordovician Tiñú Formation of southern Mexico is key for identifying sediment sources along the northern margin of Gondwana, enhancing our understanding of early Paleozoic paleogeography and linking it with age-equivalent units in terranes with Gondwanan affinity. This study integrates detrital zircon U–Pb ages, Hf isotope signatures, and heavy mineral chemical data. U–Pb detrital zircon ages indicate sources from Stenian–Tonian (900–1200 Ma) to Calymmian (1400–1600 Ma) ages. The Stenian to Tonian zircon population, with peak ages around 1.0 Ga and model ages ranging from 1.68 to 1.90 Ga, suggests a provenance from the metaigneous rocks of the Oaxacan and Guichicovi complexes. The presence of the Calymmian zircon population, tourmaline crystals, and rutile grains displaying lower crystallization temperatures compared to the high-temperature rutile from the Oaxacan Complex suggests additional sources. Hf isotope signatures from Calymmian-aged zircon grains, with model ages between 1.95 and 2.30 Ga, match well with the Paleo-Mesoproterozoic Catarina Unit in the southern Chiapas Massif Complex. Further potential sources may include the basement of the Putumayo Province in Colombia and igneous rocks from the western Guiana Shield and the Rio Negro-Juruena Province. The Tiñú Formation provenance is comparable to coeval metasedimentary units across the northwestern margin of Gondwana found in Belize, the southern Chiapas Massif Complex, and Guatemala. The Tiñú Formation was likely deposited adjacent to the rifted margin of the Rheic Ocean. The results also emphasize combining U–Pb–Hf isotope analysis and trace elements in detrital zircon and rutile as effective provenance tracers.

U-Pb detrital zircon ages of Cambrian–Ordovician sandstones from the Taebaeksan Basin, Korea: Provenance variability in platform shelf sequences and paleogeographic implications

Abstract The early Paleozoic paleogeography of East Gondwanan terranes, including the North China Craton (NCC), is contentious, primarily reflecting the paucity of integrated geochronological, biogeographic, and tectonic data sets. Our new sensitive high-resolution ion microprobe data from 14 sandstones of the Taebaeksan Basin, Korea, indicate that its platform shelf sequences, typified by trilobite faunal assemblages diagnostic of the NCC, record the vestige of coeval arc magmatism. Detrital zircons analyzed from the sandstones yielded Eoarchean to Early Ordovician ages, which define three distinct types of distribution patterns characterized by: (1) double peaks at ca. 1.85 Ga and 2.50 Ga diagnostic of basement rocks in the NCC; (2) minor peaks at ca. 1.75, 1.6, and 1.2–1.1 Ga in addition to double peaks; and finally (3) a scattered array of late Paleoproterozoic to Neoproterozoic zircons lacking double peaks. The marked contrasts among the three types reflect significant changes in provenance, most likely linked to variations in paleo-water depths during the “Sauk” transgression. Longshore- or onshore-directed currents, associated with an increase in water depth, apparently brought outboard oceanic detritus and benthic trilobites into the relatively flat outer shelf of the Taebaeksan Basin. As a result, fine-grained sandstones received a large amount of detritus from distal sources, yielding mixed signatures in zircon age patterns and trilobite assemblages. Excluding the basal sandstone-conglomerate unit, five siliciclastic formations contain syndepositional zircon populations, and their weighted mean 206Pb/238U ages decrease upsection from 512 ± 5 Ma to 483 ± 2 Ma, indicating a sedimentary influx from contemporaneous volcanic activity. In conjunction with arc-related bulk-rock geochemistry and juvenile Nd isotopic signature, early Paleozoic detrital zircons likely represent the first-cycle detritus supplied for ∼30 m.y. from the proto-Japan arc that initially formed at ca. 520 Ma. Together with the occurrence of ca. 700–500 Ma detrital Pacific Gondwana zircons in fine-grained sandstones, Paleozoic arc-sourced detritus suggests that the Korean Peninsula was paleogeographically linked to an ancient convergent margin, perhaps extending from the Terra Australis orogen.

U-Pb ages on detrital zircons and geochemistry of Lula paragneiss from Variscan belt, NE Sardinia, Italy: implications for source rocks and early Paleozoic paleogeography

Chemical analyses of garnet-bearing metasediments and EMP and U/Pb analyses of detrital zircons of the Lula paragneisses in the Axial Zone of the Variscan belt (NE Sardinia) give significant contribution to the reconstruction of the early Paleozoic evolution of the northern Gondwana margin. The youngest middle Ordovician (465 Ma) age of detrital zircons indicate a derivation from a fore- arc sedimentary basin along an early Paleozoic convergent margin, which collected sediments from nearby emerged lands consisting of early Paleozoic volcanic arcs and pre-Paleozoic sequences. The chemical composition of metasediments is characterized by negative Sr anomaly and depletion in heavy rare earth elements (HREE) and Y as compared to the upper crust. Normalized to chondrite values, the paragneiss shows a steep REE pattern with light-REE enrichment, negative Eu anomaly and flat heavy-REE pattern. All these features suggest a derivation form older active continental margins or island arcs. Detrital zircon ages cover a very large time span (3151 + 97 Ma to 465 + 8 Ma) and reveal a complex history of inheritance and recycling. The oldest ages obtained on relic cores and/or magmatic stages, mostly enriched in Hf (Zr / Hf ratios: 45-24) and devoid of Y, indicate a contribution from granitoid rocks of mainly crustal origin. The ages of detrital zircons highlight a derivation of the sedimentary supply from the Sahara craton and/or the Arabian-Numidian shield along the northeastern margin of Gondwana. This fit well with derivation of early Paleozoic metasedimentary formations in southern Sardinia and northern Apennine, pointing out a common origin and location of these sedimentary basins along the northern margin of Gondwana at the early Paleozoic. As regards the Variscan orogeny, the common middle Ordovician age of Lula paragneiss and nearby Lodé orthogneiss highlight the role of Variscan tectonics in the assembly of different blocks of early-middle Paleozoic margin.

Sediment grain size does matter: implications of spatiotemporal variations in detrital zircon provenance for early Paleozoic peri-Gondwana reconstructions

A comprehensive understanding of the relationship between the Sino-Korean Craton (SKC) and the Gondwana supercontinent is crucial for accurate reconstruction of the tectonic evolution and early Paleozoic paleogeography of East Asia. To explore the link between the SKC and peri-Gondwana, we provide new detrital zircon U–Pb age data from litho- and bio-stratigraphically constrained lower Cambrian to Lower Ordovician sandstone deposits from the eastern margin of the SKC (Taebaeksan Basin). Results indicate that the two distinct age spectra of detrital zircon resulted from provenance change combined with a strong function of sediment grain size within host siliciclastic rocks of the Taebaek Group. The age spectra from coarse-grained sandstones display Paleoproterozoic (1.9 Ga) and Neoarchean (~ 2.5 Ga) peaks, indicating that the sediments were supplied from the basement rocks of the SKC. Conversely, age spectra from fine-grained siliciclastics contain late Mesoproterozoic (~ 1.0 Ga) and Neoproterozoic (~ 0.6 Ga) peaks, with or without a Paleoproterozoic signal, consistent with a Gondwanan sediment origin. These different age populations have been documented in multiple Cambrian and Ordovician sequences of the SKC and are consistently well correlated with sediment grain size. Coarse-grained sediments, sourced primarily from local basement rocks, were deposited in coastal, nearshore, and shelf environments, whereas fine-grained sediments were derived from more distal sources (i.e., the Gondwana mainland and/or the Gyeonggi Marginal Belt) and deposited in inner to outer shelf settings. Therefore, the repeated occurrence of sediment with two distinct provenances in the Cambrian–Ordovician siliciclastics of the SKC is likely a result of provenance shift integrated with changing depositional environments in an epeiric platform. This yielded variations in sediment grain size and source rock provenance, with and/or without a tectonic activity. Consequently, our results indicate that the SKC was adjacent to Gondwana during the early Paleozoic.

A Cambrian mixed carbonate–siliciclastic platform in SW Gondwana: evidence from the Western Sierras Pampeanas (Argentina) and implications for the early Paleozoic paleogeography of the proto-Andean margin

The Western Sierras Pampeanas (WSP) of Argentina record a protracted geological history from the Mesoproterozoic assembly of the Rodinia supercontinent to the early Paleozoic tectonic evolution of SW Gondwana. Two well-known orogenies took place at the proto-Andean margin of Gondwana in the Cambrian and the Ordovician, i.e., the Pampean (545–520 Ma) and Famatinian (490–440 Ma) orogenies, respectively. Between them, an extensive continental platform was developed, where mixed carbonate–siliciclastic sedimentation occurred. This platform was later involved in the Famatinian orogeny when it underwent penetrative deformation and metamorphism. The platform apparently extended from Patagonia to northwestern Argentina and the Eastern Sierras Pampeanas, and has probable equivalents in SW Africa, Peru, and Bolivia. The WSP record the outer (deepest) part of the platform, where carbonates were deposited in addition to siliciclastic sediments. Detrital zircon U–Pb SHRIMP ages from clastic metasedimentary successions and Sr-isotope compositions of marbles from the WSP suggest depositional ages between ca. 525 and 490 Ma. The detrital zircon age patterns further suggest that clastic sedimentation took place in two stages. The first was sourced mainly from re-working of the underlying Neoproterozoic metasedimentary rocks and the uplifted core of the early Cambrian Pampean orogen, without input from the Paleoproterozoic Rio de la Plata craton. Sediments of the second stage resulted from the erosion of the still emerged Pampean belt and the Neoproterozoic Brasiliano orogen in the NE with some contribution from the Rio de la Plata craton. An important conclusion is that the WSP basement was already part of SW Gondwana in the early Cambrian, and not part of the exotic Precordillera/Cuyania terrane, as was previously thought.

The De Long Islands: A missing link in unraveling the Paleozoic paleogeography of the Arctic

The vast Laptev and East Siberian shelves in the eastern Russian Arctic, largely covered by a shallow sea and buried beneath sea ice for 9months of the year, remain one of the least studied parts of continental crust of the Earth and represent a big unknown when performing pre-Cenozoic reconstructions of the Arctic. The De Long Islands provide an important window into the geology of this area and are a key for understanding the Early Paleozoic history of the Amerasian Arctic. Four of them (Jeannette, Henrietta, Bennett and Zhokhov islands) were studied using structural data, petrographic and geochemical analyses and U–Pb zircon age dating to offer the following new constraints for the Early Paleozoic paleogeography of the Arctic realm. The basement beneath the De Long Islands is of Late Neoproterozoic to earliest Cambrian age, about 670–535Ma. In the Early Paleozoic, the De Long Islands were located along the broad Timanian margin of Baltica, with a clastic sediment provenance from the Timanian, Grenville–Sveconorwegian, and Baltic Shield domains. The Cambro-Ordovician volcaniclastic successions on Jeannette and Henrietta islands formed part of a continental volcanic arc with a corresponding back-arc basin located to the south (in present co-ordinates). On the continent-ward side of the back-arc basin, shallow marine shelf clastic and carbonate rocks were deposited, which are exposed today on Bennett Island in the south-west of the archipelago (in modern coordinates). The De Long Islands together with other continental blocks, such as Severnaya Zemlya, Arctic Alaska–Chukotka, and the Alexander Terrane, formed the contiguous active continental margin of Baltica during the Early Paleozoic. Today however, these terranes are spread out over a distance of 5000km across the Arctic and eastern Pacific margins due to the subsequent opening of a series of Late Paleozoic, Mesozoic and Cenozoic oceanic basins.

Detrital provenance evolution of the Ediacaran–Silurian Nanhua foreland basin, South China

We report here in-situ U–Pb and Hf isotopic results of detrital zircons from sixteen Cambrian–Silurian siliciclastic samples across the Nanhua foreland basin, South China. Together with published data from Ediacaran–Silurian sandstones in the region, we establish the temporal and spatial provenance evolution across the basin. Except for samples from northeast Yangtze, all other Ediacaran–Silurian samples exhibit a prominent population of 1100–900Ma, moderate populations of 850–700Ma and 650–490Ma, and minor populations of 2500Ma and 2000–1300Ma, grossly matching that of crystalline and sedimentary rocks in northern India. Zircon Hf isotopes further reveal four episodes of juvenile crustal growth at 2.5Ga, 1.8Ga, 1.4Ga and 1.0Ga in the source regions. Utilizing the basin history and late Neoproterozoic to early Paleozoic paleogeography of South China, we conclude that the Ediacaran–Cambrian sediments in the Nanhua foreland basin were mainly sourced from northern India and adjacent orogens, and the Ordovician–Silurian sediments were derived from both locally recycled Ediacaran–Cambrian rocks and eroded Cathaysian basement. The Wuyi–Yunkai late-orogenic magmatic rocks also contributed to the Silurian sediments in the basin. The upper-Ordovician to Silurian samples in northeast Yangtze received higher proportions of local Cryogenian (850–700Ma) magmatic rocks which were uplifted during late-Ordovician to Silurian time. We speculate that there was an Ediacaran–Cambrian collisional orogen between South China and northern India, shedding sediments to the early Nanhua foreland basin. Far-field stress during the late stage of this collisional orogeny triggered the Ordovician–Silurian intraplate Wuyi–Yunkai orogeny in South China, and erosion of the local Wuyi–Yunkai orogen further provided detritus to the late Nanhua foreland basin.

Nd isotopic study of Upper Cambrian conodonts from Korea and implications for early Paleozoic paleogeography

Correlation of the Korean Peninsula with the neighboring South and North China blocks has been one of the most important and long debated issues in East Asian tectonics. The eastward extension of the Chinese collisional belt between the South and North China blocks into the Korean Peninsula is still in dispute. The lower Paleozoic sedimentary rocks in South Korea, the Joseon Supergroup, accumulated in the Okcheon belt which has been proposed as the suture zone or the block boundary between the South and North China blocks in Korea. The Joseon Supergroup comprises five different lithostratigraphic units, and has been proposed to represent two tectonostratigraphic blocks bounded by the Honam Shear Zone (HSZ) in the Okcheon belt; among them, the Yeongweol Unit in the western part of the HSZ is correlated with South China and the Duwibong Unit in the eastern part of the HSZ with North China. To test the above geodynamic interpretation, this study analyzed the Nd isotopic composition of Upper Cambrian conodonts from the Duwibong and Yeongweol units. The difference of the ɛ Nd ( T) values between the Upper Cambrian Duwibong and Yeongweol units is about 3 ɛ units. Compared to a wide range of the ɛ Nd (0) values in the modern oceanic basins, this slight difference can be regarded as a variation in a same paleo-watermass. The ɛ Nd ( T) values of the two units are consistent with coeval values from North China, and this suggests that the Duwibong and Yeongweol units shared the same oceanic watermass with the North China. Considering current early Paleozoic paleogeographic reconstructions, the Nd isotopic signatures of North China, Duwibong and Yeongweol units may be independent of Laurentia and Baltica and thus can be indicative of another unique oceanic watermass. In contrast to the previous tectonic interpretations, the same paleoceanographic signatures shown by the Duwibong and Yeongweol units and North China and recent developments suggest that the Yeongweol Unit in the early Paleozoic Joseon Supergroup is not correlated with South China but correlated with North China, and the Korean Peninsula and North China block may have been included in a larger continental block, the Sino-Korean block. The collisional belt between the South and North China blocks may not extend into the Korean Peninsula.

Nd isotopic study of Upper Cambrian conodonts from Korea and implications for early Paleozoic paleogeography

Abstract Correlation of the Korean Peninsula with the neighboring South and North China blocks has been one of the most important and long debated issues in East Asian tectonics. The eastward extension of the Chinese collisional belt between the South and North China blocks into the Korean Peninsula is still in dispute. The lower Paleozoic sedimentary rocks in South Korea, the Joseon Supergroup, accumulated in the Okcheon belt which has been proposed as the suture zone or the block boundary between the South and North China blocks in Korea. The Joseon Supergroup comprises five different lithostratigraphic units, and has been proposed to represent two tectonostratigraphic blocks bounded by the Honam Shear Zone (HSZ) in the Okcheon belt; among them, the Yeongweol Unit in the western part of the HSZ is correlated with South China and the Duwibong Unit in the eastern part of the HSZ with North China. To test the above geodynamic interpretation, this study analyzed the Nd isotopic composition of Upper Cambrian conodonts from the Duwibong and Yeongweol units. The difference of the ɛ Nd ( T ) values between the Upper Cambrian Duwibong and Yeongweol units is about 3 ɛ units. Compared to a wide range of the ɛ Nd (0) values in the modern oceanic basins, this slight difference can be regarded as a variation in a same paleo-watermass. The ɛ Nd ( T ) values of the two units are consistent with coeval values from North China, and this suggests that the Duwibong and Yeongweol units shared the same oceanic watermass with the North China. Considering current early Paleozoic paleogeographic reconstructions, the Nd isotopic signatures of North China, Duwibong and Yeongweol units may be independent of Laurentia and Baltica and thus can be indicative of another unique oceanic watermass. In contrast to the previous tectonic interpretations, the same paleoceanographic signatures shown by the Duwibong and Yeongweol units and North China and recent developments suggest that the Yeongweol Unit in the early Paleozoic Joseon Supergroup is not correlated with South China but correlated with North China, and the Korean Peninsula and North China block may have been included in a larger continental block, the Sino-Korean block. The collisional belt between the South and North China blocks may not extend into the Korean Peninsula.

The mafic–ultramafic rock association of Loderio–Biasca (lower Pennine nappes, Ticino, Switzerland): Cambrian oceanic magmatism and its bearing on early Paleozoic paleogeography

Dismembered relics of mafic and ultramafic rock in high-grade basement rocks often record pre-collisional stages of deep lithospheric and/or oceanic mafic magmatism in an orogen. A lens of amphibolites and serpentinites, intercalated between the crystalline Simano and Leventina nappes (lower Penninic nappes, Central Alps, Switzerland) was investigated for the protolith age and chemical and isotopic composition. Despite the polyphase high-grade metamorphic overprinting, primary isotopic and chemical relationships are still preserved and are indicative of an origin in an active margin situation. Trace element geochemistry and Nd isotopes of amphibolites argue for the fractionated gabbros as protoliths, which were formed by the partial melting of the upper mantle. The rocks show a variation of ε Nd values from +7.3 to +4.2 and Nd model ages up to 2 Ga, taken as evidence for the contamination by a geochemically enriched, old lithospheric source. Sr isotopes are heavily disturbed through the percolating crustal fluids after the emplacement into the continental crust. U–Pb age determination of zircon from two amphibolites using both in situ (SHRIMP) and conventional methods converge at an age of 518±11 Ma for the crystallization of the protoliths. The rock association of Loderio–Biasca is a further example from the Alpine basement recording an oceanic domain between Gondwana and the different Gondwana-derived microcontinents in the Cambrian–Ordovician times. Remnants of this ocean were incorporated into the accretionary wedges that formed during the subduction/collision events from Ordovician to Carboniferous, commonly summarized as the Caledonian and Variscan orogeny, and are today spread over the so-called Saxothurigian and Moldanubian domain of the Variscan orogen. These domains consist, thus to large extents, of heterochronous accretionary wedge sequences.

The Early Paleozoic paleogeography of the North China block and the other major blocks of China

With the summarization of the Early Paleozoic paleomagnetic data recently obtained from the three major blocks of China, the Early Paleozoic (i.e. Cambrian and Ordovician) paleogeographic positions of the North China, South China and Tarim blocks were discussed in detail. The North China, South China and Tarim blocks were inferred to be located adjacent to East Gondwana in low latitudes of the Southern Hemisphere during the Early Cambrian. During the Early-Middle Ordovician, the South China and Tarim blocks were also located in low latitudes of the Southern Hemisphere with some affinities of the Gondwanaland, whereas the North China block may have episodically separated from the Gondwanaland, and might be sited close to the North America and Siberia. The reestablished paleogeographic configurations are in agreement with the studies on the biogeography, paleoclimate and sedimental facies of the North China and South China blocks.

Les Pyrénées centrales et orientales au début du Paléozoique (Cambrien s.l.): évolution paléogéographique et géodynamique

In order to debate of the early Paleozoic paleogeography, the repartition of the Hercynian blocks, today scattered around West-Mediterranean Sea. should be known. This is the case for the end of the Paleozoic (Fig. 1), but not for the beginning; Fig. 6 is drawn with the supposed repartition in the middle of the Carboniferous. In Central and Eastern Pyrenees and surrounding areas (Fig. 1), Upper Ordovician beds rest unconformably upon a thick (4–6 km), dominantly pelitic series known as Lower Paleozoic in the Eastern Pyrenees or Seo Formation in the Central Pyrenees. The metamorphic lower part of this series often lies over metagranilic orthogneisses, which are best interpreted as a Precambrian basement, Panafriean-Cadomian in age. By correlation with fossiliferous series of other areas, the Pyrenean Lower Paleozoic should be mainly Cambrian in age (ranging from Uppermost Proterozoic to Lowermost Ordovician). For the purpose of this paper, the complex lithostratigraphic succession of the Lower Paleozoic of the Eastern Pyrenees, with two groups and seven formations, could be summarized (Fig. 2) by a threefold division, from bottom to top: (i) a pelile-greywacke and carbonate unit, with a conspicuous plagioclasic component and a sodic composition (Uppermost Precambrian to Lowermost Cambrian?): (ii) a sandstone-pelite unit, with lithic sandstones, ending with a carbonate level, well developped in the Central Pyrenees (Lower Cambrian?): (iii) a mudstone-siltstone unit (Middle-Upper Cambrian?). Fossiliferous Lower Cambrian beds which outcrop at Terrades (south of the Eastern Pyrenees) could be a remnant of an allochthon unit which can be compared with the nappe-thrusts of the nearby Southern Montagne Noire. The pelite-greywacke and carbonate unit (Fig. 3) occurs only in the South-Eastern Pyrenees as a south to north transgressive platform bordering a basin extending southwards; not far south of Eastern Pyrenees, a volcanism of “intermediate” type supplied in plagioclasic clasts the greywackes and volcanoclastic deposits. Near the base of the sequence, a bimodal volcanism and synsedimentary faults reflect the extensional context of the basin initiation, the geochemistry of which has been related to back-arc setting. An acidic volcanism developped higher in the sequence (tufs and hypovolcanic bodies). Carbonate levels are numerous, particularly in the lower part of the unit. The upper part of the sequence is an oslistostrome made of polygenic intraformational conglomerates fed from the south: it outlines the transition to the next unit. The sandstone-pelite unit (Fig. 4) rests conformably on the previous one in the Eastern Pyrenees, and is unconformable upon the Precambrian basement to the north (North-Pyrenean massifs) and to the west (Central Pyrenees). It is characterized by arkosic lithic sandstones with clear quartz grains: they originated in the erosion of a granitic basement and/or acidic volcanic rocks. Coarseness of the sandstones and thickness (up to 2–4 km) of the unit increase from south-east to north and west. A carbonate upper level, well developped in the Central Pyrenees, can be correlated with Lower Cambrian limestones from the surrounding areas. The mudstone-siltstone unit (Fig. 5) is defined by the prevalence of mm- to cm- scale alternations of argillaceous mud and silt of a flyschoid type, representing a more basinal sedimentation. A carbonate level, the highest in the series, is intercalated in Ihe lower part ot the unit: above this level, deposits are very homogeneous and thiek (about 2 km). A poorly known formation with pelitcs and sandstones caps the muddy-silty unit: it could be Lower Ordovician in age. Thus, the Pyrenean domain shows the same depositional history as West-Mediterranean area: (i) first, a volcano-sedimentary platform or basin occurs, as in Central Spain. Eastern Pyrenees. Sardinia and axial zone of the Montagne Noire, but not further north; (ii) second, a silicoclastic platform spreads out. which becomes carbonated at the end: (iii) third. Ihe basin deepens and receives fine silicoclaslies. This evolution is not fully accounted for in recent synthesis of Pre-hercynian France or Spain, and it should appear useful for a better understanding of the south French Massif Central geological history.

Early Paleozoic paleogeography of Laurentia and western Gondwana: Evidence from tectonic subsidence analysis: Comment and Reply

Early Paleozoic paleogeography of Laurentia and western Gondwana: Evidence from tectonic subsidence analysis: Comment and Reply

Early Paleozoic paleogeography of Laurentia and western Gondwana: Evidence from tectonic subsidence analysis

Research Article| August 01, 1997 Early Paleozoic paleogeography of Laurentia and western Gondwana: Evidence from tectonic subsidence analysis Kenneth E. Williams Kenneth E. Williams 1Texaco Inc., Exploration and Production Technology Department, 3901 Briarpark, Houston, Texas 77042 Search for other works by this author on: GSW Google Scholar Geology (1997) 25 (8): 747–750. https://doi.org/10.1130/0091-7613(1997)025<0747:EPPOLA>2.3.CO;2 Article history first online: 02 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 Kenneth E. Williams; Early Paleozoic paleogeography of Laurentia and western Gondwana: Evidence from tectonic subsidence analysis. Geology 1997;; 25 (8): 747–750. doi: https://doi.org/10.1130/0091-7613(1997)025<0747:EPPOLA>2.3.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 A number of terranes were present in the early Paleozoic ocean between Laurentia and Gondwana following rifting. The precise location of these microcontinents and island arcs is unclear. We present tectonic subsidence curves from selected basins that may provide some constraints on the possible paleogeographic interpretations for this time interval. Among these tectonic blocks were the Precordillera terrane that originated in the Ouachita area of Laurentia and the composite Avalon-Carolina terrane that was derived from the Gondwana margin. Also present were the island-arc terranes of Famatina, Mixteca, and Zapoteca. The Precordillera and Famatina terranes are currently located in southern South America. The Avalon-Carolina terrane is in eastern North America. The Mixteca and Zapoteca terranes are in Central America. A review of previous work augmented by new tectonic subsidence analysis indicates that these terranes were swept up by early Paleozoic plate movements and were translated to approximately their present relative positions by the Early Carboniferous. 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.

Early Paleozoic paleogeography of the northern Gondwana margin: new evidence for Ordovician-Silurian glaciation

During the Early Paleozoic, transgressions and the distribution of sedimentary facies on the northern Gondwana margin were controlled by a regional NNW-SSE to almost north-south striking structural relief. In Early Silurian times, a eustatic highstand enabled the sea to reach its maximum southward extent. The counterclockwise rotation of Gondwana during the Cambrian and Early Ordovician caused the northern Gondwana margin to shift from intertropical to southern polar latitudes in Ordovician times. Glacial and periglacial deposits are reported from many localities in Morocco, Algeria, Niger, Libya, Chad, Sudan, Jordan and Saudi Arabia. The Late Ordovician glaciation phase was followed by a period of a major glacioeustatic sea-level rise in the Early Silurian due to the retreat of the ice-cap. As a consequence of the decreasing water circulation in the basin centers (Central Arabia, Murzuk- and Ghadames basins), highly bituminous euxinic shales were deposited. These shales are considered to be the main source rock of Paleozoic oil and gas deposits in parts of Saudi Arabia, Libya and Algeria. The following regression in the southern parts of the Early Silurian sea was probably caused by a second glacial advance, which was mainly restricted to areas in Chad, Sudan and Niger. Evidence for glacial activity and fluvioglacial sedimentation is available from rocks overlying the basal Silurian shale in north-east Chad and north-west Sudan. The Early Silurian ice advance is considered to be responsible for the termination of euxinic shale deposition in the basin centers.

Early Paleozoic paleogeography and accretionary history of the Newfoundland Appalachians

New paleomagnetic results were obtained from several units in the Central Mobile belt of the north-central Newfoundland Appalachians. Combined with recently published data, the results place important limits on interpretations of early Paleozoic paleogeography and evolution of the Appalachian-Caledonian orogen. The Ordovician Appalachian margin of North America, located at low paleolatitudes and facing roughly south, was separated from the southern margin of Iapetus (Avalon-Armorica) by ∼3500 km. Primary directions in pillowed volcanic rocks of the Moreton9s Harbour Group that are part of an Early Ordovician island arc show that these rocks were formed near the North American margin, at a paleolatitude of 12°S. Early to Middle Ordovician volcanic rocks of the Roberts Arm, Chanceport, and Summerford groups, on the other hand, were extruded at paleolatitudes of 30°-40°S. Unconformably overlying volcanics of the Silurian Botwood Group were extruded subaerially at a paleolatitude of 24°S. Combined with tectonostratigraphic data, these results suggest the following tectonic history. In Early Ordovician time, northerly subduction of the main Iapetus basin was accompanied by the formation of a volcanic arc and a back-arc basin near the North American margin. Middle Ordovician emplacement of ophiolites on the North American margin reflects the closure of this back-arc basin (Iapetus I), and continued northerly subduction in Silurian time closed the main basin (Iapetus II).

Paleomagnetic results from volcanic rocks of the Shelve Inlier, Wales: evidence for a wide Late Ordovician Iapetus Ocean in Britain

In order to shed light on the early Paleozoic paleogeography of Iapetus-bordering continents, samples for paleomagnetic study were collected from middle Ordovician (Llanvirn) volcanic rocks of the Shelve Inlier, Welsh Borderland. The folding within the inlier is constrained to late Ordovician (Ashgill) time, thus offering a fold test with tight age brackets. After stepwise thermal demagnetization, a pre-folding characteristic magnetization component was isolated from 95 specimens. The mean of 11 site mean directions for the characteristic magnetization gives D/I=116.4/+ 67.9(k = 89.4; α 95 = 4.9° ), and the paleomagnetic pole lies at 26.6°N, 36.1°E ( δp = 6.9°, δm = 8.2°). The fold test is positive at the 99% confidence level, indicating that the magnetization was acquired during the middle or late Ordovician. We infer from geological considerations that this magnetization is not a primary thermoremanence, but was acquired during late Ordovician time as a result of a thermochemical disturbance of that age. Our results indicate that southern Britain was near 51° south latitude during the later Ordovician. Since middle to late Ordovician paleolatitudes for Gondwana and Laurentia are well-determined, our result can be used to test various scenarios for the closure of Iapetus. We conclude that: (1) the Iapetus Ocean in Britain still had a latitudinal width of some 30° at this time, thus rendering a postulated Ordovician closure unlikely; (2) southern Britain, Avalon, and Hercynian Europe all occupied high latitudes during the later Ordovician, consistent with a paleoposition near the northern margin of Gondwana; and (3) the Acadian orogeny in Britain and North America could have been the result of the collision of Gondwana and Laurentia during early Devonian time.