Neoproterozoic Supercontinent Research Articles

Geochronological and isotopic constraints on the Mesoproterozoic Namaqua–Natal Belt: evidence from deep borehole intersections in South Africa

Mesoproterozoic lithologies of the Namaqua–Natal Belt are exposed in the west and east of South Africa but the central section of the belt is obscured by younger sedimentary cover. This belt is one of several Grenvillian-aged belts world-wide and is of importance in reconstructions of the Meso- to Neo-Proterozoic supercontinent of Rodinia . Zircons from granite and biotite gneiss in two deep boreholes which penetrated the Phanerozoic cover provide SHRIMP U–Pb dates of 1053 +29 / −25 Ma and 1134 +15 / −15 Ma. Sm–Nd model dates for whole-rock samples from these and two other boreholes range from ∼2400 to 1200 Ma, unlike model dates from the eastern (Natal) sector of the Namaqua–Natal Belt which are all younger than ∼1400 Ma. Model dates are similar to those noted in the Bushmanland and Richtersveld Sub-provinces of the western (Namaqua) sector of the Belt. The results are interpreted to indicate that this Proterozoic crust may be an easterly extension of the Bushmanland Sub-province or some equivalent terrane and that there must be a terrane boundary between the eastern-most borehole studied and the surface outcrops further east.

Geological complexes in the margin of the Siberian Craton as indicators of the evolution of a Neoproterozoic Supercontinent

This paper describes the Late Precambrian geologic complexes from the southern margin of the Siberian Craton, associated with the extension epochs. Analysis of the data available suggests that there were two episodes of intracontinental breakup, which resulted in the opening of the ocean (1300-900 and 850-550 million years ago). The time sequence of the rift-related volcanic rocks and terrigenous deposits ! basic dike swarms ! carbonate-terrigenous rocks ! ophiolites and island-arc rocks reflects the successive change of geodynamic environments in the marginal part of the craton. The stage of intracontinental rifting was superseded by the stage of advanced rifting which preceded the continent break and the formation of oceanic crust. This period was followed by two phases of oceanic evolution: a passive phase (sedimentary rocks of the passive margins) and an active phase (island arcs, backarc seas, and the like). Several dierent versions are oered and discussed for the extension processes in the southwestern and southeastern parts of the Siberian Craton is association with the breakup of the Rodinia Continent.

Supersequences, superbasins, supercontinents – evidence from the Neoproterozoic–Early Palaeozoic basins of central Australia

ABSTRACTNeoproterozoic sedimentary basins cover a large area of central Australia. They rest upon rigid continental crust that varies from c. 40–50 km in thickness. Whilst the crust was in part formed during the Archaean and early Palaeoproterozoic, its final assembly occurred at approximately 1.1 Ga as the Neoproterozoic supercontinent, Rodinia, came into being. The assembly process left an indelible imprint on the region producing a strong crustal fabric in the form of a series of north dipping thrusts that pervade much of the thick craton and extend almost to the Moho. Following a period of stability (1.1–0.8 Ga), a large area of central Australia, in excess of 2.5 × 106 km2, began to subside in synchroneity. This major event was due to mantle instability resulting from the insulating effect of Rodinia. Initially, beginning c. 900 Ma, a rising superplume uplifted much of central Australia leading to peneplanation of the uplifted region and the generation of large volumes of sand‐sized clastic materials. Ultimately, the decline of the superplume led to thermal recovery and the development of a sag basin (beginning at c. 800 Ma), which in turn resulted in the redistribution of the clastic sediments and the development of a vast sand sheet at the base of the Neoproterozoic succession.The superbasin generated by the thermal recovery was short lived (c. 20 M.y.) but, in conjunction with the crustal fabric developed during supercontinent assembly, it set the stage for further long‐term basin development that extended for half a billion years well into the Late Palaeozoic. Following the sag phase at least five major tectonic episodes influenced the central Australian region. Compressional tectonics reactivated earlier thrust faults that had remained dormant within the crust, disrupting the superbasin, causing uplift of basement blocks and breaking the superbasin into the four basins now identified within the central Australian Neoproterozoic succession (Officer, Amadeus, Ngalia and Georgina Basin). These subsequent tectonic events produced the distinctive foreland architecture associated with the basins and were perhaps the trigger for the Neoproterozoic ice ages. The reactivated basins became asymmetric with major thrust faults along one margin paralleled by deep narrow troughs that formed the main depocentres for the remaining life of the basins. The final major tectonic event to influence the central Australian basins, the Alice Springs Orogeny, effectively terminated sedimentation in the region in the Late Palaeozoic (c. 290 Ma). Of the six tectonic episodes recorded in the basinal succession only one provides evidence of extension, suggesting the breakup of east Gondwana at the end of the Rodinian supercontinent cycle may have occurred at close to the time of the Precambrian–Cambrian boundary. The central Australian basins are thus the products of events surrounding the assembly and dispersal of Rodinia.

Sedimentology and sequence stratigraphy of Neoproterozoic and Cambrian units across a craton-margin hinge zone, southeastern California, and implications for the early evolution of the Cordilleran margin

Abstract Neoproterozoic–basal Cambrian strata exposed in eastern California represent the deposits of a craton-margin hinge zone that formed in response to the fragmentation of the Neoproterozoic supercontinent, Rodinia. One unresolved question regarding the late Neoproterozoic stratigraphy in the southwestern United States has been the interpretation of paleotectonic affinity for rocks deposited above the glaciogenic Kingston Peak Formation. Of central concern has been attempts to identify the position in this stratigraphy, where rift-related sediments give way to passive-margin deposits. Subsidence analyses suggest that rifting occurred near the start of the Cambrian, perhaps coincident with the feldspathic middle member Wood Canyon Formation. It rests on a disconformity that represents the base of the Sauk Supersequence and would likely represent the break-up unconformity in subsidence analysis models. Middle member Wood Canyon and overlying Lower–Middle Cambrian strata extend far into the craton. Detailed sedimentary facies and sequence stratigraphic analysis of post-Kingston Peak, pre-middle Wood Canyon rocks indicate that depositional facies in this succession (distal alluvial through shallow subtidal) are similar to units deposited on the stable craton. Further, these pre-Sauk units, which can be divided into multiple, principally eustatically driven depositional sequences are correlated across long distances and even lap onto the edge of the stable craton. We suggest the Kingston Peak Formation is the principal rift-generated deposit and the overlying thick, predominantly siliciclastic, section represents the basal deposits of the Cordilleran passive margin. Kingston Peak strata consist of thick, coarse diamictites interbedded with turbidites; such facies are unique in the overall stratigraphy but are similar to other known rift deposits. Although the age of the Kingston Peak Formation is not well constrained and may be as young as ∼590 Ma, it may correlate with the Rapitan–Sturtian glaciation (∼720 Ma), which would place middle Wood Canyon strata some 150 Ma younger than the start of rifting.

Petrology and Isotopic Composition of a Grenvillian Basement Fragment in the Northern Appalachian Orogen: Blair River Inlier, Nova Scotia, Canada

Mesoproterozoic metaplutonic rocks in northern Cape Breton Island, INTRODUCTION Nova Scotia, occur in a tectonic inlier within the Appalachian In eastern North America, Mesoproterozoic Laurentian orogen. Although they have been multiply metamorphosed and basement rocks and their Neoproterozoic to mid-Paleovariably deformed, the petrology and geochemistry of these rocks zoic volcanic and sedimentary cover preserve a record provide insight into the tectonomagmatic evolution of easternmost of the Proterozoic to mid-Paleozoic geologic history of Laurentia. Anorthosite, syenite, and granitoid plutons eastern Laurentia. The record includes Mesoproterozoic (1100–980 Ma) intruded the Sailor Brook and Polletts Cove River orogeny on the ancient North American craton, breakgneisses. New Nd isotopic data are presented from a biotite-rich up of a Neoproterozoic supercontinent, development of part of the Sailor Brook gneiss ( Ndi = −0·7), two anorthosite a passive continental margin, and mid-Paleozoic orogeny. samples ( Ndi = +2·1 and +2·8), and a charnockite unit Exposures of Mesoproterozoic Laurentian basement in ( Ndi = −0·4). New U–Pb zircon data from the anorthosite yield easternmost Canada and the USA occur in a disPb/Pb ages between 975 and 1095 Ma. Disrupted U–Pb continuous band of inliers in the Appalachian orogen systematics preclude a unique age interpretation, but the >1095 Ma from Newfoundland to Alabama (Fig. 1). They consist single-grain date is a minimum age for the anorthosite. Field relations, mostly of rocks formed or deformed during major and trace-element geochemistry, and isotopic characteristics >1190–980 Ma Grenvillian tectonic and magmatic indicate that the anorthosite and charnockite were probably coexisting events, and are distinct from Neoproterozoic and melts, but not differentiates of a single parent magma. The lithological Paleozoic units of accreted Appalachian terranes in that and chemical characteristics of the Lowland Brook Syenite are they include granulite-facies metamorphic rocks and, similar to those of a contemporaneous belt of ultrapotassic plutons in many cases, anorthosite–charnockite–mangerite suites in the southern Grenville Province, and both have the chemical (Bartholomew, 1984, and papers therein; Pettingill et al., characteristics of certain modern continental-margin arc magmas. 1984; Rankin et al., 1989, 1993; Owen & Erdmer, 1990; These data indicate that the Mesoproterozoic units in the Blair Hughes et al., 1997). River inlier were juvenile crustal additions to eastern Laurentia The sinuous trend of the band of basement inliers during Grenville-related orogenic events. broadly reflects promontories and re-entrants that formed

Laurentia‐Kalahari Collision and the Assembly of Rodinia

The Llano Orogenic Belt along the present southern margin of Laurentia, regarded as continuation of the Grenvillian Orogen along the eastern Laurentian margin and exposed in basement uplifts in central and western Texas, records an ∼300‐m.yr. history of orogenesis culminating in arc‐continent and continent‐continent collision between ∼1150 and 1120 Ma and continuing until ∼980 Ma. The shape of the orogen and kinematics of the contractional deformation along the belt, together with the high‐P metamorphic conditions attained, indicate that a previously unidentified craton served as an indentor. It is paleomagnetically acceptable for the Kalahari Craton of southern Africa to have been opposed to this margin and within ∼1500 km of present‐day central Texas at ∼1100 Ma. Moreover, the Kalahari Craton is the correct size, and the structural and metamorphic evolution of the 1200–950 Ma Namaqua‐Natal Orogenic Belt that wraps around its present southern margin is compatible with that craton having been the indentor. The ocean basin that closed between the Laurentia and Kalahari Cratons would have been comparable to the present Pacific, with island arc/terrane accretion occurring during the Mesoproterozoic along opposing active convergent margins. The coeval 1.1 Ga Keeweenawan and Umkondo magmatic provinces of Laurentia and Kalahari, respectively, are associated with rifts at a high angle to the Llano and Namaqua Orogens. The rifts are interpreted as the result of collision‐generated extensional stresses within the two cratons. The voluminous mafic igneous rocks in both provinces, however, may reflect contemporaneous plume activity. Our reconstruction for 1.1 Ga provides a testable model for the Llano Orogenic Belt of Texas and the Namaqua Orogenic Belt of southwestern Africa as opposite sides of a Himalayan‐type collisional orogen, with the Natal Belt of southeastern Africa and the originally continuous Maudheim Belt of East Antarctica as a related Indonesian‐type ocean‐continent convergence zone. This reconstruction leads to a refinement of the paleogeography of Rodinia, with the Kalahari Craton in a position isolated from both the East Antarctic and Rio de la Plata Cratons by oceanic lithosphere. It also provides the first model for the assembly of that hypothetical early Neoproterozoic supercontinent. At least four separate cratonic entities appear to have collided along three discrete segments of the apparently anastomosing global network of “Grenvillian” orogens: the type‐Grenville Belt of eastern North America and counterparts in South America, the Llano‐Namaqua Belt, and the Eastern Ghats‐Albany/Fraser Belt of India‐East Antarctica and Australia. Over the remarkably short interval of ∼200 m.yr., this first‐order composite collisional event resulted in the amalgamation of most of Earth’s continental lithosphere and defined the close of the Mesoproterozoic Era.

The Neoproterozoic Supercontinent: Rodinia or Palaeopangaea?

The Rodinia reconstruction of the Neoproterozoic Supercontinent has dominated discussion of the late Precambrian Earth for the past decade and originated from correlation of sedimentary successions between western North America and eastern Australia. Subsequent developments have sited other blocks according to a distribution of ∼1100 Ma orogenic belts with break-up involving a putative breakout of Laurentia and rapid reassembly of continent crust to produce Gondwana by early Phanerozoic times. The Rodinia reconstruction poses several serious difficulties, including: (a) absence of palaeomagnetic correlation after ∼730 Ma which requires early fragmentation of continental crust although geological evidence for this event is concentrated more than 150 Ma later near the Cambrian boundary, and (b) the familiar reconstruction of Gondwana is only achieved by exceptional continental motions largely unsupported by evidence for ocean consumption. Since the geological evidence used to derive Rodinia is non-unique, palaeomagnetic data must be used to evaluate its geometrical predictions. Data for the interval ∼1150–500 Ma are used here to test the Rodinia model and compare it with an alternative model yielding a symmetrical crescent-shaped analogue of Pangaea (Palaeopangaea). Rodinia critically fails the test by requiring Antarctica to occupy the location of a quasi-integral Africa, whilst Australia and South America were much closer to their Gondwana configurations around Africa than implied by Rodinia. Palaeopangaea appears to satisfy palaeomagnetic constraints whilst surmounting geological difficulties posed by Rodinia. The relative motions needed to produce Gondwana are then relatively small, achieved largely by sinistral transpression, and consistent with features of Pan-African orogenesis; continental dispersal did not occur until the Neoproterozoic–Cambrian boundary. Analogies between Palaeopangaea and (Neo)pangaea imply that supercontinents are not chaotic agglomerations of continental crust but form by episodic coupling of upper and lower mantle convection leading to conformity with the geoid.

Geodynamic evolution and tectonostratigraphic terranes of northwestern Argentina and northern Chile

In Ordovician time, Gondwana in the area of northwestern Argentina and northern Chile had a west-facing active margin. The evolution of this margin culminated in the Ocloyic orogeny at the end of Ordovician time. This orogeny was caused by the collision of the allochthonous Arequipa-Antofalla terrane with this margin. The early Paleozoic evolution of northwestern Argentina and northern Chile contrasts markedly with the accretionary history of central Argentina and central Chile, where the Precordillera and Chilenia terranes docked in the Late Ordovician and Late Devonian periods, respectively. An inspection of the available stratigraphic and geochronological data on sedimentary, volcanic, and plutonic units of the southern Central Andes of northern Chile and northwestern Argentina reveals a lull in magmatic and metamorphic activity lasting for ~100 m.y., from Early Silurian to early Late Carboniferous time. This is interpreted as corresponding to a tectonic scenario in which the present Andean margin was a passive margin of Gondwana. This passive margin developed in response to the rifting off of a part of the Arequipa-Antofalla terrane; the present location of this block is unknown. Late Carboniferous time marks the renewed onset of subduction, initiating the Andean plate tectonic setting still prevalent today. Recently proposed models explain the Late Ordovician orogeny by the collision of Laurentia with western South America during Laurentia’s clockwise motion around South America and away from its position in the Neoproterozoic supercontinent. In its present form, this hypothesis is difficult to reconcile with the Paleozoic tectonostratigraphic evolution of the southern Central Andean region.

A geologic history of the north-central Appalachians; Part 1, Orogenesis from the Mesoproterozoic through the Taconic Orogeny

The north-central Appalachians lie just southwest of the boundary between the central/southern and northern Appalachians, occupying a critical position within the 3000+ km-long Appalachian orogen. The history of tectonic activity in the north-central Appalachians spans more than one billion years, from the assembly and breakup of a Neoproterozoic supercontinent, through active orogenesis during Laurentia9s Paleozoic northward journey off the western margin of West Gondwana, to the Mesozoic transformation of the active orogen into a passive margin during Pangea9s disassembly. The major tectonic events include five compressional orogenies and two extensional episodes: 1. The late Mesoproterozoic Grenville orogeny assembled several continental masses into the Neoproterozoic supercontinent, Rodinia. It was the most widespread but now least exposed tectonism, and rocks involved in this event underlie as basement most of the exposed north-central Appalachians. Large fragments of Laurentian Grenville rock were subsequently broken off and incorporated in later Appalachian orogenesis. 2. Crustal extension and rifting late in the Neoproterozoic and into the earliest Cambrian separated Laurentia from West Gondwana, thereby forming the intervening Theic ocean and two continental rifts on Laurentia9s eastern margin, the Catoctin rift and, later in the Middle? to Late Cambrian, the so-called Rome trough. The initial siliciclastic sedimentation on the margin migrated westward through time onto the craton, supplanted by a thick and increasingly wide carbonate shelf on Laurentia9s eastern margin. Two microcontinents of Grenville-age, non-Laurentian(?) continental rock became positioned east of Laurentia, thereby creating the Octoraro sea as an arm of Theia. 3. In Theia, east of the two microcontinents, magmatic arcs developed over a subduction zone late in the Cambrian. Convergence within Theia caused the Potomac orogeny, which obduced the arcs (Wilmington Complex, Cecil Amalgamate) over the microcontinents and associated Theic deposits (including accretionary wedge sediments). 4. Continued westward convergence collapsed the Octoraro sea, producing the Middle to Late Ordovician Taconic orogeny in which the Potomac-deformed magmatic arcs and associated Theic elements were obduced onto the Laurentian continental margin. This obduction: drowned the carbonate shelf with siliciclastic sediments (Martinsburg Formation); drove continental rise and basinal deposits over the carbonate shelf on the Martic thrust; slid the Hamburg klippe onto the shelf; and accreted the Potomac package of microcontinent/arc/basinal-sediments onto the Laurentian margin. This orogeny transformed the broad Early Paleozoic carbonate shelf into the Appalachian basin that persisted throughout the Middle and Late Paleozoic. 5. The Middle Devonian Acadian orogeny ended the largely paralic environment that dominated the Appalachian basin during the Late Silurian. Active orogenesis in New England probably extended southward to the north-central Appalachians, because a vast amount of terrigenous sediment was introduced into the Appalachian basin to form the Catskill delta; however, evidence of actual Acadian deformation and metamorphism is lacking at this latitude. These presumed internal Acadides have yet to be found. 6. The convergence of West Gondwana and Laurentia during the Late Carboniferous and earliest Permian produced the Permian Alleghany orogeny in the north-central Appalachians. This widespread decollement tectonism directly affected a larger area of the presently exposed central and southern Appalachians than any earlier Paleozoic tectonic event. An early layer-parallel shortening phase gave way to a fold-thrust development above a basal decollement. This Alleghany fold-and-thrust tectonism created long, arcuate folds in the Appalachian basin. Late in the Alleghany orogeny, rock thrust northward over the Carboniferous rocks in the Anthracite region of northeastern Pennsylvania caused anthracitization of the underlying coals. The internal Alleghanides are not presently exposed. 7. Crustal extension in the Late Triassic and Early Jurassic produced numerous local, closed basins along eastern North America. Igneous intrusions and effusions marked the beginning of the Jurassic. By the end of the Early Jurassic, horizontal crustal rebound in response to opening of the Atlantic Ocean rotated the basins by crustal inversion, which folded some within-basin rocks and produced a prominent topographic ridge along the Piedmont, up-dip of the basins. Subsequent erosion of this Piedmont ridge and other parts of the Appalachian orogen fed large volumes of sediment to offshore basins during the remainder of the Mesozoic and throughout the Cenozoic. Each of these orogenies affected most of the Appalachian orogen. The tectonic expression of each orogeny varied along and across the orogen. The elements and structural bodies involved in each also varied along strike. However, many common elements persist from one part of the orogen to another; only a few features are singular in time and space. The tectonic boundary between the central and northern Appalachians is one of these singular features-it is solely an Alleghanian artifact.

The early Neoproterozoic sedimentary Succession B of northwestern Laurentia: Correlations and paleogeographic significance

The Mesoproterozoic–Neoproterozoic stratigraphic record of ancestral North America (Laurentia) comprises three, unconformity-bounded sedimentary successions that are termed, from oldest to youngest, A, B, and C. Recent and ongoing detailed stratigraphic studies of Succession B, along with improved geochronology, allow extension and refinement of existing correlation schemes for northwestern Canada and Alaska. Succession B strata include the Shaler Supergroup of the Amundsen Basin, Mackenzie Mountains supergroup of the Mackenzie Mountains fold belt, Pinguicula group of the Wernecke Mountains inlier, Fifteenmile group of the Ogilvie Mountains inliers, and the lower Tindir Group of Tatonduk inlier. The Katakturuk Dolomite, in the northeast Brooks Range of Alaska, is included with Succession B on the basis of platformal character, geochronology, and inferred paleogeographic affinity. The framework for regional lithostratigraphic correlation of Succession B is built on recognition of four distinctive lithostratigraphic assemblages: two thick stromatolitic platformal carbonate assemblages separated by two largely subaerial siliciclastic assemblages. The correlation is supported by geochronology of detrital zircons from the upper quartzarenite assemblage, which indicates a maximum age of ca. 1000 Ma for the lower part of Succession B. These rocks are interpreted to be remnants of a northwesterly trending (present coordinates) early Neoproterozoic basin-margin promontory (Amundsen-Ogilvie-Mackenzie platform) that developed within an intracratonic basin on the northwest margin of Laurentia. The Neoproterozoic stratigraphic record of northwestern North America bears striking similarity to contemporaneous stratigraphy on other continents, particularly in the Amadeus Basin and Adelaide fold belt of central and southern Australia. Reconstructions of the Neoproterozoic supercontinent juxtapose the eastern margin of ancestral Australia against the western margin of Laurentia during the time these strata were being deposited. The Amundsen-Ogilvie-Mackenzie platform consequently may represent a segment (of the margin) of a large intracratonic basin that rifted apart with the breakup of the supercontinent during the latest Proterozoic. This hypothesis provides a template for future sequence stratigraphic, chemostratigraphic, biostratigraphic, paleomagnetic, and geochronologic comparisons and has implications for predictive economic geology in both areas. Capitalization of group and supergroup indicates formalization according to the International Stratigraphic Code. Noncapitalization indicates that the names have not been formalized.

700 Ma rift event in the Blue Ridge province of Virginia: A unique time constraint on pre-Iapetan rifting of Laurentia

Research Article| January 01, 1996 700 Ma rift event in the Blue Ridge province of Virginia: A unique time constraint on pre-Iapetan rifting of Laurentia Richard P. Tollo; Richard P. Tollo 1Department of Geology, George Washington University, Washington, D.C. 20052 Search for other works by this author on: GSW Google Scholar Frederick E. Hutson Frederick E. Hutson 2Department of Geological Sciences, University of Texas, Austin, Texas 78712 Search for other works by this author on: GSW Google Scholar Author and Article Information Richard P. Tollo 1Department of Geology, George Washington University, Washington, D.C. 20052 Frederick E. Hutson 2Department of Geological Sciences, University of Texas, Austin, Texas 78712 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1996) 24 (1): 59–62. https://doi.org/10.1130/0091-7613(1996)024<0059:MREITB>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 Richard P. Tollo, Frederick E. Hutson; 700 Ma rift event in the Blue Ridge province of Virginia: A unique time constraint on pre-Iapetan rifting of Laurentia. Geology 1996;; 24 (1): 59–62. doi: https://doi.org/10.1130/0091-7613(1996)024<0059:MREITB>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 Discovery of compositionally distinctive rhyolites produced from a peralkaline volcanic center within the late Neoproterozoic Robertson River batholith and which are intercalated with terrestrial deposits of the previously undated Mechum River Formation indicates that rift-related sedimentation and magmatism were ongoing at 702–705 Ma, about 130 m.y. before the breakup of Laurentia. Recognition of late Neoproterozoic age rhyolites in central Virginia indicates that rift-related magmatism was more widespread along the incipient eastern (present coordinates) margin of Laurentia than previously thought. Neoproterozoic rifting in the Blue Ridge province of Virginia appears to have been part of a broad-scale process that affected most, if not all, of the preserved margins of Laurentia. The association of similar, extension-related terrestrial deposits and compositionally distinctive felsic rocks elsewhere may provide a unique marker for testing proposed predrift configurations of the late Neoproterozoic supercontinent, Rodinia. 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.

Are Neoproterozoic glacial deposits preserved on the margins of Laurentia related to the fragmentation of two supercontinents?

Remarkably similar deposits representing two Neoproterozoic glaciations are present on the west and east sides of Laurentia. Although now located near the margins of Laurentia, these glaciogenic successions were formed within supercontinents. The older glaciogenic succession (Rapitan-Sturtian, ∼700 Ma) is preserved in a series of pull-apart basins formed when the supercontinent Kanatia fragmented to produce the proto–Pacific ocean. The younger Varangerian glaciogenic rocks (∼600 Ma) are now scattered throughout the North Atlantic region, but formed in basins that reflect the demise of a second Neoproterozoic supercontinent (Rodinia) and heralded the formation of the Iapetus ocean.

Palaeomagnetic constraints on the position of Laurentia from middle Neoproterozoic to Early Cambrian times

Abstract Most published palaeopoles from Laurentia indicate that the craton moved in equatorial regions during much of the Neoproterozoic-Cambrian period. However, recent palaeomagnetic results from the Mackenzie and Wernecke Mountains of northwestern Canada suggest that Laurentia passed over the South Pole sometime close to the Precambrian-Cambrian boundary. By this scenario, the craton remained in equatorial latitudes as part of a Neoproterozoic supercontinent until after the second and last glaciation recorded in Laurentia. It began its ascent to high southern latitudes on or before deposition of the Risky Formation, perhaps following rifting along the eastern margin of Laurentia at ∼ 615 Ma. High-latitude poles related to hematitization might evidence Laurentia's flight to higher latitudes (60–70°S). Hematitization appears to have occurred during a long hiatus in the geological record between deposition of the Risky Formation and the terminal Proterozoic Ingta Formation, and may evidence a final rifting event along the western margin of Laurentia in the late Neoproterozoic. A combined pole from the Ingta and Early Cambrian Backbone Ranges formations forms a bridge to Early Cambrian poles that trend from the Equator to mid-southern latitudes. Except for the excursion of Laurentia over the South Pole in the transition from the Proterozoic to the Phanerozoic Eons, Laurentia seems to have been at latitudes less than 60°S in the period from ∼ 900 to 500 Ma.

Paleozoic Laurentia-Gondwana interaction and the origin of the Appalachian-Andean mountain system

Laurentia, the rift-bounded Precambrian nucleus of North America, may have broken out from a Neoproterozoic supercontinent between East and West Gondwana. Several lines of evidence suggest that the Appalachian margin of Laurentia subsequently collided with the proto-Andean margin of the amalgamated Gondwana supercontinent in different relative positions during early and mid-Paleozoic time, in route to final docking against northwest Africa to complete the assembly of Pangea. Hence the Appalachian and Andean orogens may have originated as a single mountain system. The overall hypothesis retains the same paleomagnetic and paleobiogeographic controls as previous global reconstructions for the Paleozoic Era. Laurentia-Gondwana collisions may help to explain contemporaneous unconformities in the Paleozoic sedimentary cover of the Laurentian, Gondwanan, and Baltic cratons.

The changing face of late Precambrian and early Palaeozoic reconstructions

The SWEAT hypothesis, linking the Southwest US and East Antarctica as conjugate rift margins of a Neoproterozoic continent has lead to major revisions of late Precambrian and early Cambrian reconstructions. Geological evidence summarized here supports separation of Antarctica from Laurentia c. 750 Ma ago. A possible link between the break-up of a Neoproterozoic supercontinent and amalgamation of Gondwana during Pan-African times suggests that the Neoproterozoic was a time of rapid tectonic change. This conflicts with those theories that predict regular supercontinental cycles of 500 Ma from the time of disintegration of one supercontinent to its eventual reassembly.

Neoproterozoic glaciation in the Broken Hill area, New South Wales, Australia

The Neoproterozoic sedimentary rocks on the eastern margin of the Adelaide Geosyncline include two major glacigenic successions. The lower of these, the Yancowinna Sub-Group (as much as 5,000 m thick), can be divided into four stratigraphic units deposited in a northwest-trending graben. Dramatic thickness variations are attributed to contemporaneous normal fault movements. The thin basal granite-boulder diamictite/conglomerate of Unit 1 is considered to represent ice-proximal deposition in a temperate glacial setting. Unit 2 is a heterogeneous mudstone-dominated succession formed from fine material provided by meltwater streams during glacial recession when the basin was starved of coarse debris. Coarser grained facies were deposited by sediment gravity-flow mechanisms. The thick diamictites of Unit 3 are interpreted as rain-out deposits formed during a second glacial advance. Unit 4 records the terminal glacial recession. Paleo-current measurements suggest that the sediment source was the Curnamona Cratonic Complex to the northwest. These rocks are the most easterly preserved Neoproterozoic glacigenic deposits of the Adelaide Geosyncline and are therefore relevant to comparisons with regions such as western North America, which were possibly adjacent, prior to the breakup of a Neoproterozoic supercontinent.