Late Devonian-Early Carboniferous Research Articles

Initiation and evolution of intra‐oceanic subduction in the Uralides: Geochemical and isotopic constraints from Devonian oceanic rocks of the Southern Urals, Russia

Abstract The Southern Uralides are a collisional orogen generated in the Late Devonian–Early Carboniferous by the collision of the Magnitogorsk island arc (MA) generated in the Early to Middle Devonian by intra‐oceanic convergence opposite to the continental margin, and the continental margin of the East European craton. A suture zone of the arc to the continental margin, the Main Uralian Fault (MUF), is marked by ophiolites and exhumed high‐pressure–low‐temperature metamorphic rocks of continental origin. The pre‐orogenic events of the Southern Urals and their geodynamic setting are traced by means of fluid‐immobile incompatible trace elements (rare earth elements and high field strength elements) and Sr–Nd–Pb isotope geochemistry of the MA suites, in particular the protoarc suite with boninites and probably ankaramites, and the mature arc comprised of island arc tholeiitic (IAT) suites, transitional IAT to calc‐alkaline (CA), and CA suites. The MA volcanics result in genetically distinct magmatic source components. In particular, depleted normal‐mid‐oceanic ridge basalt‐type mantle sources with various enrichments in a slab‐derived aqueous fluid component are evident. The enriched component is not involved in significant amounts, as testified by the rather radiogenic Nd isotopes and unradiogenic Pb isotopes. Further information on the pre‐orogenic events is provided by the Mindyak Massif metagabbros derived from diverse gabbroic protoliths that were affected by oceanic rodingitization, and subsequently by a high‐temperature (HT) metamorphism related to the development of a metamorphic sole. The HT metamorphism has the same age as the protoarc volcanism, and constrains the initiation of subduction at approximately 410 Ma. Consequently, the maximum timespan between initial intra‐oceanic convergence and final collision is approximately 31 my, a duration consistent with that of present‐day ongoing collisions in the western Pacific. The characteristics of early volcanism and the traces of a metamorphic sole provide useful criteria to attribute most MUF ophiolites to the Tethyan type with a complex pre‐orogenic evolution.

Paleozoic tectonic evolution of medio-Europa from the example of the French Massif Central and Massif Armoricain

The French Massif Central and Massif Armoricain belong to three tectonic and paleogeographic domains of the Medio-Europa Variscan Orogen. The entire Massif Central and southern part of the Massif Armoricain belong to the North Gondwana margin, the Central Armorican Domain is a part of Armorica microcontinent and the Leon Domain is a piece of another microcontinent. The N. Gondwana margin and Leon Domain are made of a stack of metamorphic nappes, conversely, the Central Armorican Domain consists of a Proterozoic basement built up by the Neoproterozoic Cadomian orogeny and a Paleozoic sedimentary cover weakly deformed by upright folds related to wrenching. The architecture of the North Gondwana margin results of three main tectonic-metamorphic events that follow an early Late Silurian (ca 415 Ma) high-pressure metamorphism whose associated structures are poorly documented. The Early Devonian D1 event is responsible for top-to-the-SW nappes coeval with migmatization and exhumation of high-pressure rocks around 385-380 Ma. The Late Devonian-Early Carboniferous D2 event is a top-to-the-NW shearing coeval with an intermediate pressure-temperature metamorphism dated around 360-350 Ma. The Visean D3 event is a top-to-the-south shearing widespread in the south Massif Central whereas in north Massif Central, D3 corresponds to the onset of synorogenic extension. The Variscan Belt is also characterized by a widespread magmatism. The Early-Middle Devonian calc-alkaline magmatism is related to the southward subduction of the Rheic Ocean. The Carboniferous magmatic events are the crustal melting response of D2 and D3 tectonic events. Late Visean, Namurian and Westphalian magmatic stages are coeval with extensional tectonics controlled by NW-SE stretching. These structural, metamorphic and magmatic events are replaced in a geodynamic evolution model involving two cycles of microcontinent drifting, rewelding and continental collision.

40Ar/39Ar dating in the Lochaber–Mulgrave area, northern mainland Nova Scotia: implications for timing of regional metamorphism and sediment provenance in the Late Devonian – Early Carboniferous Horton Group

40Ar/39Ar dating of whole-rock samples and muscovite separates using age spectrum analysis, and of single muscovite grains using total fusion analysis, yields new insights into the timing of regional metamorphism and sediment provenance in the Late Devonian – Early Carboniferous Horton Group in the Lochaber–Mulgrave area of Nova Scotia. The time of regional metamorphism is constrained to ca. 340–335 Ma by whole-rock spectra from well-cleaved slate and shale samples from the lowermost Clam Harbour River and overlying Tracadie Road formations of the Horton Group. This ca. 340–335 Ma event may have been the result of burial and deformation of the Horton Group by older volcanic and sedimentary rocks of the Guysborough Group, which were overthrust from the south as the result of development of a positive flower structure at a restraining bend along the Cobequid–Chedabucto fault system, the boundary between the Meguma and Avalon terranes. Detrital muscovite ages of ca. 410–380 and ca. 500 Ma were obtained from single-grain analysis and from spectral analysis of separated grains. Whole-rock spectra for two samples from a mylonitic metasedimentary unit in the Cape Porcupine Complex yielded plateau ages of 364 ± 4 and 367 ± 4 Ma, providing a likely source for ca. 370–360 Ma detrital muscovite, ages that may be reflected in some of the age spectrum data. However, the Meguma terrane to the south is the most likely source for most of the detrital muscovite.

Successive shearing tectonics during the Hercynian collisional evolution of the southwestern French Massif Central

Abstract In the French Massif Central, the Devonian-Carboniferous tectonic evolution of the Rouergue-Albigeois area is characterized by three phases of low-angle ductile shearing. The first event D1, which occurred probably in the Lower Devonian, is responsible for the south-westward thrusting of the high metamorphic Lévézou nappe which belongs to the Upper Gneiss Unit above the Lower Gneiss Unit overlying itself the Para-autochthonous Unit, (locally called the St-Serninsur-Rance nappe). In the late Devonian-early Carboniferous, this stack of nappes is reworked by a second event, D2, characterized by a top-to-the-NW shearing of the Para-autochthonous Unit upon the Lower Gneiss Unit developed under medium pressure/medium temperature metamorphism. The contact between the Lower Gneiss Unit and the Para-autochthonous Unit is a top-to-the NW low-angle fault that progressively evolues into a dextral strike-slip fault from west to east. The D2 event is followed by a top-to-the south D3 thrusting dated around 330–340 Ma. The main feature of the D3 compressional stage is the emplacement of the whole stack of nappes previously structured by D1 and D2 events upon the Albigeois series. The D3 event produced south-verging recumbent folds in the Albigeois, Mont-de-Lacaune and Montagne Noire. The significance of the D2 event either as thrusting or normal faulting is discussed.

Phanerozoic tectonothermal history of the Arabian–Nubian shield in the Eastern Desert of Egypt: evidence from fission track and paleostress data

To constrain the post-Pan-African evolution of the Arabian–Nubian Shield, macro-scale tectonic studies, paleostress and fission track data were performed in the Eastern Desert of Egypt. The results provide insights into the processes driving late stage vertical motion and the timing of exhumation of a large shield area. Results of apatite, zircon and sphene fission track analyses from the Neoproterozoic basement indicate two major episodes of exhumation. Sphene and zircon fission track data range from 339 to 410 Ma and from 315 to 366 Ma, respectively. The data are interpreted to represent an intraplate thermotectonic episode during the Late Devonian–Early Carboniferous. At that time, the intraplate stresses responsible for deformation, uplift and erosion, were induced by the collision of Gondwana with Laurussia which started in Late Devonian times. Apatite fission track data indicate that the second cooling phase started in Oligocene and was related to extension, flank uplift and erosion along the actual margin of the Red Sea. Structural data collected from Neoproterozoic basement, Late Cretaceous and Tertiary sedimentary cover suggest two stages of rift formation. (1) Cretaceous strike-slip tectonics with sub-horizontal σ1 (ENE/WSW) and σ3 (NNW/SSE), and sub-vertical σ2 resulted in formation of small pull-apart basins. Basin axes are parallel to the trend of Pan-African structural elements which acted as stress guides. (2) During Oligocene to Miocene the stress field changed towards horizontal NE–SW extension (σ3), and sub-vertical σ1. Relations between structures, depositional ages of sediments and apatite fission track data indicate that the initiation of rift flank uplift, erosion and plate deformation occurred nearly simultaneously.

Tectonic influence on sedimentation along the southern flank of the late Paleozoic Magdalen basin in the Canadian Appalachians: Geochemical and isotopic constraints on the Horton Group in the St. Marys basin, Nova Scotia

Research Article| July 01, 2000 Tectonic influence on sedimentation along the southern flank of the late Paleozoic Magdalen basin in the Canadian Appalachians: Geochemical and isotopic constraints on the Horton Group in the St. Marys basin, Nova Scotia J. Brendan Murphy J. Brendan Murphy 1Department of Geology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada Search for other works by this author on: GSW Google Scholar GSA Bulletin (2000) 112 (7): 997–1011. https://doi.org/10.1130/0016-7606(2000)112<997:TIOSAT>2.0.CO;2 Article history received: 23 Jun 1998 rev-recd: 13 Aug 1999 accepted: 17 Sep 1999 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation J. Brendan Murphy; Tectonic influence on sedimentation along the southern flank of the late Paleozoic Magdalen basin in the Canadian Appalachians: Geochemical and isotopic constraints on the Horton Group in the St. Marys basin, Nova Scotia. GSA Bulletin 2000;; 112 (7): 997–1011. doi: https://doi.org/10.1130/0016-7606(2000)112<997:TIOSAT>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 SocietyGSA Bulletin Search Advanced Search Abstract The Late Devonian–Early Carboniferous St. Marys basin in mainland Nova Scotia, Canada, consists of Horton Group intracontinental clastic rocks that were deposited along the Avalon-Meguma terrane boundary during the waning stages of the Acadian orogeny and prior to terminal collision in the Appalachian orogen. These rocks represent the earliest stages of deposition along the southern flank of the composite Magdalen basin (Late Devonian to Permian) that extends over much of Maritime Canada and oversteps terrane boundaries in the Canadian Appalachians. As such, the Horton Group represents deposition in an episutural basin.The Horton Group in the St. Marys basin predominantly consists of 3000–4000 m of clastic sedimentary rocks deposited in fluviatile and lacustrine nearshore environments.Geochemical analyses of clastic rocks reveal a range of SiO2 content (60–94 wt%), high total rare earth elements and initial 87Sr/86Sr, and strongly negative ϵNd(t) (t = 360 Ma). The signature of the passive margin to active continental margin implied by standard discrimination diagrams probably is inherited largely from rocks in the source region and is not an indication of the setting in which the basin formed. Although the data indicate that some lithologies contain a minor Avalonian basement component, the geochemical and isotopic signatures of the sedimentary rocks reveal mixed sources that can be attributed largely to uplift and erosion of Meguma terrane metasedimentary and granitoid rocks immediately to the south of the St. Marys basin. Regional syntheses indicate that this uplift occurred before and during Horton Group deposition and was coeval with dextral ramping of the Meguma terrane over the Avalon terrane along the southern flank of the Magdalen basin. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Late Visean thermal event in the northern part of the French Massif Central: new 40Ar/39Ar and Rb–Sr isotopic constraints on the Hercynian syn-orogenic extension

he French Massif Central belongs to the central metamorphic domain of the European Hercynian Belt. 40Ar/39Ar mica and amphibole dates have been obtained on magmatic and metamorphic rocks from the northern part of the French Massif Central (Sioule and Brevenne-Violay series). The 336- to 337-Ma dates recorded by a granodiorite (the St. Gervais pluton) and its mylonitic border along the Ste Christine fault and the 337-5-Ma muscovite ages from the Brevenne series are consistent with the age of wrenching related to the late stage of the Hercynian compression. The remaining age spectra from the Sioule area provide ages ranging from 331 to 335 Ma that are interpreted as cooling ages related to rock exhumation after the main stages of metamorphism and deformation in the studied area. Late Visean dates widespread in North Massif Central correspond to a huge magmatic event characterized by the emplacement of red granites, granophyres and sub-aerial acidic volcanics known as the Tufs anthraciferes formation. Rb-Sr isotopic data from volcanic and hypovolcanic rocks from the Sioule and Montagne Bourbonnaise areas place constraints on the source of the magmas. Simple metapelite crustal melting or a major contribution from depleted mantle sources are ruled out, and instead, mantle-derived magmas were probably involved, at least as a heat source, during the Late Visean magmatism. Exhumation and cooling of metamorphic rocks below 300°C occurred contemporaneously with this Late Visean magmatism. In the geodynamic evolution of the Hercynian Belt, the Late Visean (ca. 335-330 Ma) magmatism corresponds to a major break marking the onset of post-collisional extension in the inner zone which had been thickened by collision in Latest Devonian-Earliest Carboniferous. This Late Visean extension in the inner zone which is synchronous to compression in the northern and southern forelands of the belt appears as a syn-orogenic process.

Geochemical constraints on the origin and timing of palaeofluid flow in the Presqu’ile barrier reef, Western Canada Sedimentary Basin

Abstract The Mississippi Valley-type ore deposits at Pine Point are spatially and genetically associated with saddle dolomite cements. The origin and timing of fluid flow that produced these ore deposits are, therefore, constrained by paragenesis and geochemistry of the saddle dolomite cements. Because saddle dolomites occur continuously across the sub-Watt Mountain unconformity, dolomitization and associated mineralization must have occurred after the sub-Watt Mountain exposure during burial. The lateral continuity of saddle dolomite along the barrier for 400 km suggests that dolomitization and mineralization were probably associated with the lateral fluid migration along the barrier reef. From northeastern British Columbia to Pine Point, over a lateral distance of 400 km, saddle dolomites display remarkable trends of decreasing 87 Sr/ 86 Sr ratios (0.7106 to 0.7081) and homogenization temperatures of fluid inclusions (178°C to 92°C) with a corresponding increase in δ 18 O values (−16‰ to −7‰ PDB). These regional trends suggest that hot, radiogenic basinal fluids moved eastward up-dip along the Presqu’ile barrier reef. The movements of basinal fluids were probably related to tectonic compression and sedimentary loading on the western margin of the Western Canada Sedimentary Basin during either the late Devonian-early Carboniferous (Antler Orogeny) or the Jurassic-early Tertiary (Columbia-Laramide Orogenies). The δD values of aqueous fluid inclusions from Pine Point dolomite are very low (−80‰ SMOW to −100‰ SMOW) compared with that of Devonian seawater (−10‰ SMOW) suggesting an input of some Columbia-Laramide meteoric waters. If the low δD values are caused by a mixture of fluids from primary inclusions containing Devonian seawater with secondary inclusions that formed later during the Columbia-Laramide Orogenies, the fluid migration and associated dolomitization and mineralization could be interpreted as late-Devonian events. However, if the measured fluids were mostly from the primary inclusions, the low δD values indicate an entrapment of some Columbia-Laramide meteoric waters with Devonian formation waters at the time of dolomitization. This would suggest a Jurassic to early Tertiary age for dolomitization, which is supported by similar low δD values of present-day Devonian formation waters that consist of a mixture of Laramide meteoric waters and original connate brines. The light δD values of Pine Point dolomite inclusions could also occur as a result of reaction of fluids with organic matter associated with generation of oil and gas, which occurred at the maximum burial during the Laramide Orogeny.

Late Devonian-Early Carboniferous peak sulphide mineralization in the Western Hercynides

The Late Devonian-Early Carboniferous (Dinantian) within the Western Hercynides is marked by the formation of volcanic-hosted massive sulphide deposits: Chessy and Chizeuil in the Brevenne and Somme successions of the French Massif Central; Bodennec and La Porte-aux-Moines in the Châteaulin Basin of the French Armorican Massif; Rio Tinto, Neves-Corvo, Tharsis, etc., in the Volcano-Sedimentary formation of the Iberian Pyrite Belt; and Ketara, Draa Sfar and Hajar in the Jebilet-Guemassa district of the Moroccan Southern Meseta. Although these deposits show a slightly diachronous emplacement in response to a progressive migration of the metalliferous event from Late Devonian in France to Dinantian in Morocco, it is nevertheless possible to define an overall metalliferous ‘‘peak” around 350 Ma. The mineralization of the Armorican, Iberian and Moroccan sectors took place in epicontinental domains of the outer zone of the Hercynian belt, whereas that of the northeastern Massif Central occurred within the inner zone of the belt. This difference is registered by variations both in the geochemical characteristics of the ores (Sn in the outer zone and Mo-Ni in the inner zone) and in their lead isotopic signatures (clear mantle participation exclusively in the inner zone). In many cases the ores appear to be closely related to the felsic member of a bimodal magmatic association, although the massive sulphide deposits in the outer zone are more commonly associated with sedimentary rocks whereas those in the inner zone are hosted by felsic volcanic rocks. Another feature that should be noted is that the host sequences of the massive sulphide deposits commonly seem to be underlain by chaotic formations (notably with olistoliths) reflecting the beginning of Hercynian orogenic activity in the outer zone. It can be concluded that the peak mineralization took place within tensional domains developed during a period of plate convergence, and that it occurred around 350 Ma after a major period of Devonian compression but before the Carboniferous continental closure.

Rift‐phase extensional fabrics of the back‐arc Drummond Basin, eastern Australia

The base of the Late Devonian–Early Carboniferous Drummond Basin, a major backarc extensional feature in eastern Australia which formed in response to detachment faulting, is extensively exposed in central Queensland. Here a crystalline basin floor is overlain by the Silver Hills Volcanics, a synrift sequence of predominantly silicic ash flow tuffs and lavas ranging to over 2 km in thickness. Detailed mapping of faults and stratigraphic logging of thickness changes within the Silver Hills Volcanics have allowed the rift‐phase structural architecture that accompanied initial subsidence near the basin margin to be resolved. A complex mosaic of block faults with throws of up to 1 km is indicated. Locally developed mosaics may conform to, or depart from, the configuration predicted by the detachment faulting model. Structural fabric of the basement was a critical determinant of the extensional geometry. Distributed shear along pre‐existing penetrative planar fabrics is considered to have accommodated hangingwall extension at lower strain rates whereas the propagation of tension fractures and the development of block faults by failure on pre‐existing, brittle, basement dislocations facilitated extension at higher strain rates. The detachment fault inferred to lie beneath the extended hangingwall carapace has not been mapped at the surface and is thought to dissipate into a broad zone of distributed shear within basement to the east of the basin. Volcanism coincided with the initiation of extensional movements at which time deep crustal repositories for evolved magma were tapped by extensional fractures. The main extensional faults cutting the basinal succession were not used as conduits for magmatic products which were sourced from the basin margin and from extended hinterland to the east.

The history of Devonian-Carboniferous reef communities: Extinctions, effects, recovery

Analysis of the taxonomic composition, diversity and guild structure of five “typical” reef and mud mound communities ranging in age from Late Devonian-Early Carboniferous indicates that each of these aspects of community organization changed dramatically in relation to three extinction events. These events include a major or mass extinction at the end of the Frasnian; reef communities were also effected by less drastic end-Givetian and mid-late Famennian extinctions of reef-building higher taxa.

Paleozoic Plate-Tectonic Evolution of the Tarim and Western Tianshan Regions, Western China

The plate-tectonic evolution of the Tarim basin and nearby western Tianshan region during Paleozoic time is reconstructed in an effort to further constrain the tectonic evolution of Central Asia, providing insights into the formation and distribution of oil and gas resources. The Tarim plate developed from continental rifting that progressed during early Paleozoic time into a passive continental margin. The Yili terrane (central Tianshan) broke away from the present eastern part of Tarim and became a microcontinent located somewhere between the Junggar ocean and the southern Tianshan ocean. The southern Tianshan ocean, between the Tarim craton and the Yili terrane, was subducting beneath the Yili terrane from Silurian to Devonian time. During the Late Devonian-Early Carboniferous, the Tarim plate collided with the Yili terrane by sinistral accretional docking that resulted in a late Paleozoic deformational episode. Intracontinental shortening (A-type subduction) continued through the Permian with the crea...

Palaeozoic collisional tectonics and magmatism of the Chinese Tien Shan, central Asia

The Chinese Tien Shan range is a Palaeozoic orogenic belt which contains two collision zones. The older, southern collision accreted a north-facing passive continental margin on the north side of the Tarim Block to an active continental margin on the south side of an elongate continental tract, the Central Tien Shan. Collision occurred along the Qinbulak-Qawabulak Fault (Southern Tien Shan suture). The time of the collision is poorly constrained, but was probably in in the Late Devonian-Early Carboniferous. We propose this age because of a major disconformity at this time along the north side of the Tarim Block, and because the Youshugou ophiolite is imbricated with Middle Devonian sediments. A younger, probably Late Carboniferous-Early Permian collision along the North Tien Shan Fault (Northern Tien Shan suture) accreted the northern side of the Central Tien Shan to an island arc which lay to its north, the North Tien Shan arc. This collision is bracketed by the Middle Carboniferous termination of arc magmatism and the appearance of Late Carboniferous or Early Permian elastics in a foreland basin developed over the extinct arc. Thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin. Post-collisional, but Palaeozoic, dextral shear occurred along the northern suture zone, this was accompanied by the intrusion of basic and acidic magmas in the Central Tien Shan. Late Palaeozoic basic igneous rocks from all three lithospheric blocks represented in the Tien Shan possess chemical characteristics associated with generation in supra-subduction zone environments, even though many post-date one or both collisions. Rocks from each block also possess distinctive trace element chemistries, which supports the three-fold structural division of the orogenic belt. It is unclear whether the chemical differences represent different source characteristics, or are due to different episodes of magmatism being juxtaposed by later dextral strike-slip fault motions. Because the southern collision zone in the Tien Shan is the older of the two, the Tarim Block sensu stricto collided not with the Eurasian landmass, but with a continental block which was itself separated from Eurasia by at least one ocean. The destruction of this ocean in Late Carboniferous-Early Permian times represented the final elimination of all oceanic basins from this part of central Asia.

Late paleozoic orogeny in the northwestern Gondwana continental margin, western Argentina and Chile

During Early Carboniferous-Early Permian time, the segment of the northwestern Gondwana continental margin (western Argentina and Chile) between present-day latitudes 27°S and 50°S was structurally organized into a marginal orogen and a foreland rising into cratonic highlands. Orogenesis and magmatism were governed by subduction of an ancestral Pacific plate under Gondwana. During the Late Devonian-Early Carboniferous, former slope-rise deposits were thickened to form the orogen and were thrust slightly onto the foreland; parts of the orogen emerged above sea level. Following this early diastrophic phase, tectonic uplift in the orogen was regionally checked by erosion until the late Early Permian when uplift rates overcame erosion. The development of this orogen is peculiar in that throughout much of this time: a) the orogenic bett was partly occupied by marine areas; b) there was no reversal of provenance, so that foreland basins were continuously fed from the interior highlands; and c) the orogenic belt did not advance further onto the foreland. Thus the orogen stabilized in position and relief. Magmatism was intense during the period of orogenic stability and was dominated by plutonism; there are no remnants of a well developed volcanic arc. Reconstructions involving Late Devonian-Early Carboniferous collision of crustal masses against Gondwana and a seaward jump of the subduction trench are not entirely substantiated by available data. An alternative suggests that from the Late Devonian to the Early Permian the trench maintained approximately the same position seaward of present-day coastal exposures.

Tectonics and Hydrocarbon Potential of the Barents Megatrough

Interpretation of geophysical data shows that the geological structure of the Eastern Barents Shelf, named Barents Megatrough (BM), extends sublongitudinally almost from the Baltic shield to the Franz Josef Land archipelago. The earth crust within the axis part of the BM is attenuated up to 28-30 km, whereas in adjacent areas its thickness exceeds 35 km. The depression is filled with of more than 15 km of Upper Paleozoic, Mesozoic, and Cenozoic sediments overlying a folded basement of probable Caledonian age. Paleozoic sediments, with exception of the Upper Permian, are composed mainly of carbonates and evaporites. Mesozoic-Cenozoic sediments are mostly terrigenous. The major force in the development of the BM was due to extensional tectonics. Three rifting phases are recognizable: Late Devonian-Early Carboniferous, Early Triassic, and Jurassic-Early Cretaceous. The principal features of the geologic structure and evolution of the BM during the late Paleozoic-Mesozoic correlate well with those of the Sverdup basin, Canadian Arctic. Significant quantity of Late Jurassic-Early Cretaceous basaltic dikes and sills were intruded within Triassic sequence during the third rifting phase. This was probably the main reason for trap disruption and hydrocarbon loss from Triassic structures. Lower Jurassic and Lower Cretaceous reservoir sandstones are most probably themore » main future objects for oil and gas discoveries within the BM. Upper Jurassic black shales are probably the main source rocks of the BM basin, as well as excellent structural traps for hydrocarbon fluids from the underlying sediments.« less

Relationships between deformation and basin evolution in the intracratonic Amadeus Basin, central Australia

Tectonic subsidence curves based on the sedimentary record are used here to study basin evolution and to indicate deformational periods in the history of the intracratonic Amadeus Basin in central Australia. The basin developed during an initial period of extension at about 900 Ma in the Late Proterozoic (Stage 1), was subjected to another period of extension at about Proterozoic-Cambrian boundary time when there was also a shortening event on the southwest margin (Stage 2), and was shortened during the Late Devonian-Early Carboniferous (Stage 3). Stage 1 extension in the southwest and northwest corners of the basin was associated with rift basin sediments and volcanics previously regarded as basement to the Amadeus succession. In the metamorphic Arunta Complex on the northern margin of the basin, a dolerite dyke swarm is considered to have been emplaced during this event. Extension in a N-S direction associated with Stage 2 occurred only in the northern part of the basin; at the same time a major compressional event, the Petermann Ranges Orogeny, was occurring along the southern margin. In the north, the sediment fill at this time firstly thickens rapidly towards the northern margin and then thins dramatically at the margin, implying a half-graben structure and the presence of a major bounding fault. In the southwest, the Petermann Ranges Orogeny caused detachment of the sediments above the salt horizon in the Bitter Springs Formation, northward transport, folding of the sediment pile, and formation of major basement-cored nappes. During Stage 3 a foreland basin associated with southward-directed overthrust sheets of the Alice Springs Orogeny formed in the northern part of the basin. Horizontal shortening was of the order of 50–100 km and hence the present basin margins are structural rather than depositional. The structures that developed during this stage dominate the structural pattern of the basin.

Lithostratigraphy of the Late Devonian-Early Carboniferous Horton Group of the Moncton Subbasin, southern New Brunswick

The threefold subdivision of the Late Devonian - Early Carboniferous Horton Group in the Moncton Sub-basin of southern New Brunswick conforms to the original description and subsequent adoption of the group elsewhere in the Maritimes Basin. The Horton Group consists of the Memramcook, Albert and Moncton formations, the Moncton Formation having previously been regarded as a group. The Memramcook Formation rests unconformably on pre-Carboniferous basement and is conformably overlain by and in part the lateral facies equivalent of the Albert Formation. The Albert Formation contains five variably developed members (both spatially and, in part, temporally): the Dawson Settlement, Frederick Brook, Hiram Brook, Round Hill and Gautreau members. Of these, the Round Hill and Gautreau members have previously been the subject of much stratigraphic debate but are herein proposed simply as members of the Albert Formation. The formally proposed Moncton Formation is subdivided into a lower Weldon Member and an upper Hillsborough Member; where the contact can actually be defined it is un— conformable. The Albert Formation - Weldon Member contact is conformable and transitional. The Hillsborough Member - Windsor Group contact is marked by an abrupt facies change where Windsor Group strata are marine as distinct from non-marine in origin.&#x0D; &#x0D; RÉSUMÉ&#x0D; Le groupe Horton (Dévonien supéirieur - Carbonifère inférieur) que l'on retrouve dans le sous-bassin de Moncton au sud du Nouveau-Brunswick est divisé en trois formations, conformément à la description originale telle qu'adoptée ailleurs dans le bassin sédimentaire des Maritimes. Le groupe Horton comprend les formations de Memramcook, Albert et Moncton (la formation de Moncton était autrefois considérée comme un groupe). La formation de Memramcook repose en discordance sur un socle pré-Carbonifère et est recouverte de façon concordante par la formation d'Albert. La formation de Memramcook est également en partie un faciès latéral de la formation d'Albert. La formation d'Albert compte cinq membres dont l'emplacement à varié dans l'éspace, et em partie, dans le temps: les membres Dawson Settlement, Frederick Brook, Hiram Brook, Round Hill et Gautreau. Les membres Round Hill et Gautreau, qui par le passe ont soulevé maints débats stratigraphiques, sont ici présentés comme membres de la formation d'Albert. La formation de Moncton, présentée de façon officielle, est divisée en un membre inférieur, Weldon, et un membre supérieur, Hillsborough; la où il peut être indenting, le contact est discordant. Le contact concordant entre la formation d'Albert et le membre Weldon en est Ggalement un de transition. Le contact entre le membre Hillsborough et le groupe Windsor n'est marqué par un brusque changement de faciès que la où les strates du groupe Windsor sont distinctement d'origine marine, plutôt que non-marine.&#x0D; &#x0D; [Traduit par le journal]

Sea-level changes and the evolution of benthic marine calcareous algae during the Palaeozoic

Maximum spreads of epicontinental seas in the area now covered by the USSR correlate closely with major periods of diversification of benthic calcareous algae (especially chlorophytes and rhodophytes) during the early-middle Ordovician and the late Devonian-early Carboniferous. This is consistent with the 'species-area' concept of direct relationship between taxonomic diversity and habitat-size. The shape of the Earth's hypsometric curve makes it likely that continental flooding would enlarge the area habitable by benthic algae more than it would for benthos not limited to the photic zone, thus enhancing the species-area effect for algae at times of sea-level change. In contrast, the first occurrence of calcareous algae near the Precambrian-Cambrian boundary does not seem to correlate with a transgressive maximum. Cyanophytes are the main calcified group appearing in the early Cambrian and it is possible that their occurrence at this level reflects a different factor which resulted in the calcification of pre-existing algal groups.

Salt-Induced Growth Structures and Subsequent Overthrusts, Northeastern Amadeus Basin, Central Australia: ABSTRACT

Thicknesses of the late Proterozoic-Early Cambrian Arumbera Sandstone and Middle Cambrian Giles Creek Formation show initiation of growth of the Brumby anticline during the Middle Cambrian. Growth probably resulted from flowage of bedded salt in the late Proterozoic Bitter Springs Formation, possibly due to uneven deposition of fluvial sediments of the Arumbera. Such early growth structures are more likely to be oil prone than anticlines that formed later, during the Alice Springs orogeny (Late Devonian-Early Carboniferous), because adjacent source rocks were not buried as deeply. Positive source-rock analyses are known from several late Proterozoic units in the Northeast Amadeus basin. Four major tectonic elements formed during the Alice Springs orogeny: (1) the N'Dahla nappe in the north, (2) the Phillipson nappe in the center, (3) tectonic windows (autochthon?) southward in the Phillipson nappe, and (4) the Camel Flat nappe in the south. Isopach maps drawn for each tectonic element suggest a minimum of 10 to 20 km of southward movement for each of the two northern nappes. A strike-slip fault along the east side of Todd River anticline, with 1 to 1.5 km of left-lateral offset, forms a prominent north-trending lineament across the dominant east-northeast trend of most of the folds in the Northeast Amadeus basin. It is paralleled on both sides by closed, doubly plunging anticlines. Major strike-slip faults and north-trending anticlines were not widely recognized prev ously in the Amadeus basin. End_of_Article - Last_Page 614------------