The Skiddaw Group (English Lake District) reviewed: early Palaeozoic sedimentation and tectonism at the northern margin of Avalonia
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Abstract The Skiddaw Group is a 5 km thick sequence of Tremadoc-Llanvirn turbiditic mudstone and sandstone, including a major olistostrome, which occupies the northern part of the Lake District Lower Palaeozoic Inlier. Sporadic outcrop and borehole records indicate that similar strata extend beneath other parts of northern England. To the west, the Manx Group of the Isle of Man is a regional correlative. The Skiddaw Group was deposited on the Avalonian margin of the Iapetus Ocean, with constituent sediment derived largely from an earlier, possibly Precambrian, continental margin volcanic arc. Nd isotope data confirm the absence of juvenile detritus. Olistostrome emplacement in the late Arenig preceded subduction-related uplift of the deep-marine Skiddaw Group to form the subaerial basement to the mainly Caradoc, Borrowdale and Eycott volcanic groups. The scale of the unconformity beneath the volcanic rocks requires considerable pre-volcanic disruption and erosion of the Skiddaw Group prior to structural disturbance by volcanotectonic faulting. Volcanism ended in the late Caradoc when thermal reequilibration, coupled with possible further extension, allowed marine transgression through the early Silurian. Ultimately, convergence of Avalonia with Laurentia initiated thrust imbrication of the Skiddaw Group as the Southern Uplands thrust belt extended across the sutured Iapetus Ocean. Thrust-related hydration caused widespread resetting of Rb-Sr isotope systems during the 430–420 Ma interval. A penetrative slaty cleavage with a broadly Caledonian trend was imposed during the Early Devonian, Acadian Orogeny and cuts an earlier, bedding-parallel (compaction) fabric. Later phases of Acadian compression probably involved reactivation of thrusts within the Skiddaw Group with associated strain partitioning resulting in domainal crenulation cleavage. Granite intrusion at c. 400 Ma coincided with the final cleavage episode.Keywords:
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Research Article| December 01, 1990 I-type granitoids as indicators of a late Paleozoic convergent ocean-continent margin along the southern flank of the central European Variscan orogen F. Finger; F. Finger 1Institut für Mineralogie, Universität Salzburg, A-5020 Salzburg,Austria Search for other works by this author on: GSW Google Scholar H. P. Steyrer H. P. Steyrer 2Institut für Geologie and Paläontologie, Universität Salzburg, A-5020 Salzburg, Austria Search for other works by this author on: GSW Google Scholar Author and Article Information F. Finger 1Institut für Mineralogie, Universität Salzburg, A-5020 Salzburg,Austria H. P. Steyrer 2Institut für Geologie and Paläontologie, Universität Salzburg, A-5020 Salzburg, Austria Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1990) 18 (12): 1207–1210. https://doi.org/10.1130/0091-7613(1990)018<1207:ITGAIO>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 Email Permissions Search Site Citation F. Finger, H. P. Steyrer; I-type granitoids as indicators of a late Paleozoic convergent ocean-continent margin along the southern flank of the central European Variscan orogen. Geology 1990;; 18 (12): 1207–1210. doi: https://doi.org/10.1130/0091-7613(1990)018<1207:ITGAIO>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 belt of Carboniferous to Permian I-type granitoid bodies is in the basement thrust sheets of the Alps, which correspond to the southern flank of the central European Variscan orogen. These predominantly granodioritic plutons contrast with a contemporaneous belt of S-type granites, which extends to the north of the Alps in the Moldanubian section of the Variscan orogen. The observed regional duality of Variscan plutonism resembles the plutons along active circum-Pacific continental margins, in that there are outer I-type plutons and inner S-type granitoid belts. Therefore, central Europe could have undergone a Cordilleran-type orogenic event in late Paleozoic time, involving northwestward subdcution of the paleo-Tethys ocean. 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.
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Middle Paleozoic rocks change facies from east to west across central Idaho reflecting sedimentation in different environments of the Cordilleran geosynclinal complex and its eastern margin. A thin cratonic assemblage of Upper Devonian Jefferson Dolomite, punctuated by local diastems, unconformably oversteps Ordovician Kinnikinic Quartzite and Precambrian Belt strata in southwestern Montana and in the Beaverhead Range along the Idaho-Montana border. West of the southern Lemhi Range the importance of the Devonian regional unconformity diminishes and variable amounts of Upper Ordovician Fish Haven and Silurian dolomites are preserved below Jefferson Dolomite. The basal quartzite-carbonate succession of Kinnikinic Quartzite and Fish Haven, Laketown, and Jefferson do omites thickens markedly in the Lost River Range toward the west. This miogeosynclinal succession is replaced farther west in the Wood River region by Lower Ordovician to Silurian graptolitic shale, chert, and quartzite, the Phi Kappa-Trail Creek sequence of eugeosynclinal affinity. About 3,500 feet of interbedded shaly limestone, dolomite, shale, and quartzite of the Middle-Upper Ordovician Saturday Mountain Formation and the Silurian Laketown Dolomite are present in the Bayhorse region and appear to be transitional in facies between the time-equivalent quartzite-dolomite sequence on the east and the graptolitic shale-chert-quartzite sequence on the south. Since newly measured sections imply approximately north-south facies boundaries and thickness trends, the graptolitic shale-chert-quartzite sequence in the Wood River region lies due north and on depositional trend with transitional facies in the Bayhorse region. This eastward invasion of the graptolitic shale-chert-quartzite sequence into the miogeosynclinal carbonate belt is attributed to thrusting as has been demonstrated for corresponding facies contrasts in Nevada. Contrary to classical concepts of geosynclinal sedimentation, most of the middle Paleozoic detrital rocks on the west side of the miogeosynclinal carbonate belt and intertongued with the carbonates are of quartz sand and mature detrital fines apparently derived from eastern cratonic sources rather than from unknown orogenically active borderlands or volcanic island arcs on the west. In contrast, late Paleozoic orogenic movements in the eugeosynclinal belt caused uplifts from which a thick wedge of coarse detritus forming the Milligen and Wood River Formations spread eastward to intertongue and grade into finer clastics and carbonates of the Brazer Limestone near the craton margin. Late Paleozoic orogenic activity in central Idaho represents a northern continuation of the Antler orogeny of Nevada. The Antler orogeny thus had extremely widespread and profound effects on tectono-stratigraphic patterns of the Cordilleran geosyncline: for the first time in the Paleozoic history of Idaho and Nevada it replaced the craton as a principal source for detrital sediment; in Idaho, the orogeny brought to a close the eugeosynclinal episode of essentially depositional continuity extending from at least early Ordovician to late Devonian. End_Page 569------------------------------
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The Silurian-Mississippian time interval in northeastern North America can be subdivided into major interregional, depositional, and erosional episodes, reflecting vertical movements of the North American crustal plate. A detailed analysis of the preserved depositional record indicates the presence of 6 major unconformity-bounded sequences on the eastern craton, 3 in the transitional region of New York and Pennsylvania, and 2 on the Appalachian plate margin of the New England States and the Maritime Provinces. Good biostratigraphic and lithostratigraphic control clearly demonstrates that this decrease in the number of sequences is due to an easterly increasing change in tectonic style reflected by higher rates of subsidence, less uniform erosional fragmentation, and bette preservation. The interregional pattern of preservation and the predominance of carbonate facies suggest broad epeirogenic movements during Silurian time. Pronounced facies changes and variations in thickness during Early and early Middle Devonian time characterize the transition from epeirogenic to orogenic movements of the Acadian orogeny. Isostatic uplift and foredeep development mark the late Middle and late Devonian. The Mississippian record indicates greatly increased subsidence on the craton and tensional block faulting, with renewed volcanism on the Appalachian plate margin. End_of_Article - Last_Page 781------------
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Structurally, the Hugoton embayment is a large, southward-plunging syncline that represents a northerly extension of the Anadarko basin. It is bounded on the east by the Pratt anticline, on the northeast by the Central Kansas uplift, on the northwest by the Las Animas arch, on the west by the Sierra Grande uplift, and on the southwest by the Amarillo uplift. The embayment is approximately 150 mi wide and 250 mi long. Subsidence began during the Early Ordovician and reached a maximum from the middle Mississippi through the early middle Permian. Rocks of Paleozoic, Mesozoic, and Cenozoic ages are present in the embayment. The section thickens toward the axis of the embayment where it is about 9500 ft. The Ordovician through Cambrian section attains a thickness of about 650 ft. The Devonian and Silurian are largely absent from the area. The Mississippian and Pennsylvanian sections are about 3000 ft thick. Excluding the Permian, the Mississippian and Pennsylvanian contain the highest exploration potential. An evaluation of the deeper zones in the underexplored areas of the embayment identified several structural and stratigraphic trends that are presently untested or remain underexplored. The trends can be separated into those controlled by early structural developments whichmore » persisted through the section and later structural stratigraphic events. The probability of finding new fields in the 500,000 to 5,000,000-bbl range is good.« less
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Lake Malawi, Africa, serves as an important modern analog for understanding depositional processes in an active rift setting.This paper explores the depositional processes and stacking patterns of coarse-grained facies across a large fan delta and associated sublacustrine fan system offshore of the South Rukuru River using singlechannel seismic data coupled with deep-water vibracores and gravity cores.A companion paper (Wells et al. 1999) discusses the details of the depositional processes of the system inferred from core data.Using 2900 km of single-channel seismic data, eight genetic facies were defined based on seismic reflection character, external geometry, accompanying core data, and location within the modern geomorphic system.Five sand-dominated facies include: (1) mouth-of-canyon-fan facies; (2) progradational-fan-delta facies; (3) channel-fill facies; (4) canyon-fill facies; and (5) basin-plain-fill facies.These facies occur as surficial deposits in water depths of more than 600 m, suggesting that coarse-grained sedimentation characterizes certain localities, in even the deepest parts of Lake Malawi.Climatically driven lake-level changes influenced the internal character of these facies, their thickness, and to some extent their location within the South Rukuru study area.However, climate was generally subordinate to tectonism in controlling the temporal and spatial distribution of the facies.Tectonic controls can be categorized as: (1) orientation of the first-order border fault and intrabasinal faults; (2) syndepositional footwall uplift and rotation; and (3) temporal changes in the rate and location of maximum subsidence.These controls affect the location and stacking of the mouth-of-canyon fans, and the presence and orientation of sub-lacustrine canyons and the zone of maximum sediment accumulation, and depositional gradients.
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New data are presented about folded Ordovician and Silurian strata pierced in some bore-holes in NW Poland, reliably suggesting the presence there of foldings connected with the late Caledonian orogenic cycle.
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