Cratonic Source Research Articles

Age and Provenance of the Beardmore Group, Antarctica: Constraints on Rodinia Supercontinent Breakup

Abstract New U‐Pb ages for detrital and igneous zircons constrain the depositional age and sedimentary provenance of the Beardmore Group, a siliciclastic succession that records transformation of the East Antarctic margin during Rodinia breakup and subsequent Gondwana amalgamation. We divide rocks previously mapped as the Beardmore Group into (1) an inboard late Neoproterozoic assemblage (probably ≤670 Ma) and (2) a volumetrically dominant, outboard assemblage that is latest Early Cambrian or younger (≤520 Ma). The inboard assemblage contains mature, multicycle sediment derived from mixed cratonic sources dominated by 2.8‐ and 1.9–1.4‐Ga components. It was deposited in a platformal‐to‐shoreline setting along an existing rifted margin. A new zircon age of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepacka...

North American margin origin of Quesnel terrane strata in the southern Canadian Cordillera: Inferences from geochemical and Nd isotopic characteristics of Triassic metasedimentary rocks

New geochemical and Nd isotopic data from Triassic (ca. 220 Ma) clastic metasedimentary rocks assigned to the Quesnel terrane (Quesnellia) in southeastern British Columbia show that detritus was derived from both primitive and evolved sources. Twenty-four samples yield eNd 2 2 0 values between-9.1 and +5.6, independent of sample location. These samples have Eu anomalies between 0.6 and 1.0, La N /Yb N ratios between 3.8 and 11.4, La/Sc ratios ranging from 0.38 to 4.76, and Th/Sc ratios between 0.09 and 1.62. This range of isotopic and geochemical values overlaps that of samples from upper Paleozoic to Mesozoic rocks of the North American miogeocline and Upper Triassic Nicola Group volcanic rocks of the Quesnel terrane. The range in Nd isotopic and geochemical values supports the interpretation that detritus was derived from both continental North America (evolved cratonic source) and a volcanic arc (primitive source) developing on the continental margin. These data do not support previous interpretations of the Quesnel terrane as an intraoceanic arc. The inferred depositional link between North America and the Quesnel arc in Triassic time is ca. 40 Ma older than the hypothesized obduction of the Quesnel terrane onto the North American continental margin and, when combined with existing geological information, strongly supports a pericratonic, nonexotic origin for the Quesnel terrane in southeastern British Columbia.

Nd isotope composition of early Cambrian discrete basins

A Nd isotope map of early Cambrian epeiric basins has been inferred from the Nd isotopic signature recorded in phosphatic Small Shelly Fossils. The most radiogenic εNd(t) values characterize water reservoirs along the Avalonian and Cadomian belts, while εNd(t) values of −10 to −20 were obtained in Laurentia and East Gondwanan Australia and China. Such a distribution of Nd isotope signatures results from the different provenance of early Cambrian epeiric seas: juvenile magmatic arcs and/or cordilleran for Mongolia, Siberia, Iberia and adjacent terranes, and cratonic sources for Laurentia and East Gondwana. Biogenic apatite of Small Shelly Fossils may be a useful tool for mapping of Nd isotope composition and documenting water mass exchange between discrete basins.

Beyond whole-rock geochemistry of shales: The importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the Ouachita Mountain flysch deposits

The origin of the Ouachita Mountains has been the focus of significant debate for decades. Considerable confusion also exists concerning the provenance of the Carboniferous flysch of the Ouachitas. Trace-element geochemistry of shales from the Stanley Group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during Mississippian time. Th/Sc and Cr/Th ratios indicate a cratonic source for the majority of the Stanley Group sedimentary rocks. However, in several samples, low Th/Sc ratios and high Cr/Th ratios suggest a contribution from a mafic source. Using element ratio diagrams, all of the samples plot along a curve consistent with a two-component mixing model, consisting of a dominant felsic and a subordinate mafic source. The heavy-mineral fraction of these shales sequester many of the trace elements used in whole-rock studies. Monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock. The occurrence of monazite almost exclusively in sialic igneous rocks implies that Sm/Nd isotopic signatures are not sensitive to sediment input from more mafic sources. In some Stanley shale samples, chromite and Mn oxides were identified and positively identify an oceanic crustal component as a source of Stanley Group sediment. The results of this study emphasize the importance of determining the mineralogic sites of trace elements, and realization of specific mineralogic contributions from mafic or sialic tectonic provenances.

Beyond whole-rock geochemistry of shales: The importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the Ouachita Mountain flysch deposits

Research Article| July 01, 2000 Beyond whole-rock geochemistry of shales: The importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the Ouachita Mountain flysch deposits Matthew W. Totten; Matthew W. Totten 1Department of Geology and Geophysics, University of New Orleans, New Orleans, Louisiana 70148, USA Search for other works by this author on: GSW Google Scholar Mark A. Hanan; Mark A. Hanan 1Department of Geology and Geophysics, University of New Orleans, New Orleans, Louisiana 70148, USA Search for other works by this author on: GSW Google Scholar Barry L. Weaver Barry L. Weaver 2School of Geology and Geophysics, University of Oklahama, Norman, Oklahoma 73019, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2000) 112 (7): 1012–1022. https://doi.org/10.1130/0016-7606(2000)112<1012:BWGOST>2.0.CO;2 Article history received: 09 Dec 1998 rev-recd: 13 Oct 1999 accepted: 17 Nov 1999 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Matthew W. Totten, Mark A. Hanan, Barry L. Weaver; Beyond whole-rock geochemistry of shales: The importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the Ouachita Mountain flysch deposits. GSA Bulletin 2000;; 112 (7): 1012–1022. doi: https://doi.org/10.1130/0016-7606(2000)112<1012:BWGOST>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 origin of the Ouachita Mountains has been the focus of significant debate for decades. Considerable confusion also exists concerning the provenance of the Carboniferous flysch of the Ouachitas.Trace-element geochemistry of shales from the Stanley Group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during Mississippian time. Th/Sc and Cr/Th ratios indicate a cratonic source for the majority of the Stanley Group sedimentary rocks. However, in several samples, low Th/Sc ratios and high Cr/Th ratios suggest a contribution from a mafic source. Using element ratio diagrams, all of the samples plot along a curve consistent with a two-component mixing model, consisting of a dominant felsic and a subordinate mafic source.The heavy-mineral fraction of these shales sequester many of the trace elements used in whole-rock studies. Monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock. The occurrence of monazite almost exclusively in sialic igneous rocks implies that Sm/Nd isotopic signatures are not sensitive to sediment input from more mafic sources. In some Stanley shale samples, chromite and Mn oxides were identified and positively identify an oceanic crustal component as a source of Stanley Group sediment. The results of this study emphasize the importance of determining the mineralogic sites of trace elements, and realization of specific mineralogic contributions from mafic or sialic tectonic provenances. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

An isotopic and geochemical study of the northern Kaapvaal Craton and the Southern Marginal Zone of the Limpopo Belt: are they juxtaposed terranes?

To test existing lateral accretion models for the Archean Kaapvaal Craton in South Africa, metapelites and leucocratic granitoids from two different provinces, the granulite facies Southern Marginal Zone of the Limpopo Belt and the northern part of the adjacent greenschist to amphibolite facies Kaapvaal Craton, have been studied. Both provinces resemble each other in terms of isotope and trace element characteristics. They show a general depletion of incompatible elements independent from the grade of metamorphism. This observation conflicts with theories involving mobilisation during granulite facies metamorphism. A further common fingerprint is the unusually high Cr and Ni concentrations in the metapelites. In addition, they define a very narrow range of Nd model ages (2.9–3.05 Ga) constraining the average crustal age of their cratonic source region. The granitoid gneisses show somewhat larger variations of Nd model ages indicating some age heterogenity within the crust. However, the data from both provinces completely overlap. The Southern Marginal Zone and the Kaapvaal Craton also show uniform low 207 Pb/ 204 Pb relative to their 206 Pb/ 204 Pb ratios that differ clearly from other Southern African provinces. These results support the view that the Southern Marginal Zone represents a part of the Kaapvaal Craton exposed at a deeper crustal level; it rules out a hypothesis that both provinces are separate amalgamated terranes. Furthermore, there is very little difference between granitoids and metapelites which indicates that the latter largely derived from the former. The exposure of the granulite facies metapelites of the Southern Marginal Zone at the same level as the lower grade metamorphic rocks of the Kaapvaal Craton indicates uplift along a sharp tectonic boundary.

Stratigraphic architecture and evolution of the early Paleoproterozoic McGrath Trough, Western Australia

Palaeocurrents, provenance and stratigraphic analysis of the upper part of the Mount Bruce Supergroup and the Wyloo Group in the southwestern part of the Hamersley Province of the Pilbara region of Western Australia have been used to define an early Paleoproterozoic foreland basin, the McGrath Trough, in front of the northwards-advancing Ophthalmian fold belt. The foreland basin succession commences with the Boolgeeda Iron Formation and includes the overlying Turee Creek and lower Wyloo Groups. The basin geometry is asymmetric, thinning northwards away from the Ophthalmian fold belt, and the trough axis trends east-southeast parallel to the Ophthalmian folds. Multiple intraformational unconformities in the upper Turee Creek Group record the advance of the fold belt into the axis of the McGrath Trough in the Hardey syncline area. East-southeast-trending folds and steep southward-dipping cleavage post-date deposition of the Beasley River Quartzite, a shallow-marine to fluvial sandstone that records an interval of tectonic quiescence during basin evolution. Deposition of the Beasley River Quartzite was followed by renewed uplift of the southern hinterland, resulting in continued deposition of fluvial siliciclastics into the foreland basin, which was eventually filled with the eruption of the Cheela Springs Basalt. The age of the McGrath Trough is constrained broadly between ∼2.45 Ga, the age of the underlying Woongarra Rhyolite, and ∼2.2 Ga, the age of the Cheela Springs Basalt at the top of the succession. The sedimentary fill of the McGrath Trough was derived mainly from the south, and becomes texturally and compositionally more mature upward, reflecting its recycled orogen provenance. Two main sources are identified: a dominant cratonic source interpreted to be similar to the granitoid-greenstone basement of the Pilbara Craton, and a volumetrically lesser source from banded iron formation (BIF), and volcanic and sedimentary rocks of the Mount Bruce Supergroup. Felsic volcanic detritus, likely to have been derived from the underlying Woongarra Rhyolite, is most common in the lower Turee Creek Group and becomes increasingly less common upsection, although it is reworked from underlying formations. Chert and BIF clasts appear first in the upper Turee Creek Group, and are important components of the most proximal alluvial fan to braided stream deposits in the upper Turee Creek and lower Wyloo Groups. Grains of microplaty haematite, identical in appearance to microplaty haematite in the giant Hamersley iron-ore deposits, appear in conglomeratic units from the base of the Beasley River Quartzite upwards. These fluvial sediments were derived from the south and record erosion of ore-grade deposits from the uplifted Ophthalmia fold belt during lower Wyloo Group times.

Longitudinal fluvial drainage patterns within a foreland basin-fill: Permo-Triassic Sydney Basin, Australia

The north-south trending Permo-Triassic Sydney Basin (southern sector of the Sydney-Bowen Basin) is unique compared to many documented retro-arc foreland basins, in that considerable basin-fill was derived from a cratonic source as well as a coeval fold belt source. Quantitative analysis of up-sequence changes in sandstone petrography and palaeoflow directions, together with time-rock stratigraphy of the fluvial basin-fill, indicate two spatially and temporally separated depositional episodes of longitudinal fluvial dispersal systems. A longitudinal drainage-net similar in geometry to the modern Ganga River system (reduced to 60% original size) explains many of the palaeoflow patterns and cross-basinal petrofacies variation recorded in the basin-fill. The Late Permian to Early Triassic rocks reveal a basin-wide southerly directed fluvial drainage system, contemporaneous with east-west shortening recorded in the New England Fold Belt. In contrast, the Middle Triassic strata reveal a change to an easterly directed fluvial system, correlated to a shift in orogenic load to a NW-SE orientation in the fold belt northeast of the basin. The detailed petrofacies variation in the deposits of the second longitudinal fluvial dispersal system reveals vertical jumps in petrofacies compositions, with uniform compositions between jumps. The petrological jumps are interpreted as the result of minor fault adjustments in the fold belt, resulting in changing rates of sediment supply to the foreland basin. Uninterrupted erosion of the same terrain most likely caused the compositional uniformity between jumps. The identification of similar longitudinal fluvial systems, with transverse variation in detrital composition, is likely to help resolve the tectonic history of foreland fold belts elsewhere.

Source Terrains and Diagenetic Imprints of Cretaceous Marine Rocks of the Cordillera Oriental, Colombia

Cretaceous marine rocks of the western Cordillera Oriental of Colombia are exposed in stratigraphic sections which reveal multiple source terrains and variable diagenetic histories that were imposed by later thrusting XRD and petrographic analyses indicate that earliest Cretaceous rocks were derived from a nearly plutonic source (Triassic-Jurassic Ibague Batholith of the Cordillera Central) which provided feldspathic lithic fragments and clay-sized illite. High smectite concentrations in the overlying Hauterivian-Barremian strata reflect contemporaneous volcanism, possibly in the Cordillera Central. This signal decreased upsection to the upper Aptian, where detrital clays (kaolinite, chlorite, feldspar, amphibole) indicate a shift to a cratonic source, probably the Guayana Shield. Cratonic detrital input continues into the Turonian-Coniacian and is accompanies by high concentrations of smectite representing another period of volcanic activity. Later tectonic activity divided the area into two regions, each with unique diagenetic signatures. Three primary clastic sources are inferred for the section east of the thrust belt, however, the mineral assemblage is masked by later diagenesis. Sediments within the thrust belt show greater variability in the relative abundance of mineral assemblages and more poorly crystallized illite than occurs to the east of the thrust section. The preservation of much of the original mineralogic components within more » the thrust section indicates that these sediments have experienced only limited diagenetic overprinting as a result of a relatively short burial history. These contrasting signatures have important implications for hydrocarbon maturation within Cretaceous source rocks in a structurally complex region. « less

A combined petrographical—geochemical provenance study of the Newland Formation, Mid-Proterozoic of Montana

AbstractA provenance study was conducted on the Mid-Proterozoic Newland Formation, in which petrographical features of sandstones and geochemical characteristics of shales were integrated to arrive at an internally consistent interpretation.Sandstones of the Newland Formation are typically arkosic sands and arkoses with very-well-rounded quartz and feldspar grains and only minor amounts of extrabasinal rock fragments. The predominant feldspar types are K-spar and microcline, feldspar grains are smaller than quartz grains, and feldspars show little alteration due to weathering. Detrital modes of Newland sandstones (QFL diagrams) indicate that they were derived from a stable cratonic source. These petrographical features imply a source area dominated by granites and granitoid gneisses, semi-arid to arid climate, tectonic quiescence, and overall peneplain conditions.Shales of the Newland Formation are dominated by illite, quartz silt, and fine crystalline dolomite. They have small La/Th rations, relatively large Hf contents, and small contents of Cr, Co, and Ni, all indicative of derivation from crust of granitic composition. Small Tio2/Al2O3ratios also suggest source rocks of granitic composition. The average chemical index of alteration (CIA) for Newland shales is 71.8, which in light of the probable granitoid source indicates modest amounts of chemical weathering. Relatively large SiO2contents and large K2O/Na2O ratios reflect derivation from stable cratonic areas and tectonic quiescence.Thus, in general, the petrography of sandstones and geochemistry of shales provides the same provenance clues for the Newland Formation. One notable discrepancy between the two approaches is that the sandstones indicate an arid to semi-arid climate with very minor chemical weathering, whereas the CIA of the shales indicates at least modest amounts of chemical weathering. This indicates on one hand the need to better calibrate the CIA with a large variety of muds from modern climatic settings, and on the other hand the possibility that this discrepancy is due to transport segregation.

The provenance of Archean clastic metasediments in the Narryer Gneiss Complex, Western Australia: Trace element geochemistry, Nd isotopes, and U-Pb ages for detrital zircons

Clastic metasedimentary rocks of mid-Archean age from the Mt. Narryer and Jack Hills metasedimentary belts have REE patterns resembling those of mid- to late-Archean pelitic-quartzitic cratonic sequences elsewhere, and post-Archean continental rocks in general. Detrital zircons in the metasediments range in age from ca. 3000 to 3700 Ma. This indicates a provenance from mature cratonic sources controlled by K-rich granitic rocks. Additional minor sediment sources were identified as older, mainly chemical sedimentary sequences, ultramafic rocks, and felsic rocks characterized by low HREE contents, perhaps of tonalitic affinity. The association of the near-shore/fluviatile clastic association studied here with extensive turbiditic and chemical sedimentary sequences indicates these sources formed part of a (rifted ?) cratonic margin ca. 3 Ga ago. Differences between sedimentary REE patterns and those in the surrounding 3.73-3.0 Ga orthogneiss terrain, and between detrital zircon ages and the age distribution in the gneisses, suggest that the present association of the metasedimentary belts with the orthogneiss terrain is of tectonic origin. The occurrence of detrital zircons with U-Pb ages > 4 Ga in certain quartzites and conglomerates of the Jack Hills and Mt. Narryer metasedimentary sequences indicates a further, most likely granitic, source. ϵ Nd ( T Dep ) values in Jack Hills metasediments vary widely (+5 to −12) but have a smaller range in the Mt. Narryer belt (−5 to −9). The lowest ϵ Nd values of both sequences are interpreted to reflect the presence of detritus derived from 4.1–4.2 Ga old LREE-enriched continental crust in proportions considerably larger (≥ 10%) than estimated previously from the abundance of pre-4 Ga detrital zircons (≈3%). This would imply the former existence of significant volumes of pre-4 Ga continental crust in the provenance of the Mt. Narryer and Jack Hills metasediments.

Comparative Evolution of Pennsylvanian Platform Margins in Oklahoma and North-Central Texas

Pennsylvanian evolution of the Midland basin's eastern shelf and the northern shelves of the Anadarko and Arkoma basins demonstrates a strongly contrasting pattern with regard to the facies composition and stability of the shelf margin. For the Midland basin a carbonate ramp system developed adjacent to the Eastern shelf during the early Desmoinesian but received no coarse-grained clastic sediment until after the central Fort Worth basin was completely filled by Ouachita orogenic debris in the late Desmoinesian. At that time, a distinct north-south hingeline formed between the shelf and incipient Midland basin that allowed for subsequent vertical accretion of a Missourian-age double bank system. Due to the absence of active deltaic depocenters across the southern two-thirds of the shelf, the Missourian shelf margin did not prograde basinward nor did a submarine fan system develop adjacent to this reciprocal bank complex. Later, during the Virgilian, a single shelf-edge bank and submarine fan complex prograded the shelf edge westward. The shelf edges for the Anadarko and Arkoma basins demonstrate a significantly different pattern. Only during the late Desmoinesian (Marmaton Group) did a shelf-edge bank develop in association with shelf-slope reciprocal sedimentation. For the Anadarko basin, widespread submarine fans, fed from a northeasterlymore » cratonic source, are first seen with Red Fork deposition. Post-Tonkawa cyclic sedimentation prograded the shelf edge southward and gave rise to a more carbonate-dominated shelf sequence. In virtually all instances the regressive submarine fan units indicate eustatic lowstands of sea level.« less

Depositional Setting and Paleogeography of Ordovician Vinini Formation, Central Nevada

The eugeoclinal strata of the Ordovician Vinini Formation composes most of the Roberts Mountains allochthon (RMA). Its stratigraphy, reconstructed in the Roberts Mountains, can be precisely correlated throughout much of the RMA and into coeval strata of the autochthonous miogeocline by means of graptolite and conodont biostratigraphy. The Vinini is a mixture of clastic lithologies with some limestone and greenstone. Coarse clastics, characterized by well-rounded and well-sorted sands derived from cratonic sources, occur in two separate intervals and provide critical data on depositional and paleogeographic setting. The lower interval, hundreds of meters thick, was deposited in the latest Ibexian-earliest Whiterockian and can be closely correlated throughout central Nevada. It is a mixture of quartz sandstone, siltstone, limestone, and calcareous sandstone, deposited by turbidity flows during a lowstand of sea level. Both eastern and western sources have been interpreted for these sands. The upper interval is a prominent, pure quartzite up to 20 m thick deposited as a prograding blanket of sand in the latest Whiterockian-earliest Mohawkian. It occurs in the Vinini in the northern Toquima Range and in a parautochthonous sequence of transitional strata in the southern Toiyabe Range. This interval represents the most basinward edge of the Eureka Quartzite,more » which was also deposited across the miogeocline. The presence of sand of the Eureka Quartzite in the RMA indicates that the basin in which the RMA strata were deposited was immediately adjacent to the margin of North America in the Ordovician.« less

Depositional setting and regional relationships of basinal assemblages: Pershing Ridge Group and Fencemaker Canyon sequence in northwestern Nevada

Research Article| February 01, 1990 Depositional setting and regional relationships of basinal assemblages: Pershing Ridge Group and Fencemaker Canyon sequence in northwestern Nevada JOHN S. OLDOW; JOHN S. OLDOW 1Department of Geology and Geophysics, Rice University, Houston, Texas 77251 Search for other works by this author on: GSW Google Scholar RICHARD L. BARTEL; RICHARD L. BARTEL 1Department of Geology and Geophysics, Rice University, Houston, Texas 77251 Search for other works by this author on: GSW Google Scholar ARTHUR W. GELBER ARTHUR W. GELBER 1Department of Geology and Geophysics, Rice University, Houston, Texas 77251 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN S. OLDOW 1Department of Geology and Geophysics, Rice University, Houston, Texas 77251 RICHARD L. BARTEL 1Department of Geology and Geophysics, Rice University, Houston, Texas 77251 ARTHUR W. GELBER 1Department of Geology and Geophysics, Rice University, Houston, Texas 77251 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1990) 102 (2): 193–222. https://doi.org/10.1130/0016-7606(1990)102<0193:DSARRO>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN S. OLDOW, RICHARD L. BARTEL, ARTHUR W. GELBER; Depositional setting and regional relationships of basinal assemblages: Pershing Ridge Group and Fencemaker Canyon sequence in northwestern Nevada. GSA Bulletin 1990;; 102 (2): 193–222. doi: https://doi.org/10.1130/0016-7606(1990)102<0193:DSARRO>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 SocietyGSA Bulletin Search Advanced Search Abstract Basinal and platformal rocks of the northern part of the Mesozoic marine province of northwestern Nevada are juxtaposed along the curvilinear trace of the late Mesozoic Fencemaker thrust fault. The allochthonous rocks form a belt of basin-facies deposits that accumulated in upper- to mid-submarine fan environments that parallel the trace of the regional thrust. Lower submarine-fan or basin-floor facies are recognized but consistently are west of the more proximal deposits and lie in structurally higher positions within the Fencemaker allochthon. The thrust fault apparently follows the transitional zone between the basinal rocks composing the upper plate and the easterly parautochthonous platformal rocks.The basin facies sediments were derived from two sources in the Late Triassic and Early Jurassic periods. One source supplied siliciclastic debris, whereas the other contributed sporadic but copious amounts of shallow-marine carbonate debris. The two sources operated independently and simultaneously supplied sediments to different parts of the basinal environment.The platform assemblage was dominated by deltaic and carbonate reef and continental shelf environments. The site of deltaic sedimentation migrated with time, producing compositional differences in the detritus being fed into the adjacent basinal areas to the west.Sedimentation rates within the basinal environment exceeded subsidence, causing the basin to fill and shoal with time. The basin facies rocks are gradationally overlain by westward-prograding platform carbonate rocks and rocks representing prodeltaic environments. Early to Middle Jurassic synorogenic sediments derived both from local sources and from probable cratonic sources dominated the final episode of deposition. The synorogenic sediments accumulated in shallow-marine to subaerial environments localized by structures associated with regional extension. 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.

Regional, Three-Dimensional Permeability Distribution Within a Diagenetically Complex Fluvial Basin Fill: ABSTRACT

The Sydney basin, Australia, contains nearly 200 boreholes, many fully cored for coal resource evaluation, as well as outcrops of Early Triassic fluvial systems deposited during late-stage filling of a foreland basin. Lithofacies mapping defined three stratigraphic sequences consisting of deposits of four principal fluvial systems. Within these sequences reservoir quality is highly variable; permeability is a function of original sand mineralogy and texture and thus is closely related to paleogeography and facies of the fluvial systems. A set of visual permeability standards (encompassing five orders of magnitude) was used for continuous permeability estimation of cores from 15 geographically and geologically representative wells. Accuracy of estimates was monitored by laboratory analysis of 540 core samples. Meter-by-meter permeability estimates were combined to produce a suite of quantitative maps and cross sections showing the areal and stratigraphic distribution of reservoir quality. Contouring was strongly guided by the quantitative lithofacies maps that incorporated data from all drill holes and outcrops. Permeability mapping is an important element in ongoing prospect evaluation in the basin. Stratigraphic distribution of reservoir quality records the increasing importance of cratonic source areas through time. Within depositional systems, permeability fairways are closely associated with major fluvial channel axes. Regional west-to-eastmore » decrease reflects a pervasive diagenetic overprint on facies-related heterogeneities.« less

Origins of upper Paleozoic quartzose sandstones, American southwest

In the latter half of the Paleozoic, all margins of the North American craton were orogenic highlands except for the Cordilleran miogeocline. Rivers that drained cratonic areas northwest of the Transcontinental arch probably flowed to the topographically low Cordilleran miogeocline, but little direct sedimentary record of these ancient fluvial systems remains. The voluminous upper Paleozoic quartzose sandstone deposits of the American west are indirect evidence for these systems. Northern and central portions of the miogeocline were flooded with quartzose sand in the Pennsylvanian, and by mid-Early Permian, littoral and wind processes were transporting large volumes of quartzose sand southward, along the miogeoclinal/cratonic hingeline. Winds drove some of these sands inland, onto the disrupted western end of the Transcontinental arch, where they mixed with locally derived detritus and collected in great ergs. Calcareous siltstones that were deposited downwind of major ergs probably represent desert loess accumulations. Some eolian sands spilled across the Transcontinental arch to interfinger with carbonate and evaporite deposits in basins of the southwestern United States. Most sandstones deposited by these ancient littoral and eolian systems are fine- to very fine-grained, potash-feldspar subarkoses. Bimodal sandstones are common. The distribution, composition and volume of these sandstones suggest that the northern craton was the major source area and cratonic uplifts of the Ancestral Rockies were a secondary source. The fine grain size, high degree of sorting, and grain-size bimodality suggest that these sands were the most mobile sediments in littoral and eolian settings. A perplexing aspect of these deposits is the lack of compositionally unstable silicates, such as plagioclase, and the lack of phyllosilicate clays. Possibly this reflects great amounts of physical abrasion and sediment winnowing during protracted transport in littoral and eolian systems, and it may partially reflect weathering processes in arid coastal settings. The petrology therefore reinforces the model of a northern cratonic source and protracted southerly transport, but the degree to which the petrology reflects provenance and various physico-chemical processes remains unresolved.

Reservoir Quality, Sediment Source, and Regional Aspects of Norphlet Formation, South State Line Field, Greene County, Mississippi: ABSTRACT

South State Line field, discovered in 1970, is centrally located in the productive Jurassic Norphlet trend of the eastern Gulf Coast. The Norphlet Formation at South State Line has produced gas and condensate from normally pressured eolian sandstones at depths of more than 17,900 ft (5455 m). The 600-ft- (183-m) thick Norphlet Formation is composed of 100% sandstone and consists of two reservoir types: a poorer quality upper sandstone having low permeability (0.6 md) and a good-quality lower sandstone with better permeability (15.5 md). The upper sandstone exhibits tighter compaction of framework grains and more cement than the lower sandstone. Significantly, the upper sandstone contains authigenic illite (which promotes pressure solution), whereas the lower sandstone contains authigenic chlorite (which inhibits cementation and possibly pressure solution). On a regional scale, illite is the principal diagenetic clay mineral in the western area of the Norphlet trend (Mississippi to Texas), whereas chlorite is the principal diagenetic clay mineral in the east (Alabama to Florida). Not surprisingly, reservoir quality is poorer in the western portion of the trend. A comparison of framework grains in the upper and lower sandstones shows no significant compositional differences. Both are mature arkosic sandstones with a transitional-continental source (easternmore » Appalachians). No evidence was seen of a quartz-rich Ouachita or cratonic source. Volcanic and plutonic rock fragments are slightly more abundant in the lower sandstone, possibly reflecting a shifting of compositional terranes within a single source area along the eastern side of the Appalachians. The lower Norphlet sandstone may have been derived from Triassic volcanics, whereas the upper sandstone may have been derived from a more metamorphic source.« less

Fission track evidence for the source of accreted sandstones, Barbados

A part of the accretionary wedge associated with the Lesser Antilles arc system is exposed in an area of approximately 50 km² in northeastern Barbados. Zircon separates from sandstones collected from the Scotland District, Barbados, W. I., were analyzed using the fission track technique in order to assess the spectrum of source areas from which these terrigenous sediments were derived and to better constrain the timing of deposition. Results yielded a mixture of ages with strong groupings from 25–80 Ma, 200–350 Ma, and greater than 500 Ma. The youngest population indicates that some of the Scotland beds, previously dated by paleontologic methods as Eocene, may actually be as young as late Oligocene. Possible source areas include the Lesser Antilles arc, the Netherlands‐Venezuelan Antilles arc, and the Caribbean Mountains of Venezuela. The 200–350 Ma population may reflect partially annealed cratonic material, an Andean component, and/or material associated with a Triassic rifting event. The oldest zircons (&gt;500 Ma) and metamict zircons were likely derived from the South American craton. Detrital feldspars separated from sandstone at the base of Chalky Mount were analyzed by the 40Ar/39Ar age spectrum technique. Results yield what is interpreted to be a slow cooling gradient from 1350 Ma to 925 Ma and provides additional evidence of a cratonic source for the accreted sediments. Based on results from this study, and paleogeographical constraints, it is proposed that source areas for the Scotland sandstones of Barbados may have included the Guayana shield, Central Cordillera, uplifted areas of coastal South America, and the Lesser Antilles volcanic arc. We speculate that in Late Oligocene time an immense “proto‐Orinoco” river system flowed in a northeasterly direction from the shield through the northern Venezuelan mountain system (Cordillera de la Costa and Araya‐Paria) finally emerging into the Caribbean Sea in the area now occupied by Unare depression. Sediments comprising this deltaic complex and deep sea fan were either deposited directly into the trench or onto the sea floor where they were soon after caught up in the accretionary wedge of the Lesser Antilles arc system. This article contains supplementary material.

Inherited zircons in the Mundi Mundi Granite, Broken Hill, New South Wales

A heavy mineral concentrate from the undeformed Mundi Mundi Granite N of Broken Hill yielded very few zircons. U‐Th‐Pb measurements on microgram fractions of those extracted showed no indication of the stock's true 1500–1600 Ma intrusive event but revealed something inherited and of an age probably greater than 2 Ga. These zircons, either survivors of those inherited from the magma source or accidental inclusions from the wall rocks, may either represent sedimentary accumulations in the lower Willyama Supergroup with an older craton source i.e. provenance, or indicate the presence of a pre‐Willyama Supergroup basement. Considerable loss of Pb from the zircons is deduced to have occurred at (1) the time of granite intrusion, (2) in the lower Palaeozoic, and, (3) in the case of 208Pb, probably right up to recent time.

Regional Paleogeography and Habitat of Hydrocarbons in Ouachita Foredeep Basins: ABSTRACT

Nine present-day structural basins occur along the leading edge of the Ouachita thrust belt, a 1,400 mi (2,250 km) Paleozoic overthrust trend that extends from the Appalachians to Mexico. These basins, now separated by either subtle arches or pronounced basement uplifts, are components of a widespread late Paleozoic foredeep that formed in front of the Ouachita orogenic belt as a result of tectonic loading. This elongate depression filled during Pennsylvanian and Permian times with up to 15,000 ft (4,590 m) of sediment ranging in origin from alluvial to deep marine. An estimated 10 tcf of commercially recoverable natural gas has been discovered to date in the clastics of this foredeep basin trend. Four basins contain the bulk of these known reserves. The major conclusions of a study of late Paleozoic paleogeography, the structural style, and the habitat of hydrocarbons in this foredeep trend are: 1. The clastics were derived from cratonic or Appalachian sources, not from the rising Ouachita orogene. There appear to be a least 4 major entry points along the northern margin of the foredeep. 2. The facies range from coal-bearing deposits to deep-water turbidities. Fluvial and shallow-marine facies are found in the more stable areas; several turbidite depocenters occur in the areas of rapid, early subsidence. 3. The vast majority of the discovered hydrocarbons (gas) occurs in gas-saturated deep-basin traps. These very large fields occur in turbidites (Val Verde and Arkoma basins) and fluvial to shallow-marine deposits (Fort Worth basin). 4. Large undeveloped reserves can be documented in several basins in low-permeability reservoirs. In addition, there has been only rank wildcat exploration in 3 of the basins--Desha, Kerr, and Marfa. End_of_Article - Last_Page 287------------