Tesi: "Geology, Stratigraphic Cambrian"

1

Dilliard, Kelly Ann. "Sequence stratigraphy and chemostratigraphy of the Lower Cambrian Sekwi Formation, Northwest Territories, Canada". Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Spring2006/K%5FDilliard%5F042406.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

2

Baghiyan-Yazd, Mohammad Hassan. "Palaeoichnology of the terminal Proterozoic-Early Cambrian transition in central Australia : interregional correlation and palaeoecology". Title page, table of contents and abstract only, 1998. http://web4.library.adelaide.edu.au/theses/09PH/09phb1445.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

3

Osleger, David Allen. "Cyclostratigraphy of Late Cambrian cyclic carbonates : an interbasinal field and modelling study, U.S.A. /". Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03262008-175224/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

4

Malhame, Pierre. "Quartz arenites of the uppermost Cambrian-lowermost Ordovician Kamouraska Formation, Québec, Canada : gravity flow deposits of eolian sand in the deep sea". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101868.

Testo completo

Abstract (sommario):

The uppermost Cambrian-Lower Ordovician Kamouraska Formation in the external Humber Zone of the Quebec Appalachians consists of dominant thick massive to graded quartz arenite beds, subordinate pebble conglomerate and intercalated thin shale and siltstone beds. It was deposited by hyperconcentrated to concentrated density flows in a meandering submarine canyon on the continental slope bordering the Iapetus Ocean. Turbidity currents deposited beds with turbidite structure divisions. The sandstones consist of well sorted, well rounded quartz sand with frosted grains. Scanning electron microscopy reveals the presence of textures supporting eolian transport before redeposition in the deep sea. The Kamouraska quartz arenites are considered an ancient equivalent of Pleistocene eolian-sand turbidites on an abyssal plain off West Africa consisting of Sahara sand. Sand provenance is attributed to eolian equivalents of the Cairnside Formation of the Potsdam Group. The quartz arenites of the Kamouraska Formation provide a variant to tectonic sandstone provenance proposed in the scheme of Dickinson and Suczek (1979).

Gli stili APA, Harvard, Vancouver, ISO e altri

5

Sundberg, Frederick Allen. "Morphological diversification of the ptychopariid trilobites in the Marjumiid biomere (Middle to Upper Cambrian)". Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-07102007-142511/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

6

Eagan, Keith E. "Paleoenvironmental and Stratigraphic Interpretation of the Middle Cambrian Ute Formation, Northern Utah". DigitalCommons@USU, 1996. https://digitalcommons.usu.edu/etd/6791.

Testo completo

Abstract (sommario):

The Middle Cambrian Ute Formation includes some 200 m of cyclically alternating carbonates and mud rocks. These are arranged in eight to nine, meter-scale, shallowing-upwards packages, representing deposition under predominantly subtidal conditions. The packages consist of vertical sequences of shale, silty limestone, oncolitic packstone, and oolitic grainstone that exhibit little variance in this general pattern. Small-scale unconformities separate the packages. The inferred depositional environment consists of an intrashelf basin that has a peritidal platform near its margins. The craton, which supplied most of the terrigenous sediment, was situated to the south (Cambrian orientation), and located near the equator. One cycle includes a stromatolite biostrome that is distributed across more than 1500 km2 in northern Utah and southern Idaho. Stromatolites range from mound-like to club-shaped to columnar and reach up to 2 min vertical dimension, and 0.15 min diameter. These large columnar structures were apparently established just basinward of an oolitic shoal. These ancient stromatolites, which are in many ways similar to those stromatolites recently reported from the Bahamas, contain many clues that suggest that they grew in normal marine conditions. These findings require a rethinking of the commonly held belief that Phanerozoic columnar stromatolites are indicators of restricted, hypersaline conditions. Analysis of several orders of laminae in Ute Formation stromatolites indicates periodicity in accumulation from which yearly accumulation rates may be inferred. Values obtained for growth rate range from 4.39-4.88 cm/yr. Such rates of accumulation are in accord with those documented for ancient stromatolites from the Bitter Springs Formation. Thus, even considering the occurrence of hiatal surfaces within the stromatolites, the duration of the columnar-stromatolite horizon probably encompasses 10-2 - 10-3 yr. The biostrome's position in the sequence of cycles and the changes in stromatolite morphology across depositional dip suggest that the biostrome may be essentially isochronous across its outcrop area and, thus, may be viewed as a bioevent horizon. The stromatolites also contribute to a better understanding of the paleogeography of the study area during the Middle Cambrian by providing information on relative energy levels and flow directions. (212 pages)

Gli stili APA, Harvard, Vancouver, ISO e altri

7

Singh, Updesh. "Late Precambrian and Cambrian carbonates of the Adelaidean in the Flinders Ranges, South Australia : a petrographic, electron microprobe and stable isotope study /". Title page, abstract and contents only, 1986. http://web4.library.adelaide.edu.au/theses/09PH/09phs1792.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Tremblay, James Vincent. "Trilobites and strata of the Lower and Middle Cambrian Peyto, Mount Whyte and Naiset Formations, Alberta and British Columbia /". *McMaster only, 1996.

Cerca il testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

9

Simpson, Edward L. "Sedimentology and tectonic implications of the Late Proterozoic to Early Cambrian Chilhowee Group in southern and central Virginia". Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53660.

Testo completo

Abstract (sommario):

Few detailed facies analyses of rift to passive-margin transitions have been undertaken in exhumed orogenic belts. In the central Appalachians, the Chilhowee Group records such an evolution. The Unicoi and basal Hampton Formations record the transition from rifting to opening of the Iapetus Ocean. The majority of the Hampton Formation and the overlying Erwin Formation represent an overall regressive sequence punctuated by five progradational packages that accumulated along a passive margin. The rift to passive·margin phases of sedimentation in the central Appalachians reflect a continuum from fault·influenced to thermotectonic subsidence. Alluvial sediments and intercalated basalts of the lower Unicoi Formation developed in a rift setting. Paleontological data indicate that rifting continued into lower Cambrian time. The upper Unicoi Formation represents the incipient phase of passive-margin sedimentation related to a first-order, sea level rise. Differences in degree of crustal attenuation controlled the distribution of sedimentary environments during transgression. On the most attenuated crust to the east, initial transgressive facies consist of tidal sandwave and sandridge deposits intercalated with proximal and medial braid-pIain deposits. As transgression progressed cratonwards onto less attenuated crust, tidal sedimentation was supplanted by tide- and wave-influenced sedimentation characterized by sandwave complexes, tidal inlets and longshore bedforms. Drowning at the top of the Unicoi Formation is indicated by outer-shelf black mudstones. Deepening may have been enhanced by continued movement along listric faults throughout the incipient phase of passive-margin development. Examination of outcrops of the Hampton and Erwin Formations on different thrust sheets has permitted an across-strike reconstruction of the Early Cambrian Chilhowee shelf in space and time. Progradational packages developed under storm- and fair·weather wave conditions. Coarsening· and thickening-upward sequences on westerly thrust sheets were generated during progradation of shoreface, inner-shelf and outer-shelf environments. Outer-shelf facies predominate on easterly thrust sheets. Intertidal-flat deposits on the most westerly thrust sheet erosively overlie progradational shoreface sediments and developed during transgression in an embayment in which the tidal wave was amplified. More distal transgressive deposits consist of fining- and thinning·upward sequences with glauconitic horizons, and condensed sections in mudstones.
Ph. D.

Gli stili APA, Harvard, Vancouver, ISO e altri

10

Maguire, Henry C. "Application Of Geophysical And Geochronological Methods To Sedimentologic And Stratigraphic Problems In The Lower Cambrian Monkton Formation: Northwestern Vermont". ScholarWorks @ UVM, 2018. https://scholarworks.uvm.edu/graddis/938.

Testo completo

Abstract (sommario):

The Monkton Formation of the western shelf stratigraphic sequence in Vermont (VT) is identified as a Lower Cambrian regressive sandstone unit containing parasequences recording tidal flat progradation. Previous workers identified cycles believed to represent parasequences in a portion of a 1034' deep geothermal well drilled at Champlain College in Burlington, Vermont. For this study, both outcrop and well geophysical surveys were completed to better identify gamma emission curves and relative values for parasequences and select lithologies that are indicators of bathymetry and sea level. After using physical stratigraphic techniques to assemble a composite stratigraphic section for the Monkton Formation, analysis of the gamma emission curve and relative gamma values resulted in the identification and characterization of parasequences and select lithologies within the Monkton. Interpretation of bathymetry-sensitive lithologies along with parasequence architecture and thickness trends reveals three distinctive intervals over the thickness of the Monkton. It is recognized that the succession of these intervals represents an overall decreasing rate in accommodation space generation through Monkton deposition. Previous workers have suggested that biostratigraphic relationships of the Monkton Formation to the Potsdam Group in New York (NY) suggest that that they would be at least partially correlative. To further refine age relationships and constrain and compare the provenance of the Vermont stratigraphy locally and regionally, zircon samples were collected from the Monkton and the overlying Danby Formations and radiometric age determinations were completed by laser ablation–inductively coupled plasma mass spectrometry (LA-ICPMS) at University of Arizona Laserchron Center. Zircon age probability distribution curves show two dominate age peaks between 1.05-1.09 Ga and 1.15-1.18 Ga for the Monkton and Danby suggesting either a continuity of provenance through the Cambrian or the cycling of the Monkton's sand. The 1.05-1.09 Ga age range corresponds to rocks generated during the Ottawan Orogeny while the 1.15-1.18 Ga range is associated with the Shawinigan Orogeny and anorthosite-mangerite-charnockite-granite (AMCG) plutonism. Dominant age peaks in the Vermont samples between 1.15-1.18 Ga are similar to the 1.16 Ga age peak reported by other workers from the Altona and Ausable Formations of the Potsdam Group of New York. The shared dominant age peak and close proximity of the Vermont and New York stratigraphy may suggest a primarily shared provenance.

Gli stili APA, Harvard, Vancouver, ISO e altri

11

Dunster, John N. "Sedimentology of the Ouldburra Formation (Early Cambrian), northeastern Officer Basin". Title page, contents and abstract only, 1987. http://web4.library.adelaide.edu.au/theses/09SM/09smd926.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

12

Tawadros, Ezzat Edward. "Stratigraphy, sedimentology and petrology of the Cambrian rocks in the subsurface of Southern Alberta, Canada". Thesis, University of St Andrews, 1988. http://hdl.handle.net/10023/11694.

Testo completo

Abstract (sommario):

The Cambrian section in the subsurface of southern Alberta has a maximum thickness of 1860'. It is composed of sandstones, shales, limestones, and dolomites. The grand cycles characteristic of the Cambrian Sections in the Foothills and Front Ranges can be traced to some distance in the subsurface. However, the section changes facies eastwards into clastics and the grand cycles become less defined. The present correlations indicate that the Waterfowl-Arctomys grand cycle extends to the subsurface but is restricted to the northwest corner of the study area. Two new stratigraphic units have been informally defined in this study: The Crow Indian Formation of fine clastics and restricted to the southeast corner of Alberta. It is equivalent to the Cathedral, Stephen and Eldon Formations. The second unit is the Sakwatamau Member of the Eldon Formation, a clastic and carbonate deltaic unit restricted to the northwest corner of the study area. The Cambrian sediments were deposited in a broad shallow shelf-lagoon bordered to the east by the Canadian Shield and to the west by a shoal (the Kicking Horse Rim). Facies and thickness of the Cambrian section were controlled by six paleogeographic elements: 1) The Peace River Arch, 2) the Sweet Grass Arch, 3) the West Alberta Ridge, 4) the Kicking Horse Rim, 5) a shoal area immediately south of the Peace River Arch, and 6) a shoal area immediately north of the Sweet Grass Arch. When circulation in the shelf-lagoon was restricted, carbonate deposition dominated, especially in the shoal areas, and when open marine conditions prevailed, deposition of quartzarenites and glauconitic sandstones took place. Nine lithofacies have been recognized; 1) Mottled dolomitic mudstones and wackestones; 2) Mudstones, wackestones, and packstones; 3) Grainstones; 4) Cryptalgalaminates, cryptalgalaminate breccia, and algal-laminated sediments; 5) Flat-pebble conglomerates; 6) Glauconitic sandstones; 7) Quartzarenites; 8) Hybrid sandstones or iron-formations, and 9) Coquinas. These facies reflect deposition in environments ranging from supratidal to subtidal. Facies analysis also suggests that storms played a major role during the deposition of these sediments. Diagenesis (in both clastics and carbonates) appears to be the product of early, shallow freshwater phreatic-, marine phreatic-, and mixing zones. Dolomitization has developed in the mixing zone, as a result of pressure-solution, and/or dolomitization of glauconitic illites. Illite, kaolinite, authigenic K-feldspars, and quartz overgrowths were formed in the mixing zone depending on the K⁺ and H₄SiO₄ activity of the solutions. Fibrous calcite cement was formed in the marine-phreatic zone. Blocky calcite cement, syntaxial rims around echinoderm fragments, and fracture-filling sparry calcite were probably precipitated in the freshwater phreatic zone. Saddle dolomite occurs as burrow-filling and pore-filling in carbonates and as poikilotopic cement and in burrows (concretions) in sandstones. Saddledolomite (in carbonates and clastics) and chlorite (in clastics) were probably the last diagenetic products to form at deep burial and higher temperatures.

Gli stili APA, Harvard, Vancouver, ISO e altri

13

Gill, Benjamin Charles. "High-resolution sulfur isotope records of the Paleozoic and a detailed geochemical study of the late Cambrian SPICE event utilizing sulfur isotope stratigraphy, metal chemistry and numerial modeling". Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=78&did=1871861801&SrchMode=1&sid=1&Fmt=7&retrieveGroup=0&VType=PQD&VInst=PROD&RQT=309&VName=PQD&TS=1270232379&clientId=48051.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Nicholas, Christopher John. "Strontium isotope stratigraphy in the Cambrian system". Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321030.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

15

Stewart, William Douglas. "Stratigraphy and sedimentology of the Chancellor succession (Middle and Upper Cambrian) southeastern Canadian Rocky Mountains". Thesis, University of Ottawa (Canada), 1991. http://hdl.handle.net/10393/7628.

Testo completo

Abstract (sommario):

The Chancellor succession accumulated in a deep-water trough bordering a wide, epeiric shelf during Middle and Late Cambrian time. The Chancellor is divisible into seven major lithostratigraphic units, which are correlative with an eastern shelf assemblage comprising eight cabonate and siliciclastic formations. The deep-water carbonate and siliciclastic sediments in the Chancellor are divisible into five basic lithofacies, each of which has several variants due to a variety of depositional and diagenetic factors. Sediments in the argillite lithofacies were deposited by dilute, muddy and silty turbidity currents and hemipelagic settling. The ribbon calcilutite lithofacies was probably deposited in a similar manner, but owes its final appearance to diagenetic enhancement of rhythmic, primary variations in sediment composition. Both of these lithofacies contain a variety of synsedimentary deformation structures indicative of slope instability. The ribbon calcisiltite lithofacies is composed of interbedded silty carbonate and terrigenous mud turbidites. The calcarenite lithofacies is the product of high-concentration turbidity flows. It locally occupies large, channel-like features ("megachannels"), which are inferred to be slide scars incised into the upper slope. Most of the sediments assigned to the conglomerate lithofacies show evidence of matrix strength, and were laid down by debris flows. This lithofacies includes spectacular megaconglomerates containing Epiphyton boundstone blocks up to 50 m in maximum dimension. Periplatform talus blocks of similar size are scattered throughout the Chancellor. During most of Chancellor time, silt- and sand-sized material either bypassed the upper slope or was confined to the shelf. The high proportion of carbonate and siliciclastic turbidites in the Duchesnay and Oke units (middle Chancellor) is a direct reflection of an abrupt, regressive shift in the position of the cratonal shoreline. Spectacular cross-strike exposures have revealed that the Eldon-Pika margin and adjoining upper slope strata (Tokumm and Vermilion sub-units) are traversed by at least three megatruncation surfaces. (Abstract shortened by UMI.)

Gli stili APA, Harvard, Vancouver, ISO e altri

16

Lyon, Eva. "The Interrelationship Between the Bio- and Sequence Stratigraphy of the Middle Cambrian Spence Shale of Northern Utah and Southern Idaho". DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/1117.

Testo completo

Abstract (sommario):

The Middle Cambrian Spence Shale Member of the Langston Formation of northern Utah and southern Idaho is a fossil-rich unit that exhibits distinct cyclicity at the parasequence (meter) scale. At least seven discrete, shallowing-upwards parasequences, or cycles, can be found at the Miners Hollow and Antimony Canyon localities, each composed of calcareous shale capped by limestone. Within each cycle and within the member as a whole, predictable patterns of faunal distribution are evident. Sampling and identification of fossils from two localities have revealed that observed changes in fauna track changes in sea level throughout the section. Through cluster and principal components analyses it has been determined that those rocks of the Spence Shale representing a transgressive systems tract are home to a particular community of organisms, while those rocks of the highstand systems tract are home to another. It logically follows that the rocks of the transgressive tract represent a distinct biofacies, while those of the highstand tract represent another. The transgressive biofacies is composed of species such as agnostid and oryctocephalid trilobites and inarticulate brachiopods that are commonly found in deeper ramp settings. The highstand biofacies is distinguished by such taxa as Zacanthoides and other larger trilobite genera such as Glossopleura and Kootenia, and the eocrinoid Gogia, among others. The difference in ramp position between the Miners Hollow and Antimony Canyon localities implies a water depth gradient, with Antimony Canyon representing shallower water and Miners Hollow representing deeper water. This relationship is also reflected in the biofacies and community assignments. The stratigraphic trends explored in this study may be applied to other Spence Shale localities and possibly other Cambrian fossil deposits, such as the Burgess Shale of British Columbia. (151 pages)

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Jensen, Christopher Ryan. "Sequence Stratigraphy, Depositional Environments and Geochemistry of the middle Cambrian Bloomington Formation in Northern Utah". DigitalCommons@USU, 2015. https://digitalcommons.usu.edu/etd/4231.

Testo completo

Abstract (sommario):

The Bloomington Formation (~425 m thick) is a latest Middle Cambrian (~506.5-505 Ma), mixed, warm water, continental-shelf carbonate and fine-grained siliciclastic unit on the Cordilleran passive margin exposed in northern Utah and southern Idaho. Thicknesses of the Bloomington Formation at Calls Fort Canyon are 111 m in the Hodges Shale Member, 230 m in the middle limestone Member, and 84 m in the Calls Fort Shale Member. The Hodges Shale and Calls Fort Shale Members are shale dominated and represent outer detrital belt deposition. The Logan Canyon outcrop of the Hodges Shale Member shows an environmental change that may represent a transition form an open marine facies into what appears to be a lagoonal facies. The middle limestone member represents shallow marine carbonate deposition on the passive margin shelf. The Bloomington Formation has a low fossil abundance and diversity when compared to correlative units such as the Wheeler and Marjum Formations. There are, however, 10-50 cm thrombolite bioherms, associated with Girvanella oncoliths. These bioherms indicate a shallow-water carbonate facies that experienced a small flooding event that gives the bioherms time and proper conditions to build up. δ18O and δ13C results both show positive and negative shifts with δ13CVPDB values of 1.0 to -4.7 per mil and δ18OVSMOW values of -12.9 to -20.8 per mil. A negative δ13C excursion in the Hodges Shale may correlate to a similar excursion in the base of the Wheeler Formation that represents the DICE event. Lower and Middle Cambrian Formations in the Wellsville Range have been interpreted as being part of a second order transgressive system and containing third and higher-order cycles. The contact of the Hodges Shale Member and the underlying Blacksmith Dolomite represents a flooding surface and a sequence boundary, followed by a third order cycle. Flooding is indicated by shale deposits that overlie carbonates with a shallowing upward trend. High frequency fourth or fifth order cycles are expressed as laminated shale and thick-bedded limestones as well as thick packages of interbedded, thin limestones and shales. A PCA analysis of thin section point counts indicates that the limestone lithologies of all three members repeat throughout the entire Formation, suggesting cycles of relative sea level rise that cause repeating facies.

Gli stili APA, Harvard, Vancouver, ISO e altri

18

Schneider, Loren P. "The Sequence Stratigraphy of the Middle Cambrian Wheeler Formation in the Drum Mountains of West Central Utah". DigitalCommons@USU, 2000. http://digitalcommons.usu.edu/etd/6786.

Testo completo

Abstract (sommario):

The majority of the Middle Cambrian Wheeler Formation in the Drum Mountains was deposited during a single 3rd order sequence. Superimposed onto this sequence are three indistinct 4th order cycles and twenty distinct 5th order cycles. These higher other cycles were likely deposited within short intervals of geologic time (204 to 405 ky). The lower sequence boundary zone occurs within the Swasey Formation. The Transgressive Surface is the contact between the Swaset and Wheeler Formations. The Maximum Flooding Surface is located near the top of the lower Wheeler Formation, which also approximates the base of the Ptychagnostus atavus range zone. The upper sequence boundary is marked by stromatolites, which occur near the top of the upper member of the Wheeler Formation in the Drum Mountains. Deposition of the Wheeler Formation in the Drum Mountains was controlled by eustacy and tectonics. Local normal faulting associated with Middle Cambrian postrifting thermal subsidence may have caused some of the 5th order cycles. The cycles and surfaces defined in this stratigraphic analysis, and the base of the Ptychagnostus atavus and P. gibbus range-zones, can be used to correlate strata occurring in other localities in the eastern Great Basin. In addition, this study enables the evaluation of the effect of tectonics (faulting) versus global eustacy on the sedimentary regime occurring within the Middle Cambrian House Range Embayment. (95 pages)

Gli stili APA, Harvard, Vancouver, ISO e altri

19

Langenburg, Elizabeth S. "The Middle Cambrian Wheeler Formation: Sequence Stratigraphy and Geochemistry Across a Ramp-to-Basin Transition". DigitalCommons@USU, 2003. https://digitalcommons.usu.edu/etd/4275.

Testo completo

Abstract (sommario):

The Middle Cambrian Wheeler Formation is interpreted as having been deposited in the shallow ramp and deeper basin environments of the House Range embayment (HRE), presumably, during a single third-order sequence. In the Drum Mountains, the Wheeler Formation (295 m thick) is dominated by proximal and distal ramp deposits; at Ma~um Pass, the Wheeler Formation (190m thick) is dominated by basinal shale deposits. The Wheeler Formation contains only one biozone marker; the first appearance of Ptyhagnostus atavus. Lack of other chronostratigraphic markers and distinctive stratal patterns in the basinal facies makes correlation along this ramp-to-basin transect difficult. Therefore, carbon-isotope stratigraphy and total organic carbon analysis were tested for their utility as intra basinal correlation tools. 813Ccarbonate isotope values range from -1.7% to 0.07%o (PDB) at Marjum Pass and -1.1% to 1.4% (PDB) in the Drum Mountains; previously reported 813Ccarbonate values in the Great Basin for this time interval range between -2% to 2% (PDB). Both localities show small-scale isotope variability, however, this variability is thought to be the result of local isotopic effects and was not used for correlation. TOC values obtained from both sections increase upsection, define a distinct peak, then decrease upsection. These peaks are associated with shale facies and occur near the maximum flooding surface in both sections, indicating that the TOC results could be used for correlation between sections. The lithologic cyclicity recognized in the shallow-water deposits at the Drum Mountains locality have also been recognized in the deeper-water deposits at Ma~um Pass. At each locality the meter-scale cycles shallow upward and display similar stacking patterns. Because cyclicity is preserved in both sections and the total stratigraphic thickness and cycle thickness decrease toward the embayment-controlling fault, it is probable that the cyclicity was the result of small-scale eustatic changes in sea level rather than episodic tectonism. This ramp-to-basin correlation also supportS the validity of P. atavus as a global biostratigraphic marker. The first appearance of Ptydnagostus atavus has been found below the interpreted maximum flooding surface and was coeval with transgression in both localities, indicating that its appearance was likely synchronous.

Gli stili APA, Harvard, Vancouver, ISO e altri

20

Wright, Scott H. "Sequence Stratigraphy and Paleoecology of the Middle Cambrian Spence Shale Member of the Langston Formation of Northeastern Utah and Southeastern Idaho". DigitalCommons@USU, 1999. https://digitalcommons.usu.edu/etd/6542.

Testo completo

Abstract (sommario):

The Middle Cambrian Spence Shale Member contains meter-scale, shallowing-up cycles (parasequences) and record approximately 360 ky of deposition. These meter-scale cycles are nested within transgressive systems tracts (TST) and highstand systems tracts (HST) which reflect different stages of a lower-order, higher-magnitude sea-level excursion. Fossil assemblages are located in stratigraphic positions within the Spence Shale Member that can be predicted on the basis of sequence architecture. The cycle architecture, taphonomy, and geochemistry of the Spence parasequences confirm synthetic sections and theoretical models of meter-scale cycles developed in other studies. Delineation of meterscale cycles, based on taphonomic and sedimentologic criteria, allows high-resolution (100-500 ky) correlation. This study also documented the Cambrian existence of the Tooele and Arco Arches and aided in further understanding paleoenvironmental conditions within the Spence Shale Member.

Gli stili APA, Harvard, Vancouver, ISO e altri

21

Makhlouf, Issa Mohamed. "The stratigraphy and sedimentation of Upper Cambrian, Permo- Triassic and Lower Triassic rocks along the North Eastern margin of the Dead Sea basin, Jordan". Thesis, University of Newcastle Upon Tyne, 1987. http://hdl.handle.net/10443/552.

Testo completo

Abstract (sommario):

A thick sequence of predominantly terrigenous clastic sediments ranging from Cambrian to Cretaceous in age is exposed along-the northeastern margin of the Dead Sea, Jordan. The present study is confined to rocks of Upper Cambrian, Permo - Triassic (Um Irna Formation)-and Lower Triassic (Ma'in Formation) age, -which attain a total thickness of about 150 m. The lithology, stratigraphy, sedimentary structures, lithofacies and depositional environments of these sediments have been studied in detail. Early After deposition of the'Middle Cambrian marine Burj Formation, a major regressive event occured punctuated by minor transgressive phases, during which the Upper Cambrian sediments were laid down. These lie conformably on the Burj Formation, and are unconformably overlain by the Permo - Triassic Um Irna Formation. The Upper Cambrian succession consists of a medium - to coarse - grained quartzarenite facies and a subordinate heterolithic facies of siltstone and mudstone with sandy lenses. Internally the arenites are structured by trough cross - bedding arranged in cosets or solitary sets. Foreset dip directions show a unidirectional northwesterly mode. Most of the trough cross - beds are deformed giving rise to penecontemporaneous overturning of the foresets in the down-current direction. This is attributed to shear stress exerted by a dense sediment - laden current of water moving over the top of seismically liquefied cross - bedded sand. The Upper Cambrian sediments were, deposited on a braidplain and adjacent tidal flats due to periodic shifting of the active part of the braidplain. Reworking of the inactive part of the braidplain by tidal currents and subsidence led to marine incursions and the devel - opment of tidal flats. The Permo - Triassic Um Irna Formation is conformably overlain by interbedded sandstone, siltstone and mudstone of the Lower Triassic Ma in Formation. Um Irna Formation can be divided into a lower and upper member according to grain size and the proportion of sandstone to siltstone and shale in succession. The lower member attains a thickness of 10 m and is characterised by the presence of five sandstone-dominated fining - upward sequences from 0.75 to 2.15 m thick comprising an erosively - based coarse-to fine-grained sandstone overlain by, and laterally intertonguing with, maroon silt - stone and shale. The sandstones are internally structured by small - scale (< 20 cm thick) trough cross - bedding. Foreset azimuths show a unidirectional trend towards the north - northwest. The upper member also consists of five fining - upward sequences from .4 to 14.5 m thick, each sequence comprising an erosively - based pebbly sandstone grading up through medium-and fine-grained sandstone into maroon siltstone and silty - shale. Trough cross - bedding is the dominant internal structure with foresets directed towards the north - northwest. A characteristic feature of the silty - shale is the presence of abundant ferruginous concretions (pisoliths). Both members were deposited by fluvial processes. The lower member is attributed to deposition mainly by shallow, low sinuosity sand bed channels draining the distal reaches of a low gradient alluvial plain. The upper member contains a higher proportion of overbank fines (silt and mud) consistent with deposition by a mean - dering fluvial system, while the dominance of pebbly components in the sandy facies and their multilateral and multistorey nature suggests deposition by low sinuosity channels on the more proximal reaches of the braidplain. The nature of the concretions (Fe- pisoliths)- suggests that the diagenetic (pedogenic) environment was complex with alternating episodes of leaching, cementation and fracturing during their growth. The Lower Triassic Ma'in Formation is overlain by the shallow marine Dardur Formation. Two facies are recognised within the Ma'in Formation. The lower Himara Member comprises two facies which are deep maroon in colour and highly bioturbated: a lower sandy facies and an upper heterolithic facies (sand, silt and mud). This member is thought to have been deposited on a-tidal flat as evidenced by rhythmic beds of sand, silt and clay, flaser, wavy and lenticular bedding, herringbone cross - bedding, mudcracks, raindrop imprints, superimposed ripple marks showing interference, and ladder back forms reflecting shallowing and late stage emergence run off features. The depositional model proposed is one of a microtidal to mesotidal coastline, with a palaeotidal range of 0.45 m to 2.35 m. The coastline is inferred to have been interacting with a braided fluvial plain, which fed in quartzitic sediment from the southeast as indicated by the palaeocurrent pattern. The upper, more sandy, Nimra Member is cream in colour, more fossiliferous and more calcareous. The proposed depositional model is that of a shallow subtidal shelf receiving clastic sediment by way of river mouths extending seawards as subtidal channels. The shallow open marine nature of the environment is indicated by the presence of oold'si ,foraminifers, lamellibranchs, echinoids, bryozoars and gastropod fragments cemented mainly by dolomite. The overall model proposed for the Ma'in Formation is that of an intertidal flat (Hirnara Member) located between a braided alluvial plain (Um Irna Formation) and a subtidal marine shelf (Nimra Member).

Gli stili APA, Harvard, Vancouver, ISO e altri

22

Smith, Douglas D. "Sequence Stratigraphy of the Middle Cambrian Marjum Formation: Response of Sedimentary Facies and Biota to Sea-level Changes". DigitalCommons@USU, 2007. https://digitalcommons.usu.edu/etd/6744.

Testo completo

Abstract (sommario):

Research on the Marjum Formation provides insight into facies transitions in the House Range embayment of southwestern Utah during the Middle Cambrian. Sections of the Marjum Formation and equivalents were measured in strata representing shallow- (Drum Mountains), intermediate- (Wheeler Amphitheater), and deep-ramp (Marjum Pass) environments. This traverse across the embayment reveals strong litho- and biofacies changes. The Drum Mountains strata (343 m thick) are dominated by thickbedded shallow-water limestone facies containing polymerid trilobites and stromatolites. The Wheeler Amphitheater locality (392 m thick) provides an example of intermediate deposits between deep-water and shallow-water environments and is characterized by limestone and subordinate shale facies containing polymerid and agnostid trilobites, brachiopods, and sponge spicules. The Marjum Pass locality (424 m thick) contains equal parts shale and limestone facies with abundant fossils that include polymerid and agnostid trilobites, sponge spicules and soft bodied algae, representing deep-water environments. Migration of litho- and biofacies observed within Marjum Formation sections across the embayment shows carbonate ramp build-up and progradation from the Drum Mountains to the Swasey Peak, Wheeler Amphitheater area. Lateral migration of deepwater shale and rhythmite-producing turbidite facies can also be observed on a larger timescale from the Drum Mountains, during the early Bolaspidella time (Wheeler Formation deposits), to the Marjum Pass area (Marjum Formation deposits) by late Bolaspidella time. The Marjum Formation records two, third order shoaling-upward sequences. Fourth, fifth, and higher-frequency (rhythmite) cycles superimposed on these third order sequences can also be identified within the formation and are best preserved within the relatively deep-water deposits at Marjum Pass. Identification of sampled trilobites allowed correlation of known fauna! turnovers found by Robison and Vorwald with observed strata and systems tracts from this study. Stratigraphic locations of trilobite fauna! turnovers were found to be associated with transgressive systems tracts in the Drum Mountains and Marjum Pass localities. Fauna! turnover associated with significant sea-level events within these systems tracts suggests change in water depth altered the local environment forcing extinction and/or migration of organisms. Peak values of total organic carbon (TOC) at each measured section were also found to have a close relationship with maximum flooding zones. Associations of peak TOC values and fauna! turnovers with significant sea-level events demonstrate the value of these tools for correlation across the embayment.

Gli stili APA, Harvard, Vancouver, ISO e altri

23

Laneville, Michael Warren. "Subsurface Depositional Systems Analysis of the Cambrian Eau Claire Formation in Western Ohio". Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu154220482332536.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

24

Fielder, Gordon W. "Lateral and vertical variation of depositional facies in the Cambrian Galesville Sandstone, Wisconsin Dells". 1985. http://catalog.hathitrust.org/api/volumes/oclc/12327897.html.

Testo completo

Abstract (sommario):

Thesis (M.S.)--University of Wisconsin--Madison, 1985.
Thirteen folded leaves of illustrative matter are in pocket. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 154-168).

Gli stili APA, Harvard, Vancouver, ISO e altri

25

Botsford, Jack W. "Depositional history of middle Cambrian to lower Ordovician deep water sediments, Bay of Islands, western Newfoundland /". 1987. http://collections.mun.ca/u?/theses,94181.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

26

Wilbur, Bryan Charles. "A revision of helicoplacoids and other early Cambrian echinoderms of North America". Thesis, 2005. http://www.lib.utexas.edu/etd/d/2005/wilburb11838/wilburb11838.pdf#page=3.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

27

Pyle, Leanne. "Stratigraphy, conodont taxonomy and biostratigraphy of Upper Cambrian to Lower Silurian platform to basin facies, northern British Columbia". Thesis, 2000. https://dspace.library.uvic.ca//handle/1828/9100.

Testo completo

Abstract (sommario):

This study establishes the stratigraphic framework and conodont biostratigraphy of Lower Paleozoic strata of the Northern Canadian Cordilleran Miogeocline, which document a non-passive tectonic evolution of the rifted margin of Laurentia. Only a few reconnaissance stratigraphic studies have been conducted previously in the study area. Nine key sections span an east-west transect from the Macdonald Platform to the Kechika Trough (platform-miogeocline-basin) and 3 key sections comprise a transect across the parautochthonous Cassiar Terrane. Over 12 000 m of strata from the Kechika and Skoki formations and Road River Group in northeastern British Columbia were measured and described, from which a total of 405 conodont samples (4-5 kg each) were taken. A total of 39 526 conodonts have been used to refine the Upper Cambrian to Lower Silurian conodont biostratigraphy across the transect. The stratigraphy is revised to divide the Kechika Formation (late Cambrian to early Arenig in age) into 5 formal members: Lloyd George, Quentin, Grey Peak. Haworth and Mount Sheffield members. The Skoki Formation (early to late Arenig in age) comprises 3 new formal members defined as: Sikanni Chief. Keily and Redfern members. The Road River Group is divided into 3 new formations: Ospika (early Arenig to Llanvim in age), Pesika (Lower Silurian in age) and Kwadacha (formerly the Silurian Siltstone). The Ospika Formation is further subdivided into 5 formal members: Cloudmaker, Finlay Limestone, Chesterfield, Finbow Shale and Ware. Conodonts of Late Cambrian to Early Silurian age are described taxonomically from the Kechika, Skoki, Ospika and Pesika formations across the transect. A total of 39 526 identifiable conodonts recovered from 142 productive samples indicate high species diversity and abundance in shallow water facies and less diversity and abundance with in deeper water facies. Elements are moderately to well preserved, typically with a colour alteration index (CAl) of 3-5. A total of 197 species, representing 73 genera are identified and illustrated among which 6 new genera and 39 new species are described. Fifteen of the 39 new species had too little material and were described in open nomenclature. The new genera are Graciloconus, Kallidontus, Planusodus and 3 new genera (A, B, C) treated in open nomenclature. The new species are Acodus kechikaensis n. sp., A. quentinensis n. sp., A. warenesis n. sp., Cordylodus delicatus n. sp., Colaptoconus greypeakensis n. sp., ?Diaphorodus n. sp., Drepanoistodus minutus n. sp., Graciloconus concinnus n. gen. n. sp., Kallidontus serratus n. gen. n. sp., K. nodosus n. gen. n. sp., K. princeps n. gen. n. sp., Laurentoscandodus sinuosus n. sp., Macerodus cristatus n. sp., M lunatus n. sp., Microzarkodina n. sp., Oepikodus n. sp., Oistodus n. sp., Paroistodus n. sp., Planusodus gradus n. gen. n. sp., ?Prioniodus n. sp., Protoprioniodus n. sp., Rossodus kwadachaensis n. sp., R. muskwaensis n. sp., R. sheffieldensis n. sp.. R. subtilis n. sp., Scolopodus amplus n. sp., Striatodontus strigatus n. sp., Triangulodus akiensis n. sp., Tricostatus infundibulum n. sp., T. terilinguis n. sp., 3 unnamed new genera and 3 new species and 5 new species of Drepanoistodus (A, B. C, D, E). The conodont zonation for Upper Cambrian to Lower Silurian strata is refined, using Sections 4, 5, 13 and Grey Peak as reference sections. It allows close dating of stratigraphic boundaries. The oldest zones in the Kechika are cosmopolitan and include the Eoconodontus Zone (upper Cambrian), Cordylodus proavus and Cordylodus lindstromi zones (uppermost Cambrian) and lapetognathus Zone (base of Tremadoc). Ten higher zones are recognized and redefined for shallow water platform facies containing faunas of the Midcontinent Realm. Four of these are new (Polycostatus falsioneotensis, Rossodus tenuis, Scolopodus subrex and Acodus emanualensis zones) and 10 new subzones are established. Those for the Kechika Formation include, in ascending order, the Polycostatus falsioneotensis Zone (lower Tremadoc). Rossodus tenuis Zone (lower Tremadoc); Rossodus manitouensis Zone with R. muskwaenesis and R. sheffieldensis subzones (middle Tremadoc), Low diversity interval (upper Tremadoc), Scolopodus subrex Zone with Graciloconus concinnus and Colaptoconus bolites subzones (lower Arenig) and Acodus kechikaensis Zone with Kallidontus serratus. Diaphorodus russoi and Kallidontus nodosus subzones (lower Arenig). Those for the Skoki Formation include the Oepikodus communis Zone with Tropodus sweeti, Bergstroemognathus extensus and Juanognathus variabilis subzones (middle Arenig). The O. communis Zone spans the Kechika-Skoki boundary and the uppermost Kechika lies within the lowermost part of the O. communis zone underlying the T. sweeti Subzone. The Skoki Formation also contains the Jumudontus gananda Zone (middle Arenig) and Tripodus laevis Zone (upper Arenig). The Phragmodus undatus Zone (Upper Ordovician) lies within the Road River Group in the Cassiar Terrane. Thirteen deep water zones are recognized for basinal facies containing faunas of predominantly the North Atlantic Realm. Five new zones are established (Drepanoistodus nowlani, Acodus deltatus, Paracordylodus gracilis, Paroistodus horridus and Dzikodus tableheadensis zones) and one new subzone within the P. gracilis Zone is proposed. Those within the Kechika Formation include Cordylodus angulatus Zone (lower Tremadoc), Paltodus deltifer Zone (middle Tremadoc), Drepanoistodus nowlani Zone (middle Tremadoc), Acodus deltatus Zone, (middle Tremadoc), Paroistodus proteus Zone (upper Tremadoc), Paracordylodus gracilis Zone with Oelandodus elongatus Subzone (upper Tremadoc) and Prioniodus elegans Zone (base of Arenig). Those within the Skoki and Ospika formations include Oepikodus evae Zone (Skoki Formation, middle Arenig), Paroistodus originalis Zone (Skoki and Ospika formations, upper Arenig), Paroistodus horridus and Dzikodus tableheadensis zones (both within the Ospika Formation, lower Llanvim). The Amorphognathus tvaerensis Zone lies within the Road River of the Cassiar Terrane (Upper Ordovician). The Distomodus staurognathoides Zone lies within the Pesika Formation (middle Llandovery). The conodont faunas therefore provide detailed temporal constraints for the stratigraphic framework. Some evolutionary remarks are made for selected species involved in radiations, especially in the Tremadoc and Arenig, that are useful in further refining the standard Midcontinent Realm zonation. The Midcontinent Realm conodont faunas are used for regional correlations within North America and those of the Atlantic Realm provide calibration on an interregional scale, for example, with Baltica.
Graduate

Gli stili APA, Harvard, Vancouver, ISO e altri

28

Blanco, Gaucher Gonzalo Homero. "Provenance analysis of the Neoproterozoic-Cambrian Nama Group (Namibia) and the Arroyo del Soldado Group (Uruguay) : implications for the palaeogeographic reconstruction of SW Gondwana". Thesis, 2012. http://hdl.handle.net/10210/7257.

Testo completo

Abstract (sommario):

D.Phil.
The amalgamation of SW Gondwana after the break-up of Rodinia supercontinent during the Neoproterozoic-early Palaeozic was one of the most active tectonic periods of the earth history and its geological evolution remains controversial. Recently, diverse hypotheses such as mantle plume activity, orthogonal continent-continent and strike-slip collisions according to different models try to explain the complex evolution of the Pan-African Brasiliano orogens and the associated sedimentary basins. In order to get insight of the SW Gondwana reconstruction, provenance analyses were performed on two Neoproterozoic-early Palaeozic sedimentary units: (1) the Arroyo del Soldado Group representing a —5000 meter thick platform succession unconformably overlying the mainly Archaean to Neoproterozoic rocks of the Rio de la Plata Craton in Uruguay and, (2) the Nama Group, a —2000 meter thick shallow marine to fluvial deposit interpreted as a foreland basin in response to tectonism in the adjacent northern Damara and western Gariep Orogenic Belts and unconformably overlying the mainly Mesoproterozoic rocks of the Kalahari Craton in Namibia. Several techniques including petrography, heavy mineral analysis, geochemistry, Sm-Nd isotope analysis and zircon dating were applied to both sedimentary basins. The petrographic, heavy mineral analyses and geochemical results from the Nama Group indicate a recycled upper crust composition characterized by metamorphic and granitic sources and minor mafic rocks. Palaeocurrent analyses of the chromian spinet bearing sandstones of the Nama Basin point to a volcanic island arc source located in the Damara Belt. Detrital zircon dating of the Nama Group display major peaks of Neoproterozoic and Mesoproterozoic ages suggesting a provenance from the Damara/Gariep Belts and their basements. Palaeocurrents from the west and the dominance of Neoproterozoic-Cambrian detrital zircon ages (76%) in the "Molasse" stage of the foreland evolution probably indicate exhumation of the felsic volcanic arc root which probably occurred after the time indicated by the younger zircon dated at 531 ±9 Ma. The petrographic and geochemical results from the Arroyo del Soldado Group indicate a recycled upper crust composition characterized by source diversity composed of granite-gneissic and mafic-metamorphic rocks. On average, Nd isotopes account for negative ENd values and TDM ages in a range of variation found elsewhere within SW Gondwana. Detrital zircon dating indicate sources dominated by Palaeoproterozoic (1.7-2.0-2.2 Ga) and subordinate Archaean ages (2.5-2.9-3.5 Ga). The scarcity of Mesoproterozoic and Neoproterozoic zircons and palaeocurrent directions towards the east indicate that the Arroyo del Soldado Group was fed by detritus from the Rio de la Plata Craton favouring a passive margin tectonic setting for their deposition. Deformation of the Arroyo del Soldado Group took place ca. 530 Ma, after strike-slip collision with an African affinity terrane. Finally, based on the palaeogeographic evaluation, the provenance of Nama foreland basin and the passive margin deposit of the Arroyo del Soldado basin suggest that continent-continent collision of the Kalahari/Congo Cratons with the Rio de la Plata Craton and the Cuchilla Dionisio Pelotas Terrane most likely occurred due to strike slip accretion related to a component of N—S shortening in the period between 530 and 495 Ma.

Gli stili APA, Harvard, Vancouver, ISO e altri

29

White, MJ. "Stratigraphy, volcanology and sedimentology of the Cambrian Tyndall Group, Mount Read volcanics, western Tasmania". Thesis, 1997. https://eprints.utas.edu.au/21968/7/whole_White_thesis_ex_pub_mat.pdf.

Testo completo

Abstract (sommario):

The Tyndall Group is a Cambrian, dominantly submarine, volcano-sedimentary succession that occurs in the upper part of the Mount Read Volcanics, western Tasmania. The Tyndall Group comprises a relatively complex assemblage of lithofacies including crystal- and lithic-rich volcaniclastic breccia, conglomerate and sandstone, welded ignimbrite, rhyolite lava and/or intrusions, laminated mudstone and carbonate. Problems with the previously defined stratigraphic nomenclature have prompted development of a new stratigraphic scheme, based on detailed mapping and facies analysis of major Tyndall Group exposures in the central Mount Read Volcanics. The Tyndall Group is herein divided into two formations, the Comstock Formation and the overlying Zig Zag Hill Formation. The Comstock Formation is further subdivided into the Lynchford Member and the overlying Mount Julia Member. This stratigraphic scheme is based on regional lithological variations, which largely reflect different provenance characteristics. Volcanogenic sedimentary lithofacies are abundant in the Tyndall Group and were largely deposited from low- to high-density turbidity currents, implying that the depositional setting was dominantly subaqueous and below storm wave base. An in situ limestone unit containing abundant shallow marine fossils (Jago et al. 1972) occurs at the base of the Comstock Formation at Comstock, and indicates that at least part of the group was deposited in water less than a few hundred metres deep. Sources of the volcaniclastic components in the Tyndall Group are not exposed or have been eroded away. However, syn-eruptive volcaniclastic facies in the Comstock Formation provide a record of the character and setting of volcanic activity in the source. The high proportion of juvenile pyroclasts in these facies (e.g. crystals, crystal fragments, shards, pumice) indicates the occurrence of voluminous explosive magmatic and/or phreatomagmatic eruptions in the source, and that the source areas were in subaerial to shallow marine environments. Pyroclasts were probably transported to the marine setting by pyroclastic flows which transformed into water-supported sediment gravity flows after sufficient interaction with water, forming crystal-rich volcaniclastic sandstone. Occurrences of welded ignimbrite in the Comstock Formation represent relicts of primary deposits from pyroclastic flows that did not interact with water. Although the welded ignimbrites could be deposits from hot, gas-supported submarine pyroclastic flows, two other emplacement mechanisms are suggested: 1) a thick delta of crystal-rich volcaniclastic sand, generated by interaction of voluminous subaerial pyroclastic flows with sea water, caused temporary shallowing and allowed subsequent pyroclastic flows to deposit welded ignimbrite across the shallowly submerged (or sub aerial?) top of the delta; 2) large allochthonous blocks of welded ignimbrite were transported in giant submarine sediment gravity flows, forming units of ignimbrite-block-bearing breccia. Rhyolite lava dome complexes also built up on the sea floor during the Comstock Formation stage. The lower part of the Comstock Formation (Lynchford Member) has an andesitic to dacitic provenance and the overlying Mount Julia Member is more silicic in character. Distinctive bedding-parallel alteration banding in the crystal-rich volcaniclastic sandstone facies is thought to have originated during diagenetic alteration and compaction of the vitric-rich ash matrix. In contrast to the Comstock Formation, the overlying Zig Zag Hill Formation records post-eruptive erosion and reworking of the subaerial to shallow marine source areas, resulting in the influx of wellrounded, polymict, epiclastic and reworked pyroclastic aggregates to the marine setting. The palaeogeographic setting for the Tyndall Group comprises a subaerial to shallow marine volcanic terrain adjacent to the sea. The central North Island and offshore Bay of Plenty in New Zealand, and the Grenada Basin and Lesser Antilles arc, are considered to be two modem geographic and volcanic analogues. The source magmas for the Comstock Formation were probably derived from melting of Proterozoic crust (Crawford and Berry 1992), and the Zig Zag Hill Formation probably formed in response to tectonic uplift in the source. In summary, the Tyndall Group is the submarine record of active volcanism (Comstock Formation) and subsequent erosion (Zig Zag Hill Formation) of a subaerial to shallow marine volcanic terrain that is not preserved.

Gli stili APA, Harvard, Vancouver, ISO e altri

30

Myrow, Paul Michael. "Sedimentology and depositional history of the Chapel Island Formation (late Precambrian to early Cambrian) southeast Newfoundland /". 1987. http://collections.mun.ca/u?/theses,97100.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

31

Baghiyan-Yazd, Mohammad Hassan. "Palaeoichnology of the terminal Proterozoic-Early Cambrian transition in central Australia : interregional correlation and palaeoecology / Mohammad Hassan Baghiyan-Yazd". Thesis, 1998. http://hdl.handle.net/2440/21668.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

32

Zaw, Khin. "The effect of Devonian metamorphism and metasomatism on the mineralogy and geochemistry of the Cambrian VMS deposits in the Rosebery-Hercules district, Western Tasmania". Thesis, 1991. https://eprints.utas.edu.au/21917/1/whole_ZawKhin1992_thesis.pdf.

Testo completo

Abstract (sommario):

The Rosebery, Hercules and South Hercules deposits in western Tasmania are composed of polymetallic massive to disseminated sulphide mineralisation hosted in felsic volcanics of the Cambrian Mt Read Volcanic belt. The deposits have been affected by regional metamorphism of upper greenschist facies and associated tectonic deformation related to the Devonian Tabberabberan Orogeny. The Devonian tectonic movement has resulted in folding, shearing and faulting (thrusting) of the ore lenses which caused significant changes in the overall configuration of the original strati.form ores and underlying stringer zones. In addition, the south-end of the Rosebery deposit has undergone metasomatic replacement related to a postorogenic Devonian granite intrusion. The VMS mineralisation at Rosebery consists of three primary sulphide-sulphate zones: lowermost pyrite-chalcopyrite zone (>4% Cu), overlain by a sphalerite-galena ± pyrite ± chalcopyrite zone, and followed by an uppermost massive barite zone. The south-end of the orebody has been overprinted by Devonian transgressive metasomatic mineral assemblages. Three major replacement zones can be distinguished: (1) magnetite-biotite ± chalcopyrite zone, (2) pyrrhotite-pyrite zone and, (3) tourmaline-quartz± magnetite zone. Othermetasomatic minerals such as fluorite, garnet and helvite are present. The main Hercules deposit occurs 10 km south along strike from Rosebery and lies in a similar tuffaceous shale unit The deposit consists of a number of disconnected stratabound Zn-Pb-Cu-Ag-Au ore lenses with ~imilar metal distribution and alteration features to the Rosebery ores. The Hercules deposit shows a zonation from a massiye to disseminated pyritechalcopyrite zone (>4% Cu) at the footwall through a massive sphalerite-galena ±pyrite zone and spotty sphalerite-galena ± pyrite zone to a carbonate ± barite zone at the top. The South Hercules deposit is located about one kilometer south of the main Hercules ore lenses at the same stratigraphic level. The deposit displays comparable mineralogical zonation with Rosebery and Hercules but contains low-grade lead and zinc, and has a low copper content ( <1 wt % Cu) and relatively high (Au+Ag)/(Pb+Zn) ratio. The deposit consists of a disseminated to stringer sulphide zone with variably altered carbonate assemblages. Metal zonation studies indicate that zinc occurs dominantly as blanket-like enrichment in the Rosebery district deposits and silver broadly follows zinc. Gold is largely concentrated at the top of the ore lenses. In the transgressive pyrrhotite-pyrite replacement zone of the Rosebery south-end, zinc is conspicuously depleted but gold values of more than 20 g/t Au are noted. In contrast, the other biotite-, magnetite-, and tourmaline-bearing replacement zones contain low gold grades (generally less than 5.0 g/t Au). Like zinc, silver is also depleted in the replacement zones but a significant amount of copper is present Copper values as high as 2% are observed in the biotite-magnetite zone as well as the pyrrhotite-pyrite zone. This indicates that although zinc and silver were dissolved and removed during the Devonian replacement event, gold and copper appear to have been redistributed and recrystallised. A detailed mineralogical study of gold in the F(J) lens indicates that the gold occurs as electrum inclusions in pyrite, as individual electrum grains in pyrrhotite, and in chalcopyrite veins cutting pyrrhotite. Similar mineragraphic investigations at Hercules and South Hercules show that gold occurs as individual electrum grains locked in the pyrite, and as patches or blebs in the remobilised and recrystallised sphalerite, galena and tetrahedrite. The Devonian metamorphic and metasomatic processes resulted in significant recrystallisation and remobilisation of these gold grains as indicated by their texture, grain size, and fineness variation. The Devonian overprinting processes also resulted in the redistribution of FeS in sphalerites from the Rosebery district deposits. The sphalerite-hexagonal pyrrhotite-pyrite assemblages from the Rosebery south-end were used to apply the sphalerite geobarometer to estimate the pressure conditions during the Devonian replacement process. The estimated pressure is 3.0 ± 0.5 kb for the requilibration of sphalerite in the F(J) lens which would correspond to a depth of 8.0 ± 1.0 km. The correlation of the mole % FeS in sphalerite and the gold grades at the Rosebery, Hercules and South Hercules deposits displays complex patterns owing either to later Devonian metamorphic and metasomatic recrystallistion or to variation of the initial depositional conditions. The VMS carbonates from both north- and south-ends of the Rosebery deposit display tightly constrained and similar isotopic patterns. The isotopic patterns imply that no later isotopic changes have taken place although the south-end of the Rosebery deposit was strongly overprinted by the high temperature (> 300°C), pervasive Devonian replacement process. The 0180 values of biotite and magnetite from the F(J) lens replacement zone were used to calculate the oxygen isotopic composition of the Devonian hydrothermal fluid. The calculated o1 80CH.z0) values for the overprinting Devonian hydrothermal fluid vary from 8.0%0 to 12.0%0 and are consistent with a magmatic fluid. Detailed sulphur isotopic investigations on the hand specimen scale indicate that there are no obvious o34S variations between the lead-zinc lenses of Cambrian volcanogenic origin and the pyrrhotite-pyrite assemblages of Devonian origin. The sulphur isotope values of the sulphide minerals from the South Hercules deposit range from o34S values of 8.2o/oo to 14.1 o/oo and the calculated 034J\S values in the ore fluids display a permissible correlation with gold grades. This correlation suggests the possibility of using the sulphur isotopic composition as a guide to assist in targeting the gold-rich sections of massive sulphide systems. Fluid inclusion studies indicate that early formed low-temperature (ea 200'C), low-salinity ( <5 NaCl equiv. wt % ) Type I inclusions with no appreciable C02 may be interpreted as primary, Cambrian exhalative fluids that have survived the Devonian recrystallisation. Fluid inclusion characteristics of necking down and healed microfractures together with trapped carbonate and barite daughter minerals identified by laser Raman spectroscopy suggest an extensive remobilisation and recrystallisation of carbonate minerals during the Devonian overprinting processes, which corroborates with the redistribution and recrystallisation of primary Cambrian sulphides (e.g. sphalerite) and gold, during Devonian metamorphic and metasomatic processes. Although the VMS deposits in the Rosebery-Hercules area display no evidence for large-scale chemical remobilisation of ore constituents during metamorphism, the postorogenic Devonian granite intrusion below the south-end of the Rosebery mine resulted in chemical remobilisation of the ore lenses. The early replacement assemblages in the F(J) lens formed from interaction of moderate to high temperature(~ 330°C), saline (~0 NaCl equiv. wt % ) fluid with the original lead-zinc mineralisation. The later stage tourmaline veining and associated replacement assemblages resulted from lower temperature (~ 300°C), less saline (~0 NaCl equiv. wt%) fluid. During the Devonian metasomatic event gold may have been remobilised and recrystallised either as Au(HS)2 - or AuC12 - complexes but the high temperature and salinity conditions favour the AuC1i-complex. Copper also appears to have been recrystallised during the replacement process with minor remobilisation. In comparison to copper and gold, zinc, lead and silver have been dissolved and removed as the very soluble chloride complexes.

Gli stili APA, Harvard, Vancouver, ISO e altri

33

Wade, Benjamin P. "Unravelling the tectonic framework of the Musgrave Province, Central Australia". Thesis, 2006. http://hdl.handle.net/2440/57768.

Testo completo

Abstract (sommario):

The importance of the Musgrave Province in continental reconstructions of Proterozoic Australia is only beginning to be appreciated. The Mesoproterozoic Musgrave Province sits in a geographically central location within Australia and is bounded by older and more isotopically evolved regions including the Gawler Craton of South Australia and Arunta Region of the Northern Territory. Understanding the crustal growth and deformation mechanisms involved in the formation of the Musgrave Province, and also the nature of the basement that separates these tectonic elements, allows for greater insight into defining the timing and processes responsible for the amalgamation of Proterozoic Australia. The ca. 1.60-1.54 Ga Musgravian Gneiss preserves geochemical and isotopic signatures related to ongoing arc-magmatism in an active margin between the North Australian and South Australian Cratons (NAC and SAC). Characteristic geochemical patterns of the Musgravian Gneiss include negative anomalies in Nb, Ti, and Y, and are accompanied by steep LREE patterns. Also characteristic of the Musgravian Gneiss is its juvenile Nd isotopic composition (ɛNd1.55 values from -1.2 to +0.9). The juvenile isotopic signature of the Musgravian Gneiss separates it from the bounding comparitively isotopically evolved terranes of the Arunta Region and Gawler Craton. The geochemical and isotopic signatures of these early Mesoproterozoic felsic rocks have similarities with island arc systems involving residual Ti-bearing minerals and garnet. Circa 1.40 Ga metasedimentary rocks of the eastern Musgrave Province also record vital evidence for determining Australia.s location and fit within a global plate reconstruction context during the late Mesoproterozoic. U-Pb detrital zircon and Sm-Nd isotopic data from these metasedimentary rocks suggests a component of derivation from sources outside of the presently exposed Australian crust. Best fit matches come from rocks originating from eastern Laurentia. Detrital zircon ages range from Palaeoproterozoic to late Mesoproterozoic, constraining the maximum depositional age of the metasediments to approximately 1.40 Ga, similar to that of the Belt Supergroup in western Laurentia. The 1.49-1.36 Ga detrital zircons in the Musgrave metasediments are interpreted to have been derived from the voluminous A-type suites of Laurentia, as this time period represents a “magmatic gap” in Australia, with an extreme paucity of sources this age recognized. The metasedimentary rocks exhibit a range of Nd isotopic signatures, with ɛNd(1.4 Ga) values ranging from -5.1 to 0.9, inconsistent with complete derivation from Australian sources, which are more isotopically evolved. The isotopically juvenile ca. 1.60-1.54 Ga Musgravian Gneiss is also an excellent candidate for the source of the abundant ca. 1.6-1.54 Ga detrital zircons within the lower sequences of the Belt Supergroup. If these interpretations are correct, they support a palaeogeographic reconstruction involving proximity of Australia and Laurentia during the pre-Rodinia Mesoproterozoic. This also increases the prospectivity of the eastern Musgrave Province to host a metamorphised equivalent of the massive Pb-Zn-Ag Sullivan deposit. The geochemical and isotopic signatures recorded in mafic-ultramafic rocks can divulge important information regarding the state of the sub continental lithospheric mantle (SCLM). The voluminous cumulate mafic-ultramafic rocks of the ca. 1.08 Ga Giles Complex record geochemical and Nd-Sr isotopic compositions consistent with an enriched parental magma. Traverses across three layered intrusions, the Kalka, Ewarara, and Gosse Pile were geochemically and isotopically analysed. Whole rock samples display variably depleted to enriched LREE patterns when normalised to chondrite ((La/Sm)N = 0.43-4.72). Clinopyroxene separates display similar depleted to enriched LREE patterns ((La/Sm)N = 0.37-7.33) relative to a chondritic source. The cumulate rocks display isotopically evolved signatures (ɛNd ~-1.0 to .5.0 and ɛSr ~19.0 to 85.0). Using simple bulk mixing and AFC equations, the Nd-Sr data of the more radiogenic samples can be modelled by addition of ~10% average Musgrave crust to a primitive picritic source, without need for an enriched mantle signature. Shallow decompressional melting of an asthenospheric plume source beneath thinned Musgravian lithosphere is envisaged as a source for the parental picritic magma. A model involving early crustal contamination within feeder zones is favoured, and consequently explorers looking for Ni-Cu-Co sulphides should concentrate on locating these feeder zones. Few absolute age constraints exist for the timing of the intracratonic Petermann Orogeny of the Musgrave Province. The Petermann Orogeny is responsible for much of the lithospheric architecture we see today within the Musgrave Province, uplifting and exhuming large parts along crustal scale E-W trending fault/shear systems. Isotopic and geochemical analysis of a suite of stratigraphic units within the Neoproterozoic to Cambrian Officer Basin to the immediate south indicate the development of a foreland architecture at ca. 600 Ma. An excursion in ɛNd values towards increasingly less negative values at this time is interpreted as representing a large influx of Musgrave derived sediments. Understanding the nature of the basement separating the SAC from the NAC and WAC is vital in constructing models of the amalgamation of Proterozoic Australia. This region is poorly understood as it is overlain by the thick sedimentary cover of the Officer Basin. However, the Coompana Block is one place where basement is shallow enough to be intersected in drillcore. The previously geochronologically, geochemically, and isotopically uncharacterised granitic gneiss of the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. U-Pb LA-ICPMS dating of magmatic zircons provides an age of ca. 1.50 Ga, interpreted as the crystallisation age of the granite protolith. The samples have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. ɛNd values are high with respect to surrounding exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The tectonic environment into which the granite was emplaced is also unclear, however one possibility is emplacement within an extensional environment represented by interlayered basalts and arenaceous sediments of the Coompana Block. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the “Australian magmatic gap” of ca. 1.52-1.35 Ga, and is a possible source for detrital ca. 1.50 zircons found within sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2006

Gli stili APA, Harvard, Vancouver, ISO e altri

34

Wade, Benjamin P. "Unravelling the tectonic framework of the Musgrave Province, Central Australia". 2006. http://hdl.handle.net/2440/57768.

Testo completo

Abstract (sommario):

The importance of the Musgrave Province in continental reconstructions of Proterozoic Australia is only beginning to be appreciated. The Mesoproterozoic Musgrave Province sits in a geographically central location within Australia and is bounded by older and more isotopically evolved regions including the Gawler Craton of South Australia and Arunta Region of the Northern Territory. Understanding the crustal growth and deformation mechanisms involved in the formation of the Musgrave Province, and also the nature of the basement that separates these tectonic elements, allows for greater insight into defining the timing and processes responsible for the amalgamation of Proterozoic Australia. The ca. 1.60-1.54 Ga Musgravian Gneiss preserves geochemical and isotopic signatures related to ongoing arc-magmatism in an active margin between the North Australian and South Australian Cratons (NAC and SAC). Characteristic geochemical patterns of the Musgravian Gneiss include negative anomalies in Nb, Ti, and Y, and are accompanied by steep LREE patterns. Also characteristic of the Musgravian Gneiss is its juvenile Nd isotopic composition (ɛNd1.55 values from -1.2 to +0.9). The juvenile isotopic signature of the Musgravian Gneiss separates it from the bounding comparitively isotopically evolved terranes of the Arunta Region and Gawler Craton. The geochemical and isotopic signatures of these early Mesoproterozoic felsic rocks have similarities with island arc systems involving residual Ti-bearing minerals and garnet. Circa 1.40 Ga metasedimentary rocks of the eastern Musgrave Province also record vital evidence for determining Australia.s location and fit within a global plate reconstruction context during the late Mesoproterozoic. U-Pb detrital zircon and Sm-Nd isotopic data from these metasedimentary rocks suggests a component of derivation from sources outside of the presently exposed Australian crust. Best fit matches come from rocks originating from eastern Laurentia. Detrital zircon ages range from Palaeoproterozoic to late Mesoproterozoic, constraining the maximum depositional age of the metasediments to approximately 1.40 Ga, similar to that of the Belt Supergroup in western Laurentia. The 1.49-1.36 Ga detrital zircons in the Musgrave metasediments are interpreted to have been derived from the voluminous A-type suites of Laurentia, as this time period represents a “magmatic gap” in Australia, with an extreme paucity of sources this age recognized. The metasedimentary rocks exhibit a range of Nd isotopic signatures, with ɛNd(1.4 Ga) values ranging from -5.1 to 0.9, inconsistent with complete derivation from Australian sources, which are more isotopically evolved. The isotopically juvenile ca. 1.60-1.54 Ga Musgravian Gneiss is also an excellent candidate for the source of the abundant ca. 1.6-1.54 Ga detrital zircons within the lower sequences of the Belt Supergroup. If these interpretations are correct, they support a palaeogeographic reconstruction involving proximity of Australia and Laurentia during the pre-Rodinia Mesoproterozoic. This also increases the prospectivity of the eastern Musgrave Province to host a metamorphised equivalent of the massive Pb-Zn-Ag Sullivan deposit. The geochemical and isotopic signatures recorded in mafic-ultramafic rocks can divulge important information regarding the state of the sub continental lithospheric mantle (SCLM). The voluminous cumulate mafic-ultramafic rocks of the ca. 1.08 Ga Giles Complex record geochemical and Nd-Sr isotopic compositions consistent with an enriched parental magma. Traverses across three layered intrusions, the Kalka, Ewarara, and Gosse Pile were geochemically and isotopically analysed. Whole rock samples display variably depleted to enriched LREE patterns when normalised to chondrite ((La/Sm)N = 0.43-4.72). Clinopyroxene separates display similar depleted to enriched LREE patterns ((La/Sm)N = 0.37-7.33) relative to a chondritic source. The cumulate rocks display isotopically evolved signatures (ɛNd ~-1.0 to .5.0 and ɛSr ~19.0 to 85.0). Using simple bulk mixing and AFC equations, the Nd-Sr data of the more radiogenic samples can be modelled by addition of ~10% average Musgrave crust to a primitive picritic source, without need for an enriched mantle signature. Shallow decompressional melting of an asthenospheric plume source beneath thinned Musgravian lithosphere is envisaged as a source for the parental picritic magma. A model involving early crustal contamination within feeder zones is favoured, and consequently explorers looking for Ni-Cu-Co sulphides should concentrate on locating these feeder zones. Few absolute age constraints exist for the timing of the intracratonic Petermann Orogeny of the Musgrave Province. The Petermann Orogeny is responsible for much of the lithospheric architecture we see today within the Musgrave Province, uplifting and exhuming large parts along crustal scale E-W trending fault/shear systems. Isotopic and geochemical analysis of a suite of stratigraphic units within the Neoproterozoic to Cambrian Officer Basin to the immediate south indicate the development of a foreland architecture at ca. 600 Ma. An excursion in ɛNd values towards increasingly less negative values at this time is interpreted as representing a large influx of Musgrave derived sediments. Understanding the nature of the basement separating the SAC from the NAC and WAC is vital in constructing models of the amalgamation of Proterozoic Australia. This region is poorly understood as it is overlain by the thick sedimentary cover of the Officer Basin. However, the Coompana Block is one place where basement is shallow enough to be intersected in drillcore. The previously geochronologically, geochemically, and isotopically uncharacterised granitic gneiss of the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. U-Pb LA-ICPMS dating of magmatic zircons provides an age of ca. 1.50 Ga, interpreted as the crystallisation age of the granite protolith. The samples have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. ɛNd values are high with respect to surrounding exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The tectonic environment into which the granite was emplaced is also unclear, however one possibility is emplacement within an extensional environment represented by interlayered basalts and arenaceous sediments of the Coompana Block. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the “Australian magmatic gap” of ca. 1.52-1.35 Ga, and is a possible source for detrital ca. 1.50 zircons found within sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1261003
Thesis(PhD)-- University of Adelaide, School of Earth and Environmental Sciences, 2006

Gli stili APA, Harvard, Vancouver, ISO e altri

35

Hogan, Eric Gordon. "Sedimentologic and Stratigraphic Analysis of Units Defining the Basal Sauk Supersequence Across the Craton Margin Hinge Zone, Southeastern California". 2011. http://trace.tennessee.edu/utk_gradthes/880.

Testo completo

Abstract (sommario):

In the Death Valley and Mojave Desert regions of southeastern California, the contact separating the lower and middle members of the Wood Canyon Formation (WCF) is currently interpreted as a regional scale unconformity coincident with the base of the Sauk Sequence. Regional mapping of this surface, however, reveals a nonconformable contact with underlying crystalline basement in cratonic settings, and a relatively conformable contact atop a northwest thickening wedge of miogeoclinal strata that is capped by the lower member of the WCF. Consistent with an unconformity, the progressive loss of three carbonate units within the lower member of the WCF has been attributed to incision by the base of the middle member WCF. However, fossil evidence and correlation based on carbon isotope compositions of each lower member WCF dolostone units rejects top-down erosion to describe their loss and overall cratonward thinning. Results from multiple detailed, measured, stratigraphic sections of a conglomerate found at the base or low in the middle member WCF also do not support a top-down erosion model because the conglomerate has variable stratigraphic position and absence in some locations. Middle member WCF conglomerate clasts also reveal variation in composition and grain size across the regions. Sequence stratigraphic architecture indicates that filling of available accommodation space and short period normal regression, as opposed to a forced regression, are the causal mechanisms for formation of the basal middle member WCF unconformity, and that the base of the Sauk Sequence rests lower in the stratigraphic section.

Gli stili APA, Harvard, Vancouver, ISO e altri

36

Kamali, Mohammed Reza. "Sedimentology and petroleum geochemistry of the Ouldburra Formation, eastern Officer Basin, Australia / by Mohammad Reza Kamali". 1995. http://hdl.handle.net/2440/18732.

Testo completo

Abstract (sommario):

Copies of author's previously published works inserted.
Bibliography: leaves 153-165.
ix, 165, [153] leaves, [10] leaves of plates : ill. (chiefly col.), maps ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, National Centre for Petroleum Geology and Geophysics, 1996

Gli stili APA, Harvard, Vancouver, ISO e altri

37

Nedin, C. "The nature of the Precambrian-Cambrian transition in the northern Flinders Ranges, South Australia". Thesis, 1990. http://hdl.handle.net/2440/119917.

Testo completo

Abstract (sommario):

This item is only available electronically.
Previous investigations into the Ediacara Member of the late Proterozoic Rawnsley Quartzite in the Flinders Ranges have produced differing interpretations of the depositional environment. Studies at Nilpena Hills indicate that deposition was influenced by back barrier lagoonal conditions with the intermittent influx of fluidised sands which mantled lagoonal muds. Re-interpretation of the Ediacara assemblage shows a hitherto unrecognised benthonic bias. This abundance of sessile, benthonic forms supports a sub-tidal depositional environment. However, the increase in the numbers of motile forms compared with sessile forms, preserved towards the top of the member, accords well with one of two inferred shallowing upward cycles within the sequence. A recent re-evaluation of the nature of the Precambrian-Cambrian boundary in the Flinders Ranges suggests a conformable relationship between the Pound Subgroup and the overlying Early Cambrian beds. This is at odds with previous interpretations, which proposed that a regional disconformity occurs at the boundary. Mapping at Mt. Scott Range, Puttapa Syncline and Red Range provided ample evidence that several periods of at least partial lithification occurred within the Pound Subgroup, before the onset of Cambrian deposition. Erosive downcutting marks the contact of the Pound Subgroup-Uratanna Formation at Mt. Scott Range, Red Range and Puttapa Syncline. Erosive downcutting of the Parachilna Formation into the Uratanna Formation was mapped at Mt. Scott Range. The Pound Subgroup-Parachilna Formation contact was mapped as a disconformity which becomes a high angle unconformity near the Beltana Diapir.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 1990

Gli stili APA, Harvard, Vancouver, ISO e altri

Tesi sul tema "Geology, Stratigraphic Cambrian"

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili