No description available.

The Denault Formation (2.1-1.9 Ga) outcrops in the Labrador Trough, northeastern Quebec and western Labrador. The Denault crops out around the town of Schefferville and at Marion Lake, fifty kilometers east-northeast of Schefferville. In June 2007, four stratigraphic sections were measured and samples were collected from eight locations. Occurrences of the Denault near the town of Schefferville contain textural characteristics consistent with deposition on the middle and outer portions of a storm-influenced shallow ramp. Mid-ramp facies consist of intraclastic grainstones with hummocky cross-stratification (HCS), swaley cross-stratification (SCS), current ripples, and graded event beds. Further outboard, grainstones grade into deeper water laminites that are composed of even, mm-scale couplets of flat-lying organic and micritic laminae. Scours within the laminites suggest occasional storm activity. Laminites gradually grade into outer ramp deep-water shales. Separated from these ramp facies by 50km (present day) is an isolated eastern stromatolitic accumulation. This outcrop can be interpreted as the remnant of a near-continuous margin or may simply represent an isolated accumulation that developed on a pre-existing topographic high. Microscopic (2-10µm) lathes of dolomite are interpreted to be pseudomorphs after gypsum. The presence of such pseudomorphs and solution-collapse breccias provide evidence for evaporative conditions during the deposition and early diagenesis of the Denault. Seepage-reflux of brines generated through evaporation during the deposition of the Denault and the overlying Fleming Formation are interpreted to have caused early, mimetic dolomitization in a shallow burial setting. Subsequent burial diagenesis resulted in recrystallization of some rock to fabric-destructive, anhedral dolomite. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2009-01-07 15:09:43.994

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No description available.

A Dissertation Submitted tc the Faculty of Science, University of the Witwatersrand, Johannesburg, for the degree of Doctor of Philosophy. Johannesburg 1981 / An area of about 200 'sq km has been mapped at a scale of 1 : 25 000 between Messina and Tshipise. Subsequent laboratory work has included petrographic, whole-rock and mineral analysis in order to describe the Precambrian rock-types and lithologies, their structure, and their metomorphic history. The Precambrian lithologies underlying the study area consist of grey banded basement gneisses of granodioritic composition, together with a large variety of supracrustal rocktypes. These include quartzo-feldspathic gneiss, Singeleletype granitoid gneiss, garnet-cordierite-sillimunite gneiss, sapphirine-bearing rock, garnet-orthopyroxene-plagioclase symplectite, pyroxenitic amphibolite, quartzite, banded magnetite quartzite, amphibolite, calc-silicate gneiss and marble. These supracrustal rocks may belong to a geosynclinal-type series of depv .» Led or extruded lithologies. Intrusive rocks of the Messina Layered Intrusion consist of gabbroic and anorthositic gneiss. Metapyroxenites and serpentinites also occur. Both ancient deformed and you ger fabric-free mafic dykes transect this stratigraphy. Polyphase deformation has produced complex and intense folding of the area. Early isoclinal and ductile folds, now manifest as tight intrafolial folds, have been refolded around later structures. Most fold hinges plunge moderately to the south-west. Considerable flattening, attenuation and alongstrike boudinaging of the units occurs in the region, probably as a result of regional simple shear The assymetry of the folds in the region suggest that this simple shear was left lateral. Peorce-type variation diagrams for data from the Messina Layered Intrusion show plagioclase fractionation trends, and support the argument that these rocks are of plutonic igneous origin. The anorthcsites were the earliest cumulates, with the gabbros forming by subsequent fractionation. Rayleigh's law indicates that about 70 per cent fractionation has occurred in these rocks. The parental liquid appears to have been anomalously enriched in rubidium. The supracrustal units have experienced a high-grade metamorphism between about 3 100 m.y. ago and 2 400 m.y. ago. The P-T conditions for this metamorphism range from about 9 kbar and 900 C at the 'peak' of the metamorphism, to about 4 kbar and 650°C, and thus represents a retrogression within the field of medium pressure granulites. Earlier high-pressure granulite metamorphism is indicated by assemblages reported from other regions in t.ie Central Zone of the Limpopo Mobile Belt. These data suggest that the supracrustal rocks were subjected to burial into regions of the lower crust up to 40 km depth, and geothermal gradients between 15°C/km and 35°C/km were experienced. Water activities were low durin.j this high-grade metoeorphism, with water making up not more than 10 per cent of the fluid present during this event. The onset of relative tectonic stability and the end of high-grade metamorphism was achieved by about 2 200 m.y. 0go.

Precambrian stromatolites in South Australia are almost entirely restricted to the folded rock sequence of the Adelaide Geosyncline, a large, deeply subsiding basin with predominantly shallow - water sediments. The history of research into the age and fossils of the Precambrian rocks is reviewed, and a possible time - framework is suggested on the basis of available radiometric data. Stromatolites, laminated structures formed by trapping of detritus and precipitation of chemical sediment by algae and bacteria, have been studied by other workers from at least two points of views : most Western authors regard stromatolite morphology to be purely environmentally determined, while one Russian school maintains that it is largely controlled by the algae present, and that stromatolites evolve as a consequence of the evolution of the algae forming them. They concluded this from an empirical study of widespread stromatolites of different ages, which made possible the biostratigraphic subdivision and correlation of many Late Precambrian sections. The Russian methods of study and taxonomy have now been applied to South Australian stromatolites for the first time. Of the eighteen forms of columnar stromatolites described, five are identical or nearly identical to Russian forms. Nine forms are new, but sufficiently similar to Russia forms to allow inclusion in the same groups as these. Groups and forms must be defined on the basis of numerous characters, which may be given different relative weighting for different taxa. The taxa so defined have restricted ranges in geological time. Stromatolite correlation with the Russian sequence suggests that the Early Adelaidean ( i.e. pre - tillite ) beds are middle Riphean ; the Skillogalee Dolomite is youngest middle Riphean, i.e. older than the Late Riphean Bitter Springs Formation of Central Australia. The Late Adelaidean Umberatana Group assemblage, correlated with the youngest Late Riphean, has seven groups in common with the Bitter Springs Formation, but unlike the latter, it overlies the lower tillite. A comparison with available radiometric data shouts good agreement for the Umberatana Group, but some conflict with one recent age determination exists for the Early Adelaidean. A study of the environments of growth of South Australian stromatolites shows that at least three forms, of widespread distribution, grew under a variety of conditions of energy, oxidation, type of sediment influx, and possibly salinity. The taxa defined are stable under these varying conditions, but there are minor modifications due to differences in environmental energy. Skillogalee Dolomite stromatolites grew under varying energy conditions on a very extensive and level carbonate depositing platform, frequently under hypersaline conditions. Umberatana Group stromatolites inhabited a marine environment, either in marginal littoral zones in the south - western and north - eastern Flinders Ranges, or on off - shore carbonate banks interpreted to be related to rising diapirs. In both cases, stromatolites formed during episodes of shallowing water depth. / Thesis (Ph.D.)--Department of Geology and Mineralogy, 1971.

Samples from more than two hundred and twenty wells penetrating basement rock have been examined and described from a 61,000 square mile area in adjoining parts of Oklahoma, Kansas, Missouri, and Arkansas. Twenty-five isotopic age determinations were made on twenty samples of basement rock from wells and outcrop areas. Nine basement rock units can be defined within the study area on the basis of petrography and isotopic age. 1. "Older granite and gneiss" is a loose association of granitic rocks considered to be older than 1400 million years. The unit cannot be precisely defined within the study area. 2. The Lyon County Quartzite is a micaceous quartzite restricted to relatively small areas in the buried basement of Kansas. The age of deposition is unknown but preceded the 1400 million year age of metamorphism. 3. The Chase County Granite Group is composed largely of granite and gneissic granite. Rocks of this group underlie most of the Nemaha Uplift in Kansas and also occur considerably east and west of the Uplift. The rocks were intruded at about 1400 million years, probably as a composite batholith. At about 1200 million years, four petrographically related rock units were intruded or extruded. The age difference between these units cannot be distinguished by isotopic ages. The four units are assembled into the Northeast Oklahoma Province, a petrographic grouping of volcanic rocks and chemically equivalent hypersolvus type epizone granites. 4. The Washington County Volcanic Group is composed mostly of rhyolite but also contains andesite and metarhyolite. The majority of the rhyolites were probably extruded as welded tuffs. 5. The Spavinaw Granite Group is composed of generally micrographic granite porphyries. The intrusions are considered to be largely sills on textural evidence and by analogy with outcrop areas elsewhere. 6. The Woodson County Granite is texturally variable. Samples from drill holes in Kansas are petrographically identical to boulders found at Rose Dome in Woodson County, Kansas. 7. The Osage County Microgranite is the most uniform unit in the area. The microgranite occurs in a roughly circular area in Osage County, Oklahoma. The unit was probably intruded as a sill within rhyolite flows. Two other petrographic units are interpreted as being younger than parts of the Northeast Oklahoma Province, although in the same 1200 million years isotopic age range. 8. The Vernon County Metamorphic Group is composed mostly of low rank metamorphic rocks derived from clastic sediments. The grade of metamorphism is from incipient to middle greenschist facies. Rhyolite detritus occurs in some samples. 9. The Central Oklahoma Granite Group is composed of two feldspar mesozone type granites. The unit is not distinguishable from the Chase County Granite Group on the basis of petrography. Uplift and erosion followed the intrusion of the Central Oklahoma Granite Group. The main uplifts were along the present Nemaha Uplift and along a northeast-southwest axis from southwest Missouri to central Oklahoma. There is no evidence for any igneous or metamorphic activity between 1200 million years and the deposition of lower Paleozoic sediments. / text

2 v. : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Mineralogy, 1971

Precambrian stromatolites in South Australia are almost entirely restricted to the folded rock sequence of the Adelaide Geosyncline, a large, deeply subsiding basin with predominantly shallow - water sediments. The history of research into the age and fossils of the Precambrian rocks is reviewed, and a possible time - framework is suggested on the basis of available radiometric data. Stromatolites, laminated structures formed by trapping of detritus and precipitation of chemical sediment by algae and bacteria, have been studied by other workers from at least two points of views : most Western authors regard stromatolite morphology to be purely environmentally determined, while one Russian school maintains that it is largely controlled by the algae present, and that stromatolites evolve as a consequence of the evolution of the algae forming them. They concluded this from an empirical study of widespread stromatolites of different ages, which made possible the biostratigraphic subdivision and correlation of many Late Precambrian sections. The Russian methods of study and taxonomy have now been applied to South Australian stromatolites for the first time. Of the eighteen forms of columnar stromatolites described, five are identical or nearly identical to Russian forms. Nine forms are new, but sufficiently similar to Russia forms to allow inclusion in the same groups as these. Groups and forms must be defined on the basis of numerous characters, which may be given different relative weighting for different taxa. The taxa so defined have restricted ranges in geological time. Stromatolite correlation with the Russian sequence suggests that the Early Adelaidean ( i.e. pre - tillite ) beds are middle Riphean ; the Skillogalee Dolomite is youngest middle Riphean, i.e. older than the Late Riphean Bitter Springs Formation of Central Australia. The Late Adelaidean Umberatana Group assemblage, correlated with the youngest Late Riphean, has seven groups in common with the Bitter Springs Formation, but unlike the latter, it overlies the lower tillite. A comparison with available radiometric data shouts good agreement for the Umberatana Group, but some conflict with one recent age determination exists for the Early Adelaidean. A study of the environments of growth of South Australian stromatolites shows that at least three forms, of widespread distribution, grew under a variety of conditions of energy, oxidation, type of sediment influx, and possibly salinity. The taxa defined are stable under these varying conditions, but there are minor modifications due to differences in environmental energy. Skillogalee Dolomite stromatolites grew under varying energy conditions on a very extensive and level carbonate depositing platform, frequently under hypersaline conditions. Umberatana Group stromatolites inhabited a marine environment, either in marginal littoral zones in the south - western and north - eastern Flinders Ranges, or on off - shore carbonate banks interpreted to be related to rising diapirs. In both cases, stromatolites formed during episodes of shallowing water depth. / Thesis (Ph.D.)--Department of Geology and Mineralogy, 1971.

No abstract included. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate