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

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No description available.

No description available.

Bibliography: pages 346-370. / A regional study of highly metamorphosed supracrustal rocks was undertaken in the western portions of the Namaqualand Metamorphic Complex. The study area was essentially restricted to a north-south section some 50 kilometres wide and 220 kilometres long. Eight east-west-trending belts of supracrustal rocks were examined, together with several smaller paragneiss remnants, in an area dominated by quartzo-feldspathic gneisses of granitic composition. The supracrustal rocks were classified into seven major lithological groups: quartzitic rocks, metapelitic and metapsammitic rocks, quartzo feldspathic rocks, metabasites, metacarbonate rocks, magnesium-rich cordierite rocks and iron formations. Further subdivision, based on variations in mineral constituents within each group, also occurred, as well as the presence of lithologies with compositions transitional between certain groups. The various supracrustal sequences were subdivided into formations containing minor distinctive members on an informal lithostratigraphic basis. Correlation between the major supracrustal belts was then undertaken. Four subgroups were identified across the study area, comprising a quartzo feldspathic gneiss subgroup and an overlying feldspathic quartzite/garnetcordierite gneiss subgroup that both predominate in the southern and central part of the area, a glassy quartzite/mica- sillimanite schist subgroup that predominates in the northern part, and a cordierite gneiss/metacarbonate subgroup that is restricted to the Geselskapbank synform. The supracrustal rocks appear to have been emplaced on a basement of augen gneisses. This relationship is, however, complicated by the intrusion of granit i c rocks within the contact zone.

No description available.