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The stratigraphy of the late Precarnbrian upper Brachina Subgroup has been studied in detail throughout the southern and central Flinders Ranges of South Australia. Ten stratigraphically significant facies associations are readily recognisable within which 18 separate and distinct lithotypes have been defined and described. The complex regional strati - graphic arrangement has been simplified by using a Markov Chain technique of analysis. The resultant lithotype stratigraphy is used as the base upon which the palaeogeographic history of the upper Brachina Subgroup is reconstructed. A detailed sedimentologic analysis of each lithotype was undertaken in order to ascertain their individual palaeoenvironments of deposition. This involved a petrologic analysis of the arenaceous component of each lithotype, the analysis of the suite of sedimentary structures contained within each lithotype, and the analysis of all directional structures for palaeocurrent directions. For this latter analysis a new computer technique was developed whereby up to 3 individual populations can be separately analysed from any one distribution. Deposition of the upper Brachina Subgroup succession was due to a phase of uplift tectonism and minor accompanying basic volcanism. Within this succession two distinct depositional episodes are readily discernable. During the first episode a massive sand influx flowed from a westerly source region ( the Gawler Craton ) into a shallow submerged, though possibly tidally influenced mudflat as a prograding deltaic succession ( the " Alligator River Delta " ). This initial delta developed in the western region of the Adelaide ' Geosyncline ' as a fluvial and tide modified, wave dominated system which was fed by stable outlet channels, protected by barrier - bars and surrounded by a low intertidal aerobic mudflat. Preserved wi - bhin this mudflat deposit are the probable body fossils of primitive cup - shaped coelenterates ( ? ), which were possibly the ancestral organisms of the Ediacara assemblage. With, continued sediment influx and basin shallowing, this initial delta system evolved to an unbarred fluvial modified, tide - dominated delta which was fed by migrating channels and surrounded by an intertidal mudflat. This mudflat was anaerobic, possibly due to the activity of abundant microscopic organisms. The second depositional episode of the upper Brachina Subgroup developed when tectonic instability affected a portion of the basin's western margin ( Uplift I ). As a result, part of the previously deposited deltaic succession was eroded and reworked into a vast, thin intertidal sandflat which extended through the central region, and into the northern region of the Adelaide ' Geosyncline '. A second phase of tectonic instability ( Uplift II ) caused renewed activity along the basin ' s western margin, and also induced the emergence of at least two islands within the basin. Around these islands a thin, dominantly fluvial deposit was generated. The final phase of tectonic instability ( Uplift III ) affected only the western margin of the basin, and produced a narrow sand deposit of probable beach origin. Meanwhile, within the basin gradual subsidence induced the development of a shallow, possibly tidal aerobic mudflat and marked the end of the upper Brachina Subgroup phase of sedimentation. / Thesis (Ph.D.)--Department of Geology and Mineralogy, 1978.

During deposition of the mixed carbonate - clastic sequence of the Mundallio Subgroup, the " Adelaide Geosyncline " was a very shallow, elongate sedimentary basin, flanked to the west and east by older Precambrian basement. In much of the southern and northern Flinders Ranges, clastic deposition predominated in the lower Mundallio Subgroup. In the north, alternating development of shallow mudflats and sandflats ( Nankabunyana Formation ) depended on the interplay between the sediment supply and winnowing processes, while dolomite mudstones were locally deposited in the shallowest areas. In the eastern half of the Willouran Ranges, massive shales were deposited as the environment remained persistently below wave base ( Camel Flat Shale ), but a renewed sand influx led to deposition of the Tilterana Sandstone. In the southern Flinders Ranges, terrigenous clay and silt were deposited on submergent mudflats which shallowed into intermittently exposed dolomite mudflats ( Nathaltee Formation ). Dolomite mudflats were a more persistent feature in areas more distal from the terrigenous source, and sometimes contained isolated, ephemeral lakes which were sites of magnesite deposition ( Yadlamalka Formation ). Dolomite and magnesite mudstone deposition of the Yadlamalka Formation became wide spread in the northern and southern Flinders Ranges in the upper Mundallio Subgroup, as shallowing and retreat of the basin margin led to the formation of semi - isolated lakes, separated and enclosed by exposed carbonate mudflats. The elastics deposited in association with these carbonate mudstones consisted largely of sand sized detritus, probably derived from the reworking of aeolian deposits. In the eastern Willouran Ranges, the greater influx of sand and the slightly deeper, largely submergent environments, led to the deposition of the sandstones, dolomites and siltstones of the Mirra Formation. Because of little clastic influx into the northern Mt. Lofty Ranges, shallow to occasionally exposed environments were largely sites of dolomite deposition ( Skillogalee Dolomite ). To the south, shales were deposited in slightly deeper environments ( Woolshed Flat Shale ), although local dolomite deposition occurred in the Adelaide region ( Castambul Formation, Montacute Dolomite ). In the uppermost part of the subgroup, the area of shale deposition extended northward, encroaching over the dolomite mudflats of the upper Skillogalee Dolomite. Dolomite, occurring largely as mudstones, is the major carbonate mineral present in the Mundallio Subgroup, but magnesite is also widespread. Limestones are not present. The carbonates experienced minor replacement by early diagenetic chert, initially precipitated as both crystalline and amorphous phases. Within the upper Mundallio Subgroup, the preservation of fine details of the detrital texture of dolomite mudstones and peloidal dolomites, and the high Sr contents of dolomites ( largely in the range of 400 - 650 ppm ), suggest that these sediments consisted of Ca - Mg carbonates ( protodolomite, Mg - calcite ) at the time of deposition. Slightly greater recrystallisation of dolomites in the lower Mundallio Subgroup resulted in their lower Sr and higher Mn and Fe contents. Magnesite mudstones may have initially precipitated as hydrated Mg - carbonates. Lithification of surface sediments as a result of subaerial exposure, led to the formation of micritic magnesite. Much of this magnesite was subsequently reworked into intraclastic beds. The carbonate mineralogy of this sequence, and the evidence of only rare sulphates, indicate that the carbonates were precipitated from alkaline, Mg - Ca - C03 waters, with a higher carbonate and lower sulphate content than seawater. / Thesis (Ph.D.)--Department of Geology and Mineralogy, 1980.

8 fold. maps in end pocket of v.2 Includes bibliographical references (p. 227-234)

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