Lithostratigraphic revision and correlation of the Oligo‐Miocene Murray Supergroup,Western Murray Basin,South Australia

The Murray Basin in southeastern Australia is a large, shallow, intracratonic basin filled with laterally extensive, undeformed, Cenozoic carbonate and terrigenous clastic sedimentary rocks that constitute regional and locally important groundwater aquifers. The marine Oligo‐Miocene strata distributed throughout the southwestern portion of the basin are here encompassed within the Murray Supergroup. The Murray Supergroup (formerly Murray Group) incorporates the marginal marine marl and clay of the Ettrick Formation, Winnambool Formation and Geera Clay in the western and northern portions of the Murray Basin in South Australia, in addition to the limestone that outcrops along the banks of the River Murray in nearly continuous section for 175 km. The stratigraphic nomenclature of these rocks is revised as follows. The boundary between the lower and upper members of the Mannum Formation is redefined and a new Swan Reach Dolomite Member is erected. The Finniss Clay is revised to Finniss Formation possessing three new members: the Cowirra Clay Member, Portee Carbonate Member and Woolpunda Marl Member. The ‘Morgan Limestone’ is raised to Morgan Group and contains three new formations: the Glenforslan Formation, Cadell Formation (with Murbko Marl Member and Overland Corner Clay Member) and Bryant Creek Formation. The Pata Formation is redefined and described. Type and reference sections are erected for each new and revised unit, and are lithostratigraphically correlated to illustrate their stratigraphic architecture.     

Mineralogical characteristics and mineral economics of kaolinite deposit of Sawa area,Chittaurgarh, Rajasthan

A large deposit of low-grade kaolinite is occurring within the rocks of Lower Vindhyan Supergroup southwest of Chittaurgarh, Rajasthan. The deposit is being utilised by open-cast, manual to semi-mechanised methods of mining. Kaolinite produced is being marketed without processing. Earlier, nearly 60% of the kaolinite produced from the area was consumed by cement industries, but in recent past, utilisation of low-grade kaolinite has been minimised by cement industries in production of ordinary cement and hence its production has significantly declined. Mineralogical studies reveal that kaolinite is the main clay-mineral and quartz, calcite, iron-oxides and biotite are present as non-clay minerals in clay deposit of the area. Chemical analysis of the kaolinite show that alumina ranges from 15 to 35% while, silica and iron varies from 51 to 78% and 0.25 to 2.50% respectively.     

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

The sparse Archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post-mortem silicification. Hitherto as an exception, sedimentary carbonate rocks from the Neoarchean Nauga Formation of South Africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria (Chroococcales and Pleurocapsales). Their remains, visible under the scanning electron microscope (SEM) after etching of polished rock samples, comprise capsular envelopes, mucilage sheaths, and groups of cells mineralized by calcium carbonate with an admixture of Al–K–Mg–Fe silicates. The capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the Neoarchean microbiota described and their modern analogues. The new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the Neoarchean, and offer a solution to the problem of the origin of Archean carbonate platforms, stromatolites and microbial reefs.     

Geochemistry of sericite deposits at the base of the paleoproterozoic aravalli supergroup, Rajasthan, India: Evidence for metamorphosed and metasomatised precambrian paleosol

Fine grained sericite deposits occur at the interface between Archean Mewar Gneiss Complex and the Proterozoic Aravalli Supergroup independent of shearing. They show a gradational contact with the basement granites and gneisses and a sharp contact with the overlying quartz pebble conglomeratic quartzites. Rip-up clasts of these sericite schists are found in the overlying conglomerates. The sericite schists are rich in sericite towards the top and contain chlorite towards the base. The sericite in these schists was formed by metasomatic alteration of kyanite and not from the feldspars of the basement granitoids and gneisses. Uni-directional variations of SiO₂ and Al₂O₃, high Al₂O₃ content (>30%), positive correlation between Al₂O₃ and TiO₂, Ti/Al and Ti/Zr ratios, high pre-metasomatic chemical indices of alteration (> 90), and enrichment of heavy rare earth elements relative to the parent granites and gneisses—all these chemical characteristics combined with field evidence suggest that the sericite schists are formed from a paleosol protolith, which developed on Archean basement between 2.5 and ~2.1 Ga in the Precambrian of Rajasthan. The superimposed metasomatic alteration restricts the use of Fe²⁺/Ti and Fe³⁺/Ti ratios of these paleosols for interpretation of PO₂ conditions in the atmosphere.     

Paleomagnetic Constraints on the Permian-Triassic Boundary in Terrestrial Strata of the Karoo Supergroup, South Africa: Implications for Causes of the End-Permian Extinction Event

The closure of the Palaeozoic witnessed the greatest biotic crisis in earth history. Surprisingly little is known about the effects and timing of the terrestrial counterpart of the well-described End-Permian mass extinction from known marine successions worldwide. In the present study, reliable paleomagnetic results were obtained from a PT boundary section in the terrestrial Karoo Basin of South Africa. Permo-Triassic aged mudstones from a locality in the Eastern Cape Province yielded two magnetic chrons, reverse followed by normal (with the boundary possibly close to the reversal). This extends to results from a previous study: thereby jointly identifying a R/N/R polarity pattern for this boundary interval. The PTB interval is constrained below the red mudstones of the Beaufort Group at the present locality and within reverse-magnetised green mudstone, implying a diachronic relation between the marine and terrestrial End-Permian mass extinction events.     

Newly Discovered Fish Faunas from the Early Triassic, Karoo Basin, South Africa, and their Correlative Implications

Recent collecting in exposures of the lowermost Burgersdorp Formation (Beaufort Group), of the Karoo Basin of South Africa, has revealed a previously unknown fish fauna from the Early Triassic (Scythian), lowermost Cynognathus Assemblage Zone (CAZ), which forms an important component of the total vertebrate assemblage. The newly discovered fish material includes lungfish, saurichthyids, and a large microfauna that includes numerous isolated chondrichthyan teeth, two fin spine fragments, and actinopterygian scales and teeth. The latest fish finds, together with the lowermost Cynognathus Assemblage Zone vertebrate faunas, make this Karoo Basin Assemblage Zone one of the most diverse Early Triassic faunal assemblages, comparable in faunal diversity to those from the Czatkowice Formation (Poland) and the Arcadia Formation (Australia). The presence of the lungfish Ptychoceratodus phillipsi in the early Middle Triassic Cynognathus Assemblage Zone (Subzone B), and in the underlying latest Early Triassic Cynognathus Assemblage Zone (Subzone A), indicates that these lungfish could serve as range index fossils within the CAZ, and thus are potentially useful biostratigraphic markers across the Early-Middle Triassic boundary. Furthermore the ‘new’ fish fauna provides a vital marine realm link in particular with the faunas of Madagascar and Australia, that is unavailable using the tetrapod faunal elements of the lower CAZ.     

Provenance ages of the Neoproterozoic Katanga Supergroup (Central African Copperbelt), with implications for basin evolution

New age data on detrital zircons and micas are presented from key units within the Neoproterozoic Katanga Supergroup, which hosts the major stratiform Cu–Co deposits of the Central African Copperbelt. Detrital zircon ages indicate a mainly Palaeoproterozoic (between 2081 ± 28 and 1836 ± 26 Ma) provenance for the Katanga basin, derived from the Lufubu Metamorphic Complex of the Kafue Anticline and the Bangweulu Block to the north of the outcrop belt. Detrital zircons and clasts from the Grand Conglomerat glacial diamictite indicate a source from the Palaeoproterozoic metavolcanic porphyries and granitoids of Luina Dome region, which was a basement high during Nguba Group deposition. Minor zircons of Mesoproterozoic age may have been derived from the Kibaran belt. Finally, ⁴⁰Ar/³⁹Ar age data from detrital muscovites from Biano Group siltstones give a maximum age of sedimentation of 573 Ma, strongly supporting previous models that the Biano Group was deposited in a foreland basin of the Lufilian Orogen.     

Ant composition and activity patterns as determined by pitfall trapping and other methods in three habitats in the semi-arid Karoo

The diversity and abundance of epigaeic ant species were determined across three habitats (riverine areas, gently sloping grassland areas and steep slope areas) in summer (November–December) and winter (May–June) of 1998 at Tussen die Riviere Nature Reserve in the Karoo, to determine temporal and spatial variations in the availability of potential prey species of the aardvark (Orycteropus afer). Pitfall trapping, dig sampling and quadrat sampling were used to ensure as complete a sampling effort as possible. Forty-five ant species of five sub-families and 17 genera were recorded. The grassland habitat yielded the highest abundance and diversity, followed by the steep slope and riverine areas. Ant abundance and diversity were higher during summer than winter in all three habitats. Anoplolepis custodiens was the most abundant species in summer, whilst Monomorium albopilosum was the most abundant species in winter. Pitfall trapping was responsible for recording more species than dig sampling or quadrat sampling. No method recorded all of the species present.     

Age of the Vindhyan Supergroup: A review of recent findings

The Vindhyan Supergroup of India is one of the largest and thickest sedimentary successions of the world. Deposited in an intra-cratonic basin, it is composed mostly of shallow marine deposits. It is believed to have recorded a substantial portion of Proterozoic time and therefore, likely to contain valuable information on the evolution of the atmosphere, climate, and life on our planet. It also contains some of the most disputed fossils of earliest animal life. Despite their importance, the absolute age of these rocks had remained unknown until recently. In this work I evaluate all the recent chronological information and discuss their implications. From the present findings it appears that the issues surrounding the age of the Lower Vindhyans in the Son valley are now resolved, whereas problems with the age of the Upper Vindhyans and that with the stratigraphic correlations remain to be answered.     

Chuaria circularis from the early Mesoproterozoic Suket Shale, Vindhyan Supergroup, India: Insights from light and electron microscopy and pyrolysis-gas chromatography

Chuaria circularis (Walcott 1899) from the Suket Shale of the Vindhyan Supergroup (central India) has been reinvestigated for its morphology and chemical composition using biostatistics, electron microscopy and pyrolysis-gas chromatography. Morphology and microscopic investigations provide little clues on the specific biological affinity ofChuaria as numerous preservational artifacts seem to be incorporated. On the contrary, the predominance of η aliphatic pyrolysates of presently studiedChuaria from India rather supports an algal affinity. Moreover, the reflectance ofC circularis can be used to obtain a comparative maturity parameter of the Precambrian sediments. The review of the age and geographical distribution ofC circularis constrains that this species cannot be considered as an index fossil for the Proterozoic time.