Volume 15 1973

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Browsing Volume 15 1973 by Author "McLachlan, I. R."

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    PROBLEMATIC MICROFOSSILS FROM THE LOWER KARROO BEDS IN SOUTH AFRICA
    (BERNARD PRICE INSTITUTE FOR PALAEONTOLOGICAL RESEARCH, 1973) McLachlan, I. R.
    A problematic group of microfossils has recently been recovered from strata of Permian age, in the northern part of the Karroo basin in South Africa. This article attempts to present the information that is presently known about them. They have been found in a wide variety of sediments in the Lower, Middle and Upper Ecca stages, and in carbonaceous sediments in the lower part of the Beaufort series. The external morphology of the microfossils is extremely varied, but they are characterized by a regular cup-shaped organ. They closely resemble forms called Anellotubulata by O. Wetzel (1959), who described them from the Upper Lias (c) of Germany. Other workers have recovered, but not described, similar microfossils from Permian, Triassic and Cretaceous strata in Australia. In this paper, the microfossils are referred to as anellotubulates. They are remarkable in a number of respects, the most extraordinary of which is their composition. Electron-microprobe and X-ray diffraction tests have shown the shell to consist of a non-crystalline mineral or minerals, composed mainly of iron and phosphorus, with minor calcium. It has not been possible to demonstrate clearly whether this is the original shell composition, or whether it has resulted from replacement. The available information, including that provided by associated fossils, which has bearing on the palaeoenvironment of the anellotubulates, is discussed. It is hoped that, when more information is available, these problematic microfossils will contribute towards a better understanding of the depositional environment of the sediments in which they occur.
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    A REVIEW OF THE EVIDENCE FOR MARINE CONDITIONS IN SOUTHERN AFRICA DURING DWYKA TIMES
    (BERNARD PRICE INSTITUTE FOR PALAEONTOLOGICAL RESEARCH, 1973) McLachlan, I. R.; Anderson, Ann
    The faunas of the three major Dwyka basins in southern Africa are listed in the form of tables. Marine invertebrates have been recorded from the western part of the Kalahari basin and from the Warmbad basin, but had not previously been confirmed within the Great Karroo basin. A new fauna from the base of the Upper Dwyka shales near Kimberley is described. Cephalopods, brachiopods and lamellibranchs are found in calcareous concretions, which also contain palaeoniscoid fish, coprolites, fossil wood and the mineral glauberite. The marine invasion into South West Africa postulated by Martin & Wilczewski (1970) therefore extended into the Great Karroo basin as well. By the time of accumulation of the White Band at the top of the Upper Dwyka shales, conditions were probably non-marine; with the possible exception of the Notocarid crustaceans, the White Band fossils are not, in themselves, indicative of marine conditions. The only other significant indication of marine conditions in the Great Karroo basin is the glauconite in the deltaic Coal Measures of the Ecca in the northern part of the basin. It is possible then that the fossiliferous marine shales near Kimberley accumulated as a fine-grained offshore facies of the Ecca deltaic sequence.