PROBLEMATIC MICROFOSSILS FROM THE LOWER KARROO BEDS IN SOUTH AFRICA
Date
1973
Authors
McLachlan, I. R.
Journal Title
Journal ISSN
Volume Title
Publisher
BERNARD PRICE INSTITUTE FOR PALAEONTOLOGICAL RESEARCH
Abstract
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.