INVERTEBRATE AND PLANT TRACE FOSSILS FROM THE TERRESTRIAL LATE TRIASSIC OF ZIMBABWE

Abstract

ABSTRACT Late Triassic invertebrate and plant trace fossils are described from the Pebbly Arkose Formation of the Upper Karoo Group (Gwembe Sub-basin, Mid-Zambezi Basin), Zimbabwe. These ichnofossils appear in pedogenically modified siltstone and silty mudstone floodplain deposits and overbank fluvial channels. The ichnofossil-bearing sites show variability in their pedogenic features, maturity and preservation. Invertebrate ichnofossils are primarily recorded as horizontal, vertical and inclined burrows, sometimes branched, lined or unlined and may have an active meniscate infill. The common forms documented are Taenidium, Beaconites, Palaeophycus, Skolithos, and Planolites ispp. with some rare and more unusual morphologies (i.e., ‘Y’-shaped burrow type). Ichnofossil-bearing sites show a low-diversity but high-density of traces commonly dominated by Taenidium and Planolites ispp. The greatest diversity of invertebrate ichnofossils are within interbedded overbank sandstones in weakly pedogenically modified overbank sites. Rhizohalos and rhizoliths are common and often include carbonate infilled roots. Given the abundance and dimensions of fossilized wood and the rhizohalos and rhizoliths, the Pebbly Arkose Formation supported both large and small stature plants. Overall, the studied Pebbly Arkose Formation overbank areas are typically well-drained, calcic palaeosols subject to variable discharge, subaerial exposure, and supporting a diversity of plant and invertebrates tracemakers that lived in a semi-arid to sub-humid environment.