Sedimentology and taphonomy of cenozoic vertebrates from Langebaanweg, Cape West Coast, South Africa; with palaeoecological interpretations

Doctoral Thesis


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University of Cape Town

The fossil locality Langebaanweg, is world renowned for its vast abundance and diversity of fauna. Langebaanweg is the only fossil site in South Africa that preserves remains from the Late Miocene to Early Pliocene. The Mio-Pliocene is a period of major climatic change, with global temperatures falling, and increased aridity and seasonality across the African continent. Langebaanweg, located on the coastal platform of Southern Africa, is ideally placed to investigate how these major changes in climatic conditions in the Mio-Pliocene affected ecology, environment and animals in south-western Africa. The majority of fossils from Langebaanweg were recovered from the early Pliocene Varswater Formation. Specifically, the two major fossil bearing horizons, the Langeberg Quartz Sand Member (LQSM) and the overlying Muishond Fontein Pelletal Phophorite Member (MPPM). The Varswater Formation has been reconstructed as a fluvio-estuarine environment with localised tidal-flats and marshes. The relationship between the MPPM and the LQSM and their relative ages and depositional environments is controversial. This thesis sought to investigate the depositional environment of the MPPM and LQSM in Langebaanweg E-Quarry, with the aim of identifying the relationship and comparative ages of the two members. In order to investigate this, three test pits were excavated at Langebaanweg and the lithology, sedimentology and taphonomy of remains recovered from the test pits was studied. The test pits were located in the sivathere bonebed, the 1976/2 excavation and in a new locality positioned 200 m to the south of the 1976/2 excavation. The depositional environment of the bonebed and 1976/2 were investigated as well as their relationship to each other. The taphonomic pathways by which bones came to be interred in each test pit was identified. Sedimentologically, the MPPM and LQSM were found to be almost identical and the only major distinguishing characteristic was the lack of phosphate in the latter deposit. This indicates that the two horizons were deposited in the same setting and/or by the same depositional process. Additionally the MPPM and LQSM sediments were dominated by fine to very fine sand grains and muds and silts were virtually absent (except in the MPPM in one test pit). This, together with the texture of the sediments, lead to the conclusion that the MPPM and LQSM, in Langebaanweg EQuarry, had a marine origin. Langebaanweg E-Quarry is here interpreted as a barrier-island estuary formed on a wave-dominated coast. Given the consistency of sediments, taxa and taphonomic characters between the MPPM and the LQSM they are interpreted as representing a single unit or depositional event where the upper parts (MPPM) have been secondarily phosphatised. Under this scenario, there is no unconformity or age gap between the MPPM and the LQSM. Investigations of the depositional environment of the 1976/2 excavation concur with Hendey's (1980) reconstructions for a river channel. The results of this study reject previous reconstructions of the sivathere bonebed as a lag deposit of a river channel (Roberts et al. 2011; Smith & Haarhoff 2006). This study shows that the bonebed was deposited in a low energy freshwater pool associated with the river. No evidence was found for an aquifer-fed spring as suggested by Brumfitt et al. (2013). The MPPM sediments of the test pit located to the south of 1976/2 displayed a dominance of fine muds and silts with a possible high organic content. This was interpreted as a possible marsh habitat. This is the first study to identify a marsh environment at Langebaanweg since the 1980's and all other examples of this type of environment have been destroyed by mining. The identification of this locality will provide exciting new opportunities for future research. Taphonomic analysis has shown that the influence of fire and predation on faunal remains excavated in this study was small and internment in all cases was quick. As a final note, this thesis conducted a review of previous research and excavations at Langebaanweg E-Quarry by Dr Brett Hendey and identified the location of some fossil collecting localities that had been lost. These were plotted onto aerial photographs, which will be beneficial to future researchers trying to identify old locals or identify new deposits.