Herries_Kromdraai_geo micromorphology

Kromdraai is the type site of Paranthropus robustus, the first fossil of which was found in 1938 from what is now known as the Holotype Block. The site was more systematically excavated in the 1950s, 19702 and since the 1990s. Despite this, the age of the site remains unknown beyond estimates from biochronology and a preliminary palaeomagnetic study in the early 2000s. This palaeomagnetic study was only conducted on a small number of samples from a restricted area of the site in and around where the type specimen was recovered. Since this time extensive new deposits have been uncovered at Kromdraai, with a complete reanalysis of the stratigraphy of the classic southern wall deposits. A recent analysis of where the original palaeomagnetic samples have come from, along with a preliminary in situ analysis of the stratigraphy indicate that the results and conclusions of this original study maybe flawed. Firstly, it is clear that reversed polarity samples KBM7 and KBM8 come from a speleothem that was heavily eroded and truncated before the deposition of apparently overlying normal polarity sediments (KRM6). It is likely that a significant time gap occurs between these two units. Secondly, an apparent reversal from normal to reversed polarity in sample KBM2 that was used to suggest the occurrence of the end of the Olduvai SubChron at 1.78 Ma is only seen in a single sample from the Type site block area of the site. To confirm the presence of such a reversal more than a single sample is needed. Moreover, an analysis of the sample location suggests that this apparent reversal might be instead related to the core intersecting more than 1 deposit, one of which may actually be an eroded block within the sequence. Such reworked Brecia blocks are commonly seen throughout these deposits and have in the past been misinterpreted as a separate in situ unit. To fully understand the nature of this reworked material and to confirm recent stratigraphic analysis we aim to conduct micromorphological analysis across the site to better characterize the sedimentary sequence and formational history and to make sure that similar misinterpretations of the sequence and palaeomagnetic analysis do not occur. This, along with other analysis being conducted (Palaeomagnetism, uranium series dating, cosmogenic nuclide burial dating, electron spin resonance, luminescence) will provide the first comprehensive age for the southern wall deposits and Type specimen.

In addition to a focus on the classic southern wall deposits at Kromdraai, including the Holotype Block, we have also taken samples from more recently exposed northern deposits. This includes an extensive series of siltstone and sandstone deposits on the eastern side of the site and at a similar level to the Holotype Block. This also includes the newly discovered Units O and P from the centre of the site, including a large in situ stalagmite that may have formed on Unit O and been covered by Unit P. Again, all the above stated methods will be conducted on these deposits and blocks to establish the nature of the stratigraphic sequence and its age. In particular we aim to establish the age of the stalagmite itself as this is a key marked in the sequence as well as establish the relationship between calcified deposits under and overlying the stalagmite and decalcified bone bearing breccia that fills much of the centre of the site. Furthermore, we want to establish the age and relationship of a series of speleothems that are associated with a heavily calcified breccia deposit that has yielded a new hominin cranium KW11000.

For all this to be a success micromorphological analysis is critical to understanding the relationships of the various deposits at the site (speleothem, sandstones and siltstones, breccia). We have taken samples from contact points between these different units to help understand the stratigraphic relationships. This will enable us to determine the formational history and sequencing of the deposits (i.e did sediments form over or under flowstones, or whether older deposits have been reworked). Such issues have been a significant source of debate at other sites in the region, like Sterkfontein, where stratigraphic studies have focused only on in situ stratigraphic descriptions, and no thin section analysis has been undertaken to confirm the suggested relationships of different deposits. It is critical to know the relationship of material being dated, e.g. flowstones, to the fossils we want to know the age of.


Methodology (short):

Micromorphology will be conducted on the block samples so that specific stratigraphic features can be identified. The blocks will be resin impregnated and then cut into thin section slides for examination on a polarizing geological microscope.

Statement why this study cannot be done in South Africa: There are no researchers undertaking this type of analysis in South Africa.