Littérature scientifique sur le sujet « Jacovich »

The fossiliferous deposits within the lower-lying Jacovec Cavern in the locality of Sterkfontein yielded valuable hominin remains, including the StW 578 specimen. Because StW 578 mainly preserves the calotte, the taxonomic status of this specimen has been a matter of discussion. Within this context, here we employed high-resolution microtomography and a landmark-free registration method to explore taxonomically diagnostic features in the external surface of the StW 578 calotte. Our comparative sample included adult humans and common chimpanzees as well as one Australopithecus africanus specimen (Sts 5). We partially restored the StW 578 calotte digitally and compared it to extant specimens and Sts 5 using a landmark-free registration based on smooth and invertible surface deformation. Our comparative shape analysis reveals morphological differences with extant humans, especially in the frontal bones, and with extant chimpanzees, as well as intriguing specificities in the morphology of the StW 578 parietal bones. Lastly, our study suggests morphological proximity between StW 578 and Sts 5. Given the intimate relationship between the brain and the braincase, as well as the integration of the hominin face and neurocranium, we suggest that cranial vault shape differences between StW 578 and extant humans, if confirmed by further analyses, could be either explained by differences in brain surface morphology or in the face. Besides providing additional information about the morphology of the Jacovec calotte that will be useful in future taxonomic discussion, this study introduces a new protocol for the landmark-free analysis of fossil hominin cranial shape.

Sterkfontein is the most prolific single source of Australopithecus fossils, the vast majority of which were recovered from Member 4, a cave breccia now exposed by erosion and weathering at the landscape surface. A few other Australopithecus fossils, including the StW 573 skeleton, come from subterranean deposits [T. C. Partridge et al. , Science 300, 607–612 (2003); R. J. Clarke, K. Kuman, J. Hum. Evol. 134, 102634 (2019)]. Here, we report a cosmogenic nuclide isochron burial date of 3.41 ± 0.11 million years (My) within the lower middle part of Member 4, and simple burial dates of 3.49 ± 0.19 My in the upper middle part of Member 4 and 3.61 ± 0.09 My in Jacovec Cavern. Together with a previously published isochron burial date of 3.67 ± 0.16 My for StW 573 [D. E. Granger et al. , Nature 522, 85–88 (2015)], these results place nearly the entire Australopithecus assemblage at Sterkfontein in the mid-Pliocene, contemporaneous with Australopithecus afarensis in East Africa. Our ages for the fossil-bearing breccia in Member 4 are considerably older than the previous ages of ca. 2.1 to 2.6 My interpreted from flowstones associated with the same deposit. We show that these previously dated flowstones are stratigraphically intrusive within Member 4 and that they therefore underestimate the true age of the fossils.

PT. Natarang Mining merupakan tambang emas bawah tanah yang menerapkan metode sublevel open stoping. Untuk memaksimalkan kapasitas produksi akan dibuat open stope pada Drift West Level 4 di kedalaman 165 m. Penelitian ini dlakukan untuk mengevaluasi kestabilan sill drift dan optimalisasi dimensi stope pada lokasi Drift West Level 4 dengan menggunakan metode Mathews Stability Graph dan Mining Rock Mass Rating (Laubscher and Jacovec, 2001). Metode ini dipilih karena penentuan parameter disesuaikan dengan kondisi tambang bawah tanah seperti efek peledakan, tegangan terinduksi, tingkat pelapukan, kondisi air dan orientasi kekar. Dalam karaketerisasi massa batuan, terdapat tiga jenis batuan pada lokasi penelitian yaitu andesitic massive, prophylitic andesitic vulcanic breccia dan brecciated quartz vein. Berdasarkan pendekatan empiris MRMR dan Mathews Stability Graph lokasi drift west dalam kondisi stabil dengan nilai hydraulic radius 1.16 m. Optimalisasi dimensi pada perencanaan open stope dapat dilakukan dengan memaksimalkan nilai hydraulic radius dengan perencanaan tinggi stope adalah 50 m. Berdasarkan pendekatan empiris MRMR panjang optimal stope dalam kondisi stabil adalah 39 m pada hanging wall dan 28 m pada vein. Sedangkan pada metode Mathews Stability Graph diperoleh nilai panjang optimal sebesar 15 m pada hangingwall dan 12.5 m pada vein. Kata-kata kunci : MRMR, Q System, Stability Graph, Hydraulic Radius

A dissertation submitted to the School of Geosciences, Faculty of Science University of the Witwatersrand, Johannesburg for the degree of Master of Science. March 2017.
Since the first fossil discovery in the late 1800s Sterkfontein has become one of the most productive palaeoanthropological sites in the world. This cave network has produced abundant fossil material that has provided insight to Plio-Pleistocene ecology, environments and hominid behaviour. Although the site is rich in fossil material, various post-depositional processes that occurred over time have made the deposits very complex and difficult to decipher. At the centre of understanding this complex site, extensive geological work has been done to place the fossil material in the best possible context. This has led to the establishment of a cave stratigraphic framework, namely the Sterkfontein Formation, which has arranged fossiliferous deposits from some of the chambers in the Sterkfontein Cave System. However, some of the lowerlying chambers were not included within this stratigraphic framework and thus required investigation. After the discovery of a partial cranium of Australopithecus sp. in this cavern, the primary research focus was on taphonomy, palaeoecology, biostratigraphy as well as chronostratigraphy; minimal sedimentological work was undertaken. This research involved a sedimentological facies analysis in a lesser known chamber of the cave network, the Jacovec Cavern, which is one of the deepest caverns in the Sterkfontein Cave System. The examinations of the sediment yielded a detailed depositional history as well as provided the opportunity to test previously proposed karstification models. This provides a better comprehension for the formation and development of the Jacovec Cavern and its relation to the entire Sterkfontein Cave System. The observation of sediment halt (blockage from a palaeo-karst wall) suggested the presence of two depositionally independent chambers, namely the north western Main Jacovec Chamber and the newly-differentiated eastern (sediment-rich) Thulasizwe Chamber. Work in the Thulasizwe Chamber helped revise the proposed stratigraphy by identifying four distinct units and reconciling the previously-proposed reverse stratigraphy of the upper brecciated (Brown and Orange breccia) units. These four units begin with a basal slackwater (laminated) unit overlain by a debris flow unit followed by a fossiliferous Brown Breccia and, finally, a channel-derived Orange Breccia. The Main Jacovec Chamber contains two small sedimentary units whose depositional histories are harder to decipher. These sediments have been subject to a large degree of alteration (from both biotic and abiotic factors), which has led to the identification of cave access and phreatic stages. The lithology of the sediments (especially the presence of a distinct tuff seam) in both chambers has assisted in restricting the provenance of the sediments to localized deposits most likely coming from the south-southeast of the cave system. Furthermore, the presence of ghost rock remnants proved useful in providing a detailed karstification model (which suggests a long-lived stage of chemical dissolution before mechanical erosion and removal of cave earth) for the chamber and supports early works by Wilkinson (1985) of a deep phreatic network. This has implications for the stratigraphic interpretations on the cave system and sequence of filling.
LG2018