South African Journal of Geology最新文献

{"title":"Lithostratigraphy of the Mesoproterozoic Twakputs Gneiss","authors":"S. Doggart, P. Macey, D. Frei","doi":"10.25131/SAJG.124.0041","DOIUrl":"https://doi.org/10.25131/SAJG.124.0041","url":null,"abstract":"","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46260373","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A new lithostratigraphic framework for portions of the Pongola Supergroup within the Nkandla sub-basin, southern Kaapvaal Craton, South Africa; insights into Mozaan Group stratigraphy","authors":"N. Hicks, D. Gold, M. Ncume, L. Hoyer","doi":"10.25131/SAJG.124.0039","DOIUrl":"https://doi.org/10.25131/SAJG.124.0039","url":null,"abstract":"","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43954779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A proposed chronostratigraphic framework for the late Quaternary of southern Africa","authors":"J. Knight, J. Fitchett","doi":"10.25131/SAJG.124.0030","DOIUrl":"https://doi.org/10.25131/SAJG.124.0030","url":null,"abstract":"\u0000 The principles of chronostratigraphy can inform the process of correlation between different palaeoclimate records, enabling the coherence of spatial and temporal patterns of past climates and environments to be identified based on the physical, chemical, biological and isotopic properties of individual depositional units. This study presents a chronostratigraphic framework for the late Quaternary of southern Africa, based on the integration of palaeoclimatic and palaeoenvironmental proxy data from key records across the country from the start of Marine Isotope Stage 6 (~191 ka BP) to present. The methodology adopted in this study involves, first, wiggle-matching between sufficiently long and continuous records from different regions across southern Africa, informed by radiometric age controls from individual records. Based on interpretive limitations of these records, we then integrate different geomorphic and archaeological data types in proposing successive chronostratigraphic time periods that collectively extend through the late Quaternary of southern Africa. These time periods correspond to phases in which, within them, a certain set of (relative) stable climates or environments existed in different regions of southern Africa, as recorded in different ways in different proxy records. The boundaries between successive time periods are identified where there is evidence for a significant change in the workings of the climate or environmental system as reflected in the preserved proxy record found in a certain locality. These chronostratigraphic units are interpreted as reflecting the impacts of external forcing that is of regional extent, synchronous, and are not merely an outcome of local environmental variability. These chronostratigraphic phases identified for the late Quaternary period also correspond to distinctive technological and cultural phases in the southern African archaeological record, demonstrating links between coeval climate and environmental change and phases of human evolutionary development. This chronostratigraphic approach provides both a correlative framework for understanding the varied late Quaternary records of southern Africa, and a testable hypothesis for considering the synchroneity or otherwise of different records and thus their associated forcing factors.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42759469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The late Quaternary stratigraphy of coastal dunes and associated deposits in southern Africa","authors":"C. E. Knight","doi":"10.25131/SAJG.124.0032","DOIUrl":"https://doi.org/10.25131/SAJG.124.0032","url":null,"abstract":"Coastal sand dune sediments with associated intraformational aeolianite, palaeosols and beachrock are found throughout much of the southern African coast, and have important roles as both Quaternary environmental archives and in recording the interplay of sediment supply, coastal processes and sea-level change. This paper examines the stratigraphy and palaeoenvironmental significance of coastal sand dunes and associated sediments, using examples mainly from South Africa but also with reference to the sandy coasts of Namibia and southern Mozambique. Based on morphological, sedimentary and dating evidence reported in the diverse literature, the stratigraphic relationship of coastal sand dune sediments to Marine Isotope Stages (MIS) is summarized, and a chronostratigraphic diagram for the period MIS 6 to 1 along the South African coast is used to identify spatially coherent sedimentary units that correspond to different regional climatic and sea-level phases. This framework provides a stratigraphic context to better examine the relationship between coastal sand dunes and external forcing during the late Quaternary in southern Africa, and to guide future field studies.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42752357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A new lithostratigraphic framework and unified nomenclature for the Nsuze Group of the Nkandla sub-basin, southern Kaapvaal Craton, South Africa","authors":"N. Hicks, D. Gold, M. Ncume, L. Hoyer","doi":"10.25131/SAJG.124.0027","DOIUrl":"https://doi.org/10.25131/SAJG.124.0027","url":null,"abstract":"","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42012228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stratigraphy and palaeoenvironmental interpretation of late Quaternary colluvial slope deposits in southern Africa","authors":"J. Knight","doi":"10.25131/SAJG.124.0031","DOIUrl":"https://doi.org/10.25131/SAJG.124.0031","url":null,"abstract":"\u0000 Slope and lowland sediment systems throughout southern Africa are dominated by the presence of colluvium with interbedded palaeosols and hardground duricrusts. These sediments correspond to phases of land surface instability and stability, respectively, during the late Quaternary. This study examines the stratigraphy and environmental interpretation of slope sediment records from specific sites in southern Africa for the period of marine isotope stages (MIS) 6 to 1 (~191 ka to present), informed by theoretical ideas of the dynamics of slope systems including sediment supply and accommodation space. Based on this analysis, phases of land surface instability and stability for the period MIS 6 to 1 are identified. The spatial and temporal patterns of land surface conditions are not a simple reflection of climate forcing, but rather reflect the workings of slope systems in response to climate in addition to the role of geologic, edaphic and ecological factors that operate within catchment-scale sediment systems. Considering these systems dynamics can yield a better understanding of the usefulness and limitations of slope sediment stratigraphies.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49012749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A reinterpretation of the Archaean stratigraphy south of Nkandla, southern Kaapvaal Craton, South Africa: Geophysical and stratigraphic constraints on a sheared granitoid-greenstone remnant","authors":"N. Hicks, D. Gold","doi":"10.25131/SAJG.124.0025","DOIUrl":"https://doi.org/10.25131/SAJG.124.0025","url":null,"abstract":"","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46691672","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A LA-ICPMS zircon record of magmatic crystallization and compositional alteration in meta-igneous rocks of the eastern Kaapvaal Craton","authors":"R. Bolhar, A. Hofmann, C. Allen, R. Maas","doi":"10.25131/SAJG.124.0042","DOIUrl":"https://doi.org/10.25131/SAJG.124.0042","url":null,"abstract":"","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44560003","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Occurrence and probable source of chromium enrichment in Permian coals, South Africa","authors":"N. Wagner, M. Mokwena, A. Kolker","doi":"10.25131/sajg.124.0013","DOIUrl":"https://doi.org/10.25131/sajg.124.0013","url":null,"abstract":"\u0000 The trace element data pool for South African coals is limited. However, certain elements are reported as occurring in considerably higher concentrations than global average values. These elements include chromium (Cr), as well as manganese (Mn), cobalt (Co), and molybdenum (Mo), with Cr showing the most consistent enrichment. The aim of this study was to investigate the occurrence of Cr in South African coals sampled from five coalfields, and to assess the possible source of Cr. A total of 21 run-of-mine (ROM) coal samples from the Waterberg, Soutpansberg, Witbank, Highveld, and the Nongoma Coalfields were obtained from active mines. Coal characterization, mineralogy, and geochemical data were compiled. The Cr values for the Waterberg (23 to 28 ppm), Soutpansberg (4.7 to 43 ppm), Witbank (24 to 37 ppm), and Highveld (33 to 37 ppm) coal samples are higher than those for the Nongoma coals (1.2 to 2.5 ppm), and, in nearly every case, higher than the Clarke value for hard coals (17 ppm). Correlation coefficients, density fractionation, and selective leaching were used to infer (indirect) modes of occurrence. A dominant silicate (clay) affinity was determined with Cr, as well as an organic affinity in the ROM samples. The Nongoma coals, with illite and no kaolinite, have extremely low Cr values. The other samples are enriched in kaolinite and also have a high Cr content. Chromium values as high as 67 ppm were reported for 1.4 RD float fraction samples, indicating a positive correlation with organic matter. A Cr - silicate association was observed following selective leaching. These results imply multiple modes of occurrence of Cr in the South African samples, in agreement with studies conducted globally. Chromium in the South African coals could have originated from the Bushveld Complex (approximately two billion years old), the largest Cr reserve in South Africa, which predates coal formation (approximately 299 to 252 million years ago) and is proximal to the coalfields. The Cr, seemingly not associated with chromite, may have been redistributed in the peat swamps during peat deposition, accumulating in the sediments and organic material. The Nongoma Coalfield is the farthest distance from the possible Bushveld Complex Cr source, and these samples are depleted in Cr.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41719625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geomechanical properties of the Permian black shales in the southern main Karoo Basin: lessons from compositional and petrophysical studies","authors":"C. Geel, S. Nolte, E. M. Bordy","doi":"10.25131/sajg.124.0026","DOIUrl":"https://doi.org/10.25131/sajg.124.0026","url":null,"abstract":"\u0000 Permian black shales from the lower Ecca Group of the southern main Karoo Basin (MKB) have a total organic carbon (TOC) of up to ~5 wt% and have been considered primary targets for a potential shale gas exploration in South Africa. This study investigates the influence of shale composition, porosity, pressure (P) and temperatures (T) on their geomechanical properties such as compressive strength and elastic moduli. On average, these lower Ecca Group shales contain a high proportion, ~50 to 70 vol%, of mechanically strong minerals (e.g., quartz, feldspar, pyrite), ~30 to 50 vol% of weak minerals (e.g., clay minerals, organic matter) and ~0 to 50 vol% of intermediate minerals (e.g., carbonates), which have highly variable mechanical strength. Constant strain rate, triaxial deformation tests (at T ≤100°C; P ≤50 MPa) were performed using a Paterson-type high pressure instrument. Results showed that the Prince Albert Formation is the strongest and most brittle unit in the lower Ecca Group in the southern MKB followed by the Collingham and then the Whitehill Formation. Compressive strength and Young’s moduli (E) increase with increasing hard mineral content and decrease with increasing mechanically weak minerals and porosity. On comparison with some international shales, for which compositional and geomechanical data were measured using similar techniques, the lower Ecca Group shales are found to be geomechanically stronger and more brittle. This research provides the foundation for future geomechanical and petrophysical investigations of these Permian Ecca black shales and their assessment as potential unconventional hydrocarbon reservoirs in the MKB.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.8,"publicationDate":"2021-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46266384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}