Journal of African Earth Sciences (1983)最新文献

{"title":"East African rift and northeast lineaments: continental spreading—transform system?","authors":"M.B. Katz","doi":"10.1016/0899-5362(87)90111-4","DOIUrl":"10.1016/0899-5362(87)90111-4","url":null,"abstract":"<div><p>Seafloor spreading and transform faulting processes are also likely to be operative during continental rifting events. Continental lines of old weakness oriented at high angles to the direction of continental rifting may be reactivated by transform faulting. These older continental transform faults, which predate and accomodate the rifting, will continue to propagate as younger oceanic transform faults as the rift develops into seas and oceans. This model is applied to the East African Rift which is postulated to be a continental spreading rift that is accommodated by east-northeast continental transform lineaments that are reactivated older crustal defects of appropriate orientation. At least five continental transform lineaments can be tentatively identified by empirical best fits to oceanic transform directions of the South Atlantic Ocean and to various continental African northeast-trending structures: (1) Cape Town-Maputo (CT-LM); (2) Orange River-Beira (OR-B); (3) Luderitz-Lindi (L-Li); (4) Walvis Bay-Mombasa-Mogadishu (WB-M-Mo); and (5) Luanda-Afar (Lu-Af). As these postulated lineaments are perennial deep seated crustal defects they may also control the development of mineral deposits.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 1","pages":"Pages 103-107"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90111-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53877742","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Apatite as a paleoenvironmental indicator in the Precambrian-mesozoic clastic sequence of the Middle East","authors":"Tuvia Weissbrod ,&nbsp;Ithamar Perath ,&nbsp;Joseph Nachmias","doi":"10.1016/0899-5362(87)90036-4","DOIUrl":"10.1016/0899-5362(87)90036-4","url":null,"abstract":"<div><p>Apatite, either detrital or authigenic, or both, occurs in the Precambrian arkoses and Cambrian subarkoses, grits and quartz-arenites in Israel, Sinai, southern Jordan and northwest Arabia. However, no apatite is found in the sandstones that overlie the sub-Carboniferous unconformity (often superceded by a sub-Cretaceous unconformity) throughout the Middle East.</p><p>Within the Precambrian-Cambrian sequence, apatite distribution is not uniform and varies between 0–80% of transparent heavy minerals. The detrital apatite was derived from the acid igneous terrain that supplied the sands. Authigenic apatite was formed by recrystallization of the detrital apatite.</p><p>Until its abrupt stratigraphic termination, apatite accompanies the ultrastable minerals zircon-tourmalinerutile without displaying, like the semi- and nonstable heavy minerals, vertical trends of gradual disappearnce. Therefore its disappearance cannot be explained by repeated reworking and transportation which, by themselves, are not known to result in the complete elimination of a heavy mineral from an assemblage.</p><p>Numerous heavy-mineral studies, and especially the experimental work of Nickel (<em>Contr. Sedimentol.</em><strong>1</strong>, 1–68, 1973) have shown that apatite dissolves under conditions of low (&lt; 6) pH, which may develop in well-leached humic soils, pedalfers and laterosols, but which are not known in intrastratal groundwaters. The apatite distribution suggests, together with clay-mineral indications, that pedogenesis of this type developed with the spread of terrestrial floras over the Arabo-Nubian land surfaces during the Late Paleozoic. Various lines of evidence, including paleomagnetic data, indicate that the present-day Near East area was in a temperate-humid zone during the Cambrian. After drifting through subpolar latitudes during the Ordovician-Silurian-Devonian, it moved again into a tropical-humid zone toward the Late Paleozoic. This coincided with the appearance of plant fossils in the clastic section, and the disappearance of apatite. Since the dissolution of apatite is inhibited in the presence of carbonate or Ca²⁺ ions, its removal must already have been completed before the Permian, when carbonate deposition became gradually dominant.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 6","pages":"Pages 797-805"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90036-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53876557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Trace fossils assemblage and depositional environment of Turonian calcareous sandstones in the southern Benue Trough, Nigeria","authors":"Etie B. Akpan,&nbsp;Eyo E. Nyong","doi":"10.1016/0899-5362(87)90059-5","DOIUrl":"10.1016/0899-5362(87)90059-5","url":null,"abstract":"<div><p>A calcareous sandstone sequence that forms part of the Eze-Aku Formation (Reyment) features an assemblage of ichnofossils in a section exposed on a quarry face. The traces encountered include horizontal burrows, some of which are preserved as casts, lined with organic matter and belonging to the ichnogenera <em>Gyrolithes, Pholeus</em> and <em>Arthrophycus</em>. Three other types of trace fossils are described as horizontal crawling trails, flat impressions and cylindrical shafts without formal names. <em>Gyrolithes</em> are by far the dominant traces in this sequence. The degree of bioturbation is high in every horizon. Body fossils are very rare except for scattered occurrence of fragments of calcitic pelecypod shells.</p><p>Ichnological and lithological considerations suggest that the sediments were deposited in an aerated shallow shelf environment which supported an assemblage of decapods, worms and other shallow water marine benthos. Deposition was generally below wave base under a continuous but relatively slow rate of sedimentation.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 2","pages":"Pages 175-180"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90059-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53876974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nouvelle découverte de Miocène supérieur à Abidjan, Côte d'Ivoire","authors":"M. Báldi-Beke ,&nbsp;S. de Klasz ,&nbsp;I. de Klasz ,&nbsp;J.P. Tastet ,&nbsp;C. Tissot","doi":"10.1016/0899-5362(87)90001-7","DOIUrl":"10.1016/0899-5362(87)90001-7","url":null,"abstract":"<div><p>The discovery of Upper Miocene marine layers in a water-borehole in Abidjan, to the north of the great tectonical fault zone dividing lengthwise the terrestrial part of the Ivory Coast sedimentary basin, incited us to study their microfauna, palynoflora and nannoflora in detail. To our knowledge it is for the first time that fossils of the two last named groups of such age have been studied in Ivory Coast and none of the characteristic species of the three groups illustrated up to now. The study has been carried out within the geological and sedimentological framework of the borehole.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 5","pages":"Pages 617-631"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90001-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53876349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A gravity and magnetic traverse from Port Sudan to Abu Hamad, NE Sudan","authors":"Abdel Ati Sadig ,&nbsp;David C. Almond ,&nbsp;Farouk Ahmed","doi":"10.1016/0899-5362(87)90039-X","DOIUrl":"10.1016/0899-5362(87)90039-X","url":null,"abstract":"<div><p>Gravity and magnetic measurements were recorded while making a geotraverse from the Red Sea at Port Sudan to the River Nile at Abu Hamad. Much of the region is poorly known geologically and the geophysical interpretations have been constrained by new observations along and near to the traverse line. There are close correlations between gravity, magnetics and many of the major geological features of the region. Western, central and eastern blocks can be distinguished on the basis of combined geology and geophysics. The largely metasedimentary western block shows flat geophysical profiles, whereas the batholith which composes most of the central block shows minor anomalities related to its inhomogenous primary composition and to zones of later N-S shearing. The eastern block is composed largely of low-grade metavolcanic rocks but has a local basement of higher grade rocks, and there are numerous intrusions of granite and gabbro, with ophiolitic lenses within the NE-trending Nakasib shear zone. The strong geophysical anomalies over the Nakasib zone are in keeping with interpretation of this zone as a reworked oceanic suture. Other strong anomalies relate to the presence of basic intrusions and the distribution of basic basement rocks. The regional gravity profile is similar to those measured elsewhere on the flanks of the Red Sea and reflects thinning of the lithosppheric units as the Red Sea axis is approached.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 6","pages":"Pages 823-832"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90039-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53876614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Depositional environment and facies relationships of the Cretaceous ironstone of the Agbaja Plateau, Nigeria","authors":"Ezigbo Michael Umeorah","doi":"10.1016/0899-5362(87)90081-9","DOIUrl":"10.1016/0899-5362(87)90081-9","url":null,"abstract":"<div><p>The Maastrichtian oolitic ironstone examined caps the mesas of the Agbaja Plateau, which covers an area approximately 150 km² and is situated NW of Lokoja, near the confluence of the Benue and Niger rivers, in the Cretaceous Middle Niger Basin of Nigeria. This basin is one of six depositional (Mesozoic to Recent) basins in Nigeria and is a shallow trough filled with Campanian to Maastrichtian, marine to fluviatile strata on the Pre-Cambrian basement.</p><p>Four major lithofacies of ironstone may be discerned on the basis of semi-quantitative X-ray diffraction analyses of borehole samples. These are from oxidized to more dehydrated and reduced conditions: (1) goethite + kaolinite; (2) hematite + geothite + kaolinite; (3) maghemite/magnetite + goethite + kaolinite; (4) siderite + magnetite + kaolinite. The maghemite/magnetite + geothite + kaolinite facies is dominant.</p><p>The ironstone was deposited during a major transgression. It overlies either a carbonaceous mudstone/shale or clay/sandstone, which is underlain by a fluviatile sandstone. Primary oxidized ironstone minerals were formed in nearshore fluviatile environment, and transported into deeper water. Through re-working and diagenesis, ironstone deposition continued under estuarine and reducing conditions with evidence of low energy wave action at the top of the ironstone.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 4","pages":"Pages 385-390"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90081-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53877346","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Resédimentations d'âge sénonien dans le Rif central (Maroc): conséquences sur les divisions paléogéographiques et structurales de la chaîne","authors":"Lahcen Asebriy,&nbsp;Patrick de Luca,&nbsp;Jacques Bourgois,&nbsp;Pierre Chotin","doi":"10.1016/0899-5362(87)90103-5","DOIUrl":"10.1016/0899-5362(87)90103-5","url":null,"abstract":"<div><p>The occurence of resedimented gypsiferous polygenic breccias in Senonian marls of the central Rif (Morocco) leads us to refute current paleogeographic and structural subdivisions of the Rifian Range. We propose to regroup zones such as the internal and external Mesorif and Ketama-Tangier unit into a single zone named Subrif. From a tectonic point of view, NE-SW and NW-SE strike-slip faults are considered as taking the prominent part, contrary to thrust faulting (= nappe), which restricts the degree of allochtony of the Central Rif nappes.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 1","pages":"Pages 9-17"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90103-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53877641","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"La structure du rif externe (Maroc): mise au point sur le rôle des décrochements des chevauchements et des glissements gravitaires","authors":"Dominique Frizon de Lamotte","doi":"10.1016/0899-5362(87)90011-X","DOIUrl":"10.1016/0899-5362(87)90011-X","url":null,"abstract":"<div><p>Regional structural field evidence in the Temsamane area, forming the eastern part of the Rifian external zones, indicate that deformation of this area results from N75° left lateral wrenching. The structural data do not fit the nappe interpretation pointed out in Western part of external zone. A review of the geological frame appears necessary; it forms the subject of the present paper.</p><p>Structurally, the external zones are subdivided into three groups of tectonic units: (a) the olistostromes and associated gravity-driven nappes which crop out all around the Rifian belt (‘slided external Rif’); (b) The tectonic windows situated beneath olistostromes and nappes (‘basal external Rif’); (c) The central area bounded by NW-SE thrust faults in the Western parts of the belt and by N75° (then N45°) wrench faults in the Eastern parts (‘Central Rif’).</p><p>Concerning the paleogeographic evolution, the deposits of external Rif show a different evolution from their direct foreland but comparable with areas actually situated far eastward: (a) the ‘tellian-like domain’ shows basinal-type facies similar to facies of the epitellian nappes into Algeria^b, (b) the ‘Ker Ker-like domain’ shows platform facies similar to facies known in West Algerian and Northeast Moroccan forelands.</p><p>Thus, structural and paleogeographic data show that the all external zones of Rif moved westward along the African margin before sliding southward.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 5","pages":"Pages 755-766"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90011-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53876480","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Potential groundwater discharges and safe yields of drainage basins in southwestern Nigeria","authors":"O.O. Ogunkoya","doi":"10.1016/0899-5362(87)90033-9","DOIUrl":"10.1016/0899-5362(87)90033-9","url":null,"abstract":"<div><p>The potential safe yields of aquifers in the rocks and saprolites of third-order drainage basins on the Pre-Cambrian Basement Complex of southwestern Nigeria are determined and presented using the Total Potential Groundwater discharge (<em>Q</em>_TP) model of Butler (1957) and Meyboom (1961). The safe yield values range from 22 1 min⁻¹ to 2156 1 min⁻¹. These values compare with those from the Basement Complex in some other parts of Nigeria but most of them appear very low when compared with yields of between 640 and 1740 1 min⁻¹ reported for sedimentary rocks within the same region. The relatively high values of between 642 and 2156 1 min⁻¹ reported in this study were obtained from aquifers located within the highly fissured quartzitic rocks and their associated coarse grained saprolites.</p><p>The potential safe yield values from the basins may thus show that apart from those areas underlain by quartzites and such other highly fissured rocks overlain by coarse grained saprolites e.g. porphyritic/coarse grained granites (and these are not widespread on the Basement Complex), the Basement Complex is an area of poor groundwater yield.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 6","pages":"Pages 773-779"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90033-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53876513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diagnetic pyrite framboids in the phosphate deposits of Abu-Tartur area, Western Desert, Egypt","authors":"Mohamed A. El-Dahhar","doi":"10.1016/0899-5362(87)90037-6","DOIUrl":"10.1016/0899-5362(87)90037-6","url":null,"abstract":"<div><p>The pyrite framboids enclosed in the phosphate deposits of Abu-Tartur area, Western Desert, Egypt, occur as discrete individuals and as clustered aggregates. They are intimately associated with the organic matter contained in the phosphates. The morphology and other characteristics of these framboids are presented.</p><p>A biogenic mode of formation is suggested for such framboids. Bacterial action on soft organic rich sediments resulted in formation of local concentration of hydrogen sulfide. By the increase in activity of the latter in presence of Fe²⁺ and organic matter, a hydrophobic sulfide gel might have formed. It is considered possible that precipitation of the sulfide around bacteria in the gel would promote formation of globular pyrite rather than other forms, and clustering of the globules may be a result of precipitation of the sulfide around bacterial growths. However, the possibility of forming the framboids as an internal consequence of pyrite crystallization by increasing forces of surface tension is not completely excluded.</p></div>","PeriodicalId":100749,"journal":{"name":"Journal of African Earth Sciences (1983)","volume":"6 6","pages":"Pages 807-811"},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(87)90037-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53876580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}