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A Tertiary age for Upper Nubian Sandstone Formation, central Sudan
Abstract
In central and northern Sudan, oil exploration is now active in the basins containing sediments of the Nubian Sandstone Formation. On the evidence of planned pipeline construction, significant volumes of oil appear to have been discovered in southwestern Sudan. A newly discovered flora from the upper Nubian Sandstone Formation near Khartoum in central Sudan is Tertiary in age. The flora is well preserved, and comprises leaves, flowers, and fruits, many not yet described. At the generic level, they are comparable to forms that are known fro the Eocene to Miocene. Aquatic plants indicate a lacustrine paleoenvironment; humid tropical forests thrived on the lakeshores. The Nubian Sandstone Formation of Sudan had been considered to be entirely of Cretaceous age; this new flora shifts the upper boundary into the Tertiary. The Tertiary Hudi Chert, found in scattered outcrops in the region of Atbara, was considered to overlie the Nubian Sandstone Formation. The authors suggest that the Hudi Chert is partly age equivalent to the Tertiary upper Nubian Sandstone at Jebel Mudaha.
... Stratigraphical observations provided insights into the late Pleistocene to mid-Holocene sedimentary record to which artefact layers can be attached with varying chronological precision. The 43 Whiteman 1971;Medani 1972;Prasad et al. 1986. At MOG105 a large flat pebble of Hudi chert was excavated from an insitu pebble bed which would suggest the former existence of a local fossiliferous chert formation. ...
... The basement consists mostly of granitoid rocks, together with a series of metamorphic rocks and magmatic intrusive sequences (Shang et al. 2010). These are overlain by the continental sands (and minor intercalated silts) of the Nubian Sandstone, which were largely deposited during the Cretaceous period and perhaps slightly later (Prasad et al. 1986;Klemm et al. 2001;Gardiner 2010). While the Nubian Sandstone Formation is exposed frequently within the Nubian Shield, younger fluvial sediments related to the Nile drainage system dominate the Nile Valley area. ...
This study presents the results of integrated mineralogical, petrographic and chemical analyses of different ceramic assemblages and local sediments from Sai Island, northern Sudan, dating to between the seventh and the third millennium bc, and highlights a significant variability in the raw materials and technology of these productions. Although archaeometric analyses of ceramics are widely employed in many parts of the world, a lamentable scientific gap exists for African pottery, which this paper aims to bridge with new and compelling results.
In this paper, I discuss issues of time resolution and time-averaging in fossil megafloras from Late Cretaceous (Cenomanian) to Oligocene age. The sites are predominantly from North America with some examples from other continents. The purpose of this paper is to explicate the methods used to resolve the age and duration of fossil floras and to discuss the uncertainties associated with these methods. The age of floras is most important for their evolutionary, paleoclimatic and paleoaltitudinal applications, while the duration of floras (here defined as the time represented by individual assemblages, florules, or quarries) is critical for paleoecological and paleoenvironmental applications. Levels of time resolution of both the age and the duration of fossil floras are subject to time-averaging. Behrensmeyer et al. (1992, p. 75) have defined two types of time-averaging: analytical time-averaging which is artificial and results from techniques of analysis and taphonomic time-averaging which is natural and results from the taphonomic history of the assemblage.
The Jebel Mudaha locality southwest of Khartoum yielded the following leaf fossils: Aristolochites cf. dentata, Nelumbites ? sp. (cf. N. aff. minimus), Annonophyllum cf. ellipticum, Magnoliaephyllum sp. (cf. Magnolia auriculata), cf. Laurus coloradensis, Laurus cailliaudi, Ulmiphyllum cf. brookense, Celtidophyllum sp. and Dewalquea grandifolia. In accordance with AWAD (1994) the age of this assemblage is interpreted to be Late Cretaceous (not younger than ?Turonian to early Senonian) and not Tertiary as previously concluded in the literature. Presence of small-sized Annonaceae, Lauraceae, Magnoliaceae and Ulmaceae in the leaf assemblage together with taphonomic and sedimentological features like rolled leaf margins and breccia-like sediments suggest seasonally dry (semiarid) conditions during the time of deposition of the Jebel Mudaha succession.
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A new fossil wood species of Caesalpiniaceae: Cassinium dongolense sp. nov., from the Nubian (Wadi Howar Formation), Northern Sudan is presented. The structures show similarities with the living Cassia L. (Cassia siamea Lamarck) from the Africano-Asiatic area. This genus was described for the first time in Upper Cretaceous sediments of Sudan. The new species was living in a warm climate with alternating dry and wet seasons.RésuméCe travail concerne l'étude de bois fossiles attribués à laa famille des Caesalpiniaceae: Cassinium dongolense n. sp. Ils proviennent de la Formation Wadi Howar dans le Soudan septentrional. Ces structures s' apparentent au genre actuel Cassia L., en particulier à l'espèce africano-asiatique C. siamea Lamarck. Ce genre est décrit pour la première fois dans le Crétacé supérieur du Soudan. Cette nouvelle espèce croissait sous un climat chaud avec une alternance de saisons sèches et humides.
During Cretaceous times, NE Africa was covered by clastic sediments. These sandy deposits correspond to the so-called "Nubian Sandstones" of Sudan, and the equivalent series of Egypt, Ethiopia and Somalia. In Central Sudan, the sandstone are alluvial, deposited from braided rivers under a dry tropical climate. They grade into alluvial plain and beach deposits in northern and eastern Sudan, Egypt, Ethiopia and Somalia. The source province was a north-south basement high, the Butana Massif, which extended northward into Egypt and eastward into Ethiopia and Somalia (Ethiopia-Sudan High, Harar-Nogal Swell). Nubian Sandstones were deposited in extensional tectonic framework. Old lineaments were rejuvenated as normal and strike-slip faults. Several geodynamics event could have interfered: northward drift of the African craton and downwarping of its northern margin as evidenced by Tethys transgressions, Indian Ocean opening and progressive uplift of the eastern margin of Africa, eastern updoming preceding the Red Sea and Aden Gulf opening.
The basalt of Jebel Et Toriya near Khartoum/Sudan has been studied in order to discover the mode of emplacement. For this purpose the chemical composition of an altered horizon in the bassalthas been analysed. Losses of Na, Mg, Ca,and the related gains of Al, Fe, Ti, V and Zr show element depletion and enrichment, which are common for rock weathering. This evidence permits a re-interpretation of the basalt mass comprising of two surface flows, separated from each other, by a period of chemical weathering.Some geological models of emplacement have been suggested and discussed to explain the occurrence of centripetally dipping flow banding and surface weathering.
Premise of the study:
Koelreuteria (Sapindaceae) has four extant deciduous tree species, disjunctly distributed in eastern Asia and the Fiji Islands. While K. paniculata is widely cultivated, the biogeographic origin and evolutionary history of Koelreuteria remain unclear.
Methods:
Fruits, pollen, wood, and leaves of closely related extant taxa were examined in comparison with fossil remains to evaluate the fossil record and biogeographic history of Koelreuteria.
Key results:
Overall, characters of capsular fruits are more diagnostic than other organs for this genus. We describe two new species of fruit remains from the Eocene, K. taoana sp. nov. (northeastern China and far eastern Russia) and K. dilcheri sp. nov. (western United States), and give emended descriptions of three species: K. allenii (Lesq.) W. N. Edwards (early-late Eocene of the United States), K. macroptera (Kováts) W. N. Edwards (late Oligocene-early Pliocene of Europe), and K. miointegrifoliola Hu et R. W. Chaney (Miocene of eastern Asia).
Conclusions:
Reliable fossil records of capsules and ring-porous wood indicate that Koelreuteria may have originated in North Pacific-Rim area of the northern hemisphere by the early Eocene, representing an early temperate lineage in Sapindaceae adapted for wind dispersal. The fossils herein place a minimum age (ca. 52 Ma) for the divergence of Koelreuteria from tropical genera that appear more basal in the molecular phylogeny of Sapindaceae. Regional extinctions after the Eocene in North America and the Pliocene in Europe, reduced the range of Koelreuteria to eastern Asia, where three species occur today. The present distribution of another species in the Southern Pacific may be explained by long-distance dispersal.
The main result of geological work of our group in Egypt and Sudan was the subdivision of the so-called Nubian Sandstone in its type-area Nubia and in the surroundings of Nubia. More than 20 formations have been identified, ranging in age from Cambrian to Paleocene and comprising an impressive number of facies variations. The only characteristic these strata have in common is their position near the northern edge of the African craton. This position caused similiarities within the continental facies and it also influenced marine sedimention, which in general took place in shallow to very shallow seas. The former Nubian Sandstone is strata deposited on both sides of shallow transgressions or in shallow, purely continental basins. Variations of facies were mainly influenced by changes of climate. Except for shallow marine carbonates of Early Tertiary age present in a larger area in northwestern Sudan, all sediments formenly called Nubian Sandstone are of clastic nature including thick sequences of paleosols.
Analyses of physiognomy of Late Cretaceous leaf assemblages and of structural adaptations of Late Cretaceous dicotyledonous woods indicate that megathermal vegetation was an open-canopy, broad-leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year, with a moderate increase at about 40–45°N. Many dicotyledons were probably large, massive trees, but the tallest trees were evergreen conifers. Megathermal climate extended up to paleolatitude 45–50°N. Mesothermal vegetation was at least partially an open, broad-leaved evergreen woodland (perhaps a mosaic of woodland and forest), but the evapotranspirational stress was less than in megathermal climate. Some dicotyledons were large trees, but most were shrubs or small trees; evergreen conifers were the major tree element. Some mild seasonality is evidenced in mesothermal woods; precipitational levels probably varied markedly from year to year. Northward of approximately paleolatitude 65°N, evergreen vegetation was replaced by predominantly deciduous vegetation. This replacement is presumably related primarily to seasonality of light. The southern part of the deciduous vegetation probably existed under mesothermal climate. Comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational-climatic patterns suggested from North American data. Limited data from equatorial regions suggest low rainfall.
This paper presents an overview of the Cenozoic stratigraphic record in the Sahara, and shows that the strata display some remarkably similar characteristics across much of the region. In fact, some lithologies of certain ages are exceptionally widespread and persistent, and many of the changes from one lithology to another appear to have been relatively synchronous across the Sahara. The general stratigraphic succession is that of a transition from early Cenozoic carbonate strata to late Cenozoic siliciclastic strata. This transition in lithology coincides with a long-term eustatic fall in sea level since the middle Cretaceous and with a global climate transition from a Late Cretaceous–Early Eocene “warm mode” to a Late Eocene–Quaternary “cool mode”. Much of the shorter-term stratigraphic variability in the Sahara (and even the regional unconformities) also can be correlated with specific changes in sea level, climate, and tectonic activity during the Cenozoic. Specifically, Paleocene and Eocene carbonate strata and phosphate are suggestive of a warm and humid climate, whereas latest Eocene evaporitic strata (and an end-Eocene regional unconformity) are correlated with a eustatic fall in sea level, the build-up of ice in Antarctica, and the appearance of relatively arid climates in the Sahara. The absence of Oligocene strata throughout much of the Sahara is attributed to the effects of generally low eustatic sea level during the Oligocene and tectonic uplift in certain areas during the Late Eocene and Oligocene. Miocene sandstone and conglomerate are attributed to the effects of continued tectonic uplift around the Sahara, generally low eustatic sea level, and enough rainfall to support the development of extensive fluvial systems. Middle–Upper Miocene carbonate strata accumulated in northern Libya in response to a eustatic rise in sea level, whereas Upper Miocene mudstone accumulated along the south side of the Atlas Mountains because uplift of the mountains blocked fluvial access to the Mediterranean Sea. Uppermost Miocene evaporites (and an end-Miocene regional unconformity) in the northern Sahara are correlated with the Messinian desiccation of the Mediterranean Sea. Abundant and widespread Pliocene paleosols are attributed to the onset of relatively arid climate conditions and (or) greater variability of climate conditions, and the appearance of persistent and widespread eolian sediments in the Sahara is coincident with the major glaciation in the northern hemisphere during the Pliocene.
The poorly fossiliferous Late Cretaceous clastic series of Northwestern Sudan has been studied palynologically for the first time. Clay samples, rich in kaolinite, from the El Ghaba well, about 370 km NW of Khartoum, contain two terrestrial palynomorph assemblages dominated by tricolpate angiosperm pollen, but also include some gymnosperms (Inaperturopollenites, Steevesipollenites) and, very rarely, pteridophyte spores. The presence of Foveotricolpites giganteus, F. gigantoreticulatus, F. tienabaensis, Tricolpites sp. CI.13, and T. sp. SCI.294 suggests a Lower Senonian (Coniacian) age for the El Ghaba samples. Their sedimentary facies favours a possible correlation with the upper Wadi Howar or lower Kababisch Formation of the Gebel Abyad Basin in Northwestern Sudan.
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