Recent studies have been able to pin point the timing of the Nile’s initiation as a major river from a more proximal catchment area (Fielding et al., 2018). Knowledge of the evolution of the Nile brings with it potential insights into the predicted reservoir quality of the offshore Oligocene to recent Nile Delta sediments. This paper will focus on an investigation into multi-disciplinary studies and how they are key in correctly interpreting the detrital provenance signatures of ancient clastic sediment wedges and their implications for reservoir quality whilst overcoming bias from effects such as diageneses and hydraulic sorting.
One place exceptionally well suited to carry out such an investigation is the thick Oligocene to recent sedimentary succession in the offshore Nile delta (Craig et al., 2011). In this article, we compare the compositional signatures of Nile River and Nile delta sediments – using two provenance techniques: 1) Heavy mineral analysis and petrography and; 2) U/Pb zircon geochronology. Petrographic analysis was carried out on samples from before and after the construction of the Aswan High Dam in 1964 and transported as bedload and suspended load (Garzanti et al., 2006, 2015; Fielding et al., 2017) – with those of partly lithified Oligocene to Pleistocene Nile delta sands, silts, and muds cored offshore by BP Egypt (Fig. 1; Fielding et al., 2018). Fielding et al., (2018) focuses principally on provenance, whereas Garzanti et al., 2018 illustrates the stratigraphic trends shown by petrographic modes and heavy-mineral suites and thoroughly discusses their potential controlling factors. Particular focus was given to comparing heavy mineral assemblages in samples with grain sizes from cohesive mud to upper-medium sand, to evaluate differences in the intensity of diagenetic effects in strata characterized by different porosity and permeability to intrastratal fluids.
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We outline a novel workflow for utilising hinterland datasets to predict reservoir quality and distribution in frontier exploration regions and apply this methodology to a case study in the Nile Delta. Geochemical data is intersected with drainage areas to derive first-order bulk chemical compositions. Drainage polygons are modified using thermochronological data and paleocurrent information to create paleo-drainage areas. Volume of denuded sediment is then estimated from uplift data and integrated with stratigraphies to verify the link between hinterland and offshore geology. Finally, chemical data are used to predict the modal composition of sediment within key reservoir and seal horizons. The workflow presented utilises datasets otherwise overlooked in the exploration process and reduces the reliance on more speculative inputs such as paleogeographic reconstructions and paleoclimate modelling. The workflow provides quantitative predictions with percentage certainties, allowing explorers to understand the degree to which results can be relied upon.
To demonstrate this workflow we look at the offshore Nile Delta sediments in the Eastern Mediterranean. The Nile’s vast hinterland is comprised of sediments derived from the Congo Craton and Saharan Metacraton, Cenozoic Flood Basalts and Phanerozoic sediments from the Ethiopian Highlands, and Phanerozoic sediments and Cenozoic carbonates from the Egyptian Red Sea Hills. Recent detrital studies on the offshore Nile Delta have shown the provenance of the Oligocene-to-Pleistocene sediments remained the same since the Rupelian, 31 Ma (Fielding et al., 2017). Fluctuations in the amount of mafic material recorded in the delta during the Oligocene and Pliocene versus the Miocene and Pleistocene have implications for discontinuous reservoir quality in the basin. Using the workflow outlined above and incorporating additional datasets and methods, we aim to quantify this variation in mafic sediments and its implications for predicting reservoir quality in the offshore Nile delta.
The Nile is generally regarded as the longest river in the world. Knowledge of the timing of the Nile’s initiation as a major river is important to a number of research questions. For example, the timing of the river’s establishment as a catchment of continental proportions can be used to document surface uplift of its Ethiopian upland drainage, with implications for constraining rift tectonics. Furthermore, the time of major freshwater input to the Mediterranean is considered to be an important factor in the development of sapropels. Yet the river’s initiation as a major drainage is currently constrained no more precisely than Eocene to Pleistocene.
Within the modern Nile catchment, voluminous Cenozoic Continental Flood Basalts (CFBs) are unique to the Ethiopian Highlands; thus first detection of their presence in the Nile delta record indicates establishment of the river’s drainage at continental proportions at that time. We present the first detailed multiproxy provenance study of Oligocene–Recent Nile delta cone sediments. We demonstrate the presence of Ethiopian CFB detritus in the Nile delta from the start of our studied record (c. 31 Ma) by (1) documenting the presence of zircons with U–Pb ages unique, within the Nile catchment, to the Ethiopian CFBs and (2) using Sr–Nd data to construct a mixing model which indicates a contribution from the CFBs. We thereby show that the Nile river was established as a river of continental proportions by Oligocene times. We use petrography and heavy mineral data to show that previous petrographic provenance studies which proposed a Pleistocene age for first arrival of Ethiopian CFBs in the Nile delta did not take into account the strong diagenetic influence on the samples.
We use a range of techniques to show that sediments were derived from Phanerozoic sedimentary rocks that blanket North Africa, Arabian–Nubian Shield basement terranes, and Ethiopian CFB’s. We see no significant input from Archaean cratons supplied directly via the White Nile in any of our samples. Whilst there are subtle differences between our Nile delta samples from the Oligocene and Pliocene compared to those from the Miocene and Pleistocene, the overall stability of our signal throughout the delta record, and its similarity to the modern Nile signature, indicates no major change in the Nile’s drainage from Oligocene to present day.
This Nile Delta case study provides quantitative information on a process that we must understand and consider in full before attempting provenance interpretation of ancient clastic wedges. Petrographic and heavy-mineral data on partly lithified sand, silt, and mud samples cored from the up to 8.5 km-thick post-Eocene succession of the offshore Nile Delta document systematic unidirectional trends. With increasing age and burial depth, quartz increases at the expense of feldspars and especially of mafic volcanic rock fragments. Heavy-mineral concentration decreases drastically, transparent heavy minerals represent progressively lower percentages of the heavy fraction, and zircon, tourmaline, rutile, apatite, monazite, and Cr-spinel relatively increase at the expense mainly of amphibole in Pliocene sediments and of epidote in Miocene sediments. Recent studies have shown that the entire succession of the Nile Delta was deposited by a long drainage system connected with the Ethiopian volcanic highlands similar to the modern Nile since the lower Oligocene. The original mineralogy should thus have resembled that of modern Delta sand much more closely than the present quartzose residue containing only chemically durable heavy minerals. Stratigraphic compositional trends, although controlled by a complex interplay of different factors, document a selective exponential decay of non-durable species through the cored succession that explains up to 95% of the observed mineralogical variability. Our calculations suggest that heavy minerals may not represent >20% of the original assemblage in sediments buried less than ~1.5 km, >5% in sediments buried between 1.5 and 2.5 km, and >1% for sediments buried >4.5 km. No remarkable difference is detected in the intensity of mineral dissolution in mud, silt, and sand samples, which argues against the widely held idea that unstable minerals are prone to be preserved better in finer-grained and therefore presumably less permeable layers. Intrastratal dissolution, acting through long periods of time at the progressively higher temperatures reached during burial, can modify very drastically the relative abundance of detrital components in sedimentary rocks. Failure to recognize such a fundamental diagenetic bias leads to grossly mistaken paleogeographic reconstructions, as documented paradigmatically by previous provenance studies of ancient Nile sediments.
This research uses analyses from Nile catchment rivers, wadis, dunes and bedrocks to constrain the geological history of NE Africa and document influences on the composition of sediment reaching the Nile delta. Our data show evolution of the North African crust, highlighting phases in the development of the Arabian–Nubian Shield and amalgamation of Gondwana in Neoproterozoic times. The Saharan Metacraton and Congo Craton in Uganda have a common history of crustal growth, with new crust formation at 3.0 – 3.5 Ga, and crustal melting at c. 2.7 Ga. The Hammamat Formation of the Arabian–Nubian Shield is locally derived and has a maximum depositional age of 635 Ma. By contrast, Phanerozoic sedimentary rocks are derived from more distant sources. The fine-grained (mud) bulk signature of the modern Nile is dominated by input from the Ethiopian Highlands, transported by the Blue Nile and Atbara rivers. Detrital zircons in the Nile trunk are predominantly derived from Phanerozoic cover rocks. Most detritus from the upstream White Nile is trapped in the Sudd marshes and contributes little to the Nile trunk. Therefore, the White Nile downstream is dominated by locally derived Phanerozoic cover. The White Nile proximal to the Gezira Fan is influenced by the fan’s Blue Nile signature.
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We have reconstructed long-term shifts in catchment sediment sources by analysing, for the first time, the strontium (Sr) and neodymium (Nd) isotope composition of dated floodplain deposits in the Desert Nile. The sediment load of the Nile has been dominated by material from the Ethiopian Highlands for much of the Holocene, but tributary wadis and aeolian sediments in Sudan and Egypt have also made major contributions to valley floor sedimentation. The importance of these sources has shifted dramatically in response to global climate changes. During the African Humid Period, before c. 4.5 ka, when stronger boreal summer insolation produced much higher rainfall across North Africa, the Nile floodplain in northern Sudan shows a tributary wadi input of 40–50%. Thousands of tributary wadis were active at this time along the full length of the Saharan Nile in Egypt and Sudan. As the climate became drier after 4.5 ka, the valley floor shows an abrupt fall in wadi inputs and a stronger Blue Nile/Atbara contribution. In the arid New Kingdom and later periods, in palaeochannel fills on the margins of the valley floor, aeolian sediments replace wadi inputs as the most important secondary contributor to floodplain sedimentation. Our sediment source data do not show a measurable contribution from the White Nile to the floodplain deposits of northern Sudan over the last 8500 years. This can be explained by the distinctive hydrology and sediment delivery dynamics of the upper Nile basin. High strontium isotope ratios observed in delta and offshore records – that were previously ascribed to a stronger White Nile input during the African Humid Period – may have to be at least partly reassessed. Our floodplain Sr records also have major implications for bioarchaeologists who carry out Sr isotope-based investigations of ancient human remains in the Nile Valley because the isotopic signature of Nile floodplain deposits has shifted significantly over time.
The cratons of Central Africa are formed of various blocks of Archaean and Palaeoproterozoic crust, flanked or truncated by Palaeoproterozoic to Mesoproterozoic orogenic belts. The geology of east Africa has largely been shaped by the events of the Pan-African Orogeny when east and west Gondwana collided to form ‘Greater Gondwana’ at the end of the Neoproterozoic. The Pan-African orogeny in NE Africa involved the collision of Archaean cratons and the Saharan Metacraton with the Arabian Nubian Shield, a terrane comprising Neoproterozoic juvenile oceanic island arcs. Phanerozoic cover sedimentary rocks, eroded from the Pan-African orogenies, blanket much of NE Africa. Detrital data from these Phanerozoic cover sedimentary rocks, and modern rivers draining both the cover the basement, provide a wealth of information on basement evolution, of particular relevance for regions where the basement itself is poorly exposed due to ancient or modern sedimentary cover. From samples collected in Uganda, Ethiopia, Sudan and Egypt, we provide combined U-Pb and Hf-isotope zircon, U-Pb rutile and Ar-Ar mica datasets, heavy mineral analyses, and bulk trace element data, from Archaean basement, Phanerozoic cover and modern river sediment from the Nile and its tributaries to document the evolution of the North African crust. The data document early crust-forming events in the Congo Craton and Sahara Metacraton, phased development of the Arabian Nubian Shield culminating in the Neoproterozoic assembly of Gondwana during the Pan African Orogeny, and the orogen’s subsequent erosion, with deposition of voluminous Phanerozoic cover.
The Meratus Complex, located in SE Kalimantan, records accretion and collision along the Sundaland margin during the mid-Cretaceous. Several authors have suggested that the resultant suture continues northwards beneath the Kutai Basin, possibly extending as far north as Sabah, where ophiolitic and arc-type rocks are well documented. Prominent features such as the Kutai Lakes Gravity High, have been suggested to be the expression of the Meratus Suture as it is downthrown towards the north beneath the Kutai Basin. This paper presents a suite of observations from literature review, satellite mapping, biostratigraphy, well and seismic data; and builds upon a previous IPA manuscript that proposed a new model for the uplift history of the Meratus Complex. We discuss the results of structural mapping of onshore East Kalimantan derived from SRTM, Landsat 7 ETM+ and Bouguer Gravity data. Structural trends are presented, highlighting lineations and basement lineaments which have previously been interpreted to cross Borneo. We integrate these observations with biostratigraphy and subsurface data, to provide a framework for better understanding the deformation of East Kalimantan from a regional perspective. We interpret structural trends across Borneo that reflect distinct mechanisms for deformation under compressional forces. The Adang Line-Paternoster Fault lies in the approximate location of a basement high which separates the Barito Basin to the south from the Kutai Basin in the north. We interpret this lineament as a Paleogene feature that later facilitated differing responses to compression associated with the Australia-Eurasia collision from the Miocene onwards. To the south of the Adang-Paternoster, approximate NW-SE compression was bulwarked against the newly emergent Schwaner Mountains, causing concentrated uplift in the Meratus. North of the Adang-Paternoster, deformation in the lithosphere was distributed more widely, resulting in less dramatic uplifts and detachment faulting and folding, as observed in the Samarinda Anticlinorium.
This study documents the palaeodrainage history of the Nile River, in particular the time of its transition from a small locally sourced drainage network to the initiation of an extensive catchment. Today, the Nile drains as far south as Lake Victoria, with the White Nile draining largely cratonic rocks of Archean to Proterozoic age and the Blue Nile draining Cenozoic Ethiopian Continental Flood Basalts and Neoproterozoic basement. However, the timing of catchment expansion to the river’s current extent is highly debated. Two end member models are: A) The Blue Nile did not connect with the lower Nile until the Late Messinian, and the White Nile not until 0.5 Ma. In this model, the pre-Messinian Nile delta sediments are locally derived from the Red Sea Hills (RSH) (Issawi and McCauley 1992). B) The Blue Nile has been connected to the lower Nile since the Oligocene (Burke and Wells 1989). Onshore fieldwork characterised each possible source area (Ethiopian flood basalts, Archean craton, and Neoproterozoic basement and Phanerozoic cover sequences of the RSH) using petrography, geochemistry and isotope studies. Tertiary-aged Nile delta sediments provide a unique archive of the river’s palaeodrainage history, which were analysed from conventional core from exploration and appraisal wells in order to identify the occurrence (if any) of these sources in the delta geological record. Heavy mineral, petrographic, U/Pb rutile and Lu/Hf zircon analyses indicate Blue Nile and/or RSH input to the Nile delta since at least the Oligocene with very little input from the White Nile. Sr and Nd whole-rock analyses of mud samples allow discrimination between the Blue Nile and RSH sources and may, subject to further analyses, confirm Blue Nile input to the delta since the Oligocene. U-Pb zircon analyses reveal the presence of 20-30 Ma zircons in both the modern river sediments from the Ethiopian Highlands and the Nile Delta core from the early Miocene to present day indicating a connection between the lower Nile and the Blue Nile since at least the early Miocene.
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This study documents the palaeodrainage history of the Nile River, in particular the time of transition from a small locally sourced drainage network to the initiation of an extensive Nile catchment, by conducting a provenance study of the well-dated Nile cone sediments. The identification of specific source inputs into the Nile cone has important implications for the prediction of reservoir quality and connectivity in hydrocarbon reservoirs. Presently, the Nile river drains as far south as south of Lake Victoria, with the White Nile draining largely Cratonic basement rocks of Archean to Proterozoic ages and the Blue Nile draining Cenozoic continental flood basalts and Neoproterozoic basement in Ethiopia. However, the timing of catchment expansion to its current extent is highly debated. There are a number of proposed palaeodrainage reconstructions, two of which are: A) The Blue Nile did not connect with the main (lower) Nile until the Late Messinian, and the White Nile did not connect with the lower Nile until at 0.5 Ma (e.g. Issawi and McCauley, 1992). In this model, the pre-Messinian Nile cone sediments are derived exclusively from the northern part of the present drainage basin, from the Red Sea Hills. B) The Blue Nile and Atbara Rivers have been connected to the main (lower) Nile since the Oligocene, simultaneous with large scale regional uplift and volcanism in the Ethiopian Highlands; with the river following a similar course to present day (Burke and Wells 1989). The palaeo-Nile cone sediments have the capacity to provide a unique archive of the river’s highly debated palaeodrainage history. Our first objective was to characterise petrographically, geochemically and isotopically each possible source area (Ethiopian Flood Basalts, African Craton and Red Sea Hills) using a multidisciplinary approach in order to identify the presence (if any) of sediment from these sources in the delta core samples. Heavy mineral, petrographic, U-Pb zircon and rutile analyses so far support the hypothesis of the Blue Nile and/or the Red Sea Hills contributing detritus to the Nile delta since the Oligocene with very little input from the White Nile throughout the core. XRF, Sm-Nd and Rb-Sr analyses also point to a significant mafic (Blue Nile or Red Sea Hills) source since the Oligocene. More recent analytical work has involved studying the Lu/Hf of zircon. This is being carried out to assess the occurrence of the 30Ma zircons identified in the core, the Ethiopian Highlands and at Faiyum in the Western Desert. These results are preliminary, and the Red Sea Hills region in particular is subject to on-going work to more completely characterise its geochemical and isotopic signature.