@phdthesis{Kukulus2004, author = {Kukulus, Matthias}, title = {A quantitative approach to the evolution of the central Walvis Basin offshore NW-Namibia : structure, mass balancing, and hydrocarbon potential}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-11075}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2004}, abstract = {Rifting and breakup of Westgondwana in the Late Jurassic/ Early Cretaceous initiated the formation of the South Atlantic and its conjugated pair of passive continental margins. The Walvis Basin offshore NW-Namibia is an Early Cretaceous to recent depositional centre with a typically wedge-shaped postrift sedimentary succession covering an area of 105000km2. A 2D model transect across the central Walvis Basin and adjacent onshore areas is used as a case study to investigate quantitatively the denudational history of the evolving passive margin and the related contemporaneous depositional postrift evolution offshore. The database for both the onshore and offshore part of the model traverse is well constrained by own field work, published data as well as by seismic and well data supported by samples. The ultimate goal of this project is to present an integrated approach towards a quantitative link between surface processes and internal processes in terms of a mass and process balance.}, subject = {Namibia }, language = {en} } @phdthesis{Wanke2000, author = {Wanke, Ansgar}, title = {Karoo-Etendeka Unconformities in NW Namibia and their Tectonic Implications}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-3234}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2000}, abstract = {In north-western Namibia the fills of the Karoo-Etendeka depositories can be subdivided into (1) a Carboniferous-Permian, (2) a Triassic-Jurassic and (3) a Cretaceous megasequence, each recording extensional periods related to successive rifting phases in the evolving South Atlantic. The tectonic environment of the depositories in north-western Namibia changes successively from the coast towards the continental interior, which is reflected by the facies distribution and the position of time-stratigraphic gaps. Close to the present-day coastline synsedimentary listric faults, trending parallel to the South Atlantic rift (N-S), caused the formation of wedge shaped sediment bodies. Here, the Karoo Supergroup is only represented by the Permian succession in the Huab area. A hiatus within the Permian can be recognised by the correlation with the main Karoo Basin in South Africa and the Brazilian Paran{\´a} Basin. This stratal gap correlates with a pre-Beaufort Group unconformity in the main Karoo Basin that might be related to an orogenic pulse in the Cape Fold Belt. The Permian succession itself is unconformably overlain by the Lower Cretaceous Etendeka Group. This hiatus extending from the Upper Permian to the Lower Cretaceous has probably been induced by a combination of rift shoulder uplift and additional crustal doming associated with Etendeka flood volcanism. The enhanced tectonism during the Early Cretaceous controlled accommodation space for the alluvial-fluvial and aeolian deposits of the lower Etendeka Group. Disconformities within those deposits and the overlying lava succession attribute to distinct phases of tectonic and volcanic activity heralding the South Atlantic breakup. Towards the south-east, the Karoo succession becomes successively more complete. In the vicinity of Mt. Brandberg Early Triassic strata (Middle Omingonde Formation) follow disconformably above the Upper Permian/Lowermost Triassic Doros Formation. The sedimentation there was essentially controlled by the SW-NE trending Damaraland Uplift. South of the Damaraland Uplift the SW-NE trending Waterberg-Omaruru Fault zone is interpreted as a sinistral oblique-slip fault that compartmentalised the South Atlantic rift. This fault controlled accommodation space of the entire Triassic Omingonde Formation and the Early Jurassic Etjo Formation in its associated pull-apart and transtension structures. A locally well developed angular unconformity defines a hiatus between the two formations. Correlation with the main Karoo Basin in South Africa confirms that this gap is of a regional extent and not only a local, fault induced feature. Furthermore, it might also correlate with an orogenic pulse of the Cape Fold Belt. In general, the Mesozoic megasequences record the long-lived history of the southern Atlantic rift evolution. Rifting has been controlled by orogenic pulses derived from the Samfrau active margin throughout the Mesozoic. The associated intracratonic E-W extension caused the formation of grabens and conjugated oblique-slip zones. The generation of voluminous flood basalts marks the climax of intracratonic extension that was accompanied by enhanced uplift of the rift shoulders.}, subject = {Namibia }, language = {en} } @phdthesis{Krapf2003, author = {Krapf, Carmen}, title = {Ephemeral river systems at the Skeleton Coast, NW-Namibia - Sedimentological and geomorphological studies on the braided river dominated Koigab Fan, the Cenozoic succession in the Uniabmond area and comparative studies on fluvio-aeolian interaction between ephemeral rivers and the Skeleton Coast Erg}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-6013}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2003}, abstract = {The Skeleton Coast forms part of the Atlantic coastline of NW Namibia comprising several ephemeral rivers, which flow west-southwest towards the Atlantic Ocean. The area is hyper-arid with less than 50 mm average annual rainfall and a rainfall variability of 72\%. Therefore, the major catchment areas of the rivers are about 100-200 km further inland in regions with relatively high annual rainfall of 300-600 mm. The coastal plain in the river downstream areas is characterized by a prominent NNW trending, 165 km long belt of 20-50 m high, locally compound, barchanoid and transverse dunes. This dune belt, termed Skeleton Coast Erg, starts abruptly with a series of barchans and large compound dunes 15 km north of the Koigab River and extends from 2-5 km inland sub-parallel to the South Atlantic margin of NW Namibia over a width of 3-20 km. As the SSE-NNW trending dune belt is oriented perpendicular to river flow, the dunefield dams and interacts with the west-southwestward flowing ephemeral river systems. This study focused on three main topics: 1) investigation and classification of the Koigab Fan, 2) the investigation of the Cenozoic succession in the Uniabmond area and 3) comparative studies of fluvio-aeolian interaction between five ephemeral rivers and the Skeleton Coast Erg. Sedimentological and geomorphological investigations show that the Koigab Fan represents a yet undocumented type of a braided fluvial fan system, which operates in an arid climatic, tropical latitude setting, is dominated by ephemeral mixed gravel/sand braided rivers, lacks significant vegetation on the fan surface, has been relatively little affected by human activity, is a perfect study site for recording various types of fluvio-aeolian interaction and thereby acts additionally as a model for certain Precambrian and Early Palaeozoic fan depositional systems deposited prior to the evolution of land plants. The Cenozoic succession in the Uniabmond area consists of three major unconformity-bounded units, which have been subdivided into the Red Canyon, the Whitecliff, and the Uniabmond Formation. The Tertiary Red Canyon Fm. is characterized by continental reddish sediments documenting an alluvial fan and braided river to floodplain depositional environment. The Whitecliff Fm. displays a wide variety of continental and marine facies. This formation provides the possibility to examine fluvio-aeolian interactions and spectacular, steep onlap relationships towards older sediments preserved in ancient seacliffs. The Whitecliff Fm. has been subdivided into four sedimentary cycles, which resulted from sea level changes during the Plio- to Middle Pleistocene. The following Uniabmond Fm. provides a unique insight into the depositional history of the NW Namibian coast during the Last Pleistocene glacial cycle. The formation has been subdivided into four units, which are separated by unconformities controlled by sea level changes. Unit 1 represents deposits of an Eemian palaeo-beach. The overlying Units 2-4 build up the sedimentary body of the Uniab Fan, again a braided river dominated fan, which is nowadays degraded and characterized by deeply incised valleys, deflation surfaces and aeolian landforms. The Uniabmond Fm. is overlain by the dunes of the Skeleton Coast Erg, whose development is related to the Last Glacial Maximum (LGM). The damming of river flow by aeolian landforms has been previously recognized as one of several principal types of fluvio-aeolian interaction. Five ephemeral rivers (from S to N: Koigab, Uniab, Hunkab, Hoanib, Hoarusib), which variously interact with the Skeleton Coast Erg, were chosen for the purpose of this study to consider the variability of parameters within these fluvio-aeolian systems and the resulting differences in the effectiveness of aeolian damming. The fluvio-aeolian interactions between the rivers and the dune field are controlled by the climate characteristics and the geology of the river catchment areas, the sediment load of the rivers, their depositional architecture, the longitudinal river profiles as well as the anatomy of the Skeleton Coast Erg. Resulting processes are 1) aeolian winnowing of fluvially derived sediments and sediment transfer into and deposition in the erg; 2) dune erosion during break-through resulting in hyperconcentrated flow and intra-erg mass flow deposits; 3) the development of extensive flood-reservoir basins caused by dune damming of the rivers during flood; 4) interdune flooding causing stacked mud-pond sequences; and 5) the termination of the erg by more frequent river floods.}, subject = {Namibia }, language = {en} }