Andreas Nduutepo’s research while affiliated with Ministry of Mines and Energy and other places

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Publications (2)


Transport of ‘Nama’‐type biota in sediment gravity and combined flows: Implications for terminal Ediacaran palaeoecology
  • Article

November 2024

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177 Reads

Sedimentology

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Andreas Nduutepo

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[...]

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The lower Nama Group in southern Namibia contains trace fossils and soft‐bodied and biomineralized macro‐organisms from the terminal Ediacaran Period ( ca 550 to 539 Ma), offering insights into early metazoan evolution. Interpretation of the fossilized Nama Group organisms as being preserved in, or very close to, the environments in which they originally lived has yielded insights into organism feeding habits, reproduction and life histories. Sedimentological evidence presented here reveals that typical ‘Nama‐type’ Ediacaran macro‐fossils ( Cloudina , Ernietta , Pteridinium and Rangea ) in the Dabis and Zaris formations of the Witputz Sub‐basin seldom preserve organisms in life position in their original palaeoenvironments. Both soft‐bodied and biomineralizing organisms were transported in sediment gravity flows (debris flows, turbidity flows and transitional debris flow‐turbidity flow ‘hybrid’ event beds) or combined flow (hummocky cross‐strata) to their terminal environment of deposition in shoreface and offshore shelf settings. Transport has placed studied beds and their associated macro‐organisms in depositional settings detached from the original life habitat, with macro‐organisms sourced from shallower‐water, up‐slope environments. Integrated sedimentological and palaeontological data indicate that the Nama Group may not provide a high‐fidelity record of original Nama ecosystems. Individual macro‐organisms are clasts within beds, and can be horizontal, imbricated or chaotic in orientation. Transport can blend different communities at various scales (bed, outcrop and basin), complicating interpretations of life habitats, species interactions and taxon‐specific ecology, such as feeding behaviour and life position of organisms. Recognition of organism transport also impacts datasets used for comparing global Ediacaran fossil assemblages, with implications for tracking spatial and temporal patterns in early animal evolution.


Fig. 1. (a) Study area in the Orutanda Fjord in northern Namibia, showing the location of study sections examined in recently published work and in the present paper. The lack of geographical overlap between these studies should be noted. In the present study, loose sand prevented our access to the sections of Rosa et al. (2023) and hence the possibility to reappraise them. (b) and (c) are two oblique aerial views from Google Earth (image © 2024 Airbus) with ×3 vertical exaggeration, emphasizing the geomorphology of the Orutanda Fjord. The location of the Dwyka Group outcrops within the valley are indicated in pink, along with the location of our three key outcrops and associated figures throughout this paper. Source: Rosa et al. (2023).
Fig. 2. (a) Orthomosaic and (b) map interpretation of our northernmost study section (Outcrop 1), which aims to characterize the deformation styles in the heterolithic facies association comprising folded sandstone, siltstone and lonestone-bearing shale.
Fig. 3. (a-c) Three sedimentary logs of the Dwyka Group deposits in the southern Orutanda Fjord, arranged from north to south. We recognize at least three levels of diamictite in the succession. At the northern section, large-scale soft-sediment deformation characterizes the succession (mapped in Fig. 2). At the Impala section, gravelly sandstones and sandstones crop out, and express both humpback dune bedforms interpreted as the products of supercritical flows together with trough and planar cross strata. At the southern section, a lithologically diverse succession is exposed, including a diamictite with large striated boulders at the base of the succession. Source: humpback dune bedforms from Lang et al. (2021).
Fig. 4. Aspects of the soft-sediment deformation structures preserved in the northern logged section (Fig. 3a). (a) Refolded folds developed in sandstone, with evidence for shear bands on the fold limbs. (b) Recumbent stack of intrabed folds with local evidence for reverse faulting. (c) Basal surface of a sandstone bed with bounce marks and primary current lineations overprinted by shear bands. (d) Folded and overturned sandstone bed showing normal grading.
Fig. 7. (a-e) Aspects of the cross-bedded sandstone facies at our southernmost study site (see Fig. 1 for location and Fig. 3 for sedimentary profile).
Anatomy of a 300-million-year old fjord in Namibia
  • Article
  • Full-text available

October 2024

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106 Reads

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1 Citation

Journal of the Geological Society

Namibia is remarkable in terms of its network of approximately 300-million-year-old fjords, cut by Gondwanan glaciers at high palaeolatitudes during the Late Palaeozoic Ice Age (LPIA). A classic suite of structures is preserved on Proterozoic bedrock, including striations, roches moutonnées and other subglacial features within many of these palaeovalleys. Some palaeovalleys are plastered with comparatively thin diamictites (a few metres) of presumed subglacial origin, in turn capped by ice marginal delta successions (tens of metres). Close examination of deposits in the outer Orutanda Fjord palaeovalley reveals an architecture that shows departure from this trend. There, boulder-bearing diamictites pass laterally into highly contorted heterolithic successions comprising folded and faulted sandstones, siltstones and shales. Aerial imagery from UAVs in tandem with traditional field observations permits mapping of assemblages of soft-sediment deformation structures (tight to recumbent folds, deformation bands, faults, sheath folds) together with spatial mapping of the long-axis of boulders in diamictite. Collectively, this assemblage of structures points towards subglacial deformation, and hence an origin as a “deforming bed” beneath a glacier. Whilst several open questions remain regarding the precise deformation mechanisms, the concept of glacial re-advances into a deeply incised palaeovalley is proposed, by direct analogy to similar stratigraphic architectures in the LPIA record of South America.

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