Browsing by Author "Abrahams, Miengah"

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    Evaluation of tridactyl theropod tracks in southern Africa: quantitative morphometric analysis across the Triassic–Jurassic boundary
    (2020) Abrahams, Miengah; Bordy, Maria Emese; Knoll, Fabien
    In the Mesozoic, dinosaur abundance and diversity steadily increased from the Carnian to the Triassic booming soon after the end Triassic Mass-Extinction event (ETE), marking a key period in archosaur history. In southern Africa, the Triassic–Jurassic Boundary (TJB) is contained in the richly fossiliferous, fluvio-lacustrine-aeolian Upper Triassic to Lower Jurassic strata of the Stormberg Group. More specifically, the middle Norian – Pliensbachian Elliot and Clarens formations (upper Stormberg Group) of main Karoo Basin, host a diverse tetrapod osteological and ichnite record. Due to an absence of high resolution radioisotopic age determinations, the exact stratigraphic placement of the TJB remains unknown. Although diverse ichnofossils attributed to Saurischians and Ornithischians are preserved in the Stormberg Group, the record is dominated by isolated tridactyl tracks that can be assigned to common ichnogenera like Grallator, Eubrontes and Kayentapus. Ideally, these track morphologies would reflect the trackmaker's autopod morphology, but complex interactions between the trackmaker and tracking substrate may affect the final footprint shape. Tracks with a high morphological preservation grade may be used to infer information (e.g., body length, hip height, weight) about the trackmaker, which is especially useful when skeletal remains are scarce, as is the case with theropod body fossils in the Elliot and Clarens formations. Herein, we present the findings of an extensive southern African field-based study to quantify the morphological variation of Grallator, Eubrontes and Kayentapus tracks across the TJB in the upper Stormberg Group. Furthermore, this study produced the first detrital zircon Uranium–Lead (U-Pb) LA-ICPMS ages of the major ichnosites from this region, and confirmed that the TJB is within the Elliot Formation, near the boundary of the lower and upper Elliot Formation (i.e., near the contact of the informal lEF and uEF). Across this contact, the considered tridactyl tracks become more abundant, larger and have a less pronounced medial digit projection. These morphological changes are gradational, with tracks from the Clarens Formation being distinct to tracks from the lEF, while the uEF tracks being intermediate between the lEF and Clarens Formation. A decrease in the mesaxony (Dp/TS ratio) and a decrease in medial digit projection relative to track length can be detected in both small and large tridactyl tracks. These apparent trends in the upper Stormberg Group are consistent with global tridactyl trends, which suggest an overall increase in theropod abundance and body size across the Jurassic. Moreover, the reason for the less prominent medial pedal digit is linked to a better weight distribution across the autopod in the increasingly larger theropods. Last but not least, Grallator, Eubrontes and Kayentapus ichnogenera which may be attributed to at least three different groups of theropod-like trackmakers, suggest a higher palaeo-diversity and abundance of tridactyl dinosaurs in southern Africa than is known from the osteological record.
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    From grains to tracks: high-resolution sedimentology of track-bearing Stormberg strata, southern Africa
    (2023) Mpangala, Loyce Elesia; Abrahams, Miengah; Bordy, Emese
    Tracks registration is influenced by the dynamic interplay between the pedal anatomy of the trackmaker, its behaviour, and the substrate conditions it interacts with. Differences in substrate conditions, especially those linked to grain size and moisture content, often result in the most dramatic variations in track morphology. In the upper Stormberg Group, main Karoo Basin of southern Africa, diverse trace fossils, primarily comprising Upper Triassic– Lower Jurassic dinosaur tracks, are preserved. Extensive studies have been carried out to document these individual tracksites and to examine the variations between sites and through time, with recent studies suggesting that track abundance and anatomical fidelity increase up-stratigraphy. Despite the well-established understanding of the effects of substrate on track registration and preservation, these past studies have not specifically focused on the substrate conditions, and when substrate conditions were considered, the emphasis was primarily on macro-sedimentary features. Here, we examine the microsedimentary features of track-bearing units in the upper Stormberg Group using petrographic techniques, to better understand the palaeosubstrate and its effect on fossil track registration and preservation. The analysis revealed that very fine-grained sands and substrates modified by microbial activity tend to preserve tracks with greater abundance and higher anatomical fidelity. Furthermore, the prevalence of very fine-grained and microbially modified strata, and their associated track trends, increases in younger stratigraphic units. Across the Triassic– Jurassic boundary of southern Africa, there was a proliferation of dinosaur populations, possibly linked to the end–Triassic mass extinction events, which has been credited globally for track abundance increases in the Lower Jurassic. However, our findings suggest that, locally, the observed increase in track abundance (and anatomical fidelity) up-stratigraphy may also be linked to substrate–composition differences, which were ultimately controlled by large-scale changes in the palaeoenvironment from high-energy meandering fluvial to lowerenergy aeolian-lacustrine settings in the Late Triassic and Early Jurassic, respectively
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    The geochemistry of fossil termite nests in Calitzdorp, Western Cape, South Africa
    (2025) Jacobs, Rabia; Abrahams, Miengah; Harris, Chris
    Termites alter soil profiles by gathering nutrient-rich materials to construct their nests, known as termitaria. Certain termite species also fortify their termitaria using a combination of saliva and excrement (frass), resulting in geochemically distinct termitaria relative to the host soils. The enrichment of exchangeable bases derived from organic matter, including termite frass, and upward groundwater movement frequently leads to post-construction carbonate precipitation within termitaria. Fossil termitaria near Calitzdorp, Western Cape, South Africa, were described nearly two decades ago, but no detailed work has been performed on them until now. Here, these calcretised Quaternary features, which are largely composed of calcite and dolomite, are investigated to 1) determine whether there is evidence of nutrient mining or preferential nutrient enrichment in the fossil termitaria compared to their host palaeosols and 2) assess the palaeoenvironmental conditions at the time of carbonate precipitation. The fossil termitaria are distinct from their host palaeosols, being enriched in CaO, MgO, MnO, and P₂O₅ and depleted in Al₂O₃, Cu, Fe₂O₃, K₂O, and Zn, suggesting that the termites enriched their termitaria by depositing organic matter. However, there is no evidence of termites selectively mining materials, as observed in modern termitaria. The termitaria's unique geochemical signature is attributed to post-construction carbonate precipitation facilitated by termite activity. The enrichment of CaO and MgO can be linked to the termites' localised deposition of organic matter, rich in exchangeable base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺). While calcite is present in other termitaria, the dolomite found in the termitaria in this study is distinctive and likely resulted from secondary carbonate precipitation aided by magnesium-rich organic matter. This exchangeable base enrichment, enhanced by termite activity, likely led to the preferential calcretisation of the termitaria, setting them apart from their host palaeosols. The pedogenic carbonate within the termitaria and some palaeosols indicates an arid environment at the time of carbonate formation. The δ¹³C values of the termitaria range from 0 to -8‰, indicating a mixed C₃-C₄ vegetation matrix, with a more pronounced C₄ signature at the northern ichnosite and a stronger C3 signature in the southern ichnosite. This mixture suggests a close association with year-round rainfall, with a higher proportion of arid-adapted vegetation in the north and a lower proportion in the south. Furthermore, the δ¹⁸O values indicate a similar water source between the two ichnosites and reflect palaeotemperatures ranging from ~20 to 35 °C.