Rapide Versenkung eines trockenen Sandsteins - die besondere kompaktionsdominierte Diagenese der Twyfelfontein Formation, NW Namibia
Zusammenfassung der Projektergebnisse
The main goal of this project was to understand the effect of pronounced mechanical compaction on the diagenesis of an eolian sandstone. Target of investigation was the Lower Cretaceous Twyfelfontein Formation in NW Namibia, that was quickly buried by the Paraná-Etendeka flood basalts at around 130 Ma. Due to the outbreak of the Covid-19 pandemic, fieldwork had to be postponed for two years, which stripped the project from its basis. As an alternative, it was decided to focus on existing samples of the Jurassic Etjo Formation, i.e. another Namibian aeolian sandstone that was also affected by the Etendeka volcanic extrusion. The reliance of samples and data collected by someone else a decade ago made the analysis and interpretation challenging and time-consuming. A first manuscript that includes a detailed petrographic description of this sandstone at three key outcrop localities distributed across central Namibia and a proposed regional diagenetic evolution is submitted. Core of this work is the presentation of a sandstone that spatially exhibits a very high variability of diagenetic properties. This is assigned mainly due to spatially varying thicknesses of the Etendeka volcanic province. A second manuscript is currently being finalized and includes numerical prediction modeling on diagenesis. This will provide a quantification of the Etendeka rock column thickness that might have been emplaced above the Etjo Formation. The investigation of the Twyfelfontein Formation was started after Covid-19 travel restrictions were eased and fieldwork was undertaken in 2022 and 2023. The analysis of samples collected of the Twyfelfontein Formation is still ongoing, yet preliminary observations hint towards a high variability of mechanical compaction throughout this sandstone. The findings of calcite-cemented sandstone bodies as well as calcite veins cutting through the sandstone allowed for U-Pb calcite dating and clumped isotope thermometry. Preliminary results show a calcite precipitation in the Cenozoic (<64 Ma) at low temperatures (<61°C). As the calcite cement is a late diagenetic imprint in the paragenetic sequence, these results are very helpful in pinning the timing of quartz cementation and grain breakage to the Cretaceous. This will also improve the accuracy of the diagenetic prediction modeling to elucidate the burial depth/temperature history of the Twyfelfontein Formation. Overall, the present results from both the Etjo and Twyfelfontein Formations highlight the diagenetic variability a sandstone can attain underneath a volcanic province and demonstrate the importance of understanding local and regional parameters for the prediction of sandstone reservoir quality. Further, the analytical results and the diagenetic prediction modeling will provide important constraints on the post-continental breakup exhumation paths of rock in Namibia and will help in refining thermochronologic models.
Projektbezogene Publikationen (Auswahl)
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Diagenetic evolution of aeolian sandstone under a massive sheet of flood basalts – the case of the upper Etjo Formation, Namibia. School on Sandstone Diagenesis, Erlangen, Germany.
Salomon, E., Caracciolo, L., Stollhofen, H., Bonnell, L., Lander, R.H. & Kittel, M.
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The impact of Etendeka flood basalts on the diagenesis of the fluvio-aeolian Jurassic Etjo Formation, Namibia. Geological Society of London Energy Group, "The impacts of volcanism on sedimentary basins and their energy resources", London, United Kingdom.
Salomon, E., Caracciolo, L., Stollhofen, H., Bonnell, L., Lander, R.H. & Kittel, M.
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Thickness estimates of the Etendeka volcanic province based on diagenesis of the Jurassic Etjo Formation, Namibia. 29th Colloquium of African Geology, Windhoek, Namibia.
Salomon, E., Stollhofen, H., Caracciolo, L., Bonnell, L., Lander, R.H. & Kittel, M.
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Burial of a sand sea: Heterogeneous compaction and cementation of the jurassic Etjo Formation, Namibia and what it tells. Marine and Petroleum Geology, 168, 107044.
Salomon, Eric; Stollhofen, Harald; Caracciolo, Luca; Bonnell, Linda M.; Lander, Robert H. & Kittel, Mario
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Calcite veins as local fluid flow barriers in reservoir rock? The odd occurrence of veins in highly porous aeolian sandstone in Namibia. EGU General Assembly, Vienna, Austria.
Salomon, E., Meckler, A.N. & Stollhofen, H.
