Source to sink systems of Senegal

  • Monty Pearson

Student thesis: Phd

Abstract

“In geology, as in history, the material in hand remains silent if no questions are asked. The nature of these questions depends on the "school" to which the geologist belongs and on the objectivity of his investigations.� - Reinout Willem van Bemmelen. In terms of sedimentary provenance, the answers to these questions can be unravelled through the identification, discrimination and correlation of minerals within a given sediment. Defining changes in sediment provenance can aid in the modelling of source to sink dynamics. Paleo source to sink system analysis requires a complete earth systems model approach, utilising regional geology, tectonics, climate, and modern-day source to sink analogues. This study examines the Cretaceous source to sink systems of Senegal, NW Africa, integrating a broad regional dataset using an integrated mineralogical approach. A multidisciplinary mineralogical approach to sedimentary provenance utilizes several analytical methodologies, to create as higher-resolution modelling as possible. These analytical methodologies include whole-rock powder X-ray diffraction, < 2 μm clay X-ray diffraction, heavy mineral analysis through optical microscopy, petrographic analyses, single mineral speciation by scanning electron microscopy, Sr and Nd isotopic analyses of clay and U/Pb zircon geochronology. Modelling of Cenozoic to modern-day source to sink systems allows reconstruction of the provenance of sediment denuded from the West African Craton, and the role of sediment recycling within the onshore basins. This research has developed the first high-resolution source to sink model for the Senegal part of the MSGBC Basin during the Cretaceous and has wider implications in understanding the role of climate and tectonics in sediment delivery into basins. The most significant regional geological and tectonic events to affect the Senegal since the Pan African orogenies (800-520 Ma) are the Early-Permian Mauritanide orogeny (320-290 Ma), Pangea break-up and rifting between S. America and Africa, with associated CAMP volcanism (200 Ma) and uplift of the Mauritanides between the Albian and Maastrichtian (113-66 Ma). In addition to tectonic controls, climate is another principal driver for paleo-drainage reorganisation. During the Cretaceous an antithetical shift in climate from warm and arid (145-115 Ma), to hot and humid (100-88 Ma), increased fluvial catchment and energy. Understanding the compositional changes of clay-mineralogy in basinal neritic sediments and deep-sea sediments allows us to better constrain the timing and evolution of hydroclimatic processes of NW Africa during the Cretaceous. Transportation of chlorite-illite during the very-Early Cretaceous was restricted to modest intra-basinal river systems within an arid environment, whilst aeolian processes transported smectite from higher altitude regions of the West African Craton. During the Albian, continued fragmentation of Pangea resulted in the opening of the juvenile equatorial Atlantic gateway and the associated evolution of the paleo-intertropical convergence zone contributed towards the increased humidity within the tropics. This increase in humidity is reflected in increases in kaolinite deposition in both nearshore and offshore basins. The Cenomanian-Turonian was host to the Cretaceous Thermal maximum which witnessed extreme temperatures and humidity with larger river systems extending further into the West African Craton sourcing and transporting smectite into the Senegalese Basin. The occurrence of palygorskite in deep-sea sediments are representative of ocean anoxia OAE2 and OAE3 through the authigenesis of pre-existing seafloor smectite. The catchment of the paleo-Senegal River remained relatively static throughout the Cretaceous, actively eroding the northern-extent of the Senegalese Mauritanides throughout the Albian. A southern paleo-system, analogous to the modern-day Gambian River was eroding the highland terrane of the Fouta Djal
Date of Award1 Aug 2025
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorJonathan Redfern (Supervisor) & Stefan Schroeder (Supervisor)

Keywords

  • Mineralogy
  • Climate
  • Provenance
  • Senegal
  • Heavy mineral

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