Controls on stratigraphic development of shelf margin carbonates: Jurassic Atlantic margin - Essaouira-Agadir Basin, Western Morocco

  • Aude Marie Luce Fran Duval-Arnould

Student thesis: Phd


The Jurassic succession along the Atlantic margin offshore Morocco and on the Nova Scotia conjugate margin is marked by development of extensive carbonate platforms, alternating with siliciclastic influx. This thesis aims to improve understanding of the development and architecture of carbonate dominated sequences along a passive margin, and the relative controls of eustasy, climate and tectonics on facies distribution. Early-post rift deposition started with development of a carbonate ramp during the Upper Sinemurian to Lower Pliensbachian, later exhumed and tilted before deposition of a fluvial package. This is interpreted to mark an important regional inversion event of Toarcian age, with a fluvial system eroding down to Triassic deposits. This is followed by an upper Toarcian transgression that established a shallow marine carbonate platform, dominated by peritidal deposits. These conditions persisted throughout the Middle Jurassic in the Essaouira part of the basin, while around Agadir a siliciclastics influx from the south occurred. The origin of the siliciclastic intervals can be linked to uplift of the Anti-Atlas documented by recent thermochronology studies. The Middle to Upper Jurassic interval is dominated by carbonate ramp deposits with development of discrete bioherm buildups. This is a proven reservoir offshore Morocco and Nova Scotia, however facies distribution and geometry is poorly documented. The interval has been extensively sampled for biostratigraphy, with the existing collections re-evaluated, resulting in new data that improves dating. Detailed sedimentological logging of extensive outcrops has identified the establishment of a carbonate ramp during the Callovian transgression containing two potential reservoir intervals: the lower Callovian oolities and middle Oxfordian buildups. Biostratigraphic analysis has identified a previously unrecognised upper Callovian to middle Oxfordian hiatus. The age of the buildups has been more precisely constrained to middle Oxfordian, suggesting their establishment was broadly synchronous. The buildups show a range of sizes and geometries, with a typical evolution from low relief microsolenid colonies to higher relief diversified colonies. The major bioherms are fringed by a rubble facies that forms clinoforms. Highly dolomitised, these deposits enhance the reservoir potential of the formation by creating connections between the coral buildup. This formation is followed during the upper Oxfordian by a major regression that established peritidal conditions. This study provides the first detailed analysis of the entire lower to upper Jurassic interval undertaken using a unified systematic analysis. The influence of tectonics at certain times is shown by the repeated influx of siliciclastics and deformation of the basin. At outcrop scale, integrated mapping has allowed the facies relationships and control of facies development to be addressed. The results provide further insight into the size of bioherms in the Oxfordian and their typical distribution, that can be extrapolated to the subsurface to give a better understanding of buildup geometries Offshore Morocco and the Scotian Basin, where they are potential hydrocarbon reservoirs.
Date of Award1 Aug 2019
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorJonathan Redfern (Supervisor) & Stefan Schroeder (Supervisor)


  • Callovian transgression
  • Buildup
  • Essaouira-Agadir Basin
  • Central Atlantic
  • Jurassic
  • Carbonates
  • Passive Margin

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