Palaeoenvironmental and palaeoclimatic characterization of Upper Jurassic sedimentary sequences with dinosaur footprints of the M'Goun Geopark (High Atlas, Morocco)

Abstract

The Iouaridène Formation (Upper Jurassic, High Atlas, Morocco) is a relevant area for the study of dinosaur footprints, but up to now little is known about the palaeoenvironmental conditions at the time of its formation. This work consists of a sedimentological, geochemical, and mineralogical study of part of the sedimentary succession of the Iouaridène Formation, especially Units B and C. The cyclic sedimentation pattern in Unit B, characterized by alternating soft claystones and siltstone layers and hard sandstone layers with ripples and mudcracks, reflects a dynamic environment shaped by recurring flooding and emersion events. This cyclicity is marked by fluctuations in quartz, clay and analcime content, leading to sedimentary sequences capped by silcretes, which indicate sedimentation hiatuses. The formation of mudcracks and the preservation of dinosaur footprints further highlight the depositional conditions. Mineralogical and geochemical analyses reveal an upwards trend to increasingly arid conditions during the deposition of Unit B, with an increase in quartz and decrease in kaolinite, as well as palaeoclimatic geochemical proxies. The presence of analcime supports a lacustrine environment under arid or semi-arid conditions and fluctuations in the alkalinity of pore waters. The CIA and CIW values reflect moderate to weak weathering congruent with the arid conditions indicated by other proxies. Decreasing C-values towards the top of the section points to environmental changes from semi-arid toward more arid conditions. Other indexes of salinity and aridity (Sr/Ba and Zr/Rb ratios), also support the trend towards increasing aridity in Unit B. In contrast to this, Unit C indicates more humid and deeper conditions, marked by the record of cross-bedding, lacustrine ostracods and fish bones, and the absence of mudcracks, silcretes, and dinosaur footprints. This variability underscores the dynamic climatic and environmental history of the Iouaridène Formation, reflecting the final phase of the Atlasic Basin fill during the Late Jurassic. This is the first work on the palaeoclimatic conditions of the Iouaridène Formation and the first study that integrates sedimentology, geochemistry and mineralogy of this formation. These findings enhance the understanding of the geological evolution of the Jurassic of the M'Goun Geopark and set the background for future research on the area to explore the interactions between climatic conditions, sedimentary processes, and biological activity in Jurassic lacustrine environments.