The Lithostratigraphy, Palaeontology, and Palaeoenvironmental Interpretation of the Non-marine, Lower Cretaceous Wessex Formation (Wealden Group, Upper Berriasian-Upper Barremaian) of the Isle of Purbeck, Dorset, Southern England

Abstract

The non-marine, Lower Cretaceous (upper Berriasian – upper Barremian) Wessex Formation (Wealden Group) of the Wessex Sub-basin, southern England, represents approximately 18 million years of fluviatile deposition. Two hundred years of geological examination has resulted in the palaeoenvironmental interpretation of a semi-arid wetland and the documentation of a diverse, dinosaur-rich biota. Given the scarcity of Early Cretaceous aquatic and terrestrial strata globally, analysis of the Wessex Formation’s palaeontological content and depositional settings remains prominently at the forefront of geological research. Although historically well-documented, the Wessex Formation of Dorset remains largely disconnected from modern geological analysis;
consequently, palaeoenvironmental examination, contemporary lithostratigraphical documentation, and biotic analysis have been employed with an aim of providing a more complete palaeoecological and depositional understanding of Dorset’s Early Cretaceous wetlands. Collectively, extensive lithostratigraphical logging and the bulk sampling of fossiliferous horizons facilitated the production of a formalised lithostratigraphy that benefits from detailed palaeoenvironmental interpretation, and comprehensive palaeoecological analysis.
The lithostratigraphical documentation of eight coastal sections on the Isle of Purbeck, Dorset, results in the erection of a comprehensive new lithostratigraphy that documents the depositional evolution of the Wessex alluvial plain as sedimentation responded to both local and global tectono-climatic controls, as well as relative sea level change. Documentation of the succession’s lithological composition, internal bed framework, and sedimentological architecture has resulted in the production of a refined regional depositional model that accommodates both medial braidplains and more distal, meanderplain settings. Furthermore, the targeted examination of both plant debris beds and newly discovered microvertebrate-rich gutter casts permits the biotic documentation of Dorset’s Early Cretaceous wetlands elucidating the regions palaeoecological diversity, and trends within palaeobiogeographical distribution. Importantly, ostracod biostratigraphy confirms the presence of the basal Wessex Formation in east Dorset; consequently, the biotic analysis undertaken at Dungy Head represents the first account of pre-Hauterivian faunal diversity within the formation. Several genera recorded represent either a first occurrence within the Wessex Formation (albuliform fish), or confirm a taxon’s presence within the Early Cretaceous of southern England (Parvodus celsucuspus).
Collectively, the lithological, sedimentological, and biotic examination of Dorset’s World Heritage designated Wessex Formation provides palaeoecological and palaeoenvironmental context that benefits from the development of a comprehensive, regional lithostratigraphy. This new lithostratigraphical scheme elucidates the dynamic depositional settings of the Wessex alluvial plain, whilst also providing a formalised framework that accommodates both the palaeontological and geological data presented in this thesis.

Date of Award	28 Apr 2024
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Anthony Butcher (Supervisor), David Loydell (Supervisor) & Steve Sweetman (Supervisor)