Reconstructing Late Holocene Environmental Change in the Pevensey Levels: Stratigraphic and Paleoenvironmental Insights from Horse Eye and North Eye, UK

Abstract

This thesis investigates the stratigraphic framework and paleoenvironmental evolution of the Pevensey Levels, focusing on the depositional histories of the sediment covering the bedrock-cored islands Horse Eye and North Eye in East Sussex, United Kingdom (UK). Low-lying coastal systems such as the Pevensey Levels are sensitive to climatic variability, geomorphological changes, and human interaction, yet detailed stratigraphic and environmental reconstructions are limited for these landscapes. By combining field observations, sedimentological analyses, and laboratory analyses, this research enhances the understanding of climatic events, geomorphological factors, and anthropogenic influences that have shaped this low-lying coastal-lagoonal landscape over the Holocene. A multiproxy laboratory approach- including laboratory methods that include laser diffraction grain size analysis, portable X-ray fluorescence (pXRF), loss on ignition (LOI), X-ray diffraction (XRD), and AMS radiocarbon dating- was applied to create a stratigraphic framework for reconstructing the stratigraphy and environmental history of the sediment on these bedrock-cored islands. The stratigraphic analyses reveal a broadly consistent depositional sequence across both islands, transitioning from lower marine silty clays at the base to organic-rich peat layers and finally to upper terrestrial clayey silts. Despite this similarity, there are differences that emerge: North Eye’s stratigraphy includes sand-dominated units, attributed to its thinner sediment cover, bedrock exposure, and localized sediment contributions during episodic higher-energy depositional events. In contrast, Horse Eye’s thicker sediment cover and more continuous peat layers indicate prolonged lower-energy deposition and water-logged conditions. Additionally, the lithologic and stratigraphic analyses conducted in this thesis offer a higher level of detail compared to earlier studies, providing localized depositional variability. These findings distinguish this research from earlier work in the area, which provided generalized stratigraphic data for North Eye and focused on broader regional depositional sequences within the Pevensey Levels. The integration of results from the different techniques identified a temporal alignment between localized responses in the sediment with key climatic events, such as the globally recognized 4.2 ka event- a period characterized by dry climates in some regions but has remained poorly understood in Western Europe. At the Pevensey Levels, the stratigraphy during this period reveals an increase in sand content, indicative of heightened depositional energy and fluctuating hydrological conditions, providing new insights into how this global climatic phase may have influenced low-lying coastal landscapes in the UK. The findings also align temporally with documentation of human modifications during the late Holocene, including drainage and land reclamation. For example, lenticular laminations and an increase in sand content in the upper stratigraphy align with documented medieval drainage efforts in this region. This thesis situates these modifications within a regional context, noting how anthropogenic activities may have influenced sedimentary processes in dynamic coastal environments. This thesis provides a new framework for understanding the evolution of the Pevensey Levels within a broader regional context by drawing comparisons with adjacent systems such as the Romney Marsh and Somerset Levels. While the Pevensey Levels exhibit broadly similar depositional patterns to adjacent systems, including marine-to-terrestrial transitions, there are localized differences in sediment depositional processes due to geomorphological controls, such as the differences in size and shape of the bedrock islands, as well as their location with respect to their proximity to sediment sources. The Pevensey Levels’ stratigraphy is more influenced by bedrock-controlled sedimentation near the bedrock-cored islands, landforms that are not present in the Romney Marsh. These regional comparisons reveal variations in depositional energy, peat development, and anthropogenic modifications, offering new insights into the factors shaping coastal-lagoonal systems during the Holocene.