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Title: Linking source and sink in an active rift : quantifying controls on sediment export and depositional stratigraphy in the Gulf of Corinth, central Greece
Author: Watkins, Stephen
ISNI:       0000 0004 7659 2380
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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The stratigraphic record is broadly assumed to be a fundamental archive of past climate and tectonic regimes and is routinely used by geologists to decipher the Earth's history. The sedimentary record in basins is formed from sediments that are produced in onshore catchments, transported by sediment routing systems and ultimately exported and deposited in the basin. However, in recent years there has been considerable discussion on the reliability of this record in documenting climatic and tectonic events. Outstanding research questions include whether sediment routing systems are able to respond to and transmit high-frequency signals (104-105 years) of climate change; whether final grain-size distributions of sediment supply near catchment outlets actually record tectonic or lithological signals, even if these signals are initially generated and observed upstream; the extent to which sediment delivery impacts on basin sedimentary architecture; and whether changes in basin sediment distribution record changes in tectonics or sediment supply. To yield detailed insights into these questions an integrated study of a real-world source-to-sink system is required. In this thesis I use the Corinth Rift, central Greece, as a case study, integrating multiple catchments, to address these questions at a regional scale. The Corinth Rift basin (the Gulf of Corinth) has been a closed underfilled basin throughout the Late Pleistocene and Holocene with a well-constrained tectonic and climatic history. In this thesis I adopt a multi-disciplinary approach that utilises a 30 m ASTER Digital Elevation Model, available seismic datasets, fieldwork and existing literature to holistically investigate this source-to-sink system. In the first part of this thesis I investigate the ability of sediment routing systems draining the Corinth Rift to transfer high-frequency climate change signals (104 yrs) into the basin. I interpret basin sediment volumes over the last 130 kyrs to investigate if sediment accumulation rates have varied. Additionally, I predict sediment fluxes to the basin using the BQART model and compare to the observed accumulation rates. I find that sediment accumulation rates and sediment supply have varied over the last 130 kyrs and are higher in the Holocene by approximately 30%. These results therefore imply that the Corinth Rift sediment routing systems are sensitive to high-frequency (104 yr) climate change. The second part of the thesis focuses on the present-day grain-size distributions being exported at the river mouths entering the Corinth Gulf. I undertook in-situ sieving of high-flow channel bars at the river outlets for 47 catchments that drain approximately ~83 % of the Corinth Rift. In addition, Wolman Point Counts and measurements of channel geometries were carried out. I find that simple geomorphic parameters, such as catchment area or maximum catchment relief, or tectonics have relatively little control on final grain-size distributions. Instead, lithology appears to be the dominant control on sediment size at the river mouth. In addition, I show that the sieved sediment is transported in bedload during bankfull conditions and I infer that mode of transport is a first order control on the modern basinal stratigraphy seen in the Gulf of Corinth. Finally, I use my data to derive the entire bedload sediment budget for the rift for the first time. In the final part of the thesis I investigate sediment distribution patterns within the basin throughout the last 130 kyrs to better understand the interactions of sediment supply and tectonics. This analysis subsequently aids a high temporal resolution investigation (104 yrs) of basin sediment distribution patterns to make inferences on short-term strain variability in the Gulf of Corinth. The sediment distribution maps reveal that over longer time periods (0-130 kyrs) the rift is behaving asymmetrically and that the majority of sediment is being deposited within the hanging-wall of the Lykoporia fault. However, I find that smaller scale North- and South-dipping faults within the basin affect sediment distribution patterns and results in areas of localised greater sediment thickness. In addition, the sediment distribution pattern over the last 12 kyrs reveals three distinct depocentres throughout the Gulf of Corinth, which does not reflect patterns of modern geodetic extension rates that suggest the majority of extension is currently located in the far West of the Rift. The data therefore highlights the potential pitfalls of using modern extension rate data to infer longer geological tectonic trends. Overall, this thesis shows that the Corinth Rift is highly responsive to climate and tectonics over 104 year timescales and that lithology appears to be a dominant control on fluvial grain-size distributions exported to the basin. These results reveal that the sedimentary archive is recording changes in climate, tectonics and rock type in terms of sediment characteristics, distribution patterns and volumes.
Supervisor: Bell, Rebecca E. ; Whittaker, Alexander C. Sponsor: Imperial College London ; Natural Environment Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral