Date of Award
Master of Science in Coastal Marine and Wetland Studies
Coastal and Marine Systems Science
Till J.J. Hanebuth
Richard F. Viso; Jenna C. Hill
Holocene mud accumulation on the continental shelf in northern Gulf of Cadiz, from the Guadalquivir River to the Tinto-Odiel Estuary, is described as two types of mud depocenters (MDCs): a sheet-like prodelta and mud belt. Despite a substantial number of investigations of this continental shelf (Somoza et al., 1997; Hernández-Molina et al., 2000; Lobo et al., 2001; synthesis: Lobo et al., 2015), information on Holocene sediment facies and a robust stratigraphic age model remained unestablished (Lobo et al., 2002; and Lobo and Ridente, 2014). Objectives of this study are to describe the dynamics of MDC formation in a chrono- and litho-stratigraphic approach as well as to calculate a sediment budget. Research cruise POS482 on the German RV Poseidon collected 2,040 km of seismo-acoustic profiles and forty sediment cores in March 2015 with collaborative partners of the CADISED project. X-ray fluorescence core scanning, used in combination with magnetic susceptibly, porosity, high resolution core imaging, lithology description, and radiography depict five successive sedimentary facies since 9.0 cal ka BP. Boomer data sets from 1992 and 1986 combined with new CADISED seismo-acoustic profiles provide detailed insight to the geometric formation of this depocenter. Of particular surprise is that the sheet-like prodelta MDC is locally subsiding as a result of semi-recent active extension faults related to local salt diapir uplift. 14C and 210Pb dating are used to provide age control to the history of mud accumulation. Grain density and sedimentation rates determine accumulation trends in the range of 0.03 to 0.46 grams per cubic millimeter a year (g mm-2 yr-1) from early Holocene times until 2.7 cal ka BP. The following 1500 yrs showed rates increasing by up to ninety times (0.32 to 2.66 g mm-2 yr-1), correlating with a widespread humid climate period from 2.6 to 1.6 cal ka BP and enhanced mining and agricultural activity by the Roman Empire. Since 1.0 cal ka BP, accumulation rates increased even further due to industrialization and intense land use (1.09 to 28.63 g mm-2 yr-1). Smaller climatic events also contributed to changes in sediment accumulation. For example, the Medieval Climate Anomaly (MCA) coincided with a decrease from 1.05 to 0.7 cal ka BP. The total volume of the MDCs is 5.80 km3 with a total and dry sediment mass of 12,971 Mt. Total Organic Carbon (TOC) mass of 85 Mt and a 0.038 km3 volume with a CaCO3 mass of 3,637 Mt and a 1.63 km3 volume makes this depocenter an important quasi-modern sink in the marine sector of the regional carbon cycle.
King, Mary Lee, "Holocene Formation History of Mud Depocenters on the Continental Shelf in the Gulf of Cadiz, Southwestern Spain" (2018). Electronic Theses and Dissertations. 29.