45 D11. Hydrogeology, Karst, Limnogeology, and Marine Geoscience (Posters)

Sunday, 19 March 2023
8:00 AM - 12:00 PM
Grand Ballroom A–D

ULTRA-HIGH RESOLUTION ANALYSIS OF INTER-ANNUAL NATURAL AND ANTHROPOGENIC VARIABILITY USING FLUVIOGENIC FLOOD LAYERS OVER THE PAST 600 YEARS DOCUMENTED BY A PRODELTAIC DEPOCENTER IN THE GULF OF CADIZ, SPAIN

Paper number: 45-17
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Mud depocenters (MDCs) on the continental shelf are composed of fine-grained fluvially sourced material and can provide an exceptional opportunity to examine natural and anthropogenic processes in ultra-high resolution. The prodeltaic record of the Guadalquivir River in the eastern Gulf of Cadiz is one such place to decipher the variability over the past centuries. This region has a rich history of anthropogenic disturbances, particularly from the Industrial Revolution, and is influenced by both the Atlantic and Mediterranean climate systems; both of which affect the Guadalquivir River basin and the regional coastal-marine system.

To determine the magnitude and temporal scale of changes and impacts, a 5-m long sediment core was taken at 23 m water depth from the Guadalquivir MDC spanning the past 645 ± 25 cal yrs CE. Both radiography images and XRF element distribution core scanning at 1 cm resolution suggest three types of sedimentary facies within the core: hemipelagic (83%), fluviogenic flood (15%), and storm layers (2%). Flood layers (10-year return period with ~50 events) were targeted for high-resolution grain size analysis at a 0.25 cm resolution to determine the frequency as well as the specific supply and transport dynamics of the flood events. In addition, end-member modeling analysis (EMMA) using a non-parametric fit of the mean grain size of all facies revealed three dominant modes describing 99.5% of the variance. EM1, which describes 83.0% of the total variance, illustrates the hemipelagic fine-silt sub-population (7.6 ± 1.5 μm) of the prodeltaic record. EM2 and EM 3 have mean grain sizes of 11.5 ± 2.3 μm (97.7% of the total variance) and 17.3 ± 3.1 μm (99.5% of the total variance), respectively, and contribute the highest percentage of abundance to the flood layers. The EMMA simulation, in combination with elemental proxies, organic C and N stable isotopes, and foraminifera assemblages, reveals both an oscillatory pattern in flood layer frequency and magnitude as well as an increased sedimentation rate and an overall upward-fining of the sediment record. These changes are likely the result of regional climatic changes and human-linked environmental impacts on the river system, its estuary, and the nearshore hydrodynamics from the Little Ice Age to modern times, particularly since the Industrial Revolution.

Geological Society of America Abstracts with Programs. Vol. 55, No. 2

doi: 10.1130/abs/2023SE-386126

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