Sedimentological processes occurring in the deep basins of the South Aegean Sea
Loading...
Date
2025-07-08
Authors
Manta, Kyriaki
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Investigating deep-sea sediments is essential for understanding climate variability and marine ecosystems. The sediments serve as a natural archive, preserving records of past environmental conditions such as ocean temperature, salinity, and biological activity. Furthermore, deep-sea sediments contain valuable information about ocean currents and tectonic movements, aiding researchers in studying seafloor dynamics, earthquake results, tsunami impacts and underwater volcanic activity.
The South Aegean region is characterized by a complex geomorphology involving interactive basins, steep canyons and an intricate network of active faults, making the area a “natural laboratory” for sediment dynamics investigation. The geological events recorded in the sediment layers in the area (ranging from major earthquakes and tsunami deposits to episodes of volcanic activity and landslides) have attracted global scientific interest for decades. These studies not only enhance the understanding of regional geology but also contribute to broader knowledge related to past reconstruction of geological events, sediment transportation and accumulation processes in a tectonically active area and models of geo-hazard risks.
Overall, deep-sea sediment investigation in the South Aegean offers a multifaceted window into past marine conditions and geological events and informs about future geo-hazard mitigation strategies. Thus, the addition of new scientific results related to such a unique marine compartment has high research, academic and societal impact.
The scope of the dissertation was the contribution to deepening the understanding of sediment dynamics in the complex marine compartment of the South Aegean Sea, and more specifically in the deep basins, by studying the sediment accumulation mechanisms and the factors that influence and control the different sedimentation process, as well as the potential relationship between the sedimentological and geochemical signatures.
In order to accomplish the objectives of the study, six sediment cores, with lengths up to 3.9 meters, were examined for their physical, sedimentological, and geochemical properties, followed by statistical analysis. The cores were scanned with a multi-sensor core logger (Geotek), described, photographed, and subjected to X-radiography. A total of 1,072 samples were taken for the various laboratory analyses (grain size, dating, major and trace elements, TOC and nitrogen) and statistical analysis was performed.
Several sediment deposits, were identified, including hemipelagites, contourites, turbidites, and mass transport deposits (MTDs).
In two of the four basins, specifically, the Cretan and Kamilonisi Basins, the deposition of turbidites and MTDs indicates that their gravity-driven downslope deposits were mobilized during different periods. Additionally, both basins contain volcanoclastic deposits with similar characteristics. In contrast, contourites were identified in the shallower Zafora Basin, suggesting the influence of bottom currents in this area. Magnetic susceptibility serves as an effective proxy for distinguishing between volcanoclastic deposits, turbidites, MTDs and contourites. Furthermore, the onset of sapropel S1 began around 9,000 years ago (ka BP) in our study area. Moreover, in the Zafora Basin as in the Cretan Sea, Minoan tephra and sapropel S1 have been detected in a similar depth interval, although their sedimentation processes are completely different.
Conversely, the Amorgos Basin and south of Anafi Island, MTDs are the dominant deposits. These MTDs are linked to the 1956 earthquake, with thicknesses ranging from 55 to 100 cm in the sediment cores. The predominant sediment fraction consists of clay, followed by sand. These deposits are characterized by a gray color, sharp boundaries, and a mixture of cohesive and non-cohesive flows. Additionally, values of gamma density, p-wave velocity, and magnetic susceptibility are elevated compared with the above and underlying sediments. They are characterized as lithoclastic, with a lack of foraminiferal material and calcite dilution. Additionally, they present low amounts of calcium (Ca) and strontium (Sr) and elevated values in potassium (K), rubidium (Rb). All the physical and chemical signatures allow us to distinguish the MTD deposits from 1956 from the overlying and underlying sediments. The differences in sedimentological characteristics of the MTDs are attributed to their proximity to the main seismic event.
Although a statistical analysis took place it was difficult to establish some proxies for the different sedimentary facies, due to the different geology of the islands that are neighboring.
Hemipelagic sedimentation is negligible especially in the basins (Cretan, Kamilonisi, Zafora, and Amorgos), and are composed mostly of reworked sediments (contourites, turbidites, MTDs). A more detailed study has to be done with emphasis on contourites, to help unravel the palaeoclimatology and the palaeoceanography of the Aegean Sea. Moreover, denser sampling for major and trace elements can help to identify geochemical proxies useful to distinguish pelagic sediments from the reworked sediments in the Aegean Sea. Finally, a numerical modeling of the 1956 tsunami, combined with the sediment characteristics, is essential for evaluating the impact of tsunamis and providing predictive insights for future seismic events.
Description
Keywords
Sediment processes, Gravity flows, Deep basins, South Aegean, Amorgos 1956