Multi-proxy analysis for deciphering the Holocene record and mass transport processes at the Dor Disturbance in the Southeastern Mediterranean continental slope

Sedimentary records from passive continental margins can be used to reconstruct regional climate–ocean trends while identifying mass transport deposits (MTD) and elucidating their characteristics and timing in relation to regional paleoclimate and paleoseismicity. This study used two radiocarbon-dated piston cores from the Southeastern Mediterranean continental slope that cover the Holocene period. The cores were collected from the shelf edge (122 m depth) and the mid slope (588 m depth) to the north east of the Nile Delta at the Dor Disturbance off-shore Israel.

Computed Tomography (CT) scanning showed the sedimentary record evolved along the Holocene representing a gradual change in the sediment grain size and composition, while detecting units of MTD. The base of the cores was dated to 10-11 ka BP, and the shelf edge core captured the transgression on the continental shelf. The Early Holocene sediments are characterized by coarser grain size, higher content of biogenic material and highest foraminiferal abundances that reflect stable and favorable environmental conditions. Sapropel S1 is recorded as the lowest Ti/Al and the highest Si/Al values and TOC content that indicate higher precipitation in the source region and the high discharge of Nile. The disappearance of benthic foraminifera in the slope core point to the development of bottom water anoxia. During the time interval of sapropel formation, a clear interruption is observed by a decrease in TOC and a moderate presence of benthic foraminifera indicating re-oxygenation of the see-floor in corresponds with the ~8.2 ka BP cold event. Towards the mid Holocene the Ti/Al ratio and Fe contend increase in association with the increase of weathering rates in the Ethiopian Highlands at the Nile watershed as a result of reduced rainfall, and thus reduced vegetation cover. This trend aligns well and correlates with the many studies documenting a middle to late Holocene orbital change that led to the decrease of solar insolation forcing southward migration of the summer ITCZ and a gradual decrease of monsoon precipitation making this region increasingly arid.

In the slope core, four units were identified in the CT scanning as relatively higher bulk density sediments, which is consistent with enhanced consolidation and reduction in porosity, observed in MTDs. Older and out of stratigraphical order radiocarbon ages within these MTD units point to deposition of recycled sediments. Interestingly, the Ca/Fe ratios showed prominent peaks and distinct changes are observed in the benthic foraminifera community including the total number of individuals per gram dry sediment (BF/g), species richness, dominance, and species composition. Furthermore, within all the MTD units a noticeable increase in broken BF shells is also detected. It is noteworthy that the abundances of the opportunistic benthic species stay moderately high in between MTD events, probably reflecting the instability of the benthic habitat.