Depositional patterns and Late Quaternary evolution of two Mediterranean submarine fans: A comparison

Abstract

This study contrasts the Late Quaternary evolution of the Rosetta Fan in the eastern and the Menorca Fan in the western Mediterranean. The lithofacies patterns of these fans resulted from the interplay of four controlling factors: (a) structural setting and associated physiography, (b) sediment input, (c) physical oceanographic parameters, and (d) climate-eustatic oscillations. Consideration of the spatial and temporal distribution of the two fan facies shows that these four controlling factors have not exerted equal influence. The structural framework has been the primary factor and has largely controlled physiography and sediment input. The other factors, climatic control and directly related eustatic oscillations and physical oceanographic parameters, also are important. They determined specific transport processes, the nature of sediment types, and facies distribution patterns observed in the two fans. Time and spatial variations have resulted in major differences in the depositional patterns characteristic of each fan. The Rosetta Fan on the Nile Cone records the transport of a large supply of terrigenous fine-grained sediment onto a gentle surface in a relatively tranquil structural setting. Sediment is supplied to the fan across broad sectors of the Egyptian Shelf edge and slope. Associated with rapid deposition is a surface of low relief and a poorly defined channel network restricted to the lower fan sectors. The absence of well-marked lobes is noteworthy. The above factors and the significant imprint of the climatic and eustatic oscillations on sediments accumulating in a closed silled basin, account for the overall characteristics of the Rosetta Fan. In contrast, the Menorca Fan formed on the Balearic Rise, a zone affected by fault displacement and salt tectonics; sediment input, primarily coarse-grained bioclastic sand, has been low. In response, this fan is typified by an irregular relief with pinnacles and other topographic complexities, a major canyon-fan channel system, and marked lobe development. The role of bottom currents is important in this fan. During the Late Quaternary there has been a parallel depositional evolution in the two sectors and this has resulted in some basic similarities between the Rosetta and Menorca lithofacies. However, differences in the sedimentation rates, general facies types and spatial distribution patterns serve to distinguish these two fans, and these differences have remained during the time span considered. This study also serves to identify the sedimentary sections of the Menorca Fan from those of the Rosetta Fan.