Carlo Bartolini

Morphology and recent sediments of the Western Alboran Basin in the Mediterranean Sea

Abstract The Western Alboran Basin Plain, lying around 4°20′ and 35°40′ N, 90 km south of Malaga, at an average depth of over 800 fathoms (1,436 m), was chosen by the Saclant Research Centre (Saclantcen), at La Spezia, for sound propagation experiments, because a preliminary survey had revealed the presence of a plain with an apparently simple sub-bottom structure. The present study consists mainly of precise echo-sounding surveys (3,200 km) to record the detailed sub-bottom structure to a depth of 30 m and extensive large diameter coring (49 cores). The results of core analysis were matched together with the sub-bottom structures revealed by the echo-sounding surveys, in order to correlate the turbiditic graded and laminated layers found in most of the collected cores. The sedimentological evolution of such layers basinward was studied by means of the grain-size and petrographic properties. A swift change in such properties has been observed on basin slopes, while in the basin plain, where the “sediment ponding” occurs, on appreciable selective power of the currents has been inferred. The sand layers sampled with some cores collected from the northern (Spanish) slopes have been interpreted as possibly derived from the Serrania de Ronda basic and ultrabasic complex. Most of the sand and silt layers fall within the range of feldspathic graywackes. The grain-size distributions of the turbiditic layers are more or less positively skewed. Only a few samples from the proximal areas are relatively clean silts or sands, featuring a nearly symmetrical frequency distribution. The others contain a large quantity of fines. The stratigraphy of the cores was studied by means of the foraminiferal, nannoplankton (Bartolini, 1970) and paleotemperature analysis. Furthermore the vegetal debris found in the bottom section of core 80 were studied from the botanical point of view and were utilized for a 14C dating. By relying on the isochronous turbiditic layers the sedimentation rates inferred by the stratigraphic analysis were extrapolated to the whole cored area. These appeared to range from about 20 cm 1,000 years in the marginal areas to 40 cm 1,000 years in the central, deeper part of the Basin Plain.

Tracing nearshore bottom currents with sea-bed drifters

Abstract The experience acquired during 36 Woodhead drifter releases performed along the Tuscan coast is briefly reported. Without a costly apparatus, residual current patterns may be easily obtained with this method. Care should be taken, however, when sediment dispersal patterns are required, since weak currents which drag drifters slowly, displace only finer sediments.

Evidence of sedimentation by gravity-assisted bottom currents in the Mediterranean Sea

Abstract Differences in the sedimentation rates of (hemipelagic) muds in the western Mediterranean have been inferred. Within a water depth difference of 9 m, corresponding to a distance on the sea bottom of only 5 nautical miles, the sedimentation rate doubles from about 20 cm/1,000 year towards the basin rims, to 40 cm/1,000 year in the topographic lows of the basin centre. The “rain of sediment” process is ruled out as the principal deposition agent. The turbidity-current and normal-current hypotheses are briefly discussed as the most realistic alternatives. The lateral variations of the sedimentation rates are rather constant during the investigated time span, approaching 15,000 years.