Floyd W. McCoy

New findings of Bronze Age homogenites in the Ionian Sea: Geodynamic implications for the Mediterranean

Abstract Holocene homogenites similar in character and stratigraphic position to those previously recorded in the Ionian Basin, and related to the gigantic tsunami originating from Santorini (Bronze Age eruption) are described from a core transect crossing the deformation front of the Mediterranean Ridge east of Victor Hensen Seahill. Investigations on grain sizes and carbonate content carried out on three cores from three different areas of the Ionian Basin, encompassing the Bronze Age homogenite, revealed important similarities and some differences. The most obvious difference concerns the carbonate content, which is minimum at the base of the unit in a core close to the Messina Abyssal Plain, whereas it is maximum in cores from the Western Mediterranean and Calabrian Ridges, characterized by the typical “cobblestone topography”. A terrigenous versus pelagic nature of the components is documented, and a distal versus local provenance is inferred. Homogenites are critically compared with unifites, a type of re-sediment recently described from the eastern Mediterranean. Comparison includes in particular: (a) source and sediment transport; and (b) triggering mechanism. A substantial difference exists between the sedimentation patterns of the Ionian and Levantine Basins seaward of the Calabrian and Hellenic Arcs in the latest Quaternary, and the difference contains a clear geodynamic message: sedimentation rates increase from the Late Pleistocene to the Holocene in the Ionian Basin, whereas they decrease in the Levantine Basin. The glacio-eustatic signal is well expressed in the Levantine Basin, where the source areas are situated consistently in the south, or on a passive-type, aseismic continental margin (north African margin). In the Ionian Basin on the contrary the glacioeustatic signal is totally obscured by the strong tectonic signal from the active northern continental margin of the Mediterranean.

Turbidites and megaturbidites from the Herodotus abyssal plain (eastern Mediterranean) unrelated to seismic events

Abstract A transect of 9 piston and gravity cores was taken across the southeast flank of the Mediterranean Ridge. The transect extends from the abyssal plain to a location 290 m shallower than the abyssal plain and 50 km north of the edge of the ridge. Each core contains two or more turbiditic layers, which belong to two discrete types, here called A and B. Type A essentially consists of black plastic clays rich in smectite, with silt fraction of terrigenous nature; source area is the Nile cone, and age is middle or late Pleistocene. Type B turbidites are pale brown to whitish in color, coarse-grained, carbonate-rich and bioclastic in composition with shallow-water fossils dominant. They are poor in smectite, and the silt fraction is very rich in carbonates (calcite and aragonite). The source area is the North African shelf, south of the abyssal plain. A megabed belonging to Type B turbidites is correlatable from core to core, with a thickness in excess of 10 m in the abyssal plain, and an estimated volume of 10 km 3 . Its stratigraphic position in the latest Pleistocene suggests that its origin is related to a sudden collapse of bioclastic sediments accumulated in a canyon head, during a low sea-level stand. The source areas of the two discrete turbidite types belong to the essentially aseismic North African continental margin. Although they are presently recorded on the tectonically active Mediterranean Ridge, no seismic events are required to account for the presence of either type of turbidite.

Physiography and structure of Bacino Bannock (eastern mediterranean)

Detailed analysis of the morphology of Bacino Bannock, a deep-sea basin filled by a hypersaline brine, shows with unusual detail the effect on the ocean floor topography of the deformation and dissolution of a salt body under tectonic stress. Although salt diapirism occurs in the central part of the investigated area, the major cause of basin formation is dissolution of subsurface evaporites which creates negative relief that exceeds by about one order of magnitude the positive relief. The true shape of the deformed salt deposit is preserved as a result of the absence of a thick post-evaporites sedimentary cover.

Floating megalitter in the eastern Mediterranean

Concentrations of floating megalitter—floating debris that is large enough for sighting by eye or with binoculars—were measured from a ship in a small area (8.3 km2) of the eastern Mediterranean Sea over a 22 day period. Suggested concentrations are on the order of 0.012 g m−2, based upon a limited data base, but are close to values determined elsewhere in the Mediterranean. If these values are representative of regional concentrations, then as many as 3.6×106 objects may be afloat per day as megalitter in the Mediterranean Sea. Most of the observed megalitter was plastic debris; all of the litter was man-made.

Photographic analysis of coring

Abstract Photographs taken by cameras mounted on piston corers at 132 sampling stations provide a dramatic documentation of the coring process. While being lowered through the water column, corers rotate between 1°–30° per 5 sec (the time interval between pictures) and hang from the wire at inclinations or at deviations from vertical of up to 12°. With tripping, free-fall and penetration, rotational movements increase considerably: during 49% of the stations, rotations were between 31° and 150° per 5 sec; during 43% of the stations, rotations were 1°–30°; only 8% of the stations indicated slight or no rotational movement. Inclinations increased from descent to full penetration by up to 8° on 70% of the stations, between 9° and 12° on 11% of the stations, and was greater than 12° on 15% of the stations; no increase was recorded on only 4% of the stations. Additional corer movement such as continued slow penetration or abrupt rotations followed initial penetration on approximately one-third of the 102 stations where good photographs were taken while the equipment remained in the sea-floor. Comparisons between measured penetration of the piston corer and recorded mud-line levels on core barrels, indicate mud-line measurements were within ± 5% of penetration on 78% of the stations, demonstrating the value of the mud-line as a penetration indicator. Core-recovery ratios (core recovered: penetration) averaged 0.78 for 75 stations where piston-corer penetration was measurable. Not considering stations where flow-in, pre-tripping, bending of pipes, sub-surface hard grounds, etc., produced disturbed sedimentary sequences in cores or inhibited penetration, average recovery ratios were 0.86 (49 stations); no relationship to sediment type is apparent. Recovered core lengths exceeded penetration (recovery ratios > 1.00) on five stations although stratigraphic disturbances were not noticeable in the cores. Recovery ratios of

SPECULATIONS ON THE ORIGIN OF THE ALGODONES DUNES, CALIFORNIA

The Algodones dune belt, which lies on the southeastern border of the Imperial Valley in southeastern California, represents a coastal dune system probably derived from the shore lines of fresh-water and marine inundations of the Cahuilla Basin. The estimation of the volume of sand in the dune belt is 380,000 million cubic feet. Assuming climatic conditions similar to those of today existed during formation of the dune belt, computations of wave regimen and resultant longshore currents showed that fresh-water and marine inundations of the basin aggregating a minimum of 160 thousand years would be required to provide and transport this volume of sand from the source areas to the present site of the dunes. Inundations of the Cahuilla Basin during part of the Pleistocene as well as the Recent are necessary for such a formation of the dune belt.

The hydrostatic motor: Utilization of hydrostatic pressure differentials in the deep sea

A hydrostatic motor that converts hydrostatic pressure gradients in the deep sea into harnessable mechanical energy has been developed and successfully tested. Controlled equalization between higher ambient hydrostatic pressures at oceanic depths and lower pressures retained from atmospheric or sea-level conditions—sealed within a chamber as part of the motor assembly—produces reciprocating motion of a piston. This motion is utilized for power or work requirements. Our needs have been directed toward oceanographic instrumentation requirements but many other applications are likely.

Acoustic horizons in the Argentine Basin, southwestern Atlantic Ocean: New evidence from deep-sea drilling

Acoustic horizons previously described in the Argentine Basin, southwestern Atlantic Ocean, have been correlated with the stratigraphic sequence drilled at Deep Sea Drilling Project site 358. Horizon B is associated with the transition from basal marly chalks to siliceous mudstones in the middle Eocene at 730 m subbottom. Horizon A, at 460 m subbottom, occurs in the upper Oligocene section and is correlated with a diagenetic boundary between diatom-radiolarian mudstones above and siliceous mudstones below in which biogenic opal has been converted to amorphous silica. Similarly, horizon F at 155 m subbottom correlates with a middle Miocene change from diatom-radiolarian mud above to siliceous mud below. Horizon A at site 358 in the Argentine Basin differs in age from a similar horizon in the Malvinas Outer Basin (site 328) and differs in age and character from horizon A in the North Atlantic. It is possible that silica diagenesis responsible for acoustic horizons A and F at site 358 occurred at or near the sediment-water interface during times of relatively slow sedimentation or that the degree of diagenesis is controlled by the composition of the host sediment.

The hydrostatic corer

Abstract Successful coupling of the hydrostatic motor to a corer has resulted in a promising new sampler for recovering deep-sea sediments. The hydrostatic motor converts hydrostatic pressure differentials between near-surface or atmospheric conditions and those found at deeper water depths into harnessable mechanical energy. Controlled use of this energy has driven a gravity (open-barreled) corer into stiff marls where penetration by a conventional gravity corer was unsuccesful. In this prototype design, corehead weights were mechanically coupled to the motor and used as a pile-driver to ensure significant sea-floor penetration. The successful testing of the hydrostatic corer revitalizes an old design and promises to be a significant advance in sediment sampler design for deep-ocean use.