Search

Variations in the earth's magnetic intensity, fluctuations in atmospheric radiocarbon activity, and climatic changes of the earth surface and of the ocean during the last 7000 yr are correlated. Variations in magnetic intensity, fluctuations in magnetic inclination, and climatic changes in deep-sea sediment cores are correlated for the last 470,000 yr. We tentatively conclude that magnetism may modulate climate.

Igneous and sedimentary rocks recently dredged and cored from the steep western slope of the Beata Ridge provide important data on the composition, age and details of crustal evolution of the rock-types responsible for recorded compressional wave velocities. The sedimentary rock samples also provide new data concerning the age and depositional environment of overlying sedimentary reflectors. The deepest (4,100 m) dredge haul contains deeply weathered coarsegrained igneous rocks. Nine other hauls, distributed between 4,000–2,300 m, contain holocrystalline basalts and diabases. The compressional wave velocity of air-dried samples of two holocrystalline basalts and a diabase at atmospheric pressure ranges from 5.0–5.6 km/sec. Sampling in depths less than 2,300 m shows that the crest of the Beata Ridge is capped by Quaternary deposits underlain by consolidated carbonate sediment of at least Middle Eocene age. The faunal assemblages of the Mid-Eocene samples are the product of normal accumulation in a shallow shelf environment. The dredging results coupled with previously published seismic reflection and refraction data, suggest that the 5.4–5.7 km/sec crust is composed of a layer of basalt and diabase which outcrops below 2,300 m, on a fault-generated escarpment that was produced in the Late Cretaceous-Early Tertiary. The shallow shelf samples of Eocene age indicate that the Beata Ridge was higher in the Early Tertiary and has subsided subsequently to its present depth.

Crustal shortening of the ocean floor in the eastern Mediterranean is recognized by a marked thickening of the sedimentary layer seaward of the Hellenic and Calabrian island arcs. Steep gradients and large negative free-air anomalies in the gravity field along with a highly uniform, low regional heat flow are manifestations of the thickened crust. Bodies of recently deformed sediment in and seaward of the Hellenic Trough reveal the style, polarity, and dynamics of the thickening mechanism. A linear buried anticlinal structure, inferred from analysis of surface ship gravity profiles, may mark the site of contemporary intrabasinal underthrusting. The distribution of earthquakes beneath the Mediterranean Ridge supports the interpretation that the Anaximander, Ptolomy, and Strabo Mountains are features comparable to large basement nappes. Cyprus is one such structure, offset to the south, where the oceanic crust and part of the upper mantle have been involved in the decollement.

A semiquantitative X-ray diffraction study of the finer-than-2μ-size fraction of the surface sediments of the eastern Mediterranean Sea has been carried out. On the basis of the abundances and the distributional patterns of the different clay minerals six mineral assemblages are distinguished. These assemblages have distinctive sources and their dispersal reflects different agents of transport in the eastern Mediterranean Sea. A Nile assemblage with very high amounts of well-crystallized smectite (> 50%) and 15–25% kaolinite is found on the eastern Nile cone and within the eastern Levantine Basin. Its distribution has resulted from the dispersal by the easterly directed surface water currents which form part of the counter-clockwise gyre in the eastern Mediterranean Sea. The Levantine intermediate water has transported from the southeast Aegean Sea on to the Mediterranean ridge southeast of Crete a southeast Aegean assemblage characterized by 40–60% well-crystallized smectite and higher contents of chlorite and illite than in the Nile assemblage. A kaolinite-rich assemblage (20%– > 30% kaolinite), coinciding with high carbonate values, occurs on the western section of the Mediterranean ridge and to some extent in the western Nile cone, as a consequence of transport by wind from North Africa. The restriction of Kithira and Messina assemblages (illite- and chlorite-rich assemblages) to deep parts of the Ionian Basin is chiefly due to water movements involved in deep circulation. A Sicilian assemblage with 20– > 30% kaolinite and 30–50% smectite in the westernmost part of the Ionian Basin south of Sicily, has mainly resulted from the dispersal by easterly moving surface waters from the western Mediterranean Sea.

Our investigation of deep-sea climatic and magnetic records showing that high eccentricity of the earth's orbit, low magnetic field intensity and warm climate occur together indicates the relative importance of eccentricity as perhaps the phenomenon which has most consistently modulated both climate and magnetism for at least the past 2,000,000 years. A speculative hypothesis regarding the mechanism which may be responsible for a relationship between the eccentricity of the earth's orbit, geomagnetism, and climate is suggested.

CORRELATION between the variations of the Earth's magnetic field, fluctuations in atmospheric radiocarbon activity, and climatic changes during the past 7,000 yr has been discussed extensively in the past1–7. In addition, Harrison8 has suggested that reversals of the Earth's magnetic field could cause climatic changes. With an associate we have recently9 been able tentatively to conclude on the basis of studies of deep-sea sediment cores that in the past 470,000 yr the magnetism of the Earth has modulated climate. We have now extended the correlation between variations of the magnetic intensity and evidence of climatic change from deep-sea sediment cores back to 1.2 m.y.

Deep-towed side-scan and bathymetric data have been merged to present a 3-D view of the lower continental slope and upper continental rise offshore Atlantic City, New Jersey. Carteret Canyon narrows and becomes nearly stranded on the lower slope where it leads into one of two steep-walled, flat-floored erosional chutes. The floors of the chutes, cut into semilithified middle Eocene siliceous limestones, are marked by downslope-trending grooves. The grooves are interpreted to be gouge marks formed during rock and sediment slides. On the uppermost rise, beneath the chutes, is a 40-m deep depression. The origin of the depression is believed to be related to material moving downslope and encountering the change in gradient at the slope/rise boundary. Downslope of the depressi n are channels, trails, and allochthonous blocks. The lack of significant post-early Miocene deposits implies that the lower slope offshore New Jersey has yet to reach a configuration conducive to sediment accumulation. The age of erosion on the lower slope apparently ranges from late Eocene-early Miocene to the recent geologic past.

Sedimentary rocks of Triassic-Neogene age are present on the Malta Escarpment of the eastern Mediterranean. Upper Triassic dolomitic limestones of shallow-water origin, at depths between 2.5 and 3.5 km, are similar in lithofacies to coeval platform carbonates of the Siracusa (Syracuse) belt of southern Sicily. Jurassic rocks include lower-middle Liassic shallow-water limestones followed by condensed hemipelagic lime deposits indicative of sinking and starving of the former platform. Cretaceous materials are represented by both red marls rich in planktonic faunas and reworked volcaniclastic breccias including shallow-water skeletal material. Paleogene rocks are both shallow-water limestones with corals, algae, and bivalves, and redeposited calcarenites of lithofacies similar to those from surface and subsurface of the Ragusa zone. Oligocene-?lower Miocene rocks from the escarpment are also similar in lithology to the coeval Ragusa deposits. Tortonian is represented by hemipelagic marls indicating open-marine environment. Pervasive dolomitization on lime crusts and on initial-stage fissure fillings with strongly positive isotopic oxygen ratio is thought to be a product of Messinian evaporitic drawdown. Pliocene sediments belong to the Trubi facies and consist of pelagic foraminiferal chalk. An impressive vertical relief existed by Miocene times, as attested by Messinian crusts and veins on or in rocks as old as Late Triassic. Our data do not provide evidence that this morphologic feature necessarily coincides with a continent-ocean transition. The present escarpment was produced by faulting, erosion, and defacement.

The shaping of the ocean floor is dependent not only on the local geological setting and the nature of the substrate, but it is also influenced by the overlying water mass. The purpose of this paper is to explore various physical, chemical, and biological factors that can be responsible for subaqueous erosion and landslides. Because oceanographic conditions change in response to both global climate fluctuations and the continuous rearrangements of the size, shape, and depth of the ocean basins, submarine erosion has a certain degree of time dependency, Knowledge of the so-called “paleo-oceanographic events” is made available primarily from the results of deep-sea drilling and seismic reflection profiling.

8 pages, 5 figures, The northern continental slope off the Ebro Delta has a badland topography indicating major slope erosion and mass movement of material that deposits sediment into a ponded lobe. The southern slope has a low degree of mass movement activity and slope valleys feed channel levee-complexes on a steep continental rise. The last active fan valley is V-shaped with little meandering and its thalweg merges downstream with the Valencia Valley. The older and larger inactive channel-levee complex is smoother, U-shaped, and meanders more than the active fan valley. © 1985 Springer-Verlag New York Inc.

ABSTRACT Seven ALVIN submersible dives were made into three submarine canyons that incise the slope region of Georges Bank off the New England coast. Forty-eight samples were collected and detailed dive tracks reconstructed. Our visual observations coupled with our sampling indicate that older Lower Cretaceous carbonate and mixed carbonate clastic platform facies rocks are exposed in portions of the canyons. This older sequence of rocks has been eroded and incised by canyons prior to the Middle Eocene and possibly prior to Maastrichtian times. Canyon cutting has been a process that has been reactivated over spans of tens of millions of years. The regions of the canyons are characterized by a complexity of stratigraphic/erosional discontinuities, various sequences of older canyon fill deposits that exhibit rapid facies changes, and chaotic mixing of units that would be impossible to understand without the submersible tool. INTRODUCTION During a ten day expedition in the summer of 1977 we explored three selected New England submarine canyons using the research submersible ALVIN. The submersible is self-contained, battery powered, has a depth capability to 3650 meters and carries two observers in addition to the pilot. Our program was designed to traverse the narrow axial tha1wegs of the canyons in the regions where they deeply incise the continental slope. We anticipated that we would encounter bedrock outcrop of old continental shelf strata that had been exposed by the retreat of the slope, principally as the consequence of intense phases of regional erosion. Several dives were made up a wall of each canyon on tracks more or less perpendicular to the thalweg. These reconnaissance routes gave us a chance to observe if the present sculpturing of the canyons was pervasive on the slope or was restricted to the region of the valley floor. Submarine canyons on the continental slope of the Atlantic side of North America (Fig. 1) were discovered and initially sampled some four decades ago (Shepard et a1.. 1934; Veatch and Smith, 1939). Down cutting in the canyon regions exceeds one kilometer giving rise to deep gorges along a branching dendritic-type drainage network. Some geologists have matched this morphologic pattern to counterparts on land. While speculating about a hypothetical sub aerial origin prior to the subsidence of the continental edge (Stetson. 1936; Shepard, 1952). Upon arrival at our dive sites, each canyon was surveyed with 12 kHz echo sounding in systematic grids, both previous to and between our dives. Navigation was obtained with Loran-C at approximate 15 minute intervals and at all course changes. Our bathymetric maps were constructed with our survey data supplemented by other available tracks, all shown by dotted lines in Figs. 2,3 and 4. The canyons we visited are of different sizes and shapes. Oceanographer Canyon (Fig. 2) is the largest and cuts the furthest back into the shelf edge. Its lower part exhibits large right angle bends. The "tributaries" of this canyon are fairly linear and form two orthogonal systems suggesting control by pre-existing structures in the bedrock.

8 pages, 6 figures, The Valencia Valley is a Quaternary, 200 km long deep-sea valley in the Valencia Trough, Western Mediterranean Sea. A swathmapping survey approximately mid-way along the valley length, where the floor has an average gradient of 1:250 (0.2°), shows valley walls that rise 200 to 350 m above the valley floor, with slopes of 2 to 18°. Sediment forming the walls is undergoing retrogressive, upslope-directed slumping with increasing bedding disruption along steeper walls. The valley exhibits a winding course with steep outer and gentler inner walls around bends, and bedforms on the valley floor. Lateral migration around bends is less than 5 km and the valley is deeply entrenched into Quaternary-bedded sediments. © 1985 Springer-Verlag New York Inc.

Avalanche scars, landslide scree and debris flow tongues have been imaged in plan view on the continental slope of the western margin of the North Atlantic. Their detection and mapping has been accomplished with a tethered deep-ocean side-scan sonar having a swath width of 5 km. The sonar was constructed to search for and locate the wreck of the S. S. TITANIC (Wilford, 1980). We have subsequently used it in cooperation with the U.S. Geological Survey to explore the continental slope of New England and the mid-Atlantic margin of the United States (Robb et al., 1981, a, b; McGreggor et al., 1981).

The second Maurice Ewing Symposium was devoted to the implications of deep drilling results in the Atlantic Ocean. This subject was chosen for two reasons. First, Maurice Ewing was one of the leaders of JOIDES (Joint Oceanographic Institutions for Deep Earth Sampling) the association of oceanographic institutions that was formed to organize and sponsor drilling in the deep ocean, and which has continued to provide scientific advice to the Deep Sea Drilling Project. Second, the first phase of International Program of Ocean Drilling in the Atlantic was finished and it seemed a good time to assess the implications of drilling results in the Atlantic that had been obtained over almost a decade. During the time this volume was being prepared, discussions were taking place about a new initiative in oceanic drilling, in which a drilling vessel with much enhanced capability might be used. The results presented in this volume thus represent the base on which new drilling plans can be built.

The mixing of cyanamide and KNO2 produced changes from white solids to yellow liquid and then to orange solid. The gases cyanogen and ammonia were formed. No external energy was used. The reactions were carried out with a small amount of O2. The presence of proteins in the reaction product formed 13 months after the mixing was indicated by the positive reactions of the cyanamide-KNO2 reaction product with ninhydrin, microbiuret, and Folin reagent; the ultraviolet absorption at about 280 nm; the yield of 24% of 15 amino acids; and molecular weight measurements of more than 160,000. The presence of nucleosides, nucleic acid bases, hydrocarbons, and organic esters in the reaction product formed 2 months after the mixing was indicated by ultraviolet absorption at about 260 nm, and the results of ligand-exchange chromatography, paper chromatography, infrared analysis, mass spectral analysis, and NMR spectroscopy. Possible cyanamide-mediated dehydration reactions and mechanisms are discussed.

A dense layer of suspended particulate matter exists below a depth of 1,900m in the Atlantis II Deep in the Red Sea. This layer was detected with a light scattering meter (nephelometer) at two locations within this deep and was found to conform generally to the zone of hot brines. The nepheloid layer scatters light with a constant intensity except for a few very thin internal layers of greater light scattering which correlate with the interface between the different temperature and salinity brines. The intensity of light scattering is found to increase gradually over an interval of eighty meters in the transition zone between the hot brine and the normal Red Sea deep water. The particles which produce the light scattering are interpreted as the colloidal suspensions and mineral precipitates created by the interaction of the reducing, acidic, and metal-containing hot brine with the oxidizing and alkaline overlying normal Red Sea deep water.

The initiation of dedicated databases for the U.S. National Science Foundation (NSF)-supported Ridge2000 and MARGINS programs provides the opportunity to develop a data management system capable of handling the primary data types of marine geoscience research. Ridge2000 and MARGINS are broad initiatives focused on fundamental problems of crustal creation, evolution, and destruction along the world’s tectonic plate boundaries.These programs involve the collection of a wide range of geophysical data types, as well as rock, fluid, and biological samples, and time series data. An effective data management scheme is essential for the success of the Ridge2000 and MARGINS programs, to facilitate integration of the broad suite of studies carried out within

Sandy submarine braid plains, like their fluvial counterparts on land, are sand-rich depositional environments that may display excellent reservoir characteristics in terms of sediment volume, porosity, and permeability. The submarine examples may be laterally associated with potential source rocks such as the fine-grained levee deposits of deep-sea channels. A side-scan sonar study of the central Labrador Sea revealed the existence of a more than 700 km long and up to 120 km wide submarine sand and gravel plain that has been supplied with sediment by high-density turbidity currents, possibly resulting from subglacial lake outburst flooding in the Hudson Strait. The side-scan imagery of parts of the plain displays a conspicuous streaky pattern of alternating high and low backscatter intensity. High-resolution 3.5 kHz seismic profiles and 12 kHz bathymetric profiles show that the pattern represents a furrow-and-ridge (erosional) or channel-and-bar (depositional) topography, similar to a braided alluvial plain. The furrows or channels have low acoustic backscatter, are less than 10 m deep, and are separated by ridges or bars having high backscatter. Some channels terminate in depositional lobes. Individual channels and bars (or furrows and ridges) are less than 100 m wide and can be followed up to 40 km downcurrent. On sleeve-gun seismic profiles, the total sand thickness appears to be between 200 m (proximal) and 100 m (distal). Piston cores from the plain recovered massive sand layers up to 4 m thick, buried under 1 m of Holocene hemipelagic ooze. Texturally, the sands and gravelly sands display a trend of improving sorting with increasing mean grain size. Some very coarse grained samples are moderately well sorted and almost matrix free. The flooding events that deposited the sands might be the submarine counterpart of Heinrich events but need not be restricted to such events. Radiocarbon ages of about 10 k.y. from the base of the ooze overlying the youngest sand gave a minimum age for the sand that is similar to the age of Heinrich event 0. Estimates for the discharge volume of individual events are poorly constrained and range from 103 to 105 km3. Braided channel patterns in deep-water (Begin page 1500) sandy depositional environments are not restricted to high latitudes but also have been identified in various submarine fan settings in the lower latitudes, for example, the Orinoco, Var, and Monterey deep-sea fans and in the Santa Monica Basin. The largest examples, however, are known from high latitudes, suggesting that melt-water discharge from continental ice sheets may favor the formation of this habitat of giant sands in the deep sea. The occurrence of sandy braided deep-water environments having favorable reservoir characteristics in a variety of tectonic settings makes this type of environment a potentially interesting deep-water target.

The disastrous 1999 earthquakes in Turkey have spurred the international community to study the geometry and behavior of the North Anatolian Fault (NAF) beneath the Marmara Sea. While the area is considered mature for a large earthquake, the detailed fault geometry below the Marmara Sea is uncertain, and this prevents a realistic assessment of seismic hazards in the highly-populated region close to Istanbul. Two geological/geophysical surveys were recently conducted in the Marmara Sea: the first in November 2000 with the R/V Odin Finder, and the second in June 2001 with the R/V CNR-Urania. Both were sponsored and organized by the Institute of Marine Geology of the Italian National Research Council (CNR), in cooperation with the Turkish Council for Scientific and Technical Research (TUBITAK) and the Lamont-Doherty Earth Observatory of Columbia University Multi-beam bathymetry, multi-channel seismic reflection profiling, magnetometry high-resolution CHIRP sub-bottom profiling, and bottom imaging were carried out with a remotely operated vehicle (ROV). Over 60 gravity and piston cores were collected.

The width of and along-axis variations within the plate boundary zone of the southern segment of the Endeavour Ridge of the Juan de Fuca Ridge System have been quantified using Sea MARC I sidelooking sonar imagery. The sonar imagery was calibrated with video and photographic surveying to provide visual corroboration of the activity, spacing, and offset of faults and fissures. This ridge segment contains an axial high bisected along its length by a summit depression whose width, relief of its rims, depth of its floor, and spacing of faults and fissures vary systematically away from the midpoint of the ridge segment toward its tips. The axial high and its summit depression are likened to an elongated shield volcano that is being disrupted by collapse of its crest into a widening linear caldera. The observed distribution of faults and fissures could be produced by mechanisms which stretch young ocean crust which is characterized by rheological properties which vary with distance from the center of the elongated volcano. Reprints. (jhd)

Sea MARC I side-looking sonar images and Sea Beam bathymetry along a 400-km stretch of the Juan de Fuca Ridge crest provide evidence that excessive extrusive volcanism periodically builds a crestal ridge along the axis of seafloor spreading. An elongate summit depression (ESD), or rift valley, is commonly observed in the spine of this crestal ridge. The crestal ridge volcanic landform has a distinctive shape that is recognized in bathymetric contours both along the spreading axis and at least up to 30 km away from the axis. The landform has a plan-form shape that resembles a side view of an archer's bow with the long dimension of the bow form parallel to the strike of the ridge. In cross section, the bow form is flat on top and has steep flanks. These bow-form shapes can be explained by magma that rises into the crust at a discrete center and flows laterally into belts of ridge-parallel dikes, similar to Icelandic fissure eruptions. Both the variable dimensions of the ESD along axis of the Juan de Fuca Ridge and the relationship among volcanic flow morphologies within and beyond the ESD suggest the four different segments of the Juan de Fuca Ridge presented in detail here display different stages in a cycle of oceanic crust accretion. This cycle includes episodes in which there is (1) extrusive volcanic construction which widen the crestal ridge prior to the collapse of the summit depression, (2) collapse within the summit region of the crestal ridge to form an ESD during a phase of volcanic inactivity, and (3) renewed magmatism in the ESD as its floor widens by extension and brittle fracture of the upper crust. This episodic model implies that the width of the young seafloor affected by volcanic extrusion or dominated by tectonic stretching varies through time.

The precipitous (28° to 40°) Bahama Escarpment is characterized by abundant low-energy, restricted peritidal and lagoonal rocks and scarce high-energy, bank-margin rocks of Early and middle Cretaceous age at depths of >2,000 m. This indicates significant erosional modification of the slope. All models of carbonate platforms have high-energy facies at platform edges, with low-energy and restricted facies confined to platform interiors. Erosion has removed marginal deposits that constituted the original slope of the Bahama Platform and exposed peritidal and lagoonal facies rocks. On the basis of widths of facies belts of middle Cretaceous carbonate platforms in eastern Mexico and of erosional benches apparent in seismic profiles across the Bahama and Blake Escarpments, an estimated 5 km of material has been eroded from the base of the escarpment. Greatest erosion occurred between the Cenomanian and Maastrichtian, with additional erosion in the Paleocene and Oligocene, as documented by Tertiary and Late Cretaceous pelagic and forereef deposits that unconformably drape and fill fissures in the older shallow-water rocks. It is unclear whether erosion of the escarpment is occurring at present. Erosion of the slope deeper than 2,500 m is effected, in part, by spalling of joint blocks from shattered exposures. Jointing probably results from expansion of previously buried rocks exposed at the sea floor by erosion. Erosion of the Bahama Escarpment may have occurred by other processes acting in concert, or individually at different times, as well. Dissolution by corrosive water below the calcite compensation depth (CCD) and removal of sediments at the base of the slope by abyssal currents probably contributed most to erosional modification of the Bahama Escarpment. Bioerosion and jointing may aid dissolution by increasing surface area exposed to corrosive waters. Tectonic activity related to movements along fracture-zone trends might have contributed locally to erosion of the Bahama Escarpment. Erosion of the Bahama Escarpment shallower than 2,500 m has been less extensive and apparently proceeds by slumping of large, allochthonous blocks, as indicated by the presence of an apparently intact Eocene forereef deposit in the interval from 3,590 to 3,430 m off Eleuthera Island.

Six seamounts and many small constructional volcanic cones were recently investigated during a combined Sea MARC 1 and Seabeam survey of the East Pacific Rise (EPR) axis between 9.5°N and 13°N as part of an overall program funded by the National Science Foundation designed to characterize the along-strike morphology and structure of the axis of the EPR [Rise Axis Tectonic Team, 1983]. The larger seamounts studied fall into two principal categories: those that exhibit purely constructional volcanic terrain and those where the summits and flanks show significant structural and erosional features such as summit calderas (cover photo) and collapse craters and edifice flanks which have been extensively modified owing to mass-wasting processes (Figure 1). The seamounts studied include three volcanos just west of the EPR axial graben at 9°52′, which form a linear group that trends N60°W. The flanks and summits of these seamounts were insonified on overlapping traverses by using Sea MARC 1 side-scan sonar and Seabeam, multi-beam echosounding. Sea MARC 1 is a midrange side-scan system developed by International Submarine Technology of Redmond, Washington, and Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York. It can insonify swaths of seafloor as great as 5 km (full width) and depicts seafloor morphology and structure as small as a few meters with great accuracy. The resulting bathymetric base a n d sonar images have clearly identified an evolutionary pattern in the progressive structural and morphological development of these seamounts as one moves away from the EPR axis, with the details of the sonar records having important implications for constructional volcanism on the flank of the EPR.

A SeaBeam and SeaMARC I survey of a seamount group located several kilometres west of the axis of the East Pacific Rise (EPR) at lat 9°53′N defines the existence of a large submarine lava field at the base of one of the volcanoes (MIB). The field must be relatively young with respect to the surrounding terrain because lavas lap up against the base of MIB seamount, obscuring older erosional terrain, and extend out over the faulted, sedimented terrain of the flank of the EPR. Volcanic cones within the lava field are aligned with the strike of fault scarps that are buried by the lavas. MIB seamount is characterized by a large, well-developed caldera, and we suggest that the lava field was created during a recent volcanic episode when magmas migrated laterally away from the seamount9s reservoir along preexisting faults parallel to the ridge axis. The withdrawal of magmas from the MIB reservoir into the flanking parasitic eruptive plumbing system created the lava field and deflated the seamount summit. This event contributed to the development of the MIB caldera. Draining of shallow-level magma chambers under seamounts by pressure-controlled basal-flank eruptions that form lava fields is an important mechanism for the development of seamount morphology.

As many as 20 air-borne tephra layers have been identified in the upper Quaternary sequence of deep-sea cores from the eastern Mediterranean. Petrographical examination based on refractive index, phenocryst content, and chemical composition of the volcanic glass distinguishes the parent magma types: (1) tephritic, (2) alkalic-trachytic, (3) peralkalic-pantelleritic, and (4) calc-alkalic andesitic to rhyodacitic and alkali-basaltic. Tephra layers could be correlated with the following source volcanoes: Somma-Vesuvius, Roman district, Phlegraean Fields and Ischia, Pantelleria, Aeolian Islands, Mount Etna, and Aegean arc. The distribution for single layers has been traced over more than 2,000 km.

Coring and acoustic-reflection data show that coarse-grained sediment layers are remarkably continuous throughout the Tyrrhenian Abyssal Plain. Contrasts in acoustic impedance at the interfaces of these layers with the finer pelagic clay produce discrete sub-bottom echoes that have been correlated with the in situ strata by coring. Observations of grain size, bed thickness, and mineralogy have been used to identify the origin and transportation routes for two distinct types of sand. One type consists of eolian-transported tephra; several individual beds have been tentatively correlated with historic volcanic eruptions. The other type appears to have been transported through submarine canyons to the abyssal plain by turbidity currents. Three extensive turbidite layers have been traced to Naples Canyon, and one layer to a canyon originating off the eastern coast of Sardinia. Photographs of the sea floor on the abyssal plain show no evidence of bottom currents; however, those at the mouth of Naples Canyon depict large sand waves and drifted sediments which suggest that strong transient currents have recently flowed there. The vast areal extent of the individual turbidite layers within the abyssal plain supports the hypothesis that the turbidity currents arrive at the abyssal plain with sufficient energy to pond their suspension over the basin floor. Seismic-reflection records indicate that this process has been active throughout the modern history of the Tyrrhenian Basin, and more than 1000 m of sediment has accumulated in its deepest depression.

A prominent system of submarine canyons has been discovered in the Ionian Sea south of the Strait of Messina. The canyons are from 2 to 5 miles wide and more than 100 fathoms deep. Below the base of the continental slope, the canyons widen and develop flat floors as they extend southward 150 miles across a large cone to the Messina Abyssal Plain. On December 28, 1908, the Strait of Messina was affected by a severe earthquake which devastated the city of Messina and nearby communities. Only two of the eight submarine cables which linked Italy and Sicily within the area of maximum intensity were damaged. Ten hours after the quake, a cable from Malta to Zante parted 120 miles to the south in 1800 fathoms depth at a point where the cable crossed the submarine canyon leading from the Strait to the abyssal plain. The earthquake apparently generated a slump which initiated a turbidity current which broke the two successive cables as it traveled downslope through the canyon at an average speed of 12 knots. The tsunami which swept repeatedly against the surrounding coasts appears to have been produced by the slump and the turbidity current. The cables lying in shallower parts of the Strait, although directly within the epicentral area, did not break because the strong currents through the Strait had removed essentially all the unconsolidated sediments. Multiple sub-bottom echoes, observed beneath the canyon floors and beneath the abyssal plain but absent from the cone, are reflections from coarse-grained layers of sediment deposited by turbidity currents. Cores from within the canyons contain graded beds of sands and silts. Cores from isolated topographic locations show a pelagic record of stagnations and tephra falls which may be correlated.