Minerals, native metals, and intermetallides in bottom sediments of the Markov Deep, Mid-Atlantic Ridge

Bottom sediments of the Markov Deep contain rather large (>0.1 mm) grains of native minerals and intermetallides of noble and nonferrous metals that can be concentrated in placers. Intermetallides of Pt and Fe are likely to be derivates of the gold-hematite-barite assemblage that forms at late (low-depth) stages of hydrothermal massive sulfide formation. Mineral association of native forms of lead, tin, and copper with Zn-bearing copper may be related to hydrothermal transformation of ultrabasic and basic rocks accompanied by massive sulfide copper mineralization. The association of these minerals of native elements in bottom sediments can also serve as a prospecting guide for sulfide mineralization both at the Sierra Leone site, in particular, and on the seafloor, in general.

Holocene sedimentation in the Strait of Otranto, Mediterranean Sea

An extensive radiograph study of 24 undisturbed, up to 206-cm long box and gravity cores from the western part of the Strait of Otranto revealed a great variety of primary bedding structures and secondary burrowing features. The regional distribution of the sediments according to their structural, textural, and compositional properties reflects the major morphologic subdivisions of the strait into shelf, slope, and trough bottom (e.g., the bottom of the northern end of the Corfu-Kephallinia Trough, which extends from the northeastern Ionian Sea into the Strait of Otranto): (1) The Apulian shelf (0 to -170m) is only partly covered by very poorly sorted, muddy sands without layering. These relict(?) sands are rich in organic carbonate debris and contain glauconite and reworked (?Pleistocene) ooids. (2) The slope sediments (-170 to -1,000 m) are poorly sorted, sandy muds with a high degree of burrowing. One core (OT 5) is laminated and shows slump structures. An origin of these slumped sediment masses from older deposits higher on the slope was inferred from their abnormal compaction, color, texture, organic content, and mineral composition. (3) Cores from the northern end of the Corfu-Kephallinia Trough (-980 to -1,060 m) display a few graded sand layers, 2-5 cm (maximum 30 cm) thick with parallel and ripple-cross-laminations, deposited by oceanic bottom or small-scale turbidity currents. They are intercalated with homogeneous lutite. (4) Hemipelagic sediments prevail in the more southerly part of the Corfu-Kephallinia Trough and on the "Apulian-Ionian Ridge", the southern submarine extension of the Apulian Peninsula. Below a core depth of 160 cm, these cores have a laminated ("varved") zone, representing an Early Holocene (Boreal-Atlanticum) "stagnation layer" (14C age approximately 9,000 years). The terrigenous components of the surface sediments as well as those of the deeper sand layers can be derived from the Apulian shelf and the Italian mainland (Cretaceous Apulian Plateau and Gargano Mountains, southern Apennines, volcanic province of the Monte Vulture). Indicated by the heavy mineral glaucophane, a minor proportion of the sedimentary material is probably of Alpine origin. If this portion is considered to be first-cycle clastic material it reaches the Strait of Otranto after a longitudinal transport of 700 km via the Adriatic Sea. The lack of phyllosilicates in the coarse- to medium-grained shelf samples might be explained by the activity of the "Apulian Current" (surface velocities up to 4 knots) which in the past possibly has affected the bottom almost down to depths of the shelf edge. The percentage of planktonic organisms, and also the plankton: benthos ratio in the sediments is a useful indicator for bathymetry (depth zonation).

Heavy and light minerals in turbidites from DSDP Hole 19-183, the Aleutian abyssal plain

The Aleutian abyssal plain is a fossil abyssal plain of Paleogene age in the western Gulf of Alaska. The plain is a large, southward-thinning turbidite apron now cut off from sediment sources by the Aleutian Trench. Turbidite sedimentation ceased about 30 m.y. ago, and the apron is now buried under a thick blanket of pelagic deposits. Turbidites of the plain were recovered at site 183 of the Deep Sea Drilling Project on the northern edge of the apron. The heavy-mineral fraction of sand-sized samples is mostly amphibole and epidote with minor pyroxene, garnet, and sphene. The light-mineral fraction is mostly quartzose debris and feldspars. Subordinate lithic fragments consist of roughly equal amounts of metamorphic, plutonic, sedimentary, and volcanic grains. The sand compositions are arkoses in many sandstone classifications, although if fine silt is included with clay as matrix, the sand deposits are feldspathic or lithofeldspathic graywacke. The sands are apparently first-cycle products of deep dissection into a plutonic terrane, and they contrast sharply with arc-derived volcanic sandstones of similar age common on the adjacent North American continental margin. The turbidite sands are stratigraphically remarkably constant in composition, which indicates derivation from virtually the same terrane through a time span approaching 20 m.y. Comparison of Aleutian plain data with the compositions of coeval sedimentary rocks from the northeast Pacific margin shows that the Kodiak shelf area includes possible proximal equivalents of the more distal turbidites. Derivation from the volcaniclastic Mesozoic flysch of the Shumagin-Kodiak shelf is unlikely; more probably the sediments were derived from primary plutonic sources. The turbidites also resemble deposits in the Chugach Mountains and the younger turbidites of the Alaskan abyssal plain and could conceivably have been derived from the coast ranges of southeastern Alaska or western British Columbia. The Aleutian plain sediment most likely was not derived from as far south as the Oregon-Washington continental margin, where coeval sedimentary deposits are dominantly volcaniclastic.

Sedimentation and mineral analysis on sediment cores from the Lena Delta

Core and outcrop analysis from Lena mouth deposits have been used to reconstruct the Late Quaternary sedimentation history of the Lena Delta. Sediment properties (heavy mineral composition, grain size characteristics, organic carbon content) and age determinations (14C AMS and IR-OSL) are applied to discriminate the main sedimentary units of the three major geomorphic terraces, which form the delta. The development of the terraces is controlled by complex interactions among the following four factors: (1) Channel migration. According to the distribution of 14C and IR-OSL age determinations of Lena mouth sediments, the major river runoff direction shifted from the west during marine isotope stages 5-3 (third terrace deposits) towards the northwest during marine isotope stage 2 and transition to stage 1 (second terrace), to the northeast and east during the Holocene (first terrace deposits). (2) Eustasy. Sea level rise from Last Glacial lowstand to the modern sea level position, reached at 6-5 ka BP, resulted in back-filling and flooding of the palaeovalleys. (3) Neotectonics. The extension of the Arctic Mid-Ocean Ridge into the Laptev Sea shelf acted as a halfgraben, showing dilatation movements with different subsidence rates. From the continent side, differential neotectonics with uplift and transpression in the Siberian coast ridges are active. Both likely have influenced river behavior by providing sites for preservation, with uplift, in particular, allowing accumulation of deposits in the second terrace in the western sector. The actual delta setting comprises only the eastern sector of the Lena Delta. (4) Peat formation. Polygenetic formation of ice-rich peaty sand (''Ice Complex'') was most extensive (7-11 m in thickness) in the southern part of the delta area between 43 and 14 ka BP (third terrace deposits). In recent times, alluvial peat (5-6 m in thickness) is accumulated on top of the deltaic sequences in the eastern sector (first terrace).

Composition of suspended matter and bottom sediments from the Atlantic Ocean and its seas

The book summarizes data on distribution and composition of sedimentary material suspended in waters of the Atlantic Ocean and its seas. Results of observations of Soviet and foreign expeditions are given. Distribution of suspended matter in sections across the ocean, as well as in the most studied seas are shown. New data on grain size, mineral and chemical composition of suspended matter are published. Summary of history of investigation of bottom sediments from the Atlantic Ocean from the first scientific cruises to the present is done. A brief description of sediment types in the ocean and a detailed description of Mediterranean Sea sediments are given.

Composition of sediments, hydrothermal manifestations, interstitial waters, and aeolian material from the TAG Hydrothermal Field and Central Atlantic

The book is devoted to regularities of spatial distribution, mineralogy and geochemistry of hydrothermal and hydrothermal-sedimentary manifestations of the Mid-Atlantic Ridge rift zone.