758 D. Submarine Geology and Geophysics OLR (1987) 34 (9)

and Hawaii were sampled and dated radiometrically. Recognition that the terraces are tilted 5 m/km toward the locus of volcanic loading on Hawaii, permits assignment of such terraces from 150 to 1300 m depth to eight general reef platforms, drowned by combined island subsidence and sea level rise at the end of successive glacial stages from 13 to 647 Ka. Dating of slope change at the end of active volcanic shield building provides independent evidence that shield building ended at about the time eruptions changed from tholeiitic to alkalic basalt, and the depth variation of the dated, tilted reefs indicates that the end of subsidence follows that of shield building by about one half million years. During the last half million years the SE migration rate for the end of subsidence and tholeiitic volcanism has apparently increased, implying increased eruption rates. USGS, 345 Middlefield Rd., Menlo Park, CA 94025, USA.

D120. Sedimentary processes (deposition, diagenesis, etc.)

87:5047 Canfield, D.E. and R.A. Berner, 1987. Dissolution

and pyritizatlon of magnetite in anoxic marine sediments. Geochim. cosmochim. Acta, 51(3): 645-659.

Concentrations of magnetite were determined, with depth, in sediments of varying H2S content from Long Island Sound and the Mississippi Delta. For the three Long Island sites, dissolution of magnetite during burial is clearly demonstrated, and for all four sites the rate of dissolution is proportional to dissolved pore water sulfide. Under typical condi- tions, the 'half-life' of magnetite in anoxic marine sediments ranges from ~50-1000 yr. Magnetite dissolution may be accompanied by extensive pyrite replacement if the magnetite is in contact with high H2S concentrations for several hundred years. This feature may prove to be a useful paleosulfide indicator. Dept. of Geol. and Geophys., Yale Univ., P.O. Box 6666, New Haven, CT 06511, USA.

DI30. Sediments (rocks, formations, type, composition, etc.)

87:5048 Chassefiere, B. and A. Monaco, 1987. Geotedmical

properties and sedimentological processes of the Rhone continental margin. Mar. Geol., 74(3- 4):225-235. Geol. et Geochimie, Univ. de Nice, 06034 Nice Cedex, France.

87:5049 Jansen, J.H.F., C.F. Woensdregt, M.J. Kooistra and

S.J. van der Gaast, 1987. lludte pseudomorphs in the Zaire deep-sea fan: an intermediate between calcite and porous calcite. Geology, geol. Soc. Am., 15(3):245-248. Netherlands Inst. for Sea Res., P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands.

87:5050 Kitano, Yasushi, 1986. Geochemical study on the

formation of carbonate sediment. Lecture by the member awarded the Oceanographical Society of Japan Prize for 1986. J. oceanogr. Soc. Japan, 42(5):402-420. (In Japanese, English abstract.)

A review of the study on crystal form and minor element distribution in marine biogenic carbonate (for which the prize was awarded) is presented. Discussed are the goals and basic information used for the research; the influence of chemical con- stituents in the parent solution on polymorphic crystallization of CaCO3; crystal form and type of marine biogenic carbonates; synthesis of magnesian calcite in aqueous solution; distribution of minor elements in solution and precipitate; and the amount and role in the geochemical balance of biogenic carbonate deposited annually in the ocean. Sugi- yama Jogakuen Univ., 17-3, Hoshigaoka Moto- machi, Chikusa-ku, Nagoya 464, Japan.

87:5051 Perissoratis, C. et al., 1987. The geology and

geochemistry of the surficial sediments off Thraki, northern Greece. Mar. Geol., 74(3-4):209-224. Inst. of Geol. and Mineral Exploration, 70 Mesoghion St., Athens, Greece.

87:5052 Prusak, Deanne and Jim Mazzullo, 1987. Sources

and provinces of Late Pleistocene and Holocene sand and silt on the Mid-Atlantic continental shelf. J. sedim. Petrology, 57(2):278-287.

Studies of the shapes and surface textures of quartz and silt grains from the mid-Atlantic shelf indicate two distinct sources of sediment: the Atlantic Coastal Plain and Appalachian Highlands. Their distribution is controlled to a great extent by late Quaternary paleogeography. The Appalachian sands are generally found in the estuaries, shelf valleys, and deltas of the river systems which drain the Appalachian Highlands. Coastal plain sands are found in areas proximal to exposures of coastal-plain strata. The distribution of silt is controlled largely by prevailing Holocene coastal and shelf currents. Five sedimentary provinces can be defined by areal variations in the abundances of sand; the Hudson,