Postglacial deposition of sand in the Eckernfoerder Bay, western Baltic Sea

At the NW-slope of Eckernforder Bay (Western Baltic) between 14 and 21 m water depth 7 sand cores were taken with a vibrocorer. The cores were between 85 and 250 cm long. The sand was analysed for grain size distribution, proportions of organic carbon and carbonate, and contents of microfossils. The radiometric age and stable carbon isotope ratios were determined on organic material from 14 sample. With regard to benthic foraminifera and other microorganisms four different types of depositional conditions could be distinguished: Types 1 and 2: two types of offshore sand areas. Type 3: lagoon and nearshore. Type 4: subaerial or limnic. Using sedimentological and geochemical parameters two formation areas could be distinguished with the aid of a discriminant analysis: offshore (types 1 and 2) and nearshore (types 3 and 4). A juxtaposition of core sections indicated two distinct profiles. Their ages fit into the picture of the assumed postglacial sea-level rise. The lagoon- and nearshore sands are interpreted as the result of sea-level stagnation at 17-18 m below present sea-level. The accumulation rates of the sand in the offshore areas are, with a maximum of 0.15 mm/yr., an order of magnitude smaller than in the mud areas, located several hundred metres away.

Chemistry of sulfide deposites of ODP Site 106-649

The Snake Pit active hydrothermal field was discovered at 23°22'N on the Mid-Atlantic Ridge during ODP Leg 106. Among the ten holes drilled in the mound at the foot of an active chimney, only three (649B, 649F, and 649G) had substantial recovery, and produced cores of unconsolidated hydrothermal deposit made up of porous sulfide fragments with minor talc pellets and biological debris, and a few pieces of brassy massive sulfides. Eight representative samples from the 6.5-m-long core from Hole 649B were analyzed for bulk chemistry, both by XRF (major elements) and NAA (trace elements). Major elements average compositions show high Fe (36 wt%), S (37 wt%), and Cu (12 wt%) contents, and minor Zn (6.7 wt%), reflecting a mostly high-temperature deposit. Trace elements are characterized by a high Au content (600 ppb) which could express the maturity of the mound. Mineralogical assemblages show evidence of sequential precipitation, and absence of equilibrium. Major sulfide phases are pyrrhotite, pyrite, Fe, Cu sulfides, marcasite, and sphalerite. Three types of samples are distinguished on the basis of textures and mineral assemblages: type 1, rich in pyrrhotite, with approximately equivalent amounts of Cu, Fe sulfides, and sphalerite and minor pyrite; type 2, rich in Cu, Fe sulfides, which are cubic cubanite with exsolutions and rims of chalcopyrite; and type 3, essentially made up of sphalerite. Type 2 samples likely represent fragments of the inner chimney wall. The presence of talc intergrown with cubic cubanite/chalcopyrite in one big piece from Hole 649G is probably related to mixing of the hydrothermal fluid with seawater.

Composition of bioclastic sands, carbonates and pyroclastic rocks of the Great Meteor and Josephine Seamounts, eastern North Atlantic

1. Great Meteor Seamount (GMS) is a very large (24,000 km**3) guyot with a flat summit plateau at 330-275 m; it has a volcanic core, capped by 150-600 m of post-Middle-Miocene carbonate and pyroclastic rocks, and is covered by bioclastic sands. The much smaller Josephine Seamount (JS, summit 170- 500 m w. d.) consists mainly of basalt which is only locally covered by limestones and bioclastic sands. 2. The bioclastic sands are almost free of terrigenous components, and are well sorted, unimodal medium sands. (1) "Recent pelagic sands" are typical of water depths > 600 m (JS) or > 1000 m (GMS). (2) "Sands of mixed relict-recent origin" (10-40% relict) and (3) "relict sands" (> 40% relict) are highly reworked, coarse lag deposits from the upper flanks and summit tops in which recent constituents are mixed with Pleistocene or older relict material. 3. From the carbonate rocks of both seamounts, 12 "microfacies" (MF-)types were distinguished. The 4 major types are: (1) Bio(pel)sparites (MF 1) occur on the summit plateaus and consist of magnesian calcite cementing small pellets and either redeposited planktonic bioclasts or mixed benthonic-planktonic skeletal debris ; (2) Porous biomicrites (MF 2) are typical of the marginal parts of the summit plateaus and contain mostly planktonic foraminifera (and pteropods), sometimes with redeposited bioclasts and/or coated grains; (3) Dense, ferruginous coralline-algal biomicrudites with Amphistegina sp. (MF 3.1), or with tuffaceous components (MF 3.2); (4) Dense, pelagic foraminiferal nannomicrite (MF 4) with scattered siderite rhombs. Corresponding to the proportion and mineralogical composition of the bioclasts and of the (Mgcalcitic) peloids, micrite, and cement, magnesian calcite (13-17 mol-% MgCO3) is much more abundant than low-Mg calcite and aragonite in rock types (1) and (2). Type (3) contains an "intermediate" Mg-calcite (7-9 mol-X), possibly due to an original Mg deficiency or to partial exsolution of Mg during diagenesis. The nannomicrite (4) consists of low-Mg calcite only. 4. Three textural types of volcanic and associated gyroclastic rocks were distinguished: (1) holohyaline, rapidly chilled and granulated lava flows and tuffs (palagonite tuff breccia and hyaloclastic top breccia); (2) tachylitic basalts (less rapidly chilled; with opaque glass); and (3) "slowly" crystallized, holocrystalline alkali olivine basalts. The carbonate in most mixed pyroclastic-carbonate sediments at the basalt contact is of "post-eruptive" origin (micritic crusts etc.); "pre-eruptive" limestone is recrystallized or altered at the basalt contact. A deuteric (?hydrothermal) "mineralX", filling vesicles in basalt and cementing pyroclastic breccias is described for the first time. 5. Origin and development of GMS andJS: From its origin, some 85 m. y. ago, the volcano of GMS remained active until about 10 m. y. B. P. with an average lava discharge of 320 km**3/m. y. The volcanic origin of JS is much younger (?Middle Tertiary), but the volcanic activity ended also about 9 m. y. ago. During L a t e Miocene to Pliocene times both volcanoes were eroded (wave-rounded cobbles). The oldest pyroclastics and carbonates (MF 3.1, 3.2) were originally deposited in shallow-water (?algal reef hardground). The Plio (-Pleisto) cene foraminiferal nannomicrites (MF 4) suggest a meso- to bathypelagic environment along the flanks of GMS. During the Quaternary (?Pleistocene) bioclastic sands were deposited in water depths beyond wave base on the summit tops, repeatedly reworked, and lithified into loosely consolidated biopelsparites and biomicrites (MF 1 and 2; Fig. 15). Intermediate steps were a first intragranular filling by micrite, reworking, oncoidal coating, weak consolidation with Mg-calcite cemented "peloids" in intergranular voids and local compaction of the peloids into cryptocrystalline micrite with interlocking Mg-calcite crystals up to 4p. The submarine lithification process was frequently interrupted by long intervals of nondeposition, dissolution, boring, and later infilling. The limestones were probably never subaerially exposed. Presently, the carbonate rocks undergo biogenic incrustation and partial dissolution into bioclastic sands. The irregular distribution pattern of the sands reflects (a) the patchy distribution of living benthonic organisms, (b) the steady rain of planktonic organism onto the seamount top, (c) the composition of disintegrating subrecent limestones, and (d) the intensity of winnowing and reworking bottom current

(Table T1) Fluid inclusions in siltstone and sandstone grains from ODP Hole 210-1276A

Twenty samples of siltstones and sandstones were taken from Ocean Drilling Program Site 1276 during Leg 210 for fluid inclusion studies. With the exception of one sample of vein calcite, all inclusions were in quartz grains. The results of fluid-inclusion petrology and microthermometry indicate the presence of three fluid inclusion types (Types 1, 2, and 3). Type 1 fluid inclusions are two-phase (liquid + vapor) aqueous inclusions, and Type 2 inclusions are monophase fluid inclusions (liquid or vapor). These are common in all samples and are formed either as primary isolated inclusions or as secondary inclusions as trails along annealed fractures in the grain. Type 3 fluid inclusions are three-phase (liquid + vapor + solid) inclusions. Type 3 inclusions are rare and are observed as isolated inclusions or in a cluster with other types (i.e., Types 1 and 2). The predominant population throughout the different units sampled is two-phase (liquid + vapor) aqueous fluid inclusions (i.e., Type 1). The temperature of homogenization (TH) bivariate plots for Type 1 inclusions shows dominance throughout the hole of low- to medium-salinity fluids with minimum trapping temperatures between 150° and 400°C.

Chromatographic fractionation of bitumen from sediments and presence of glycerol ethers in immature sediments (Table 2)

Alkanes having unusual saturated isoprenoidal and methyl-branched structures have been isolated from the bitumen of several sediments. The methanogenic biomarkers 2,6,10,15,19-pentamethyleicosane and squalane were found in sediments which also contained bacteriogenic glycerol ethers. However, in one ether-containing sediment, 2,6,10,13,17,21-hexamethyldocosane was tentatively identified and this compound was found in place of the established alkane biomarkers. Other hydrocarbons found were regular C21 and C23 isoprenoid alkanes, compounds which cannot be derived from phytol; two isoprenoids of the type 3,7,11.-polymethylalkane, previously reported only in petroleums; 8-methylheptadecane, a probable biomarker for cyanobacteria and a number of its homologs and other methyl-branched alkanes. Ubiquitous branched-chain alkylbenzenes and a homology of trimethylalkylbenzenes were also isolated. Most, or all, of the compounds reported here are probably not catagenetic products but may represent direct algal or bacterial bioinputs.

(Table 1) Magnetozone boundaries, age and sedimentation rate at DSDP Hole 93-605

Natural Remanent Magnetization (NRM) was measured for regularly spaced samples from the 620-m-thick, lower middle Eocene to upper Maestrichtian section of DSDP Site 605. The total NRM of the Eocene chalks was too low (5-50 µA/m) to establish a reliable magnetic polarity stratigraphy. However, the results from the somewhat more clayrich Paleocene-upper Maestrichtian section are useful. A fourfold quality classification of the results of progressive demagnetization studies aided in determining the polarity of the original remanence. Two types (1 and 2a) showed a Characteristic Remanent Magnetization (ChRM) direction with reversed and normal polarity, respectively; the third type (2b) can be interpreted as having a reversed ChRM, which could not be cleaned, whereas the fourth type (3) is considered to be unreliable. The Site 605 magnetic polarity stratigraphy compares well with published sections, adding important detail to the correlation with planktonic microfossil zones and, hence, to the resolution of this portion of the time scale (C24-C32 on the Berggren et al., 1985, scale). The Cretaceous/Tertiary boundary occurs in a reversed polarity zone that has been correlated with Subchron C29r. We suspect the presence of an unconformity at the boundary between lithostratigraphic Units Va and IV a location which is also the level of Reflection Horizon A*.