Cladorhiza corona sp. nov. (Porifera : Demospongiae : Cladorhizidae) from the Aleutian Islands (Alaska)

A new species of Cladorhizidac, front the Aleutian Islands is described and compared with all known species of Cladorhizza worldwide. Cladorhiza corona sp. now has a unique growth form with two planes of differently shaped appendages. Appendages are Inserted directly at the stalk; a spherical or conical body at the stalk is lacking. It is the only species reported where different spicule types occur in three morphologically different areas of the sponge. The spiculation of the basal plate is characterized by the occurrence of short, thick anisoxcas and the lack of anisochelae. Anisochelac arc found in the stalk and the basal appendages only. Flattened sigmancistras and (sub-)tylostyles are restricted to the crown. The arrangement of spicules is different in the basal plate, the stalk with the basal appendages, and in the distal append ages. The dimensions and combination of spicule types separate C. corona sp. nov. from all known members of the genus.

Mineralogy and nannoplankton distribution in ODP Hole 194-1195A

Significant synchronous shifts in the chemistry, mineralogy, grain sizes and color of the sediments at 6 m below sea floor (mbsf) at ODP Site 1195 on the Marion Plateau (NE Australia) are interpreted to reflect a major regional paleoceanographic change: the initiation of the southern province of the Great Barrier Reef (GBR). The onset of this massive carbonate production centre nearby resulted primarily in increased deposition of carbonate-rich sediments of neritic origin. Both sedimentation rate and terrigenous input record a coincident decline attributed to inshore trapping of materials behind the reefs. Our best estimate places the development of reef framework in the southern part of the GBR between 560 and 670 kyr B.P., based on an age model combining magnetostratigraphic and biostratigraphic data. The proposed estimation agrees with previous studies reporting an age between 500 and 930 kyr B.P., constraining more tightly their results. However, it does not support research placing the birth of the GBR in Marine Isotope Stage (MIS) 11 (~400 kyr), nor the theory of a worldwide modern barrier reef development at that time.

(Table 1) Counts and ratios of microfossils at DSDP Hole 64-480

We examined the relative abundance of various components in the coarse fraction (> 150 µm) from a selected portion of the DSDP Site 480 piston core. The components consist mainly of diatoms, radiolarians, benthic and planktonic foraminifers with minor amounts of sponge spicules, terrigenous material, volcanic glass(?), dehydrated gypsum crystals, and spines of unknown biological origin. The examination shows that the siliceous organisms abound in the laminated sediments and that the calcareous organisms are more abundant in the nonlaminated sediments. Seasonal upwelling is responsible for the deposition of laminated sediments. The upwelling creates a strong oxygen-minimum zone, restricting the occurrence of burrowing benthic organisms and benthic foraminifers.

Lithology and geochemistry of ODP Leg 198 sites, Shatsky Rise

Samples of chert, porcellanite, and chalk/limestone from Cretaceous chert-bearing sections recovered during Leg 198 were studied to elucidate the nature and origin of chert color zonations with depth/age. Sedimentary structures, trace fossils, compactional features, sediment composition, texture, geochemistry, and diagenetic history were compared among lithologies. Trends in major and minor element composition were determined. Whereas geochemical analyses demonstrate systematic elemental differences among the different lithologies, there are less distinct patterns in composition for the colored cherts. The color of the chert appears to be related primarily to the amount of silica and secondarily to the proportion of other components. Red cherts are almost pure silica with only minor impurities. This may allow pigmentation from fine Fe oxides to dominate the color. These red cherts are from places where geophysical logs indicate that chert is the dominant rock type of the section. These red chert intervals cannot be unequivocally distinguished from surrounding chert-bearing lithologies in terms of sedimentary structures.

Siliceous fossils in sediments of the Ibero-Moroccan shelf and adjacent deep sea plains

Siliceous skeletons were investigated in two core profiles (9 cores), one off Cap de Sines, Portugal and the other off Cap de Mazagan, Morocco. Total number of skeletons was determined per gram of dried sediment at different core depths of the fraction >21 µ. Results are compared with a core profile from the Arabian Sea. Diatoms are of four groups: (A) marine-planktonic, B) marine-benthic, (C) freshwater and (D) Tertiary species (Trinacria e.g.). Species from groups (B), (C) and (D) are redeposited in all cores taken at a water depth of greater than 100 m. Small numbers of Silicoflagellates and Radiolarians were found throughout the cores from the Ibero-Moroccan shelf. In the Arabian Sea core, Radiolarians were concentrated in distinct horizons in which Tertiary material was redeposited (40-50, 140-150, 250-260 cm). The number of siliceous skeletons per gram of dried sediment decreases more or less rapidly with increasing depth in all cores. Whereas about 2500 skeletons were found in sediments close to the surface, approximately 100 skeletons only were found in deeper (>40 cm) layers. Deeper horizons with more than 100 specimens were interpreted as redeposited material. This sediment contained robust skeletons, resistant against dissolution, as well as benthic and Tertiary material. The decrease of siliceous skeletons relative to core depth depends upon the sedimentation rate. Where the sedimentation rate is high, the opal dissolution zone extends down to 30-60 cm, where the sedimentation rate is low, it is located at 10-30 cm. Below these depths opals disappears. These zones also have approximately the same age (4000 years) everywhere. Siliceous skeletons dissolve differentially, first the Silicoflagellates disappear, second the Diatoms, third the Radiolarians, and fourth the Sponge Spicules. Surface structure of skeletons from near the opal dissolution zones are similar to those of skeletons treated with NaOH. Tertiary diatoms (Trinacria e. g.) and benthic diatoms (Campylodiscus e.g.) dissolve less rapidly than skeletons of modern planktonic diatoms (Coscinodiscus e.g.). The time control of the opal dissolution zones appeared rather independent of various oceanic influences. No evidence was found for effects from upwelling either off Portugal or off Morocco. No difference in dissolution rates was recorded between the abyssal plains lying off these two areas. Likewise, there was no change in solution rates from Pleistocene to Holocene within either one of the abyssal plains. The Mediterranean outflow, which is enriched in dissolved silica, apparently had no effect on dissolution rates of siliceous skeletons in the sediment.

Pliocene and Pleistocene abundance of siliceous microfossil assemblages in ODP Leg 127 sites

A close examination of the siliceous microfossil assemblages from the sediments of ODP Leg 127, Japan Sea Sites 794, 795, and 797, reveals that upper Pliocene and Pleistocene assemblages have been subjected to more dissolution than have lower Pliocene assemblages. This conclusion is based on semiquantitative observations of samples processed for diatoms and radiolarians. Although preservation of opaline microfossils in some upper Pliocene and Pleistocene samples is better than others, in general, the poorly preserved state of these assemblages supports the notion that opal dissolution, in response to lowered productivity, is responsible for the paucity of siliceous microfossils in upper Pliocene and Pleistocene sediments. The lithological transition from diatomaceous oozes to silts and clays corresponds to a change between dominantly well preserved to more poorly preserved siliceous assemblages, and is termed the late Pliocene Japan Sea opal dissolution transition zone (ODTZ). The base of the ODTZ is defined as the uppermost occurrence of high abundances of moderately to well preserved valves of the diatom Coscinodiscus marginatus. The dissolution transition zone is characterized by partially dissolved refractory assemblages of radiolarians, the presence of C. marginatus girdles, C. marginatus fragments, siliceous sponge spicules, and a general decrease in weakly silicified, less solution resistant diatoms upward in the section. The top of the dissolution transition zone marks the level where whole C. marginatus valves and C. marginatus fragments are no longer present in significant numbers. Dissolution of the late Pliocene and Pleistocene opaline assemblages is attributed mainly to changes in paleoceanographic circulation patterns and decreased nutrient (dissolved silicon) contents of the water column, and possibly dissolution at the sediment/water interface, rather than to post-depositional dissolution or diagenesis. We suggest that the transition from silica-rich to silica-poor conditions in the Japan Sea was due to fluctuations of deep-water exchange with the Pacific through the Tsugaru Strait between 2.9 and 2.3 Ma.

Median grain size and distribution of sand in ODP Hole 108-660A (Fig. 5)

50 m of Middle Eocene pure radiolarian ooze were drilled at ODP Site 660 in the equatorial East Atlantic, 80 km northeast of the Kane Gap. The oozes comprise a 10 m high and 2 km broad mound of seismic reverberations, covered by manganese-rich sediment, and contain trace amounts of sponge spicules and diatoms, negligible organic carbon (0.15%), clay, and variable amounts of pyrite. The yellow to pale brown silty sediments are relatively coarse-grained (30-45% coarser than 6 µm), little bioturbated, and commonly massive or laminated on a cm-scale. The unlithified radiolarian ooze may indicate an interval of high oceanic productivity, probably linked to a palaeoposition of Site 660 close to the equatorial upwelling belt during Middle Eocene time. The absence of organic matter, however, and both the laminated bedding and the mound-like structure of the deposit on the lower slope of a continental rise indicate deposition by relatively intense contour currents of oxygen-rich deep water, which passed through the Kane Gap, winnowed the fine clay fraction, and prevented the preservation of organic carbon. The ooze may be either a contourite-lag deposit, or a contourite accumulation of displaced radiolarians, originating south of the Kane Gap and being deposited in its northern lee, thus documenting the passage of a strong cross-equatorial bottom-water current formed near Antarctica. These Eocene contourites may be an analogue for ancient radiolarites in the Tethyan Ocean.

Sedimentology and origin of lower Cretaceous pelagic carbonates and redeposited clastics at DSDP Hole 76-534A

Drilling at Site 534 in the Blake-Bahama Basin recovered 268 m of Lower Cretaceous, Berriasian to Hauterivian, pelagic carbonates, together with volumetrically minor intercalations of claystone, black shales, and terrigenous and calcareous elastics. Radiolarian nannofossil pelagic carbonates accumulated in water depths of about 3300 to 3650 m, below the ACD (aragonite compensation depth) but close to the CCD (calcite compensation depth). Radiolarian abundance points to a relatively fertile ocean. In the Hauterivian and Barremian, during times of warm, humid climate and rising sea level, turbiditic influxes of both terrigenous and calcareous sediments, and minor debris flows were derived from the adjacent Blake Plateau. The claystones and black shales accumulated on the continental rise, then were redeposited onto the abyssal plain by turbidity currents. Dark organic-rich and pale organic-poor couplets are attributed to climatic variations on land, which controlled the input of terrigenous organic matter. Highly persistent, fine, parallel lamination in the pelagic chalks is explained by repeated algal "blooms." During early diagenesis, organic-poor carbonates remained oxygenated and were cemented early, whereas organic-rich intervals, devoid of burrowing organisms, continued to compact later in diagenesis. Interstitial dissolved-oxygen levels fluctuated repeatedly, but bottom waters were never static nor anoxic. The central western Atlantic in the Lower Cretaceous was thus a relatively fertile and wellmixed ocean basin.

Macrobenthos from the Novaya Zemlya Trough, Kara Sea

During Cruise 54 of R/V Akademik Mstislav Keldysh macrobenthos of the Novaya Zemlya Trough was studied with use of a Sigsby trawl along a submeridional transect near 75°30'N at depth range from 68 to 362 m. In total 140 species of bottom animals were found. Relative role of taxons was assessed using three parameters: abundance, biomass, and energy flow. Similarity of the parameters was used for comparison of samples. New material greatly contributes to data on composition of fauna and structure of communities of the studied region. It was revealed that small scyphozoid polyps and sipunculoids play an important role in the trough's community. Presence of a community dominated by Ophiocten sericeum (with important role of small bivalves) was revealed for the first time not only at the eastern by also at the western slope of the Novaya Zemlya Trough. The sharpest changes in composition and structure of the bottom community were confined to a zone of transition from the trough floor to the slope. These changes are determined by specificity of the macrorelief (of the floor and slope), composition of ground (soft brown silts abound in rhizopods and dense gray silts with admixture of pebbles), and possibly by hydrodynamic processes near the bottom.

Chemistry of interstitial waters of samples from DSDP Leg 25

Interstitial water analyses from sediments collected during Leg 25 of the Deep Sea Drilling Project have revealed that in the southwest Indian Ocean, great chemical activity exists in sediments in various depositional environments. Variable sedimentation rates allow us to set some interesting boundary conditions on chemical and transport processes in these interstitial waters, particularly with regard to the distribution of dissolved sulfate. In terrigenous rapidly deposited sediments, large depletions are observed in magnesium and potassium, whereas relatively small decreases in dissolved calcium occur. In slowly deposited detrital sediments, also, large decreases in potassium and magnesium coincide with very large calcium increases. In truly pelagic sediments, a one to one replacement of magnesium by calcium is observed in the interstitial waters, presumably due to reactions in the basal sediment layers. Biogenous deposits have great influence on dissolved silica (sponge spicules and radiolarians) and on dissolved strontium (carbonate recrystallization). Otherwise, dissolved silica reflects the clay mineralogy and shows variations which seem particularly dependent on the presence or absence of kaolinite. Variable dissolved manganese values reflect reducing conditions and/or availability of manganese in the solid phases for mobilization in reducing sediments.

Radiolarian stratigraphy across the Oligocene/Miocene transition in low latitudes

Recently the International Union of Geological Sciences (Commission on Stratigraphy, Working Group on the Paleogene/Neogene Boundary) proposed that the Oligocene/Miocene boundary be placed at the base of Chron C6Cn2n at 23.8 Ma on the Cande and Kent (1992) magnetic time scale, where it is approximated by planktic foraminifera at the first occurrence of Globorotulia kugleri, and by calcareous nannofossils at the last occurrence of Sphenolithus ciperoensis and the first and last occurrences of Sphenolithus delphix and S. capricornutus. Herein we show that, in terms of radiolarians, the base of Chron C6Cn2n can be correlated with the upper part of the Lychnocanoma elongata Zone between the last occurrence of Artophormis gracilis (23.94 Ma) and the first occurrence of Cyrtocapsella tetrapera (23.69 Ma). Since the proposed stratotype at Lemme-Carrosio (Italy) does not contain radiolarians at the boundary, we re-examined 13 DSDP sites and established the stratigraphic sequence of 29 first and last radiolarian occurrences and one evolutionary transition across the boundary. Nine of these sites contain both calcareous and siliceous microfossils and thus allow for an integrated biostratigraphy. Paleomagnetic stratigraphy is not available for any of the DSDP cores examined. However, use of Hodell and Woodruff's (1994) strontium isotope curve from DSDP Site 289 has permitted calibration of several low latitude microfossil datum levels against the geomagnetic polarity scale. Two new species, Lychnocanoma apodora and Eucyrtidium plesiodiaphanes, are described.

Late Cretaceous dinoflagellate cysts of ODP Hole 120-748C

At Ocean Drilling Program Hole 748C in the Southern Indian Ocean, a total of 171 Late Cretaceous dinoflagellate taxa were encountered in 38 productive samples from Cores 120-748C-27R through 120-748C-62R (407-740 mbsf). Four provisional dinoflagellate assemblage zones and five subzones were recognized based on the character of the dinoflagellate flora and the first/last occurrences of some key species. Isabelidinium korojonense and Nelsoniella aceras occur in Zone A together with Oligosphaeridium pulcherrimum and Trithyrodinium suspect urn. Zone B was delineated by the total range of Odontochitina cribropoda. Zone C was separated from Zone B by the presence of Satyrodinium haumuriense, and Zone D is dominated by new taxa. The dinocyst assemblages bear a strong affinity to Australian assemblages. Paleoenvironmental interpretations based mainly on dinocysts suggest that during the ?Santonian-Campanian to the Maestrichtian this portion of the Kerguelen Plateau was a shallow submerged plateau, similar to nearshore to offshore to upper slope environments with water depths of tens to hundreds of meters, but isolated from the major continents of the Southern Hemisphere. Starting perhaps in the late Cenomanian (Mohr and Gee, 1992, doi:10.2973/odp.proc.sr.120.196.1992), the Late Cretaceous transgression over the plateau reached its maximum during the late Campanian. The plateau may have been exposed above sea level and subjected to weathering during the latest Maestrichtian. The studied dinocyst assemblages characterized by species of Amphidiadema, Nelsoniella, Satyrodinium, and Xenikoon together with abundant Chatangiella (the large-size species) and Isabelidinium suggest that a South Indian Province (tentatively named the Helby suite) may have existed during the Campanian-Maestrichtian in comparison with the other four provinces of Lentin and Williams. One new genus, three new species, and two new subspecies of dinocysts are described.

Distribution of Cretaceous redeposited benthic foraminifers at DSDP Site 89-585

Cretaceous benthic foraminifers from Site 585 in the East Mariana Basin, western Pacific Ocean, provide an environmental and tectonic history of the Basin and the surrounding seamounts. Age diagnostic species (from a fauna of 155 benthic species identified) range from late Aptian to Maestrichtian in age. Displaced species in sediments derived from the tops and flanks of nearby seamounts were deposited sporadically on the Basin floor well below the carbonate compensation depth (CCD) at abyssal depths of 5000 to 6000 m. These depths, characterized by an indigenous assemblage of benthic foraminifers, recrystallized radiolarians, fish debris, and sponge spicules, existed in the Mariana Basin from late Aptian to the present. Early Albian and older edifice-building volcanism had reached the photic zone with associated shallow-water bank or reef environments. By middle Albian, the dominant source areas subsided to outer-neritic to upper-bathyal depths. Major volcanic activity ceased and fine-grained sediments were deposited by distal turbidites, although intermittent volcanism and the influx of rare neritic material continued until the late Albian. By the Cenomanian to Turonian, upper- to middle-bathyal depths were reached by the dominant source areas, and the sediments recovered from this interval include organic carbon-rich layers. Rare benthic foraminifers from the Coniacian-Santonian interval indicate a continuation of dominantly middle-bathyal source areas. A change in sedimentation during the Campanian-Maestrichtian from older zeolitic claystone to abundant chert in the Campanian, and nannofossil chalk and claystone in the Maestrichtian resulted from migration of the site beneath the equatorial productive zone due to northwestward plate motion. The appearance of rare middle-neritic and upper-bathyal species in the Maestrichtian interval associated with volcanogenic debris gives evidence of the remobilization and downslope transport of pelagic deposits due to thermally induced uplift. Episodic redeposition of shallow-water material during the Aptian-Albian was produced by edifice-building volcanism perhaps combined with eustatic lowering of sea level. The Cenomanian-Turonian pulse coincided with a low global sea-level stand as does the transported material during the Coniacian-Santonian. The Maestrichtian pulse was caused by renewed midplate volcanism that extended over a large area of the central Pacific.