Submarine Exposure Research Articles

Submarine exposure guideline recommendations for carbon dioxide based on the prenatal developmental effects of exposure in rats.

To protect crewmember health, the U.S. Navy sets exposure limits for more than 200 components of submarine atmospheres. The addition of females to nuclear submarines required a reevaluation of these exposure limits, originally established for all-male crews. In the case of carbon dioxide (CO2 ), the only available data suitable for deriving an exposure limit were from a 2010 study sponsored by the British Royal Navy that reported a debatable interpretation casting doubt on whether current U.S. Navy exposure limits served to protect fetal developmental health. About 120 time-mated female Sprague-Dawley rats (Crl: CD[SD]) were exposed to CO2 at levels of 1.5%, 2.0%, 2.5%, and 3.0% from gestation days 6 to 20. Dams were euthanized and fetuses were examined. Findings with implications for exposure limits for CO2 during pregnancy were an increased mean litter proportion of early resorptions and a lower mean litter proportion of viable fetuses in the 3.0% CO2 group. The results yield a No Observed Adverse Effect Level (NOAEL) of 2.5% and a Lowest Observed Adverse Effect Level (LOAEL) of 3.0%. The results reasonably allow a point of departure of 2.5% CO2 for deriving an exposure recommendation. An interspecies uncertainty factor was applied to derive a recommended 90-day continuous exposure limit (CEL) of 0.8% for CO2 . As reproductive endpoints that are developmental in nature must be assumed to result from a single exposure at a critical point during gestation, it is further recommended that the 24-hr emergency exposure limit (EEL) also be 0.8%.

Hydrothermal contributions to global biogeochemical cycles: Insights from the Macquarie Island ophiolite

Hydrothermal circulation is a fundamental process in the formation and aging of the ocean crust, with the resultant chemical exchange between the crust and oceans comprising a key component of global biogeochemical cycles. Sections of hydrothermally altered ocean crust provide time-integrated records of this chemical exchange. Unfortunately, our knowledge of the nature and extent of hydrothermal exchange is limited by the absence of complete oceanic crustal sections from either submarine exposures or drill core. Sub-Antarctic Macquarie Island comprises ~10Ma ocean crust formed at a slow spreading ridge, and is the only sub-aerial exposure of a complete section of ocean crust in the ocean basin in which it formed. Hydrothermally altered rocks from Macquarie Island therefore provide a unique opportunity to evaluate the chemical changes due to fluid–rock exchange through a complete section of ocean crust. Here we exploit the immobile behavior of some elements during hydrothermal alteration to determine the precursor compositions to altered Macquarie whole rock samples, and evaluate the changes in bulk rock chemistry due to fluid–rock interaction throughout the Macquarie crust. The extent to which elements are enriched or depleted in each sample depends upon the secondary mineral assemblage developed, and hence the modal abundances of the primary minerals in the rocks and the alteration conditions, such as temperature, fluid composition, and water:rock ratios. Consequently the chemical changes vary with depth, most notably within the lava–dike transition zone where enrichments in K, S, Rb, Ba, and Zn are observed. Our results indicate that hydrothermal alteration of the Macquarie crust resulted in a net flux of Si, Ti, Al, and Ca to the oceans, whereas the crust was a net sink for H2O, Mg, Na, K, and S. Our results also demonstrate the importance of including the contribution of elemental uptake by veins for some elements (e.g., Si, Fe, Mg, S). Extrapolation of our results, assuming a crustal production rate of 3km2/yr, yields estimates of the hydrothermal contribution to global geochemical cycles. For example, the Mg flux to the crust is estimated to be 3.3±1.1×1012mol/year, sufficient to balance the riverine Mg input to the oceans given the uncertainties involved. However, the relationship between spreading rate and hydrothermal chemical exchange fluxes remains poorly understood, and the approach described here should be applied to crust produced at a range of spreading rates to refine the global hydrothermal flux estimates.

Ophiolite Tectonics, Rock Magnetism and Palaeomagnetism, Cyprus

Magnetic properties of minerals may be sensitive indicators of provenance. Remanence-bearing minerals (RBM) such as iron–titanium oxides, and matrix-forming minerals such as paramagnetic phyllosilicate or diamagnetic calcite yield different clues to provenance, strain history and tectonics, and are essential supplements for the full interpretation of palaeomagnetic data. Moreover, mineral magnetic properties provide magnetic-petrofabric indicators of tectonic strain, determine the suitability of sites for palaeomagnetism, and permit the restoration of palaeomagnetic vectors in some strained rocks. In the Cretaceous Troodos ophiolite (~88 Ma) magnetic properties are dictated by the relative importance of mafic silicates and largely primary, ophiolite-derived RBM. In its cover of deformed pelagic sedimentary rock, magnetic properties are dictated by the balance of clastic RBM versus matrix calcite and in some cases clay. The two larger Cretaceous ophiolite outcrops (Troodos & Akamas) share a common orientation of their plutonic flow fabrics, determined by magnetic methods. The dike complex shows fabrics indicating plume-like feeders spaced along and perpendicular to the spreading axis, with longevities >0.5 Ma. South of the ophiolite, its Cretaceous-Miocene limestone cover possesses ubiquitous tectonic petrofabrics inferred from anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent susceptibility (AARM). Its foliation and maximum extension dip and plunge gently northward, sub-parallel to a common but previously unreported North-dipping stylolitic cleavage. In well-known localized areas, there are S-vergent thrusts and overturned folds. The S-vergent deformation fabrics are due to Late Miocene (pre-Messinian ~8 Ma) deformation. The structures are geometrically consistent with overthrusting of the Cretaceous Troodos-Akamas ophiolite, and its sedimentary cover, onto the underlying Triassic Mamonia terrane. The northern limit of pre-Messinian tectonic fabrics, the Troodos-Mamonia terrane boundary and the Arakapas-Transform fault form an approximate E–W composite boundary that we term the Troodos Tectonic Front. Miocene deformation remagnetized the ophiolite and its sedimentary cover in many places and also affects the Mamonia terrane to the SW, with which the Troodos terrane docked in the late Cretaceous. Magnetic mineralogy, particularly of the RBM traces the progressive un-roofing of the ophiolite during the deposition of its sedimentary cover. During the submarine exposure and erosion of the ophiolite, the contribution of RBM clasts to the overlying sedimentary cover changed qualitatively and quantitatively. Thus, magnetic mineralogy of the sedimentary rock cover records the progressive denudation of the ophiolite from lavas, down through dikes, to gabbros and deeper mantle rocks. Palaeomagnetic studies previously revealed the anticlockwise rotation of the Troodos terrane and its northwards migration. Characteristic remanent magnetism (ChRM) is most reliable for lavas and dikes although it is usually carried by recrystallized RBM. These correspond to the age of greenschist facies ocean-floor metamorphism, perhaps 7–15 Ma after igneous crystallization with an extent and depth dependent on depth and degree of hydrothermal circulation. The gabbros and mantle rocks commonly bear young ( 8 Ma), the remagnetizing effects of penetrative strain have been under-estimated. Where strain has occurred, un-tilting procedures produce erroneous restorations for the remanence vectors, and thus for the associated paleopoles. We find that de-straining of limestone sites most appropriately restores ChRM vectors to their original orientation. The best-determined and restored ChRMs define an apparent polar wander path (APWP). Since the APWP terminates at the present N-pole, we inverted it to determine the true plate-motion of the Troodos-terrane. Thus, in present-day coordinates, Troodos rocks moved ~1,000 km South; then ~4,500 km East and finally ~900 km North at an approximate rate of 75 km/Ma [1 km/Ma = 1 mm/a]. This true motion path commenced ~88 Ma ago and rates of motion since 65 Ma may be too high due to the limited precision of strain-corrections of the ChRM orientations in limestone. This true motion path is compatible with the eastward and then northward rotation of Africa relative to Europe although other workers show relative motion paths.

Development of rudist lithosomes in the Coniacian–Lower Campanian carbonate shelves of central-southern Italy: high-energy vs low-energy settings

The Late Cretaceous shallow-water depositional areas of southern Tethys were complexes of unprotected shelves occupied by foramol assemblages that produced loose, diagenetically stable bioclastic debris not involved in significant in situ cementation processes. Both storm- and wind-induced currents and waves exercised a strong control on the distribution of the shifting biogenic sediments which covered the open sea-floor, constituting large coalescing sheets of winnowed fine to coarse skeletal sands. Rudists spread over all shelf sectors, from more open and external areas to more internal ones, occupying different substrata and furnishing the bulk of the skeletal component by means of bioerosion processes. They colonised mobile sediments giving rise to complex bodies with peculiar characteristics related to environmental parameters of the different sectors of the shelf. On the basis of detailed sedimentological, taphonomic and palaeontological data, we recognised two main rudist-rich depositional settings (‘end members’) in the southern Italy Senonian rudist-bearing successions. In successions pertaining to hypothesised marginal shelf sectors, characterised by high-energy regime deposits, rudist lithosomes are metric in thickness and lateral extent and lens-like in morphology, rich in bioerosion-derived skeletal sand and silt. Rudists are highly diversified. Large elongated cylindro-conical hippuritids (mostly pertaining to the genera Hippurites and Vaccinites), thick-shelled radiolitids and plagioptychids largely dominate. Rudists clustered in life position are subordinate; they often form small bouquets. More commonly these organisms appear fallen but only barely reworked. The rudist-rich bodies laterally pass into clean bioclastic grainstone in which sedimentary structures, related to current and/or storm erosional action, are common. No evidence of significant original relief of the rudist bodies in respect of the neighbouring sediment can be recognised. The submarine erosion and/or the high-energy processes operating presumably inhibited the aggradation of the tidal sediments above the marginal ones. As a consequence the vertical facies organisation shows widespread subtidal cycles, as commonly recognised in open shelves with ramp-like morphologies. In successions pertaining to more internal and/or low-energy sectors, rudist-rich beds rhythmically alternate with finer-grained foraminiferal limestones. Small elevator radiolitids with oligospecific diversity are dominant, mostly concentrated in clumps. Rudists in growth position are abundant, although a large quantity of shells appear toppled with little reworking. They may form laterally continuous biostromal shell beds. Sedimentary structures such as cross-lamination and gradation are only occasionally present. The resulting facies are commonly arranged in peritidal/shallow subtidal cycles in which evidence of subaerial (up to pedogenic modifications on a large and small scale) and, less frequently, submarine exposure is common. Intermediate successions have been recognised, characterised by deposits of silty-sand plains, which present intercalations of graded, bioclastic, storm-related beds. Sedimentological characteristics seem to document more open conditions in which submarine erosion was intermittently prevalent. In these successions rudist species that are commonly found both in high-energy and low-energy assemblages coexist.

Upper Cretaceous ramp limestones from the Sorrento Peninsula (southern Apennines, Italy): micro- and macrofossil associations and their significance in the depositional sequences

Abstract The Upper Cretaceous limestones of the Sorrento Peninsula are primarily characterized by wackestone/packstone with benthic foraminifers, thaumatoporellaceans and Aeolisaccus sp. and by rudist floatstones. Rudists in growth position are rare; most of them appear toppled and locally oriented but not reworked. In some cases they form small bouquets no more than 30 cm thick. The successions analyzed in the Sorrento Peninsula encompass a variety of facies representative of inner shelf environments in a ramp-like depositional setting. On the basis of lithologic and sedimentologic characteristics and on a qualitative analysis of the biofacies, three major facies associations have been recognized corresponding to: (a) intertidal silty-sand flats and shallow lagoons; (b) subtidal mobile foraminiferal sand sheets; (c) subtidal rudist dwelt sand plain. In the lower part of the successions periodic (more or less prolonged) emersions (subaqueous with fresh/brackish waters or subaerial exposure) are documented. The upper part of each succession lacks any emersion evidence; submarine exposure surfaces are testified by firmground-related features. The periodic influence of high-energy regimes (some storm-related events) is documented by wave- and cross-laminations, HCS and the lack of fine sediments. Lithofacies are arranged in depositional cycles that may correspond to individual beds. The boundaries of the depositional cycles show evidence of subaerial or submarine exposures. The nature and position of these discontinuity surfaces in the successions provide an important clue to interpretation in terms of both depositional environment and vertical evolution. The increase in thickness of the depositional cycles and the gradual change from peritidal/shallow-subtidal cycles to dominantly subtidal cycles, document an increase in the amount of accommodation space which resulted from a long-term rise in relative sea-level. A detailed study of benthic associations (micro- and macrofauna) has been carried out in order to identify accurately further signs of periodicity contained within the successions as a whole. These Upper Cretaceous limestones are abundantly fossiliferous with only a moderately diverse fauna. There are no significant differences in terms of species, the assemblages simply reflecting differences in abundance of the same species. Taphonomic studies of rudist-rich beds permit seven major shell-bed types to be distinguished. Six main foraminiferal assemblages have been detected, and the distribution and relative abundance of the species have been examined within the environments inferred through facies analysis. The taphonomic data and the foraminiferal assemblage abundance and diversity, have been compared with lithologic and sedimentologic data in order to elucidate their distribution within depositional cycles and throughout the successions. The successions show little up-section changes in lithology and in taxonomic composition of the foraminiferal assemblages. It is therefore difficult to establish a paleoenvironmental trend independent of the rudist shell concentrations, which do change up-section. We noticed an overall increase in thickness and abundance of the shell beds and a shift in types of shell concentration and in taxonomic composition. These characteristics, associated with the upward disappearance of emersion surfaces, the higher frequency of storm and/or wave intercalations, the increase in thickness of the depositional sequences and the gradual change from peritidal/shallow-subtidal cycles to dominantly subtidal cycles, document a general deepening-upward trend. More open water conditions with a depth between fairweather and storm wave-base became established as a result of relative sea-level rise and to a consequent increase in the available accommodation space.

Senonian rudist limestones in the Sorrento Peninsula sequences (Southern Italy)

Senonian carbonate sediments rich in rudists are widespread throughout central-southern Italy. TheConiacian-Santonian series, analyzed in the Lattari Mountains (Sorrento Peninsula), are almost completely composed of limestones, with very subordinate dolomitic beds. On a field scale we can distinguish rudist-rich beds rhythmically alternating with finer-grained foraminiferal beds. The studied series testify to a deposition in shallow-sea environments. In the lower part of the series periodical, more or less prolonged emersions (subaqueous with fresh/brackish waters or subaerial exposure) are documented. The upper part of the series lacks emersion evidence; submarine exposure surfaces are testified by firmgrounds or hardgrounds. Wave- and cross-laminations, HCS and the lack of fine sediments document an overall deposition under influence of occasional high-energy water regimes with some storm-related events. The sedimentology and taphonomic signature of the rudist shell beds have been described in order to get a better understanding of depositional environment and the physical processes that controlled the Senonian sedimentation. Monospecific tabular beds mainly characterize the lower part of the series; more complex rudist concentrations, characterized by moderate species diversity, increase up-section. The recognized lithofacies are organized in shallowing-upward depositional cycles that show a gradual change from peritidal/shallow-subtidal cycles to dominantly subtidal cycles up-section; this change records a general deepening-upward trend as a possible result of an increase of the accommodation space provided by a relative sea-level rise, according to what is suggested for other coeval Apennine and Sardinia series.

Depositional Gradient Analysis in Transgressive Systems Tracts and Highstand Systems Tracts, Eocene of the Brazos River Valley Section, Texas

Middle-late Eocene third-order sequences in the Brazos River section are composed of transgressive and highstand systems tracts of shelfal marine and marginal marine sediments. Diagenesis has destroyed most fossils (except palynomorphs, arenaceous forams, and traces), but sedimentary structures and fabric provide evidence for determination of depositional gradient. Tidalite deposits dominate shallower parts of the gradient and proximal and distal storm deposits dominate deeper parts of the gradient. As seen in the Weches, Crockett, Yegua, Caddell, and Manning formations, a characteristic shoaling gradient consists of a coarsening-upward section of deeper water mudstones with thin distal storm deposits overlain by sediment with proximal storm deposits (with upward-increasing storm bed content), by planar cross-bedded sands and by intensely bioturbated shore-zone sands. A characteristic deepening gradient is a fining-upward section of cross-bedded sands overlain by flaser bedded (and plant-fragment rich) tidalites, by proximal storm deposits (usually fossil and glauconite rich), and by shales with thin distal storm deposits. Maximum flooding surfaces (associated with sediment starvation) are indicated by submarine exposure surfaces and zones of amalgamated storm beds. The lithologic character of storm deposits varies with availability of grains (sand, shell, glauconite pellets, silt) and distance of transport. Gradient analysis was used to locate themore » maximum flood of the Jackson Stage in the Brazos River section. It lies in a parasequence within the lower lignite-bearing portion of the Manning Formation, as verified by the last appearance datum of Textularia hockleyensis.« less

Neptunian dykes along a drowned carbonate platform margin: an indication for recurrent extensional tectonic activity?

ABSTRACTThree successive Mesozoic neptunian dyke generations and related unconformities suggest recurrent extensional fracturing and periods of relative sea‐level rise along the NW Trento Plateau margin in the Southern Alps, Italy. The first neptunian dyke generation was induced by NNW–SSE directed extension of Early Jurassic skeletal oolitic periplatform deposits generating micritic early Middle Liassic neptunian dykes with orthogonal orientation. The second generation of neptunian dykes was possibly caused by marginal extension at the drowned platform edge penetrating Late Jurassic, red pelagic limestones with a pelagic matrix of Albian/Cenomanian age and nearly orthogonal fracture orientation. The third generation of neptunian dykes occurred after a prolonged period of submarine exposure and erosion (Aptian/Albian to Late Maastrichtian) during the rapid burial of the submarine Trento Plateau margin relief. The Late Maastrichtian neptunian dykes were caused by extension of Early to Middle Jurassic oolitic periplatform limestones along steep (inclination > 10°) submarine slopes.Generally successive neptunian dyke generations along drowned carbonate platform margins could be caused by repeated extensional brittle fracturing of lithified periplatform deposits and the filling of micritic matrix derived from overlying pelagic sediment sequences under substantial hydrostatic pressure. This would suggest that recurrent extensional fracturing is continuously recorded by neptunian dyke formation which could be used to indicate extensional tectonic activity at a foundering deep‐marine carbonate platform edge.

Carbonate Hardgrounds: Their Use as Stratigraphic Markers and Their Significance in Porosity Development in the Lower Cretaceous Edwards Limestone, Word Field Complex, Lavaca County, Texas

ABSTRACT Edwards gas production at the Word Field Complex is from backreef carbonate environments associated with a broad regional arch and is anomalous along the Cretaceous Shelf Margin. Over 3000 feet of core was utilized to determine the factors controlling porosity development and to calibrate electric log responses for reservoir zonation. The depositional facies in the cores include open marine, lagoon, and island paleoenvironments. The island complex (which include beaches, tidal flats, and tidal channels) controls the distribution of the production. Numerous episodes of syndepositional exposure are recognized in the cores. The most porous zones in the sequence are below the exposure surfaces in the grainstone shoal deposits of the beach environment. The evolution and identification of these exposure surfaces is critical to understanding reservoir quality and to subdividing and correlating the Edwards into hydraulic units. Hard grounds in the Edwards evolve during both subaerial and submarine exposure. The leaching and cementing processes below these exposure surfaces have a strong control on the distribution of porosity and permeability. The dominant porosity type is intraparticle microporosity, formed preferentially in micritic or micritized grains and in the patches of interparticle lime mud. Some microporosity later converted into moldic porosity due to leaching. The influence of these exposure surfaces on the porosity trends is significant in determining the connectivity of the reservoir. The original fabric of each lithofacies is modified by the exposure processes. Three types of exposure surfaces are recognized in the cores by their structure, color, and texture: 1) Submarine hard grounds characterized by encrustations, borings, vertical burrows, and marine cements 2) Subaerial exposure surfaces characterized by caliche crusts and pisolites, dessication features, vadose cement, brecciation, dissolution vugs and channels, and multiple episodes of infilling and 3) Pedolithic surfaces (related to prolonged post-depositional emergent conditions) characterized by clay paleosols with caliche nodules overlying rooted caliche crusts, and occasionally red sediment-filled fissures. The hard grounds in the Edwards Limestone are widely traceable in the Word Field Complex and form an integral part of the porosity development cycles. The correlation of the porosity trends in the cores as delineated by the hard grounds correspond to reservoir units interpreted on electric logs. The sonic porosity logs show close agreement with core measured and visual porosity estimates, while the gamma log responds to lithofacies changes. The consistent physical recognition of these hard grounds and their stratigraphic relationship to porosity trends permits their usage as field wide stratigraphic markers. The carbonate hard grounds define hydraulically connected porosity zones within the Edwards reservoir and therefore, can be utilized to better define the in-place reserves. End_of_Record - Last_Page 495-------

Submerged forest off Nyuzen, Kurobegawa alluvial fan, Toyama Bay, Central Japan

Remnants of a submerged ancient forest have been found on the continental shelf of NW Japan off the Kurobe alluvial fan in Toyama Bay. The remains, standing tree stumps and roots, are located at depths between 20 and 40 m and ages of 8,000 years B.P. to 10,000 years B.P. have been determined by the 14C method. Alnus and Salix are the most commonly preserved genera and the trees grew on the now sub‐merged seaward margin of the alluvial fan. Pollen analysis permits an estimate of palaeo‐temperatures 2°C to 4°C lower than at present. Diatoms give some indication of salinity variations at the time of forest development and suggest brackish water, possible lagoonal conditions. The distribution of the stumps and roots suggests that there were probably two separate forests which were overwhelmed by rising sea‐level and flash flood deposits. The present day submarine exposures may be due to recent submarine erosion related to the seaward movement of flood waters which passed from the fan into the upper reaches of the Toyama submarine canyon system.

Ophiolitic breccias associated with allochthonous oceanic crustal rocks in the East Ligurian Apennines, Italy — a comparison with observations from rifted oceanic ridges

In the East Ligurian segment of the North Apennines, eugeosynclinal sequences which contain ophiolitic rocks have been tectonically emplaced onto approximately coeval miogeosynclinal sediments. These allochthonous sequences represent the floor of a Mesozoic ocean which closed during the early Tertiary. The ophiolitic rocks consist of serpentinite, gabbro, pillowed and massive basalts, and breccias derived from these lithologies. They are overlain with depositional contacts by Upper Jurassic-Cretaceous pelagic cherts, limestones, and a shale/limestone sequence. The ophiolitic breccias attain thicknesses up to 100 m and strike lengths up to a few kilometres, and consist largely of unorganized accumulations of sand- to block-sized clasts. Compositions at specific horizons may range from oligomict breccias containing gabbro, basalt, or serpentinite fragments, to polymict breccias consisting of any mixture of these lithologies. Most of the breccias probably represent slow talus accumulations at the base of major submarine fault scarps which have exposed gabbro and serpentinite to submarine erosion. Direct exposure of gabbro and serpentinite on the ocean floor is also indicated by the occurrence of stratigraphically intact contacts between these lithologies and overlying pelagic sediments (generally cherts). The distribution and thickness of the breccias and volcanics, and the distribution of the gabbro and serpentinite, can vary greatly within distances of a few kilometres, thus producing complex heterogeneous sequences consisting of laterally impersistent lithological units. Recent observations and deep drilling of the Mid-Atlantic Ridge and other rifted ridges have revealed occurrences of significant thicknesses of basaltic, serpentinitic, and gabbroic breccias upon and within the volcanic layer of the oceanic crust, as well as the direct submarine exposure of plutonic rocks. It is therefore likely that the East Ligurian sequences represent parts of rifted ridge-generated crust. If so, then the complexity of the East Ligurian sequences suggests that the upper part of rifted ridge-generated crust may in places possess large variations in its stratigraphy over small (<10 km 2) areas. Smooth, non-rifted (fast-spreading) ridges, which have very reduced topography and lack major fault scarps, should form ophiolitic complexes deficient in breccias containing fragments of plutonic igneous rocks. Most large ophiolitic complexes do not contain plutonic rock-bearing breccias, and were therefore probably formed at smooth ridges. The apparently preferential preservation of this type of ophiolitic complex, as opposed to the rifted ridge-type crust in East Liguria, may be related to the less pervasive and less intense fracturing of smooth ridges. This resulted in greater “cohesion” and lateral continuity of smooth ridge-generated crust during later tectonic emplacement into allochthonous positions in orogenic belts.

Siliceous Dinoflagellates in the Northeast Pacific Rim

Siliceous dinoflagellates of the species Actiniscus pentasterias (Ehrenberg) are described from more than 20 outcrops and submarine exposures in the northeast Pacific rim area. Trends in the geographic and stratigraphic distribution of this taxon are recorded with respect to the documented abundance of the siliceous marine microflora in the interval from the Middle Miocene to the Lower Pliocene. Scanning electron micrographs of specimens illustrate the remarkable symmetry and geometry of this little-known group of microfossils. INTRODUCTION In the course of studying siliceous microfloras represented by diatoms and silicoflagellates in the northeast Pacific area, we have consistently encountered spicules of the siliceous dinoflagellate Actiniscus pentasterias (Ehrenberg). Specimens are never abundant, but their frequency is notably higher in those sediments with large quantities of biogenous silica. We found the highest incidence of the spicules in marine diatomites of Middle Miocene to Early Pliocene age in the Oregon and California coastal region and continental shelf. The literature on this group is rare and is to be found primarily in European journals. Ehrenberg (1854) originally named some five species of the genus Actiniscus, and systematic work on the group since that time has been limited to around a dozen authors. Considerable variation is to be found in the taxonomic treatment of the siliceous dinoflagellates. The confusion here may be attributed to the morphological similarity of siliceous dinoflagellates to other marine plankton groups. The spicules of these dinoflagellates bear a remarkable resemblance not only to those of members of the Radiolaria and Silicoflagellata but to broken fragments of diatoms as well. Four extant genera have been reported (Chatton, 1 953), and there can be no doubt of their affinities to the Dinoflagellata. Much of the literature on the group consists of scattered references to specimens that were encountered with other siliceous marine microfossils. The most definitive work of the group to date is that of Dumitrica (1968, 1973). In the latter paper, Dumitrica described siliceous dinoflagellates from cores recovered on Leg 21 of the Deep Sea Drilling Project in the southwestern Pacific. In addition to presenting frequency and range charts for the floras from the Oligocene through the Holocene, Dumitrica produced excellent illustrations of the flora and named three new genera and eight species. It is significant that Dumitrica (1973, text-fig. 2) recorded an interval from the Middle Miocene to the Early Pliocene particularly rich in siliceous dinoflagellates. SYSTEMATICS Division PYRROPHYTA Class DINOPHYCEAE Order GYMNODINIALES Family ACTINISCACEAE Kitzing Genus ACTINISCUS Ehrenberg Type species: Dictyocha (Actiniscus) pentasterias Ehrenberg, 1841. Actiniscus pentasterias (Ehrenberg) Ehrenberg, 1854 Plate 1, figures 1-11; plate 2, figures 1-6 Dictyocha (Actiniscus) pentasterias EHRENBERG, 1841, pp. 111, 149. Actiniscuspentasterias (Ehrenberg).-EHRENBERG, 1854, pl. 18, fig. 61; pl. 19, fig. 45; pl. 33 (XVII), fig. 1; pl. 35A (XXIII), fig. 1. micropaleontology, vol. 22, no. 1, pp. 92-99, pls. 1-2, january, 1976 92 This content downloaded from 157.55.39.112 on Wed, 07 Sep 2016 05:24:32 UTC All use subject to http://about.jstor.org/terms

Surficial Sediments of Barkley Sound and the Adjacent Continental Shelf, West Coast Vancouver Island

The bathymetry and sediment distribution of Barkley Sound and the adjacent continental shelf off the west coast of Vancouver Island have been markedly affected by the late Pleistocene glaciation and modern sedimentary processes. Several fjords widen and coalesce to form the sound, which is continuous with glacially eroded basins on the inner continental shelf. These basins are flanked by flat-topped banks, the larger of which merge with the outer shelf—a gently sloping plain that terminates at the 200 m isobath, 58 km from shore.Modern sediments are restricted mainly to Barkley Sound where the glaciated "basin and sill" bathymetry and an estuarine circulatory system prevent the predominantly muddy detritus from reaching the continental shelf. Relict sands and gravels cover most of the shelf except within basins and drowned river valleys where muds prevail. This relict cover was initially dispersed by glaciers and meltwater streams, then later inundated during the Holocene Transgression, and is now being partly reworked by the present hydraulic regime. Near the shelf-break relict sediments are sparse and authigenic sands (glaucontized mudstone pellets) predominate together with residual sediments derived from submarine exposures of Tertiary mudstone.

Pacific northwest siliceous phytoplankton

Submarine exposures of silica-rich claystones from widespread areas on Heceta Bank and offshore from Cape Arago on the Orego coast have yielded a diverse flora of diatoms and silicoflagellates. A similar and apparently synchronous flora was recovered from a small exposure of diatomite on the coast south of Bandon, Oregon. The floral diversities from these claystone are comparable to those from many Neogene diatomites in California, and a temperate shallow marine environment is indicated by the presence of many middle latitude, littoral and neritic benthonic forms. Several species of diatoms and silicoflagellates present in the floras are unreported elsewhere from sediments either older or younger than Late Miocene. The Oregon floras are correlative with several lithologically comparable diatomaceous sediments in the northeast Pacific area. The closest of these adjacent exposures is the Wildcat group in Humbolt County, California, of which the floras of the Delmontian Pullen formation display the greatest similarities to the Oregon material.

The corrosion of ocean communications cable

THE FIRST structurally practicable submarine telegraph cable was manufactured in about 1850, and for the following 100 years the basic submarine cable design remained unchanged. In the 1950's, the development of new submarine cable of armourless design and using modern materials was begun, and this is now in widespread use in new cables. The lack of information on cable performance led to the initiation of a submarine cable recovery programme by the Bell Telephone Laboratories, with the object of investigating the effect of submarine exposure on existing ocean cable materials. Specimens are obtained from cables in service, taken whenever repairs or replacement require that a cable is raised. Since submarine telegraph cables have been in use for over 100 years, the systematic examination of such specimens gives an invaluable source of information on the performance of materials and the effect of environment.