Deep-water Mud Research Articles

Multibeam Bathymetry of the Håkon Mosby Mud Volcano

The Hakon Mosby Mud Volcano is a natural laboratory to study geological, geochemical, and ecological processes related to deep-water mud volcanism. High resolution bathymetry of the Hakon Mosby Mud Volcano was recorded during RV Polarstern expedition ARK XIX/3 utilizing the multibeam system Hydrosweep DS-2. Dense spacing of the survey lines and slow ship speed (5 knots) provided necessary point density to generate a regular 10 m grid. Generalization was applied to preserve and represent morphological structures appropriately. Contour lines were derived showing detailed topography at the centre of the Hakon Mosby Mud Volcano and generalized contours in the vicinity. We provide a brief introduction to the Hakon Mosby Mud Volcano area and describe in detail data recording and processing methods, as well as the morphology of the area. Accuracy assessment was made to evaluate the reliability of a 10 m resolution terrain model. Multibeam sidescan data were recorded along with depth measurements and show reflectivity variations from light grey values at the centre of the Hakon Mosby Mud Volcano to dark grey values (less reflective) at the surrounding moat.

Characteristics of the wedge-top depozone of the southern Taiwan foreland basin system

The wedge-top depozone in the southern Taiwan foreland basin system is confined by the topographic front of the Chaochou Fault to the east and by a submarine deformation front to the west. The Pingtung Plain, Kaoping Shelf and Kaoping Slope constitute the main body of the wedge-top depozone. In a subaerial setting, the alluvial and fluvial sediments accumulate on top of the frontal parts of the Taiwan orogenic wedge to form the Pingtung Plain proximal to high topographic relief. In a submarine setting, fine-grained sediments accumulate on the Kaoping Shelf and dominant mass wasting sediment forms the Kaoping Slope. Wedge-top sediments are deformed into a series of west vergent imbricated thrusts and folds and associated piggyback basins. A major piggyback basin occurs in the Pingtung Plain. Four smaller piggyback basins appear in the shelf-slope region. Many small sized piggyback basins developed over ramp folds in the lower slope region. Pliocene-Quaternary deep marine to fluvial sediments about 5000m thick have been deposited on top of the frontal orogenic wedge in southern Taiwan. Sedimentary facies shows lateral variations from extremely coarse fluvial conglomerates proximal to the topographic front (Chaochou Fault) to fine-grained deep marine mud close to the deformation front near the base of the slope. The stratigraphic column indicates that offshore deep-water mud is gradationally overlain by shallow marine sands and then fluvial deposits. The transverse cross- section of the wedge-top depozone in the southern Taiwan is a doubly tapered prism. The northern boundary of the wedge-top depozone in southern Taiwan is placed along the southern limit of the Western Foothills where the frontal orogenic wedge progressively changes southward to a wedge-top depozone (Pingtung Plain), reflecting ongoing southward oblique collision between the Luzon Arc and the Chinese margin. The wedge-top depozone is bounded to the south by the continent-ocean crust boundary. The deep slope west of the Hengchun Ridge can be viewed as an infant wedge-top depozone, showing initial mountain building and the beginning of wedge-top depozone.

Geological, geochemical, and microbial processes at the hydrate-bearing Håkon Mosby mud volcano: a review

Submarine mud volcanoes are point sources of fluid expulsion and oases of active geological, geochemical, and microbial processes in the deep ocean. The results of multidisciplinary investigations at the Håkon Mosby mud volcano (HMMV) in the Norwegian Sea at ∼1250 m water depth are reviewed in this paper. Seafloor morphology, lithotypes, geochemical, and biological processes at the HMMV are concentrically zoned. The zonation is controlled by ejection of sediment, water, and gases (mainly methane) accompanied by high heat flow in the mud volcano crater. A structural gas hydrate accumulation is associated with the HMMV. Gas hydrate is abundant only in a relatively narrow zone where optimal conditions (low temperature and high gas concentration) exist for gas hydrate crystallization. Authigenic minerals, bacterial mats, and chemosynthetic communities typical of cold seep environments are present. Rapid anaerobic sulfate-dependant oxidation of methane is thought to be mediated by a consortium of methanogens and sulfate-reducing bacteria. Although methane is oxidized in sediments at high rates, a significant portion of this gas may escape into the ocean, mainly as diffuse flux. In the water column, methane is rapidly dissolved and oxidized. This observation supports the hypothesis that gas flux from deep-water mud volcanoes contributes to the oceanic carbon pool, but not to the atmosphere. The HMMV represents an important natural laboratory and provides insight to processes at the interface of methane-rich sediments and cold bottom water in the deep ocean. Future studies may best focus on accurate direct measurements of gas flux and quantification of the biogeochemical cycling of major chemical elements in shallow sediment.

Mud volcanism in the Gulf of Cadiz: results from the TTR-10 cruise

A new deep water mud volcano field (between 2000 and 3500 m water depth) was discovered in the deep South Portuguese margin, as well as several new mud volcanoes in the South Spanish and Western Moroccan margins of the Gulf of Cadiz, during the TTR-10 (Training Through Research, UNESCO/IOC) cruise, in July/August 2000. This work followed the discovery of a large mud volcano field in the Gulf of Cadiz, first investigated during the TTR-9 cruise [Gardner (2001) Geophys. Res. Lett. 28, 339–342; Kenyon et al. (2000) IOC, Technical series no. 56]. The discoveries were made based on a SEAMAP side-scan sonar mosaic and multibeam bathymetry (SEABEAM) collected in the area by the Naval Research Laboratory (NRL), Washington, DC, USA, in 1992, kindly released for this purpose. Single-channel seismics, long-range side-scan sonar (OKEAN), TV-controlled grab, hull-mounted 3.5-kHz profiler and coring were used to investigate several seafloor features observed on the side-scan sonar imagery, in the South Iberia, Spanish and Moroccan margins of the Gulf of Cadiz, which were confirmed to be mud volcanoes. The typical structures related to fluid venting in the Gulf of Cadiz are essentially represented by conical mud volcanoes with diameters ranging from several tens of meters to 4 km and heights that can reach 200 m. Some of these structures appear to be aligned along major conjugate NE–SW and NW–SE trending faults that can be identified on the side-scan sonar imagery. The new field discovered in the South Portuguese margin is the deepest in the Gulf of Cadiz area and includes three new mud volcanoes – Bonjardim, Olenin and Carlos Ribeiro – which seem to be quite active, with near-surface gas hydrate occurrence and a high saturation in H 2S and hydrocarbon gases (mainly methane) in the mud breccia and overlying pelagic sediments. Gas hydrates were recovered from the Bonjardim mud volcano. An intensely gassified mud breccia, with one fragment of semi-consolidated claystone with a thin bituminous veneer at the surface, was recovered from the Carlos Ribeiro mud volcano. The fauna recovered consists mainly of pogonophoran worms belonging to several species and undetermined species of Foraminifera. Three new mud volcanoes were also discovered in the NW Moroccan margin: Rabat, Student and Jesus Baraza. These show a richer fauna that includes several species of molluscs, polychaetes, pogonophoran worms, crustaceans, echinoderms and some fragments of dead coral ( Madrepora and Lophelia). Carbonate crusts were recovered from the Student mud volcano. The Ginsburg mud volcano, discovered during the previous TTR-9 cruise, was revisited and gas hydrates recovered once again. A new mud volcano was also discovered in the Spanish margin, Tasyo, where evidence was found of coral build-ups on the hard substratum of the mud volcanic edifice.

Shallow to deep-water deposition in a Cratonic basin: an example from the Proterozoic Penganga Group, Pranhita–Godavari Valley, India

The unmetamorphosed Proterozoic succession dominated by deep-water lithographic limestone and shale in the western flank of the Pranhita–Godavari Valley is designated as the Penganga Group. The succession in different parts of the Valley includes the Pranhita Sandstone (25–400 m), the Chanda Limestone (300 m), and the Sat Nala Shale (>2000 m) in ascending order. The Pranhita Sandstone and the Chanda Limestone reveal considerable variations in the character of the stratal packages and depositional settings from Mancherial in the south to Adilabad in the north. The Sat Nala Shale in both southern and northern outcrop belts is completely devoid of sand. It is brown to purple in colour and resembles present-day deep-water mud deposits. In the Mancherial area, the Pranhita Sandstone consists of 25–400 m thick conglomerate, pebbly red arkose and quartzose sandstone succession of coastal alluvial fan to shallow shelf origin. The Chanda Limestone is micritic and locally includes interbedded lenses of cross-stratified quartzose sandstone in the lower part. The depositional milieu varies from shallow shelf to below wave base outer ramp carbonate platform. Around Adilabad, the Pranhita Sandstone (25 m) lacks the conglomerate–pebbly arkose association at the base and comprises only quartzose sandstone and shale of shoreface to muddy shelf settings. The Chanda Limestone is essentially micritic but, in contrast to the Mancherial area, includes several interbedded intervals of slope-related, autoclastic debris flow limestone conglomerates and calciturbidites, and represents deep, outer ramp to slope and basinal settings. A predominantly deep-water micritic limestone and deep-water shale succession suggests that the Penganga basin evolved to a vast, deep epicratonic sea connected to an open ocean. The absence of a coastal alluvial fan association at the lower part of the Pranhita Sandstone and presence of a slope to basinal association in the Chanda Limestone in the northern outcrop belts around Adilabad indicates a northward transition from coastal to deep shelf, slope and basinal conditions and a northerly paleoslope of the basin.

Are reefs and mud mounds really so different?

Although both ‘ecologic reefs’ and mud mounds are demonstrably rigid, framework reefs, they are still considered to be distinct in terms of their dominant processes of formation and preferred environmental settings. This distinction has rested largely upon the assumption that ecologic reefs are dominated by skeletal metazoans growing in shallow waters, in contrast to the complex autochthonous micrite-supported cavity systems that characterise deep-water mud mounds, now considered to represent either organomineralic deposits (where carbonate precipitation has taken place in association with nonliving organic substrates to form ‘automicrite’) or various types of microbialite (where carbonate forms as a direct result of the physiological activity or decay of benthic microorganisms). Yet, such autochthonous micrite is increasingly recognised as an important component of many ancient shallow ecologic reefs as well as some modern coral reefs, and indeed may contribute locally up to 80% of the reef rock. These observations raise doubts as to the validity of current fabric-based definitions used to distinguish between mud mounds and ecologic reefs. Whether the autochthonous micrite in mud mounds proves to be dominated by either automicrite or microbialite, both require particular environmental conditions for their formation. Automicrites form where surplus organic matter from metazoans has degraded to release quantities of acidic amino acids with a significant ability to bind Ca2+ , and microbialite formation also often requires either unusual marine chemistries or ecological conditions. Such conditions might include changes in terrigenous influx, ground water seepage, local anoxia, and increases in the pH of interstitial reef waters or in nutrient concentration.

Worldwide distribution of submarine mud volcanoes and associated gas hydrates

Abstract The list of known and inferred submarine mud volcanoes is presented in this paper. They occur worldwide on shelves, continental and insular slopes and in the abyssal parts of inland seas. Submarine mud volcanoes are distributed on the Earth more extensively than their subaerial analogs. The estimated total number of known and inferred deep-water mud volcanoes is 103–105. There are two key reasons for the formation of submarine mud volcanoes—high sedimentation rate and lateral tectonic compression. Submarine mud volcanoes form by two basic mechanisms: (1) formation on the top of a seafloor-piercing shale diapir; (2) formation due to the rise of fluidized sediments along faults. Fluid migration is critical to the formation of a mud volcano. Gas hydrates are often associated with deep-water mud volcanoes and have many common features from one accumulation to another. Gas hydrates form by conventional low-temperature hydrothermal process around the central part of a mud volcano and by metasomatic processes at its periphery. A preliminary global estimate of methane accumulated in gas hydrates associated with mud volcanoes is about 1010–1012 m3 at standard temperature and pressure.

Ovarian Maturation and Spawning of the Deep-Water Mud Shrimp Solenocera Melantho De Man, 1907 (Decapoda, Penaeoidea, Solenoceridae) in Kagoshima Bay, Southern Japan

The deep-water mud shrimp Solenocera melantho is one of the most dominant species in the benthic community of Kagoshima Bay, southern Japan, and is commercially important as the main target species for small-scale trawlers. The reproductive aspects such as ovarian maturation, size at sexual maturity, and spawning season were examined using a large number of female specimens collected from the central area of the bay. This species exhibits an asynchronous type of ovary that contains oocytes of various developmental stages. Ovarian maturity stages were divided into four categories based on the developmental stage of the most advanced oocytes in the ovary: quiescent, developing, early ripe, and ripe. The ripe ovaries contain prematuration-stage oocytes where cortical crypts are found in the peripheral part. Females with ripe ovaries were defined as mature females which would spawn within a few days. The size at sexual maturity of females was estimated to be 25.3 mm in carapace length (1-year old). The gonadosomatic index (GSI = 100 x gonadal weight/body weight) was significantly increased with the progress of ovarian maturation, and most females with GSI 12 were mature. The spawning season was estimated to continue from June to December with its peak during October and November. In the early spawning season, only the 2- and 3-year old groups of females matured. Young females in the 1-year old group matured from July to December.

Hydrothermal origin of Devonian conical mounds (kess-kess) of Hamar Lakhdad Ridge, Anti-Atlas, Morocco

Various interpretations have been proposed for the origin of peculiar cone-shaped, finely crystalline, Devonian carbonate mounds of the Hamar Lakhdad Ridge, Anti-Atlas, Morocco, ranging from shallow-water reefs to deep-water mud mounds, formed by biogenic and/or hydrodynamic processes. This study is the first integrated sedimentological and geochemical analysis of these structures. The mounds are cone shaped, steep sided, circular to subelliptical in plan view, and exhibit internal crude bedding parallel to the mound9s outer surface. They occur in a cluster of 48 mounds on top of a volcanic massif. Stable isotope analyses of first-stage isopachous nonluminescent cement have yielded marine values. In contrast, the finely crystalline carbonate that makes up the bulk of the mound and the internally sedimented mud between crusts of early marine cements have significantly lower δ 18 O values, whereas values of δ 13 C are similar to those of the early marine cement. Strontium isotope ratios also clearly distinguish the nonluminescent early marine cements from the finely crystalline material. The 87 Sr/ 86 Sr values for the former (0.707 934–0.709 392) are in or near the Devonian marine range, whereas the ratios for the latter (0.708 515–0.709 656) indicate a more radiogenic Sr source. On the basis of their lithology, architecture, isotope geochemistry, and clustered occurrence on top of a volcanic pile, we propose that the finely crystalline material that forms the mounds and the intermound beds was precipitated from hydrothermal fluids, and that accretion of the material was driven by hydrothermal venting.

Growth of the Deep-Water Mud Shrimp Solenocera Melantho De Man, 1907 (Decapoda, Penaeoidea, Solenoceridae) in Kagoshima Bay, Southern Japan

The deep-water mud shrimp Solenocera melantho is commercially important as the main target species for small-scale trawlers in Kagoshima Bay, southern Japan. A total of 4,837 specimens were collected from the central area of the bay from January 1993 to June 1994. Length frequency analysis was used to examine the growth and longevity of S. melantho. Both males and females were first recruited in winter with modal sizes of around 15 mm carapace length. Growth was best described by the Pauly & Gaschutz growth equation as Lt = 33.09{1 - exp[-0.857(t/12 + 0.525) - (0.538/2π) sin(2π (t/12 - 0.404))]} for males and Lt = 45.76{1- exp[-0.777(t/12 + 0.401) - (0.452/2π) sin(2π (t/12 - 0.583))]} for females, where Lt is carapace length (mm) at age t (months). Females grow faster and reach larger sizes earlier than males of the same age group. Growth rates and the occurrence of soft-shelled individuals in both sexes were highest between winter and spring, and lowest during the spawning season between summer and early winter (June to December). The longevity of both malc and female S. melantho was estimated to be around 37 months. The allometric relationship between body weight and carapace length was represented by significantly different equations between sexes.

Temperate Carbonates on a Modern, Low-Energy, Isolated Ramp: The Balearic Platform, Spain

ABSTRACT This paper presents a depositional model for a temperate, low-energy carbonate ramp based on descriptive studies of five areas around the Balearic Islands of Mallorca and Menorca. This low-energy ramp differs significantly from other present-day temperate carbonate platforms that are primarily high-energy open shelves. It is characterized by the following lithofacies (from shore to basin): (1) lagoon, (2) barrier island, (3) shallow subtidal, (4) inner ramp, (5) middle ramp, and (6) distal ramp. Subaqueous carbonate dunes are present near slope breaks off Menorca and Cabrera, but they are not representative of the entire ramp. Balearic ramp sediments differ in composition, texture, biology, and degree of cementation from those on modern low-energy, tropical ramps. Balearic ramp carbon tes lack ooids and peloids, hermatypic coral buildups, and calcareous green algae (except in one restricted bay where Halimeda is relatively common). Red algal sands and gravels extend to depths of up to 90 m, and are coarser than their strandplain-equivalent lime sands. Skeletal allochems consist of the bryomol-rhodalgal association, marine cementation is rare, and the carbonate fraction of deep-water muds is mainly Mg-calcitic and calcitic in composition. Aragonite is rare. Except for the red alga Peyssonnelia, which is composed of aragonite, it is neither a dominant skeletal constituent nor common as a cement. The Mediterranean Sea off Mallorca and Menorca is a low-energy, temperate, oligotrophic, clear-water environment. The depositional model for the region is an isolated platform configured as a homoclinal ramp. Ancient counterparts of the Balearic ramp are present in the Neogene of the Mediterranean Tethys and the Paratethys, and though the constituents of fossil assemblages vary with time, the biota of the Balearic ramp, such as bryozoans, red algae, echinoderms, and mollusks, ranges from the Paleozoic Era to the present. Echinodermal bryomols passing to basinal muds on carbonate ramps are particularly characteristic of the Early Carboniferous in North America and Europe. This suggests that the Balearic Islands temperate ramp may be more representative of some ancient carbonate sequenc s than either temperate, high-energy, open shelves or tropical ramps in the present oceans.

Quaternary sedimentation and marine placers along the North Shore, Gulf of St. Lawrence: Reply

Offshore areas, along the North Shore of the St. Lawrence Estuary, have major lithostratigraphic and seismostratigraphic units that relate to the advance or retreat of the Late Wisconsinan Ice Sheet, subsequent marine transgression or regression, and reworking of postglacial deposits. Glacial diamicton and glaciomarine units (acoustic units 1 and 2) were emplaced between >18 and 14.5 ka, by basal meltout or ice-marginal sedimentation; they reflect ice-proximal sedimentation associated with ice-terminal stillstands. Deep-water muds (acoustic unit 3) represent ice-distal accumulation of glaciomarine sediment from glaciofluvial plumes between 13.5 and 11 ka. After this time exceptionally thick nearshore coarse-grained deltaic and estuarine successions (acoustic unit 4) were deposited. The uppermost postglacial sediment (acoustic unit 5) forms the seabed and reflects a reworking phase concomitant with a lowering sea level and ablating Late Wisconsinan ice sheets.Glacioisostatic rebound, which occurred about 2...

Quaternary sedimentation and marine placers along the North Shore, Gulf of St. Lawrence

Offshore areas, along the North Shore of the St. Lawrence Estuary, have major lithostratigraphic and seismostratigraphic units that relate to the advance or retreat of the Late Wisconsinan Ice Sheet, subsequent marine transgression or regression, and reworking of postglacial deposits. Glacial diamicton and glaciomarine units (acoustic units 1 and 2) were emplaced between >18 and 14.5 ka, by basal meltout or ice-marginal sedimentation; they reflect ice-proximal sedimentation associated with ice-terminal stillstands. Deep-water muds (acoustic unit 3) represent ice-distal accumulation of glaciomarine sediment from glaciofluvial plumes between 13.5 and 11 ka. After this time exceptionally thick nearshore coarse-grained deltaic and estuarine successions (acoustic unit 4) were deposited. The uppermost postglacial sediment (acoustic unit 5) forms the seabed and reflects a reworking phase concomitant with a lowering sea level and ablating Late Wisconsinan ice sheets.Glacioisostatic rebound, which occurred about 23 ka to the present, uplifted glacial and marine deposits and resulted in extensive reworking and production of modern placers. Heavy-mineral concentrations vary as follows: terrestrial tills, 9–20%; modem storm-berm and delta top deposits, 43–60%; delta slope deposits, 25–55%; and deep (170+ m) offshore sediments, 0–2%. Three stages occurred in marine placer formation: (1) 6700 BP, fluvial discharge was high, and fluvial-dominated deltas were built; marine limit was 30 m asl, with progradation of deltas and delivery of sediments with at most 2% heavy minerals; (2) 5200 BP, fluvial discharge was reduced; marine limit was 15 m asl, deltaic sediments were reworked, increasing heavy mineral concentration to 2–8%; (3) 2800 BP, fluvial input was greatly reduced, waves and tides were more influential, a strong littoral current system developed, causing significant reworking of nearshore sediments, heavy mineral concentrations increased, with values exceeding 20% locally. Mass budget calculations show that the second-cycle reworked sediment (acoustic unit 5) is a potential economic target (1 km3, or 1700 Mt). If 7% (using atomic weights) of this target sediment is ilmenite (FeTiO3). then 27 Mt of titanium may be available.

Seabed geology of the Canadian eastern continental shelf

The physiography of the continental shelf off eastern Canada is irregular, developed by glacial erosion of a previously fluvially-dominated landscape. Northern shelves are deeper than southern shelves. Most surficial sediments on the shelf are relict or palimpsest. The principal modern source of sediment to the northern shelves is ice rafting and iceberg scour reworking of Quaternary sediments. Southern shelves receive sediment through erosion of Quaternary sediments; only small amounts of fine-grained sediment derived from coastal erosion and rivers escape from the coastal zone. Regional maps of sediment texture, carbonate content and heavy mineralogy consequently show differences between the northern and southern shelves. Large areas of the shelf show little net deposition. On the northern shelves, there is a surface veneer up to 0.5 m thick derived from ice rafting and iceberg turbation of underlying Quaternary sediment, modified by south-flowing currents [ Woodworth-Lynas et al. (this issue) Continental Shelf Research, 11, 939–961]. The overall effects of former iceberg turbation may extend to a depth of 10 m sub-bottom. On the southern shelves, bioturbation and perhaps storm-related currents rework exposed Quaternary sediments more slowly. Muds accumulate in deep basins on the shelves at rates of about 0.5 m per 1000 years; this accumulation is probably episodic and related to major storms reworking sediment from the surface sediment veneer in shallower areas of little net deposition. In water depths less than 110 m sand and gravel have formed as a result of reworking in the coastal zone during the post-glacial transgression. Over large areas of Georges Bank, the eastern Scotian Shelf and the Grand Banks of Newfoundland, such sands are mobilized during storms to form a wide suite of bedforms [ Amos and Judge (this issue) Continental Shelf Research, 11, 1037–1068]. Elsewhere, particularly in deeper water, sandy surfaces appear moribund or inactive and large bedforms are relict. Armoured gravel surfaces are common on the banks of the western Scotian Shelf. In areas of coastal transgression, barrier beach and foreshore sediments are superimposed on partially eroded estuarine and lagoonal sediments. In areas of coastal regression, deep water muds are being reworked by waves as relative sea level falls, to produce a surface lag of coarser sediment.

Cyclic Ramp-to-Basin Carbonate Deposits, Lower Mississippian, Wyoming and Montana: A Combined Field and Computer Modeling Study

ABSTRACT The Lower Mississippian Lodgepole/lower Madison Formations (20-225 m thick) developed along a broad (> 700 km), storm-dominated pericratonic ramp. Three types of fifth-order upward-shallowing cycles are recognized across the ramp-to-basin transition. Peritidal cycles consist of very shallow subtidal facies overlain by algal-laminated tidal flat deposits, which are rarely capped by paleosol/breccia layers. Shallow subtidal cycles consist of stacked ooid grainstone shoal deposits, or deeper subtidal facies overlain by ooid-skeletal grainstone caps. Deep subtidal cycles located along the outer ramp consist of basal sub-storm wave base limestone-argillite, overlain by storm-deposited limestone, which are capped by hummocky stratified to massive skeletal-ooid grainstone. Deep subtidal c cles pass downslope into ramp-slope facies composed to rhythmically interbedded limestone and argillite, with local deep-water mud mounds; no upward-shallowing cycles occur within the ramp-slope facies. Average cycle durations calculated along the outer ramp are between 30-110 ky. The fifth-order cycles are stacked to form three third- to fourth-order depositional sequences, which are recognized by regional transgressive-regressive facies trends and cycles stacking patterns. Ramp-margin wedges (RMW) developed during long-term sea-level fall and lowstand and consist of cyclic crinoidal bank and oolitic shoal facies, which pass downdip into deep subtidal cycles. Transgressive systems tracts (TST), which onlapped the ramp during long-term sea-level rise, include thick shallow and deep subtidal cycles; peritidal cycles are restricted to the inner ramp. Highstand systems tracts (HST) developed during long-term sea-level highstand and fall, and along the ramp are composed of early HST shallow subtidal cycles overlain by late HST peritidal cycles; shallow through deep subtidal cycles characterize the HST along the ramp-slope. Two-dimensional computer modeling of the cyclic sequences suggests that for the assumed water depths of facies, fifth-order sea-level oscillations of at least 20-25 m were required to generate deep subtidal cycles along the ramp-slope. Synthetic sequences run with fifth-order sea-level amplitudes End_Page 1194----------------------- and TST deposition, a feature not observed in the actual sequences. Other factors, in addition to fifth-order sea-level oscillations, likely played a role in generating synchronous peritidal and deep subtidal cycles during HST deposition. These factors may include short-term climatic changes, which influenced the depths to storm-wave reworking. The moderate-amplitude sea-level oscillations suggested by the cyclic sequences may reflect the initial effects of Carboniferous glaciation that was occurring in Gondwana.

Acanthochaetetidae (Hadromerida, Demospongiae) fromthe Coniacian of Vera de Bidasoa (basque pyrénées, Northern Spain)

Acanthochaetetes specimens from the Coniacian brecciated limestones near Vera de Bidasoa (Northern Spain) are described. It is the first report of acanthochaetetids from Coniacian strata. The specimens are very small and probably lived in fissures and crevices in fore-reef breccias and deep water mud mounds. The family Acanthochaetetidae Fischer is placed in the order Hadromerida (Tetractinomorpha, Demospongiae). The order Tabulospongida Hartman & Goreau was abandoned.

PATTERNS OF MOLLUSK SHELL BIODEGRADATION IN BATHYAL AND ABYSSAL SEDIMENTS

Shells settled on deep-water muds were heavily bored by various microorganisms. Their morphological aspects in situ and the structural weathering of shells are described. The geographical and bathymetric distribution of the boring or endolithic microorganism is considered and their ecological and oceanographic role tentatively outlined.

Distribution and structure of benthic assemblages in Puget Sound, Washington, USA

Benthic infauna was collected with a 0.2 m2 van Veen grab at 48 stations in Puget Sound, Washington, USA during February–March 1969. All the crustaceans, lamellibranchs, and echinoderms were identified and counted. Particle size distributions and nitrogen contents of the sediments, depths, and temperature and salinity of the bottom water were determined at all stations. The first three factors of a factor analysis applied to between-stations measures of affinity, explained 41.26% of the total variance. The first factor had representative stations on shallow-water mud bottoms, the second factor on bottoms dominated by coarse sediments, and the third factor had representative stations on deep-water mud bottoms. The multiple correlation coefficients for each of the three factors with depth and mean particle size of the sediments were 0.752, 0.897, and 0.706, respectively. The factor analysis did not result in clusters of stations that could be interpreted as discrete benthic communities. The number of species per 0.6 m2 ranged from 8 to 55 species, with a mean of 26.4 species. The frequency distribution of specimens among the species was in good agreement with a log-normal distribution. The number of specimens per 0.6 m2 ranged from 57 to 1733 specimens, with a mean of 584.0 specimens. The species diversity ranged from 0.34 bits/individual to 4.35 bits/individual, and there was a weak trend of increasing diversity towards coarser sediments. The first three factors applied to the matrix of between-species correlation coefficients explained 43.72% of the total variance. With each factor there was one group of species with high positive loadings and one group with high negative loadings. Each group of species could be identified with particular environments. The standing crop, measured as ash-free dry weight, ranged from 0.490 to 54.093 g/m2, with a mean of 13.752 g/m2. Only about 24% of the variability in standing crop could be attributed to variability in sediment types, nitrogen content in the sediments, salinity of the bottom water, and depth.

Effect of Climatic Changes on Chemical Content of Deep-Water Muds Exemplified by Deposits of Arctic and Atlantic Oceans: ABSTRACT

1. Within deep-water deposits formed in different Quaternary physiographic environments, characteristic changes in mud chemical content are observed. 2. Investigations of the Arctic Ocean deposits (Makarov basin) showed compositional variation in absorbed complexes. For cold epochs (during Sartan, Zyryan, and Samar glaciations, as well as during the Boreal transgressions), the K content of absorbed complexes ranges from 14 to 15.5%. For warm epochs (postglacial time, Kargin transgression, Boreal transgression) the K content is between 16 and 17.5%. 3. While studying the Atlantic Ocean deposits (50°28^primeN and 26°23^primeW), it was observed that the higher absorbed K content was related to higher carbonate content of the deposits. Relative K content of 18-20% corresponds to warm periods, whereas that of 9.5-17.5% is connected with cold periods; carbonate content (CaCO + MgO weight %) is 23-40% for warm periods, and 9-16.5% for cold periods. 4. Investigations in the Caribbean showed that the higher relative carbonate content correlates with an increase in seawater temperatures. 5. Compositional variations in absorbed complexes and relative carbonate contents also may be correlative with physiographic conditions. If true, it may be possible to correlate the values of various chemical components End_Page 2505------------------------------ of deep-water muds with the physiographic conditions. End_of_Article - Last_Page 2506------------

Sedimentation in an Arctic Lake

ABSTRACT Stanwell-Fletcher Lake is 400 miles north of the Arctic Circle, covers 131 square miles, and is over 100 m deep. Its size and the severe climate restrict summer melting of ice to the margins. The ice insulates the water, which remains essentially isothermal, warming slightly from 1.3 to 1.6°C. during the summer. Inflowing water is nearer 4°C, and therefore sinks and mixes with the lake water, a process which maintains thermal and chemical homogeneity in the lake and oxygenates the surficial bottom sediment. Sedimentation is very slow because of the short period of stream flow and the low organic activity in the lake. Silty sand derived from river bed loads accumulates on shallow marginal deltas and shelves. The sediment is poorly sorted because ice cover prevents wave action and removal of the fine material to deeper water. Mud, derived largely from the suspended loads of rivers, settles slowly in the central part of the lake. Faint laminae in the shelf sands may be varves, but the deep water mud is structureless. Evidently seasonal sedimentary variations do not affect the center of the lake, probably because ice cover minimizes transporting currents. The oxidation-reduction boundary in the sediment is at 5-20 cm, deeper than in temperate lakes, because of oxidation at the lake bottom and slower reduction within the sediment.