Deep-sea gastropods (Mollusca: Gastropoda) in soft sediments of the Colombian Pacific Ocean: Biodiversity and ecology

The stability of the Upper Continental Slope sediments of the northern Gulf of Mexico was examined by estimating the degree of consolidation of the sediments. Geotechnical properties of 14 piston cores coupled with analysis of deposition rates provided the data base for the interpretations. Degree of consolidation was estimated by using two independent methods. The first method was based on a comparison of measured and empirically derived shear strength values, where the derived values were representative of expected strengths in normally consolidated sediment. Disagreement, therefore, signified a departure from normal consolidation. The second method permitted direct computation of degree of consolidation by using the sedimentation rates in conjunction with consolidation theory. Results from both methods indicate that in general the sediment on the upper slope is normally consolidated to slightly underconsolidated, although examples of moderate underconsolidation and overconsolidation may be found. These deviations are rare, thus most areas are considered essentially stable with respect to the surficial sediment. Local variability precludes extrapolation of this conclusion to sites not covered in this study. INTRODUCTION As the petroleum industry has breached the shelf break and moved onto the upper Continental Slope, its offshore technology has been challenged by a new set of problems. Some of these problems, such as the greater water depths and increased gradients, can be solved without specific environmental data; others, such as the prospect of large or even smallscale deformation cannot. The most basic difficulty lies within this second category, for design factors, such as efficiency, safety, and pollution prevention, cannot be handled effectively from an engineering standpoint unless the circumstances are defined. As yet, such definition is rarely possible on the slope. This unfortunate circumstance was never more center-stage than in the northern Gulf of Mexico, currently the site of 25% of all the world offshore petroleum activity, where the encroachment onto the upper slope (200–1000 m water depth) is already well in progress. Emplacing various structures and pipelines in this "frontier" environment requires detailed information, particularly of the geotechnical variety; thus, this move to deeper water must mark time while site-specific data are gathered and evaluations made. A further complication is that this upper slope, through its variety of depositional environments, may represent a spectrum of bottom-stability conditions. The extremes of this spectrum are erosional areas, which may be very stable, and areas subjected td high rates of deposition, such as within the Mississippi depocenter, which may be considerably unstable. This local variability also implies that the potential for mass movement or deformation is likewise inconstant. Our research, therefore, sought to evaluate sediment stability at selected sites on the upper slope of the northern gulf. This evaluation is based on one facet of the stability problem: stability as related to consolidation states of the sediment mass. Other aspects, such as tectonic activity or conventional slope stability analysis, are not included in paper.

The occurrence, acoustic characteristics, and significance of submerged reefs on the continental shelf edge and upper slope, northern South China Sea

The mud lobsters of the family Axiidae are represented in the eastern tropical Pacific by seven species. Only one of these species belongs to the genus Acan thaxius Sakai & De Saint Laurent, 1989 (cf. Hendrickx, 1995a), although a second species, A. spinulicauda (Rathbun, 1902) is known from British Columbia and Cal ifornia. Originally described from the Pacific coast off Colombia in the genus Ax iopsis Borradaile, 1903, Acanthaxius caespitosus (Squires, 1979) was transferred to the genus Acanthaxius by Sakai & De Saint Laurent (1989). Acanthaxius caespi tosus and Axiopsis baronai Squires, 1979, a second species of Axiidae also origi nally described from Pacific Colombia, have both been reported from a much wider geographic area by Hendrickx (1987) on the basis of material mostly collected in shrimp trawls. Acanthaxius caespitosus is currently known from the west coast of the Gulf of California, Mexico, off R?o San Juan del Sur, Colombia (type locality), and off Mancora, Peru, thus leaving a wide gap of approximately 22 degrees of latitude with no records (from the southern Gulf of California to southern Colom bia). A recent search in the crustacean holdings of the Invertebrate Collection at Scripps Institution of Oceanography, La Jolla, California, led to the discovery of yet another small series of unidentified specimens of A. caespitosus from locali ties previously not included in the distribution range of this species. Abbreviations used are: TL, total length; CL, carapace length; coll., collector; SIO-C, Scripps Institution of Oceanography Crustacea collection.

Biostratigraphy has a significant role in petroleum exploration, especially for correlation and depositional environment analysis. This research located in Kedinding Hill Area, Blora, Central Java, Indonesia. We uses semiquantitative graphic correlation method and quantitative constrained cluster analysis with data taken from measuring section of Kedinding River Track (Section-1) and Kalen River Track (Section-2). Both sections generate crossover in biostratigraphic event sequence that trouble the biozonation determination which resolved by Graphic Correlation Method and generate FAD Neogloboquadrina humerosa – LAD Globorotalia merotumida – LAD Globigerina venezuelana as regional biostratigraphic event sequence. Constrained Cluster Analysis method generate five cluster for depositional environment in both Section-1 and Section-2. Depositional environment of each cluster in Section-1 are: Cluster 1 (unpredictable), Cluster 2 (deep middle – outer shelf), Cluster 3 (outer shelf), Cluster 4 (outer shelf), Cluster 5 (outer shelf – upper slope), meanwhile in Section-2: Cluster 1 (inner shelf), Cluster 2 (deep middle – outer shelf), Cluster 3 (deep middle shelf), Cluster 4 (deep middle shelf), Cluster 5 (outer shelf – upper slope).

Geochemistry of sediments from the Mangalore-Cochin shelf and upper slope off southwest India: Geological and environmental factors controlling dispersal of elements

This paper describes the use of a 3D, layered, numerical current model to simulate hurricane driven currents on the continental shelf and slope. A novel feature of the model is its ability to represent the intersection of the thermocline with the sea bed. This allows for a realistic representation of the current response on the shelf and upper slope during intense hurricane forcing. Hindcast currents are compared with an extensive set of current measurements recorded during the passage of two hurricanes (Frederic and Belle). Water depths at the measurement sites (30-470 m) encompass both the shelf and slope. Model error statistics are presented and the effect of these errors on calculated platform loads is discussed. INTRODUCTION Calculation of loads due to winds, waves and currents is an important aspect in offshore structure design. Measurements of these environmental factors are rarely of sufficient duration to determine design criteria for installations that will remain in place for decades. To circumvent this, it is necessary to simulate these factors for past storm events using the available meteorological data base. Techniques for hindcasting storm winds and waves are well developed. Considerable attention has been given to establishing accuracy, and the techniques have been routinely used as a basis for establishing offshore design criteria for over a decade. However, the development and verification of storm current hindcasting techniques have lagged somewhat behind. Historically, work on hindcasting techniques for storm driven currents has focused on two regimes the inner continental shelf and the deep ocean. On the inner shelf, the density throughout the water column is uniform. Consequently, density stratification plays no role in the dynamics of the storm response. During hurricane season in the Gulf of Mexico, this well-mixed zone typically extends from the coast out to water depths on the order of 30 m. In this regime, the response is dominated by the effects of wind and bottom stresses, Coriolis acceleration and topography. Fairly reliable current model predictions can be made using relatively simple, single layer models [1]. In the deep ocean (typically, water depths greater than about 1,000 meters), topography is of little or no importance, but stratification is important. The response is dominated by the effects of the local wind stress, Coriolis acceleration, inertia and entrainment. Reliable predictions can be made using multilayer models that do not include topography [2]. Little attention, however, has been paid to the regimes between the inner shelf and deep ocean (water depths from roughly 50 to 1,000 meters) where the complicating effects of both stratification and topography can be important. Recently, Cooper and Thompson [3] (subsequently referred to as CT) have developed a multilayer current model that has shown good success in reproducing the observed storm response in this regime. While their model is quite general, it is limited in its representation of shelf topography. This restricts the use of the model to water depths greater than about 200 m. This paper presents a multilayer model that builds on the work of CT.

The upper insular slope of southwest Puerto Rico is defined as extending from the shelf break at ~20 m water depth down to a depth of ~160 m where there is a pronounced change in geomorphic character and the basal slope begins. The upper slope is divided into two geomorphic zones separated by a pronounced break in slope gradient at ~90 m water depth. Descending from the shelf break, these are Zone I (20–90 m) and Zone II (90–160 m). As orientation of the shelf margin changes, geomorphology of Zone I shows systematic variations consistent with changes in exposure to prevailing waves. Within Zone I, exposed southeast-facing slopes have a gentler gradient and lower relief than more sheltered southwest-facing slopes, which are steep and irregular. Mesophotic coral ecosystems (MCEs) are largely restricted to Zone I and concentrated on topographic highs removed from the influence of active downslope sediment transport. Accordingly, MCEs are more abundant, extensive and diverse on southwest-facing slopes where irregular topography funnels downslope sediment transport into steep narrow grooves. MCEs are more sporadic and widely spaced on southeast-facing slopes where topographic highs are more widely spaced and downslope sediment transport is spread over open, low-relief slopes inhibiting coral recruitment and growth. Relict features formed during preexisting sea levels lower than present include deep buttresses at ~45–65 m water depth and a prominent terrace at ~80 m. Based on correlations with existing reef accretion and sea-level records, it is proposed that the 80-m terrace formed during the last deglaciation ~14–15 ka and subsequently drowned during a period of rapid sea-level rise associated with meltwater pulse 1A at ~14 ka and deep buttresses at ~45–65 m formed between ~11.5 and 13.5 ka and then drowned during a period of rapid sea-level rise associated with meltwater pulse 1B at ~11.3 ka.

Seasonal experimental trawl surveys were carried out in the Northern Aegean and Thracian seas (NE Mediterranean, Greece), from summer 1990 to autumn 1993, during which a total of 172 fish species were caught. In these areas, fishing pressure is very high, since approximately 50% of the Greek otter trawl fleet operates there, producing more than 57% of the total demersal landings. Different statistics were used to assess spatial structure, seasonal changes and diversity of the demersal fish assemblages on the continental shelf and upper slope. The following measures were applied to the species abundance matrix: species diversity, species richness, evenness and dominance. The analysis of 501 bottom trawls revealed that, in general, species diversity, richness and evenness decreased with water depth, with the highest values at depths 200 m. The effect of depth on the diversity patterns observed was always significant, while seasonal trends were similar with those described for the overall diversity characteristics in each area. Classification and ordination methods showed the existence of 4 groups associated with the continental shelf and upper slope in each area. Classification of the top ranking species at each group and area revealed that commercially important species were dominant in the shallowest zone (

Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73°S: Distribution, ecology and fossilization potential

The Kidnappers Slide complex, on the 1–5° upper continental slope of eastern North Island, New Zealand, consists of several, very large translational slides and rotational slumps. They are of several Late Quaternary phases, range from 20 to 140 m thick, and cover a total area of 720 km2. The main, early Holocene (c. 8000–10,000 yr) phase involved a coast‐parallel sedimentary prism that was deposited on the outer shelf and upper continental slope at a rate of 1–3 m/1000 yr during the last glacial age. Irregularly blanketing the slump, and also locally slumped, is the thin, outer edge of the post‐glacial (< 16,000 yr) prism, deposited on the upper slope at rates ranging from 0.3 to 0.7 m/1000 yr. The sediments consist essentially of terrigenous hemipelagic olive gray mud, along with minor sandy mud, volcanic ash, and pumiceous mud. They are low in calcium carbonate and are inorganic, with high plasticity and low sensitivity. Minor variations occur in the mass physical properties of the post‐glacial...

&lt;em&gt;Abstract .&lt;/em&gt;— Trophic relationships of dominant fishes associated with hard-bottom features of the upper continental slope of the southeastern United States are linked to pelagic prey occurring throughout the water column. Deflection of the Gulf Stream by the Charleston Bump is often associated with upwelling and increased water column productivity in this region of the southeastern Atlantic coast of the United States, leading to increased food availability along the shelf/slope margin. Planktivorous reef fishes take advantage of Zooplankton that is swept onto the outer shelf and upper slope, and are abundant in upper slope rocky habitats of the Charleston Lumps (~ 200 m depth). While upper slope reefs are numerically dominated by yellowfin bass &lt;em&gt; Anthias nicholsi, &lt;/em&gt;a demersal planktivore, large predators of the upper slope, including snowy grouper &lt;em&gt; Epinephelus niveatus &lt;/em&gt;and blueline tilefish &lt;em&gt; Caulolatilus microps, &lt;/em&gt;primarily feed on benthic invertebrates. Blake Plateau reefs in the vicinity of the Charleston Bump (400-600 m depth) are dominated by vertically migrating predators such as alfonsinos &lt;em&gt; Beryx &lt;/em&gt;spp., mesopelagic fishes and squids, and the large demersal wreckfish &lt;em&gt; Polyprion americanus. &lt;/em&gt;Stomach contents of wreckfish reveal that vertically migrating organisms support dense aggregations of this large predator in areas of elevated topography at depths that are usually food poor.

Demersal Continental Shelf and Upper Slope Cephalopod Assemblages from the Balearic Sea (North-Western Mediterranean). Biological Aspects of Some Deep-Sea Species

&lt;p&gt;The Turnagain Area covers the continental shelf and slope off the east coast of North Island, New Zealand between Napier and Castlepoint. Its late Quaternary stratigraphy, tectonic history, sedimentation and foraminiferal distribution are described with the aid of continuous seismic profiles, sediment samples and cores. Results are presented in seven papers and a chart. The first three papers deal mainly with sub-bottom layers revealed by continuous seismic profiles; the next three papers describe dried sediment samples and cores and the last paper is a study of foraminifera in alcohol-preserved sediment samples. The topics discussed in each of the seven papers are as follows: 1. stratigraphy, sedimentation rates and origin of present topography on the continental shelf and upper slope; 2. rates of tectonic processes; 3. slumping; 4. distribution of sediments; 5. ages of indurated sediments; 6. ash horizons and rates of deposition on the lower part of the continental slope. 7. the distribution of living and dead foraminifera. The chart shows bathymetry and nature of sediment at the seabed. The sediments beneath the sea have been folding since Miocene times in the same way as marine sediments on the adjacent land. On the seabed anticlinal crests are preserved as ridges and banks and synclines form depressions. The present land area is rising and much of the seabed is sinking; the zero isobase between then is situated on the inner continental shelf. It has been at about the same position throughout Late Quaternary times, being always close to the dividing line between net erosion and net deposition. Rates of tilting have ranged from 2 to 36 microdegrees/thousand years and rates of vertical movement from +1.7 to -1.5 m/thousand years. Seaward of the zero isobase the continental shelf and upper slope has been built upwards and outwards by prisms of sediment, each prism representing a phase either of low sea level or of high sea level. Prisms deposited during periods of glacially lowered sea level are at their thickest beneath the upper slope; prisms deposited during periods of relatively high sea level are at their thickest beneath the continental shelf. Parts of the youngest prism on the upper slope have slumped on gradients as low as 1 [degree]. The topography and sediments formed during the last 20 thousand years have received the most attention. The present continental shelf if a composite feature. The inner part has been formed by wave-planation of hard rock near shore and deposition of the latest prism of sediment offshore. The outer part and the shelf break were formed by wave-planation and by deposition during the last low sea level about 20 thousand years ago. At that time the shelf break ranged in depth from about 40m to about 70m, being shallowest where eroded into soft sediment and deepest where deposited beyond the seaward edge of erosion. In adjacent areas the shelf break was probably formed at depths of less than 20m being eroded into hard rock. The inner part of the wave-planed surface formed at that time is now deeply buried by the latest prism of sediment but the outer part is covered by only a thin veneer. The outer shelf is still essentially a drowned low sea level feature. At the thickest part of the prism on the mid continental shelf, rates of deposition above an 8 thousand year old seismic reflector range from about 1 to about 4 m/thousand years, being most rapid south of major rivers. Rates are too slow to be measured at some places near the shelf break and at ridges on the continental slope. In depressions on the continental slope, sedimentation rates are indicated by the depth of the 3.4 thousand year old Waimihia ash and range from 0.36 m/thousand years in a depression relatively near land to 0.02 m/thousand years in the depression furthest from land. Sediments range from fine sand near shore to clayey fine silt on the lower slope. Many sediments are bimodal because they were deposited as a mixture of floculated and unfloculated grains. Rapidly deposited sediment on the continental shelf is predominantly detrital sand and silt; slowly deposited sediment near the shelf break and on ridges consists mostly of volcanic ash, foraminifera, and glauconite Muddy sediment in continental slope depressions contains sandy turbidite layers. Different environments are characterised by sediment types and foraminiferal faunas that can be matched in Tertiary Rocks.&lt;/p&gt;

&lt;p&gt;The Turnagain Area covers the continental shelf and slope off the east coast of North Island, New Zealand between Napier and Castlepoint. Its late Quaternary stratigraphy, tectonic history, sedimentation and foraminiferal distribution are described with the aid of continuous seismic profiles, sediment samples and cores. Results are presented in seven papers and a chart. The first three papers deal mainly with sub-bottom layers revealed by continuous seismic profiles; the next three papers describe dried sediment samples and cores and the last paper is a study of foraminifera in alcohol-preserved sediment samples. The topics discussed in each of the seven papers are as follows: 1. stratigraphy, sedimentation rates and origin of present topography on the continental shelf and upper slope; 2. rates of tectonic processes; 3. slumping; 4. distribution of sediments; 5. ages of indurated sediments; 6. ash horizons and rates of deposition on the lower part of the continental slope. 7. the distribution of living and dead foraminifera. The chart shows bathymetry and nature of sediment at the seabed. The sediments beneath the sea have been folding since Miocene times in the same way as marine sediments on the adjacent land. On the seabed anticlinal crests are preserved as ridges and banks and synclines form depressions. The present land area is rising and much of the seabed is sinking; the zero isobase between then is situated on the inner continental shelf. It has been at about the same position throughout Late Quaternary times, being always close to the dividing line between net erosion and net deposition. Rates of tilting have ranged from 2 to 36 microdegrees/thousand years and rates of vertical movement from +1.7 to -1.5 m/thousand years. Seaward of the zero isobase the continental shelf and upper slope has been built upwards and outwards by prisms of sediment, each prism representing a phase either of low sea level or of high sea level. Prisms deposited during periods of glacially lowered sea level are at their thickest beneath the upper slope; prisms deposited during periods of relatively high sea level are at their thickest beneath the continental shelf. Parts of the youngest prism on the upper slope have slumped on gradients as low as 1 [degree]. The topography and sediments formed during the last 20 thousand years have received the most attention. The present continental shelf if a composite feature. The inner part has been formed by wave-planation of hard rock near shore and deposition of the latest prism of sediment offshore. The outer part and the shelf break were formed by wave-planation and by deposition during the last low sea level about 20 thousand years ago. At that time the shelf break ranged in depth from about 40m to about 70m, being shallowest where eroded into soft sediment and deepest where deposited beyond the seaward edge of erosion. In adjacent areas the shelf break was probably formed at depths of less than 20m being eroded into hard rock. The inner part of the wave-planed surface formed at that time is now deeply buried by the latest prism of sediment but the outer part is covered by only a thin veneer. The outer shelf is still essentially a drowned low sea level feature. At the thickest part of the prism on the mid continental shelf, rates of deposition above an 8 thousand year old seismic reflector range from about 1 to about 4 m/thousand years, being most rapid south of major rivers. Rates are too slow to be measured at some places near the shelf break and at ridges on the continental slope. In depressions on the continental slope, sedimentation rates are indicated by the depth of the 3.4 thousand year old Waimihia ash and range from 0.36 m/thousand years in a depression relatively near land to 0.02 m/thousand years in the depression furthest from land. Sediments range from fine sand near shore to clayey fine silt on the lower slope. Many sediments are bimodal because they were deposited as a mixture of floculated and unfloculated grains. Rapidly deposited sediment on the continental shelf is predominantly detrital sand and silt; slowly deposited sediment near the shelf break and on ridges consists mostly of volcanic ash, foraminifera, and glauconite Muddy sediment in continental slope depressions contains sandy turbidite layers. Different environments are characterised by sediment types and foraminiferal faunas that can be matched in Tertiary Rocks.&lt;/p&gt;

Morphosedimentary features and recent depositional architectural model of the Cantabrian continental margin