Miocene Blanca Fan, Northern Channel Islands, California: Small fans reflecting tectonism and volcanism

Blanca fan is a submarine fan composed of Miocene volcaniclastic strata. Parts of the fan system are exposed on Santa Cruz and Santa Rosa Islands, and possibly correlative strata crop out on San Miguel and Santa Catalina Islands. The Blanca fan and underlying breccia reflect regional transcurrent faulting in the California Continental Borderland and development of a system of rapidly subsiding basins and uplifted linear ridges during early and middle Miocene time. Erosion of uplifted crystalline basement rocks followed by the onset of silicic volcanism created linear sediment sources for the alluvial and submarine fans, respectively. Margin setting represents fan and/or source area     

Recreational boaters value biodiversity: The case of the California Channel Islands National Marine Sanctuary

Marine ecosystems provide a range of valuable services, some of which come with market prices to quantify value and others for which markets have not set prices. Lacking perfect information, policy makers are at risk of undercounting non-priced values and services, leading to biases in policy decisions in favor of services valued through markets. Furthermore, understanding users’ valuation of specific site attributes, such as marine biodiversity, can contribute to effective policy decisions. This paper presents a non-market valuation of private recreational boaters (PRBs) in the Channel Islands National Marine Sanctuary located in California, USA, using data from an intercept survey conducted in 2006 and 2007. A Random Utility Model is used to estimate PRBs’ daily trip values and the importance of specific site attributes. The average consumer surplus was estimated at $48.62 per trip, with a total non-market value of non-consumptive private recreational boating of $86,325 annually. PRBs show a preference for visiting locations with lower exposure to prevailing winds and greater species richness and abundance, which to the authors’ knowledge is the first time that PRBs have been found to value biological diversity in site choices. Furthermore, this suggests that improved biodiversity and productivity of marine ecosystems contribute to better recreational experiences. The results from this study reveal the importance of including non-market services and stakeholder's preferences into policy decisions.     

Navy Fan, California Borderland: Growth pattern and depositional processes

Navy Fan is a Late Pleistocene sand-rich fan prograding into an irregularly shaped basin in the southern California Borderland. The middle fan, characterized by one active and two abandoned “distributary” channels and associated lobe deposits, at present onlaps part of the basin slope directly opposite from the upper-fan valley, thus dividing the lower-fan/basin-plain regions into two separate parts of different depths. Fine-scale mesotopographic relief on the fan surface and correlation of individual turbidite beds through nearly 40 cores on the middle and lower fan provide data for evaluating the Late Pleistocene and Holocene depositional processes. Margin setting represents fan and/or source area     

Navy Fan,California Borderland: Growth pattern and depositional processes

Navy Fan is a Late Pleistocene sand-rich fan prograding into an irregularly shaped basin in the southern California Borderland. The middle fan, characterized by one active and two abandoned “distributary” channels and associated lobe deposits, at present onlaps part of the basin slope directly opposite from the upper-fan valley, thus dividing the lower-fan/basin-plain regions into two separate parts of different depths. Fine-scale mesotopographic relief on the fan surface and correlation of individual turbidite beds through nearly 40 cores on the middle and lower fan provide data for evaluating the Late Pleistocene and Holocene depositional processes.     

Geology of Macdonald Seamount region,Austral Islands: Recent hotspot volcanism in the south Pacific

The southeastern extension of the Austral Islands volcanic chain terminates near 29°S, 140°W at the active Macdonald Seamount. The hotspot region near Macdonald consists of at least five other volcanic edifices each more than 500 m high, included in an area about 50–100 km in diameter. On the basis of the sea-floor topography, the southeastern limit of the hotspot area is located about 20 km east of the base of Macdonald, where it is defined by the 3950 m isobath. At the edge of the hotspot area, there is a marked deepening of the seafloor from c.3900 m down to 4000–4300 m. The deeper sea-floor is faulted and heavily sedimented. The Macdonald volcano itself stands 3760 m above the surrounding seafloor, and has a basal diameter of 45 km. Its summit in January 1987 was 39 m below sea level, and it seems likely that Macdonald will emerge at the surface in the near future.Recent (March and November 1986) phreatic explosions on Macdonald Seamount erupted fragments of ultramafic and mafic plutonic blocks together with basic lapilli (volcaniclastic sand). The plutonic blocks have been variably altered and metamorphosed, and in some cases show signs of mineralisation (disseminated sulphides). The blocks presumably come from deeper levels in the volcanic system. The volcanics so far dredged from Macdonald consist of olivine and clinopyroxene cumulus-enriched basalts, evolved basalts, and mugearite. On the basis of incompatible element variations, simple crystal fractionation seems to be controlling the chemical evolution of Macdonald magmas.     

Ferrelo Fan,California: Depositional system influenced by Eustatic sea level changes

Remnants of an Eocene fan system are preserved onshore at San Diego and in the central part of the southern California borderland. Even though faults and erosion have truncated its margins, geophysical data and exploratory wells indicate that remaining parts of the fan extend beneath an offshore area nearly 400-km long and 40- to 100-km wide. Environments representing fluvial, fan-delta, shelf-channel, overlapping inner- to outer-fan, and basin-plain facies are recognized or inferred. Three progradational cycles onshore and two distinct pulses of sand accumulation offshore are attributable to eustatic low sea-level stands rather than to tectonic uplift or shifts in depositional patterns.     

Synsedimentary structural control on foredeep turbidites: An example from Miocene Marnoso-arenacea Formation, Northern Apennines, Italy

This work discusses the synsedimentary structural control affecting the turbidites of the Marnoso-arenacea Formation (MAF) deposited in an elongate, NW-stretched foredeep basin formed in front of the growing Northern Apennines orogenic wedge. The stratigraphic succession of the MAF (about 4000 m thick) records the progressive closure of the Apennine foredeep basin due to the NE propagation of thrust fronts. In this setting, Langhian to Serravallian turbidites are overlain by Tortonian mixed turbidite deposits, i.e. sandstone-rich low-efficiency turbidites. The high-resolution stratigraphic framework of basin-plain turbidites has made it possible to identify five informal stratigraphic units (I, II, III, IV, V) mainly on the basis of the structural control highlighted by: 1) the presence of topographic highs and relative depocentres detected through a progressive flattening approach, and 2) the presence of thrust-related mass-transport complexes and the progressive appearance and disappearance of five bed types (Types 1, 2, 3, 4, 5) considered important to understand the interaction between flow efficiency and basin morphology. By contrast, the upper part of the MAF succession (Tortonian in age) is formed by more sandstone-rich systems characterized by beds whose origin is likely to depend, at least in part, upon flow decelerations related to topographic confinement due to the progressive closure of the foredeep. The vertical and lateral distribution of these types of beds is, therefore, useful for the reconstruction of the morphological evolution of structurally controlled basins; in the MAF example, this is mainly due to the progressive narrowing of the foredeep caused by the propagation of the main thrust fronts toward the foreland.     

Evolution and stratigraphic architecture of marine slope gully complexes: Monterey Formation (Miocene), Gaviota Beach,California

Three small headlands in the sea cliffs west of Gaviota Beach, California, are the remnant fill of three discrete submarine gullies incised into the late Miocene submarine slope environment. These promontories provide excellent, three-dimensional exposure of the gully fill in outcrop, permitting documentation of their complex internal stratigraphic architecture. Detailed study of these exposures elucidates the sedimentologic processes that occur in the filling of slope gullies, guides interpretation of the acoustic records of otherwise unsampled modern gully systems on continental slopes, and provides insight into the heterogeneity that may characterize slope gully petroleum reservoirs.     

舟山马岙峡道的水文泥沙特性和峡道效应

根据舟山本岛北部马岙峡道实测水文泥沙资料和沉积物采样分析结果以及对马岙岸段岸滩的现场踏勘结果，分析了马岙峡道的水文泥沙特性及其峡道效应。文章认为，受峡道地形限制，马岙岸段水流呈现显著的往复流特性，潮流流速较强，水体含沙量较低，泥沙淤积较弱，岸滩处于冲淤平衡状态；受峡道内涨落潮流分流和汇流的共同作用，马岙小泥糊礁附近发育水下沙嘴，该沙嘴是以落潮流作用为主形成的浅滩，受涨潮流改造而形成的，并将在涨落潮流作用下逐渐增长，形成连岛沙嘴，使小泥糊礁附近岸线发展成弧形岸线，并达成新的平衡。     

Side-scan sonar mapping and computer-aided interpretation in the Santa Barbara Channel,California

We have experimented with digital processing of side scan sonar data taken in a 14 sq-km area of continental shelf offshore Southern California. The data were FM tape recorded during the survey and digitized and processed later in the laboratory. The digital image processing included both image correction and image enhancement. Geometric corrections were applied to correct for image distortions due to variable ship position and speed and sonar slant range. Enhancements that were tried included contrast stretching, band-pass filtering, image restoration (inverse filtering), and various edge enhancements such as density slicing and standard deviation filters. Interpretive procedures were also attempted and included digital mosaicking, stereoscopic viewing, and falsecolor display. The most effective processing was geometric correction combined with contrast stretching. Mosaicking proved difficult due to imprecise navigation (±50 m), but was very effective in increasing the understanding of the geologic structure in the survey area.     

Subsea Channels and Incidence of Thermogenic Hydrocarbons in the Mid-proximal Bengal Fan, West of the Andaman-Nicobar Islands

Mid-fan areas in the Bay of Bengal to the west of the Andaman-Nicobar Islands and to the east of the 90 E ridge display remarkable channel-levee and interlevee characteristics over the seabed. These subsea channels at 3,000 m or more water depth have specific orientations along NNE or NNW. Most of these major and minor channels are at present inactive, except one running along the eastern part of the area following the reported subduction suture (Currey et al., 1979). The other channels in the western part retain the configuration of a floor-bank combination but are covered with a thin deposition of pelagic organisms without any significant terrigenous inputs to a depth of around 25 cm below the seabed. On the other hand, the active channel to the east is filled with continuous hemipelagic to terrigenous inputs up to at least 1.5 m bsf. The pelagic organisms of the upper 25 cm of seabed over the inactive channels as well as in their banks and interlevee areas are mainly represented by foraminiferal tests and thus constitute foraminiferal ooze. Most of the seafloor is covered by such ooze except in the easternmost part, where the active channel brings a terrigenous influx in the form of turbidites. The fan deposition has been restricted to the easternmost active channel since the early Holocene. The age of the pelagites that constitute the 25-cm top sediment slice is assumed to represent about 8,000 years, calculated at the rate of deposition of 3 cm 1,000 years (Kennet, 1982). Thus, most of the western seabed has not experienced any fan deposition during the last 8,000 years. However, below 25 cm, the entire area is seen to have experienced fan deposition as evidenced by occurrence of terrigenous silt and clay. Significantly, incidence of thermogenic hydrocarbons is proved in the levee-in terlevee complexes of the central part. Being closer to the subduction zone, gas seepages through pervasive fissures are perhaps more pronounced here.     

Correlation of Miocene strata on the submarine St. Croix Ridge and onland St. Croix,US Virgin Islands

The nannofossils of an hydraulic piston core from the steep scarp between the St. Croix Ridge and Virgin Islands Basin were restudied. Formerly thought to represent a Pliocene debris flow, we interpret it as an early Miocene (NN1/2) hemipelagic deposit. We correlate the seismic unit sampled by piston core with the Kingshill-Jealousy Formation present on St. Croix. These sediments likely belong to an extensive, thick, deep marine cover of the St. Croix Ridge, deposited on a metamorphic—igneous basement between early Eocene and early Miocene time. Faulting did not evidently affect this sediment cover until the late Neogene.     

Fatty Acid Composition and Community Structure of Plankton from the San Lorenzo Channel, Gulf of California

The structure of the plankton community and fatty acid composition of nano-, micro- and zooplankton are described during four seasons of 1994 from the San Lorenzo Channel. During August, the warmest temperature in the surface water was observed and a thermocline developed between 20 and 30 m. In the remaining months, a well-mixed layer occurred in the upper 30 m. The chlorophyllacontent of the nanoplankton fraction (<38 μm) was higher than the microplanktonic fraction (38–200 μm) year round. Maximal chlorophyll values (1·5–3 μ l⁻¹) occurred in January, which may be associated with organic matter, since phytoplankton was lower than at other seasons. The relative abundance of diatoms increased from January (57% of phytoplankton) to November (99%). The increment was mainly due toNitzschiaandChaetoceros. Dinoflagellates were always low (0·03–1·36 cells ml⁻¹). Copepods (mainlyEucalanus) dominated the zooplankton in winter and fall, while in spring and summer, the abundance of doliolids was similar to the copepods (Nannocalanus minordominated).Four fatty acids (16:0, 16:1, 18:0, 18:1) were the most conspicuous in the plankton, representing usually between 40 and 80% of the total fatty acids throughout the water column. In winter, higher fatty acid content and higher relative amounts of 16:0 and 16:1 were observed than in the warm months. Stearic acid (18:0) peaked during fall. The major seasonal differences occurred in the nanoplankton, which had peaks of 20:5 during January, and 16:4 in April. A strong decrease in polyunsaturated fatty acids (PUFA) occurred during the warm months. The fatty acid composition of microplankton and larger zooplankton was similar in winter–spring. Individual copepods of selected species (Eucalanus sewelli,Rhincalanus nasutus,Centropages furcatusandLabidocera acuta) showed fatty acid profiles similar to the mixed zooplankton, with some differences in content of PUFA.     

Social indicators of vulnerability for fishing communities in the Northern Gulf of California,Mexico: Implications for climate change

Marine fisheries support the livelihoods of millions of people worldwide. These fisheries and the communities that depend on them are highly vulnerable to climate change and other interacting anthropogenic threats. The cumulative and interacting effects of these stressors could potentially produce declines in fish production, which would significantly impact artisanal fishers. Assessing relative vulnerability of fishing communities to anthropogenic stressors is an important first step to identifying mitigation or adaptation strategies. This study assessed the vulnerability of 12 coastal communities in the Northern Gulf of California to disruptions in fishing activities from anthropogenic stressors, including climate change. The Northern Gulf is a megadiverse area and a major source of fishery resources. Quantitative indicator indices based on secondary and primary data were developed to assess the three aspects of vulnerability: sensitivity, exposure, and adaptive capacity. The key components of vulnerability varied amongst communities. Vulnerability was higher in communities with higher fishing dependence and lower socioeconomic diversification. The approach presented here provides important insights into the type of policy actions that might be needed in different communities for adaptation and mitigation.     

The Bengal Fan: morphology, geometry, stratigraphy, history and processes

The Bengal Fan is the largest submarine fan in the world, with a length of about 3000 km, a width of about 1000 km and a maximum thickness of 16.5 km. It has been formed as a direct result of the India–Asia collision and uplift of the Himalayas and the Tibetan Plateau. It is currently supplied mainly by the confluent Ganges and Brahmaputra Rivers, with smaller contributions of sediment from several other large rivers in Bangladesh and India.The sedimentary section of the fan is subdivided by seismic stratigraphy by two unconformities which have been tentatively dated as upper Miocene and lower Eocene by long correlations from DSDP Leg 22 and ODP Legs 116 and 121. The upper Miocene unconformity is the time of onset of the diffuse plate edge or intraplate deformation in the southern or lower fan. The lower Eocene unconformity, a hiatus which increases in duration down the fan, is postulated to be the time of first deposition of the fan, starting at the base of the Bangladesh slope shortly after the initial India–Asia collision.The Quaternary of the upper fan comprises a section of enormous channel-levee complexes which were built on top of the preexisting fan surface during lowered sea level by very large turbidity currents. The Quaternary section of the upper fan can be subdivided by seismic stratigraphy into four subfans, which show lateral shifting as a function of the location of the submarine canyon supplying the turbidity currents and sediments. There was probably more than one active canyon at times during the Quaternary, but each one had only one active fan valley system and subfan at any given time. The fan currently has one submarine canyon source and one active fan valley system which extends the length of the active subfan. Since the Holocene rise in sea level, however, the head of the submarine canyon lies in a mid-shelf location, and the supply of sediment to the canyon and fan valley is greatly reduced from the huge supply which had existed during Pleistocene lowered sea level. Holocene turbidity currents are small and infrequent, and the active channel is partially filled in about the middle of the fan by deposition from these small turbidity currents.Channel migration within the fan valley system occurs by avulsion only in the upper fan and in the upper middle fan in the area of highest rates of deposition. Abandoned fan valleys are filled rapidly in the upper fan, but many open abandoned fan valleys are found on the lower fan. A sequence of time of activity of the important open channels is proposed, culminating with formation of the one currently active channel at about 12,000 years BP.     

Miocene to recent Cariaco basin, offshore Venezuela: Structure, tectonosequences, and basin-forming mechanisms

The Cariaco basin, located ∼40 km off the central part of the coast of Venezuela, is the largest (∼4000 km²) and bathymetrically deepest (1400 m BSL) Neogene fault-bounded basin within the right-lateral strike-slip plate boundary zone that separates the Caribbean and South American plates. Using subsurface geophysical data, we test two previously proposed tectonic models for the age, distribution and nature of east-west-striking, strike-slip faults, and basin-forming mechanism for the two main depocenters of the Cariaco basin. The earliest interpretation for the opening of the twin Cariaco depocenters by Schubert (1982) proposes that both depocenters formed synchronously by extension along transverse (north-south) normal faults at a ∼30-km-wide rhomboidally-shaped pull-apart basin between the right-lateral, east-west-striking, and parallel San Sebastian and El Pilar fault zones. A later model by Ben-Avraham and Zoback (1992) proposes that both depocenters formed synchronously by a process of ”transform-normal parallel extension”, or rifting in a north-south direction orthogonal to the east-west-striking and parallel strike-slip faults.We use more than 4000 km of 2D single- and multi-channel seismic data tied to 11 wells to map 5 tectono-stratigraphic sequences and to produce a series of structural and isopach maps showing how the faults that controlled both Cariaco depocenters evolved from Paleogene to the present. Comparison of fault and isopach maps for dated horizons from Paleogene to late Neogene in age show three main phases in basin development: 1) from middle Miocene to Pliocene, the West Cariaco basin formed as a rhomboidally-shaped pull-apart at a 30-km-wide stepover between the northern branch of the San Sebastian fault and the El Pilar fault zone; 2) during the early Pliocene, a new strike-slip fault transected the West Cariaco basin (southern branch of the San Sebastian fault) and caused extension to cease; and 3) during the early Pliocene to recent, a “lazy-Z” shaped pull-apart formed along the curving connection between the southern branch of the San Sebastian and El Pilar fault zones.     

Top-down modeling and bottom-up dynamics: Linking a fisheries-based ecosystem model with climate hypotheses in the Northern California Current

In this paper we present results from dynamic simulations of the Northern California Current ecosystem, based on historical estimates of fishing mortality, relative fishing effort, and climate forcing. Climate can affect ecosystem productivity and dynamics both from the bottom-up (through short- and long-term variability in primary and secondary production) as well as from the top-down (through variability in the abundance and spatial distribution of key predators). We have explored how the simplistic application of climate forcing through both bottom-up and top-down mechanisms improves the fit of the model dynamics to observed population trends and reported catches for exploited components of the ecosystem. We find that using climate as either a bottom-up or a top-down forcing mechanism results in substantial improvements in model performance, such that much of the variability observed in single species models and dynamics can be replicated in a multi-species approach. Using multiple climate variables (both bottom-up and top-down) simultaneously did not provide significant improvement over a model with only one forcing. In general, results suggest that there do not appear to be strong trophic interactions among many of the longer-lived, slower-growing rockfish, roundfish and flatfish in this ecosystem, although strong interactions were observed in shrimp, salmon and small flatfish populations where high turnover and predation rates have been coupled with substantial changes in many predator populations over the last 40 years.     

Interactions Between Small Sciaphilous Scleractinians and Epizoans in the Northern Mediterranean, With Particular Reference to Bryozoans

Abstract. Two small sclcractinians, Lepfopsummiu pruvoti (solitary) and Hoplungiu dur-olrix (colonial, aggrcgatcd or not), which arc common pcrcnnial componcnts of Mcditcrrancan submarinc cavcs and dccp vcrtical walls, bcar many cpibionts on thc lowcr part of thcir corallitcs. Samplcs were collectcd ncar Marscillcs (7–58 in) undcr various cnvironmcntal conditions and coral densitics. Frequency of occurrencc of thc major cpizoan groups and of individual bryozoan spccics overgrowing the corallites varies according to habitat charactcristics and to acccssibility of the individual corallitcs for adjaccnt epizoans. Thc most frcqucnt colonizcrs arc: bryozoans (by vcgctative growth and larval settlcrnent), sponges (mainly by vcgctativc growth), and scrpulids. Among the 40 recorded bryozoan species (26 on Leptopsammia, 28 on Hoplangiu), 15 spccics are relatively frequent on each host. Comparisons of data from the corallites with thosc obtained from adjoining samples indicatc the preference for coral substratc of Pucflina radiata. This encrusting bryozoan is highly predominant on both Leptopsammia and Hoplangiu as well as on other scleractinian species. SEM observations show that overgrowth processcs are reversible and that corals may control the invading encruSters by embedding them in their sclerenchyme. The balance and benefits of this epizoan/host system are discussed.     

Numerical Study of a Kyucho and a Bottom Intrusion in the Bungo Channel,Japan: Disturbances Generated by the Kuroshio Small Meanders

The generation and propagation mechanisms of a Kyucho and a bottom intrusion in the Bungo Channel, Japan, have been studied numerically using the hydrostatic primitive equations by assuming density stratification during summer. The experiments are designed to generate a Kuroshio small meander in Hyuga-Nada, which acts as a trigger for these disturbances. After the current speed of the Kuroshio is changed, a small meander is generated. At the head of the small meander, warm Kuroshio water is engulfed, and encounters the southwest coast of Shikoku. However, convergence of heat flux on the bump off Cape Ashizuri suppresses the generation of a warm disturbance, if the current speed is large. As the cold eddy associated with the small meander approaches Cape Ashizuri, the heat flux diverges on the bump. This heat source forces a warm disturbance, which intrudes along the east coast of the Bungo Channel as a baroclinic Kelvin wave (a Kyucho). After the cold eddy passes off Cape Ashizuri, the Kuroshio approaches the bump again. Strong convergence of heat flux then occurs on the bump, which forces a cold disturbance. This disturbance propagates as a topographic Rossby wave along the shelf break at the mouth of the channel. After the topographic wave reaches the west end of the shelf break, it intrudes along the bottom layer of the channel as a density current (a bottom intrusion). These results suggest that a Kyucho and a bottom intrusion are successive events associated with the propagation of the small meander.     

Clay-mineral suites,sources, and inferred dispersal routes: Southern California continental shelf

Clay mineralogy is useful in determining the distribution, sources, and dispersal routes of fine-grained sediments. In addition, clay minerals, especially smectite, may control the degree to which contaminants are adsorbed by the sediment. We analyzed 250 shelf sediment samples, 24 river-suspended-sediment samples, and 12 river-bed samples for clay-mineral contents in the Southern California Borderland from Point Conception to the Mexico border. In addition, six samples were analyzed from the Palos Verdes Headland in order to characterize the clay minerals contributed to the offshore from that point source. The <2 microm-size fraction was isolated, Mg-saturated, and glycolated before analysis by X-ray diffraction. Semi-quantitative percentages of smectite, illite, and kaolinite plus chlorite were calculated using peak areas and standard weighting factors. Most fine-grained sediment is supplied to the shelf by rivers during major winter storms, especially during El Ni?o years. The largest sediment fluxes to the region are from the Santa Ynez and Santa Clara Rivers, which drain the Transverse Ranges. The mean clay-mineral suite for the entire shelf sediment data set (26% smectite, 50% illite, 24% kaolinite+chlorite) is closely comparable to that for the mean of all the rivers (31% smectite, 49% illite, 20% kaolinite+chlorite), indicating that the main source of shelf fine-grained sediments is the adjacent rivers. However, regional variations do exist and the shelf is divided into four provinces with characteristic clay-mineral suites. The means of the clay-mineral suites of the two southernmost provinces are within analytical error of the mineral suites of adjacent rivers. The next province to the north includes Santa Monica Bay and has a suite of clay minerals derived from mixing of fine-grained sediments from several sources, both from the north and south. The northernmost province clay-mineral suite matches moderately well that of the adjacent rivers, but does indicate some mixing from sources in adjacent provinces.