New evidence of slope instability in the Outardes Bay delta area, Quebec, Canada

The Outardes Bay delta constitutes one of the best sites to study the formation of failure deposits in a modern lowstand environment. These deposits are located in a pseudo-shelf-edge position along the northern part of the Laurentian Channel in the St. Lawrence Estuary. The site has been investigated over the past 20 years with a Raytheon model RTT1000 boomer (3.5 kHz, 400 J) on the shelf, and most recently with a Simrad model EM 1000 multibeam sonar (95 kHz) on the slope to provide high-resolution seismic and bathymetric data. The seismic data show wavy, chaotic and contorted reflectors which are typical in marine environments characterised by instability features. The multibeam sonar data have revealed many slope instability features such as creep folds, channel incisions, debris flows, and rotational slide scars. Thus, these interpreted features are in direct relationship with the seismic interpretation of the data collected upslope. These geomorphological and geophysical signatures express both past and present sedimentological processes. Some of the mass movement signatures observed in the surveyed area are believed to be related with the great MS~7 Charlevoix earthquake in 1663.     

Evidence for slope instability and current-induced sediment transport,the RMSTitanic wreck search area,Newfoundland rise

The first map of the sea bed morphology and sedimentary features within the RMSTitanic search area is proposed from the interpretation of SAR side-scan sonar images. Downslope sedimentary features such as erosional furrows and crown scarps constitute a 7 km wide instability corridor. A large field (15 km²) of asymmetrical sediment waves indicating a downslope transport is identified. Current-induced features corresponding to associated sand ribbons and barchan dunes resulting from the Western Boundary Undercurrent action are mapped. The morphology of theTitanic Canyon is also precised from the SAR images. Finally, the origin of the sea bed features is discussed in an attempt to link each bed form to a sedimentary process.     

Large-scale in situ rotational failure on a low-angle delta slope: The Foreslope Hills,Fraser Delta,British Columbia,Canada

The Foreslope Hills are a series of ridges and troughs covering over 60 km² of the sea floor at the base of the Fraser Delta slope. Internally, the hills consist of blocks of prodelta and delta slope sediment (> 10.6 km³) bounded by offshore dipping faults and shear planes. Stratification within each block generally dips landward, indicating rotational failure. The amount of downslope translation of delta slope sediments was relatively minor. Deformation is restricted to a deep structural trough, suggesting failure resulted from yielding of soft underlying (early Holocene) prodelta sediments in the trough.     

Sustainability of wilderness sea kayaking in the Bay of Fundy,Canada

A study was undertaken to investigate the potential long-term sustainability of sea kayaking in the Bay of Fundy, Canada. The biological and physical state of the environment of four islands frequently visited by sea kayakers was measured in spring, summer, and fall, 1997. Information was also collected on the quality of kayakers’ wilderness experience, and whether encounters with other groups of people or the quality of the environment affected that experience.The kayakers’ impact on the bio-physical states of the islands was found to be minimal. Few impacts were recorded, and most of these were in areas that were frequently and readily modified by waves and tides. All respondents indicated that their wilderness experience was good to excellent, with 97% indicating a very good to excellent experience. More than 80% of respondents indicated that the quality of the natural environment had either a positive or very positive impact on their wilderness experience. Nearly half (43%) of respondents indicated that encounters with other groups of people had a negative or very negative effect on their wilderness experience.Recommendations have been developed for the management of islands in maritime environments with the goal of long-term sustainability.     

福建省三都湾赤潮监控区福宁湾浮游植物的生态

本文于2002～2003年对福宁湾海域浮游植物进行分析,共鉴定浮游植物5个门54属共156种,其中硅藻门为主要门类.季度平均生物量为8.92×103μg/dm3,其年高峰出现于夏季为2.55×104μg/dm3.主要优势种于夏秋和春冬之间演替明显.没赤潮时主要优势种为中肋骨条藻(Skeletonemacostatum)、尖刺菱形藻(Nitzschiapungens)、旋链角毛藻(Chaetoceroscurvisetus),赤潮时主要优势种为具齿原甲藻(Prorocentrumdentatum)、夜光藻(Noctilucascientillans)、米金裸甲藻(Gymnodini ummikimotoi).在常规监测中,活性磷酸盐、硝酸氮、总氮为福宁湾浮游植物生物量的营养盐限制因子.赤潮时,活性磷酸盐是福宁湾及其邻近海域赤潮生物的生物量主要营养盐限制因子之一.     

Composition and conditions for formation of neogene deposits at the Primorye continental slope in the area of Vladimir Bay in the Sea of Japan

The petrographic and micropaleontological studies of the rocks in the sedimentary cover of the Primorye continental slope in the area of Vladimir Bay in the Sea of Japan made it possible to establish that the sedimentary cover is represented in this area by two different facial complexes of Late Miocene rocks. The first facial complex consists of terrigenous rocks (siltstones, sandstones, and conglomerates) that were accumulated under relatively shallow-water conditions of the shelf and the uppermost part of the continental slope. The second one is formed by diatomaceous-clayey rocks under more deep-water conditions, mainly in the upper part of the continental slope. The carbonate nodules that are widely distributed among the deposits of the first complex but are also recorded in the second one were formed as a result of diagenetic processes in the terrigenous or silicious-terrigenous sediments that had been formed. With respect to their age, the Late Miocene deposits are characterized by a full succession of diatomaceous zones over 10.0–5.5 mln yr. The sediments of the first facial complex accumulated during the first third of the Late Miocene (10.0–8.5 mln yr), while those of the second began to accumulate somewhat later, but their accumulation continued until the late Miocene (9.2–5.5 mln yr).     

Macrobenthos of Kakinada Bay in the Godavari delta, East coast of India: comparing decadal changes

A one-year study (1995–1996) on the macrobenthos over a spread of (37) hydrographically differing GPS-fixed sites in Kakinada Bay (mean salinity 27.16±0.4) and adjacent mangrove channels (14.78±0.55) in the Godavari delta, one of India's largest estuarine systems, revealed a great preponderance of benthic life. There were 11 diverse taxa represented by 95 species collected through several (303) grab and dredge hauls. Based on Bray-Curtis similarity through hierarchical clustering implemented in PRIMER, it was possible to distinguish the benthos into four assemblages each of which represented sites in the Central and North bay (Paphia textrix – Typhlocarcinus sp. Assemblage), South-East bay (Protankyra similis – Paphia malabarica Assemblage), Mangrove Outlets (Cerithidea cingulata Assemblage) and Mangrove channels (Diopatra neapolitana Assemblage). Benthos densities (mean nos. dredge haul⁻¹) were highest (299 individuals) at sites close to mangrove outlets. Species diversity (Margalef, d; Shannon-Wiener, H′) was low in general (d 1.244 to 2.251 and H′ 0.038 to 1.502). Sediments were mostly clayey-silt in nature except in southeast bay where they are silt-sand. Organic matter (mean) was at or near 1.3%. The observations have revealed marked changes in benthic community structure relative to an earlier investigation held in 1958–1963 in this area. Over the years, species such as Turritella duplicata, Tonna dolium and Placuna placenta found in considerable numbers previously have dwindled. Anomia, Bursa and Atrina and echinoderms, Astropecten indica, Echinodiscus auritus and Temnopleurus toreumaticus and the brachiopod, Lingula sp. of common occurrence in early 60s are absent altogether attributable to long-term natural trends during the intervening years and/or events accompanying human impingement (e.g. industrial and urban growth, port expansion measures, aquaculture, mangrove denudation etc.). Despite such large-scale alterations in benthos community structure, there were no significant changes in “biodiversity” measured through Average Taxonomic Distinctness (AvTD) and Variation in Taxonomic Distinctness (VarTD). The investigation revealed that AvTD (Δ⁺) and VarTD (Λ⁺) for previous years and the present study remained well within the 95% confidence funnel implying taxonomic stability. It was found that species, which had replaced the earlier forms, were drawn from comparable (Linnean) hierarchy i.e. same phylum/class.     

Patterns and variability in sediment accumulation rates,Fraser River delta foreslope,British Columbia,Canada

Minimum sediment accumulation rates on the Fraser River delta foreslope exhibit a high degree of spatial variation, with accumulation rates ranging from 0.50 to 3.0 cm/yr. Accumulation rates generally increase towards Sand Heads channel, the active foreslope depocenter. Sedimentation rates and patterns and micropaleontological assemblages are interpreted to reflect reintroduction of older sediment from upslope via slumping and sedimentgravity flow processes. Such processes account for the bulk of sedimentation in much of the subaqueous delta. These processes provide a mechanism for sand bypassing of the delta plain and foreslope and for delivery of coarse-grained sediment directly to prodelta and basinal environments.     

海湾开发利用强度分析——以宁波市杭州湾、象山港与宁波市三门湾为例

海湾开发利用强度评估可反映海湾利用程度,是海湾开发潜力及其可持续开发研究的基础,对发展湾区经济意义重大.以1990—2015年每隔5 a共6期TM/ETM/OLI影像为数据源,提取宁波市杭州湾、象山港和宁波市三门湾各时期的岸线及土地利用数据,基于此从海湾岸线开发和土地利用两方面综合分析海湾开发利用强度及其变化特征.结果表明:1990—2015年间,宁波3湾岸线人工化程度不断加深,岸线人工化指数最高的海湾由象山港(0. 16)转变为宁波市三门湾(0. 61),部分淤泥岸段(尤其是宁波市杭州湾岸段)滩涂围垦强度弱于泥沙淤积强度,削弱了岸线人工化程度.整个研究期间,宁波市三门湾和宁波市杭州湾的岸线开发利用结构始终为单一主体结构,象山港则呈现出由单一主体依次向二元、多元结构演变的趋势. 1990—2015年间,宁波3湾的岸线和土地利用强度均有所增加,其中象山港岸线开发利用强度指数最大,达0. 42;宁波市杭州湾区域土地利用变动最为强烈,土地利用程度指数最大,达292. 300.区位和资源禀赋、社会经济水平及政策因素是造成宁波3湾区域开发利用程度差异的重要因素.     

Geology and geotechnical characteristics of sediments in east bay area,Mississippi delta

Abstract

Deltaic sedimentation has produced an accumulation of clay and silt with a maximum thickness of 90 m in East Bay area. Sediments in the upper 50 m grade from interbedded sand, silt, and clay near South Pass and Southwest Pass to predominantly clay in the central part of the area. The variation in the types of sediments and rates of deposition greatly affected the engineering properties of these deposits. Sediments from boreholes in the central part of the area have shear strengths of less than 10 kPa to a depth of at least 50 m. Near the distributaries, shear strength increases with depth; values as high as 43 kPa were measured in sediments in the upper 50 m. These sediments are generally stronger and coarser, and have a lower water content and liquid limit than do sediments at comparable depths in the central part of the area.     

海南三亚湾海域水质状况评价

本文根据1998年10月至1999年8月海南三亚湾海域水质监测结果，分析了各水质参数的周年变化，在对各水质参数进行污染指数计算的基础上，应用水质综合评价模式，对该海域进行水质评价。结果表明：（1）受河口和高含量测值的影响，三亚湾海域水质呈现轻度污染状态，河口水质已接近严重污染；（2）除重金属Pb外，该海域其它水质参数均未超出一类海水水质标准；（3）除重金属Pb外，该海域其它水质参数变化的控制因子。     

Pockmarks and seafloor instability in the Olbia continental slope (northeastern Sardinian margin, Tyrrhenian Sea)

The seafloor morphology and the subsurface of the continental slope of the Olbia intraslope basin located along the eastern, passive Sardinian margin (Tyrrhenian Sea) has been mapped through the interpretation of high-resolution multibeam bathymetric data, coupled with air-gun and sparker seismic profiles. Two areas, corresponding to different physiographic domains, have been recognized along the Olbia continental slope. The upper slope domain, extending from 500 to 850 m water depth, exhibits a series of conical depressions, interpreted as pockmarks that are particularly frequent in seafloor sectors coincident with buried slope channels. In one case, they are aligned along a linear gully most likely reflecting the course of one of the abandoned channels. The location of the pockmarks thus highlights the importance of the distribution of lithologies within different sedimentary bodies in the subsurface in controlling fluid migration plumbing systems. A linear train of pockmarks is, however, present also away from the buried channels being related to a basement step, linked to a blind fault. Two bathymetric highs, interpreted as possible carbonate mounds, are found in connection with some of the pockmark fields. Although the genetic linkage of the carbonate mounds with seafloor fluid venting cannot be definitively substantiated by the lack of in situ measurements, the possibility of a close relationship is here proposed. The lower slope domain, from 850 m down to the base of the slope at 1,200 m water depth is characterized by a sudden gradient increase (from 2° to 6°) that is driven by the presence of the basin master fault that separates the continental slope from the basin plain. Here, a series of km-wide headwall scars due to mass wasting processes are evident. The landslides are characterized by rotated, relatively undeformed seismic strata, which sometimes evolve upslope into shallow-seated (less than 10 m), smaller scale failures and into headless chutes. Slope gradient may act as a major controlling factor on the seafloor instability along the Olbia continental slope; however, the association of landslides with pockmarks has been recognized in several continental slopes worldwide, thus the role of over-pressured fluids in triggering sediment failure in the Olbia slope can not be discarded. In the absence of direct ground truthing, the geological processes linked to subsurface structures and their seafloor expressions have been inferred through the comparison with similar settings where the interpretation of seafloor features from multibeam data has been substantiated with seafloor sampling and geochemical data.     

厦门湾口外近岸陆架区海底沙波发育特征

利用2014–2017年在台湾海峡西部采集的多波束、单道地震剖面、沉积物粒度样品及海流监测资料,在厦门湾近岸陆架区识别出一系列海底沙波,并对沙波的形态特征、分布规律和沉积物组成特征进行分析,探讨水动力条件及其对沙波发育的影响.结果表明沙波发育区水深一般为10～60 m,地形较平缓开阔,坡度一般为0°～1°;平面上沙波区...     

象山港潮滩坡度对潮动力影响的数值研究

象山港属于狭长型半封闭港湾,湾内分布有大面积潮滩。多年以来象山港内实施了大量海岸工程及养殖工程,湾内潮滩坡度发生了显著变化。基于非结构网格和有限体积数值模式（FVCOM）建立象山港三维潮动力模型,研究湾内不同区域潮滩坡度变化对象山港潮动力过程的影响机理。结果表明：潮滩坡度下降将增大湾内纳潮量,进而增大M2分潮振幅和迟角,反之则反。铁港潮滩坡度的减小（增大）,将改变底部耗散项,进而增大（减小）M4分潮振幅。由于M2和M4分潮的振幅在湾顶较大,所以湾顶（铁港）潮滩坡度对象山港潮动力过程的影响明显大于侧岸（西沪港）。西沪港潮滩坡度对象山港潮动力过程的影响是局部的。铁港、西沪港潮滩坡度对湾内潮汐不对称、余流及潮能影响显著。铁港潮滩坡度的改变均会减弱湾内落潮占优程度。西沪港区域潮滩坡度的减小将减弱湾内落潮占优趋势,反之则反。铁港和西沪港潮滩坡度的减小,将增大余流大小及潮能密度,进而潮能耗散增大,反之则反。研究结果对河口海岸潮滩区域的工程建设及生态修复有重要参考价值。     

Seasonal metal remobilization in the sediments of Great Bay,New Hampshire

Concentrations of dissolved iron, manganese, molybdenum, copper, and organic carbon (DOC) were measured in the pore waters from surficial sediments of a temperate estuary to delineate seasonal metal remobilization from 1978 through 1980. Iron and DOC data were collected for 31 months and covaried inversely and exponentially. Iron dissolution occurred during the spring and during periods of active bioturbation with concentrations as high as 18 mg 1^?1. Iron values were low during winter due to oxidation to ferric oxides. The lack of active bioturbation during the summer of 1978 allowed for the nearly complete removal of iron as a monosulfide precipitate. However, bioturbation resumed during the summer of 1979 and 1980 and dissolved iron concentrations as high as 10 mg 1^?1 were observed at those times. The iron and DOC data were a qualitative measure of bioturbation activity. Dissolved manganese, molybdenum, and copper data were collected for 18 months during 1978 and 1979. All three metals displayed spring maxima covariate with iron, suggesting that they behaved chemically like iron and/or were associated with iron- or manganese-rich phases during this time of the year. In general, manganese and molybdenum varied temporally with iron while copper concentrations mimicked iron variations only during the spring.     

Three-dimensional forward stratigraphic modelling of the gravel-to mud-rich fan-delta in the slope system of Zhanhua Sag,Bohai Bay Basin,China

An important hydrocarbon reservoir is hosted by the third member of the Shahejie Formation (Es₃) in the Zhanhua Sag, Bohai Bay Basin. Seismic stratal slices reveal different characteristics of channels and fan-delta lobes between the south (slope break belt) and southwest (gentle slope) areas combined with lithology, wire-line logs and three-dimensional (3-D) seismic data in the southern slope of Zhanhua Sag. And an excellent analogue has been provided for understanding various key depositional evolution of fan-deltas in the slope system (from base to top: Es₃^L, Es₃^M and Es₃^U). The Sedsim, a three-dimensional stratigraphic forward modelling programme, is applied to simulate the evolution of fan-deltas in the southern slope break systems and southwestern gentle slope systems of the Zhanhua Sag by considering a number of key processes and parameters affecting the fan-deltaic deposition from 43 Ma to 38.2 Ma. Modelling results indicate that depositional types and scales evolved from the thickest medium-scale gravel- or sand-rich fan deltas (43 Ma ∼41.4 Ma, Es₃^L) to the thinnest small-scale mud-rich fan deltas and lacustrine mud (41.4 Ma ∼39.8 Ma, Es₃^M), and lastly to less thicker larger-scale mixed sand-mud fan deltas (39.8 Ma ∼38.2 Ma, Es₃^U). The types of slope system, sediment supply and lake-level change are three controlling factors for determining the source-to-sink architecture of the gravel-to mud-rich fan-deltas and sediment-dispersal characteristics. This study has demonstrated that the process-based modelling approach can be effectively used to simulate complex geological environments and quantify controlling factors.     

Hydrocarbon accumulation model for Neogene traps in the Chengdao area,Bohai Bay Basin,China

Chengdao is an offshore area in the Bohai Bay Basin that contains approximately 25.7 × 10⁸ bbl of oil and gas reserves within the sandstone reservoirs in Neogene strata. However, previous predictions of hydrocarbon accumulation in Neogene traps are inaccurate, resulting in a current failure rate of 50% when drilling for hydrocarbons in this area. To build an improved exploration model for Neogene traps, we select 92 traps from Neogene strata in the Chengdao area to quantify the filling degree, which is an indicator of hydrocarbon accumulation efficiency. The quantified filling degree is based on actual geological and exploration data and differs significantly among various trap types. The filling degree of traps also varies significantly with their structural locations and decreases generally from the northwest to the southeast along the Chengbei Fault zone. Vertically, the filling degree is highly heterogeneous, initially increasing from the bottom to the middle of Neogene strata and then decreasing towards the top of the strata. These Neogene hydrocarbon reservoirs are sourced from the Paleogene, and as they lay vertically away from the source rocks, their hydrocarbon enrichment is constrained largely by hydrocarbon migration distance and vertical migration pathways. The sealing capacity of faults and cap rocks, sandbody orientation and reservoir sedimentary facies determine the maximum column height, which in turn affects the amount of hydrocarbon accumulation within these traps. A scatter plot analysis of individual controls and volumetric filling for each trap type is compiled using multivariate linear regression analysis to quantify controls and the dominant control of hydrocarbon accumulation is determined.