青海湖近岸现代沉积滩坝主要类型及沉积特征*

滩坝是隐蔽油气藏最重要的沉积储集层类型之一,已成为陆相断陷盆地油气勘探的重要领域。现代沉积滩坝的研究是深入认识滩坝沉积相的有效手段。环湖考察研究发现青海湖近岸滩坝类型多样,主要发育了废弃三角洲前缘处滩坝、三角洲侧缘处滩坝、湖岸线拐弯处滩坝、开阔滨浅湖处滩坝和冲积扇改造处滩坝5种类型。通过对各种类型滩坝剖面的详细分层及沉积物室内矿物组成分析等,发现不同类型滩坝砂体沉积特征存在很大差异。整体而言,青海湖近岸滩坝沉积物粒度较粗,黏土含量低,结构成熟度较高,沉积构造多见平行层理、交错层理和冲洗交错层理,垂向上表现出上粗下细的反韵律特征。同时,选取了青海湖南岸规模较大的坝相,分别对坝主体、坝间和坝侧缘进行详细的探槽剖面分析,得出坝主体单旋回厚度较坝间和坝侧缘大,沉积物粒度也相对较粗,黏土含量最低,分选性也最好,是发育为隐蔽油藏最有利的区域。     

苏北盆地高邮凹陷古近系阜宁组一段浅水三角洲和滩坝沉积模式*

通过对苏北盆地高邮凹陷古近系阜宁组一段38口取心井的岩心观察和薄片鉴定, 识别出岩性、结构、构造标志, 进一步分析了高邮凹陷阜一段的相标志和沉积展布特征。研究认为其具有浅水三角洲和滩坝相的沉积特征, 其中浅水三角洲可进一步分为浅水三角洲平原和浅水三角洲前缘2个沉积亚相, 前者包括分流河道、河口坝、天然堤3个沉积微相, 后者包含水下分流河道、水下天然堤、支流间湾、河口坝4个沉积微相。在湖平面频繁变化过程中, 浅水三角洲的水下分流河道向湖泊轴心方向推进, 形成多个叠置的朵叶体;而在浅水三角洲侧缘, 由于湖浪和沿岸流的改造, 形成多条沿湖岸线和浅水三角洲呈狭长带状展布的滩坝。在上述研究基础上, 建立了湖平面频繁变化时期浅水三角洲和滩坝混合沉积的沉积模式。     

Limnology of nine Westland beech forest lakes

Lakes in the beech (Nothofagus sp.) forest foothills between Greymouth and Hokitika, Westland, are characterised by amber‐coloured waters. Microbiological, biochemical, and chemical analyses of samples from nine such lakes during March 1976 indicate that they are unproductive. Microbial biomass was intensively investigated in heavily stained Lakes Haupiri and Lady and in least‐stained Lake Brunner. A combination of adenosine triphosphate assays, Utermöhl phytoplankton counts, and autoradiographic biomass determinations revealed a greater bacterial than algal biomass in heavily stained lakes, a highly unusual phenomenon which suggests that most of the production of organic matter was allochthonous. Autochthonous productivity was low, probably because biologically available phosphorus was very scarce and because discoloration reduced the transparency of the water. Hypqlimnetic oxygen depletion was slight during this period of maximum thermal stratification; decomposition of organic matter was apparently incomplete. Reactive phosphorus did not increase appreciably in partially deoxygenated hypolimnia. Much of the allochthonous organic matter originating from beech forests and their soils may be partially resistant to biodegradation.     

Stability of an artificially nourished beach,Balaena Bay,Wellington Harbour,New Zealand

Balaena Bay, Wellington Harbour, New Zealand, has a small pocket beach that was covered originally by pebbles and cobbles. In February and October 1982, the beach was nourished with sandy granular gravel, the stability of which was monitored until February 1984. Although isolated from oceanic swell, the new beach readily responded to locally generated wind waves which induced both northwards and southwards longshore drift. The net effect was erosion of the southern beach, aggradation over the central beach, and minor fluctuations at the northern end. Yet despite this mobility nearly all the nourishment sediment was retained in the littoral zone. Beach volumes, calculated for each survey, varied little and sediment distribution patterns revealed negligable transport of nourishment sediment to adjacent beaches and offshore areas. Stability is further confirmed by compositional data which record no preferential loss of the sandstone, argillite, and quartz components. The only compositional changes were the incorporation into the new beach of small (< 10%) quantities of sediment derived from the old beach surface and from biogenic productivity.     

Crustorhabditis chitwoodi sp. nov. (Nematoda: Rhabditidae): An intertidal species from the coast of New South Wales,Australia, with observations on its ecology and life history

A new species, Crustorhabditis chitwoodi, was discovered in nutrient agar plates inoculated with beach sand collected from an ocean beach in New South Wales, Australia. The three other known species of the genus have all been found as commensal inhabitants of ocypodid shore crabs. It is suggested that the sand inoculum was seeded with dauer larvae of the nematode that had been dispersed by scavenging crabs. The new species is distinguished from the three previously described species by possessing a smaller number of differently arranged bursal papillae, eight rather than 10. The species is amphimictic, oviparous, and produces abundant dauer larvae in culture, which can be sustained indefinitely on sea water nutrient agar in which it feeds on associated bacteria.     

Erosion and Accretion of a Placer Mining Beach of SW Indian Coast

The erosion/accretion pattern in a placer mining beach on the southwest Indian coast was monitored for five years to study the role of different driving forces. The beach has maximum width during the fair weather months and least in the rough monsoon months. Apart from hydrodynamic processes, sand mining and presence of sea wall are found to be the driving forces for erosion/accretion. Impact of sand mining is not felt on the beach when the mining is within an optimum level, equivalent to the natural replenishment. It is concluded that, though sand mining will cause erosion in the innershelf, the time taken for a measurable impact can be long if the mining volumes are much less than the annual volume changes.     

Observations of Tsunami Impact on the Coast of Kerala,India

The tsunami generated by the December 2004 Sumatra-Andaman earthquake had a devastating effect on some parts of Kerala coast, which is a coast located in southwest India. Results of post-tsunami field surveys carried out to understand the changes in coastal morphology and sediment characteristics in the worst affected Kayamkulam region of Kerala coast are documented in this study. Analysis of offshore bathymetric data indicates the shifting of depth contours towards shore, indicating erosion of sediments and deepening of innershelf due to the tsunami. Depth measurement along the backwater (T-S canal) in the hinterland region indicates siltation due to the inundation of the canal.     

福建崇武半月湾渔港防波堤建成后下游海滩地形变化及养护对策研究

渔港硬式构筑物如防波堤等对海岸的影响显著。以福建泉州崇武半月湾渔港防波堤修建前后的海滩变化为例,通过对2003²011年不同阶段海滩地貌形态、岸线变化分析以及2个海滩剖面多期监测比较发现,防波堤修建后海湾下游西侧海滩发生显著蚀退,西端侵蚀强度最大,向东(靠近防波堤遮蔽段)逐渐减小,中东部遮蔽段转为淤涨。海滩变化的主要原因:1)E2011年不同阶段海滩地貌形态、岸线变化分析以及2个海滩剖面多期监测比较发现,防波堤修建后海湾下游西侧海滩发生显著蚀退,西端侵蚀强度最大,向东(靠近防波堤遮蔽段)逐渐减小,中东部遮蔽段转为淤涨。海滩变化的主要原因:1)E^SE向主入射波浪受到防波堤的阻挡作用,在堤头发生绕射,港内波影区动力变弱;2)防波堤阻碍了从东向西的沿岸流运动,形成东向为主的沿岸输沙,使得东端发生堆积,造成下游的西侧海岸的沉积物亏损,发生侵蚀。针对海岸变化机理提出了海滩养护防御措施,并通过数值模拟预测说明养护海滩以由西向东输沙为主,年均输沙量约3万m3,堆积于遮蔽段,最后,提出采用周期性抽取遮蔽段养护沙补充到西端的方法来实现海滩循环养护。     

Mining Sand on the Continental Shelf of the Atlantic and Gulf Coasts of the U.S.

Essentially all marine mining along the East and Gulf coasts of the U.S. is for sand used in beach nourishment projects. The current minimal commercial production of sand and aggregate may increase as conventional, on-shore sources become exhausted or are lost to competing land use. Studies published in the late 1990s document a history of nearly 900 individual episodes of beach nourishment having a total cost in excess of $2 × 10⁹ with several hundred million cubic meters of sand placed along over 645 km (400 mi) of shoreline. As exemplified by studies in Florida, prospecting for sand for use in beach nourishment can begin before site specific needs are identified. A full prospecting starts with assimilation of pertinent literature, local knowledge, and an understanding of the geologic and geomorphic settings in which suitable deposits of sand or aggregate occur. High-resolution seismic profiling follows to outline the three dimensional extent of the sand bodies. Finally, vibratory cores are collected to verify the interpretation of the seismic data and to provide samples for geotechnical, especially granulometric, analyses. The actual method of production often is determined by the local availability of different dredge types. Because the mining of marine sands disturbs meaningful areas of the sea floor, environmental concerns must be considered. While it generally is assumed that dredged areas will be left barren, it is possible to assess the likely rate of recolonization. The disruption of bottom habitat also can affect feeding and spawning areas for fishes and other organisms. Alteration in local currents and wave transformation processes need to be modeled and their consequences assessed.     

Spatial and temporal variability of seawater properties,current velocity and SPM concentration off Cassino Beach-Rio Grande-Southern Brazil

Water column profiles and near-bed time series of pressure, current velocity, suspended-particulate matter (SPM) concentration and seawater temperature and salinity were collected during three short cruises carried out in May 2005 in the shoreface and inner shelf area adjacent to Cassino Beach, southern Brazil. The measurements were part of the Cassino Experiment, a project conducted at an open, sandy coastal area known for the occurrence of patches of fairly large amounts of muddy sediments that are sporadically fluidized, transported onshore and eventually stranded on the beach. The study area is close to the Patos Lagoon mouth, being influenced by its water and suspended-sediment discharge. The presence of the Patos Lagoon outflow on the inner shelf was detected in one of the cruises (May 13) through measurements of near-surface salinity: while close to shore salinity was 29.4, a minimum value of 13.8 was measured at ∼10 km from the coast. Four days later, no trace of the plume was detected in the area. Regarding seawater temperature, no large temporal or spatial variability was documented with measured values ranging from 19.3 to 20 °C. Water column currents were prominently to N and NE, except at the outermost station, located ∼42 km from the coast, where NW-directed flows were observed at surface and mid-depth. Maximum near-bed current velocity oscillated between 18 and 42 cm s⁻¹ in the east–west direction and between 14 and 42 cm s⁻¹ in the north–south direction. Near-surface concentration of SPM oscillated between 11 and 99 mg L⁻¹, in general one order of magnitude lower than near-bed values. However, near-bed concentration of SPM showed large spatial variability: the highest value (2200 mg L⁻¹) was yielded by a water sample collected at ∼8 m water depth, at a station located ∼2 km away from the shoreline; two water samples collected 500 m, apart from this station, yielded SPM concentrations of 148 and 205 mg L⁻¹, one order of magnitude lower. Spectral analyses of near-bed current speed and SPM concentration indicate the relevance of oscillations in the low-frequency (<0.05 Hz) range. Detailed sampling of bottom sediment indicated that in May 2005 the mud patch was centered at ∼8.5 m water depth.