Hard Mud Research Articles

Stratigraphic sequence and episodes of the ancient Huanghe Delta along the southwestern Bohai Bay since the LGM

Abstract The sedimentary evolution of the ancient Huanghe (Yellow River) Delta in China is not well documented due to frequent river-avulsions and limited deep cores. In this paper, 22 cores with lengths of > 20 m at the coastal plain along the southwestern Bohai Bay were used. The sedimentary facies were determined by grain size and microfossil analysis, and Carbon-14 dating. The strata in the study area since the Last Glacial Maximum (LGM) are divided into lowstand system tract (LST), transgressive system tract (TST), highstand system tract (HST), and retrograding system tract (RST). The LST, which formed during the LGM to 10.8 ka BP, consists of hard mud layer, and overlying interfluvial lowland and flood plain deposits. The TST that formed during 10.8–8.5 ka BP, mainly include coastal marsh, onshore sand bars, and filled incised valleys. The HST that formed during 8.5–2.6 ka BP mainly includes flood plain, river channel, delta front, mouth bar and prodelta. The RST that formed after 2.6 ka BP mainly includes crevasse splay, interfluvial lowlands and distributary channel. About eight episodes of the ancient Huanghe (delta) are observed during the Holocene and the names of the deltas are given by corresponding location names of cheniers: (1) during 10.8–8.5 ka BP, around YS3 and NP1 cores, without formation of cheniers during the transgression, (2) during 8.5–7.4 ka BP, around YS1, YS4 and NP3 cores, the Dongsun-Shuiyicheng delta, (3) during 7.4–6.1 ka BP, around CK1 core, the Mashanzi delta, (4) during 6.9–5.7 ka BP, around GZ3 core, the Miaozhuang-zhaizhuang delta, (5) during 4.6–3.5 ka BP, around YS4 core, the Wuditai delta, (6) during 3.0–2.6 ka BP, around HH4 and HH1 cores, the Qikou delta, (7) during 2.6–1.9 ka BP, around YS7 and NP1 cores, the Nanpaihe delta, and (8) during 1034 BC–1099 BC, around Wangzidao and Dakouhe, the Wangzidao delta.

Effects of substrate character of Lake Gehu on the growth of <i>Potamogeton crispus</i> and <i>Elodea nattalii</i>

通过模拟试验,研究滆湖3种沉积物(表层湖泥、硬底湖泥、表层覆岸泥)对菹草和伊乐藻生长的影响.结果表明,生长于表层湖泥、硬底湖泥、表层覆岸泥的菹草和伊乐藻生物量分别为4.07、1.98、3.69kg/m²和1.86、1.27、1.74kg/m²,表层湖泥较适合这两种沉水植物生长.3种沉积物对菹草和伊乐藻的干湿比影响显著,硬底湖泥 > 表层湖泥 > 表层覆岸泥.在表层覆岸泥和表层湖泥中,两种沉水植物的叶绿素含量均较高,伊乐藻在不同沉积物中差别最大,叶色区别明显.丙二醛的测定结果进一步表明硬底湖泥不适宜植物生长.试验结果表明菹草和伊乐藻在滆湖不同的沉积物上能够正常生长,表现出良好的适应性,菹草适合在表层湖泥中生长,伊乐藻更适合在表层覆岸泥中生长,通过对滆湖不适宜的底质环境进行改造,以利于沉水植物的生长繁殖,为滆湖生态修复中的基质修复与沉水植被重建提供理论指导.;Using mesocom experiment, this paper studied the effects of three different sediments (surface mud, hard mud and surface mud of bank sediment) of Lake Gehu on the growth of two submerged macrophytes, Potamogeton crispus and Elodea nattalii. When grown on surface mud, hard mud and surface mud of bank sediment, the mean biomass of P. crispus and E. nattalii were 4.07, 1.98, 3.69 kg/m² and 1.86, 1.27, 1.74 kg/m², respectively. All the tested species grown on hard mud had the lowest biomass and shoot height. The wet and dry ratio of P. crispus and E. nattalii was affected significandy by the sediments followed with an order of hard mud > surface mud > surface mud of bank sediment. The contents of chlorophyll-a and chlorophyll-b on the surface mud with bank sediment and surface mud were both higher than those cultured on the hard mud. The difference of leaf colour of E. nattalii between the three sediments was remarkable. The measurement of malondialdehyde further sugested that hard mud was not good for the growth of the two submerged macrophytes. Finally the results showed that the two submerged macrophytes were able to grow normally under conditions of different sediments from Lake Gehu. P. crispus grew well on surfurce mud while E. nattalii was more adapted to surface mud of bank sediment. Sediment rehabilitation should be made in order to facilitate the growth of submerged macrophytes of Lake Gehu and give a guide on sediment rehabilitation and the submerged macrophjrtes restoration of Lake Gehu.

Evo/Devo and the lungfish: the last gasp of intelligent design

Evo/Devo and the lungfish: the last gasp of intelligent design

Seasonal variation in habitat use by salmon, Salmo salar, trout, Salmo trutta and grayling, Thymallus thymallus, in a chalk stream

Abstract A portable multi‐point decoder system deployed in a tributary of the River Itchen, a southern English chalk stream, recorded the habitats used by PIT‐tagged juvenile salmon, Salmo salar L., trout, Salmo trutta L. and grayling, Thymallus thymallus L., with a high degree of spatial and temporal resolution. The fishes’ use of habitat was monitored at 350 locations throughout the stream during September/October 2001 (feeding period) and January/February 2002 (over‐wintering period). Salmon parr tended to occupy water 25–55 cm deep with a velocity between 0.4 and 1.0 m s−1. During both autumn and winter, first year salmon (0+ group) were associated with gravel substrate during the daytime and aquatic weed at night. In autumn, 1+ salmon were strongly associated with hard mud substrates during the day and with marginal tree roots at night. In winter, they were located on gravel substrate by day and gravel and mud at night. Trout were associated with a greater range of habitats than salmon, generally occupying deeper and faster water with increasing age. During the autumn, 0+ trout were located along shallow (5–10 cm) and slow (−0.1–0.4 m s−1) margins of the stream, amongst tree roots by day and on silty substrates at night. During winter the 0+ trout occupied silty substrates at all times. As age increased, trout increasingly used coarse substrates; hard mud, gravel and chalk, and weed at night. All age groups of grayling (0+, 1+ and 2+) tended to occupy hard gravel substrate at all times and used deeper and faster water with increasing age. The 1+ and 2+ groups were generally found in water 40–70 cm deep with a velocity between 0.3 and 0.5 ms−1, whilst the 0+ groups showed a preference for shallower water with reduced velocity at night, particularly in the winter. There were greater differences in the habitats used between species and age groups than between the autumn and winter periods, and the distribution of fish was more strongly influenced by substrate type than water depth or velocity. The results are discussed in relation to the habitat requirements of mixed salmonid populations and habitat management.

Foraging Ecology of the Black-fronted Plover on Saline Lagoons in Australia: the Importance of Receding Water Levels

The conditions that determine habitat suitability for waterbirds on temporary wetlands in Australia are poorly understood. This study describes the foraging behavior of the Black-fronted Plover (Elseyornis melanops) on two shallow saline lagoons with variable water depths. When water levels were receding, areas were left exposed around the periphery of the lagoons, which formed a succession from substrates still covered by water, to wet mud with a surface layer of water, to moist firm mud and eventually to dry, hard mud. The plovers showed a strong preference for feeding in areas of moist, firm mud and their prey capture rates were highest in this substrate type. When water levels rose following rainfall, previously exposed areas were partially flooded and the birds’ prey capture rates fell significantly. Most abandoned the lagoon. The species was thus highly dependent on receding water levels to provide suitable foraging conditions.

Composition and spatial organization of a cold seep community on the South Barbados accretionary prism: Tectonic, geochemical and sedimentary context

Deep faunal assemblages were observed on cold seeps, between 1000 and 2000m depth, along the southern termination of the Barbados accretionary prism, during the Caracolante II and Diapicar cruises. Faunal composition and microdistribution of a cold seep community were analyzed at one site using deep-sea photographs and seismic (3.5 Kz) profiles. The community is dominated by large mussels up to 20cm long (possibly related to the genus Bathymodiolus), tiny vesicomyid clams, and vestimentiferan clusters in which animals are up to 2m long. There is a high density of sponges (three species), bryozoans and gorgonians. Other taxa occasionally associated with this assemblage include galatheid crabs, anemones, holothurians and possibly pennatulaceans which are numerous at boundaries of the site. A typical deep-sea fauna of fish, asteroids and ophiuroids is also scattered about the vicinity. This seep community is distributed as a band of discontinuous colonies, 40–50m in width and more than 10km in length. Living colonies alternate with accumulations shells and bare areas. The substratum is hard mud covered by a ferrugineous crust and cemented by carbonates. The early diagenetic character of the bottom and the occurrence of biological assemblages indicate that seepages of sulphur and/or methane, which have been revealed along the decollement zone of the Barbados prism, must diffuse through the sea floor. These biological and geological features are located on the crests of NE-SW anticlinal ridges and mud volcanoes which have been built by diaprism.

Casing Wear Caused by Tooljoint Hardfacing

Summary Casing wear caused by new tooljoint hardfacings, such as fine-mesh tungsten-carbide hardfacing and a hardfacing covered with a layer of relatively soft material, has been investigated in the laboratory. The tests were performed on a full-scale test facility with field conditions—forces, motions, and fluids—simulated as closely as possible. It was found that the major mechanisms responsible for casing wear by tooljoints are adhesive wear, abrasive wear, and ploughing. Wear mechanisms can be classified as mild, normal, and severe. A thorough understanding of these mechanisms could lead to measures for lessening casing wear. This can be achieved with (1) tooljoints that have a sufficiently large, smooth, round, and uniform surface and (2) an appropriate mud that has a sufficiently high content of soft solid particles, such as barites, to form a layer in the tooljoint/casing contact area so that metal-to-metal contact is avoided and small, hard mud particles are embedded.

Burst Resistance of Pipe Cemented Into the Earth

Abstract A mathematical study has been made of the amount of support a cement sheath could provide to casing cemented into the earth. Several assumptions were required to make the analysis, but only two of them are limiting:the pipe must be completely surrounded with cement, andany mud filter cake between the cement and formation has the same physical properties as either the cement or formation. The calculations showed that little support would be provided to the pipe before an unsupported cement sheath failed in tension; however, when the cement is confined between the pipe and wellbore and is loaded in compression, the pipe could receive a considerable amount of support. In fact, the theoretical results indicate the lower grades and larger sizes of pipe could have their working pressures doubled when reasonable compressive loads were applied to a surrounding cement sheath. These data are shown in six charts. Other down-hole conditions such as setting the cement under pressure, increased temperature and cement confinement all tend to increase the potential usefulness of the sheath. Because of size limitations, a laboratory program to verify the most important results of this mathematical study would be very difficult. However, small-scale field tests would be practicable. This paper shows that, if a solid cement sheath can be obtained in the field by either primary cementing or by repair after detection of flaws by surveys such as the new cement-bond logs, the use of this approach to reducing pipe costs merits further consideration. Introduction A modification in casing design practices is proposed which may either reduce the amount and grade of steel required to contain a specified internal pressure or permit the working pressure to be increased for a specified weight and grade of pipe. One of the more important considerations in casing design is its resistance to collapse; however, Bowers' and, more recently, O'Brien and Goins have shown many casing programs are unnecessarily conservative in this respect, and they have indicated how savings can be made by designing for more realistic down-hole conditions. Earlier, Saye and Richardson showed that pipe costs could be reduced by considering the cement sheath as a part of the casing string when collapse resistance was being calculated. More recently, Rogers has raised the question as to whether a cement sheath might be considered in the design for burst resistance of the cemented casing. Calculations have been made for the increased burst resistance a cement sheath would provide for casing in a wellbore, and the results show that a sizable amount of support could be obtained in some instances. These data are presented in addition to a discussion of several other factors that are considered to affect the burst strength of pipe supported by cement. Two types of support are treated: Case I for tensile loading of the unconfined cement sheath, and Case II for compressive loading of the confined cement sheath. ANALYTICAL TREATMENT AND RESULTS CASE I-TENSILE STRESSES IN AN UNCONFINED CEMENT SHEATH Conditions like this would most likely occur in a greatly enlarged portion of the hole where the cement was not in immediate contact with either the formation or a thin and hard mud cake. The mathematical analysis for this condition, as shown in the Appendix, rests on the following concepts. Pressure inside a unit length of pipe causes:a tensile or tangential stress to be exerted over the longitudinal cross-sectional areas of the pipe and cement; andan equal amount of strain in both the pipe and cement that is uniformly distributed over the wall thickness of each. This analysis was then used to make several calculations for a cement sheath around 5 1/2-in. OD pipe. The results are illustrated in Fig. 1, which shows that a tensile stress of 500 psi is imposed on a 5-in. thick sheath when the casing contains a pressure of only 1,450 psi. It also shows that a 10-in. thick sheath would be stressed to 500 psi in tension when the pipe contained a pressure of only 2,350 psi. Alternatively, if the stress analysis is made by means of the Lame thick-wall cylinder theory, the inner fibers of the 10-in. thick sheath will be stressed to 500 psi in tension when the pressure in the pipe is only 990 psi. This, of course, reveals that an unconfined sheath is of little support to the pipe in burst; however, an entirely different result is obtained when the cement is confined between the pipe and formation. JPT P. 1033^

Swarming of Nereis succinea (Leuckart) off the east coast of Canada.

IN June 1952 the crew of a fisheries patrol boat cruising in Miramichi Bay, New Brunswick, observed what they took for a sand-bar in an unexpected situation. On closer inspection they found that there was no such bar, but that the surface of the sea over a wide area was in a state of violent turmoil (“a sort of boiling”) due to the presence of enormous numbers of polychaetes. The area covered was some 150 yards in radius and was broken up into several minor patches. The largest one, from which they took a sample of the polychaetes, was estimated to be 75 ft. long and 15 ft. wide, and the polychaetes seemed to extend to about 2 ft. deep. The tide was low at the time and the depth of the water about 7 ft. The bottom consisted of hard mud. The observation was made on a fine, warm day.