Experimental Study on Landslides of Loose Sediment Slope Induced by Stream Bed Incision

Uplift of the Qinghai-Tibetan Plateau has resulted in rapid incision of rivers along the margin of the plateau. Landslides occur frequently as a consequence of increasing bank slope and potential landslide energy due to stream bed incision or lateral bank erosion on the concave banks at bends. The Fencha Gully is on the eastern margin of the Qinghai-Tibetan Plateau and is developing on a huge landslide body. Flume experiments were conducted on the base of the field investigation to study the mechanism of landslides induced by stream bed incision. The experiments were designed with a length scale ratio of 1:20. Landslides and stream bed incision with loose sediment were observed and analyzed. The results show that landslides are induced as a result of stream bed incision. The potential landslide energy is defined, which increases quickly with an effective incision depth coupling vertical incision and lateral bank erosion. The occurrence of landslides can be attributed to increasing incision depth and potential landslide energy. Results indicate that the critical effective incision depth is 4.0–6.0 m. A critical value of the potential landslide energy is found from the experiments. Landslides occur if the potential energy exceeds the critical energy, which is 2.24×104 t·m/s2 for the Fencha Gully. The incision depth and potential energy of landslides from the Fencha Gully agree well with the results.

Foraminifera On The Beach Of Malalayang Dua

Beach as one on the landform that reflects the work of hydro-oceanographic factors, generally in the form of loose sedimentary material. Loose sediment is a collection of organic and inorganic particles that accumulate widely and are irregular in shape. One example of organism in marine waters that contributes to the availability of organic particles in the beach landform is foraminifera. Foraminifera is a single-celled organism that has the ability to form shells from substances of CaCO3 which originate from itself or from the surrounding environment. This study was aimed to classify physical sediments on the Malalayang Dua beach according to the points of sediment sampling, and see how the composition of foraminifera in the beach area and analyze the presence of foraminifera in relation to the granulometry of beach sediments. From the result of the study, it is found that the composition of grain size of sediment on the beach of Malalayang Dua is different, in stasion 1A, 1B, 2A, and 2B the sediment were mostly composed by fine grains while in station 3A and 3B were of coarse-grained sediment. A number of a species of foraminifera (dead test) was found in the study, and the number of tests was highes in fine sediments compared to coarse sediment.Keywords : Beach Landform, Malalayang Dua Coast, Foraminifera ABSTRAKGisik sebagai salah satu bentuklahan yang merefleksikan kerja faktor-faktor hidro-oseanografi, umumnya berwujud material sedimen lepas. Sedimen lepas adalah kumpulan partikel organik dan anorganik yang terakumulasi secara luas dan bentuknya tidak beraturan. Salah satu organisme di perairan laut yang berkontribusi terhadap ketersediaan partikel organik di gisik adalah foraminifera. Foraminifera merupakan organisme bersel tunggal yang mempunyai kemampuan membentuk cangkang dari zat-zat CaCO3yang berasal dari dirinya sendiri atau dari lingkungan sekitarnya. Penelitian ini bertujuan untuk mengelompokkan sedimen gisik di pantai Malalayang Dua menurut titik-titik pengambilan sampel sedimen, dan melihat bagaimana komposisi foraminifera di kawasan gisik serta menganalisis keberadaan foraminifera dalam kaitannya dengan granulometri sedimen gisik. Dari hasil penelitian komposisi ukuran butir sedimen pada lahan gisik di pantai Malalayang Dua berbeda menurut stasiun yang ditetapkan, di ruang pantai ke arah Timur yaitu stasiun 1A, 1B, 2A, 2B komposisi sedimennya berukuran halus, sedangkan di ruang pantai ke arah Barat yaitu stasiun 3A dan 3B komposisi sedimennya berukuran kasar, komposisi sedimen di setiap stasiun gisik litoral dan sublitoral menampilkan adanya perbedaan tingkat kekasaran partikel sedimen. Dari hasil penelitian ditemukan 9 cangkang foraminifera. Pada komposisi sedimen gisik yang berukuran halus ditemukan jumlah cangkang foraminifera yang lebih banyak dibandingkan dengan gisik yang komposisi sedimen berukuran kasar.Kata kunci : Lahan Gisik, Pantai Malalalayang Dua, Foraminifera

Experimental Measurements of Forces on Loose Particle in Motion Over Rough Bed Under Waves Using Oblique Particle Image Velocimetry

Magnitude and phase of major forces that act on a loose non-cohesive particle (sediment) on single layer fixed rough bed (longitudinal slope 2%) were determined from experiments in a laboratory flume under waves. The loose particles were glass spheres of diameter 1.58 ± 0.1 mm and specific gravity 2.5. The range of wave-height-to-water-depth (H/h) ratio in the experiments was 0.366 < H/h < 0.521. The measurement plane was parallel to the bed and located at a height of ½ loose particle diameter (ds) above the rough bed. Grayscale morphological image processing methods were used to separate the fluid and loose sediment phases from the same oblique particle image velocimetry (OPIV) image based on their signature sizes. The OPIV calibration method is presented and validated with conventional particle image velocimetry (PIV) method. Loose particle velocity and accelerations along with the associated fluid velocity and fluid total accelerations in the wave direction were determined simultaneously by processing OPIV used to compute magnitude and phase of major forces that act on the loose sediment particle. It was observed that for same wave period (T), an increase in H/h ratio has a dominant effect on sediment displacements onshore. The phase along with magnitude of the major driving force (drag and fluid accelerations) plays an important role at initiation of loose sediment from its rest position. It is suspected that the loose particle overcomes a critical bed friction force with higher H/h ratio as magnitude of drag force is higher. The resultant force then displaces the sediment onshore which experiences sliding and or rolling motions very close to bed, in a thin fluid layer over maximum protrusion of bed sediments. At the instance, the gravitational force plus bed frictions overcomes the lift force the loose particle attains a new position onshore.

Metallogenetic Model of Bauxite Deposit in WZD Area, Northern Guizhou, China

Through the research on field macrofeature and microscopic feature we found that forming process of the WZD bauxite have experienced three stages: at first, Hanjiadian formation and Huanglong formation take lateritization generate laterite, laterite is the precursor of the bauxite; In the second, laterite has been transported and deposited in WZD area; At last, loose sediment outcrops accompanying regression, and then accept eluviation, in the process of eluviation disadvantage elements as iron and silica have a great scale of runoff, aluminum has the least loss result in the forming process of high grade bauxite.

Physicochemistry and Vegetation of Piccaninnie Ponds, a Coastal Aquifer-fed Pond in South-eastern South Australia

The aquatic vegetation and physicochemistry of Piccaninnie Ponds are described and recent annual losses of aquatic vegetation investigated. The aquifer-derived waters of the Ponds are characterized by their clarity, low nutrient content, low salinity, and lack of thermal and chemical stratification. In 1985, large areas of aquatic vegetation within the Ponds degraded and were lost. Subsequent faster regeneration of denuded areas by Ruppia polycarpa resulted in the displacement of Lepilaena cylindrocarpa. The annual uprooting of R. polycarpa, which has occurred since, results from Ruppia's comparatively poorer anchorage capacity in the loose sediment floc. Gradual expansion of L. cylindrocarpa into freshly uprooted regions restricts the regrowth of R. polycarpa and hence the area susceptible to denudation in the following year. It is expected that the displacement of R. polycarpa will continue until only small isolated stands remain, which will be prevented from uprooting by the root matrix of surrounding vegetation.

The role of marine cementation in the preservation of Lower Palaeozoic assemblages

Many workers have emphasized recently the taphonomic processes involved in the preservation of fossil assemblages, and some have doubted that invertebrate assemblages have ever been preserved that reflect closely the living community. Yet there are many examples in the literature in which invertebrate assemblages have been interpreted in just such a fashion. Many of the most confident reconstructions have been based upon assemblages in early Palaeozoic limestones. What was it about some early Palaeozoic environments that led at times to such exquisite preservation? Carbonate petrologists have stressed the importance of marine cements in some modern environments (especially reefs). Our observations in Ordovician shelf carbonates suggest that such marine cementation may have been more common in a wider range of environments in the early Palaeozoic. The reason was a sufficiently different marine water chemistry at that time. Marine cementation effects accumulating biotic assemblages in three ways: (i) the formation of true hardgrounds with establishment of a specialized biota on the completely lithified surface; (ii) production of peculiar ‘mixed’ assemblages by incremental, patchy hardground formation during accumulation leading to a mixture of encrusting forms in the same bed as loose-sediment forms; and (iii) preservation of fossils in life position, or retardation of transportation and mixing, caused by early immobilization of skeletons by cement fringes. Our thesis is that early Palaeozoic carbonate shelf communities are better preserved than those of other environments and other times because the fossils were more often ‘locked’ in place by very early, marine cements.