Eason Hong

Mechanisms Influencing the Spatial Distribution of Trace Metals in Surficial Sediments off the South-Western Taiwan

Abstract Surficial sediments collected from the south-western coast off Taiwan were determined for the grain size, organic carbon contents (OC), carbonate and leachable trace metals (Co, Cu, Fe, Mn, Ni, Pb and Zn). The sediments in the study area were mostly the very fine sands (0.125–0.0625 mm, φ =3–4). However, muds (0.0625–0.0156 mm, φ =4–6) were observed in the trough area located in the south of the Waisanding Barrier Island. Concentration ranges of organic carbon, carbonate and leachable trace metals in the sediments were: OC, 0.06–0.49% (mean, 0.2%); carbonate, 1.48.6–3.68% (2.23%); Fe, 0.41–1.52% (0.85%); Co, 4.6–18.2 mg/kg (8.9 mg/kg); Cu, 0.4–16.7 mg/kg (4.39 mg/kg); Mn, 186–625 mg/kg (338 mg/kg); Ni, 2.1–10.2 mg/kg; Pb, 0.73–21.8 mg/kg (6.8 mg/kg) and Zn, 3.6–56.4 mg/kg (22.1 mg/kg). Normalization technique and comparison with the results obtained in other marine environment around Taiwan are used to assess the contaminated status of the study area. The results suggest that the sediment of the south-western coast off Taiwan has not been contaminated by trace metals. The distribution patterns of trace metals and OC are fairly similar, and oppositely correlated with that of sediment mean grain-size. That is the finer the sediment, the higher the concentrations of trace metals and OC. Moreover, higher concentrations of trace metals and OC were found in the trough located in the south of the Waisanding Barrier Island while lower values were in the near-shore area. The sediment grain size is probably the most crucial parameter which controls the spatial distribution of trace metals, except Mn, in the south-western coast off Taiwan. Although, the maximum contour of Mn also occurs in the trough, the concentration of Mn does not correlate well with the sediment grain size. In contrast, concentration of Mn significantly correlates with the carbonate, which may suggest that Mn is adsorbed or co-precipitated with the calcium carbonate and forms rhodochrosite-calcite (MnCO3–CaCO3) in the water column.

Echo characters and sedimentary processes along a rifting continental margin, northeast of Taiwan

The northeastern o!shore of Taiwan, including the southern-most East China Sea continental margin, Ilan Shelf, Ilan Ridge and the western tip of the Okinawa Trough, is characterized by active rifting and an energetically complex hydrodynamic #ow regime. In this study, sedimentary processes on the sea #oor were inferred from regional mapping of 3.5 kHz echo characters. Eight distinct echo types were mapped, and based on echo type distribution, analysis of sediments and regional bathymetry, these were interpreted as deposits that had been formed under the in#uence of various local hydrodynamic processes. Di!erent sedimentary processes, interpreted from the lithology and distribution pattern of sediments, were found to prevail on di!erent physiographic provinces. In the southern East China Sea continental shelf margin, it is the out#ow of Taiwan Strait Water and the on-shelf intrusion, upwelling and countercurrent induced by the impinging and turning of the Kuroshio Current that largely determine the distribution of sediments. On the narrow Ilan continental shelf, the deposition is mainly in#uenced by subaqueous deltaic and shallow marine processes. Over the rifting tip of the Okinawa Trough, including the Okinawa Trough Basin and its nearby slopes, the primary sea#oor-shaping agents have been the mass-wasting processes and turbidity currents. Since the observed sediment data is in good consistency with other hydrographic data, the studies of transportation and deposition patterns of sediment can provide good constraints for the interpretation of physical oceanographic data. ( 2000 Elsevier Science Ltd. All rights reserved.

Evolution of Pliocene to Pleistocene sedimentary environments in an arc-continent collision zone: Evidence from the analyses of lithofacies and ichnofacies in the southwestern foothills of Taiwan

Abstract Lithofacies and ichnofacies analyses reveal an excellent example of gradually subsiding and rapid infilling and uplifting of the sedimentary basin in the southwestern foothills of Taiwan, along the strike of the active Plio-Pleistocene orogeny. Ten well-exposed sections, roughly evenly distributed along a southwestern transect, were studied to construct the three-dimensional distribution of lithofacies and ichnofacies. Basin evolution is discussed in terms of temporal and spatial facies variations. In early Pliocene time, the shallow marine facies of the northern part of the study area were deposited on the passive Eurasian continental shelf. The sedimentary basin was deeper in the south, with a lower slope and/or basin floor setting. The ongoing arc-continent collision caused flexural bending of the crust, inducing gradual subsidence of the basin during Pliocene and early Pleistocene time. Around 0.98 Ma, the onset of more rapid orogenic movements accelerated the basin subsidence, as indicated by rapid deepening of the facies northward along the basin axis, as well as by the widespread development of mass-gravity transportation deposits and channel cutting structures. However, the basin was soon infilled and uplifted as part of the orogen within 0.8 my. Basin subsidence is much greater than previously indicated.

The Influence of the Beach Environment on the Digging Success and Nest Site Distribution of the Green Turtle, Chelonia mydas, on Wan-an Island, Penghu Archipelago, Taiwan

Abstract Wan-an Island is one of the most stable green sea turtle nesting sites in Taiwan. Each of the 11 beaches is characterized by various width, slope, grain size, and vegetation coverage. The digging success of the gravid female turtles on this island varies a great deal, and the average value is not high. Many investigations have demonstrated that the nest environment can influence the nest site distribution. The major environmental factors include: substratum compactness, vegetation coverage, grain size, and porewater content. Results of this study indicated that the substratum compactness is directly or indirectly influenced by other factors. This, in turn, would affect the digging success directly. The vegetation coverage can not only influence the substratum compactness but may act as an inducing factor for digging. As a result, the substratum compactness and vegetation coverage may be the most important environmental factors that influence the nest site distribution on Wan-an Island. The different combinations of various environmental factors might result in the high variation in digging success. Based on the result of this study, a hypothesis of nesting behavior of the green turtle on Wan-an Island is proposed. This is the first study ever that has demonstrated quantitatively the influence of beach characteristics on the nest site selection of the green sea turtles.

Schaubcylindrichnus formosus isp. nov. in Miocene Sandstones from Northeastern Taiwan

Sheaves of smooth, thickly lined, vertically curved burrows occur abundantly in certain Tertiary strata in northern Taiwan. The burrows belong to the ichnogenus Schaubcylindrichnus, and they show several characteristics distinguishing them from previously established ichnospecies of this genus. The typical form in Taiwan is a sheaf converging into a crossing point in the lower part. This form is clearly different from the congruent sheaves and the loose bundles described for S. coronus and S. freyi, respectively. The observed Schaubcylindrichnus are significantly larger than other ichnospecies. The wide regional and stratigraphic spread of the ichnogenus Schaubcylindrichnus, together with the facies distribution ranging from shallow water to deep water settings and the distinct variation in morphology and size of the trace fossils motivate the proposition of a new species name, Schaubcylindrichnus formosus. The deposit feeder behavior proposed for other forms of Schaubcylindrichnus seems unlikely because of the successive, spreite-like overlap of burrows in the lower part of the system that would mean a repetitive exploitation of the same substrate. Schaubcylindrichnus formosus is interpreted as the work of a filter feeding worm living in offshore bar and shoreface environments.

Geomorphic evolution of a barrier island reflects the history of natural sediment supply and human intervention in Taiwan.

Abstract We report on the integration of subaerial and subaqueous surveys, on the basis of, respectively, SPOT satellite images and data acquired from a combined side-scan and profiler sonar system, of a barrier island on the west-central coast of Taiwan. Our results establish a case study of a natural barrier island (i) the morphology and position of which have been dramatically affected by human alteration of a sediment-supplying river during the 200-year interval 1790–1990, but (ii) whose partial destruction and migration have been mitigated significantly in recent years by a combination of tectonic and climatic events. These events have been shown elsewhere to have increased riverborne supply of sediment to the Taiwan coast, and we propose that this development, in turn, contributed to the observed stabilization of the barrier island in size and location.