PETROLOGICAL CHARACTERISTICS OF SEDIMENTS IN SEA AREA BETWEEN DAGONG-ZHAITANG ISLANDS, SHANDOVIG PROVIVICE

Abstract: A systematic petrological research has been made on nearshore surficial sedi-ments(the mazimum depth is 30m)of southern Shandong Peninsula(the area is located between the mouth of liaozhou Bay- and Rizhao County).The nearshore surficial sedimentsare divided into three sedimentary regions as follows,Recent coastal sedimentary region:This is distributed within the depth of 10-15m，and presents a striped form parallel to the coastline.The sediments are mainly sand. muddy silt and sand-silt-mud.Their granulometric parameters vary within a large range because of the、一arious types of sediments.T he sediments are rich in feldspar, but owing to the difference of the characters of coastal source rock，the Q/F ratio is less than 1 in the south and 1一3 in the north.The content of nemetamorphic quartz is more in the south and less in the north.The mean round-ss of quartz of coarse sand grain is 0.29(according to Power standard)，so it is subangular.almost all the sediments consist of terrigenous materials, with a little-organic and authigenic components.Common organisms are Forominifera and Pelecypoda.Recent shelf sedimentary- region:This is located at the northeast of the studied area, where the water depth is more than 15 m.The sediments are principally sand-silt-mud and muddy- silt(Mz=6.38-7.59Φ)，for hydrodynamic effect is weak.Since there is not only one source, the sediments are very poorly sorted(σ₁=2.70-3.-12).After CaCo₃ being removed, sorting coefficient rises, but ii is still greaterthan 2 .It is positively skew and its kurtosis smooth.In> 0.063mm fraction,Q, F ratio is high(4-8).The content of metamorphic polycrystalline quartz is medium, less than 10% at bathvmetric line of about 20 m，and it increases outward to 10-20% T he roundness of coarse sand fraction(Ms=0.30) is higher than that of recent coastal sedimentary region.Basically, there is little glauconite and calca-reous concretion,but organic content is higher than that in the coastal region, com-monly 5-10% in sand fraction.Foraminifera is major organism and its principal species is Ammonia compressiuscula.residual sedimentary region:This is situated in the south of the studied area, where water depth is more than 10-15 m.The sediments(except calcareous concretion)are conglomeratic sand and san(Mz=0.98-3.51Φ).Granulometric parameters are extremely abnormal, such as very poor sorting(σ₁=3.98-4.78)，positive or extre-mely positive skewness(SK=0.15-0.39)and commonly abnormal kurtosis.The types of sediment compositions are conglomeratic arkose and arkose(Q, F<2).The con-tent of metamorphic polycrystalline quartz is rather high near the shore，but drops rapidly outward to less than 10%.The roundness of quartz is high, belonging to subrounded class(Mρ = 0.34)，much higher than that in the other two regions.The content of iron-staining quartz of tile region is also high(> 40%).The sedimen-ts of this region are rich in calcareous concretion which belongs to terrigenous authigenic component, so the content of CaC03 is commonly higher than 12%.The content of glauconite is also much higher than that in the other two regions.Organ-ic association is characterized by the appearance of oyster-bryozoa and contains Candoniella sp.The textures of sediments in recent coastal and shelf sedimentary regions are is equilibrium with the water depth where they are.Palimpsest sediments are origin-ally of intertidal zone-coastal facies, and were formed 30,000 yrs B.P.They ex-perienced reformation in a continental envionment because of regression.Calcareous concretions were formed during this period(¹⁴C dating is 17,870±260 yr).They were not submerged until the Holocene transgression and they have received little sediments since then。