Statistical Analysis of Dispersion and Geochemical Patterns of Sedimentary System...
409
tocene Wlirm Glaciation, as evidenced by the intertidal shells with a radiocarbon age of 15-20 Ka B.P. (Yan and Jin 1985). The finer parts of the sediments
are mainly modern terrigenous origin, mixed in from region A.
In this region the spatial variation in geochemical composition does not coincide with the variation in grain-size features. The geochemical regionalization includes regions III!> III z , and sandwiched region Il3 (Fig.6). Boundaries
of the regions are subparallel to the coastline. Region III is characterized by
predominant class 3 sediments, and differs from region II by higher CaC0 3
and lower SiOz. The geochemical composition of these relict sediments may
be controlled by the sedimentary environment of their formation. For example, regions IIII and III z might represent the neritic zone during the climax of
the Wurm Glaciation and some later glaciation, respectively. The lowest
coastline of the Wurm Glaciation is suggested to be the underwater terrace at
130-155 m present water depth (Yang and Jin 1985).
3. An ancient delta is exposed at the seabed about 50 km southwest of the Zhujiang River Mouth (region D-l in Fig. 5, also region III in Fig. 6). It is a small
area of 160 km long and 50 km wide southwest of the Zhujiang River mouth.
There exist all types of grain-size, with type III coarse-sediments dominating.
Geochemically these sediments are SiOz-enriched class 4. We interpret these
as ancient deltaic sediments, similar to the Lower Holocene encountered by
drilling in the Zhujiang River delta. These relict sediments have been protected from modern terrigenous sedimentation by an upwelling current in the
area (Huang and Huang 1985).A similar environment is found in a very small
area near the coast SW ofYangjiang (region D-2), and is also observed along
the 50-km -long, SE-striking underwater extension of the Zhujiang River (Region D-3), indicating an uncovered ancient river channel.
4. A modern high-energy sedimentation environment is characterized by subtype IIl-l well-sorted medium-coarse sand. There are two districts of such an
environment: The shelf break sedimentation zone (region C-l in Fig. 5, also
part of region IIl z in Fig. 6), where sediments are calcareous class 3. The finger delta of the Qiongzhou Strait and the underwater extension of the sand
beach east of the Hainan Island (Region C-2 in Fig. 5, also region lIz and part
of Il3 in Fig. 6), where sediments are relatively siliceous class 4.
7
Dominant Directions of Sediment Dispersion
To determine the predominant direction of sediment dispersion, the method of
the one-tail Z test proposed by McLaren and Bowles (1985) was adopted. For
n(n-l) pairs of n specimens in a possible direction of dispersion, the parameters
of grain-size distribution are compared. Denoting the mean size decrease as F,
increase as C; standard deviation increase as P, decrease as B, and skewness increase as +, decrease as -, then for each pair of sediment samples there are eight
possible events FB-, FB+, FP-, FP+, CB-, CB+, CP-, and CP+. Based on stochastic modeling, only FB- and CB+ are indicative for transportation direction. FB-
409
tocene Wlirm Glaciation, as evidenced by the intertidal shells with a radiocarbon age of 15-20 Ka B.P. (Yan and Jin 1985). The finer parts of the sediments
are mainly modern terrigenous origin, mixed in from region A.
In this region the spatial variation in geochemical composition does not coincide with the variation in grain-size features. The geochemical regionalization includes regions III!> III z , and sandwiched region Il3 (Fig.6). Boundaries
of the regions are subparallel to the coastline. Region III is characterized by
predominant class 3 sediments, and differs from region II by higher CaC0 3
and lower SiOz. The geochemical composition of these relict sediments may
be controlled by the sedimentary environment of their formation. For example, regions IIII and III z might represent the neritic zone during the climax of
the Wurm Glaciation and some later glaciation, respectively. The lowest
coastline of the Wurm Glaciation is suggested to be the underwater terrace at
130-155 m present water depth (Yang and Jin 1985).
3. An ancient delta is exposed at the seabed about 50 km southwest of the Zhujiang River Mouth (region D-l in Fig. 5, also region III in Fig. 6). It is a small
area of 160 km long and 50 km wide southwest of the Zhujiang River mouth.
There exist all types of grain-size, with type III coarse-sediments dominating.
Geochemically these sediments are SiOz-enriched class 4. We interpret these
as ancient deltaic sediments, similar to the Lower Holocene encountered by
drilling in the Zhujiang River delta. These relict sediments have been protected from modern terrigenous sedimentation by an upwelling current in the
area (Huang and Huang 1985).A similar environment is found in a very small
area near the coast SW ofYangjiang (region D-2), and is also observed along
the 50-km -long, SE-striking underwater extension of the Zhujiang River (Region D-3), indicating an uncovered ancient river channel.
4. A modern high-energy sedimentation environment is characterized by subtype IIl-l well-sorted medium-coarse sand. There are two districts of such an
environment: The shelf break sedimentation zone (region C-l in Fig. 5, also
part of region IIl z in Fig. 6), where sediments are calcareous class 3. The finger delta of the Qiongzhou Strait and the underwater extension of the sand
beach east of the Hainan Island (Region C-2 in Fig. 5, also region lIz and part
of Il3 in Fig. 6), where sediments are relatively siliceous class 4.
7
Dominant Directions of Sediment Dispersion
To determine the predominant direction of sediment dispersion, the method of
the one-tail Z test proposed by McLaren and Bowles (1985) was adopted. For
n(n-l) pairs of n specimens in a possible direction of dispersion, the parameters
of grain-size distribution are compared. Denoting the mean size decrease as F,
increase as C; standard deviation increase as P, decrease as B, and skewness increase as +, decrease as -, then for each pair of sediment samples there are eight
possible events FB-, FB+, FP-, FP+, CB-, CB+, CP-, and CP+. Based on stochastic modeling, only FB- and CB+ are indicative for transportation direction. FB-