Fig. 1

Regional map of the study area (a) and topographic features and workload distribution of the study area (b)"

Tab. 1

Main parameters of the geophysical surveying system"

Fig. 2

Vertical distribution of marine sand-gravel body and research methods used in the study area. The blue mark represents the extent to which stratigraphic information was obtained by the study method. SCH: single-channel seismic; SBP: sub-bottom profiler; SSS: side-scan sonar; SBES: single-beam echo-sounder; G: grab sampling; and D: geological drilling. The penetration thickness of the sub-bottom profile to sand and gravel is less than 10 m. The surface sand-gravel body is divided into upper and lower parts"

Fig. 3

Topographic features in the study area revealed by typical depth profiles. The red line indicates water depth changes of the survey lines A-A′, B-B′, and C-C′, and the locations of the survey lines are shown in Fig. 1b"

Fig. 4

Side-scan sonar revealing seafloor geomorphic features. (a) shows the distribution of survey lines in the study area; (b), (c), and (e) reveal the strike of sand wave ridges; (d) reveals the flat seabed topography in the middle of the study area; (f) reveals the intersecting seafloor trawling marks; and (g) reveals the sand ripples superposed on the sand waves"

Fig. 5

Sub-bottom profile revealing the characteristics of thick argillaceous overlying strata and the distribution of the surface sand-gravel body. (a) shows the distribution of thick argillaceous overlying strata, (b) indicates the gradual interchange between thick argillaceous overlying strata and the surface sand-gravel body, (c) displays the characteristics of the surface sand-gravel body near submarine sand ridge, and (d) gives the characteristics and variation of thick argillaceous overlying strata"

Fig. 6

Characteristics of surface and buried sand-gravel bodies. (a) shows seismic response characteristics of the sand-gravel body revealed by single-channel seismic profile. U1~U4 are identified seismic sequence units. R0~R3 are the main seismic reflection interfaces. (b) is a drawing of (a), revealing the surface sand-gravel body (corresponding to U1), buried sand-gravel body (U3) and mud body (U2 and U4). There are also areas in the buried sand bodies that are not suitable for the occurrence of sand bodies. The blue dashed line is the sand-mud interface (corresponding to R1~R3), and the black dashed line is the interface between the upper (U1-1) and lower (U1-2) surface sand-gravel bodies. (c) Sub-bottom profiles reveal the characteristics of the upper surface sand body, which is a supplement to the seismic characteristics of the surface sand body in the single-channel seismic profile"

Tab. 2

Seismic sequence unit division and seismic response characteristics of marine sand body"

Fig. 7

Sand and gravel content ratio and sand body location distribution of the three boreholes along the survey line G—G′. (a), (b), and (c) are the data of cores ZK1, ZK2, and ZK3, respectively. The black dots are the sampling points and test results, and the red lines are the connecting lines of the test results. The yellow shading block is the stratigraphic position of the sand body; and the white block is the stratigraphic position of argillaceous bodies"

Fig. 8

Comparison of sand body stratigraphic position revealed by borehole and sand body identified by single-channel seismic. The dark yellow block is the sand and gravel layer revealed by the borehole. The light yellow block and the gray block are the sand-gravel body and argillaceous body identified by single-channel seismic respectively. R0~R3 are the main seismic reflection interface"

Fig. 9

Occurrence mode of submarine sand body in the study area"

Tab. 3

Geophysical characteristics and favorable occurrence signs of marine sand bodies in the study area"