Sinian system in Xuzhou area, northern Jiangsu Province

Figure 5-2 is the comprehensive stratigraphic histogram of Sinian system in northern Jiangsu. Jiayuan Formation (Z2jy), Zhaowei Formation (Z2zw) and Niyuan Formation (Z2ny) are based on Zhaowei section. Jiudingshan Formation (Z2jd), Zhang Qu Formation (Z2zq) and Wiki Formation (Z2wj) are based on the section of Wiki White Mountain. The profiles are all measured, and the scales of the profiles are different. Wiki group is 1:2000, which is convenient for discussing the relationship between Shi Jia group and Wiki group. See ③, ①, ⑨ and ⑩ in Figure 5- 1 for the profile position.

Figure 5-2 Zhaowei-Wiki Profile in Tongshan County, Jiangsu Province (Measured) (Catastrophe Event and Sequence)

Jiayuan Formation (Z2jy) and Zhaowei Formation 1 and Member 2 (Z2zw 1, Z2zw2) are micrite limestone containing quartz sand, which is characterized by a series of superimposed waterways and constitutes the TST on the profile. Jiayuan Formation and the second member of 1 and Zhaowei Formation are seismites, and the surrounding rocks inside and outside the waterway are filled with liquefied micrite limestone veins (Figure 5-3). The 9 ~ 13 layer of the second member of Zhaowei Formation is basal cemented breccia limestone, and the gravel only accounts for 4% ~ 5% of the rock content, which is equivalent to sporadic deposition at the outlet of carbonate gentle slope channel. The 14 ~ 17 layer consists of shallow cemented vein limestone and layered limestone (located on the river bank).

Jiayuan Formation (Z2jy) and Zhaowei Formation 1 and 2 (Z2zw 1 and Z2zw2) are rock formations with frequent strong earthquake records, and their macroscopic characteristics are very obvious, which left a deep impression on geologists. This earthquake disaster event rock layer records the in-situ liquefaction (various micrite veins) in carbonate rocks during the earthquake, the mound layer formed at the gentle slope of carbonate rocks by the tsunami storm caused by the earthquake, the debris flow, turbidite and the waterway formed by the tsunami wave back flushing the gentle slope (Figures 5-2 and 5-3). The channel width can reach1~1.5m; Depth 50cm；; The smallest waterway is only a few centimeters wide and a few millimeters deep, and it is composed of bag molds and groove molds. (The numbers in Figure 5-2 are 1, 4, 5, 6, 17, etc. ). Without exception, the river channel cuts the underlying liquefied micrite vein limestone, and the sediments in the river channel are striated limestone with Jin Lang hills, depressions and fishbone bedding. Liquefied carbonate argillaceous veins and silty veins are filled in waterways. The superposition of waterways recorded many strong earthquakes and their induced waves.

The third and fourth members of Zhaowei Formation are sand-bearing tabular micrite limestone and argillaceous banded micrite limestone, which are generally gentle slope-basin facies, forming a sequence. 19 yellow extremely thin micrite limestone mixed with silty sand (5 ~ 7 cm thick) and thin micrite limestone (thickness 10cm) are interpreted as CS profile.

The dolomite of Niyuan Formation constitutes a single sequence, which is a lithofacies transition surface with underlying and overlying sequences.

The fourth member of Zhaowei Formation (Z2zw4) and the lower member of Niyuan Formation (Z2ny) are two typical storm event rocks. Lenticular in-situ storm rocks (layer 2 1 ~ 27 in Figure 5-2) are composed of flaky gravels of carbonate rocks, interbedded with yellow argillaceous banded limestone in normal weather, and 20 in-situ carbonate storm event layers can be identified in the field. The records of carbonate storm events in the fourth member of Zhaowei Formation and the lower member of Niyuan Formation are completely different from the records of earthquake and tsunami events in the underlying Zhaowei Formation and Jiayuan Formation. They live in different environments: earthquake disasters occur on shallow gentle slopes, which are shallow carbonate environments, while storm events occur on deep gentle slopes or basins. It is very important to distinguish between the records of general strong storm events and the records of tsunami and wave action induced by earthquakes in strata!

From Wiki to Baishan, Zhang Qu Formation and Wiki Formation are completely exposed, and Jiudingshan Formation is covered by Quaternary, so it can only be measured along the plain valley, which is not ideal, but the top-bottom interface is clear.

Jiudingshan Formation is a set of seismite strata, and two sequences can be identified in the field. Zhang Qu Formation is divided into upper and lower sections, and the lower section is red tabular argillaceous banded micrite limestone with in-situ storm deposits. The upper member is dolomitic limestone containing seismite. The two members of Zhang Qu Formation constitute two sequences respectively. The bottom of the lower sequence (No.9 layer) is lithologic conversion surface, and the top boundary is conglomerate. The top of the upper member (layer 65438 +00) sequence is oolitic dolomite.

Eight upward shallowing sequences (PS 1 ~ PS 8 in Figure 5-2) can be identified in the Wiki Formation. The lower unit of each subsequence is subtidal shale, and the upper unit is layered limestone (intertidal zone-supratidal zone), dolomite or micritic vein limestone (seismite). PS 1 ~ PS 5 constitutes retrogradation sequence. The lower unit of PS6 is shale and deep-water conical stromatolite, and the upper unit is red columnar stromatolite (widely used as architectural decorative stone, commonly known as "Xuzhou Red"). The lower part of PS8 is shale mixed with clay, and the upper part is supratidal columnar stromatolite (gymnosperms) and striated limestone. Obviously, PS6~PS8 constitute a progressive subsequence group. The bottom surface of PS6 is equivalent to the maximum submerged surface.

Figure 5-3 Macroscopic Characteristics of Backwater Scouring Waterway in Jin Lang of Zhaowei Formation

Below: overlapping waterways; Middle: The waterway cuts the hills and depressions in Jin Lang; Above: Liquefied mud veins in the waterway (middle photo is enlarged in the waterway).