Jiudingshan Formation is dolomite, which can be divided into four lithologic sections, which is generally consistent with the lithology of Jiudingshan Formation in northern Jiangsu. The first and third sections are rock formations of two earthquake events, and the second and fourth sections are dolomite and stromatolite. Two sequences can be identified in Jiudingshan Formation.
(2) Zhang Qu Group
Zhang Qu Formation is divided into two sections, the lower section is tabular micrite limestone containing three sponges, and the upper section is dolomite. The whole Zhang Qu Formation is a cataclysmic event group (storm event and earthquake event).
The lower member (I) is a storm event layer, which is a long-distance storm turbidite and is characterized by a granular layer with a thickness of one centimeter. It is isochronous with the original storm rock of Zhang Qu Formation in Wiki, Shendian and Damiao in Tongshan County, northern Jiangsu Province, and it is more than 70 kilometers to the north. Zhang Qu Formation in northern Jiangsu is located on the carbonate uphill and northern Anhui is located on the carbonate downhill. The ratio of wavelength to height of storm mound in Zhang Qu Formation in two areas is different. According to Bose, the wavelength/wave height in the profile of Zhang Qu Village is 10 or 1 1 (Figure 5- 12). The wavelength/height in northern Jiangsu is 15 or 14, and the water depth is less than 40m. Excerpted from Bose( 1988) abstract map (the Bose map is reproduced on page 45 of Sinian-Lower Cambrian Genesis Stratigraphy in Southern Liaodong Peninsula edited by Qiao Xiufu and Song et al.). ), it also shows that the Zhangqu Village section is in a deeper position than the sea water in northern Jiangsu (the wavelength/wave height is relatively low).
The upper member (Ⅱ member) dolomite belongs to the seismic event rock group (Figure 5- 12), which shows a sequence of upward shallowing, from the upper gentle slope clastic flow dolomite to the relatively deep-water stromatolite (subtidal zone) and then to the shallow-water beach oolitic dolomite (Figure 5- 13).
Table 5-5 lists the distribution of some elements on the profile of Zhang Qu Formation, and the geochemical data also provide the information that Zhang Qu Formation becomes shallower upward.
Table 5-5 Some Element Values of Zhang Qu Formation
Note: The samples in the table are analyzed by Institute of Rock and Mineral Testing, Chinese Academy of Geological Sciences; The number of layers is the same as that in Figure 5- 12.
Figure 5- 12 Profile of Sequence Stratigraphy and Catastrophe Events of Jiudingshan Formation and Zhang Qu Formation in Zhang Qu Village, Lingbi County, Anhui Province (actually measured)
Fig. 5- 13 Seismic Event Record of Upper Member of Zhang Qu Formation in Liquefied Carbonate Vein
Left: It shows the pulse phenomenon in the 7th floor of Figure 5- 12No. ; Right: Liquefied carbonate veins in No.22 oolitic dolomite (Zhang Qu Village).
(1) The combination degree of boron (b) and clay increases with the depth, so the content of insoluble b in sediments increases with the depth. The Zhang Qu Formation lacks argillaceous rocks, so the content of b is very low, but the relative content is 34.00× 10-6 in the 6th layer and 2.75× 6556 in the 8th layer. Layer 6 is clastic flow breccia limestone, and the backflow caused by the earthquake carries clay to the gentle slope, which is mixed with carbonate sediments, showing a high B content.
(2) Some trace elements in sediments, such as cobalt, copper, barium, neodymium, cerium, lead and strontium. , which can indicate the depth of seawater (Toure Day,1961; Nichols,1967; Benedict, 1978). The contents of the above elements in Table 5-3 are too low to indicate the specific depth, but two pieces of information are provided: First, the Sr/Ba ratio is greater than 1, indicating the marine environment; Second, the Sr content is more than 16 and less than 50× 10-6, but it is186×10-6 ~1621×1on No.6 and No.8.
(3) The manganese content in carbonate sediments increased with depth. Judging from the manganese content, the lower member of Zhang Qu Formation is deeper than the upper member. The relative content of No.8 layer in the upper member is high, but the upward content is relatively reduced.
(4) The Ca/Mg values of No.6 and No.8 layers are 77 and 96.45, respectively, and the ratio in the upper part of the profile decreases rapidly (the ratio is less than 2). With the increase of seawater depth, the amount of low magnesium calcite increases, while the amount of high magnesium calcite decreases, and the Ca/Mg value increases with the depth.
Zhang Qu Formation can recognize two sequences, the lower member is a sequence, No.2 ~ No.3 is an upward deepening sequence (TST) and No.4 ~ No.5 is an upward shallowing sequence (HST). The system tract interface is selected between storm turbidites (between No.3 and No.4). The upper member is sequence, No.6 ~ No.7 is TST, and No.8 ~ No.23 is high water level system tract. The eighth floor represents the deepest period of the upper water body, and geochemical data also show the same information.