CAUSE OF THE PARTIAL MISSING OF GRAPTOLITE ZONES IN WUFENG AND KAOCHIAPIEN FORMATIONS OF WELL GD-1, CHAOHU AREA, LOWER YANGTZE REGION
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摘要:
鼓地1井位于安徽巢湖鼓山,该井开口层位即为高家边组地层,在770.5~1 234.5 m处钻遇高家边组(下段)和五峰组黑色笔石页岩,笔者据此开展了该井笔石生物地层研究及其部分笔石带缺失的原因分析。鼓地1井由下而上能鉴定出Dicellograptus complexus-Paraorthograptus pacificus带(WF2—WF3)、疑似Akidograptus ascensus带(LM2)、Coronograptus cyphus带(LM5)、Demirastrites triangulatus带(LM6,未见顶)4个生物地层单元。与下扬子区连续沉积的五峰-高家边组笔石生物带相比,鼓地1井缺少Metabolograptus extraordinarius-Metabolograptus persculptus带(WF4—LM1)和Parakidograptus acuminatus-Cystograptus vesiculosus带(LM3—LM4)。分析认为,受“江南古陆”扩展的影响,鼓地1井可能在WF4—LM1时期存在沉积间断,并未接受沉积;而LM3—LM4在邻区可见,推测是由于鼓地1井位于逆冲推覆构造带上,受构造滑脱的影响致使该段地层缺失;这些原因也导致了该井五峰-高家边组有利黑色页岩厚度小。Coronograptus cyphus带和Demirastrites triangulatus带(LM5和LM6)厚度大,应是受逆冲推覆构造的影响,地层出现了重复。
Abstract:The well GD-1, located in Gushan, Chaohu of Anhui Province, is a well initiated from the Kaochiapien Formation. From 770.5 m to 1234.5 m, there occur black graptolite shale of the Kaochiapien Formation and Wufeng Formation. Graptolite biostratigraphy reveals that there are four graptolite biozones in an ascending order, say Dicellograptus complexus-Paraorthograptus pacificus (WF2-WF3) zones, Akidograptus ascensus (LM2?) zone, Coronograptus cyphus (LM5) and Demirastrites triangulatus (LM6) zones (No apical in LM6). Compared with the Wufeng and Lungmachi (Kaochiapien) Formations in the Yangtze Region, the graptolite biozones of Metabolograptus extraordinarius-Metabolograptus persculptus (WF4-LM1) zones and Parakidograptus acuminatus-Cystograptus vesiculosus(LM3-LM4)zones are lacking in the well GD-1, but found in other holes nearby. It is suspected that the WF4-LM1 zones may not have been deposited in the area surrounding the well GD-1 due to the expansion of ‘Jiangnan Oldland’. The fact that the LM3-LM4 zones can be seen in the adjacent area but absence in well GD-1 may suggest the influence of the decollement structure, which also leads to the thinning of the black shale. The LM5 and LM6 zones are relatively thicker than the others in the Yangtze region, possibly due to the strata repetition affected by the thrust nappe tectonics.
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图 3 鼓地1井五峰-高家边组部分典型笔石[16]
Figure 3.
表 1 扬子区奥陶−志留系之交笔石带序列[1]
Table 1. Subdivision of the Ordovician-Silurian graptolitebiozones in the Yangtze region[1]
表 2 扬子区钻井生物地层划分及厚度对比
Table 2. Graptolite biozones and thickness correlation of the Yangtze area
地层 下扬子地区 上扬子地区 阶 笔石带 鼓地1井(本文) 皖含地1井[14] 仑山5井[13] 新地2井[23] 宁211井[24] 威202井[25] 焦页1井[26-27] 巫溪2井[28-29] 井深/m 厚度/m 井深/m 厚度/m 井深/m 厚度/m 井深/m 厚度/m 井深/m 厚度/m 井深/m 厚度/m 井深/m 厚度/m 井深/m 厚度/m 特列
奇阶N2 未见顶 未见顶 未见顶 未见顶 LM9/N1 1 915.5 2 180 2 541.63 >6? 未见顶 1 564.2 >53.79 埃隆阶 LM8 1 968.49 52.99 2 213.16 33.16 2 546.79 5.16 2 344.19 >44.19 1 599.1 34.9 LM7 未见
顶底未见
顶底未见
顶底2 009.14 40.65 2 251.73 38.57 2 551.08 4.29 2 348.22 4.03 1 610.91 11.81 LM6 1 175.5 405 1 280 13.95 9.6 9.6 2 045.67 36.53 2 313.44 61.71 2 561.6 10.52 2 367.43 19.21 1 613.86 2.95 鲁丹阶 LM5 1 224.5 49 1 290 10 27 17.4 2 047.77 2.1 2 326.97 13.53 2 567.34 5.74 2 390.58 23.15 1 620.47 6.61 LM4 缺失 1 300.25 10.25 33.2 6.2 2 056.97 9.2 2 337.21 10.24 2 571.79 4.45 2 404.27 13.69 LM3 缺失 1.3(破碎带) 35.6 2.4 2 064.55 12.4 2 342.2 4.99 2 407.76 3.49 1 624.67 4.2 LM2 1 226.2
(?)1.7 39.4 3.8 2 069.37 2 346.33 4.13 赫南
特阶LM1 缺失 40.2
(?)0.8 2 070.44
(?)1.07 2 349.04 2.71 2 412.1 4.34 1 628.9 4.23 WF4 44.3 14.1 2 080.1 9.66 2 351.67 2.63 2 579.6 7.81 2 412.52 0.42 1 629.1 0.2 凯迪阶
(上部)WF3 1 234.5 8.3 1 308 6.45 2 353.99 2.32 1 636 6.9 WF2 1 309.15 1.15 2 080.94 0.84 2 357.5 3.51 2 415.2 2.68 WF1 1 309.95 0.8 2 081.62 0.68 2 415.36 0.16 总厚度 464 43.9 54.3 166.12 177.5 >115.36 >125.59 注:表中井深代表底界深度 -
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