四川盆地及周缘震旦系灯影组岩性—碳同位素地层划分及意义<sup>*</sup>

doi:10.7605/gdlxb.2023.06.050

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四川盆地及周缘地区灯影组厚度变化巨大,给地层划分与对比带来极大困难; 同时,绵阳—长宁拉张槽成因问题的实质也是地层归属不清。在此背景下,基于2条露头和3口钻井开展了系统的岩性—碳同位素地层划分对比工作,将灯影组划分为6个可等时对比的岩性段,共包含3次碳同位素正偏(DP1、DP2、DP3)和3次碳同位素负偏(DN1、DN2、DN3)。地层划分结果为:(1)灯一段以泥晶白云岩为特征; (2)灯二下亚段发育各种藻白云岩,伴生葡萄状构造,且下部发育DP1碳同位素正偏,中部发育DN1碳同位素负偏,上部向DP2碳同位素正偏过渡; (3)灯二上亚段岩性为泥晶白云岩夹少量藻白云岩,下部发育DP2碳同位素正偏,中上部发育DN2碳同位素负偏,且该亚段中部在局部地区发育混合沉积; (4)灯三段普遍具有混积特征,局部地区为碎屑岩,发育特征管状化石; (5)灯四下亚段以大套泥晶白云岩为特征,碳同位素稳定在1‰左右,上部向DP3碳同位素正偏过渡; (6)灯四上亚段主要发育藻纹层白云岩和叠层石白云岩,底部见DP3碳同位素正偏,向上逐渐负偏过渡为DN3。地层对比发现,灯二上亚段顶部的不整合面可对应547 Ma左右的冰期,灯四段顶部的不整合面对应震旦纪—寒武纪之交(541 Ma左右)的冰川事件。位于绵阳—长宁拉张槽内部的蓬探1井、蓬深3井不同程度地缺失灯二上亚段之上的地层,缺失厚度可达600 m以上(缺至灯二下亚段底部),且上覆麦地坪组厚度最大、最完整,说明绵阳—长宁拉张槽的主体形成时间可以约束到灯二下亚段底部沉积之后和拉张槽内部麦地坪组开始沉积之前。

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	陈明思
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	徐少立
	丁一

关键词 ：四川盆地, 灯影组, 碳同位素, 地层划分对比, 绵阳&#x02014, 长宁拉张槽

Abstract：

The division of the Dengying Formation is controversial due to great variation in its stratigraphic thicness. Moreover,the formation mechanism of the Mianyang-Changning intracratonic sag is poorly understood due to the controversy in stratigraphic division. Based on investigations of two outcrop sections and three drilling wells,this paper conducted a systematic lithol and carbon isotopic δ¹³C stratigraphic division and correlation of the Dengying Formation,and divided it into six isochronous lithologic units with three positive(DP1,DP2,DP3)and three negative(DN1,DN2,DN3)carbon isotopic excursions: (1)The Member 1 of Dengying Formation is marked by dolomudstone;(2)the lower submember of Member 2 of Dengying Formation consists of various microbial dolomite with grape-like structures,showing DP1 in its lower part,and DN1 in its middle part,which passes upward into DP2 gradually;(3)the upper submember of Member 2 of Dengying Formation is marked by dolomudstone and minor microbial dolomite,locally with mixed carbonate and siliciclastic sedimentation,showing DP2 in its lower part and DN2 in its middle-upper part;(4)the Member 3 of Dengying Formation is typical of mixed carbonate and siliciclastic sedimentation,locally solely with siliciclastic rocks,containing characteristic tubular fossils;(5)the lower submember of Member 4 of Dengying Formation is composed of thick dolomudstone with δ¹³C around 1‰in the lower part and positively shifting into DP3 upward;(6)the upper submember of Member 4 of Dengying Formation consists mainly of microbial dolomite,exhibiting DP3 in the base with a negative shift trend towards the Ediacaran-Cambrian boundary as DN3. The unconformities above the upper submember of Member 2 of Dengying Formation and Member 4 of Dengying Formation can be correlated with the glaciations during 547 Ma and Ediacaran-Cambrian boundary,respectively. The missing of the strata above the lower submember of Member 2 of Dengying Formation of varying degree is identified in the Wells Pengtan 1 and Pengshen 3 in the Mianyang-Changning intracratonic sag. The strata missing of the Dengying Formation in the Mianyang-Changning intracratonic sag up to 600 m(to the basal Lower submember of Member 2 of Dengying Formation), and the largest thickness of the overlying Maidiping Formation and the most complete strata there,collectively suggest that the majority of Mianyang-Changning intracratonic sag of the Dengying Formation formed after the deposition of the basal lower submember of Member 2 of Dengying Formation and before the deposition of the Maidiping Formation.

Key words： Sichuan Basin Dengying Formation carbon isotope stratigraphic division and correlation Mianyang-Changning intracratonic sag

收稿日期: 2022-11-29

ZTFLH:

P521

基金资助:

*国家自然科学基金项目(编号: 41902105,U19B6003)资助

通讯作者: 李智武,男,1976年生,成都理工大学教授,博士生导师,主要从事构造地质、石油地质方面研究。E-mail: lizhiwu06@mail.cdut.edu.cn。丁一,男,1987年生,成都理工大学研究员,主要从事碳酸盐岩沉积学、地球化学方面研究。E-mail: Dingyi@cdut.edu.cn。

作者简介: 陈明思,男,1997年生,成都理工大学硕士研究生,专业为地质学。E-mail: 1369635589@qq.com。

引用本文:

陈明思,张本健,李智武等. 四川盆地及周缘震旦系灯影组岩性—碳同位素地层划分及意义^*[J]. 古地理学报, 2023, 25(6): 1347-1363.

CHEN Mingsi,ZHANG Benjian,LI Zhiwu et al. Lithol and carbon isotopic stratigraphic division and its sighificance of the Sinian Dengying Formation in Sichuan Basin and surrounding area[J]. JOPC, 2023, 25(6): 1347-1363.

链接本文:

http://journal09.magtechjournal.com/gdlxb/CN/10.7605/gdlxb.2023.06.050 或 http://journal09.magtechjournal.com/gdlxb/CN/Y2023/V25/I6/1347

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