塔里木盆地下寒武统玉尔吐斯组沉积特征及有机质富集模式

doi:10.19657/j.geoscience.1000-8527.2023.103

摘要/Abstract

摘要：

塔里木盆地是我国西北部规模最大的含油气盆地,盆内下寒武统玉尔吐斯组为一套富含有机质的泥岩和碳酸盐岩沉积,构成盆内最重要的烃源岩之一。本文基于露头、钻测井、地震、岩心岩屑等资料综合分析,简述玉尔吐斯组的岩相、沉积相和古地理分布特征,揭示富有机质沉积的分布及其控制因素。玉尔吐斯组以古暴露面为界可划分为三个层序,总体形成于被动陆缘混积的缓坡陆棚环境。可识别出10种岩相和7个岩相组合以及4种主要的沉积相类型;沉积古地理编图揭示由南西向北东方向依次展布混积潮坪、浅水内陆棚、深水外陆棚到深水盆地的沉积相带分布。富有机质沉积主要发育于深水外陆棚相带,以发育具有异常高的TOC值和丰度极高的微量元素的黑色泥页岩为特征。有机质的富集与高的古生产力和保存条件有关。热液活动带来了丰富的营养元素;上升洋流促进营养元素与正常海水的混合和扩散,形成富营养化的表层水;深水外陆棚区缺氧条件有利于有机质的保存富集。

关键词: 沉积古地理, 富有机质沉积, 制约因素, 玉尔吐斯组, 塔里木盆地

Abstract:

The Tarim Basin is the largest oil-bearing basin located in Northwestern China.The Lower Cambrian Yuertusi Formation comprises mudstone and carbonate deposits rich in organic matter, making it one of the most important source rocks in the basin.We conducted a comprehensive analysis of outcrops, including logging data, seismic data, cores, and cuttings, to reveal the lithofacies, sedimentary facies, and paleogeographic distribution characteristics of the Yuertusi Formation and to understand the distribution and constraints on organic-rich deposits.The Yuertusi Formation can be divided into three sequences based on the boundaries of the exposed surfaces, and it generally formed in a mixed ramp shelf environment on a passive continental margin.Ten lithofacies, seven facies associations (Fa), and four major sedimentary facies have been identified in the Yuertusi Formation.The sedimentary palaeogeography map shows the distribution of sedimentary facies belts from southwest to northeast, including mixed tidal flat, shallow inner shelf, deep outer shelf, and deep basin.The organic-enriched deposits mainly developed in the deep outer shelf zone and are characterized by black mud shales with unusually high TOC values and extremely high trace element abundances.The enrichment of organic matter is related to high paleo-productivity and favorable preservation conditions.Hydrothermal activities introduced many nutrient elements, and upwelling currents promoted the mixing and diffusion of these nutrients with normal seawater, leading to the formation of eutrophic surface water.Additionally, the anoxic conditions in the deep outer shelf are conducive to the preservation and enrichment of organic matter.

Key words: sedimentary palaeogeography, organic-rich deposit, constraint factor, Yuertusi Formation, TarimBasin

中图分类号:

P618.1

蔡振忠, 徐帆, 杨果, 李浩, 胡方杰, 林畅松. 塔里木盆地下寒武统玉尔吐斯组沉积特征及有机质富集模式[J]. 现代地质, 2024, 38(05): 1258-1269.

CAI Zhenzhong, XU Fan, YANG Guo, LI Hao, HU Fangjie, LIN Changsong. Sedimentary Characteristics of the Lower Cambrian Yuertusi Formation and the Organic Matter Enrichment Model in the Tarim Basin[J]. Geoscience, 2024, 38(05): 1258-1269.

图/表 11

图1 塔里木盆地构造单元图[21]

Fig.1 Tectonic unit map of the Tarim Basin [21]

表1 玉尔吐斯组岩相组合和沉积相类型主

Table 1 Facies associations and sedimentary facies of the Yuertusi Formation

岩相组合	岩相类型	岩相描述	沉积相
Fa1	粉砂岩+泥质粉砂岩/(粉砂质)泥岩+云质粉砂岩+灰色含泥白云岩	成分成熟度高,分选性差,白云岩中含粉砂石英	混积潮坪
Fa2	深灰色含泥白云岩+颗粒白云岩	发育泥质纹层和粉砂级石英颗粒,含海绵骨针	浅水陆棚
Fa3	深灰色泥质灰岩+灰色含泥灰岩/灰岩	发育水平层理,含少量钙质海绵骨针和石英颗粒	浅水陆棚
Fa4	黑色硅质岩+黄色磷质岩+黑色页岩	硅质岩与磷质岩混杂堆积,呈厚板状,页岩段较薄	深水陆棚,具热液和上升流活动
Fa5	黑色硅质岩+黑色页岩	硅质岩呈薄板状,页岩段厚,含黄铁矿、生物碎屑	深水陆棚,具热液沉积
Fa6	灰黑色泥岩/深灰色含灰泥岩+灰色含泥灰岩	含硅质放射虫和海绵骨针	深水陆棚
Fa7	黑色泥岩+泥质灰岩	泥岩厚度较大,含黄铁矿颗粒,夹薄层泥质灰岩	深水盆地

图2 玉尔吐斯组岩相类型 (a) 粉砂岩岩心照片,中寒1井,约7475 m;(b) 泥质粉砂岩岩屑微观照片,中寒1井,约7484 m,单偏光(plane-polarized light, PPL),50倍;(c) 粉细晶白云岩,部分晶间缝充填沥青(黑色浸染状部分),什艾日克剖面,PPL,25倍;(d) 粉细晶白云岩,含钙质海绵骨针,什艾日克剖面,PPL,25倍;(e) 含泥白云岩,什艾日克剖面,PPL,25倍;(f) 泥晶灰岩微观照片,含海绵骨针,旗探1井,约5965 m,PPL,50倍;(g) 含泥灰岩岩心照片,轮探1井,约8648 m;(h) 含泥灰岩岩心微观照片,含大量海绵骨针,轮探1井,约8648.55 m,PPL,50倍;(i) 泥岩的岩心照片,旗探1井,约5998 m;(j) 泥岩,含放射虫,旗探1井,约5998 m,PPL,50倍;(k) 含灰泥岩的岩屑微观照片,轮探1井,约8658 m,PPL,50倍;(l) 泥岩的岩屑微观照片,轮探1井,约8675 m,PPL,50倍;(m) 黑色硅质岩被黄色磷质岩包裹,硅质岩可呈块状或卵状,什艾日克剖面;(n) 磷质岩,含有大量硅质海绵骨针和放射虫,PPL,50倍;(o) 薄层状黑色硅质岩和页岩互层,什艾日克剖面;(p) 薄层状的黑色页岩,易破碎,什艾日克剖面;(q) 硅质泥岩,含黄色磷质团块和黄铁矿,什艾日克剖面,PPL,50倍;(r)与图(q)同视域下正交偏光照片(cross-polarized light, XPL);(s) 泥岩,含顺层厘米级黄铁矿颗粒,塔东2井;(t)图(s)的微观照片,PPL,25倍

Fig.2 Lithofacies of the Yuertusi Formation

图3 塔里木盆地玉尔吐斯组沉积演化模式

Fig.3 Sedimentary evolution model of the Yuertusi Formation in the Tarim basin

图4 塔里木盆地玉尔吐斯组底部削截和顶部底超结构的地震剖面(a)及解释(b)(剖面位置见图1)

Fig.4 Seismic profile (a) and interpretation (b) ofthe bottom truncation and top downlap of the Yuertusi Formation in the Tarim Basin (see Fig.1 for profile location)

图5 塔里木盆地玉尔吐斯组层序-沉积微相对比和总有机碳含量(TOC)变化(剖面位置见图1)

Fig.5 Changes of sequence-sedimentary microfacies and total organic carbon (TOC) content in the Yuertusi Formation, Tarim Basin (see Fig.1 for profile location)

图6 塔里木盆地下寒武统玉尔吐斯组残余厚度图

Fig.6 Residual thickness map of the Lower Cambrian Yuertusi Formation in Tarim Basin

图7 塔里木盆地下寒武统玉尔吐斯组岩相古地理图

Fig.7 Lithofacies paleogeographic map of the Lower Cambrian Yuertusi Formation in the Tarim Basin

图8 旗探1井玉尔吐斯组元素丰度、U/Th比值、古水温与TOC的垂向变化(深水陆棚相带内有机质更富集,各项指标明显高于浅水陆棚相带;古水温基于全岩氧同位素恢复)

Fig.8 Vertical variations in element abundance, U/Th ratios, paleotemperature, and TOC values in the Yuertusi Formation of QT1 (Organic matter is more abundant in the deep shelf zone compared to the shallow shelf; Palaeotemperatures are estimated from bulk oxygen isotopes)

表2 旗探1井玉尔吐斯组碳、氧同位素数据

Table 2 C-O composition of the Yuertusi Formation in well QT1

深度 (m)	δC_VPDB (‰)	δO_VPDB (‰)	深度 (m)	δC_VPDB (‰)	δO_VPDB (‰)
5955	-0.6	-9.3	5978	-1.2	-8.8
5957	-0.1	-9	5980	-1.6	-8.7
5959	-0.7	-8.5	5982	-1.6	-9.3
5961	0.2	-8.9	5984	-1.5	-10.3
5962	0.1	-9.6	5986	-1.7	-8.9
5964	0.1	-8.8	5989	-1.9	-10.2
5966	-0.9	-8.8	5991	-2.5	-9.1
5968	-1.4	-8.8	5993	-2.1	-9.7
5970	-1.2	-8.5	5995	2.0	-14.1
5972	-1.0	-8.5	5997	-0.3	-8.6
5974	-0.7	-8.2	5999	0.9	-7.5
5976	-1.6	-8.8	6000	1.7	-7.9

图9 塔里木盆地下寒武统玉尔吐斯组“热液+上升流+缺氧”富有机质沉积模式

Fig.9 Hydrothermal+upwelling+anoxic organic-rich sedimentary model of the Lower Cambrian Yuertusi Formation in the Tarim Basin

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