-
上扬子地区震旦系灯影组不仅是南华纪冰期结束以后全球气候回暖的海洋沉积物响应,而且记录了早寒武世骨骼动物大爆发前夕地球早期动物的演化过程(Zhang Shihong et al.,2005;Zhu Maoyan et al.,2007;Xiao Shuhai et al.,2016),同时其大量发育的微生物云岩构成的丘滩体沉积目前正成为四川盆地深层古老碳酸盐岩油气勘探的重要目标(刘树根等,2013;杜金虎等,2016;帅燕华等,2021)。对于上扬子地区震旦系灯影组,前人在岩石学特征及成因(林孝先等,2015;赵东方等,2018;Cui Huan et al.,2019)、沉积相类型和古地理演化(李英强等,2013;刘静江等,2015;周进高等,2015;赵文智等,2017;魏国齐等,2018)等方面开展了比较深入的研究,这些研究为分析其沉积环境演化奠定了良好的基础。对其剖面沉积序列及沉积环境演化特征亦有报道,但由于不同地区沉积环境的差异以及研究方法、研究深入程度的不同,目前对于灯影组沉积环境的演化仍存在分歧(Zhu Maoyan et al., 2007;Jiang Ganqiang et al.,2011;文龙等,2016),对其沉积环境演化缺乏较为细致的分析解释,对海平面变化缺乏精细刻画,严重制约了上述研究的进展。如前人通过研究认为灯影组优质储层的发育受沉积相和成岩作用共同控制,由于缺乏清晰的沉积相演化特征认识,灯影组优质储层的分布规律仍然不清(李凌等,2013;周进高等,2014;宋金民等,2018;杨跃明等,2019;夏青松等,2021)。
-
埃迪卡拉纪晚期,上扬子地台西北缘位于当时华南板块的边缘,为陆缘海沉积环境,相比于克拉通内部,对全球海平面的变化响应有更高敏感性(图1a)(谷志东等,2016;杨跃明等,2016;李智武等,2019;苏桂萍等,2020)。本文报道的上扬子西北缘绵竹清平剖面,起点坐标:N:30°36′06.29″E:104°05′24.94″;终点坐标:N:31°35′55.889″E:104°06′09.745″,震旦系灯影组地层出露完整连续、界线清楚,真厚度约达780m,其沉积记录完整丰富,几乎发育了前人报道的灯影组所有岩石类型,是研究该时期沉积环境演化难得的剖面(图1b)。本文通过对该剖面灯影组详细野外沉积学解剖以及室内微相分析、解释,刻画出详细的沉积序列、沉积环境演化以及海平面变化历程并建立了相应的沉积模式。该研究不仅对深入探索埃迪卡拉纪晚期全球海平面变化具有一定理论意义,而且对进一步明确灯影组优质储层纵向分布规律指导油气勘探具有实用价值。
-
图1 上扬子地区灯影期古地理格局及川西清平剖面震旦系地层柱状图
-
Fig.1 The paleogeographic pattern of Dengying Age in the Upper Yangtze area and the stratigraphic column of the Sinian strata in Qingping section, western Sichuan
-
(a)—灯三、四段沉积期上扬子地区古地理格局(据侯明才等,2017);(b)—川西清平剖面震旦系地层柱状图
-
(a)—Paleogeographic pattern of the Upper Yangtze area during the deposition periods of the third and fourth members of the Dengying Formation(after Hou Mingcai et al.,2017); (b)—Sinian stratigraphic column of Qingping section in western Sichuan
-
1 区域地质背景
-
本文选择的清平剖面位于四川盆地西缘的绵竹市清平乡小木岭林场境内,属于上扬子克拉通西北缘,构造位置位于龙门山逆冲推覆断裂带中段(图1a)。南华纪冰期结束,全球气候回暖、海平面上升,上扬子地台开始接受陡山沱组沉积,其岩性以黑色页岩、碳酸盐岩、硅质岩和磷块岩为主(邓双林等,2020)。灯影组是继陡山沱组沉积之后发育的一套海侵沉积序列,以浅水碳酸盐台地沉积为主(李勇等,2019)。其下部与喇叭岗组或陡山沱组整合接触,上部与寒武系麦地坪组或宽川铺组之间不整合接触,存在沉积间断;内部地层在上扬子地区主要采用四段的划分方案(邓胜徽等,2015)。灯一段主要为一套泥微晶云岩沉积,表现为海侵序列;灯二段沉积期,海水退却,以大套的微生物云岩为主,沉积厚度大,是整个灯影组沉积的主体;灯二段末期,受全球海平面以及区域构造运动影响,上扬子地台整体暴露,形成区域性分布的不整合面;灯三段沉积期,海水再次侵入,形成了一套以碎屑岩为主的沉积;灯四段沉积期,海平面降低,以微生物云岩沉积为主,灯四段另一特色便是其发育大量的硅化纹层和硅质条带;灯影组顶部由于构造运动,产生暴露,存在明显的不整合面,与上覆寒武系地层之间不整合接触。综上所述,上扬子地区埃迪卡拉纪灯影组是南华纪冰期结束以后,陡山沱组海侵序列之上的一套以微生物云岩为主的浅水碳酸盐岩台地相沉积。
-
2 主要岩石微相类型描述及解释
-
根据野外露头精细解剖和室内岩石薄片鉴定结果,参考Flügel(2010)沉积微相划分方案,确定出清平剖面灯影组白云岩共发育21种微相类型(以下简称MF)(表1)。按照沉积水体深度由深到浅的序列对其进行排序,MF1~MF9常出现在潮下带;MF10~MF16潮间带常见;MF17~MF18主要为潮上带沉积;MF19~MF20为陆上沉积环境。其中MF9、MF11、MF12、MF13、MF14与蓝细菌生物活动有着直接关系。下面将具体介绍主要岩石微相的特征及分析解释结果。
-
(1)MF1砾屑漂砾云岩:灯四段中部发育,露头上呈灰白色中层状,砾屑层顺层产出,厚度在10~20cm之间(图2a);样品中砾屑含量在50%左右,基质支撑,分选磨圆均差(图2b);砾屑颗粒多为撕裂状,呈菊花状、放射状杂乱分布,但总体上仍顺层延伸,呈现向上变细的粒序层理(图2c);砾屑颗粒成分为近源硅质碎屑(图2d),其长轴可达7~8cm,但短轴不超过1cm,粒度范围0.5mm~8cm,呈双峰态分布。由硅质砾屑的菊花状、撕裂状外形以及正粒序分布特征,认为砾屑是风暴作用将已经选择性硅化的弱固结薄层碳酸盐岩打碎所致(Davis et al.,2012),根据该微相分选磨圆差、颗粒长轴顺层延伸以及粒度双峰态分布,推测MF1是当风暴作用缓和时,离岸回流以密度流的形式带着砾屑沿海底向下搬运至潮下低能环境沉积下来所形成(Flügel,2010)。
-
(2)MF3放射鲕颗粒云岩:灯四段上部发育,露头上表现为深灰色中—厚层,可见多个粒度向上变粗的沉积旋回(图2e);镜下鲕粒的丰度在60%左右,砂屑颗粒在15%左右,颗粒之间点接触,亮晶胶结;鲕粒类型全部为放射鲕,颗粒周缘发育等厚的暗色泥晶包壳,厚度在5~30 μm之间;鲕粒核心多为微晶白云石,原始结构被破坏;包壳为均质包壳,核壳比值在0.1~1之间,均为正常鲕;鲕粒的粒度范围在0.2~0.5mm之间,平均值为0.3mm,分选好(图2f、g)。放射鲕是中低能沉积环境的标志,并且与其伴生的砂屑颗粒也是弱振荡环境中形成的,颗粒周缘存在透光带的蓝细菌钻孔形成的泥晶包壳,颗粒被亮晶胶结,所以认为其形成于潮下带的弱动荡的水体中(赵东方等,2018)。
-
(3)MF6集合粒颗粒云岩:灯一段顶部发育,露头上呈浅灰色厚层-块状产出;镜下集合粒丰度在80%左右,颗粒支撑、亮晶胶结;集合粒发生塑性变形,呈椭球形—不规则形;集合粒由多个砂屑颗粒构成,部分砂屑颗粒破碎,砂屑颗粒粒度在100 μm左右,分选磨圆较好,部分重结晶;集合粒的粒度范围在0.3~2.5mm之间,平均值为0.7mm,呈单峰态分布(图2h、i、j)。由集合粒内部破碎的砂屑颗粒认为,集合粒的形成是砂屑云岩在弱固结阶段,由于水体能量增强,对其进行冲刷淘洗后再沉积形成的,根据其分选磨圆,粒度分布形态以及亮晶胶结等特征,认为其就近在潮下带的中等振荡环境中沉积(Flügel,2010)。
-
(4)MF10纹层状微生物黏结云岩:灯二段、灯四段常见的微相类型之一,露头上表现为灰白色薄层云岩被暗色平直层隔开,两者纵向上呈韵律状相间沉积;灰白色薄层云岩内部又表现为密集平直的明暗相间纹层沉积(图2k、l);镜下亮层为藻丝体黏结灰泥形成的纹层在纵向上平直排列,暗层为亮晶胶结物以及微生物生长、矿化形成的残余有机质共同构成(图2m)。亮暗互层沉积为席状微生物群落间歇性生长所形成,根据纹层平直的形态判断,认为其形成于水深不断变化的潮间带低能环境;对其形成过程的解释为微生物群落会伴随着每次涨潮而黏结灰泥形成平直的纹层,而随着每次退潮停止生长、甚至死亡,细暗色纹层为正常潮落暴露所致,粗暗色纹层可能受每月几次的大潮所控制(王文之等,2016)。
-
(5)MF14凝块状微生物黏结云岩:该微相是灯二段下部常见的微相之一,在剖面上呈现为灰白色中—厚层沉积;样品特征为微生物捕获黏结沉积物以及自身矿化,整体形成一个块体,构成岩石骨架(图2n),块体内部残余不规则的外形的空腔,空腔被纤状环边胶结物胶结,凝块自身依然可见微生物黏结形成结构(图2o、p)。由其连续稳定的格架结构,认为其形成于潮间带局限环境弱震荡水体中,对其形成过程的解释为潮间带局限水体环境中,水体轻微振荡,特定的微生物群落会黏结灰泥形成具有一定形态特征的格架结构黏结岩,其与泡沫绵层状微生物黏结云岩一起,构成灯影组凝块石的主体,两者形态的差异,推测是由于微生物群落类型或水动力条件的差异所导致的(李安鹏等,2019)。
-
(6)MF15葡萄状白云岩:灯二段中部发育,露头上葡萄状白云岩主要顺层产出,呈暗色条带状,厚度在数毫米—数厘米之间,侧向延伸很远(图3a)。葡萄状白云岩在垂向上由明暗相间且轻微下凹的纹层构成,沿层面剥开,可见由大量半球形单体葡萄石顺层拼切构成的葡萄石集合体,葡萄体多形成于岩石的下层面(图3b、c);单个葡萄石半径在毫米至厘米级之间,表面光滑,易破碎(图3d);镜下特征表明其核心为黏结形成的暗色团块,壳体由半球形明暗相间的同心圈层所构成,其核壳比值很小,单个圈层的厚度由核心向边缘增厚,从几微米可增厚至几十微米,壳体的成分为延长的自行纤维状白云石晶体,在正交偏光下呈典型的带状消光(图3e、f)。根据葡萄体位于岩层下层面、向下生长以及放射纤状晶体扇构成的穹顶状外形,认为葡萄石形成于自由表面之上,受到大气淡水的影响,其生长过程与现代岩溶洞穴中石钟乳类似(林孝先等,2015);对其的解释为潮间带形成的叠层状微生物黏结岩,层间发育顺层裂隙,裂隙在向下渗流的大气淡水的影响下会形成的淡水-海水混合带的重力型胶结物,该胶结物便构成葡萄状白云岩,其形成于潮间-潮上环境(Cui Huan et al.,2019)。
-
图2 川西清平剖面震旦系灯影组MF1、MF3、MF6、MF10、MF14微相野外产状及镜下显微特征
-
Fig.2 Field feature and microscopic characteristics of microfacies MF1, MF3, MF6, MF10, MF14of Sinian Dengying Formation in Qingping section, western Sichuan
-
MF1: (a)—中观结构,见多个砾屑层旋回;(b)—单个砾屑层特征;(c)—砾屑宏观特征,砾屑呈条状,分选磨圆差;(d)—砾屑显微特征(正交偏光),砾屑为硅质,98层,灯四段。MF3:(e)—鲕粒云岩露头特征;(f)—鲕粒手标本特征;(g)—鲕粒显微特征(单偏光),鲕粒周缘存在泥晶包壳,100层,灯四段。MF6:(h)—集合粒宏观特征;(i)、(j)—集合粒显微特征(单偏光),内部砂屑颗粒破碎,亮晶胶结,6层,灯一段。MF10:(k)—纹层状微生物黏结云岩中观结构;(l)—灰白色薄层云岩局部放大;(m)—薄层云岩显微特征(单偏光),10层,灯二段。MF14:(n)—凝块状微生物云岩剖光面特征;(o)—格架结构显微特征(正交偏光),空腔被多期胶结物充填;(p)—凝块内部见微生物黏结特征(单偏光),14层,灯二段。
-
MF1: (a)—meso structure, see multiple gravel layer cycles; (b)—characteristics of single gravel layer; (c)—macroscopic characteristics of gravel debris, gravel debris in strip shape, poor sorting and rounding; (d)—microscopic characteristics of gravel debris (orthogonal polarization), gravel debris is siliceous, 98th layer, the fourth Member of Dengying Formation.MF3: (e)—outcrop characteristics of oolitic dolomite; (f)—characteristics of oolitic hand specimens; (g)—microscopic characteristics of oolites (plane polarized light), there is argillaceous cladding around oolites, 100th layer, the fourth Member of Dengying Formation.MF6: (h)—macro characteristics of aggregate particles; (i), (j)—microscopic characteristics of aggregate particles (plane polarized light), broken internal sand debris particles and bright crystal cementation, 6th layer, the first Member of Dengying Formation.MF10: (k)—mesostructure of laminated microbial cohesive dolomite; (l)—local amplification of gray white thin-layer dolomite; (m)—microscopic characteristics of thin-layer dolomite (plane polarized light), 10th layer, the second Member of Dengying Formation.MF14: (n)—sectional characteristics of clotted microbial dolomite; (o)—microscopic characteristics of the grid structure (orthogonal polarization), the cavity is filled with multi-stage cement; (p)—microbial bonding characteristics (plane polarized light) can be seen inside the clot, 14th layer, the second Member of Dengying Formation
-
图3 川西清平剖面震旦系灯影组MF15、MF16、MF19、MF20微相野外产状及镜下显微特征
-
Fig.3 Field feature and microscopic characteristics of microfacies MF15、MF16、MF19、MF20of Sinian Dengying Formation in Qingping section, western Sichuan
-
MF15:(a)—葡萄状白云岩剖面垂向特征;(b)—手标本下垂向特征,由轻微下凹的纹层构成;(c)—葡萄状云岩层面特征;(d)—手标本下层面特征, 大量半球形凸起顺层组成洞穴白云石化学沉积物;(e)、(f)—葡萄石镜下显微特征(单偏光),核心为黏结形成的暗色团块,壳体由半球形明暗相间的同心圈层所构成,22层,灯二段。MF16:(g)—花边状云岩野外中观特征,可见杂乱的空腔体被亮晶胶结物充填;(h)—野外中观特征,空腔被葡萄状胶结物充填;(i)—空腔体内葡萄状胶结物的镜下显微特征(单偏光),14层,灯二段。MF19:(j)—豆粒云岩野外中观特征,可见其形态多为扁球状;(k)—豆粒云岩手标本特征;(l)—豆粒显微特征(单偏光),见向上和向下的凸起(红色箭头)、新月形胶结物(黄色箭头),122层,灯四段。MF20:(m)—角砾岩中观照,角砾呈灰白色,基质呈暗色;(n)—角砾岩显微特征(单偏光),分选磨圆均差;(o)—颗粒边缘悬挂重力形胶结物(红色箭头),31层,灯二段
-
MF15: (a)—vertical characteristics of grapevine dolomite profile; (b)—vertical characteristics of hand specimen, which is composed of slightly concave laminae; (c)—characteristics of grapevine dolomite layer; (d)—characteristics of lower layer of the rock specimen, which shows a large number of hemispherical protrusion form dolomite speleothems along the layer; (e) (f)—microscopic characteristics of grapevine (single polarized light), the core is a dark mass formed by bonding, and the shell is composed of a hemispherical concentric circle of light and dark, 22th layer, the second Member of Dengying Formation.MF16: (g)—field mesoscopic characteristics of lace dolomite, it can be seen that the disordered cavity is filled with bright crystal cement; (h)—field meso features, the cavity is filled with grape cement; (i)—microscopic characteristics of grape cement in cavity (single polarized light), 14th layer, the second Member of Dengying Formation.MF19: (j)—field mesoscopic characteristics of dolostone, it can be seen that its shape is mostly flat spherical; (k)—characteristics of dolostone rock specimens; (l)—microscopic characteristics of bean particles (single polarized light), see upward and downward bulges (red arrow), crescent cement (yellow arrow), 122th layer, the fourth Member of Dengying Formation.MF20: (m)—viewed in breccia, the breccia is gray white and the matrix is dark; (n)—microscopic characteristics of breccia (plane polarized light), poor sorting and rounding; (o)—hanging gravity cement (red arrow) at the edge of particles, 31th layer, the second Member of Dengying Formation
-
(7)MF16花边状白云岩:灯二段下部发育,露头上与凝块石伴生;花边状白云岩主要产出在凝块石形成的空腔内部,在剖面上成层分布,单层厚度在5~100cm之间;空腔最大内径可达数厘米,空腔可占原岩体积的40%以上(图3g、h);由镜下观察可知体积较小的空腔被亮晶白云石胶结物充填,胶结物首先为纤状环边胶结物,厚度在50 μm左右,剩余主体被粒状胶结物充填;体积较大的空腔被葡萄状的重力型胶结物所充填,葡萄状胶结物沿环边向空腔内部生长(图3i),直至相互贴合,在正交光下呈带状消光。格架结构的微生物黏结云岩在其内部形成大量形态不规则的空腔,空腔在平面上多表现为向内贴合的多边外形,为原生形成。残留的不规则的空腔会被海水或大气淡水-海水混合水所胶结,形成亮晶胶结物或葡萄状重力型胶结物,便构成花边状白云岩,其形成于潮间-潮上带环境(Ding Yi et al.,2019)。
-
(8)MF19渗流豆粒白云岩:灯四段的上部发育,紧邻E-C(埃迪卡拉纪—寒武纪)暴露不整合面,露头上表现为灰白色中厚层状。样品中豆粒丰度在75%左右(图3j),颗粒之间多边贴合,亮晶胶结;豆粒多为扁球状,可见向上和向下的凸起,颗粒周缘可见新月形胶结物(图3l);豆粒核心为泥质颗粒或纤状-放射状胶结物结壳,部分豆粒有多个核心;包壳为多个规则的、密集的且明暗相间的同心圈层;颗粒的大小在1mm~1cm之间,呈双峰态分布,主要集中在2mm和8mm左右,具有逆粒序特征(图3k)。由豆粒大多具有向上和向下的凸起形态、新月形胶结物、亮晶胶结、粒度双峰态分布以及逆粒序特征等微相标志判断其为典型的渗流豆粒。渗流豆粒是由于地表暴露,大气降水溶解碳酸盐岩,饱和的碳酸钙溶液沿着缝洞系统向下渗流过程中所形成的,所以认为该微相形成于陆上沉积环境(Flügel,2010)。
-
(9)MF20岩溶角砾云岩:发育在灯二段上部古溶洞的底部,角砾的岩性为全部为碳酸盐岩,粒度范围包括砂屑级至中砾级,分选不好,圆度多为棱角状,表现为大量的棱角状碳酸盐岩碎屑嵌入到泥晶基质或/和胶结物组成的填隙物中(图3m、n),部分碎屑颗粒边缘可见悬挂形重力胶结物(图3o)。根据其分选、磨圆认为其为原地形成,并根据镜下观察到的在颗粒边缘存在悬挂形重力胶结物认为其形成于自由表面之上,加上其野外产状,认为该微相为原地碳酸盐岩经淡水溶解—蒸发—崩塌形成的非沉积角砾岩,形成于陆上沉积环境(Flügel,2010)。
-
3 典型沉积序列描述与环境分析
-
研究发现清平地区灯一段—灯二段、灯四段发育若干向上变浅的沉积序列以及米级沉积旋回;沉积序列表现为相对海平面的逐渐降低,其形成可能是由于海平面下降或沉积速率大大超过沉降速度所导致;沉积旋回反映水体深度高频次、周期性地不断波动,单个旋回厚度在0.5~10m之间,厚度为2~3m的居多。沉积序列和沉积旋回类型主要共有五种:序列类型Ⅰ(S1)潮下带—潮间带—潮上带的完整潮坪序列,序列类型Ⅱ(S2)为潮下带—潮间序列,序列类型Ⅲ(S3)为潮间带—潮上序列(图4);旋回类型Ⅰ(C1)为潮下颗粒滩旋回,旋回类型Ⅱ(C2)为潮间微生物丘旋回(图5)。
-
(1)序列类型Ⅰ(S1) 根据不同的微相组合分为2个亚类。S1-1发育在灯二段中部,表现为MF5→MF7→MF12→MF15→MF20的沉积序列,反映了从浅潮下带高能环境—潮间带局限水体环境—潮上暴露环境的演化序列。S1-2发育在灯四段的上部,表现为MF3→MF10→MF11→MF19的沉积序列,反映了从潮下带弱振荡水体环境—潮间带频繁暴露环境—潮上带大气淡水沉积环境的演化序列。
-
(2)序列类型Ⅱ(S2)根据不同的微相组合分为2个亚类。S2-1发育在灯一段—灯二段下部,表现为MF5→MF6→MF10→MF11→MF14的沉积序列,反映了从浅潮下带高能环境—潮间带频繁暴露环境—潮间带局限水体环境的演化序列。S2-2发育在灯三段以及灯四段下部表现为MF0→MF5→MF10→MF11的沉积序列,反映了从浅海—潮下带高能环境—潮间带频繁暴露环境的演化序列。
-
(3)序列类型Ⅲ(S3)(MF12→MF15→MF17→MF18):该序列发育在灯二段上部,单序列厚度为2~3m,表现为多个叠层状微生物黏结云岩—葡萄状白云岩—泥晶云岩—鸟眼孔、窗孔状泥晶云岩的沉积序列,反映了从潮间带局限环境—潮上蒸发环境的演化序列。
-
(4)颗粒滩沉积旋回(C1)进一步分为C1-1砂屑滩、C1-2鲕粒滩、C1-3核形石滩三种类型。其中C1-1砂屑滩在灯一、灯四段可见,C1-2鲕粒滩在灯二段发育,C1-3核形石滩在灯二段可见,旋回厚度在2~10m之间,主要表现为下部砂屑颗粒,上部集合粒、鲕粒或核形石颗粒的沉积序列,反映了浅潮下带高能环境沉积。
-
图4 川西清平剖面震旦系灯影组典型沉积序列演化示意图
-
Fig.4 Schematic diagram of the evolution of the typical sedimentary sequence of the Sinian Dengying Formation in the Qingping section, western Sichuan
-
图5 川西清平剖面震旦系灯影组典型沉积旋回演化示意图
-
Fig.5 Schematic diagram of typical sedimentary cycle evolution of Sinian Dengying Formation in the Qingping section, western Sichuan
-
(5)微生物丘沉积旋回(C2)主要在灯二段发育,单个完整序列厚度为3~6m。完整沉积序列由丘基—丘核—丘坪、丘翼构成。丘基主要为团块状微生物黏结云岩、砂屑粒泥云岩;丘核是微生物丘的主体部分,主要为凝块状微生物黏结云岩、泡沫绵层状微生物黏结云岩;丘翼分布于微生物丘两侧,为微生物丘间的过渡区域,主要微相为泥晶白云岩、砂屑粒泥云岩,为微生物丘之间的低能区域;丘坪为微生物丘的顶部区域,受微生物丘快速生长或高频海平面下降而造成暴露,其横向连续性较差,主要微相为纹层状微生物黏结云岩、花边状白云岩、葡萄状白云岩,受大气淡水溶蚀作用影响明显。
-
4 沉积环境演化及海平面变化
-
通过对清平剖面灯影组详细的沉积相演化分析,认为其沉积相类型主要以潮下带颗粒滩沉积、潮间带微生物丘沉积以及潮上暴露环境下的蒸发沉积和岩溶沉积为主;沉积物类型受潮汐、波浪、风暴等作用强烈控制,沉积环境演化受全球海平面波动、区域构造活动以及碳酸盐岩沉积速率综合影响;相对海平面变化经历了四次海侵—海退次级旋回以及两次全区可对比的暴露侵蚀,详细沉积环境演化过程及海平面变化历程如下所述(图6)。
-
图6 川西清平剖面震旦系灯影组沉积演化综合地层柱状图
-
Fig.6 Synthetic stratigraphic histogram of the sedimentary evolution of the Sinian Dengying Formation in the Qingping section, western Sichuan
-
次级旋回Ⅰ 由灯一段—灯二段下部构成,厚度约220m,演化序列为泥晶云岩(海侵)浅潮下带颗粒滩沉积(海侵)、潮间带微生物丘沉积;次级旋回Ⅱ 由灯二段中上部—灯二段顶部构成,厚度约300m,演化序列为潮间带纹层状微生物云岩沉积(海侵)、浅潮下带颗粒滩沉积(海退)、潮间带局限环境沉积(海退)、潮上带蒸发环境沉积(海退),灯二段顶部暴露不整合面;次级旋回Ⅲ 由灯三段—灯四段下部构成,厚度约120m,演化序列为深潮下带静水环境沉积(海侵)、浅潮下带颗粒滩沉积(海退)、潮间带微生物丘沉积;次级旋回Ⅳ 由灯四段中上部—灯四段顶部构成,厚度在100m左右,演化序列为潮下带风暴沉积(海侵)、潮下带颗粒滩沉积(海退)、潮间带微生物丘沉积(海退)、潮上带暴露环境沉积(海退)、灯四段顶部的风化壳以及不整合面。
-
5 沉积模式及其地质意义
-
灯影组为隐生宙-显生宙交接期的沉积,体现了宏体生物即将出现之前,以微生物主导的海洋生态系统中的碳酸盐岩沉积特征,该时期海洋以潮汐作用为主,波浪作用较弱,偶尔发生风暴作用(胡安平等,2021)。据此,根据对清平剖面沉积微相特征、微相组合特征、沉积相演化规律的研究以及在前人建立的沉积模式的基础上,建立了上扬西北缘灯影组的浅水碳酸盐岩台地的沉积模式。该模式依据海水深度以及波浪、潮汐作用影响的范围,将其沉积环境划分为浅海、潮下带、潮间频繁暴露环境、潮间局限环境(弱暴露)、潮上蒸发环境以及陆上大气淡水影响环境,详细沉积环境分布如图7所示。
-
综上所述,埃迪卡拉纪灯影组在上扬子西北缘表现为以丘滩体、颗粒滩、潮坪相为典型沉积特征的受次级海平面波动影响的浅水微生物碳酸盐岩台地沉积;该层位为四川盆地安岳气田主要油气勘探层位,也是目前四川盆地深层古老碳酸盐岩油气勘探的重要目标(邹才能等,2019),对灯影组沉积环境演化详细刻画有利于明确优质储层的纵向分布特征。每一个次级旋回上部会发生明显的同生期或表生期岩溶作用,形成典型格架孔、层间孔、铸膜孔以及不整合面岩溶裂缝,这些孔缝均是油气储集和疏导的有效空间(文龙等,2016;王文之等,2019),因此,位于灯影组内部每一个次级旋回的中上部可能成为灯影组优质储层发育的主要层位。同时,在纳米比亚板块埃迪卡拉系中上部(等同于灯二段顶部)发育一次小型冰期(Vingerbreek glaciation)(Hofmann et al.,2015),在西伯利亚板块、纳米比亚、哈萨克斯坦地区埃迪卡拉系顶部(等同于灯四段顶部)发育一次小型冰期(Baikonur glaciation)(Chumakov,2011),这些冰期均与灯影组内部的不整合可能相关;因此,其可以进一步佐证扬子台地灯影组内部的两次暴露不整合可能与冰期事件导致的海平面下降有关。
-
图7 川西清平剖面震旦系灯影组沉积模式图
-
Fig.7 Sedimentary model of the Sinian Dengying Formation in the Qingping section, western Sichuan
-
6 结论
-
(1)根据不同岩石类型的组构特征差异以及碳酸盐岩微相分类原则,将清平剖面灯影组划分为21种岩石微相。最为常见的微相类型包括:MF3放射鲕颗粒云岩、MF7核形石砾状云岩、MF8切向鲕颗粒云岩、MF10纹层状微生物黏结云岩、MF12叠层状微生物黏结云岩、MF14凝块状微生物黏结云岩、MF15葡萄状白云岩、MF16花边状白云岩、MF18鸟眼孔、窗格孔状泥晶云岩、MF20岩溶角砾云岩。
-
(2)基于微相解释和纵向组合关系,发现清平剖面灯影组存在若干向上变浅的米级沉积旋回;包括:S1潮下—潮间—潮上沉积序列、S2潮下—潮间沉积序列、S3潮间—潮上沉积序列以及C1颗粒滩沉积旋回、C2微生物丘沉积旋回等。
-
(3)沉积环境演化研究认为,灯影组经历了四次海侵-海退旋回,次级旋回Ⅰ由灯一段—灯二段下部构成、次级旋回Ⅱ由灯二段中上部—灯二段顶部构成、次级旋回Ⅲ由灯三段—灯四段下部构成、次级旋回Ⅳ由灯四段中上部—灯四段顶部构成;并且发生了两次全区可对比的暴露侵蚀作用,分别导致灯二段以及灯四段顶部存在沉积间断。
-
(4)灯影组沉积环境受全球海平面波动、区域构造活动以及碳酸盐岩沉积速率综合影响,沉积物类型由潮汐作用、波浪作用以及风暴作用等控制,反映了一个以丘滩体、颗粒滩、潮坪相为典型沉积特征的浅水碳酸盐岩台地形成过程。灯影组内部每一个次级旋回的中上部可能成为灯影组优质储层发育的主要层位,并且灯影组内部的两次暴露不整合可能与冰期事件导致的海平面下降密切相关。
-
参考文献
-
Chumakov N M. 2011. Late Proterozoic African glacial era. Stratigraphy & Geological Correlation, 19(1): 1~20.
-
Cui Huan, Xiao Shuhai, Cai Yaoping, Peek S, Plummer R E, Kaufman A J. 2019. Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China. Geological Magazine, 156: 1924~1948.
-
Davis R A, Dalrymple R W. 2012. Principles of Tidal Sedimentology. Dordrecht: Springer.
-
Deng Shenghui, Fan Ru, Li Xin, Zhang Shiben, Zhang Baomin, Lu Yuanzheng. 2015. Subdivision and correlation of the Sinian(Ediacaran) system in the Sichuan basin and its adjacent area. Journal of Stratigraphy, 39(3): 239~254 (in Chinese with English abstract).
-
Deng Shuanglin, Song Jinmin, Liu Shugen, Luo Ping, Li Zhiwu, Yang Di, Sun Wei, Li Jinxi, Yu Jingjie, Li Liji. 2020. Mixed sedimentary characteristics of the third member of Dengying Formation, Sichuan basin, and its geological significance. Acta Sedimentologica Sinica, 38(3): 598~609 (in Chinese with English abstract).
-
Ding Yi, Chen Daizhao, Zhou Xiqiang, Guo Chuan, Huang Taiyu, Zhang Gongjing. 2019. Cavity-filling dolomite speleothems and submarine cements in the Ediacaran Dengying microbialites, South China: responses to high-frequency sea-level fluctuations in an ‘aragonite-dolomite sea’. Sedimentology, 66(6): 2511~2537.
-
Du Jinhu, Wang Zecheng, Zou Caineng, Xu Chunchun, Shen Ping, Zhang Baomin, Jiang Hua, Huang Shipeng. 2016. Discovery of intra-cratonic rift in the Upper Yangtze and its coutrol effect on the formation of Anyue giant gas field. Acta Petrolei Sinica, 37(1): 1~16 (in Chinese with English abstract).
-
Flügel E. 2010. Microfacies of Carbonate Rocks: Analysis, Interpretation and Application, 2nd edn. New York: Springer, 1~984.
-
Gu Zhidong, Yin Jifeng, Jiang Hua, Li Qiufen, Zhai Xiufen, Huang Pinghui, Peng Ping, Yang Fan, Zhang Hang. 2016. Discovery of Xuanhan-Kaijiang Paleouplift and its significance in the Sichuan basin, SW China. Petroleum Exploration and Development, 43(6): 893~904 (in Chinese with English abstract).
-
Hofmann M, Linnemann U, Hoffmann K H, Germs G, Gerdes A, Marko L, Eckelmann K G, Rtner A, Krause R. 2015. The four Neoproterozoic glaciations of southern Namibia and their detrital zircon record: the fingerprints of four crustal growth events during two supercontinent cycles. Precambrian Research, 259: 176~188.
-
Hou Mingcai, Xing Fengcun, Xu Shenglin, Lin Liangbiao, Liu Xinchun, Xiong Fuhao, Huang Hu. 2017. Paleogeographic patterns of E-C transition period in the Upper Yangtze and the geodynamic mechanism. Acta Sedimentologica Sinica, 35(5): 902~917 (in Chinese with English abstract).
-
Hu Anping, Shen Anjiang, Zheng Jianfeng, Wang Xin, Wang Xiaofang. 2021. The classification, facies and sedimentary models of microbialites. Marine Origin Petroleum Geology, 26(1): 1~15 (in Chinese with English abstract).
-
Jiang Ganqiang, Shi Xiaoying, Zhang Shihong, Wang Yue, Xiao Shuhai. 2011. Stratigraphy and paleogeography of the Ediacaran Doushantuo Formation (ca. 635–551 Ma) in South China. Gondwana Research, 19(4): 831~849.
-
Li Anpeng, Zhou Lingbao, Zhong Kang, Xiong Yi, Zhang Lele, Da Gao. 2019. Depositionfabrics and environment analysis of the fourth member of the Dengying Formation in Gaoshiti Area, central Sichuan basin. Advances in Geosciences, 9(5): 376~382 (in Chinese with English abstract).
-
Li Ling, Tan Xiucheng, Zeng Wei, Zhou Tao, Yang Yu, Hong Haitao, Luo Bing, Bian Lizeng. 2013. Development and reservoir significance of mud mounds in Sinian Dengying Formation, Sichuan basin. Petroleum Exploration and Development, 40(6): 666~673 (in Chinese with English abstract).
-
Li Yingqiang, He Dengfa, Wen Zhu. 2013. Palaeogeography and tectonic-depositional environment evolution of the Late Sinian in Sichuan basin and adjacent areas. Journal of Palaeogeography, 15(2): 231~245 (in Chinese with English abstract).
-
Li Yong, Wang Xingzhi, Feng Mingyou, Zeng Deming, Xie Shengyang, Fan Rui, Wang Liangjun, Zeng Tao, Yang Xuefei. 2019. Reservoir characteristics and genetic differences between the second and fourth members of Sinian Dengying Formation in northern Sichuan basin and its surrounding areas. Petroleum Exploration and Development, 46(1): 52~64 (in Chinese with English abstract).
-
Li Zhiwu, Ran Bo, Xiao Bin, Song Jinmin, Zhang Ling, Li Jinxi, Wang Han, Xiao Bin, Ye Yuehao, Cai Qixin, Liu Shugen. 2019. Sinian to Early Cambrian uplift-depression framework along the northern margin of the Sichuan basin, central China and its implications for hydrocarbon exploration. Earth Science Frontiers, 26(1): 59~85 (in Chinese with English abstract).
-
Lin Xiaoxian, Peng Jun, Yan Jianping, Hou Zhongjian. 2015. A discussion about origin of botryoidal dolostone of the Sinian Dengying Formation in Sichuan basin. Journal of Palaeogeography(Chinese Edition), 17(6): 755~770 (in Chinese with English abstract).
-
Liu Jingjiang, Li Wei, Zhang Baomin, Zhou Hui, Yuan Xiaohong, Shan Xiuqin, Zhang Jing, Deng Shenghui, Gu Zhidong, Fan Ru, Wang Yongjun, Li Xin. 2015. Sedimentary palaeogeography of the Sinian in Upper Yangtze region. Journal of Palaeogeography(Chinese Edition), 17(6): 735~753 (in Chinese with English abstract).
-
Liu Shugen, Sun Wei, Luo Zhili, Song Jinmin, Zhong Yong, Tian Yanhong, Peng Hanlin. 2013. Xingkai taphrogenesis and petroleum exploration from Upper Sinian to Cambrian strata in Sichuan basin, China. Journal of Chengdu University of Technology (Science & Technology Edition), 40(5): 511~520 (in Chinese with English abstract).
-
Shuai Yanhua, Liu Keyu, Hu Guoyi, Wang Tongshan, Tian Xingwang, Zhang Bin, Chen Zhuxin. 2021. Gas accumulation mechanisms of the Sinian reservoir in the Sichuan basin and their significance for deep gas exploration. Acta Geologica Sinica, 95(11): 3400~3412 (in Chinese with English abstract).
-
Song Jinmin, Luo Ping, Liu Shugen, Li Zhiwu, Sun Wei, Tang Xuan, Yang Di, Yu Jingjie. 2018. The deposition and reservoir characteristics of Dengying Formation in western Sichuan basin, China. Journal of Chengdu University of Technology(Science & Technology Edition), 45(1): 27~44 (in Chinese with English abstract).
-
Su Guiping, Li Zhongquan, Ying Danlin, Li Gen, Ying Wenfeng, Yang Yuanyu, Liu Henglin, Ding Xiao, Tang Huaqiang. 2020. Formation and evolution of the Caledonian paleo-uplift and its genetic mechanism in the Sichuan basin. Acta Geologica Sinica, 94(6): 1793~1812 (in Chinese with English abstract).
-
Wang Wenzhi, Yang Yueming, Wen Long, Luo Bing, Luo Wenjun, Xia Maolong, Sun Sainan. 2016. A study of sedimentary characteristics of microbial carbonate: a case study of the Sinian Dengying Formation in Gaomo area, Sichuan basin. Geology in China, 43(1): 306~318 (in Chinese with English abstract).
-
Wang Wenzhi, Wen Long, Yao Jun, Li Kunyu, He Yuan, Zhou Hongfei, Nie Jing, Li Ya. 2019. Sequence classification and discovery of multi-stage platform margin belts of Sinian Dengying Formation, Sichuan basin. Natural Gas Exploration and Development, 42(4): 46~54 (in Chinese with English abstract).
-
Wei Guoqi, Yang Wei, Xie Wuren, Jin Hui, Su Nan, Sun Ai, Shen Juehong, Hao Cuiguo. 2018. Accumulation modes and exploration domains of Sinian-Cambrian natural gas in Sichuan basin. Acta Petrolei Sinica, 39(12): 1317~1327 (in Chinese with English abstract).
-
Wen Long, Yang Yueming, You Chuanqiang, Zhang Xihua, Peng Hanlin, Wang Wenzhi, Luo Bing, Luo Wenjun. 2016. Characteristics of Dengying Fm. sedimentary sequence in the central-western Sichuan basin and their controlling effect on gas accumulation. Natural Gas Industry, 36(7): 8~17 (in Chinese with English abstract).
-
Xiao Shuhai, Narbonne G M, Zhou Chuanming, Laflamme M, Grazhdankin D V, Moczydlowska V M, Cui Huan. 2016. Towards an Ediacaran time scale: problems, protocols, and prospects. Episodes, 39(4): 540~555.
-
Xia Qingsong, Huang Chenggang, Yang Yuran, Peng Jun, Tao Yanzhong, Zhou Xiang. 2021. Reservoir characteristics and main controlling factors of oil and gas accumulation of Dengying Formation, Sinian System, in Gaoshiti-Moxi area, Sichuan basin. Geological Review, 67(2): 441~458 (in Chinese with English abstract).
-
Yang Yueming, Wen Long, Luo Bing, Song Jiarong, Chen Xiao, Wang Xiaojuan, Hong Haitao, Zhou Gang, He Qinglin, Zhang Xiaoli, Zhong Jiayi, Liu Ran, Shan Shujiao. 2016. Sedimentary tectonic evolution and reservoir-forming conditions of the Dazhou-Kaijiang paleo-uplift, Sichuan basin. Natural Gas Industry, 36(8): 1~10 (in Chinese with English abstract).
-
Yang Yueming, Yang Yu, Yang Guang, Song Jiarong, Wen Long, Deng Chuanguang, Xia Maolong, Ran Qi, Duan Guobin, Luo Bing, Xie Bing. 2019. Gas accumulation conditions and keyexploration & development technologies of Sinian and Cambrian gas reservoirs in Anyue gas field. Acta Petrolei Sinica, 40(4): 493~508 (in Chinese with English abstract).
-
Zhang Shihong, Jiang Ganqing, Zhang Junming, Song Biao, Kennedy M J, Christie B N. 2005. U-Pb sensitive high-resolution ion microprobe ages from the Doushantuo Formation in South China: constraints on late Neoproterozoic glaciations. Geology, 33(6): 473~476.
-
Zhao Dongfang, Hu Guang, Zhang Wenji, Wang Lichao, Li Fei, Tan Xiucheng, Lian Chengbo. 2018. Sedimentary Characteristics of Ooids of Sinian(Ediacaran) Dengying Formation on the Yulin section in Wuxi, Chongqing, and geological implications. Geological Review, 64(1): 191~202 (in Chinese with English abstract).
-
Zhao Wenzhi, Wei Guoqi, Yang Wei, Mo Wuling, Xie Wuren, Su Nan, Liu Mancang, Zeng Fuying, Wu Saijun. 2017. Discovery of Wanyuan-Dazhou intracratonic rift and its exploration significance in the Sichuan basin, SW China. Petroleum Exploration and Development, 44(5): 659~669 (in Chinese with English abstract).
-
Zhou Jingao, Fang Chao, Ji Hancheng, Zhang Jianyong, Zhao Fei. 2014. A development rule of Lower Cambrian Longwangmiao grain beaches in the Sichuan basin. Natural Gas Industry, 34(8): 27~36 (in Chinese with English abstract).
-
Zhou Jingao, Zhang Jianyong, Deng Hongying, Chen Yana, Hao Yi, Li Wenzheng, Gu Mingfeng, Luo Xianying. 2017. Lithofacies paleogeography and sedimentary model of Sinian Dengying Fm. in the Sichuan basin. Natural Gas Industry, 37(1): 24~31 (in Chinese with English abstract).
-
Zhu Maoyan, Zhang Junming, Yang Aihua. 2007. Integrated Ediacaran (Sinian) chronostratigraphy of South China. Palaeogeography, Palaeoclimatology, Palaeoecology, 254(1-2): 7~61.
-
Zou Caineng, Yang Zhi, Wang Hongyan, Dong Dazhong, Liu Honglin, Shi Zhensheng, Zhang Bin, Sun Shasha, Liu Dexun, Li Guizhong, Wu Songtao, Pang Zhenglian, Pan Songqi, Yuan Yilin. 2019. “Exploring petroleum inside source kitchen”: Jurassic unconventional continental giant shale oil & gas field in Sichuan basin, China. Acta Geologica Sinica, 93(7): 1551~1562 (in Chinese with English abstract).
-
邓胜徽, 樊茹, 李鑫, 张师本, 张宝民, 卢远征. 2015. 四川盆地及周缘地区震旦(埃迪卡拉)系划分与对比. 地层学杂志, 39(3): 239~254.
-
邓双林, 宋金民, 刘树根, 罗平, 李智武, 杨迪, 孙玮, 李金玺, 余晶洁, 李立基. 2020. 四川盆地灯影组三段混积特征及其地质意义. 沉积学报, 38(3): 598~609.
-
杜金虎, 汪泽成, 邹才能, 徐春春, 沈平, 张宝民, 姜华, 黄士鹏. 2016. 上扬子克拉通内裂陷的发现及对安岳特大型气田形成的控制作用. 石油学报, 37(1): 1~16.
-
谷志东, 殷积峰, 姜华, 李秋芬, 翟秀芬, 黄平辉, 彭平, 杨帆, 张航. 2016. 四川盆地宣汉—开江古隆起的发现及意义. 石油勘探与开发, 43(6): 893~904.
-
侯明才, 邢凤存, 徐胜林, 林良彪, 刘欣春, 熊富浩, 黄虎. 2017. 上扬子E-C转换期古地理格局及其地球动力学机制探讨. 沉积学报, 35(5): 902~917.
-
胡安平, 沈安江, 郑剑锋, 王鑫, 王小芳. 2021. 微生物碳酸盐岩分类、沉积环境与沉积模式. 海相油气地质, 26(1): 1~15.
-
李安鹏, 周灵宝, 仲康, 熊意, 张乐乐, 高达. 2019. 川中高石梯地区灯影组四段微生物碳酸盐岩结构类型及沉积环境分析. 地球科学前沿, 9(5): 376~382.
-
李凌, 谭秀成, 曾伟, 周涛, 杨雨, 洪海涛, 罗冰, 边立曾. 2013. 四川盆地震旦系灯影组灰泥丘发育特征及储集意义. 石油勘探与开发, 40(6): 666~673.
-
李英强, 何登发, 文竹. 2013. 四川盆地及邻区晚震旦世古地理与构造—沉积环境演化. 古地理学报, 15(2): 231~245.
-
李勇, 王兴志, 冯明友, 曾德铭, 谢圣阳, 凡睿, 王良军, 曾韬, 杨雪飞. 2019. 四川盆地北部及周缘地区震旦系灯影组二段、四段储集层特征及成因差异. 石油勘探与开发, 46(1): 52~64.
-
李智武, 冉波, 肖斌, 宋金民, 郑玲, 李金玺, 王瀚, 肖斌, 叶玥豪, 蔡其新, 刘树根. 2019. 四川盆地北缘震旦纪—早寒武世隆—坳格局及其油气勘探意义. 地学前缘, 26(1): 59~85.
-
林孝先, 彭军, 闫建平, 侯中健. 2015. 四川盆地震旦系灯影组葡萄状白云岩成因讨论. 古地理学报, 17(6): 755~770.
-
刘静江, 李伟, 张宝民, 周慧, 袁晓红, 单秀琴, 张静, 邓胜徽, 谷志东, 樊茹, 王拥军, 李鑫. 2015. 上扬子地区震旦纪沉积古地理. 古地理学报, 17(6): 735~753.
-
刘树根, 孙玮, 罗志立, 宋金民, 钟勇, 田艳红, 彭瀚霖. 2013. 兴凯地裂运动与四川盆地下组合油气勘探. 成都理工大学学报(自然科学版), 40(5): 511~520.
-
宋金民, 罗平, 刘树根, 李智武, 孙玮, 唐玄, 杨迪, 余晶洁. 2018. 四川盆地西部震旦系灯影组沉积储层特征. 成都理工大学学报(自然科学版), 45(1): 27~44.
-
苏桂萍, 李忠权, 应丹琳, 李根, 应文峰, 杨渊宇, 刘恒麟, 丁啸, 唐华强. 2020. 四川盆地加里东古隆起形成演化及动力学成因机理. 地质学报, 94(6): 1793~1812.
-
帅燕华, 刘可禹, 胡国艺, 王铜山, 田兴旺, 张斌, 陈竹新. 2021. 四川盆地深层前寒武系天然气超晚期成藏及勘探意义. 地质学报, 95(11): 3400~3412.
-
王文之, 杨跃明, 文龙, 罗冰, 罗文军, 夏茂龙, 孙赛男. 2016. 微生物碳酸盐岩沉积特征研究——以四川盆地高磨地区灯影组为例. 中国地质, 43(1): 306~318.
-
王文之, 文龙, 姚军, 李堃宇, 和源, 周红飞, 聂晶, 李亚. 2019. 四川盆地震旦系灯影组层序划分及多期台缘带的发现. 天然气勘探与开发, 42(4): 46~54.
-
魏国齐, 杨威, 谢武仁, 金惠, 苏楠, 孙爱, 沈珏红, 郝翠果. 2018. 四川盆地震旦系—寒武系天然气成藏模式与勘探领域. 石油学报, 39(12): 1317~1327.
-
文龙, 杨跃明, 游传强, 张玺华, 彭瀚霖, 王文之, 罗冰, 罗文军. 2016. 川中—川西地区灯影组沉积层序特征及其对天然气成藏的控制作用. 天然气工业, 36(7): 8~17.
-
夏青松, 黄成刚, 杨雨然, 彭军, 陶艳忠, 周翔. 2021. 四川盆地高石梯—磨溪地区震旦系灯影组储层特征及主控因素. 地质论评, 67(2): 441~458.
-
杨跃明, 文龙, 罗冰, 宋家荣, 陈骁, 王小娟, 洪海涛, 周刚, 何青林, 张晓丽, 钟佳倚, 刘冉, 山述娇. 2016. 四川盆地达州-开江古隆起沉积构造演化及油气成藏条件分析. 天然气工业, 36(8): 1~10.
-
杨跃明, 杨雨, 杨光, 宋家荣, 文龙, 邓传光, 夏茂龙, 冉崎, 段国彬, 罗冰, 谢冰. 2019. 安岳气田震旦系、寒武系气藏成藏条件及勘探开发关键技术. 石油学报, 40(4): 493~508.
-
赵东方, 胡广, 张文济, 王利超, 李飞, 谭秀成, 连承波. 2018. 渝北巫溪鱼鳞剖面灯影组鲕粒沉积特征及其地质意义. 地质论评, 64(1): 191~202.
-
赵文智, 魏国齐, 杨威, 莫午零, 谢武仁, 苏楠, 刘满仓, 曾富英, 武赛军. 2017. 四川盆地万源—达州克拉通内裂陷的发现及勘探意义. 石油勘探与开发, 44(5): 659~669.
-
周进高, 房超, 季汉成, 张建勇, 赵菲. 2014. 四川盆地下寒武统龙王庙组颗粒滩发育规律. 天然气工业, 34(8): 27~36.
-
周进高, 张建勇, 邓红婴, 陈娅娜, 郝毅, 李文正, 谷明峰, 罗宪婴. 2017. 四川盆地震旦系灯影组岩相古地理与沉积模式. 天然气工业, 37(1): 24~31.
-
邹才能, 杨智, 王红岩, 董大忠, 刘洪林, 施振生, 张斌, 孙莎莎, 刘德勋, 李贵中, 吴松涛, 庞正炼, 潘松圻, 袁懿琳. 2019. “进源找油”: 论四川盆地非常规陆相大型页岩油气田. 地质学报, 93(7): 1551~1562.
-
摘要
上扬子地区震旦系灯影组不仅记录了埃迪卡拉纪晚期环境与生命的协同演化,而且大量发育的丘滩体沉积正成为四川盆地深层古老碳酸盐岩油气勘探的重要目标。因此分析灯影组沉积环境演化不仅可以约束埃迪卡拉纪晚期全球海平面变化、古海洋环境演化,而且对于四川盆地深层油气勘探具有重要意义。前人对于上扬子地区震旦系灯影组的沉积环境演化、相对海平面变化仍缺乏较为精细的刻画和解释,严重制约了以上研究的进展。本文通过对上扬子西北缘绵竹清平剖面灯影组详细的野外沉积学解剖及室内微相分析解释,识别出以各类颗粒云岩、微生物云岩为主的21类岩石微相;根据微相组合关系分析,认为发育多种向上变浅的潮下—潮间—潮上沉积序列以及若干颗粒滩、微生物丘沉积构成的米级沉积旋回;以此为基础详细刻画出灯一段—灯二段下部、灯二段中上部—灯二段顶部、灯三段底部—灯四段下部、灯四段中上部—灯四段顶部构成的四次海侵—海退次级旋回以及灯二段和灯四段顶部暴露侵蚀的沉积环境演化及海平面变化历程,并建立了扬子台地西缘绵竹地区埃迪卡拉纪晚期以潮坪相、微生物丘滩体、颗粒滩为典型沉积特征的浅水碳酸盐岩台地沉积模式。综合沉积微相特征、微相组合特征及剖面沉积相演化规律认为,该地区沉积环境演化主要受次级海平面波动影响,海侵—海退次级旋回的中上部可能为灯影组优质储层发育的主要层位,其内部的两次暴露不整合可能与冰期事件导致的海平面下降密切相关。
Abstract
The Ediacaran Dengying Formation in the Upper Yangtze area not only recorded the co-evolution of environment and life at the end of the Precambrian, but the massively developed mound-shoal deposits are currently becoming an important target for oil and gas exploration in deep ancient carbonate rocks in the Sichuan basin. Therefore, analyzing the evolution of the Dengying Formation sedimentary environment can not only constrain the global sea level change and the evolution of the paleo-ocean environment in the late Ediacaran, but also has important value for deep oil and gas exploration in the Sichuan basin. Previous studies lack detailed description and explanation of the sedimentary environment evolution and relative sea level changes of the Dengying Formation at the end of the Ediacaran in the Upper Yangtze area, which severely limited the progress of the above studies. Based on detailed field sedimentology and microfacies analysis and interpretation of Dengying Formation in Qingping section of Mianzhu in the northwestern margin of the Upper Yangtze, 21 types of rock microfacies were identified, mainly composed of granular and microbial dolomites. According to the analysis of microfacies assemblage relationship, it is considered that there are several shallower subtidal-intertidal-supratactic sedimentary sequences and meter-level sedimentary cycles composed of several grain banks and microbe mounds. On this basis, the sedimentary environment evolution and sea level change process of four transgression-regressive secondary cycles and two exposed erosions are described in detail. The sedimentary model of shallow water carbonate platform in the Mianzhu area in the western margin of Yangtze Platform in Late Ediacaran is established, which is characterized by tidal flat facies, microbial mound bank body and grain bank. Based on the characteristics of sedimentary microfacies, combination of microfacies and vertical evolution of sedimentary facies, it is believed that the evolution of the sedimentary environment in this area is mainly affected by secondary sea level fluctuations, and the middle and upper part of the transgression-regression secondary cycle may be high-quality reservoirs in the Dengying Formation. The two exposure unconformities in the main development horizon may be closely related to the sea level drops caused by ice age events.