-
生物礁是由固着生物“建造”的一种特殊的生物沉积体。国内外勘探实践表明,生物礁是许多大中型油气藏的重要储集层,因而生物礁常常成为油气勘探的重要对象(卫平生等,2008)。同时,生物礁中蕴藏着丰富的生物化石,是重要的“化石库”,可以反映当时的古气候、古生态、古环境。因此,对于生物礁研究有利于恢复古气候、古环境,对研究生物演化也具有重要意义(巩恩普等,2021)。此外,近年来学界对于礁灰岩的工程地质特征研究也取得了一定进展,对我国南海岛礁的工程建设有一定指导意义(钟毓等,2020;王振亭等,2021)。
-
二叠纪是继泥盆纪之后,又一个生物礁发育的高峰期,这一时期的造礁生物多样、礁体类型丰富(范嘉松等,2005)。其中,北美著名的二叠盆地发育世界闻名的Capitan生物礁(Wood,1999;Playton et al.,2018;Bryant et al.,2022),我国华南地区晚二叠世也广泛发育海绵生物礁(刘冬洋等,2017;李阳等,2018)。据野外观察,塔里木盆地西北缘(简称“塔西北”)乌拉尔世地层中广泛发育生物礁,其中,巴立克立克组中上部更是发育厚度>200 m的藻礁,这是塔里木盆地二叠系生物礁发育的一大特色。前人对于塔西北的乌拉尔世生物礁也有一定程度研究。王黎栋等(2006)初步研究了柯坪地区苏巴什剖面康克林组生物礁特征,罗金海等(2007)从整体角度研究了塔西北二叠系生物礁的时空分布和油气地质意义,王庆同等(2021)研究了塔西北的二叠系藻礁的地球化学特征及其环境意义。目前,国内地质学界对于塔西北乌拉尔世生物礁的研究较为宽泛,侧重于宏观演化,缺乏对于单个礁点的深入解析,在礁体的发育模式、成岩作用等方面的工作也较为粗浅,以至于制约了对于塔西北二叠纪沉积环境的深入研究,更制约了塔西北二叠系生物礁油气藏的勘探。
-
基于此,笔者于2021年初对塔西北克孜勒布拉克南沟中的巴立克立克组生物礁进行了详细的观察、描述、采样。本文基于对礁体的宏微观地质特征的观察,对该礁体的结构、成岩作用等进行了深入解析,结合地化分析的结果和前人对石炭系—二叠系造礁生物古生态、塔里木大火成岩省的相关研究,尝试探讨塔西北巴立克立克组礁滩复合体的成因及演化阶段,并分析乌拉尔世塔西北造礁环境的普遍性,希望为塔西北乌拉尔世古气候、古环境的深入研究提供有益借鉴。同时,本文还对塔西北巴立克立克组礁滩体的物性进行了相关分析,尝试对塔西北二叠纪生物礁储层的预测提供科学依据。
-
1 区域地质背景
-
前人的研究表明,塔西北柯坪—温宿一带在石炭纪为古隆起,自宾夕法尼亚亚系卡西莫夫阶的康克林组开始,塔里木盆地发生自西向东的海侵,柯坪—温宿古隆起多被海水淹没,碳酸盐岩台地开始形成。到了巴立克立克组沉积时期,随着塔里木盆地陆内火山喷发,塔里木大火成岩省开始形成,柯坪地区与巴立克立克组大体等时的库普库兹曼组和开派兹雷克组也发育厚度较大的火成岩。与此同时,海侵范围达到最大,开始沿着克孜勒布拉克南沟—阿合奇—奥衣布拉克山一带发育了规模巨大的台地边缘的礁滩体(贾进华等,2018)。其中,巴立克立克组的台缘礁滩体以克孜勒布拉克南沟的出露程度较好,发育较为典型。
-
塔西北主要包括乌什凹陷(属于库车凹陷向西延伸的部分,可分为东西两个次凹)、柯坪隆起、温宿凸起以及南天山造山带4个部分。而克孜勒布拉克南沟剖面位于乌什西次凹以北的南天山造山带南缘,为一条季节性河道下切形成。该区域构造变形强烈,逆冲推覆体广泛发育,使得该区域广泛出露古生代地层,其中以石炭系—二叠系的出露面积最大(图1)。
-
克孜勒布拉克南沟出露跨石炭系密西西比亚系卡西莫夫阶—二叠系乌拉尔统萨克马尔阶康克林组至巴立克立克组的地层。其中,康克林组下部岩性主要为扇三角洲相的砾岩、含砾粗砂岩,上部主要为局限台地相的生屑滩和滩间海泥晶灰岩,局部夹三角洲相的碎屑岩。巴立克立克组下部主要出露泥岩、泥质粉砂岩、细砂岩等陆棚相的碎屑岩夹少量泥灰岩、泥晶灰岩、生屑灰岩,中上部主要出露厚约400 m的礁灰岩(图2)。前人将该剖面的巴立克立克组下部的碎屑岩段单独划分,将其定为“卡克组”,而将该剖面巴立克立克组上部的礁灰岩定名为“昆克拉契组”(罗金海等,2007)。但是,为了避免繁杂的分层术语引发混乱,本文还是采用“巴立克立克组”来进行统层。
-
2 生物礁结构特征
-
整体上看,礁灰岩的岩性主要为黄灰—褐灰色藻灰岩、藻屑泥晶灰岩等,它们和生屑滩在纵向上呈不等厚互层产出,形成了一套礁滩复合体。从野外观察来看,礁灰岩在宏观露头上产出形态较为多样,大致可以分为如下几种类型:
-
(1)含“藻斑点”泥晶灰岩:野外露头的礁灰岩中可见大量“藻斑点”密集分布;藻斑点多呈暗色,形状多呈圆状—次圆状,有时也可见多个“藻斑点”聚集呈团聚体状,宽一般为0.2~0.8 cm(图3a);斑点间为灰泥充填。该种“藻斑点”的形态与近年来一些研究“微生物岩”的文献中提到的由蓝绿藻(或蓝细菌)控制形成的“卵球形颗粒”较为类似(王建功等,2020)。
-
(2)具“枝状体”藻灰岩:野外露头的礁灰岩中有时可见藻类呈暗色树枝状向垂直层面方向上延伸。其周围往往可见一些“间断”的藻叠层,且每个“间断”的部分往往会呈现周缘“上凸”、中央“下凹”的形态特征(图3b),呈现出“帐篷构造”的特征,有文献(张静等,2022)将其称之为“锅状体”,认为它是潮间带间歇性暴露导致微生物席干裂收缩形成。
-
(3)具“网状体”藻灰岩:野外露头上,暗色的藻类往往呈“网状”密集穿插于泥—微晶基质中(图3c),“网状体”内部结构较为均一,类似于一些文献中提到的“均一石”的特征(吴亚生等,2018)。
-
除此之外,在该套藻礁中,发育大量毫米~厘米级的由亮晶方解石充填的不规则的孔洞(图3a~c),这些孔洞是藻丝体进行光合作用过程中形成的“气体逃逸通道”或藻类埋藏腐烂后形成的气室,后被亮晶方解石充填。
-
根据野外和镜下观察,克孜勒布拉克南沟剖面二叠系巴立克立克组的礁灰岩在纵向上至少发育4期礁滩体,其总厚度约400 m。具体每一期礁相的特征如下:
-
图1 克孜勒布拉克南沟位置图
-
Fig.1 Location of Kezilblak Nangou
-
(a)—塔西北构造分区图(据贾进华等,2018改);(b)—克孜勒布拉克南沟卫星影像图(黄框为生物礁大致出露范围)
-
(a) —structural zoning map of the northwest margin of the Tarim basin (modified after Jia Jinhua et al., 2018) ; (b) —satellite image of Kezilblak Nangou (the place where reefs cropped out approximately is indicated by the yellow box)
-
(1)礁基:每一期礁体底部都可见厚10~20 m的生屑灰岩,其中富含大量䗴类、叶状藻、棘皮生屑等,约占岩石总体积的50%~70%。但是,即使在生屑滩中,已经普遍可见生屑颗粒被蓝绿藻包绕,形成核形石(图4f、i),生屑周围可见大量破碎的微凝块,甚至局部出现藻叠层(图4b),这些具有藻黏结和缠绕结构的生屑滩构成了礁基。
-
图2 塔里木盆地西北缘克孜勒布拉克南沟巴立克立克组生物礁沉积相柱状图
-
Fig.2 Sedimentary facies histogram of the reef of the Baliklik Formation at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(2)礁核:其中,每一期礁核的下部造礁生物主要为蓝绿藻,岩性主要为凝块石灰岩(部分被打碎成为微凝块,图4d),局部发育藻叠层灰岩(图4a),可见少量的苔藓虫、管壳石、叶状藻等,各种附礁生物较少,礁灰岩的颜色多为黄灰色;礁核上部叶状藻比重开始增大并逐渐占据主导地位,且礁体的颜色也逐渐变成褐灰—灰褐色,与此同时苔藓虫、管壳石等造礁生物含量有所增加,䗴类、棘皮动物、腹足等各类附礁生物含量也明显增多,甚至局部富集形成滩体。在镜下可见礁核上部的样品中局部有着褐红色的铁染灰泥充填(图4n),指示氧化环境,藻纹层中也常见指示间歇性暴露的“锅状体”,局部甚至出现了“顺层岩溶”的现象,说明此时的礁体已经时常暴露于大气中。
-
(3)礁后低能带:第一套斜坡相角砾状灰岩之下,发现厚约15 m的灰—深灰色泥晶生屑灰岩,局部夹深灰色核形石灰岩(图3h),有时可见局部介壳富集成层(指示风暴沉积,图3f),整体特征为礁后低能沉积。
-
(4)礁顶—礁前斜坡:该套礁滩复合体的顶底部还可见两套厚约10 m厚的角砾状灰岩,而其中的角砾成分多为藻黏结灰岩、藻团块灰岩,且角砾周围仍可见藻丝体缠绕的特征。其中,沿着礁体顶部的第二套斜坡角砾岩侧向追索,还可见明显的暴露构造,其间可见大量的渗流豆粒、钙结壳和角砾等(图3j~l)。据此可以判断,这两套角砾状灰岩为台缘礁体生长到一定规模后暴露在大气中,遭受大气淡水淋滤和风化剥蚀后,产生的礁角砾,由礁顶沿斜坡滑塌形成,属于礁前斜坡相沉积。此外,在顶部的角砾状灰岩之下约20 m处,发育的顺层的、被多期方解石胶结的溶蚀孔洞(图3m~o),带有古岩溶分带中的“水平潜流带”或“径流溶蚀带”的特征(何江等,2013;邹胜章等,2016)。
-
据4期礁相特征,本文断定,克孜勒布拉克南沟巴立克立克组的礁滩体在纵向上出现了两次“进积—退积”的旋回。这一方面说明巴立克立克组沉积时期的沉积环境有利于礁滩体的发育;另一方面也说明此时海平面升降较为频繁,使得每一期礁滩体都频频暴露在大气淡水中,遭受岩溶改造,对于礁滩体稳定发育有一定消极影响。基于此认识,绘制出了克孜勒布拉克南沟二叠系生物礁结构剖面图(图5)。
-
3 礁体古生物特征
-
3.1 造礁生物
-
3.1.1 蓝绿藻(蓝细菌)
-
蓝绿藻(蓝细菌)作为最主要的造礁生物,在巴立克立克组生物礁发育的各个阶段都有其参与建造,且产出形式较为多样。主要包括:① 呈不规则的纹层状藻丝体包绕,形成单独的藻团块,在礁核上部,蓝绿藻会被铁染灰泥浸染呈褐红色(图6a);② 完全包覆某个生屑颗粒或泥粒,形成具有同心层状内部结构的核形石(图6b),常见于礁基,在礁核上部也较为富集,在礁后低能带中也局部可见;③ 藻丝体和微晶碳酸盐在纵向上互层产出,形成叠层状构造(图4a,图6c),但在该套礁滩体中,叠层石相对较少,且主要见于礁核下部;④ 以生屑滩为基础向上生长、定殖,在滩体表面形成结壳(图4b);⑤ 蓝绿藻包裹在某些生屑、泥粒乃至角砾的表面形成包壳状纹层(图6d),且包壳状纹层的厚度大于被包裹的物质,这与吴亚生(2023)定义的“包壳石”的特征高度吻合;⑥ 呈内部结构相对均一的凝块石产出,当凝块石被打碎时,呈现出明显的微凝块的特征(图6e、f),这是该套礁滩体中数量最多的微生物岩类型,主要出现在礁核下部。
-
蓝绿藻的这些产出形式呈现出典型的“微生物岩”的特征(郝雁等,2018;吴亚生等,2018,2021)。根据前人对微生物岩的生态研究显示,凝块石灰岩形成于较弱的水动力条件下,常位于每个微生物岩旋回的底部,而叠层石形成的环境要稍高于凝块石;核形石灰岩往往形成于能量周期性变化的水动力环境中(齐永安等,2017;李莹等,2020)。因此,通过对于该套礁滩体中的藻类产出形式可以大致推测当时的水动力条件。
-
3.1.2 叶状藻
-
为宏观钙质藻类,藻片厚约1 mm,延伸最大可达4~5 cm。作为石炭纪—二叠纪的重要造礁生物,巴立克立克组的礁滩体中也局部富集叶状藻(图7a),往往在礁核上部局部富集,在礁基和礁后低能带中也较为常见。叶状藻片的形态多呈卷曲的片状,有时也呈近似椭圆的环状(图4g)。在单偏光下隐约可见边缘灰白色的皮层和褐黄色的髓部,二者之间有时可见“暗线”为界(图7c),这应为叶状藻原始的管状细胞被灰泥充填的产物,可作为其重要的识别标志。
-
前人对叶状藻生态学特征的研究显示,叶状藻往往生态适应范围较窄,水动力太弱或太强都不利于叶状藻的发育,且不能适应浑浊的水体,因此叶状藻常出现于水动力条件中等、温暖清洁、水体略深的浅海环境中,且在环境适宜的条件下,可在短时间内迅速繁盛,表现出惊人的生产力,并且还能聚集大批附着生物参与造礁(张永利等,2007;巩恩普等,2009;高永娟等,2018),这可以很好地解释礁核上部叶状藻周围往往有大量棘皮生屑伴生(图7b)。因此,当叶状藻大量出现时,可以判断当时的水动力条件处于中等水平,且水体的较为干净。值得一提的是,在露头和镜下常见叶状藻片被蓝绿藻(蓝细菌)黏结/结壳形成类似“核形石”的特征,且叶状藻片往往较为破碎且中间有分段的现象(图7b、c),藻片之间也往往被铁染的灰泥大量充填(图4j,图7d),这意味着叶状藻礁在生长过程中,可能遭遇水动力的周期性变化,间歇性的高能动荡的水体对于叶状藻礁的稳定发育有着消极影响。这应该是巴立克立克组礁灰岩中尽管局部发育叶状藻礁,但其并不占主体地位的重要原因。
-
3.1.3 苔藓虫
-
苔藓虫作为重要的造礁生物,在礁基(生屑滩)中较为常见,在礁体上部也时有出现,以隐口目苔藓虫为主。苔藓虫的形态较为多样,镜下常呈链状、长条状,有时候在横切面上呈似圆状和双层对称状。虫室的形态多呈似圆状,有时也呈三角状。镜下显示,苔藓虫颗粒大多被蓝绿藻丝体所黏结/结壳(图4i)。
-
3.1.4 管壳石
-
管壳石(Tubiphytes)在礁基和礁核上部较为常见。相关研究认为它是属于“蓝藻—有孔虫共生体”(Popa et al.,2014)。在显微镜下,管壳石的横切面为圆形且往往具有同心圈层构造,其纵切面往往呈长条状,其中心有一圆形空腔(图8a、d)。有时管壳石也长成枝状乃至无定形状(图4e,图8c)。它常常黏附在苔藓虫等生屑的硬体表面(图8b),起着黏结造礁作用,管壳石周围常见凝块石破碎形成的微凝块。
-
3.1.5 海绵
-
海绵作为造礁生物,克孜勒布拉克南沟巴立克立克组的礁灰岩中数量较少。在镜下可识别出蠕虫状海绵(Vermispongiella)、管形海绵(Solenolmia)等。其中,蠕虫状海绵发育较多的蠕虫状、粗的出水沟道,使得海绵在宏观上呈“脑纹状”的形态产出(图4k);管形海绵的横切面呈似圆状,发育中央腹腔,房室内发育呈网格状填充的泡沫组织(图4l)。
-
3.2 附礁生物
-
克孜勒布拉克南沟巴立克立克组生物礁中的附礁生物类型较为多样。其中,䗴类和棘皮动物的数量最多。其中,在镜下可以识别出䗴类主要为皱壁䗴属(Rugosofusulina),其旋壁起波状皱折,发育较粗的蜂巢层,隔壁皱折较强,往往在轴部呈网状—泡沫状密集排列(图9a、b);部分皱壁䗴壳体中部隔壁褶皱微弱,但在轴部褶皱较强(图9c)。䗴类是石炭纪—二叠纪重要的化石门类,因其演化迅速、演化性状易识别,生物地层序列清楚,因而是石炭纪—二叠纪重要的定年生物(沈树忠等,2019)。根据近年来的研究表明,皱壁䗴属(Rugosofusulina)往往集中出现在乌拉尔世阿瑟尔期晚期—萨克马尔期(Okuyucu et al.,2020),据此可以将该套礁滩复合体的时代定为乌拉尔世阿瑟尔期晚期—萨克马尔期。
-
此外,棘皮动物也较为常见,主要为海百合,常以骨板的形式出现(图3d、e),有时还可以见到海胆棘刺(图4j),有时甚至局部富集成层。此外,还可见双壳、腕足、非䗴有孔虫等(图9d、e)。偶见腹足类,腹足类的壳体在纵向上主要呈圆锥形,其体腔往往被粒状方解石充填(图9f)。
-
图3 塔里木盆地西北缘克孜勒布拉克南沟二叠系巴立克立克组礁灰岩宏观照片
-
Fig.3 Macroscopic photos of reef limestone of Permian Baliklik Formation at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(a)—黄灰色藻灰岩(礁核下部),可见纤柱状-葡萄状胶结物充填孔洞,巴立克立克组,克孜勒布拉克南沟;(b)—黄灰色藻灰岩(礁核上部),可见垂向生长的呈“枝状”的藻团聚体和呈“锅状体”的藻纹层;(c~e)—褐灰色藻黏结灰岩(礁核上部),可见大量海百合茎,巴立克立克组,克孜勒布拉克南沟;(f)—生屑灰岩(礁后),可见大量介壳富集,巴立克立克组,克孜勒布拉克南沟;(g)—生屑灰岩(礁基),可见大量䗴类富集,巴立克立克组,克孜勒布拉克南沟;(h)—灰色核形石灰岩(礁后),巴立克立克组,克孜勒布拉克南沟;(i)—褐红色角砾状灰岩(礁体之下),巴立克立克组,克孜勒布拉克南沟;(j)—褐灰色角砾状灰岩(礁体之上),巴立克立克组,克孜勒布拉克南沟;(k、l)—礁顶的暴露构造,可见大量胶结物充填的溶蚀孔洞、渗流豆粒和角砾等;(m~o)—顺层岩溶孔洞,孔洞中可见齿状—马牙状胶结物垂直洞壁生长、紧密排列,形成栉壳结构
-
(a) —yellowish-grey algal limestone (at the lower zone of the reef core) , with pores and vugs filled by fibrous-columnar and botryoidal cement, from the Baliklik Formation at Kizilbulak Nangou; (b) —yellowish-grey algal limestone (at the upper zone of the reef core) , with dendritic algal aggregates and concave algal lamina growing vertically; (c~e) —brownish-grey algal boundstone (at the upper zone of the reef core) , with an abundance of crinoid stems visible, from the Baliklik Formation at Kizilbulak Nangou in the northwest margin of the Tarim basin; (f) —bioclastic limestone (at the reef back) , with an abundance of shells visible, from the Baliklik Formation at Kizilbulak Nangou in the northwest margin of the Tarim basin; (g) —bioclastic limestone (at the reef base) , with an abundance of fusulinids visible, from the Baliklik Formation at Kizilbulak Nangou in the northwest margin of the Tarim basin; (h) —grey oncolitic limestone (at the back reef) , from the Baliklik Formation at Kizilbulak Nangou in the northwest margin of the Tarim basin; (i) —brownish-red breccia limestone (under the reef) , from the Baliklik Formation at Kizilbulak Nangou; (j) —brownish-grey breccia limestone (over the reef) , from the Baliklik Formation at Kizilbulak Nangou in the northwest margin of the Tarim basin; (k, l) —the exposure structure of the reef cap, with a large number of dissolution pores and vugs filled by cement, and of vadose pisolite and breccia; (m~o) —bedding dissolution pores and vugs, with dentate or ditrigonal scalenohedral cement growing vertically and closely along the wall to form the ctenoid texture
-
综上所述,克孜勒布拉克南沟巴立克立克组的造礁生物主要为蓝绿藻(蓝细菌),约占造礁生物数量的40%~50%左右,它们主要以凝块石和破碎的微凝块的方式产出,局部可见叠层石,主要分布于礁核下部。此外,在礁基中常见蓝绿藻丝体包绕灰泥基质或生屑颗粒,形成核形石;其次为叶状藻,约占造礁生物数量的20%~30%,在礁基中较为常见,在礁核上部也局部富集。其余还可见苔藓虫、管壳石、海绵等骨架生物,它们约占造礁生物数量的20%,常见于礁基和礁核上部。此外,还可见䗴类、棘皮生屑、腕足、腹足等附礁生物,约占岩石总量的10%~20%。其中,在礁基中局部富集䗴类和苔藓虫,棘皮生屑则常见于礁核上部。
-
4 礁体的成岩作用
-
4.1 礁灰岩的阴极发光特征
-
巴立克立克组的礁灰岩形成后,也经历了复杂的成岩作用改造,这些成岩作用可直接或间接通过胶结物表现出来。通过野外观察和镜下薄片观察发现,巴立克立克组礁灰岩中发育大量被方解石胶结物全充填的孔洞。其中,方解石胶结物的形态较为多样,可识别出如下类型:
-
(1)纤状方解石。该种胶结物往往紧贴颗粒边缘的泥晶套垂向生长,晶体较为细小,部分已重结晶为细晶方解石,仅残留纤状晶体的外形。在正交偏光下,纤维状方解石没有统一的消光位。不同岩石类型孔洞中胶结物生长状态也不同,亮晶颗粒灰岩中,纤维状方解石纤柱状方解石胶结物围绕似圆状的颗粒生长成栉壳状略等厚的环边(图4c),厚度通常为0.02~0.10 mm。
-
(2)放射纤维状方解石。该种方解石易出现在藻灰岩的小孔洞中,且往往以纤状方解石为基础向孔隙中间生长,晶体粗大,不具明显的波状消光,可形成厚达2.0~3.0 mm的环边。其胶结作用一般可使礁灰岩中的原生孔隙减少10%~30%,甚至可填满大部分的孔隙空间。该种方解石往往和纤状方解石一起在宏观上形成类似“葡萄花边”的形态(图4b)。
-
(3)叶片状—棱柱状方解石。当孔洞较大时,该种方解石晶体较为发育。方解石晶体往往沿着它们的延长方向宽度有所增加,显得“上宽下窄”,顶端外形类似马牙状,长度约为0.5~2 mm,较之纤状和放射纤状方解石胶结物,该种方解石胶结物表面较为干净且单个晶体较为粗大(图4d中第Ⅲ期胶结物),这种胶结物很可能是在同生期海水胶结物的基础上重结晶而来的。
-
(4)粒状方解石。主要见于孔洞中央,晶粒较为粗大,可达毫米级,为埋藏期成因(图4d中第Ⅳ期胶结物)。此外,在部分孔洞中央,有时可见少量白云石晶体呈紧密镶嵌接触,它们的晶粒较为细小,粒径多<100 μm,自形程度普遍较差,它们往往分布于埋藏期形成的粗粒状方解石中,因而推断其为埋藏期方解石胶结物遭受埋藏白云石化改造的产物(图4l、m)。
-
为了深入研究巴立克立克组礁灰岩的成岩作用及恢复其原岩结构,本次研究中选取了部分礁灰岩的薄片进行了阴极发光测试。发现了如下特征:
-
(1)各种生屑颗粒往往发弱—中等橘红色光,破碎的凝块石(微凝块)往往发亮红色光。不同期次的胶结物也有着不同的阴极发光特征。其中,颗粒周围的纤状胶结物发弱橘红色光,棱柱状胶结物发弱橘红色光—不发光,孔隙中央的晶粒状方解石胶结物多不发光,部分晶粒有橘黄色亮边(图10a~f);
-
图4 塔里木盆地西北缘克孜勒布拉克南沟二叠系巴立克立克组礁灰岩微观照片(Ⅰ、Ⅱ、Ⅲ、Ⅳ代表方解石的期次)
-
Fig.4 Micro photos of the Permian Baliklik Formation reef limestone at Kizilbulak Nangou in the northwest margin of the Tarim basin (Ⅰ, Ⅱ, Ⅲ and Ⅳ are indicators of corresponding calcite phases)
-
(a)—藻灰岩,可见纹层状的藻丝体垂向生长形成藻叠层,藻格架间可见两期胶结物充填,单偏光;(b)—生屑泥晶灰岩,可见苔藓虫、管壳石等生屑颗粒,颗粒周围可见大量微凝块,顶部可见藻丝体包覆,藻丝体之上可见葡萄状胶结物充填孔洞,单偏光;(c)—泥晶灰岩,受成岩改造较为强烈,仅见少量的管壳石和藻片,孔隙中可见两期胶结物充填,单偏光;(d)—藻灰岩,受成岩改造较为强烈,仅见少量管壳石(图中粉色箭头所示),周围可见微凝块,可见4期胶结物充填孔洞,单偏光;(e)—藻灰岩,受成岩改造较为强烈,仅见少量管壳石,孔隙中可见两期胶结物充填,正交光;(f)—藻灰岩,可见蓝绿藻(绿色箭头所示)和叶状藻(紫色箭头所示)丝体包绕,藻格架间被灰泥充填,还可见少量苔藓虫(黄色箭头所示)碎片,单偏光;(g)—生屑泥晶灰岩,可见叶状藻(紫色箭头所示)和链状苔藓虫(黄色箭头所示),其中双壳内部还可见示顶底构造,单偏光;(h)—泥晶生屑灰岩,局部可见藻团块(绿色箭头所示)和䗴类(蓝色箭头所示)富集,藻团块被铁染泥质浸染呈褐红色,还可见少量苔藓虫(黄色箭头所示),单偏光;(i)—泥晶生屑灰岩,可见大量隐口目苔藓虫(黄色箭头所示)富集,且苔藓虫多被蓝绿藻丝体(绿色箭头所示)包绕,局部可见少量叶状藻(紫色箭头所示),单偏光;(j)—叶状藻灰岩,可见大量叶状藻片(紫色箭头所示)密集分布,局部可见海胆棘刺(深蓝色箭头所示),且叶状藻和海胆棘刺周围往往被蓝绿藻丝体(绿色箭头所示)包绕,单偏光;(k)—生屑泥晶灰岩,可见脑纹状海绵(橘色箭头所指)、叶状藻(紫色箭头所指)、管壳石(粉色箭头所指)等,受构造作用影响,发育构造裂缝,裂缝被方解石全充填,单偏光;(l、m)—藻灰岩,受成岩改造较为强烈,孔洞中被亮晶胶结物全充填,孔隙中央局部可见自形程度较差的白云石富集(黄箭头所指);图l中还可见管形海绵属(Solenolmia,红色箭头所指);(n)—生屑泥晶灰岩,可见管壳石富集,局部可见铁染的灰泥充填其中
-
(a) —algal limestone, with lamellar algal filaments growing vertically to form algal stromatolith, and the grids of the algal framework filled by cement of two phases, under plane polarized light; (b) —bioclastic micritic limestone, with such bio-particles as bryozoans and Tubiphytes visible and an abundance of microclots around those bio-particles; the top covered and wrapped by algal filaments; the pores and vugs over the algal filaments filled by botryoidal cement, under plane polarized light; (c) —micritic limestone, relatively strongly transformed by diagenesis, with only a few Tubiphytes and algal fragments, and the pores filled by cement of two phases, under plane polarized light; (d) —algal limestone, relatively strongly transformed by diagenesis, with a few Tubiphytes (indicated by pink arrows) , and some microclots around them; the pores and vugs filled by cement of four phases, under plane polarized light; (e) —algal limestone, relatively strongly transformed by diagenesis, with a few Tubiphytes; the pores filled by cement of two phases, under cross polarized light; (f) —algal limestone, wrapped by the filaments of Cyanobacteria (indicated by the green arrow) and phylloid algae (indicated by the purple arrow) ; the grids of the framework filled by marl; a small number of bryozoan fragments visible (indicated by the yellow arrows) , under plane polarized light; (g) —bioclastic micritic limestone, with phylloid algae (indicated by purple arrows) and catenulate bryozoans (indicated by the yellow arrows) visible; the geopetal structure visible inside the bivalves, under plane polarized light; (h) —micritic bioclastic limestone, locally with an abundance of oncolite (indicated by green arrows) and Fusulinids (indicated by blue arrows) ; the oncolite is brownish-red due to the presence of ferrous marl; a small number of bryozoans (indicated by the yellow arrow) are visible, under plane polarized light; (i) —micritic bioclastic limestone, with a large number of Cryptostomata (indicated by yellow arrows) visible, and most of them wrapped by Cyanobacteria filaments (indicated by green arrows) ; a small number of Phylloid algae (indicated by purple arrows) visible locally, under plane polarized light; (j) —phylloid algal limestone, with a large number of phylloid algal fragments (indicated by purple arrows) densely distributed, and sea urchin spines (indicated by the blue arrow) locally distributed; the phylloid algae and sea urchin spines mostly wrapped by Cyanobacteria filaments (indicated by green arrows) , under plane polarized light; (k) —bioclastic micritic limestone, with striated sponges (indicated by orange arrows) , phylloid algae (indicated by purple arrows) , and Tubiphytes (indicated by pink arrows) ; the structural fractures incurred by tectonism are fully filled by calcite, under plane polarized light; (l, m) —algal limestone, relatively strongly transformed by diagenesis; the pores and vugs entirely filled by sparry cement; poorly euhedral dolostone locally abundant in the middle of the pores (indicated by the yellow arrow) ; Solenolmia (indicated by the red arrows) can also be seen in Fig.4l; (n) —bioclastic micritic limestone, with an abundance of Tubiphytes, and locally filled by ferrous marl
-
图5 塔里木盆地西北缘克孜勒布拉克南沟巴立克立克组生物礁结构剖面图
-
Fig.5 Structural profile of the Baliklik Formation reefs at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(2)骨架颗粒周围被纤状—放射纤维状方解石胶结物充填的区域在阴极发光下有时呈现出亮暗相间的“纹层”,整体呈现藻丝体缠绕的“幻影”特征(图10a~h)。根据与受成岩改造较弱的礁灰岩样品进行对比后发现,礁灰岩中生屑颗粒受蓝绿藻包绕的情况较为普遍(图4i、j)。由此证实,纤状胶结物所在区域为沉积期形成的藻黏结岩中的藻丝体腐烂后形成的“气室”,在随后的海底渗流带被纤状—放射纤状的高镁方解石所充填,这可能指示了冷海水的成岩环境。
-
(3)纤状胶结物外侧的棱柱状胶结物在阴极发光下有时呈现出明显细直的针状和放射状排列特征(图10i、j),这和同生期海底成因的“葡萄状胶结物”的形态较为类似。通过与受成岩改造微弱的样品对比显示,藻叠层之上的孔洞中普遍充填同生期海底成因的“葡萄状胶结物”(图4b)。因此可以判断,那些棱柱状胶结物为同沉积期葡萄状胶结物重结晶或新生变形的结果。
-
总体而言,克孜勒布拉克南沟巴立克立克组生物礁灰岩遭受成岩改造的程度中等。但是,礁灰岩中不同的组分遭受成岩改造的程度却存在着明显的非均质性。其中,礁核中的凝块石灰岩遭受成岩改造的程度较大,多被亮晶胶结物所取代,而诸如苔藓虫、管壳石一类的生屑颗粒则受成岩作用的影响较小,形态往往能得到较好保存。此外,具有叠层构造的藻灰岩受成岩改造的程度较低,其层纹结构往往能得到较好保存。
-
图6 塔里木盆地西北缘克孜勒布拉克南沟巴立克立克组蓝绿藻微观照片
-
Fig.6 Micro photos of Cyanobacteria from the Permian Baliklik Formation at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(a)—可见褐红色藻团块和䗴类,藻团块被铁染泥质浸染呈褐红色,单偏光;(b)—可见藻丝体包覆泥粒,形成核形石,单偏光;(c)—藻丝体和微晶碳酸盐岩纵向上互层产出,单偏光;(d)—可见藻黏结角砾,形成包壳石,单偏光;(e)—藻灰岩,局部可见结构相对均一的凝块石和破碎的微凝块,单偏光;(f)—藻灰岩,可见大量破碎的微凝块,裂缝贯穿其中,被方解石充填,单偏光
-
(a) —brownish-red oncolite (due to the presence of ferrous marl) and fusulinids, under plane polarized light; (b) —mud particles wrapped by algal filaments to form oncolite, under plane polarized light; (c) —algal filaments and microcrystalline carbonate rocks interbedded vertically, under plane polarized light; (d) —algae-bound breccia to form crustolite, under plane polarized light; (e) —algal limestone, with thrombolite of relatively uniform structure and broken-up microclots, under plane polarized light; (f) —algal limestone, with a large number of broken-up microclots, which fractures run through and are filled with calcite, under plane polarized light
-
4.2 礁灰岩的成岩阶段划分
-
(1)准同生—同生成岩阶段:克孜勒布拉克南沟巴立克立克组生物礁灰岩中可识别的准同生—同生成岩阶段的成岩标志主要有:① 蓝绿藻类对各种生物碎屑和灰泥基质的黏结和缠绕;② 藻丝体腐烂后,形成的空腔被同生海底期成因的葡萄状胶结物充填;③ 准同生期礁体生长到一定阶段抬升暴露,遭受大气淡水淋滤,使得礁体中发育渗流豆粒、礁角砾等。
-
(2)早成岩阶段:克孜勒布拉克南沟巴立克立克组生物礁灰岩在成岩过程中主要经历了淡水潜流和淡水渗流环境。淡水潜流环境的主要成岩标志包括:① 发育平行于岩层方向的顺层岩溶孔洞,期间可见齿状或马牙状胶结物紧密排列呈栉壳结构(图3m~o);② 充填于孔洞中心的亮晶方解石胶结物。这些胶结物往往显示出淡水胶结物的环带状阴极发光,即具有不发光—弱发光的核部和明亮的发光边缘(图10b、d、f);③ 重结晶作用,主要表现为细长的葡萄状胶结物新生变形成为粗大的棱柱状胶结物。淡水渗流环境的成岩标志主要为示底构造等。
-
图7 塔里木盆地西北缘克孜勒布拉克南沟巴立克立克组叶状藻宏微观照片
-
Fig.7 Macro and micro photos of phylloid algal from the Permian Baliklik Formation at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(a)—叶状藻灰岩露头照片,可见大量叶状藻片富集,礁核上部;(b)—生屑灰岩,可见大量的海百合茎,局部可见叶状藻片被蓝绿藻丝体包绕(紫色箭头所指),礁核上部;(c)—可见大量叶状藻片,藻片呈卷曲片状,隐约可见分化的皮层和髓部,藻片间被铁染的灰泥充填,单偏光;(d)—叶状藻周围可见蓝绿藻黏结缠绕,藻片呈卷曲片状,藻片间被铁染的泥晶和无定形生屑充填,单偏光
-
(a) —photos of phylloid algal limestone outcrop, with an abundance of phylloid algal fragments visible, in the upper zone of reef core; (b) —bioclastic limestone, with an abundance of crinoid stems, and locally phylloid algal fragments wrapped by Cyanobacteria filaments (indicated by purple arrows) , in the upper zone of the reef core; (c) —an abundance of phylloid algal fragments, curly and lamellar; separated cortex and pith vaguely visible; the spaces between the fragments filled by ferrous marl, under plane polarized light; (d) —phylloid algal fragments (curly and lamellar) bound and wrapped by Cyanobacteria; the spaces between the fragments filled by ferrous marl and amorphous bioclasts, under plane polarized light
-
(3)中—晚成岩阶段:中—晚成岩阶段的主要成岩标志包括:① 生长于溶蚀孔隙中心、晶体较粗大的方解石,局部还出现了埋藏白云石化,形成了自形程度较差的白云石(图4l、m);② 发育构造裂缝,且沿裂缝有明显扩溶现象(图11a),部分裂缝被紧密镶嵌状接触的粒状方解石全充填(图11b);③ 少量生屑颗粒的钙质骨骼、亮晶方解石等被硅质交代(图11c、d)。
-
图8 塔里木盆地西北缘克孜勒布拉克南沟巴立克立克组管壳石微观照片
-
Fig.8 Micro photos of Tubiphytes from the Permian Baliklik Formation at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(a)—典型的似同心圆状的管壳石黏附凝块石,其周围可见破碎的微凝块,单偏光;(b)—管壳石黏附于苔藓虫颗粒之上,周围常见微凝块,单偏光;(c)—无定形的管壳石,管壳石;(d)—管壳石的纵切面,呈长条状,周围可见微凝块,单偏光
-
(a) —typical concentric-like Tubiphytes can be seen to adhere to thrombolite, with broken-up microclots around, under plane polarized light; (b) —Tubiphytes can be seen to adhere to the bryozoan particles, with typically clotted algal particles around, under plane polarized light; (c) —amorphous Tubiphytes can be seen, under plane polarized light; (d) —longitudinal sections of Tubiphytes can be seen in the form of long strips, with microclots around, under plane polarized light
-
5 讨论
-
5.1 关于碳氧同位素的测试结果解析
-
生物礁发育往往和当时的古气候、古环境以及海平面变化密切相关,这往往通过碳氧同位素(尤其是δ13C值变化)来表征。基于此,本次研究分别采集了7块巴立克立克组的藻礁灰岩和4块巴立克立克组之下的康克林组的泥晶灰岩进行碳氧同位素测试。样品在西南石油大学油气地质与勘探实验教学中心的Isoprime100型同位素质谱仪上进行测试。
-
碳氧同位素分析结果如表1所示,大多数样品的δ18O的数值>-10‰,说明该批样品受成岩作用的改造程度较弱,其δ13C和δ18O的数值能够代表沉积期海水的碳氧同位素组成,计算出来的Z值也能大致反映沉积期的古盐度特征(李文正等,2019)。
-
有机碳埋藏速率是影响碳酸盐岩δ13C值变化的重要因素。由于有机碳中往往富集12C,因此当大量有机碳快速埋藏的时期,更多的12C进入埋藏的有机碳中,将使同期海相碳酸盐岩的13C值向正向偏移,反之则负向偏移。因此,如果海相碳酸盐岩的δ13C升高,说明这一时期的海洋生物产率较高;反之,则表明海洋生物产率较低。其中,藻类是影响海水中碳同位素的重要因素,具体表现为藻类在光合作用过程中优先吸收轻同位素12C,使得海水中重同位素13C的含量相对增加(姚春彦等,2011;杨雪琪等,2017)。表1中的结果显示,康克林组沉积时期δ13C值皆为负值,而巴立克立克组的藻礁的δ13C值大多为正值,说明相对于康克林组沉积时期,巴立克立克组时期藻类的繁盛使得同时期的海水中13C相对富集,个别藻礁样品的δ13C数值偏低甚至为负值,可能与礁体抬升,遭受暴露淋滤和准同生白云岩化的改造有关。
-
图9 塔里木盆地西北缘克孜勒布拉克南沟巴立克立克组附礁生物微观照片
-
Fig.9 Micro photos of accessary reef organisms from the Permian Baliklik Formation at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(a~c)—泥晶生屑灰岩,局部富集皱壁䗴(Rugosofusulina),单偏光;(d)—生屑泥晶灰岩,可见双壳,壳体内可见示顶底构造,单偏光;(e)—泥晶生屑灰岩,富集叶状藻(紫红色箭头所示)、非䗴有孔虫(绿箭头所示)等,单偏光;(f)—泥晶生屑灰岩,可见腹足动物壳体,单偏光
-
(a~c) —micritic bioclastic limestone, with Rugosofusulina locally abundant, under plane polarized light; (d) —bioclastic micritic limestone, with bivalves and geopetal texture within the shells visible, under plane polarized light; (e) —micritic bioclastic limestone, with abundant phylloid algae (indicated by purple arrows) and non-fusulinid foraminifera (indicated by green arrows) , under plane polarized light; (f) —micritic bioclastic limestone, with gastropod shells visible, under plane polarized light
-
5.2 关于礁滩体的成因和发育过程探讨
-
前人普遍认为,有机碳的埋藏量增减和海平面的变化息息相关,因而δ13C的变化往往可以间接地反映海平面的变化(陈鹤等,2008;窦衍光等,2022),按照这种观点,克孜勒布拉克南沟巴立克立克组的这套台缘礁滩复合体是在海平面上升的过程中发育起来的。而且,巴立克立克组的这套巨厚礁滩体并非孤立存在,而是在整个塔西北的巴立克立克组中上部普遍发育,区域上绵延可达数百公里(贾进华等,2018)。此外,在柯坪地区苏巴什剖面的巴立克立克组中部同样发育厚度>10 m的台内核形石滩体;向上靠近巴立克立克组顶部,也发育厚度<10 m的台内礁滩体,礁基中富集叶状藻、腕足和核形石(图12a~c),造礁生物为横板珊瑚亚纲中国孔珊瑚属(Sinopora),珊瑚格架间为灰泥充填(图12d~f),它整体上为一枝状珊瑚障积礁(图12g)。由此可见,塔里木盆地西北缘巴立克立克组沉积时期,在区域上,无论是台地边缘还是局限台地,皆有利于造礁。因此,从区域海平面上升的角度来解释这套礁滩体的成因也较为合理。
-
图10 塔里木盆地西北缘克孜勒布拉克南沟二叠系巴立克立克组礁灰岩阴极发光照片
-
Fig.10 Cathodoluminescence images of reef limestone of Permian Baliklik Formation at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(a)—藻灰岩,受强烈的成岩改造,可见少量管壳石,周围孔隙中可见两期胶结物充填,单偏光;(b)—图a的阴极发光图像,管壳石发弱—中等橘红色光,颗粒周围可见藻包绕的“幻影”(发弱橘红色光,黄色箭头所指),孔隙中央的粒状方解石整体上不发光,部分粒状方解石有橘黄色亮边;(c)—泥晶生屑灰岩,受成岩改造较为强烈,仅见少量苔藓虫颗粒,孔隙中可见两期胶结物充填,单偏光;(d)—图c的阴极发光图像,苔藓虫颗粒发中等橘红色光,颗粒周围可见藻包绕的“幻影”(发弱橘红色光),孔隙中央的粒状方解石多不发光,部分粒状方解石颗粒有橘黄色亮边;(e)—藻灰岩,受成岩改造较为强烈,仅见少量管壳石和苔藓虫颗粒碎片,孔隙中可见两期胶结,单偏光;(f)—图e的阴极发光图像,苔藓虫和管壳石颗粒周围可见藻包绕的“幻影”(发中等橘红色光),颗粒周围可见藻包绕的“幻影”(发弱橘红色光),孔隙中央的粒状方解石多不发光,部分粒状方解石颗粒有橘黄色亮边;(g)—生屑泥晶灰岩,遭受强烈成岩改造,仅剩少量苔藓虫颗粒和破碎的凝块石(凝粒),可见两期胶结物充填孔隙,单偏光;(h)—图g的阴极发光图像,其中苔藓虫和凝粒发弱—中等橘红色光,周围显示藻包绕的“幻影”(发弱橘红色光),孔隙中央的粒状方解石多不发光,部分粒状方解石颗粒有橘黄色亮边;(i)—泥晶生屑灰岩,遭受强烈的成岩改造,仅见少量管壳石,其周围可见纤状—棱柱状胶结物环边,单偏光;(j)—图i的阴极发光图像,其中管壳石发中等橘红色光,纤状胶结物发暗红色光,外侧的棱柱状胶结物则呈现出葡萄状胶结物的“幻影”(极弱—不发光,图中白色箭头所指);(k)—藻灰岩,遭受强烈的成岩改造,仅局部可见少量苔藓虫、管壳石和破碎的凝块石(凝粒),单偏光;(l)—图k的阴极发光图像,其中凝粒发亮红色光,管壳石和苔藓虫发中等橘红色光,纤状胶结物发暗红色光,外侧的棱柱状胶结物不发光
-
(a) —algal limestone, strongly transformed by diagenesis, with a few Tubiphytes visible, and the pores around filled by cement of two phases, under plane polarized light; (b) —CL image of (a) , in which the Tubiphytes emit weak-to-medium orange light; “phantoms” (emitting weak orange light and indicated by yellow arrows) loom vaguely out of the algae-wrapping of particles; the granular calcites in the center of the pores generally do not emit light, with some having orange edges; (c) —micritic bioclastic limestone, relatively strongly transformed by diagenesis, with only a few bryozoan particles visible, and pores filled by cement of two phases, under plane polarized light; (d) —CL image of (c) , in which the bryozoan particles emit medium orange light; “phantoms” (emitting weak orange light) loom vaguely out of the algae-wrapping of particles; the granular calcites in the center of the pores are mostly nonluminous, with some having orange edges; (e) —algal limestone, relatively strongly transformed by diagenesis, with some Tubiphytes and bryozoan particle fragments visible; the pores filled by cement of two phases, under plane polarized light; (f) —CL image of (e) , in which “phantoms” (emitting medium orange light) loom vaguely out of the algae-wrapping of the particles of bryozoans and Tubiphytes; “phantoms” (emitting weak orange light) loom vaguely out of the algae-wrapping of the particles; granular calcites in the center of the pores are mostly nonluminous, with some having orange edges; (g) —bioclastic micritic limestone, strongly diagenetically transformed, with only a few bryozoan particles and broken thrombolite (or thrombolite particles) left; pores filled by cement of two phases, under plane polarized light; (h) —CL image of (g) , in which the bryozoans and thrombolite particles emit weak-medium orange light; “phantoms” (emitting weak orange light) loom vaguely out of the algae-wrapping of the particles; the granular calcites in the center of the pores are mostly nonluminous, with some having orange edges; (i) —micritic bioclastic limestone, strongly diagenetically transformed, with only a few Tubiphytes visible, surrounded by fibrous-prismatic cement, under plane polarized light; (j) —CL image of (i) , in which the Tubiphytes emits medium orange light; the fibrous cement emits dark red light, and the prismatic cement on the outside assumes a “phantom” of botryoidal cement (extremely weak-nonluminous, indicated by the white arrow) ; (k) —algal limestone, strongly diagenetically transformed, with a few bryozoans, Tubiphytes and broken thrombolites (or thrombolite particles) visible locally, under plane polarized light; (l) —CL image of (k) , in which the thrombolites emit bright red light; Tubiphytes and bryozoans emit medium orange light; the fibrous cement emits dark-red light; the prismatic cement on the outside is nonluminous
-
图11 塔里木盆地西北缘克孜勒布拉克南沟巴立克立克组构造裂缝和硅质交代
-
Fig.11 Macro and micro photos of structural fracture and siliceous mineral metasomatism from the Permian Baliklik Formation at Kezilblak Nangou in the northwest margin of the Tarim basin
-
(a)—藻灰岩,可见构造裂缝,沿裂缝有扩溶现象;(b)—藻灰岩,局部可见被方解石全充填的裂缝(黄色箭头所示),正交偏光;(c)—苔藓虫颗粒,局部可见钙质骨骼被石英交代(黄色圈所示),正交偏光;(d)—叶状藻灰岩,局部可见石英交代亮晶方解石(黄色圈所示),单偏光
-
(a) —algal limestone, with structural fractures and diffused dissolution along the fractures; (b) —algal limestone, with fractures fully filled by calcite locally (indicated by the yellow arrow) , under cross polarized light; (c) —bryozoan particles, calcareous skeleton are metasomatized by quartz (shown in yellow circles) , under cross polarized light; (d) —phylloid algal reef limestone, crystal calcites are locally metasomatized by quartz (shown in yellow circles) , under plane polarized light
-
注:δ13CPDB、δ18OPDB分别为13C、18O同位素组成代号;Z=2.048×(δ13CPDB+50)+0.498×(δ18OPDB+50),Z>120时,为海相灰岩;Z<120时,为淡水灰岩。
-
但是,δ13C值的变化本质上还是反映有机碳埋藏量增减,至于其是否和海平面变化相关,需要具体问题具体分析。现代环境科学的研究表明,各种藻类的繁盛往往和水体遭受污染导致的富营养化有关(邵志平等,2023),推断巴立克立克组沉积时期藻类的繁盛乃至形成藻礁或微生物岩也和海水遭受了某种“污染”导致的富营养化有关。
-
图12 塔里木盆地西北缘苏巴什剖面巴立克立克组上部枝状珊瑚障积礁
-
Fig.12 Branched coral barrier reef in upper Baliklik Formation of Subashi section in the northwest margin of the Tarim basin
-
(a)—生屑灰岩,可见腕足(绿色箭头所示)、叶状藻(红色箭头所示)等;(b)—生屑灰岩,局部可见核形石(黄色箭头所示);(c)—叶状藻灰岩,单偏光;(d、e)—珊瑚障积岩野外照片,珊瑚类型为中国孔珊瑚(Sinopora),形似喇叭状;(f)—中国孔珊瑚镜下照片,其横截面似圆状,纵截面似喇叭状,珊瑚格架间被灰泥充填;(g)—礁体结构图
-
(a) —bioclastic limestone, brachiopods (shown by the green arrows) , phylliod algal (shown by the red arrows) , etc. can be seen; (b) —bioclastic limestone, oncoids can be seen locally (shown by the yellow arrows) ; (c) —phylloid algal limestone, monopolarized; (d, e) —cropout photos of coral bafflestone, with the flared Sinopora as the coral type; (f) —micro image of Sinopora, whose cross sections are circular, and whose longitudinal sections are flared, the grids of the coral frameworks are filled by marl; (g) —profile of reef
-
如前所述,克孜勒布拉克南沟巴立克立克组的台缘礁滩体的时间年限为乌拉尔世阿瑟尔期晚期—萨克马尔期。近年来的研究表明,这一时期正值塔里木大火成岩省岩浆作用的第一阶段,柯坪地区库普库兹曼组(大体上和巴立克立克组等时)的火山岩为其典型代表(余星等,2017;田伟等,2018)。近年来,也有相关学者提到火山活动对于微生物岩的影响,主要包括:① 火山灰中富含K、P等微生物生长所需要的营养元素,有利于微生物的爆发,进而有利于微生物岩的形成;② 火山活动后,由于岩浆房内的压力释放,易导致区域沉降,进而导致局部海平面上升,这可以为微生物的发育提供可容空间,但海平面上升过快也可能导致微生物被“淹死”(陈虹宇,2018;李泯星等,2020)。因此,巴立克立克组的藻礁或微生物岩的发育,极有可能和当时的塔里木大火成岩省事件给南天山洋残余海盆带来了富含K、P等营养元素的火山灰,使得南天山洋残余海盆中的水体富营养化,从而刺激了藻类的繁殖有关。藻类的繁盛,有利于海水中13C的相对富集,更有利于吸引诸如棘皮动物、䗴类、腹足等以微生物为食的海生底栖生物前来定居,从而在区域上(无论台内还是台缘)普遍发育礁滩体(图13)。这可以作为今后微生物岩研究的重要方向。
-
而且,如前所述,即使是与藻礁或微生物岩互层的滩体中,藻丝体也大量发育,且诸如棘皮动物、䗴类、苔藓虫等生物碎屑也往往和藻团块共生,甚至被藻丝体大量包绕形成核形石。而棘皮动物、䗴类、苔藓虫、海胆等都属于滤食藻类的生物,据此可以判定,藻类的繁盛吸引了上述的食藻动物前来定居,并开始形成生屑滩。简而言之,从食物链的角度来看,应该是先有藻类大量繁殖形成“礁”,而后才逐渐形成“滩”。当礁滩体生长到一定阶段后,暴露在水面之上,开始遭受大气淡水的淋滤,发育同生岩溶,形成大量的溶蚀孔洞。
-
据此,可以将每一期礁滩体的发育过程概括如下(图14):
-
(1)礁基形成:蓝绿藻(蓝细菌)、叶状藻等微生物或宏观钙质藻类的大量繁殖,吸引了棘皮动物、䗴类和非䗴有孔虫、苔藓虫、腹足类等食藻动物前来栖居。这一过程中,藻类和食藻动物之间达成了某种“动态平衡”,生屑滩开始逐步形成,部分改变了海底的地形、光照条件。
-
(2)蓝绿藻造礁阶段:在滩体的高部位,由于水深相对较浅、光照和含氧量相对充足,吸引了营光合作用的藻类大量繁殖。藻类主要以凝块石的方式产出,当波浪能量稍高时,凝块石经常被破碎成微凝块,同时也易发育藻叠层。当水体变浅、藻叠层暴露在大气中时,藻叠层易干裂收缩,形成“帐篷构造”或“锅状体”。此时的水动力条件总体较低。
-
图13 塔里木盆地西北缘巴立克立克组时期沉积相模式图
-
Fig.13 Sedimentary facies model of the Baliklik Formation in the northwest margin of the Tarim basin
-
图14 克孜勒布拉克南沟巴立克立克组生物礁演化阶段示意图
-
Fig.14 Schematic diagram of the evolution stages of the Baliklik Formation reefs at Kizilbulak Nangou
-
(3)蓝绿藻—叶状藻造礁阶段:随着波浪能量升高,适应中等水动力条件的宏观钙质藻类—叶状藻开始大量定殖,结束了蓝绿藻在礁生态中“一家独大”的地位。由于叶状藻的发育,吸引了大量底栖生物(如䗴类、棘皮动物)等前来定居。但是,此时的水动力条件存在着周期性变化,间歇性的高能动荡水体使得叶状藻礁的发育并不稳定,蓝绿藻(蓝细菌)依旧在礁体生态中占有重要地位,并且大量包绕叶状藻片和各类生物碎屑进行生长。
-
(4)礁体消亡阶段:礁体生长到一定阶段,暴露在浪基面之上,在碎浪的作用下,礁体发生破碎形成大量礁角砾,但礁角砾周围依然可见蓝绿藻包绕现象。与此同时,在大气淡水作用下,礁体开始遭受岩溶改造,发育大量溶蚀孔洞,岩溶分带开始出现。
-
5.3 礁体的物性特征
-
储层物性是储层的基本特征之一,通常用孔隙度和渗透率来表征。本次研究分别选取了44块克孜勒布拉克南沟和8块苏巴什剖面巴立克立克组生物礁样品进行孔隙度和渗透率的测试。
-
测试结果显示,来自克孜勒布拉克南沟和苏巴什剖面的所有巴立克立克组生物礁样品的孔隙度皆<4%;渗透率方面,绝大多数样品的渗透率<1×10-3 μm2,根据《油气储层评价方法》(SY/T6285—2011)中对于碳酸盐岩物性的划分来看(表2),塔西北巴立克立克组礁灰岩属于特低孔—特低渗储层的范畴。在孔渗相关性方面,基质样品的孔渗相关性较好(R>0.6),仅少数裂缝样品的渗透率>10×10-3 μm2,个别裂缝样的渗透率甚至>100×10-3 μm2,出现了“低孔—中高渗”的特征(图15)。由此可见,从区域上看,巴立克立克组的礁灰岩的基质部分较为致密,储渗性较差,而构造裂缝对于改善礁灰岩储层的渗透性起着至关重要的作用。
-
图15 塔里木盆地西北缘巴立克立克组礁灰岩孔渗相关性统计图(红色、蓝色散点分别为克孜勒布拉克南沟裂缝样、基质样;紫色、绿色散点分别为苏巴什剖面裂缝样、基质样)
-
Fig.15 Correlation of porosity and permeability of reef limestone in Baliklik Formation in the northwest margin of the Tarim basin (the red and blue scattered points are respectively the fracture samples and matrix samples at Kezilblak Nangou; the purple and green scattered points are respectively the fracture samples and matrix samples of Subash section)
-
6 结论
-
(1)克孜勒布拉克南沟发育巨厚的、多期次的礁滩复合体。其中,生屑滩组成了礁基,藻类是主要的造礁生物。其中,礁核下部主要为蓝绿藻造礁,以凝块石及破碎的微凝块为主,次为藻叠层,此时的水动力条件较弱;礁核上部开始出现叶状藻等宏观钙质藻类造礁,生屑含量开始有所增加,此时的水动力条件总体中等,但存在间歇性高能动荡水体干扰,使得叶状藻礁无法稳定发育。当礁体生长到一定阶段,礁体开始暴露在浪基面之上和大气淡水中,发育礁角砾岩、暴露岩溶等。
-
(2)根据䗴类定年的结果,该套礁滩体的时代为乌拉尔世阿瑟尔期晚期—萨克马尔期,这与塔里木大火成岩省的早期(柯坪地区库普库兹曼组火成岩形成阶段)大致相当,火山活动形成的火山灰可以为海水带来丰富的K、P等元素,使得海水发生“富营养化”,有利于藻类爆发,藻类的光合作用使得海水中的13C相对富集。与此同时,藻类的繁盛吸引了大量食藻的宏体生物前来定居,从而发育礁滩体。因此,巴立克立克组的礁滩体发育和塔里木大火成岩省的关系可以作为今后研究的一个重要方向。
-
(3)克孜勒布拉克南沟巴立克立克组的台缘礁滩体局部遭受了强烈的成岩改造。例如,礁灰岩的孔洞(包括藻类腐烂形成的气室、暴露淋滤形成的溶蚀孔洞)大多被多期方解石胶结物充填;苏巴什剖面巴立克立克组台内礁滩体的原生孔隙也多被沉积期的灰泥充填,这使得生物礁致密化,储渗性较差。总而言之,区域上巴立克立克组礁滩体受胶结作用等建设性成岩作用的影响,有利于“成岩”,但不利于“成储”。唯有通过构造裂缝的改造,方能形成高渗储层。可以断定,塔西北二叠系巴立克立克组的礁滩储层的发育程度、分布范围和相带的关系不大,主要受后期构造裂缝的制约和控制,即主要发育裂缝性储层。这是今后塔西北二叠系生物礁油气藏勘探中应特别注意的问题。
-
致谢:中石油塔里木油田分公司勘探开发研究院的王斌、黄智斌、左小军3位主任在野外工作方面给予了很大帮助;南京大学地球科学与工程学院王向东教授和史宇坤副教授在䗴类的精确鉴定和定年方面给予了有益的指导;西南石油大学地球科学与技术学院谭秀成教授的学生陈虹宇硕士和芦飞凡博士分别在微生物岩的识别、演化以及碳氧同位素的环境响应方面给予了较多的指导,极大地开拓了写作思路;东北大学资源与土木工程学院张永利副教授在叶状藻的环境意义以及微生物岩的特征方面给予了较多提点,对我的研究助益颇多;审稿专家也提出了非常宝贵的修改意见和建议,让本文能够不断完善。在此一并致以衷心的感谢!
-
参考文献
-
Bryant R N, Present T M, Ahm A C, McClelland H L O, Razionale D, Blattler C L. 2022. Early diagenetic constraints on Permian seawater chemistry from the Capitan Reef. Geochimica et Cosmochimica Acta, 328: 1~18.
-
Chen He, Gong Enpu, Guan Changqing, Sun Baoliang, Zhang Yongli. 2008. Application of constitution of carbon, oxygen and strontium isotopes and trace elements in study of paleoenvironment of reefs. World Geology, 27(2): 130~136 (in Chinese with English abstract).
-
Chen Hongyu. 2018. Impact of volcanic activity on the development of microbial rocks. Master's thesis of Southwest Petroleum University (in Chinese with English abstract).
-
Dou Yanguang, Li Qing, Wu Yonghua, Zhao Jingtao, Sun Chenghui, Cai Feng, Chen Xiaohui, Zhang Yong, Fan Jiahui, Shi Xuefa. 2022. Carbon and oxygen isotopic characteristics of benthic foraminifera in the Okinawa trough since MIS6 and their palaeoceanographical significance. Earth Science Frontiers, 29(4): 84~92 (in Chinese with English abstract).
-
Fan Jiasong, Wu Yasheng. 2005. Main features of the Permian reefs of world and their palaeogeographic distribution. Journal of Palaeogeography, 7(3): 287~304 (in Chinese with English abstract).
-
Gao Yongjuan, Lin Shiliang, Qin Yadong, Lou Xiongying, Cheng Jinxiang. 2018. Discovery of the Middle Permianphylloid algal reefs in Huize area of Yunnan Province, and its palaeoenvironmental significance. Geological Review, 64(3): 701~710.
-
Gong Enpu, Dong Xuming, Zhang Yongli, Guan Changqing, Sun Baoliang. 2009. Paleoecological characteristics of the Carboniferous phylloid algal buildups in southern Guizhou. Geological Review, 55(5): 731~736 (in Chinese with English abstract).
-
Gong Enpu, Huang Wentao, Guan Changqing, Zhang Yongli, Wang Lifu, Yang Zhenyuan, Li Xiao, Wang Junjie, Miao Zhuowei. 2021. The coupled relationship between Carboniferous reefs and the Late Paleozoic iceage. Acta Geologica Sinica, 95(6): 1671~1692 (in Chinese with English abstract).
-
Hao Yan, Zhang Xunan, Zhang Demin. 2018. Research status and progress of microbial carbonate rocks. Journal of Chengdu University of Technology (Science & Technology Edition), 45(4): 415~427 (in Chinese with English abstract).
-
He Jiang, Fang Shaoxian, Hou Fanghao, Yan Ronghui, Zhao Zhongjun, Yao Jian, Tang Xiujun, Wu Guorong. 2013. Vertical zonation of weathered crust ancient karst and reservoir evaluation and prediction: A case study of M55—M51 sub-members of Majiagou Formation in gas fields, central Ordos basin, NW China.Petroleum Exploration and Development, 40(5): 534~542.
-
Jia Jinhua, Zhang Liping, Chen Xiuyan. 2018. Sedimentary evolution of the Carboniferous-Permian in western Wushi sag, Tarim basin. Journal of Paleogeography, 20(3): 423~434 (in Chinese with English abstract).
-
Li Minxing, Qu Haizhou, Cheng Xi, Yang Xun, Yang Dongfan, Zhang Benjian, Zhang Yunfeng, Li Xiao. 2020. Influence of volcanism on carbonate sedimentation and diagenesis. Acta Sedimentologica Sinica, 38(4): 810~825.
-
Li Quanquan, Bao Zhidong, Xiao Yuxiang, Chen Jianyang, Li Zhongzhong, Wang Zhenjun, Liu Minzhao, Li Zhuolun, Xu Xiting, Cao Fan. 2021. Research advances and prospect of mixed deposition. Acta Sedimentologica Sinica, 39(1): 153~167 (in Chinese with English abstract).
-
Li Yang, Wu Yasheng, Jiang Hongxia. 2018. Taphonomic characteristics of a Permian calcisponge reef in Lichuan, Hubei Province and its paleoenvironmental significance. Acta Palaeontologica Sinica, 57(2): 212~227 (in Chinese with English abstract).
-
Li Ying, Pan Wenqing, Wu Yasheng, Yang Guo, Sun Chonghao, Jiang Hongxia. 2020. Fabric types of microbialites from the Stage 3 of Cambrian Series 2 in Sugaitebulake section, Tarim basin. Journal of Paleogeography (Chinese Edition), 22(4): 663~679.
-
Liu Dongyang, Yu Meiyi, Lehrmann D J. 2017. Lithofacies and palaeoecosystem of an Upper Permian reef and its implication in palaeoenvironment, in Gantian'ao, Luodian, Guizhou Province, South China. Acta Palaeontologica Sinica, 56(2): 201~213 (in Chinese with English abstract).
-
Luo Jinhai, Che Zicheng, Zhou Xinyuan, Li Yong, Li Jianli, Zhang Jingyi. 2007. Spatio-temporal distribution and its oil-gas significances of Permian reef limestones on the northwestern margin of the Tarim basin. Geological Review, 53(5): 600~607 (in Chinese with English abstract).
-
Okuyucu C, Tekin U K, Bedi Y, Sayit K. 2020. Biostratigraphy of Lower Permian foraminiferal assemblages from platform-slope carbonate blocks within the Mersin Mélange, southern Turkey: Paleogeographical implications. Geobios, 59: 61~77.
-
Playton T E, Kerans C. 2018. Architecture and genesis of prograding deep boundstone margins and debris-dominated carbonate slopes: Examples from the Permian Capitan Formation, Southern Guadalupe mountains, west Texas. Sedimentary Geology, 370: 15~41.
-
Popa L, Cristina E P, Eugen G. 2014. An early Middle Anisian (Middle Triassic) tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): Facies, depositional environment and diagenesis. Acta Geologica Polonica. 64(2): 189~223.
-
Qi Yong'an, Sun Xiaofang, Dai Mingyue, Zhang Xiyang. 2017. The Microbialite cycles and their evolution from the cambrian Mantou Formation, Lushan, western Henan Province, central China. Journal of Micropaleontology, 34(2): 170~178.
-
Shao Zhiping, Lai Jiangling, Yuan Hongying, Zheng Xiaoxu, Jiang Hongxiang, Wang Cong, Huang Zhenhua, Wang Jinglin, Wang Dongsheng, Xu Shengjun. 2023. Analysis on the change of microbial community structure during the outbreak of algal bloom in different kinds of eutrophic micro water bodies. Acta Scientiae Circumstantiae, 43(3): 490~502.
-
Shen Shuzhong, Zhang Hua, Zhang Yichun, Yuan Dongxun, Chen Bo, He Weihong, Mu Lin, Lin Wei, Wang Wenqian, Chen Jun, Wu Qiong, Cao Changqun, Wang Yue, Wang Xiangdong. 2019. Permian integrative stratigraphy and timescale of China. Science China Earth Sciences, 62: 154~188.
-
Tian Wei, Wang Lei, Pan Lu, Gong Mingyue. 2018. A giant felsic pyroclastic flow eruption in the Tarim Flood Basalt Province. Acta Petrologica Sinica, 34(1): 63~74.
-
Wang Jiangong, Zhang Daowei, Bai Yadong, Sun Xiujian, Li Xiang, Wang Aiping, Zhang Shiming, Yi Dinghong, Yang Wei. 2020. Saline lacustrine palustrine sediments and microbialite in the upper Youshashan Formation in the western Qaidam basin. Acta Geologica Sinica, 94(11): 3228~3248 (in Chinese with English abstract).
-
Wang Lidong, Yu Bingsong, Zhang Yongwang, Miao Jijun. 2006. Characteristics of reef and beach facies in the Kangkelin age from western Tarmi basin——A case study from the Subashi outcrop section in the Keping area. Geoscience, 20(2): 291~298 (in Chinese with English abstract).
-
Wang Qingtong, Wang Zhijun, Wang Haigen, Wang Lizhi, Liu Shibin, Zhang Xiaolei. 2021. Geochemical characteristics and geological significance of Permian reef limestone in the northwest of Tarim basin. Northwestern Geology, 54(4): 49~58 (in Chinese with English abstract).
-
Wang Zhenting, Liu Xuyang, Li Xiaoze, Qu Jianjun 2021. Anti-erodibility ofcoral reef limestones on the Xisha-Nansha Islands. Marine Geology Frontiers, 37(6): 71~76.
-
Wei Pingsheng, Liu Quanxin, Zhang Jinglian, Chen Qilin, Zhang Huquan. 2008. Re-discussion of relationship between reef and giant oil-gas fields. Acta Petrolei Sinica, 27(2): 38~42 (in Chinese with English abstract).
-
Wood R. 1999. Paleoecology of the Capitan Reef. Special Publications, 65: 129~137.
-
Wu Yasheng. 2023. Classification of biolith (biogenic rocks). Journal of Paleogeography, 25(3): 511~523 (in Chinese with English abstract).
-
Wu Yasheng, Jiang Hongxia, Yu Gongliang, Liu Lijing. 2018. Conceptions of microbialites and origin of the Permian-Triassic boundary microbialites from Laolongdong, Chongqing, China. Journal of Paleogeography, 20(5): 737~775 (in Chinese with English abstract).
-
Wu Yasheng, Jiang Hongxia, Li Ying, Yu Gongliang. 2021. Microfabric characteristics of microbial carbonates. Journal of Paleogeography, 23(2): 321~334 (in Chinese with English abstract).
-
Yao Chunyan, Ma Dongsheng, Ding Haifeng, Zhang Xiaoyong. 2011. Reconstruction of the Early Cambrian carbonate sedimentary environment in Akesu area of Xinjiang, China: Evidences from trace elements and carbon isotope excursion. Geochimica, 40(1): 63~71 (in Chinese with English abstract).
-
Yu Xing, Yang Shufeng, Chen Hanlin, Li Zilong, Li Yinqi. 2017. Petrogenetic model of the Permian Tarim Large Igneous Province. Scientia Sinica (Terrae), 47(10): 1179~1190.
-
Zhang Jing, Zhang Baomin. 2022. Microscopic fabrics and microbial lithogeneous processes of Mesoproterozoic carbonate rocks in the Ordos basin. Acta Geologica Sinica, 96 (4): 1397~1411 (in Chinese with English abstract).
-
Zhang Yongli, Gong Enpu, Guan Changqing, Samankassou E, Sun Baoliang. 2007. Carboniferous phylloid algal reefs in Ziyun County, Guizhou (South China): Evidence of algal blooms. Acta Sedimentologica Sinica, 25(2): 177~182 (in Chinese with English abstract).
-
Zhong Yu, Wang Ren, Li Qi, Wei Houzhen, Li Xiaying. 2020. Physical and engineering characteristics of reef limestone: A review. Science & Technology Review, 38(20): 57~70.
-
Zou Shengzhang, Xia Riyuan, Liu Li, Tang Jiansheng, Liang Bin. 2016. Vertical zone characteristics and identification standard of Ordovician Karst reservoirs in the Tahe oifield. Acta Geologica Sinica, 90(9): 2490~2501.
-
陈鹤, 巩恩普, 关长庆, 孙宝亮, 张永利. 2008. C、O、Sr同位素及微量元素组成在生物礁礁体环境研究中的应用. 世界地质, 27(2): 130~136.
-
陈虹宇. 2018. 火山活动对微生物岩发育的影响. 西南石油大学硕士学位论文.
-
窦衍光, 李清, 吴永华, 赵京涛, 孙呈慧, 蔡峰, 陈晓辉, 张勇, 范佳慧, 石学法. 2022. 冲绳海槽MIS6期以来底栖有孔虫碳氧同位素特征及其古海洋指示意义. 地学前缘, 29(4): 84~92.
-
范嘉松, 吴亚生. 2005. 世界二叠纪生物礁的基本特征及其古地理分布. 古地理学报, 7(3): 287~304.
-
高永娟, 林仕良, 秦雅东, 娄雄英, 程锦翔. 2018. 云南会泽地区中二叠世叶状藻礁的发现及其古环境意义. 地质论评, 64(3): 701~710.
-
巩恩普, 董旭明, 张永利, 关长庆, 孙宝亮. 2009. 贵州南部石炭纪叶状藻礁古生态学特征. 地质论评, 55(5): 731~736.
-
巩恩普, 黄文韬, 关长庆, 张永利, 王立芙, 杨臻元, 李骁, 王俊杰, 苗卓伟. 2021. 石炭纪生物礁与晚古生代冰期的耦合关系. 地质学报, 95(6): 1671~1692.
-
郝雁, 张哨楠, 张德民. 2018. 微生物碳酸盐岩研究现状及进展. 成都理工大学学报(自然科学版), 45(4): 415~427.
-
何江, 方少仙, 侯方浩, 阎荣辉, 赵忠军, 姚坚, 唐秀军, 吴国荣. 2013. 风化壳古岩溶垂向分带与储集层评价预测: 以鄂尔多斯盆地中部气田区马家沟组马五5—马五1亚段为例.石油勘探与开发, 40(5): 534~542.
-
贾进华, 张立平, 陈秀艳. 2018. 塔里木盆地乌什凹陷西部石炭系—二叠系沉积演化. 古地理学报, 20(3): 423~434.
-
李泯星, 屈海洲, 程曦, 杨迅, 杨东凡, 张本健, 张云峰, 李晓. 2020. 火山作用对碳酸盐岩沉积及成岩的影响. 沉积学报, 38(4): 810~825.
-
李泉泉, 鲍志东, 肖毓祥, 陈建阳, 李忠诚, 王振军, 刘敏昭, 李卓伦, 许西挺, 操凡. 2021. 混合沉积研究进展与展望. 沉积学报, 39(1): 153~167.
-
李文正, 张建勇, 郝毅, 倪超, 田瀚, 曾乙洋, 姚倩颖, 山述娇, 曹脊翔, 邹倩. 2019. 川东南地区洗象池组碳氧同位素特征、古海洋环境及其与储集层的关系. 地质学报, 93(2): 487~500.
-
李阳, 吴亚生, 姜红霞. 2018. 湖北利川二叠纪生物礁的埋藏学特征及其环境意义. 古生物学报, 57(2): 212~227.
-
李莹, 潘文庆, 吴亚生, 杨果, 孙崇浩, 姜红霞. 2020. 塔里木盆地苏盖特布拉克剖面寒武系第二统第三阶微生物岩结构类型. 古地理学报, 22(4): 663~679.
-
刘冬洋, 喻美艺, Lehrmann D J. 2017. 贵州罗甸干田坳晚二叠世生物礁基本特征研究. 古生物学报, 56(2): 201~213.
-
罗金海, 车自成, 周新源, 李勇, 李建立, 张敬艺. 2007. 塔里木盆地西北缘二叠系礁灰岩的时空分布特征及其油气地质意义. 地质论评, 53(5): 600~607.
-
齐永安, 孙晓芳, 代明月, 张喜洋. 2017. 豫西鲁山寒武系馒头组微生物岩旋回及其演化. 微体古生物学报, 34(2): 170~178.
-
邵志平, 赖姜伶, 苑宏英, 郑效旭, 蒋红翔, 王聪, 黄振华, 王靖霖, 王东升, 徐圣君. 2023. 不同类型富营养化微型水体藻华暴发期微生物群落结构变化分析. 环境科学学报, 43(3): 490~502.
-
沈树忠, 张华, 张以春, 袁东勋, 陈波, 何卫红, 牟林, 林巍, 王文倩, 陈军, 吴琼, 曹长群, 王玥, 王向东. 2019. 中国二叠纪综合地层和时间框架. 中国科学: 地球科学, 49(1): 160~193.
-
田伟, 王磊, 潘路, 弓明月. 2018. 塔里木溢流玄武岩省的巨型长英质热火山碎屑流爆发记录. 岩石学报, 34(1): 63~74.
-
王建功, 张道伟, 白亚东, 孙秀建, 李翔, 王爱萍, 张世铭, 易定红, 杨巍. 2020. 柴西地区上油砂山组咸化湖沼沉积与微生物岩.地质学报, 94(11): 3228~3248.
-
王黎栋, 于炳松, 张永旺, 苗继军. 2006. 塔里木盆地西部康克林组沉积期生物礁滩体——以柯坪地区苏巴什露头剖面为例. 现代地质, 20(2): 291~298.
-
王庆同, 王志军, 王海根, 王立志, 刘世彬, 张晓磊. 2021. 塔西北二叠纪生物礁灰岩地球化学特征及其地质意义. 西北地质, 54(4): 49~58.
-
王振亭, 刘旭阳, 李孝泽, 屈建军. 2021. 西沙—南沙珊瑚礁礁灰岩抗蚀性特征. 海洋地质前沿, 37(6): 71~76.
-
卫平生, 刘全新, 张景廉, 陈启林, 张虎权. 2006. 再论生物礁与大油气田的关系. 石油学报, 27(2): 38~42.
-
吴亚生. 2023. 生物岩的分类. 古地理学报, 25(3): 511~523.
-
吴亚生, 姜红霞, 虞功亮, 刘丽静. 2018. 微生物岩的概念和重庆老龙洞剖面P-T界线地层微生物岩成因. 古地理学报, 20(5): 737~775.
-
吴亚生, 姜红霞, 李莹, 虞功亮. 2021. 微生物碳酸盐岩的显微结构基本特征. 古地理学报, 23(2): 321~334.
-
杨雪琪, 钟大康, 任影, 谢瑞, 姜杨锦丰, 蒲强, 钟泞聪, 唐自成. 2017. 重庆东部地区寒武系龙王庙组碳、氧同位素特征及其意义. 古地理学报, 19(5): 865~878.
-
姚春彦, 马东升, 丁海峰, 张晓勇. 2011. 新疆阿克苏地区早寒武世碳酸盐岩沉积环境: 微量元素和碳同位素证据. 地球化学, 40(1): 63~71.
-
余星, 杨树锋, 陈汉林, 厉子龙, 励音骐. 2017. 塔里木乌拉尔世大火成岩省的成因模式. 中国科学: 地球科学, 47(10): 1179~1190.
-
张静, 张宝民. 2022. 鄂尔多斯盆地中元古界碳酸盐岩微观组构与微生物造岩作用. 地质学报, 96(4): 1397~1411.
-
张永利, 巩恩普, 关长庆, Samankassou E, 孙宝亮. 2007. 贵州紫云石炭纪叶状藻礁: 藻类繁盛的标志. 沉积学报, 25(2): 177~182.
-
钟毓, 汪稔, 李琦, 魏厚振, 李霞颖. 2020. 珊瑚礁灰岩物性特征及工程性质研究进展. 科技导报, 38(20): 57~70.
-
邹胜章, 夏日元, 刘莉, 唐建生, 梁彬. 2016. 塔河油田奥陶系岩溶储层垂向带发育特征及其识别标准. 地质学报, 90(9): 2490~2501.
-
摘要
塔里木盆地西北缘二叠系巴立克立克组广泛发育具有油气勘探意义的巨厚台地边缘生物礁,本文对塔西北克孜勒布拉克南沟出露的典型的二叠系巴立克立克组生物礁进行了详细的宏微观研究。该套生物礁以生屑滩为礁基,礁核下部主要为蓝绿藻建造的各类微生物岩,其结构组分主要为凝块及破碎的微凝块,次为叠层石,此时的水体能量较低;礁核上部局部发育叶状藻礁,并伴生大量的海生底栖动物,此时礁体开始暴露在浪基面之上,大量发育角砾状灰岩,并遭受大气淡水岩溶的改造。除了台缘带外,塔西北柯坪地区同期的局限台地中也发育小规模的、具微生物岩特征的台内礁滩体,说明该时期区域上的环境条件普遍适宜造礁。巴立克立克组的该套礁滩体的形成时间为乌拉尔世阿瑟尔期晚期—萨克马尔期,这与乌拉尔世塔里木大火成岩省早期阶段相当,因此,推测该套礁滩体的形成和当时的火山活动产生的火山灰导致南天山洋残余海盆的海水“富营养化”有关。藻类的爆发使得巴立克立克组礁滩体的δ13C值较之康克林组的碳酸盐岩呈现显著正偏移。但是,巴立克立克组的礁滩体受胶结作用等建设性成岩作用的改造程度较深,利于“成岩”,不利“成储”,使得区域上巴立克立克组的礁滩体尽管相带较好,但储渗性极差,唯有受构造裂缝改造部分可发育高渗层。因此,可以确定:塔西北乌拉尔世巴立克立克组的礁滩储层基本不受相控,主要发育裂缝型储层。因此,今后对于塔西北二叠系礁滩油气藏的勘探应重点关注构造裂缝发育段。本研究对今后塔西北巴立克立克组生物礁优质储层预测提供了科学依据,对于我国乃至世界范围内二叠系微生物岩的研究也有一定助益。
Abstract
At the Permian Baliklik Formation in the northwest margin of the Tarim basin, there developed massively thick reef limestone that bears oil and gas exploration significance. This paper makes macro and micro examinations of the reefs which cropped out at Kizilbulak Nangou in the northwest margin of the Tarim basin. This set of reefs had bioclastic shoals as reef bases. The lower zone of the reef core is mainly composed of microbialite of various types formed by Cyanobacteria, with thrombolite and broken-up microclots as its most dominant structural components, followed by stromatolites. At this time, the hydraulic energy is low. In the upper zone of the reef core locally developed phylloid algal reefs, with a large quantity of marine benthic fauna among them. At this time, the reef body began to expose itself above the wave base, with a large number of brecciated limestone developed, and it was subjected to the transformation of atmospheric freshwater karstification. In addition to the platform margin zone, the synchronous restricted platform in the Keping area in the northwest Tarim basin also developed small-scale intra-platform reef-shoal complexes, with microbial rock characteristics, indicating that the environmental conditions in the region during this period were generally favorable for reef building. The set of reef-shoal complexes in the Baliklik Formation formed in the Late Atherian period of the Cisuralian to the Sa kmarian age, contemporary with the early stage of large igneous provinces of Cisuralian Tarim basin. Therefore, it is speculated that the forming of this set of reef-shoal complexes was related to the “eutrophication” of the sea water in the residual basin of the south Tianshan ocean; the “eutrophication” had been caused by the volcanic ash spurted out by volcanic activities at that time. As a result of the outbreak of algae, the δ13C value of the reef-shoal complexes in the Baliklik Formation shows a significant positive shift compared with that of the carbonate rocks in the Kangkelin Formation. However, the reef-shoal complexes of the Baliklik Formation was much transformed by cementation and other constructive types of diagenesis, unfavorable to the forming of reservoirs. In other words, the reef-shoal complexes of the Baliklik Formation in the region, despite their desirable facies belts, possess poor reservoir permeability; high permeability layers only developed where structural fractures occurred. Therefore, it can be theorized that reef-shoal reservoirs of the Cisuralian Baliklik Formation in the northwest margin of the Tarim basin are, generally speaking, not controlled by facies, and that fractured reservoirs were dominant. Thereupon, exploration of Permian reef-shoal oil and gas reservoirs in the northwest margin of the Tarim basin should focus on the structural fractured members. In brief, this study is an attempt to provide some scientific basis for the prediction of high-quality reservoirs in the Baliklik Formation reefs of the Tarim basin, and to promote further research into Permian microbial rocks in China and throughout the world.