自四川盆地西北部(川西北)泥盆系观雾山组油气勘探取得重要进展以来,观雾山组的沉积储层研究受到了广泛重视。然而,由于观雾山组地层划分方案的变动和地层的穿时性,导致目前对观雾山组的时代分布和充填过程认识不清,从而影响了沉积古地理格局的恢复。本文以四川广元西北乡、潜溪河剖面泥盆系观雾山组牙形石生物地层研究为基础,结合区域古生物地层资料,认为江油马角坝以北的观雾山组绝大多数沉积于晚泥盆世早—中弗拉期,且地层沉积时间自南西向北东逐渐变晚。龙门山北段观雾山组具有自西向东、自南向北地层厚度减薄和地层时代变新的特征,表明来自扬子地台西部的古特提斯洋海水向东侵入龙门山地区,因地形差异和渐进式海侵形成了自南西向北东的超覆沉积。由于岩相分异,超覆沉积形成的观雾山组与金宝石组在区域上既表现为上下叠置关系,也表现为同期异相的相变关系。该研究不仅对约束川西北地区观雾山组地层时代提供了可靠的古生物证据,而且对认识龙门山地区泥盆系的充填过程、沉积古地理格局均具有重要意义。

The study on sedimentation and reservoir of the Guanwushan Formation has been widely investigated in recent years since a great breakthrough was obtained in hydrocarbon exploration of the Devonian Guanwushan Formation in northwestern Sichuan basin. However, the stratigraphic age distribution and sedimentary filling pattern of the Guanwushan Formation remains controversial due to disputed stratigraphic division and stratum diachronism, which has hindered the reconstruction of the Devonian palaeogeographic configuration in the Longmenshan area. Based on the results of conodont biostratigraphy of the Guanwushan Formation at the Xibeixiang and Qianxihe sections in combination with regional geological material, this study reveals that the Guanwushan Formation distributed in the north of Majiaoba area (Jiangyou County) were generally deposited from the early to middle Frasnian (Late Devonian), and the depositional age trends are younger from the southwest toward the northeast. The Devonian strata in the Longmenshan area tend to be younger in stratigraphic age but decrease in thickness from the west to the east, suggesting that the Devonian seawater in Longmenshan area came from the Palaeotethys ocean that was located in the western margin of the Yangtze Platform. During the early to middle Frasnian, the episodic transgressions and topographic height differences caused sedimentary overlap in the Guanwushan Formation from the southwest to northeast at the northern segment of Longmenshan area. On the influence of overlap deposition, both superimposed and syndepositional relationships between the Guanwushan and Jinbaoshi formations in different areas could be identified due to facies differentiation. This study provides a robust palaeontological evidence for constraining the stratigraphic age of the Guanwushan Formation, which is of great significance in understanding of the depositional filling process of the Devonian strata as well as important for reconstructing the Devonian palaeogeographic configuration in the Longmenshan area.

泥盆系 ； 观雾山组 ； 金宝石组 ； 牙形石生物地层 ； 超覆沉积 ； 龙门山

Devonian ； Guanwushan Formation ； Jinbaoshi Formation ； conodont biostratigraphy ； sedimentary overlap ； Longmenshan Mountains

近年来随着四川盆地西北部(川西北)地区上古生界油气勘探的突破,特别是双探3井泥盆系观雾山组试气获得日产数十万方天然气,预示着川西北地区观雾山组具有巨大的勘探潜力(邓虎成等, 2008; 沈浩等, 2016)。川西北西缘的龙门山地区是观雾山组出露的重要区域,针对该区域观雾山组的沉积、储层特征,不少学者开展了大量研究工作(熊连桥等, 2019; 熊绍云等, 2020; 林怡等, 2021)。然而,不同学者对龙门山地区泥盆系观雾山组的地层时代分布和充填过程尚未达成共识,使得不同学者对该地区观雾山组沉积古地理格局的认识存在较大差异(侯鸿飞等, 1988b; 沈浩等, 2016; 熊绍云等, 2020)。这主要与两方面因素有关:一方面与龙门山地区泥盆系的零散分布有关,多数泥盆系呈断块或飞来峰出露(四川省地质矿产局, 1991),研究难度大;另一方面与龙门山泥盆系区域研究程度差异有关,除唐王寨—仰天窝一带的泥盆系具有较高研究程度外(乐森璕, 1956; 侯鸿飞等, 1988a; 蒋武等, 1990; 郑荣才等, 1997; Li Fengjie et al.,2017),自江油马角坝向北东和南西方向出露的观雾山组的地层时代、沉积环境以及充填过程仍不清楚。

尽管前期不少学者对龙门山地区泥盆系岩石地层(陈源仁, 1974; 万正权, 1983; 侯鸿飞等, 1988a)、生物地层(蒋武等, 1990; Ma Xueping et al.,2006; Edwards et al.,2018)、层序地层(鲜思远等, 1995; 李祥辉等, 1998; Chen Yuanren et al.,2005)开展了大量研究,但是绝大多数的研究集中在北川甘溪剖面,缺少区域地层时代对比研究,特别是广元地区的泥盆系研究程度较低。基于龙门山地区泥盆系沉积和分布特征,本文提出了观雾山组地层划分新方案,结合广元西北乡、潜溪河剖面观雾山组牙形石生物地层、沉积微相、层序地层研究以及区域地层资料分析,确定了龙门山北段观雾山组的穿时规律和泥盆纪海侵方向,总结了观雾山组沉积充填模式,为认识龙门山地区沉积古地理格局提供了重要的等时地层格架。

龙门山地区位于上扬子地台西北缘,四川盆地与松潘—甘孜造山带之间,北接秦岭构造带,南临康滇构造带(图1a)。龙门山地区自北西向南东发育的4条主干断裂将龙门山造山带分隔为3个变形带(图1b):后山带、前山带、山前带(前陆扩展变形带)(龙学明, 1991; 李智武等, 2008; 刘树根等, 2009)。根据冲断带的基底性质及展布、地层演化历史、构造变形特征、沉降与隆升特征以及活动构造等在走向上的差异性,龙门山造山带自北向南分为3段:北段、中段、南段(李智武等, 2008; 刘树根等, 2009)。自扬子地台形成统一基底以来,龙门山地区经历了两大构造演化阶段(龙学明, 1991; 罗志立等, 1992; Chen Shefa et al.,1996; 郭正吾等, 1996; Jia Dong et al.,2006),即震旦纪—中三叠世以拉张背景为主的被动大陆边缘阶段和晚三叠世至今以挤压背景为主的冲断隆升和前陆盆地阶段。

志留纪—中三叠世的裂陷活动形成了龙门山北东—南西向主干断裂的雏形,并控制了龙门山地区沉积物的类型和分布特征(龙学明, 1991; 罗志立等, 1992; 刘文均等, 1999; Jia Dong et al.,2006)。由于受加里东晚幕运动的影响,上扬子地台整体抬升为陆,龙门山地区泥盆系沉积于受断裂控制的上扬子古陆西缘,呈北东—南西向带状分布于广元朝天驿至天全—二郎山一带,其中以龙门山北段的唐王寨—仰天窝一带地层发育最完整,并向南西和北东方向急剧减薄至尖灭(四川省地质矿产局, 1991)。龙门山地区完整泥盆系自下而上划分为3统11组(厚约4700m)(图1c):平驿铺组至白柳坪组为砂质海岸环境下的陆源碎屑沉积序列,由石英砂岩、泥质粉砂岩及部分杂砂岩组成;甘溪组至金宝石组为陆源碎屑岩与海相碳酸盐岩混合型地层,代表混积陆棚沉积;观雾山组至长滩子组为碳酸盐岩夹生物礁灰岩地层,代表碳酸盐岩台地沉积 (侯鸿飞等, 1988a; 鲜思远等, 1995)。

晚三叠世以来,受中国大陆主体拼合和印度—欧亚板块碰撞作用的综合影响,龙门山及其以西的松潘—甘孜地区地层发生变形—变质和冲断隆升(Burchfiel et al.,1995; Jia Dong et al.,2006),其东侧发生强烈沉降形成前陆盆地,沉积了巨厚的陆相碎屑岩(罗志立等, 1992; Chen Shefa et al.,1996; Li Yong et al.,2003)。由于受构造层次、变形程度差异的影响,自北西向南东依次形成松潘—甘孜褶皱带、龙门山冲断带、川西前陆盆地三个相互独立而又密切联系的构造单元。

在龙门山泥盆系标准剖面(北川甘溪剖面)早期地层研究中,原观雾山组(“观雾山组”)被定义为养马坝组之上、沙窝子组之下的一套富含腕足类和苔藓虫的黑色石灰岩及暗色厚层或块状的镁质石灰岩地层(乐森璕, 1956),其下部为砂岩页段(后命名为金宝石组)(万正权, 1983),上部为碳酸盐岩段(对应本文的观雾山组)(图2)。陈源仁(1974)根据腕足类的研究,将甘溪剖面“观雾山组”顶部腕足类Stringocephalus(鸮头贝)消失、Cyrtospirifer(弓石燕)出现之前的一套富集Leiorhynchus(秃嘴贝)动物群的灰岩—泥质灰岩地层命名为沙窝子组土桥子段,并将上覆厚层白云岩夹生物礁灰岩、泥灰岩地层命名为沙窝子组水井湾段。侯鸿飞等(1988a)从岩性角度将土桥子段提升为土桥子组,并将土桥子组限定为白云质灰岩之上、藻纹层灰岩之下的一套灰黑色中—薄层泥晶灰岩、团块团粒生屑灰岩地层(对应原土桥子段中上部)。此外,侯鸿飞等(1988a)将白云岩之下发育层孔虫泥晶灰岩、含生屑泥晶灰岩、藻纹层泥晶灰岩段从沙窝子组水井湾段中分出,命名为小岭坡组。

由于受相变的影响,除甘溪剖面外,土桥子组和小岭坡组在龙门山北段大部分地区都不发育,故本文按照原始定义将土桥子组和小岭坡组分别划归观雾山组顶部和沙窝子组底部。按照本文划分方案,观雾山组自下而上分为下、中、上三段,分别对应侯鸿飞等(1988a)划分方案中观雾山组鸡公岭段、海角石段、土桥子组(图2)。从标准剖面岩性特征来看,观雾山组下段主要为深灰色厚层泥晶生屑灰岩、层孔虫礁灰岩,中段主要为灰色—深灰色中—厚层生屑泥晶灰岩、白云质灰岩、白云岩夹薄层泥晶灰岩,上段主要为灰黑色中—薄层泥晶灰岩、团块团粒生屑灰岩夹泥灰岩(图1c)。本文研究区观雾山组岩性主要为灰色—深灰色中—薄层泥晶灰岩、生屑泥晶灰岩、泥晶生屑灰岩,对应于本组上段地层。

图1 龙门山及邻区大地构造位置(a)(据汤良杰等, 2008)、泥盆系分布(b)(据刘树根等, 2009,马角坝以北的泥盆系地层年代来自本研究)和地层序列图(c)(据侯鸿飞等, 1988a)

Fig.1 Tectonic setting of the Longmenshan Mountains and adjacent area (a) (after Tang Liangjie et al.,2008), distribution of the Devonian (b) (after Liu Shugen et al.,2009,stratigraphic age of the Devonian strata distributed in the north of Majiaoba area came from this study) and stratigraphic succession of the Devonian strata(c)(after Hou Hongfei et al.,1988a)

Ⅰ-1—龙门山后山带;Ⅰ-2—龙门山前山带;Ⅰ-3—龙门山山前带

Ⅰ-1—Back range of Longmen Mountain;Ⅰ-2—front range of Longmen Mountain; Ⅰ-3—foreland of Longmen Mountain

本文实测的西北乡、潜溪河剖面的大地构造位置处于上扬子地台西北缘的龙门山冲断带(前山带)北段(图1b)。由于受古地貌的影响,虽然研究剖面泥盆系发育不完整,但是剖面岩性序列与甘溪剖面具有相似性(图1c),也显示出碎屑滨岸向碳酸盐岩台地演化过程。

西北乡剖面位于四川省广元市朝天区西北乡南东约2km附近的公路旁,剖面泥盆系自下而上仅发育金宝石组、观雾山组、沙窝子组,总厚约151.49m(图3,图4)。泥盆系与下伏志留系纱帽组、上覆二叠系栖霞组均呈平行不整合。观雾山组与下伏金宝石组呈整合接触,与上覆沙窝子组呈整合接触(图3d)。金宝石组出露厚度约3.43m,主要为浅黄色中—薄层石英粉砂岩夹泥岩,石英分选好,磨圆差,偶见棘皮类生屑。观雾山组厚约54.59m,根据岩性和古生物特征分为2个小段:第Ⅰ段底部为含石英泥晶生屑灰岩,中上部为浅灰色中—薄层含生屑泥晶灰岩、瘤状灰岩夹泥岩(图3a、b),生物扰动(生物扰动指数BI=2~3)(Taylor et al.,2003)和示顶底构造发育,顶部为灰色中层泥晶生屑灰岩,部分层位发生白云岩化;第Ⅱ段下部为深灰色薄层泥晶灰岩夹泥晶生屑灰岩,见水平层理、生物扰动(BI=2~3)和示顶底构造,上部为深灰色中层生屑泥晶灰岩,发育粒序层理和生物扰动(BI=2~3)构造,顶部为灰色中层生物漂浮岩。沙窝子组下部为灰色中层生屑泥晶灰岩夹薄层泥晶灰岩和泥岩(厚约6.12m),上部为灰色中—厚层粉—细晶白云岩(厚约87.35m)。

图2 龙门山地区观雾山组划分沿革

Fig.2 History of stratigraphic division of the Guanwushan Formation in the Longmenshan area

潜溪河剖面位于四川省广元市朝天区东约5km附近的龙洞背大桥公路旁,剖面泥盆系岩性序列特征与西北乡十分相似,自下而上发育金宝石组和观雾山组(图3,图5)。泥盆系与下伏志留系、上覆二叠系栖霞组均呈平行不整合接触。金宝石组厚12.50m,由多个向上变浅旋回组成(图3e):旋回底部为灰色—灰绿色薄层泥岩、石英粉砂岩,石英颗粒分选中等,磨圆较差,见水平层理;旋回上部为灰白色中层石英细砂岩,石英含量高达80%以上,石英颗粒分选较好,磨圆中等,见楔状交错层理。观雾山组厚18.39m,底部为含石英泥晶生屑灰岩和薄层瘤状灰岩(图3f),中部为生屑泥晶灰岩夹泥晶灰岩,见水平层理和生物扰动构造(BI=2~3),顶部为含生屑泥晶灰岩,具白云岩化现象,见示顶底和生物扰动构造(BI=3)。

本研究参考Dunham(1962)和冯增昭(1989)的碳酸盐岩分类方案,根据支撑类型、颗粒含量、颗粒类型、生物化石及沉积组构等特征,在西北乡和潜溪河剖面观雾山组中识别出7种岩石微相类型(图6),各沉积微相的结构、沉积构造及环境解释见表1。根据沉积微相的特征和沉积环境的差异,上述7种沉积微相可归入3种相组合,分别形成于深潮下带、浅潮下带和潮间带环境。

(1)深潮下带相组合:主要由泥岩、泥晶灰岩、含生屑泥晶灰岩、生屑泥晶灰岩组成,少数为生物漂浮岩。各岩石微相均为泥晶基质支撑,泥晶基质含量大于50%。颗粒类型以生物碎屑为主,生物碎屑以腕足类、腹足类为主,少数为竹节石、介形类,大小为0.2~8mm。基质支撑结构和较低的碳酸盐颗粒含量,反映较弱的水动力环境,受正常风浪的影响较小。较发育的生物扰动构造(图6c、d、f),显示水体氧气较充分。部分层位发育水平层理(图6b)未见暴露构造,指示非潮上的低能环境。生物组合以底栖生物为主,偶有浮游生物为特征,反映具有一定的离岸环境。上述特征反映该组合主要沉积于正常浪基面以下,风暴浪基面以上的低能沉积环境。

图3 四川广元西北乡和潜溪河剖面观雾山组野外宏观岩性特征

Fig.3 Field photographs of lithology in the Guanwushan Formation at the Xibeixiang and Qianxihe sections, Guangyuan, Sichuan

(a)—西北乡剖面下部含生屑泥晶灰岩夹泥岩;(b)—西北乡剖面下部瘤状灰岩;(c)—西北乡剖面上部泥晶灰岩,发育水平层理;(d)—西北乡剖面观雾山组与沙窝子组界线附近景观;(e)—潜溪河剖面全景,黄圈中铁锤长约30cm;(f)—潜溪河剖面第8层底部瘤状灰岩,黄色虚线之下为含石英泥晶生屑灰岩,红色记号笔长约14cm

(a)—Bioclasts-bearing wackestones intercalated with mudstones from the lower succession of the Xibeixiang section; (b)—nodular limestones from the lower succession of the Xibeixiang section; (c)—micritic limestones with horizontal bedding from the upper succession of the Xibeixiang section; (d)—the boundary between the Guanwushan Formation and Shawozi Formation at the Xibeixiang section; (e)—overview of outcrop at the Qianxihe section, hammer in the yellow circle is about 30cm in length; (f)—nodular limestones from the lower part of Bed 8overlaid on bearing-quartzs packstones (below the yellow dashed lines) at the Qianxihe section, red marker is about 14cm in length

(2)浅潮下带相组合:主要由生屑泥晶灰岩和泥晶生屑灰岩组成。颗粒含量25%~72%,颗粒类型主要为生物碎屑,多破碎,颗粒之间主要为灰泥基质。生屑主要以腹足类、棘皮类、腕足类为主。该组合以颗粒支撑结构和破碎的生屑颗粒发育为主要特征,反映动荡的高能环境。生物碎屑组合中以广盐度生物占优势,浮游生物稀少,底栖生物相对丰富,但分异度低,显示水体受到一定程度的限制。生物扰动构造发育(图6h、j),显示水体氧气较丰富。该组合主要沉积于平均低潮线至正常浪基面之间的浅潮下带沉积环境。

图4 四川广元西北乡剖面金宝石-观雾山组地层、层序及沉积微相特征

Fig.4 The columnar stratigraphic section with lithological units, sequences, and microfacies data of the Jinbaoshi-Guanwushan Formation at the Xibeixiang section, Guangyuan, Sichuan

M—泥岩;W1—含颗粒灰泥岩;W2—颗粒质灰泥岩;P—灰泥颗粒岩;G—颗粒灰岩

M—Mudstone; W1—grain-bearing wackestone; W2—wackestone; P—packstone; G—grainstone

(3)潮间带相组合:主要由含石英泥晶生屑灰岩组成,少数为含生屑的白云质泥晶灰岩。颗粒含量为50%~60%,颗粒类型主要为生屑,以棘皮类、腹足类为主,生屑多数破碎。基质为灰岩,灰泥内充填少量的石英粉屑(5%~10%),粒径50~100 μm,呈次棱角状—次圆状,分选中等(图6a)。该相组合通常叠覆于滨岸碎屑沉积(金宝石组)之上,位于泥晶灰岩之下。以颗粒支撑结构和灰泥基质混入陆源石英粉屑为主要特征,反映受陆源输入影响的高能动荡水体环境。滨岸滩颗粒灰岩中含陆源砂被认为是古代镶边台地的重要特征(金振奎等, 2013)。生物分异度较低,以广盐度腹足类、棘皮类为主,反映水体较局限。部分层位云化的灰泥基质中发育溶蚀面(图6l),显示沉积暴露特征。这些特征反映该相组合形成于平均低潮线之上的潮间带环境。

图5 四川广元潜溪河剖面金宝石-观雾山组地层、层序及沉积微相特征

Fig.5 The columnar stratigraphic section with lithological units, sequences, and microfacies data of the Jinbaoshi-Guanwushan Formation at the Qianxihe section, Guangyuan, Sichuan

M—泥岩;W1—含颗粒灰泥岩;W2—颗粒质灰泥岩;P—灰泥颗粒岩

M—Mudstone; W1—grain-bearing wackestone; W2—wackestone; P—packstone

综合沉积微相类型及环境的变化,在西北乡和潜溪河剖面中分别识别出2幕和1幕海侵-海退旋回(图4,图5)。在西北乡剖面的两幕海侵-海退旋回中,沉积环境从浅水的潮间带逐渐向较深的浅潮下带→深潮下带演变,最后在旋回顶部回落到浅潮下带—潮间带 (图4)。在潜溪河剖面中,沉积环境从较浅的潮间带向浅潮下带→深潮下带演变,最后在旋回顶部回落到浅潮下带(图5)。在两个剖面的海侵-海退旋回中,海侵体系域中的生物分异度较高,不仅有广盐度生物(如,腹足类、双壳类、介形类等),也有窄盐度生物(如,腕足类、竹节石、牙形石)。在高位体系域中,广盐度生物较窄盐度生物更富集。这些特殊的古生物学和沉积学特征是识别层序的重要标志。

通过对剖面观雾山组开展牙形石生物地层工作,在西北乡剖面共鉴定出牙形石4属10种: Ancyrodellarugosa, Mesotaxis sp., Polygnathus cf.pennatus, Pol.decorosus, Pol.alatus, Pol.dubius, Pol.praepolitus, Pol.aspelundi, Icriodusexpansus, I.subterminus, I.symmetricus(图7)。在潜溪河剖面共鉴定出牙形石3属6种:Ancyrodellacurvata early form, I.cf.difficilis, I.symmetricus, I.cf.symmetricus, Pol.decorosus, Pol.webbi(图7)。

图6 四川广元西北乡和潜溪河剖面观雾山组显微镜下岩性和古生物特征

Fig.6 Photomicrographs of lithology and palaeontology in the Guanwushan Formation at the Xibeixiang and Qianxihe sections, Guangyuan, Sichuan

(a)—含石英泥晶生屑灰岩(MF-7,样品XB-2-1),方解石被茜素红染红,正交光;(b)—具水平层理的泥晶灰岩(MF-2,样品XB-18-1),单偏光;(c)—具生物潜穴充填(黄色箭头)的泥晶灰岩(MF-2,样品XB-12-1),单偏光;(d)—含生屑泥晶灰岩(MF-3,样品QXH-8-1),其中骨骼碎屑(腕足类和腹足类)因生物扰动呈旋涡状排列(黄色虚线内),单偏光;(e)—生屑泥晶灰岩(MF-5,样品QXH-9-2),单偏光;(f)—生屑泥晶灰岩(MF-5,样品XB-23-1),其中骨骼碎屑(腹足类)因生物扰动呈旋涡状(黄色箭头)排列,单偏光;(g)—泥晶生屑灰岩(MF-6,样品XB-17-1),其中腹足类和介形类壳体中示顶底构造(白色箭头)充填球粒和生屑微粒,方解石被茜素红染红,单偏光;(h)—具生物扰动构造(黄色箭头)的泥晶生屑灰岩(MF-6,样品XB-16-1),单偏光;(i)—横板珊瑚漂浮岩,灰泥基质中充填生屑微粒(MF-4,样品XB-28-2),单偏光;(j)—泥晶生屑灰岩(MF-6,样品XB-16-3),其中骨骼碎屑(棘皮类和腹足类)因生物扰动呈旋涡状排列(黄色箭头),单偏光;(k)—泥晶生屑灰岩(MF-6,样品XB-19-2),单偏光;(l)—含生屑泥晶灰岩(MF-3,样品QXH-10-2),灰泥基质被白云石微晶交代(白色虚线表示溶蚀边界),方解石被茜素红染红,单偏光;A—横板珊瑚;B—腕足类;E—棘皮类;G—腹足类;T—竹节石;O—介形类;样品编号“XB”和“QXH”分别代表样品来自西北乡和潜溪河剖面

(a)—Quartz-bearing packstone (MF-7, sample XB-2-1), calcites were stained red with alizarin red, in cross-polarized light (CPL); (b)—micritic limestone with horizontal bedding (MF-2, sample XB-18-1), in plane-polarized light (PPL); (c)—micritic limestone (MF-2, sample XB-12-1) with burrow filling (yellow arrows), in PPL; (d)—skeletal debris (brachiopod and gastropod fragments) in bioclast-bearing wackestone (MF-3, sample QXH-8-1) arranged as swirls due to bioturbation (inside yellow dashed lines), in PPL; (e)—bioclastic wackestone (MF-5, sample QXH-9-2), in PPL; (f)—skeletal debris (gastropod fragments) in bioclastic wackestone arranged as circular swirls (yellow arrows) due to bioturbation (MF-5, sample XB-23-1), in PPL; (g)—packstone with geopetal deposition (white arrows) of peloids, fine bioclasts in gastropod and ostracod (MF-6, sample XB-17-1), calcites were stained red with alizarin red, in PPL; (h)—packstone (MF-6, sample XB-16-1) with bioturbation (yellow arrow), in PPL; (i)—tabulate coral floatstone with fine-grained bioclasts filling in marl matrix (MF-4, sample XB-28-2), in PPL; (j)—skeletal debris (echinoderm and gastropod fragments) in packstone arranged as circular swirls (yellow arrows) due to bioturbation (MF-6, sample XB-16-3), in PPL; (k)—packstone (MF-6, sample XB-19-2), in PPL; (l)—bioclast-bearing wackestone (MF-3, sample QXH-10-2) with marl matrix replaced by micritic dolomites (the white dashed line labeled dissolution interface), calcites were stained red with alizarin red, in PPL; A—auloporid; B—brachiopod; E—echinoderm; G—gastropod; T—tentaculitid; O—ostracod;sample number “XB” and “QXH” indicates sample came from the Xibeixiang and Qianxihe sections, respectively

表1 四川广元西北乡和潜溪河剖面观雾山组碳酸盐岩沉积特征及微相类型

Table1 Sedimentary characteristics and microfacies classification of carbonates in the Guanwushan Formation at the Xibeixiang and Qianxihe sections, Guangyuan, Sichuan

目前国际层型剖面中—上泥盆统界线以牙形石Ancyrodellarotundiloba演化序列中的早期形态类型Ancyrodellapristina首现来确定(Klapper et al.,1987; Becker et al.,2012),Ancyrodella属的演化特征对确定中—晚泥盆世之交的地层时代具有重要意义。虽然不同学者建立的Ancyrodella属演化序列存在差异(Klapper, 1985; Sandberg et al.,1989; 丁干等, 2000; Aboussalam et al.,2007),但是Ancyrodella总体演化趋势具相似性:齿台不断变宽、变大,两侧齿叶由不发育逐渐向前、向后伸,口面瘤齿不断复杂化,形成二级齿脊;反口面基腔不断变小、二级龙脊逐渐延伸至齿叶边缘。

西北乡剖面观雾山组底部的Ancyrodella rugosa具有心形齿台和向前伸的二级齿脊,齿台表面具大小一致的齿瘤,反口面的二级龙脊侧向延伸至齿叶边缘等特征(图7中的10和11)。这些特征显示A.rugosa为Ancyrodellarotundiloba晚期形态演化类型,代表了晚泥盆世分子。A.rugosa通常首现于晚泥盆世早弗拉期上Mesotaxisguanwushanensis (=falsiovalis)带,延伸至 Palmatolepis punctata带(Klapper, 1988; Ziegler et al.,1990; Ji Qiang et al.,1993)。Pol.alatus从晚吉维特期中Pol.varcus带延至中弗拉期下Pa.hassi带。Pol.cf.pennatus和Pol.dubius常从晚吉维特期延至早弗拉期Pa.transitans带(龚大明, 1990)。I.subterminus主要分布于吉维特期下M.guanwushanensis带至晚弗拉期Pa.rhenana带(Sandberg et al.,1984)。牙形石组合的生物年代学结果显示,西北乡剖面观雾山组沉积于晚泥盆世早弗拉期上M.guanwushanensis带至Pa.transitans带。

图7 四川广元西北乡和潜溪河剖面观雾山组牙形石生物组合

Fig.7 Conodont assemblage of the Guanwushan Formation at the Xibeixiang and Qianxihe sections, Guangyuan, Sichuan

1,2—Polygnathus cf.pennatus,1口视,2反口视,标本号XB-18-1-008,采自西北乡剖面第18层;3—Polygnathusdubius,口视,标本号XB-7-1-001,采自西北乡剖面第7层;4~7—Polygnathus decorosus,4口视,标本号QXH-9-2-010,5侧视,标本号QXH-9-2-008,6口视,7反口视,标本号QXH-9-2-009,采自潜溪河剖面第9层;8,9—Ancyrodellacurvata early form,8口视,9反口视,标本号QXH-9-2-001,采自潜溪河剖面第9层;10,11—Ancyrodella rugosa,10口视,11反口视,标本号XB-7-1-004,采自西北乡剖面第7层;12—Mesotaxis sp.,口视,标本号XB-7-1-002,采自西北乡剖面第7层;13—Polygnathusaspelundi,口视,标本号XB-18-1-010,采自西北乡剖面第18层;14—Polygnathusdubius,口视,标本号XB-18-1-005,采自西北乡剖面第18层;15,16—Polygnathus praepolitus,15口视,16反口视,标本号XB-7-1-003,采自西北乡剖面第7层;17,18—Polygnathus alatus,17口视,18反口视,标本号XB-18-1-006,采自西北乡剖面第18层;19,20—Polygnathus webbi,19侧视,20反口视,标本号QXH-9-2-006,采自潜溪河剖面第9层;21—Icriodussymmetricus,口视,标本号XB-18-1-003,采自西北乡剖面第18层;22—Icriodusexpansus,口视,标本号XB-18-1-009,采自西北乡剖面第18层;23,24—Icriodus subterminus,23口视,标本号XB-18-1-001,24口视,标本号XB-18-1-002,采自西北乡剖面第18层;25—Icriodus cf.symmetricus,口视,标本号QXH-9-2-011,采自潜溪河剖面第9层;26,30—Icriodus cf.difficilis,26口视,标本号QXH-9-2-002,30口视,标本号QXH-9-2-003,采自潜溪河剖面第9层;27~29—Icriodus symmetricus,27口视,标本号QXH-9-2-005,28口视,标本号QXH-9-2-007,29口视,标本号QXH-9-2-004,采自潜溪河剖面第9层

1,2—Polygnathus cf.pennatus,1oral view,2aboral view,number XB-18-1-008,from Bed 18at the Xibeixiang section;3—Polygnathusdubius,oral view,number XB-7-1-001,from Bed 7at the Xibeixiang section;4~7—Polygnathus decorosus,4oral view,number QXH-9-2-010,5lateral view,number QXH-9-2-008,6oral view,7aboral view,number QXH-9-2-009,from Bed 9at the Qianxihe section;8,9—Ancyrodellacurvata early form,8oral view,9aboral view,number QXH-9-2-001,from Bed 9at the Qianxihe section;10,11—Ancyrodella rugosa,10oral view,11aboral view,number XB-7-1-004,from Bed 7at the Xibeixiang section;12—Mesotaxis sp.,oral view,number XB-7-1-002,from Bed 7at the Xibeixiang section;13—Polygnathusaspelundi,oral view,number XB-18-1-010,from Bed 18at the Xibeixiang section;14—Polygnathusdubius,oral view,number XB-18-1-005,from Bed 18at the Xibeixiang section;15,16—Polygnathus praepolitus,15oral view,16aboral view,number XB-7-1-003,from Bed 7at the Xibeixiang section;17,18—Polygnathus alatus,17oral view,18aboral view,number XB-18-1-006,from Bed 18at the Xibeixiang section;19,20—Polygnathus webbi,19lateral view,20aboral view,number QXH-9-2-006,from Bed 9at the Qianxihe section;21—Icriodussymmetricus,oral view,number XB-18-1-003,from Bed 18at the Xibeixiang section;22—Icriodusexpansus,oral view,number XB-18-1-009,from Bed 18at the Xibeixiang section;23,24—Icriodus subterminus,23oral view,number XB-18-1-001,24oral view,number XB-18-1-002,from Bed 18at the Xibeixiang section;25—Icriodus cf.symmetricus,oral view,number QXH-9-2-011,from Bed 9at the Qianxihe section;26,30—Icriodus cf.difficilis,26oral view,number QXH-9-2-002,30oral view,number QXH-9-2-003,from Bed 9at the Qianxihe section;27~29—Icriodus symmetricus,27oral view,number QXH-9-2-005~29,28oral view,number QXH-9-2-007,29oral view,number QXH-9-2-004,from Bed 9at the Qianxihe section

潜溪河剖面观雾山组底部出现的A.curvata early form为梯形齿台,齿台前缘发育前侧齿脊,齿台表面具稀疏的齿瘤,后侧齿叶微发育,反口面二级龙脊延伸至前侧齿叶边缘,基腔后部有向侧后方延伸趋势的次级龙脊,延伸距离极短(图7中的8和9)。这些特征显示A.curvata early form是相对于Ancyrodella rugosa更晚演化出来的分子。A.curvata early form通常首现于中弗拉期Pa.punctata带上部,延伸至Pa.jamieae带(Klapper, 1988; Ziegler et al.,1990)。I.symmetricus常分布于Pa.transitans带至下Pa.rhenana带(Ziegler et al.,1990)。Pol.decorosus和Pol.webbi从晚吉维特期下M.guanwushanensis带延至晚弗拉期Pa.linguiformis带(Ji Qiang et al.,1993)。潜溪河剖面牙形石生物组合特征显示观雾山组沉积于晚泥盆世中弗拉期Pa.punctata带至Pa.jamieae带。

早期区域地质资料显示,自江油马角坝向北东至朝天驿一带分布的泥盆系均被定为“观雾山组”(观雾山组原始定义)(四川省地质局, 1966❶),然而,地层的穿时性和划分方案的变动导致对这些地区泥盆系的充填时间认识不清。北川甘溪剖面牙形石生物地层研究结果显示,观雾山组下段至中段为吉维特期Pol.varcus带(对应侯氏划分方案鸡公岭段至海角石段中下部),观雾山组中段上部为晚泥盆世早弗拉期下M.guanwushanensis带至Pa.transitans带(对应侯氏划分方案的海角石段顶部),观雾山组上段为中弗拉期Pa.punctata带至Pa.hassi带(对应侯氏划分方案的土桥子组)(侯鸿飞等, 1988a; Ma Xueping et al.,2006)(图8)。龚大明(1990)通过对江油马角坝地区观雾山组白云岩顶部牙形石动物群研究,将马角坝地区观雾山组确定为晚泥盆世早弗拉期地层。最新牙形石生物地层研究表明,西北乡、清风峡、朝天驿等地观雾山组开始沉积于晚泥盆世早—中弗拉期(黄程等, 2021;本文)。龙门山北段不同地区牙形石生物地层对比结果显示,观雾山组为横跨中—上泥盆统的穿时地层,并且江油马角坝以北的观雾山组绝大多数应沉积于晚泥盆世弗拉期,而非中泥盆世吉维特期。岩性对比结果显示,龙门山北段观雾山组厚度具有自南向北逐渐变薄的特征:甘溪剖面观雾山组自下而上分别为厚层礁灰岩、厚层白云岩(或白云质灰岩)、中—薄层灰岩(厚约695m);马角坝地区观雾山组主要为厚层白云岩(厚约200m);西北乡、清风峡、朝天驿观雾山组主要为中—薄层灰岩(厚约20~60m)。综合生物地层、地层厚度、剖面位置(图1b)等证据,本文认为龙门山北段观雾山组充填时间具有自南向北逐渐变晚的趋势。

由于早期“观雾山组”同时包含了金宝石组和观雾山组(下段、中段、上段),金宝石组与观雾山组之间通常为整合接触,两者组成一个完整的海侵-海退旋回,因此,金宝石组地层时代对认识龙门山地区泥盆系沉积充填过程具有十分重要的意义。牙形石生物地层结果表明,甘溪剖面金宝石组中下部为艾菲尔期Eognathodusbipennatus-Polygnathusparawebbi组合带,金宝石组顶部为早吉维特期下Pol.varcus带(侯鸿飞等, 1988a)。然而,李星学等(1982)在广元后高坪、猫儿塘、阳泉等地的金宝石组中发现了以Leptophloeumrhombicum(斜方薄皮木)为代表的晚泥盆世古植物群,认为这些地区金宝石组沉积于晚泥盆世弗拉期。由于广元西北乡、潜溪河、清风峡等地金宝石组总体厚度较薄(3~13m)且为滨岸快速沉积(黄程等, 2021),与上覆观雾山组地层时代相差不会太大。从沉积厚度来看,金宝石组地厚度具有从甘溪地区向西北乡、潜溪河等地逐渐减薄的趋势,并与下伏志留系或寒武系呈假整合接触,显示超覆沉积特征。综合牙形石、古植物、沉积学等证据表明,金宝石组与观雾山组相似,地层时代也具有自南向北逐渐变新的特征。由于后高坪、猫儿塘、阳泉等地金宝石组已沉积于晚泥盆世弗拉期,因此,位于北东侧的西北乡、潜溪河、清风峡等地金宝石组应也沉积于晚泥盆世弗拉期。

虽然龙门山地区泥盆系的研究自20世纪30年代开始至今已有近90多年的历史(赵亚曾等, 1931; 乐森璕, 1956; 侯鸿飞等, 1988a),但是对于龙门山泥盆纪海侵方向却悬而未解。目前关于龙门山区泥盆纪海侵方向的观点可归纳为3类:① 从南往北,即从广西经云南到泸定冷碛,向北进入北川、江油、广元(王钰等, 1983);② 从北往南,即从西北的康、滇、藏向东南进入龙门山区(侯鸿飞等, 1988b);③ 从南向北(如考虑泥盆纪时华南板块的旋转,即对应现在的南西→北东向)沿古陆周缘侵入龙门山地区(陈源仁, 1990)。

图8 龙门山北段上泥盆统金宝石-观雾山组层序地层对比图(甘溪剖面资料据侯鸿飞等, 1988a; 李祥辉等, 1998编绘)

Fig.8 Sequence stratigraphy correlation of the Upper Devonian Jinbaoshi-Guanwushan Formation in the northern segment of Longmenshan area (data of the Ganxi section compiled after Hou Hongfei et al.,1988a; Li Xianghui et al.,1998)

M—泥岩;W1—含颗粒灰泥岩;W2—颗粒质灰泥岩;P—灰泥颗粒岩;G—颗粒灰岩;C—灰砾岩;Pa.—掌鳞刺属;Pol.—多颚刺属; M.—中列刺属

M—Mudstone; W1—grain-bearing wackestone; W2—wackestone; P—packstone; G—grainstone; C—calcirudite; Pa.—Palmatolepis;Pol.—Polygnathus; M.—Mesotaxis

海侵方向与沉积古地理格局密切相关,早期学者推测的泥盆纪海侵方向是将龙门山区作为海湾环境为分析前提(王钰等, 1983; 侯鸿飞等, 1988b)。生物古地理分区研究结果表明,龙门山地区的泥盆纪古生物面貌与湘、黔、桂等地区非常相似,代表浅水陆棚或开阔台地沉积(侯鸿飞等, 1988a),说明都受广海古特提斯洋的影响。大地构造和沉积学分析结果显示,在中三叠世以前,扬子地台西缘与古特提斯洋相连,在北川-映秀断裂以西形成以冒地槽型建造为主的深水斜坡-盆地相泥盆系沉积,该断裂以东形成以地台型建造为主的浅水陆棚相泥盆系沉积(龙学明, 1991; 刘树根等, 2009)。虽然龙门山地区出露的地层多数都受中生代逆冲推覆的影响(潘桂棠等, 1983; Burchfiel et al.,1995; 郭正吾等, 1996; Zheng Yong et al.,2014),但是通过平衡剖面恢复研究结果表明泥盆系沉积厚度明显受古生代同沉积断裂的控制(龙学明, 1991; 陈竹新等, 2005; 熊连桥等, 2019)。在龙门山北段,北东向的北川-映秀断裂、马角坝断裂以及北西向断裂的发育,使得该区形成西低东高的菱形断陷式沉积(龙学明, 1991),从而在唐王寨—仰天窝一带沉积了巨厚的泥盆系,过江油雁门坝后向北呈透镜状断续出露,至广元朝天驿附近全部尖灭(四川省地质局, 1966❶)。

由于同沉积断裂和地形的影响,龙门山北段的泥盆系厚度不仅从唐王寨—仰天窝一带向北东—南西减薄至尖灭,而且自西向东也迅速减薄至尖灭。从地层充填时间来看,虽然江油马角坝以北出露的观雾山组主要形成于晚泥盆世,但是广元后高坪、西北乡、朝天地区观雾山组的充填时间晚于其南西侧的江油马角坝地区(李星学等, 1982; 龚大明, 1990; 黄程等, 2021)。从垂直泥盆系展布方向来看,观雾山组自西向东从中泥盆世吉维特期穿时至晚泥盆世弗拉期。在龙门山中段和南段,泥盆系虽然在南北向的时代变化规律不清楚,但是都具有自西向东变新的特征。目前重建的泥盆纪古地理特征显示,龙门山北段的海水深度具有自西向东逐渐变浅的特征 (刘树根等, 2009; 熊绍云等, 2020)。此外,观雾山组底部的砂岩交错层理恢复的古流向也指示海水自西向东侵入(张立军等, 2009)。龙门山泥盆系的穿时变化规律和重建的古地理环境模式,显示海水来自于西部的古特提斯洋,而地形的差异使泥盆系充填具有自西向东逐渐变晚而呈超覆沉积特征。

中—晚泥盆世之交全球海平面上升导致扬子地台边缘和南秦岭地区广泛分布中—上泥盆统碳酸盐岩,由于局部构造的影响,不同地区的最大海侵时间存在较大差异(杜远生等, 1996; 李祥辉等, 1998)。在扬子地台南缘(陈代钊等, 1994)和南秦岭地区(杜远生等, 1996),最大海侵出现于晚弗拉期(相当于牙形石Pa.rhenana带—Pa.linguiformis带),与西欧和北美(Johnson et al.,1985)最大海侵时间较为一致。扬子地台西缘的龙门山地区最大海侵出现于早弗拉期(李祥辉等, 1998),这与目前江油马角坝以北广泛分布的观雾山组时代结果较为一致(黄程等, 2021;本文)。由于晚泥盆世早弗拉期阶段性海侵,导致扬子地台西缘的古特提斯洋海水自西向东渐进式侵入龙门山地区,使得晚泥盆世地层逐渐向东超覆于寒武系或志留系之上。在超覆沉积过程中,不同沉积位置存在明显的岩相差异:在靠近滨岸带附近,由于陆源影响形成以粉砂岩和细砂岩为主的滨岸碎屑岩沉积,即对应金宝石组;在远离陆源影响区,形成以灰岩或白云岩为主的碳酸盐岩沉积,即对应观雾山组(图8,图9)。因此,观雾山组与金宝石组在区域上不仅表现为上下叠置关系,而且还表现为同期异相的相变关系。

海侵超覆导致观雾山组穿时性十分明显,从吉维特期穿时至早弗拉期,其中水体深度和地形是重要控制因素。通过广元西北乡、潜溪河剖面观雾山组碳酸盐岩的组分和结构分析,识别出的7个碳酸盐岩微相多数形成于深潮下带(介于正常浪基面与风暴浪基面之间)低能环境,个别微相形成于浅潮下带至潮间带较高能环境。潜溪河剖面观雾山组发育4种微相类型(MF-2、MF-3、MF-5、MF-7),其中以MF-5生屑泥晶灰岩较发育;而西北乡剖面观雾山组中MF-1至MF-7都有发育,其中以MF-2、MF-3最多,显示泥质含量相对较高,代表沉积水体更深。从地层接触关系来看,潜溪河剖面观雾山组顶部与上覆中二叠统栖霞组之间呈平行不整合接触,并且在观雾山组顶部出现了暴露溶蚀现象,侵蚀界面之上的灰泥基质被溶蚀,充填半自形的白云石微晶,仅保留生屑颗粒(图6l)。虽然潜溪河剖面观雾山组白云质灰岩与上覆二叠系栖霞组灰岩之间的平行不整合界线指示了抬升暴露证据,但是西北乡剖面观雾山组与沙窝子组之间的整合界线代表了连续沉积过程(图9)。沉积微相和地层之间的接触关系表明,潜溪河剖面沉积位置的地形高于西北乡剖面,显示龙门山北段具有南低北高的地形特征(图9),这与其他学者恢复的古地貌结果较为一致(龙学明, 1991; 熊绍云等, 2020)。

在龙门山北段渐进式海侵过程中,由于地形和水深的差异,导致上泥盆统充填时间和层序数量存在差异(图8),并体现为超覆沉积特征。西北乡剖面观雾山组开始沉积于晚泥盆世早弗拉期(M.guanwushanensis带至Pa.transitans带),比潜溪河剖面观雾山组的沉积时间(中弗拉期Pa.punctata带至Pa.jamieae带)至少早1个牙形石带(~1Ma)。层序地层研究结果显示(李祥辉等, 1998),龙门山北段断陷沉积中心(甘溪剖面)的观雾山组中段上部至上段可划分出3个三级层序(图8)。在断陷边缘地区,通过海平面变化分析在西北乡和潜溪河剖面金宝石-观雾山组中分别识别出2个和1个三级层序(图4,图5)。从层序的充填特征与地形、水深之间的关系来看,水体越深、地形越低,地层充填越早、层序越完整、厚度越大,即水体深度和地形控制了龙门山北段观雾山组充填过程。综合生物地层、层序地层、区域地层结果表明,西低东高、南低北高的地形导致龙门山北段的观雾山组不仅具有自西向东的超覆沉积过程,而且具有从南向北超覆的沉积特征,即从南西向北东超覆沉积(图9)。综上所述,由于龙门山北段观雾山组穿时和超覆沉积的普遍性,在利用观雾山组岩性重建龙门山地区沉积古地理过程中,需明确目标区观雾山组的时代是否相同。

图9 龙门山北段泥盆系观雾山组沉积充填模式

Fig.9 Depositional filling pattern of the Devonian Guanwushan Formation in the northern segment of Longmenshan area

Pa.—掌鳞刺属; Pol.—多颚刺属; M.—中列刺属

Pa.—Palmatolepis; Pol.—Polygnathus; M.—Mesotaxis

(1)通过西北乡和潜溪河剖面观雾山组牙形石生物地层研究,结合区域古生物和地层资料,明确了江油马角坝以北的观雾山组主要沉积于晚泥盆世早—中弗拉期,不同与以往所认识的中泥盆世吉维特期,并且地层充填时间从南西向北东逐渐变晚。

(2)龙门山地区的泥盆系自西向东具有厚度减薄、地层逐渐变新特征,显示龙门山地区的海水来自西部的古特提斯洋。综合观雾山组区域地层对比、沉积微相、层序地层研究认为,由于受龙门山北段西低东高、南低北高的地形影响,渐进式的海侵导致观雾山组同时具有自西向东和自南向北的超覆沉积特征,即自南西向北东超覆。

(3)由于同沉积断裂和地形的影响,在断陷中心区,形成了厚度巨大、层序完整的观雾山组沉积;在地形较高的边缘区,形成了厚度较薄、层序不完整的观雾山组沉积。在超覆沉积过程中,由于岩相分异,导致观雾山组与金宝石组在不同区域不仅表现为上下叠置关系,而且还表现为同期异相的相变关系。

致谢:野外工作中得到了西南石油大学唐浩博士、研究生周力、李明隆、金值民的帮助,在此表示感谢。

注释

❶ 四川省地质局.1966.1∶20万中华人民共和国地质图《广元幅》(I-48-XXXIV).

Aboussalam Z S, Becker R T. 2007. New upper Givetian to basal Frasnian conodont faunas from the Tafilalt (Anti-Atlas, Southern Morocco). Geological Quarterly, 51(4): 345~374.

Becker R T, Gradstein F M, Hammer O. 2012. The Devonian Period. In: Gradstein F M, Ogg J G, Schmitz M, Ogg G, eds. Geological Time Scale 2012. Amsterdam: Elsevier, 559~601.

Burchfiel B C, Chen Zhiliang, LiuYupinc, Royden L H. 1995. Tectonics of the Longmen Shan and adjacent regions, central China. International Geology Review, 37(8): 661~735.

Bureau of Geology and Mineral Resources of Sichuan Province. 1991. Regional and Geological Annals of Sichuan Province. Beijing: Geological Publishing House, 1~730(in Chinese).

Chen Daizhao, Chen Qiying. 1994. Devonian sedimentary evolution and transgression-regression patterns in South China. Scientia Geologica Sinica, 29(3): 246~255(in Chinese with English abstract).

Chen Shefa, Wilson C J L. 1996. Emplacement of the Longmen Shan Thrust—Nappe Belt along the eastern margin of the Tibetan Plateau. Journal of Structural Geology, 18(4): 413~430.

Chen Yuanren. 1974. The Middle-Upper Devonian boudary at the middle part of Longmen Mountain in Sichuan Province: from the perspective of brachiopod fossils. Journal of Chengdu College of Geology, (1): 46~52(in Chinese).

Chen Yuanren. 1990. Where did sea water of the Longmen Mountain area come from during the Devonian? Sedimentary Facies and Palaeogeography, (1): 19~27(in Chinese with English abstract).

Chen Yuanren, Li Xianghui. 2005. Paleocommunity replacements of benthic brachiopod in the Middle-Upper Devonian in the Longmenshan area, southwestern China: responses to sea level fluctuations. Acta Geologica Sinica, 79(3): 313~324.

Chen Zhuxin, Jia Dong, Zhang Qie, Wei Guoqi, Li Benliang, Wei Dongtao, Shen Yang. 2005. Balanced cross-section analysis of the fold—thrust belt of the Longmen Mountains. Acta Geologica Sinica, 79(1): 38~45(in Chinese with English abstract).

Deng Hucheng, Zhou Wen, Qiu Dongzhou, Xie Runcheng. 2008. Oil sand-forming conditions and evaluation on resource of oil sand in Tianjingshan structure in northwest part of Sichuan basin. Journal of Jilin University(Earth Science Edition), 38(1): 69~75(in Chinese with English abstract).

Ding Gan, Jiang Dayong, Bai Shunliang. 2000. Evolution lineage of conodont Ancyrodella and the Middle-Upper Devonian boundary at Liujing, Guangxi. Acta Palaeontologica Sinica, 39(2): 197~204(in Chinese with English abstract).

Du Yuansheng, Gong Yiming, Liu Benpei, Feng Qinglai, Wu Yi. 1996. Devonian sequence stratigraphy and sea-level changes within the South China Plate. Sedimentary Facies and Palaeogeography, 16(6): 14~23(in Chinese with English abstract).

Dunham R J. 1962. Classification of carbonate rocks according to depositional textures. In: Ham W E, ed. Classification of Carbonate Rocks—A Symposium. Tulsa: American Association of Petroleum Geologists, 108~121.

Edwards D, Li Chengsen. 2018. Further insights into the Lower Devonian terrestrial vegetation of Sichuan Province, China. Review of Palaeobotany and Palynology, 253: 37~48.

Feng Zengzhao. 1989. Lithofacies Paleogeography of Carbonate Rocks. Beijing: Petroleum Industry Press, 47~57(in Chinese).

Gong Daming. 1990. Conodonts from the top of the Guanwushan Formation in Majiaoba, northern Sichuan. Journal of Chengdu College of Geology, 17(4): 10~15(in Chinese with English abstract).

Guo Zhengwu, Deng Kangling, Han Yonghui. 1996. The Formation and Development of Sichuan Basin. Beijing: Geological Publishing House, 1~200(in Chinese with English abstract).

Hou Hongfei, Wan Zhengquan, Xian Siyuan. 1988a. Devonian Stratigraphy, Paleontology and Sedimentary Facies of Longmenshan, Sichuan. Beijing: Geological Publishing House, 1~487(in Chinese with English abstract).

Hou Hongfei, Wang Shitao. 1988b. The Devonian System of China. In: Chinese Academy of Geological Sciences, ed. Stratigraphy of China(No. 7). Beijing: Geological Publishing House, 292~306(in Chinese).

Huang Cheng, Shen Yuwei, Wen Xin. 2021. Sedimentary characteristics and palaeoenvironmental significance of the Upper Devonian storm deposits at Qingfengxia section in Guangyuan City, Sichuan Province. Journal of Palaeogeography, 23(6): 1094~1109(in Chinese with English abstract).

Ji Qiang, Ziegler W. 1993. The Lali section: an excellent reference section for Upper Devonian in South China. Courier Forschungsinstitut Senckenberg, 157: 1~183.

Jia Dong, Wei Guoqi, Chen Zhuxin, Li Benliang, Zeng Qing, Yang Guang. 2006. Longmen Shan fold-thrust belt and its relation to the western Sichuan basin in Central China: new insights from hydrocarbon exploration. AAPG Bulletin, 90(9): 1425~1447.

Jiang Wu, Deng Tao. 1990. Biostratigraphical research overthrust nappe of Tangwangzhai area in Longmen Mountain. Journal of Southwestern Petroleum Institute, 12(3): 14~41(in Chinese with English abstract).

Jin Zhenkui, Shi Liang, Gao Baishui, Yu Kuanhong. 2013. Carbonate facies and facies models. Acta Sedimentologica Sinica, 31(6): 965~979(in Chinese with English abstract).

Johnson J G, Klapper G, Sandberg C A. 1985. Devonian eustatic fluctuations in Euramerica. Geological Society of America Bulletin, 96(5): 567~587.

Klapper G. 1985. Sequence in conodont genus Ancyrodella in Lower asymmetricus zone (earliest Frasnian, Upper Devonian) of the Montagne Noire, France. Palaeontographica Abteilung A, 188(1-3): 19~34.

Klapper G. 1988. The Montagne Noire Frasnian (Upper Devonian) conodont succession. Devonian of the World: Proceedings of the 2nd International Symposium on the Devonian System, Memoir 14(3): 449~468.

Klapper G, Feist R, House M R. 1987. Decision on the boundary stratotype for the Middle/Upper Devonian series bounday. Episodes, 10(2): 97~101.

Li Fengjie, Zhang Hao, Jing Xigui, Cheng Xiaoyu. 2017. Paleoenvironmental analysis of the ichnogenus Zoophycos in the Lower Devonian tempestite sediments of the Longmenshan area, Sichuan, China. Palaeogeography, Palaeoclimatology, Palaeoecology, 465: 156~167.

Li Xianghui, Liu Wenjun, Zheng Rongcai. 1998. Frequency, amplitude, and pattern of sea-level changes in Devonian in Longmen Mountains, western Yangtze. Journal of Chengdu University of Technology, 25(4): 3~5(in Chinese with English abstract).

Li Xingxue, Wang Hongfeng. 1982. On the occurrence of Late Devonian plants from MT. Longmenshan, north Sichuan. Acta Palaeontologica Sinica, 21(1): 87~95(in Chinese with English abstract).

Li Yong, Allen P A, Densmore A L, Qiang X. 2003. Evolution of the Longmen Shan foreland basin (western Sichuan, China) during the Late Triassic Indosinian Orogeny. Basin Research, 15(1): 117~138.

Li Zhiwu, Liu Shugen, Chen Hongde, Liu Shun, Guo Bing, Tian Xiaobin. 2008. Structural segmentation and zonation and differential deformation across and along the Lomgmen thrust belt, west Sichuan, China. Journal of Chengdu University of Technology (Science & Technology Edition), 35(4): 440~454(in Chinese with English abstract).

Lin Yi, Chen Cong, Xu Shiyu, Yang Fan, Zeng Yiyang, Li Yang, Zhao Chunni, Yang Jing, He Kailai. 2021. Characteristics and formation mechanism of ultra-deep carbonate reservoirs in the Devonian Guanwushan Formation, northwestern Sichuan basin. Natural Gas Geoscience, 32(6): 794~805(in Chinese with English abstract).

Liu Shugen, Li Zhiwu, Cao Junxing, Liu Shun, Deng Bin, Wang Guo Zhi, Deng Bin. 2009. 4-D textural and structural characteristics of Longmen intracontinental composite orogenic belt, southwest China. Chinese Journal of Geology, 44(4): 1151~1180(in Chinese with English abstract).

Liu Wenjun, Zheng Rongcai, Li Xianghui. 1999. Reconstruction of palaeogeography and palaeotectonics of a Devonian sedimentary basin in the Longmenshan area, Sichuan. Acta Geologica Sinica, 73(2): 109~119(in Chinese with English abstract).

Long Xueming. 1991. Several questions of geochronic evolution in the mid-northern segment of Longmenshan mountains. Journal of Chengdu College of Geology, 18(1): 8~16(in Chinese with English abstract).

Luo Zhili, Long Xueming. 1992. The uplifting of the Longmenshan orogenic zone and the subsidence of the west Sichuan foreland basin. Acta Geologica Sichuan, 12(1): 1~17(in Chinese with English abstract).

Ma Xueping, Becker R T, Li Hua, Sun Yuanyuan. 2006. Early and Middle Frasnian brachiopod faunas and turnover on the South China shelf. Acta Palaeontologica Polonica, 51(4): 789~812.

Pan Guitang, Xu Yaorong, Wang Peisheng. 1983. The Cenozoic tectonics at the eastern margin of Qinghai-Xizang Plateau. Contribution to the Geology of the Qinghai-Xizang (Tibet) Plateau, 4: 129~142(in Chinese with English abstract).

Sandberg C A, Dreesen R. 1984. Late Devonian icriodontid biofacies models and alternate shallow-water conodont zonation. In: Clark D L, ed. Conodont Biofacies and Provincialism. Boulder: Geological Society of America, 196: 143~178.

Sandberg C A, Ziegler W, Bultynck P. 1989. New standard conodont zones and early Ancyrodella phylogeny across Middle-Upper Devonian boundary. Courier Forschungsinstitut Senckenberg, 110: 195~230.

Shen Hao, Wang Hua, Wen Long, Ma Hualing, Li Yi, Zhang Benjian. 2016. Natural gas exploration prospect in the Upper Paleozoic strata, NE Sichuan basin. Natural Gas Industry, 36(8): 11~21(in Chinese with English abstract).

Tang Liangjie, Yang Keming, Jin Wenzheng, Lü Zhizhou, Yu Yixin. 2008. Multi-level decollement zones and detachment deformation of Longmenshan thrust belt, Sichuan basin, southwest China. Science in China Series D: Earth Sciences, 38(S1): 30~40(in Chinese).

Taylor A, Goldring R, Gowland S. 2003. Analysis and application of ichnofabrics. Earth-Science Reviews, 60(3): 227~259.

Wan Zhengquan. 1983. New advance in the study of Devonian System and establishment of a new stratigraphic unit—Jinbaoshi Formation in Longmenshan area, Sichuan. Bulletin of the Chengdu Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences, 4: 111~118(in Chinese with English abstract).

Wang Yu, Yu Changmin. 1962. Devonian System of China. In: All China Commission of Stratigraphy, ed. Compliation of Academic Reports on the National Stratigraphical Conference of China. Beijing: Science Press, 1~186(in Chinese).

Wang Yu, Rong Jiayu. 1983. Yukiangian (early Eamsian) brachiopod zoogeography. In: Editorial Board of the Basic Theory of Paleontology, ed. Paleobiogeographic Province in China. Beijing: Science Press, 53~63(in Chinese).

Xian Siyuan, Chen Jirong, Wan Zhengquan. 1995. Devonian ecostratigraphy, sequence stratigraphy and sea-level changes in Ganxi, Longmen Mountain, Sichuan. Sedimentary Facies and Palaeogeography, 15(6): 1~47(in Chinese with English abstract).

Xiong Lianqiao, Yao Genshun, Xiong Shaoyun, Shen Anjiang, Hao Yi. 2019. A method of stratum restoration for fault belt based on balanced cross-section: a case study of the Middle Devonian Guanwushan Formation in the Longmenshan area, western Sichuan basin, China. Geotectonica et Metallogenia, 43(6): 1079~1093(in Chinese with English abstract).

Xiong Shaoyun, Hao Yi, Xiong Lianqiao, Zhou Gang, Li Wenzheng, Yao Qianying, Zhang Jianyong. 2020. Sedimentary evolution of the Middle Devonian Guanwushan Formation and its control on reservoir development in western Sichuan. Marine Origin Petroleum Geology, 25(2): 181~192(in Chinese with English abstract).

Yoh S S. 1956. Subdivision zonation and correlation of the Devonian formations in Longmenshan area, northwestern Sichuan. Acta Geologica Sinica, 36(4): 443~476(in Chinese with English abstract).

Zhang Lijun, Gong Yiming. 2009. New discovery of Late Devonian plant and trace fossils in Hougaoping, Guangyuan, Sichuan. Journal of Stratigraphy, 33(2): 138~146(in Chinese with English abstract).

Zhao Yazeng, Huang Jiqing. 1931. The Geology of the Tsinglingshan and Szechuan. Geological Memoirs, Series A, (No. 9): 1~287(in Chinese with English abstract).

Zheng Rongcai, Liu Wenjun. 1997. Carbon and strontium isotopic effects of the Devonian sequence in the Longmen Mountains area. Geological Review, 43(3): 264~272(in Chinese with English abstract).

Zheng Yong, Kong Ping, Fu Bihong. 2014. Time constraints on the emplacement of klippen in the Longmen Shan thrust belt and tectonic implications. Tectonophysics, 634: 44~54.

Ziegler W, Sandberg C. 1990. The Late Devonian standard conodont zonation. Courier Forsehungsinstitut Senekenebrg, 121: 1~113.

陈代钊, 陈其英. 1994. 华南泥盆纪沉积演化及海水进退规程. 地质科学, 29(3): 246~255.

陈源仁. 1974. 从腕足动物化石来看四川龙门山中段中上泥盆统的界线. 成都地质学院学报, (1): 46~52.

陈源仁. 1990. 四川龙门山区泥盆纪海水来自何方. 岩相古地理, (1): 19~27.

陈竹新, 贾东, 张惬, 魏国齐, 李本亮, 魏东涛, 沈扬. 2005. 龙门山前陆褶皱冲断带的平衡剖面分析. 地质学报, 79(1): 38~45.

邓虎成, 周文, 丘东洲, 谢润成. 2008. 川西北天井山构造泥盆系油砂成矿条件与资源评价. 吉林大学学报(地球科学版), 38(1): 69~75.

丁干, 江大勇, 白顺良. 2000. 牙形石Ancyrodella早期演化与广西六景中上泥盆统界线. 古生物学报, 39(2): 197~204.

杜远生, 龚一鸣, 刘本培, 冯庆来, 吴诒. 1996. 华南板块泥盆纪层序地层及海平面变化. 岩相古地理, 16(6): 14~23.

冯增昭. 1989. 碳酸盐岩岩相古地理学. 北京: 石油工业出版社, 47~57.

龚大明. 1990. 马角坝泥盆系观雾山组顶部的牙形石. 成都地质学院学报, 17(4): 10~15.

郭正吾, 邓康龄, 韩永辉. 1996. 四川盆地形成与演化. 北京: 地质出版社, 1~200.

侯鸿飞, 万正权, 鲜思远. 1988a. 四川龙门山地区泥盆纪地层古生物及沉积相. 北京: 地质出版社, 1~487.

侯鸿飞, 王士涛. 1988b. 中国的泥盆系. 见: 中国地质科学院著, 中国地层(7). 北京: 地质出版社, 292~306.

黄程, 沈宇葳, 文馨. 2021. 四川广元清风峡剖面上泥盆统风暴岩沉积特征及其古环境意义. 古地理学报, 23(6): 1094~1109.

蒋武, 邓涛. 1990. 龙门山唐王寨地区逆冲推覆体生物地层学研究. 西南石油学院学报, 12(3): 14~41.

金振奎, 石良, 高白水, 余宽宏. 2013. 碳酸盐岩沉积相及相模式. 沉积学报, 31(6): 965~979.

乐森璕. 1956. 四川龙门山区泥盆纪地层分层分带及其对比. 地质学报, 36(4): 443~476.

李祥辉, 刘文均, 郑荣才. 1998. 龙门山地区泥盆纪海平面升降规程、频幅及对比. 成都理工学院学报, 25(4): 3~5.

李星学, 王洪峰. 1982. 四川龙门山晚泥盆世植物的发现. 古生物学报, 21(1): 87~95.

李智武, 刘树根, 陈洪德, 刘顺, 郭兵, 田小彬. 2008. 龙门山冲断带分段-分带性构造格局及其差异变形特征. 成都理工大学学报(自然科学版), 35(4): 440~454.

林怡, 陈聪, 徐诗雨, 杨帆, 曾乙洋, 黎洋, 赵春妮, 杨京, 何开来. 2021. 川西北部泥盆系观雾山组超深层碳酸盐岩储层特征及形成机制. 天然气地球科学, 32(6): 794~805.

刘树根, 李智武, 曹俊兴, 刘顺, 邓宾, 王国芝, 邓斌. 2009. 龙门山陆内复合造山带的四维结构构造特征. 地质科学, 44(4): 1151~1180.

刘文均, 郑荣才, 李祥辉. 1999. 龙门山泥盆纪沉积盆地的古地理和古构造重建. 地质学报, 73(2): 109~119.

龙学明. 1991. 龙门山中北段地史发展的若干问题. 成都地质学院学报, 18(1): 8~16.

罗志立, 龙学明. 1992. 龙门山造山带崛起和川西陆前盆地沉降. 四川地质学报, 12(1): 1~17.

潘桂棠, 徐耀荣, 王培生. 1983. 青藏高原东部边缘新生代构造. 青藏高原地质文集, 4: 129~142.

沈浩, 汪华, 文龙, 马华灵, 李毅, 张本健. 2016. 四川盆地西北部上古生界天然气勘探前景. 天然气工业, 36(8): 11~21.

四川省地质矿产局. 1991. 四川省区域地质志. 北京: 地质出版社. 1~730.

汤良杰, 杨克明, 金文正, 吕志洲, 余一欣. 2008. 龙门山冲断带多层次滑脱带与滑脱构造变形. 中国科学(D辑: 地球科学), 38(S1): 30~40.

万正权. 1983. 四川龙门山泥盆系研究进展与金宝石组的建立. 中国地质科学院成都地质矿产研究所所刊, 4: 111~118.

王钰, 俞昌民. 1962. 中国的泥盆系. 全国地层委员会著, 全国地层会议学术报告汇编. 北京: 科学出版社, 1~186.

王钰, 戎嘉余. 1983. 就郁江期腕足动物群的特征论其古动物地理的性质. 古生物学基础理论丛书编委会著, 中国古生物地理区系. 北京: 科学出版社, 53~63.

鲜思远, 陈继荣, 万正权. 1995. 四川龙门山甘溪泥盆纪生态地层、层序地层与海平面变化. 岩相古地理, 15(6): 1~47.

熊连桥, 姚根顺, 熊绍云, 沈安江, 郝毅. 2019. 基于平衡剖面对断裂带地层展布恢复的方法——以川西地区中泥盆统观雾山组为例. 大地构造与成矿学, 43(6): 1079~1093.

熊绍云, 郝毅, 熊连桥, 周刚, 李文正, 姚倩颖, 张建勇. 2020. 川西中泥盆统观雾山组沉积演化及其对储层发育的控制作用. 海相油气地质, 25(2): 181~192.

张立军, 龚一鸣. 2009. 四川后高坪地区晚泥盆世植物和遗迹化石的新发现. 地层学杂志, 33(2): 138~146.

赵亚曾, 黄汲清. 1931. 秦岭山及四川之地质研究. 地质专报, 甲种(第9号): 1~287.

郑荣才, 刘文均. 1997. 龙门山泥盆纪层序地层的碳、锶同位素效应. 地质论评, 43(3): 264~272.