天然气地质学

三水盆地布心组湖相碳酸盐岩沉积特征及相模式

  • 唐鑫萍 , 1, 2 ,
  • 雷栋 3 ,
  • 宋效文 1, 3
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  • 1. 中国石油大港油田公司勘探开发研究院,天津 300280
  • 2. 中油(天津)国际石油勘探开发技术有限公司,天津 300280
  • 3. 中国石油南方石油勘探开发有限责任公司,海南 海口 570216

唐鑫萍(1987-),男,广西桂林人,工程师,硕士,主要从事石油地质研究. E-mail: .

收稿日期: 2020-11-04

  修回日期: 2021-01-21

  网络出版日期: 2021-04-27

Sedimentary characteristics and facies model of lacustrine carbonate rocks of Buxin Formation, Sanshui Basin

  • Xin-ping TANG , 1, 2 ,
  • Dong LEI 3 ,
  • Xiao-wen SONG 1, 3
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  • 1. Research Institute of Exploration and Development,Dagang Oilfield Company,CNPC,Tianjin 300280,China
  • 2. PetroChina (Tianjin) International Petroleum Exploration & Development Technology Co. Ltd. ,Tianjin 300280,China
  • 3. PetroChina South Petroleum Exploration and Development Co. Ltd. ,Haikou 570216,China

Received date: 2020-11-04

  Revised date: 2021-01-21

  Online published: 2021-04-27

Supported by

The China National Science and Technology Major Project(2016ZX05026003)

the China National Petroleum Corporation Science and Technology Project(2019D-0707)

本文亮点

运用岩心、岩石薄片、扫描电镜、X⁃射线衍射和微量元素等资料,分析三水盆地布心组湖相碳酸盐岩沉积特征及相模式。结果表明:①三水盆地布心组碳酸盐岩主要有泥灰岩、生物灰岩、泥晶灰岩3类,岩性总体较细,基质含量高、颗粒含量较低,胶结物主要为泥晶,单层厚度较薄。②布心组碳酸盐岩形成于贫外物源的湖盆缓坡背景,总体水动力较弱;形成于贫氧—缺氧条件下的半咸水—咸水沉积环境;表现为总体较弱水动力条件下的咸水化学沉积和局部生物沉积。③建立了受控于古地形与湖浪的缓坡碳酸盐岩沉积模式,碳酸盐岩主要发育于滨湖—浅湖区域,滨湖可分为砂泥坪、灰泥坪2个微相,浅湖可分为生物浅滩、灰泥浅湖、泥质浅湖3个微相,不同微相的碳酸盐岩发育情况具有较明显的分异性,灰泥坪优势岩性为泥灰岩、生物浅滩优势岩性为生物灰岩、灰泥浅湖优势岩性为泥晶灰岩。研究成果可为该区碳酸盐岩沉积相工业化制图和储层分布预测提供依据。

本文引用格式

唐鑫萍 , 雷栋 , 宋效文 . 三水盆地布心组湖相碳酸盐岩沉积特征及相模式[J]. 天然气地球科学, 2021 , 32(5) : 675 -684 . DOI: 10.11764/j.issn.1672-1926.2021.01.015

Highlights

This paper aims at the sedimentary characteristics and sedimentary facies model of lacustrine carbonate rocks of Buxin Formation in Sanshui Basin. Petrological characteristics were analyzed by using core, thin section, scanning electron microscope and X-ray diffraction data. Combined with trace element data, sedimentary environment analysis was carried out. The carbonate sedimentary facies model is established based on the analysis of continuous well profile. The results are as follows: (1)The carbonate rocks of Buxin Formation in Sanshui Basin are mainly composed of muddy limestone, biological limestone and micrite limestone. The overall lithology of carbonate rocks is fine, with high matrix content and low particle content. The cement is mainly mud crystal. The thickness of single layer is thin. (2)The carbonate rocks of Buxin Formation were formed in the gentle slope environment of lake basin with poor provenance. The overall hydrodynamic force is weak. It is formed in the oxygen-poor and anoxic environment. It is characterized by saline water chemical deposition and local biological deposition under relatively weak hydrodynamic conditions. (3)The sedimentary model of gentle slope carbonate rock controlled by paleotopography and lake wave is established. Carbonate rocks are mainly developed in the lakeside shallow lake area. The lakeside can be divided into two microfacies: sand mud flat and muddy lime flat. The shallow lake can be divided into three microfacies: biological shoal, muddy lime shallow lake and muddy shallow lake. The development of carbonate rocks with different microfacies has obvious differentiation. The dominant lithology of muddy lime flat is muddy limestone. The dominant lithology of biological shoal is biolimestone. The dominant lithology of muddy lime shallow lake is micritic limestone. The research results can provide basis for industrial mapping of carbonate sedimentary facies and prediction of reservoir distribution.

0 引言

湖相碳酸盐岩广泛发育于国内外诸多具湖相沉积背景的盆地之中。近年来,在我国的准噶尔盆地1、柴达木盆地2、四川盆地3、渤海湾盆地4,美国的Great Salt Lake 盆地5、Ridge 盆地6、Pyramid Lake盆地7,东非大裂谷Tanganyika盆地8-9,玻利维亚Palaeo-Andean盆地10,阿根廷Andina盆地11等的湖相碳酸盐岩均已获得工业油流,展现出了巨大的勘探潜力。与海相碳酸盐岩相比,湖相碳酸盐岩的沉积研究还比较少,是当前沉积学研究的重点攻关方向12
三水盆地是一个中新生代内陆湖相盆地,其中古近系布心组地层中大面积发育碳酸盐岩。早在1976—1980年,唐天福等13对布心组碳酸盐岩进行了野外调查及室内研究,在碳酸盐岩中发现了介形虫、螺、藻类等化石及叠层石、波状层理等构造,明确其形成于湖相环境,这是我国较早期的湖相碳酸盐岩沉积学的专门研究。近期前人研究认为三水盆地碳酸盐岩是湖盆演化过程中贫外物源阶段内源沉积的产物,呈条带状分布于盆地的斜坡区域14-15。前人16研究也为该区碳酸盐岩油气勘探提供了重要基础。随着油气勘探的深入,湖相碳酸盐岩单层薄、岩性变化快、分布规律不明确等问题日益凸显,故很有必要对该盆地湖相碳酸盐岩的岩石学特征、沉积环境及沉积模式进行研究。

1 地质背景

三水盆地位于广东省珠江三角洲西北部,北起清远市,南至佛山市,西抵肇庆市,东至广州市,面积为3 375 km2[17-19。盆地构造位置处于华南陆缘,形成于晚白垩世华南陆缘伸展与破裂作用,受控盆断裂的影响,盆地呈近南北向展布,总体为不规则菱形20。盆地内包括东西2个斜坡、南北2个凹陷、中北部宝竹背斜5个构造单元(图1)。盆地以上古生界—中生界海相碳酸盐岩为基底,沉积了白垩系、古近系和第四系。古近系从老到新依次发育古新统莘庄组、始新统布心组、西布组、华涌组。盆地在渐新世后发生强烈隆升剥蚀,原有盆地边缘被剥蚀,形成现今三水残余盆地。前人21在宝竹背斜发现了宝月、竹山岗2个油气田,主要的油气产层为古近系布心组。研究表明,布心组亦是盆地烃源岩的主要发育层段,该组岩性主要为泥岩、灰岩和砂岩,从下往上可分为布一段、布二段和布三段,其中碳酸盐岩主要发育于布二段和布三段22-23
图1 三水盆地古近系构造区划

Fig.1 Tectonic division map of Paleogene in Sanshui Basin

2 岩石学特征

碳酸盐岩的沉积特征以岩石学特征、沉积环境特征、沉积相特征为主要研究内容,其中岩石学特征是沉积研究的基础24-27。综合12口井、54个岩心样品的岩心描述、薄片鉴定、扫描电镜分析表明,三水盆地布心组碳酸盐岩岩性主要为泥灰岩、云质泥灰岩、生物灰岩和泥晶灰岩4种类型(图2)。
图2 三水盆地布心组碳酸盐岩岩心、显微镜和扫描电镜照片

Q5井,604.9 m,泥灰岩:(a)岩心为灰色荧光泥灰岩,见波状不规则分布的裂缝被黑色有机质及方解石晶体充填;(b)岩石薄片单偏光下见泥晶方解石与部分碎屑石英小颗粒(箭头);(c)扫描电镜下见它形方解石与片状黏土矿物(箭头)。Q5井,592.8 m,白云质泥灰岩:(d)岩心为灰白色荧光泥灰岩;(e)岩石薄片单偏光下见斑块状白云石(箭头);(f)扫描电镜下见菱形白云石(白箭头),晶间发育针状硬石膏(红箭头)。Q5井,829.5 m,介壳灰岩:(g)岩心为深灰色油斑灰岩,裂缝被原油(箭头)及方解石晶体充填;(h)岩石薄片单偏光下见泥晶介壳灰岩,生物化石主要为以介形虫(箭头);(i)扫描电镜下见介形虫碎片(箭头)。Q5井,843.6 m,生物灰岩:(j)岩心为深灰色油迹灰岩,裂缝被原油(箭头)及方解石晶体充填;(k)岩石薄片单偏光下见泥晶藻灰岩,生物化石以红藻(箭头)、枝管藻为主,含介形虫;(l)扫描电镜下见方解石溶蚀(箭头)。H1A井,1 461.8 m,泥晶灰岩:(m)岩心为灰黑色油斑泥晶灰岩,裂缝被原油(箭头)及方解石晶体充填;(n)岩石薄片单偏光下见深灰色泥晶方解石;(o)扫描电镜下见灰岩内方解石晶间孔隙2~6 μm(箭头)。H1A井,1 463.5 m,含砂屑泥晶灰岩:(p)岩心为灰黑色油斑泥晶灰岩,裂缝被原油(箭头)及方解石晶体充填;(q)岩石薄片单偏光下见带泥晶套的粉砂粒级内碎屑(箭头),由方解石矿物组成;(r)扫描电镜下见灰岩内方解石晶间孔隙2~5 μm(箭头)

Fig.2 Core, microscope and SEM photos of carbonate rocks of Buxin Formation in Sanshui Basin

(1)泥灰岩颜色为灰色—灰白色,油气显示级别一般为荧光,发育波状层理、水平层理,发育干裂及结核构造,偶见生物化石[图2(a)];矿物成分主要由方解石和黏土矿物组成[图2(b)],少量碎屑石英、白云石;方解石多呈它形、少量半自形[图2(c)],含量为28%~35%;黏土矿物以片状高岭石、伊利石、伊/蒙混层为主,含量为25%~33%;白云石多与黏土矿物颗粒混杂出现,含量约为5%。
(2)部分泥灰岩含较多白云石,其含量约为20%,形成云质泥灰岩[图2(d)]。岩石薄片观察表明,其中的白云石矿物多呈斑块状分布[图2(e),图2(f)]。云质泥灰岩中的白云石晶粒较为细小,以泥晶为主,未见大颗粒的白云石晶体;白云石分布较为局限,常与泥晶方解石、黏土矿物颗粒混杂出现,晶体表面多呈浑浊状,未见较纯白云岩;泥晶白云石常被黑色有机质侵染。这些特征表明白云石形成于成岩阶段较早时期。扫描电镜观察表明,半自形的泥晶白云石晶体分布于岩石粒间孔之中;结合其斑块状分布的特点,初步推测,白云石的形成与原始粒间富镁咸化的孔隙水有关。
(3)生物灰岩颜色为灰色—深灰色,油气显示较活跃,显示级别一般为油迹,岩心出筒时常见原油从裂缝处渗出[图2(g),图2(j)];发育叠层石等生物成因构造,生物十分发育,常见红藻、枝管藻、蓝绿藻、螺、介形虫等生物化石,从而形成介壳灰岩、藻灰岩等岩石类型[图2(h),图2(i),图2(k)];矿物成分上方解石占绝对优势,达90%左右[图2(l)];胶结物主要为泥晶方解石、局部亮晶方解石。
(4)泥晶灰岩颜色为深灰色,油气显示活跃,显示级别一般为油斑,岩心出筒时常见原油从裂缝出渗出[图2(m),图2(p)];发育生物搅动构造,见少量介形虫、螺等生物化石;矿物成分主要为方解石、少量黏土矿物;方解石晶粒较细,多为泥晶级别[图2(n),图2(o),图2(q),图2(r)]。部分泥晶灰岩含砂屑—粉砂屑级别的内碎屑颗粒,从而形成含(粉)砂屑的泥晶灰岩。
研究区碳酸盐岩有以下共同点:一是岩性较细、基质含量高或颗粒含量较低,仅部分生物灰岩的颗粒含量超过50%;二是胶结物的粒径主要为泥晶级,仅部分岩石裂缝和部分生物腔体内发育亮晶胶结物;三是单层厚度较薄,一般为1~8 m,总体表现为较弱水动力的细粒岩沉积环境。
X-射线衍射(XRD)分析表明,岩石矿物成分主要为方解石,部分白云石、黏土矿物,少量石英、长石、黄铁矿、硬石膏、铁白云石、菱铁矿(表1)。矿物成分中石英、长石、黏土矿物与陆源沉积物有关28-29,多发育于泥灰岩(或云质泥灰岩)中,而生物灰岩、泥晶灰岩中这类矿物比较少,说明泥灰岩沉积时受陆源沉积物影响较明显,具混源沉积特征,而生物灰岩、泥晶灰岩受陆源沉积物影响较小,主要为内源沉积。
表1 三水盆地布心组碳酸盐岩XRD矿物分析

Table 1 XRD mineral analysis table of carbonate rocks of Buxin Formation in Sanshui Basin

井号 样品深度/m 岩性 矿物含量/%
黏土 硬石膏 石英 斜长石 方解石 铁白云石 白云石 菱铁矿 黄铁矿
Q5 604.9 泥灰岩 28.7 3.4 18.6 3.2 31.1 6.5 3.4 5.1
Q5 592.8 云质泥灰岩 32.9 2.5 5.4 2.1 28.8 2.5 23.3 2.5
Q5 829.5 介壳灰岩 1.6 2.8 90.4 0.9 3.1 1.2
Q5 843.6 藻灰岩 1.7 91.7 1.3 2.8 2.5
H1A 1 461.8 泥晶灰岩 5.7 0.8 87.6 2.7 3.2
H1A 1 463.5 含砂屑泥晶灰岩 8.5 1.9 1.3 84.6 1.4 2.3

3 沉积环境

前人对于三水盆地湖相碳酸盐岩沉积环境的研究主要包括2个方面的内容。一是以测井相—地震相联合分析为基础的古物源、古地貌等宏观沉积背景研究,认为布心组沉积时期碎屑物源主要来自西北方向,而东部和西南部为贫外物源环境,故碳酸盐岩沉积发育;在碳酸盐岩沉积的构造背景上,碳酸盐岩主要发育于东部斜坡和西部斜坡南部,其沉积底形均为缓坡背景14-15。二是以岩性与古生物化石组合为基础的沉积水体性质与古气候环境分析揭示,三水盆地布心组沉积时期为咸化沉积水体、古气候较为炎热、总体为温湿—干旱气候环境13-1421
微量元素可以作为碳酸盐岩海/陆相成因标志,并可反映沉积环境的水体盐度、氧化还原性等特征30-32。本文在前人研究基础上,进一步开展了岩矿的微量元素分析,深化认识了三水盆地布心组的沉积环境。
据前人研究,B元素在海相沉积物中含量通常在100×10-6以上,而Ga元素在陆相沉积物中含量较高,因此B/Ga值常作为古盐度的标志。海相沉积物的B/Ga 值一般大于4.5,而陆相沉积物B/Ga值普遍小于3.333-36。研究区碳酸盐岩样品介于1.03~6.85之间,平均值为2.91(表2)。总体反映陆相沉积特征,也显示出湖水咸化的特点。
表2 三水盆地布心组碳酸盐岩微量元素分析

Table 2 Trace element analysis table of carbonate rocks of Buxin Formation in Sanshui Basin

井号 深度/m 岩性 B/10-6 Ga/10-6 B/Ga Sr/10-6 Ba/10-6 Sr/Ba V/10-6 Ni/10-6 V/(V+Ni)
平均值 33.02 6.97 2.91 855.07 159.40 5.99 31.32 10.57 0.68
Q5 604.9 泥灰岩 56.5 11.2 5.04 1 905.4 240.2 7.93 23.7 9.1 0.72
Q5 592.8 云质泥灰岩 3.9 2.6 1.50 1 059.2 110.7 9.57 8.2 5.3 0.61
Q5 829.5 介壳灰岩 2.3 1.2 1.92 646.8 159.3 4.06 7.4 5.9 0.56
Q5 843.6 藻灰岩 6.3 6.1 1.03 447.6 186.5 2.40 17.5 12.6 0.58
SS40 1 537.5 泥晶灰岩 126.7 18.5 6.85 557.9 204.1 2.73 87.3 21.2 0.80
SS40 1 554.2 泥晶灰岩 2.4 2.2 1.09 513.5 55.6 9.24 43.8 9.3 0.82

注:微量元素测试采用电感耦合等离子体质谱(ICP⁃MS),最低检测限为0.01×10-6,分析测试工作在中国石化胜利油田分公司地质科学研究院石油地质测试中心完成

陆相沉积物中的Ba含量高于海相沉积物,海相碳酸盐岩中Ba含量通常为(10~30)×10-6,研究区白云岩中Ba含量介于(55.6~240.2)×10-6之间,平均为159.4×10-6,也说明了研究区碳酸盐岩非海相沉积,而是陆相沉积。Sr/Ba值也可用来区分淡水和咸水沉积环境,一般淡水沉积的Sr/Ba<1,咸水沉积的Sr/Ba>137-40。区内白云岩的Sr/Ba值在2.4~9.57之间,平均值为5.99(表2),反映沉积时水介质盐度较高。
V元素在氧化水体多以HVO4 2-或H2VO4 -形式存在,而在还原水体中多形成V2O3或V(OH)3固体氧化物沉淀,因此V/(V+Ni)值可用于反映沉积物原始沉积环境的氧化还原性:V/(V+Ni)值小于0.45反映沉积水体为氧化环境,V/(V+Ni)值介于0.45~0.6之间时反映沉积水体为贫氧环境,V/(V+Ni)值大于0.6时,反映沉积水体为缺氧环境41-43。研究区样品V/(V+Ni)值在0.56~0.82之间,平均值为0.68(表2),指示贫氧—缺氧的沉积环境。其中介壳灰岩、藻灰岩的V/(V+Ni)值介于0.45~0.6之间,为贫氧指征;其他碳酸盐岩样品V/(V+Ni)值大于0.6,为缺氧指征。说明在总体缺氧的环境下,生物灰岩的沉积环境具有“相对含氧”的特征。
综合上述分析,布心组碳酸盐岩微量元素指示为湖相半咸水—咸水的盐度环境,与前人古生物、古气候研究相符。咸水环境有利于碳酸钙的沉淀,是碳酸盐岩形成的有利条件44。微量元素指示贫氧—缺氧的沉积环境,与前文岩石学研究反映的总体较弱水动力条件相符。
按照湖泊构造成因,可分为断陷湖泊型、坳陷湖泊型、前陆湖泊型;按照沉积物主要类型,可分为陆源碎屑型、内源型、混合沉积型;按照湖水盐度,可分为淡水湖型、半咸水湖型、咸水湖型、盐湖型5-10。前人20-23对三水盆地构造演化研究表明,布心组沉积时期属于坳陷湖泊发育期,湖盆处于逐渐扩张阶段;三水盆地布心组西北部发育碎屑岩沉积、东部斜坡与西部斜坡南部发育内源碳酸盐岩沉积,总体属于混合沉积型湖泊。地球化学分析表明,其湖泊水体总体处于半咸水—咸水型水体环境。

4 沉积微相

在岩石学和沉积环境分析的基础上,本文开展了碳酸盐岩的井间对比研究。首先通过岩心—测井的响应分析,明确碳酸盐岩具有低自然伽马(GR)、高电阻率(RD)特征,与泥岩高自然伽马(GR)、低电阻率(RD)具有明显的区别。生物灰岩的测井曲线形态为箱型,泥灰岩、泥晶灰岩测井曲线形态均为指型(图3)。以此为基础,开展了井间沉积特征对比。
图3 三水盆地Q5井布心组测井相分析

Fig.3 Log facies analysis of Well Q5 of Buxin Formation in Sanshui Basin

依据泥岩颜色及泥地比划分了半深湖、浅湖、滨湖3个沉积亚相。半深湖岩性主要为泥岩、少量深色泥灰岩,泥岩颜色为灰黑色至黑色;浅湖岩性主要为泥晶灰岩、生物灰岩与泥岩互层,泥岩颜色为深灰色;滨湖岩性主要为泥灰岩、云质泥灰岩、钙质砂岩与泥岩互层,泥岩颜色为灰色—杂色。
井间对比结果表明,碳酸盐岩主要发育于滨浅湖区域,从滨湖至浅湖,碳酸盐岩类型具有一定的分异性:滨湖主要为泥灰岩;浅湖主要为生物灰岩、泥晶灰岩,少量泥灰岩。泥灰岩、泥晶灰岩井间可对比性较强,在井间具有一定的连续性;纵向上各类碳酸盐岩与泥岩形成间互沉积(图4),垂向变化较快。
图4 三水盆地东部斜坡布心组碳酸盐岩连井沉积相分析

(钻井位置见图1连井线;GR指自然伽马,API;RD指深侧向电阻率,Ω·m)

Fig.4 Sedimentary facies analysis chart of carbonate rocks of Buxin Formation in the east slope of Sanshui Basin

上述分析表明,除了生物灰岩具有一定的生物沉积特色外,研究区碳酸盐岩总体表现为咸化湖的化学沉积。此外,岩性分布随沉积区域而表现出的分异性也说明,岩石的沉积受古地形或湖浪环境的影响。综合上述因素,建立了受控于古地形与湖浪的缓坡碳酸盐岩沉积模式(图5)。
图5 三水盆地布心组碳酸盐岩沉积相剖面模式

Fig.5 Sedimentary microfacies model of carbonate rocks of Buxin Formation in the east slope of Sanshui Basin

按照碳酸盐岩通常的沉积亚相分类45,滨湖亚相位于洪水面与枯水面之间,浅湖亚相位于浪基面与枯水面之间,半深湖亚相位于浪基面之下。鉴于岩相和沉积环境在碳酸盐岩沉积中的重要作用,微相的命名原则为岩相组合+沉积环境46。滨湖亚相按照这一原则分为砂泥坪、灰泥坪2个微相;浅湖亚相分为灰泥浅湖、泥质浅湖2个微相。以灰泥浅湖为例,这一术语用来表示发育于浅湖的灰岩泥岩间互沉积46-47。灰泥浅湖与灰泥坪的区别本质上是指浅湖灰泥间互沉积和滨湖灰泥间互沉积的区别,浅湖的水体更为开放,沉积的灰岩岩性更纯,且浅湖水深相对深,泥岩的颜色更暗。
砂泥坪微相以钙质砂岩为优势岩性,靠近湖盆边缘,岩相为钙质砂岩、泥灰岩、泥质粉砂岩等混合沉积。泥灰岩颜色为灰白色,发育干裂结核构造,偶见生物化石。灰泥坪发育于滨湖泥坪基底上,以泥灰岩为优势岩性,表现为泥灰岩与泥岩交互沉积的特点,泥灰岩颜色为灰白色—灰色,发育波状层理、水平层理,见少量介形虫、螺等生物化石(图5)。
生物浅滩微相以藻灰岩、介壳灰岩等生物灰岩为优势岩性,灰岩颜色为灰色,发育叠层石等生物成因构造,生物十分发育,常见枝管藻、蓝绿藻、螺、介形虫等生物化石(图5)。生物浅滩微相的颗粒含量较高,为30%~60%;相应地,泥晶基质含量相对较低,为40%~70%,发育少量亮晶胶结物。在研究区碳酸盐岩总体表现为颗粒含量低、泥晶含量高、水动力较弱的情况下,生物浅滩的沉积水体能量较强,结合前述的生物灰岩V/(V+Ni)值指示的贫氧(即“相对含氧”)沉积环境指征,推测生物浅滩发育于浅湖水下隆起区,通常这类型隆起发育于枯水面与平均湖水面之间,具有较强的水体交换条件,利于生物繁殖48-49
灰泥浅湖微相以泥晶灰岩为优势岩相,岩相主要为泥晶灰岩、泥灰岩、部分含生屑灰岩,灰岩颜色为深灰色,发育生物搅动构造,见少量介形虫、螺等生物化石(图5)。泥质浅湖微相与半深湖亚相相邻,主要为灰黑色泥质岩相,碳酸盐成分较少发育。
研究区湖相碳酸盐岩具有单层较薄、相变较快、岩性较复杂的特点,与海相碳酸盐岩“规模性发育、广覆式沉积”有着鲜明的区别4550。上述微相分析表明,研究区碳酸盐岩总体形成于缓坡背景下的咸水沉积环境,而不同古地形、水深、水动力造就了各个微相的岩石学特征的明显差异。

5 结论

通过对三水盆地布心组湖相碳酸盐岩沉积特征与相模式的研究,取得了以下认识:
(1)岩石学特征方面:岩性主要为泥灰岩、生物灰岩、泥晶灰岩3类;岩石内部基质含量高,主要为泥晶级方解石;颗粒含量较低,主要成分为生物化石、内碎屑;总体单层厚度较薄、岩性较细。
(2)沉积环境方面:碳酸盐岩总体形成于贫外物源的湖盆缓坡环境,沉积水动力总体较弱;形成于半咸水—咸水、贫氧—缺氧的沉积水体;综合反映了较弱水动力条件下的咸水化学沉积环境以及局部生物沉积环境。
(3)相模式方面:在滨湖—浅湖区域划分了滨湖分为砂泥坪、灰泥坪微相、浅湖分为生物浅滩、灰泥浅湖、泥质浅湖微相5个微相。其中:碳酸盐岩主要分布于灰泥坪、生物浅滩、灰泥浅湖3个微相内;不同微相的碳酸盐岩发育情况具有较明显的差异,灰泥坪优势岩性为泥灰岩、生物浅滩优势岩性为生物灰岩、灰泥浅湖优势岩性为泥晶灰岩。文章综合沉积环境与岩性分布的分异规律,建立了受控于古地形与湖浪的缓坡碳酸盐岩沉积模式。
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