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1.
《古地理学报》2016,(3)
华南地区下奥陶统仑山组为奥陶系最底部的岩石地层单位之一,其以大套白云岩为主要特征,广泛分布于下扬子区。通过对安徽池州洪家剖面仑山组的系统分析,并结合下扬子区多个相关剖面的资料,进一步确定仑山组岩性为白云岩、灰质白云岩和白云质灰岩,夹有部分亮晶颗粒灰岩和亮泥晶颗粒灰岩。整体上以亮晶生屑灰岩或泥晶生屑灰岩的出现作为仑山组顶界,在下扬子区内部、北部及东南部地区以白云质灰岩或灰质白云岩出现为其底界,而在下扬子区西南部大部分地区则以白云岩化出现为其底界。整个仑山组所含生物化石种类和数量较少,自下而上可建立5个牙形石带,分别是Monocostatus sevierensis带、Acanthodus lineatus-A.costatus带、Scolopodus?pseudoplanus带、Glyptoconus quadraplicatus带和Paltodus deltifer-Tripodus proteus带,推测其时代为早奥陶世特马豆克早期。仑山组主要形成于浅潮下带至深潮下带环境中,其地层总厚度和其中的白云岩厚度受到古地理因素的控制。通过岩石学特征分析,推断仑山组白云岩主要为准同生条件下的多种白云岩化作用叠加中等埋藏条件下的白云岩化形成。 相似文献
2.
《地层学杂志》2016,(4)
华南上扬子区桐梓组为下奥陶统最底部的岩石地层单位之一。通过贵州习水吼滩剖面桐梓组的系统分析,并结合上扬子区多个相关剖面的资料,确定桐梓组以中厚层白云岩、白云质灰岩、页岩为主,偶夹薄层生屑灰岩。桐梓组主要形成于浅潮下带至深潮下带环境,其沉积厚度具由西向东逐渐增大的趋势,白云岩所占比例由西向东逐渐减少。通过对白云岩岩石学特征分析,初步得出桐梓组白云岩成因:在台地浅滩附近以混合水白云岩化为主,在台地内部以回流渗透作用为主。整个桐梓组自下而上可以建立5个牙形石带,分别是Cordylodus angulatus带、Glyptoconus quadraplicatus-Scolopodus?pseudoplanus带、Paltodus deltifer-Triangulodus proteus带、Triangulodus bifidus带、Serratognatus divers带。桐梓组上下界线均为穿时界线,底界由西向东向上穿时,顶界向下穿时。 相似文献
3.
滩相是碳酸盐台地内、台地边缘的地貌高点,在纵向上、横向上与开阔台地相(或局限台地相)、上斜坡相呈过渡关系,其岩性多为亮晶颗粒灰岩,亦有亮泥晶、泥亮晶颗粒灰岩以及颗粒泥晶灰岩,中、下扬子区下奥陶统滩相地区均如此。中、上寒武统的滩相多因形成于台地内部地貌高点,水流不如台地边缘那么通畅而白云化,其岩石类型多为残余颗粒含白云质灰岩或残余颗粒含灰、灰质白云岩。湖南石门杨家坪剖面因其地层连续、沉积厚度大、岩石类型齐全、标志层明显而被定为标准剖面。前人,如湖南省403地质队、武汉地质学院、江汉石油学院等单位均在此做过一些工作,但多局限于古生物地层方面,在岩石学方面尚无人做过深入的研究。本文首次对该剖面的岩石学特征、成岩作用及其孔隙演化、成岩序次做了全面的、深入的研究,并重 相似文献
4.
贵阳乌当地区中、上奥陶统沉积学研究 总被引：1，自引：0，他引：1
贵阳乌当地区上奥陶统碳酸盐岩地层与扬子地区同时代地层相比具有其特殊性,黄花冲组与宝塔组"龟裂纹"灰岩时代相当.通过对该地区中、上奥陶统碳酸盐岩的研究,划分出亮晶生屑灰岩相、泥晶生屑灰岩相、含生屑泥晶灰岩相、生屑泥晶灰岩相和页岩-粉砂岩相5种沉积相;根据沉积相组合推断此时期乌当地区黄花冲组处于局限潮下低能环境. 相似文献
5.
对南京湖山地区黄龙组地层剖面微相的研究有助于理解晚石炭世下扬子地区的沉积环境、构造运动,对恢复下扬子板块古地理、古气候具有重要意义.研究表明,湖山地区黄龙组的岩石以泥晶颗粒灰岩为主,其次为亮晶颗粒灰岩和泥晶灰岩.根据岩石薄片特征识别出6大类、18种岩石微相类型,再根据各种微相类型的形成原因与条件及其在垂向上的变化规律,共划分出5种微相序列组合.主要微相类型及微相序列组合反映了黄龙组的沉积环境为开阔潮下带、局限潮下带、潮坪及浅滩环境. 相似文献
6.
湖南桑植仁村坪剖面茅口组中—上段地层的牙形l类资料显示,该剖面具有相对完整的卡匹敦阶(Capitanian)牙形类化石带,但缺失瓜德鲁普统-乐平统界线附近的Jinogondollela granti-Clarkina postbitteri postbitteri的3个牙形类化石带。该阶底部Jinogondollela postserrata牙形类化石带起始于茅口组下段顶部的礁边缘相生屑灰岩沉积的底部(-4.1m处);茅口组中段"孤峰组"硅(泥)质岩段属于牙形类J.shannoni化石带的沉积;茅口组上段含白云质团块的巨厚层亮晶灰岩基本属于牙形类J.xuanhanensis化石带的沉积。该剖面卡匹敦阶的层序地层分析显示出一个完整的三级层序变化过程。其底界SB3位于茅口组下段顶部9cm厚度的薄层白云岩之顶,代表东吴运动的第二幕(鸣山运动);后继高水体系域沉积表现为茅口组中段的硅(泥)质沉积岩段,属于牙形类J.shannoni化石带;茅口组上部灰岩段代表低水位体系域的碳酸盐台地边缘相灰泥丘沉积,属于牙形类J.xuanhanensis化石带,可与广西"来宾灰岩"的生物时代和沉积环境相对比;茅口组顶部覆盖的"王坡煤系"代表二级层序界面(SB2),与东吴运动的主幕(第三幕)相对应。 相似文献
7.
塔里木盆地柯坪地区奥陶系鹰山组台内滩沉积特征 总被引：2，自引：0，他引：2
通过对柯坪地区蓬莱坝剖面奥陶系鹰山组的野外实测可以将其划分为下、中、上三段,每段都具有不同的相序结构和沉积特征,下段主要以含陆源泥质的泥晶粗砂屑灰岩为主,中段为亮晶粉-细砂屑灰岩和层纹石灰岩互层出现,上段主要为中-厚层状似球粒泥晶灰岩,台内颗粒滩主要发育在中、下两段;柯坪水泥厂剖面也可以划分为三段,但界限没有蓬莱坝剖面明显,主体表现为中层状的亮晶砂屑灰岩和泥晶砂屑灰岩交互出现。通过对蓬莱坝剖面和柯坪水泥厂剖面的岩石进行野外露头、偏光显微镜、扫描电镜等不同尺度的观测及沉积微相分析,理清了柯坪地区鹰山组的岩石类型和相序结构,建立了柯坪地区颗粒滩沉积模式:由于水体深度和能量的差异,柯坪地区发育了四种相带类型--高能颗粒滩相带、滩间洼地沉积相带、低能颗粒滩相带、开阔浅海沉积相带。中-低能颗粒滩相带主要发育泥晶中-粗砂屑颗粒滩,高能颗粒滩相带主要发育亮晶细-中砂屑颗粒滩,并且两种颗粒滩都可以划分出3种亚相--滩主体、滩翼和滩内洼地;在微生物主导的碳酸盐建造向后生动物主导的碳酸盐岩建造转换的地质背景下,柯坪地区在奥陶系鹰山组沉积时期总体处于大面积发育微生物似球粒的浅水环境,沉积物的形成与改造受微生物活动的影响,微生物作用一方面为颗粒滩的发育提供了良好的物质基础,另一方面也控制了该时期颗粒滩的沉积特征。 相似文献
8.
川北地区下寒武统龙王庙组沉积相 及与储层的关系 总被引：1，自引：0，他引：1
以四川盆地北部下寒武统龙王庙组为研究对象,利用野外露头、测井及岩心等资料,探讨了川北地区下寒武统龙王庙组的沉积相类型及特征,并分析了其对储层的影响。研究认为:川北地区在早寒武世龙王庙期的沉积环境为碳酸盐台地,发育潮坪、局限台地和开阔台地等3种相带,这些相带又进一步细分为混积潮坪、台内点滩、潟湖和滩间海等4种亚相。其中,混积潮坪亚相主要发育砂质白云岩坪、白云岩坪等,部分地区可见潮道;台内点滩亚相以砂屑白云岩最为常见,沉积厚度不大;潟湖亚相以白云质潟湖沉积和白云质灰质潟湖沉积为主,分布面积大;滩间海亚相沉积物以深灰色块状石灰岩为主,局部夹白云质豹斑灰岩。纵向上,大部分地区龙王庙组沉积由2次海退旋回构成,潟湖主要发育在单个沉积旋回的中下部;台内点滩主要发育在沉积旋回的中、上部,单个滩体厚度较薄;混积潮坪发育在旋回顶部,即旋回末期。平面上,由于受古陆影响,研究区自西向东具有物源供应减少、沉积水体逐渐变深,以及沉积相从潮坪—局限台地—开阔台地过渡的特征,台内点滩主要围绕局限潟湖分布。结合不同沉积相带储层物性的分析,认为台内点滩的颗粒白云岩储集性能最好,晶粒白云岩次之,膏盐岩最差。龙王庙组储层发育的最有利沉积环境为台内点滩。 相似文献
9.
达县-宣汉地区长兴组-飞仙关组礁滩相特征及其对储层的制约 总被引：38，自引：1，他引：38
通过对普光2井、普光6井和毛坝3井等钻井资料以及地震剖面的详细研究,可知长兴组—飞仙关组生物礁相在地震剖面上,形态为透镜状,具有透镜体、中强变振幅、杂乱影像特征。岩性为灰色障积海绵礁灰岩、灰色障积海绵礁白云岩、灰色骨架海绵礁灰岩、灰色骨架海绵礁白云岩等组成。滩相在地震剖面上表现为透镜体、中强变振幅、不连续影像特征,其岩性主要为浅灰色厚块状亮晶鲕粒白云岩、亮晶含砾鲕粒白云岩、亮晶含豆粒鲕粒白云岩、亮晶生屑白云岩及亮晶砂屑白云岩等。两者在空间上相伴生,沿着台地边缘分布,形成台地边缘礁滩相带,该相带控制了达县—宣汉地区储层的岩性、储集性及其空间分布。 相似文献
10.
中扬子地区是我国碳酸盐岩最为发育的地区,从古生代到中生代都有碳酸盐岩地层发育,其中寒武系滩相碳酸盐岩发育最好,与之对应的岩石类型齐全、沉积环境与成岩环境多变,储集性能较好。 湖北省寒武系十分发育,露头面积占全省面积的7％～8％,其中鄂西寒武系分布于秭归、长阳、宜都一带,其中尤以宜昌为代表的峡东地区最为齐全,露头亦较连续、完整,故可作为滩相研究的典型地区。本区寒武系碳酸盐岩地层既有石灰岩,也有白云岩。石灰岩中既有颗粒灰岩、(含)颗粒泥晶灰岩及泥晶灰岩。颗粒类型包括鲕粒、核形石、砂屑、砾屑及生屑,颗粒间的填隙物多为亮晶,少为泥晶,亦有二者共存者(亮泥晶、泥亮晶)。白云岩中既有准同生白云岩(泥粉晶白云岩)也有准同生后白云岩(残余颗粒白云岩、晶粒白云岩)。本区 相似文献
11.
The Jubaila Formation (Upper Jurassic) in central Saudi Arabia has been divided into lower, middle, and upper parts purely on lithologic grounds. Each part consists of a major lower unit of lime mudstone and a minor upper unit of grainstone. This persistent change in the limestone facies is interpreted as a reflection of repeated shoaling up in the depositional shelf environment. It is a normal marine carbonate sequence that varies in thickness from 85 to 126 m. In the Hanifa Formation, the lowermost brown ledges in the section comprise a series of coarsening upward sequences which generally terminate in a fossiliferous/peloidal packstone and grainstone and subordinately lime mudstone facies. The middle slope member is yellow, blocky weathered shale and marl. Above this slope member are several thick beds of brown-coated fossiliferous wackestone, packstone, and grainstone with the association of lime mudstone in certain levels. These are fairly resistant ledges due to the occurrence of stromatoporoids. Dedolomitization occurs in the Jubaila Formation in various textural forms which include composite calcite rhombohedra, zonal dedolomitization, regeneration of predolomitization fabric of the limestone, and coarsely crystalline calcite mosaics with or without ferric oxide rhombic zones. Rhombohedral pores commonly occur in intimate association with dolomite, possibly resulting from the leaching of calcitized dolomite rhombohedra. The regional dedolomitization was most likely brought about by calcium sulfate solutions reacting with dolomites. The source of sulfate solutions is the dissolved anhydrite deposits of the Arab–Hith Formations, sometime before their erosion, and it takes place at or near an exposed surface. The Hanifa Formation shows various diagenetic features. These include dolomitization, dedolomitization, micritization, cementation, and recrystallization. Most of the examined samples of the Hanifa carbonates are dolomitized and subsequently dedolomitized as evidenced by the presence of iron-coated dolomite rhombs partially or completely calcitized. Dolomite also occurs in the lime mudstone, wackestone, packstone, and grainstone facies, while leaching of wackestone and packstone and dedolomitization of dolomite and dolomitic limestone followed by recrystallization are common processes. 相似文献
12.
下奥陶统白云岩是塔里木盆地最现实的重点勘探领域。文中在分析塔里木盆地早奥陶世构造、沉积及古气候等地质背景的基础上,以前人对白云岩的结构分类为基础,从白云岩发育产状出发,将塔里木盆地下奥陶统白云岩划分为灰岩中零散白云石、灰岩中斑状白云石、层状白云岩和沿断裂分布白云岩4类,白云石含量层位上自下而上具有总体减少的趋势。各类白云岩在岩石学特征和发育分布上具有较为明显的差异,局部可重叠出现。灰岩中零散白云石和斑状白云石的岩石学和地球化学及发育分布特征均反映其主要由浅埋藏白云石化作用形成;层状白云岩和沿断裂分布白云岩形成于中深埋藏白云石化作用;各类白云岩的产状特征差异受控于沉积期海平面变化、海水性质及埋藏条件等因素。沿断裂分布白云岩的形成和分布与断裂密切相关,是重要的储集岩石类型。白云岩储集层的形成主要是后期改造的结果,埋藏白云石化作用并未对大规模白云岩储集层的形成起到建设性作用,伴生或后期流体再运移导致的溶蚀作用为其主要成因。 相似文献
13.
The Lower Ordovician La Silla Formation of the Precordillera of west‐central Argentina is part of the west‐facing early Palaeozoic, tropical carbonate platform succession that comprises the core of the Cuyania terrane. Up to 360 m thick, it is exposed in several thrust sheets over a distance of some 250 km along and across depositional strike over a palinspastically unrestored distance of about 35 km. La Silla Formation is a strikingly pure limestone with subordinate finely crystalline dolomite and rare chert. It accumulated on a more or less uniformly subsiding passive margin. Copious precipitation of microcrystalline calcite, probably influenced by microbial activity to varying degrees, led to the generation of peloids, ooids and aggregates of these grains, as well as small amounts of lime mud, intraclasts, stromatolites and thrombolites. Rare bioclasts are limited mostly to scattered gastropods and trilobite sclerites; bioturbation is present locally. The array of carbonate rock types is grouped into eight recurring lithofacies, in order of decreasing abundance: (i) peloidal grainstone; (ii) laminated dolostone; (iii) intraclastic rudstone; (iv) microbial laminite; (v) peloidal packstone; (vi) ooidal grainstone; (vii) thrombolite boundstone; and (viii) mudstone. These facies represent sediments that formed solely in a shallow subtidal marine environment, with no evidence of restricted conditions, hypersalinity or subaerial exposure. No events of eustatic sea‐level change are recorded. By far the dominant facies is grainstone composed of well‐sorted, fine sand‐sized peloids and peloidal aggregates in homogeneous, tabular to gently undulating, medium to thick beds; cross‐lamination is scarce. Clusters of sub‐metre‐sized microbial patch reefs developed sporadically. The shallow platform is envisaged to have been covered by extensive peloidal sand flats and low‐relief banks, and little lime mud was generated. The setting was probably microtidal and may not have been affected by strong trade winds. It was washed by frequent, relatively gentle wave action but without experiencing powerful storms. In the middle member, anomalous lenses of intraclastic rudstone and laminated dolostone occur as graded beds overlying sharply downcut scoured surfaces up to 20 cm deep; these are interpreted to indicate a phase when accretion was punctuated occasionally by tsunamis generated from rift‐faulting seaward of the platform margin. The remarkably uniform peloidal grainstone composition over a broad area shows that, given the appropriate combination of climate, environmental and ecological factors, large portions of some early Palaeozoic platforms were dominated by grainy sediment and remained under well‐agitated conditions within fair‐weather wave‐base, without distinct lateral facies differentiation or tidal‐flat aggradation. 相似文献
14.
“仑山灰岩”标准地点在江苏南部句容县的仑山。1933年,俞建章在研究“仑山灰岩”中的头足类动物群时,曾指出:“仑山灰岩”的时代应属于早、中奥陶世。1935年,李捷等在系统研究宁镇山脉地质时,对“仑山灰岩”重新进行划分,把上部含鞘角石(Vaginoceras)动物群的灰岩归入中奥陶统,称汤山灰岩。 相似文献
15.
对研究程度较高的北美奥陶系碳酸盐岩油气田特征参数作了统计和分析,对比中国下古生界碳酸盐岩油气田,分析了古老碳酸盐岩油气储层的特点及主要控制因素。北美大陆奥陶纪沉积环境以环潮坪—浅水陆棚为主,储集岩可简单地划分为四种岩相类型,包括泥晶灰岩、粒泥灰岩、泥粒灰岩以及颗粒灰岩。晶间孔、角砾岩相关孔隙及溶蚀孔隙是最主要的孔隙类型,其中尤以晶间孔最为普遍。中国下古生界碳酸盐岩油气储层的演化更为复杂,原生孔隙损失殆尽。北美和中国的研究都表明,岩溶储层和白云岩储层是主要的有效储层。当埋深超过3000m时,白云岩是主要的储层岩石类型。在埋深增大的情况下白云岩保持更好的储集性能,这是一个基本的趋势。中国下古生界碳酸盐岩埋深较大,所以白云岩储层是一个特别值得关注的领域。 相似文献
16.
Osman Salad Hersi 《Arabian Journal of Geosciences》2011,4(1-2):147-160
The boundary separating Maastrichtian Sharwayn Formation from late Paleocene Eocene Umm Er Radhuma (UER) Formation in Dhofar, southern Oman, is characterized by a regionally extensive unconformity. The Jabal Samhan escarpment, north of Marbat-Sadh transect, preserves this unconformable boundary. This paper addresses the lithologic and diagenetic differences of the strata across the boundary and discusses their significance and link to the development of the upper Maastrichtian to lower Paleocene unconformity. The upper part of the Sharwayn Formation is characterized by lower thickly bedded, bioclastic, and peloidal mudstone to wackestone lithofacies overlain by a thick ledge (~5.5 m) of medium to coarse crystalline, (sucrosic) dolostone. Poorly preserved outlines of the framework grains suggest an original peloidal and bioclastic grainstone texture for the dolostone unit. The contact with the overlying UER Formation is sharp. The UER Formation is characterized by thickly bedded, bioclastic mudstone to wackestone overlain by coarse-grained, foraminiferal grainstone. The dolomitization process of the dolomite unit at the top of the Sharwayn Formation is envisaged to a shallow subsurface mixed meteoric and sea water diagenetic realm. This interpretation is supported by an inferred timing of dolomitization of latest Maastrichtian (post-Sharwayn Formation) to early Paleocene (pre-EUR Formation), preservation (although poorly recognizable) of the original depositional texture and diagenetic features that postdate the sucrosic dolomite. Pervasive dolomitization of the dolomite unit was controlled by its original grainstone texture, which permitted efficient percolation of the dolomitizing fluids. Correlation between the reference section of the formation and the section studied in this work raises the thickness of the formation to 28.5 m (relative to a thickness of 22 m at the reference section). Analysis of the new composite section suggests that deposition of the formation took place in a shallowing-upward setting where low-energy subtidal sediments (the lower limestone unit) were succeeded by a high energy sand shoal (upper dolomitized unit).This shallowing-upward succession is attributed to a third-order sea-level drop. The later is also recognized in many parts of the Arabian Peninsula, as well as globally, and interpreted as eustatic sea-level fluctuation. 相似文献
17.
The Neogene carbonate rocks have relatively small exposure relative to the siliciclastic and evaporite rocks in Rabigh and Ubhur areas, north Jeddah, Red Sea coastal plain of Saudi Arabia. The Miocene carbonates form small hills in both areas, which conformably overlie the siliciclastics, whereas the Pleistocene coral reefs form terraces facing the Red Sea in Rabigh area. The Neogene carbonates are represented by the following microfacies types: (1) dolomitic, oolitic, foraminiferal packstone; (2) sandy, dolomitic, intraclastic, foraminiferal packstone; (3) dolomitic and oolitic wackestone; (4) dolomitic, foraminiferal, intraclastic wackestone; (5) dolomitic mudstone; (6) coral boundstone; and (7) grainstone. The diagenetic processes affecting these carbonates are compaction, dissolution, aggrading neomorphism, and replacement that took place during deposition, shallow burial, and uplift. Pervasive dolomitization by the seepage reflux mechanism is responsible for the mimic replacement of the calcite of the original component of the limestone with dolomite. Sediments, biota, and lithofacies characteristics of the studied carbonate rocks of Rabigh and Ubhur areas indicate the presence of three facies zones; these are (1) FZ 5 platform margin reefs, (2) FZ 6 (platform margin sand shoals), and (3) FZ 7 platform interior-normal marine. The standard microfacies types are represented by (1) SMF 12, limestone with shell concentration; (2) SMF 15, oolitic wackestone and packstone; and (3) SMF 18, bioclastic grainstone and packstone with abundant benthic foraminifera. 相似文献
18.
四川盆地下奥陶统桐梓组白云岩的成因研究较少,模式存在多样性,尚未达成共识.通过系统的岩心观察、薄片鉴定、地球化学分析等方法,在四川盆地桐梓组识别出晶粒白云岩、颗粒白云岩和含石英白云岩及含白云质石英砂岩等与白云石相关的岩石类型.地球化学分析揭示不同类型白云岩具有不同的地球化学特征及白云石化机理,晶粒白云岩的MgO含量与CaO含量呈现出明显的正相关性,具有相对高的δ18OPDB值、δ13CPDB值、Sr值及较高的Mg/Ca比值,Fe、Mn含量较低,为准同生期蒸发泵白云石化成因;A类含石英白云岩及含白云质石英砂岩具有与晶粒白云岩相似的地球化学特征,也主要为准同生期白云石化成因;颗粒白云岩的MgO含量与CaO含量表现出弱负相关性,δ13CPDB值和δ18OPDB值与同期海水碳、氧同位素值分布范围基本一致,Sr含量相对较高,为回流渗透白云石化成因;B类含石英白云岩及含白云质石英砂岩只在研究区靠近物源的局部地区发育,其MgO含量与CaO含量呈正相关,δ13CPDB值和δ18OPDB值表现为明显负偏,与其他两类白云岩相比具有较高的Al2O3、Fe、Mn含量和相对较低的Sr含量,且受到陆源碎屑混入的影响,认为是混合水白云石化成因.四川盆地桐梓组具有3种白云石化机理共存的特征,总体继承了上寒武统白云石化机理. 相似文献
19.
陕西镇安西口石炭系/二叠系界线剖面碳酸盐岩微相特征与沉积环境的研究 总被引：18，自引：0，他引：18
在陕西镇安西口从上石炭统逍遥阶和下杨家河阶到下二叠统上杨家河阶、范家河阶、垭口阶和隆林阶的地层剖面上,区分出10种碳酸盐岩微相类型,即含生物碎屑灰泥灰岩、生物碎屑粒泥灰岩、生物碎屑泥粒灰岩、粒泥灰岩—泥粒灰岩、粗枝藻粒泥灰岩—粗枝藻泥粒灰岩、腕足棘皮粒泥灰岩—腕足棘皮泥粒灰岩、生物碎屑颗粒灰岩、团块颗粒灰岩、核形石颗粒灰岩和含鲕粒团块颗粒灰岩。它们形成于开阔台地和台地边缘浅滩2种沉积环境,开阔台地又进一步分为较浅水的开阔台地浅滩和较深水的开阔台地滩间,台地边缘浅滩内则局部发育藻丘。在此基础上,识别出在晚石炭世逍遥期至早二叠世隆林期研究区发生过12次相对海平面波动,它们构成5次明显的相对海平面升降;最后讨论了三里冲剖面上各阶界线与海平面变化的关系。 相似文献
20.
Well‐exposed Mesozoic sections of the Bahama‐like Adriatic Platform along the Dalmatian coast (southern Croatia) reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding Late Jurassic (Tithonian) shallow platform‐interior (over 750 m thick, ca 5–6 Myr duration). Facies within parasequences include dasyclad‐oncoid mudstone‐wackestone‐floatstone and skeletal‐peloid wackestone‐packstone (shallow lagoon), intraclast‐peloid packstone and grainstone (shoal), radial‐ooid grainstone (hypersaline shallow subtidal/intertidal shoals and ponds), lime mudstone (restricted lagoon), fenestral carbonates and microbial laminites (tidal flat). Parasequences in the overall transgressive Lower Tithonian sections are 1–4·5 m thick, and dominated by subtidal facies, some of which are capped by very shallow‐water grainstone‐packstone or restricted lime mudstone; laminated tidal caps become common only towards the interior of the platform. Parasequences in the regressive Upper Tithonian are dominated by peritidal facies with distinctive basal oolite units and well‐developed laminate caps. Maximum water depths of facies within parasequences (estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences) were generally <4 m, and facies show strongly overlapping depth ranges suggesting facies mosaics. Parasequences were formed by precessional (20 kyr) orbital forcing and form parasequence sets of 100 and 400 kyr eccentricity bundles. Parasequences are arranged in third‐order sequences that lack significant bounding disconformities, and are evident on accommodation (Fischer) plots of cumulative departure from average cycle thickness plotted against cycle number or stratigraphic position. Modelling suggests that precessional sea‐level changes were small (several metres) as were eccentricity sea‐level changes (or precessional sea‐level changes modulated by eccentricity), supporting a global, hot greenhouse climate for the Late Jurassic (Tithonian) within the overall ‘cool’ mode of the Middle Jurassic to Early Cretaceous. 相似文献