中上扬子石炭系某些宏观地质信息分析

本语文以某些大胆设想、结合当代地学科学前沿研究,分析了发育于早石炭世的玄武质火山岩和热液活动时空分布特征和已有的古地磁资料相印证,论述地壳热膨胀与沉积基底地的关系;通过沉积物厚度获取的沉积速率时分布,探讨了沉积基底形变程度和性质,认为全球海平面变化、地壳热膨胀引起地壳微型扩张中上扬子在石炭纪纬度的迁移等是控制沉积古地理的主要因素,并以此对中上扬子石灰纪进行沉积古地理宏观演化分析。     

西秦岭造山带泥盆纪沉积地质学和动力沉积学:造山带沉积地质学研究的思想、内容与方法

造山带沉积地质学是融造山带地层学、沉积学、大地构造学及地球物理、地球化学等为一体的综合性分支学科，被誉为近年来自层序地层学诞生之后，沉积学领域又一次Ｂｅｎｃｈｍａｒｋ式的跃进．本文着重介绍了造山带沉积地质学研究中应坚持以活动论思想为指导，借鉴沉积盆地分析中整体分析、综合分析、背景分析和演化分析的学术思想和工作原理，并结合造山带结构和盆地及古海洋格局，确定造山带沉积地质学研究内容和技术路线、造山带沉积地质学包括造山带区域地层学、区域沉积学、区域构造学、地层层序和沉积演化、古地理和古海洋格局、动力沉积学和动力演化模式等内容和多层次综合研究的技术路线。     

在庆贺国际古地理学会成立大会上的申请工作汇报

近代地球科学的发展和大陆动力学前沿领域研究的活跃．向古地理研究者提出新的挑战,亟需编制新一代具找矿效应的等时的、活动论的古地理图。在地学领域中活动论和固定论是相对的,在今后相当长的时限内．尚不能完全以非当争界限编绘古地理图。当前活动论古地理的研究．首要的是转变思路．不仅要从沉积区反馈盆地的构造活动,同时还要从非沉积压的古地理演化获得造陆、造山的佐证,以此编制全球性的中小比例尺的构造-古地理复原图。层序地层学的出现不仅为编制以层序不整合面、高位体系域和凝缩段为标志的等时性古地理图提供了条件．而且还使穿时体系域的时空演化研究成为可能。露头古地理图相对于古地理复原图而言．对找矿预测和油气盆地选区评价更具实际意义,     

全球旋回地层学

全球旋回地层学是指在对全球沉积岩进行综合系统研究之基础上，通过估算沉积盆地中源于物源区的沉积物类型和沉积环境条件变化，来预测地层学特征的一种过程一结果模型。其研究内容包括对全球地质演化时期全球海平面变化、全球气候条件、全球构造运动、全球古地理背景、全球沉积环境特征、全球古生物事件及全球矿产形成过程进行动态模拟，强调古气候在地质记录中的意义，注重沉积记录的全球同时性研究；强调各种事件在沉积作用中的意     

《全球沉积地质计划》——一次国际学术讨论会报告

种种有利条件的组合鼓励着开展一项新的国际研究的尝试——全球沉积地质计划。当代,有关全球性趋势在通讯、运输、商业和政治等方面是很明显的;这种趋势在地球科学的板块构造、古海洋学、古气候学和地震学等领域内也是看得到的。沉积地质学——一门研究未固结的沉积物和其石化了的对应物的科学—参与这一扩展的地球观已具备了成熟的条件。 沉积物和沉积岩是地球大部分历史和生命演化的档案记录。在这些沉积层中含有人类所必需的大多数资源——燃料、水、金属矿床和建筑材料。古老沉积岩是地球运动的一种脉冲“心电图”,而且在这些岩石中记录着大约30亿年来的水圈、生物圈和大气圈的演化。 近四十年来,在沉积地质学方面取得了一系列的显著进展,这为扩展到全球性问题的新方法和新概念提供了基础,这些进展包括:精确的定时;各类沉积模式的建立;海洋与大气的循环;板块构造;同位素地球化学;地震地层学和遥感等。 值此发展沉积地质学的有利的大好时机,需要有一个国际研究计划,以便为全球规模的研究和分析提供重点、机会和动力。对这个新研究计划确定出三个研究主题:(1)全球性韵律与事件;(2)全球性演化的沉积学记录;(3)全球性的沉积岩相分析。利用上述每个主题中的一些基本问题去概括出一些全球性研究的实例,这     

贵州古地理的演变

贵州已知的最老地质记录距今约１４００Ｍａ，在这漫长的地质历史时期中，古地理及其演变具如下特点：（１）可分为前震旦纪、震旦纪－志留纪、泥盆纪－晚三叠世中期及晚三叠世中期以后四个阶段，每个阶段的古地理格局具明显的继承性和一致性，而各个阶段又有显著的差异，这种差异是在相对短的地质时期内完成的。（２）演化的总趋势地壳由洋壳演化为陆壳、其厚度增大、活动性减弱，沉积盆地由洋盆转化为克拉通内陆盆地；古环境由海洋转化为陆地；沉积物由海相深水碎屑岩演化为陆相红色碎屑；沉积类型由海相活动性组合演化为陆相活动性组合。（３）贵州地壳经历了由北向南及由南向北的漂移，但始终位于低、中纬地区，气候以温湿为主。（４）沉积物具明显的大规模的旋回性，这种旋回性显示出古地理演变的周期性。（５）影响贵州古地理格局及其演变的主导因素是古构造及构造运动。     

板块聚合活动带及其研究

板块构造观的中心思想是；全球构造和地壳演化由岩石圈板块相互作用而引起，不存在构造作用的全球共同时空性。大陆造山带是古板块构造研究的重要区域，研究时应首先区别出稳定和活动两类不同的地壳构造类型，分别针对其特点进行侧重不同的研究。板块聚合活动带的重点问题是：（１）识别和研究夹杂其中的构造块体；（２）区分和恢复次级聚合活动带；（３）复原次级聚合活动带中不同性质地质体的原始状态。板块聚合活动带研究是从其组成的物质基础（沉积、岩浆建造）和变形动力学着手，综合生物古地理、大陆边缘沉积学、古地磁、地球物理等学科的成果，总结构造演化规律，建立具体板块聚合活动带的地质演化模式。     

层序岩相古地理编图在岩相古地理分析中的应用

岩相古地理图既是记录和说明地质作用过程中构造演化和沉积历史的重要图件，又是反映沉积学研究现状的标志之一。早期岩相古地理研究中，经典的年代地层单元编图为古地理研究奠定了基础。以板块理论为指导、以岩石地层为单元的优势相编图是第二代岩相古地理编图的标志，层序地层学理论的提出和发展，为岩相古地理编图研究提供了新的思路。作者以川滇黔桂地区泥盆系为例，在对中国南方部分地区泥盆系海相层序地层学研究的基础上，选择了层序、体系域、层序界面或相关界面为编图单元，进行了编制层序岩相古地理图的尝试。实践表明，层序岩相古地理图能够用更客观的动态变化来反映盆地的充填和演化历史，具有等时性、成因连续性和实用性等优点。     

湖南泥盆纪沉积盆地的演化与层序地层沉积模式

湖南泥盆纪沉积盆地的演化与层序地层沉积模式牟传龙（地矿部成都地质矿产研究所）层序地层学的诞生，给沉积地质学研究领域注入了新的研究思路和方法，迫使人们不得不去重新认识地质历史中的一些地质现象和问题。“层序地层学”的创立被地质学家称为地学中的一次里程碑事...     

怀念敬爱的王鸿祯先生

今年是敬爱的王鸿祯先生百岁诞辰纪念,我们怀着崇高的敬意,深深怀念这位为中国地质事业做出了重大贡献的前辈大师。 王鸿祯先生博学多才,学术造诣深厚,研究领域包括古生物学、地层学、古地理学、前寒武纪地质学、大地构造学和地质学史。在地层古生物和古地理方面,建立了四射珊瑚的系统分类和演化阶段;提出了以年代地层和岩石地层为主的地层分类观点,将沉积相与构造背景相结合,区别不同的古地理格局和古构造框架,主编出版了《中国古地理图集》;提出了层序地层学的分类级别体系及其与天文周期之间的可能联系。在大地构造与全球构造方面,提出了构造名词体系和中国及全球的基底构造单元和构造发展阶段的划分;提出了以泛大陆（联合古陆）为准的大陆聚散周期的认识和地球史上不同类别和不同级别的节律及可能的天文控制因素;进行了全球古大陆再造的研究,由此形成了全球构造活动论和历史发展阶段论相结合的地球史观。在地质学史方面,提倡以学科史和学科思想史为主要研究内容,以求“以史为鉴,继往开来”（参看《王鸿祯文集》第465页）。 （1）     

前陆盆地层序地层学研究简介

前陆盆地层序地层学是将层序地层学理论应用于构造活动的前陆盆地分析的一个特例。前陆盆地三级层序成因并非受全球统一的海平面变化控制，而是与盆缘造山带区域本报特约记者运动、盆内沉积作用和相对海平面变化的联合作用有关，代表了前陆分地一个成盆期的不同发育阶段。层序界面是相对海平面下降和区域构造隆的联合作用面。在盆地演化的不对称沉降阶充填阶段，邻造山带区为低水位浊积扇沉积层序；远离造山带区，低水位体系域不发育     

长周期层序形成机制的探索:层序地层学进展之二

将不整合面所限定的地层单位定义为层序,赋予这种层序以"构造旋回"的概念;将"不整合面及其可以对比的整合面"所限定的地层单位定义为"沉积层序",简称为"层序",并将沉积层序的形成过程解释为海平面变化过程。如果将前者作为"构造层序",则这种层序代表了二级层序,新定义的"沉积层序"则属于三级层序。概念的调整和变化意味着层序存在一个级别或序次问题。地质学家长期研究的结果表明,海平面变化主要存在两种基本的驱动机制,一种是由于构造运动所造成的"洋盆体积"的变化,另一种是气候变化所造成的地球极地冰盖消长而最终产生的海水体积的变化;前者所造成的变化以周期长、速度慢为特征,被简称为"构造型海平面变化",后者所产生的变化则以高频率和高速率为特征,被简称为"冰川型海平面变化"。根据上述概念,显生宙可识别出两个一级旋回,并可以进一步划分为6个二级层序(Sloss模型)或13个二级层序(Vail模型),显生宙二级层序划分的差别反映了长周期层序形成机制研究的一些重要变化和进展。对长周期层序形成机制的研究,除了考虑地球本身的构造活动所造成的洋盆体积的变化以外,地质学家们还将一级旋回与银河年旋回对应、二级旋回与银道面旋回对应、三级旋回与奥尔特星系旋回对应起来进行更大范围的思考和探索,也为研究长周期层序形成的最终驱动机制提供了一个重要的思考途径。如果把对Exxon层序地层模式概念体系不协调的研究而产生的各种层序地层模式作为层序地层学的第1个进展,长周期层序形成机制的研究则可以作为层序地层学的第2个进展。包括:(1)把来自于显生宙的一些重要模型和概念应用到前寒武纪,由此在更长的时间框架内探索一级旋回与超大陆旋回的成因联系;(2)二级旋回与地球水圈和大气圈演变的成因关联;(3)进一步总结三级旋回的形成机制。追索这方面的进展,可以更加深入地理解当年Exxon科学家们将层序形成机制归因于海平面变化的初衷以及所包含的科学意义,从而有利于今后的深入研究。     

Depositional bias and environmental change—important factors in sequence stratigraphy

Differences among depositional systems, here called depositional bias, strongly influence sequence patterns. Siliciclastics and shallow-water carbonates, for instance, shed most of their sediment during opposite phases of a sea-level cycle (lowstand shedding and highstand shedding, respectively). Furthermore, the two systems generate their own, system-specific relief on the sea floor, disperse their sediment load along different avenues and differ in the way they are deactivated: reefs and carbonate platforms can be drowned, whereas siliciclastic deposition can be shut off and renewed at any depth. As a consequence of these differences, pronounced unconformities (drowning unconformities) develop where carbonate platforms are terminated and buried by siliciclastics (the siliciclastic-to-carbonate transition tends to be more gradual). Drowned platforms and drowning unconformities appeared world-wide in great abundance in the Miocene, Cretaceous (Valanginian-Turonian), Jurassic (Toarcian) and Devonian (Frasnian/Famennian). Examples of drowning unconformities interpreted as sequence boundaries, include those of the Early Cretaceous platforms off New Jersey and off Morocco, the mid-Cretaceous unconformity in the Gulf of Mexico and Miocene unconformities on top of reefs in the Far East.

The eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms: either the rates of rise are an order of magnitude lower than the growth potential of platforms, or cycle amplitudes are too small, or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone. The critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems. Thus, drowning unconformities demonstrate the importance of environmental change as a control on sequence development. Other examples of dominantly environment-controlled sequences include slope deposits shaped by shifting currents (e.g. Florida and Blake Plateau) and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland (e.g. Gulf of Mexico).

Environmental change must be considered as a third, independent factor that competes with eustatic and tectonically driven regional changes of sea-level for control of sequences. The definition of sequences and sequence boundaries should be broad enough to include the possibility of non-sea-level controls.     

Upper Carboniferous to Lower Permian transgressive–regressive sequences of central Spitsbergen,Arctic Norway

Investigation of the Upper Carboniferous to Lower Permian sedimentary strata of central Spitsbergen shows that this highly cyclic rock succession is composed of four long-term transgressive–regressive cycles. These long-term cycles are themselves composed of stacked higher order cycles. Transgressive phases are characterized by increasing accommodation space, and include a basal transgressive part of marked retrogradation of facies belts and thickening-upward component cycles. Regressive phases are characterized by decreasing accommodation space, displayed by progradation of facies belts, overall shallowing and increased restriction of the depositional environment, influx of coarse terrigenous sediments and increasing evidence of exposure and/or non-deposition. The oldest transgressive–regressive sequence identified, Sequence 1, is of Serpukhovian to Bashkirian age and represents a syn-rift sequence. Also composed of syn-rift sediments is the transgressive–regressive Moscovian to mid-Gzhelian-aged Sequence 2. The late Gzhelian to late Asselian Sequence 3 is mainly a post-rift sequence. The youngest sequence, Sequence 4, is of Sakmarian to possible Artinskian age, and is also composed of post-rift sediments. The individual transgressive–regressive cycles are defined as second-order cycles, based on lithological signatures, lateral extent of bounding unconformities, and the actual time period the cycles span. Local tectonic activity is believed to control to some extent the development of short-term cycles in the syn-rift succession. However, cyclicity within the long-term cycles is mainly controlled by eustatic sea-level fluctuations, and therefore enables them to be correlated to other Circum-Arctic regions. Copyright © 1999 John Wiley & Sons, Ltd.     

Tectonic controls on sequence stacking pattern and along-strike architecture in the Pleistocene Mejillones Formation,northern Chile: Implications for sequence stratigraphic models

In the Mejillones Formation, a shallow-marine Pleistocene succession of northern Chile, the cyclic stratigraphic record is the result of the complex interaction of regional uplift, glacio-eustasy, local tectonics, sediment supply, and sedimentary processes. Stratal geometries, characteristics of sedimentary facies, and nature of sequence-bounding unconformities have been investigated to evaluate the influence of: (i) intrabasinal, short-term normal faulting on both along-strike variations in sequence architecture and genetic complexity of key stratal surfaces; and (ii) long-term regional uplift on sequence stacking pattern. The stratigraphic succession, dissected by small-displacement (few meters) normal faults striking obliquely with respect to the palaeo-shoreline trends, displays systematic variations in sequence architecture and the nature of bounding surfaces across them. Indeed, depending on position with respect to the fault plane, two basic types of internal organisation can be recognised in the examined shallow-marine, almost clastic-starved sequence. Within grabens it consists of a siliciclastic-rich transgressive systems tract (TST), which is bounded beneath by a transgressively modified, Glossifungites-demarcated sequence boundary (SB/RS), overlain by a mollusc-bearing falling-stage systems tract (FSST). The erosional downlap surface that separates the TST from the FSST is the regressive surface of marine erosion (RSME). On the footwall crests the combination of marine regressive erosion, during falls in relative sea-level, and uplift has resulted in complete removal of the sediments of the TST from these sites, leading to the formation of a tectonically enhanced basal unconformity composed of the RSME superimposed onto the previous SB/RS (SB/RS/RSME). The prominent lateral change in component units (systems tracts) and nature of bounding surfaces within the studied sequence is directly related to the presence of normal faults and indicates that fault activity had a major impact on the sequence stratigraphic evolution of the Mejillones Formation, enhancing subsidence within the grabens and promoting unconformities in the horsts.Overall, the Mejillones Formation records a long-term sea-level fall driven by the contemporaneous regional uplift, punctuated by repeated, high-frequency eustatic sea-level changes. The effect of this superimposition was that glacio-eustatic sequences were displaced progressively downward and basinward and stacked in a distinct downstepping, tectonically enhanced falling-stage sequence set, which reflects basin-wide loss in accommodation space. The sequence set is underlain by a composite RSME that becomes progressively younger basinward and is made up by the lateral and down-dip connection of a series of lower-rank sequence boundaries including hanging-wall SB/RSs and footwall SB/RS/RSMEs of successive sequences.     

Third-order depositional sequences controlled by synsedimentary extensional tectonics: evidence from Upper Triassic carbonates of the Carnian Prealps (NE Italy)

ABSTRACT The Upper Triassic platform-margin deposits of the Carnian Prealps fail to show the succession of the two global sea-level lowerings predicted for the Norian and Rhaetian by the Haq global sea-level curve. In both cases a relative sea-level rise occurs, a discrepancy that can be explained by an increase in tectonically controlled subsidence, a consequence of the plate-scale rifting in the NW Tethys Gulf preceding oceanic spreading in the Jurassic. Pulses of tectonic subsidence followed by relative quiescence are capable of generating depositional sequences similar in gross geometry and duration to the third-order eustatic cycles of Haq et al . The Late Triassic part of the Exxon global sea-level curve, partly derived from correlatable strata within the same palaeogeographical domain, is likely to reflect pulses of tectonically induced subsidence rather than eustatic sea-level changes.     

Tectonic, sea-level, and climatic controls on Late Paleozoic sedimentation in the western basins of Argentina

Tectonic activity, sea-level changes, and the climate controlled sedimentation in Late Paleozoic basins of western Argentina. The role of each factor is investigated from the geologic record of the Río Blanco and Paganzo basins using three hierarchical orders of stratigraphic bounding surfaces. First-order surfaces correspond to regional unconformities, second-order ones to local unconformities with a lesser regional extent, and third-order surfaces represent locally extended sedimentary truncation. Using this methodology, the Carboniferous–Permian record of the Paganzo and Río Blanco basins may be divided into two megasequences, four sequences, and 12 stratigraphic sections. Megasequences are bounded by regional unconformities that result from tectonic events important enough to cause regional paleogeographic changes. Sequences are limited by minor regional extension surfaces related to local tectonic movements or significant sea-level falls. Finally, stratigraphic sections correspond to extended sedimentary truncations produced by transgressive events or major climatic changes. Sequence I is mainly composed of marine deposits divided into basal infill of the basin (Section 1) and Tournaisian–Visean transgressive deposits (Section 2). Sequence II is bounded by a sharp erosional surface and begins with coarse conglomerates (Section 3), followed by fluvial and shallow marine sedimentary rocks (Section 4) that pass upward into shales and diamictites (Section 5). The base of Sequence III is marked by an extended unconformity covered by Early Pennsylvanian glacial sedimentary rocks (Section 6) that represent the most important glacial event along the western margin of Gondwana. Postglacial deposits (Section 7) occur in the two basins and comprise both glaciolacustrine (eastern region) and transgressive marine (central and western regions) deposits. By the Moscovian–Kasimovian, fluvial sandstones and conglomerates were deposited in most of the Paganzo Basin (Section 8), while localized volcanic activity took place in the Río Blanco Basin. Near the end of the Carboniferous, an important transgression is recorded in the major part of the Río Blanco Basin (Section 9), reaching the westernmost portion area of the Paganzo Basin. Finally, Sequence IV shows important differences between the Paganzo and Río Blanco basins; fluvial red beds (Section 10), eolian sandstones (Section 11), and low-energy fluvial deposits (Section 12) prevailed in the Paganzo Basin whereas volcaniclastic sedimentation and volcanism dominated in the Río Blanco Basin. Thus, tectonic events, sea-level changes and climate exerted a strong and complex control on the evolution of the Río Blanco and Paganzo basins. The interaction of these allocyclic controls produced not only characteristic facies association patterns but also different kinds of stratigraphic bounding surfaces.     

Tectonic,sea-level,and climatic controls on Late Paleozoic sedimentation in the western basins of Argentina

Tectonic activity, sea-level changes, and the climate controlled sedimentation in Late Paleozoic basins of western Argentina. The role of each factor is investigated from the geologic record of the Río Blanco and Paganzo basins using three hierarchical orders of stratigraphic bounding surfaces. First-order surfaces correspond to regional unconformities, second-order ones to local unconformities with a lesser regional extent, and third-order surfaces represent locally extended sedimentary truncation. Using this methodology, the Carboniferous–Permian record of the Paganzo and Río Blanco basins may be divided into two megasequences, four sequences, and 12 stratigraphic sections. Megasequences are bounded by regional unconformities that result from tectonic events important enough to cause regional paleogeographic changes. Sequences are limited by minor regional extension surfaces related to local tectonic movements or significant sea-level falls. Finally, stratigraphic sections correspond to extended sedimentary truncations produced by transgressive events or major climatic changes. Sequence I is mainly composed of marine deposits divided into basal infill of the basin (Section 1) and Tournaisian–Visean transgressive deposits (Section 2). Sequence II is bounded by a sharp erosional surface and begins with coarse conglomerates (Section 3), followed by fluvial and shallow marine sedimentary rocks (Section 4) that pass upward into shales and diamictites (Section 5). The base of Sequence III is marked by an extended unconformity covered by Early Pennsylvanian glacial sedimentary rocks (Section 6) that represent the most important glacial event along the western margin of Gondwana. Postglacial deposits (Section 7) occur in the two basins and comprise both glaciolacustrine (eastern region) and transgressive marine (central and western regions) deposits. By the Moscovian–Kasimovian, fluvial sandstones and conglomerates were deposited in most of the Paganzo Basin (Section 8), while localized volcanic activity took place in the Río Blanco Basin. Near the end of the Carboniferous, an important transgression is recorded in the major part of the Río Blanco Basin (Section 9), reaching the westernmost portion area of the Paganzo Basin. Finally, Sequence IV shows important differences between the Paganzo and Río Blanco basins; fluvial red beds (Section 10), eolian sandstones (Section 11), and low-energy fluvial deposits (Section 12) prevailed in the Paganzo Basin whereas volcaniclastic sedimentation and volcanism dominated in the Río Blanco Basin. Thus, tectonic events, sea-level changes and climate exerted a strong and complex control on the evolution of the Río Blanco and Paganzo basins. The interaction of these allocyclic controls produced not only characteristic facies association patterns but also different kinds of stratigraphic bounding surfaces.     

Interplay of orbital forcing and tectonic pulses in the Cambrian Iberian platform, NE Spain

The stratigraphy of carbonate/shale couplets, cycles and cycle-stacking patterns in a Cambrian shallow water platform (Iberian Chains, NE Spain) are related to sea-level changes driven by orbital forcing and by tectonic pulses. The interplay of both effects can be discriminated in the Iberian fault-controlled platform, in which the tectonic activity can be analysed by accurate and detailed biostratigraphic correlations based on trilobite zonation. The stratigraphic hierarchy of rhythmically interbedded limestones and shales, in two coeval but structurally separated geodynamic settings, yields cycle ratios of 1.44 :1. This ratio is supported by time thickness and spectral analysis, which is based on a graphic method of analysis: the Map of Grey Lines. The cycle ratio seems to be evidence for orbital forcing by obliquity and precession cycles predicted for early Paleozoic time. Carbonate/shale couplets, the smallest rhythmic units recognisable in the field, represent short-term, periodic fluctuations in supply of terrigenous sediments and carbonate productivity of uncertain origin, which could be associated with one of several harmonics of the former orbital cycles. The pulsating tectonic activity was approximated by using a quantitative analysis of tectonically induced subsidence (Shaw method). Recurrence frequencies of tectonic pulses were estimated and dated by biostratigraphy. As a result, tectonic disturbances in the Cambrian Iberian platform show an episodic periodicity comparable to that of orbital eccentricity cycles, which could mask their recognition. Received: 15 November 1999 / Accepted: 9 February 2000     

Syn‐rift sequence development in a fault‐controlled embayment (Early Permian Irwin River Coal Measures,Northern Perth Basin,Western Australia)

Stratigraphic patterns and sequence development in tectonically active extensional basins remain poorly documented in comparison with passive‐margin settings. Rift basin fills are generally characterized by coarsening‐upward trends in response to the rapid creation of accommodation by extensional faulting, and the progressive filling of graben during more quiescent periods. The Early Permian Irwin River Coal Measures in the Northern Perth Basin (Western Australia) record a complex stratigraphic arrangement of conglomerate, sandstone, mudstone and coal, and have been attributed to delta plain depositional environments that developed in a cool–temperate climatic setting during syn‐rift activity. Sedimentary analysis of outcrop and core data from the fault‐bounded Irwin Terrace is used to distinguish nine facies associations reflecting deposition in braided rivers, fixed‐anastomosed channel belts, tide‐influenced coastal environments and storm‐affected distal bays. The broader depositional system is interpreted as a morphologically asymmetrical tide‐dominated embayment with a fluvial and wave influence. The stratigraphic architecture of the Irwin River Coal Measures was strongly influenced by the evolving rift basin margin. Fault reactivation of the major basin‐bounding Darling Fault in the early syn‐rift phase caused footwall uplift and the inception of transverse palaeo‐valleys occupied by braided fluvial systems. Fault block subsidence during the subsequent balanced, backstepping and drowning phases resulted in a dominantly retrogradational stacking pattern indicating progressive flooding of marginal‐marine areas and culminating in deposition of distal marine elements. In the active rift basin, it is proposed that preservation of a shallow‐marine syn‐rift sequence was promoted by the geomorphological confinement of the embayed system increasing tidal current acceleration and hampering transgressive ravinement. The proposed sequence model demonstrates that transgressive successions can develop in the early syn‐rift phase in response to footwall uplift and tectonic subsidence. The syn‐rift sequence recording the filling of an embayment on a rift basin margin may be applied in similar tectonic and/or depositional contexts worldwide.