3-D Modeling for Flexural Subsidence and Deposition Process of Foreland Basin

前陆盆地是在造山带负荷作用下岩石圈发生挠曲沉降而形成的,并且被主要从造山带搬运的沉积物所充填.为了更好地理解和认识前陆盆地的形成演化机制,特别是受控于周缘多个造山带活动所形成的前陆盆地的演化机制,本文通过建立前陆盆地挠曲沉降与沉积过程的3-D模型,模拟展示了造山带逆冲推覆作用、岩石圈挠曲沉降响应及在山盆体系中由于动力地形变化而导致的河流体系的发育变化及其产生的剥蚀和沉积过程.模型的建立和实验完整体现了逆冲推覆、弹性挠曲沉降和沉积物搬运这三者之间的耦合机制,为全面深入研究前陆盆地动力学提供了理论依据和方法.     

前陆盆地沉降机理和地层模型

前陆盆地形成的主要原因是造山带负载导致的岩石圈挠曲。逆冲作用造成地壳增厚,造山带的巨大质量又导致下部岩石圈的区域均衡沉降,从而临近和平行于造山带发育了凹陷。另外,前陆盆地的演化也受到沉积物供应、盆地内沉积物扩散能力、岩石圈强度、造山带逆冲速率、全球海平面变化、和俯冲有关的动力沉降及俯冲负载等众多其它因素的影响。本文阐述了这些因素与前陆盆地沉降的关系,介绍了与幕式逆冲有关的地层模型和欠补偿-过补偿地层模型。希望本文能够对中国西北地区前陆盆地的研究起到一定的借鉴意义。     

前陆盆地构造-热演化:以龙门山前陆盆地为例

前陆盆地油气资源丰富但构造变形十分复杂,使得前陆盆地构造-热演化模拟面临挑战。前陆盆地演化过程中构造与热的耦合体现在多个层面:岩石圈热演化对岩石圈强度时空分布及其挠曲的影响;逆冲推覆作用的浅部温度效应;快速沉积作用对盆地温度场的影响等。首先,前陆盆地形成时的岩石圈热背景及其造成的岩石圈强度空间变化对盆地后期的演化具有重要影响。同时早期热事件的热扰动也会叠加在前陆盆地的构造-热演化过程中,并不断衰减,影响岩石圈的流变结构,从而带来一系列的影响。热与构造演化相耦合在前陆盆地定量模拟中非常重要。其次,还需特别关注岩石圈深部过程与近地表构造过程的耦合。造山带逆冲推覆、抬升和剥蚀是与前陆盆地形成相关的重要构造活动,这种运动引起的热对流对造山带的热结构、前陆逆冲带以及前渊地区的温度场的分布有着重要影响。最后,前陆盆地形成演化过程中的快速沉积作用对盆地温度场和地表热流产生强烈的压制作用,对前陆盆地浅部热演化的影响不容忽视。因此,在浅部热演化(包括造山带逆冲推覆、快速沉积压实等)与盆地下伏岩石圈挠曲、深部热演化的联合作用下,使得前陆盆地构造-热演化颇为复杂,二者的耦合使得前陆盆地构造-热演化模拟颇具挑战。     

前陆盆地形成的力学机制

前陆盆地挠曲沉降的主要控制因素包括：逆冲带负荷，地壳内部水平挤压，盆地沉积负荷和地壳力学性质，描术前陆盆地挠曲过程的主要参数为：逆冲楔状体初始宽度，逆冲前缘推进速度，地表坡度，拆离面倾角，搬运系数，地壳的有效弹性厚度，地壳内部作用力，前陆盆地力学模型极两种：一种依据造山带深部岩石圈是破裂的，其力学模型为中间破裂的无限宽度线弹性薄板的水平挤压和垂向负荷作用下的挠曲，另一种假设造山带深部岩石圈是连续的     

前陆盆地挠曲过程模拟的理论模型

本文讨论了前陆盆地形成的主要控制因素，包括逆冲负荷、盆地沉积物负荷、地壳内部水平挤压力和地壳力学性质，介绍了前陆盆地弹性和粘弹性挠曲力学模型的基本特征。在此基础上，结合典型实例，探讨了运用粘弹性和弹性挠曲模型模拟前陆盆地沉降和沉积过程的基本方法和基本原理，揭示了造山带与前陆盆地系统演化的动力作用过程。     

四川盆地盆-山耦合系统和沉积响应特征

依据四川盆地晚三叠世须家河期至白垩纪盆地构造和沉积演化史的综合分析结果,认为该盆地属于发育在大型周缘前陆盆地基础上的陆内压性叠合盆地,具类前陆盆地性质。盆地形成和演化受周边龙门山、米仓山-大巴山和雪峰山3个造山带多期次非同步异方位的逆冲推覆活动控制,可划分为受盆缘造山带逆冲推覆作用控制的川西、川东北和川东南3个盆-山耦合次系统,区域上构成了独具特色的"三坳围一隆"构造-沉积格局。对应各造山带异方位的交替逆冲推覆活动,盆-山耦合过程又可划分为早期周缘前陆盆地(T3m→T3xt)、中期类前陆盆地(T3x→J3)、晚期萎缩衰亡(K)3个演化阶段。各演化阶段盆-山耦合过程的沉积学响应具有特征的异同性:差异性为对应各造山带逆冲推覆应力方位的变化,各亚阶段沉降-沉积中心位置各异,往复迁移于川西、川东北和川东南3个坳陷带;相似性为各次系统地层分布都呈自前缘坳陷带向前陆斜坡带和前陆隆起带上超减薄变细的楔状体,具有相似的沉积组合、相带展布和油气地质特征。     

Basin-Mountain Coupling Syestem and Its Sedimentary Response in Sichuan Analogous Foreland Basin

依据四川盆地晚三叠世须家河期至白垩纪盆地构造和沉积演化史的综合分析结果,认为该盆地属于发育在大型周缘前陆盆地基础上的陆内压性叠合盆地,具类前陆盆地性质.盆地形成和演化受周边龙门山、米仓山-大巴山和雪峰山3个造山带多期次非同步异方位的逆冲推覆活动控制,可划分为受盆缘造山带逆冲推覆作用控制的川西、川东北和川东南3个盆-山耦合次系统,区域上构成了独具特色的“三坳围一隆”构造-沉积格局.对应各造山带异方位的交替逆冲推覆活动,盆-山耦合过程又可划分为早期周缘前陆盆地(T3m→T3 xt)、中期类前陆盆地(T3x→J3)、晚期萎缩衰亡(K)3个演化阶段.各演化阶段盆-山耦合过程的沉积学响应具有特征的异同性:差异性为对应各造山带逆冲推覆应力方位的变化,各亚阶段沉降-沉积中心位置各异,往复迁移于川西、川东北和川东南3个坳陷带;相似性为各次系统地层分布都呈自前缘坳陷带向前陆斜坡带和前陆隆起带上超减薄变细的楔状体,具有相似的沉积组合、相带展布和油气地质特征.     

造山作用与沉积响应

造山造与沉积盆地是大陆上最基本的两个构造单元,具有盆山转换和盆山耦合的地质特征。造山作用主要体现为逆冲作用和走滑作用,造山带逆冲推覆作用所产生的构造负荷是前陆盆地生长的构造动力,控制前陆盆地的沉降,形成２可容空间,并提供物源,导致盆地的沉降和物源在垂直造山带方向的迁移;造山带走滑作用不仅控制造山带瞳滑挤压盆地的形成,而且控制前陆盆地的沉降和物源在平行造山方向的迁移,以及盆地的抬升与侵蚀。沉积盆地地     

试论龙门山逆冲推覆作用的沉积响应─—以成都盆地为例

本文根据现今龙门山前陆盆地（成都盆地）沉积特征和龙门山冲断带第四纪以来的逆冲推覆事件，研究了龙门山逆冲推覆作用对成都盆地沉积的控制作用和成都盆地沉积对龙门山逆冲推覆作用的响应，总结了龙门山冲断带逆冲推覆作用的沉积响应模式和地层标识，为研究龙门山冲断带地质演化提供了新的思路和方法。     

陆-陆碰撞造山带双前陆盆地模式——来自大别山、喜马拉雅和乌拉尔造山带的证据

大陆碰撞造山带不同的构造演化阶段往往形成不同成因类型的周缘前陆盆地 (系统 )。根据对几个典型大陆造山带的研究 ,我们把大陆碰撞造山带的构造演化过程分为陆 -陆拼接和大规模陆内逆冲推覆 (陆内俯冲 )两个阶段 ;早期陆 -陆拼接阶段直接在俯冲板块被动大陆边缘基础上形成的前陆盆地称为“原前陆盆地” ,后期大规模陆内逆冲 -推覆 (或陆内俯冲 )阶段在俯冲板块内部形成的前陆盆地称为“远前陆盆地”(它比原前陆盆地距主缝合带远 )。原前陆盆地和远前陆盆地是同一大陆碰撞造山带不同构造演化阶段的产物 ,是两种不同成因类型的周缘前陆盆地 ,它们构成了同一大陆造山带的双前陆盆地 ,而不是传统概念的单一成因类型前陆盆地。     

叠加于弧后前陆盆地挠曲沉降之上的另一类沉降——动力沉降

弧后前陆盆地挠曲沉降包括逆冲负载沉降和盆地沉积物负载沉降。叠加于挠曲沉降之上还存在另一类沉降,即动力沉降。动力沉降是动力地形的一种,即动力地形低。动力地形一般认为具有两种成因,一种为与超大陆集聚和分散有关的动力地形,另一种为与大洋板片俯冲有关的动力地形。由大洋板块俯冲产生的动力沉降往往分布于弧后前陆盆地区,其幅度、波长与板块俯冲角度、俯冲速率、俯冲板块在地幔中通过的位置和俯冲岩石圈的热年代密切相关。将通过弧后前陆盆地沉积地层的去压实得到的总沉降减去盆地模拟获得的逆冲带负载和盆地沉积物负载沉降可以得到剩余沉降,即动力沉降。从地层资料中定量分离出动力沉降为改进和限制长期以来悬而未决的由洋壳俯冲导致的地幔-粘性流动构造模型提供理论基础和实际资料。     

Foredeep submarine fans and forebulge deltas: orogenic off-loading in the underfilled Karoo Basin

Third-order sequence stratigraphic analysis of the Early Permian marine to continental facies of the Karoo Basin provides a case study for the sedimentation patterns which may develop in an underfilled foreland system that is controlled by a combination of supra- and sublithospheric loads. The tectonic regime during the accumulation of the studied section was dominated by the flexural rebound of the foreland system in response to orogenic quiescence in the Cape Fold Belt, which resulted in foredeep uplift and forebulge subsidence. Coupled with flexural tectonics, additional accommodation was created by dynamic loading related to the process of subduction underneath the basin. The long-wavelength dynamic loading led to the subsidence of the peripheral bulge below base level, which allowed for sediment accumulation across the entire foreland system.A succession of five basinwide regressive systems tracts accumulated during the Artinskian (5 My), consisting of foredeep submarine fans and correlative forebulge deltas. The progradation of submarine fans and deltaic systems was controlled by coeval forced and normal regressions of the proximal and distal shorelines of the Ecca interior seaway respectively. The deposition of each regressive systems tract was terminated by basinwide transgressive episodes, that may be related to periodic increases in the rates of long-wavelength dynamic subsidence.     

库车前陆盆地白垩系层序地层样式及控制因素分析

白垩系库车坳陷是在南天山强烈逆冲导致的挠曲沉降背景下发育的前陆盆地。综合地震、钻井和露头资料对白垩系进行了层序地层划分,共分出2个区域性的沉积旋回或构造层序、8个三级层序;区内各层序及其内部体系域总体呈现东西向展布、南北向分异的特点;建立了两种层序地层学框架模式:卡普沙良群构造层序具有典型前陆盆地挤压深陷特征,沉积构成反映了从前陆逆冲挠曲沉降到回弹上隆的演化过程;巴什基齐克组构造层序具有宽缓、伸展的特点,层序地层框架模式及内部地层构成样式有其独特性。白垩系前陆盆地的层序地层格架和沉积体系域的配置受到前陆构造作用的控制,而气候及湖平面变化则主要影响层序地层格架内的沉积相类型。      

The South Westland Basin: seismic stratigraphy, basin geometry and evolution of a foreland basin within the Southern Alps collision zone, New Zealand

This paper develops further the case for a foreland basin origin of South Westland Basin, located adjacent to the Southern Alps mountain belt. Geohistory analyses show Middle Miocene initiation of subsidence in the basin, with marked increases at 5–6 Ma. Five seismic reflection horizons, including basement, Middle Miocene (top Awarua Limestone), top Miocene, mid-Pliocene (PPB) and mid-Pleistocene (PPA) have been mapped through the grid of seismic data. A series of five back-stripped structure contour maps taken together with five isopach maps show that prior to the Middle Miocene, subsidence and sedimentation occurred mainly along the rifted continental margin of the Challenger Plateau facing the Tasman Sea; subsequently it shifted to a foredeep trending parallel to the Southern Alps and located northwest of them. Through the Late Miocene–Recent this depocentre has progressively widened, and the loci of thickest sediment accumulation have moved northwestward, most prominently during the Late Pliocene and Pleistocene with the progradation of a shelf–slope complex. At the northern end of the basin the shelf–slope break is currently located over the forebulge, which appears not to have migrated significantly, probably because the mountain belt is not advancing significantly northwestwards. Modelling of the lithospheric flexure of the basement surface normal to the trend of the basin establishes values of 3.1 to 9.8×10²⁰ N m for the flexural rigidity of the Australia Plate. This is at the very low end of rigidities for plates, and 1–2 orders of magnitude less than for the Australia Plate beneath the Taranaki Basin. Maps of tectonic subsidence where the influence of sediment loading is removed also clearly identify the source of the loading as lying within or beneath the mountain belt. The basin fill shows a stratigraphic architecture typical of underfilled ancient peripheral foreland basins. This comprises transgressive (basal unconformity, thin limestone, slope-depth mudstone, flysch sequence) and regressive (prograding shelf–slope complex followed by molasse deposits) components. In addition the inner margin of the basin has been inverted as a result of becoming involved in the mountain building, as revealed earlier by fission track thermochronological data. The timing and degree of inversion fits well with the geometrical and stratigraphic development of the basin. That the inversion zone and the coastal plain underlain by molasse deposits are narrow, and most of the basin is beneath the sea, highlights this as an underfilled active foreland basin. The basin is geodynamically part of the Southern Alps collision zone.     

Concept and styles of reciprocal stratigraphies: Western Canada foreland system

The late Cretaceous–Palaeocene Western Canada foreland system provides a record of high-frequency cycles of reciprocal flexural tectonics superimposed on longer term changing dynamic subsidence. Initial dominance of dynamic subsidence during the deposition of the Bearpaw marine succession resulted in continual subsidence with differential rates across the flexural hinge line. Subsequent dominance of flexural tectonics resulted in opposite base-level changes between the proximal and distal reaches of the foreland system during the deposition of the post-Bearpaw nonmarine succession. In both cases, the contrasting base-level changes generated out-of-phase stratigraphic sequences, which defines the concept of reciprocal stratigraphies. Two styles of reciprocal stratigraphies have been identified in relation to the pattern of base-level changes across the foreland system. The Bearpaw style consists of a conformable succession of correlative transgressive and regressive systems tracts, suggesting continuous basin-wide sedimentation with the rates within the range of variation of the rates of base-level rise. The post-Bearpaw style shows sequences correlative to age-equivalent sequence boundaries related to coeval rising and falling base-level, respectively. The succession of Bearpaw and post-Bearpaw sequences corresponds to a cycle of marine to nonmarine foreland sedimentation controlled by changing ratios between dynamic subsidence and flexural tectonics. The amount of sediment supply derived from the orogen to the foreland system may also reflect the rates of dynamic subsidence, as a decrease in dynamic loading may lead to accelerated denudation of the sediment source areas.     

前陆盆地挠曲沉降正演模型的设计与实现——以库车古近纪陆内前陆坳陷沉降分析为例

本文以二维薄板弹性挠曲模型为基础,对模型进行简化和参数优化选取,并在VC++6.0环境下采用Windows视窗设计,实现了前陆盆地挠曲沉降的正演模拟系统.应用这一系统模拟分析了库车古近纪-新近纪前陆盆地的挠曲沉降过程.模拟结果表明,库车古近纪-新近纪前陆盆地的沉降曲线总体呈上凸型,具有典型前陆盆地沉降的特点,根据沉降速率变化可以把整个沉降过程分为四个部分,分别对应盆地的四个构造层序发育阶段,每一阶段呈不同的沉降特征,相邻两阶段之间存在一盆地回弹隆升、逆冲构造活动终止期,盆地遭受广泛剥蚀形成两个构造层序之间的不整合界面.正演模拟通过将沉降过程时间离散,精细设定不同时间段的构造负载,能够精细恢复前陆盆地的沉降过程和演化.     

Tectonically-driven underfilled–overfilled cycles,the middle Cretaceous in the northern Cordilleran foreland basin

It is shown that the middle Cretaceous succession in the northern Cordilleran foreland basin consists of several-million-year tectonically-driven cycles comprising two components: strata deposited in an underfilled basin with a prominent forebulge zone and strata deposited in an overfilled basin lacking evidence of a forebulge. The episodic thrusting of the Cordilleran orogenic wedge and its rich sediment supply to the basin are two main controlling factors for the formation of these cycles. A qualitative model of several-million-year tectonically-driven underfilled–overfilled cycle for migration and stratigraphic fill in this basin is proposed. During the early underfilled period (orogenic loading period), due to orogenic loading of emplaced thrust sheets, flexural subsidence is created in the region proximal to the mountain belt and a prominent forebulge is developed. During the late underfilled period (early orogenic unloading period), as the cratonward migration of the subsidence center of sediment loading in the foredeep zone, forebulge zones and backbulge zones migrate cratonwards, forming a diachronic erosion surface in the central basin. During the overfilled period (late orogenic unloading period), a prominent erosion forms in the proximal basin and a peripheral sag develops above the forebulge area of the previous underfilled period. This model may provide a pattern to subdivide sedimentary successions in the Cordilleran foreland basin. Using this model, alternative interpretations are suggested for some important, but controversial stratigraphic phenomena in the Cretaceous Cordilleran foreland basin: traditionally defined eustatic highstands, wide sedimentation area of the basin, erosion surfaces and widespread subtle topographic uplifts in the central basin, high-frequency coarsening-up cycles, extensively distributed erosive-based sandstones and conglomerates enclosed in marine mudstones.     

从前陆盆地充填地层分析盆山耦合关系

根据前陆盆地充填地层分析盆地和造山带的耦合关系，研究区域包括四川中生代前陆盆地和鄂尔多斯中生代前陆盆地。研究表明，前陆盆地和造山带具有较好的耦合关系。前陆盆地充填沉积物特征是造山带形成演化和盆地沉降的响应。向上变粗的沉积序列以及地层不整合盆地方向的迁移反映了造山带向前陆不断隆升的演化过程，前陆盆地沉积物的岩石学特征反映了双物源供给和造山带的剥蚀。层序地层的体系域构成和地层堆积方式主要受控于前陆盆地沉降速度的变化。     

库车前陆盆地早白垩世岩石圈粘弹性变形的地层记录

基于前陆盆地岩石圈弹性与粘弹性挠曲变形的不同特点,提出应用前隆斜坡带地层结构获取岩石圈力学性质及变形过程信息的思路。对库车前陆盆地的实例分析表明,研究区早白垩世历经了两个逆冲期至宁静期的构造演化,卡普沙良群、巴什基奇克组分别为逆冲期和宁静期的地层记录。在单个逆冲期,随着逆冲加载和岩石圈挠曲变形,岩石圈性质从弹性转化为粘弹性,盆地由向克拉通方向扩展变宽转变为向逆冲带变窄加深。相应地,前隆斜坡带的地层记录为:逆冲早期,地层向克拉通方向渐进超覆和退积;逆冲晚期,地层向逆冲带收缩和前积,形成底面上超/削截和顶面削截—顶超两个重大不整合面。宁静期盆地宽浅,地层平行连续,临近冲断带因岩石圈回弹产生少量削截不整合。