准噶尔西北缘前陆冲断带三叠纪-侏罗纪逆冲断裂活动的沉积响应

笔者从冲断活动的产物———各种成因扇体(冲积扇、水下扇、扇三角洲)出发,由160口单井剖面、15条联井剖面、8个层位平面渐次展开了准噶尔西北缘前陆冲断带三叠—侏罗纪逆冲断裂活动的沉积响应研究。三叠纪扇体在乌尔禾—夏子街地区发育叠置程度最好,T1b到T3b,其由盆内向盆缘老山方向退缩迁移明显,并具T1b到T2k1由盆缘向盆内、T2k2到T3b由盆内向盆缘迁移的2个进退波动变化。侏罗纪扇体在八道湾组最为发育,总体叠置关系较差,J1b到J2t,均呈由盆内向盆缘老山退缩沉积的退覆式迁移特征。三叠纪到侏罗纪,总体为由强到弱的退覆式冲断活动及扇体迁移模式,即随主要同生控扇断裂分布由盆缘向老山方向退缩迁移,冲断活动强度由盆缘向盆地方向逐渐减弱直至停息;相应地,各期扇体平面上分布规模渐小,总体呈由盆内向盆缘老山退缩迁移的沉积响应,两者耦合性良好。各类扇体的沉积分布受不同时期同生断裂活动的严格控制,其时空叠置及迁移规律的差异是红山嘴—车排子、克拉玛依—百口泉及乌尔禾—夏子街各构造带冲断作用地域性及作用强度差异性的沉积响应。进而引入“活动性指数”的概念与方法,对前陆冲断带同生断裂的冲断活动强度进行了定量化统计分析,并根据冲断推覆事件的地层、沉积标识划分出T1b-T3b、J1b-J2x、J2t三套构造层序,识别出三叠—侏罗纪的3个逆冲推覆幕、6次逆冲推覆事件。     

准噶尔盆地西北缘扇体形成演化与扇体油气藏勘探

准噶尔盆地西北缘广泛发育二叠纪-侏罗纪冲积扇、水下扇、扇三角洲等砾质粗碎屑沉积,其形成演化严格受不同时期活动的同生断裂控制.二叠纪以乌尔禾组扇体最为发育,呈由盆缘向盆地方向逐渐增强的前展式推覆冲断及渐进式扇体迁移响应模式.三叠纪-侏罗纪以百口泉组、克拉玛依组扇体最为发育,呈由盆内向盆缘方向逐渐减弱的退覆式冲断活动及后退式扇体迁移响应模式.已知扇体油气藏主要富集于水下扇扇根及扇中、扇三角洲平原及前缘4个亚相带,及二叠系佳木河组、乌尔禾组、三叠系百口泉组、克拉玛依组、侏罗系八道湾组、头屯河组6个层位.二叠-三叠纪扇体含油层多、规模大、储量丰度高,侏罗纪扇体反之.受断裂、不整合、岩相岩性、物性4种因素控制,扇体主要形成断块、地层不整合及构造岩性油气藏.断阶带及扇根-扇中相带主要发育构造(断块)油藏,为扇体与断层相配置的垂向运聚成藏模式;斜坡区及扇中-扇缘相带主要发育岩性油藏,为扇体与不整合相配置的侧向运聚成藏模式.西北缘扇体成藏条件好,探明程度总体较低,剩余资源潜力大,进而指出了七大有利勘探区块和方向.     

准噶尔盆地乌夏地区二叠纪构造控扇作用

乌夏前陆冲断带二叠系构造层序特征、沉积相特征及断裂特征研究表明,二叠纪乌夏地区系受到推覆体严格控制的周缘前陆盆地,主要发育水下扇-扇三角洲-冲积扇-湖泊沉积体系,其中扇体发育代表了最典型的沉积特征.受海西运动晚期的影响,构造演化经历了强烈俯冲碰撞造山期、弱冲断夹短暂伸展火山期和强烈冲断复活期3个阶段,并形成了众多走向不同却又彼此相互切割叠加的逆冲断裂,影响了地层的沉积与剥蚀,控制了断裂带的形成和演化.由早至晚扇体由山前向盆内呈前展式夹短暂退覆式叠置迁移,相应地,二叠纪以北东东向断裂为主,并从山前向盆地方向依次发育,其间夹杂短暂后展式发育,构造活动强度逐渐由西向东、由北向南迁移,因此,绝大多数同生断裂控制了扇体的沉积边界和分布,部分控制了其厚度和发育方向,扇体的迁移与控扇断裂的活动迁移具有很好的吻合性,断裂活动是控制乌夏地区沉积的主要因素.     

准噶尔盆地西北缘玛北地区百口泉组扇三角洲沉积模式

准噶尔盆地西北缘二叠纪-三叠纪强烈的同生断裂活动和逆冲推覆构造使西北缘三叠系为大型内陆坳陷湖盆沉积, 发育多级坡折, 大型坳陷湖盆坡折带控制了玛北地区扇体的发育。通过岩芯、铸体薄片及测井资料, 结合地层超覆叠置、岩性纵向组合及砂体的展布分析可知玛北地区三叠系百口泉组发育典型的扇三角洲沉积, 根据沉积相标志和扇三角洲内部成因沉积单元的精细刻画, 识别出3种亚相和11种微相:即扇三角洲平原亚相的水上泥石流砾岩微相、辫状河道砂砾岩微相、平原河道间砂泥岩微相;扇三角洲前缘亚相的水下主河道砾岩微相、水下河道砂砾岩微相、水下泥石流砂砾岩微相、水下河道间砂泥岩微相、水下河道末端砂岩微相、河口坝-远砂坝砂岩微相;前扇三角洲亚相的前扇三角洲粉砂岩微相和前扇三角洲泥岩微相。玛北地区三叠系是在湖侵背景下多级坡折控制的扇体, 扇三角洲是重力流与牵引流综合沉积作用的结果, 向北东物源方向呈退积沉积, 是一种典型的湖侵退积型扇三角洲。     

准噶尔盆地乌夏前陆冲断带构造活动—沉积响应

通过研究乌夏前陆冲断带二叠系构造层序特征、沉积相特征、断裂特征及最具断裂构造活动指向性的扇体发育特征,认为二叠纪构造演化受海西运动晚期的影响经历了强烈俯冲碰撞造山期、弱冲断夹短暂伸展火山期和强烈冲断复活期三个阶段,并形成了众多走向不同却又彼此相互切割叠加的逆冲断裂,影响着地层的沉积与剥蚀,控制着断裂带和扇体的形成和演化。结果表明由早至晚扇体由山前向盆内呈前展式夹短暂退覆式叠置迁移特点,相应地,二叠纪以形成北东向和北东东向断裂为主,并从山前向盆地方向依次发育,其间夹杂短暂的后展式发育,构造活动强度逐渐由北西向南东方向迁移。因此,绝大多数同生断裂控制了扇体的沉积边界和分布,部分控制了其厚度和发育方向,扇体的迁移与控扇断裂的活动迁移具有很好的吻合性,断裂活动是控制乌夏地区沉积的主要因素。结果表明:二叠纪时期乌夏地区主要发育水下扇—扇三角洲—冲积扇—湖泊沉积体系,从下至上经历了饥饿深水阶段、复理石阶段和磨拉石阶段构造,其中扇体发育代表了最典型的沉积特征。     

羌塘盆地东部晚三叠世-侏罗纪构造-沉积演化

本文以野外实测剖面为基础,结合区域地质调查,通过地层学、岩石组合特征及沉积盆地分析,并综合区域构造演化背景及年代地层学等最新研究成果,对羌塘盆地东部上三叠统-侏罗系岩石组合、沉积类型和沉积相特征进行了对比研究,明确了羌塘盆地东部晚三叠世-侏罗纪的地层分布特征、沉积相类型、展布特征及构造-沉积演化过程。以区域性角度不整合为标志,将羌塘盆地东部上三叠统-侏罗系划分为2个构造层(卡尼阶-诺利阶构造层和瑞替阶-基默里阶构造层),并详细叙述了不同构造层内各地层的分布范围、厚度变化及岩性特征。研究区上三叠统-侏罗系以海陆过渡相和海相沉积为主,其中海陆过渡相包括三角洲相和潮坪-泻湖相,海相包括碳酸盐缓坡、蒸发台地、局限台地、滨海、浅海、半深海和深海相沉积。卡尼期主要发育滨海-浅海-半深海-深海相沉积(北羌塘坳陷)和滨浅海沉积(南羌塘坳陷)。诺利期早期以碳酸盐岩缓坡-混积陆棚沉积为主,诺利期晚期、赫塘期-巴柔期、卡洛期和基默里期主要发育潮坪-三角洲相沉积(北羌塘坳陷)和滨浅海沉积(南羌塘坳陷),巴通期和牛津期以蒸发台地-局限台地-混积陆棚沉积为主。沉积相东西向带状展布,东部低隆起是分割南北相带的重要构造单元,并在巴通期及牛津期为水下隆起,控制着羌塘东部局限台地、蒸发台地及台地边缘的分布。将区域构造背景与沉积记录相结合,总结出5个构造-沉积演化阶段:活动陆缘阶段(卡尼期,Ⅰ_1)、前陆盆地演化阶段(诺利期,Ⅰ_2)、裂陷-坳陷阶段(瑞替期-巴柔期,Ⅱ_1)、被动陆缘-坳陷阶段(巴通期-卡洛期,Ⅱ_2)和被动陆缘-坳陷阶段(牛津期-基默里期,Ⅱ_3)。     

新疆尼勒克坳陷侏罗系沉积演化及与铀成矿的关系

尼勒克坳陷位于我国砂岩型铀矿产基地伊犁盆地东北部,具铀源、层间氧化带、地球化学障等砂岩型铀矿成矿条件,由于构造变形较强、工作程度偏低,该区铀成矿潜力不明晰。以铀矿勘查钻孔岩心观测、典型钻孔剖面沉积相分析为基础,结合伊犁盆地构造背景及断陷湖盆演化规律,分析尼勒克坳陷侏罗系沉积演化及铀成矿作用。研究表明,尼勒克坳陷侏罗系主要发育湖泊-扇三角洲沉积,八道湾-三工河沉积期尼勒克地区整体处于浅湖环境,吉林台等局部地区发育有滨浅湖滩坝砂体;西山窑沉积期为扇三角洲-湖泊沉积,发育有较大规模平原沼泽。尼勒克坳陷铀成矿潜力集中于构造相对稳定的吉林台及以西地区,铀矿体赋存于该区西山窑组扇三角洲分流河道砂体中。     

准噶尔盆地西北缘前陆冲断带二叠纪逆冲断裂活动的沉积响应

笔者从160口单井剖面、15条联井剖面及5个层位平面渐次展开了准噶尔西北缘前陆冲断带二叠纪逆冲断裂活动的沉积响应研究。各种成因扇体(冲积扇、水下扇、扇三角洲)在佳木河组和上乌尔禾组地层中最为发育，其沉积分布严格受不同时期活动的同生断裂控制。由早二叠世佳木河期至晚二叠世上乌尔禾期，扇体在克拉玛依-夏子街地区叠置程度较好，由盆缘向盆内迁移、推进明显；在车排子中拐地区叠置程度相对较差，局部略呈向盆缘老山收缩、后退趋势，表明红山嘴车排子断裂带与克拉玛依-百口泉断阶带、乌尔禾-夏子街断褶带逆冲活动的强度及地域迁移性有明显差异。二叠纪总体为一由弱到强的前展式推覆冲断及渐进式扇体迁移模式，即随同生控扇断裂由老山向盆缘的前展式推覆活动，相应地，各构造带扇体逐渐由盆缘向盆地方向发育、推进，扇体面积不断扩大，显示出明显的渐进式迁移的沉积响应，两者形成良好的耦合性。进而引入“活动性指数”的概念与方法，对前陆冲断带同生断裂的冲断活动强度进行了定量化统计分析，据二叠纪冲断推覆事件的地层、沉积标识，识别出3个逆冲推覆幕、7个逆冲推覆事件，划分出P1j-P1f、P2x—P2w、P3w三套构造层序，并指出在P1f、P2x及P2 3w各时期，由红山嘴-车排子→克拉玛依-百口泉→乌尔禾-夏子街构造带，同生断裂活动性趋于增强；在乌尔禾-夏子街断褶带，由早二叠世佳木河期到中、晚二叠世乌尔禾期，冲断推覆强度逐渐增大。     

河套盆地临河坳陷白垩纪-古近纪沉积环境演化及油气地质意义*

河套盆地沉积环境演化的研究程度较低,尤其是针对具有重要油气勘探潜力的临河坳陷白垩系和古近系。通过对地震和钻井资料的详细分析,对河套盆地临河坳陷白垩系和古近系沉积演化开展系统研究,并探讨其油气地质意义。结果表明: (1)白垩纪和古近纪,河套盆地临河坳陷处于亚热带干旱-半干旱气候条件,沉积水体整体富氧但局部贫氧-厌氧,并且淡水和半咸水环境交替出现。(2)坳陷内的白垩系和古近系共发育5类沉积相,包括冲积扇、辫状河、辫状河三角洲、扇三角洲及湖泊相,又进一步划分为12类沉积亚相及22类沉积微相。坳陷西北侧断控构造活动较强,地形高差较大,发育冲积扇、扇三角洲、湖泊沉积体系;东南侧构造活动弱,地形较缓,发育辫状河、辫状河三角洲、湖泊沉积体系。各期沉积格局整体相似,仅表现在盆缘扇体和盆内湖相沉积规模的此消彼长。(3)坳陷内的白垩系和古近系沉积作用表现为“弱幕式构造主控下的干旱浅水双物源沉积”特征。在盆地发育的初期,构造活动较强,但盆地规模较小且水体较浅,两侧碎屑物质快速向盆内推进,并在盆地中心汇合,形成“满盆砂”的沉积格局。随着构造活动减弱和水平面快速上升,碎屑物质供应不足,湖泊的沉积和改造作用占据主导,从而形成以湖泊相占优势的沉积格局。(4)坳陷内的沉积相带控制着砂体的宏观发育规模、叠置关系和垂向演变,进一步决定了有效储集层的空间分布特征。在沉积相带和断裂作用双重主控因素下,坳陷内的白垩系和古近系有利储集层多分布于以滨-浅湖和三角洲前缘沉积为主并且断层发育的中央断垒带。     

塔里木盆地库车坳陷三叠纪沉积相与古地理研究

库车坳陷继晚二叠世的厚层磨拉石沉积之后,三叠纪开始进入封闭的挤压挠曲型盆地发展阶段,拉开了中生代前陆盆地发展的序幕,构造格局和构造样式较古生代发生很大转变。盆地内三叠纪气候湿热,沉积相类型多样。靠近北部山前发育大套冲积扇、扇三角洲和辫状三角洲沉积,向坳陷中心有辫状三角洲、曲流河和湖泊沉积。河漫沼泽上发育多套煤层。其滨湖、沼泽相炭质泥岩及煤系建造是库车坳陷重要的烃源岩。在整个三叠纪演化的不同时期,逆冲挤压应力逐渐增强又逐渐减弱,各时期盆地的古地理特征不同。从早三叠世到晚三叠世,盆地的沉积和沉降中心持续南迁,前缘隆起则持续向前陆方向后退。三叠纪前缘隆起和北部逆冲带在轮台以东连通,该连通古陆从早三叠世至晚三叠世持续由东向西移动,但迁移幅度不大,在晚三叠世时期成为一个次要物源区。      

广西蓬莱滩地区合山组盆底扇上的异地煤

蓬莱滩地区合山组中的煤层产在深水盆底扇上部，是在低水位期由水下重力流从海岸带带入盆地的植物碎屑在盆底扇上二次堆积而成。由于有机碎屑物质的密度低，在二次搬运和沉积过程中经过重力分异，有机碎屑通常富集在扇体顶部，形成异地煤层。     

滇西耿马盆地构造—沉积综合分析

滇西耿马盆地位于三江褶皱系保山褶皱带的耿马—澜沧复背斜,面积１９５ｋｍ２,接受广泛的河湖相沉积,为典型的第三系小型陆相盆地。盆地内沉积受构造控制明显,沿边界断层主要发育冲积扇、近岸水下扇沉积,远离断层发育深湖相或半深湖相沉积。耿马盆地的构造样式与沉积展布在滇西具有极好的代表性,故从构造－沉积相互作用角度对其分析,对于指导滇西其他第三系盆地的勘探有重要意义。     

干旱环境河流扇概念与鄂尔多斯盆地延长组“满盆砂”成因新解

河流扇是陆相盆地中近年来日益受到重视的一种新沉积模式,其主要形成于干旱气候环境中。该文阐述了河流扇的概念演变与发展由来、沉积特征、鉴别标志与控砂机理等,讨论了河流扇与分支河流体系、末端扇及浅水三角洲等相关概念之间的区别与联系,认为河流扇形成主要受“分支型”河道控制,而末端扇及浅水三角洲主要受“分流型”河道控制。在对鄂尔多斯盆地晚三叠世古气候环境深入分析的基础上,运用河流扇概念对延长组“满盆砂”形成机制进行了重新解释。主要结论是:1）延长组沉积时期,古气候具有三分性——早期为干旱环境,中期为湿润环境,晚期再次转变为半干旱—半湿润环境;2）在干旱气候环境下,缺少大面积汇水区,以洪水搬运—事件沉积作用为主,形成了别具特色的河流扇体系,这可能是造成延长组“满盆砂”的主要原因之一;3）干旱环境河流扇砂体与潮湿环境水进域富含有机质泥岩相匹配,有利于形成大型岩性油气藏,从而使延长组由“满盆含砂”变为“满盆含油”。该研究改变了以往大型坳陷湖盆以“三角洲模式”为主导的传统认识,对丰富发展我国陆相盆地沉积理论认识及指导油气勘探实践均有积极意义。     

Soil-landscape and climatic relationships in the middle Miocene of the Madrid Basin

The Miocene alluvial-lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors on sedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonically active area, soils were weakly developed in aggrading alluvial fans, dominated by mass flows, reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed; the former were associated with Mg-poor fan sediments while the latter formed on Mg-rich lake clays exposed during minor lake lowstands. The north-east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream flood deposits, sourced by carbonate terrains. Floodplain and freshwater lake deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential development of calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones. The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quaternary fans, which are characterized by climatically induced periods of stability and instability.     

Sedimentation and extensional basin evolution in a Miocene metamorphic core complex setting, Alvord Mountain, central Mojave Desert, California, USA

The Lower Miocene Clews Formation at Alvord Mountain, Mojave Desert, California, comprises an upward coarsening sequence of synextensional continental deposits of variable thickness; this sequence pinches out to the west against the Alvord Mountain pre-Tertiary basement complex and thickens eastward to c.300 m over a distance of 7 km. Two stages of sedimentation are recognized in the formation. During the initial stage of sedimentation, the depocentre was delineated by a lacustrine system that was bounded to the west by small, sheetflood-dominated alluvial fans and to the north by a southerly flowing fluvial braidplain. Lacustrine mudstone, siltstone and carbonate suggest an initially closed basin. Conglomerate to the west represents small, sheetflood-dominated fans. Igneous clasts and a south-east palaeoflow direction suggest a proximal, low-relief source in the western Alvord Mountain area. Pebbly sandstone of the southward-prograding braidplain has a metasedimentary provenance in the Paradise Range to the north. The second stage of deposition was dominated by coarse conglomerate and breccia. West to southwest palaeotransport indicators and a distinctive metaigneous petrofacies indicate a provenance in the Cronese Hills, 8 km to the east. These strata reflect rapid westward progradation of sheetflood- and debris flow-dominated alluvial fans that advanced across the axial braidplain and lacustrine system. Basin development is interpreted to have been controlled by regional NE-directed extension on a detachment fault associated with the central Mojave metamorphic core complex. 30 km to the west. The Alvord Mountain - Cronese Hills region was initially transported as a single hangingwall block on the E-dipping detachment. Initial lacustrine sedimentation reflects the development of a flexural or sag basin in the hangingwall. Subsequent westward progradation of alluvial fans out of the Cronese Hills is believed to record the propagation of a NW-striking, SW-dipping normal fault antithetic to the low-angle E-dipping detachment fault.     

Sedimentation,tectonism and volcanism relationships in two Andean basins of southern Peru

The intermontane basins of the Central Andes, formed from the first episode of the andine tectonic (peruvian phase, Santonian), are characterized by a clastic continental sedimentation, settled in a compressive tectonic context and containing volcanic intercalations. The two basins presented in this paper, have distinct ages and a different geodynamic context, each:

1. The Cuzco-Sicuam Basin, Maestrichtian-Paleocene in age, is a back-arc basin. A coarse grained red bed sedimentation appeared at the same time as the synsedimentary tectonic and volcanic activity increased in the source area.
2. The Moquegua Basin, Oligocene in age, is a fore-arc basin. After a compressive phase, the northeastern border of the basin shows high mobility, characterized by superposed alluvial fans. Within the basin, the coarse grained sediments are associated with volcanic tuffs.

In the two basins, the tectonism, the volcanism and the coarse grained sedimentation occured simultaneously. The coarse grained sedimentation does not appear to be linked with climatic changes, but with the increasing mobility of the source area. The relationship between tectonic regime and volcanic activity in the basin and in the source area is considered.     

Morphotectonic analysis of alluvial fan dynamics: comparative study in spatio-temporal scale of Himalayan foothill,India

Alluvial fan is a depositional fluvial landform that is characterised by sediment flow and hydrological processes and is also controlled by tectonic activity. These extraordinary features have always attracted researchers since the past as they preserve the past records, but now, this study is focused on the formation meso-level fans with its spatio-temporal dynamic nature. These tributaries have formed secondary alluvial fans at their debouching points. The dynamics of the fans are controlled by the hydrological responses and tectonic base and also by the sedimentation processes. The origin of these tributaries and their respective fans are related to the last stage of Himalayan uplift. This is the region of Himalayan foreland basin which contains the main frontal thrust and makes the region tectonically very active. The region is drained by many large rivers and their numerous tributaries. The active tectonism, the configuration of the basin and also the deposition of the sediments carried by these rivers have formed alluvial fans where the channel debouches into the widened valley. In the present study, the meso-level alluvial fans formed by River Gish and the Rivers Neora and Murti have been studied. Both these fans are present in the piedmont region of the Himalayas, but they deliver different characteristics, and the nature of their deposition is also different. This is mainly because of the influence of the minor faults in the region which control the channel pattern and also have a great influence in the sediment delivery to the downstream section of the channels. Thus, in order to understand the influence of tectonics in the dynamics of these fans, some morphotectonic parameters have been taken into consideration. These include mountain front sinuosity index, valley floor width-to-depth ratio, and tectonic tilt. The calculated hypsometric integral also depicts that the two fans are at different stages of development.     

Coarse-grained submarine fan and slope apron deposits in a Cretaceous back-arc basin, Antarctica

The Cretaceous of west James Ross Island, Antarctica represents the proximal fill of a late Mesozoic back-arc basin that was probably initiated by oblique extension during the early development of the Weddell Sea. The succession records sedimentation in two contrasting depositional systems: a laterally persistent slope apron flanking the faulted basin margin interrupted both spatially and temporally by coarse-grained submarine fans. Slope apron deposits are dominated by thinly interbedded turbiditic sandstones and mudstones (mudstone association), interspersed with non-channelized chaotic boulder beds, intraformational slump sheets and isolated exotic blocks representing a spectrum of mass-flow processes from debris flow to submarine gliding. Localized sand-rich sequences (sandstone-breccia association) represent sandy debris lobes at the mouths of active slope chutes. The submarine fan sediments (conglomerate association) are typified by coarse conglomerates and pebbly sandstones, interpreted as the deposits of high-density turbidity currents and non-cohesive debris flows. Three assemblages are recognized and are suggested to represent components of the inner channelled zone of coarse-grained submarine fans, from major fan channels through ephemeral, marginal channels or terraces to levee or interchannel environments. The occurrence of both slope apron and submarine fan depositional systems during the Early and Mid-Cretaceous is attributed to localized input of coarse arc-derived sediment along a tectonically active basin margin. Periods of extensive fan development were probably linked to regional tectonic uplift and rejuvenation of the arc source region; cyclicity within individual fan sequences is attributed to migration or switching of fan channels or canyons. Slope apron sedimentation was controlled largely by intrabasinal tectonics. Local unconformities and packets of amalgamated slide sheets and debris flow deposits probably reflect episodic movement on basin margin faults. Differential subsidence across the basin margin anchored the basin slope for at least 20 Myr and precluded basinward progradation of shallow marine environments.