碎屑岩沉积构型研究若干进展

近10年来,国内外的沉积构型研究从之前的以精细表征为主扩展到成因机制分析。文中以同生逆断层控制的冲积扇、可容空间影响下的曲流河点坝、浅水缓坡背景下的三角洲指状砂坝以及大陆斜坡微盆地背景下的重力流沉积等为例介绍相关研究进展。(1)挤压盆地边缘复杂的同生逆断裂构造活动控制了冲积扇的构型要素类型、叠置样式、分布演化及定量规模,表现出有别于构造稳定条件下的冲积扇构型模式;(2)曲流河在可容空间较小的情况下可发育顺流迁移型点坝,表现出特殊的微相类型、分布样式及旋回特征,而随着A/S值的不断增大,曲流河点坝可由鳞片状逐步演变为条带状,最后变为点状;(3)浅水三角洲中可发育类似于河控较深水三角洲中的指状砂坝沉积,其平面形态、微相组合样式、定量规模等特征受气候、沉积物供给、沉积水体等多因素的影响;(4)大陆斜坡微盆地内部可发育重力流水道、朵叶体、块状搬运体等多种构型要素类型,不同构型要素的空间分布样式、定量规模及构型演化模式受复杂地形地貌及构造活动的影响较为明显。综合原型模型分析、沉积物理模拟及数值模拟开展系统的定量化研究,建立定量的、可预测的碎屑岩沉积构型模式,是今后碎屑岩沉积构型研究的发展趋势。     

鄂尔多斯盆地上三叠统延长组三角洲沉积及演化

鄂尔多斯盆地上三叠统延长组广泛发育曲流河三角洲沉积,其总体沉积特征为：沉积体系及相带发育完整;成分成熟度及结构成熟度较高;发育各种沉积构造、动植物化石及生物遗迹构造。曲流河三角洲平原的分流河道具有复杂分支与决口历史,因此常呈交织状,受分流河道冲蚀作用的影响,河口坝不发育。曲流河三角洲主要形成于湖盆坳陷回返期。通过对岩相组合、骨架砂体的几何形态及盆地古地理背景的综合分析,认为延长组的环境演化反映了浅水台地型三角洲逐渐转变为陆上平原的过程。曲流河三角洲可形成良好的储层,是油气勘探的有利相带。     

黑龙江北部孙吴——嘉荫盆地沉积相类型及其演化

通过对孙吴-嘉荫盆地淘淇河组、永安村组、太平林场组、鱼亮子组、乌云组和孙吴组露头剖面详细的沉积学研究,查明该盆地从淘淇河组到孙吴组发育的沉积相类型有冲积扇、辫状河、曲流河、扇三角洲、辫状河三角洲、曲流河三角洲、湖底扇和湖泊。冲积扇及扇三角洲主要发育于淘淇河组和孙吴组;辫状河及辫状河三角洲主要发育于鱼亮子组和乌云组;曲流河及曲流河三角洲主要发育于永安村组和太平林场组,各组均有湖泊相沉积发育。孙吴-嘉荫盆地从淘淇河组到乌云组,具有冲积扇-扇三角洲-湖泊→曲流河-曲流河三角洲-湖泊→辫状河-辫状河三角洲-湖泊→冲积扇-扇三角洲-湖泊的沉积演化规律,反映晚白垩-古新世构造活动性减弱,中-上新世孙吴组沉积时重又趋于活动。     

鄂尔多斯盆地及周缘地区下二叠统沉积特征

通过大量的野外剖面观察和盆地内钻井岩心的详细描述,综合测井资料,从岩石类型、结构、沉积构造、古生物化石及测井曲线响应特征等方面对鄂尔多斯盆地及周缘地区下二叠统太原组和山西组沉积相特征进行了全面分析研究。结果表明,太原组主要发育陆棚、海岸、冲积扇和三角洲等沉积相,海岸沉积相包括障壁岛、潟湖和潮坪沉积,三角洲沉积相可划分为三角洲平原、三角洲前缘和前三角洲沉积。山西组主要发育冲积扇、河流、曲流河三角洲、湖泊和海岸沉积相,其中河流沉积相包括辫状河和曲流河沉积,曲流河三角洲沉积相可划分为曲流河三角洲平原、曲流河三角洲前缘和前三角洲沉积,而湖泊沉积相以浅湖沉积为主,海岸沉积主要为潟湖沉积。太原期,海相沉积占主导,主要分布于银川-榆林北部一线以南广大地区,并且从东西两侧至中部地区由浅海陆棚沉积和滨浅海过渡为潟湖沉积和潮坪沉积,其间发育障壁岛。盆地西北缘发育冲积扇和扇三角洲沉积,北部广大地区以三角洲沉积为主,自北向南依次为三角洲平原和三角洲前缘沉积。山西期,海水从盆地东南部退却,整体演变为海陆过渡相沉积,盆地北部乌达-杭锦旗-鄂尔多斯一线发育冲积扇沉积,向南至靖边一带依次发育辫状河和曲流河沉积,靖边以南至延安以北地区以三角洲平原沉积为主,向南至同心-庆阳一线发育三角洲前缘沉积,盆地南部彭阳-泾阳地区主要为浅湖沉积,再向南发育物源来自南部的三角洲沉积,在东南部武乡-义马一带为潟湖沉积。     

河控浅水三角洲沉积构型

自浅水三角洲的概念提出以来,已经历了60多年的研究历史。虽然在诸多方面取得了较大的研究进展,但在浅水三角洲的概念内涵、砂体成因类型及沉积构型样式等方面仍存在一定的分歧。本文探讨了浅水三角洲概念的内涵,并总结和分析了其沉积构型特征和样式。根据浪基面和河-盆水深比(初始河道深度与河口盆地水体深度比值),可将三角洲分为极浅水三角洲、较浅水三角洲和较深水三角洲。典型的浅水三角洲为极浅水三角洲,发育于河-盆水深比值大于或等于1的浅水水体,分流河道可下切至下伏的前三角洲沉积。根据三角洲前缘分流河道与河口坝的组合样式,将河控浅水三角洲的端元类型分为分流砂坝型和指状砂坝型。分流砂坝型三角洲为河道入海(湖)后形成的多级分叉的河口坝与分流河道系统,平面上呈扇状,河—坝组合呈现“河在坝间”的样式,而指状砂坝型三角洲为指状砂坝与分流间湾相间分布的系统,平面上呈枝状,河—坝组合呈现“河在坝内”的样式。     

鄂尔多斯盆地及周缘地区下二叠统沉积特征*

通过大量的野外剖面观察和盆地内钻井岩心的详细描述,综合测井资料,从岩石类型、结构、沉积构造、古生物化石及测井曲线响应特征等方面对鄂尔多斯盆地及周缘地区下二叠统太原组和山西组沉积相特征进行了全面分析研究。结果表明,太原组主要发育陆棚、海岸、冲积扇和三角洲等沉积相,海岸沉积相包括障壁岛、潟湖和潮坪沉积,三角洲沉积相可划分为三角洲平原、三角洲前缘和前三角洲沉积。山西组主要发育冲积扇、河流、曲流河三角洲、湖泊和海岸沉积相,其中河流沉积相包括辫状河和曲流河沉积,曲流河三角洲沉积相可划分为曲流河三角洲平原、曲流河三角洲前缘和前三角洲沉积,而湖泊沉积相以浅湖沉积为主,海岸沉积主要为潟湖沉积。太原期,海相沉积占主导,主要分布于银川—榆林北部一线以南广大地区,并且从东西两侧至中部地区由浅海陆棚沉积和滨浅海过渡为潟湖沉积和潮坪沉积,其间发育障壁岛。盆地西北缘发育冲积扇和扇三角洲沉积,北部广大地区以三角洲沉积为主,自北向南依次为三角洲平原和三角洲前缘沉积。山西期,海水从盆地东南部退却,整体演变为海陆过渡相沉积,盆地北部乌达—杭锦旗—鄂尔多斯一线发育冲积扇沉积,向南至靖边一带依次发育辫状河和曲流河沉积,靖边以南至延安以北地区以三角洲平原沉积为主,向南至同心—庆阳一线发育三角洲前缘沉积,盆地南部彭阳—泾阳地区主要为浅湖沉积,再向南发育物源来自南部的三角洲沉积,在东南部武乡—义马一带为潟湖沉积。     

鄂尔多斯盆地子洲地区上三叠统延长组长1段沉积相和浅水三角洲河口坝发育规律

鄂尔多斯盆地上三叠统延长组沉积时期为大型坳陷湖盆,具有坡缓、水浅和构造相对稳定的特点,有利于浅水三角洲的形成。通过野外露头观察发现,鄂尔多斯盆地子洲地区大理河剖面三叠系延长组长1段发育浅水三角洲沉积。其中,三角洲前缘沉积中发育河口坝,河口坝内部具明显3期下细上粗反韵律,而且每期河口坝内部具泥质夹层厚度具有向上增加的趋势,指示可容纳空间向上增大。总结了浅水三角洲河口坝发育规律,认为河口坝的形成由可容纳空间与沉积物供给共同决定:(1)在可容纳空间变大的情况下,河口坝的形成由沉积物供应量决定,若有一定量的沉积物供给,则形成具湖侵退积序列的河口坝沉积;(2)在可容纳空间变小的情况下,河口坝的形成由剩余可容空间决定,若有剩余可容纳空间,则形成具湖退进积序列的河口坝沉积;(3)当没有可容纳空间时,河口坝不发育。鄂尔多斯盆地子洲地区延长组长1段河口坝的形成属于可容纳空间变大且有沉积物供给的情况。     

川西前陆盆地上侏罗统蓬莱镇组沉积特征

经岩性、岩石组合、沉积韵律等综合分析认为川西前陆盆地上侏罗统蓬莱镇组主要为冲积扇、曲流河、三角洲和湖泊沉积.其中冲积扇发育扇中和扇端两个亚相,扇根不发育;曲流河发育河道和洪泛平原两个亚相;三角洲发育三角洲平原、三角洲前缘以及前三角洲三个亚相;而湖泊相主要发育滨浅湖和半深湖沉积,深湖在研究区内不发育.在龙门山前缘的盆地边缘发育冲积扇相带.大小不同的冲积扇体连接或叠覆构成冲积扇群.并依次出现扇中、扇端的微相分带.同时砾石由粗变细,逐渐过渡到河流的砂岩相;由河流往东则进入湖泊沉积区,并在河流入湖处形成三角洲相沉积.根据冲积扇-曲流河-三角洲一湖泊的时空展布规律,建立了本区蓬莱镇组的沉积模式.     

冯地坑-洪德地区延长组长6沉积相特征研究

结合整个鄂尔多斯盆地的构造及沉积演化特征,对鄂尔多斯盆地冯地坑-洪德地区上三叠统延长组长6油层组沉积相类型和特征进行分析,建立长6油层组沉积模式,对其岩石类型、砂岩的岩石结构、沉积构造、古生物及测井相等相标志进行详细研究。研究表明,冯地坑-洪德地区长6沉积时期发育着一套曲流河三角洲沉积体系,曲流河三角洲发育三角洲前缘和三角洲平原2种亚相;三角洲平原沉积砂体以细砂和粉砂为主,最粗可达到中砂级,其中可见到分支河道微相,陆上天然堤微相及沼泽微相。三角洲前缘砂体以细砂-粉砂为主,发育有水下分支河道、水下天然堤、支流间湾、河口砂坝和前缘席状砂5种微相。     

小型箕状断陷盆地构造—沉积模式与油气成藏——以苏北管镇次凹为例

管镇次凹位于苏北盆地洪泽凹陷中部,是一个典型的箕状断陷,由南向北可划分为4个构造带:陡岸带、深凹带、断裂构造带和缓坡带.识别出5种沉积体系,即曲流河三角洲沉积体系、滨浅湖沉积体系、半深湖-深湖沉积体系、冲积扇(扇三角洲)沉积体系、水下扇沉积体系;在缓坡带发育三角洲沉积体系,深凹带发育湖相沉积体系,陡坡带发育冲积扇(扇三角洲)-水下扇沉积体系.研究区主要目的层存在2种沉积体系组合:水下扇-半深湖(深湖)-曲流河三角洲沉积体系组合和冲积扇(扇三角洲)-滨浅湖-小型三角洲沉积体系组合;阜宁组沉积时期,第1种沉积体系组合模式下更有利于烃源岩的发育;戴南组沉积时期,第2种沉积体系组合模式下容易形成一定规模的低水位扇(扇三角洲).因此在这2种沉积体系组合的有机配置下,极有利于岩性油气藏的形成.     

准噶尔盆地玛湖凹陷夏子街扇区三叠系百口泉组沉积演化特征*

玛湖凹陷是准噶尔盆地最具规模的油气聚集带与勘探区,发育以砾岩为主、具有较强非均质性的粗粒沉积复杂地层。对粗粒沉积体的精细刻画有助于研究沉积体内部的非均质性特征。应用储层构型分析法,结合研究区岩心、测井、录井资料,对玛湖凹陷夏子街扇区三叠系百口泉组沉积体内部9个级次构型要素的几何形态、大小、方向以及相互之间的叠置关系进行了表征,识别出12种岩石相类型以及10种由岩石相组合而成的沉积微相类型。通过分析沉积微相在垂向、平面上的不同组合特征,扇体的类型受沉积环境影响发生变化,逐渐由冲积扇、河流扇转换为扇三角洲,整体反映了湖平面上升或沉积物供给量逐渐减小的沉积背景。分析夏子街扇区各期次的扇体特征,包括长轴、短轴距离、长轴短轴比、扇根与扇缘厚度变化、扇体坡度变化、扇体最大粒径变化等,认为扇体顺物源方向有以下变化趋势: 沉积物粒径大小随河道搬运逐渐减小,减小的幅度受扇体坡度影响,坡度越陡沉积物粒径减小的越快;河道数量减少,流量降低;河道沉积物在横向和纵向上的连通性逐渐降低;砂岩、砾岩厚度逐渐减小,泥岩厚度逐渐增加,湖相沉积变得较为发育。总结玛湖凹陷百口泉组的各期次扇体共可归纳出6种扇体模式: 冲积扇、冲积—河流扇、河流—末梢扇、河流扇—扇三角洲、扇三角洲、大型河流扇。     

Large‐scale architecture in non‐marine basins: the response to the interplay between accommodation space and sediment supply

Sedimentary successions of non‐marine basins can be considered in terms of accommodation space and sedimentary supply changes. Changes in accommodation space controlling the large‐scale architecture of non‐marine basins are different in areas with high and low sedimentary supplies. Uplift of intrabasinal monoclines and anticlines reduced the available accommodation space, resulting in changes in both the geometry of the depositional sequences and the large‐scale architecture of fluvial, mudflat and shallow carbonate lacustrine deposits. Main drainage fluvial systems record areas with a high sedimentary supply, while mudflats and shallow fluctuating lakes represent areas that received less sediment. Two end members in the large‐scale architecture of main drainage fluvial system in the Almazán Basin (Spain) are: (i) ribbon‐shaped channel fills with low interconnectivity which pass laterally into mudflats dominated by mudstones and evaporites and into palustrine and shallow carbonate lacustrine deposits (mainly in the A2 depositional sequence); and (ii) sheet‐like channel fills with high interconnectivity laterally correlated with stacked calcretes in the marginal mudflats (in the upper part of A3). Ribbon‐shaped channel fills formed in areas of high accommodation space and sheet‐like channel fills formed in areas of reduced accommodation space.     

鄂尔多斯盆地镇-泾地区中侏罗统延安组沉积体系及聚煤特征

在前人研究的基础上,结合大量新的钻井、测井资料,以鄂尔多斯盆地镇原-泾川地区中侏罗统延安组为例,运用沉积学的方法详细阐述了研究区目的层位的沉积体系,以及重点沉积微相的发育特征。延安组自下而上由河流沉积体系逐渐过渡为三角洲沉积体系。沉积微相主要发育有河流体系的心滩、边滩、河漫滩和岸后沼泽,以及三角洲体系的分流河道、洪泛平原和平原沼泽等。另对研究区延安组的聚煤特征给予了分析,并从构造、环境、气候及古地形等方面讨论了该区的成煤控制因素。     

Progressive changes in sedimentary facies and stratal patterns along the strike-slip margin,northeastern Jinan Basin (Cretaceous), southwest Korea: implications for differential subsidence

In strike-slip basins, proximal stratal patterns are a function of displacement on basin-bounding faults. In order to better understand factors that control changes in sedimentary facies and stratal patterns of the northeastern part of the Jinan Basin (Cretaceous), a strike-slip basin, we made a detailed analysis of sedimentary facies, depositional architecture and paleoflows. The sedimentary successions can be grouped into five facies associations representing five depositional environments: (1) facies association FA I (alluvial fan); (2) FA II (small-scale Gilbert-type delta); (3) FA III (large-scale, steep delta slope); (4) FA IV (base of large-scale, steep delta slope and prodelta); and (5) FA V (lacustrine plain). The successions are divided into two distinct sedimentary fills on the basis of facies associations, depositional architecture and paleocurrents: (1) marginal fill and (2) longitudinal fill. The marginal fill (ca. 3.2 km thick) is present along the strike-slip basin-bounding fault. The lower part of the marginal fill (ca. 1.3 km thick) consists of alluvial-fan deposits (FA I) along the bounding fault which are transitional northward to small-scale Gilbert-type delta (FA II) and lacustrine plain (FA V) deposits. The upper part of the marginal fill (ca. 1.9 km thick) contains large-scale, steep delta slope (FA III) and base of delta slope/prodelta (FA IV) deposits accompanied with a northward change in facies associations. In the marginal fill, the successive alluvial fan, small-scale Gilbert-type delta and large-scale, steep delta/prodelta deposits are overlapped (shingled) northeastward. The longitudinal fill (ca. 2 km thick) is characterized by eastward overlapped stacks of large-scale, steep delta slope (FA III) and base of delta slope/prodelta (FA IV) deposits with a westward progradation. The longitudinal fill was overstepped by the marginal fill. The northeastward shingled geometry of the marginal fill was most likely caused by sinistral strike-slip displacements on the basin-bounding fault. The slightly oblique (northward) progradation of the marginal fill was due to the northward basin-floor tilting. In the marginal fill, the progressive changes in facies and depositional architecture from the lower alluvial fan/small-scale Gilbert-type delta to the upper large-scale, steep delta/prodelta are suggestive of increase in basin subsidence along the strike-slip basin margin that was closely related to the variation in displacement on the basin-bounding fault. The sinistral strike-slip movements on the bounding fault also caused the eastward overlapping of the longitudinal fill.     

塔里木盆地库车坳陷与塔西南坳陷早白垩世沉积相与油气勘探

塔里木盆地库车坳陷与塔西南坳陷的白垩系沉积厚度大,岩石类型多,既有碎屑岩,又有蒸发岩和碳酸盐岩。沉积相类型丰富,包括海相、海陆交互相和陆相,并以陆相碎屑岩沉积为主。库车坳陷与塔西南坳陷在早白垩世虽为分隔性的沉积盆地,但其陆相碎屑沉积具有几乎相同的特征：均以冲积沉积体系发育为主,相带分布和储层发育具有明显的相似性。对应山前断陷盆地的不对称性,冲积扇-扇三角洲、辫状河三角洲沉积体系发育在靠近山前的陡坡一侧,正常河流三角洲沉积体系发育在湖盆缓坡一侧。冲积扇-扇三角洲沉积体系由冲积扇、扇三角洲平原、扇三角洲前缘等构成,辫状河三角洲沉积体系由辫状河三角洲平原、辫状河三角洲前缘等构成。储层主要发育于扇三角洲或辫状河三角洲的辫状河道、水下分流河道及分流河口砂坝中,在库车坳陷和塔西南坳陷都形成了优质的储集岩。砂体厚度大,分布广,储集条件好。冲积沉积体系的普遍发育预示了白垩系储集岩在盆地内的分布可能是十分广泛的。近年在喀什凹陷、英吉苏凹陷相继取得的勘探成果大大拓宽了其勘探领域,白垩系正逐渐成为盆地内主要的勘探目的层之一,展现了良好的勘探前景。     

An allostratigraphic approach to a non-marine basin: the north-western part of Cretaceous Kyongsang Basin, SE Korea

The north-western part of the Cretaceous Kyongsang Basin, south-east Korea, comprises alluvial deposits of conglomerate, gravelly sandstone, sandstone and mudstone which can be grouped into four allomembers bounded by stratigraphic discontinuities. The discontinuities trend NW–SE and are marked by distinct facies transitions, abrupt emplacement of conglomerate and thin but persistent mudstone beds. Sedimentary facies and architectural analyses reveal that each allomember formed a depositional system of fluvial channel networks draining toward the south-east with alluvial fans on the northern margin. Each allomember can be characterized by distinctive architecture of channel-fills, clast composition of conglomerate and sandstone/mudstone ratio. Successive units show an eastward shift in the locus of deposition, suggesting basinward relocations of alluvial systems. Such variations with time and space are interpreted to reflect changes in accommodation space and sediment supply during basin evolution, probably caused by fault movements. This study shows that detailed mapping, combined with architectural analysis, and the establishment of alluvial allostratigraphy can help assess changes in alluvial systems and structural development of the basin.     

滇西洱源县军马场下三叠统青天堡组冲积扇-三角洲沉积体系研究

滇西洱源县位于扬子地块西南缘丽江拗陷盆地南侧。在详细野外剖面测量和室内分析的基础上,对研究区下三叠统青天堡组地层的宏观特征（颜色、原生沉积构造）、物质组分、岩石结构及古生物特征等进行了系统研究,划分出冲积扇、河流、三角洲3类沉积相,并进一步划分出河道充填、三角洲前缘和前三角洲3个沉积亚相及辨状河道、洪泛平原、水下分流河道、分流河道间、河口砂坝、席状砂6个沉积微相。研究表明,军马场下三叠统青天堡组垂向上表现为冲积扇—河流—三角洲的退积型沉积特征,表明在早三叠世青天堡时期盐源-丽江盆地发生了大规模海侵,盆地水体加深,军马场地区经历了由陆相到海相的沉积演化序列。     

Alluvial architecture of the Holocene Rhine–Meuse delta (the Netherlands)

Ancient fluvial successions often act as hydrocarbon reservoirs. Sub‐surface data on the alluvial architecture of fluvial successions are often incomplete and modelling is performed to reconstruct the stratigraphy. However, all alluvial architecture models suffer from the scarcity of field data to test and calibrate them. The purposes of this study were to quantify the alluvial architecture of the Holocene Rhine–Meuse delta (the Netherlands) and to determine spatio‐temporal trends in the architecture. Five north–south orientated cross‐sections, perpendicular to the general flow direction, were compiled for the fluvial‐dominated part of the delta. These sections were used to calculate the width/thickness ratios of fluvial sandbodies (SBW/SBT) and the proportions of channel‐belt deposits (CDP), clastic overbank deposits (ODP) and organic material (OP) in the succession. Furthermore, the connectedness ratio (CR) between channel belts was calculated for each cross‐section. Distinct spatial and temporal trends in the alluvial architecture were found. SBW/SBT ratios decrease by a factor of ca 4 in a downstream direction. CDP decreases from ca 0·7 (upstream) to ca 0·3 (downstream). OP increases from less than 0·05 in the upstream part of the delta to more than 0·25 in the downstream delta. ODP is approximately constant (0·4). CR is ca 0·25 upstream, which is approximately two times larger than in the downstream part of the delta. Furthermore, CDP in the downstream Rhine–Meuse delta increases after 3000 cal yr BP. These trends are attributed to variations in available accommodation space, floodplain geometry and channel‐belt size. For instance, channel belts tend to narrow in a downstream direction, which reduces SBW/SBT, CDP and CR. Tectonics cause local deviations in the general architectural trends. In addition, the positive correlation between avulsion frequency and the ratio of local to regional aggradation rate probably influenced alluvial architecture in the Rhine–Meuse delta. The Rhine–Meuse data set can be a great resource when developing more sophisticated models for alluvial architecture simulation, which eventually could lead to better characterizations of hydrocarbon reservoirs. To aid such usage of the Rhine–Meuse data set, constraints for relevant parameters are provided at the end of the paper.     

Middle Miocene to Pleistocene sedimentary record of rift evolution in the southern Albert Rift (Uganda)

This study presents an almost complete Middle Miocene to Pleistocene sequence of synrift sediments in the western branch of the East African Rift. The studied succession is exposed in several patches on an eastward tilted block between the northern tip of the Rwenzori Block and the eastern shoulder of the Albert Rift. In this position, it reaches a maximum thickness of 600 m of which 350 m have been logged systematically by analysing lithofacies and sediment architecture. Stratigraphic subdivision of the succession relies on published biostratigraphic data of endemic mollusc associations and their correlation across East Africa. The synrift sediments encountered are siliciclastics ranging from clay to coarse gravel with gypsum and ferrugineous interlayers or impregnations. Lithofacies and architectural analysis indicate alluvial plain, delta plain, nearshore, delta front, or lacustrine depositional environments. Based on the vertical stacking pattern, prograding and retrograding trends of the depositional environments, and climatic indicators (e.g. conservation of feldspar, gypsum, and/or iron hydroxide precipitation), four evolutionary phases can be distinguished: (i) a first phase between ca. 14.5 and 10.0 Ma is characterised by bedload-dominated fluvial environment with massive sandy to gravelly bedforms, feldspar-rich sands, rare iron impregnations and relatively low accommodation space. This phase is interpreted as pre- and early synrift sedimentation under a semiarid climate. (ii) From ca. 10.0 to 4.5 Ma predominantly fine-grained siliciclastics were deposited in a distal fluvial plain to lacustrine setting characterised by limited accommodation space. Fluctuation of thin beds, dominance of clay and frequent iron impregnations point to a more humid climate with seasonality and weak tectonic activity. (iii) During the third phase between 4.5 and 2.0 Ma delta plain and nearshore deposits with frequent ferrugineous impregnations and rich mollusc associations occurred, indicating a humid period with lake-level highstands and accelerated subsidence. (iv) During the final sedimentary interval between 2.0 and 1.5 Ma gravel units reoccurred with less iron- but more carbonate and gypsum impregnations, and arkosic sandstones. This phase recorded a general aridisation trend most probably caused by the upcoming rain barrier of the Rwenzori Mountains together with accelerated rift-flank uplift and strong subsidence of the rift floor. The results of this study are of particular importance for delineating key controls on sedimentation in the Albert Rift.