江苏如东潮滩微地貌及现代沉积速率

在江苏如东洋口港东侧长沙镇外宽10余千米的粉砂质潮滩上进行潮滩微地貌调查,在低潮滩设置 3个沉降板,在中、低潮滩采集4个柱状样（长度92~151 cm）,并对其进行垂向上的粒度和微相分析及210 Pb 测量。希望通过上述调查,揭示研究区近几十年来由于强烈的人类活动导致的潮滩冲淤调整状态。调查结果表 明,低潮滩尤其是低潮滩下部是微地貌变化最活跃的场所,表现为潮滩表面凹凸不平、多冲蚀洼槽,沉降板试 验结果显示低潮滩约２个月的沉积量向水边线方向显著减小;中潮滩表面平坦,微地貌相对比较稳定。柱状样 研究结果显示,低潮滩早期为向上变细的进积层序,但近期沉积物粗化,呈现退积层序,且该现象在低潮滩下 部尤其明显;中潮滩柱状样显示向上细化层序,反映稳定持续的加积和进积。柱状样的210 Pb测试结果表明,中 潮滩中部（米草滩中部） 沉积速率为4.40cm/a,中潮滩下部（米草滩前缘） 为1.85cm/a,低潮滩中部为1.54 cm/a,低潮滩下部无法获得沉积速率。该沉积速率结果还显示低潮滩退积层序的开始时间和研究区米草的引种 时间基本吻合。上述研究结果反映近30a来在人类活动尤其是米草的作用下,研究区中潮滩稳定淤积,但低潮 滩却因缺乏充足泥沙而加剧侵蚀。     

渤海莱州湾凹陷南部古近系混合沉积特征及发育模式*

渤海莱州湾凹陷南部古近系沙三下亚段广泛发育陆源碎屑与碳酸盐混合沉积。通过对井壁取心、测井及综合化验资料的分析,对研究区混合沉积特征、发育模式及控制因素进行分析。结果表明: 研究区既发育同一岩层内的混合沉积,又发育碳酸盐岩与陆源碎屑的互层混合沉积。混合沉积形成于两大物源注入背景下的湖泊滨岸环境,可进一步分为泥坪、砂质滩坝、浅滩和半深湖等混合沉积亚相,主要体现为波浪和湖流作用的双重影响。沙三下亚段整体呈现出水退式发育的特点,主要发育湖侵域和高位域,湖侵域主要发育半深湖混合沉积和浅滩混合沉积,高位域主要发育砂质滩坝混合沉积。混合沉积物受古地貌、古气候、古物源和湖平面变化的控制,优势储集亚相为砂质滩坝混合沉积亚相和浅滩混合沉积亚相。该研究成果不仅为莱州湾凹陷南部古近系优质动用储量研究提供了指导,而且为下一步勘探指明了方向。     

渤海莱州湾凹陷南部古近系混合沉积特征及发育模式

渤海莱州湾凹陷南部古近系沙三下亚段广泛发育陆源碎屑与碳酸盐混合沉积。通过对井壁取心、测井及综合化验资料的分析,对研究区混合沉积特征、发育模式及控制因素进行分析。结果表明:研究区既发育同一岩层内的混合沉积,又发育碳酸盐岩与陆源碎屑的互层混合沉积。混合沉积形成于两大物源注入背景下的湖泊滨岸环境,可进一步分为泥坪、砂质滩坝、浅滩和半深湖等混合沉积亚相,主要体现为波浪和湖流作用的双重影响。沙三下亚段整体呈现出水退式发育的特点,主要发育湖侵域和高位域,湖侵域主要发育半深湖混合沉积和浅滩混合沉积,高位域主要发育砂质滩坝混合沉积。混合沉积物受古地貌、古气候、古物源和湖平面变化的控制,优势储集亚相为砂质滩坝混合沉积亚相和浅滩混合沉积亚相。该研究成果不仅为莱州湾凹陷南部古近系优质动用储量研究提供了指导,而且为下一步勘探指明了方向。     

辽河盆地冷家油田沙河街组三段储层岩相古地理

辽河盆地在沙河街组三段早期水体较深,主要形成扇三角洲及盆底扇;沙三晚期水体较浅,发育湖泊砂体.依据沉积相分布规律,沙三早、中、晚3个时期可进一步分别划分出湖泊扩张和收缩阶段.盆地西部凹陷的冷家油田为东陡西缓的箕状洼陷.研究区内沙三段的古地理格局是决定相分布的关键因素,河流和湖泊能量相对强弱决定扇体沉积的规模.受相对湖平面变化的影响,纵向扇三角洲主要形成于湖泊扩张时期,并且有相带窄、过渡快、以粗碎屑沉积为主的特点.扇体沉积中主要发育前缘分流河道充填沉积,但位于河口前缘或侧缘的滩坝及前三角洲中的盆底扇局部也较发育.     

薄互层滩坝砂体的定量预测——以东营凹陷古近系沙四上亚段（Es上4）为例

薄互层砂体的定量预测是沉积学研究的难点之一.滩坝是滨浅湖区典型的薄互层砂体,其预测和勘探难度大.通过对东营凹陷古近系沙四上亚段滩坝的沉积特征、平面分布及控制因素等研究,认为滩坝的形成与分布主要受不同波浪带控制,即冲浪回流带控制沿岸滩坝(包括砾质滩坝)、碎浪带控制近岸滩坝、破浪带控制远岸滩坝.在建立了东营凹陷风动力砂体分布模型基础上,通过分析不同波浪带波浪参数变化,建立了破浪带和碎浪带砂体定量预测模型,对东营凹陷博兴洼陷南部缓坡带近岸坝、远岸坝单砂体的厚度及宽度进行了定量预测计算,并对砂体的延伸长度通过微地貌恢复+风动力技术结合进行了计算.然后通过统计单个坝砂体厚度和连井对比对预测砂体厚度、宽度及长度进行了检验验证,二者吻合较好,证明预测方法切实可行.最后认为,6～8级风力最有利于滩坝的形成.该方法为薄互层砂体的定量预测研究提供了一种新的分析思路,对隐蔽油藏勘探有指导作用,但该方法不适用于明显受物源控制薄砂体的预测.     

长江下游落成洲河段洲滩联动关系与航道浅滩碍航机制

航道浅滩演变与边心滩形态调整具有强关联性,叠加河道冲淤不均衡性、上游河段冲刷供沙等综合影响,使得航道浅滩碍航机制更趋复杂。本研究以长江感潮段内落成洲河段为对象,通过1959—2021年洲滩形态、河床冲淤特征、水动力环境与浅滩碍航特性等分析,明确边心滩—浅滩演变联动关系、上游河床冲刷供沙及对浅滩演变的影响机制。研究结果表明：(1) 1981年以来落成洲河段所在的扬中河段由淤积转为1991年以来的持续冲刷,1981—2021年枯水河槽冲刷量为3.97亿m³,占洪水河槽冲刷量的95.9%;(2)三峡工程运行前嘶马弯道崩退—落成洲左缘淤积—三益桥边滩未发育,即嘶马弯道崩退是洲滩联动演变的主要诱因;(3)三峡工程运行后至航道整治工程实施前的来沙量减少引起洲滩整体冲刷,落成洲冲刷为三益桥边滩提供了发育空间,逐渐淤涨的三益桥边滩与水沙条件共同使得落成洲冲刷和右汊冲刷发展,即三益桥边滩形态变化逐渐由被动淤涨转为洲滩联动演变的主因;(4) 1981—2010年三益桥边滩淤涨、落成洲洲头与左缘冲刷等决定着三益桥浅滩碍航程度,由于流域来沙量减少引起的河床冲刷使得碍航程度减弱,2011—...     

薄互层滩坝砂体的定量预测——以东营凹陷古近系沙四上亚段(Es_4~上)为例

薄互层砂体的定量预测是沉积学研究的难点之一。滩坝是滨浅湖区典型的薄互层砂体,其预测和勘探难度大。通过对东营凹陷古近系沙四上亚段滩坝的沉积特征、平面分布及控制因素等研究,认为滩坝的形成与分布主要受不同波浪带控制,即冲浪回流带控制沿岸滩坝(包括砾质滩坝)、碎浪带控制近岸滩坝、破浪带控制远岸滩坝。在建立了东营凹陷风动力砂体分布模型基础上,通过分析不同波浪带波浪参数变化,建立了破浪带和碎浪带砂体定量预测模型,对东营凹陷博兴洼陷南部缓坡带近岸坝、远岸坝单砂体的厚度及宽度进行了定量预测计算,并对砂体的延伸长度通过微地貌恢复+风动力技术结合进行了计算。然后通过统计单个坝砂体厚度和连井对比对预测砂体厚度、宽度及长度进行了检验验证,二者吻合较好,证明预测方法切实可行。最后认为,6～8级风力最有利于滩坝的形成。该方法为薄互层砂体的定量预测研究提供了一种新的分析思路,对隐蔽油藏勘探有指导作用,但该方法不适用于明显受物源控制薄砂体的预测。     

惠民凹陷中央隆起带沙四上亚段滩坝与风暴岩组合沉积

惠民凹陷沙四上亚段沉积时期,盆地边缘发育三角洲和扇三角洲沉积,受波浪和沿岸流的影响,在中央隆起带滨浅湖区形成了与岸线走向平行或斜交的滩坝砂体和风暴沉积。滩坝沉积成熟度较高,泥质含量少,岩性以中细砂岩和粉砂岩为主,也有少量砾石,砂岩中常见含双壳类化石、生物碎屑和炭屑。滩坝沉积可分为砂坝、砂滩和滩坝间微相,平面上该区滩坝砂体可分为近岸砂滩、近岸砂坝、坝间砂滩、远岸砂坝、远岸砂滩、水下隆起处砂坝和水下隆起处砂滩。此外,受风暴浪的影响,在浪基面和风暴浪基面之间的地带形成风暴沉积,主要由块状层理段、递变层理段、丘状交错层理段、平行层理段和块状泥岩段构成。该组合沉积体系的形成主要受古地形、物源性质、湖平面变化等方面的影响。     

扇三角洲沉积模式探讨:以准噶尔盆地玛北地区下三叠统百口泉组为例*

扇三角洲是一类非常重要的油气聚集场所,准确可靠的扇三角洲沉积模式,对储集层预测具有重要意义。准噶尔盆地玛北地区三叠系百口泉组发育一套扇三角洲沉积体系,虽然前人做了大量的研究,但在沉积模式方面仍存在一些争议。通过现代沉积考察、前人水槽模拟实验、研究区测井、岩心等资料综合分析发现: (1)玛北地区百口泉组扇三角洲平原发育3类微相,即辫状河道微相、砾质漫滩微相、水上朵前泥微相,同时可见泥石流沉积;玛北地区百口泉组扇三角洲前缘发育2种微相,即砾质浅滩微相、砂质浅滩微相,同时可见碎屑流沉积;(2)扇三角洲平原河道与河道间均为砂砾岩,河道砂砾岩的分选性明显好于河道间砂砾岩;(3)扇三角洲前缘不发育水下分流河道,扇三角洲前缘的砂砾岩主体是由扇三角洲平原片流入湖形成的,呈席状。     

波浪作用下砂质滩坝的沉积过程与沉积模式

受波浪及沿岸流影响,在滨岸地区形成的滩坝砂体是滨海（湖）带发育的主要砂体类型。目前国内外学者对滩坝沉积砂体的认识多来自于现代沉积和油气地质特征,对滩坝砂体的沉积机制和内部结构研究相对较弱。基于沉积水槽实验,采用规则波浪对沙质斜坡滨岸带进行模拟实验,观测波浪作用下滨岸带滩坝形成过程和波浪运动特征,记录波浪作用下滨岸带沙质滩坝在不同浪带平面时空演化规律。实验结果显示:波浪是改造湖岸原有沉积物的关键驱动力,波浪作用下沙质岸滩床面泥砂将发生输移运动,而滩坝是陆湖（海）泥沙在水动力驱动下搬运沉积的结果,水动力的强弱及水流结构引起泥沙在空间上的不均匀输运和分布,进而塑造不同的滩坝形态。与强波浪相关的高水位可以加速滩坝系统的形成并最终形成大规模的滩坝砂;相比之下,与较弱波浪相关的低水位只能略微改变初始沉积物形态。根据不同的沉积物特征可将实验中的滩坝系统分为三类:冲浪带和碎浪带滩坝系统近端部分的大规模厚层坝砂,破浪带和升浪带滩坝系统中部分布广泛的薄滩砂,以及位于滩坝系统中远端的弧形或平行排列的脊状、砂纹坝砂。建立了水槽实验模式下滩坝沉积模式,可用于指导油气勘探开发。     

Large-scale rhomboid bed forms and sedimentary structures associated with hurricane washover*

Hurricane washover fans from the Texas Gulf Coast exhibit large-scale rhomboid bed forms developed on washover deposits of fine sand with varying shell content. Washover processes inferred from aerial photographs, storm characteristics, and physical settings suggest that these bed forms are the product of (1) storm surge flooding or (2) high wind shear stress. Multiple bed forms, including large-scale rhombs, are responsible for sedimentary structures preserved in washover deposits. Proximal channels exhibit scour and fill sequences capped by mud drapes. Mid-channel fan deposits also have scour bases marked by shell lags which are overlain by horizontal laminations and foreset and backset laminae. Distal fan sediments are relatively shell free and are interbedded with tidal flat deposits characterized by bioturbated, alternating sand and mud laminae. Rhomboidal patterns can form on the free surface of water in response to five processes: (1) wave interference from two externally independent sources, (2) wave interference from refraction of a single set of wave fronts, (3) standing oblique waves caused by bed roughness elements, (4) standing oblique waves formed at channel boundaries and channel transitions, and (5) wind stress. Geologically, standing oblique waves from unidirectional nearly supercritical flow is probably the most important process in rhomboid bed form development.     

陆相盆地水下扇扇中亚相的微相细分--以东营凹陷史南地区沙二9梁家楼水下扇为例

通过对东营凹陷史南地区沙二9砂层组的小层精细对比和微相细分,可以将梁家楼水下扇扇中亚相进一步划分出辫状水道、辫状砂坝、“边滩”、侧缘砂坝、侧缘分支沟道、末端砂坝、冲溢扇、低阶地、高阶地等9个微相。不同微相之间的砂体粒度变化、平面发育位置都有明显的不同,尤其是其中的辫状砂坝、“边滩”、侧缘砂坝是在水下地形较平坦,坡度较小的情况下,由辫状沟道侧向迁移形成的。对水下扇扇中亚相的微相细分和重新厘定,不仅有助于对水下扇沉积过程的进一步了解,而且也将有助于油田对水下扇砂体剩余油的分布研究和开发方案的调整。      

黄河三角洲东营港潮坪上的贝壳沉积

黄河三角洲东营港的泥质潮坪上发育大量的贝壳沉积。贝壳的特殊形态使其很容易被水流搬运,波浪的簸选、泥坪表面的侵蚀坑穴和植物根、堤坝等障碍物对贝壳的拦阻、与地形地貌或涨潮流的水流形态有关的流速降低都可以形成贝壳堆积。潮坪表面贝壳的沉积形态包括:与涨潮流有关的坑穴状、密集窝状、陡坎状、垄沟状、席状、带状以及潮汐水道中的混合沉积等类型;与波浪作用有关的堤坝状、堤坝遮挡沉积等类型。涨潮流流速降低的方式不同,贝壳沉积形态也会相应有较大的差别。另外,潮坪表面的细微起伏、潮坪底质类型和粘结性都会对贝壳的沉积形态造成较大影响,其中尤其是以密集窝状和陡坎状为特征。从东营港贝壳的沉积特征上看,潮坪上贝壳沉积的水动力条件与常见的砂砾滩、鲕粒滩、内碎屑滩有很大的不同,不能将介壳的富集一概归为滩坝相沉积。     

Bedform and stratification characteristics of some modern small-scale washover sand bodies

Washover sand bodies commonly develop along microtidal coastlines in beach/barrier island or spit settings. Wave runup, usually in conjunction with an abnormally high water level, may overtop the most landward berm of the beach and the foredune crest, if one exists, to produce overwash and subsequent runoff across the more landward subaerial surface. Two main elements of the resulting deposit are the washover fan and runoff channel. Newly formed, small-scale washover deposits were examined along the Outer Banks, North Carolina, near Pt Mugu, California, and at Presque Isle (Lake Erie), Pennsylvania. The fans were formed in response to unidirectional landward transport, and the runoff channels in response to unidirectional flow usually in a landward direction, but sometimes in shore-parallel then seaward direction. Where overwash carried across the fan surface and entered a pond or lagoon, a small-scale delta (microdelta) developed. In this case, the washover fan consisted of two subfacies, the wetted, but ‘subaerial’ part of the fan and the subaqueous washover delta. Flow associated with the development of the fan and runoff channel produced distinctive sets of bedforms and internal stratification. High velocity discontinuous surges moving across the fan surface resulted in the development of a plane bed and subhorizontal to low-angle (landward dipping) planar stratification which comprised the major part of the fan. Similarly, rhomboid forms were produced by high velocity sheet flow across the fan surface. Where flow carried into a standing body of water, delta-type foreset strata developed. For this case, the lateral structural sequence was subhorizontal, planar stratification merging landward into landward dipping, delta (tabular) foreset strata. In the runoff setting, where flow became channelized and continuous, both upper-flow and lower-flow regime currents were typical. Upper-flow regime bedforms included antidunes, standing waves, and plane beds. The most commonly observed lower-flow regime bedforms included microdelta-like bars, low-amplitude bars, linguoid ripples, and sinuous-crested current ripple trains. The sets of sedimentary structures comprising modern washover sand bodies provide criteria for the identification of similar deposits in ancient sediments and for more specific interpretation of the environment.     

琼东南盆地崖南凹陷海湾扇三角洲体系沉积构成及演化模式

本文以琼东南盆地崖南凹陷陵水组三段扇三角洲体系为例，详细讨论了进积于海湾背景环境下扇三角洲体系的岩性相、成因相及其空间配置关系。研究区海湾扇三角洲体系自下而上潮汐作用越来越强，其垂向演化可划分为三个阶段，早期为以河流作用占优势阶段，中期为河流和潮汐混合作用阶段，晚期为以潮汐作用占优势逐渐过渡为以潮汐作用占优势。     

Transgression of an estuarine channel and tidal flat complex: the Lower Triassic of Barles, Alpes de Haute Provence, France

The Lower Triassic succession of Barles, Alpes de Haute Provence, France, comprises an unconformable quartz arenite sand body of 90m thickness. The succession may be informally divided into (i) lower channellized cross-bedded member overlain by (ii) an upper fining upward member. The lower member comprises vertically stacked, subtidal channel units separated into five major sand bodies by thin developments of fine grained channel margin and shoal deposits. Subtidal channel fill deposits are dominated by varying scales of cross bedding. These scales vary systematically from the base to the top of the member, with large scale planar sets dominating the lowest channel sand body (sand body 1), medium scale planar and trough cross bedding characterizing sand bodies 2-4, the largest scale planar sets in the highest sand body (sand body 5). This upward change in cross bedding scale is concomitant with a decrease in both the relief of major channel sand body erosion surfaces, and the proportion of preserved interchannel shoal deposits. The succeeding fining upward member comprises small scale tidal channel units overlain by channel shoal and tidal flat deposits. Tidal flat sequences are characterized by parallel laminated, wave and current rippled sandstones separated by bioturbated, fine grained siltstones and mudstones. The vertical variation in facies of the Lower Triassic succession suggests two main periods of deposition. The lower member is considered to preserve successively more seaward components of a transgressive estuarine complex. The overlying upper member records the seaward progradation of tidal channel, shoal and tidal flat environments. The unconformity bounded nature of the lower member, combined with its systematic variation in facies, suggests it may represent an incised valley-estuarine fill developed in response to an early Triassic relative sea level fall and subsequent rise. Succeeding tidal channel and tidal flat deposits forming the upper fining upward member reflect a change in sediment supply and/or rate of relative sea level rise comparable with a progradational shoreline. It is unclear whether this final depositional episode represents a period of highstand progradation or a later lowstand shoreline system developed following a further period of relative sea level fall and rise.     

Sedimentology of the Ekwan Shoal,Akimiski Strait,James Bay,Canada

One of the steepest depositional coasts of western James Bay is found along the west shores of Akimiski Strait, north of the mouth of the Ekwan River. This shore receives considerable amounts of sediment during the spring break-up of the rivers. The sediments are stored on the steep narrow tidal flats and marshes, and in thinner (up to 80 cm) drapes on till-cored shoals that parallel and protect the coast. The low areas between the shoals and the mainland are swept and reworked by relatively powerful (2 m s^?1) reversing currents due to flooding and ebbing of tides into the strait.A series of distinct environments and sedimentary facies develop on this western coast and its antecedent longshore shoal. The outer part of the shoal is characterized by tidal bedding, Macoma balthica burrows and considerable ice scour. The inner part of the shoal has winnowed sand, the greatest abundance of Macoma, and well-developed flaser bedding. The longshore tidal channel separating the shoal from the mainland has coarse sand lags in the shallower parts and silty sand in deeper protected areas. The steep tidal flats develop laminated silty sands locally saturated and slumping toward the channel. The high saturation of the sediments inhibits colonization of the flats by Macoma. The narrow marshes have characteristic vegetation zonation, with Puccinellia phryganodes colonizing the lower marsh. The sedimentary sequence of the marsh displays irregular, bioturbated laminated sequences of silt, silty sand and organic matter.     

辽河西部凹陷曙北地区沙四段薄砂层成因类型及分布规律

为了明确辽河西部凹陷曙北地区沙河街组四段薄砂层成因类型及分布规律,从岩心、测井响应和地震反射特征等方面总结了各类成因薄砂层的识别标志,并预测了各砂层组的砂体展布,探讨了砂体发育的控制因素,总结了沉积模式.研究结果表明,曙北地区沙四段为扇三角洲-湖泊的沉积体系,薄砂层发育水下分流河道、河口坝、低隆滩坝、沿岸浅滩4种成因类型,其中以水下分流河道和低隆滩坝为主.古地貌、古物源和古水深控制了各类砂体的展布.以曙光和兴隆台古潜山一线为界,南部为扇三角洲体系沉积区,主要发育前缘水下分流河道和河口坝;北部（包括低隆区）为无明显水流注入的半封闭湖湾区,主要发育低隆滩坝砂体和灰/云坪,在西侧沿岸局部地区还发育沿岸浅滩.储量区外大面积发育的低隆滩坝砂体,是下一步碎屑岩增储上产的潜在接替区域.     

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。     

Shallow marine sand bar sequences: an example from the late Precambrian of North Norway

Five coarsening upward shallow marine sandstone sequences (2–10 m thick), are described from the late Precambrian of North Norway, where they occur in a laterally continuous and tectonically undeformed outcrop. The sequences consist of five facies with distinct assemblages of sedimentary structures and palaeocurrent patterns. Each facies is the product of alternate phases of sedimentation during relatively high- and low-energy periods. Facies 1 to 4 are interpreted as representing prograding, subtidal sand bars. Sand bar progradation occurred during the highest energy periods when unidirectional currents flowed to the northwest, depositing trough cross-bedded sandstones (facies 3 and 4) on the bar crests and flanks, and sheet sandstone beds (facies 1 and 2) in the offshore environments. Weaker northwesterly flowing currents continued during moderate energy fair weather periods. Low energy fair weather periods were dominated by wave processes, which formed largescale, low-angle, westerly inclined surfaces on the bar flanks (facies 4) and wave rippled sandstone beds (facies 2) and flat laminated siltstone layers (facies 1) in the offshore environments. One sand bar was dissected by channels and infilled by tabular cross-bedded sandstones (facies 5). Bipolar palaeocurrent evidence, with two modes separated into two laterally equivalent channel systems, suggests deposition by tidal currents in mutually evasive ebb and flood channels. The inferred processes of these sand bars are compared with those associated with modern storm-generated and tidal current generated linear sand ridges. Both are influenced by the interaction of relatively low and high energy conditions. The presence of the tidal channel facies, however, combined with the inferred strong bottom current regime, is more analogous to a tidal current hydraulic regime.