Holocene sedimentation of a wave-dominated barrierisland shoreline: Cape Lookout, North Carolina

The sedimentary record of 130 km of microtidal (0.9 m tidal range) high wave energy (1.5 m average wave height) barrier island shoreline of the Cape Lookout cuspate foreland has been evaluated through examination of 3136 m of subsurface samples from closely spaced drill holes. Holocene sedimentation and coastal evolution has been a function of five major depositional processes: (1) eustatic sea-level rise and barrier-shoreline transgression; (2) lateral tidal inlet migration and reworking of barrier island deposits; (3) shoreface sedimentation and local barrier progradation; (4) storm washover deposition with infilling of shallow lagoons; and (5) flood-tidal delta sedimentation in back-barrier environments.

Twenty-five radiocarbon dates of subsurface peat and shell material from the Cape Lookout area are the basis for a late Holocene sea-level curve. From 9000 to 4000 B.P. eustatic sea level rose rapidly, resulting in landward migration of both barrier limbs of the cuspate foreland. A decline in the rate of sea-level rise since 4000 B.P. resulted in relative shoreline stabilization and deposition of contrasting coastal sedimentary sequences. The higher energy, storm-dominated northeast barrier limb (Core and Portsmouth Banks) has migrated landward producing a transgressive sequence of coarse-grained, horizontally bedded washover sands overlying burrowed to laminated back-barrier and lagoonal silty sands. Locally, ephemeral tidal inlets have reworked the transgressive barrier sequence depositing fining-upward spit platform and channel-fill sequences of cross-bedded, pebble gravel to fine sand and shell. Shoreface sedimentation along a portion of the lower energy, northwest barrier limb (Bogue Banks) has resulted in shoreline progradation and deposition of a coarsening-up sequence of burrowed to cross-bedded and laminated, fine-grained shoreface and foreshore sands. In contrast, the adjacent barrier island (Shackleford Banks) consists almost totally of inlet-fill sediments deposited by lateral tidal inlet migration. Holocene sediments in the shallow lagoons behind the barriers are 5–8 m thick fining-up sequences of interbedded burrowed, rooted and laminated flood-tidal delta, salt marsh, and washover sands, silts and clays.

While barrier island sequences are generally 10 m in thickness, inlet-fill sequences may be as much as 25 m thick and comprise an average of 35% of the Holocene sedimentary deposits. Tidal inlet-fill, back-barrier (including flood-tidal delta) and shoreface deposits are the most highly preservable facies in the wave-dominated barrier-shoreline setting. In the Cape Lookout cuspate foreland, these three facies account for over 80% of the sedimentary deposits preserved beneath the barriers. Foreshore, spit platform and overwash facies account for the remaining 20%.     

Barrier island stratigraphy and Holocene history of west-central Florida

Although the morphology of the barrier-inlet system along the west-central Florida coast is quite complicated, the stratigraphy of these barriers is rather simple. The basal Holocene unit in most cores is an organic-rich, muddy sand that represents a vegetated, paralic marine, coastal environment similar to that which is north and south of the present barrier system. Above that unit is a muddy, bioturbated sand that displays a marine fauna at most locations but also contains Crassostrea virginica in a few places. These sediments accumulated in a low-energy marine setting that may or may not have been protected by a barrier island. Much of this facies also represents sediment that was delivered as washover deposits in an intertidal or subtidal setting and was subsequently bioturbated. The facies that can be attributed to a barrier island with some certainty are no more than 3000 years old, and on most islands, are much younger. These are the shelly sand and sorted sand facies. The shelly strata represent deposition in nearshore, beach, supratidal washover or intertidal spillover environments, and tidal inlet and tidal delta channels, whereas the sorted sand is typical of eolian deposition in dunes or the backbeach and some tidal delta elements. The presence of Holocene oyster beds offshore of a present barrier suggests that some of these islands formed significantly offshore and moved to their present position through washover. It is likely that most of these barriers initially formed through upward shoaling by waves. Although there is significant morphologic difference between the wave-dominated and mixed-energy, drumstick barrier islands, their stratigraphy is quite similar. The only significant difference is the presence of extensive progradation on at least part of the drumstick islands and a relatively high amount of former washover deposits on the wave-dominated type.     

Sedimentary records of intense storms in Holocene barrier sequences, Maine, USA

Coastal-morphological, geophysical (ground-penetrating radar [GPR]), and sedimentological data document extreme storm events along the sandy barriers of Maine's south–central (Hunnewell and Flat Point barriers) and southwestern (Saco Bay barriers) coastal compartments. The Hunnewell barrier contains four equally spaced buried storm scarps behind the exposed scarp of the Blizzard of 1978, a 100-year storm that eroded more than 100 m of shoreline, causing extensive property loss. These scarps dip 3–5° steeper than the normal beachface slope and consist of sands with more than 50% heavy minerals. The heavy minerals produce distinct subsurface reflections that facilitate the location of buried supratidal parts of storm scarps and the mapping of ancient poststorm shoreline positions. The imaged scarps likely formed within the past 1.5–2.0 ka BP. The Flat Point barrier consists of a prograded sequence overlain by a laterally extensive, seaward-thinning layer of freshwater peat and capped by aeolian sands. This stratigraphy suggests that the bog varied in size through time, contracting during overwash events and aeolian deposition and expanding across washover sheets during extended periods of barrier stability. The main overwash event accompanied by barrier planation and wetland expansion may be linked to the first historical storm in New England, the “Great Colonial Hurricane” of 1635.

Evidence of near-modern and mid-Holocene storm events along Saco Bay includes washover units and marsh ridges. Washovers interfinger with saltmarsh peat that ranges in age from 4.5 ka BP to modern. The presence of isolated sandy ridges behind existing and former tidal inlets reflects overtopping of marshes and high intertidal mudflats during major storms. Radiocarbon ages indicate that this process took place at different locations along the Saco Bay barrier complex from 3 to 1 ka BP.     

Morphostratigraphy of an ebb-tidal delta system associated with a large spit in the Piedras Estuary mouth (Huelva Coast,Southwestern Spain)

The Piedras Estuary is one of the most significative estuarine systems on the mesotidal Huelva Coast, in the Northwestern portion of the Cadix Gulf. The river mouth is presently an estuarine lagoon partially closed by a large spit constructed from an old barrier island system. This estuary is in an advanced state of infilling and its tidal prism has decreased during the Holocene causing instability and clogging of old inlets and transforming the barrier island chain into a spit. Sedimentation is controlled by the interaction of ebb tide currents and the prevailing SW waves. The main sediment supply is provided by an intensive West-to-East longshore current, transporting sand material from Portuguese cliffs and the Guadiana River. Tidal range is mesotidal (2.0 m) and the mean significant wave height is 0.6 m with an average period of 3.6 s.A boxcore study allowed five depositional facies to be distinguished in the Piedras Estuary mouth: (1) main ebb channels; (2) marginal flood channels; (3) ebb-tidal delta lobes; (4) marginal levees; and (5) curved spits. The recent evolution studied in this area suggests a cyclic evolutionary model for the ebb-tidal delta system. The architectural facies relations shown by the vibracore/boxcore study confirm that the apical growth of the spit occurred over the innermost of these ebb-tidal deltas. Consequently the preserved sequence shows the ebb-tidal delta facies under the spit facies.     

Stratigraphy of washover deposits in Florida: implications for recognition in the stratigraphic record

Twelve washover deposits were cored on the west-central Gulf Coast of Florida to provide data to permit development of a model to help identify washover facies in the stratigraphic record. Typical modern washover stratigraphy displays landward-dipping plane beds comprised of well-sorted sand with distinct laminae of shells and heavy minerals. Five subfacies are delineated which show variations in composition, texture, and bioturbation throughout the washover facies. These subfacies represent differences in flow conditions during overwash, position relative to sea level, and variable degrees of reworking after deposition. Three shell assemblages aid in identification of washover deposits. Backbarrier sediments composed of shoreface/open water species or mixed shoreface/backbarrier species may potentially be washover in origin. Sediments with purely backbarrier/quiet water shell species are likely to have been deposited independently of washover activity. Examination of washover deposits of differing ages reveals that preservation of washover stratigraphy is not exclusively a function of time. Reworking of small-scale stratification can occur in as short as a decade; however, this same stratification was found to be preserved in deposits several hundred years old. Destruction of original washover signatures is related to the position of the deposits relative to sea level, and the rate and depth of burial. Even after the destruction of small-scale stratigraphic features, washover deposits may still be identified as such due to their texture, composition, and shell assemblages. Key features in recognizing the facies after bioturbation and reworking are: (1) the presence of clean sand in otherwise muddy backbarrier sediments, (2) the landward thinning of the facies, and (3) the presence of shoreface shells or mixed shoreface/backbarrier shells on landward portions of the barrier island system. If reworking is severe and/or there are limited subsurface data, distinguishing washovers from genetically similar deposits (e.g. flood tidal deltas and spillover deposits) in the stratigraphic record is difficult and when considered out of stratigraphic context may not be recognizable.     

Facies architecture of the mixed carbonate/siliciclastic inner continental shelf of west-central Florida: implications for Holocene barrier development

Sediment vibracores and surface samples were collected from the mixed carbonate/siliciclastic inner shelf of west–central Florida in an effort to determine the three-dimensional facies architecture and Holocene geologic development of the coastal barrier-island and adjacent shallow marine environments. The unconsolidated sediment veneer is thin (generally <3 m), with a patchy distribution. Nine facies are identified representing Miocene platform deposits (limestone gravel and blue–green clay facies), Pleistocene restricted marine deposits (lime mud facies), and Holocene back-barrier (organic muddy sand, olive-gray mud, and muddy sand facies) and open marine (well-sorted quartz sand, shelly sand, and black sand facies) deposits. Holocene back-barrier facies are separated from overlying open marine facies by a ravinement surface formed during the late Holocene rise in sea level. Facies associations are naturally divided into four discrete types. The pattern of distribution and ages of facies suggest that barrier islands developed approximately 8200 yr BP and in excess of 20 km seaward of the present coastline in the north, and more recently and nearer to their present position in the south. No barrier-island development prior to approximately 8200 yr BP is indicated. Initiation of barrier-island development is most likely due to a slowing in the Holocene sea-level rise ca. 8000 yr BP, coupled with the intersection of the coast with quartz sand deposits formed during Pleistocene sea-level highstands. This study is an example of a mixed carbonate/siliciclastic shallow marine depositional system that is tightly constrained in both time and sea-level position. It provides a useful analog for the study of other, similar depositional systems in both the modern and ancient rock record.     

Distribution characteristics of delta reservoirs reshaped by bottom currents: A case study from the second member of the Yinggehai Formation in the DF1-1 gas field,Yinggehai Basin,South China Sea

The Dongfang1-1 gas field (DF1-1) in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources. The second member of the Pliocene Yinggehai Formation (YGHF) is the main gas-producing formation and is composed of various sedimentary types; however, a clear understanding of the sedimentary types and development patterns is lacking. Here, typical lithofacies, logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling, logging, analysis and testing data. Based on 3D seismic interpretation and attribute analysis, the origin of high-amplitude reflections is clarified, and the main types and evolution characteristics of sedimentary facies are identified. Taking gas formation upper II (IIU) as an example, the plane distribution of the delta front and bottom current channel is determined; finally, a comprehensive sedimentary model of the YGHF second member is established. This second member is a shallowly buried “bright spot” gas reservoir with weak compaction. The velocity of sandstone is slightly lower than that of mudstone, and the reflection has medium amplitude when there is no gas. The velocity of sandstone decreases considerably after gas accumulation, resulting in an increase in the wave impedance difference and high-amplitude (bright spot) reflection between sandstone and mudstone; the range of high amplitudes is consistent with that of gas-bearing traps. The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps, and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps. The study area is a delta front deposit developed on a shallow sea shelf. The lithologies of the reservoir are mainly composed of very fine sand and coarse silt, and a variety of sedimentary structural types reflect a shallow sea delta environment; upward thickening funnel type, strong toothed bell type and toothed funnel type logging facies are developed. In total, 4 stages of delta front sand bodies (corresponding to progradational reflection seismic facies) derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF; these sand bodies are dated to 1.5 Ma and correspond to four gas formations. During sedimentation, many bottom current channels (corresponding to channel fill seismic facies) formed, which interacted with the superposed progradational reflections. When the provenance supply was strong in the northwest, the area was dominated by a large set of delta front deposits. In the period of relative sea level rise, surface bottom currents parallel to the coastline were dominant, and undercutting erosion was obvious, forming multistage superimposed erosion troughs. Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.     

Oligocene sequence stratigraphy and basin development in the Danish North Sea sector based on log interpretations

Five sequences are defined in the Oligocene succession of the Danish North Sea sector. Two of the sequences, 4.1a and 4.3, have been identified onshore Denmark.Two types of prograding lowstand deposits are recognized. Sand-dominated deposits occur proximally, comprising sharp-based forced regressive deposits covered with prograding low-stand deposits. Clay-dominated prograding lowstand deposits occur distally in the sequences. The highstand deposits are proximally represented by thick prograding sandy deposits and distally by thin and condensed intervals.The main sediment input direction was from the north and the northeast. A succession oif lithofacies, from shallow marine facies dominated by sand to outer shelf facies dominated by clay, is mapped in each of the sequences. An overall southward progradation of the shoreline took place during the Oligocene, interrupted only by minor shoreline retreats.     

Two-dimensional time dependent hurricane overwash and erosion modeling at Santa Rosa Island

A 2DH numerical, model which is capable of computing nearshore circulation and morphodynamics, including dune erosion, breaching and overwash, is used to simulate overwash caused by Hurricane Ivan (2004) on a barrier island. The model is forced using parametric wave and surge time series based on field data and large-scale numerical model results. The model predicted beach face and dune erosion reasonably well as well as the development of washover fans. Furthermore, the model demonstrated considerable quantitative skill (upwards of 66% of variance explained, maximum bias − 0.21 m) in hindcasting the post-storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied. The prediction skill ranged between 0.66 and 0.77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied. The sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay. The model sensitivity to the sheet flow sediment transport limiter, which served as a proxy for unknown factors controlling the resistance to erosion, was significantly greater than the sensitivity to the hydraulic forcing parameters. If no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response.     

Ground penetrating radar for facies architecture and high-resolution stratigraphy: Examples from the Mesoproterozoic in the Chapada Diamantina Basin,Brazil

Ground Penetrating Radar (GPR) surveys were conducted on Mesoproterozoic eolian, fluvial, deltaic, estuarine, and shallow marine successions in the Chapada Diamantina Basin. The subsurface continuation of facies and facies architecture exposed on road cuts was imaged using the GPR signal of a 400-MHz antenna penetrating 8 m in depth, even with mudstone intervals. Reflection patterns in the GPR profiles that were compared with photo mosaics of outcrops and supporting data from vertical sections and gamma ray logs, reveal sedimentary, stratigraphic, and structural features, such as sedimentary structures, the external geometry of architectural elements, stratigraphic surfaces, folds and tension gashes. The patterns most likely reflect the response from low-weathered, non-porous muscovite-illite-rich mudstone and quartzarenite sandstone in which authigenic and detrital illite and sericite are prevalent clay minerals.Measured vertical sections and radar stratigraphy indicate high-frequency cyclic successions of estuarine and shoreface intervals are present at the base of the Tombador Formation. The shoreface intervals are composed of heterolithic strata and offshore tidal bars deposits. The heterolithic shoreface strata exhibit tabular geometry that can be easily identified throughout the outcrop and in the subsurface. Such intervals represent the end of high-frequency transgressive cycles, and hence they are potential candidates for including the maximum flooding surfaces and for defining genetic sequences. Therefore, GPR proved to be an independent method for studying facies architecture and the establishment of a high-resolution stratigraphic framework even in the Precambrian.     

Control of barrier island shape by inlet sediment bypassing: East Frisian Islands, West Germany

A study of the East Frisian Islands has shown that the plan form of these islands can be explained by processes of inlet sediment bypassing. This island chain is located on a high wave energy, high tide range shoreline where the average deep-water significant wave height exceeds 1.0 m and the spring tidal range varies from 2.7 m at Juist to 2.9 m at Wangerooge. An abundant sediment supply and a strong eastward component of wave power (4.4 × 10³ W m⁻¹) have caused a persistent eastward growth of the barrier islands. The eastward extension of the barriers has been accommodated more by inlet narrowing, than by inlet migration.

It is estimated from morphological evidence that a minimum of 2.7 × 10⁵ m³ of sand is delivered to the inlets each year via the easterly longshore transport system. Much of this sand ultimately bypasses the inlets in the form of large, migrating swash bars. The location where the swash bars attach to the beach is controlled by the amount of overlap of the ebb-tidal delta along the downdrift inlet shoreline. The configuration of the ebbtidal delta, in turn, is a function of inlet size and position of the main ebb channel. The swash bar welding process has caused preferential beach nourishment and historical shoreline progradation. Along the East Frisian Islands this process has produced barrier islands with humpbacked, bulbous updrift and bulbous downdrift shapes. The model of barrier island development presented in this paper not only explains well the configuration of the German barriers but also the morphology of barriers along many other mixed energy coasts.     

应用探地雷达方法对海南岛博鳌海岸沙坝的研究

了解海岸沙坝的内部结构对于动态地恢复海岸沙坝与海平面变化的相互关系具有重要的意义，探地雷达（GPR）为海岸沙坝的研究提供了一种快速、经济和高分辨率的地球物理方法；探地雷达利用高频电磁波在介电特性不均匀的沉积体中产生反射获得图像，通过解译可确定地下沉积体的性质和结构；在海南岛东部博鳌玉带滩海岸沙坝的近口门处、决口堤处和南岗村东侧玉带滩海岸沙坝顶部进行了探地雷达反射剖面的测量；研究结果表明自然堆积的沙体反射波连续，受风暴浪改造的沙体同相轴错断，反射波杂乱不连续，无法进行对比；运用探地雷达相分析方法并结合钻孔资料，认为5－6m以上的平行反射波形可能代表中细砂沉积，以下的丘状或杂乱反射波形可能代表中粗砂沉积，并显示砂砾或细小卵砾等粗颗粒含量的增加。     

渤中凹陷西斜坡BZ3-8区块东营组东二下高分辨率井震层序及地震沉积学

渤海海域凹陷由于资料的限制,其沉积相研究多为宏观的区域性研究,制约了储层的精细解释。基于最新采集的高精度地震三维资料,结合地震地层学、层序地层学、地震沉积学等理论方法,开展渤中凹陷西斜坡BZ3-8区块东营组重点目的层,东二下层序高分辨率井震层序分析及其地震沉积学研究。结果表明,研究区南北两侧具有不同的物源体系和沉积相模式。低水位体系域(LST)和高水位体系域(HST)时期,研究区北部物源均形成扇形、朵形的地震多属性及振幅切片异常,对应于扇三角洲沉积;南部物源均形成NE向展布的条带状地震多属性及振幅切片异常,对应于辫状河三角洲沉积。海进体系域(TST)时期,湖平面快速上升导致扇体不发育,仅在研究区北部局部发育小规模的扇三角洲沉积。东二下层序LST(富砂)-TST(富泥)-HST(富砂)的岩相演化规律,充分反映了经典层序地层学理论层序格架中的地层岩相组合分布规律,对储层和烃源岩的预测具有指示意义。     

A backbarrier overwash record of intense storms from Brigantine, New Jersey

Analysis of aerial photographs and historic charts indicates that the barrier beach at Brigantine, NJ has migrated landward 300 to 400 m since 1869, primarily as a result of overwash during hurricanes and winter storms. A series of vibracores from the backbarrier salt marsh reveals a millennial-scale stratigraphic record of overwash deposition. Carbon-14 (C-14) and Cesium-137 (Cs-137) radioisotopic methods were used to date overwash deposits (washovers). The ages of recent washovers are consistent with deposition during intense storms in 1938, 1944, 1950, and 1962. An additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788. Two prehistoric overwash fans were likely deposited by intense storms striking the New Jersey Coast in the 7th to 14th centuries and 6th to 7th centuries A.D. The landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans. The greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period, the hurricane of 1821. The spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments.     

中全新世以来长江口北支环境的演变

从古环境演变的角度,对崇明岛北侧的永隆沙钻孔进行了系统的采样和粒度分析、微体古生物分析、环境磁学分析以及14C测年等。大致恢复长江口北支古地理环境演变的过程,中全新世以来,长江口北支由浅海沉积环境,逐渐演变为三角洲平原环境。但通过环境磁学和微体古生物分析,揭示了在2080~2000 aB.P.,700~625 aB.P.这两段历史时期,长江口北支表现为河口砂坝亚环境和河口河槽亚环境。这两次环境变异事件记录了长江主泓南北迁移的事实。     

Near-surface seismic facies at the Korea Strait shelf margin and trough region

High-resolution seismic profiles across the shelf margin and trough region of the Korea Strait reveal five shallow, near-surface facies units. These are relict coastal deposits, relict delta deposits, slumps and slides, and trough lag deposits. Most deposits represent a lowstand systems tract, formed during the last lowstand of sea level. Relict coastal deposits represent a linear sediment body along the present shelf margin at water depths of 120–150 m, whereas relict delta deposits occur on the gentle, southwestern slope of the trough at water depths of about 150–200 m. Slumps and slides are dominant at the base of slope in the central trough region. Sediments on the central trough floor were partly eroded and redistributed by strong currents, resulting in lag deposits.     

Evidence for storm-dominated early progradation of Castle Neck barrier, Massachusetts, USA

Washovers, dune scarps and flattened beach profiles with concentrations of coarse-grained sediment or heavy minerals are the diagnostic geological signatures of large storms on barriers today. It is clear that storms are a major force driving transgressive barriers onshore, but what is not as well understood is the role these powerful erosive events play in the evolution of prograding barriers. Application of ground-penetrating radar (GPR) and a combination of coring techniques have significantly improved our ability to image barrier architecture. Results of these studies reveal a more complex evolution than previously recognized. It is now possible to precisely locate and map storm deposits within prograded barrier lithosomes.

A comprehensive study of northern Castle Neck, Massachusetts was performed using 15 km of GPR surveys, a 120-m-long seismic line, 11 cores, and several radiocarbon dates. Storm-related layers are the most prominent horizons contained in the barrier stratigraphy. The geometry and sedimentology of these layers closely resembles those of a present-day post-storm beach. Twenty closely spaced, curvilinear heavy mineral layers imaged in the landward portion of the barrier suggest that the Castle Neck barrier was heavily influenced by storms during its initial phase of progradation beginning 4000 years BP. Approximately 1800 years BP, two intense storms impacted the coast depositing two extensive coarse-grained units. These layers mimic the flat-lying sand and gravel deposits that occur in front of a nearby eroding till outcrop following major storms. The great number of storm deposits in the early history of Castle Neck is related to either a period of greater storm activity and/or a slow rate of barrier progradation. The occurrence and preservation of these earlier storm layers are likely a product of the exposure of nearby drumlins resulting in greater availability of iron oxide and ferromagnesian sands. The supply of heavy-mineral sands has gradually diminished as the barrier prograded and the proximal drumlin source was buried by beach and dune sands.     

连云港海域废黄河水下三角洲北翼的沉积特征与空间分布

基于连云港海域浅地层剖面资料解释和16个站位柱状岩心的剖面观察、粒度分析、微体化石鉴定、有孔虫和腹足类纹沼螺的AMS 14C年龄,分析废黄河水下三角洲北翼的沉积结构、厚度和沉积物组成,划分沉积单元及其分布范围;识别海侵沉积区的沉积相,认识其沉积环境特征。结果表明,水下三角洲沉积体可分为三角洲前缘和前三角洲两个沉积单元,两者沿连云港海岸线呈并置关系。三角洲前缘位于埒子口至新淮河口外,为一NNE向进积、NW向倾斜的扇形楔状体,可识别出灌河叶瓣及其以东的叶瓣两个沉积中心。该沉积单元以砂质沉积为主,两个叶瓣之间的分流间湾分布有泥和砂质泥。前三角洲位于三角洲前缘西北侧,大致从埒子口外侧沿海岸带向海州湾展布。该单元为泥质沉积,厚度较薄,其北部的两个柱状岩心所揭示的沉积厚度分别为1.8 m和1.5 m。水下三角洲以北,海侵沙席分布广泛,厚度通常在20 cm左右。其分布在本区具有普遍性,只是在连云港海域被黄河泥沙所覆盖,由此也构成了废黄河水下三角洲的底界面。该界面具有侵蚀残留地貌特征。海侵沙席之下为晚更新世MIS 3阶段中早期的海陆过渡相沉积。沉积物多由黄色粉砂或砂质粉砂组成,含有较丰富的有孔虫、介形虫等,可见淡水纹沼螺。