A method to define the palaeowind strength from lacustrine parameters

Gravelly beach ridges, which are formed solely by swash processes, may accurately reflect past wave conditions. The thickness (or height) of a gravelly beach ridge approximately equals the height of wave inundation, which is the sum of the surge and wave run‐up. Their ancient counterparts, if well‐preserved and identified, can be used to estimate palaeowave conditions, which can later be converted to palaeowind intensities based on wind–wave relationships. A technique is described for estimating the palaeowind speed in this paper, which is referred to as the gravelly beach‐ridge thickness technique. By comparing these estimates with instrumental wind records obtained at a modern lake, Qinghai Lake in north‐western China, the beach‐ridge thickness technique is shown to be useful for estimating the average wind speed (V _avg). When applying this method to ancient fetch‐limited basins, five parameters are necessary: (i) the thickness of the isolated gravelly beach ridge; (ii) the average depth of the water body; (iii) the palaeofetch; (iv) the angle between the palaeowind direction and the normal to the shoreline; and (v) the particle size. This technique was applied to an ancient example in the Eocene Dongying Depression, located in eastern China. The results indicate that the average wind speed of the northern wind ranged between 2·27 m sec⁻¹ and 8·36 m sec⁻¹ from 45·0 Ma to 42·0 Ma, and displayed a generally decreasing trend that included early strengthening followed by weakening and later strengthening during this period. The beach‐ridge thickness technique provides a new perspective on delineating palaeowind conditions and can be applied to ancient fetch‐limited basins with gravelly beach ridges worldwide. Generally, if a water body is sufficiently large (fetch exceeding 40 km), deep (average depth exceeding 10 m) and waves (or winds) are determined to approach the shoreline with high angles (angle of incidence <35°), then the calculation errors will be small to negligible.     

利用马尔可夫链分析识别内蒙古正镶白旗额里图组沉积特征

通过野外地质剖面实测识别了额里图牧场额里图组各层岩性特征,利用马尔可夫链分析方法分析该剖面下岩段地层的沉积旋回,综合地质基础资料,进一步分析了沉积环境.结果识别出一个以砂岩-粉砂质泥岩-粉砂岩-泥岩为特征和一个以砂岩-灰岩-泥岩为特征的两个岩性旋回,分别代表浅海陆棚-深水浊积岩相序和陆棚浅海礁滩相沉积.结合剖面分别划分出陆棚、斜坡和盆地（海槽）3个相,进一步识别出潮坪滩相、滩前斜坡相、浊积滩坝相、滩相、斜坡盆地相、缓坡相、深水海槽相和礁滩相等亚相.整个剖面由两次海侵半旋回和一次完整的海侵海退旋回组成.研究认为古亚洲洋的最终闭合时限应该在额里图组时期之后.     

海南高隆湾海滩生物碎屑分布及其对沉积物粒度特征的影响

在热带砂质海岸,生物碎屑是海滩沉积物的重要组成部分,其分布和变化影响海滩沉积物的粒度特征。采用添加过量盐酸和双氧水的方法对海南高隆湾海滩表层沉积物进行了去生物碎屑前后粒径分布的对比,并结合海滩高程测量分析,结果表明:（1）海滩剖面上沉积物中生物碎屑的含量主要受到海水动力的影响,且生物碎屑颗粒较粗、重量较大,在高潮时由波浪流推上海滩并滞留。（2）海滩沉积物中生物碎屑的分布主要受三方面影响:一是地形及常涌浪向;二是区域中养殖业产生的生物碎屑;三是岸外发育的珊瑚礁坪。（3）海滩沉积物中生物碎屑的含量随季节变化,冬季至春季由海水供给的生物碎屑减少、进一步分解,使得北部海滩生物碎屑含量减少;而珊瑚碎屑的稳定供给和春季较强的波浪动力条件又使研究区南部断面的生物碎屑含量增加。（4）海滩沉积物中粗颗粒所含生物碎屑多于细颗粒中的生物碎屑,生物碎屑粒径主要为-1~2,即粗砂至细砾。沉积物中生物碎屑含量愈大,对粒径参数的影响也愈大。     

Discrimination of particle zonation on a pebble beach

The extent to which pebble shapes are zonally sorted on a pebble beach is examined. On the basis of comprehensive point samples from a pebble beach in west Wales, and using factor analysis, a pebble shape index for each point sample is derived. It is proposed that the sum of squares (%RSS) explained by a linear trend surface of shape index values, approximates to the degree to which the second derivative of pebble shape with respect to distance downbeach, tends towards zero. If the second derivative is zero there is no zonation of sample shape values but, rather, a uniform trend. Strength of zonation on one beach is calculated for eight beach samples during 1971. A heterogeneity index (Ht) is introduced to show the degree of difference between clustered point samples on the basis of shape and size. On the basis of %RSS and Ht value, discrimination between pebble facies type on the sample beach over time can be made.     

Seasonal changes and morphodynamic behavior of a high-energy mesotidal beach: case study of Charf el Akab beach on the North Atlantic coast of Morocco

The morphodynamic behavior of a mesotidal sandy beach was monitored during both calm and energetic conditions. Two years of seasonal surveys were carried out on Charf el Akab, a gently sloped beach in the North Atlantic coast of Morocco. The method of survey consisted of a 3D study of the beach morphological changes and provided 2 cm vertical accuracy. During the surveyed period, Charf el Akab beach underwent very energetic wave conditions, and the breaking wave height was of H _b ≥ 1.5 m. The beach is characterized by a nonpermanent swash bar and composed of well-sorted medium sand. The application of environmental parameters revealed a dissipative state with very low beach gradient which did not vary significantly over the studied period. Morphological changes consist of beach erosion and bar decay under high-energy waves, whereas the intertidal bar re-established and the beach recorded an accentuated accretion due to relatively fair weather conditions. The beach volume reveals a seasonal behavior; the sand accumulated during summer is dramatically removed during winter season. The range in beach sand volume from the most accreted to the most eroded conditions observed is about −5,493 m³. The average sand volume flux between surveys reaches −1 and 0.4 m²/day during peak erosion and accretion periods. The relationships between the wave forcing and the sand volume adjustments were examined. The sand volume change was found to be highly correlated (0.91) with the wave energy flux. The highest correspondence (0.95) was found between the sand flux rate and the wave energy flux. The wave forcing is expected to be the main factor governing beach morphodynamics at Charf el Akab site.     

辽河盆地西部凹陷古近系沙四上亚段沉积相及演化

薄互层砂体研究是湖盆沉积学的研究难点。本文针对辽河西部凹陷沙四上亚段（Es^4上）薄互层砂体,以层序地层学、沉积学、测井地质学等理论为指导,综合岩心、测录井和地震等多种资料,对西部凹陷的薄互层砂体进行精细描述和深入剖析。结果表明,研究区主要发育辫状河三角洲和湖泊沉积相,其中,滩坝砂体是湖泊相的主力砂体。通过考虑不同沉积背景下滩坝在岩相组合、发育位置和成因机理的差异性,将滩坝划分成侧缘改造型滩坝、前缘改造型滩坝、基岩改造型滩坝、淹没改造型滩坝和风暴改造型滩坝5种沉积模式;对薄层滩坝砂体的控制因素进行分析,认为其受到"风场-物源-盆地"三端元的控制。     

Factors influencing human beach choice on three South African beaches: A multivariate analysis

Knowledge of recreational use patterns, preferences and opinions of beach users can be useful in developing beaches in such a way as to ensure quality recreational experiences. This paper investigated, by means of questionnaire survey, a) the factors influencing human beach choice on three beaches with different levels of development and b) whether respondents on the different beaches considered different characteristics important on an ideal beach. By means of multiple discriminant analysis, visitors could be classified according to the beaches they were interviewed on, based solely on the different reasons given for visiting the beach as well as on the characteristics they considered important on a beach.Although factors relating to level of beach development were the most important in influencing beach choice on highly developed King's Beach and undeveloped Sardinia Bay, traditional/historical, socio-economic factors and accessibility (all unrelated to beach development) were more important on semi-developed Joorst Park, visited by people of a lower-socio-economic level. These people considered Joorst Park underdeveloped but were prevented by socio-economic restraints from visiting a beach of their choice, eg King's Beach. The highly and semi-developed beaches were visited for their facilities, social activities and accessibility. The undeveloped beach was visited for experiencing nature, peace and quiet, its few people and because dogs were allowed there. In addition, respondents' opinions were obtained on litter, additional facilities, preferred distances between groups on the beach and in the surf and whether dogs and off-road vehicles should be allowed on beaches. More basic facilities (toilets and refuse bins) were considered necessary on all beaches, especially on the semi-developed beach. Beyond a minimal level of amenities, additional comforts were undesired by users on the undeveloped beach and limited funds should rather be used to upgrade and improve beaches such as Joorst Park, that are already developed to attract people with greater demands for a wider range of facilities. However, beaches with different levels of development are necessary to cater for people who desire different recreational experiences. Limiting beach access beyond a certain number of visitors seems to be unpopular with the public.     

Effects of a Beach Nourishment Project in Jamaica Bay,New York,on Horseshoe Crab (<Emphasis Type="Italic">Limulus polyphemus</Emphasis>) Spawning Activity and Egg Deposition

Restoration of horseshoe crab spawning habitats through beach nourishment may be considered as a potential strategy to enhance reproductive success in areas where estuarine beaches have been lost to coastal erosion and development. The US Army Corps of Engineers performed a beach nourishment project at Plumb Beach (Jamaica Bay, Brooklyn, NY) in 2012 to stabilize the shoreline. While the addition of sand was done to protect infrastructure, it created an opportunity to examine the responses of American horseshoe crabs (Limulus polyphemus) to beach nourishment using a BACI (before-after control impact) design. During Spring 2012, before beach nourishment, horseshoe crabs made minimal use of the highly degraded western section of Plumb Beach in comparison to a nearby reference site, as quantified by numbers of spawning adults at high tide and densities of horseshoe crab eggs in core samples. In the first post-nourishment field season (Spring 2013), there was no detectable increase in horseshoe crab spawning activity on the newly restored beach. In 2014 and 2015, the density of spawning females began to increase at the nourished beach, although their numbers and especially the density of horseshoe crab eggs remained much lower than at the reference site. Three years after beach nourishment, differences in sediments texture (mean grain diameter, percent gravel, sorting, skewness, and hardness) were still evident between the nourishment and reference sites. Our results suggest that (1) at this site, beach nourishment appeared to bring about only slow increases in horseshoe crab spawning density after several seasons and (2) subtle differences in beach geomorphology over relatively short distances can be detected by horseshoe crabs and may underlie their selection of specific nesting sites.     

华南海岸沙丘岩的特征及其与海滩岩的区别

沙丘岩是热带亚热带的一种特殊的岩石类型，尽管外貌相似，但它们成因和特征上有别于海滩岩。作者通过对西沙石岛、海南岛文昌和临高、广东阳江青洲岛、汕头广澳等处具一定代表性的沙丘岩的研究，总结了沙丘岩的沉积学、岩石学特征及其与海滩岩的区别。华南沙丘岩由岛屿上的灰砂和含生物碎屑的海岸风成沙丘物质胶结而成。分布高程可达＋６０ｍ以上，岩石中发育板状交错层理、大型槽状交错层理、上凸层理、似水平层理以及根管构造；其物质来源与海滩砂具继承关系，兼具风成砂的特点，部分沙丘岩还混有坡积物及陆生生物壳体。沙丘岩的颗粒多为中砂粒径，普遍分选好，（ＳＫ１）偏度变化比较大，ＫＧ峰度较小，Ｙ１值为负值，与海滩砂、海滩岩差别较大。沙丘岩中发育各种淡水渗流环境中特有的胶结物和胶结组构。虽然沙丘岩与现代海滩岩相比，其Ｃａ、Ｍｇ、Ｓｒ元素的含量及比例不同，但可以完全与上升海滩岩相似。本文作者认为:辨别沙丘岩主要从产状、沉积构造、粒度分析、胶结物及组构诸方面进行研究。     

Genetic type,distribution patterns and controlling factors of beach and bars in the second member of the Shahejie formation in the Dawangbei Sag,Bohai Bay,China

As an important reservoir type in the Bohai Bay Basin, China, lacustrine beach and bar sands which refer to the shallow water complex deposited mainly by nearshore, delta‐rim and buried hill‐related beaches as well as longshore bars were developed in a particular stage in the evolution of those faulted Cenozoic continental depressions. In the Chezhen Depression, for example, the Second Member of the Oligocene Shehejie Formation (abbr. as Es2 hereafter) formed during the rifting‐to‐thermal subsidence transitional stage. Although well developed in Es2, beach and bar sands are difficult to recognize owing to their relative thinness. The paper summarizes sedimentary characteristics of lacustrine beach and bar sands on cores and logs. Low‐angle cross‐stratification, swash stratification, as well as occasional small‐scale hummocky cross‐stratification resulted from storms can be observed in beach and bar sands. The paper distinguishes bars and beaches from each other in Es2 mainly based on the grain‐size, bed thickness, facies succession and log responses. In order to predict the distribution of beach and bars, a chrono‐stratigraphic correlation framework of Es2 in the study strata is established using a high‐resolution sequence stratigraphic approach. Es2 strata are sub‐divided into six medium‐scale cycles and the mapping of the high‐frequency cycles allows the geographic and stratigraphic distribution of both beach and bar sands to be predicted. The study shows that beach and bars are better developed in times of base‐level fall than in base‐level rise. Factors such as lake‐level fluctuation, sediment supply, palaeogeomorphology and palaeowind direction have exerted control on the formation and distribution of beach and bar sands. Finally, the genetic pattern of beach and bar sands in the Es2 unit has been constructed, which provides a foundation for the prediction of beach and bars reservoir in continental basins in general. Copyright © 2011 John Wiley & Sons, Ltd.     

山东峡山湖东岸现代滩坝沉积模式及控制因素*

滩坝作为发育于滨岸带非常重要的沉积储集层类型之一,已成为隐蔽油气藏勘探的目标。为进一步明确峡山湖东岸滨浅湖滩坝沉积模式,以现代沉积考察为基础,结合探地雷达技术和粒度分析资料,对东岸研究区滩坝砂体的沉积特征以及控制因素进行详细分析。结果表明: 峡山湖东岸主要发育风成沙丘及滩坝2种沉积体系。早期风成沉积物以发育连续性好的大型板状交错层理细砂为主,分选较好,粒度概率曲线以两段式为特征;滩坝沉积物以发育连续性差的板状交错层理、平行层理中砂为主,主要为反粒序或者复合粒序,具冲刷构造,岩性较混杂并以砂泥薄互层为特征,发育大量植物根系,粒度概率曲线以三段式为主,跳跃组分分为2段,分选较好。探地雷达资料表明研究区下部主要以厚层层状反射结构砂体为主,与风成沙丘沉积反射特征较为一致,环境敏感粒度组分对滩坝沉积较强的水动力作用有较好的指示。总体上,风力作用控制了风成砂体的沉积发育并且改变了古地貌条件,风浪作用冲刷改造了早期砂体,为滩坝的发育提供了物源,控制了滩坝发育的规模和地理位置,可概括为“风运—湖改”滩坝沉积模式,可为滩坝体系的识别和有利储集层预测提供指导。     

埃迪卡拉系微生物碳酸盐岩沉积特征及其地质意义:以川中磨溪8井区灯影组四段为例*

四川盆地高石梯—磨溪地区埃迪卡拉系灯影组广泛发育一套微生物碳酸盐岩。以磨溪8井区灯影组四段(灯四段)为例,通过精细解析高频向上变浅序列的岩石学特征,发现灯四段微生物云岩及序列建造具有如下特征: (1)向上变浅序列主要由凝块石云岩、叠层石云岩和(含微生物)泥晶云岩3类构成,伴以少量微生物粘结颗粒云岩;(2)完整的典型向上变浅序列自下而上由(含微生物)泥晶云岩(A段)、平直状叠层石云岩(B段)、小型丘状叠层石云岩(C段)、分散状凝块石云岩(D段)、格架状凝块石云岩(E段)、微生物粘结颗粒云岩(F段)等6个岩性单元构成,但大量的序列由A-C-E、A-C-D、B-D、B-C-D-E等不完整的岩性单元构成,且序列顶底皆以凝块石云岩/(含微生物)泥晶云岩、叠层石云岩/(含微生物)泥晶云岩等不平整的岩性突变面或暴露面区分;(3)埃迪卡拉系微生物碳酸盐岩发育于浪基面之上至平均海平面附近的相对高能区域,且凝块石云岩较叠层石云岩形成的环境能量高。该研究结果不仅揭示出较高能的浅水环境控制了规模性微生物岩分布这一规律,而且对区域储集层预测具有指导意义,同时也因建立了有别于现代微生物的环境分布模式而具有重要的沉积学意义。     

The age and stratigraphic context of the Easington Raised Beach, County Durham, UK

The Easington Raised Beach, in Shippersea Bay, County Durham, is the most northerly known interglacial beach deposit in England. It lies directly on Magnesian Limestone bedrock at 33 m O.D. and is covered by glacial sediments attributed to the Devensian. Detailed sedimentological analysis suggests that it is an interglacial beach, which is supported by the presence of pebbles bored by marine organisms and littoral, temperate-climate, marine macro- and micro-fossils. It comprises beds of unconsolidated, bedded, imbricated, well-rounded sands and gravels, overlain by similar, but calcreted, deposits. The gravel fraction is dominated by Magnesian and Carboniferous limestone, with orthoquartzite, flint, and porphyries also present; these are far-travelled erratics that must have derived from the erosion of older glacially transported sediments. Previous workers have described erratics derived from the Oslofjord region of Norway in the raised beach gravel, although rocks diagnostic of a Scandinavian origin have not been recovered as part of this study. The heavy-mineral suite is rich in epidote, dolomite, clinopyroxenes, garnet, tourmaline, and micas. The beach was dated previously by conventional amino acid analysis of the shells, which suggested a Marine Isotope Stage (MIS) 7 age, albeit with a reworked component from MIS 9. This has been confirmed by new optically stimulated luminescence (OSL) dates, which indicate that the beach formed between 240 and 200 ka BP. New amino acid racemisation analyses, using a modified technique, broadly support this interpretation but must await more comparative data before they can be assessed fully. The strong indication of an MIS 7 age for the formation of the beach has implications for the uplift history of northeastern England during the Pleistocene, and indicates an uplift rate of 0.19 mm a⁻¹. The stable isotope geochemistry indicates that the cementation occurred during an interglacial period, whilst U-Series dating of the cement indicates that cementation occurred mostly during the Holocene, and is genetically related to the overlying Devensian till. This work has formed part of a full re-appraisal of the glacial sequence in eastern County Durham, the results of which suggest that the Warren House Formation pre-dates the raised beach, and that the Devensian Horden Till overlies the raised beach.     

Shoreline variability of an urban beach fronted by a beachrock reef from video imagery

This contribution presents the results of a study on the shoreline variability of a natural perched urban beach (Ammoudara, N. Crete, Greece). Shoreline variability was monitored in high spatio-temporal resolution using time series of coastal video images and a novel, fully automated 2-D shoreline detection algorithm. Ten-month video monitoring showed that cross-shore shoreline change was, in some areas, up to 8 m with adjacent sections of the shoreline showing contrasting patterns of beach loss or gain. Variability increased in spring/early summer and stabilized until the end of the summer when partial beach recovery commenced. Correlation of the patterns of beach change with wave forcing (as recorded at an offshore wave buoy) is not straightforward; the only discernible association was that particularly energetic waves from the northern sector can trigger changes in the patterns of shoreline variability and that increased variability might be sustained by increases in offshore wave steepness. It was also found that the fronting beachrock reef exerts significant geological control on beach hydrodynamics. Hydrodynamic modelling and observations during an energetic event showed that the reef can filter wave energy in a highly differential manner, depending on its local architecture. In some areas, the reef allows only low-energy waves to impinge on the shoreline, whereas elsewhere penetration of higher waves is facilitated by the low elevation and limited width of the reef or by the presence of an inlet. Wave/reef interaction can also generate complex circulation patterns, including rip currents that appeared to be also constrained by the reef architecture.     

论湖相滩与坝的成因差异

滩坝是滨浅湖地区常见的一种沉积体系类型,自20世纪90年代起,滩坝作为良好的油气储集体受到人们重视。本文在国内外大量文献资料查阅以及现代沉积考察的基础上,追溯滩坝定义来源,并从水动力搬运和沉积方式上对湖相滩与坝的差异进行重新讨论,将滩与坝划分为两种能够完全区分的沉积体。滩是自浪基面至最大湖泛面范围内,碎屑物质在波浪作用下垂直于湖岸搬运和沉积的、与岸大致平行的席状(或条带状)沉积体,向陆地方向直接与湖岸平原相连。滩可以呈大面积席状展布,也可以呈滩脊、滩槽状相间分布,沿岸沙坝本质是形成于水下的滩脊。坝是在沿岸流作用下,碎屑物质平行湖岸搬运并沉积于岸线向陆弯折处、一端与岸相连、另一端向湖区自由伸展的沉积体,坝与湖岸平原常有湖湾或泻湖相隔。滩与坝的形成水动力条件不同,平面上无法共生,不应该将坝砂作为滩砂的特殊类型进行研究。厘清滩与坝的成因和差别,将有助于陆相含油气盆地滩坝砂储层的精确勘探与开发。     

Stratigraphy and chronology of Provo shoreline deposits and lake‐level implications,Late Pleistocene Lake Bonneville,eastern Great Basin,USA

The Provo shoreline of Lake Bonneville formed following the Bonneville flood, and, based on previous dating, was formed during a period of overflow from about 17.5 to 15.0 cal. ka. In many places the Provo shoreline consists of a pair of distinct shorelines, one ～3 m higher than the other. We present data from two cuts through double beaches to show that the upper beach is younger and represents sedimentation after a lake‐level rise. In addition, the lower beach deposits are internally stratified by beds that suggest three more lake‐level rises during its development. The Provo beach complex thus appears to have been built during rising lake levels, which can be explained by rises in the overflow threshold by sequential landslide deposition. Evaluation of beach altitudes demonstrates that the two beach crests throughout the Bonneville basin experienced equivalent rebound from removal of the lake load, and therefore they formed after the rebound associated with the Bonneville flood occurred in early Provo time. However, radiocarbon ages on gastropods collected within the beach deposits suggest both that the sequence of five beach deposits formed from c.18.1 to c. 17.0 cal. ka, and that the Bonneville flood occurred before 18 cal. ka. These ages are discordant with previous dates on shells within offshore sands, and raise questions about the validity of radiocarbon ages for shells in Lake Bonneville as well as about the age of the Bonneville flood and Provo shoreline. The timing for maximum Provo lake depths and its association with climate stages during deglaciation remain unresolved.     

Reply to the Discussion by John Nott on ‘Coarse‐sand beach ridges at Cowley Beach,north‐eastern Australia: Their formative processes and potential as records of tropical cyclone history’ by Tamura et al. (2018), Sedimentology,65, 721–744

Tamura et al. (2018) refined our understanding of formative processes that have resulted in a series of coarse‐sand beach ridges at Cowley Beach in north‐eastern Australia. Nott (2018) claimed that there are several shortcomings in the findings Tamura et al. (2018) presented. However, his criticism mostly derived from his misunderstanding of the data and discussion presented in Tamura et al. (2018), which thus should be clarified here. This reply also reiterates how his method for estimating the magnitude of past tropical cyclones from beach ridges is inconsistent with our observations of beach morphology and beach‐ridge formative processes.     

Sea level control of stacked late Quaternary coastal sequences, central Great Barrier Reef

Lithofacies analysis, pollen assemblages and radiocarbon age dates of 20 stratigraphic drill holes are used to develop an evolutionary history for late Quaternary sedimentation in two coastal embayments landward of the central Great Barrier Reef. Different physiographic settings of the embayments result in two contrasting styles of sedimentary sequence: (a) an exposed, moderate energy, beach barrier-lagoon system (Wyvuri Embayment) and (b) a protected, low energy, muddy inlet fill sequence (Mutchero Inlet). Despite sharp contrast in sequence style, similar depositional cycles occur in both embayments in response to late Quaternary sea level fluctuations including: (1) a last interglacial highstand (+2 m; c. 125 000 yr bp ) beach barrier (Wyvuri); (2) an early to mid-Holocene (8000–6100 yr bp ) transgressive beach barrier-lagoon (Wyvuri) and estuarine infill (Mutchero); and (3) mid-Holocene to present highstand beach barrier (Wyvuri) and estuarine (Mutchero) progradation. Preservation of such cycles in the stratigraphic record would produce a series of vertically stacked and offset linear barrier sands surrounded by lagoonal mud and fine grained shoreface sediment juxtaposed to muddy, estuarine infills. Sea level elevations are well recorded by the upward transition from Rhizophora-dominated intertidal mangrove mud to freshwater swamp (clearly identified by pollen analysis) and by the basal contacts of beach barrier sediments which sharply overlie the upper shoreface. Transgressive sedimentation is interrupted in both embayments by a constructional beach barrier (Wyvuri) and abbreviated progradation (Mutchero) corresponding to a — 5 m pause in relative sea level rise at c. 6800 yr bp . Sea level control of fine scale coastal sedimentation patterns is beginning to be widely recognized and provides an accurate analogue for stacked ancient sequences.     

A data-driven approach for analyzing dynamics of tide–aquifer interaction in coastal aquifer systems

Analysis of tidal effects on aquifer systems plays an important role in coastal aquifer management owing to various hydrological, engineering and environmental problems in coastal areas. Using the real-world data of unconfined and confined aquifers, a data-driven approach is presented in this study for the analysis of tide–aquifer interaction in coastal aquifers. Six analytical tide–aquifer interaction models were selected which take into account the effects of vertical beach, sloping beach, tidal loading, aquifer leakage, outlet capping, and combined leakage and outlet capping on tide-induced groundwater fluctuations. The tide–aquifer interaction datasets were obtained from the Konan groundwater basin (unconfined aquifer) of Japan and the Dridrate groundwater basin (confined aquifer) of Morocco. The analysis of the results obtained by the sloping beach model revealed that for a given beach slope, the amplitude of groundwater level increases with an increase in aquifer diffusivity and a decrease in aquifer thickness. However, no significant effect of beach slope was observed in this study at unconfined sites for all the datasets. The influence of tidal loading was found to be considerably less for all the three confined sites. Further, the analysis of the results of the leakage model indicated that with an increase in leakage into the aquifer, the amplitude of groundwater level as well as the phase shift (time lag) decreases. Of all the confined and unconfined datasets, only two confined sites were found to be affected by outlet capping. Overall, it is concluded that the coastal beach bordering the Konan basin is not significantly sloping, the contribution of tidal loading to tide-induced groundwater fluctuations in the Dridrate aquifer is not appreciable, and that the aquifer leakage and outlet capping do not exist at the unconfined sites under investigation.     

Perception of the rip current hazard on Galveston Island and North Padre Island,Texas, USA

The hazard posed by a rip current depends in part on the ability of beach users to identify a rip current and to associate surf conditions with the potential for rip currents. Understanding which visual features beach users associated with rip currents is an important step in the development of appropriate programs and educational materials aimed at improving the ability of beach users to identify a rip current. A face-to-face survey (n = 392) was conducted to assess the ability of beach users to identify a rip current using five near eye-level photographs that simulate the view of the beach and surf zone as the respondent approached the beach. The survey was conducted on three heavily used public beaches in Texas (Galveston, Port Aransas, and Corpus Christi) at the height of the summer beach season in 2012. Only 13 % of respondents correctly selected the photograph showing the most hazardous conditions and correctly identified the precise location of the rip current on the photograph. The majority of beach users (87 %) incorrectly indicated that the photograph with the heaviest surf represented the most hazardous surf conditions and greatest potential for the development of rip currents, or failed to identify rip currents in photographs. Respondents who were able to correctly identify the rip current tended to recognize the breaking wave pattern, areas of darker water, or the proximity to structures as key visual characteristics of rip currents and also had higher self-reported abilities to swim in rough water and escape a rip current.