渤海湾巨葛庄贝壳堤与下伏泥层有孔虫组合的海面变化意义

根据巨葛庄贝壳堤及下伏泥层的有孔虫研究,讨论了贝壳堤底板和下伏泥层各类沉积环境的海面意义,以此作为海面标志点重建的古海面误差范围为±0.225~±0.625m。结合该贝壳堤底板和下伏泥层顶板的年龄数据,重建了3900~3300cal BP时的海面高度为-2.955~-2.715m。     

Sediments and water fluxes in a muddy coastline: interplay between waves and tidal channel hydrodynamics

Tidal channels are ubiquitous in muddy coastlines and play a critical role in the redistribution of sediments, thus dictating the general evolution of intertidal landforms. In muddy coastlines, the morphology of tidal channels and adjacent marshes strongly depends on the supply of fine sediments from the shelf and on the resuspension of sediments by wind waves. To investigate the processes that regulate sediment fluxes in muddy coastlines, we measured tidal velocity and sediment concentration in Little Constance Bayou, a tidal channel in the Rockefeller State Wildlife Refuge, Louisiana, USA. The tidal measurements were integrated with measurements of wave activity in the bay at the mouth of the channel, thus allowing the quantification of feedbacks between waves and sediment fluxes. Results indicate that the sediment concentration in the channel is directly related to the wave height in the adjacent bay during flood and high slack water, whereas the concentration during ebb depends on local channel velocity. Moreover, the sediment flux during ebb is of the same order of magnitude as the sediment flux during the previous flood, indicating that only a small fraction of transported sediments are stored in the marsh during a tidal cycle. Finally, very low tides, characterized by high ebb velocities, export large volumes of sediment to the ocean. Copyright © 2010 John Wiley & Sons, Ltd.     

渤海湾沿岸贝壳堤对潮滩有孔虫海面变化指示意义的影响

通过对渤海湾沿岸有贝壳堤发育和无贝壳堤发育的2类现代开放潮滩有孔虫组合的对比,研究了该2类潮滩环境沉积物中有孔虫的海面指示意义。5个有孔虫组合带被MHWST(平均大潮高潮位)、MHW(平均高潮位)、MHWNT(平均大潮低潮位)和MSL(平均海面)分隔,分别对应潮滩的高盐沼、低盐沼、潮间带上部、潮间带中上部和潮间带中下部5个不同亚环境。不同亚环境沉积物因其所含的有孔虫群的独特性,均可作为高精度海面标志物,误差为各亚带高差的1/2。沿岸贝壳堤可对潮滩有孔虫的属种组成产生影响,影响程度从高潮位向低潮位逐渐降低。在MHWNT潮位之下,有孔虫组合不再受到沿岸贝壳堤的影响。     

Recent effects of tidal and hydro‐meteorological changes on coastal plains near the mouth of the Amazon River

The goal of this work was to understand the main hydrodynamic processes acting on tidal flats of the coast of Amapá near the mouth of the Amazon River, and how they change over the short term (~ 20 years). The analysis of morphological and geobotanical units was carried out by applying processing and interpretation methods to optical and synthetic aperture radar (SAR) images, combined with data on water salinity, maximum flood height, sedimentary facies data, rainfall and river discharge. The temporal analysis of morphological and geobotanical units suggests the relative stabilization of savannah, ‘várzea’ and mangrove areas during the drier period and increasing tidal amplitude between 1987 to 1997. The wetter period and decreasing tidal amplitude between 1997 to 2008 led to an increase in the area of ‘várzea’ and lakes over savannah, and the expansion of mangroves mainly over the inundated field and tidal mud/mixed flats. Therefore, the decrease in rainfall index during the drier period is well‐correlated with the reduction of the Calçoene River discharge and jointly with increasing tidal amplitude favored the increase of migration rate of the mud bank and erosion profile along the littoral. It was followed by the increase of the Calçoene River discharge and jointly with decreasing tidal amplitude during the wetter period, favoring the development of mangroves on muddy substrates near the coastline. Copyright © 2013 John Wiley & Sons, Ltd.     

Subantarctic macrotidal flats, cheniers and beaches in San Sebastian Bay, Tierra Del Fuego, Argentina

San Sebastian Bay is a large, semicircular coastal embayment situated on the Atlantic coast of Tierra del Fuego, Argentina. It is a high-energy, subantarctic environment with a tidal range of 10.4 m, influenced by large waves of Atlantic and local origin and swept by constant, strong westerly winds. A 17 km long gravel spit protects the Northern part of the Bay giving rise to a gradient in sedimentary processes. From south to north, are seven distinct sedimentary environments. Coastal sedimentation started at least 5200 years before present (BP) and a rapid progradation related to a relative sea-level drop has infilled about 6 kilometres of the Bay with a sedimentary sequence 10–11 m thick. 14-C dating of unabraded shells in the Chenier ridges of the relict part of the complex allows for a precise reconstruction of the stages of the progradation, that has slowed from 2.35 m/year at 5000 years BP to 0.6 m/year at present. The possible causes of the sea-level drop are discussed.     

渤海湾贝壳堤研究现状及意义

贝壳堤是渤海湾西岸、西北岸近五六千年以来成陆过程中的一类重要地质现象。它的发育规模、时间跨度和所包含的地质古环境信息在第四纪地质研究中占有重要的位置。在整理总结前人有关贝壳堤研究的基础上，介绍了贝壳堤研究的现状、方法和意义，并指出了研究中仍需探讨的问题。     

苏北平原龙冈LG孔晚第四纪地层与环境演化记录

通过研究已经获得的苏北平原龙冈LG孔岩芯野外描述、照片、粒度、¹⁴C测年、有孔虫、孢粉、重矿物等原始测试分析数据,并参考邻区发表成果和该区新近补充的资料数据,再分析和讨论了LG孔的地层层序、年代框架和环境演化记录等内容。结果表明：① LG孔34.8 m岩芯保存了MIS 4以来沉积环境演化记录,先后经历了河漫滩、河湖相洪泛平原（第二硬黏土层）、较开放潮滩的潮间带和潮下带、较开放潮滩的潮下带、较开放潮滩的潮间带和潮上带下部、河湖相洪泛平原（第一硬黏土层）、潮上带滨海沼泽和海岸沙堤等一系列环境演化过程,其中潮滩环境的MIS 3海侵层发育;② 西冈贝壳沙堤龙冈段的全新统厚度很薄,一般在10 m以内,由于LG孔可见两个硬黏土层,应位于古河间地而非下切古河谷区,且以其第一硬黏土层顶面作为全新统底界更为合理,故原报道该孔全新统厚达25 m难以成立;③ 老于末次冰盛期的常规和加速器¹⁴C测年数据皆存在着不同程度的误差和不确定性,加之淤泥和钙质结核等测年材料易受污染等,故LG孔第二硬黏土层中的2个¹⁴C测年数据明显偏年轻,皆不宜用于解释地层年代。     

Shell bed tempestites in the Chenier Plain of Louisiana: late Holocene example and modern analogue

Hurricane Ike's storm surge deposited a concentrated shell bed in the form of a series of coalescing washover fans over backshore sand and adjoining marshland in part of southwest Louisiana's Chenier Plain. The shell bed is a tempestite and has distinctive morphological, sedimentological and biogenic characteristics that provide a modern analogue to aid interpretation of older shell bed tempestites in the geological record. The shell bed has a wedge‐shaped profile that thickens landward, is about 40 m wide, up to 27 cm thick and extends several hundred metres parallel to the shore. Shells are predominantly disarticulated valves of the common bivalve Mulinia lateralis, probably reworked and transported landward from skeletal remains offshore. The shell bed has an erosional base, is bioclast supported, normally graded and has common mud rip‐up clasts. Similarities between the modern shell bed and another concentrated shell deposit, forming part of a sandy beach ridge some 1.5 km inland, suggest that the palaeo shell deposit is also a tempestite recording hurricane washover of a former shoreline 600 a ago. These findings demonstrate that the shell bed deposited by Hurricane Ike is a valuable analogue for palaeotempestological investigations and that hurricanes have likely contributed to the construction of both modern berm ridges and palaeo beach ridges on this coastal plain. Copyright © 2011 John Wiley & Sons, Ltd.     

风暴潮贝壳堤的沉积特征及发育模式

南海北部长湾贝壳堤是一典型的风暴潮成因贝壳堤。该贝壳堤的横向、纵向露头和钻孔所显示的地层结构、层理特征、粒度特征、14C测年、物质组成、贝屑种属生境及当地风暴增水高度和地壳升降幅度表明：（1）贝壳堤由风暴沉积组成,是风暴潮增水期间海岸沉积物堆积的结果,由于堆积在平均高潮面之上,增水退却后不受正常天气下波浪的影响得以保存;（2）理想剖面由下而上分4个部分：1）潮滩堆积;2）激浪带堆积;3）增水面下波浪堆积;4）增水面上波浪爬高堆积。各个部分具有不同的沉积特征,分别代表贝壳堤向上增长的各个阶段的沉积环境和风暴作用方式;（3）风暴潮贝壳堤与非风暴潮贝壳堤不仅在发育过程,而且在沉积结构、粒度特征、贝屑种属、堆积部位、堆积高度及环境意义等方面都有所不同。     

渤海湾西岸的第一道贝壳堤的年代学研究及1千年来的岸线变化

取自堤下部的＾１４Ｃ平均校正年龄表明,渤海湾西岩沿现代海岩线展布的第一道贝壳堤（Ⅰ堤）的初始年龄约在９００～７００ｃａｌＢＰ／ＡＤ１０５０～１２５０,堤的发育延续至１８、１９世纪。以入＾１４Ｃ数据因取样位置不当（一般取自堤的中部）,不能用于支持文献中关于该堤起始时间的;但是这批数据连同文献中获自岸外残存贝壳碎屑堆积层的数据,暗示隋、唐贝壳堤存在的可能性。近１千年来该地区贝壳堤的发育反映了海岩线的重