Tidal Flat Environments Research Articles

Near-field sea-level variability in northwest Europe and ice sheet stability during the last interglacial

Global sea level during the Last Interglacial (LIG, Marine Isotope Sub-stage 5e) peaked between c. 5.5 and 9 m above present, implying significant melt from Greenland and Antarctica. Relative sea level (RSL) observations from several far- and intermediate-field sites suggest abrupt fluctuations or jumps in RSL during the LIG highstand that require one or more episodes of ice-sheet collapse and regrowth. Such events should be manifest as unique sea-level fingerprints, recorded in far-, intermediate- and near-field sites depending on the source(s) of ice-mass change involved. To date, though, no coherent evidence of such fluctuations has been reported from near-field RSL studies in northwest Europe. This is an important problem because RSL fluctuations during the LIG are portrayed as warning signs for how polar ice sheets may behave in a future, warmer than present, world. Here we review the evidence for RSL change during the LIG using stratigraphic data from the best resolved highstand records that exist in the near-field of northwest Europe, from a range of settings that include lagoonal, shallow marine, tidal flat, salt marsh and brackish-water fluviatile environments. Consideration of previously published stratigraphic records from two sites in the Eemian coastal-marine embayment that existed in the central Netherlands, yields no clear indications for abrupt RSL change during the attainment of the near-field highstand. Nor do we find any such indications common to other records from countries bordering the North Sea, the Baltic Sea and the White Sea. Two modelling experiments that explore the global signal of hypothetical sea-level oscillations caused by partial collapse and regrowth of either the Greenland or Antarctic LIG ice-sheet, show that the North Sea region is relatively insensitive to mass changes sourced from Greenland but should clearly register events with an Antarctic origin, especially those that occur late in the LIG. The lack of evidence for abrupt sea-level fluctuations at this time in northwest Europe concurs with a lack of clear near-field evidence for ice sheet collapse.

Sedimentary Environment and Sequence Stratigraphy of the Lower Cretaceous Deposits in the Bideshk Area, at North of Esfahan, Iran

Background/Objectives: Rocks of the Mesozoic era in Iran, especially Cretaceous period, have been studied frequently from stratigraphic point of view, but little research has been done from sedimentology viewpoint. This study aims to restore the sedimentation condition and the conditions governing the sedimentary basins during that period (lower Cretaceous). Methods: One stratigraphic section was measured along the outcrop in Bideshk Area, at North of Esfahan. 63 thin sections samples were studied to determine the facies and a polarized microscope was used for the procedure. Findings: Based on lithological properties, 3 lithostratigraphic units have identified in the area. Facies analysis and field observations led to identification of 10 carbonate facies, 4 terrigenous facies and also 4 mixed (terrigenous and carbonate). Bideshk area was deposited on a homoclinal ramp setting within four zones including Continental, tidal flat, lagoon and bar environments. Sequence stratigraphic analysis identified three third-order depositional sequences in the studied area. Lower boundary in the first sequence is unconformity first-type boundary (SB1) (with Jurassic deposits) and consists of Transgressive Systems Tract (TST). Sequence number 2 consists of Low stand Systems Tract (LST), Transgressive Systems Tract (TST) and High stand Systems Tract (HST). Sequence 3 also consists of LST, TST and HST. Application: These results could be used for comparison with other worldwide localities and provide additional data for lower Cretaceous paleogeographic reconstructions.

Effects of causeway construction on environment and biota of subtropical tidal flats in Okinawa, Japan

Okinawa, Japan is known for its high marine biodiversity, yet little work has been performed on examining impacts of numerous large-scale coastal development projects on its marine ecosystems. Here, we examine apparent impacts of the construction of the Kaichu-Doro causeway, which was built over 40years ago. The causeway is a 4.75km long embankment that divides a large tidal flat and has only two points of water exchange along its entire length. We employed quadrats, transects, sampling, visual surveys, and microbial community analyses combined with environmental, water quality data, and 1m cores, at five stations of two paired sites each (one on each side of Kaichu-Doro) to investigate how the environment and biota have changed since the Kaichu-Doro was built. Results indicate reduction in water flow, and site S1 was particularly heavily impacted by poor water quality, with low diversity and disturbed biotic communities.

Airborne Spectral Polarimeter for Ocean Wave Research

AbstractThe Airborne Remote Optical Spotlight System (AROSS) family of sensors consists of airborne imaging systems that provide passive, high-dynamic range, time series image data and has been used successfully to characterize currents and bathymetry of nearshore ocean, tidal flat, and riverine environments. AROSS–multispectral polarimeter (AROSS-MSP) is a 12-camera system that extends this time series capability to simultaneous color and polarization measurements for the full linear polarization of the imaged scene in red, green, and blue, and near-infrared (RGB–NIR) wavelength bands. Color and polarimetry provide unique information for retrieving dynamic environmental parameters over a larger area (square kilometers) than is possible with typical in situ measurements. This particular field of optical remote sensing is developing rapidly, and simultaneous color and polarimetric data are expected to enable the development of a number of additional important environmental data products, such as the improved ability to image the subsurface water column or maximizing wave contrast to improve oceanographic parameter retrievals of wave spectra and wave heights.One of the main obstacles to providing good-quality polarimetric image data from a multicamera system is the ability to accurately merge imagery from the cameras to a subpixel level. This study shows that the imagery from AROSS-MSP can be merged to an accuracy better than one-twentieth of a pixel, comparing two different automated algorithmic techniques. This paper describes the architecture of AROSS-MSP, the approach for providing simultaneous color and polarization imagery in space and time, an error analysis to characterize the measurements, and example color and polarization data products from ocean wave imagery.

The expansion of Spartina alterniflora marsh in response to tidal flat reclamation, central Jiangsu coast, eastern China

The central Jiangsu coast is typical of China's coastal muddy silt with an average tidal range of 4 m. The shoreline has been gradually advancing seaward as the coast was supplied by a large amount sediment from ancient Yangtze River and Yellow River. As a result, a lot of land resources are fostered in the coast. Therefore tidal flat reclamation activities gradually intensified to the demand of economic development. A large- scale reclamation plan in Jiangsu coast has been implemented since the 21 st century and Spartina alterniflora marsh has become the main target of tidal flat reclamation. Thus how Spartina alterniflora marsh will expand during the reclamation period is worthy of study. Thirteen phases of satellite imageries from 2001 to 2013 and field observation data are analyzed to quantify the expansion rate of Spartina alterniflora marsh in association with the reclamation activities. The result shows that Spartina alterniflora expansion during 2001- 2013 can be divided into three periods. During 2001- 2007,the Spartina alterniflora area outside the seawall was relatively large and the influence on the tidal flat sedimentary environment by reclamation did not hamper its expansion. As a result,both the annually increased Spartina alterniflora area and the expansion rate keep pace with reclamation. During 2008- 2010, the Spartina alterniflora area outside the seawall decreased significantly; nevertheless, the mean annual expansion rate of the Spartina alterniflora marsh was still relatively high. During 2011- 2013, the area of Spartina alterniflora marsh became small because of the reclamation activities during 2001-2007 and 2008-2010 periods. Spartina alterniflora expansion became stabilized. As such, the pattern of the marsh expansion differs in response to the reclamation rate and stages. If a sufficiently wide marsh can be maintained during reclamation, then the marsh will continue to grow. The underlying mechanism is that the Spartina alterniflora marsh is influenced by the generation of seedling and the sediment types and bed elevation, while reclamation will affect all these factors. The relationship between marsh expansion and reclamation rate for the period of 2001- 2007 indicates that, for sustainable reclamation on the Jiangsu coast, a width of 0.9-1 km for the Spartina alterniflora marsh should be maintained.

Late Quaternary sedimentary environmental evolution offshore of the Hangzhou Bay, East China—implications for sea level change and formation of Changjiang alongshore current

This study focuses on sedimentary environmental changes offshore of Hangzhou Bay, East China, since the Late Quaternary. AMS C-14 ages from core CJK10, lithologies, distribution of foraminifera, heavy minerals, and S and Cl elements show a fluvial terrace environment during similar to 23.2-11.0 cal ka BP; a littoral to tidal-flat environment during 11.0-10.2 cal ka BP; and a shallow marine environment with a relatively low sedimentation rate (0.1-0.22 cm/a) since 4.3 cal ka BP. High depositional rates (similar to 1.6 cm/a) from 10.9 to 10.2 cal ka BP resulted from sufficient accommodation space created by rapid sea level rise from -44 m to -33 m, from high sediment delivery by local rivers, and effective trapping of sediments by tidal-flat vegetation. The rate of sea level rise was variable; relatively high from 10.9 to 10.6 cal ka BP (2.1 cm/a), and lower since 10.6 cal ka BP (1.2 cm/a). The Changjiang alongshore current crossed the Hangzhou Bay to form the mud wedge on the inner shelf of the East China Sea later than 9.4 cal ka BP. The CJK10 site was a tide-dominated shelf environment and experienced erosion from approximately 9.4-9.2 cal ka BP to 4.3 cal ka BP. The depositional hiatus was caused by the Changjiang alongshore current, which was relatively weak during 9.4-7.5 cal ka BP and increased in strength during similar to 7.5-4 cal ka BP. From similar to 4.3 cal ka BP, a large amount of sediment from the Changjiang River was partly deposited on the continental shelf of Hangzhou Bay with some transported southward. Therefore, this study clarifies the history of Changjiang-derived sediment dispersal and deposition, although a detailed record of the changes in the Changjiang alongshore current since 4.3 cal ka BP is difficult to obtain because of the scarcity of evidence.

Chapter 19 Geological history of the Kaladgi–Badami and Bhima basins, south India: sedimentation in a Proterozoic intracratonic setup

Abstract The Proterozoic Kaladgi–Badami and Bhima basins are intracratonic basins occurring over the Archaean Dharwar craton. The Kaladgi–Badami Basin contains arenites, shales and carbonates with minor cherts and conglomerates deposited in continental, transitional and shallow-marine environments presumably during the late Palaeoproterozoic/Mesoproterozoic to Neoproterozoic. The lower part of the succession (Bagalkot Group) is deformed into east–west-trending elongated doubly plunging synclines and anticlines. The upper part of the succession (Badami Group) is undeformed and unconformably overlies the lower part. The evolution of the Kaladgi–Badami Basin was controlled by movements along east–west-trending normal faults under an extensional stress regime. The Bhima Basin hosts mainly limestones with subordinate arenites and shales deposited in fluvial, deltaic and tidal flat environments possibly during the Neoproterozoic. These sediments are undeformed except along faults with significant strike-slip components. The basin is exposed in narrow strips arranged in an en echelon pattern and appears to be a pull-apart basin. Inadequate data exist on the age of the basin fills, the deep basinal architecture, subsidence history and tectonic controls for both of the basins. Future research may be directed towards these aspects which will have wide implications for understanding intracratonic basin formation, reconstructing Proterozoic supercontinents and studying the evolution of the atmosphere and primitive life forms.

贵州西部二叠系主采煤层稀土元素分布特征及影响因素分析

贵州是我国煤炭资源蕴藏极为丰富的省份，是中国重要的煤炭生产基地，但煤层中元素地球化学分布情况研究程度低，对贵州煤炭资源有效利用是一项严重的欠缺。通过对贵州西部二叠系主采煤层稀土元素地球化学研究，获得了大方、黔西、威宁、赫章、织金等地主采煤层稀土元素分布特征，并得出煤中稀土元素主要来源于陆源碎屑，与峨眉山玄武岩有关。煤层中稀土元素的含量受到沉积环境和陆源区母岩性质的影响，稀土元素随着从玄武岩风化碎屑多的三角洲平原环境，到受海水影响较大的潮坪环境，稀土元素逐渐被稀释，靠近陆地的成煤环境稀土含量较高，远离陆地的成煤环境形成的煤层中稀土含量低。根据这种分布规律，提出了利用稀土元素地球化学来区分贵州西部成煤环境的新思路，这对解决贵州西部三角洲成煤还是潮坪成煤问题具有现实意义。 Guizhou has abundant coal resources which is an important coal production base in China, but few researches have been done on the element geochemistry of coal measure strata in Guizhou Province, and the effective utilization of coal resources in Guizhou is a serious defect. Based on element geochemical studies of the main Permian exploitable coal measure strata in western Guizhou, geochemical distribution characteristics of the rare earth elements in the main exploitable coal measures have been revealed in the regions of Dafang, Qianxi, Weining, Heizhang, Zhijin, etc. of Guizhou province. The REEs in coals are mainly continental origin, associated with Emeishan basalt. Contents of REEs in coal seam are affected by sedimentary environments and lithology qualitative in terrigenous areas. REEs are gradually diluted from delta plain environment, which contains more basalt weathering debris, to the tidal flat environment greatly influenced by the water. The contents of REEs are higher when coal-forming environment is closer to land, while the contents of REEs are lower when coal-forming environment is away from land. According to the rules of distribution of REEs in coal measures, a new idea has been put forward to make use of the geo-chemical composition characteristics to classify coal-forming environments, which is of great sig-nificance in dissolving the problem of whether coal measures were formed either in delta envi-ronment or in tidal-flat environment in western Guizhou.

贵州省黔西县二叠系龙潭组主采煤层微量元素分布特征及制约因素探讨

黔西县是贵州主要的产煤县之一，煤炭资源丰富，煤层主要产于二叠系上统龙潭组(P31)地层中，属于织纳煤田。通过对主要矿区主采煤层系统取样分析，研究了不同煤层、不同矿区微量元素空间分布特征；与相邻的大方、赫章等区域煤层中微量元素含量对比发现，在陆源供给多的三角洲平原环境形成的煤层中微量元素含量相对高，在受海水影响较大的潮坪环境煤层中微量元素相对含量低，揭示了研究区陆源物质供给母岩——玄武岩具有较高的微量元素地球化学背景是其主要制约因素。个别煤层中有害元素Pb、Tl等含量高，是后期热液活动和断裂构造影响的结果。 Guizhou has abundant coal resources, but little research has been done on the element geochemi-stry of coal measure strata in Guizhou Province, and the effective utilization of coal resources in Guizhou is a serious defect. Based on element geochemical studies of the main Permian exploitable coal measure strata in western Guizhou, the element geochemical distribution characteristics of the different coal seam and different mining area have been revealed, contrasting with the trace element content in Dafang, Hezhang, etc. The element contents are mainly affected by terrestrial material supply. Coal measures formed in the delta plain environment where sufficient terrestrial materials are supplied contain relatively abundant trace elements, whereas those formed in the tidal-flat environment influenced greatly by seawater have relatively low contents of trace elements, mainly controlled by the geological fact that basalts—the parent rocks of source regions contain high trace elements. The content of Tl and Pb in coal seam is higher, and it is the result of the late hydrothermal activity and the effect of the fracture structure.

Channel characterization using multiple-point geostatistics, neural network, and modern analogy: A case study from a carbonate reservoir, southwest Iran

In facies modeling, the ideal objective is to integrate different sources of data to generate a model that has the highest consistency to reality with respect to geological shapes and their facies architectures. Multiple-point (geo)statistics (MPS) is a tool that gives the opportunity of reaching this goal via defining a training image (TI). A facies modeling workflow was conducted on a carbonate reservoir located southwest Iran. Through a sequence stratigraphic correlation among the wells, it was revealed that the interval under a modeling process was deposited in a tidal flat environment. Bahamas tidal flat environment which is one of the most well studied modern carbonate tidal flats was considered to be the source of required information for modeling a TI. In parallel, a neural network probability cube was generated based on a set of attributes derived from 3D seismic cube to be applied into the MPS algorithm as a soft conditioning data. Moreover, extracted channel bodies and drilled well log facies came to the modeling as hard data. Combination of these constraints resulted to a facies model which was greatly consistent to the geological scenarios. This study showed how analogy of modern occurrences can be set as the foundation for generating a training image. Channel morphology and facies types currently being deposited, which are crucial for modeling a training image, was inferred from modern occurrences. However, there were some practical considerations concerning the MPS algorithm used for facies simulation. The main limitation was the huge amount of RAM and CPU-time needed to perform simulations.

A hybrid approach for litho-facies characterization in the framework of sequence stratigraphy: A case study from the South Pars gas field, the Persian Gulf basin

The Upper Dalan and Kangan formations with dominant lithology of limestone and dolomite associated with anhydrite nodules and interbeds form the Permo-Triassic succession of South Pars gas field (SPGF) and host the largest none-associated gas reservoir in the world. The current study focuses on preparing a comprehensive litho-facies model in the framework of sequence stratigraphy. For this purpose, Self-Organizing Map Neural Network (SOM-ANN) and hierarchical cluster analysis (HCA) were utilized as effective tools to prepare the preliminary data for litho-facies mapping. Neural networks (self-organizing maps) and hierarchical clustering approaches were applied to characterize litho-facies in un-cored but logged wells. Particularly, the powerful visualization tools of the SOM-ANN which provide more information in comparison to HCA facilitate the task of establishing an order of priority between the distinguished electro-facies groups. The mentioned method of SOM-ANN clustering algorithm showed a good performance in petrophysical data clustering and litho-facies determination. Based on the porosity and permeability maps at different depth levels, the target reservoir is ranked and classified into four litho-facies and six electro-facies. They include litho-facies 3 with good reservoir quality (equivalent of electro-facies 4–6), litho-facies 4 with moderate reservoir quality (equivalent of electro-facies 2) and litho-facies 1 and 2 with poor to bad reservoir quality (equivalent of electro-facies 1 and 3). The main litho-facies assemblages are indicative of deposition within tidal flat, lagoon, shoal and off-shoal environments. The most shoal litho-facies with best reservoir quality occurs in the high energy sub-environment within upper transgression position (HST) of the 3rd-order cycle in K4 and K2 reservoir units. Distribution of the petrophysical characteristics was analyzed in detail in the framework of electro-facies and sequence stratigraphy. The methodology is illustrated by using a case study from SPGF, Iran.

Erratum to: Neogene eastern Amazon carbonate platform and the paleoenvironmental interpretation

The Early Miocene Pirabas Formation represents extensive carbonate and siliciclastic belts deposited in marine coastal environments along the eastern Amazon coast. This formation was studied in its palynological, crustacean decapods and sedimentary facies, to develop a model of its depositional processes, faunal and floral assemblages and the sedimentary environments, as observed in the B17 mine (Capanema, Para). The sedimentary records consist mostly of light gray to greenish gray mudstones with tidal bedding, calciferous sandstones, stratified biocalcirudites and levels with conglomerates deposited in a carbonate/siliciclastic transitional system with lagoon, tidal flat, flood-tide delta and foreshore environments. 18 palynomorph species were identified in the tidal flat deposits including one alga, five pteridophytes and nine angiosperms. Among the latter, mangrove pollen and spores of Zonocostites ramonae, Zonocostites minor and Deltoidospora adriennis are reported. Nine species of crustacean decapods were recognized in the foreshore deposits, comprising one Callianassoidae, two Calappidae and six Portunidae, represented by Euphylax, †Necronectes, Portunus and Scylla, the ecology of which is associated with beaches of marginal lagoons. The main factor in the formation of these carbonate environments is assumed to have been related to the lack of a large-scale drainage system such as the Amazon River basin in the transition Oligocene–Miocene, which may also have influenced carbonate production and resulted in a strong decrease of paleodischarges from incipient river systems along the Amazon coast.

Porosity evolution within high-resolution sequence stratigraphy and diagenesis framework: outcrop analog of the upper Jurassic Arab-D reservoir, Central Saudi Arabia

The upper Jurassic Arab-D reservoir is considered as the most prolific reservoir in the Ghawar field in Saudi Arabia. Exposed strata equivalent to the Arab-D reservoir was investigated and evaluated to establish a relationship between lithofacies, sequence stratigraphy, diagenesis, and porosity evolution within the Arab-D reservoir analog. The study revealed eight lithofacies which interpreted to have been deposited in an open-marine lower-slope and upper-slope of a ramp platform, ramp-crest, distal to proximal lagoon and tidal flat environments. The diagenetic and paragenetic analysis showed early marine dissolution and cementation, followed by replacement of aragonite and high Mg calcite to low Mg calcite. Porosity enhancement started with shoaling-up of the system. This produces most of the moldic and intraporosity in the study area. Although the outcrop section showed a degree of burial compaction, there is no pronounced effect of compaction on porosity reduction. With extensive progradation of the proximal lagoon and inner ramp along with meteoric realm, near-surface dolomitization was formed and resulted in porosity increase. This was very clear at the top of each of the high-frequency sequences of the lower part of the outcrop. Later, the whole system had undergone fracturing which enhanced porosity dramatically. Although, the outcrop has little or no macro porosity due to sub aerial exposure and recent meteoric cementation, the paragenesis study provides a predictive porosity distribution model within a high-resolution sequence stratigraphy framework and its associated diagenetic events. This model could provide better understanding of porosity evolution and valuable guide for subsurface exploration.

Assessment of Sediment Quality in Jiangsu Coastal Ocean Based on Grey Clustering Method

Thirty-nine samples of surface sediments obtained from Jiangsu coastal ocean were analysed to evaluate the sediment quality. The grey clustering method is applied to assess the sediment quality and generate the classified results. Then the samples are classified into three categories (clean, light pollution and heavy pollution). Of all the thirty-nine samples, there are eleven clean samples, twenty light pollution samples, and eight heavy pollution samples. The results show that the pollution status has the regional feature of concentrating distribution. By analysing underlying reasons, pollutants discharging into the sea due to increased industrial and agricultural activities contributed to the contamination. Therefore, more emphasis should be paid on the surface tidal flat sediment environment administration, especially on the treatment of pollution source for improving the sediment quality. It is very important to enhance the marine environmental protection for sustainable development of coastal area.

Petrological and geochemical interpretation of Triassic–Jurassic boundary sections from northern Iraq

Triassic–Jurassic sedimentary successions (Baluti and Sarki formations) in northern Iraq record a variety of environmental changes that may be related to global Triassic–Jurassic (Tr/J) boundary events. The diversity of some benthic fauna decreases through the transitional boundary beds. The coastal marine environment of the lower part of the Baluti Formation is followed by shallower tidal flat and supratidal marginal marine environments at the transitional boundary with the Jurassic‐age Sarki Formation. The alternating calcareous mudrocks and dolomitic limestones of the transitional succession are overlain by a succession of calcareous mudrocks and dolomicrites that form a dolocrete bed in the latest Triassic. The early Jurassic carbonates (lower part of Sarki Formation) were deposited in a shallow‐marine to lagoonal environment. Geochemical evidence supports this interpretation. TOC% increases towards the Tr/J boundary and the lower part of the Sarki Formation. This increase can be interpreted as resulting from the primary precipitation of dolocrete as palaeosol horizons. The variations in the oxygen isotope ratios mainly reflect the facies and diagenetic effects. Th/K ratio is generally constant and shows an increase in the calcareous mudrock beds of the upper part of the Baluti Formation, possibly related to the degradation of K‐bearing clay minerals. Low Th/U ratios are due to the depletion in thorium, typical of many marine carbonates rather than to an increase in authigenic uranium. This explanation is also corroborated by the presence of abundant fossils in some of the studied carbonates. Copyright © 2013 John Wiley & Sons, Ltd.

Depositional History and Sequence Stratigraphy of Tirgan Formation (Barremian–Aptian) in Central Kopet Dagh, NE Iran

Abstract The Tirgan Formation (Barremian – Aptian) is exposed in the Kopet Dagh in northeast Iran. Two stratigraphic sections in Radkan and Chenaran were measured. Their thickness are 238 m and 119 m, respectively. This formation in measured sections consists of three parts (including lower carbonate, middle limy shale – marl and upper carbonate rocks). Based on study of 164 thin-sections, 15 carbonate and 2 siliciclastic lithofacies have been identified. Carbonate lithofacies are deposited in a ramp platform in fore shoal, shoal, lagoon and tidal flat environments. Sea level changes during lower Cretaceous led to the formation of different large-scale depositional sequences Radkan (two) and Chenaran (two) respectively. The present study highlights the reconstruction of tectonic history of the area during lower Cretaceous.

Early to mid‐Holocene rapid sea‐level rise and coastal response on the southern Yangtze delta plain, China

ABSTRACTWe used accelerator mass spectrometry (AMS) 14C‐dated sediments of the Holocene basal supratidal flat to upper tidal flat facies in 11 cores on the southern Yangtze delta plain to reconstruct relative sea levels of 8.5–8.0 cal ka BP. Three cores were further AMS 14C dated and used to examine the evolution of sedimentary geomorphological environments in response to the rapid sea‐level rise during the early to mid‐Holocene. Results demonstrate relative sea‐level rise of around 30 mm a−1 from 8.5 to 8.3 cal ka BP and around 10 mm a−1 from 8.3 to 8.0 cal ka BP. Retrogradation from supratidal to lower tidal flat environments occurred in response to the rapid sea‐level rise at 8.5–8.3 cal ka BP, and aggradation from middle to upper tidal flat occurred at 8.3–7.9 cal ka BP. Further retreat of the tidal flat at 7.9–7.2 cal ka BP implies a mean sea‐level rise rate exceeding 5 mm a−1 at this time. We suggest that the rapid relative sea‐level rise during 8.3–8.5 cal ka BP and subsequent slower rise caused drastic changes in the coastal zone and that these changes are key phenomena for understanding the coastal response to future sea‐level rise.

Depositional environments and sequence stratigraphy of the Late Carboniferous−Early Permian coal-bearing successions (Shandong Province, China): Sequence development in an epicontinental basin

This study focuses on the Late Carboniferous−Early Permian coal-bearing successions in Shandong Province, North China in order to understand the depositional processes and sequence-stratigraphic framework in an epicontinental basin. Based on detailed analysis of eleven facies, five facies assemblages (FAs) were recognized in the studied succession. FA1–3 are present mainly in the Benxi and Taiyuan formations, and consist of mixed siliciclastic and carbonate lithofacies, representing eluvial-lagoon, barrier-lagoon, and tidal-flat environments. FA4 occurs in the Shanxi formation and consists mainly of interbedded medium to fine sandstone, siltstone, mudstone, and coal lithofacies, representing river-dominated deltaic environments. FA5 is characterized by interbeds of trough cross-stratified coarse sandstone, and silty mudstone, mainly in the Lower Shihezi Formation, which was deposited in meandering river channel and floodplain. Three third-order sequences were established based on the vertical arrangement of facies assemblages and identification of physical surfaces (i.e., subaerial unconformity, transgressive surface, and regressive surface). Each sequence comprises a transgressive systems tract (TST) and a highstand systems tract (HST). TST of sequence 1 is composed of eluvial lagoonal deposits (FA1), whereas HST formed in lagoon-barrier and tidal-flat settings (FA2 and FA3). TST of sequence 2 formed in a barrier-lagoon system (FA2), whereas HST is characterized by repetitive accumulation of interbedded limestone, sandstone, mudstone, and coal, deposited under lagoonal and tidal-flat settings (FA2 and FA3). TST of sequence 3 comprises FA2, and HST mainly FA4, deposited in a river-dominated shallow-water delta system. Sequence 3 is overlain by a fluvial sequence (FA5). The three third-order sequences in the Shandong region are generally correlated with those in the Taebaeksan Basin (South Korea), the eastern part of the North China Block. The relative sea-level curves established in the two regions show a generally similar long-term rising trend.

Observations on the Biology and Sclerochronology ofTurritella leucostoma(Valenciennes, 1832; Cerithioidea: Turritellidae) from the Gulf of California

Abstract: Fossil and Recent shells of Turritella leucostoma (Valenciennes, 1832) are common in the Northern Gulf of California and, during winter months, living specimens can be found populating tidal flat environments. At San Felipe, Baja California, Mexico, T. leucostoma preferentially inhabit the sediment near the base of tidal channels and the low tide beach, where a total of 45 live specimens were gathered and documented. Most specimens were found in feeding position with the aperture exposed at the sediment surface and the apex pointed down at a low angle into the sediment. They act as predominantly stationary semi-infaunal active suspension feeders. Actively moving specimens were encountered during day and night low tides. The size distribution of the shells is narrow and no juveniles occur on the San Felipe tidal flat. Analysis of δ18O performed on three shells shows variations of up to 3.4‰ attributable to seasonal changes in water temperature, and indicates longevity of 1.5–2 years and relativel...

Sequence stratigraphy of the Early–Middle Devonian succession (Padeha Formation) in Tabas Block, East-Central Iran: Implication for mixed tidal flat deposits

The facies and sequence stratigraphic analyses of the Padeha Formation (Early–Middle Devonian) in the East-Central Iran are based on two measured stratigraphic sections in the Ozbak-Kuh (type section) and Deranjal (Dahaneh-Kalot section) Mountains in the northern Tabas Block, with a thickness of 492 and 320m respectively. The field observations and laboratory studies were used to identify sixteen lithofacies and four architectural elements. The facies associations were classified into five categories including sandstone (St, Sp, Sr, Sh, Sl), fine grained (siltstone–claystone) or mud rock (Fl), interbedded sandstone–mud rock (Sr(Fl), Sr/Fl, Fl(Sr)), dolomite (Dl and Ds), and evaporate (El, Efl, Efm, Edl). Structural (wave and interference ripples, planar cross-bedding and herringbone, flaser-wavy and lenticular beddings, tepee and stromatolite structures, entrolothic foldings, shrinkage and syneresis cracks, rain drop imprints, and salt casts) and textural (mature–supermature quartzarenite) features, as well as predominant bimodal pattern of paleocurrents in most lithofacies, show that sediments of the Padeha Formation have been deposited in a tidal flat environment. The sandstone, interbedded sandstone–mud rock, and dolomite facies (SB and LA architectural elements) are related to subtidal and intertidal settings, and fine-grained sediments and evaporate facies (consisting of FF and E architectural elements) were deposited in the supratidal and sabkha settings. Detail sequence stratigraphic study led to identification of two 3rd order complete depositional sequences (DS2 and DS3) with SB1 sequence boundaries and two incomplete sequences (DS1 and DS4). Supratidal and sabkha facies were formed during the fall of relative sea level and are related to the lowstand systems tract (LST). The intertidal facies were formed at a rise of relative sea level and are interpreted as transgressive (TST) and highstand (HST) systems tracts.