Shallow Marine Embayment Research Articles

Middle Miocene final demise of remnants of an eastern Neotethyan seaway, Naga Hills, Indo-Myanmar Range

Miocene planktonic foraminifers occur in shale intercalated with thinly bedded siltstone and sandstone of the Surma Group in the foothills of the Naga Schuppen Belt of the Indo-Myanmar Range. Fourteen species from eleven genera are the first clearly imaged middle Miocene foraminifers recorded from the Surma Group in the Naga Hills. This new M5-M6 assemblage from the upper unit of the Bhuban Formation correlates to the uppermost Burdigalian to Langhian (16–14 Ma). Biostratigraphy, paleoenvironment and paleogeography of the assemblage are all significant. They provide a basis for widespread regional and global correlation constraining the timing of elimination of the final remnants of the Neotethyan seaway between India and eastern Eurasia. Results indicate that, unlike the western and Tibetan Himalayas where similar seaways disappeared before the Miocene, a shallow marine embayment that connected to the Indian Ocean endured in eastern parts of the India-Eurasia collision zone until the Middle Miocene.

Effects of lubricant oil and diesel on macrofaunal communities in marine sediments: A five year field experiment in Antarctica

Hydrocarbons pose significant risks to marine ecosystems. A field experiment investigated the effects of four different hydrocarbon products (diesel fuel and three lubricating oils: Unused, Used and Biodegradable) on sediment macrofaunal communities over a five year period, in a shallow Antarctic marine embayment. Sediments were defaunated, treated with a hydrocarbon and deployed in trays (including a control) on the seabed. Diesel fuel had the biggest initial impact on communities, with strong effects at 5 weeks and 1 year, in particular on annelids, but also on amphipods, ostracods and cumaceans. By five years, however, the effect of diesel was less than that of lubrication oils and showed more recovery than oiled treatments and the biggest effect was from the Used oil. There was an effect of hydrocarbons on diversity, especially diesel, at 5 weeks and 1 year, but by 2 and 5 years diversity was not different or greater in hydrocarbon treatments than controls. Total abundance was always lower in hydrocarbon treatments than controls, especially for crustaceans, but annelids were more abundant in oil treatments than controls at 5 years. Oils, and in some cases diesel, enhanced the abundance of some taxa at 2–5 years, including molluscs, some polychaete families (capitellids, cirratulids, dorvilleids), oligochaetes, as well as ostracods, cumaceans and isopods. Amphipods and tanaids were most sensitive to hydrocarbons, and annelids were very sensitive to diesel. The Biodegradable oil had similar magnitude community effects to standard oil at 5 years, but annelids were more affected by Biodegradable oil, particularly at 1 and 2 years, and it did not enhance annelid or mollusc abundance at 5 years like the other oils, except for some polychaete families. Impacts of spilled hydrocarbons in Antarctica will persist well beyond 5 years, but diesel impacts will recover faster than oil.

Historic development of heavy metal contamination into the Firth of Thames, New Zealand

Near-coastal marine sediments often provide high-resolution records of various anthropogenic influences such as the release of heavy metals, which pose a potentially negative influence on aquatic ecosystems because of their toxicity and persistence. In places, the gradual onset of man-made heavy metal emission dates back to ~ 4500 years BP and is difficult to distinguish from potential natural sources. New Zealand offers a perfect setting for studies on anthropogenic impact due to its well-defined three-step development: pre-human era (until ~ 1300 CE), Polynesian era (~ 1300–1800 CE) and European era (since ~ 1840 CE). However, hardly any information exists about the degree of heavy metal input to New Zealand’s coastal areas and the ‘pristine’ natural background values. This study determines the natural background contents of lead (Pb) and zinc (Zn) in marine sediments of the Firth of Thames, a shallow marine embayment on New Zealand’s North Island, and investigates anthropogenic inputs in historic times. Eight sediment cores were analysed by X-ray fluorescence (XRF) for their element composition and temporally resolved by a pollen and radiocarbon-based stratigraphic framework. Sharp increases in Pb and Zn contents occurred simultaneously with the onset of goldmining activities (1867 CE) in the nearby catchment area. The contents of Zn (Pb) increase from very stable values around 60 (13) ppm in the older sediments, interpreted to reflect the natural background values, to an average maximum of 160 (60) ppm near the core top, interpreted to reflect a significant anthropogenic input. These findings unravel the history of contamination in the Firth of Thames and provide an urgently needed database for the assessment of its current ecological state.

A marine origin for the late Mesoproterozoic Copper Harbor and Nonesuch Formations of the Midcontinent Rift of Laurentia

The c. 1.1 Ga Copper Harbor and Nonesuch Formations of the Keweenawan Supergroup exposed along the Canadian-United States shorelines of Lake Superior are part of the surface exposures of the Laurentian Midcontinent Rift. These units have long been considered non-marine in origin and have figured prominently in ideas regarding the evolution of microbial life and the redox conditions of Earth’s ocean-atmosphere system at the close of Mesoproterozoic time. However, these rocks also host hydrothermal metal deposits, the emplacement of which may have compromised primary geochemical signals that are used to underpin those ideas. Here we highlight new sedimentological observations to provide an independent framework for assessing the depositional setting and geochemistry of those strata. We show that the totality of sedimentological features leads to the conclusion that parts of the upper Copper Harbor Formation and the entirety of the Nonesuch Formation were deposited along tide- and wave-influenced shorelines and in shallow-marine settings under evaporitic conditions. Evidence for this interpretation includes the abundance of flaser, wavy, linsen and pinstripe bedding, ubiquity of reactivation surfaces and mud drapes associated with all ripple forms, superposed sets of ripple cross-lamination showing bimodal (herring-bone) sediment transport directions, desiccation cracks and metre-scale hummocky cross-stratification. Further, evaporite fabrics and pseudomorphs after gypsum in the upper 200 m of the Copper Harbor Formation and in numerous stratigraphic positions within the Nonesuch Formation indicate that the water body was saline, not fresh. The emerging palaeogeographic image is one of a large, shallow-marine embayment with fringing sabkha-like shorelines. Ideas about late Mesoproterozoic biospheric evolution and Earth’s surface redox and oxygenation that rely on the Nonesuch Formation and Copper Harbor stromatolites having been deposited within a lacustrine setting require reassessment.

Sedimentary responses to Holocene sea-level change in a shallow marine environment of southern China

This study has examined how the sedimentary processes in the prevalent non-deltaic coastal marine environments along the southeast coast of China have responded to sea-level change and other environmental drivers during the Holocene. Three sediment cores collected from a shallow marine embayment of the Lantau Island, Hong Kong, on the northern coast of the South China Sea, were analyzed. The results of particle size, total organic carbon content, organic carbon and nitrogen ratios, organic carbon stable isotope ratios, abundance of alkenones and radiocarbon dating of these cores have helped reconstruct the sedimentary history of this site. This history shares the similarity in sedimentary processes within the deltaic environment for the early Holocene, because palaeo-incised channels exist in both environments. The first 1500 years of deposition involved rapid channel infill caused by the rapidly rising sea level and strong monsoon-driven discharge. This was followed by a period of decelerated sedimentation under strong marine influence as the sea flooded the wide accommodation space in the subsequent two millennia. Major differences between the two environmental settings occur in the past 7000 years: vertical accretion was seen in the non-deltaic coastal environment, whilst lateral shoreline advance was the dominant process in the deltaic basin. The progressively slowing down in sedimentation rate in the non-deltaic site during the middle and late Holocene was caused by the reduced monsoon discharge, intensified disturbance from tropical cyclone activity and coastal currents.

Mapping a coastal transition in braided systems: an example from the Precipice Sandstone, Surat Basin

ABSTRACTThe Precipice Sandstone is traditionally interpreted as a braided fluvial deposit that transitions upwards into meandering channel deposits responding to a rise in base level that eventually deposits the overlying alluvial to lacustrine Evergreen Formation. This study found sedimentary evidence of tidal to marine influence within the Precipice Sandstone coincident with avulsion and diversion of the system from southward to northward-flowing channels as the system was transgressed. The north-flowing channels are interpreted to debouch into a shallow restricted marine embayment with tide and wave influence, which provides an alternative insight into this unit and suggests a Lower Jurassic north or northeasterly marine connection. The Precipice Sandstone is a regional aquifer, in places hosts hydrocarbons and has been considered as a storage unit for CO2 geosequestration. Outcrop analogues can provide geometries to accompany facies interpreted from sedimentary structures that are observable in core, to assist in characterising reservoir heterogeneity.

Palynological assemblage from the Deccan Volcanic Province, central India: Insights into early history of angiosperms and the terminal Cretaceous paleogeography of peninsular India

Sedimentary deposits of the Deccan Volcanic Province (DVP), of central India are rich in fossil flora and fauna. Based on a new palynological study of Infratrappean deposits from a borehole succession located in the Ashtona village, Yeotmal District, Maharashtra (Wardha Basin), this paper attempts a reconstruction of the Late Cretaceous paleovegetation, paleoecology, depositional environment and paleogeography of central India prior to Deccan volcanism, and also seeks to evaluate the early history and timing of the angiosperm diversification relative to the Cretaceous-Paleogene (K-Pg) transition. The stratigraphic age of the Infratrappean sequence was determined on the basis of several index palynomorphs (Aquilapollenites, Jigansupollis), Azolla cretacea, Gabonisporis sp, Scollardia conferta of Maastrichtian age. Two new pollen species (Dipterocarpuspollenites cretacea sp. nov., Retiacolpites pigafettaensis sp. nov., and one new dinoflagellate species (Pierceites deccanensis sp. nov.) are described in this study. The numerical abundance of the mangrove pollen Spinizonocolpites pollen (Nypa), combined with the dinoflagellate cyst Pierceites deccanensis, indicates a brackish marine depositional setting close to low-lying coastal forests in central India during the Late Cretaceous. Furthermore, the new evidence presented here from an inland location in the Deccan province strongly suggests the existence of a shallow marine embayment in central India during the late Maastrichtian, which extended from the east coast through the Godavari rift zone, thus adding significantly to the previously described marine signatures from the Upper Cretaceous sequence of Rajahmundry area on the south-eastern coast of peninsular India. The Late Cretaceous fossil pollen of Dipterocarpaceae documented here provides compelling evidence for the evolution of these tropical rain forest elements in the insular India and their dispersal to south east Asia after the initiation of India-Asia collision, consistent with the Out of India hypothesis. The new palynomorph assemblage also has significant implications for our understanding of the floral response to the initiation of Deccan volcanism.

Tidal sedimentation preserved in volcaniclastic deposits filling a peripheral seaway embayment (early Miocene, Sardinian Graben)

The Sardinian Graben System was a part of a NE-SW-oriented extensional basin, rotated counter-clockwise into a N-S-elongate basin, as consequence of the eastward migration of the Apennine orogenic front, in the western Mediterranean during the Neogene.Starting from the early Miocene, the Sardinian Graben was inundated by marine waters, turning progressively into a seaway, characterized by a tidal circulation as consequence of the connection between the Atlantic Ocean to the west and the Paratethys Ocean to the east.In this work, we investigate an area located marginally to the mid-seaway, whose well-exposed volcaniclastic deposits record the local expression of a tidal amplification occurring in a coastal peripheral embayment of the wider Sardinian Seaway.The studied succession is ca. 140 m thick and includes three main units: (i) the 20-m-thick lowermost unit consists of fluvio-lacustrine sandstones and conglomerates belonging to lower delta-plain and delta-platform environments; (ii) the second unit is 60–70 m thick and includes heterolithic sandstones and mudstones, exhibiting a variety of tidal sedimentary structures, and lies on the previous deposits through a tidal ravinement surface; these two units are mostly volcaniclastic in composition, reflecting the dominance of a magmatic source over other extrabasinal components; (iii) the uppermost unit is ca. 50 m thick, erosionally overlies the previous deposits and is made up of shoreface sandstones and open-shelf mudstones, whose composition indicates even less volcaniclastic elements and the prevalence of other clastic alongshore-derived components.Based on the results of the facies analysis, the study succession is interpreted as the infill of an incised valley along the southern flank of a structural high. The valley was excavated during a phase of relative sea-level lowstand (Aquitanian?) preceding a subsequent stage of major transgression (Burdigalian). Initially, a fluvial system impinged the valley from the west favoring the progradation of a deltaic system in a shallow-marine embayment. During an early stage of transgression, the isolation of a part of this coastal area generated by the building of a barrier island, produced the onset of a tidal-flat sedimentation over the previous deposits. A late transgression occurred through the inundation of this coastal area by marine waters and the consequent back-stepping of beach-barrier and open-shelf strata.The sedimentological features of this stratigraphic succession indicate as this valley was filled in a tectonic setting with a high rate of accommodation, where the tidal influence progressively increased during sediment accumulation, possibly due to the marginal position respect to a wider tide-dominated marine conduit.The present paper thus: (i) documents for the first time a tidal signature in the lower Miocene strata of Sardinia; (ii) indicates new possible relationships with other, coeval seaway successions of the western and northern Mediterranean area; (iii) suggests constrains for palaeogeographic reconstructions; (iv) and throws the basis for future researches on the Sardinian Seaway.

Late Pleistocene-Holocene shoreline reconstruction and human exploitation of molluscan resources in northern Pieria, Macedonia, Greece

This study presents new stratigraphic, sedimentological, pedological dating and macro- and micro-fauna data, in order to reconstruct late Pleistocene and Holocene landscapes and shorelines of northern Pieria, northern Greece, and to discuss human exploitation of coastal environments. At the end of the Pleistocene, coastal Pieria formed part of the broad coastal plain that extended from northern Anatolia to Thessaly. Holocene marine transgression flooded the Pleistocene terrain and by the Early-Middle Neolithic (5870/5690-5720/5610BCE) brackish water reached the Korinos area. A relatively shallow marine embayment was eventually established and the shoreline was at least 3.5km west of its present position. Massive Final Neolithic alluviation (4339/3999–4039/3775BCE) resulted in marine regression and the building up of a sand barrier. An open, brackish lagoon occupied a large part of the study area at least since the Early Bronze Age (3090–2880/2870BCE). By the Late Bronze Age (1740/1505–1520/1254BCE) renewed alluviation resulted in a second phase of sea regression and the creation of marshes at the edges of the lagoon. Alluvial sediments and intercalated palaeosols cap the marine/lagoon/marsh sequence and indicate a significant increase in sediment supply that started ca. 2000years ago and culminated during the Early Christian period (4th–6th century CE). Rapid shore progradation resulted in the creation of the modern coastal plain of Korinos. Archaeomalacological data indicate that prehistoric communities exploited intensively shallow aquatic environments for food and artefact manufacture. Specialisation in the gathering of the brackish mollusc Cerastoderma glaucum (the common cockle) persisted for at least 6000years (from the Early Neolithic to the Early Iron Age), thus becoming a regional culinary tradition. Although attitudes towards molluscs were originally (7th-6th mil. BCE) shaped by natural availability and proximity to shell sources, substantial residual variability from the Late Neolithic (late 6th–early 5th mil. BCE) onwards, suggesting local preferences in food and material culture, can be attributed to cultural choices and highlights the complexity of human/environment interactions.

Sedimentology of an early Cambrian tide-dominated embayment: Quyuk formation, Victoria Island, Arctic Canada

The early Cambrian (series 2, stage 4) Quyuk formation is exposed in the Minto Inlier of western Victoria Island, Canadian Arctic Islands, and forms the base of the Phanerozoic succession. Coeval with other sandstones of this age in Laurentia, it was deposited in a shallow-marine embayment on a passive margin during the initial phase of the early Paleozoic transgression. Four facies associations are recognized: (1) offshore muds consisting dominantly of dark gray laminated mudstone with discontinuous laminae of medium- to coarse sand; (2) offshore sand dune fields characterized by laterally continuous, planar cross-stratified beds up to 1.4m thick of medium- to coarse-grained sandstone; (3) distal nearshore consisting dominantly of fine- to medium-grained bioturbated sandstone and fine- to medium-grained sandstone interbedded with laminated mudstone; and (4) proximal nearshore characterized by laterally continuous fine- to medium-grained bioturbated sandstone and medium-grained oolitic ironstone. Large scale dunes of facies association 2 record areas where tidal currents were amplified and had available sediment supply in contrast to facies association 1, which was sediment starved. Dunes are, for the most part, non-bioturbated or contain just a few individual burrows belonging to Skolithos. In nearshore settings, bioturbation in the form of a typical early Cambrian suite of shallow-subtidal ichnofossils predominated, representing a low-diversity Cruziana ichnofacies. Oolitic ironstone horizons in the proximal nearshore mark periods of low sedimentation rates when iron became concentrated and calcite was the primary cementing agent. The coastline is envisaged as a complex of bays and lagoons.

Fluvial evolution of the Rhine during the last interglacial-glacial cycle in the southern North Sea basin: A review and look forward

This paper presents the current state of knowledge on the evolution and depositional history of the River Rhine in the southern part of the North Sea basin during the upper Middle and Late Pleistocene, and its response to climate change, sea-level oscillation and glacio-isostasy. The study focuses on the development of the Eemian interglacial lower-delta in the central Netherlands and its relation to records of climate and sea-level rise, and uses the Saalian and Weichselian pre- and postdating periods to place its development in context.The Rhine fluvial system fills the gradually subsiding North Sea basin, but its development has strongly been affected by the Saalian glaciation and its remaining topography. Ice-pushed ridges originating off the limit of maximum glaciation basically divided the central Netherlands into two sedimentary depocentres: a central depocentre within the former ice-limit, and a southern depocentre south of it.The sedimentary record of the central depocentre, including an incised-valley fill, shows a 20–40 m thick stacked sequence consisting of three units. The incised-valley fill consists of a Late Saalian to early Eemian age lower fluvial unit and a Weichselian age upper fluvial unit, both composed of coarse-grained channel deposits. Sandwiched in-between is a 5–15 m thick record composed of fine-grained fluvial and estuarine (tidal) floodbasin and shallow-marine deposits. It is of Eemian interglacial and Early Weichselian age, and comprises transgressive and highstand deposits that show the drowning of a fluvial system. Inland parts transformed from fluvial to deltaic and estuarine environments, and the most downstream parts transformed to a shallow-marine embayment. Preservation of these units occurred, despite considerable sea-level fall and climate-controlled erosion taking place in the last-glacial. Preservation potential was increased by the fact that the Rhine system avulsed away to the southern depocentre, halfway the Weichselian Pleniglacial. Consequently, the infill of the southern depocentre is of an entire different nature, and last-interglacial transgressive or highstand units are hardly preserved.Because of glaciation and resulting depocentre configuration, the Netherlands in NW Europe thus offers a very good opportunity to study the transgressive interglacial lower-deltaic records and falling-stage preservation thereof – both key elements for understanding sedimentary development over full 100-ky glacial-interglacial cycles of climate and base-level change.

The palynofacies pattern for the Lower Cretaceous of central Poland

Sedimentary environments and palynofacies were identified in the Lower Cretaceous of central Poland. The study was based on lithological observations, sedimentological logging and palynological investigations in the following boreholes: Poddebice PIG2, Kolo IG3 and IG4, Wągrowiec IG1, Sarnow IG1, Ciechocinek IG3, Mszczonow IG1, Korabiewice PIG1, Czluchow IG2, Klosnowo IG1 and Tuchola IG1. Palynological observations were correlated with sedimentological, lithofacies and paleogeographical data. Sedimentary environments and palynofacies were analysed in the vertical section, and spatially in different areas: in the central basin area, in the carbonate-clastic deposition zone, in the transitional zone (deltaic sedimentation) and in a zone of an active salt pillow. The following sedimentary environments were identified in the Lower Cretaceous: upper shoreface and lower-middle shoreface with transitions to an offshore-open marine shelf, delta (?delta front) passing up into distributary channel fills on a delta plain, presumed barrier and shallow-marine embayment, lagoon and shallow carbonate-siliciclastic shelf. In case of the absence of diagnostic features for exact determination of sedimentary environments, the environments were defined as generally marine or transitional (probably deltaic). A maximum flooding surface has been identified in the Poddebice PIG2 section, represented by a thin dark-grey marl bed which seems to be dated at the Berriasian/Lower Valanginian transition. The relationships between sedimentary environments and the characteristics of the palynofacies spectrum were determined, and a palynofacies pattern for the Lower Cretaceous of central Poland was proposed in a tabular form.

Characterizing Spatial and Temporal Variability of Dissolved Gases in Aquatic Environments with in situ Mass Spectrometry

The TETHYS mass spectrometer is intended for long-term in situ observation of dissolved gases and volatile organic compounds in aquatic environments. Its design maintains excellent low mass range sensitivity and stability during long-term operations, enabling characterization of low-frequency variability in many trace dissolved gases. Results are presented from laboratory trials and a 300-h in situ trial in a shallow marine embayment in Massachusetts, U.S.A. This time series consists of over 15000 sample measurements and represents the longest continuous record made by an in situ mass spectrometer in an aquatic environment. These measurements possess sufficient sampling density and duration to apply frequency analysis techniques for study of temporal variability in dissolved gases. Results reveal correlations with specific environmental periodicities. Numerical methods are presented for converting mass spectrometer ion peak ratios to absolute-scale dissolved gas concentrations across wide temperature regimes irrespective of ambient pressure, during vertical water column profiles in a hypoxic deep marine basin off the coast of California, U.S.A. Dissolved oxygen concentration values obtained with the TETHYS instrument indicate close correlation with polarographic oxygen sensor data across the entire depth range. These methods and technology enable observation of aquatic environmental chemical distributions and dynamics at appropriate scales of resolution.

Exceptional occurrence of fossil baleen in shallow marine sediments of the Neogene Pisco Formation, Southern Peru

Fossil baleen is rare in the sedimentary record. This paper documents the exceptional occurrence of thirty seven fossil whale specimens with preserved baleen in the Neogene Pisco Formation during a transect survey in a limited area west of the Ica River Valley near the town of Ocucaje in southern Peru. The sedimentary layers consist of tuffaceous and diatomaceous sandstones, diatomaceous mudstones, and dolomites, deposited in a shallow marine embayment. Observations of modern whale carcasses on the seafloor and stranded individuals indicate that baleen detaches from the mouth of the whales very rapidly after death, and that bones deteriorate very rapidly as a result of scavenging activity and abrasion. In contrast, the bones of the Pisco Formation whales are exceptionally well preserved, and their baleen is often found in life position suspended from the rostrum. Sedimentary structures found associated with some skeletons indicate tidal and storm processes, suggesting that the environment was not anoxic. This exceptional occurrence of fossil baleen suggests early mineralization of the baleen attachment to the rostrum or rapid burial of the skeletons before any detachment or loss could occur.

Quaternary depositional patterns and sea-level fluctuations, northeastern North Carolina

A detailed record of late Quaternary sea-level oscillations is preserved within the upper 45 m of deposits along an eight km transect across Croatan Sound, a drowned tributary of the Roanoke/Albemarle drainage system, northeastern North Carolina. Drill-hole and seismic data reveal nine relatively complete sequences filling an antecedent valley comprised of discontinuous middle and early Pleistocene deposits. On interfluves, lithologically similar marine deposits of different sequences occur stacked in vertical succession and separated by ravinement surfaces. Within the paleo-drainage, marine deposits are separated by fluvial and/or estuarine sediments deposited during periods of lowered sea level. Foraminiferal and molluscan fossil assemblages indicate that marine facies were deposited in a shallow-marine embayment with open connection to shelf waters. Each sequence modifies or truncates portions of the preceding sequence or sequences. Sequence boundaries are the product of a combination of fluvial, estuarine, and marine erosional processes. Stratigraphic and age analyses constrain the ages of sequences to late Marine Isotope Stage (MIS) 6 and younger (∼ 140 ka to present), indicating multiple sea-level oscillations during this interval. Elevations of highstand deposits associated with late MIS 5 and MIS 3 imply that sea level was either similar to present during those times, or that the region may have been influenced by glacio-isostatic uplift and subsidence.

Early Weichselian palaeoenvironments reconstructed from a mega‐scale thrust‐fault complex, Kanin Peninsula, northwestern Russia

A section, almost 20 km long and up to 80 m high, through alternating layers of diamict and sorted sediments is superbly exposed on the north coast of the Kanin Peninsula, northwestern Russia. The diamicts represent multiple glacial advances by the Barents Sea and the Kara Sea ice sheets during the Weichselian. The diamicts and stratigraphically older lacustrine, fluvial and shallow marine sediments have been thrust as nappes by the Barents Sea and Kara Sea ice sheets. Based on stratigraphic position, OSL dating, sea level information and pollen, it is evident that the sorted sediments were deposited in the Late Eemian‐Early Weichselian. Sedimentation started in lake basins and continued in shallow marine embayments when the lakes opened to the sea. The observed transition from lacustrine to shallow marine sedimentation could represent coastal retreat during stable or rising sea level.

Holocene palaeogeographies of the Astakos coastal plain (Akarnania, NW Greece)

This paper deals with Holocene coastal changes of the Astakos plain in Akarnania, NW Greece. Palaeoenvironmental scenarios are based on the analysis of the lateral and vertical distribution patterns of sedimentary facies. Sediments from vibracorings were studied using geomorphological, sedimentological, microfaunal, palaeobotanical and geochemical methods. A geochronostratigraphy was achieved by 14C-AMS-dating of organic matter. We present palaeogeographical maps for different points in time since the mid-Holocene. The evolution of the coastal area was generally controlled by the migration of a complex system of a shallow marine embayment, an adjacent lagoonal environment and an adjoining coastal lake forced by the interaction of sea level rise, tectonic movements, and sediment supply from the hinterland. The maximum transgression of the Ionian Sea took place at circa 5500 cal BC reaching approx. 1.1 km inland. The lagoon as well as the coastal lake had their largest dimensions around 4500 cal BC indicating a more humid climatic period. In the course of a long-lasting regression, an asymmetric sedimentation pattern developed. Around 2500 cal BC it was characterized by strong fluvial deposition of the Xeropotamos in the western plain and a small and narrow marine embayment with associated lagoonal to limnic coastal water bodies in the eastern plain. The latter were related to karstic springs draining the adjacent Rigani ridge. Around 500 cal BC the coastline lay about 200 m landward of its present position. Possible harbour sites for the ancient polis of Astakos are (a) the area of modern Astakos where a mole in a position seawards of the present coast would have guaranteed deep water conditions for anchoring, or (b) the southeastern fringe of the plain where deep water prevailed and the nearby freshwater outlet protected the site from rapid siltation. We found increased torrential activity (i) for the 6th–5th millennium BC, (ii) for the 2nd half of the 1st millennium BC until Roman times, and (iii) at the end of the 19th century AD. At least the two younger phases are mostly due to anthropogenic soil erosion. Between the 4th and the 2nd millennium BC a period of ecological stability existed. Relative changes in sea level for the Bay of Astakos were reconstructed for the first time. Since the mid-Holocene, the relative sea level has never reached a higher position than today. It rose from 12.50 m b.s.l. at 6200 cal BC via 2.20 m b.s.l. at 500 cal BC to its present level. Besides eustatic reasons, tectonic subsidence due to the half graben structure of the area is the main trigger of the relative rise in sea level.

Role of microbial mats in Sulaibikhat Bay (Kuwait) mudflat food webs: evidence from δ13C analysis

Although microbial mats are known worldwide to contribute to trophic bases in shallow marine embayments, their role has yet to be ascertained for similar habitats in the Arabian Gulf region. In this study, stable carbon isotope analysis in conjunction with faecal and gut analyses were employed to evaluate the relative importance of microbial mats in the nutrition of macrofaunal consumers and their contribution to the exceptional biodiversity, abundance and biomass of species inhabiting Sulaibikhat Bay mudflats (2000-2001) in the absence of extensive macro-vegetation. Microbial mats were mainly composed of diatoms and cyanobacteria (approx. 70 and 30% respectively), with a reduction in the latter with decreasing intertidal gradient. Faeces of 5 out of the 6 species analysed contained both mat components at varying degrees. Diatoms occurred rarely in faeces of the high intertidal consumers, while cyanobacteria dominated the faeces of those occurring at lower levels. Gut analysis revealed that 6 out of the 9 species analysed contained mat residues. Primary producers had distinct δ 13 C values with microbial mats showing a heavy signature (-15.3%o) in comparison to the halophyte Salicornia herbacea (-24.7%o), phytoplankton (-21.6%o) and the mangrove Avicennia marina (-28.1%). The δ 13 C values for herbivorous, omnivorous and carnivorous macrofauna ranged between -9.4 and -15.3%o. It appears from this investigation that microbial mats form the primary source of nutrition for both benthic and pelagic macrofaunal species within the bay including commercially important species, and that selective assimilation/digestion of cyanophytes from the mats is the likely explanation for the relatively high enrichment in the δ 13 C signatures of species located along the higher intertidal zone.

Validation of accumulation rates in Teluk Banten (Indonesia) from commonly applied 210Pb models, using the 1883 Krakatau tephra as time marker

Teluk Banten is a tropical shallow marine embayment on the north coast of Java, close to the Krakatau volcanic complex. The tsunami generated by the 1883 Krakatau eruption resulted in the deposition of a tsunamite tephra layer on the bottom of Teluk Banten. The Krakatau Event Layer has been used as a time marker to validate 210Pb geochronological dating models. This validation was performed to answer the question: Why should we believe excess 210Pb derived mass accumulation rates? The commonly used models have therefore been applied to 210Pb activity profiles from 25 gravity cores. Models that have been validated are the Constant Flux and Constant Sedimentation (CF/CS) (with and without a surface mixed layer), the Constant Initial Concentration (CIC), the Constant Rate of Supply (CRS), and the Flux Balance model. After comparison of the mass accumulation rates (MARs) of the different models with the MARs obtained from the Krakatau-layer, the following could be concluded. Firstly, activity profiles without a surface mixed layer gave CF/CS–MARs which were on average a factor 1.4 ± 0.3 ( n = 8) too high. Including a mixing-rate of 0.5 ± 0.4 cm 2 yr − 1 into the model could explain this overestimation. Secondly, for 210Pb activity profiles with a surface mixed layer, the MARs were in good comparison (1.0 ± 0.3, n = 12) with the MARs derived from the Krakatau Event Layer. Thirdly, increased accumulation instead of reworking had to be the main cause of the comparatively thick upper layer of five cores with very high inventories. Fourthly, assuming a variable accumulation rate and applying the CIC model and CRS model for these five cores, the weighted average CIC–MARs were in general more accurate than the CRS–MAR. Finally, the Flux Balance model, which is not often used, gave MARs that were a factor 1.3 ± 0.2 ( n = 25) too high. The advantage of this model is that it is independent of the profile shape. The disadvantage is that a reliable and accurate initial activity over longer time scales has to be obtained.

Gradient analysis of faunal distributions associated with rapid transgression and low accommodation space in a Late Pennsylvanian marine embayment: Biofacies of the Ames Member (Glenshaw Formation, Conemaugh Group) in the northern Appalachian Basin, USA

The Ames Sea, situated in a shallow marine embayment in the Appalachian Basin, was the result of the most extensive marine transgression of the Pennsylvanian in this region. Gradient analysis of the proportional abundance of taxa reveals an environmental continuum across the Ames embayment along which four biofacies were distributed. Biofacies distribution is interpreted to be controlled by salinity, turbidity, and oxygen gradients associated with the geometry of the Ames depositional basin and relative sea-level change. The eastern portion of the Ames Sea resembled a foredeep trough located on the detrital slope of the recently uplifted Appalachian Highlands. Biofacies 1 and 2 occur exclusively in the eastern part of the Ames depositional basin and are dominated by eurytopic molluscs tolerant of terrigenous influx. Biofacies 3 occurs in both the eastern and western portions of the Ames depositional basin. This biofacies is dominated by the opportunistic brachiopod Neochonetes, which would quickly colonize the seafloor in the wake of transgression.d Biofacies 4 occurs exclusively in the western part of the Ames depositional basin and is composed primarily of stenotopic crinoids, bryozoans, brachiopods, and epifaunal bivalves that inhabited a clear water, cratonic ramp on the eastern flank of the Cincinnati Arch. Vertical variations of faunal assemblages in the Ames Member were the result of variations in relative sea level associated with glacio–eustatic cycles. Biofacies 3, dominated by Neochonetes, was deposited at the base of the Ames Member during the initial rapid transgression in a mostly dysoxic environment with low turbidity and marine salinity. During the first regression, low-density surface water from eastern sources restricted vertical circulation, established a stratified water column, and promoted estuarine conditions in the Ames Embayment. Well-oxygenated surface waters were unable to circulate to the benthic habitat, which led to periodically dysoxic conditions and the establishment of Biofacies 1 and 2, composed of diminutive eurytopic molluscs. A second, stratigraphically-higher occurrence of Biofacies 3 is interpreted to represent a second transgression. However, unlike the first transgression, lithologic and faunal data suggest that the benthic habitat was well-oxygenated. Above the mid-Ames marine zone occurrence of Biofacies 3, Biofacies 1 and 2 were deposited in the final regressive phase as local terrigenous source areas brought increasing turbidity and fluctuating salinity to the Ames Embayment. Previous paleoecological research on the Ames Member cited freshwater and/or clastic influx as the major controls on biotic distribution, but the results of the present study suggest that oxygen availability was also a major control. Stratification of the water column during the Ames sea-level cycle promoted estuarine circulation that prevented well-oxygenated surface waters from reaching the benthic habitat. This led to the deposition of dark gray to black fissile shales that contain fossil assemblages dominated by diminutive molluscs and brachiopods that were tolerant of low-oxygen conditions.