Marine Embayment Research Articles

Latest Carboniferous–earliest Permian transgressive deposits in the Paganzo Basin of western Argentina: Lithofacies and sequence stratigraphy of a coastal-plain to bay succession

The upper Paleozoic rocks of Gondwana record a complex paleoclimatic history related to the migration of the supercontinent over high latitudes. Changes in climate and relative sea level can be traced through detailed sedimentologic and sequence-stratigraphic analysis. Our study focuses on transgressive deposits of Stephanian–Early Permian age in the lower member of the Tupe Formation with the objective of characterizing lithofacies and sedimentary environments within a sequence-stratigraphic framework in order to achieve a better understanding of the sedimentary history of the Paganzo Basin and the nature of transgressive deposits. Sixteen lithofacies grouped in eight assemblages were defined and arranged in two complete sequences. A sequence boundary (SB) is identified at the base of the Tupe Formation. Coastal-plain deposits capped by marine embayment lithofacies are included within sequence 1. A relative sea-level fall (SB) is recorded by an abrupt change into braided alluvial-plaine deposits (LST). The beginning of the TST is characterized by the appearance of coal and deltaic lithofacies. Late TST deposits occur above a ravinement surface and comprise bay-margin to distal-bay deposits forming a retrogradational stacking package. These lithofacies are replaced upwards by HST deposits. A relative sea-level fall (SB) is recorded by the presence of fluvial deposits overlying marine lithofacies. The Tupe Formation illustrates the transition of a coastal-plain to a marine embayment. The detection of a transgressive surface within the coastal-plain deposits of sequence 1 expanded significantly the volume of deposits now included as part of the latest Carboniferous–earliest Permian transgression, and underscores the importance of searching for transgressive signatures in non-marine environments. The presence of two sequences supports a punctuated shoreline trajectory with an overall retrogradational stacking pattern. An abrupt relative sea-level fall and increased aridity is recorded at the end of the transgressive event.

Sedimentary facies and sequence stratigraphy of coarse-grained Gilbert-type deltas within the Pliocene thrust-top Potenza Basin (Southern Apennines, Italy)

Coarse-grained, fluvially-dominated Gilbert-type braid deltas represent a volumetrically significant component of the Potenza Basin sedimentary infill, a small thrust-top structural depression that developed during the Pliocene in the Southern Apennines (Italy). Excellent exposure shows vertical and lateral relationships among facies assemblages that identify a suite of deltaic and non-deltaic depositional environments occupying semi-confined marine embayments along the southern–western basin margin. The succession is around 50 m thick and consists mainly of shoreface and offshore sands and clays, moderately wave-worked and covered by shoal-water deltaic clinostratified gravels. The deltas are organized into two vertically-stacked sequences that display well-developed angular-to-tangential foresets and poorly-preserved topsets, and a suite of internal depositional architectures consisting of alternating progradational and aggradational geometries that were controlled by high-frequency, relative sea-level changes in a relatively slowly subsiding basin. The common element that characterizes all the depositional architectures detected within the two main studied sections is the constant influence of coastal uplift on the deltaic systems during sediment accumulation. The tectonic control of the basin margin from which the deltas were sourced forced a forward-stepping (basinward) arrangement of stacked Gilbert-type braid deltas, and these produced clinoforms that become progressively younger toward the basin depocentre. The deltaic sequences show different offsets in their along-dip arrangement suggesting that the coastal margin was inclined at varying angles depending on the rates of the tectonic uplift. Two end-members of Gilbert-type delta architectures are represented by concave- and flat-bottom deltas, prograding onto a mudstone and calcareous substrate, respectively. These two different Gilbert-type models reflect a different style of delta accretion during progradation, due to the response of the substrate to the erosion exerted from gravel avalanches.

Plio-Pleistocene drainage development in an inverted sedimentary basin: Vera basin, Betic Cordillera, SE Spain

The Vera basin is one of a series of interconnected Neogene–Quaternary sedimentary basins located within the Internal Zone of the Betic Cordillera (southeast Spain). Since the Pliocene the Vera basin has been subjected to low uplift rates (11–21 m Ma − 1 ) and inverted via compressive tectonics that are related to the ongoing oblique collision between the African and Iberian plates. Within this paper the sedimentary and geomorphic response to basin inversion is explored. Sedimentary processes and environments are established for key stratigraphic units of the Pliocene/Plio-Pleistocene basin fill and Pleistocene dissectional landscape. These data are subsequently utilised to reconstruct an evolving basin palaeogeography. Fault and uplift data are employed to discuss the role of tectonically driven basin inversion for controlling the resultant palaeogeographic changes and associated patterns of drainage development. During the Early-Mid Pliocene the Vera basin was characterised by shallow marine shelf conditions (Cuevas Formation). A major palaeogeographic reorganisation occurred during the Mid-Late Pliocene. Strike-slip movement along the eastern basin margin, coupled with uplift and basin emergence created a protected, partially enclosed marine embayment that was conducive for Gilbert-type fan-delta sedimentation from fluvial inputs along the northern and eastern basin margins (Espíritu Santo Formation). The Vera basin then became fully continental and internally drained through the development of a consequent drainage network that formed following the withdrawal of marine conditions during the Late Pliocene to Early Pleistocene. Alluvial fans developed along the northern and western basin margins, grading to a bajada and terminating in a playa lake in central basin areas (Salmerón Formation). During the Early-Mid Pleistocene a switch from basin infilling to dissection took place, recorded by alluvial fan incision, a switch to braided river sedimentation and fluvial incision into the underlying basin fill sediments and basin margin mountainous topography. Fluvial incision, headwards erosion, expansion and modification of the consequent drainage network is documented within a series of up to four major inset river terrace levels and associated landforms. Fluvial incision and drainage network expansion are attributed to differential uplift and the creation of regional gradients between adjacent basins. The relatively low Plio-Pleistocene uplift rate of the Vera basin (11–21 m Ma − 1 ) in comparison to adjacent basins (Sorbas: 80–160 m Ma − 1 ; Huercal–Overa: > 50 m Ma − 1 ) resulted in a switch from internal to external basin drainage. Ancestral forms of the principal drainage systems within the Vera basin: the Ríos Almanzora, Aguas and Antas, captured basins and mountain catchment areas to the north (Huercal–Overa basin), southwest (Sorbas basin) and west (Sierra de los Filabres range). The switch from basin infilling to fluvial dissection is coincident with a phase of Early-Mid Pleistocene compressional tectonics, expressed by extensional faulting. This deformation is probably linked to accelerated strike-slip movement along the Palomares Fault Zone. The faulting is superimposed onto the longer term pattern of Plio-Pleistocene uplift and basin inversion.

Ostracod assemblages, palaeoenvironment and cyclicity of Purbeck-type sediments of the Münder Formation (Lower Cretaceous, Hils Syncline, N-Germany)

Berriasian marlstones in the upper part of the Münder Formation (“Purbeck”) of the Hils Syncline have been regarded as freshwater deposits with minor brackish influence. However, similar to some marlstones of the English Purbeck Limestone Group, it remained unclear whether these deposits rich in non-marine ostracods are lacustrine or marine-lagoonal in origin. Facies analysis of the sediments revealed strikingly symmetric cycles composed of (1) red-brown massive marlstones of distal alluvial plains, (2) greenish-grey bedded marlstones with microbial lamination of the supralittoral zone, (3) dark-grey charophyte marlstones and (4) light-grey charophyte limestones with scattered porostromate oncoids of the eulittoral zone, (5) poorly bedded light-grey micritic limestones and (6) clayey marlstones of the sublittoral zone. Ostracod associations revealed by cluster analysis and associated microfossils indicate cyclic salinity changes coincident with lithofacies alternations. A Theriosynoecum-association is restricted to eulittoral and shallow sublittoral lithofacies types and reflects freshwater to oligohaline conditions. This association is accompanied by the freshwater gastropods Gyraulus and Provalvata as well as charophytes of the genera Atopochara, Clavator and Globator. Supralittoral marlstones are characterized by a mixed Cypridea-association, composed of autochthonous Cypridea of ephemeral freshwater pools and transported faunal elements. Increased salinities of miohaline to mesohaline conditions are indicated for sublittoral lithofacies types by a Mantelliana-association. Maximum flooding is indicated by the appearance of small foraminifera. Variations of monospecific ostracod stable isotope ratios coincide with the cyclic salinity fluctuations interpreted from ostracod assemblages along the section. This correlation of lithofacies types and ostracod faunas implies that salinities increased with increasing water level and vice versa. Consequently, a coupling of the water level of the Hils Basin to short-term eustatic sea-level changes must be assumed. Therefore, the Hils Basin is interpreted as a marine embayment during the Berriasian with freshwater spreading out on top of marine-brackish water, but not a lake. A similar approach combining micropalaeontological and sedimentological evidence may help to distinguish between marginal-marine sediments affected by cyclic sea-level changes and lacustrine sediments displaying climatically-driven cyclicity in the Purbeck-type area and elsewhere in Europe.

Environmental control of short-term variation in the plankton community of inner Tokyo Bay, Japan

Water temperature, salinity, nutrient concentrations and the composition of the plankton community were recorded at three stations in inner Tokyo Bay over a period of 328 days (from June 8, 1995 to April 30, 1996) with a nominal sampling frequency of once per day. Inspection of the results revealed that the data could be divided into two blocs as an aid to analysis: the period from June to October was characterized by the development of stratification of temperature and salinity (stratification period), and November to March was characterized by uniform temperature and salinity in the water column due to vertical mixing (mixing period). Oxygen-depleted water forms in the bottom layer during the stratification period, but vertical mixing of the water column, due to changing wind and rainfall conditions caused by passing weather fronts, results in the breakdown of the oxygen-depleted water mass. Nutrient loads are high in the surface water due to the freshwater supply, but occasional pulses of primary production cause a depletion of phosphate in the surface water, suggesting that the phosphorus becomes a limiting nutrient for phytoplankton growth in this period. Several short-term peaks of plankton abundance (blooms) occurred as responses to temporal changes in water quality from June to November, with consequent species succession. Significant fluctuations in the densities of the diatom Skeletonema costatum and several species of ciliates corresponded to the daily changes in the physical and chemical characteristics of the coastal environment. During the mixing period, when water temperature and solar radiation decreased, there were no short-term variations in water quality and although nutrient concentrations gradually increased from November to February, primary production remained low. This study shows that the short-term dynamics of the phytoplankton community are closely coupled to fluctuations in environmental forcing, and that the degree of coupling is stronger during periods when solar radiation is greater. The results provide a novel typological understanding of seasonal plankton dynamics in a shallow, eutrophicated marine embayment, and suggest how such systems may be treated in simulation modeling.

Late Mesozoic transgressions of eastern Heilongjiang and their significance in tectonics, and coal and oil accumulation in northeast China

The spatial and temporal distribution of Late Mesozoic marine and brackish-water sediments in eastern Heilongjiang records three main transgressive interludes: The late Middle Callovian–Valanginian, Barremian–Aptian and Albian marine invasion phases. The Callovian–Valanginian transgressions were limited to the northeastern corner of eastern Heilongjiang, but the others intermittently extended northwest-, southwest- and westwards along the Yunshan shallow embayment, which opened into and deepened towards the northwestern Palaeo-Pacific. They not only flooded almost all of the subsiding basins surrounding the embayment, but during peak transgressions also widely flooded areas outside eastern Heilongjiang, such as the Yanji, Beipiao–Fuxin and Songliao basins along the Tan–Lu fault system of northeast China. All the transgressions came from the northwestern Palaeo-Pacific Ocean, and probably the Arctic Sea as well. In addition to the eustatic sea level changes, the late Early Cretaceous transgressions of northeast China were closely related to the tectonic movements within the Tan–Lu fault system and the circum-Paleo-Pacific, which were very pronounced and went hand in hand with a strong volcanic activity and ongoing subsidence. During the late Early Cretaceous, the long-term existence of a marine embayment in eastern Heilongjiang, successive marine transgressions, and flooding along the Tan–Lu fault system in northeast China ensured a humid climate across all of northeast China. These transgression and climatic conditions produced a number of extensive and long-lasting swamps and marsh lands in both paralic and limnic environments. Luxuriant plant and thriving animal growth led to the accumulation of abundant organic matter in the deposits. As a result, a number of late Early Cretaceous coal basins and oil fields formed in eastern Heilongjiang, the Yanji basin of eastern Jilin, Beipiao–Fuxin basin of western Liaoning, and the Songliao basin, northeast China.

Upper Cretaceous depositional environments and bivalve assemblages of far-east Asia: the Himenoura Group, Kyushu, Japan

The depositional environments and bivalve assemblages are determined for the Upper Cretaceous Hinoshima Formation of the Himenoura Group, Kamishima, Amakusa Islands, Kyushu, Japan. The Hinoshima Formation is characterized by a thick transgressive succession that varies from incised-valley-fill deposits to submarine slope deposits with high aggradation rates of depositional systems. The incised valley is filled with fluvial, bayhead delta, brackish-water estuary, and marine embayment deposits, and is overlain by thick slope deposits. Shallow marine bivalves are grouped into five fossil assemblages according to species composition: Glycymeris amakusensis (foreset beds of a bayhead delta), Nippononectes tamurai (foreset beds of a bayhead delta), Ezonuculana mactraeformis– Nucula formosa (central bay), Glycymeris amakusensis– Apiotrigonia minor (slope), and Inoceramus higoensis– Parvamussium yubarensis (slope). These bivalve assemblages all represent autochthonous and parautochthonous conditions except for a Glycymeris amakusensis– Apiotrigonia minor assemblage found in debris flow and slump deposits. The life habitats of these bivalves and the compositions of the assemblages are discussed in terms of the ecological history of fossil bivalves of the mid- to Late Cretaceous.

The northern sector of the last British Ice Sheet: Maximum extent and demise

Strongly divided opinion has led to competing, apparently contradictory, views on the timing, extent, flow configuration and decay mechanism of the last British Ice Sheet. We review the existing literature and reconcile some of these differences using remarkable new sea-bed imagery. This bathymetric data provides unprecedented empirical evidence of confluence and subsequent separation of the last British and Fennoscandian Ice Sheets. Critically, it also allows a viable pattern of ice-sheet disintegration to be proposed for the first time. Covering the continental shelf around the northern United Kingdom, extensive echosounder data reveals striking geomorphic evidence – in the form of tunnel valleys and moraines – relating to the former British and Fennoscandian Ice Sheets. The pattern of tunnel valleys in the northern North Sea Basin and the presence of large moraines on the West Shetland Shelf, coupled with stratigraphic evidence from the Witch Ground Basin, all suggest that at its maximum extent a grounded ice sheet flowed from SE to NW across the northern North Sea Basin, terminating at the continental-shelf edge. The zone of confluence between the British and much larger Fennoscandian Ice Sheets was probably across the northern Orkney Islands, with fast-flowing ice in the Fair Isle Channel focusing sediment delivery to the Rona and Foula Wedges. This period of maximum confluent glaciation (c. 30–25 ka BP) was followed by a remarkable period of large-scale ice-sheet re-organisation. We present evidence suggesting that as sea level rose, a large marine embayment opened in the northern North Sea Basin, as far south as the Witch Ground Basin, forcing the two ice sheets to decouple rapidly along a north–south axis east of Shetland. As a result, both ice sheets rapidly adjusted to new quasi-stable margin positions forming a second distinct set of moraines (c. 24–18 ka BP). The lobate overprinted morphology of these moraines on the mid-shelf west of Orkney and Shetland indicates that the re-organisation of the British Ice Sheet was extremely dynamic — probably dominated by a series of internally forced readvances. Critically, much of the ice in the low-lying North Sea Basin may have disintegrated catastrophically as decoupling progressed in response to rising sea levels. Final-stage deglaciation was marked by near-shore ice streaming and increasing topographic control on ice-flow direction. Punctuated retreat of the British Ice Sheet continued until c. 16 ka BP when, following the North Atlantic iceberg-discharge event (Heinrich-1), ice was situated at the present-day coastline in NW Scotland.

Lizard eggs from Upper Cretaceous Lameta Formation of Jabalpur, central India, with interpretation of depositional environments of the nest-bearing horizon

A nest with eleven relatively large-sized eggs of lacertilian affinity has been recovered from the Lower Limestone horizon exposed at the type section of the Lameta Formation, Jabalpur (Madhya Pradesh, India). Morpho-structurally, the eggs probably represent a new family as they share common features with the eggs of the living varanid lizard Varanus indicus and a shell microstructure described for geckonids. The close association of a lizard nest and titanosaurid (Sauropoda) eggs raises interesting questions regarding the egg-laying strategies of these differently-sized reptiles. Sedimentological data suggest that the Lower Limestone of Lameta Ghat was deposited in an alkaline lagoon that was connected to a marine embayment by channels. The massive limestone, sandy limestone, and calcareous sandstone lithofacies forming coarsening upward sequence represents sedimentation from deeper to marginal parts of the lagoon that were densely vegetated. Pre-burial meteoric diagenesis of the sediments indicates humid climate. Such conditions might have provided a suitable habitat supporting a large variety of terrestrial life.

Size compositions and reproductive biology of an important bycatch shark species (Heterodontus portusjacksoni) in south-western Australian waters

Heterodontus portusjacksoniwas obtained from the catches of commercial trawl, gillnet and longline fisheries operating in south-western Australian waters, in which this shark is an abundant bycatch species. Ninety per cent of theH. portusjacksonicaught by commercial trawling in a marine embayment were <400 mm in total length, whereas 99 and 100%, respectively, of the individuals taken by commercial gillnet and longline outside that embayment were >400 mm. Although the differences between the size compositions in the catches obtained by trawling vs both gillnetting and longlining, which were similar, are partly attributable to gear selectivity, they also reflect a use by juvenileH. portusjacksoniof protected nearshore waters as nursery areas and a tendency for larger juveniles and adults to occupy reef/rock habitats in a range of water depths. The fact that all but one of the numerousH. portusjacksoni>800 mm were females is reflected in the ratio of females to males differing significantly from parity in the gillnet and longline samples. Yolked oocytes usually take one year to develop to ovulatory size. Ovulation occurs in late winter to early summer and hatching takes place a year later when the embryo is 180–220 mm. The claspers of males commence rapid growth at a total length of ~450 mm, coincident with the onset of clasper calcification and gonadal maturation. The rate of clasper growth relative to total length reached a maximum at ~570 mm and then declined precipitously as the claspers approached full calcification. Based on gonadal criteria, theL50at maturity for females (805 mm) was nearly 40% greater than that for males (593 mm). Values of the deviance information criterion and marked overlap in their 95% confidence intervals demonstrate that theL50of 581 mm derived for males using full clasper calcification as the index of maturity was equally valid as the aboveL50derived for males at maturity using gonadal criteria. The capture of substantial numbers of juveniles by trawling and of females <L50at maturity by gillnetting and longlining may be having localized effects on the population structure ofH. portusjacksoniin south-western Australian waters.

Radium isotopes reveal seasonal groundwater inputs to Cockburn Sound, a marine embayment in Western Australia

Summary The mass balance and activity ratios of naturally occurring radium (Ra) iso-topes ( 223 Ra, 224 Ra, 226 Ra, 228 Ra) were investigated in Cockburn Sound (Western Australia)to further understand submarine groundwater discharge (SGD) into these coastal waters.Water samples from 11 marine stations and 20 groundwater sites (encompassing threeaquifer layers) were analysed for Ra at four times, at the end of winter (September2003), early summer (December 2003), late summer (March 2004) and mid-winter (July2004). Variable isotopic signatures of groundwater suggested that vertical mixing mayoccur between different aquifer layers and two isotopically different water sources wereidentified in marine waters both inside and outside of Cockburn Sound. A mass balance ofthe long lived radium isotopes ( 228 Ra and 226 Ra) produced a range of discharge estimatesfrom 0.8 · 10 7 L day 1 in late summer to 2.7 · 10 7 L day 1 at the end of winter. Signaturesof radium isotopes in the coastal waters suggested that groundwater discharge was notconfined to the shoreline and may have occurred from a number of aquifer sources at atemporally variable scale.a 2007 Elsevier B.V. All rights reserved.

Foraminiferal reconstruction of mid- to late-Holocene ocean circulation and climate variability in Disko Bugt, West Greenland

Benthic foraminifera from two cores collected from Disko Bugt, a large marine embayment in West Greenland, are used to investigate hydrographic changes during the mid to late Holocene. The records document fluctuations in the West Greenland Current (WGC) linked to large-scale changes in North Atlantic circulation and, for one core, impacts of local climate changes. In particular, changes in the cold East Greenland Current (EGC) and the warm, more saline Irminger Current (IC) influence the WGC and propagate into Disko Bugt. The cores record subsurface warming associated with the `Holocene Thermal Maximum' (HTM) from c. 6 to 5 ka cal. BP. Gradual cooling of WGC from 5 ka cal. BP was interrupted by an abrupt warm interval from 3.9 to 3.5 ka cal. BP, before cooling became more prominent from 3.5 to 2 ka cal. BP. This cold period corresponds to the well-documented Northern Hemisphere cooling of the neoglacial and we interpret it as reflecting enhanced flux from the EGC and reduced IC flux to the WGC in Disko Bugt. Colder subsurface conditions from 3.5 ka cal. BP correspond to major hydrographic and climate changes elsewhere in West Greenland, reflecting the final transition from HTM to the neoglacial in this region. Relatively warm conditions identified from c. 2.0 to 1.4 ka cal. BP are followed by gradual cooling to 0.7 ka cal. BP, interrupted by a brief warm episode around 1 ka cal. BP. The late-Holocene fluctuations in WGC recorded in Disko Bugt can be linked to North Atlantic oceanographic changes identified on the East Greenland and North Icelandic shelf.

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.

The nature of Miocene Amazonian epicontinental embayment: High-frequency shifts of the low-gradient coastline

A sedimentological and ichnological data set that covers the Lower-Upper Miocene sedimentary series of western Amazonian foreland basin indicates that widespread, restricted marine ingressions shaped western Amazonia throughout the Miocene. The late Lower–early Upper Miocene sedimentary series (Pebas Formation) consists of stacked, 3- to 10-m-thick, tidally influenced, brackish to freshwater, bay-margin sequences. The overlying Upper Miocene (“post-Pebas”) strata bear tidally influenced, low-salinity, channel deposits that are interbedded with continental deposits. The data suggest that several tens of high-frequency ingressions reached the basin during the Miocene. The ingressions were shallow and restricted, and were interspersed with rapid progradation. Along with the prograding shorelines, the continental environments—swamps, lagoons, floodplains and forests—constrained the extent of the marginal marine embayment. Consequently, the Miocene marginal marine and continental strata are closely interbedded throughout the basin. These results refine the recent depositional models for Miocene Amazonia, and challenge the theory that marine ingressions shaped the area only during one brief time interval (late Middle-early Late Miocene) during the epoch. Much of recent literature has documented fossils of mangrove pollen, brackish-euryhaline fish and brackish-water ostracods, brackish-water trace fossil assemblages, and tidal deposits from various Miocene stratigraphic levels. Commonly, these data sets are collected from the same outcrops as those for which data sets imply freshwater conditions. We propose that these seemingly contrasting data sets can be unified, if the repetitive nature of the ingressions is considered, and all the paleoenvironmental data are presented in a detailed lithological and stratigraphical context.

Habitat partitioning by five congeneric and abundant Choerodon species (Labridae) in a large subtropical marine embayment

The habitats occupied by the juveniles and adults of five morphologically similar, diurnally active and abundant Choerodon species in the large subtropical environment of Shark Bay, a “World Heritage Property” on the west coast of Australia, have been determined. The densities of the two life cycle stages of each Choerodon species in those habitats were used in various analyses to test the hypotheses that: (1) habitats are partitioned among these species and between their juveniles and adults; (2) such habitat partitioning is greatest in the case of the two Western Australian endemic species, i.e. Choerodon rubescens and Choerodon cauteroma; and (3) the extent of habitat partitioning between both of these two species and the only species that is widely distributed in the Indo-West Pacific, i.e. Choerodon schoenleinii, will be less pronounced. Initially, catches of each of the five congeneric species, obtained during other studies in Shark Bay by angling, spearfishing and otter trawling, were collated to elucidate the broad distribution of these species in that embayment. Underwater visual census was then used to determine the densities of the juveniles and adults of each Choerodon species at sites representing the four habitat types in which one or more of these species had been caught, i.e. reefs in marine waters at the western boundary of the bay and seagrass, reefs and rocky shorelines in the two inner gulfs. The compositions of the Choerodon species over marine (entrance channel) reefs and in seagrass were significantly different and each differed significantly from those in both inner gulf reefs and rocky shorelines, which were, however, not significantly different. Choerodon rubescens was restricted to exposed marine reefs, and thus occupied a different habitat and location of the bay than C. cauteroma, the other endemic species, which was almost exclusively confined to habitats found in the inner gulfs. Choerodon cauteroma differed from other Choerodon species in being relatively abundant in each inner gulf habitat and undergoing an ontogenetic change in habitat. Thus, while its juveniles lived predominantly in seagrass, its adults occupied mostly reefs and rocky shorelines. Choerodon cephalotes occurred almost exclusively in seagrass, while C. cyanodus was relatively most abundant along rocky shorelines. Choerodon schoenleinii, the only one of the five Choerodon species to be widely distributed outside Australia, occupied reefs and, to a lesser extent, rocky shorelines in the inner gulfs. The above differences in habitat among Choerodon species would reduce the potential for competition for spatial resources among these abundant and similar species and between the juveniles and adults of one of the species.

The Holocene history of George VI Ice Shelf, Antarctic Peninsula from clast-provenance analysis of epishelf lake sediments

The Antarctic Peninsula has experienced a dramatic increase in temperature and the loss of ca. 14,000 km 2 of ice-shelf area in recent years. During this time George VI Ice Shelf (GVIIS) has remained relatively intact, but it is now reaching its theoretical limit of viability. Epishelf lakes, formed when ice shelves dam the mouths of marine embayments, accumulate sediments that can be used to constrain past ice-shelf behaviour. They are stratified water bodies with an upper layer of fresh meltwater overlying a marine layer of water. Multi-proxy analysis of a sediment core from Moutonnée Lake, an epishelf lake dammed by GVIIS on the east coast of Alexander Island, has recently shown that it retreated to at least the Ablation Point area in the early Holocene, ca. 9600–7500 years BP, demonstrating its vulnerability to periods of atmospheric and oceanic warmth. This study tests this interpretation of ice-shelf collapse through detailed analyses of granulometric, geochemical and Sr and Nd isotope provenance data for > 8 mm clasts from the same cores. Clast data from Moutonnée Lake were compared with geological reference data from two further lakes on Alexander Island (Ablation Lake and Citadel Bastion Lake) and an extensive archive of rocks and isotope-geochemical provenance data from the Antarctic Peninsula region. Underpinning this provenance analysis is the contrast between the plutonic/igneous outcrops in Palmer Land on the western side and the predominantly sedimentary strata of Alexander Island on the eastern side of George VI Sound, and the different patterns in their deposition that would be expected at Moutonnée Lake during periods of ice-shelf presence and absence. Results show that changes in clast distribution and provenance reflect the early Holocene retreat and reformation of George VI Ice Shelf at Moutonnée Lake. The period of ice-shelf retreat was marked by the onset of marine conditions in the basin followed by a rapidly deposited zone of clasts whose provenance, distribution, varied lithology and larger than average clast size are indicative of a period of lake ice disintegration and ice-rafted debris deposition between ca. 9600–8450 years BP. Igneous clasts in the ice-rafted debris have a close affinity with the plutonic provinces of western Palmer Land suggesting transport to the site by icebergs or recycling through Alexander Island strata/moraines. When epishelf lake conditions returned after ca. 7500 years BP, the clasts were smaller, the number of lithologies more limited and the assemblage dominated by olive-green vitric tuff and pale-green rhyolitic clasts that isotope data link to Early Cretaceous volcanic activity in Palmer Land. Their dominance in the upper part of the core most likely relates to increased erosion of Palmer Land ash/tuffs from volcanic outcrops on the floor of Moutonnée Valley and implies a downturn in climate after ca. 7500 years BP and the reformation of George VI Ice Shelf.

The effects of differential subsidence and coastal topography on high-order transgressive–regressive cycles: Pliocene nearshore deposits of the Val d'Orcia Basin, Northern Apennines, Italy

This study focuses on the lowstand and early transgressive systems tracts of a basin-fill sequence of lower Pliocene nearshore deposits in the Val d'Orcia Basin of the Northern Apennines, Italy. The basin at that time was a semi-enclosed marine embayment, and, in the study area, its margin was subject to highly variable subsidence along the depositional strike, attributed to a decrease in tectonic displacement. The nearshore succession in the more rapidly-subsiding segment of the basin is around 20 m thick, comprising three storeys of laterally-stacked Gilbert-type delta lobes overlain by a shoal-water delta, whereas the nearshore succession in the adjacent, more slowly-subsiding segment, is up to 9 m thick. This succession is characterised by alternation of shoreface and offshore deposits, moderately wave-worked and covered by shoal-water deltaic facies. These coeval nearshore successions consist of several transgressive–regressive cyclothems. The development and lateral variation of the cyclothems was controlled by the local subsidence rate and coastal topographic gradient. Some of the cyclothems are considered to be higher-order sequences and others to be parasequences, with the former passing laterally into the latter in the area where the sea-level fall was countered by fast local subsidence. Some of the bounding surfaces are of limited lateral extent, with two parasequences passing laterally into a single one. Coastal topography controlled particularly the thickness of transgressive deposits. In the low-gradient setting of a delta plain, the relative sea-level rises caused major landward shifts of the shoreline and reduced fluvial sediment supply, with the formation of a transgressive lag in sediment-starved conditions. In the high-gradient coastal setting of the non-deltaic zone, the shoreline shift was minimal and had relatively little impact on local sediment supply, which promoted an accretionary transgression. At the end of the lowstand stage, the rate of sediment accumulation in the non-deltaic nearshore zone was lower, allowing the onset of subsequent transgression to be recorded considerably earlier than in the deltaic nearshore zone. This diachroneity suggests that facies criteria alone may not necessarily be a reliable basis for the recognition of systems tract boundaries.

TOWARD A BETTER UNDERSTANDING OF THE "TRANSVERSE RANGE BREAK": LINEAGE DIVERSIFICATION IN SOUTHERN CALIFORNIA

The Transverse Ranges in southern California have been identified as having a prominent phylogeographic role. Numerous studies have identified distinct north-south and/or east-west lineage breaks involving the Transverse Ranges. However, in evaluating their findings, most authors have regarded this complex system somewhat simplistically. In this study we more deeply investigate these breaks using two approaches: first we examine the phylogeographic history of Sepedophilus castaneus (Coleoptera: Staphylinidae) and then implement a comparative phylogeography approach applying Brooks parsimony analysis to the topologies of nine additional taxa. Phylogenetic analysis, nested clade analysis, and AMOVAs for S. castaneus agree that there is a major lineage break between the eastern and western Transverse Ranges, localized between the Sierra Pelona and the San Gabriel Mountains. The comparative phylogeographic analysis supports a generally strong concordance of area relationships with geographic proximity. It is notable, however, that the Transverse Ranges as a group do not show phylogenetic cohesion, but rather they are split into three main regions: an eastern region (San Gabriel, San Bernardino, and San Jacinto Mountains), a central region (central Transverse Ranges and Sierra Pelona) that is often grouped with the Tehachapi and Sierra Nevada populations, and a western region (northwestern Transverse Ranges and Santa Ynez Mountains) that is consistently grouped with coast range areas to the north. The lineage break between east and west Transverse Ranges is attributable to the presence of a marine embayment in what is now the Santa Clara River valley 5-2.5 million years ago.

Production and fate of extracellular polymeric substances produced by benthic diatoms and bacteria: A laboratory study

It is well known that benthic diatoms and bacteria are able to affect the stability of cohesive sediments. Their production of new extracellular polymeric substances (EPS) increases the erosion threshold and decreases the erosion rate. To predict this build up of biostability in cohesive sediments, it is therefore vital to understand the EPS production rates for both diatoms and bacteria under different ecological conditions. The present study examined the production of EPS as function of light intensity and linked this to biostabilisation. Microbenthos was sampled from a Danish marine embayment at 5-m depth. A 10-day comparison of EPS production under light and under dark conditions showed that the bacterial EPS production hardly changed during the experiment, while the algal EPS production was significantly high already from day 1 and reached a maximum production on day 10. Erosion threshold of natural cohesive sediments was determined in annular flumes after variable consolidation periods under similar light/dark conditions. The evolutions of erosion threshold and EPS concentration correlated well under light conditions, while the development in dark conditions showed no significant correlation, indicating that diatoms are more efficient in sediment stabilisation than bacteria. Further it seems, that the studied biological-sedimentary system needs 2–3 days of acclimatisation before the production of EPS can be well correlated with the increase of sediment stability.

Isotopic and elemental indicators of nutrient sources and status of coastal habitats in the Caribbean Sea, Yucatan Peninsula, Mexico

Nutrient inputs associated with coastal population growth threaten the integrity of coastal ecosystems around the globe. In order to assess the threat posed by rapid growth in tourism, we analyzed the nutrient concentrations as well as the δ 15N of NO 3 − and macrophytes to detect wastewater nitrogen (N) at 6 locations along a groundwater-dominated coastal seagrass bed on the Caribbean coast of Mexico. We predicted that locations with greater coastal development would have higher concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (P), as well as δ 15N of NO 3 −, reflecting wastewater sources of N. However, concentrations of NO 3 − were not significantly different between developed (3.3 ± 5.3 μM NO 3 −) and undeveloped (1.1 ± 0.7 μM) marine embayments. The most important control on DIN concentration appeared to be mixing of fresh and salt water, with DIN concentrations negatively correlated with salinity. The δ 15N of NO 3 − was elevated at an inland pond (7.0 ± 0.42‰) and a hydrologically-connected tide pool (7.6 ± 0.57‰) approximately 1 km downstream of the pond. The elevated δ 15N of NO 3 − at the pond was paralleled by high δ 15N values of Cladophora sp., a ubiquitous green alga (10 ± 1‰). We hypothesize that inputs of nitrogen rich (NO 3 − > 30 μM) groundwater, characterized by 15N enriched signatures, flow through localized submarine groundwater discharges (SGD) and contribute to the elevated δ 15N signatures observed in many benthic macrophytes. However, changes in nitrogen concentrations and isotope values over the salinity gradient suggest that other processes (e.g. denitrification) could also be contributing to the 15N enrichments observed in primary producers. More measurements are needed to determine the relative importance of nitrogen transformation processes as a source of 15N to groundwaters; however, it is clear that continued inputs of anthropogenic N via SGD have the potential to severely impact ecologically and economically valuable seagrass meadows and coral reefs along the Caribbean coast of Mexico.