Marine Palaeoenvironments Research Articles

The Pennsylvanian palynoflora of the Pando X-1 Borehole, northern Bolivia

Palynological analysis of ten core samples obtained from 867–729 m depth in the Pando X-1 Borehole (11° 36′07″ S, 67° 56′45″ W), northern Bolivia, is presented. Palynomorphs are fairly well-preserved although many contain abundant pyrite. The whole assemblage is composed of 48 species of which six are spores. Among the pollen grains, 21 are monosaccate and 19 bisaccate (11 striate species). Scarce scolecodonts, microforaminifera and algae are also present. Two assemblages are recognized on the basis of the stratigraphic distribution of species, mainly of the striate pollen grains. The lower assemblage (A1) is dominated by amorphous organic matter and scarce monosaccate pollen grains, trilete spores and microforaminifera. The upper assemblage (A2) is dominated by tracheids and brown and black phytoclasts and characterized by more diverse palynomorphs, mainly striate and non-striate pollen grains. The geographical and stratigraphic distribution of taxa reveals that many species are recorded from Pennsylvanian and Permian palynofloras elsewhere in Gondwana and Euramerica. The presence of Lahirites segmentatus, Limitisporites scitulus, Lunatisporites onerosus and Vittatina species, common with Brazilian palynofloras, supports a Moscovian age for the assemblage 2. This age is also supported by calcareous microfossils previously found in the same interval of this borehole. Twenty two species are first records in the Pennsylvanian of Bolivia (e.g., Florinites eremus, Protohaploxypinus varius, Striatopodocarpites antiquus, S. gondwanensis, S. solitus, Vittatina sp.). Palynofacies features of both assemblages are indicative of a shallow marine palaeoenvironment. Qualitative changes on the floral composition between A1 and A2 may reflect broadly local palaeoclimatical changes. The dominance of Cordaitales and Coniferales in A1 indicates a relatively more humid local condition than during A2 time, which is characterized by the appearance of abundant and diverse striate pollen grains related to new groups of Pteridosperms. These features are in agreement with a lower humidity or seasonally arid conditions prevailing in the terrestrial landscape near to the Copacabana marine palaeoenvironment.

A comparative analyses of microstructures from Late Jurassic diamictic units, near Helmsdale, northeast Scotland and a Pleistocene diamicton from near Milton, southern Ontario, Canada – a differential diagnostic method of sediment typing using micromorphology

AbstractMicromorphology is used to examine and compare a Late Jurassic diamictite from northeast Scotland with a Pleistocene diamict from southern Ontario, Canada in order to test if a statistical difference between diamicts can be recognized and used to separate differing types of diamicts/diamictites. The diamictites from Scotland have been ascribed to various depositional agencies occurring in several distinctly differing terrestrial and marine palaeoenvironments. In contrast, the Pleistocene diamicton is regarded as a subglacial till. Both diamicts appear remarkably similar visually and contain many corresponding features such as macrostructures, and exotic and fractured subangular to subrounded clasts. Micromorphology is used to re-examine these diamicts/diamictites at the microscopic level to detect if the palaeoenvironments within which they were deposited can be ascertained. In this paper a quantitative assessment of microstructures using micromorphology is developed. Comparative statistical analyses of these diamicts, using micromorphological features, reveals that the Jurassic diamictites are non-glacigenic, non-terrestrial and most likely deposited within a marine environment as a result of subaquatic debris mass movement, while, in contrast, the Pleistocene diamicts were most likely subglacial tectomicts deposited beneath the active base of the Laurentide Ice Sheet.

Separation of sedimentary micron-sized particles for palaeoceanography and calcareous nannoplankton biogeochemistry

A protocol is described for separating sub-20 microm-sized particles contained in sedimentary rocks into size fractions. Geochemical data from manually isolated foraminifera are commonly used in the interpretation of marine palaeoenvironments; problems associated with the isolation of calcareous nannofossils hampers their geochemical exploitation. However, geochemistry performed on calcareous nannofossil monotaxic assemblages should provide more meaningful data sets than those generated from the highly heterogeneous bulk carbonate. This protocol is based on cascade filtering steps, using polycarbonate membranes with well-calibrated pores. Strong ultrasonic treatment can further be applied to selectively reduce the size of particles for greater enrichment. Obtained residues frequently comprise near-monotaxic nannofossil assemblages. The application of this technique, which can be achieved within less than 2 days, has provided distinct fractions of coccoliths, calcareous dinoflagellate shells and also diagenetic monocrystals. This protocol is designed for application in reconstructing the history of water-column physicochemistry and diagenesis. It also has the potential to provide insights into the biogeochemistry of calcareous nannoplankton, including vital effects.

A note on two occurrences of inferred microbial mat features preserved in the c. 2.1 Ga Magaliesberg Formation (Pretoria Group, Transvaal Supergroup) sandstones, near Pretoria, South Africa

A complex variety of casts of sand cracks occurs at two study areas near Pretoria, within mature, thin sandstone beds of the c. 2.1 Ga Magaliesberg Formation (Pretoria Group, Transvaal Supergroup). This formation is ascribed to deposition within the littoral, sandy portions of a low-energy epeiric sea, then covering much of the Transvaal preservational basin. Reticulate networks of these sand crack casts (which equate to petee ridges) and lesser vermiform geometries, the latter commonly associated with ripple troughs ( cf. Manchuriophycus ), reflect a degree of cohesiveness which is difficult to envisage in sands unless there were either thin muddy interbeds between sandy strata, or the sandy beds were bound by microbial mats growing in their upper portions. In the absence of any observed mudstone interbeds, a genetic role for microbial mats can be supported. Several of these inferred microbially-induced sand cracks appear to have “healed”, presumably having become overgrown by re-establishment of a new mat following partial desiccation of an earlier one. Associated “oncolites”, found at one of the sites, confirm this general model of microbially-mediated “sand-cracking” having taken place. Such microbial mat features appear to be relatively widespread within the Magaliesberg Formation, most likely reflecting the shallow epeiric marine palaeoenvironment which would have favoured their preservation.

Reconstruction of late Bajocian–Bathonian marine palaeoenvironments using carbon and oxygen isotope ratios of calcareous fossils from the Polish Jura Chain (central Poland)

Oxygen and carbon isotope analyses were carried out on Upper Bajocian – Bathonian calcitic belemnite rostra and oyster shells as well as aragonitic ammonite, nautiloid and trigoniid shells from the “Ore-bearing Częstochowa Clay Formation” in south-central Poland. All samples were studied by means of cathodoluminscence microscopy, trace element, X-ray, and scanning electron microscope (SEM) analysis in order to select best-preserved material. SEM studies allowed classifying some aragonitic ammonite and nautiloid shells (> 99% aragonite) as diagenetically altered. Average δ 18O values of oysters, belemnites and trigoniids translate into relatively low palaeotemperatures of 10.1, 9.2 and 7.4 °C, respectively. The comparable δ 18O values of bivalves and belemnites indicate that belemnites had a nectobenthic lifestyle and did not record surface water temperatures. The ammonite fauna is interpreted to have been nektonic, however, palaeotemperatures derived from ammonite δ 18O (around 18.6 °C) may be overestimated due to a lower, than normal marine, salinity of surface waters. The reduced salinity is inferred as well from sedimentological observations and faunal composition. The obtained δ 18O values indicate cool climatic conditions during the Late Bajocian–Bathonian in south-central Poland, which may have been linked with the occurrence of a cold climatic episode. Despite the fact that all studied shells were not precipitated in carbon isotope equilibrium with ambient waters, the δ 13C shell values enabled us to roughly estimate isotope composition of dissolved inorganic carbon (DIC) in the Late Bajocian–Bathonian sea of south-central Poland. Water δ 13C DIC values calculated from ammonite δ 13C are lower in comparison to δ 13C DIC values calculated from oyster and belemnite carbon isotope ratios, which in conjunction with ammonite δ 18O values indicates lower salinity of surface or shallow near-coastal waters.

Late Quaternary marginal marine palaeoenvironments of northern Australia as inferred from cluster analysis of coccolith assemblages

Cluster analyses (R- and Q-mode) were applied to upper Quaternary coccolith assemblages in a sediment core (MD972132) collected in the Gulf of Carpentaria, northern Australia. This shallow gulf is influenced by the Australian monsoon, is tectonally stable and represents an important link between marine and terrestrial palaeoenvironments. The Gulf of Carpentaria is linked to the Pacific Ocean to the east by Torres Strait (12 m water depth) and to the Indian Ocean to the west by the Arafura Sill (53 m water depth), and therefore has been separated from both oceans during sea-level low-stands, resulting in the formation of Lake Carpentaria. Coccolith assemblages in the gulf are similar to modern assemblages in the region, and correspond to typical assemblages in marginal seas. The cluster analysis defines six species assemblages (R-mode), and six groups of samples (i.e., defined by depth in core depth; Q-mode), some with sub-groups, which were deposited under similar environmental conditions. We thus recognised, four major environmental facies over the past 125 ka, corresponding to closed Lake Carpentaria stages, the transitional periods while active channels sporadically connected Lake Carpentaria to the Indian Ocean, and the opening of the Gulf of Carpentaria to the ocean over either one, or both of the sills. Lake Carpentaria was isolated from both oceans through Marine Isotope Stages (MIS) 5d, MIS 4 and MIS 2, and the Gulf of Carpentaria was connected to both oceans during MIS 5c and MIS 1. Torres Strait was emergent during MIS 5b, was flooded again during MIS 5a and persisted as land bridge from MIS 4 to MIS 1. The Arafura Sill was opened from MIS 5c to MIS 5a and episodically connected the Gulf to the Indian Ocean during MIS 3.

FOSSILDIAGÊNESE E GEOQUÍMICA DOS CRUSTÁCEOS DECÁPODES DA FORMAÇÃO MARIA FARINHA (PALEOCENO), ESTADO DE PERNAMBUCO, BRASIL

This study includes fossildiagenetical and geochemical analysis of the decapod carapaces and the host rocks, sampled at the Poty quarry, outcrop of the Maria Farinha Formation, State of Pernambuco, Brazil. In this geological setting the brachyura are envolved by biomicrites mineralogically composed by quartz, calcite, hidroxylapatite, dolomite and kaolinite. The allocheme elements in these biomicrites are represented by decapod crustaceans, benthonic and planktonic foraminifera, ostracods, microbivalves, microgastropods, calcareous algae, microbryozoans, corals, diatoms and spines of echinoids. Six presumebly simultaneous eodiagenetic processes were identified: (1) replacement of the skeletal aragonite by calcite; (2) pyritization of the organic matter; (3) phosphatization of the organic matter; (4) mechanical compactation; (5) formation of CaC03 fringe; and (6) local dissolution of CaC03 precipitated in pores. The δ13C e δ18O values suggested marine palaeoenvironment with high oxidation of the organic matter in the benthos during times of the low sea level and the continental influence.

FOSSILDIAGÊNESE E GEOQUÍMICA DOS CRUSTÁCEOS DECÁPODES DA FORMAÇÃO MARIA FARINHA (PALEOCENO), ESTADO DE PERNAMBUCO, BRASIL

This study includes fossildiagenetical and geochemical analysis of the decapod carapaces and the host rocks, sampled at the Poty quarry, outcrop of the Maria Farinha Formation, State of Pernambuco, Brazil. In this geological setting the brachyura are envolved by biomicrites mineralogically composed by quartz, calcite, hidroxylapatite, dolomite and kaolinite. The allocheme elements in these biomicrites are represented by decapod crustaceans, benthonic and planktonic foraminifera, ostracods, microbivalves, microgastropods, calcareous algae, microbryozoans, corals, diatoms and spines of echinoids. Six presumebly simultaneous eodiagenetic processes were identified: (1) replacement of the skeletal aragonite by calcite; (2) pyritization of the organic matter; (3) phosphatization of the organic matter; (4) mechanical compactation; (5) formation of CaC03 fringe; and (6) local dissolution of CaC03 precipitated in pores. The δ13C e δ18O values suggested marine palaeoenvironment with high oxidation of the organic matter in the benthos during times of the low sea level and the continental influence.

Late Paleocene foraminiferal faunas with Chapmanina and Reticulophragmium from offshore southeastern Australia: a Tethyan influence

Samples from off southern New South Wales in approximately 1750 m water depth have yielded late Paleocene faunas of benthic and planktonic foraminifera and other invertebrates. Two faunal associations with a strong Tethyan influence, dominated respectively by Chapmanina conjuncta sp. nov. and Reticulophragmium naroomaensis sp. nov., are described; this is the first formal record of these genera from Australasia. The age of the host sediment is based on both benthic species and few planktonic foraminifera. The environment at the time was warm temperate to subtropical at the southwestern extremity of a counter-clockwise Pacific Ocean gyre. The new occurrence extends the record of Palaeogene marine sediments and palaeoenvironments along the eastern margin of Australia and confirms earlier observations that conditions in the marine environment at that time were considerably warmer along the east coast of Australia than those along the southern margin; the biogeographic association was Tethyan. The circulation model may go some way to explaining coeval warmth along the east Antarctic coast.

Palynofacies and calcareous nannofossils in the Upper Kimmeridgian, southeastern Paris basin (France)

AbstractThe Upper Kimmeridgian Members “Calcaires blancs supérieurs” and the “Marnes à exogyres supérieures” of the southeastern Paris basin were investigated for their palynofacies and calcareous nannofossils. These members display alternating limestone-marl lithotypes and represent shallow marine palaeoenvironments. The lower carbonate member is interpreted as a proximal palaeoenvironment (palaeobathymetry = 5 to 10 m), where storm and swell deposits were prevalent and the salinity was occasionally weak. The relative richness of brown phytoclasts in this part is favoured by good preservation related to restricted conditions. These conditions would explain the dominance of the nannofossil Cyclagelosphaera margerelii in the nannofossil assemblages. The palynological data as those of the nannofossil assemblages show variations in the shift from carbonate member to marly member. The dominance of brown phytoclasts over black phytoclasts, the presence of amorphous organic matter (AOM), and the highest abundance and diversity observed within the nannofossil assemblages suggest that the maximum of distality occurred during this transition, at the basal part of the Marnes à Exogyres supérieures. The upper part of the section (marly member) characterized by storm deposits and storm-coquina beds is deeper (palaeobathymetry probably between 10 and 40 m depth) than the lower part. Oxidizing depositional conditions prevailed and explained the abundance of black particles found in this upper part, while proximate cysts and elevated non-placolith coccolith abundances indicate that relationships with the open sea were probably more significant compared to the lower part. Towards the top of the section, recurrences of restricted conditions are reflected by relatively elevated amounts of AOM and the abundance peak of the nannofossil Biscutum ellipticum. This study shows that micropalaeontological signals can be well recorded in vast lagunal domains. We speculate that salinity, nutrient supply, and oxygenation of the waters control microfossil associations. In shallow environments, these parameters are particularly fluctuating, especially when freshwater dilutes marine waters in surface, on the occasion of rainy periods or of intense arrival of continental waters.

The global Mio–Pliocene climatic equability and coastal ostracod faunas of southeast Australia

This study on the Mio–Pliocene ostracod successions of southeast Australia outlines several faunal events indicative of climate warming and/or increased rainfall events. Ostracod faunas associated with a late Late Miocene sea level rise event suggest that the climate of this time in southeast Australia was similar to, or slightly warmer than that of present day southeast Australia. However, it was probably wetter and significantly warmer than immediately preceding (mid Late Miocene) palaeoclimatic conditions within the region. Evidence for a change to wetter and warmer conditions during the late Late Miocene is seen in the appearance of various extant euryhaline and semi-thermophilic ostracod species in coastal ostracod faunas. The appearance of euryhaline species, which are mostly absent from older shallow marine Cenozoic strata of the Bass Strait hinterland, suggests a major influx of fresh water into coastal marine settings, which contributed to the initial phase of development of the southeast Australian late Neogene barrier coastline and associated marginal marine palaeoenvironments. During the time interval latest Miocene to earliest Pliocene, and during the early Late Pliocene, two subsequent global sea level rise events are also preserved in the southeast Australian coastal plain. Many of the species present in ostracod faunas associated with these two events are the same as in older local late Late Miocene faunas. In earliest (?) Pliocene faunas, there is minor evidence for the reappearance of semi-thermophilic ostracods. Faunas of early Late Pliocene age often exhibit a conspicuous faunal dominance by, or large abundance of euryhaline species, indicating the particularly strong influence of fresh water influxes into coastal marine palaeoenvironments. This may reflect the presence of especially wet local temperate palaeoclimatic conditions during a time of equable global climates. Succeeding estuarine, lagoonal and coastal embayment ostracod faunas of late Late Pliocene age are associated with marginal marine sediments that are interbedded with coastal dune aeolianites. This suggests an overall seaward retreat of marginal marine environments that was initiated by a major global sea level fall linked to the onset of cooler Late Pliocene and Quaternary global climates.

Loess, and the Dust Indicators and Records of Terrestrial and Marine Palaeoenvironments (DIRTMAP) database

Mineral dust is an important constituent of the solid load in Earth's atmosphere, the total atmospheric aerosol loading being both a function of, and a factor affecting climatic change. Human actions have progressively enhanced atmospheric dust loading, especially in the past century, so that both natural and human-induced effects of atmospheric dust on climatic change require more detailed research. Records of changing climate are preserved in cores from the ocean floors, glaciers and ice sheets, as well as in terrestrial sedimentary sections. Quantitative data on the present-day distribution of atmospheric dust are sparse, but simulation of dust transport and deposition has been modelled with some success. The dust indicators and records of terrestrial and marine palaeoenvironments (DIRTMAP) database was designed to serve as a global validation data set for use with earth system models of the palaeo-dust cycle. Loess, a wind-borne silt deposited on the continents particularly in the past 2.6 Myr, is an important potential source of information on past atmospheric dust accumulation. A recent initiative sought to improve the terrestrial data coverage within the existing DIRTMAP database by involving representatives from key loess regions in coordinating the data synthesis process, so as to facilitate interaction between the dust modelling and the data collection communities. The results are presented in this issue. In order to compare past minerogenic dust records (loess) with those in ice and ocean cores, mass accumulation rates (MARs) have been calculated as fluxes (in g/m 2/yr). The loess regions covered include North and South America, Europe, Siberia, eastern Asia, and Australasia. It is acknowledged that provision of age models for the calculation of realistic MAR values depends upon a number of conditions, most notably sound chronostratigraphy and realistic values of loess dry bulk densities. The MAR data sets presented here show some notable variation, both within and between the studied regions. Regional MAR coverage also varies, reflecting differences in the availability of key data on loess from one world region to another. Loess facies vary according to specific site and source conditions, as well as in response to post-depositional re-working of primary (wind-lain) loess by surface geomorphic processes. Mean particle size consistently declines downwind, and terrace, valley and upland sites generally yield the highest MAR values, characteristics noted in all regions discussed here. The loess accumulations in two major world regions, central and eastern Asia and the Great Plains region of North America, differ in some important respects from loess elsewhere in that they lie peripheral to deserts and are remote from the former sites of major Quaternary ice sheets. It is concluded that the MARs for terrestrial sites obtained from loess are consistently higher than those obtained from ocean and ice cores, so that future climatic models designed to study the role of global atmospheric dust will have to take full account of the present and past dust records over the continents.

The Triassic and Jurassic of Warwickshire: report of a 2002 Weekend Field Meeting

Triassic and Jurassic strata were examined in southern Warwickshire and the county town of Warwick. The succession demonstrates a range of non-marine and marine palaeoenvironments. The field sessions were augmented by a visit to the Warwickshire Museum.

Mineralogy of the Upper Albian sediments from the Kirchrode I borehole with special emphasis on the clay mineralogy

The mineralogy of a 245 m thick section of Upper Albian marly clay stones to clayey marlstones from the Kirchrode I borehole (Lower Saxony basin of NW Germany) has been studied by X-ray diffractometry, infrared spectrometry, chemical analysis and microscopy. The investigations were carried out on bulk samples and grain-size fractions. The mineralogy of the sediments is characterised by biogenous carbonates, mainly calcite, by terrigenous-detrital components and diagenetic minerals, often enriched in concretions. The calcite content fluctuates considerably (between 20 and 50%), most probably because of changes in the marine palaeoenvironment. Illite, montmorillonite, and kaolinite are the predominant clay minerals, but in changing portions. Chlorite and alkali feldspars were detected only in traces. Mixed-layer minerals such as illite/smectites (I/S) are also present, in higher amounts in the lower part and less in the upper part of the core. Reworked Upper Carboniferous mudstones and siltstones are interpreted to have delivered part of the well crystallised illite, kaolinite, chlorite and quartz. Montmorillonites and mixed-layer minerals together with kaolinite and illite may be inherited from weakly consolidated Jurassic sediments, Aptian and Albian claystones and marlstones, and from palaeosols. The increase in the proportion of montmorillonite among the clay minerals in the upper part of the Upper Albian may be due to redistribution of volcanic sediments after either terrestrial or submarine alteration of volcanic ash. Volcanic activity is known in this area (e.g. the Middle to Upper Albian Flammenmergel at the southern margin of the Lower Saxony basin) and around the North Atlantic throughout Aptian–Albian time. But in the Kirchrode I core, ash fall was identified as a source for montmorillonite in only one layer, namely at 87.25 m, where high Zr and Nb concentrations were also found. The mineralogical composition of the concretionary material is generally a mixture of biogenous calcite, siliciclastic debris (quartz and clay minerals), and microcrystalline, diagenetically formed Fe–Mn carbonates (rhodochrosite, siderite) and carbonate–fluorapatite (francolite). Rhodochrosite is more abundant in the lower part, Mn-siderite in the upper part of the core. Concretions with fluorapatite (francolite) occur sporadically.

DIRTMAP: the geological record of dust

Atmospheric dust is an important feedback in the climate system, potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems. Yet the potential impact of dust on the climate system, both in the anthropogenically disturbed future and the naturally varying past, remains to be quantified. The geologic record of dust provides the opportunity to test earth system models designed to simulate dust. Records of dust can be obtained from ice cores, marine sediments, and terrestrial (loess) deposits. Although rarely unequivocal, these records document a variety of processes (source, transport and deposition) in the dust cycle, stored in each archive as changes in clay mineralogy, isotopes, grain size, and concentration of terrigenous materials. Although the extraction of information from each type of archive is slightly different, the basic controls on these dust indicators are the same. Changes in the dust flux and particle size might be controlled by a combination of (a) source area extent, (b) dust emission efficiency (wind speed) and atmospheric transport, (c) atmospheric residence time of dust, and/or (d) relative contributions of dry settling and rainout of dust. Similarly, changes in mineralogy reflect (a) source area mineralogy and weathering and (b) shifts in atmospheric transport. The combination of these geological data with process-based, forward-modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates, their controlling mechanisms, and how those mechanisms may vary regionally. The Dust Indicators and Records of Terrestrial and MArine Palaeoenvironments (DIRTMAP) data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150,000 years.

Warmer or cooler late Holocene marine palaeoenvironments?: interpreting southeast Australian and Brazilian sea-level changes using fixed biological indicators and their δ18O composition

Relic inter-tidal assemblages of sessile organisms, which are referred to as fixed biological indicators (FBIs), are shown to be useful proxies for late Holocene climatic and environmental changes as well as direct indicators of short term fluctuations in sea-level. A detailed comparison of change in the inter-tidal assemblages of two Southern Hemisphere sites at comparable latitudes (Port Hacking, New South Wales, south–east Australia and the Laguna-Imbituba region of southern Brazil) indicates periods of marked similarities in the timing and nature of changes at ∼5200, ∼3800 cal. years BP and differences after ∼2400 cal. years BP. There is sufficient concurrence of cooling phases and falling sea-levels to strongly suggest that in some cases global rather than regional forcing factors are at work. The value of inter-tidal organisms as indicators of changed environments is developed by identifying the past and present distributions of the common marker species: tubeworms, barnacles and mussels. The δ 18O content of these extant specimens at Port Hacking confirmed changes in ocean water temperature and associated sea-level behaviour corresponding to invasion or extinction of temperature-sensitive species. A similar pattern is repeated, although in a less marked fashion, in the Laguna-Imbituba region of southern Brazil.

Intracolony variation in zooid size in cheilostome bryozoans as a new technique for investigating palaeoseasonality

Variation in zooid size within colonies of fossil cheilostome bryozoans is presented as a potential source of information on palaeoseasonality. We base our approach on the inverse relationship between temperature and zooid size in bryozoans, and analyse the mean intracolonial coefficient of variation (CV) in zooid length, zooid width and zooid area (length×width) in a number of Recent bryozoan species collected from many seasonally different environments. A highly significant, positive correlation was obtained between the mean annual range of temperature (MART) experienced by the colonies and the mean intracolonial CVs in zooid lengths ( R 2=74.7%), zooid widths ( R 2=58.9%) and zooid areas ( R 2=80.0%). An algebraic equation derived from regression analysis of mean intracolonial CV of zooid area and MART is proposed as a new method of investigating the MART of ancient seas by assessing variation in zooid area within fossil cheilostome colonies. This technique is then applied to bryozoan colonies from two Neogene shallow-water deposits in Western Europe. Results from the Coralline Crag in south-eastern England reveal a moderate level of seasonality, in keeping with previous estimates of seasonality for British seas during the Pliocene. Results from the middle Miocene ‘faluns’ in north-west France suggest less seasonal variation in temperature than occurs in comparable seas today. We conclude that the technique represents a useful new approach that offers some benefits over other techniques of assessing seasonality in marine palaeoenvironments.

Mineralogy of the Lower Aptian sediments from the borehole Hoheneggelsen KB 40 with special emphasis on the clay mineralogy

Lower Aptian sediments from the borehole Hoheneggelsen KB 40 in the southeastern part of the Lower Saxony Basin have been studied. The succession consists of dark claystones with intercalated black, finely laminated paper shales with the fish shale as the final black shale event followed by theHedbergellamarl. The mineralogy of the sediments is characterized by biogenic components, mainly calcite and variable amounts of organic carbon, by siliciclastic detritus, and diagenetically formed minerals such as pyrite. The calcite content fluctuates considerably throughout the profile because of changes in the marine palaeoenvironment. The terrigenous detritus (quartz and clay mineral) was obviously supplied to the shallow marine epicontinental basin by the continent to the south. Reworked Upper Carboniferous mud- and siltstones may have delivered part of the illite, kaolinite, chlorite and quartz. Terrigenous detritus including the randomly interstratified vermiculite/illites may have been derived from reworked pre-Aptian sediments or palaeosols of the hinterland. The change in the mineralogical composition of the terrigenous detritus observed in the highest dark claystone horizon directly below the fish shale is most probably the result of changes in the source area and of the depositional regime.

Le comblement de la ria de Gernika (golfe de Gascogne) à l'Holocène terminal

A study of the recent sedimentation of the ria de Gernika (Bay of Biscay) is undertaken to characterise different steps of its Holocene filling. Sedimentological and micropalaeontological analysis of six cores sampled in the ria, completed with absolute dating ( 14C, and based upon 210Pb exc.), allow us to identify three phases in the filling of the ria that are limited by two transgressive shifts (3500 and 2500 yr. B.P.) already described in other areas of the Bay of Biscay. In the first phase, lithologies as well as benthic foraminifera and ostracode assemblages are typical of coastal marine palaeo-environment. During the second phase the euryhaline waters progessively occupy the central area of the estuary. Here the presence of allochthonous microfauna, particularly of planktonic foraminifera, indicates an increase of exchanges with marine waters that can reach the inner areas of the estuarine system. The last phase (2500 yr. B.P. to the present), which corresponds to the recent and active sedimentation, is marked by an impoverishment of the microfaunas, the filling of some channels and the increase of salt marshes. The estimated sedimentation rate for the upper decimetres of the cores (0.73-1.29 cm·yr −1) shows faster sedimentary filling of the ria with anthropic action evidenced by the presence of metallic contaminants and hypohaline microfauna.

Neogene mollusk faunas fromStrymon basin, Macedonia, Greece. First results for biochronology and palaeoenvironment

Several fossiliferous sites with mollusk faunas have been located in Strymon basin. The faunal characters of the so far determined fossils and the lithology of the fossiliferous sediments allow the distinction of two groups. A. Fossiliferous sites, indicating a shallow marine palaeoenvironment with clastic sedimentation linked with the proximity of a palaeocoast. These sites have been dated to Pliocene and can be correlated with an early Pliocene marine transgression. B. Fossiliferous sites with fine grained clastic sediments and indications of a complicated (shallow marine — brackish — lagoonal to lacustrine) palaeoenvironment. These sites include lenses of euryhaline marine fossils alternated with marine, brackish and fresh water faunas. The fossiliferous deposits of this group, possibly overlie those of group A and could be dated to Pliocene.