The upper Quaternary sedimentary sequence at the Rieti Basin (central Italy): a record of sedimentation response to climatic changes

Lithostratigraphy, chronology and depositional environments of sixteen Holocene alluvial fill sediment cores from the southern part of the Conca of Rieti (central Italy) was established by sedimentological, palaeontological and ¹⁴C analyses. The study area experienced a lacustrine (or palustrine) conditions and the water level was effectively controlled by a natural damming of the valley due to intermitted travertine deposition at Le Marmore site. Apart from cores S10, S13, S14 and S8 which, at their bottom, cored sediments referable to ?Upper Pliocene and Middle Pleistocene which are not the object of this paper, as a rule the drilled sediments can be referred, bottom to top, to the following four episodes: interval a, corresponding to freshwater lacustrine/palustrine environment affected by alluvial fan progradations from the edges of the valley and active by ?Middle/?Late Pleistocene to early Holocene; in this interval, several hiatuses are supposed but are not evidenced by the bad state of preservation of the sediment cores; interval b, from 361 to 371–376 m a.s.l., recording a decrease of the water level, bracketed between the ¹⁴C ages of 6000 and 2700 yr B.P., which produced the formation of distinct shallow ponds/bogs, rich in aquatic vegetation; interval c, from 381 to 384 m a.s.l., indicating a further rise of the water level, recorded by sediments containing abundant molluscs and ostracods; interval d, the upper part of the cores, records an almost continuous drying up the area as shown by abundant hydrophilic land molluscs; and interval e, the top of all sediment cores, representing the present-day soil. It has been found that the water level fluctuations occurring in the ancient Conca are chronologically consistent with the postglacial climate pattern. It is further noticed that the episodes of water highstand correspond to the Boreal–Atlantic and Subatlantic climatic ameliorations, respectively, and that the water level dropped during the global cooling episodes recurred from ca. 6000 to 2100 yr B.P. The resulting palaeoenvironmental history agrees with that previously reported for the northern reach of the Conca of Rieti, thus suggesting a common setting for the whole area.     

Evidence for Late Glacial and Holocene environmental changes from subfossil assemblages in sediments of Lake Neuchâtel, Switzerland

Ostracod and diatom assemblages, mollusc remains, plus pollen and sediment stratigraphy from three cores taken at sites 40, 80 and 135 m deep in Lake Neuchâtel, Switzerland, show distinct changes since deglaciation. Shifts are interpreted in terms both of climatic change and major changes in the catchment input caused by the Aar River entering or bypassing Lake Neuchâtel. Three palaeoenvironmental phases are recognized: (1) the Late Glacial, with the inflow of the river before 10,000 yr B.P.; (2) the early to mid-Holocene, with temporary bypassing of the river between 10,000 and 4850 yr B.P.; and (3) the mid- to late Holocene, without river input after approx. 4850 yr B.P. During periods with river input, rhythmites were deposited. Ostracods indicate a well oxygenated hypolimnion, suggesting deep ventilation enhanced by the river inflow. The diatom assemblage indicates eutrophic to mesotrophic conditions and is dominated by generally well preserved periphytic species. The high number of unidentifiable pollen suggests oxidation during transport in the river. During periods without river input, a massive calcareous silt with abundant authigenic calcite was deposited, diatoms indicate a change to mesotrophic and oligotrophic conditions, and decreased sedimentation rates and higher alkalinity enhanced the dissolution of diatoms. Terrestrial and littoral molluscs as well as periphytic diatoms indicate erosion of the shore when the lake level rose or fell with onset or offset of the river inflow. Before 12,600 yr B.P., the patchy vegetation cover led to intensive soil erosion and high sedimentation rates. The lake was still frozen during the winter months. After approx. 12,600 yr B.P. the sediment changed from clastic rhythmites to thinly bedded, non-glacial rhythmites, the vegetation cover became denser, the abundance of ostracods increased, and molluscs started to colonize the profundal zone of the lake. The Younger Dryas (approx. 10,700–10,000 yr B.P.) displays maximum abundance of ostracods, indicating deep ventilation. The transition to the Holocene is characterized by a change in the ostracod assemblage and the river bypassed the lake between approximately 10,000 and 8900 yr B.P. When the river reentered the lake after approximately 8900 yr B.P., a new ostracod species appeared. After two short periods of river bypassing between approximately 7200 and 6950 yr B.P., diatoms indicate a higher trophic level about 6000–5000 yr B.P. associated with higher erosion rates and increased nutrient input due to Neolithic agricultural activities. After approximately 4850 yr B.P. the river bypassed the lake again and the trophic level decreased. In contrast to the early to mid-Holocene periods of decreased oxygen supply, the mid- to late Holocene is characterized by deep ventilation. This is attributed to the northward retreat of the polarfront and enhanced westerlies consequent to decreased insolation after 6000 yr B.P. The change of the river flow pattern correlates with glacier oscillations and may suggest a climatic control. The final cessation of the inflow is attributed to diversion of the river consequent to isostatic uplift and late Neolithic clearance activity.     

Lacustrine sedimentation in the diapir-controlled Miocene Bicorb Basin, eastern Spain

The Miocene Bicorb Basin is a small elongated basin developed by normal faulting of a thick Jurassic–Cretaceous carbonate succession and subsequent diapirism of Upper Triassic mudstones and evaporites. The basin fill comprises a sequence over 650 m thick formed by two units. The lower, alluvial unit consists of a complex alternation of conglomerates, sandstones, mudstones, and minor lacustrine limestones. The upper unit comprises marginal alluvial and lacustrine deposits in which seven lacustrine facies associations have been distinguished. The inner lacustrine deposits comprise mudstones and carbonates with minor evaporitic deposits. At the northeast and southwest basin edges, alluvial inputs led to the development of delta and fan-delta environments where sandstone and conglomerate deposits dominate. The latter stages of the lake evolution are represented by an expansive thick limestone sequence which close to the NW fault-bounded margin pass laterally to breccias. The hierarchical arrangement of the upper unit shows five different orders of sequences. The first-order sequence defines a major vertical trend of lake expansion whereas three second-order sequences are linked to major flooding-expansion episodes. All these sequences are related to the tectonic evolution of the diapir. Metre-scale, third- and fourth-order sequences and fifth-order sequences, which consist of finely laminated rhythmite deposits probably record climatically forced processes. The diapir–graben system evolution and the climatic variations have exerted major controls on the sequential arrangement and evolution of the lacustrine system. Both factors have also strongly influenced the changes in the gastropod assemblages.     

Late glacial and early Holocene palaeoenvironmental changes in Geneva Bay (Lake Geneva, Switzerland)

Detailed interdisciplinary investigations demonstrate that Geneva Bay (Lake Geneva) sediments clearly record important palaeoenvironmental and palaeoclimatic changes occurred during the Late glacial and early Holocene. Sediments are in fact differentiated by changes in texture, mineralogical and geochemical composition. Distal turbidite and glacial rhythmite deposition associated with wind-transported sediment supply dominate during the Oldest Dryas. These were replaced during the Allerød by detrital settling of sediment from turbid water and by endogenic calcite precipitation. The Younger Dryas climate reversal (for the first time in Lake Geneva well documented by a pollen record) was characterized by an increase in detrital supply owing to increased run-off from the bay slopes surrounding and within the catchment area, caused by thinning of vegetation cover. A brief pause in endogenic precipitation related to decreased productivity also occurs at this time. Endogenic carbonate sedimentation abruptly resumed at the start of the Preboreal biozone in response to the rapid global climatic warming. In the middle Preboreal, renewed detrital sedimentation is interpreted as the sedimentological response to increased erosion in high-altitude regions of the catchment area, caused by a minor early Holocene cooling phase (Preboreal oscillation), and interrupts the trend towards increasing endogenic calcite precipitation. Favourable limnic conditions are reached during the late Preboreal, when diatom–calcite rhythmites begin to form. Stable isotope analysis (δ¹⁸O, δ¹³C) in bulk carbonate highlight the transition from clastic-dominated to endogenic-dominated sedimentation. Endogenic calcite deposition continues during the Boreal biozone, occasionally interrupted by local high-energy sedimentary processes (wave-induced erosion and reworking of littoral deposits) enhanced by progressive lake-level lowering. During the Older Atlantic biozone, sedimentation was mainly dominated by low-energy deposition, creating enhanced conditions for the development of benthic fauna. We will discuss the factors that make Geneva Bay an important site for recording the Late glacial–Holocene climate and environmental changes. The comparison with other Swiss Plateau lacustrine systems allowed us to emphasize the role played by the particular geographical and morphological setting of the site investigated and links with climate-sensitive regions in the catchment area.     

Severe drought in the early Holocene (10,000–6800 BP) interpreted from lake sediment cores, southwestern Alberta, Canada

Six lake sediment vibracores from the foothills and mountain valleys of southwestern Alberta were analysed on the basis of AMS radiocarbon dates, tephrochronology and sediment geochemistry. From these results, the magnitude, timing and duration of the early Holocene warm period are presented. At about 10,000 BP, immediately following the Younger Dryas cold period, climate warmed dramatically, precipitation decreased and surface evaporation increased. Previous research has identified this warm interval, but new results have improved resolution of regional scale effects, specific timing and severity. Sedimentation changed from extra-basinal clastic to intra-basinal organic between 10,000 and 9400 BP. Changes in subalpine lakes from sand/silt deposition to biogenic carbonate precipitation suggest decreases in suspended sediment load caused by complete ablation of glacial sediment sources. Peat which formed in lakes of less than 4 m (present depth) indicates climate-induced lake level lowering in the foothills. Water depth and stratigraphic position of the peat suggest that regional water table levels decreased by up to 6.5 m. At Cartwright Lake, an erosional unconformity 6.5 m below the modern lake surface indicates the lake had completely dried out either during or immediately after Mazama tephra time (6800 BP).     

The use of the microalga Botryococcus in the interpretation of lacustrine environments at the Jurassic–Cretaceous transition in Sweden

Ultrastructural studies of developmental stages, shapes and size of fossil microalgal Botryococcus colonies, found in the Vitabäck clays at Eriksdal in southern Sweden, have been carried out. The results of this study, by analogy with the modern alga, suggest that for these lacustrine environments short limited periods of stable, uniform climatic conditions were interspersed with longer periods of seasonal climatic changes during the deposition of the Jurassic–Cretaceous transition sediments in Sweden.     

Magnetostratigraphy and sedimentologically derived geochronology of the Quaternary lacustrine deposits of a 3000 m thick sequence in the central Qaidam basin, western China

The Qaidam basin is a large basin in western China where the thickness of Quaternary deposits has a range of 2000–3000 m at its subsiding depocentre. This study investigated the chronology of the Quaternary deposits, including palaeomagnetics, biostratigraphic correlation, rates of sediment accumulation, seismic reflection surveys and electrical property correlations. The results give a full interpretation of ages for the sequence from bottom to top. The oldest sequence age was defined by the first appearance of Microlimnocythere sinensis Huang, and was placed in the Gauss Epoch, estimated at approximately 3 Ma by extrapolation of accumulation rates. The M/G boundary occurs at the base of the third fossil zone of Ostracoda (the first appearance of Qinghaicypris crassa Huang), or at the marker layer K₁₀ of the electrical log in the Sebei anticline area, considered here to be 2.48 Ma. The Olduvai event in the fifth fossil zone, spanning electrical layers K₄ and K₃ in the Sebei area, occurs at reflection layer T₀⁻¹ of seismic stratigraphy which could be stratigraphically correlated in the whole basin. The boundary of Early/Middle Pleistocene such as the Brunhes and Matsuyama (B/M) boundary, falls within the eighth fossil zone and coincides with electrical marker K₀¹. Two boundaries corresponding to Middle/Late Pleistocene and Pleistocene/Holocene occur at the bases of the 11th and 12th biozones respectively, neither of which can be correlated with seismic stratigraphy and electrical logs in the basin due to the lack of widely distributed lacustrine deposits since the Middle Pleistocene. The ages of the boundaries can be tested by deposition rates of different facies derived from the varves and synchronous deposits. As a result, geochronological sequences of subsurface stratigraphy could be established within a basin-wide area on the synchronology of seismic reflectors and correlations of electrical logs as well as biozones.     

The syn-volcanic Naajaat lake, Paleocene of West Greenland

The Naajaat lake in the Nuussuaq Basin on Disko and Nuussuaq formed in a geological setting between cratonic crystalline Precambrian rocks overlain by Cretaceous sediments and an actively forming Paleocene volcanic province. The lacustrine deposits, shales as well as hyaloclastite breccias, accumulated in low-lying areas inundated by fresh water and sealed off from marine transgressions by a broad subaerial volcanic terrain. Foreset-bedded hyaloclastite breccias demonstrate water depths of up to 450 m, and the area of the lake was 2500 km² at its maximum extent. The lake probably existed for less than 0.5 million years. The lake received clay and silt from two provenance areas. Quartz contents of more than 25% in the majority of the sediment samples indicate that large amounts of material were continuously supplied to the lake from the crystalline terrain, whereas the volcanic terrain supplied smectite and mixed-layer minerals to the lake. High kaolinite contents stem from the crystalline or both provenance areas. The shales are characterized by high TOC (up to 11%), lack of pyrite, presence of terrestrial spores and pollen and lack of marine dinoflagellates. The lacustrine sediments rest on an erosional unconformity and its correlative conformity. The unconformity developed during the latest Cretaceous and Early Paleocene. Five stages are recognized in the geological development of the lake. Stages 1–4 are characterized by accumulation of hyaloclastite breccias, rise in lake level, and eventual transgression of subaerial terrains. The rises in lake level were caused by stemming of fluvial run-off behind the aggrading volcanic pile. Stage 5 corresponds to cessation of volcanic activity, a stable lake level, and progradation of clastic sediments, resulting in infilling of the lake. During the lacustrine transgression only sediment in suspension was transported into the central parts of the lake.     

Continental, brackish and marine carbonates from the Lower Cretaceous of Kolone–Barbariga (Istria, Croatia): stratigraphy, sedimentology and geochemistry

During the Early Cretaceous, wide areas of the Dinaric–Adriatic Carbonate Platform emerged for long periods. The Hauterivian–Barremian carbonates from Kolone–Barbariga show a few typical examples of lacustrine facies with dinosaur bones and brackish/palustrine facies. The sequence of the platform is made for the most part by subtidal and intertidal limestones. The bone levels are located in a large depression few meters deep in the uppermost Hauterivian marine limestones. The filling facies of this depression are made by oncolitic rudstones and algal boundstones, which represent marginal lacustrine facies, and by laminated limestones, thin stromatolitic levels and distal fringes of rudstones which represent relatively open lacustrine facies. The fossil content is characterized by rare charophyte stems, ostracods, gastropods and plant remains, while typical marine fauna is absent. At the Hauterivian–Barremian boundary a major emersion event has been observed, then a slow transgressive phase occurred. The transgressive facies are primarily made by mudstones with ostracods, charophytes and Spirillina (brackish and probably freshwater facies), wackestones with Ophtalmidiidae and rare dasyclad algae, storm layers with gastropods and miliolids and breccia-like dinoturbated beds. Wackstones, packstones and very rich in dasyclad grainstones outcrop at the top of the section, representing the maximum of the transgression. Trace elements content, carbon and oxygen stable isotope analyses have been performed to aid the palaeoenvironmental interpretation. In this geological setting, Barium seems to discriminate between brackish and freshwater facies. The isotopic values of the marine carbonates appear to depend on early diagenetic processes, meanwhile lacustrine facies seem to show a weak signal of the depositional environment.     

A Late Triassic lake system in East Greenland: facies, depositional cycles and palaeoclimate

The Upper Triassic Fleming Fjord Formation of the Jameson Land Basin in East Greenland contains a well-exposed succession, 200–300 m thick, of lake deposits. The Malmros Klint Member, 100–130 m thick, is composed of cyclically bedded intraformational conglomerates, red siltstones and fine-grained sandstones and disrupted dolomitic sediments (paleosols). The cyclicity is composite with cycles having mean thicknesses of (25), 5.9 and 1.6 m. The overlying Carlsberg Fjord beds of the Ørsted Dal Member, 80–115 m thick, are composed of structureless red mudstones rhythmically broken by thin greyish siltstones. This unit also has a composite cyclicity with cycles having mean thicknesses of 5.0 and 1.0 m. The uppermost Tait Bjerg Beds of the Ørsted Dal Member, 50–65 m thick, can be divided into two units. A lower unit is composed of cyclically bedded intraformational conglomerates or thin sandstones, red mudstones, greenish mudstones and yellowish marlstones. An upper unit is composed of relatively simple cycles of grey mudstones and yellowish marlstones. Recognized cycles have mean thicknesses of 5.6 and 1.6 m. The lake deposits contain evidence of seasonal, orbital and long-term climatic change. Seasonal change is documented by numerous desiccation surfaces especially in the Malmros Klint Member and Carlsberg Fjord beds, orbital change is suggested by the composite cyclicity, and long-term climatic change is indicated by the systematic upwards change in sedimentary characteristics of the lake deposits. The sedimentary features of the Malmros Klint Member suggest lacustrine deposition in a dry climate that fluctuated between desert and steppe conditions, the Carlsberg Fjord beds probably record lacustrine lake deposition in a rather constant dry (steppe) climate, while the Tait Bjerg Beds record lake sedimentation in a climate that fluctuated between dry (steppe) and warm moist temperate. In the Tait Bjerg Beds the upward change in cycle characteristics indicates a shift towards more humid conditions. Climatic deductions from sedimentary facies are in good agreement with climate maps of Laurasia, as simulated by numerical climate models. Palaeomagnetic data indicate a northward drift of East Greenland of about 10° from ca. 25°N to ca. 35°N in the Middle to Late Triassic. The Fleming Fjord Formation which represents ca. 5 m.y. of the Late Triassic interval was deposited during latitudinal drift of 1–2°. It is possible that the observed long-term upward shift in climatic indicators within the formation can be ascribed to plate drift, but southward shift of climatic belts could also have been of importance.     

Tectonic and volcanic controls on Early Jurassic rift-valley lake deposition during emplacement of Karoo flood basalts, southern Namibia

The Karoo Igneous Province of southern Africa is one of the classic Mesozoic flood basalt provinces of the world. In the case of the early Jurassic Kalkrand Formation of Namibia the succession comprises three major flood basalt units that are separated by two stratigraphically important fluvio-lacustrine interlayers. These horizons preserve a record of the complex interplay between sedimentation, effusion of Karoo flood basalts and extensional tectonics that predated and accompanied the break-up of Gondwanaland. Both sediment layers start with the dominantly local derivation of weathered and eroded lava debris, followed by the emplacement of subaqueous mass flows and subsequent deposition of chemical sediments. The latter are characterised by interbedded stromatolitic carbonates, grass-like structured gypsum, and plane-bedded sandstones and mudstones containing euhedral displacive gypsum crystals that grew in the subsurface as well as rosettes which nucleated on the sediment surface. The central parts of the lacustrine units are overlain by thin deltaic sandstones showing bottomset, foreset, and topset layering and, finally, braided fluvial, trough cross-bedded sandstones. Evidence of subsidence synchronous with the formation of lake bodies can be explained by two principal mechanisms. The first acted in localised areas only and is reflected by the development of small, centrally subsiding basins. From the repeated occurrence of onlapping geometries within such a pool, a multiphase history of sagging is deduced, being most likely related to periodic magma withdrawal and reduction in magmatic pressures in subsurface lava feeders beneath the basin floor. Abundant syn-subsident fracture features at lava–sediment contacts, such as sediment-, hydrothermal calcite-, and sometimes basic lava-filled fissure systems indicate the pronounced interaction between the underlying volcanics and these small areas of pronounced subsidence. Fluids passing through the volcanic pile exhaled into the lake, giving it the characteristics of alkaline lake systems described from more recent flood basalt areas associated with the modern African Rift System. On the regional scale, however, northerly trending extensional fault systems controlled half-graben basin geometries and both facies and thickness variations across faults indicate that tectonism operated contemporaneously with volcanism and lacustrine sedimentation. The analysis of faults and associated structures, such as regularly aligned sediment-filled fissures, sets of micro-faults, folds and basaltic dykes constrains the extensional opening direction for the Karoo graben structures in this area that heralded the opening of the South Atlantic and thus provides a basis to discuss the extensional history of the Namibian coastal margin within the regional tectonic framework.     

Comparative sequence stratigraphy of low-latitude versus high-latitude lacustrine rift basins: seismic data examples from the East African and Baikal rifts

Lakes Baikal, Malawi and Tanganyika are the world's three largest rift valley lakes and are the classic modern examples of lacustrine rift basins. All the rift lakes are segmented into half-graben basins, and seismic reflection datasets reveal how this segmentation controls the filling of the rift basins through time. In the early stages of rifting, basins are fed primarily by flexural margin and axial margin drainage systems. At the climax of syn-rift sedimentation, however, when the basins are deeply subsided, almost all the margins are walled off by rift shoulder uplifts, and sediment flux into the basins is concentrated at accommodation zone and axial margin river deltas. Flexural margin unconformities are commonplace in the tropical lakes but less so in high-latitude Lake Baikal. Lake levels are extremely dynamic in the tropical lakes and in low-latitude systems in general because of the predominance of evaporation in the hydrologic cycle in those systems. Evaporation is minimized in relation to inflow in the high-latitude Lake Baikal and in most high-latitude systems, and consequently, major sequence boundaries tend to be tectonically controlled in that type of system. The acoustic stratigraphies of the tropical lakes are dominated by high-frequency and high-amplitude lake level shifts, whereas in high-latitude Lake Baikal, stratigraphic cycles are dominated by tectonism and sediment-supply variations.     

Monitoring detrital input and resuspension effects on sediment trap material using mineralogy and stable isotopes (δO and δC): the case of Lake Neuchâtel (Switzerland)

Isotopic analyses on bulk carbonates are considered a useful tool for palaeoclimatic reconstruction assuming calcite precipitation occurring at oxygen isotope equilibrium with local water and detrital carbonate input being absent or insignificant. We present results from Lake Neuchâtel (western Switzerland) that demonstrate equilibrium precipitation of calcite, except during high productivity periods, and the presence of detrital and resuspended calcite. Mineralogy, geochemistry and stable isotope values of Lake Neuchâtel trap sediments and adjacent rivers suspension were studied. Mineralogy of suspended matter in the major inflowing rivers documents an important contribution of detrital carbonates, predominantly calcite with minor amounts of dolomite and ankerite. Using mineralogical data, the quantity of allochthonous calcite can be estimated by comparing the ratio ankerite + dolomite/calcite + ankerite + dolomite in the inflowing rivers and in the traps. Material taken from sediment traps shows an evolution from practically pure endogenic calcite in summer (10–20% detrital material) to higher percentages of detrital material in winter (up to 20–40%). Reflecting these mineralogical variations, δ¹³C and δ¹⁸O values of calcite from sediment traps are more negative in summer than in winter times. Since no significant variations in isotopic composition of lake water were detected over one year, factors controlling oxygen isotopic composition of calcite in sediment traps are the precipitation temperature, and the percentage of resuspended and detrital calcite. Samples taken close to the river inflow generally have higher δ values than the others, confirming detrital influence. SEM and isotopic studies on different size fractions (<2, 2–6, 6–20, 20–60, >60 μm) of winter and summer samples allowed the recognition of resuspension and to separate new endogenic calcite from detrital calcite. Fractions>60 and <2 μm have the highest percentage of detritus. Fractions 2–6 and 6–20 μm are typical for the new endogenic calcite in summer, as given by calculations assuming isotopic equilibrium with local water. In winter such fractions show similar values than in summer, indicating resuspension. Using the isotopic composition of sediment traps material and of different size fractions, as well as the isotopic composition of lake water, the water temperature measurements and mineralogy, we re-evaluated the bulk carbonate potential for palaeoclimatic reconstruction in the presence of detrital and re-suspended calcite. This re-evaluation leads to the following conclusion: (1) the endogenic signal can be amplified by applying a particle-size separation, once the size of endogenic calcite is known from SEM study; (2) resuspended calcite does not alter the endogenic signal, but it lowers the time resolution; (3) detrital input decreases at increasing distances from the source, and it modifies the isotopic signal only when very abundant; (4) influence of detrital calcite on bulk sediment isotopic composition can be calculated.     

Palaeoenvironmental analysis of Early Pleistocene brackish marshes in the Rieti and Tiberino intrapenninic basins (Latium and Umbria, Italy) using ostracods (Crustacea)

Recent palaeontological and sedimentological studies on the Upper Pliocene–Lower Pleistocene continental deposits of the Rieti and Tiberino basins (Latium and Umbria, Italy) showed the existence of brackish marshes influenced by the Early Pleistocene Tyrrhenian sea. The micropaleontological analyses carried out on five sections cropping out in the northern sector of the Rieti Basin and on one section cropping out in the southwestern branch of the Tiberino Basin showed the repeated alternance of two ostracod assemblages. The first is characterized by a very abundant ostracod association dominated by Cyprideis torosa, typical of brackish waters; the second one is less rich in specimens and dominated by several species of freshwater Candoninae. This alternance allowed the recognition of several changes in the water salinity that could be related to many Early Pleistocene sea-level changes. Palaeosalinities were estimated for both the Tiberino and the Rieti Basin using the morphological analysis of the shell of Cyprideis torosa (ornamentation, nodosities and percentages of sieve-type pore canals). The obtained palaeosalinity values, ranging from freshwater to oligohaline, show slightly higher salinities for the Tiberino Basin, located nearer the ancient coastline, than for the Rieti Basin.     

Contribution to the lithostratigraphy and history of Lake Ladoga

New geological data from Lake Ladoga are presented and an interpretation of the Late Pleistocene and Holocene history of the lake is given. The deglaciation of the southern part of the lake and an origin of the first ice margin Lake Ladoga took place at ca. 14,000 yr B.P.     

Timing and temperature of decollement on hydrocarbon source rock beds in cyclic lacustrine successions

The generation of hydrocarbons causes lubrication of source rock bedding planes which can enhance deformation during basin subsidence and subsequent tectonic events. Deformation includes decollement, i.e. gravitational sliding of rocks above the lubricated horizon. In cyclic sequences, such as occur in many lacustrine basins, decollement is generally restricted to the organic-rich beds of the cycle. Case studies in lacustrine successions in the Devonian Orcadian Basin, Scotland, and the Triassic–Jurassic Hartford–Deerfield Basin, USA, show that movement of material associated with the decollement surface occurred in the current down-dip direction. These extensional basins experienced rapid subsidence and a high heat flow such that hydrocarbon generation, and therefore decollement, occurred early in the basin histories. During extension, half-graben rotation ensured that the beds were dipping during hydrocarbon generation, facilitating decollement. Inversion of the Orcadian Basin reactivated decollement surfaces, involving thrust motion in some cases. Minerals precipitated in tension cavities associated with decollement yield fluid inclusion homogenization temperatures in the ranges 96–139°C and 85–96°C for the Orcadian and Hartford–Deerfield basins, respectively. These data are consistent with burial into the oil window at depths of between 1.5 and 2.0 km.     

A 12 000-year record of environmental change in the Lomond Hills, Fife, Scotland: Vegetational and climatic variability

The Lomond Hills of Fife, an isolated upland area rising to over 500 m, provide an opportunity to investigate the effect of altitude on vegetation and climate in an area otherwise dominated by lower-lying land. The West Lomond site contains sediments of the Devensian Late-glacial period; they reveal a well-defined sequence of Bolling-Older Dryas-Allerod-Younger Dryas events, commencing ca. 12 190 radiocarbon years B.P. and a probable Amphi-Atlantic Oscillation between ca. 11 040 and 10 800 B.P. The Holocene record is constrained by low sediment input but does reveal a woodland presence at this altitude, dominated byBetula andCorylus. Size statistics forBetula pollen are presented and the implications of the vegetational and climatic record are discussed. The traditional view of a smooth progress towards more temperate conditions following the Younger Dryas is not supported; between 10 180 and 9120 B.P., three cooler periods are inferred, the earliest of which may belong to a terminal phase of the Younger Dryas. Comparative pollen ‘influx’ data strongly suggest thatQuercus,Ulmus andAlnus were not present locally. As a working hypothesis, it is suggested that the demise of woodland, from ca. 5950 B.P., was a result of exposure. Pollen indicative of human impact was probably derived from areas of lowland agricultural activity from ca. 5330 B.P. onwards.     

The Effect of the Lipogenic Inhibitor Cerulenin, on Macrostomal Cell Formation in Tetrahymena vorax

ABSTRACT. Macrostomal cell formation is blocked by the antibiotic cerulenin at levels of 15 μg/ml or higher. Inhibition can be reversed up to 4 h following cerulenin addition by washing and resuspending cells in new, noncerulenin-treated transforming principle. In these latter cases, additional time equal to the time spent in the inhibitor, is needed for cells to reach control values of transformation. Neither the addition of saturated or unsaturated fatty acids, cholesterol added alone or in combination with stearic acid, nor a mixture of lipids extracted from Tetrahymena vorax reversed the cerulenin effect. Radioisotope incorporation data showed while protein synthesis was reduced by the end of 1 h and tetrahymanol synthesis by the end of 2 h, little or no effect of this inhibitor occurred on RNA or fatty acid synthesis during these times. One interpretation of these results is that cerulenin, by preventing first protein synthesis and later tetrahymanol synthesis, interferes with synthesis and formation of membranes required for the microstome to macrostome transition.     

Autogenic succession, land-use change, and climatic influences on the Holocene development of a kettle-hole mire in Northern Poland

We reconstructed the Holocene developmental history of a kettle-hole peatland in the Tuchola Forest of Northern Poland, using pollen, testat amoebae and plant macrofossil indicators. Our aims were to determine the timing and pattern of autogenic succession and natural and anthropogenic influences on the peatland. Northern Poland is under mixed oceanic and continental climatic influences but has so far been less studied in a palaeoecological context than more oceanic regions of Europe. In the first terrestrial developmental phase of the mire, the testate amoebae-inferred depth to water table revealed two major dry shifts at ca. 9400 (end of lake phase) and ca. 7100 cal BP (a period of global cooling and dry shift in Western Europe). Conditions became wetter again in two steps at ca. 6700 and ca. 5800 BP after a dry event at ca. 6100 BP. The timing of the wet shift at 5800 BP corresponds to wet periods in Western Europe. Peat accumulation rates were low (0.1 mm yr^− 1) between ca. 5600 and ca. 3000 BP when sedges dominated the peatland. In the last 2500 yrs surface moisture fluctuated with wet events at ca. 2750–2400, and 2000 BP, and dry events at ca. 2250–2100 and 1450 BP. After 1450 BP a trend towards wetter conditions culminated at ca. 500 cal BP, possibly caused by local deforestation. Over the mire history, pH (inferred from testate amoebae) was mostly low (around 5) with two short-lived shifts to alkaline conditions (7.5) at ca. 6100 and 1450 BP indicating a minerotrophic influence from surface run-off into the mire. Up to about 1000 BP the ecological shifts inferred from the three proxies agree with palaeoclimatic records from Poland and Western Europe. After this date, however correlation is less clear suggesting an increasing local anthropogenic impact on the mire. This study confirms that kettle-hole peatlands can yield useful palaeoenvironmental data as well as recording land-use change and calls for more comparable studies in regions are the interface between major climate influences.     

The leech excitatory peptide, a member of the GGNG peptide family: isolation and comparison with the earthworm GGNG peptides

A member of the GGNG peptide family was isolated from Hirudo nipponia (leech). GGNG peptides had only been isolated previously from earthworms. The C-terminus structure of the leech peptide, LEP (leech excitatory peptide), was –Gly–Gly–Asn–amide, while that of the earthworm peptides, EEP (earthworm excitatory peptide), was –Gly–Gly–Asn–Gly. LEP exerted 1000-fold more potent activities on leech gut than did EEP-2. On the other hand, EEP-2 was 1000-fold more potent than LEP on the crop-gizzard of the earthworm. Analog peptides of LEP and EEP-2 were synthesized, and the myoactive potency of each analog on the leech and earthworm tissues was compared.