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1.
The Quaternary sediments of the West Sussex Coastal Plain have produced a wide range of floral, faunal and archaeological remains. These sediments consist of marine sands and gravels exhibiting transgressive and regressive trends which occur from present day sea-level to c. +43.0 m O.D. and are overlain by terrestrial silts and cold climate periglacial sediments. At the present day coastline, channel fill deposits occur below modern beach levels. New field observations, coupled with a re-investigation of old sites and literature, suggest that five discrete high stands of sea-level may be preserved in the area of the West Sussex Coastal Plain. Age estimates for these deposits suggest that they span large parts of the Middle and Upper Pleistocene (Oxygen Isotope Stages 13 to 5). Conformable relationships between many of the marine and terrestrial sediments suggest that the potential exists within the area to correlate the marine and terrestrial Quaternary stratigraphic records. In addition sediments associated with two of these high sea-level stands are associated with extensive buried landsurfaces covering large areas of the coastal plain. At some locations these intact landsurfaces are associated with evidence for human activity and represent stratigraphic and cultural resources of international importance.  相似文献   

2.
Stream-sediment and soil geochemical data from the Upper and Lower Coastal Plains of South Carolina (USA) were studied to determine relationships between soils and stream sediments. From multi-element associations, characteristic compositions were determined for both media. Primary associations of elements reflect mineralogy, including heavy minerals, carbonates and clays, and the effects of groundwater. The effects of groundwater on element concentrations are more evident in soils than stream sediments. A “winnowing index” was created using ratios of Th to Al that revealed differing erosional and depositional environments. Both soils and stream sediments from the Upper and Lower Coastal Plains show derivation from similar materials and subsequent similar multi-element relationships, but have some distinct differences. In the Lower Coastal Plain, soils have high values of elements concentrated in heavy minerals (Ce, Y, Th) that grade into high values of elements concentrated into finer-grain-size, lower-density materials, primarily comprised of carbonates and feldspar minerals (Mg, Ca, Na, K, Al). These gradational trends in mineralogy and geochemistry are inferred to reflect reworking of materials during marine transgressions and regressions. Upper Coastal Plain stream-sediment geochemistry shows a higher winnowing index relative to soil geochemistry. A comparison of the 4 media (Upper Coastal Plain soils and stream sediments and Lower Coastal Plain soils and stream sediments) shows that Upper Coastal Plain stream sediments have a higher winnowing index and a higher concentration of elements contained within heavy minerals, whereas Lower Coastal Plain stream sediments show a strong correlation between elements typically contained within clays. It is not possible to calculate a functional relationship between stream sediment–soil compositions for all elements due to the complex history of weathering, deposition, reworking and re-deposition. However, depending on the spatial separation of the stream-sediment and soil samples, some elements are more highly correlated than others.  相似文献   

3.
Analysis of sediment and aquatic vegetation samples collected along the Onkaparinga estuary, South Australia, revealed the distribution patterns of benthic and epi-benthic micro-organisms, specifically foraminifera and ostracods. The total assemblage provided an assemblage ‘snap shot,’ contemporaneous with the environmental conditions at the time of sampling, as well as seasonally and time-averaged distribution information. Species richness is low in the upper reaches of the estuary and favours species with a wide salinity tolerance. Observed species richness increases seawards. Species richness and abundance within species is greater where there is conspicuous aquatic vegetation. Thus, species richness and distribution appear to be related to the proximity to the sea and the provision of diverse habitable substrate. Foraminiferal species, Ammonia beccarii and Elphidium excavatum, and ostracods belonging to the genera Paracypria, Xestolebris and Leptocythere dominate the total assemblage. These species are characteristic of euryhaline conditions. The mutual maximum occurrences of Reophax barwonensis, Ammobaculites barwonensis and Trochammina inflata signify mid-estuarine conditions. In the lower regions of the estuary, the appearance of shallow marine species of foraminifera such as Elphidium crispum and Quinqueloculina poeyana, and ostracods Bairdoppilata sp., Hemicytherura spp. and Paranesidea spp. signifies interactions with the adjacent inner shelf coastal waters. Throughout the entire length of the estuary, the presence of vegetal substrate created a strong numerical bias towards live occurrences of the ostracods Paracypria sp. and Xestolebris cedunaensis. These species are potentially useful as proxies for paleoenvironmental interpretations of estuarine sediments.  相似文献   

4.
In southeastern South Australia, the River Murray debouches through a coastal barrier separating euryhaline estuarine-lagoonal waters from the Southern Ocean. Depending upon the relative freshwater outflow of the river and ingress of the ocean, water salinity varies greatly within the lower estuary. Ammonia beccarii and Elphidium articulatum are euryhaline species of foraminifera that characterize the estuary and back-barrier Coorong Lagoon. The inner-shelf marine environment hosts an assemblage in which Discorbis dimidiatus, E. crispum, E. macelliforme, and various cibicidid species predominate. In cored sediments recovered from the shallow lower estuary, the relative abundance of A. beccarii + E. articulatum was compared with that of D. dimidiatus + E. crispum + E. macelliforme + other species. These data, and AMS radiocarbon ages determined for foraminifera and ostracods, provide evidence of a change from maximum oceanic influence (5255 ± 60 yr B.P.) to maximum estuarine influence (3605 ± 70 yr B.P.). Over this same time interval, sea level fell relatively by about 2 m. However, the event was also contemporaneous with falling water levels in several Victorian lakes, and it is thus attributed to onset of climatic aridity. Reduced precipitation in the River Murray catchment and reduced freshwater outflow enhanced development of the flood-tide delta and constriction of the mouth.  相似文献   

5.
Lower Pleistocene sediments recovered in boreholes from the Aberdeen Ground Formation in the central North Sea indicate that the unit was deposited in a delta front to prodelta/shallow, open shelf marine setting. Possible estuarine and clastic nearshore marine deposits have been identified on the western margin of the basin. The delta front sediments consist of interbedded, structureless to laminated sands and muds with organic debris, ferruginous nodules and common soft sediment deformation structures. Sporadic rippled and graded beds, basal scours to beds and starved ripples suggest periodic wave–current reworking. Prodelta/shelf marine sediments are predominantly argillaceous with only occasional thin sand beds and rare phosphatic bands. One exceptionally thick sand body or submarine channel-fill although this remains uncertain. The estuarine/clastic nearshore marine sediments include coarse channel-lag deposits and rippled and laminated subtidal sands. A rich microfossil assemblage recovered from the prodelta/shelf marine sequence indicates that deposition occurred under fluctuating climatic conditions.  相似文献   

6.
Marine Isotope Stage 11 (MIS 11) is considered one of the best analogues for the Holocene. In the UK the long lacustrine sequence at Marks Tey, Essex, spans the entirety of the Hoxnian interglacial, the British correlative of MIS 11c. We present multiproxy evidence from a new 18.5‐m core from this sequence. Lithostratigraphy, pollen stratigraphy and biomarker evidence indicate that these sediments span the pre‐, early and late temperate intervals of this interglacial as well as cold climate sediments that post‐date the Hoxnian. The δ18O signal of endogenic carbonate from this sequence produces several clear patterns that are interpreted as reflecting the climatic structure of the interglacial. As well as providing evidence for long‐term climate stability during the interglacial and a major post‐Hoxnian stadial/interstadial oscillation the δ18O signal provides strong evidence for abrupt cooling events during the interglacial itself. One of these isotopic events occurs in association with a short‐lived increase in non‐arboreal pollen (the NAP phase). The results presented here are discussed in the context of other MIS 11 records from Europe and the North Atlantic, particularly with respect to our understanding of the occurrence of abrupt climatic events in pre‐Holocene interglacials. Copyright © 2016 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.  相似文献   

7.
Assemblages of foraminifers, ostracods and molluscs from temperate Ipswichian Stage (last temperate stage) sediments and overlying cold Devensian Stage (last cold stage) sediments at Somersham in the southern Fenland of Cambridgeshire have been analysed. The Ipswichian sediments contain faunas consistent with temperate brackish water conditions under tidal influence. The Devensian assemblages were recovered from a series of sands and gravels laterally accreting in a channel cutting into Ipswichian sediments. In contrast to the Ipswichian faunas, the faunas of particular Devensian samples show a complex mixture of temperate freshwater, brackish and marine taxa. The molluscs are mainly freshwater, with few land snails; they occur together with foraminifers and ostracods. Freshwater, brackish water and marine ostracods are present with foraminifers. A sample of Devensian fine laminated sediment in the channel was analysed for pollen; only abundant pre-Quaternary spores were present, with abundant foraminifers in the same sample. The taphonomy of the assemblages and the difficulties of their interpretation in environmental terms are discussed. The importance of taphonomy in assessing environments, climate, range of taxa and dating is stressed.  相似文献   

8.
There has been considerable debate concerning the origin of the Spearwood Dunes on the Swan Coastal Plain in Western Australia. In general, it is believed that the Spearwood Dunes are a complex of calcareous coastal dunes deposited during the Quaternary and now consist of an aeolianite core (the Tamala Limestone) plus tracts of surficial residual sand from dissolution thereof. However, in the mid‐seventies a counter view was presented suggesting that the sand was not residual but was transported by aeolian processes from inland sources. At 11 sites on the Swan Coastal Plain a combination of grainsize analysis and heavy‐mineral analysis was used to demonstrate that the sand of the Spearwood Dunes has evolved as a result of in situ weathering of the underlying Tamala Limestone. This supports previous work on the Swan Coastal Plain and other sandplains in Western Australia, suggesting that there has been very little long‐range aeolian transport of sands during the Late Pleistocene.  相似文献   

9.
The Pliocene Norwest Bend Formation is a well‐preserved succession of terrestrial and shallow‐marine deposits in the Murray Basin, South Australia. Sediments in this unit consist of two discrete terrigenous clastic‐rich, decametre‐scale sequences, or informal members, which record episodes of marine incursion during the Early and Late Pliocene respectively. The base of each sequence is a transgressive lag and/or strandline deposit that is transitional upwards into a highstand, subtidal, terrigenous clastic and cool‐water carbonate sediment accumulation. The top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea‐level fell and terrestrial environments prograded basinward. Sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy. Differences in sedimentary style between these two sequences, however, reflect a major climatic change that took place in southern Australia during the mid‐Pliocene. The lower quartzose sand member is formed of siliciclastic sediment derived from prolonged, deep, subaerial weathering and contains a bivalve‐dominated, cool‐temperate, open‐marine mollusc assemblage. These sediments accumulated under an equitable, relatively warm, humid climate. The Murray Basin during this time, because of high fluvial discharge, was a salt‐wedge estuary with typical estuarine circulation. In contrast, the upper, oyster‐rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments. Strandline deposits contain a warm‐temperate skeletal assemblage. Contemporaneous aeolian sediments accumulated under warm, semi‐arid climatic conditions. Well‐developed ferricrete, silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern Australia today. Highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed. These Pliocene sediments support the notion that mollusc‐rich facies are the signature of cool‐water carbonate accumulations in inboard neritic environments. Unlike bryozoans that dominate the outer parts of Cenozoic cool‐water carbonate shelves, molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates.  相似文献   

10.
Nearly 6 m of uncompacted muddy sediment was recovered from the floor of the northern Coorong Lagoon in the core Coorong #5. Radiocarbon analyses of molluscan shells indicate that sedimentation at the core site commenced before 6830 ± 90 yr cal BP, and the presence of Pinus pollen confirms a modern age for the uppermost 0.5 m. Microfossils extracted from the core sediment samples, 2 cm slices at 10 cm intervals, included the foraminifera Ammonia sp., Elphidium excavatum and Elphidium gunteri; the ostracods Osticythere baragwanathi and Leptocythere lacustris; and charophyte oogonia. Shell fragments of the estuarine bivalve Spisula (Notospisula) trigonella in the lowermost 0.7 m of the core are evidence that these sediments were subject to some marine influence, but the absence of foraminifera and ostracods from this same interval indicates that at the core site salinity was not sufficient to support populations of these organisms. Thus, prior to 6830 ± 90 yr cal BP the Younghusband Peninsula was in place, in part isolating the northern lagoon from the Southern Ocean. The initial recorded salinity event is signified by abundant Ammonia sp. at a core depth of 5.2 m. The duration of this event was relatively brief; foraminifera were mostly absent in the immediately overlying 2 m, representing ca 700 yr of sedimentation. This observation is attributed to substantial inflow of freshwater from the River Murray. In the upper 3.0 m, Ammonia sp. was present in most core samples indicating that for most of the past 6000 years the Coorong Lagoon has been sufficiently saline to support a continuing population of this species. At a core depth of 1.3 m, the sediment sample yielded >2000 tests of Ammonia sp., and they were accompanied by maximum pre-modern numbers of E. excavatum, O. baragwanathi and oogonia. Taken together, these data signify the maximum pre-modern salinity event recorded in the core sediments, probably correlating in time with regional drought conditions at ca 3500 yr BP. Elphidium gunteri is confined to the modern sediments where it is abundant and accompanied by equally large numbers of Ammonia sp., E. excavatum, O. baragwanathi and L. lacustris. These data collectively indicate water conditions that are significantly changed from those that prevailed in the Coorong Lagoon for most of the Holocene.  相似文献   

11.
In the lower part of sections at Skilvika and Linneelva, western Svalbard, marine silts and sands characterized by infinite radiocarbon ages (<40,000 BP) on shells are found. These sediments are covered by at least one basal till of Late Weichselian age. The till is overlain by marine sediments from the last deglaciation (12,800-10,000 BP) which contain shallow-water, subarctic foraminiferal assemblages, similar to modern near-glacial faunas from western Svalbard. The most common foraminifera in all zones in the sub-till sediments are Cassidulina reniforme, Astrononion gallowayi and/or Elphidium excavatum . The richest zones at both localities are found in the sub-till units and contain more than 20 foraminiferal species, including some boreal-arctic species. These faunal assemblages are similar to the living faunas on the west coast of Svalbard. Faunas from the postglacial climatic optimum are not yet described. We suggest that the foraminiferal assemblages in the sub-till sediment reflect Early or Middle Weichselian interstadial environments, although an Eemian interglacial cannot be excluded.  相似文献   

12.
In the Lake Frome area of South Australia there is a sedimentary sequence of non‐marine (or possibly distant marginal marine) pale‐green to grey, fine elastics and carbonates (Namba Formation). The base of these deposits is Medial Miocene in age and they are overlain unconformably by Pleistocene (and ? Pliocene) sediments. The Miocene sequence is equivalent to the Etadunna Formation of the Lake Eyre Basin, and the clay mineralogy is similar.

Combining evidence from mineralogy, palynology, and vertebrate palaeontology, a warm high‐rainfall climate operating on a subdued topography is indicated for the lower part of the Miocene Lake Frome sequence. This caused the illite‐chlorite‐kaolinite suite of the largely Precambrian provenance to be transformed to smectite and randomly‐interstratified clay. A palygorskite‐dolomite assemblage accumulated in alkaline lakes of extreme marginal marine situation during periods of seasonal dry intervals superposed on the previous climate.

A change to illite‐dominated clay, stratigraphically about halfway up the sequence, occurred simultaneously with initial uplift of the Flinders Ranges. These ranges were previously represented by, at the most, a region of low hills. Uplift, without intervention of climatic change, is sufficient to alter the clay mineralogy by promoting increased leaching. Higher in the sequence, and correlated with the major phase of uplift in the Flinders Ranges, smectite re‐appears. In this case the clay suite is believed to have resulted from increased aridity. The smectite‐rich sediments accumulated above the water table in extensive fan and mud‐flow deposits.

The Neogene sequence records a major palaeogeographic change from low energy rivers, swamps, and lakes in a low relief terrain, probably connected to the sea, to a landscape approaching that of the present during Miocene‐Pliocene times. When the Pleistocene Millyera Formation accumulated, the landscape resembled the present, though the ancestral Lake Frome was larger, and rainfall higher.  相似文献   

13.
Past geomorphological models assume that erosion of sediments from old mountain belts occurred at a relatively constant rate, based on comparatively uniform isostatic adjustment caused by unloading. Late Miocene strata of the south‐eastern United States provide an example of pulsed tectonism resulting in a surge in siliciclastic sediment production and transport. Regional tectonism (uplift of the southern Appalachian Mountains) and climatic conditions during the Late Miocene resulted in the long‐distance (up to 1000 km) fluvial transport of coarse siliciclastic sediments onto a stable carbonate platform in southern Florida. The sediments are unusual in that they are significantly coarser than marine‐transported sands in southern Florida, with discoidal quartz and quartzite clasts up to 40 mm in diameter locally present, and have relatively high potassium feldspar contents (up to 16% in some sample fractions), whereas feldspar is rare in modern Florida beach sands. It is suggested that previously documented rejuvenation of the southern Appalachian Mountains during the Middle to Late Miocene time, coupled with the Messenian sea‐level low, generated the increased rate of sediment production and necessary hydraulic gradient to allow rapid transport of coarse sediments. Tectonic influence on the river pathway in Florida, as well as in the southern Appalachian Mountains, may have maintained the river on the narrow carbonate platform. The Florida Platform during the Late Miocene must also have had a sufficiently wet climate to cause episodic transport of the coarse sediments. Siliciclastic sediment transport on the Florida Platform during the Late Miocene greatly differed from Pleistocene to modern conditions, which are dominated by the transport of fine‐grained sands by longshore marine processes.  相似文献   

14.
Owing to proximity of the North Atlantic Stream and the shelf, the Andøya biota are assumed to have responded rapidly to climatic changes taking place after the Weichselian glaciation. Palynological, macrofossil, loss‐on‐ignition, tephra and 14C data from three sites at the northern part of the island of Andøya were studied. The period 12 300–11 950 cal. yr BP was characterized by polar desert vegetation, and 11 950–11 050 cal. yr BP by a moisture‐demanding predominantly low‐arctic Oxyria vegetation. During the period 11 050–10 650 cal. yr BP, there was a climatic amelioration towards a sub‐arctic climate and heaths dominated by Empetrum. After 10 650 cal. yr BP the Oxyria vegetation disappeared. As early as about 10 800 cal. yr BP the bryozoan Cristatella mucedo indicated a climate sufficient for Betula woodland. However, tree birch did not establish until 10 420–10 250 cal. yr BP, indicating a time‐lag for the formation of Betula ecotypes adapted to the oceanic climate of Andøya. From about 10 150 to 9400 cal. yr BP the summers were dry and warm. There was a change towards moister, though comparatively warm, climatic conditions about 9400 cal. yr BP. The present data are compared with evidence from marine sediments and the deglaciation history in the region. It is suggested that during most of the period 11 500–10 250 cal. yr BP a similar situation as in present southern Greenland existed, with birch woodland in the inner fjords near the ice sheet and low‐arctic heath vegetation along the outer coast.  相似文献   

15.
Seventeen vibrocores from the inner part of Joseph Bonaparte Gulf off northwestern Australia penetrate a range of marine and marginal‐marine sediments deposited in the post‐glacial transgression and highstand. Ranging from gravelly sand to fine silt, these sediments contain a diverse fossil biota dominated by molluscs and bryozoans, but also including ostracods and foraminifers. Minor components include solitary corals, echinoids, soft coral and sponge spicules, wood debris and bone fragments. The biota can be divided into five major marine or marginal‐marine environments (intertidal, lagoonal, estuarine, strandline and shelf) and one terrestrial (riverine) environment. The intertidal environment contains four sub‐assemblages (mangroves, salt marsh, mud flat and sand flat) and the shelf environment six sub‐assemblages (hard substrate inner shelf, sandy substrate inner shelf, muddy substrate inner shelf, epiphytic, inshore and oceanic). The most useful organisms for palaeoenvironmental reconstruction are bryozoans for differentiating various shallow‐marine substrates, and foraminifers and ostracods for defining water depths, euryhaline, freshwater and oceanic influences. Palynomorphs were the only microfossils capable of providing control on terrestrial environments. The scarcity of marine plankton and the dominance of terrestrial palynomorphs in these marine sediments provides a salutary warning of the dangers of relying on plant microfossils alone when no independent environmental data are available to test the interpretation. The mollusc and bryozoan biota in the inner part of Joseph Bonaparte Gulf superficially resembles the bryomol assemblage of cool‐water shelves. This biotic assemblage is the result of turbidity rather than water temperature. The turbidity suppresses the photosynthetic, zooxanthellate and hermatypic organisms allowing molluscs, bryozoans and other apparently cool‐water biotic elements to dominate.  相似文献   

16.
An outcrop study of uplifted marine terraces provides information on the climate of past sea‐level maxima, supplementing existing palaeoclimatological archives. The western coast of the Akamas Peninsula shows several uplifted and intricately stacked Quaternary marine terraces. This study focuses on the sedimentology, petrography and sequence stratigraphy of the last three recent terraces and provides palaeoclimatological reconstruction and chronological framing. All three terraces display basically the same stratigraphic succession, which consists of regressive sequences ranging from bioturbated, storm‐influenced, subtidal high‐energy sands to subaerial exposure and aeolian deposition. Each sequence differs in petrography, reflecting contemporaneous climatic conditions. The first studied sequence (Marine Isotope Stage 9 or 11?) was deposited in a warm, arid climate, with oligotrophic water favouring ooid formation. The second sequence (Marine Isotope Stage 7) displays colder but humid conditions, with lower carbonate production and strong detrital input. The third sequence (Marine Isotope Stage 5e) records warm, humid conditions, with high carbonate production combined with significant detrital input. These littoral terraces offer high‐quality outcrops of glacioeustatic‐dominated, littoral sedimentology, together with evidence indicative of the regional climate during the late Pleistocene.  相似文献   

17.

Holocene sediments from southern Spencer Gulf are cool‐water carbonate‐rich gravels and sands, dominated by molluscs and Bryozoa. Five sedimentary fades are recognized: (i) molluscan gravel; (ii) branching coralline‐algal gravel, associated with shallow partially protected environments; (iii) molluscan‐biyozoan sand; (iv) mixed bioclastic sand, representative of the deeper central region of the lower gulf; and (v) bryozoan gravel, an isolated fades developed in a semi‐protected micro‐environment. The southern gulf is characterized by complex oceanographic conditions together with variations in water depth and substrate. The sediments share the characteristics of both the southern shelf and upper Spencer Gulf. Grain‐size distribution and sedimentary facies are controlled by a combination of all the above processes. Past sea level fluctuations are recognized from sea floor strand‐line deposits. The relic component of the palimpsest sediments has eroded from the Pleistocene aeolianite dunes. The sediments, therefore, reflect both the modern marine and past environments.  相似文献   

18.
Current high‐resolution palaeoenvironmental records reveal short‐term Holocene coolings. One of these major Holocene rapid climate changes occurred between 3.2 and 2.7 cal. ka BP. The sensitivity of river systems vis‐à‐vis slight and short‐term Holocene climatic variations is a subject of controversy in the scientific community. In this paper, we present a 4.0 to 1.4 cal ka BP palaeoflood record from the Lower Moulouya River (northeastern Morocco) to demonstrate the high sensitivity of semiarid rivers in the southwestern Mediterranean towards Holocene environmental changes. The Lower Moulouya flood deposits are characterised by thick, well‐stratified, predominantly clayey to silty overbank fine sediments. These cohesive sediments show evidence of excellent preservation conditions against fluvial erosion and contain a continuous record of mid to late Holocene flood sequences. The Moulouya palaeoflood record can be interpreted in the context of regional and global high‐resolution proxy data, revealing a strong coupling with Holocene rapid climate changes. The centennial‐scale Moulouya palaeohydrological history will be discussed with palaeoenvironmental data from the same record (palaeomagnetics, sedimentary charcoal record, anthracological analyses, snail analyses) to generate new ideas about the mid to late Holocene hydrological cycle in the southwestern Mediterranean. The deduced features of pronounced Lower Moulouya flooding and the decreased fire recurrence during Holocene cooling remain somewhat inconsistent with the interpretation of other palaeohydrological and paleaoecological records from the southwestern Mediterranean. However, enhanced Lower Moulouya flood frequencies between 3.2 and 2.7 cal. ka BP agree with increased floodplain aggradation in other major river systems of Mediterranean North Africa. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

19.
Lake Ladoga hosts preglacial sediments, although the Eurasian ice sheet overrode the area during the LGM. These sediments were first discovered by a seismic survey and are investigated using a 22.75‐m‐long core. Its upper 13.30 m comprise Holocene and Lateglacial sediments separated from the lower 11.45 m of preglacial sediments by a hiatus. They consist of highly terrigenous lacustrine sediments, which according to OSL dating, were deposited during an early stage of the last ice age (MIS 5). The palynological data allow a first reconstruction of the Early Weichselian environmental history for northwestern Russia. Birch and alder forests with broad‐leaved taxa dominated during MIS 5d (c. 118–113 ka), suggesting a climate more favourable than in the Holocene. A high content of well‐sorted sands and poorly preserved palynomorphs indicates a shallow‐water environment at least temporarily. More fine‐grained sediments and better preserved organic remains suggest deeper water environments at the core location during MIS 5c (c. 113–88 ka). Pine and spruce became dominant, while broad‐leaved taxa started to disappear, especially after c. 90 ka, pointing to a gradual climate cooling. An increase in open herb‐dominated habitats at the beginning of MIS 5b (c. 88–86 ka) reflects a colder and dryer climate. However, later (c. 86–82 ka) pine and spruce again became more common. Birch and alder forests dominated in the area c. 82–80 ka (beginning of MIS 5a). Although open treeless habitats also became more common at this time, a slight increase in hazel may point to somewhat warmer climate conditions coinciding with the beginning of MIS 5a. The studied sediments also contain numerous remains of freshwater algae and cysts of marine and brackish‐water dinoflagellates and acritarchs documenting that the present lake basin was part of a brackish‐water basin during the Early Weichselian, probably as a gulf of the Pre‐Baltic Sea.  相似文献   

20.
In a sequence of glacigenic sediments at Aberdaron, Foraminifera were obtained from samples located specifically in order to differentiate between opposing models of depositional environment. All the diamict samples yielded remarkably uniform assemblages, with similar numbers of benthic specimens and benthic species per unit weight of sediment, similar planktic : benthic ratios, and similar ratios of clearly allochthonous to possibly autochthonous elements. This is precisely as predicted by the terrestrial model of sedimentation, where all of the sediments are interpreted as being derived from the melting of glacier ice rich in marine debris entrained during passage along the Irish Sea Basin. The results lend no support to a glacial marine model, since no faunal responses to increasingly distal sedimentary environments are observed. However, the fauna is dominated by the Foraminifera Elphidium excavatum (Terquem) forma clavata Cushman, which is commonly assumed to indicate glacial marine conditions. The modern distribution of similar assemblages suggests that it is just as likely to represent the cold, reduced salinity conditions that would have prevailed in the northern Irish Sea Basin for much of the Quaternary.  相似文献   

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