Mollusc Successions Research Articles

Alpine travellers in the Carpathians: The story of two rock‐dwelling snails told by genes and fossils

AbstractAimVarious species distributed in the Alps have their disjunct occurrences in the Carpathians. Fossil evidence for some woodland snails of Alpine distribution suggests that they colonized the Carpathians during the Holocene forest optimum or later. Here, we focus on disjunct Carpathian populations of the rock‐dwelling alpine snail Pyramidula saxatilis. As it occupies very stable habitats, that is, high‐elevation limestone rocks, one can assume its potential survival in Carpathian refugia over the glacial period(s). For comparison, the more widespread and warm‐climate P. pusilla is analysed.LocationEurope.TaxonPyramidula saxatilis and P. pusilla.MethodsWe analysed the genetic diversity of P. saxatilis and P. pusilla populations across their entire ranges using mitochondrial DNA and nuclear DNA markers. Seven fossil mollusc successions from the area where P. saxatilis occurs in the Carpathians were analysed and dated using the radiocarbon method. Habitat suitability models of both species were calculated for selected time periods since the Last Glacial Maximum.ResultsAll Carpathian P. saxatilis populations were genetically homogeneous and similar to those from the Eastern Alps. In P. pusilla, we found a genetically distinct lineage in the southern Western Carpathians. Both species were found in three fossil profiles since the Middle Holocene, and in one already in the Late Glacial. Habitat suitability models suggested the fluctuations of suitable conditions in the Carpathians driven by summer precipitation, especially for P. saxatilis.Main ConclusionsOur results suggest that the Carpathian populations of P. saxatilis represent a post‐LGM colonization from the Eastern Alps triggered by climatic changes, mainly by the increase in summer precipitation during the Late Glacial interstadials and Middle Holocene. The evidence for P. pusilla is similar, but also suggests rare long‐term survival in the Carpathian microrefugia. The palaeoecological evidence indicates a possible threat to high‐elevation species from future fluctuations in precipitation regimes.

Holocene transformation of natural steppe into an agricultural landscape in the Polabí and Pojizeří Lowlands, Czech Republic, based on mollusc evidence

Recent zonal steppes of Eastern Europe and South-West Asia have their origin in the glacial steppe with its specific continental climate. The westernmost edge of the steppe belt in Central Europe has been climatically shifted from a continental course during the Last Glacial to a rather oceanic one during the Holocene. Steppe enclaves could survive only locally in the driest parts of this area, but as we have confirmed, early arrival of Neolithic agriculture played a significant role in their preservation as well. While pollen analyses can provide the main pattern of landscape development, mollusc successions provide more information about landscape details we need for a better understanding of a steppe transformation towards the recent agricultural ecosystems. Based on the study of 18 mollusc successions in two neighbouring lowlands in the chernozems and alluvial areas of Central and North Bohemia, we described a postglacial development of these two climatically different agricultural landscapes. Based on mollusc evidence, we illustrated the impoverishment of forest communities and the continual occurrence of open habitats throughout the forest climatic optimum of the Holocene. Since the Neolithic colonisation, several erosion events were observed in many profiles documented by a lack of preserved fossil molluscs and layer redeposition which are in excellent agreement with the reconstruction of the fluvial sedimentation and vegetation in the Elbe River floodplain and with the continual settlement of this area. Because we have evidence of a fully developed forest fauna in the Eem interglacial from the Polabí lowland we know that the impoverishment of forest communities and the occurrence of open habitats during the interglacial forest climatic optimum is characteristic only of the Holocene.

Habitat conditions of molluscs in the valleys of the Talaya and Bartat Rivers (Krasnoyarsk forest steppe, Russia) in the middle and late-Holocene

Here we have analysed the Holocene mollusc successions in the valleys of the Talaya and Bartat rivers (Krasnoyarsk forest-steppe), which, based on three radiocarbon dates, cover at least the last 6000 years. By studying more than 8700 mollusc shells, we aimed to reconstruct the development of alluvial conditions. Existing palynological data from the nearby Eleneva Cave provide deeper insights into the reconstruction of habitat conditions. A total of 13 freshwater and 18 terrestrial mollusc species were identified. Some of the land snail species are the first records for the region, with the finding of Vertigo substriata pushing its distribution limit eastward. The Talaya sequence consisted of five successional stages recognised based on Coniss analysis. The major successional pathway in the mollusc record reflects an increase in temperature and fluctuations in precipitation during the Middle Holocene. Over time, an abundant assemblage of freshwater molluscs was gradually replaced by the dominance of open-country and wetland terrestrial snails. In contrast, cooling at the beginning of the Late-Holocene resulted in a reduction in terrestrial snail species diversity at the expense of aquatic molluscs, again indicating increased moisture in riparian habitats. Although the Bartat River succession covered only the last 600 years, it showed a fairly stable mollusc community composition with some terrestrialization observed in the most recent part of the succession.

Mollusc successions reveal northward postglacial shifts of Alpine species ranges (Bohemian Massif, Czech Republic)

The Alps are an important hotspot of species diversity and endemism, as well as a presumed glacial refugium of several species’ groups including land snails. The recent ranges of Alpine endemics are well known, but their fluctuations during the postglacial period mirroring local climate changes are understudied. By analysing five Late Glacial and Holocene mollusc successions from two areas in the southernmost part of the Bohemian Massif (Czech Republic) situated about 100 km north of the Alps, we reveal details of these fluctuations. The Alpine endemic rocky dweller Chilostoma achates had reached the southern part of the Bohemian Massif already in the Late Glacial and disappeared in the Mid-Holocene canopy forest optimum. On the contrary, the northern boundaries of Alpine canopy forest epigeic snails extended further north than today at the turn of the Middle and Late-Holocene, pointing to a more favourable forest microclimate. The earliest known occurrences of several temperate canopy forest central European species, especially Causa holosericea and Discus perspectivus, imply the role of different areas in the Alps as their glacial refugia.

High‐resolution mollusc record from the Mituchovci tufa (western Slovakia): a reference for the Holocene succession of Western Carpathian mid‐elevation forests

The Western Carpathian Mountains have been attracting palaeoecologists for a long time, recently mainly to seek direct evidence of northern cryptic refugia in this region. We investigated a rich Holocene mollusc record in the White Carpathian Mountains, capturing a gradual development of forest malacofaunas under stable environmental conditions. To obtain precise data about colonization and extinction events for particular species, we applied a high‐resolution depth‐age model. Early Holocene assemblages revealed both the presence of Early Holocene relics and an early appearance of closed‐canopy forest species that might indicate a cryptic glacial refugium nearby. Many forest species peaking at the Holocene forest optimum, including anthropophobic arboricole land snails (Bulgarica cana and Macrogastra borealis), were present since the Early Holocene as well. After 4000 cal. a BP, forest vegetation composition changed, and the environment became less suitable for woodland snails (i.e. calcium and moisture level decreased). This change was indicated by the disappearance of many sensitive forest species. Most of the exclusively forest species reappeared during the early Middle Ages because of dense beech forest development. However, in the late Middle Ages, the study site was deforested and became an open wetland. The existence of pollen, plant macro‐remains, and stable isotope data allowed us to compare the recorded mollusc succession to the signal derived from these proxies. Hence, we propose that the Mituchovci site should be considered a model for the Holocene development of mollusc woodland faunas in the (Outer) Western Carpathians and one of the main reference sites for central European mollusc succession.

Colonisation dynamic and diversity patterns of Holocene forest snail fauna across temperate Europe: The imprint of palaeoclimate changes

The development of biotic communities since the last glaciation has been shaped by both dramatic climate changes and pathways of species colonisation from glacial refugia. Although the growing body of literature has emerged recently on possible scenarios of postglacial colonisation, less is known about the effect of climate. We analysed the dynamics of Holocene mollusc succession with an undetected human impact using three well-dated sequences from spring tufa deposits across temperate Europe. For the first time, the detailed Holocene mollusc successions can be compared with climate parameters in the corresponding time windows. High-resolution palaeoclimate data accompanied the species data, and the data derived from stable isotope analyses. The number of closed-canopy forest species that colonised the sites until 5000 cal BP and the maximum number of species per sample systematically increased towards the interior of the continent. We also observed earlier colonisation of forest snail species in the Western Carpathians. While the aridity index was the best predictor of local species richness in Normandy and Luxembourg, minimum January temperature drove the variation in snail data in Slovakia. The short period of an abrupt cooling and drying around 8500 cal BP was found to stop the colonisation, sharply reducing the number of local species across the continent. Our results document the importance of climate for the colonisation and development of forest biota during the first half of the Holocene, both at continental and local scales. They also elucidate processes shaping the current distribution of forest snail fauna across the European temperate zone.

Did humans and natural forests coexist in close proximity? A case study of the Lateglacial and Holocene Mollusca in the Moravian Karst, Czech Republic

Prehistoric settlements are usually perceived as being in opposition to the natural development of the landscape. Indeed, for woodland snail assemblages in anthropogenic landscapes in central Europe, considerable impoverishment is typical. However, it remains unclear whether this has been caused by humans only or also by climate effects. From an archaeological point of view, the Moravian Karst is one of the classic prehistorical locations in central Europe, but with a more humid climate than the previously studied anthropogenic areas. To learn more about coexistence of humans and natural forests during the Lateglacial and Holocene, we analysed 11 mollusc successions covering this entire area, a unique data set for such a relatively small area. These mollusc successions show several specific features compared to the standard development known from other mid‐European areas. One is that although the Moravian Karst is not far from the Western Carpathians, Carpathian species appeared relatively late, only during the second half of the Holocene climatic optimum. Similarly, some western European and Alpine elements appeared later than expected. In contrast to this, however, a number of forest species with central European range appeared relatively early during the Lateglacial or Early Holocene. Two even survived the Last Glacial Maximum in the Moravian Karst. This would suggest an early occurrence of forest patches in a mosaic landscape. Humans have apparently inhabited this area since the Lateglacial amongst islands of forests, which later changed during the Boreal and then the climatic optimum into humid canopy forests. Thus, a mosaic of anthropogenic and natural habitats persisting in close vicinity was possible in rugged and humid landscapes practically until the Industrial Revolution.

Holocene succession patterns of land snails across temperate Europe: East to west variation related to glacial refugia, climate and human impact

Although Holocene mollusc succession has been described from many temperate European sites, no attempt to analyse diversity patterns across the continent from east to west has yet been done. Here, we assembled and quantitatively analysed 54 most representative Holocene successions categorized into five climatic and geomorphological regions. These were defined along a longitudinal transect across temperate Europe, i.e. West Carpathians, Bohemian Massif, West Continental, Atlantic France, and Atlantic England. We found a clear east-west gradient in the Holocene dynamic of land snail assemblages, correlating mainly with the changes in strictly forest species richness. Representation of these species increased towards the east in accordance with known position of glacial refugia in the Carpathian Mountains. The West Carpathians acted as a unique refugium, expressing the highest temporal stability of Holocene snail assemblages, with a sharp increase in strictly forest species richness already in the Early Holocene. In contrast, Atlantic regions, characterized by low elevation and low topographical heterogeneity, were always poor in number of strictly forest species with no or only shallow increase of their richness in the Holocene climatic optimum. Further reduction in the second half of the Holocene, along with the increase of strictly open-country species richness correlates with higher human impact on mollusc faunas in lowland and flat regions. These factors can explain the previously reported impoverishment of modern western European forest fauna and have apparently also contributed to regional diversity patterns throughout the Holocene. Among the regions, we found three types of successional trajectories in the composition changes of Holocene molluscs, mirroring the above mentioned east-west gradient, with the West Carpathians having the most distinctive fauna. Our results show that distance from glacial refugia, landscape topography, and also human impact importantly shaped the species richness dynamic and successional pathways of Holocene land-snail fauna across temperate Europe.

Response of a spring-fed fen ecosystem in Central Eastern Europe (NW Romania) to climate changes during the last 4000 years: A high resolution multi-proxy reconstruction

We document the long-term development of a spring-fed fen assessing its sensivity to climate changes over the last ca. 4000 years. Our investigation is based on high-resolution, continuous plant macrofossil remains and mollusc records, complemented by pollen, geochemical analysis and radiocarbon dating of Valea Morii, located in the Feleac Hills (Transylvanian Depression) in NW Romania, Central Eastern Europe. Based on our palaeocological data we have distinguished three stages of wet habitat conditions: two stages between 4000 and 2450 cal yr BP and one in the last 800 cal yr BP, and one dry stage between ca. 2450 and 800 cal yr BP. These local habitat conditions appear to reasonably reflect regional climate characteristics. High-resolution analysis of two replicated cores documented a mostly comparable pattern of local plant and mollusc succession, and stable isotope values from ca. 500 cal yr BP. The appearance of C. mariscus during the last two centuries may be related to increased wetness and associated active CaCO3 precipitation, which allowed this plant to colonise the spring-fed fen studied. However, it can be not excluded that the occurrence and spread of a Cladium mariscus population at this site during the last two centuries might have been partly favoured by the warming of the climate after the Little Ice Age. The potential of carbonate oxygen stable isotope values as an indicator of major trends in climatic change, both temperature and humidity, in mountain spring-fed fen deposits is shown. Carbon isotopes in the carbonates were found to be useful in reconstruction of changes in vegetation, soil development and the dissolution of bedrock carbonates, primarily as a reaction to changes in climate humidity.

River Floodplains as Habitat and Bio-Corridors for Distribution of Land Snails: Their Past and Present

Abstract River floodplains of Czech rivers serve as refugia to woodland or hydrophilous gastropods, in current intensively agriculturally utilised, urbanised and largely fragmented landscape. This habitat often form one of the last refuge and replace the natural habitat of these species. River floodplains also represent linear bio-corridors in landscape and allow gastropods to spread through the landscape in both directions, up and down the stream. We showed based on available fossil mollusc successions that development of the floodplain mollusc fauna took place quite different way in various river floodplains, depending on their specifics and geographical location, because especially the ones situated in the chernozem area of the Czech Republic had very different history in comparison with those in higher altitudes. The species richness and composition of recent floodplain malacofauna arises from historical development of particular area/site and depends also on environmental factors such as an elevation, humidity gradient, vegetation type and its biomass, light conditions of the site and soil reaction. Recently, the invasive plants represent a serious problem for current floodplain ecosystems; species richness and abundances of terrestrial mollusc floodplain assemblages are changing due to their effect. The impact on gastropods is species-specific and was described for the following species: Impatiens glandulifera, Fallopia japonica subsp. japonica, F. sachalinensis, F. ×bohemica.

Patterns of land-snail succession in Central Europe over the last 15,000 years: main changes along environmental, spatial and temporal gradients

Land snail shell assemblages have been used since the pioneering days of palaeoecology to describe Quaternary environmental changes. Despite the many advantages of this proxy, it has recently been rather overlooked. There are more than 300 mollusc successions from localities throughout the Czech and Slovak Republics, making this a globally unique archive. We selected 91 of these successions for radiocarbon dating and further detailed processing. Based on analyses of 828 mollusc assemblages we found a significant increase in both total species richness and number of forest species since the Lateglacial, with a decrease in both after the Middle Holocene. In contrast, the opposite response was found for open-country species and the proportion of xerophilous species. The proportion of forest and open-country species reversed at the Pleistocene/Holocene transition (approx. 11,500 cal yrs BP). Changes in species richness were rather stable across the study area and at different elevation, contrary to changes in species composition. MDS ordination based on presence/absence data show four main patterns of species composition associated with the number of forest species in a sample, position of site along the west–east direction, the proportion of hygrophilous species and, finally, with the age of the mollusc assemblage. The number of forest species indicates the main pattern of changes in the composition of Central European land snail assemblages from the Lateglacial to the present. We confirmed the application and temporal stability of ecological groups of snails as a useful tool for reconstruction of the terrestrial palaeoenvironment.

List of malacologically treated Holocene sites with brief review of palaeomalacological research in the Czech and Slovak Republics

The complete list of all Holocene mollusc succession sites sampled by standard techniques in the area of the Czech and Slovak Republics is presented, 30 years after the last one. All sites are commented upon, and geographical, geomorphological, and vegetation conditions are described including other important information. A complete literature review was done and crucial research moments pointed out. Altogether, 302 Holocene mollusc successions were sampled in this area during the period 1948–2013. To date, 272 successions are published, but only 240 of them were processed in detail; 62 sampled profiles remained unprocessed; 129 successions were numerically dated. We believe that this is a globally unique dataset with great research potential.

Direct evidence of central European forest refugia during the last glacial period based on mollusc fossils

Although there is evidence from molecular studies for the existence of central European last glacial refugia for temperate species, there is still a great lack of direct fossil records to confirm this theory. Here we bring such evidence in the form of fossil shells from twenty strictly forest land snail species, which were recorded in radiocarbon-dated late glacial or older mollusc assemblages of nine non-interrupted mollusc successions situated in the Western Carpathians, and one in the Bohemian Massif. We proposed that molluscs survived the last glacial period in central Europe in isolated small patches of broadleaf forest, which we unequivocally demonstrate for two sites of last glacial maximum age.

Mollusc succession of a prehistoric settlement area during the Holocene: A case study of the České středohoří Mountains (Czech Republic)

Some Central European areas were attractive for the first agricultural settlements due to their suitable natural conditions. The Holocene development of such areas was thus under long-term human pressure, whose impact on the whole landscape is still poorly understood. One of such areas is the České středohoří Mountains. While pollen analyses can provide the general pattern of the landscape development, the analyses of mollusc succession provide landscape details, which are important primarily in landscapes with high habitat diversity. Based on the study of 11 mollusc successions situated at the České středohoří Mountains, we describe the postglacial development of the area and show the moderate fluctuation of woodland, wetland and open country habitats without any distinct succession peaks of particular habitat types during the whole Holocene. However, a detailed look of species exchange has provided additional information of succession pattern. The impoverishment of woodland communities is probably caused by human pressure, not natural processes, because fully developed woodland assemblages had occurred there during the past interglacials. It seems for now that humans had affected the whole landscape of the prehistoric settlement area, including hard-to-access sites, not only the nearby surroundings of their settlement.

Nivní malakofauna povodí Úštěckého potoka a její vývoj během holocénu [The floodplain mollusc fauna of the Úštěcký Brook catchment basin and its development during the Holocene (North Bohemia, Czech Republic)

This paper presents a research of floodplain mollusc assemblages of the Úštěcký Brook catchment basin (Elbe tributary, North Bohemia, Czech Republic). Altogether, 71 mollusc species (69 species of Gastropoda, 2 species of Bivalvia) were recorded in the study sites between 2007 and 2011, representing 29% of the total Czech malacofauna. The common forest species dominated (41% of all recorded species) and included some rare woodland species as Daudebardia rufa, Discus perspectivus, Macrogastra ventricosa, and Sphyradium doliolum. Rare wetland species protected by the NATURA system Vertigo angustior and endangered wetland species Vallonia enniensis were also found. The richest assemblages occurred on the upper part of the brook, while the lower part was very species poor due to agriculture land use in this fertile floodplain. A small calcareous moorland, situated in the northeastern vicinity of Úštěk Town (north Bohemia) includes a Holocene mollusc succession that was subdivided into three local mollusc zones: I – basal zone with marked numbers of Discus ruderatus, Vertigo geyeri and numerous aquatic taxa, II – with forest species including Platyla polita and III – dominated by open-ground and catholic species. Despite the specific conditions of the moorland habitat the succession largely corresponds with the standard developmental pattern of the mollusc fauna in the zone of mid-European uplands. Of particular interest is the developmental break reflected by the poor fauna in the layer 3. The malacofauna of the Úštěcký Brook can be used as a model of alluvial mollusc assemblages of the brook floodplain that is situated in the warm area of Central Europe with long-term history of agriculture land use.

Holocene succession and biogeographical importance of mollusc fauna in the Western Sudetes (Czech Republic)

The location of the Sudetes Mts. between the Alpine and Scandinavian ice-sheets during the Quaternary Period makes this area interesting from a biogeographic point of view. Little information was known about the Holocene mollusc and vertebrate fauna of this area up to now. Despite some regional differences among particular mountain areas, it seems that Sudetes Holocene mollusc succession follows a similar but moderate course to that of the standard central European Holocene succession. The Stárkov–Vápenka sequence can be used as a standard succession pattern for this area. Some woodland species can survive the Glacial in talus slope debris with suitable microhabitats (e.g. Oxychilus depressus). The structure of the vertebrate assemblage suggests that the valleys of Krkonoše Mts. might provide favourable conditions for a diversified mammalian community and could take the role of a glacial refugee. This study indicates that isolated occurrences of Alpine and Carpathian elements, such as Cochlodina dubiosa corcontica endemic in Krkonoše Mts., are not relics of a former, much wider distribution, but modern immigrants of the younger half of the Holocene and thus its spreading was very slow. It seems that the Western Sudetes Mts. (except for the Ještěd Ridge) were an island of low mollusc diversity, not human-induced but natural, during the whole Holocene.

Impoverishment of recent floodplain forest mollusc fauna in the lower Ohře River (Czech Republic) as a result of prehistoric human impact

Analyses of fossil mollusc successions have rarely been used to study the development of floodplain forests during the Holocene. The Ohře River, located in a prehistorically settled chernozem area in the Czech Republic, is partly situated in Cretaceous marlstones, yielding sediments suitable for fossilization directly in floodplain deposits. We analysed five fossil mollusc successions situated in the lower stretch of the Ohře River and compared the results with recent mollusc assemblages studied along the entire 256 km of the river. Fossil samples were composed mostly of open‐country species throughout the Holocene or the whole preserved succession. Only some samples also contained woodland assemblages, but these were always greatly impoverished, with a very low frequency of strictly woodland species. Although the natural‐looking appearance of the present‐day floodplain forests of the lower river stretch has resulted in its being declared a nature reserve, modern floodplain forest mollusc assemblages there are also impoverished. This reduction in the distribution of strictly woodland species compared with modern assemblages in the upper stretch of the river seems to be the result of an ancient human settlement and continuous disturbances of the floodplain forest development since the Neolithic. Thus, fully developed floodplain forest assemblages occur recently only in the upper non‐impacted stretch of the river. Based on the studied fossil successions we can conclude that the lower Ohře River floodplain was probably a mosaic of open and disturbed forest habitats throughout the Holocene. This area is part of a central European landscape island, where forests probably never fully developed and open patches from the early Holocene continually developed into an agricultural landscape.

Malacological characteristics of the Middle to Upper Pleistocene transitional interval (MIS 7–5) observed in the Batajnica locality (Serbia)

The Batajnica loess section is one of the most complete Middle and Late Pleistocene records known in the Vojvodina region (Serbia). The main aim of the malacological investigations was to study the latest Middle Pleistocene cold interval and to see how the mollusc successions reacted to the climate changes during the cold–warm transition. The deposits which belong to the upper part of pedocomplex V-S2, V-L2 loess and partly to the V-S1 soil were sampled. The penultimate glacial loess V-L2 of the Batajnica site corresponds to the cold interval Marine Isotope Stage (MIS 6). The molluscs indicate moderate or sometimes warm climate and dry or moderate steppe-like environment composed of adjacent mosaics of drier and humid habitats. The mollusc complexes of V-S2 soil (MIS 7c), V-L2 loess (MIS 6) and V-S1 paleosol (MIS 5e) show almost the same species composition, which suggests the existence of a comparatively moderate or warm climate during the late Middle Pleistocene cold interval. In contrast, the mollusc complexes (MIS 6) from Western and Eastern Europe have less species and few individuals compared with the Batajnica section. Comparison with the late Middle Pleistocene mollusc associations from the northern and southern margins of the Fruška Gora Mountain confirms its environmental originality. The northern side of the mountain was characterized by a humid and relatively colder environment than the other areas of the Vojvodina region (Batajnica, Irig and Ruma). The mollusc fauna obtained in the Batajnica site suggests that this adjacent area represented a refugium for the thermophilous and arid tolerant species where they were able to survive during the cold periods of the Pleistocene and thus confirms the hypothesis of P. Sümegi.

Late Pleistocene mollusc assemblages and inferred paleoenvironments from the Andean piedmont of Mendoza, Argentina

This paper is focused on the paleoecological analysis of a mollusc succession cropping out on the right margin of La Estacada stream in the Andean piedmont of Mendoza, Argentina (33°28′ S, 69°03′ W). The stratigraphic section, mainly composed of fine sands, interbedded with levels of silty clays and organic matter, records the interval between 35.2–35.5 14C ka B. P. and 31.5–31.6 14C ka B.P. The mollusc succession is represented by freshwater and land snails: Biomphalaria peregrina (Planorbidae), Lymnaea viator (Lymnaeidae), Succinea meridionalis (Succineidae), Rotadiscus amancaezensis (Charopidae) and Radiodiscus sp. aff. Radiodiscus quillajicola (Charopidae). The dominance of semi-aquatic and hygrophilous land snails, suggests the development of a vegetated shallow water body, probably a damp habitat occasionally submerged, with four main stages of evolution related to fluctuating water levels. The abundance of shells together with the stable isotope composition of carbonate shells of L. viator ( δ 13C and δ 18O) and the presence of Radiodiscus sp. aff. Radiodiscus quillajicola and R. amancaezensis suggest relatively warm and wet conditions. Based on its radiocarbon chronology and the paleoecological reconstruction, the studied section is recording a mild interval corresponding to an interstadial (Marine isotope stage 3) of the last glacial cycle.

Three detailed, radiocarbon-dated, Holocene tufa and alluvial fan mollusc successions from southern Ontario: The first in northeastern North America

Fossil mollusc remains, particularly those of land snails, provide a wealth of detailed information concerning local Quaternary paleoenvironments and regional paleoclimatic conditions. However, this important resource is generally overlooked in North America and consequently quantitative, well-dated terrestrial mollusc successions are extremely rare here. In an attempt to redress this imbalance, a project examining the Holocene molluscan faunal history of northeastern North America has been initiated. Thus far, detailed mollusc successions and associated radiocarbon age determinations have been obtained from three sites in southern Ontario; two alluvial fans (Chine Drive Fan and Cudia Park Fan, both from the Scarborough Bluffs east of Toronto) and a tufa (West River Road, near Cambridge). The observed land snail successions to provide an initial view of the molluscan faunal history of this region during the period from the late glacial to the mid Holocene, between approximately 10,500 and 5000 radiocarbon years BP (yr BP). The molluscan data have also been used to reconstruct the paleoenvironmental history of southern Ontario during this time, documenting the progression from exposed, open habitats characterised by species such as Vertigo modesta, Vallonia albula, Columella columella and Vitrina angelicae limpida, to closed woodland biotopes indicated by the presence of taxa including Carychium nannodes, Nesovitrea binneyana, Paravitrea multidenta and Helicodiscus parallelus. This study has already demonstrated the potential of this technique in the study of Quaternary climatic and environmental change in eastern North America and represents a strong foundation for extending the analysis of fossil land snail successions to other sites throughout this region. It has also provided new and important insights into the establishment of the modern molluscan fauna, which are essential to the understanding of present day distributional patterns and environmental associations.