The position of the Rupelian/Chattian boundary in the southern Upper Rhine Graben based on new records of microfossils

This study analyses the regressive phase of the marine Froidefontaine Subgroup and the subsequent fluvio-lacustrine Niederroedern formation in the southern Upper Rhine Graben during the Late Rupelian and the position of the Rupelian/Chattian boundary. The study is based on the sedimentary record and several microfossil groups from two boreholes, with a focus on new records of fish otoliths, Bolboforma and Charophyta. The biostratigraphic evaluation of these groups provides evidence for a position of the Rupelian/Chattian boundary within the upper Niederroedern Formation. This is contrary to the results from a previous sedimentological approach, which places the boundary at the base of the Niederroedern Formation. The fish fauna indicates a biogeographic relation to southern France, the Molasse Basin of Switzerland and southern Germany.     

Evidence for pre-orogenic,Early Devonian rifting in the Variscan belt: stratigraphy and structure of the Palaeozoic cover of the Mauges Unit (Upper Allochthon,Armorican massif,France)

The Palaeozoic sediments from the Mauges Unit (Armorican Massif, France) are the best-preserved pre-orogenic sequences belonging to the Upper Allochthon. Two coherent sequences are identified. The southern unit (Chateaupanne Unit) represents the cover of the Proterozoic basement and consists of Ordovician sediments unconformably overlain by Emsian carbonates followed by Emsian to earliest Eifelian immature sandstones. The northern unit (Tombeau Leclerc Unit) consists of an Hirnantian to Emsian condensed sequence, in reverse position, that has been thrust over the southern unit. The Devonian unconformity is interpreted as evidence for an Early Devonian extension, recorded by normal faults affecting both the Early Devonian limestones and the underlying Ordovician series. This crustal extension, recorded here for the first time, is possibly related to the opening of a back-arc basin (Saint-Georges-sur-Loire) associated with the subduction of an ocean located further south (Galicia-Brittany-Massif Central Ocean).     

The grain-size characterisation of coastal sand from the Somme estuary to Belgium: Sediment sorting processes and mixing in a tide- and storm-dominated setting

Sand-rich Holocene to modern clastic deposits in the eastern English Channel and the southern North Sea coasts of France and Belgium occur extensively as nearshore-sand bank, estuarine-tidal flat, aeolian dune and beach sub-environments. Sand samples (n = 665) collected from these deposits suggest the presence of three different populations: a largely dominant (83%) medium to fine quartz sand population (“b”), and finer- (14%) and coarser-grained (4%) populations (respectively “c” and “a”). The distribution of these populations among the four sub-environments reflects tide- and storm-dominated sorting and transport processes and a variable degree of mixing. These populations are derived from a mixture of very fine- to very coarse-grained fluvial, outwash and paraglacial sediments deposited on the beds of the eastern English Channel and southern North Sea during the late Pleistocene lowstand. The nearshore-sand bank environment, which also corresponds to the main offshore source area of the coastal deposits, exhibits population heterogeneity reflecting the variability of hydrodynamic conditions and sediment sorting in this zone. The nearshore topography of tidal ridges, banks and troughs in these tidal seas leads to variable bed and tide- and storm-induced shear stress conditions. These conditions only allow for the mobilisation and onshore transport of some of the finer fractions (populations “b” and “c”), leaving an offshore mixture of these finer populations with coarser, less mobilisable sediments (population “a”). Once in the coastal zone, these two finer populations undergo further hydrodynamic sorting and segregation. Variably sorted very fine sands to silts (population “c”) are trapped in the low-energy estuarine-tidal flat sub-environment, while the highly homogeneous population “b” is further sorted in aeolian dune and beach sub-environments. This sorting occurs via a coastal sand transport pathway linking the Somme estuary mouth to the southern North Sea bight where tidal range and wave energy decrease relative to the English Channel. Since this sand transport pathway enables longshore transport of hydrodynamically sorted medium to fine sand derived directly from the immediate nearshore zone, it has further contributed to a net flux of this sand population from the eastern English Channel sea bed to the southern North Sea.     

Is there a close spatial relationship between faults and plutons?

Using spatial relationships between individual plutons and faults to support genetic correlations between faulting and magmatism is meaningless since even random magmatic or tectonic processes will result in some plutons adjacent to faults. Our initial analyses of populations of faults and Carboniferous plutons in the Armorican Massif, France and faults and Alleghanian plutons in the southern Appalachians, USA indicate that plutons have broad distributions with respect to faults but with a tendency for plutons to occur away from faults. Maxima of integrated pluton areas occur at 1/4 (Appalachians) and 1/2 (Armorican) of the distance between the average fault spacing in these orogens. Although there is a great need for statistical evaluations of relationships between populations of igneous bodies and structures in a wide variety of settings and crustal depths, our initial studies suggest that faults do not preferentially channel magma during ascent or emplacement and that these are relatively unfocused processes within orogenic belts.     

Lateglacial palaeoenvironments and palaeoclimates from Conty and Houdancourt, northern France, reconstructed from Beetle remains

Two Lateglacial insect sequences are described (a) from Conty, in the Selle valley and (b) from Houdancourt in the Oise valley, both in northern France. These investigations are part of a multidisciplinary investigation involving archaeology, sedimentology, geomorphology, geochronology and palaeontology (pollen, macroscopic plant remains, vertebrates, molluscs and insect fossils). The sequences of insect assemblages date from the latter part of the Bølling to the end of the Allerød periods. Environmental analysis of these faunas shows that rivers with riffles and pools meandered across flood plains. The river was extensively fringed with reedy vegetation. The only trees growing close to the river were of Salix and/or Populus. All the insect assemblages indicate that the thermal climates during the Bølling and Allerød periods were similar to one another and during both periods were very nearly as warm as that of the present day. No insect fossils were recovered from the sediments attributed to the Older Dryas interval though other evidence from these sites suggests that this event was decidedly colder than those immediately preceding and succeeding it. Comparisons are made between Lateglacial climatic patterns in northern France with those elsewhere in Europe.     

Stratigraphy,paleontology, and age of Lake Algonquin sediments in southwestern Ontario,Canada

Molluscs, ostracodes, diatoms, pollen, plant macrofossils, peat, and wood have been found in glacial Lake Algonquin sediments, and estuarine-alluvial sediments of the same age, in southern Ontario. Molluscs and ostracodes are particularly abundant and widespread. Pollen analysis of Lake Algonquin sediments, bogs on the Algonquin terrace, and upland bogs above the Algonquin terrace, indicate that Lake Algonquin was still in existence at the time of the spruce-pine pollen transition, previously dated at an average of 10,600 yr BP at a number of sites in Michigan, Ohio, and southern Ontario. Wood in estuarine-alluvial sediments graded to the Algonquin level is of similar radiocarbon age. Evidence from several sites in the eastern Great Lakes area suggests the presence of a preceding low-water stage (Kirkfield outlet stage); drowned and alluviated valleys and fining-upward sediment sequences have been identified in this study as further supporting evidence. Lake Algonquin drained from the southern sites by isostatic tilting and eventual opening of the “North Bay outlet” some time shortly after 10,400 yr BP.Our radiocarbon dates suggest the low-water stage has an age of about 11,000 yr BP, and that Lake Algonquin drained 10,000–15,000 y. a. Dates previously published for the Lake Michigan basin are generally too young in comparison with ours, and dates on the Champlain Sea are generally too old. More critical evaluation of all dating results is desirable.From fossil remains we suggest a rapidly expanding fauna in the waters of Lake Algonquin. The spruce pollen period was a time of rapid faunal and floral migration, when the ice front was retreating from Kirkfield to North Bay, Ontario. Diversity of some species and fossil numbers increased substantially at the transition from spruce to pine just before Lake Algonquin drained.     

Genetic transition between northern and southern populations of the estuarine isopod,Cyathura polita,and the discovery of a new species ofCyathura

Previous work on the genetics ofCyathura polita populations along the Atlantic coast indicated that northern and southern populations have diverged significantly. We used starch gel electrophoresis to study the transition between northern and southern populations for gene frequencies at four enzyme loci.Cyathura from three sites in the Carolinas were compared with those from representative populations in the north (Massachusetts) and south (Florida).Cyathura polita from the northern and southern populations were fixed for different alleles at three of the four loci assayed.C. polita from a population in North Carolina had the northern electromorph for two loci and were polymorphic at theEst locus for the northern and southern electromorphs, whileC. polita from a population in South Carolina had the southern electromorphs for two loci and were polymorphic at theMdh-1 locus for northern and southern electromorphs. Thus, there appears to be gene flow between the genetically differentiated populations in the north and south. One population ofCyathura from North Carolina had unique electromorphs at the four loci assayed and appears to be a new species.     

南京汤山直立人头骨的复原和更新世中期直立人的地理变异

现代中国人体质特征可分为南北两大地区类型。这两大类群的形成可追溯到全新世的新石器时代 ,甚至更新世晚期。 1993年在南京汤山发现一具更新世中期的带有面骨的直立人头骨。为追索中国人群南北两大类型的形成历史 ,对汤山头骨作了重新复原 ,对汤山头骨与周口店头骨作了形态比较。结果表明 ,汤山头骨与周口店头骨相同的特征几乎全是直立人共有的形态特征。汤山头骨不同于周口店头骨的诸特征 ,如浅的眶上圆枕上沟、不呈发髻状的枕骨水平轮廓、较短宽的面部、特宽的鼻型和接近低眶的眶型等 ,提示中国人群南北两大类型的形态差别可能早在更新世中期汤山直立人生存时已显出端倪     

Paleomagnetic results from the Permian Rodez basin implications: the Late Variscan tectonics in the southern French Massif Central

A paleomagnetic study has been carried out on three sedimentary formations of the Permian Rodez basin in the southern France. Two of them yield paleomagnetic poles of Saxonian and Thuringian age showing counterclockwise rotation of moderate amplitude, during or after the Thuringian deposition. For the French Massif Central, contrary to its stable southern (Lodève basin) and eastern (Largentière basin) borders, on its southwestern border, in a large area including the Rodez, Saint-Affrique and perhaps Brive basins suffered rotations due to the extensional tectonics during the Late Variscan period.     

Distribution and chronology of Pleistocene permafrost features in France: Database and first results

Numerous periglacial features (polygons, nets, soil stripes, ice‐wedge pseudomorphs and sand‐wedge casts, involutions) have been recorded in France by examining bibliographical sources and aerial photographs. These data show that a large part of France was affected by permafrost during the Pleistocene and only the southern Aquitaine Basin and Languedoc seem to have been beyond its maximum extent. The first OSL ages obtained from the aeolian infill of wedge structures indicate that at least two phases of thermal contraction cracking occurred in southwestern France between ～25 and 36 ka. Chronostratigraphical data from loess in northern France indicate that these episodes correspond to the formation of ice‐wedge networks associated with tundra gleys. In the latter region, two additional permafrost episodes probably occurred during the Last Glacial, the older one corresponding to the end of Marine Isotope Stage (MIS) 4 around 60 ka and the more recent one to MIS 2 around 19–16 ka. Although stratigraphical data indicate that these episodes were relatively short (about one millennium), relict permafrost may have existed for longer periods in northern France.     

Apport de la modélisation géophysique pour la compréhension de la structuration du pas de Calais

This study is based on an analysis of seismic, gravimetric and magnetic data to model the structure of the Dover Straits area. The Dover Straits are set in a transitional position within the Brabant para-autochthon, which lies between the Ardennes allochthon to the south and the Brabant Massif to the north. The seismic profiles show that this area is characterised by several superimposed Mesozoic basins, whose evolution has been controlled by the reactivation of Lower Palaeozoic faults. In common with the adjacent Weald–Wessex and southern North Sea basins, the Dover Straits area records a Jurassic extensional phase and a post-Cretaceous tectonic inversion. The geophysical modelling reveals the presence of a basement to these Mesozoic basins that exhibits Ordovician to Silurian structures, which cannot be detected on the seismic reflection profiles. In contrast to earlier interpretations, the modelling presented here suggests that the Brabant Massif continues southward beyond the Dover Straits and under the Brabant para-autochthon. Gravity data also provides evidence for the presence of granitic body at depth, in the vicinity of Km 27 on the seismic profile, which may have driven the uplift of the Silurian rocks in the area of the Straits. Similar granitic intrusions have been proposed to explain gravity anomalies along the Rhenohercynian Margin in Belgium, eastern and southern England. The geophysical modelling demonstrates the continuity of the basement and Mesozoic basin structures across the Dover Straits, suggesting a common geological evolution of the adjacent southern England–northern France regions. To cite this article: B. Minguely et al., C. R. Geoscience 337 (2005).     

Intraspecific Variability and Problematic Dimorphism in the Early Cretaceous (Valanginian) Ammonite Saynoceras verrucosum (d’Orbigny, 1841)

The population of Saynoceras verrucosum (d’Orbigny) from the Polish basin (W?wa? section, central Poland) shows no significant intraspecific variability. Dimorphism has not been found in this population. Statistical analyses of material from the shallow epicratonic Polish basin and the relatively deep Vocontian basin (southeastern France) indicated two populations. Forms from the Polish basin are somewhat more inflated and smaller than forms from the Vocontian basin.     

Quantitative evaluation of the depth of the western Mediterranean before, during and after the Late Miocene salinity crisis

Quantitative geophysical calculations which take into consideration the isostatic loading of sediment overburden, the overlying water cover, and the thermal cooling history of the continental edge, and its adjacent oceanic lithosphere, demonstrate the foundering of the margins of the western Mediterranean had already commenced in the Aquitanian stage of the early Miocene. The calculations are based on magnitudes and rates of sediment accumulation observed along a profile of three commercial boreholes into the subsurface of the continental shelf of southern France. By the time of the late Miocene (Messinian) salinity crisis, the depth of the seafloor within the Balearic basin exceeded 2.5 km. Sea-level fluctuations induced by evaporitic draw-down permitted the exposure of large tracts of the former submerged continental margins to subaerial processes. The measured magnitude of sediment removal by erosion and channel incision near the outer shelf of the modern Gulf of Lion surpasses 1 km. The subsidence history of this shelf platform south of France provides new evidence that the continental lithosphere behaves as if it is rigidly coupled to its oceanic counterpart commencing with the initial phase of the pull-apart. No major vertical fault displacements have subsequently offset their overlying crustal layers. The sedimentary shaping and construction of the margin seaward of the Rhône delta resulted in a pronounced shelf edge migration and slope progradation during the pre-salinity crisis Miocene. It has taken 5 million years of predominant upbuilding to establish a new equilibrium profile similar in cross-section to the precrisis depositional surfaces created by outbuilding.     

Environmental variability during the Last Interglacial: a new high‐resolution pollen record from Tenaghi Philippon,Greece

A new high‐resolution Last Interglacial pollen record from the Tenaghi Philippon peatland, northeast Greece, documents variability in forest composition and cover, which we attribute to changes in temperature and moisture availability. The declining stage of the interglacial was marked by a stepwise decrease in temperate tree populations and culminated in the complete collapse of forest at the onset of the ensuing stadial. The coincidence of the onset of the stepwise declining trend with the increased prominence of North Atlantic ice‐rafting events suggests that ecological thresholds in southern Europe were only crossed once ice rafting events intensified, and implies that changes in North Atlantic ocean circulation were an important contributing factor to the declining temperate forest cover in southern Europe. Our results provide evidence for intra‐interglacial variability in the low mid latitudes and suggest a coupling between the high northern latitudes and the northeast Mediterranean during this interval. Copyright © 2013 John Wiley & Sons, Ltd.     

Pleistocene fluvial terraces from northern France (Seine,Yonne, Somme): synthesis,and new results from interglacial deposits

The Seine, Yonne and Somme are the main rivers draining northwestern France and flowing into the Channel. During Pleistocene cold stages they were tributaries of the “Fleuve Manche”. They are characterised by well-developed stepped terrace systems showing up to 10 incision steps for the last 1 Ma. After 15 years of research and the synthesis of stratigraphical, sedimentological, bioclimatical data and numerical dating, these terrace systems are interpreted as the response of the fluvial environments to climatic cyclicity, superimposed on a background of slow tectonic uplift. The comparison of these three terrace systems shows that the incision budget is similar within the studied area (about 55–65 m/1 Ma), implying relative homogeneity of uplift. In the main part of the area, beyond marine influence, the analysis of each stepped alluvial formation shows regular sediment balance generally composed of coarse periglacial gravels (pleniglacial), covered by fine-grained sediments locally overlain by calcareous tufa (interglacial). However, in the Lower Seine valley, close to the present coast, the low terrace includes two estuarine interglacial units interbedded within periglacial gravel units. Nevertheless, until recently evidence of full interglacial conditions remained elusive in fluvial contexts, especially in the Somme. To address these issues a new research programme has been launched on tufa deposits that are the best candidate to register the climatic optimum. Initial results from la Celle (Seine), Saint-Acheul and Caours (Somme) allow palaeoenvironmental reconstructions of MIS 11 and 5e, and thus confirm the importance of calcareous tufa to define a reference record of Pleistocene Interglacials for northern France. Moreover, it has been previously demonstrated that the main incision leading to terrace formation can be attributed to the transition between interglacial and glacial (during early glacial phases). The new results from interglacial records have important implications concerning the precise occurrence of the major incision phases within the climatic cycle as they provide the starting point immediately preceding downcutting.     

Molluscan successions from the Holocene tufa of St Germain‐le‐Vasson,Normandy (France) and their biogeographical significance

A detailed molluscan succession from a 10 m thick deposit of Holocene tufa at St Germain‐le‐Vasson, Normandy, provides the most complete record from northern France and has shed new light on the historical biogeography of several species of land snail. The succession has been reconstructed from four profiles and a chronology provided by accelerator mass spectrometry radiocarbon dating of charcoal, wood and shell. The onset of tufa formation occurred after 9700±90 yr BP and persisted until 4213±77 yr BP. The tufa appears to have accumulated at a remarkably constant rate (14.4–16.5 cm 100 yr^?1), except for the upper levels, where the rate increases fourfold. The succession has been divided into six local molluscan zones. An early assemblage consisting of ecologically tolerant species and those indicative of marshy grassland is replaced by a sequence of shade‐demanding taxa, reflecting the encroachment of woodland. Shaded conditions persist until the end of the sequence but the most hygrophilous elements decline after 5422±60 yr BP (zone 5), a change also reflected in the tufa lithology by the development of silty grey horizons. Notable species recovered from the tufa include Acicula fusca, Vertigo substriata, V. alpestris, V. moulinsiana (all rare or unknown living in northern France). Hygromia limbata, a twentieth century introduction to Britain, was previously thought to be a relatively recent arrival in northern France, but its record at St Germain shows that it has been present in Normandy since 6500 yr BP. Azeca goodalli, another shade‐demanding species, appeared at St Germain much later, just after 4420±65 yr BP. Several other species present in the tufa, such as Pomatias elegans, no longer live on the site, adding to the evidence for a distributional decline in Normandy and elsewhere. Perhaps the most noteworthy record is that of Leiostyla anglica, between about 8500 yr BP and 5000 yr BP, because this constitutes its only Holocene occurrence from mainland Europe. Following this discovery it seems likely that further Holocene sites with L. anglica may be found along the western seaboard of Europe connecting populations in Iberia with those of the British Isles. Copyright © 2004 John Wiley & Sons, Ltd.     

藏北南羌塘安多县鄂斯玛地区早白垩世孢粉化石Dicheiropollis的发现及其地质意义

报道南羌塘盆地鄂斯玛地区首次发现早白垩世Dicheiropollis花粉。根据这一花粉的出现和整个孢粉中大量出现Clas-sopollis的组合特征,其时代可确定为晚侏罗世—早白垩世早期。这不仅为藏北南羌塘盆地晚白垩世地层的存在提供了依据,而且为今后进一步的地质工作提供了线索,具有重要的研究意义。     

藏北南羌塘安多县鄂斯玛地区早白垩世孢粉化石 Dicheiropollis的发现及其地质意义

报道南羌塘盆地鄂斯玛地区首次发现早白垩世Dicheiropollis花粉。根据这一花粉的出现和整个孢粉中大量出现Classopollis的组合特征,其时代可确定为晚侏罗世—早白垩世早期。这不仅为藏北南羌塘盆地晚白垩世地层的存在提供了依据,而且为今后进一步的地质工作提供了线索,具有重要的研究意义。