Bidart Section Research Articles

Volcanic origin of the mercury anomalies at the Cretaceous-Paleogene transition of Bidart, France

Abstract The timing and mechanisms of the climatic and environmental perturbations induced by the emplacement of the Deccan Traps large igneous province (India) and their contribution to the Cretaceous-Paleogene (K-Pg) mass extinction are still debated. In many marine sediment archives, mercury (Hg) enrichments straddling the K-Pg boundary have been interpreted as the signature of Deccan Traps volcanism, but Hg may also have been derived from the Chicxulub (Mexico) impact. We investigated the Hg isotope composition, as well as the behavior of iridium (Ir) and other trace elements, in K-Pg sediments from the Bidart section in southwest France. Above the K-Pg boundary, Ir content gradually decreases to background values in the Danian carbonates, which is interpreted to indicate the erosion and redistribution of Ir-rich fallouts. No significant enrichment in Ir and W, or Zn and Cu, is observed just below the K-Pg boundary, excluding the hypothesis of downward remobilization of Hg from the boundary clay layer. Positive Δ199Hg and slightly negative values in the upper Maastrichtian and lower part of the early Danian are consistent with the signature of sediments supplied by atmospheric Hg2+ deposition and volcanic emissions. Up section, large shifts to strongly negative mass-dependent fractionation values (δ202Hg) result from the remobilization of Hg formerly sourced by the impactor or by a mixture of different sources including biomass burning, volcanic eruption, and asteroid impact, requiring further investigation. Our results provide additional support for the interpretation that the largest eruptions of the Deccan Traps began just before, and encompassed, the K-Pg boundary and therefore may have contributed to the K-Pg mass extinction.

Mercury anomaly, Deccan volcanism, and the end-Cretaceous mass extinction

The contribution of the Deccan Traps (west-central India) volcanism in the Cretaceous-Paleogene (KPg) crisis is still a matter of debate. Recent U-Pb dating of zircons interbedded within the Deccan lava flows indicate that the main eruptive phase (>1.1 × 106 km3 of basalts) initiated ∼250 k.y. before and ended ∼500 k.y. after the KPg boundary. However, the global geochemical effects of Deccan volcanism in the marine sedimentary record are still poorly resolved. Here we investigate the mercury (Hg) content of the Bidart (France) section, where an interval of low magnetic susceptibility (MS) located just below the KPg boundary was hypothesized to result from paleoenvironmental perturbations linked to the paroxysmal Deccan phase 2. Results show Hg concentrations >2 orders of magnitude higher from ∼80 cm below to ∼50 cm above the KPg boundary (maximum 46.6 ppb) and coincident with the low MS interval. Increase in Hg contents shows no correlation with clay or total organic carbon contents, suggesting that the Hg anomalies resulted from higher input of atmospheric Hg species into the marine realm, rather than organic matter scavenging and/or increased runoff. The Hg anomalies correlate with high shell fragmentation and dissolution effects in planktic foraminifera, suggesting correlative changes in marine biodiversity. This discovery represents an unprecedented piece of evidence of the nature and importance of the Deccan-related environmental changes at the onset of the KPg mass extinction.

Asteroid impact vs. Deccan eruptions: The origin of low magnetic susceptibility beds below the Cretaceous–Paleogene boundary revisited

The respective roles of an asteroid impact and Deccan Traps eruptions in biotic changes at the Cretaceous–Paleogene (K–Pg) boundary are still debated. In many shallow marine sediments from around the world, the K–Pg boundary is marked by a distinct clay layer that is often underlain by a several decimeter-thick low susceptibility zone. A previous study of the Gubbio section, Italy (Lowrie et al., 1990), attributed low magnetization intensity in this interval to post-depositional dissolution of ferrimagnetic minerals. Dissolution was thought to be a consequence of downward infiltration of reducing waters that resulted from rapid accumulation of organic matter produced by mass extinctions after the K–Pg event. We compare the magnetic properties of sediments from the Gubbio section with those of the Bidart section in southern France. The two sections are similar in their carbonate lithology and the presence of a boundary clay and low susceptibility zone. When compared to background Cretaceous sediments, the low susceptibility zone in both sections is marked by an absence of biogenic magnetite, a decrease in total ferrimagnetic mineral content, and a preferential loss of magnetite with respect to hematite – features that are consistent with reductive dissolution. However, unlike the Gubbio section, where the low susceptibility zone starts immediately below the boundary clay, the low susceptibility zone and the clay layer at Bidart are separated by a ∼4-cm carbonate interval that contains abundant biogenic magnetite. Such separation casts doubt on a causal link between the impact and sediment bleaching. More likely, the low susceptibility layer marks a different environmental event that preceded the impact. An episode of increased atmospheric and oceanic acidity associated with Deccan Traps volcanism that occurred well before the K–Pg impact is argued here to account for the distinct magnetic properties of the low susceptibility intervals.

Lower Maastrichtian cyclostratigraphy of the Bidart section (Basque Country, SW France): A remarkable record of precessional forcing

Cyclostratigraphic analysis of the Maastrichtian limestone–marl alternations of Bidart (SW France) allows the hypothesis of orbital control on lithological cycles to be evaluated. Magnetic susceptibility (MS), oxygen and carbon isotope measurements, sampled at a high resolution, are analyzed using various cyclostratigraphic tools. A statistically significant orbital signal is detected, with a remarkable record of the precession corresponding to the limestone–marl couplets. This well expressed orbital forcing allows the building of a relative cyclostratigraphic time scale for the MS and δ13C records based on the 100kyr eccentricity cycle. The total duration of the section is estimated at 1.44±0.22Myr. Correlation based on calcareous nannofossil biostratigraphy and comparison of the scaled Bidart δ13C record to the astronomically calibrated δ13C signal of ODP Hole 762C shows that the studied section extends from −71.5 to −70Ma, covering the upper part of Chron C32n.1n and 2/3 of Chron C31r. Oxygen isotope data suggest a 2°C cooling of sea-surface temperatures during the studied interval. When placed on the long-term δ18O trend of the Bidart section, this interval is here recognized as the onset of the early Maastrichtian cooling event. With its excellent record of the precessional forcing, the Bidart section, along with other sections of the Basque Country, is a useful tool for the refinement of the Maastrichtian timescale.

Planktonic Foraminiferal Biostratigraphy and Correlation Across the Cretaceous-Paleogene Transition at the Tethyan and the Atlantic Realms

Based on high-resolution planktonic foraminiferal biostratigraphical analysis at El Kef stratotype section (GSSP for the K/Pg boundary), Ellès section in Tunisia, and Agost and Caravaca sections in Spain (Tethyan realm), we attempt to compare biozones and subzones with those of the Bidart section (SW France) (Atlantic realm). TheAbathomphalus mayaroensiszone of the upper Maastrichtian corresponds to the taxon range interval of the nominate species. We have identified thePlummerita hantkeninoidessubzone. This species is present and associated withPseudoguembelina hariaensisat the Tethyan realm. However, this species is absent at the middle latitude of the Atlantic realm (Bidart section, SW France). ThePseudoguembelina hariaensisspecies had larger paleogeographic spread, as it was present in both the Tethys and the Atlantic paleoceans. It is more relevant to be considered as the biomarker of a nominate uppermost Maastrichtian subzone instead ofPlummerita hantkeninoides. The Danian stage is characterized by theGt. cretaceazone,Pv. eugubinazone, and theParasubbotina pseudobulloideszone. The deposition thickness of the zones and subzones at El Kef stratotype section and Ellès section is more expanded than at Agost and Caravaca sections (Spain) and Bidart section (France). They would be controlled by the sedimentary basin morphology.

A new sedimentary benchmark for the Deccan Traps volcanism?

[1] The origin of the Cretaceous-Paleogene boundary (KPB) mass extinction is still the center of acrimonious debates by opposing partisans of the bolide impact theory to those who favored a terrestrial origin linked to the Deccan Traps volcanism. Here we apply an original and high-resolution environmental magnetic study of the reference Bidart section, France. Our results show that the KPB is identified by an abrupt positive shift of the magnetic susceptibility (MS), also observed by others at the KPB elsewhere. In addition, an anomalous interval of very low MS, carried by an unknown Cl-bearing iron oxide similar to specular hematite, is depicted just below the KPB. Grain-size and morphology of the Cl-iron oxide are typically in the range of hematitic dust currently transported by winds from Sahara to Europe. This discovery is confirmed in the referenced Gubbio section (Italy) suggesting a global scale phenomenon. As a conjecture we suggest an origin by heterogeneous reaction between HCl-rich volcanic gas and liquid-solid aerosols within buoyant atmospheric plumes formed above the newly emitted Deccan flood basalts. Based on this hypothesis, our discovery provides a new benchmark for the Deccan volcanism and witnesses the nature and importance of the related atmospheric change.

Ichnological analysis of the Bidart and Sopelana Cretaceous/Paleogene (K/Pg) boundary sections (Basque Basin, W Pyrenees): Refining eco-sedimentary environment

Ichnological analysis of two Cretaceous–Paleogene boundary sections at Bidart (SE France) and Sopelana (N Spain) has been conducted in order to refining eco-sedimentary environment, and to a make comparison with previous interpretations based on microfossils. In both sections, trace fossil assemblage is low diverse, consisting of Chondrites, Planolites, Thalassinoides, Trichichnus, Zoophycos, and ? Phycosiphon, ascribed to the Zoophycos ichnofacies, however, with distinct differences. In the Bidart section, early Danian dark-filled trace fossil assemblage is more abundant in large Thalassinoides, Zoophycos and larger Chondrites, and less abundant in Trichichnus and small Chondrites in comparison to the Sopelana section. Sopelana is thus interpreted as a more offshore, deeper section than Bidart although both were located in the upper bathyal zone of the basin. Oxygenation below the sediment–water interface was enough to favour a generalized total bioturbation of sediments. The presence of chemichnia and trace fossils which tracemakers sequestered sediments from the sea floor in deep burrows ( Zoophycos) suggests at least periodical food deficiency. The distribution and content of trace fossils across the K/Pg boundary do not change significantly, revealing minor incidence of the K/Pg boundary event on the macrobenthic environment. The K/Pg boundary transition, including the boundary layer, is nearly totally bioturbated; hence a redistribution of microbiotic and abiotic components by tracemakers is possible.

Bioturbational redistribution of Danian calcareous nannofossils in the uppermost Maastrichtian across the K-Pg boundary at Bidart, SW France

In this paper we present the effects of different tracemakers on the redistribution of calcareous nannofossils throughout the K-Pg boundary at the Bidart section (SW France), along with their consequences for our knowledge of the K-Pg boundary event. Danian calcareous nannofossil assemblages are present in Maastrichtian samples due to infiltration into dark trace fossil infillings proceeding from the earliest Paleogene. This is evidenced by the appearance of abundant paleogene calcareous nannofossils just below the K-Pg boundary, showing the relevance of the trace fossil infillings in the context of the K-Pg boundary event.

Catastrophic mass extinction and assemblage evolution in planktic foraminifera across the Cretaceous/Paleogene (K/Pg) boundary at Bidart (SW France)

A high-resolution biostratigraphic analysis of planktic foraminifers confirms that the Bidart section at the eastern margin of the Atlantic Ocean exhibits a continuous and complete Cretaceous/Paleogene (K/Pg) transition interval. The biozones and subzones recorded in this section are less expanded than their equivalent in Tunisian sections: El Kef (Global Stratotype Section and Point: GSSP for the K/Pg boundary) and Ellès (auxiliary section), but they are sufficiently thick to allow a detailed analysis of the evolution of the planktic foraminiferal assemblages across the K/Pg transition. Throughout the uppermost 4 m Maastrichtian, the planktic foraminiferal assemblages are highly diversified, containing up to 72 species. These Maastrichtian assemblages are rich in cosmopolitan taxa (70%), dominated by small biserial morphotypes which belong mainly to the genus Heterohelix which coexist with less abundant but highly diverse tropical and subtropical species. The extinction pattern at the Bidart section suggests a sudden catastrophic mass extinction at the K/Pg boundary which affected at least 53 out of 72 species. The species becoming extinct include globotruncanids (e.g. Contusotruncana spp., Globotruncana spp., Globotruncanita spp.) and complex heterohelicids (e.g. Racemiguembelina spp., Pseudotextularia spp., Gublerina spp.). At the Bidart section, only Archaeoglobigerina cretacea disappears 2 m below the K/Pg boundary event. Specimens of 18 small and even tiny Maastrichtian species, are found at the lowermost Danian. Only a few of these species belonging to the genera of Guembelitria, Hedbergella and Heterohelix are considered to be real “Cretaceous survivor species”, whereas the specimens belonging to the rest, are most probably reworked, because they differ in their preservation. Throughout lowermost Danian, the planktic foraminiferal assemblages are dominated by “opportunistic” species of the genus Guembelitria. These opportunists are associated to small and poorly diversified pioneer globigerinids ( Palaeoglobigerina spp. and Parvularugoglobigerina spp.). These assemblages became progressively more diversified across the early Danian containing species with cancellate walls ( Eoglobigerina spp., Parasubbotina spp., Subbotina triloculinoides and Praemurica spp.) and new taxa of biserial heterohelicids ( Woodringina spp. and Chiloguembelina spp.) suggesting a paleoenvironmental recovery.

Multiproxy approach for determination of nature and origin of carbonate micro-particles so-called “micarb” in pelagic sediments

Carbonate fractions of pelagic and hemipelagic sediments may contain significant proportions of microcrystalline (≤ 6 µm) calcitic particles with no specific structure so-called micarb. Depending on the authors, this term is related to different descriptions and yet there is no clear consensus on their origin. Although, micarb can dominate the sediment compositions in the pelagic realm, their isolation from the other carbonate particles is not easy due to their small size. The use of a granulometric separation method of the main carbonate particles allows the characterization and quantification of the compositions of the carbonate phases of the sediments and gives access to the geochemical signatures (oxygen and carbon stable isotopes) and mineralogical characteristics of each type of carbonate particles in the sediments. This approach was applied to three sections: the Mid-Pliocene Punta Piccola section (South Sicily), the Upper Campanian Bidart section (SW France) and the Aptian sediments from La Marcouline Quarry (SE France). The quantifications showed quite important proportions (up to 70% of the carbonated phases) of micarb in the sections studied excepted in the mid-Pliocene Punta Piccola samples. However, depending on the sedimentary context, it appears that those fine calcitic particles may result from fine biogenic fragmentation (Aptian, La Marcouline Quarry), authigenic precipitation in the water column (Mid-Pliocene, Punta Piccola section), or they may have an allochthonous origin (Upper Campanian Bidart section). Based on these interpretations, it is then possible to estimate precisely the composition of the carbonate fractions in each studied section. This work shows that except for the Bidart sediments which are dominated by fine exported carbonate mud, the other sections mainly consist in biogenic carbonates.

Recovery of the deep-sea floor after the Cretaceous−Paleogene boundary event: The benthic foraminiferal record in the Basque–Cantabrian basin and in South-eastern Spain

A detailed analysis of the Upper Cretaceous and lower Paleogene benthic foraminiferal assemblages (> 63 μm) from the middle bathyal Loya section (Basque–Cantabrian Basin, Southwestern France) has been carried out. The benthic foraminiferal and palaeoenvironmental turnover across the K/Pg boundary at Loya has been compared to that observed in the nearby Bidart section. Both sections exhibit mesotrophic conditions in the uppermost Maastrichtian, and a drastic decrease in the nutrient supply to the sea floor in coincidence with the K/Pg boundary. Moreover, a faunal recovery of the assemblages is observed through the lowermost Danian. The pattern of faunal and palaeoenvironmental recovery in the Basque–Cantabrian Basin has been compared to that observed in the middle bathyal Agost and Caravaca sections (South-eastern Spain), where a similar decrease in the food supply to the sea floor is observed in coincidence with the K/Pg boundary. However, whereas low oxygen conditions have been recorded in the lowermost Danian in these two sections, no evidence for oxygen deficiency has been found in the Basque–Cantabrian Basin, thus pointing to the regional – and not global – nature of low oxygen conditions following the K/Pg boundary event. Benthic foraminifera from the G. cretacea Biozone suggest environmental instability in the Basque–Cantabrian Basin and in Southeastern Spain. Such environmental stress has been related not only to the collapse of the food web due to the extinction of calcareous primary producers, but also to a rapidly changing food supply driven by phytoplankton blooms. Although stabilization of the ecosystems in surface waters probably occurred towards the upper part of the G. cretacea Biozone, data available from the Ps. pseudobulloides Biozone at Bidart and Agost indicate that food supply to the benthos had not completely recovered, at least, 200 kyr after the K/Pg boundary.

Paleoenvironmental Recovery After the Cretaceous/ Paleogene Boundary Crisis: Evidence From the Marine Bidart Section (SW France)

Abstract The study of Upper Cretaceous and Lower Paleogene benthic foraminifera from the Bidart section (SW France) provides detailed data on the paleobathymetry as well as paleoenvironmental conditions across the Cretaceous/Paleogene (K/Pg) boundary. A quantitative analysis of benthic foraminiferal assemblages from the Upper Maastrichtian Abathomphalus mayaroensis Biozone and the Danian Guembelitria cretacea, Parvularugoglobigerina eugubina, and Parasubbotina pseudobulloides Biozones was performed. Benthic foraminifera indicate that the upper Maastrichtian and lower Danian sediments at Bidart were deposited in the upper–middle part of the slope. Benthic foraminiferal assemblages indicate mesotrophic conditions during the late Maastrichtian and a strong decrease in the food supply to the sea floor coincident with the K/Pg boundary. This change in the trophic regime was related to the collapse of the food web triggered by the mass extinction of calcareous primary producers. Benthic assemblages in the lower...

Changes in the pelagic fine fraction carbonate sedimentation during the Cretaceous–Paleocene transition: contribution of the separation technique to the study of Bidart section

The Bidart section (southwestern France) displays an almost complete Late Maastrichtian–Early Danian transition. As the Cretaceous–Paleocene (K/P) crisis mainly affects carbonate producers, the aim of this study is to precisely evaluate the evolution of pelagic sediments composition across the boundary. A new protocol for separation of fine carbonates into discrete size fractions was used (1) to precisely evaluate (in weight of carbonate and not only number of particles per gram of rock) the contribution of each carbonate component type (foraminifera, calcareous nannofossils and “nonbiogenic” carbonates, calcite microparticles, and calcareous macrocrystals), and (2) to measure their isotopic signature and thus constrain the origin of these carbonate particles. The Maastrichtian pelagic carbonates are mostly biogenic (70% of the bulk carbonate) but also contain “nonbiogenic” carbonates: calcite microparticles (<4 μm) and calcareous macrocrystals (>4 μm). Due to their isotopic signature, calcite microparticles cannot result from fragmentation and partial dissolution of biogenic remains, and the most likely origin appears to be early diagenetic processes and/or export from shallow-water platforms. The calcareous macrocrystals derive from an early diagenetic process. The lowermost Danian sediments are dominated by “nonbiogenic” carbonates (between 50% and 80% of the bulk carbonate). Nevertheless, two kinds of biogenic components are present: Thoracosphaera operculata and Maastrichtian-like calcareous nannofossils. Thoracosphaera operculata is an opportunistic calcareous dinoflagellate, which frequently occurs at high abundances in basal Danian sediments and is certainly in situ, this is confirmed by it showing a Danian isotopic signature. The Maastrichtian-like calcareous nannofossils are nannofossils of taxa that indisputably occur in the Maastrichtian, but which do not occur consistently in later Danian strata, they show a Maastrichtian-type isotopic signature, which strongly supports the inference that they are mainly reworked from the Maastrichtian. This study shows that “nonbiogenic” carbonates are important components of the pelagic carbonate even during periods of normal sedimentation. In the “crisis interval”, the biogenic carbonate production drops sharply, while calcite microparticles and carbonate macrocrystals remain almost unaffected and represent the major part of the carbonate in the earliest Danian sediments. Finally, the sediments return to a composition similar to that of the Maastrichtian in M. pseudobulloides foraminifera zone.

Palaeoenvironmental implications and diagenesis of inoceramid shells (Bivalvia) in the mid-Maastrichtian beds of the Sopelana, Zumaya and Bidart sections (coast of the Bay of Biscay, Basque Country)

Inoceramid bivalve shells from the mid-Maastrichtian beds of the Sopelana, Zumaya and Bidart sections in the Basque Country, were tested for their post-depositional diagenetic alteration. Petrography, cathodoluminescence (CL) and scanning electron microscope (SEM) observations together with geochemical analyses, indicate that the coarsely prismatic calcite of the shells from the Sopelana and Zumaya sections have undergone diagenetic alteration, without there being substantial textural changes in the original prismatic microstructure. A generalized bright yellowish to red colour is seen in all the samples observed by CL. The δ 18O values obtained from the shell prisms range from −2.94‰ to −5.18‰, with a mean value of −3.6±0.5‰ in the Sopelana section, whereas in the Zumaya section they range from −1.88‰ to −4.71‰, with a mean value of −3.2±0.3‰. These values are clearly lower than those from the Bidart section (from −0.32‰ to −1.48‰; mean value −0.7±0.3‰). Other evidence of diagenetic alteration is inferred from both whole-shell geochemistry and microprobe analysis. A complementary zonation in the distribution of `diagenetic tracers' can be detected from the inner shell layer (ISL) to the outer shell layer (OSL) of inoceramid shells, together with a rare earth element (REE) enrichment in the shells which have lighter δ 18O values. In contrast, the inoceramid bivalve shells and their host-rock from the Bidart section were less altered. The calculated mean palaeotemperature (15°C) and the value of 13°C estimated from the non-luminescent middle shell layer seem to be consistent with palaeolatitudes about 30°N for deep marine waters of mid-Maastrichtian time, as the last step of the long-term climatic cooling of the Late Cretaceous `greenhouse'.

An iridium rich layer at the Cretaceous/Tertiary boundary in the Bidart Section (southern France)

We have measured an anomalous iridium concentration in the clays of the Cretaceous/Tertiary boundary in the Bidart section, thus confirming the planetary character of this anomaly. The iridium anomaly is synchronous with a very sharp minimum of the 13C/12C ratio and there is no evidence of any other iridium enrichment in marly concentrations away from the boundary. The integrated iridium content is of the same order of magnitude as that calculated from deep sea cores in the Pacific Ocean. In spite of a careful search, we have found no evidence of any exotic material.

THE QUATERNARY VEGETATIONAL HISTORY OF THE FRENCH PAYS BASQUE

SUMMARYThis paper presents macrofossil data and additional pollen analyses from the Quaternary sites previously described in Oldfield (1967). Pollen evidence presented in that paper from Bidart Plage Series B (Bidartian) and Senix Series 1 (Moulignan and Senixian) is amplified and extended by more detailed and comprehensive diagrams. The additional pollen‐analytical evidence from the Bidart section confirms the importance of a Castanea‐dominated pollen assemblage zone within the Bidartian Interglacial. The new diagram from Senix shows that the Moulignan major biostratigraphic subdivision is likewise interglacial in character. The late‐temperate and post‐temperate stages of this interglacial are well represented by the Senix and Mouligna Cliff pollen sequences now published.The macrofossil evidence from Bidart Series B(Bidartian), Mouligna Cliff MC3 (Ilbarritzian) and Marbella (Marbellan) is represented on a quantitative basis using large and volumetrically equivalent samples from each level. The main additions to the flora from these macrofossil diagrams are a wide variety aquatic and semi‐aquatic species including, for the Bidartian, Ludwigia palnstris and for the Marbellan, Aldrovandra vesiculosa and Proserpinaca cf. palnstris a North American species not previously recorded in Post‐Tiglian deposits from Europe. From Bidart, there are also interesting macrofossil records of woody warm temperate taxa, for example Chamaecyparis thyoides, Cotoneaster acuticarpa and Ostrya cf. carpinifolia. The non‐aquatic macroflora from Marbella is dominated by Erica species the seeds of which have been identified largely on the basis of the fine detail of their seed coats revealed by Scanning Electron Microscopy (Huckerby, Marchant and Oldfield, 1972).The macrofossil diagram from Marbella gives a detailed picture of the complex hydroseral changes taking place during the late‐ and post‐temperate stages of the interglacial. Along with the stratigraphic and pollen‐analytical evidence from the site it allows a rather comprehensive reconstruction of ecological changes taking place around the site in response to factors such as climate and soil deterioration and rising sea‐level.Macrofossil records are presented from the early pleistocene Bidart Series A, the oldest material studied. The richness of the narrow peat lens in ericaceous remains strongly supports the inference from the stratigraphic and pollen‐analytical record that the site represents the organic part of the ‘A’ Horizon of an acid, wet heath soil profile. Other suites of macrofossil records from Senix, Series 1, and Mouligna Cliff, MC 1 (Moulignan and Senixian), from Chabiague (Chabiaguian) and from Mouligna Plage (mid‐Flandrian) are tabulated. Sediment from the coldest totally deforested episodes of each of the major cold phases considered to be contemporary with glaciation at higher latitudes and altitudes, either completely lacks or is exceptionally poor in macroscopic plant remains. At no site are the identified remains incompatible with the ecological interpretation of the apparently deforested intervals advanced on the basis of the pollen‐analytical evidence (Oldfield, 1967). The macroflora from the Artemisia‐rich, supposedly cool, dry episodes of low but not minimal tree pollen‐representation, such as Ilbarritzian III includes open ground species of southern (e.g. Valeriana tuberosa) as well as northern affinities and tends to support previous suggestions that the flora during such periods was geographically mixed.With the completion of the macrofossil analyses from the sites, it is proposed to publish a final paper summarizing all the Quaternary palaeobotanical evidence from the area and commenting briefly on its general ecological and biogeographical significance.

THE QUATERNARY VEGETATIONAL HISTORY OF THE FRENCH PAYS BASQUE

SUMMARY This paper presents macrofossil data and additional pollen analyses from the Quaternary sites previously described in Oldfield (1967). Pollen evidence presented in that paper from Bidart Plage Series B (Bidartian) and Senix Series 1 (Moulignan and Senixian) is amplified and extended by more detailed and comprehensive diagrams. The additional pollen-analytical evidence from the Bidart section confirms the importance of a Castanea-dominated pollen assemblage zone within the Bidartian Interglacial. The new diagram from Senix shows that the Moulignan major biostratigraphic subdivision is likewise interglacial in character. The late-temperate and post-temperate stages of this interglacial are well represented by the Senix and Mouligna Cliff pollen sequences now published. The macrofossil evidence from Bidart Series B(Bidartian), Mouligna Cliff MC3 (Ilbarritzian) and Marbella (Marbellan) is represented on a quantitative basis using large and volumetrically equivalent samples from each level. The main additions to the flora from these macrofossil diagrams are a wide variety aquatic and semi-aquatic species including, for the Bidartian, Ludwigia palnstris and for the Marbellan, Aldrovandra vesiculosa and Proserpinaca cf. palnstris a North American species not previously recorded in Post-Tiglian deposits from Europe. From Bidart, there are also interesting macrofossil records of woody warm temperate taxa, for example Chamaecyparis thyoides, Cotoneaster acuticarpa and Ostrya cf. carpinifolia. The non-aquatic macroflora from Marbella is dominated by Erica species the seeds of which have been identified largely on the basis of the fine detail of their seed coats revealed by Scanning Electron Microscopy (Huckerby, Marchant and Oldfield, 1972). The macrofossil diagram from Marbella gives a detailed picture of the complex hydroseral changes taking place during the late- and post-temperate stages of the interglacial. Along with the stratigraphic and pollen-analytical evidence from the site it allows a rather comprehensive reconstruction of ecological changes taking place around the site in response to factors such as climate and soil deterioration and rising sea-level. Macrofossil records are presented from the early pleistocene Bidart Series A, the oldest material studied. The richness of the narrow peat lens in ericaceous remains strongly supports the inference from the stratigraphic and pollen-analytical record that the site represents the organic part of the ‘A’ Horizon of an acid, wet heath soil profile. Other suites of macrofossil records from Senix, Series 1, and Mouligna Cliff, MC 1 (Moulignan and Senixian), from Chabiague (Chabiaguian) and from Mouligna Plage (mid-Flandrian) are tabulated. Sediment from the coldest totally deforested episodes of each of the major cold phases considered to be contemporary with glaciation at higher latitudes and altitudes, either completely lacks or is exceptionally poor in macroscopic plant remains. At no site are the identified remains incompatible with the ecological interpretation of the apparently deforested intervals advanced on the basis of the pollen-analytical evidence (Oldfield, 1967). The macroflora from the Artemisia-rich, supposedly cool, dry episodes of low but not minimal tree pollen-representation, such as Ilbarritzian III includes open ground species of southern (e.g. Valeriana tuberosa) as well as northern affinities and tends to support previous suggestions that the flora during such periods was geographically mixed. With the completion of the macrofossil analyses from the sites, it is proposed to publish a final paper summarizing all the Quaternary palaeobotanical evidence from the area and commenting briefly on its general ecological and biogeographical significance.