574 RESEARCH REPORTS

Copyright Q 2004, SEPM (Society for Sedimentary Geology) 0883-1351/04/0019-0574/$3.00

Paleoenvironmental Recovery After the Cretaceous/Paleogene Boundary Crisis: Evidence From the Marine

Bidart Section (SW France)

LAIA ALEGRETDepartment of Earth Sciences, University College London, London WC1E 6BT, United Kingdom, E-mail: laia@unizar.es

MICHAEL A. KAMINSKIDepartment of Earth Sciences, University College London, London WC1E 6BT, United Kingdom

EUSTOQUIO MOLINADepartamento de Ciencias de la Tierra, Facultad de Ciencias, Universidad de Zaragoza. 50009-Zaragoza, Spain

PALAIOS, 2004, V. 19, p. 574–586

The study of Upper Cretaceous and Lower Paleogene ben-thic foraminifera from the Bidart section (SW France) pro-vides detailed data on the paleobathymetry as well as pa-leoenvironmental conditions across the Cretaceous/Paleo-gene (K/Pg) boundary. A quantitative analysis of benthicforaminiferal assemblages from the Upper MaastrichtianAbathomphalus mayaroensis Biozone and the DanianGuembelitria cretacea, Parvularugoglobigerina eugubina,and Parasubbotina pseudobulloides Biozones was per-formed. Benthic foraminifera indicate that the upper Maas-trichtian and lower Danian sediments at Bidart were de-posited in the upper–middle part of the slope.

Benthic foraminiferal assemblages indicate mesotrophicconditions during the late Maastrichtian and a strong de-crease in the food supply to the sea floor coincident with theK/Pg boundary. This change in the trophic regime was re-lated to the collapse of the food web triggered by the massextinction of calcareous primary producers. Benthic assem-blages in the lower Danian are strongly dominated by fewspecies, and suggest that primary productivity was domi-nated by blooms of non-calcareous primary producers, cre-ating a stressful environment for the benthic fauna. Thefaunal turnover, together with the geochemical evidence, iscompatible with an asteroid impact scenario. Benthic fora-miniferal assemblages suggest that primary productivityhad not completely recovered more than 200 kyr after theK/Pg boundary event.

INTRODUCTION

The Cretaceous/Paleogene (K/Pg) boundary marks oneof the major mass extinctions in Earth’s history. Most au-thors now accept that a large meteorite impacted the Yu-catan Peninsula in Mexico (Alvarez et al., 1980; Smit andHertogen, 1980; Hildebrand et al., 1991) and triggered thecatastrophic mass extinction of calcareous plankton (e.g.,Luterbacher and Premoli-Silva, 1964; Smit, 1982, 1990;Molina et al., 1998), as well as an anomalous enrichmentin Ir and other extraterrestrial impact evidence, such asmicrospherules (interpreted as altered microtektites) andshocked quartz grains in the boundary sediments globally

(Alvarez et al., 1980; Smit and Hertogen, 1980; Smit andten Kate, 1982; Sharpton et al., 1992). Furthermore, d13Cand d18O values in bulk sediment and in tests of benthicand planktic foraminifera show abrupt changes just afterthe K/Pg extinction (Zachos and Arthur, 1986; Kaminskiand Malmgren, 1989; Kaiho et al., 1999), and reflect im-portant environmental changes that occurred immediate-ly after the impact. Nevertheless, there are still some re-searchers who do not support a catastrophic mass extinc-tion model (Keller, 1989 a, b; Keller et al., 1995; Abramov-ich and Keller, 2002), but an extended pattern ofextinction generated by multiple causes that may be dueto the Signor-Lipps effect and reworking processes affect-ing microfossils in the sediments immediately below andabove the K/Pg boundary (Huber et al., 2002; Soria et al.,2001, Molina et al., 2002).

Whereas planktic foraminifera suffered a catastrophicmass extinction coincident with the K/Pg boundary (e.g.,Molina et al., 1998), benthic foraminifera do not show sig-nificant extinctions, as reviewed by Culver (2003). Deep-sea benthic foraminifera show drastic, temporal changesin their community structure coincident with the K/Pgboundary, followed by a gradual, staggered pattern of re-covery across the early Danian (see review by Culver,2003). These temporary changes in benthic foraminiferalassemblages have been interpreted as resulting from thecollapse of the pelagic food web and the subsequent drop infood supply to the benthos (e.g., Kuhnt and Kaminski,1993; Thomas, 1990a, b; Alegret et al., 2001, 2003; Culver,2003).

The Bidart section (southwestern France, Fig. 1) is con-sidered as one of the most complete K/Pg boundary sec-tions in southwestern Europe (Seyve, 1990; Haslett,1994). Nevertheless, the paleoenvironmental turnoveracross the K/Pg boundary in this area remains unclear,and benthic foraminifera from Bidart have not been stud-ied previously. Kuhnt and Kaminski (1993) analyzed theagglutinated benthic foraminiferal changes in the nearbyZumaya and Sopelana sections (Basque Basin, NorthernSpain), and concluded that deep-water agglutinated fora-miniferal turnover indicates a drastic decrease in surfaceproductivity and a collapse of the food-web coincident withthe K/Pg boundary. Apart from that study, no detailedanalyses on benthic foraminifera have been performed in

RECOVERY POST CRETACEOUS/PALEOGENE BOUNDARY, BIDART, FRANCE 575

FIGURE 1—Paleogeographical reconstruction of the Pyrenean do-main during the Paleocene (modified from Pujalte et al., 1994), andlocation of the Bidart section.

this area, so the results presented here provide importantdata to infer environmental changes across the K/Pgboundary.

In addition to its completeness and excellent exposure,the Bidart section is particularly important because of itspaleogeographical location—between the Tethys and theNorth Atlantic—during the Late Cretaceous and EarlyPaleogene. According to Renard et al. (1982), the Maas-trichtian of Bidart was deposited under Tethyan influenc-es, whereas the Paleocene was influenced primarily by theNorth Atlantic. Consequently, the Bidart section has beenthe focus of various studies, such as stable isotope analysis(Romein and Smit, 1981; Renard et al., 1982; Nelson et al.,1991), iridium content (Smit and Ten Kate, 1982; Dela-cotte, 1982; Bonte et al., 1984), or biostratigraphy (Bonteet al., 1984; Delacotte et al., 1985), among others. Detailedbiostratigraphical studies across the K–Pg interval havebeen based on calcareous nannofossils (Perch-Nielsen,1979; Seyve, 1990) and planktic foraminifera (Haslett,1994; Fondecave-Wallez et al., 1995; Apellaniz et al.,1997). Nevertheless, benthic foraminifera from Bidarthave not been studied in detail, as pointed out by Haslett(1994).

The aim of this study is to perform a detailed, quantita-tive study of Upper Cretaceous and Lower Paleogene ben-thic foraminiferal assemblages from the Bidart section(SW France). Benthic foraminifera, which are closely re-lated to the sea-bottom conditions, provide detailed dataon the paleobathymetric setting of the uppermost Creta-ceous and lowermost Paleogene sediments at Bidart, aswell as on the paleoenvironmental changes across the K/Pg boundary.

MATERIAL AND METHODS

The Bidart section is situated between Hendaye andBiarritz (southwestern France), within the Basque-Can-tabric Basin. The outcrop is located behind the beach of Bi-dart, towards the north of this village (for a more preciselocation of the outcrop, see Peybernes et al., 1996). The up-per 4 m of the Maastrichtian and the lower 3.6 m of the Pa-

leogene were studied at Bidart. The Maastrichtian sedi-ments correspond to the ‘‘Bidart marls’’ (Seunes, 1891),which consist of gray marls and calcareous marls contain-ing abundant foraminifera and scarce macrofossils suchas echinoids. The uppermost two centimeters of the Maas-trichtian consist of gray clayey marls. The K/Pg boundaryis marked by a sharp contact between the Maastrichtianmarls and a 6-cm-thick layer of dark clays with a 2-mm-thick, red ferruginous level at its base (Fig. 2). The rest ofthis clay layer consists of brownish clays towards its lowerpart, and thinly laminated dark gray clays towards thetop. Delacotte (1982) and Bonte et al. (1984) identified aniridium anomaly in the dark clay layer, coinciding exactlywith a drop in the d13C curve and in the d18O values (Pey-bernes et al., 1996). Apellaniz et al. (1997) documented thepresence of microspherules with Ni-rich crystals in themiddle part of the clay layer. This layer is overlain by a;25-cm-thick level of gray to brown clays, which becomemore grayish and calcareous towards the top, reflecting anincrease in total bulk carbonate after a drastic reductionidentified just above the K/Pg boundary (i.e., in the darkclay layer; Renard et al., 1982). Fish teeth were observedtowards the upper part of this level, which is overlain by1.30 m of massive gray limestones. Higher in the section, a50-cm-thick, tabular breccia was identified (Fig. 2); thematrix has a mudstone texture, and the pebbles are cal-careous, poorly sorted (the maximum length ranges from 1mm to 10 cm), and subangular to rounded. This body isoverlain by two tabular, 60-to-90-cm thick levels of mas-sive gray limestones, each of which is strongly bioturbatedtowards the top.

The K/Pg boundary at Bidart, as well as in other K/Pgboundary sections from the Bay of Biscay, is includedwithin a single depositional sequence (Maastrichtian–Danian Depositional Sequence; e.g., Apellaniz et al.,1997). According to these authors, the base of this se-quence is located 10 m below the K/Pg boundary, whereasthe top of the sequence is erosive.

Flysch deposition persisted from Albian to Eocene timesin this area, which was situated in close proximity to a pa-leoslope to the northeast (Seyve, 1984). A distal deep-seafan environment with a 40-mm/kyr sedimentation rate(Nelson et al., 1991) prevailed in this area during theMaastrichtian, whereas an increase in the activity on theslope is recorded in the Paleocene (Haslett, 1994), there-fore, the Paleocene sediments are locally slumped (Seyve,1990). According to Peybernes et al. (1996), the brecciaidentified at Bidart was deposited under conditions of lowsea level, whereas the underlying limestones were depos-ited under high sea-level conditions. Alternatively, thisbreccia could be interpreted as a slump triggered by localtectonics during the early Danian. In spite of this geologi-cal context, the Paleocene foraminifera from Bidart areunlikely to have been affected by major reworking process-es, although the microfossils found in the breccia have notbeen taken into account in the paleoenvironmental inter-pretations.

The studies by Hasslet (1994), Peybernes et al. (1996),and Apellaniz et al. (1997) have been followed for bio-stratigraphic control. These authors identified the upperCretaceous Abathomphalus mayaroensis Biozone, as wellas the Danian Guembelitria cretacea, Parvularugoglobi-gerina eugubina and Parasubbotina pseudobulloides Bio-

576 ALEGRET ET AL.

FIGURE 2—Occurrence and relative abundance of infaunal morphogroups across the K–Pg transition at Bidart. (A) Most-characteristic infaunaltaxa. (B) Relative percentage of infaunal and epifaunal morphogroups. G. c.5 G. cretacea Biozone; Pv. eugu.5 Pv. eugubina Biozone.Biostratigraphy by Haslett (1994), Peybernes et al. (1996), and Apellaniz et al. (1997). See legend in Figure 4.

zones (Figs. 2–3). Foraminiferal assemblages from thelowermost 10 cm of the Danian are dominated by benthicforaminifera, and planktic foraminifera are almost absent.Haslett (1994) and Apellaniz et al. (1997) suggested thatthis level may correspond to the Guembelitria cretaceaBiozone of Smit (1982); the first appearance of Pv. eugubi-na 10 cm above the K/Pg boundary marks the Pv. eugubi-na Biozone, and the base of the Ps. pseudobulloides Biozo-ne is located ;1 m above the K/Pg boundary.

Twenty samples were studied in the upper 4 m of theMaastrichtian and the lower 3.5 m of the Danian. Accord-ing to the biomagnetostratigraphic correlation and cali-bration recently proposed by Arenillas et al. (2004), thebase of the Ps. pseudobulloides Biozone has an estimatedage of 64.945 Ma (based on the calibration by Berggren etal., 1995, who placed the K/Pg boundary at 64.745 Ma) or

65.436 Ma (based on the astronomical calibration by Rohlet al., 2001, who placed the K/Pg boundary at 65.5 Ma).Arenillas et al. (2004) subdivided the Ps. pseudobulloidesBiozone into the Eoglobigerina trivialis Interval Subzone,which has a duration of 171.5–201.1 kyr (based on the cal-ibrations proposed by Berggren et al., 1995 and by Rohl etal., 2001, respectively) and the Subbotina triloculinoidesInterval Subzone. Although these subzones have not beenidentified by Hasslet (1994), Peybernes et al. (1996), orApellaniz et al. (1997) at Bidart, comparison of this sectionto the nearby Zumaya section, where the E. trivialis Sub-zone spans 2.75 m, suggests that at least this subzone isrepresented at Bidart. Further biostratigraphical studiesare needed to test the presence of the Subbotina triloculi-noides Subzone at Bidart. However, in the lack of a betterbiostratigraphical analysis, it may be tentatively inferred

RECOVERY POST CRETACEOUS/PALEOGENE BOUNDARY, BIDART, FRANCE 577

FIGURE 3—Occurrence and relative abundance of the most-characteristic epifaunal benthic foraminiferal taxa across the K–Pg transition atBidart. G. c.5 G. cretacea Biozone; Pv. eugu.5 Pv. eugubina Biozone. Biostratigraphy by Haslett (1994), Peybernes et al. (1996), and Apellanizet al. (1997). See legend in Figure 4.

that, at least, the whole E. trivialis Subzone is representedat Bidart. These data suggest that the top of the studiedinterval corresponds, approximately, to the top of the E.trivialis Subzone, 225.6–264.5 kyr after the K/Pg bound-ary (according to the calibrations proposed by Berggren etal., 1995 and by Rohl et al., 2001, respectively); if the S.triloculinoides Subzone were partially represented at Bi-dart, the top of the studied section would be even younger.

Samples were collected at one-meter intervals at thelower part of the section and at decimeter intervals to-wards the top, with closer sampling in the uppermostMaastrichtian and the lowermost Danian (Appendix 1).Only one micropaleontological sample from the basal 5 cmof the breccia was analyzed, but the results were not con-sidered for paleoenvironmental interpretations due to thepossible reworking processes affecting the microfossils inthis unit. Samples were disaggregated in water with dilut-ed H2O2, washed through a 63-mm sieve, and dried at508C. Species richness calculations and quantitative stud-ies were based on representative splits (using a modified

Otto micro-splitter) of approximately 300–400 specimensof benthic foraminifera larger than 63-mm. All represen-tative specimens were mounted on microslides for a per-manent record and identification. Classification at the ge-neric level follows Loeblich and Tappan (1988); when pos-sible, benthic foraminifers were identified to the specificlevel largely following the taxonomy of Alegret and Thom-as (2001), since the Mexican faunas studied by these au-thors contain around 80% of the benthic foraminiferal spe-cies identified at Bidart. Moreover, 90% of the speciesidentified in this study were reported from the Upper Cre-taceous and lower Paleogene at the Agost section (south-eastern Spain) by Alegret et al. (2003). Benthic foraminif-eral counts are presented in Appendix 1.

The Fisher-a diversity index and the H(S) Shannon-Weaver information function, another index of diversity,were calculated in order to observe possible changes in di-versity across the K–Pg interval. High values of H(S) in-dicate an even distribution of specimens over species;

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FIGURE 4—Characteristics of benthic foraminiferal assemblagesacross the K–Pg transition at Bidart. (A) Percentages of calcareousand agglutinated benthic foraminiferal tests. (B) Shannon-Weaver het-erogeneity index. (C) Fisher-a diversity index. G. c.5 G. cretacea Bio-zone; Pv. eugu.5 Pv. eugubina Biozone. Biostratigraphy by Haslett(1994), Peybernes et al. (1996), and Apellaniz et al. (1997).

Murray (1991) calls H(S) the index of heterogeneity, withhigh heterogeneity values indicating high diversity.

In order to infer probable microhabitat preferences andenvironmental parameters such as the nutrient supply tothe sea floor and seawater oxygenation (e.g., Bernhard,1986; Jorissen et al., 1995; Fontanier et al., 2002), all ben-thic foraminiferal taxa were allocated into morphogroupsfollowing Corliss (1985, 1991), Jones and Charnock (1985),and Corliss and Chen (1988). According to these authors,there is a general relationship between test morphologyand the microhabitat preferences of benthic foraminifera.Thus, benthic foraminifera with plano-convex, biconvex,and rounded trochospiral tests, as well as tubular andcoiled flattened tests, have an inferred epifaunal mode oflife, living at the sediment surface. Infaunal foraminifera,living in deeper layers of the sediment, have cylindrical orflattened tapered, spherical, rounded planispiral, flat-tened ovoid, globular unilocular, or elongate multiloculartests. Major changes in percentages of these morpho-groups (Fig. 2), as well as in the abundance of selectedtaxa (Figs. 2–3), and the comparison of fossil and recentcommunities of benthic foraminifera have been consideredin this study to infer the paleoenvironmental turnoveracross the K/Pg boundary. Nonetheless, one should becareful with these interpretations due to the complex andnot fully understood ecology of modern faunas, and theirquestionable comparison to Upper Cretaceous and lowerPaleogene faunas (Alegret et al., 2003).

PALEOBATHYMETRY

Benthic foraminiferal assemblages are dominated bycalcareous tests (;97%) through the whole section, exceptfor the upper 10 cm of the Maastrichtian, where theymake up 75% of the assemblages (Fig. 4). These values in-dicate deposition well above the calcite compensationdepth. The planktic/benthic ratio is high (85–90%) in allsamples except for those from the lowermost Danian,which are dominated by benthic foraminifera.

Paleobathymetric assignments were obtained mainlyfollowing the depth distributions and upper depth limits ofbenthic foraminiferal species, as reviewed by Alegret et al.(2003). Benthic foraminiferal assemblages contain abun-dant representatives of the bathyal and abyssal Velasco-type fauna (Berggren and Aubert, 1975), namely Aragoniavelascoensis, Cibicidoides velascoensis, Nuttallides truem-pyi, or Stensioeina beccariiformis, as well as other deep-water species such as Bulimina trinitatensis, Cibicidoideshyphalus, or Marssonella oxycona. The upper depth limitof some of the most abundant species at Bidart (e.g., Buli-mina trinitatensis, Nuttallides truempyi, Stensioeina bec-cariiformis) is located at 500–700 m depth (Alegret et al.,2003). These data suggest that the upper Maastrichtianand lower Danian sediments at Bidart were deposited inthe upper–middle part of the slope.

An increase in the percentage of Loxostomum eleyi hasbeen observed in the uppermost meter of the Maastrich-tian (Fig. 2). The preservation of these specimens is verysimilar to that of other species in the same samples, andthere is no apparent size sorting. These data indicate thatthe abundant specimens of Loxostomum eleyi identified inthe uppermost Maastrichtian sediments are unlikely tohave been reworked. Although Loxostomum eleyi is typical

of outer-shelf environments (MacNeil and Caldwell, 1981;Nyong and Olsson, 1984), its depth occurrence may in-crease under a high food supply, as suggested by Alegretet al. (2003) at the Agost section. The high relative abun-dance of infaunal morphogroups in the Maastrichtian atBidart (Fig. 2) indicates an abundant food supply to thesea-bottom floor, as in Agost. Under these conditions, thedepth of occurrence of L. eleyi may have been somewhatgreater than at other locations.

RECOVERY POST CRETACEOUS/PALEOGENE BOUNDARY, BIDART, FRANCE 579

FIGURE 5—Scanning electron micrographs of two opportunistic ben-thic foraminiferal species. Scale bar 5 50mm. (A) Glomospira serpenscalcareous isomorph. (B) Spirillina.

BENTHIC FORAMINIFERAL TURNOVER

Upper Maastrichtian assemblages are diverse and het-erogeneous (Fisher-a index ;21, Shannon-Weaver indexH(S) ;3.5; Fig. 4B, C), and they consist of a mixture of in-faunal (;58%) and epifaunal morphogroups (Fig. 2B).Among the infaunal morphogroups, species with cylindri-cal-tapered (e.g., Praebulimina cf. P. reussi, laevidentalin-ids), flattened-tapered (e.g., Loxostomum eleyi, Bolivino-ides draco), and spherical tests dominate (Fig. 2), whereastaxa with trochospiral-planoconvex (e.g., Cibicidoides hy-phalus, Cibicidoides proprius) and biconvex (Nuttallidestruempyi) tests dominate among the epifaunal morpho-groups (Fig. 3). These data suggest mesotrophic conditionsduring the uppermost Maastrichtian, and a nutrient sup-ply to the sea-bottom floor enough to sustain both infaunaland epifaunal morphogroups.

Only three species (Bolivinoides draco draco, Loxosto-mum eleyi, and Praebulimina cf. P. reussi) disappear at Bi-dart in coincidence with the K/Pg boundary (Fig. 2). Twospecimens of Bolivinoides draco draco were found two cen-timeters above the K/Pg boundary, but the different colorof the sediment inside their shells as compared to the oth-er foraminifera in the same sample suggests that they arereworked. Although benthic foraminiferal assemblageswere not significantly affected by the K/Pg extinctions, thepercentage of infaunal morphogroups (Fig. 2) and the di-versity of the assemblages (Fig. 4) drastically decreasedjust after the K/Pg boundary. Lowermost Danian assem-blages (dark clay layer) contain up to 74% of epifaunalmorphogroups, which are dominated mainly by the tro-chospiral planoconvex Stensioeina beccariiformis and Cib-icidoides hyphalus (Fig. 3). Such a decrease in the abun-dance of infaunal taxa and the presence of peaks in theabundance of two epifaunal species suggest a drastic de-crease in the food supply to the sea floor related to the cat-astrophic mass extinction of calcareous plankton at theK/Pg boundary (Zachos and Arthur, 1986; Thomas 1990a,b; Widmark and Malmgren, 1992; Kuhnt and Kaminski,1993; d’Hondt et al., 1998; Widmark, 2000; Alegret et al.,2001, 2002a, b, 2003). Under oligotrophic conditions, theepifaunal Stensioeina beccariiformis and Cibicidoides hy-phalus, living at the sediment surface, bloomed togetherwith the infaunal species Coryphostoma incrassata formagigantea.

Benthic foraminifera from the lower Pv. eugubina Bio-zone are still dominated by epifaunal morphogroups (Fig.2B), especially by trochospiral biconvex (Osangulariaspp.) and planoconvex (Globorotalites spp.) tests (Fig. 3). Itmay be argued that this interval is dominated by epifau-nal taxa not because of the paleoecological characteristicsat that time, but only due to the fact that they correspondto the solution-resistant forms. Nevertheless, both infau-nal and epifaunal species show evidence of dissolution, notonly in these samples but also in the upper two centime-ters of the Maastrichtian and through the whole Danianpart of the section. Moreover, in spite of the fact that epi-faunal species are more susceptible to dissolution in themodern oceans, a peak in the abundance of epifaunal mor-phogroups is observed in the lower Danian, thus suggest-ing that the percentage of epifaunal morphogroups mayhave been even greater and that dissolution was presentbut not overwhelming. In addition, a wide range of sizes

may be observed in all the studied samples, which containboth thick-walled, solution-resistant forms, and thin-walled benthic foraminiferal tests. Two taxa, namely Glo-mospira serpens calcareous isomorph and Spirillina (Fig.5), first appear during this interval. Both taxa morpholog-ically are very similar to Glomospira serpens and Ammo-discus, respectively, which have been documented to bemobile epifaunal forms that feed on organic detritus (Lyand Kuhnt, 1994) and tolerate environmental instability,thus blooming whenever other taxa cannot compete (Ka-minski et al., 1996). The Glomospira serpens calcareousisomorph and Spirillina were not the only taxa in the Pv.eugubina Biozone and in the lower part of the Ps. pseudob-ulloides Biozone, but their appearance and increase inabundance, together with the low diversity and low per-centage of infaunal morphogroups, possibly indicate envi-ronmental instability at the sea floor (Figs. 2–3) An in-crease in the relative abundance of the infaunal Spiroplec-tammina israelskyi and Aragonia velascoensis also is re-corded in the Pv. eugubina Biozone (Fig. 2). Thepercentages of Spirillina and Paralabamina hillebrandtisignificantly increase towards the lower part of the Ps.pseudobulloides Biozone, at which point, their abundancerapidly starts to decrease (Fig. 3).

Higher in the section, benthic foraminiferal assemblag-es from the rest of the Ps. pseudobulloides Biozone aredominated by the epifaunal Stensioeina beccariiformis,Cibicidoides hyphalus, Nuttallides truempyi, and Nuttalli-nella spp. (Fig. 3). The percentage of infaunal morpho-groups increases slightly, but remains low (Fig. 2), as dothe diversity and heterogeneity indices (Fig. 4B, C). Theabundance of typically bathyal, oligotrophic species, to-gether with the dominance of epifaunal morphogroups to-wards the top of the studied interval, suggest that the foodsupply to the sea floor had not completely recovered atthat time, at least more than 200 kyr after the K/Pgboundary.

DISCUSSION

The dominance of calcareous benthic foraminiferathrough the whole section (Fig. 4A) may indicate a smallsupply of terrigenous sediment at Bidart as compared tothe coeval north Spanish Sopelana and Zumaya sections

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(Kuhnt and Kaminski, 1993), where agglutinated forami-nifera make up two-thirds of the benthic foraminiferal as-semblages. Upper Cretaceous benthic foraminiferal as-semblages are diverse at Bidart, and consist of a mixtureof both infaunal and epifaunal morphogroups, suggestingmesotrophic conditions during the late Maastrichtian.

The drastic decrease in the relative abundance of infau-nal taxa and in the diversity and heterogeneity of the as-semblages coincident with the K/Pg boundary indicates ol-igotrophic conditions, which are related to the decrease inthe organic flux from surface waters as the result of themass extinction of primary producers (e.g., Kuhnt and Ka-minski, 1993; d’Hondt et al., 1998; Alegret et al., 2001,2003). Under conditions of very limited food supply to thesea floor, food particles were consumed at the sedimentsurface by epifaunal species, whereas the percentage of in-faunal species decreased due to the lack of organic matterin the underlying sediment. The drastic reorganization ofbenthic foraminiferal assemblages, together with the geo-chemical evidence at Bidart (e.g., Delacotte, 1982; Bonte etal., 1984; Peybernes et al., 1996), are compatible with anasteroid impact at the K/Pg boundary.

Peybernes et al. (1996) documented the rapid increasein the abundance of the dinoflagellates Thoracosphaeraoperculata, Cyclagelosphaera reinhardii, and Braaduros-phaera bigelowii in the dark clay layer (G. cretacea Biozoneand lower part of the Pv. eugubina Biozone) at Bidart.Such blooms would have provided large amounts of foodthat reached the sea floor even in the absence of pellet-producing zooplankton, which suffered a mass extinction(e.g., Ittekot, 1993; Verity et al., 1996). According to thesedata, the following questions arise: why do benthic fora-minifera indicate oligotrophic conditions just after the K/Pg boundary, when phytoplankton blooms suggest animportant food supply to the sea floor? Under these high-productivity conditions driven by non-calcareous phyto-plankton blooms, why are lowermost Danian benthic fo-raminiferal assemblages apparently stressed, of low diver-sity, and dominated by few species? Speculatively, the ob-served peaks of the epifaunal species Stensioeinabeccariiformis and Cibicidoides hyphalus, and the increasein the percentage of the infaunal Coryphostoma incrassataforma gigantea just after the K/Pg boundary (Figs. 2–3),may be related to the drastic increase in the abundance ofdinoflagellates documented in the lowermost Danian atBidart. Although the species composition of the assem-blages and the low percentage of infaunal morphogroups(Fig. 2), as well as the drop in the d13C curve and in totalbulk carbonate (Renard et al., 1982; Bonte et al., 1984), in-dicate a drastic decrease in primary productivity just afterthe K/Pg boundary, some of the benthic foraminiferal spe-cies that bloomed just after the K/Pg boundary might havebeen able to feed on short-lived, local phytoplanktonblooms that occurred even in the absence of carbonate-richsediment contributed by nannoplankton, as described byAlegret et al. (2003) in the Agost section (southeasternSpain). In the Modern oceans, many organisms do not con-sume dinoflagellates, and the unusually low-diversity fau-nas live under a stressful environment because of thischange in the composition of food directly supplied fromthe photic zone (Peryt et al., 2002). Therefore, most of thebenthic foraminiferal species could not easily use the foodnutrients supplied by the abundant dinoflagellates, thus

accounting for the low diversity and heterogeneity of thelowermost Danian benthic foraminiferal assemblages. Itmay be concluded that it was not only the drastic decreasein primary productivity, but also the changes in phyto-plankton type (from calcareous to organic-walled phyto-plankton) just after the K/Pg boundary that caused thelow-diversity, high-dominance benthic foraminiferal as-semblages from the lower part of the dark clay layer.

The appearance of the opportunistic taxa Spirillina andGlomospira serpens calcareous isomorph, together withthe high percentages of epifaunal taxa such as Globorotal-ites or Paralabamina hillebrandti during the Pv. eugubinaBiochron and the early Ps. pseudobulloides Biochron (Fig.3), suggest that the food supply was still low, and probablydominated by non-calcareous phytoplankton.

The percentage of infaunal taxa increases slightlythrough the studied part of the Ps. pseudobulloides Bio-zone, although it does not reach the high values of the lateMaastrichtian (Fig. 2). Benthic foraminiferal assemblagesfrom this interval are dominated by the deep-water spe-cies Nuttallides truempyi, Stensioeina beccariiformis, andCibicidoides hyphalus (Fig. 3), which are common inbathyal settings with a scarce nutrient supply to the seafloor (Van Morkhoven et al., 1986; Widmark and Malm-gren, 1992; Speijer and Van der Zwaan, 1996; Alegret etal., 2001). The species composition, together with the lowdiversity and heterogeneity of the assemblages (Fig. 4 B–C), suggests that primary productivity had not completelyrecovered by that time—more than 200 kyr after the K/Pgboundary.

Kuhnt and Kaminski (1993) reported a similar faunalturnover in the northern Spanish Zumaya and Sopelanasections, including Gavelinella and Stensioeina-dominatedcalcareous assemblages in the lower part of the boundaryclay and a strong increase in the abundance of Spiroplec-tammina israelskyi at the top of this clay layer. They doc-umented a drastic increase in the relative abundance ofopportunistic species just after the K/Pg boundary duringa period of reduced primary productivity, and a gradualreestablishment of a normal trophic structure that tookplace, at least several hundred thousand years after the K/Pg boundary. A similar pattern of recovery has been re-ported from the South Atlantic (Widmark and Malmgren,1992), Mexico (Alegret and Thomas, 2001; Alegret et al.,2001, 2002a, b), Austria (Peryt et al., 1997), Tunisia (Spei-jer and Van der Zwaan, 1996; Peryt et al., 2002), andsoutheastern Spain (Alegret et al., 2003). The benthic fo-raminiferal turnover is compatible with the collapse andrecovery of surface productivity as the result of the K/Pg-boundary mass extinction of calcareous primary produc-ers (Zachos and Arthur, 1986; Kuhnt and Kaminski, 1993;d’Hondt et al., 1998; Alegret et al., 2001, 2003). The lack ofsignificant extinction of benthic foraminifera at a time ofmass extinction of planktic fauna suggests a weak bentho-pelagic coupling at that time (Thomas et al., 1999; Alegretet al., 2001). Nevertheless, the drastic reorganization ofbenthic foraminiferal assemblages coincident with the K/Pg boundary at Bidart, and at many other sections world-wide is compatible with a geologically instantaneous,widespread, and catastrophic event, such as the impact ofa large asteroid at the K/Pg boundary.

RECOVERY POST CRETACEOUS/PALEOGENE BOUNDARY, BIDART, FRANCE 581

CONCLUSIONS

Upper Maastrichtian and lower Danian benthic forami-niferal assemblages from the Bidart section (southwesternFrance) are dominated by calcareous taxa, and indicateupper–middle bathyal depths of deposition for the wholestudied interval.

Upper Maastrichtian benthic foraminiferal assemblag-es are diverse and heterogeneous, and contain a mixtureof infaunal and epifaunal morphogroups, thus indicatingmesotrophic conditions during the latest Cretaceous. Thestrong decrease in diversity and heterogeneity of the as-semblages, as well as the drastic drop in the percentage ofinfaunal morphogroups, indicate a dramatic decrease inthe food supply to the sea-bottom floor coincident with theK/Pg boundary, which is related to the collapse of the foodweb triggered by the mass extinction of primary produc-ers. The benthic foraminiferal turnover, together with thegeochemical and mineralogical evidence, is compatiblewith an asteroid impact at the K/Pg boundary.

Primary productivity during the early Danian was dom-inated by blooms of non-calcareous primary producers;such a change in phytoplankton composition induced astressful environment for the benthic fauna. The low di-versity of the assemblages, as well as the low percentage ofinfaunal morphogroups through the Pv. eugubina and Ps.pseudobulloides Biozones, suggests that primary produc-tivity had not completely recovered more than 200 kyr af-ter the K/Pg boundary.

ACKNOWLEDGEMENTS

This research was funded by the DGES BTE2001–1809project (Spanish Ministry of Science and Technology), andthe DGA 2002–4 project. L. Alegret thanks the SpanishMinisterio de Educacion, Cultura y Deporte for her post-doctoral grant EX2003–0007. We thank S. J. Culver andM. B. Hart for their constructive reviews.

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2 1 25 214 3

92

93

1A

nom

alin

oide

ssp

p.A

rago

nia

sp.

Ara

gon

iave

lasc

oen

sis

Are

nobu

lim

ina

sp.

Ast

acol

us

cf.

jarv

isi

4 4

8 2

15

2 2

5

2

2 3

3

2 1

2 7 120 3

28 8

5 10 1

3 12 2

9 2 2

7 8 2

22 6

Ast

acol

us

spp.

Bat

hysi

phon

sp.

Bat

hysi

phon

sp.

CB

oliv

inoi

des

deli

catu

lus

Bol

ivin

oide

sd

raco

2 11 1

1 2 11

2 2 1 6

1 1 47

1 7

1 4

1 23

7 2 4

1 1 5

4 12 13

4

1

11

Bol

ivin

oide

ssp

.B

uli

min

am

idw

ayen

sis

Bu

lim

ina

pale

ocen

ica

Bu

lim

inia

spp.

Bu

lim

ina

trin

itat

ensi

s1

11

7 51 3 1 1

1

22

4 811

3 84

4 64 9

15 8B

uli

min

ave

lasc

oen

sis

Bu

lim

inel

lacf

.be

aum

onti

Bu

lim

inel

lasp

.C

auda

mm

ina

sp.

Cib

icid

oide

scf

.ab

udu

rben

sis

1

3 71 1

2 1

44 1

12

Cib

icid

oide

scf

.ek

blom

iC

ibic

idoi

des

cf.

nar

anjo

ensi

sC

ibic

idoi

des

dayi

Cib

icid

oide

sho

wel

liC

ibac

idoi

des

hyph

alu

s

1 51 7

3 2 15

8 1 253

4124

2 35

10 90

6

221

4151

2027

13 15

2 36

5 31

1 45

1 19C

ibic

idoi

des

prop

riu

sC

ibic

idoi

des

sp.

Cib

icid

oide

sve

lasc

oen

sis

Cla

vuli

noid

esam

orph

aC

.am

orph

aju

ven

ile

form

2312 1

10 36

9 5

8 4

14 1 1 15

15 6 1217

418 5

12 9

4 21 247

12 12

31 56 15

23 52 8

Cla

vuli

noid

essp

.C

lavu

lino

ides

tril

ater

aC

.tr

ilat

era

juve

nil

efo

rmC

anor

bin

asp

.C

oryp

host

oma

decu

rren

s

3 12

11

1 2

6 45

25

3 5

4 2

1

10

24 3

7

Cor

ypho

stom

ain

cras

sata

C.

incr

assa

tafo

rma

giga

nte

aC

oryp

host

oma

sp.

Den

tali

na

sp.

Dor

oth

iabu

llet

a

16 8 2

3 1 1 1

3 1 3

18 13 2

4 1

3 1

19 1

6910

0 1

657 1

5 14

1

RECOVERY POST CRETACEOUS/PALEOGENE BOUNDARY, BIDART, FRANCE 585

AP

PE

ND

IXC

onti

nu

ed. K

240

0K

230

0K

220

0K

210

0K

250

K2

25K

262

10K

202

2T

101

2T

131

6T

113

117

T1

251

29T

150

T1

117

T1

155

T1

165

T1

210

T1

300

T1

360

Dor

oth

iabu

llet

aju

ven

ile

form

Dor

oth

iapu

paD

orot

hia

pupa

juve

nil

efo

rmD

orot

hia

spp.

Ell

ipso

dim

orph

ina

sp.

4 2 53

3

7 3

2 1 11

8

1 3 11

12

Fis

suri

na

spp.

Fu

rsen

koin

asp

.G

aud

ryin

apy

ram

idat

aG

aud

ryin

asp

.ju

ven

ile

form

Gav

elin

ella

dan

ica

3 2

1 2

2 1 6

2 2 21

1 4 24 4

22

1 11 1

4

Gla

ndu

lin

asp

.G

lobo

rota

lite

ssp

.G

lobu

lin

apr

isca

Glo

buli

na

spp.

Glo

mos

pira

gord

iali

s

18 1 6

8 5

3 65 1 3

4 5

10 3

5 1 1 12

1 26

55 1

100

6610

11 2

244

1 8 2

12

Glo

mos

pira

serp

ens

calc

areo

us

isom

orph

Glo

mos

pira

spp.

Glo

mos

pire

lla

grzy

bow

zki

Gut

tuli

na

sp.

Gyr

oid

inoi

des

beis

seli

143 2

4 62 4

1 15

3 2 24

1 3 2232

39

3 16

2 2 28

1 1 22

9 12

15 20

14 2 17

1 1853

1 153 16

Gyr

oid

inoi

des

cf.

goud

koffi

Gyr

oid

inoi

des

depr

essu

sG

yroi

din

oide

sgi

rard

anu

sG

yroi

din

oide

sgl

obos

us

Gyr

oid

inoi

des

sp.

5 4 2

3 1 2

2 5 4 3

3 8

2 1 64 3 5

4 3 1 1

1 2 1 1

5 5 21

2 2 1

6 4 2 1

38 4 2 6

1 2 3 35 7

5 2 1

2 2 2 4 6

5 7 3H

aplo

phra

gmoi

des

prot

eus

Hap

loph

ragm

oide

ssp

.H

eron

alle

nia

lin

gula

taH

orm

osin

ave

lasc

oen

sis

Hyp

eram

min

asp

.1

21

1

11

15 1

5 3

1

31

2

Insc

ulp

tare

nula

sp.

Lae

vide

nta

lin

asp

p.L

agen

agl

obos

aL

agen

asp

p.L

enti

culi

na

spp.

26 1 21

19 2 6

25 4 10

16 2 4 7

14 10 11

9 7 4

2 24 5 20

5 4

3 6

5 7

8 13

7 17

5 8

3 2

4 2 5

4 2 42

4 7

8 7 12L

ingu

lin

asp

p.L

oxos

tom

um

eley

iM

argi

nuli

na

sp.

Mar

sson

ella

oxyc

ona

M.

oxyc

ona

juve

nil

efo

rm

1 18 5 2

39 1 2

34 3 1

24 3

18 3

14 11 6

1 242

147 2

1

1 54 2

Mar

sson

ella

sp.

Neo

flab

elli

na

sp.

Non

ione

lla

cret

acea

Non

ione

lla

sp.

Nut

tall

ides

spp.

1 1 1 5

3 1 1 1213

1227

2 1 29

1 19

2 810

1618

4138

50

2 3819

618

14N

utta

llid

estr

uem

pyi

Nut

alli

nell

aco

ronu

laN

utta

llin

ella

flore

alis

Nut

alli

nell

asp

p.O

olin

asp

p.

12 3

5 5 1

16 10

11 313 9 4

9 7

8 5

3 61 1

35

158

9

2437 4

33 36

45 7 18

586 ALEGRET ET AL.A

PP

EN

DIX

Con

tin

ued

. K2

400

K2

300

K2

200

K2

100

K2

50K

225

K2

6210

K2

022

T1

012

T1

316

T1

131

17T

125

129

T1

50T

111

7T

115

5T

116

5T

121

0T

130

0T

136

0

Ori

dors

alis

plu

mm

erae

Ori

dors

alis

sp.

Ori

dors

alis

um

bon

atu

sO

san

gula

ria

cf.

vela

scoe

nsi

sO

san

gula

ria

cf.

cord

ieri

ana

5 3

4 31

2 2

1 2 320

12 1

2 61

22 3 2

3

Osa

ngu

lari

acf

.pl

um

mer

aeO

san

gula

ria

spp.

Pal

iola

tell

aor

bign

yan

aP

alio

late

lla

sp.

Par

alab

amin

ah

ille

bran

dti

3 2

4 1 2

3 2

1 32 3

2 2 2

5 6 3

822

1939

16 35 2

18 4

8 21 47

11 3558

22 17

6 5

8 2 17P

lanu

lin

asp

.P

leu

rost

omel

lasp

.P

raeb

uli

min

acf

.re

uss

iP

raeb

uli

min

asp

.P

raeg

lobo

bulm

ina

spp.

28 1

2 142 8

2 3 12

1 5

21

14

Pse

udou

vige

rin

apl

um

mer

aeP

seud

ouvi

geri

na

sp.

Pu

llen

iacr

etac

eaP

ull

enia

jarv

asi

Pyr

amid

ina

rud

ita

2 3

2 2

1 1 7

1 93

13 6

3

3 12

21

1 11

Pyr

amid

ina

sp.

Pyr

uli

noid

essp

.Q

uad

rim

orph

ina

allo

mor

phi-

noid

esQ

uad

rim

orph

ina

sp.

Qu

inqu

eloc

uli

na

sp.

7 2

7 2

4 1

6 2

72

16

1

6 2

Ram

uli

na

spp.

Rec

urv

oide

ssp

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epm

ania

char

oide

sR

euse

lla

sp.

Rh

izam

min

asp

.

1 3 1

23

11

2 4 11

31 1

1

1S

acca

mm

ina

plac

enta

Sac

cam

min

asp

p.S

arac

enar

iasp

.S

chei

bner

ova

sp.

Sit

ella

sp.

1 13

1 11

3 41

11

2

Sli

teri

ava

rsov

ien

sis

Spi

ropl

ecta

mm

ina

cf.

den

tata

Spi

ropl

ecta

mm

ina

cf.i

srae

lsky

iS

piro

plec

tam

min

asp

ecta

bili

sS

piro

plec

tam

min

asp

p.2

1 4 1

1 33

13

65 1 1

11 3 8 5

34 1 3

299

7 2

525

15 1 2

3 2S

piro

plec

tine

lla

sp.

Spi

rill

ina

sp.

Ste

nsi

oein

abe

ccar

iifo

rmis

Ste

nsi

oein

aex

cola

taS

till

osto

mel

lasp

.

1 61 2 4

1 2

6 3 1

12 1 1

1 8 2 1

4 1 1

19 211

264 2

4 1 3

3 2

5 7 2

2 21 15 1

51 7 3

1 20 1

4 57 1 1

4 58 1

63

Tapp

anin

ase

lmen

sis

Th

alm

ann

amm

ina

sp.

Tro

cham

min

asp

.Va

ginu

lin

atr

ilob

ata

Valv

alab

amin

ale

nti

cula

3 11

11

3 1

1 1

1 6 46 4

73

1 13

2

1

TO

TA

L32

119

725

427

325

828

332

523

841

665

140

146

237

334

332

831

039

334

537

0