. 2008: Integrated magnetobiochronology of the Early/Middle Eocene transition at Agost (Spain): Implications for defining the Ypresian/Lutetian boundary stratotype. Lethaia , Vol. 41, In this paper, we present an integrated study of a 115-m-thick section that spans the Ypresian/Lutetian boundary at Agost (Betic Cordillera, SE Spain). Our study includes magnetostratigraphic results and biostratigraphic and palaeoenvironmental data derived from planktic foraminifera, small and larger benthic foraminifera, and calcareous nannofossils. Our results demonstrate that the Agost section is continuous and spans from Zones P9 to P12 (E7 to E10), Zones CP11 to CP14a (NP13 to NP16), Zones SBZ11 to SBZ15, and Chrons C22n to C19r. The first occurrence (FO) of H. nuttalli (base of P10) and the FO of G. nuttalli (base of E8) are found within Chron C20r, at a much younger age (3-5 Myr) than previously considered in standard calibration schemes. Similarly, the boundary between SBZ12 and SBZ13 is located within Chron C21n, also at a younger age than previously considered. On the contrary, the FO of B. inflatus (base of CP12b) is found within Chron C21r, which conforms to the magnetostratigraphically calibrated age of ca. 48 Ma (middle part of C21r) considered in standard calibration schemes. These results corroborate earlier studies and indicate that all the events that have been proposed to mark the Ypresian/Lutetian boundary appear at different stratigraphic intervals and have different ages. Based on our results from Agost and on data from other sections elsewhere, we suggest that the Ypresian/Lutetian boundary might be approximated by the FO of B. inflatus (base of CP12b). The Agost section might be considered as a potential candidate to locate the Global Stratotype Section and Point (GSSP) of the base of the Lutetian Stage, because it includes all the events that might be selected as marker events for the Ypresian/Lutetian boundary and it fulfils most of the geological, biostratigraphic and infrastructure requirements demanded for definition of a GSSP. ᮀ Agost , Betic Cordillera , biostratigraphy , calcareous nannofossils , Global Stratotype Section and Point , larger benthic foraminifera , magnetostratigraphy , planktic foraminifera , small benthic foraminifera , Ypresian/ Lutetian boundary .

No abstract

No abstract

ABSTRACT. --The integrated biostratigraphy of a 112 m thick exposed section near Agost (Southern Spain) was studied to assess its suitability as a Global Stratotype Section and Point (GSSP) for the Early/Middle Eocene (Ypresian/Lutetian) Boundary. This section consists of marls mterbedded with calcarenites and detrital turbidite layers deposited in a henfipelagic environment. Planktic foraminifera provided good biozonation from P8 through Pll Zones. The calcareous nannofossil Zones NP13 through NP16, respectively CPll through CP14a, could be distingmshcd. The larger foraminiferal Zones SBZ12 to SBZ14 could tentatively be distinguished. The base of the H. nuttalli (P.10) Zone, which is often used to set the boundary between the Lower and the Middle Eocene (Ypresian/Lutetian) falls at a facies change. The Agost Section can be used as a GSSP only if no better section is found.R~SUM~. -La biostratlgraphle mt6gT~e d'une coupe mesnrant 112 m d'6paisseur expos6e pros d'Agost dans le Sud de l'Espagne a 6t6 6tndi6e afin d'6valuer son ad6quation comme << Global Stratotype Section and Point (GSSP) ,> pour la limite Eocene inf6rieur/moyen (Ypr6sien/Lut6tien). La coupe est compos6e de marnes intercal6es de calcar6nites et couches d6tritiques turbidiques d6pos6es dans un environnement h6mip61agique. Les foraminif~res planctoniques permettent une bonne biozonation depuis la zone P8 ~ Pll. Pour les nannofossiles calcaires on peut distinguer les zones NP13 A NP16 et respectivement CPll ~ CP14a. Pour les grands foraminif~res il est possible de distinguer, bien que sans beaucoup de pr6cision, les zones SBZ12 h SBZ14. La base de la zone ~ H. nuttalli (P10), qui est g6n6ralement utilis6e pour marquer la linnte entre l'Eoc6ne inf6rieur et moyen (Ypr6sien/Lut6tien) coincide avec un changement de facies. Par cons6quent la coupe d'Agost pourrait ~tre choisie comme GSSP si aucune coupe plus appropri6e n'cst trouv6e.

Biostratigraphic study and re-examination of 22 late Eocene to early Oligocene sections provides data in support of three and possibly a fourth late Eocene impact events in the G. index Zone during a period of about 1 Ma of the middle Priabonian between 34.7 and 35.7 Ma. No major species extinctions or significant species abundance changes directly coincide with these impact events. Species extinctions are gradual and selective, affecting primarily cool-temperature-intolerant surface dwellers. These extinctions began with the onset of global cooling during the early middle Eocene and culminated near the Eocene/Oligocene boundary. The global cooling was associated with the isolation of Antarctica as Australia moved northward, the development of a circum-Antarctic circulation, growth of Antarctic ice sheet beginning by late middle Eocene time and a change from a thermospheric to thermohaline circulation. We find no evidence that the multiple late Eocene impact events directly contributed to the climatic deterioration already in progress.