Josep Tosquella

Did the Late Paleocene thermal maximum affect the evolution of larger foraminifers? Evidence from calcareous plankton of the Campo Section (Pyrenees, Spain)

The larger foraminifer turnover (LFT), which marks the base of the Ilerdian stage, may be related to the Late Paleocene Thermal Maximum (LPTM), or be at least nearly coeval with that climatic event. Thus, the impact of the LPTM may have been greater than hitherto realised, having also affected mid-latitude shallow-marine biota. This conclusion has been reached after a re-study of the calcareous plankton of the uppermost Paleocene and lowermost Eocene interval of the Campo section in the central southern Pyrenees. Campo is an important reference section because it contains larger foraminifers, planktic foraminifers and calcareous nannofossils, and their co-occurrence was used to intercalibrate their respective zonal schemes. Previous studies at Campo placed the onset of planktic foraminiferal Zone P5 near the base of the Ilerdian, and the calcareous nannofossil NP9/NP10 chronal boundary (sensu Bybell, L.M., Self-Trail, J.M., 1995. Evolutionary, biostratigraphic and taxonomic study of calcareous nannofossils from a continuous Paleocene/Eocene boundary section in New Jersey. US Geol. Surv. Prof. Pap. 1554, pp. 1‐36) not less than 150 m above the Ilerdian lower limit. By these estimates, the LPTM (known to have occurred in the middle part of Zone P5 and just before the NP9/NP10 boundary) would be an event much younger than the LFT. However, our reexamination of planktic foraminifers suggests that the base of the Ilerdian is probably situated at the middle of Zone P5 (a possibility proposed by Hillebrandt in 1965, but denied by later authors). For instance, Morozovella occlusa has been found for the first time in the Campo section. Its Last Appearance Datum (LAD), which in the Pyrenees was approximately coeval with that of Morozovella velascoensis (event used to place the top of Zone P5), has been identified in beds situated less than 70 m above the base of the Ilerdian. Such thickness represents a time span of a similar magnitude as the one which separated the LPTM and the LAD of M. occlusa in the deep-water hemipelagic succession of the Basque Basin, in the western Pyrenees. Autochthonous calcareous nannofossils are neither abundant nor well preserved in most of the studied interval, with Rhomboaster bramlettei (the marker of the base of Zone NP10) being extremely rare in lower and middle Ilerdian beds, a fact that makes it very difficult to fix the position of the NP9/NP10 boundary in the Campo section. However, the bases of zones NP9 and NP11 have been located, and they support the zonation with planktic foraminifers. These new data suggest that the LFT and the LPTM may have been coeval or nearly so, a possibility reinforced by correlation with sections of the Basque Basin. Specialists of larger benthic foraminifers can easily delineate the LFT in shallow water carbonate successions of the Tethys domain, and they propose to place the Paleocene/Eocene boundary at the base of the Ilerdian stage. On the other hand, the deep

Redefinition of the Ilerdian Stage (early Eocene)

The Ilerdian Stage was created by Hottinger and Schaub in 1960 to accommodate a significant phase in the evolution of larger foraminifera not recorded in the northern European basins, and has since been adopted by most researchers working on shallow marine early Paleogene deposits of the Tethys domain. One of the defining criteria of the stage is a major turnover of larger foraminifera, marked by the FO’s of Alveolina vredenburgi (formerly A. cucumiformis) and Nummulites fraasi. There is now conclusive evidence that this turnover was coeval with the onset of the Carbon Isotope Excursion (CIE) and, consequently, with the Paleocene-Eocene (P-E) boundary, a temporal correspondence that reinforces the usefulness of the Ilerdian as a chronostratigraphic subdivision of the early Eocene in a regional context. However, in addition to the paleontological criteria, the definition of the Ilerdian was also based on the designation of two reference sections in the southern Pyrenees: Tremp (stratotype) and Campo (parastratotype). In both sections, the base of the stage was placed at the lowest marine bed containing A. vredenburgi specimens. Using the CIE as a correlation tool we demonstrate that these two marine beds occur at different chronological levels, being older in Campo than in Tremp. Further, we show that both beds are in turn younger than the lowest strata with Ilerdian larger foraminifera at the deep-water Ermua section in the Basque Basin (western Pyrenees). Since the age of stage boundaries must be the same everywhere, the choice of these stratotype sections was misleading, since in practice it resulted in the Ilerdian being used as a facies term rather than as a chronostratigraphic unit. To eliminate that conflict, and yet be respectful with established tradition, we propose to redefine the Ilerdian Stage following a procedure similar to the one used by the International Commission on Stratigraphy to establish global chronostratigraphic standards, namely: by using a “silver spike” to be placed in the Tremp section at the base of the Claret Conglomerate, a widespread lithological unit that in the Tremp Graus Basin coincides with the onset of the CIE. The redefined regional Ilerdian Stage becomes thus directly correlatable to the lower part of the global Ypresian Stage, as currently defined by the International Commission on Stratigraphy.

On the age of the Early/Middle Eocene boundary and other related events: cyclostratigraphic refinements from the Pyrenean Otsakar section and the Lutetian GSSP

An integrated bio-, magneto- and cyclostratigraphic study of the Ypresian/Lutetian (Early/Middle Eocene) transition along the Otsakar section resulted in the identification of the C22n/C21r chron boundary and of the calcareous nannofossil CP12a/b zonal boundary; the latter is the main correlation criterion of the Lutetian Global Stratotype Section and Point (GSSP) recently defined at Gorrondatxe (Basque Country). By counting precession-related mudstone–marl couplets of 21 ka, the time lapse between both events was calculated to be 819 ka. This suggests that the age of the CP12a/b boundary, and hence that of the Early/Middle Eocene boundary, is 47.76 Ma, 250 ka younger than previously thought. This age agrees with, and is supported by, estimates from Gorrondatxe based on the time lapse between the Lutetian GSSP and the C21r/C21n boundary. The duration of Chron C21r is estimated at 1.326 Ma. Given that the base of the Eocene is dated at 55.8 Ma, the duration of the Early Eocene is 8 Ma, 0.8 Ma longer than in current time scales. The Otsakar results further show that the bases of planktonic foraminiferal zones E8 and P10 are younger than the CP12a/b boundary. The first occurrence of Turborotalia frontosa , being approximately 550 ka older that the CP12a/b boundary, is the planktonic foraminiferal event that lies closest to the Early/Middle Eocene boundary. The larger foraminiferal SBZ12/13 boundary is located close to the CP12a/b boundary and correlates with Chron C21r, not with the C22n/C21r boundary.

New fossils of Sirenia from the Middle Eocene of Navarre (Western Pyrenees): the oldest West European sea cow record

Postcranial remains of Sirenia from the early Middle Eocene (late Lutetian) Urbasa-Andia Formation of Navarre (Western Pyrenees) are described. The material consists of two partial atlas vertebrae, one humerus and several dorsal ribs (from Arrasate, Urbasa plateau), and partial dorsal ribs (from Lezaun, Andia plateau). The morphology of the fossils is consistent with referral to Dugongidae, the only sirenian clade known so far in the Middle Eocene of Europe. Moreover, the histological study of the ribs shows that the pachyosteosclerosis of extant Sirenia was definitively present by the early Middle Eocene. The oldest sirenian remains reported to date in the Pyrenean Realm were assigned to the Biarritzian, a regional stage that is currently ascribed either to the middle or to the lower–middle Bartonian. Therefore, the sirenian remains of Lezaun, reliably dated as late Lutetian (SBZ16 zone) in age, are definitively the earliest sirenian fossils known in Western Europe and are among the oldest sea cow records of Europe.

TRANSGRESSIVE SEQUENCES ON FORELAND MARGINS: A CASE STUDY OF THE NEOGENE CENTRAL GUADALQUIVIR BASIN, SOUTHERN SPAIN

The Guadalquivir foreland basin, located between the Iberian basement northward and the Betic orogen to the South, represents the western sector of the earlier foredeep basin of the Betic Cordillera. Along the northern foreland margin, the sedimentary fill of this basin includes a Tortonian Basal Transgressive Complex (BTC), composed of five internal sequences bounded by transgressive surfaces. Two main parts are distinguished within each sequence: the lower transgressive lag deposits, and the upper stillstand/prograding sediments. Three facies associations were distinguished within this stratigraphic succession along the central sector of this basin margin: unfossiliferous conglomerates and coarse-grained sands (A), fossiliferous conglomerates and coarse-grained sands (B), and yellow medium-coarse-grained fossiliferous sands (C). A fourth facies association (D: blue silty marlstones and shales) overlies the BTC. Deposits of alluvial sediments (facies association A) and shallow-marine/foreshore sediments (facies association C), were recurrently interrupted by transgressive pulses (facies associations B and C). Every pulse is recorded by an erosional, cemented sandy-conglomerate bar with bivalves (Ostreidae, Isognomon ), balanids, gastropods and other marine bioclasts; or their transgressive equivalents. The lateral facies changes in each individual sequence of the BTC are related to: (1) the influence on the northern foreland margin of the tectonic activity of the southern orogenic margin; (2) the palaeorelief formed by irregularities of the substrate which controls the sediment dispersal; and (3) the evolution stages of the sedimentary systems.

El género Heterostegina (Nummulitidae, Foraminifera) en el Mioceno superior del SO de España

Systematic study of specimens belonging to the genus Heterostegina from coquilla levels in the basal sandstone unit of the Neogene series in the western part of the Guadalquivir Basin (SW Spain). The specific determination of these specimens allows us to revise and emend the species Heterostegina gomez-angulensis Perconig. For the first time we describe and figure the microspheric generation of this species. The redescription of the megalospheric forms has permitted to differentiate two morphotypes. We discuss their chronostratigraphic significance.