Paleogene Chronostratigraphy of the SE Margin of the Ebro Basin: Biochronological and Tectonosedimentary Evolution Implications (Cronostratigrafia del paleogen del marge SE de la conca de l’Ebre: Implicacions biocronològiques i evolució tectonosedimentaria)

Abstract

This PhD-Thesis presents a new chronostratigraphy of the Paleogene sedimentary record of the SE margin of the Eastern Ebro Basin. It is based on a number of magnetostratigraphic sections and its integration with marine and continental biochronological data. A robust correlation with the geomagnetic polarity time scale is obtained and provides the record with absolute ages, spanning from chrons C20n to C12r (Lutetian to Rupelian stages, ca. 43.0-31.0 Ma).

Main differences with respect to the current chronostratigraphic scheme of the Eastern Ebro Basin include the age of the uppermost marine units. While earlier schemes attributed a Bartonian age to these units regarding its biostratigraphical contents, new results supports a Lower Priabonian age, yielding an interpolated age of ca. 36.0 Ma (within chron C16n.2n) for the continentalization process. This age is in concordance with a reinterpretation of earlier magnetostratigraphic data from the Western South Pyrenean Foreland Basin, and indicates that continentalization of the basin occurred as a rapid and isochronous event. The analysis of the observed sedimentation trends are used to evaluate the character of this process. Thus, contrasting sedimentation trends between the Western and Eastern sectors of the South Pyrenean foreland are proposed to indicate that basin closing preferentially affected those areas subjected to sediment bypass towards the ocean domain.

Moreover, new results provide improved temporal constraints for the sediments of the Eocene Montserrat alluvial fan and fan-delta complex. Thus a Lutetian age is ascribed to the whole La Salut Formation and the age of the Montserrat Conglomerates spans from Upper Lutetian to Lower Priabonian. The new chronological framework is used to unravel the forcing controls on the sequential arrangement of the Montserrat area at different temporal scales, and also to revise the tectonosedimentary history. Obtained results show a correlation between (tectonic) subsidence and forelimb rotation measured on deformed strata of Montserrat. Furthermore, integration of subsidence curves from different sectors of the Eastern Ebro Basin allows estimating the variable contribution of tectonic loads from the two active basin margins: the Catalan Coastal Ranges and the Pyrenees. The results support the presence of a double flexure from Late Lutetian to Late Bartonian, associated to the two tectonically active margins. From Late Bartonian to Early Priabonian the homogenization of subsidence values is interpreted as the result of the coupling of the two sources of tectonic load.

Finally, the obtained chronology contributes to the calibration of several biostratigraphic zonations to the geomagnetic polarity time scale. In the marine realm, the base of calcareous nannofossil Zone NP19-20 is pinned down to an older age than its currently accepted attribution, whereas the time span assigned to Zone NP18 is significantly reduced. A revised calibration of larger foraminifers indicates that Zone SBZ18, formerly assigned exclusively to Late Bartonian, extends its range to the earlymost Priabonian, being the Bartonian stage almost entirely represented by Zone SBZ17. A division of Zone SBZ18 into two subzones is also proposed. In the continental realm, the magnetostratigraphic record of the Eastern Ebro Basin yields accurate ages for the immediately pre- and post-Grand Coupure mammal fossil assemblages found in this basin. Thus, the Grande Coupure, a major terrestrial faunal turnover recorded in Eurasia associated with the overall climate shift at the Eocene-Oligocene transition, is found to occur with a maximum allowable lag of 0.5 Myr with respect to this boundary. Furthermore, results from this PhD-Thesis allow revisiting correlations for the controversial Eocene-Oligocene record of the Hampshire Basin (UK), and their implications for the calibration of the Mammal Paleogene reference levels MP18 to MP21.

Aquesta Tesi Doctoral presenta una nova cronologia del registre sedimentari Paleogen del marge SE del sector oriental de la Conca de l’Ebre. La cronologia obtinguda es basa en la integració d’un conjunt de sèries magnetostratigràfiques amb totes les dades biostratigràfiques dels registres marí i continental disponibles en aquest sector de la conca. L’establiment d’una correlació robusta amb l’escala de temps de polaritat geomagnètica proveeix al registre sedimentari Paleogen d’un marc cronològic amb edats absolutes que van des del cron C20n fins al cron C12r (ca. 43.0-31.0 Ma), és a dir, del Lutecià al Rupelià. Aquest nou marc cronològic proporciona les eines necessàries per a la quantificació i posterior comprensió de l’evolució tectonosedimentària dels marges adjacents a la Conca de l’Ebre. Finalment, la cronologia resultant de la present Tesi Doctoral contribueix a la calibració amb l’escala de temps geològic de les biozonacions de nanofòssil calcari i macroforaminífers (Shallow Benthic Zones), així com dels nivells de referència de mamífers paleògens europeus (European vertebrate Mammal Paleogene –MP- reference levels).