EAGE Basin Research (2012) 24, 437–455, doi: 10.1111/j.1365-2117.2011.00532.x Tectonic and climatic controls on the sequential arrangement of an alluvial fan/fan-delta complex (Montserrat, Eocene, Ebro Basin, NE Spain) M. Go´ mez-Paccard,*† M. Lo´ pez-Blanco,* E. Costa,* M. Garce´ s,* E. Beamud‡ and J. C. Larrasoan˜ a§ *Departament d’Estratigrafia, Paleontologia i Geocie`ncies Marines, Grup de Geodina`mica i Ana`lisi de Conques (GGAC), Facultat de Geologia, Universitat de Barcelona, Barcelona, Spain †Institut de Ciencie`s de la Terra Jaume Almera, ICTJA-CSIC, Barcelona, Spain ‡Laboratori de Paleomagnetisme (CCiTUB-CSIC), Institut de Ciencie`s de la Terra Jaume Almera, CSIC, Barcelona, Spain §Instituto Geolo´gico y Minero de Espan˜a, Unidad de Zaragoza, Zaragoza, Spain ABSTRACT A magnetostratigraphy-based chronological framework has been constructed in the Eocene sedi- ments of the Montserrat alluvial fan/fan-delta complex (southeast Ebro Basin), in order to unravel forcing controls on their sequential arrangement and to revise the tectonosedimentary history of the region. The palaeomagnetic study is based on 403 sites distributed along an 1880-m-thick composite section, and provides improved temporal constraints based on an independent correlation to the geomagnetic polarity time scale. The new chronological framework together with sequence stratigra- phy and geohistory analysis allow us to investigate the interplay between factors controlling the sequential arrangement of the Montserrat complex at the different temporal scales and to test for orbitally driven climate forcing. The results suggest that the internal stacking pattern in transgres- sive and regressive sequences sets within the more than 1000-m-thick Milany Composite Megase- quence can be explained as the result of subsidence-driven accommodation changes under a general increase of sediment supply. Composite sequences (tens to hundreds of metres thick) likely reflect orbitally forced cyclicity related to the 400-kyr eccentricity cycle, possibly controlled by climatically induced sea-level fluctuations. This study also provides new insights on the deformational history of the area, and shows a correlation between (tectonic) subsidence and forelimb rotation measured on basin-margin deformed strata. Integration of subsidence curves from different sectors of the eastern Ebro Basin allows us to estimate 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 with 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. INTRODUCTION ‘Bartonian transgression’ (Serra-Kiel & Trave´, 1995). Erosive processes during the Neogene and Quaternary Montserrat is a conglomeratic massif located along the have resulted in a series of long and deeply incised valleys southeastern margin of the Ebro Foreland Basin adjacent where a 2000-m-thick Eocene stratigraphic succession to the Catalan Coastal Ranges (CCR), a NE–SW oriented crops out. The excellent and continuous outcrops make and NW-verging intraplate chain resulting from Palaeo- this area particularly suitable for the study of the architec- gene convergence between the Iberian and European tural arrangement of these sediments and the interplay plates (Anado´n et al., 1985b; Guimera`, 1988; Lo´pez- between tectonics, climate, relative sea-level changes and Blanco, 2002). Tectonic activity of the CCR during the sediment supply in an active basin margin context. To Lutetian led to the development of this alluvial fan system achieve these goals, a robust chronology of the sedimen- which evolved to a fan-delta complex after the so-called tary record is essential. In an earlier work, magnetostratig- raphy was applied to establish the age of the Montserrat stratigraphic succession (Lo´pez-Blanco et al., 2000a). Correspondence: M. Go´mez-Paccard, Institut de Ciencie`sdela Terra Jaume Almera, ICTJA-CSIC, Lluı´s Sole´ i Sabarı´s s/n, However, the correlation proposed between the local E-08028 Barcelona, Spain. E-mail: [email protected] magnetostratigraphy and the geomagnetic polarity time © 2011 The Authors Basin Research © 2011 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 437 M. Go´mez-Paccard et al. scale (GPTS) was based on chronological tie points which (a) have been recently challenged (Cascella & Dinare`s- Turell, 2009; Costa et al., 2010). In addition, limited sam- EUROPEAN pling resolution in Lo´pez-Blanco et al. (2000a) yielded PLATE uncertain results regarding completeness of the magneto- Atlantic Ocean stratigraphic record. This study provides a new magnet- Alps Aquitaine ostratigraphy of the Montserrat succession that involves a Basin five-fold increase in sampling resolution and an indepen- Pyrenees dent correlation to the GPTS. The new chronology has been used to test for orbital forcing in the sequential IBERIAN Ebro Basin arrangement of the studied fan delta and to revise the PENINSULA IR tectonosedimentary evolution of the Montserrat system CCRValencia Trough and the adjacent CCR. Guadalquivir Basin Balearic Islands Betics GEOLOGICAL SETTING Mediterranean Sea Alboran Domain The Ebro Foreland Basin represents the last evolutionary Maghrebides stage of the South Pyrenean Foreland Basin (Fig. 1). It is 0300 km limited to the north by the Pyrenees, to the southwest by the Iberian Range and to the southeast by the CCR. Alpine thrust belts CCR: Catalan Coastal Ranges Enhanced tectonic loading on the Pyrenean side of the Alpine foreland basins IR: Iberian Range basin led to an asymmetrical basin where subsidence rates Rift basins study area and sedimentary thickness increased northward (Se´guret, (b) Pyrenees 1972; Choukroune & Se´guret, 1973; Puigdefa`bregas & 41º Souquet, 1986; Mun˜oz, 1992; Verge´s, 1993; Verge´s et al., Spain 1998). The Palaeogene development of the CCR and the 0º Iberian Range occurred soon after the onset of Pyrenean deformation in the Late Cretaceous (Puigdefa`bregas & Ebro Basin 3 Souquet, 1986). Tectonic uplift of the surrounding 1–2 mountain belts caused the isolation of the Ebro Basin Igualada from the open ocean by the Late Eocene, possibly in con- Barcelona currence with a mid-amplitude eustatic fall (Miller et al., 2005) peaking at 36.2 Ma (Mun˜oz et al., 2002; Pardo et al., 2004; Costa et al., 2010). Catalan Coastal Ranges Mediterranean Sea In the study area, the Palaeogene sedimentary fill is Valencia Trough divided into four lithostratigraphic units: the Mediona, El 050100 km Cairat Breccia, and La Salut Sandstone formations and Montserrat Conglomerates (Fig. 2a, b). The Mediona Formation overlies a regional unconformity on Triassic Neogene (grabens) and Quaternary rocks, and its age is constrained to the Upper Thanetian– Neogene (Ebro basin) Study area Lower Ypresian based on carophytes (Anado´n, 1978). Paleogene fault Magnetostratigraphic The El Cairat Breccia Formation mainly consists of Tri- Mesozoic sites and well-logs thrust assic-derived breccias with a Ypresian estimated age Paleozoic (Anado´n, 1978). La Salut Formation is predominantly composed of red sandstones with intercalated mudstones, Fig. 1. (a) Location of the study area and main geological units siltstones and conglomerates. This formation includes of the western Mediterranean area and (b) location of the study distal alluvial and fluvial deposits with minor palustrine area in the eastern margin of the Ebro Basin (northeast Spain). and lacustrine intervals which yielded carophytes of Late Numbers indicate locations of the magnetostratigraphic sections Ypresian–Lutetian age (Rosell et al., 1966; Anado´n et al., or well-logs cited in the text: 1, Maians-Rubio´; 2, Castelfollit; 3, Santpedor. 1992). On top of La Salut Formation rests the informal stratigraphic unit of the Montserrat Conglomerates (Riba, 1975; Anado´n, 1978), which has been divided into nine alluvial sandstones and mudstones, which in turn grade units by Anado´n et al. (1985b) (Fig. 2c). The lowermost into the marine deposits of the Santa Maria Group (Fer- Montserrat Conglomerates include syntectonic unconfo- rer, 1971; Pallı´, 1972). This group represents the submar- rmities associated with folding in the basin margin (Ana- ine part of the Montserrat fan-delta system and comprises do´n, 1978; Anado´n et al., 1985a, 1986; Lo´pez-Blanco, three main Formations: the Collba`s, Igualada and Tossa 2002). These conglomerates grade basinward into distal formations (Fig. 2a, b). © 2011 The Authors 438 Basin Research © 2011 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Tectonic and climatic controls on Montserrat fan delta (a) Igualada Montserrat -N Artés Fm Cardona Fm WSW- Les Morelles -ENE S- Priabonian Uppermost marine deposits Tossa Fm CM Igualada Fm Bartonian Milany Composite Megasequence ? SJ Santa Maria Gr Collbás Fm Monserrat Conglomerates EL La Salut Fm Lutetian Pontils Gr El Cairat Fm Ypresian Mediona Fm Orpí Fm CB WE Thanetian Mediona Fm 1 2 3 4 5 6 7 8 9 10 11 12 13 (b) Castellbell i El Vilar Rellinars BP-1101 N Monistrol Vacarisses CM CM de Montserrat N-II a BP-1213 BV-121 A-2 SJ N-II a EL El Bruc CB Collbató 0 5 km La Salut Fm Quaternary Conformity + lateral facies change Village El Cairat