Geologica Acta: an international earth science journal ISSN: 1695-6133 [email protected] Universitat de Barcelona España SANJUAN, J.; MARTÍN-CLOSAS, C.; SERRA-KIEL, J.; GALLARDO, H. Stratigraphy and biostratigraphy (charophytes) of the marine-terrestrial transition in the Upper Eocene of the NE Ebro Basin (Catalonia, Spain) Geologica Acta: an international earth science journal, vol. 10, núm. 1, 2012, pp. 1-13 Universitat de Barcelona Barcelona, España Available in: http://www.redalyc.org/articulo.oa?id=50522811002 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Geologica Acta, Vol.10, Nº 1, March 2012, 1-13 DOI: 10.1344/105.000001708 Available online at www.geologica-acta.com 1 1 2 2 3 Stratigraphy and biostratigraphy (charophytes) of the 3 4 4 5 marine-terrestrial transition in the Upper Eocene of the 5 6 6 7 NE Ebro Basin (Catalonia, Spain) 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 J. SANJUAN C. MARTÍN-CLOSAS J. SERRA-KIEL H. GALLARDO 15 16 16 17 17 18 18 19 Departament d’Estratigrafia, Paleontologia i Geociències Marines, Facultat de Geologia, Universitat de Barcelona (UB) 19 20 Martí i Franqués s/n, 08028 Barcelona, Catalonia, Spain 20 21 21 22 22 23 23 24 24 25 25 ABS TRACT 26 26 27 The onset of endorheic sedimentation in the Ebro Basin is a prominent feature of the basin’s evolution and has 27 28 recently been characterized as a rapid event occurring in the Early Priabonian. In the north-eastern part of the 28 29 basin this event coincides with the deposition of the Artés Formation (Fm.), mainly built up by red beds of alluvial 29 30 origin. The marine-continental boundary has been poorly studied up to now in the so-called Lluçanès area, and 30 31 what was previously thought to be the base of the Artés Fm. is actually a transitional unit, which we define as the 31 32 Sant Boi Formation, which covers the underlying marine Milany Depositional Sequence and passes laterally to the 32 33 Terminal Complex, extending over 15km along the eastern margin of the Ebro Basin. The Sant Boi Fm. is formed 33 34 by up to 15-20m of alternating siltstones and lutite, grading upwards to brackish and lacustrine marls and lignite, 34 35 and represents deposition in a brackish to freshwater floodplain. It is characterized biostratigraphically by the 35 36 fossil charophyte assemblage Harrisichara lineata, Harrisichara vasiformis-tuberculata and Nodosochara jorbae, 36 37 from the middle part of the Priabonian. In contrast, the overlying red beds of the Artés Fm. are characterized by 37 38 assemblages containing Harrisichara tuberculata, Nodosochara jorbae and Lychnothamnus longus from the Late 38 39 Priabonian. These results are largely consistent with recent magnetostratigraphic studies performed south of the 39 40 studied area, and have enabled us to refine the stratigraphy of the marine-continental transition in the north-eastern 40 41 Ebro Basin. 41 42 42 43 KEYWORDS Charophyta. Biostratigraphy. Ebro Basin. Eocene. Oligocene. 43 44 44 45 45 46 46 47 47 48 INTRODUCTION boundary has traditionally been located at the top of 48 49 the deltaic sandstone with reefal limestones of the Sant 49 50 The continentalization of the Ebro Basin has been Martí Xic Formation (Fm.) (Reguant, 1967). However, 50 51 a matter of debate in recent years. This event has new geological mapping, along with stratigraphic and 51 52 ARTICLEbeen described IN as PRESSoccurring over a relatively short biostratigraphic analyses of an overlying and previously 52 ARTICLE IN PRESS 53 time, affecting the entire basin at the beginning of poorly known transitional unit, called here the Sant 53 54 the Priabonian (Costa et al., 2010). In the north- Boi Fm., led us to revisit previous assumptions on the 54 55 easternmost part of the basin (Lluçanès area) the continentalization of this part of the Ebro Basin. 55 1 J . S A N J U A N e t a l . Biostratigraphy of the marine-terrestrial transition (Ebro Basin) 1 Not only is the lithostratigraphy of the study area the lowermost sedimentary sequences being incorporated 1 2 confusing, but the dating of the last marine deposits into the successive thrust sheets (Puigdefàbregas et al., 2 3 of the eastern Ebro Basin has also been controversial. 1992). 3 4 Magnetostratigraphy studies by Burbank et al. (1992) 4 5 and Taberner et al. (1999) assigned the uppermost marine The south Pyrenean foreland basin infill includes 5 6 and transitional rocks to Upper Bartonian and Lower marine and continental rocks that range from the Upper 6 7 Priabonian (chron C17n). Biostratigraphic studies based Cretaceous to the Upper Eocene. Later, exclusively non- 7 8 on foraminifera (Serra-Kiel et al., 2003) also assigned marine facies were recorded. During most of the Palaeogene 8 9 the uppermost marine and transitional rocks to the Upper the basin formed an Atlantic gulf. This situation lasted 9 10 Bartonian-Lower Priabonian (Shallow Benthic Zones until the Late Eocene, when uplift in the western Pyrenees 10 11 18 and SBZ 19?). However, recent studies on calcareous led to the final isolation from the Atlantic Ocean and the 11 12 nannofossils have revealed that only Priabonian marine definitive onset of endorheic sedimentation in the Ebro 12 13 rocks occur in this upper part of the stratigraphic record Basin (Puigdefàbregas et al., 1992). 13 14 (Zones NP18 and NP19-20) which were correlated with 14 15 chron C16/16n.2n (Cascella and Dinarès-Turell, 2009). The study area is located in the north-eastern part 15 16 Biostratigraphic studies of continental fossils, mainly of the Ebro Basin (Fig. 1). The Palaeogene sedimentary 16 17 charophytes and vertebrate remains, from the central part of succession in this part of the basin is divided into nine 17 18 the eastern Ebro Basin (Igualada-Jorba area) have attributed depositional sequences related to the emplacement of 18 19 the youngest marine units to the Upper Eocene (Anadón et the south Pyrenean thrust sheets and linked to two major 19 20 al., 1987, 1992; Choi, 1989; Feist et al., 1994). Furthermore, relative sea level rises, in the Ilerdian (Early Eocene) and 20 21 palaeomagnetic dating has recently been performed in this Bartonian (Middle-Late Eocene) (Puigdefàbregas et al., 21 22 area, attributing the youngest marine rocks to chron C16 1986). According to these authors, thrust cyclicity and 22 23 (Costa et al., 2010). In contrast, biostratigraphic markers evaporite events allow differentiation of the basin-fill into 23 24 from the marine-continental transition in the northeastern three main depositional cycles. The first cycle includes the 24 25 part of the basin have been poorly studied up to now. In the Cadí, Corones, Armàncies and Campdevànol sedimentary 25 26 Lluçanès area fossil charophytes have only been reported sequences and coincides with the submarine emplacement 26 27 by Colom et al. (1970), who found the species Harrisichara of the upper thrust sheets. The second sedimentary cycle 27 28 lineata in the Sant Boi Fm. includes the Bellmunt and Milany sequences (Lutetian 28 29 and Bartonian) and coincides with the development 29 30 Resampling the Lluçanès area has enabled us to document of an antiformal stack of thrust sheets in the central 30 31 a rich charophyte flora of biostratigraphic interest, which Pyrenees. This structure induced deltaic progradation 31 32 sheds new light on the dating of the continentalization of 32 33 the Ebro Basin in this area. The new biostratigraphic data 33 34 are significant in comparison to other margins of the Ebro 34 35 Basin, where an equivalent stratigraphic situation occurs 35 36 36 i.e. in the Riu Boix Fm., south of Igualada (Ramírez et al., N 37 Central and Eastern Pyrenees Perpinyà 37 1991) and the Campodarbe Fm., Huesca province (Canudo Jaca 38 et al., 1988). The whole of these data will allow us to test Andorra 38 39 the hypothesis of a rapid continentalization of the Ebro 39 Huesca Tremp Ripoll 40 Basin in the Priabonian from a biostratigraphic point of 40 Fig. 3 Girona 41 view, as drawn from magnetostratigraphic data. Vic 41 42 Zaragoza 42 43 Lleida 43 44 Ebro Foreland Basin 44 GEOLOGICAL SETTING Barcelona 45 Catalan Coastal Ranges 45 46 The Ebro Basin is the triangular-shaped southern Tarragona Mediterranean Sea 46 47 foreland basin of the Pyrenean Range (Fig. 1). The origin IBERIAN 47 48 of the Ebro Basin is related to flexural subsidence due to the PENINSULA 48 49 collision between the Eurasian and Iberian plates from the 0 50 100 Km 49 50 Late Cretaceous to the Miocene. Maximum compression Neogene-Quaternary Mesozoic-Paleocene thrust 50 Autochtonous Eocene-Miocene Basement blind thrust 51 occurred during the Palaeocene and Eocene and resulted in Ebro Foreland Basin 51 52 ARTICLEthe superposition IN of aPRESS number of thrust sheets in the south Allochtonous Eocene-Oligocene normal fault 52 ARTICLE IN PRESS 53 Pyrenean central zone. The main structures display an E-W 53 54 FIGURE 1 Geological sketch of the eastern part of the Ebro Foreland 54 orientation and the deformation progressed south- and Basin showing the location of the area studied (modified from Vergés 55 westwards in parallel with the basin depositional centres, et al., 1998). 55 Geologica Acta, 10(1), 1-13 (2012) 2 DOI: 10.1344/105.000001708 J . S A N J U A N e t a l . Biostratigraphy of the marine-terrestrial transition (Ebro Basin) 1 and contemporaneous migration of the basin depocentre Solsona depositional sequences, suggests that the Terminal 1 2 southwards.