Long-Term Development and Current Status of the Barcelona Continental Shelf: a Source-To-Sink Approach
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ARTICLE IN PRESS Continental Shelf Research 27 (2007) 1779–1800 www.elsevier.com/locate/csr Long-term development and current status of the Barcelona continental shelf: A source-to-sink approach C. Liquetea, M. Canalsa,Ã, G. Lastrasa, D. Amblasa, R. Urgelesa, B. De Mola, M. De Batistb, J.E. Hughes-Clarkec aGRC Geocie`ncies Marines, Dept. d’Estratigrafia, Paleontologia i Geocie`ncies Marines, Facultat de Geologia, Universitat de Barcelona, E-08028 Barcelona, Spain bRenard Centre of Marine Geology, Universiteit Gent, Krijgslaan 281 S8, B-9000 Gent, Belgium cOcean Mapping Group, Department of Geodesy and Geomatics Engineering, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5A3 Received 18 July 2006; received in revised form 16 January 2007; accepted 28 February 2007 Available online 19 March 2007 Abstract The Barcelona continental shelf, off the city of Barcelona (NE Spain), is a relatively narrow canyon-bounded shelf in the northwestern Mediterranean Sea. Three medium-size rivers (Tordera, Beso´s and Llobregat) and several ephemeral rivulets flow into this margin. Two main domains have been recognized in the Barcelona shelf: (i) a modern, river-influenced area, and (ii) a relict, sediment depleted area, both affected by a variety of human impacts. A detailed geomorphologic study based on multibeam bathymetry and backscatter data, high resolution seismic profiles, and surface sediment samples allowed mapping and interpreting the main distinctive seafloor features on the Barcelona shelf. Modern sedimentary features reveal that the Llobregat River is the main sediment source of the Barcelona prodeltaic shelf. High-discharge fluvial events result in the formation of suspended sediment plumes and sediment waves on the shelf floor. Relict (late Pleistocene–Holocene) sedimentary features reflect that an important shift occurred in the seashore direction between MIS 4 and MIS 2, and that recent neotectonic reactivation has created a set of seafloor faults. The Barcelona inner and middle shelf is severely impacted by anthropogenic activities such as the enlargement works of the Port of Barcelona, sewage pipes, dredging, anchoring and trawling. r 2007 Elsevier Ltd. All rights reserved. Keywords: Shelf sedimentary environments; Source-to-sink; Prodelta; Multibeam; River basins; Seismic reflection; Neotectonics; Sediment waves; Late Quaternary sea level change; Human impacts; Northwestern Mediterranean Sea; Barcelona continental shelf; Spain 1. Introduction the continental margins. Source-to-sink studies analyze the complex interplay of processes within Most of the processes that shape land–ocean entire sediment-dispersal systems at different tem- systems leave their imprint in the sediment record of poral and spatial scales in order to understand the evolution of continental margins and its associated ÃCorresponding author. Tel.: +34 93 402 13 60; morphology (Driscoll and Nittrouer, 1999). The fax: +34 93 402 13 40. final aim of a source-to-sink analysis is to develop a E-mail address: [email protected] (M. Canals). quantitative approach to a given margin dispersal 0278-4343/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.csr.2007.02.007 ARTICLE IN PRESS 1780 C. Liquete et al. / Continental Shelf Research 27 (2007) 1779–1800 system, so that its response to natural or human with modern and relict sedimentary features, and perturbations can be predictable. with anthropogenic impacts. The first requirement of a source-to-sink study is to compile a high-quality landscape and seascape 2. General setting data set so that sediment erosion, transport and accumulation can be analyzed as a whole. High The Catalan margin extends along 300 km from resolution swath bathymetry represented a funda- the Ebro Delta to the Cap of Creus peninsula mental breakthrough for source-to-sink studies. The (Fig. 1). It forms the western border of the northern first swath bathymetry map from a continental Valencia Trough, a 400 Â 300 km mid-Miocene margin in the western Mediterranean Sea was the extensional basin in the western Mediterranean eastern Gulf of Lions multibeam map published by Sea. The Catalan margin is underlain by a SW–NE Orsolini et al. (1981–1982). During the following oriented horst-and-graben structure (Maillard et al., years, researchers from France, Italy and Spain 1992; Roca et al., 1999). Following the Miocene added new contributions (e.g. Berne´et al., 2004; extension, the Messinian closure of the strait Canals et al., 2004b, Marani et al., 2004)toa between north Africa and the south of Iberia led general swath mapping effort that led to the recent to an event that had a dramatic influence on the multibeam bathymetry compilation of the entire shaping of Mediterranean margins: the salinity western Mediterranean Sea (Medimap Group, crisis and drying up of the basin between 5.96 and 2005). However, continental shelves were mostly 5.33 million years ago (Duggen et al., 2003). During left out of such a mapping effort mainly because of the initial stage of the Messinian event, the large fall two reasons: (i) the time consuming character of in water level caused extreme erosion and incision swath mapping in shallow areas due to much that led to the development of large canyon systems. smaller swath widths and (ii) the broadness of some The physiography and the seascape of the modern of the continental shelves in the region, such as the Catalan margin are, therefore, strongly determined Gulf of Lions (70 km) and the Ebro (50 km) by the Messinian crisis (Amblas et al., 2004). The shelves. Still today only relatively small areas of the development of the modern terrigenous shelf and continental shelves in the western Mediterranean margin started shortly after the Pliocene transgres- have been swath mapped and the results published. sion, being ultimately reshaped by Quaternary In this paper we present the results achieved so far glacioeustatic sea level changes (Bartrina et al., on the Barcelona continental shelf where a compre- 1992). hensive data set made of multibeam data, high The largest submarine canyons in the Catalan resolution seismic reflection profiles, sediment sam- margin, which clearly have Messinian ancestors, ples and geographic and hydrological data is now segment the margin in different sections. The available. First, the sediment sources and the main continental shelf is narrowest (3 km) where deeply distinctive geomorphological features are presented, incised by submarine canyon heads, and reaches its and then the origin of these features and the modern maximum width off the Ebro Delta (50 km). The seafloor zonation is discussed, regarding aspects Barcelona margin and shelf, off the city of such as fluvial sedimentation, neotectonics, sea level Barcelona, occupy the central stretch of the section changes, and human impacts. bounded by the Foix Canyon to the south and the This paper aims at providing an accurate Blanes Canyon to the north, from 41180Nto morphological description of the Barcelona con- 411320N(Fig. 1). The Barcelona continental shelf tinental shelf in the northwestern Mediterranean is 6–20 km wide with the shelf break at 110–120 m Sea following a source-to-sink perspective that links depth. Its average slope is 0.61 although it reaches fluvial inputs and physical oceanography processes up to 211 in the slope break off the Llobregat River to the development of the shelf morphosedimentary mouth and at the edge of some prominent sandy features. Mostly qualitative sedimentary analyses deposits observed to the north of the Beso´s River. have been developed at this stage due to the lack of The Barcelona shelf consists of an inner, middle and homogeneous quantitative data onshore and off- outer shelf separated by the 30–40 and the 80 m shore. The time fork considered in our study is the isobaths, respectively (ITGE, 1989). late Pleistocene–Holocene, when global sea level The Barcelona continental shelf is mainly fed by oscillations had a profound impact on continental sediment inputs from the Llobregat and Beso´s rivers shelf development. Therefore, our analysis deals (Fig. 1), mostly draining Neogene-Quaternary and ARTICLE IN PRESS C. Liquete et al. / Continental Shelf Research 27 (2007) 1779–1800 1781 1°30'E 2°0'E 2°30'E 8°W 4°W 0° 4°E 8°E 2504m Highest peak in each river basin N FRANCE Pyrenees Dams 46° (letters after Table 1) CC N Cities mentioned in ED 42° the text VT SPAIN Barcelona continental N shelf 38° C ALGERIA D Northern Current Littoral drift 1 Tordera River 2 Sant Cebrià Rivulet Faults 3 Argentona Rivulet Canyon systems 4 Besós River 5 Llobregat River Shelf break E 6 Sant Perede Ribes Rivulet Montseny 1684m 1304m A B else|csr|1585 764m Coastal642m Ranges 1 alan Cat 2 Blanes F 3 -50 Masnou -200 C. -100 4 646m Barcelona Areny 5 s C. Besós C -1000 6 Morrá Berenguer Foix C. s C. a C. Profiles in Fig.4 4550000 4600000 4650000 41°0'N400000 41°30'N 450000 42°0'N Fig. 1. Physiographic and morphological setting of the study area. Blue lines and numbers illustrate the river courses, and bold white lines mark the watersheds limits. The yellow area illustrates the Barcelona continental shelf. VT: Valencia Trough. CC: Cap of Creus. ED: Ebro Delta. Faults after Bartrina et al. (1992). Map projection is UTM Zone 31N Datum WGS 1984. Both UTM and geographic coordinates are shown for ease of reference. ARTICLE IN PRESS 1782 C. Liquete et al. / Continental Shelf Research 27 (2007) 1779–1800 Paleogene calcareous rocks, respectively, and the the study area (Calafat, 1986), while the major Tordera River eroding a predominantly granitic storm wave-face is about 30 m depth (Sorribas et al., massif (SGC, 1992). The Llobregat river basin is the 1993). most regulated in the study area (Table 1). Other ephemeral rivulets or ‘‘rieras’’ draining granitic 3. Methodology and data set rocks and a soft Plio-Quaternary cover punctually add to sediment inputs, essentially during violent Swath bathymetry and associated backscatter data eastern storms with heavy rains that mostly occur in were acquired onboard the R/V Hespe´rides and the late summer and early fall, and are locally known as 12 m fishing inspection boat Arraix during the ‘‘llevantades’’ (Martı´n Vide, 1982).