Transgressive–regressive cycles and Jurassic palaeogeography of northeast Iberia

Sedimentary Geology 162 (2003) 239 – 271 www.elsevier.com/locate/sedgeo

Transgressive–regressive cycles and Jurassic palaeogeography of northeast Iberia M. Aurell a,*, S. Robles b, B. Ba´denas a, I. Rosales b, S. Quesada b, G. Mele´ndez a, J.C. Garcı´a-Ramos c b

a Dpto. Ciencias de la Tierra, Univ. Zaragoza, 50009 Zaragoza, Spain Dpto. Estratigrafı´a y Paleontologı´a, Univ. Pais Vasco, 48080 Bilbao, Spain c Dpto. Geologı´a (Estratigrafı´a), Univ. Oviedo, 33005 Oviedo, Spain

Received 26 June 2002; accepted 25 April 2003

Abstract A correlation and sequence stratigraphy study of Jurassic successions has been carried out in the main sedimentary basins of northeast Iberia, i.e., Asturias, Basque-Cantabrian, and Iberian basins, based on the identification of transgressive – regressive cycles. The development and palaeogeographic evolution of the epicontinental carbonate platforms of northeast Iberia were largely controlled by major tectonic activity at three main intervals, at the beginning of the Jurassic, in the Lower – Middle Jurassic transition, and during the uppermost Jurassic, respectively. During Early Jurassic times, northeast Iberia was the site of a single and large carbonate ramp opened to the north. This carbonate ramp suffered a progressive drowning, evolving from an inner to hemipelagic ramp systems, with the local development of suboxic environments in the deepest areas located to the north. During the Middle Jurassic, different open carbonate platforms were formed including the development of swells in intermediate areas. During the Upper Jurassic, the outer ramp areas were progressively moving to the east Iberian Basin, and the ammonite faunas showing a markedly Tethyan affinity thereafter. Three first order T – R cycles bounded by major discontinuities associated with significant time gaps are identified. They extend respectively from the latest Rhaetian to the Early Aalenian, from the Middle Aalenian to the Early Oxfordian and from the Early Oxfordian to the Late Berriasian. Major transgressive peaks occurred at the Middle Toarcian (Bifrons Zone), at the Late Bajocian (upper Niortense and Garantiana zones) and at the mid-Kimmeridgian (Divisum Zone). Each of the first order cycles includes four second-order T – R cycles. Cycles 1.1 – 1.4 are identified in the northern basins. Cycles 2.1 – 2.4 display some differences in age of transgressive peaks from one basin to another. Cycles 3.1 – 3.4 are mainly identified in the Iberian Basin. The correlation with other separated Boreal and Thethysian basins demonstrates that the number and age of T – R cycles varies from one basin to another and are mainly controlled by the local or regional tectonic development. The transgressive peaks may reflect episodes of eustatic rise during the Jurassic. However, their different age from one basin to another is explained by different subsidence evolution. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Jurassic; Sequence stratigraphy; Eustasy; Regional tectonics; Iberia

* Corresponding author. Fax: +34-976-761088. E-mail address: [email protected] (M. Aurell). 0037-0738/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0037-0738(03)00154-4

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1. Introduction During the Jurassic, a large part of the central and western Iberian Plate formed an uplifted massif (the so-called Iberian Massif). Intracratonic basins predominantly filled with marine carbonate deposits occupied the surrounding areas. Those areas located to the northeast of the Iberian Plate include the Asturian, Basque-Cantabrian, Pyrennean and Iberian basins (Fig. 1). The Basque-Cantabrian Basin (BCB) and Asturias Basin (AB) formed a part of a large epicontinental sea, bounded by the Iberian Massif to the southwest and by the Armorican Massif to the north. These northern basins were connected to the southeast with the Iberian Basin (IB). Palaeontological data show a dominant Boreal affinity during Early and early-Middle Jurassic in this platform, whereas Tethyan affinity is more notable during the late-Middle and Late Jurassic (e.g., Atrops and Mele´ndez, 1985; Braga et al., 1988; Elmi et al., 1989; Sandoval et al., 2001). From the Late Tithonian onwards, tectonic grabens filled by continental sediments locally developed in the BCB and in the IB (Mas et al., 1993; Pujalte et al., 1996; Robles et al., 1996; Herna´ndez et al., 1999; Salas et al., 2001).

Jurassic deposits crop out widely across the northeast Iberian Peninsula (Fig. 2). Continuous field exposures supplemented with the analysis of well-log data from intervening areas (e.g., Morillo and Mele´ndez, 1979; Fontana et al., 1994) allow a detailed reconstruction of facies and thickness variations of units (Aurell et al., 2002). Jurassic rocks in northeast Iberia are bounded by important discontinuities of regional extent. These discontinuities are linked to major phases of fault reactivation (Salas and Casas, 1993; Quesada and Robles, 1995; Herna´ndez et al., 1999; Salas et al., 2001). Such tectonic activity at the Triassic – Jurassic transition was related to extensional movements leading to the westwards extension of Tethys. Extensional tectonics during the latest Jurassic – Early Cretaceous was additionally linked to the opening of Central Atlantic and the Bay of Biscay (Salas et al., 2001). Reactivation of normal faults in the basement-controlled Jurassic sedimentation in northeastern Iberia, and differential movements produced variations in both thickness and facies over space and time (e.g., Quesada et al., 1993; Salas and Casas, 1993). Additionally, widespread transgressive and regressive events recorded across the basins suggest a certain influence of regional or global sea-level

Fig. 1. Palaeogeographic reconstruction of the Iberian Plate during the Toarcian, indicating the different sedimentary basins of East Iberia. Modified from Vera (1998).

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Fig. 2. Distribution of the Jurassic outcrops in Northeast Spain, showing the location of reference key logs in Fig. 3 along the dotted line.

changes on the observed stratigraphic discontinuities and facies distribution. The stratigraphy and facies distribution of successive Jurassic sequences observed in the different northeastern basins of Iberia have been recently summarised by Aurell et al. (2002). The purpose of this paper is to present the long-term (first and second order) transgressive –regressive cycles recognised in the referred northeastern Iberian basins. Additionally, a set of palaeogeographic maps showing the Jurassic evolution of epicontinental carbonate platforms of northeast Iberia is presented. This palaeogeographic and sequence stratigraphy synthesis should supply basic information for further understanding of the different factors controlling the evolution of the studied northeastern Iberian basins during Jurassic times. This work also supplies further information on the origin and extension of the transgressive –regressive

cycles reported from sedimentary basins of other western Europe areas (Hardenbol et al., 1998; De Gracianski et al., 1998; Jacquin et al., 1998).

2. Jurassic transgressive – regressive (T –R) cycles of northeast Iberia The analysis of facies distribution and the presence of widespread discontinuities across platform areas have led to recognise of a series of first and secondorder sequences in the northeastern Iberian basins. Facies distribution in these sequences reveals the existence of a lower deepening interval, followed by a shallowing upper interval (e.g., Giner, 1980; Aurell and Mele´ndez, 1993; Quesada and Robles, 1995; Ferna´ndez-Lo´pez, 1997; Aurell et al., 2000, 2002). These two intervals are separated by a transgressive

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Fig. 3. Stratigraphy, facies distribution and T – R (transgressive – regressive) cycles of the Jurassic of northeast Iberia (see Fig. 2 for location of the transect).

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Fig. 3 (continued).

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peak, which is indicated by the maximum extension and development of the open platform facies across the studied basins. Most of the boundaries of the distinguished long-term sequences display associated stratigraphic gaps of variable extent, followed by transgressive surfaces. These gaps represent periods of no sedimentation, and sometimes erosion, linked to the uppermost regressive part of the sequences. The transgressive surfaces at the onset of the sequences are related to widespread flooding events following episodes of shallowing. The distribution of the transgressive – regressive cycles identified in the northeastern Iberia basins and the main facies patterns are shown across a northwest to southeast, more than 600 km long transect (Fig. 3). Following the terminology of Jacquin and de Gracianski (1998a,b), the first- and second-order cycles identified in northeast Iberia are refereed as major T – R (transgressive – regressive) cycles and T – R facies cycles, respectively. The duration of three first-order major T – R cycles distinguished in northeast Iberia is 28, 20 and 19 My, respectively (time scale from Hardenbol et al., 1998). The boundaries of these cycles are associated to widespread stratigraphic gaps, which extent over entire basins (Fig. 3). These gaps represent long periods of no sedimentation linked to the uppermost regressive part of the sequences, leading to local emersion of the open platform areas. The duration of most of the second-order T– R facies cycles is between 4 and 6 My. The length of the associated stratigraphic gaps of the second-order cycles is normally less than one ammonite biozone and the evidences of emersion of open platform areas are local and scarce. In accord with the model proposed by Hallam (2001), the sedimentary evolution of most of the second-order cycles reveals the existence of intervals of relative sea-level rise, which are generally followed by intervals of comparative stillstand. 2.1. Major T –R cycles of northeast Iberia Three major T – R cycles bounded by widespread and significant time gaps are identified across the sedimentary basins of northeast Iberia (Fig. 3). They extend from the latest Rhaetian to the Early Aalenian, from the Middle Aalenian to the Early Oxfordian and from the Early Oxfordian to the Late Berriasian. The

transgression peaks of these cycles are major flooding events that covered wide areas. These took place at the early-Middle Toarcian (Bifrons Zone), Late Bajocian (upper Niortense Zone in IB, Garantiana Zone in BCB) and late Early Kimmeridgian (Divisum Zone), respectively. 2.1.1. Lower Jurassic major T – R cycle Tectonic extension at the Triassic –Jurassic transition caused the break-up and local erosion of the extensive epicontinental platform formed along the northeastern margin of Iberia at the end of Triassic times (Rhaetian). This locally produced a basal Jurassic angular unconformity, such as seen in Mansilla, near Ricla, Garraf, Cedrillas or Desert de las Palmes (see Fig. 2 for location). In all these areas, the basal Jurassic unit may lie unconformably over older Triassic or, even, Palaeozoic rocks (Giner, 1980; Robles et al., 1989; San Roma´n and Aurell, 1992). Over large areas of the basin, this basal discontinuity represents a sharp transition between the shallow platform carbonates of the latest Triassic, to the evaporites, collapse breccias and massive dolomites developed at the onset of the Lower Jurassic Cycle (Fig. 3). The age of this lower discontinuity cannot be precisely established. The Rhaetian– Hettangian boundary has been placed above this unconformity on the basis of fossil bivalve and palynomorph associations (Go´mez and Goy, 1998). Therefore, the observed sharp facies change (from shallow carbonates to evaporites and associated facies) reveals the existence of a regressive event at the end of the Triassic. The transgressive interval of the Lower Jurassic Cycle (from latest Rhaetian to early-Middle Toarcian) involved the progressive deepening of the platform, from sabkha environments to a hemipelagic ramp system with local development of suboxic environments in the northern basins. This transgression is indicated by the progressive retrogradation (from north to south) of the mid-outer ramp deposits over the inner ramp facies (Fig. 3). Major flooding of the platform at the Lower – Middle Toarcian transition (Serpentinus and Bifrons zones) involved the larger extension of the open platform areas over the northeast Iberian basins (see Fig. 4). Following the transgressive peak at the Bifrons Zone, the progressive shallowing of the open platform facies during Late Toarcian – Early Aalenian times indicates a wide-

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Fig. 4. Palaeogeography of northeast Iberia during Early Jurassic times (Sinemurian to Toarcian).

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spread regressive episode. The regressive peak of the cycle is associated to an intra-Aalenian stratigraphic gap of variable extent across the Iberian basins (Fig. 3). 2.1.2. Middle Jurassic major T– R cycle The important discontinuity that roughly coincides with the Lower – Middle Jurassic boundary has been related to the reactivation of normal faults. This tectonic activity resulted in significant thickness variation (differential subsidence) over the studied basins during the Late Toarcian and Aalenian. Volcanic and pyroclastic rocks present in the southeastern IB has been related to large NW –SE faults reactivated at the Early – Middle Jurassic transition (Go´mez, 1979; Ortı´ and Vaquer, 1980; see Caudiel volcanic belt and Alcublas piroclastic belt in Figs. 4B and 5A). The lower discontinuity of this cycle is diachronous across the northeastern Iberian basins (Fig. 3). In the BCB and in the AB, this boundary is represented by a hiatus affecting the uppermost Toarcian Aalensis Zone and the base of the Aalenian Opalinum Zone (Ferna´ndez-Lo´pez and Sua´rez-Vega, 1980; Ferna´ndezLo´pez et al., 1988a; Pujalte et al., 1988; Canales et al., 1993). In central and southern areas of the IB, condensed levels with common stratigraphic gaps mark the Toarcian –Aalenian transition. The Upper Toarcian (Pseudoradiosa and Aalensis zones) and the Lower – Middle Aalenian (Opalinum and Murchisonae zones) levels are partly or completely absent (Goy and Ureta, 1990; Ferna´ndez-Lo´pez and Go´mez, 1990a,b; Sandoval et al., 2001). Ferna´ndez-Lo´pez and Go´mez (1990b) have reported evidences for the local emersion of the open platform areas of the central IB during the Aalenian (e.g., San Blas area, see Fig. 2 for location). A generalised hiatus across the open platform areas of the IB is found in the lower part of the Murchisonae Zone (Ferna´ndez-Lo´pez, 1997). During the Aalenian – Early Bajocian, a progressive onlap of the middle-outer platform facies is observed over certain marginal areas of the IB (see Catalonian Coastal Ranges in Fig. 3; Ferna´ndezLo´pez et al., 1998b). The major flooding of the platform took place at the Late Bajocian and involves the widespread deposit of marls and limestones with ammonites at the upper Niortense Zone in the IB and at the Garantiana Zone in the BCB. This flooding event has been documented by means of taphonomic

analysis (advanced deepening taphorrecods in Ferna´ndez-Lo´pez, 1997). The regressive trend of the cycle is indicated by the progressive decrease of the extension of the open platform areas and by the local progradation of oolitic and siliciclastic facies during the Bathonian and Callovian (Fig. 3). 2.1.3. Upper Jurassic major T – R cycle The lower boundary of the cycle is marked by an important sedimentary discontinuity at the Middle – Upper Jurassic boundary across the northeastern basins of Iberia. This transition has been the subject of numerous detailed studies in the open platform areas of the IB, which have demonstrated the stratigraphic gap to be of variable range (e.g., Bulard et al., 1974; Mele´ndez et al., 1983, 1990; Aurell et al., 1994a). In the open platform areas, the gap comprises at least the uppermost Callovian and lowermost Oxfordian (i.e., Lamberti and Mariae zones). Ramajo and Aurell (1997) have described emersion (paleokarst) surfaces developed above the Upper Callovian succession in the Ricla locality. In some shallow platform areas (e.g., Ejulve, Cedrillas, Obo´n, see Fig. 2 for location), a sharp erosive surface is found above the Bathonian oolitic grainstones and the Callovian and the Lower and Lower –Middle Oxfordian is completely absent (Bulard, 1972; Ramajo et al., 1999; Aurell et al., 2002). A stratigraphic gap involving a remarkable facies change and spanning the Late Callovian to the early-Middle Oxfordian is also present in the eastern BCB (Bulard et al., 1979). This unconformity has been related to an important regressive event at the end of the Callovian, which would have been responsible for widespread shallowing (and local emersion) of the open platform areas and the recorded stratigraphic gap at the Callovian – Oxfordian boundary (Aurell et al., 1994a). The onset of the Upper Jurassic Cycle is marked by the first evidence of marine flooding across open platform areas provided by the presence of ammonites of the lower Cordatum Zone. In the AB, a tectonic episode around the Middle – Upper Jurassic transition involved the doming, uplift and subaerial exposure of the entire basin. This led to the intense erosion of the underlying Jurassic deposits, followed by the development of a continental to restricted coastal basin with an irregular horst and graben relief (Fig. 3; Aurell et al., 2002).

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Fig. 5. Palaeogeography of northeast Iberia during Middle Jurassic times.

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At the end of Jurassic times, a significant extensional tectonic activity is recorded in northeastern Iberia. This tectonic activity has been related to the ‘‘Bay of Biscay early rifting episode’’ in the BCB (from Late Tithonian to Barremian; Martı´n-Chivelet et al., 2002) and to the onset of the ‘‘second rifting cycle’’ in the IB (from latest Oxfordian to Albian; Salas and Casas, 1993; Salas et al., 2001). Latest Jurassic tectonic activity involved uplift and erosion of the marine Jurassic units and the local development of continental basins in the western BCB (Aguilar and Cires basins; Herna´ndez et al., 1999; Robles et al., 1996; Fig. 3) and in the northwest IB (Cameros Basin; Platt, 1990; Platt and Pujalte, 1994; Fig. 3). The origin of these basins was controlled by the activity of ancient basement faults and other related synsedimentary faults (Alonso and Mas, 1993; Mas et al., 1993; Herna´ndez et al., 1999; Martı´n-Chivelet et al., 2002). These data suggest that the onset of the rifting may have initiated earlier westward, in the AB (from the Kimmeridgian in the Lastres – Ribadesella Basin; Sua´rez-Vega, 1974; Olo´riz et al., 1988; Aurell et al., 2002), and propagated progressively to the east, to the BCB (from Late Tithonian to Barremian in the Cires and Aguilar basins; Herna´ndez et al., 1999; Fig. 3). During Kimmeridgian, the central and eastern IB was reshaped into subsident troughs and swells, resulting in marked differential subsident and uplifted areas (Salas, 1989; Ba´denas and Aurell, 2001). The thickest development of the Kimmeridgian – Berriasian interval is recorded in the easternmost IB (i.e., Maestrat Basin, see Fig. 6C for location). A widespread discontinuity is recorded above the lowermost Cretaceous deposits (mid-Late Berriasian) which are therefore included within the Upper Jurassic Cycle. A stratigraphic gap of variable range (maximum from Late Berriasian to earliest Barremian) that increases towards the marginal (western) areas of the IB is associated to this unconformity (Salas, 1989; Aurell and Mele´ndez, 1993; Salas and Casas, 1993; Aurell et al., 1994b). The sedimentary evolution of the Upper Jurassic Cycle has been documented from the analysis of the carbonate platforms developed in the IB (Fig. 3). The lower transgressive interval is Oxfordian– Early Kimmeridgian in age. This transgression involved the setting of open platform environments across large areas of the IB. The peak transgression of this cycle

occurred at the end of the Early Kimmeridgian (Divisum Zone), and involved the widespread development of condensed sections in the rich-ammonite successions found in open platform areas (Atrops and Mele´ndez, 1985; Aurell and Mele´ndez, 1993; see Calanda area in Fig. 3). The progressive offlap and progradation (from northwest to southeast, see Figs. 3 and 6) of the Upper Kimmeridgian –Berriasian shallow platform facies observed in the marginal areas of the IB indicates the regressive trend in the upper part of this cycle. 2.2. T – R facies cycles of northeastern Iberia Second-order T – R facies cycles have been identified across the sedimentary basins of northeast Iberia. Higher-order discontinuities linked to significant transgressive events found in some of these cycles have been also indicated in Fig. 3. Four T –R cycle are recognised in the Lower Jurassic of northern Iberia (AB, BCB), whereas only two cycles are identified in the IB. In the Middle Jurassic, four T – R cycles are also recognised. These cycles show a general good correlation on the age of the boundaries but there are small discrepancies on the age of two of the transgressive peaks. In the Upper Jurassic, four T – R cycles have been identified in the carbonate platforms developed in the central and eastern part of the IB. 2.2.1. Lower Jurassic T– R facies cycles Four T – R facies cycles have been identified and dated by ammonites in the Lower Jurassic of the BCB and AB (see cycles 1.1 to 1.4 in Fig. 3 and Table 1, and references given in Table 1 for more detailed information). In the IB, cycles 1.1, 1.2 and 1.3 are not particularly differentiated and correspond to a single T – R facies cycle, which have a long-term transgressive interval up to a maximum transgressive peak at the earliest Late Pliensbachian (lower Stokesi Zone). Higher-order transgressive events at the Pliensbachian –Toarcian have been indicated in Fig. 3. The sedimentary evolution of cycle 1.1 (uppermost Rhaetian to Lower Sinemurian) has been characterised in the more open platform domains located in the BCB and AB. This cycle is transgressive up to the mid-Early Sinemurian, when middle ramp facies developed in the northwestern part of the BCB. These mid-ramp deposits consist of tabular to nodular lime-

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Fig. 6. Palaeogeography of northeast Iberia during Late Jurassic to Early Cretaceous (Berriasian) times.

stones (wackestone to packstone) including thin to thick intercalations of skeletal and oolitic grainstones, with storm-generated structures. The regressive trend at the end of the sequence is indicated in by the local development of a northward-prograding siliciclastic

sequence developed in a storm-dominated tidal flat (see Fig. 3, Reinosa area). These clastic deposits are bounded by a subaerial exposure surface. The clastic input has been related to the tectonic uplift of the southwestern marginal areas of the BCB (Robles and

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Table 1 Boundaries, tectonic events and main facies and thickness distribution of the Lower Jurassic T – R facies cycles of northeast Iberia Lower boundary/tectonics Cycle 1.1. Latest Rhaetian – Lower Sinemurian Tectonic extension at the Triassic – Jurassic transition (locally associated to volcanic rocks) caused the break-up of the Rhaetian carbonate platform, the erosion of uplifted blocks and the development of restricted, fault-controlled basins. The lower boundary is locally an angular unconformity. Local input of siliciclastic sand deposits in the southwestern BCB is related to tectonic uplift at the end of the cycle.

Cycle 1.2. Upper Sinemurian In AB and BCB, encrusted transgressive surface at the Obtusum Zone, locally (southwesternern BCB) developed above an uneven subaerial erosion surface. Not evident long-term discontinuity in the IB. Important differential subsidence in the BCB.

Cycle 1.3. Pliensbachian AB, BCB and northern IB: the lower boundary is a highly bioturbated, iron-encrusted surface (uppermost Sinemurian, upper Raricostatum Zone). Northern-central IB: other iron-encrusted surfaces developed in the mid-Jamesoni and upper Davoei zones. Maximum differential subsidence generated an arrangement of the BCB into swells and intraplatform troughs with black-shale horizons. Differential subsidence in the northern IB controls the local development of thick marly-dominated successions at the Early Pliensbachian.

Thickness and facies distribution General transgressive trend, from a coastal sabkha environment (Hettangian) to middle carbonate ramp (BCB, AB) or to shallow subtidal – intertidal flat environments (IB). Lower part (latest Rhaetian – Hettangian?) (30 – 400 m): (1) evaporites (mainly gypsum, and anhydrite in subsurface), with interbedded carbonates, (2) massive vuggy dolostones and dissolution-collapse breccias, locally alternating with stromatolitic limestones, (3) polymictic breccia, developed by the combined effect of synsedimentary block tectonics and early dissolution of interbedded evaporitic levels. Upper part (Lower Sinemurian?) (15 – 150 m): well-bedded limestones, organised in shallowing-upward sequences. They include from base to top oolitic and skeletal grainstones, mudstones or skeletal wackestones and limestones and dolostones with stromatolites. In northwestern BCB and AB (100 – 130 m), the sequence ends with tabular to nodular limestones (wackestone to packstone) including thin to thick intercalations of skeletal and oolitic grainstones, with storm-generated structures. Local siliciclastic input in the southwestern BCB on top of the cycle provides evidence for local regression.

BCB (5 – 90 m): open platform sedimentation: mudstone to bioclastic wackestone and marly limestones, with ammonites, belemnites, brachiopods, crinoids, gastropods and other benthic organisms. A shallowing event at the end of the sequence is indicated by the increase of the benthic fossil content. In southern areas, basal irregular siliciclastic unit (0 – 5 m), resulting from the filling of incised-valleys excavated on top of the early Sinemurian storm-dominated ramp. AB (30 m): alternating marls and nodular limestones, ordered in shallowing-upward cycles, with common tempestitic structures. IB (25 – 75 m): oolitic grainstones, skeletal mudstones – wackestones (brachiopods, benthic foraminifera, calcareous algae, bivalves, echinoderms) and algal-laminated facies organised in shallowing-upward sequences (shallow subtidal – intertidal flat environments).

Open platform environments dominate in AB, BCB and northern IB. BCB (30 – 130 m): Interbedded marls and skeletal nodular limestones (belemnites, brachiopods, bivalves, foraminifera, ostracods, echinoderms, ammonites). The unit includes four organic-matter-rich intervals (black shales) up to 15 m thick, earliest Pliensbachian (early-middle Jamesoni Zone), mid-Early Pliensbachian (Ibex to Early Davoei Zone) and Celebratum and Subnodosus subzones (Stockesi and Margaritatus zones, Early – Late Pliensbachian). Bioclastic limestones (packstone – grainstones) are dominant on top of the sequence. AB (ca. 40 m): well-bedded marls and limestones ordered in deepening or shallowing-upward cycles. Several black-shale episodes (Jamesoni, Ibex, Davoei zones). The main black-shale interval is Late Pliensbachian (Margaritatus Zone, up to 4 m). Northern IB: Lower Pliensbachian (15 – 50 m): well-bedded nodular fossiliferous limestones (brachiopods, bivalves, belemnites, gastropods, foraminifera, echinoderms and ammonites) with tempestites, interbedded with marly layers, organised in shallowing and deepening-upward sequences. Locally, bioclastic limestones with hermatypic coral and calcareous algae in the upper part. Northern and central IB: Upper Pliensbachian (15 – 50 m): a mostly marly unit followed by a bioclastic limestone unit (wackestone to packstone with brachiopods, bivalves, foraminifera, belemnites and echinoderms). The boundary between these two units generally within the Stokesi Zone or at the base of Margaritatus Zone. Southern IB (?20 – 100 m): peritidal carbonates and dolomites.

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Table 1 (continued) Lower boundary/tectonics Cycle 1.4. Toarcian AB, BCB, northern IB: widespread ferruginous encrusted surface (flooding surface), at the latest Pliensbachian (intra-Spinatum Zone). Central IB: virtually coincides with the Pliensbachian – Toarcian boundary. Important differential subsidence in the BCB and AB.

Thickness and facies distribution AB (30 – 40 m), BCB (25 – 125 m) and IB (10 – 70 m): Interbedded marls and micritic, fossiliferous limestones with ammonites, brachiopods, bivalves, belemnites and foraminifera. Succession of thinning and thickening upwards sedimentary sequences forming four deepening – shallowing higher order cycles at the Tenuicostatum, lower Serpentinus, upper Serpentinus – Variabilis, and Thouarsense – Aalanensis zones (Go´mez and Goy, 2000). Significant stratigraphic gap in the Thouarsense Zone in open platform areas. Maximum development of deepening-upward sequences at the upper Serpentinus – Bifrons zones. An up to 1-m-thick black-shale horizon at the upper part of the Tenuicostatum Zone in the BCB and AB. Catalonian Coastal Ranges: condensed iron-ooid limestones in the upper Lower Toarcian; 0 – 30 m of bioclastic wackestones in the Upper Toarcian – Lower Aalenian (Opalinum Zone). Local condensed oolitic ironstones and hardgrounds in the Upper Toarcian (Levesquei Subzone) in the BCB. Western-southern IB (?5 – 50 m): dolomitic or oolitic limestones.

Selected references: Goy et al. (1976), Go´mez (1979), Morillo and Mele´ndez (1979), Ferna´ndez-Lo´pez and Sua´rez-Vega (1980), Schaff (1986), Braga et al. (1985, 1988), Comas-Rengifo and Ye´benes (1988), Comas-Rengifo et al. (1988a,b, 1998, 1999), Valenzuela et al. (1989), Robles et al. (1989), Goy and Ureta (1990), San Roma´n and Aurell (1992), Quesada and Robles (1995), Borrego et al. (1996), Quesada et al. (1997), Ferna´ndez-Lo´pez et al. (1998a), Go´mez and Goy (1998, 2000), Bordonaba et al. (2000), Rosales et al. (2001), Bordonaba and Aurell (2001).

Quesada, 1995). A general transgressive evolution, from sabkha to shallow subtidal – intertidal flat environments, is observed in the IB, with no evidences of a long-term regressive trend at the Early –Late Sinemurian transition. Cycle 1.2 (Upper Sinemurian) is clearly recognised in AB and in the BCB, which starts with transgressive deposits from the Obtusum Zone (at the Early – Late Sinemurian transition). The increase of benthic fossils at the end of the sequence has been related to a shallowing event (Braga et al., 1988). Peritidal (algal laminated, micritic, oolitic) carbonates organised in shallowing-upward sequences are found in most of the IB. The progressive increase of benthic fossils in the subtidal facies of these sequences gives local evidence of the Late Sinemurian transgression. Cycle 1.3 (Pliensbachian) is bounded by a transgressive surface developed at the end of the Sinemurian (upper Raricostatum Zone). This surface is clearly observed in the AB, in BCB and in the northern IB (Fig. 3). The age of the Pliensbachian transgressive peak is different across the studied basins. In the BCB and AB, organic-rich intervals were formed under anoxic conditions during successive transgressive events in the earliest Pliensbachian (mid-Early Jamesoni Zone) and mid-Early Pliensbachian (Ibex to Early Davoei Zone). Maximum transgressive peak around the boundary between Stokesi and Margaritatus zones

(Celebratum and Subnodosus subzones) is indicated by the presence of black-shale intervals. Above these levels, the presence of bioclastic limestones (packstones) reveals a shallowing event. In AB, the presence of bioclastic limestones and shallow-water ichnofossils (e.g., Arenicolites and Diplocraterion) in the Spinatum Zone evidence an important phase of shallowing and condensation. The lowermost part of cycle 1.3 is coeval in the northern IB to the development of widespread discontinuities associated to transgressive events at the latest Sinemurian (intra-Raricostatum Zone) and at the earliest Pliensbachian (intra-Jamesoni Zone). The transgressive events at the Sinemurian – Pliensbachian boundary involved the development of open platform facies in the northern IB (see Fig. 4A). A sharp increase of marly intervals occurred in the northern IB above the earliest Pliensbachian transgressive surface (e.g., Almonacid de la Cuba area; see ComasRengifo et al., 1999). The increase of benthic fossils and the local presence of coralgal beds (Bordonaba et al., 2000; Castel de Cabra section) provides evidence for a short-term regressive event at the lower Davoei Zone. Following these levels, a widespread transgression in the upper Davoei Zone is evidenced by the presence of a iron-rich crust followed by a set of deepening-upward marly-dominated sequences (ComasRengifo et al., 1999). The transgressive peak of the

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Pliensbachian in the northern and central IB has been located above these sequences, in the lowermost Upper Pliensbachian (lower Stokesi Zone). The Late Pliensbachian regression is evidenced by the overall progradation of bioclastic limestones. No evidences of subaereal emersion on top of this cycle are found in open platform areas. Cycle 1.4 (Toarcian –Lower Aalenian) begins with a basal transgressive surface at the uppermost part of the Spinatum Zone in AB and BCB. In the northern and central IB, this transgressive surface can be locally younger (around the Pliensbachian –Toarcian boundary in Ricla or at the lower Tenuicostatum Zone in Rambla del Salto, see Fig. 2 for location). This different age has been attributed to the advance of the flooding of the basins, from north to south, and to local fault activity (Go´mez and Goy, 2000). A significant flooding event at the upper Tenuicostatum Zone involved the development of a black-shale horizon in the BCB and AB (Fig. 3). The maximum deepening interval in the Early Jurassic was reached during Early – Middle Toarcian transition. Most of the Serpentinus and Bifrons zones are represented by a set of deepening-upward sequences (from limestones to marls), whereas the uppermost Bifrons and Variabilis zones are dominated by shallowing-upward sequences (from marls to limestones). A stratigraphic gap in the Thouarsense Zone indicates the existence of a higherorder sedimentary discontinuity within this cycle. A further transgressive event resulted in the formation of a set of deepening-upward sequences at the Thouarsense – Insigne zones (Go´mez and Goy, 2000). The regression at the Pseudoradiosa and Aalensis zones culminated to a widespread hiatus at the Toarcian – Aalenian boundary in the AB and BCB. The Early Aalenian (Opalinum Zone) corresponds to a general shallowing event in the IB, culminated with a widespread stratigraphic gap at the lower part of the Murchisonae Zone (Ferna´ndez-Lo´pez, 1997). 2.2.2. Middle Jurassic T –R facies cycles The combined analysis of facies and taphonomic features of ammonite assemblages in the open platform areas of the IB (Ferna´ndez-Lo´pez, 1997) has led to the recognition of four deepening-shallowing-upwards cycles (taphocycles). The cycles 2.1 to 2.4 are bounded by widespread stratigraphic hiatuses that can be recognised across the IB and the BCB. In the AB,

only cycle 2.1 is recorded (Ferna´ndez-Lo´pez and Sua´rez-Vega, 1980). There are some differences in the age of the transgressive peaks of cycles 2.2 and 2.3 in the BCB and in the IB. The main facies distribution of the Middle Jurassic Cycles is summarised in Fig. 3 and Table 2. Detailed information is found in the references given in Table 2. Cycle 2.1 (Aalenian to Lower Bajocian) corresponds to progressive deepening from the Early Aalenian (upper Opalinum Zone) in the BCB and AB (or from Middle Aalenian, upper Murchisonae Zone in the IB) to lower Humpresianum Zone, with a short shallowing episode at the upper Humpresianum Zone. The stratigraphic record during the Aalenian – Lower Bajocian was irregular and discontinuous, showing considerable thickness and facies variations, as well as common non-sequences of variable duration and extent. This has been interpreted as a result of differential subsidence induced by local synsedimentary tectonic activity. The most subsident basins found in northern areas evolved from hemipelagic, poorly oxygenated middle – outer platform environments in the Aalenian to a pelagic platform in Early Bajocian. The stratigraphic record of the Aalenian stage is mostly irregular, sparse and discontinuous in the IB, marked by stratigraphic gaps that show different ranges in separate areas. These discontinuities may be associated with condensed levels containing phosphatic and iron ooids and may also represent subaerial exposure events, as observed in the boundary between the Murchisonae and Concavum zones in the central IB (Ferna´ndez-Lo´pez and Go´mez, 1990a,b; San Blas area). In the northern basins, the most important stratigraphic gaps are found between the Opalinum and Murchisonae zones in the AB and between the Concavum and Discites zones in the BCB (Fig. 3). The last one is interpreted as a minor order cycle boundary in the BCB. Cycle 2.2 (Upper Bajocian) starts with a widespread platform flooding at the Early – Upper Bajocian transition and includes the maximum deepening of the Middle Jurassic. The maximum development of open platform facies (marls and limestones with ammonites) occurred at the upper Niortense Zone in the IB. A shallowing phase up to the end of the Bajocian follows this deepening interval. In the BCB, the deeper facies of the succession corresponds to the Garantiana Zone, whereas at the Parkinsoni Zone,

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Table 2 Boundaries, tectonic events and main facies and thickness distribution of the Middle Jurassic T – R facies cycles of northeast Iberia Lower boundary/tectonics Cycle 2.1. Aalenian – Lower Bajocian Lower unconformity related to fault reactivation, associated to volcanic rocks in the southeastern IB. Central IB: Upper Toarcian (Pseudoradiosa and Aalensis zones) and Lower – Middle Aalenian (Opalinum – Murchisonae zones) partly or totally absent. Widespread gap at the lower Murchisonae Zone. BCB, AB: hiatus affecting the Aalensis – Opalinum boundary zone. Important differential subsidence in platform areas during the Late Toarcian – Early Bajocian that waned upwards.

Cycle 2.2. Upper Bajocian Widespread discontinuity at the Lower – Upper Bajocian boundary. Attenuated differential subsidence in platform areas.

Cycle 2.3. Bathonian Discontinuity of regional extent which partly affects the Upper Bajocian deposits (Parkinsoni Zone) and, in some areas of the IB, the lowermost Bathonian, Zigzag Zone. Attenuated differential subsidence that increases towards the Bathonian – Callovian boundary.

Cycle 2.4. Callovian Widespread stratigraphic discontinuity of variable range, with the most extreme taphonomic and stratigraphic condensation during the Late Bathonian, Discus Zone. Significant differential subsidence at the early Callovian (IB) with widespread development of sedimentary swells and troughs across platform areas. Attenuated differential subsidence at the end of the sequence.

Thickness and facies distribution BCB, AB, Soria Seaway (15 – 70 m): mostly continuous Aalenian with mudstone to wackestone (ammonites, belemnites, brachiopods and foraminifera) and interbedded marls, including ferruginous surfaces, and condensed levels. Lower Bajocian: mudstone – packstone with Zoophycos, sponges, ammonites and bivalves. Sponge mounds locally recorded in the Sauzei and Humpriesianum zones. IB, open platform areas (25 – 70 m): Aalenian – lowermost Bajocian (Discites and Leviuscula zones), irregular record with frequent stratigraphic gaps and associated condensed levels with phosphatic and ferruginous ooids. Local evidences of platform emersion. Upper Lower Bajocian (Propinquans and Humphriesianum zones), fossiliferous biomicrites (brachiopods, bivalves, ammonites belemnites, sponges, echinoids, crinoids, Zoophycos, Thalassinoides), developed as shallowing-upwards sequences.

IB and BCB (eroded in AB), open platform areas (20 – 60 m): mudstone to bioclastic wackestone (ammonites, belemnites, brachiopods, sponges, bivalves and Zoophycos), interbedded with thin marls, forming shallowing-upwards successions. Marly intervals increase progressively to become predominant during the transgressive peak of the cycle at the upper Niortense (IB) or at the upper Garantiana (BCB) zones. The shallowing at the end of the sequence involves the local development of sponge mounds, from Niortense Zone in the Castillian Platform, Garantiana Zone in the Aragonese Platform to Parkinsoni Zone in the Soria Seaway and western BCB.

BCB (eroded in AB) (20 – 70 m): a rapid deepening resulted in a general drowning of the Late Bajocian shallow spongiolitic ramp, and deposition of marls with ammonites in the Zigzag Zone. Commonly mudstone to wackestone facies with bivalves (Bositra), ammonites, belemnites, brachiopods and trace fossils (Zoophycos). IB (up to 100 m): in open platform areas, bositra-rich silty peloidal limestones. Shallow platform areas: peritidal dolomitic and grainsupported facies (bioclastic, peloidal and oolitic grainstone to packstone).

BCB (partly eroded in western BCB; eroded in AB) and IB (Soria Seaway, western Castillian and Aragonese platforms) (20 – 200 m): alternation of marls and bioclastic – peloidal limestones (mudstone to wackestone with filaments, common ammonites and belemnites, and scarcer bivalves and brachiopods). Local development of marly level rich in organic matter in the Bullatus Zone (up to 25 m) in the western BCB. IB, central-eastern Castillian and Aragonese platforms (up to 5 m): biomicritic limestones with ferruginous ooids generally Lower Callovian, also locally Middle Callovian, Anceps Zone. The Upper Callovian, Athleta and Lamberti zones deposits are either absent or extremely condensed. At the NE of the Tortosa Platform, up to 45 m of fossiliferous limestones and marly limestones, Early to Middle Callovian.

Selected references: Ferna´ndez-Lo´pez et al. (1978, 1988a,b, 1998b), Go´mez and Goy (1979), Goy et al. (1981), Schaff (1986), Pujalte et al. (1988), Ureta (1988), Ferna´ndez-Lo´pez and Aurell (1988), Robles et al. (1989), Wilde (1990), Lardie´s (1990), Quesada et al. (1990, 1993), Ferna´ndez-Lo´pez and Go´mez (1990a,b), Canales et al. (1993), Ferna´ndez-Lo´pez and Mele´ndez (1995, 1996), Ferna´ndez-Lo´pez (1997), Mele´ndez et al. (1997, 1999), Ureta et al. (1999).

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higher energy facies and spongiolitic facies are widespread, indicating shallower platform conditions above storm-wave base by the end of Bajocian times (Ferna´ndez-Lo´pez et al., 1988a; Quesada et al., 1993). In the IB, cycle 2.3 (Bathonian) includes a lower transgressive interval in the Zigzag and Progracilis zones and an upper regressive succession up to the latest Bathonian. This progressive shallowing led to the development of a general stratigraphic gap at the latest Bathonian (Discus Zone). Oolitic grainstone facies are common in shallow platform areas of the IB (e.g., Mansilla, Obo´n, Ejulve, Cedrillas). In the BCB, the cycle shows a rapid deepening trend in the Zigzag Zone, which resulted in a general drowning of the Late Bajocian spongiolitic ramp and deposition of marls at the base of the sequence. This deepening interval was followed by a progressive shallowing from the end of the Zigzag Zone (Ferna´ndez-Lo´pez, 1988; Ferna´ndez-Lo´pez et al., 1988a). Cycle 2.4 (Callovian) comprises a lower transgressive interval at the Early Callovian although local tectonics may result in the shallowing and eventual emersion of the uplifted tilted blocks (Ferna´ndezLo´pez and Mele´ndez, 1996). In the western BCB, this transgressive episode is outlined by the presence of marls rich in organic mater (up to 25 m thick) in the Bullatus Zone. Towards the end of the Callovian stage, a widespread regressive event led to a general shallowing of the open platform facies and the increase of clastic input in marginal (northwestern) areas of the IB (see Fig. 5B). The widespread stratigraphic gap at the Middle –Upper Jurassic boundary has been related to the eventual emersion of the platform. Paleokarst surfaces developed on top of the Upper Callovian succession have been described in detail in the northern IB (Ricla area: Ramajo and Mele´ndez, 1996; Ramajo and Aurell, 1997). 2.2.3. Upper Jurassic T –R facies cycles During Upper Jurassic, marine sedimentation became restricted to the eastern BCB and to the IB (Table 3). The sequential analysis of the carbonate platforms developed in the IB has resulted in the identification of four second-order T –R cycles (Salas, 1989; Aurell and Mele´ndez, 1993). Main facies distribution of these cycles is summarised in Fig. 3 and Table 3. Detailed description of these cycles is given in the references reported in Table 3. Higher-order

transgressive events found in the lower transgressive interval of cycle 3.1 and in the upper regressive interval of cycle 3.2 (Aurell et al., 2000, 2002) have been also indicated in Fig. 3. Cycle 3.1 (Oxfordian) comprises a lower transgressive interval from the Early Oxfordian (Cordatum Zone) to the earliest Late Oxfordian (Hypselum Zone). During the Early Oxfordian and early-Middle Oxfordian (Plicatilis Zone), sedimentation was irregular and discontinuous. In open platform areas, this interval is represented by a condensed succession including several iron-ooid layers in the central and eastern IB (see Fig. 5B for the distribution of the iron oolitic bed). The first evidence of marine flooding of the platform is indicated by the presence of ammonites of the lower Cordatum Zone (Bukowskii Subzone) in these condensed levels (Mele´ndez et al., 1983). Further widespread transgression over wide basin areas took place at the lower Plicatilis and lower Transversarium zones (Fig. 3). A condensed interval during the late Bifurcatus to Hypselum zones represents the maximum flooding peak of this cycle (Ferna´ndez-Lo´pez and Mele´ndez, 2003). Taphonomic features displayed by ammonites allow their categorisation in a series of so-called taphorrecords (Ferna´ndez-Lo´pez, 1997) ranging from incipient deepening taphorrecords in early Transversarium Zone to advanced deepening taphorrecords in Hypselum Zone. The latest Oxfordian regression is recognised in marginal (northwestern) areas of the IB by the progradation of siliciclastic facies (see Fig. 5A). A thick unit (ca. 50 m) of cross-bedded sandstones and conglomerates was developed at the Hauffianum –Planula Zone boundary in certain marginal areas (Veruela area; Aurell et al., 2000). The upper boundary is developed in the mid-Planula Zone, involving a local stratigraphic gap, which may partly affect the Hauffianum Zone and the lower part of Planula Zone. Cycle 3.2 (Kimmeridgian – Early Tithonian) has a lower transgressive interval from the upper Planula Zone (Planula – Galar Subzone boundary) up to a maximum flooding at the Divisum Zone. This transgressive event resulted in the local development of condensed successions in open platform areas at the end of the Lower Kimmeridgian (Calanda, Fig. 3). The regressive phase at the Late Kimmeridgian – earliest Tithonian (Hybonotum Zone) is documented by the progressive off-lap and progradation of the

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Table 3 Boundaries, tectonic events and main facies and thickness distribution of the Upper Jurassic T – R facies cycles of northeast Iberia Lower boundary/tectonics Cycle 3.1. Oxfordian Important unconformity across platform areas (IB), with a gap that comprises at least the uppermost Callovian and lowermost Oxfordian (i.e., Lamberti and Mariae zones). In AB, uplift and erosion of the marine Jurassic units related to a tectonic episode around the Middle – Late Jurassic transition. General tectonic stability during most of the Oxfordian led to the development of a wide carbonate ramp in the IB. Important tectonic reactivation and terrigenous input in marginal areas of the IB at the latest Oxfordian.

Cycle 3.2. Kimmeridgian Discontinuity at the latest Oxfordian, with an associated stratigraphic gap that partly affects the Hauffianum Zone and the lower part of Planula Zone (i.e., the Tonnerrense or Proteron Subzone). Episodes of major tectonic activity led to important differential subsidence in the eastern IB and to the uplift of the western marginal areas.

Cycles 3.3 and 3.4. Tithonian – Berriasian In the central-eastern IB, a sedimentary discontinuity between outer ramp limestones and shallow oncolitic – oolitic carbonates (intra-Hybonotum Zone?). Erosional to angular unconformity in the BCB and in the former Soria Seaway, where continental or litoral units overlie older marine Jurassic units. Major tectonic activity resulted in the formation of rapidly subsiding continental basins in the northwestern IB and in the western BCB. Important differential subsidence in the central and eastern IB. Important siliciclastic input in marginal areas of the IB, derived from the uplifted western and southern margins of the basin.

Thickness and facies distribution IB, eastern BCB: in open platform areas, a lower condensed level (up to 1 m) with abundant ammonites, belemnites, echinoderms, bivalves, foraminifera, sponges and brachiopods is found. In central and eastern IB contains abundant iron ooids and pisoids. Two ephemeral flooding episodes of the platform at the lower Cordatum and lower Plicatilis (Paturattensis Subzone) zones. Upper sucession: IB (10 – 45 m): skeletal wackestone – packstones (ammonites, sponges, brachiopods, crinoids, bivalves, beleminites, echinoids and serpulids) with interbedded marls. Locally peloidal – glauconitic packstones. Central part of the Soria Seaway (25 – 75 m): shallowing-upwards siliciclastic and carbonatic sequences (deltaic and peritidal cycles). Eastern BCB (50 – 140 m): cherty limestones (pelloidal and bioclastic packstone) with scarce echinoderms, benthic foraminifera and sponge spicules, which grade in calcareous siltstone and sandstone in the marginal areas of the basin. Erosional or non-depositional hiatus in western BCB and AB.

Central-eastern IB (50 – 500 m): marls followed by a rhythmic alternation of marls and mudstones. In the outermost platform areas (eastwards), frequent sponge-rich intervals and local presence of marls and limestones rich in organic matter (up to 300 m), which included anoxic episodes. Maximum development of open platform facies at the end of the Early Kimmeridgian (with formation of condensed sections rich in ammonites), with another transgressive interval at the Eudoxus Zone. Western IB, Soria Seaway and eastern BCB (20 – 150 m): shallow marine carbonate (oolitic, peloidal, coralgal) and siliciclastic facies. AB (up to 700 m): paleovalley fill and alluvial plain siliceous conglomerates, sandstones and mudstones followed by marls with interbedded bioclastic limestones (gastropods, bivalves) and sandstones, which resulted from vertical piling up of small deltaic, fluvially dominated systems. Occasional communication of the basin with the open sea allowed the incursion of rare ammonites of the late Early Kimmeridgian (Cymodoce Zone) and Eudoxus zones. Western BCB: erosional or non-depositional hiatus.

Central-northeastern IB (40 – 80 m): oolitic, oncolitic, reefal and bioclastic packstones – grainstones followed by peritidal (algal-laminated) carbonates. Easternmost IB (up to 900 m in the Maestrat Basin): fossiliferous bioturbated mudstone to wackestones with algae, foraminifera, bivalves and scarce calpionellids, and peloidal, oolitic and bioclastic (packstone to grainstone) intervals forming successive coarsening and thickening upwards sequences. Two T – R cycles have been defined. Cycle 3.3 is mid-Lower Tithonian – Lower Berriasian; Cycle 3.4 extends up to mid-Late Berriasian. Southwestern IB (400 – 500 m): mixed carbonate and siliciclastic unit (clays and sandstones), locally indicative of a tidal flat environment. Eastern BCB (90 – 120 m): bioclastic limestones with serpulids, gastropods, ostracods and stromatilites developed in a tidal flat. Northern continental basins (Cameros, Aguilar and Cires basins, 500 – 1500 m): alluvial to fluvial siliciclastic and palustrine carbonate facies. AB: no sedimentation.

Selected references: Go´mez and Goy (1979), Mele´ndez et al. (1983, 1990), Mas et al. (1984, 1993), Atrops and Mele´ndez (1985), Fezer (1988), Salas (1989), Alonso and Mas (1990, 1993), Garmendia and Robles (1991), Aurell and Mele´ndez (1993), Aurell et al. (1994a,b, 1998, 2000), Ba´denas (1996), Aurell and Ba´denas (1997), Pujalte et al. (1996), Robles et al. (1996), Herna´ndez et al. (1999), Ramajo et al. (1999), Ba´denas and Aurell (2001), Ferna´ndez-Lo´pez and Mele´ndez (2003).

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siliciclastic – oolitic and reefal units found in the marginal areas of the IB (see northwest Iberian Ranges in Fig. 3). A short transgressive episode at the Eudoxus Zone allows the definition of two higher-order sequences within the Kimmeridgian (Ba´denas and Aurell, 2001). Coastal and continental basins were formed in the AB during the Kimmeridgian (Table 3). Upper Jurassic (Oxfordian – Kimmeridgian) marine units in the western BCB are absent, due essentially to a latest Jurassic erosional episode (Robles et al., 1989; Aurell et al., 2002). The Tithonian – Berriasian is represented by a widespread shallowing process and progradation of carbonate and siliciclastic platforms developed in the central and eastern IB. Two T – R facies cycles have been recognised in the carbonate platforms developed in the easternmost IB (i.e., Maestrat Basin). The age of these cycles has not been confirmed by ammonites and is mainly based on larger benthic foraminifera (Salas, 1987, 1989; Ba´denas et al., 2002). Below the boundary of cycle 3.3, ammonites of the Hybonotum Zone have been recognised in the northeast IB (Calanda area, Atrops and Mele´ndez, 1985). The cycle 3.3 contains A. lusitanica and is probably middle-Early Tithonian to middle-Early Berriasian in age. The age of cycle 3.4 (middle-Lower Berriasian to the lowerUpper Berriasian), well characterised in the Maestrat Basin, is constrained by the absence of A. lusitanica and by the presence of V. miliani in the overlaying unit. The distribution of the transgressive and regressive intervals of these two cycles is based on the facies and stacking pattern analysis of two representative sections located in the most subsident areas of the Maestrat Basin (Montanejos and Salzedella sections; Ba´denas et al., 2002). The transgressive peaks around the upper-Middle Tithonian and the Lower – Middle Berriasian boundary correspond to the maximum development and thickness of the relatively deep platform facies. Highly subsident continental basins were developed in the northwest IB (Cameros Basin) and in the western BCB (Aguilar and Cires basins) at the end of the Jurassic. They were controlled by the activity of former basement faults and other related synsedimentary faults (Platt, 1990; Mas et al., 1993; Herna´ndez et al., 1999; Martı´n-Chivelet et al., 2002; Aurell et al., 2002). Lower units include fluvial and alluvial siliciclastic and palustrine carbonate facies dated, by means

of charophyte associations, as Late Tithonian to Early –Late Berriasian (Martı´n-Closas, 1989; Platt and Pujalte, 1994; Pujalte et al., 1996; Robles et al., 1996; Herna´ndez et al., 1999). Two long-term depositional sequences bounded by a stratigraphic hiatus around the mid-Lower Berriasian have been identified in the Cameros Basin (Alonso and Mas, 1993), which are tentatively correlated to the cycles 3.3 and 3.4 defined in shallow platform areas (see Fig. 3).

3. Palaeogeographic evolution The palaeogeographic evolution of northeast Iberia shows three well-differentiated episodes. In Early Jurassic times, all the studied basins formed a uniform carbonate platform opened to the north (Fig. 4). During Middle Jurassic, a number of open carbonate platforms were separated by a series of NW – SE trending sedimentary swells (Fig. 5). In contrast, during the Upper Jurassic, the progressive isolation of two separate marine areas, open respectively to the southeast and to the north, and the development of continental basins on the emerged areas to the northwestern BCB and northwestern IB (Fig. 6) took place. Differential movements of normal faults during stages of major tectonic activity at the latest Rhaetian – Hettangian, Late Toarcian– Aalenian and latest Jurassic explain the differences in the extension, overall facies distribution and orientation of the epicontinental carbonate platforms developed in the northeastern part of the Iberian Plate throughout the Jurassic. 3.1. Lower Jurassic At the Triassic –Jurassic transition, the development of restricted, shallow-water fault-controlled basins favoured the deposition of thick evaporitic– dolomitic units (San Roma´n and Aurell, 1992). Extensional fault activity weakened during Early Jurassic times, and led to the development of a wide carbonate ramp open to the north. This carbonate ramp suffered a progressive drowning, evolving from peritidal to shallow inner ramp environments during the Hettangian –Early Sinemurian interval, to an hemipelagic ramp system from Late Sinemurian to Middle Toarcian, with local development of suboxic environments

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in the deepest areas located in the BCB and in the AB. The orientation of the ramp (open to the north) would explain the dominantly central-European character of faunas within the recorded ammonite associations (Elmi et al., 1989). The shallow, inner platform environments, located in the southernmost part of the IB impeded direct connections between the Betic sedimentary domain and the IB (Sandoval et al., 2001). A mid-Early Sinemurian transgression led to the development of a middle ramp (a storm-dominated ramp deposited between fairweather and storm-wave base) in the western BCB (1 in Fig. 4A). A second transgressive event from the Early –Late Sinemurian transition (from the Obtusum Zone) led to a general flooding of the northern AB and BCB (2 in Fig. 4A). This event, though, did not reach the eastern IB so, in this area, inner ramp conditions (sabkha to intertidal environments) were maintained during the Sinemurian stage. Transgressive events at the Sinemurian – Pliensbachian transition (upper Raricostatum and Jamesoni zones) involved the setting of middle and outer ramp environments (hemipelagic conditions) in the northern IB (3 in Fig. 4A). Further transgressive episodes, which initiated at the Early – Late Pliensbachian boundary (from upper Davoei Zone) and at the Pliensbachian – Toarcian boundary (from upper Spinatum Zone) progressively reached more southerly areas (4 and 5 in Fig. 4B). The transgressive peak of the Lower Jurassic Cycle at the onset of the Middle Toarcian (i.e., Bifrons Zone) corresponds to the maximum areal extension of the open platform, hemipelagic environments over the northeast Iberian basins. However, in southwestern marginal parts of the IB, inner platform conditions were maintained during the entire Early Jurassic. A shallowing event around the Toarcian –Aalenian boundary led to the emersion of wide areas of the Lower Jurassic carbonate platform. 3.2. Middle Jurassic Synsedimentary tectonic activity increased at the Lower – Middle Jurassic transition, and resulted in the break-up of the wide Early Jurassic carbonate platform of the northeastern Iberia into different sedimentary domains (Fig. 5). The IB was reshaped into a set of NW – SE trending open platforms, separated by

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sedimentary highs where shallow sedimentation was dominant. In northeastern areas of the IB, the Tortosa Platform (TP in Fig. 5A; see Catalonian Coastal Ranges in Fig. 3 for reference sections) developed as a relatively deep and subsident open platform (Ferna´ndez-Lo´pez et al., 1996, 1998a). In the central part of the IB, there existed two open platform areas, known as the Aragonese Platform (see Ricla and Aguilo´n for reference sections in Fig. 3) and the Castillian Platform (AP and CP in Fig. 5A). These platforms were separated by a sedimentary high, which was dominated by oolitic and massive dolomitic facies from Late Bajocian onwards (Bulard, 1972; Go´mez, 1979; Aurell et al., 1999). The Aragonese and Tortosa platforms were connected through a narrow palaeogeographic corridor, in which Middle Jurassic sequences are strongly condensed (see Calanda section for reference, Fig. 3). In the southwestern marginal areas of the IB, Middle Jurassic deposits are typical of inner ramp environments. In this area, welllog data have revealed the local presence of oolitic limestones and dolostones with interbedded evaporites (Morillo and Mele´ndez, 1979). Mid-outer ramp environments were dominant in the northern BCB. These open platform areas were connected to the IB through the Soria Seaway (SS in Fig. 5A; Bulard, 1972; Wilde, 1990). The maximum transgressive interval of the Middle Jurassic at Late Bajocian times resulted in the open platform facies reaching their maximum extent (1 in Fig. 5A). A subsequent regressive phase at the end of Bajocian times (Parkinsoni Zone) and in Middle –Late Bathonian produced the widespread setting and progradation of inner platform (bioclastic, peloidal and oolitic) facies over the open platform areas. This process is underlined by the local record of siliciclastic deposits along marginal areas (2 in Fig. 5A). During the Early Callovian, a further transgressive event resulted in the flooding of the central areas of the Soria Seaway and the marginal (southwestern) areas of the IB. Callovian to early-Middle Oxfordian sedimentation was scarce and discontinuous. A condensed iron oolitic interval is found in the open platform areas located in the central part of the IB (Fig. 5B). The regression at the end of the Callovian culminated with the widespread stratigraphic gap and local open platform emersion at the Callovian – Oxfordian boundary.

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3.3. Upper Jurassic A wide, homogeneous carbonate platform gently dipping, on one side to the southeast and, on the other side, to the north was developed at the Oxfordian (Fig. 6A). Following a long period of no-sedimentation at the Callovian –Oxfordian transition, the widespread Middle to early-Late Oxfordian transgression was reflected in a general homogeneity of facies across the central and eastern IB. This allowed intense colonisation by sponges as well as by nectonic groups such as ammonites which could locally form true biological populations (Ramajo et al., 1999; Mele´ndez et al., 2002). The northern part of the Soria Seaway was occupied by relatively deep (mid-outer ramp) facies. Middle and early-Late Oxfordian outer ramp carbonate facies also reached the southwestern areas of the IB, which were occupied during Early and Middle Jurassic times by shallow, inner platform facies. The eastern part of the BCB was occupied by inner-mid carbonate ramp facies with local silicilastic input coming from the eastern land areas (Fig. 6A). The regressive impulse in the latest Oxfordian is related to the uplift of the marginal areas, which involved significant clastic input in the northern and southern margins of the Soria Seaway. The subsequent Early Kimmeridgian transgressive phase resulted in the record of rich ammonite successions in the open platform areas located in the central and eastern IB (Fig. 6B). The central part of the Soria Seaway and the eastern part of the BCB were occupied by shallow platform environments where oolitic, reefal and siliciclastic facies were deposited (Garmendia and Robles, 1991; Ba´denas, 1996; Ba´denas and Aurell, 2001). At the end of Kimmeridgian times, a tectonic reactivation of the Iberian Massif led to the uplift of the western margin of the IB. This induced the eventual emersion of the Soria Seaway and the displacement of the coastline to the east IB (Aurell and Mele´ndez, 1993; Aurell et al., 1994b). Marine sedimentation during Tithonian to Berriasian times became progressively restricted to the eastern IB, taking place on a shallow carbonate platform, which displayed important terrigenous supply in southwestern areas of the IB (Fig. 6C). In the area of the Soria Seaway, a strongly subsident continental basin was developed (Cameros Basin, Fig. 6C). Farther north, in

the western BCB, continental basins were also formed during the Jurassic – Cretaceous transition (Aguilar and Cires basins, Fig. 6C).

4. Discussion: comparison between the Iberian T – R cycles to other proposed cycles The first- and second-order sequences identified in northeast Iberia have a transgressive –regressive evolution, and were caused by first- and second-order relative sea-level changes affecting the studied basins. The origin of the inferred long-term sea-level changes can be related either to tectonic development of sedimentary basins (i.e., local to regional tectonics) or to eustatic changes. Hallam (2001) relates the major episodes of eustatic rise of the Jurassic to plate tectonics, the global Jurassic sea-level rise being associated with the opening of the Atlantic and Indian Oceans. Regional tectono-eustatic changes, including variations in the long-term subsidence evolution (induced by changes in the intraplate stress), are expected to affect different basins located in similar geodynamic settings. The comparison between the cycles defined in Iberia to those defined in other basins may give information about the origin of the Jurassic transgressive and regressive events documented in northeast Iberia, and will help to validate the currently proposed European first- and second-order sequences (Jacquin et al., 1998; De Gracianski et al., 1998; Hardenbol et al., 1998; Hallam, 2001). 4.1. Major T– R cycles Tectonic events and major T – R cycles observed in northeast Iberia are summarised in Fig. 7. Major tectonic activity at the Triassic – Jurassic transition and at the Lower – Middle Jurassic transition is outlined by the local presence of volcanic rocks. The increase of tectonic activity at the end of the Jurassic has been related to the onset of rifting episodes. Major T – R cycles characterised in northeast Iberia are compared to those proposed by Hardenbol et al. (1998) for European basins (Boreal and Tethyan areas) and by O’Dogherty et al. (2000) in the Betic Cordillera (southern Spain). There are significant discrepancies between the reference Boreal/Tethyan schemes and the three major

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Fig. 7. Tectonic evolution and major Jurassic transgressive (T) – regressive (R) cycles of the different basins of northeast Iberia and the Betics (adapted from O’Dogherty et al., 2000) compared to the Boreal and Tethyan major T – R cycles proposed by Hardenbol et al. (1998).

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T –R cycles recognised in northeastern Iberia. Hardenbol et al. (1998) propose two major T –R cycles for the Jurassic succession as a whole. The lower cycle is comparable to the one recognised in northeast Iberia, although there is discrepancy on the position of the boundaries and transgressive peak of the cycle. The upper major cycle proposed by these authors, in turn, corresponds to two major cycles in northeastern Iberia, where the Middle – Upper Jurassic unconformity is interpreted as a major T – R cycle boundary. Two long-term cycles of different age are proposed for the Middle –Upper Jurassic in the Betic Cordillera. Additional discrepancies are found on the age of the boundaries and transgressive peaks of the longer-term Jurassic Cycles proposed for Boreal domains, for Tethyan domains, for the Betics and for the different basins of northeast Iberia. The observed discrepancies suggest the imprint of local tectonics. The discussion about the origin of the major Jurassic unconformities is of special interest. The observed mismatch between the age of the major transgressive peaks is also discussed. 4.1.1. The boundaries of the Lower Jurassic Cycle The lower and upper boundaries of the Lower Jurassic Cycle have been related in Iberia to an increase of the tectonic activity at the latest Triassic and at the Early – Middle Jurassic transition, respectively. Tectonic extension at the Triassic – Jurassic transition caused the break-up of the extensive Rhaetian epicontinental platform and the development of restricted, fault-controlled basins during the latest Rhaetian– Hettangian (San Roma´n and Aurell, 1992). In the areas preserved of this tectonic activity, an important latest Rhaetian regressive event is documented (i.e., sharp transition from shallow platform sedimentation to evaporites and associated facies). A significant episode of rapid and very extensive regression, possibly global, took place at the end of the Triassic (Hallam, 2001). Therefore, the regressive event found in Iberia at the latest Triassic may have some eustatic imprint. The extension of the stratigraphic gap associated to the Lower – Middle Jurassic discontinuity varies across the northeast Iberian basins, suggesting the strong influence of local tectonic factors. In some open platform areas of IB, the Lower and Middle Aalenian are partly or completely absent. A widespread stratigraphic gap is recognised at the lower

Murchisonae Zone (Ferna´ndez-Lo´pez, 1997). In the BCB and in the AB, the major unconformity is recorded around the Toarcian – Aalenian boundary. In the AB, a further stratigraphic gap between the Opalinum and Murchisonae zones is also recognised. An unconformity with an associated stratigraphic gap at the Aalenian – Bajocian boundary is also found in the western BCB (Fig. 3). The mid-Early Aalenian represents the onset of the transgression of the long-term Middle Jurassic Cycle in the AB and in the BCB. The analysis of taphonomic features and facies of the condensed levels found in the platform areas of the IB have demonstrated that this transgression was initiated in the upper part of the Murchisonae Zone (Ferna´ndezLo´pez, 1997). Hardenbol et al. (1998) consider the Middle Aalenian as a regressive phase, followed by a major transgressive event at the onset of the Upper Aalenian. In contrast, the Aalenian is considered a long-term transgressive episode in the Betic Cordillera. Hallam (2001) describes the Aalenian as the most spectacular regressive event in Europe (in the North Sea and surrounding areas) before the end of the Jurassic, related to regional tectonics (see also Underhill and Partington, 1993). The effects of local or regional tectonic development may explain the observed discrepancies on the age of the upper boundary of the Lower Jurassic Cycle in the IB, in the AB and BCB and in other western European basins. 4.1.2. The Middle – Upper Jurassic unconformity The Callovian – Oxfordian transition is considered in northeast Iberia as a major regressive episode. In the open platform areas of the northern IB (e.g., Ricla, Fig. 3), the unconformity found on top of the Upper Callovian succession is followed by a widespread stratigraphic gap, which comprises at least the uppermost Callovian and the lowermost Oxfordian zones (Lamberti and Mariae zones). In some shallow uplifted areas located in the central IB, it can even range from Lower Callovian (upper Bullatus Zone) to Middle Oxfordian (middle Transversarium Zone) (Aurell et al., 1994a, Ramajo et al., 1999). The midEarly Oxfordian (lower Cordatum Zone) transgressive event marks the onset of the Upper Jurassic Cycle in the northeast Iberian basins. At a worldwide scale, the condensed nature of the Upper Callovian to Lower Oxfordian deposits is well

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recorded over wide areas in western Europe and in the Andes, suggesting a global phenomenon (Hallam, 2001). The interpretation of this condensed interval in terms of sea-level variation, however, has been the subject of debate. In the IB, it has been regarded as formed during a period of relative low sea-level interval (i.e., from the latest Callovian regression to the Early Oxfordian transgression) punctuated by episodic (ephemeral) flood events during lower Cordatum and lower Plicatilis zones. Facies and taphonomic analysis of the ammonite moulds found in the condensed level gives additional support to the latest Callovian – earliest Oxfordian regressive event (Aurell et al., 1994a). This interpretation is also supported by the presence of an emersion and erosion surface above the Upper Callovian shallow marine units (e.g., Ricla section, Ramajo and Aurell, 1997). The taphonomic analysis of the condensed interval in the Paris Basin and in the Jura (France) has allowed the identification of successive stages of loss of accommodation at the Callovian – Oxfordian boundary, at the mid-Early Oxfordian and at the Early – Middle Oxfordian boundary (Courbille and Collin, 2002). In the nearby Lusitanian Basin, the latest Callovian – Early Oxfordian corresponds to a time of subaerial exposure (Leinfelder and Wilson, 1993; Arruda subbasin), documented by the local presence of paleokarst surfaces, ferruginous deposits, coal and pedogenic carbonates (Azeredo et al., 1998). In contrast, the Middle Callovian and the Late Callovian – Early Oxfordian are considered as a periods of sea-level rise on a global scale (e.g., Norris and Hallam, 1995; Hallam, 2001). In the Betic Cordillera, the Middle Callovian – Oxfordian is also interpreted as a long-term transgressive period. Jacquin et al. (1998) consider a second-order peak transgression close to the Callovian –Oxfordian boundary as ‘‘one of the most correlatable drowning events of the European craton’’. It is suggested that the observed discrepancies may be largely explained by the different interpretation (in terms of sea-level variation) given by different authors to the condensed levels found around the Middle – Upper Jurassic boundary. Alternatively, all this discrepancies might indicate that, besides eustatic control, block tectonics also played an important role in separate western European basins during this interval.

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4.1.3. The first-order transgressive peaks The age of the first-order transgressive peaks is different from one basin to another (Fig. 7). A set of deepening-upward sequences are found over the northeast Iberian basins at the Serpentinus – Bifrons Zone (Go´mez and Goy, 2000). The transgressive peak at the Bifrons Zone (northeast Iberia) is age-equivalent to the Lower Jurassic transgressive peak in the Betic Cordillera and Tethyan basins, but is slightly younger than the equivalent peak proposed in Boreal basins (Serpentinus Zone). The Serpentinus Zone transgressive event is clearly recognised in such separate areas of the world as Europe, South America and western Siberia (Hallam, 2001). The transgressive peak of the Middle Jurassic Cycle is younger in the BCB (upper Garantiana Zone) than in the IB and the Betic Cordillera (upper Niortense Zone). Jacquin et al. (1998) consider a younger second-order transgressive peak at the onset of the Bathonian (lower Zigzag Zone, Boreal and Tethyan T– R cycle 7; see Fig. 8). A major transgressive peak at the end of the Early Kimmeridgian (Divisum Zone) is found in northeast Iberia (IB). A time equivalent transgressive peak has been also cited in the SE France basin and in the Provence Platform (Jacquin et al., 1998). This peak is younger than the one proposed in the Betic Cordillera (mid-Lower Kimmeridgian, Hypselocyclum Zone). A major transgressive peak in the upper Eudoxus Zone is proposed by Hardenbol et al. (1998) in Tethyan domain. This peak is slightly older than the one proposed for Boreal areas (Fig. 7). The transgression at the Eudoxus Zone has been also recognised in the IB as a third-order maximum flooding event (Ba´denas and Aurell, 2001). Some authors (Wignall, 1994; Taylor et al., 2001) also consider the Eudoxus Zone as the maximum deepening interval during the Kimmeridgian in some western European basins (south England, Greenland). Major transgressive peaks found in northeast Iberia and in other west European basins, although noncoincident, depict a general transgressive scenario at the early-Middle Toarcian, early-Late Bajocian and mid-Kimmeridgian. These transgressive intervals have been related to global episodes of sea-level rise (Hallam, 2001). The effects of local tectonics (i.e., different subsidence evolution from one basin to another) may explain the observed discrepancies at

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zone scale in the age of the major transgressive peaks. 4.2. T – R facies cycles T –R facies cycles (second-order sequences) defined in northeastern Iberia are compared to those defined by De Gracianski et al. (1998) and Jacquin et al. (1998). Only few similarities exist between both proposals (Fig. 8), suggesting a strong local or regional tectonic influence in the development of the second-order T – R cycles. 4.2.1. Lower Jurassic T – R facies cycles The number and the age of the second-order cycles defined in Iberia and in other west European basins are not the same (Fig. 8). However, some cycle boundaries and transgressive peaks identified in northeast Iberia may be correlated with those defined in other west European basins. Cycle 1.1 (characterised in the BCB and AB) is transgressive up to the mid-Early Sinemurian as the T – R cycle 4 defined in Boreal areas and in the lower cycle of the Betics. The regressive interval of the cycle is similar in all these basins. However, the precise age of the transgressive peak of cycle 1.1 has not been confirmed by ammonites in the north Iberian basins. The Early Sinemurian as been regarded as a period of global rise of sea level (Hallam, 2001). In the northern basins of Iberia the late-Lower Sinemurian (upper part of cycle 1.1) shows a regressive trend. This particular trend has been related to local tectonic uplift of the southwestern margin of the BCB (Robles and Quesada, 1995). Cycle 1.2 (Late Sinemurian) shows close correspondence to the United Kingdom cycle 4b, although the transgressive peak of cycle 1.2 is younger. The regressive interval of cycle 1.2 (characterised in the BCB and AB) is not observed in the IB, suggesting the influence of local tectonic factors. The lower boundary of cycle 1.3 (Pliensbachian) is age-equivalent to the lower boundary of United Kingdom cycle 5. The Boreal and the United Kingdom

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cycle 5 shows a transgressive peak in the Jamesoni Zone. A major marine transgression of Jamesoni Zone has been also reported from Greenland (Surlyk, 1991) as well as in other areas of the world (Hallam, 2001). Evidences of this transgressive event are also found in the AB and BCB (black-shale episode, Fig. 3) and in the northern part of the IB (transgressive surface), although the age of the stratigraphic horizon assumed as the maximum Pliensbachian transgressive peak (cycle 1.3) varies from one basin to another (Fig. 8). The origin of these disagreement may be in the complexity of the cycle 1.3 itself, because in the AB and BCB, it includes three black-shale episodes (in the Jamesoni, Ibex – Davoei and Stokesi–Margaritatus zones, respectively, Fig. 3), which can be correlated with other three transgressive events. The lower boundary of cycle 1.4 (Toarcian) is ageequivalent to the lower boundary of Tethyan cycle 6. The transgressive peak of this cycle is equivalent to the transgressive peak of cycle 6 defined in Boreal and Tethyan areas. However, as discussed above, there are significant differences in age of the upper boundary of this cycle across the northeast Iberian basins and in other western-European basins. The origin of the Lower Jurassic T –R facies cycles is discussed by De Gracianski et al. (1998). These authors explain the observed age discrepancies as recording the tectonic development of the sedimentary basins located in the western European craton. Subsidence events appear to be the cause of the secondorder transgressions. A possible tectono-eustatic effect created by a change in size of the ocean basin during the phases of rifting leading to the opening of the western Tethys is suggested by De Gracianski et al. (1998) to explain the observed match between some of the second-order transgressive peaks. Hallam (2001) considers three episodes of eustatic rise in the Early Sinemurian, Early Pliensbachian and Early Toarcian. The transgressive peaks of the Iberian cycles 1.1 (mid-Early Sinemurian) and 1.4 (earlyMiddle Toarcian) and the transgressive event found at the earliest Pliensbachian (Jamesoni Zone) are found in other Boreal basins, suggesting the influence

Fig. 8. Second-order transgressive (T) – regressive (R) facies cycles defined in the different basins of northeast Iberia compared to equivalent cycles defined in other western European basins (simplified from De Gracianski et al., 1998, Fig. 2, Jacquin et al., 1998, Fig. 2 and O’Dogherty et al., 2000, Fig. 10.A). Major episodes of eustatic rise proposed by Hallam (2001) and major third-order sequences boundaries and maximum flooding surfaces (Middle Jurassic) proposed by Hardenbol et al. (1998) are also indicated.

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of eustatic rise events. The discrepancies observed in the rest of the Late Sinemurian – Pliensbachian transgressive events suggest major control of local subsidence events. 4.2.2. Middle Jurassic T –R facies cycles In contrast with some of the Lower Jurassic T– R cycles, there is no equivalence between the four Middle Jurassic T – R facies cycles recognised in northeast Iberia and those proposed by Jacquin et al. (1998) in the Boreal and Tethyan areas (Fig. 8). The boundaries of the Aalenian to Bathonian Iberian cycles show, however, some coincidences when they are compared with the major third-order sequence boundaries (and the associated lowstand intervals) proposed by Hardenbol et al. (1998). These boundaries correspond, in fact, to discontinuities associated with stratigraphic gaps of variable extent in the northeastern Iberian epicontinental platforms (Fig. 8). On the other hand, some of the transgressive peaks of the second-order cycles of northeast Iberia correspond to major third-order flooding events in the Hardenbol et al. (1998) chart. Sandoval et al. (2002) have also demonstrated that some of the major third-order sequence boundaries and subsequent transgressive phases of the Aalenian – Lower Bajocian interval correlate with major ammonite faunal turnover events over different western Tethys basins. The widespread stratigraphic gaps associated to the lower boundary of the cycle 2.1 in the AB and BCB (lower Opalinum Zone) and in the IB (lower Murchisonae Zone) fit well with the Aa1 boundary (upper Opalinum Zone) and the Aa2 boundary (upper Murchisonae Zone) proposed in Hardenbol et al. (1998). The discontinuity recognised at the boundary between Concavum and Discites zones in the BCB correlates with the Bj1 major third-order sequence boundary. A stratigraphic gap at the Discites Zone is also locally recorded in the central IB (e.g., Ferna´ndez-Lo´pez and Go´mez, 1990b). The major transgressive peak of the cycle 2.1 (upper Humphriesianum Zone) corresponds to the first Middle Jurassic major third-order flooding event (i.e., Bj2) in the Hardenbol et al. (1998) chart. The lower and upper boundaries of cycles 2.2 and 2.3 closely match the successive transgressive surfaces associated to the Bj3, Bj5 and Bt5 major third-order boundaries defined by Hardenbol et al. (1998). The age of the transgressive peak of cycle 2.2 has been fixed in

upper Niortense Zone in the IB, while it has been dated as Garantiana Zone in the BCB. In the Hardenbol et al. (1998) chart, a major third-order flooding event is fixed in the lower Parkinsoni Zone (Bj4). The transgressive peak of cycle 2.3 (Bathonian) corresponds to the upper Zigzag Zone in the BCB and is almost equivalent to the transgressive peak of the T – R cycle 7 defined in Boreal and Tethyan areas (lower Zigzag Zone, see Fig. 8). In the IB, however, this transgressive peak is located a bit higher, at the Progracilis –Subcontractus Zone boundary (Middle Bathonian). Within the cycle 2.4 (Callovian), a major discrepancy is found in the transgressive peak (Lower – Middle Callovian boundary). In the Boreal areas, this corresponds to the boundary between T – R cycles 8a and 8b. The upper boundary of cycle 2.4 (Mariae – Cordatum Zone boundary, Early Oxfordian) is coeval with a transgressive surface associated to a medium third-order sequence boundary (Ox1). However, the transgressive peak of the Boreal cycle 8b and Tethyan cycle 8 have been located at the lower Cordatum Zone and lower Mariae Zone, respectively. This major discrepancy may be due to different interpretation of the condensed level found at the Middle – Upper Jurassic transition (see discussion above). The presence of major discontinuities associated to stratigraphic gaps in separated basins suggests the existence of a regional tectonic process affecting individual western European basins during the Middle Jurassic. According to Jacquin et al. (1998), these discontinuities are associated with major extensional tectonic activity in the North Sea. The transgressive peaks of the Bajocian– Lower Bathonian are represented in other separated basins, and are likely to reflect the existence of sea-level rise events. Hallam (2001) considers the Early Bajocian, the Late Bajocian and the Middle Callovian the periods of major eustatic rise during the Middle Jurassic. If this observation is correct, the regressive interval recognised in northeast Iberia at the Middle Callovian should reflect the imprint of local tectonic development. 4.2.3. Upper Jurassic T– R facies cycles As it is the case in the Middle Jurassic, some discrepancies can also be seen between the number and age of Upper Jurassic T – R facies cycles defined in northeast Iberia and in the Tethyan and Boreal domain (Fig. 8). This fact suggests a strong local

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tectonic control on the development of long-term sequences. Cycle 3.1 (Oxfordian) includes a lower transgressive interval from the Lower Oxfordian (Cordatum Zone) to the lowest Upper Oxfordian (Hypselum Zone). A major discrepancy is found in the transgressive peak at the Hypselum Zone, which closely corresponds to the boundary between Boreal and Tethyan cycles 8 and 9 (middle Hypselum Zone), interpreted as a regressive peak. The boundary between cycles 3.1 and 3.2 corresponds to a widespread transgressive event at the latest Oxfordian (around the Planula– Galar subzones boundary). This discontinuity, present in eastern BCB (Ba´denas, 1996) and in the IB, is associated to a sharp increase of basin subsidence at the onset of the second rifting cycle in the IB, which occurred from latest Oxfordian to early-Late Albian times (Salas et al., 2001). The lower transgressive interval of the cycle 3.2 (Kimmeridgian) would range to a major transgressive peak at the Divisum Zone. An age equivalent secondorder transgressive peak is considered in the SE France basin and for the Provence Platform (Jacquin et al., 1998). A third-order transgressive event recognised in the IB at the Eudoxus Zone (Ba´denas and Aurell, 2001) coincides with the age of the major transgressive peak in the Tethyan domain. However, in the Boreal domain, the major transgressive peak of this cycle has been defined at the uppermost Kimmeridgian Autissiodorensis Zone. The age of the lower and upper boundaries of cycles 3.3 and 3.4 has not been confirmed with ammonites. The transgressive peaks of these cycles are roughly equivalent to the transgressive peaks of the T – R facies cycles 9b and 10 defined in Boreal areas. The upper boundary of cycle 3.4, located around the middle-Upper Berriasian, may correspond to the upper boundary of the T – R cycle 10 defined in Boreal and Tethyan areas. The Late Oxfordian– Kimmeridgian period is considered a transgressive interval in Europe and in other areas of the world (e.g., Hallam, 2001). This would suggest some influence of global sea-level rise events on the three transgressive events found in eastern Iberia during this time interval. The regressive peak found at the latest Oxfordian in the IB (Bimammatum and lower Planula zones) can be related to local uplift of the western marginal areas of the IB. Additionally,

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the latest Jurassic and earliest Cretaceous are clearly regressive in northwest Europe, a fact that has been related to regional tectonic activity (Hallam, 1988; Underhill, 1991). A lowering of the sea level of that time has been also suggested (Jacquin et al., 1998). Tectonic activity at the latest Jurassic – earliest Cretaceous (Tithonian – Berriasian) is evident in northeast Iberia (i.e., onset of the second rifting cycle of Salas et al., 2001, and Bay of Biscay early rifting episode of Martı´n-Chivelet et al., 2002). This tectonic activity involved the local development of continental basins in the western BCB and in the northwest IB. Accordingly, cycles 3.3 and 3.4 may reflect the influence of local tectonic development. However, the correlation of the transgressive peaks of these cycles with other western European basins, suggest the influence of a regional controlling factor.

5. Conclusions First and second-order transgressive – regressive cycles are identified across the sedimentary basins developed in northeast Iberia. Some discrepancies found in the age of cycle boundaries and transgressive peaks between northern basins (AB and BCB) and IB are explained by the different subsidence evolution. Correlation between cycles defined in northeast Iberia and major T –R cycles and T – R facies cycles defined by Hardenbol et al. (1998), De Gracianski et al. (1998) and Jacquin et al. (1998) in other western European basins has only been possible to a certain extend in some stratigraphic intervals. The reported data give support to the idea that the number and age of T– R cycles vary from one basin to another according to the local or regional tectonic evolution. A possible influence of regional (or global) sea-level fall events is proposed for the latest Rhaetian, latest Callovian – earliest Oxfordian and latest Jurassic – earliest Cretaceous regressive intervals observed in northeast Iberia. The first order transgressive peaks (and some of the second-order transgressive peaks) can be related to the episodes of eustatic rise reported by Hallam (2001). 1. Three first order cycles have been identified in northeast Iberia, ranging respectively from latest Rhaetian to Early Aalenian, from Middle Aalenian

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2.

3.

4.

5.

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to Early Oxfordian and from Early Oxfordian to Late Berriasian. The observed long-term evolution of the relative sea level at the Jurassic is in contrast to other previous models (i.e., two first-order T –R cycles in Hardenbol et al., 1998; a more or less gradual sea-level rise through the Jurassic, followed by a fall into the earliest Cretaceous in Hallam, 1988, 2001). The regressive trend of the Late Toarcian– Middle Aalenian in the northeast Iberian basins is a common feature in other western European basins. However, discrepancies in the age of the regressive peaks and associated stratigraphic gaps from one basin to another reflect the influence of local and regional tectonics on the development of this regressive interval. The widespread discontinuity found at the Callovian – Oxfordian boundary in open and shallow platform areas of northeast Iberia (IB and eastern BCB) is regarded here as formed during a longterm regressive interval. However, other authors consider the Callovian –Oxfordian transition as a major transgressive event (e.g., Jacquin et al., 1998). It is suggested that the observed discrepancies can be partly explained by the different interpretation (in terms of sea-level variation) given by different authors for similar successions. The age of the first order transgressive peaks is early-Middle Toarcian (Bifrons Zone), Late Bajocian (Garantiana Zone in BCB, upper Niortense Zone in IB) and latest – Early Kimmeridgian (Divisum zone, IB). There is good agreement between the age of these transgressive peaks and those reported from other western European basins. Time intervals including the transgressive peaks defined in separate western European basins can be related to stages of global sea-level rise at the Lower – Middle Toarcian transition, at the Late Bajocian and at the middle part of the Kimmeridgian (see Hallam, 2001). The observed discrepancies in the age of the transgressive peaks from one basin to another throughout Western Europe (up to one or three ammonite chronozones) can be explained by different subsidence evolution. Four Lower Jurassic second-order T – R cycles have been identified in the AB and BCB. The regressive intervals of cycle 1.1 (late Early Sinemurian) and cycle 1.2 (mid-Raricostatum

Zone) are not evident in the IB and are likely to reflect local subsidence changes (pulses of tectonic uplift acting in the southwestern margin of the BCB). However, the regressive interval of the cycle 1.1 can be correlated with one equivalent in the Boreal areas. The Late Pliensbachian regression (cycle 1.3) is broadly recognised over northeast Iberia and other Tethyan basins, although it corresponds to the onset of a second-order transgressive interval in Boreal basins. There are discrepancies in the age of the Late Sinemurian – Pliensbachian second-order transgressive peaks from one basin to another. Only the transgressive events in the mid-Early Sinemurian, in the earliest Pliensbachian (Jamesoni Zone) and in the earlyMiddle Toarcian (Bifrons Zone) are found across separated basins in the Tethyan and Boreal domains, suggesting the influence of sea-level rise events. 6. The boundaries of cycles 2.1 to 2.4 (Middle Jurassic) are recognised as major discontinuities associated to stratigraphic gaps of variable range. Equivalent discontinuities are reported in other western-European basins. Accordingly, a regional tectonic control affecting wide areas is suggested for the development of the Middle Jurassic regressive events described by Ferna´ndez-Lo´pez (1997) at the end of Late Bajocian, at the latest Bajocian and at the latest Bathonian. The secondorder transgressive peaks of cycles 2.1 and 2.2 may be related to major episodes of eustatic rise at the Early and Late Bajocian (Hallam, 2001). However, the Middle Callovian episode, reported by Hallam (2001) as a further major sea-level rise, is interpreted in the IB as the onset of a regressive event, suggesting the influence of local tectonics. 7. The discrepancies on the age of the boundaries and transgressive peaks of cycles 3.1 to 3.4 (Upper Jurassic to lowermost Cretaceous) from different West Europe basins reflect the influence of local tectonics on the T – R cycles development. A major discrepancy is found in the Early –Late Oxfordian (Hypselum Zone) transgressive peak. The transgressive events recognised in the Kimmeridgian (Divisum and Eudoxus zones) are likely to reflect stages of global sea-level rise. Major tectonic activity reported in the IB at the Oxfordian– Kimmeridgian transition may explain the existence

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of a regressive peak. The progressive off-lap of uppermost Jurassic units may also be caused by the tectonic uplift of northeastern margin of Iberia.

Acknowledgements Financial support was provided by M.C.T., Spain (Projects BTE2000-1148, MCT-CSIC, BTE200204453, BTE2002-02399), Basque Government and Sociedad de Hidrocarburos de Euskadi Research Project UE-1999/8 and FICYT (Gobierno del Principado de Asturias) PC-CIS01-56. We are grateful to the two reviewers, J. Reijmer and J.A. Vera, for their constructive comments.

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