Facies models of a shallow-water carbonate ramp ... - Springer Link

Facies (2010) 56:89–110 DOI 10.1007/s10347-009-0199-z

O R I G I N A L A R T I CL E

Facies models of a shallow-water carbonate ramp based on distribution of non-skeletal grains (Kimmeridgian, Spain) Beatriz Bádenas · Marc Aurell

Received: 20 March 2009 / Accepted: 14 August 2009 / Published online: 2 September 2009 © Springer-Verlag 2009

Abstract The internal facies and sequence architecture of a Late Jurassic (Late Kimmeridgian) shallow carbonate ramp was reconstructed after the analysis and correlation of 17 logs located south of Teruel (northeast Spain). The studied rocks are arranged in Wve high-frequency sequences A–E (5–26 m thick) bounded by discontinuities traceable across the entire study area (20 £ 25 km). Facies analysis across these sequences resulted in the reconstruction of three sedimentary models showing the transition from interior ramp environments (i.e., lagoon, backshoal, and shoal) to the progressively deeper foreshoal and oVshore areas. Coral-microbial reefs (meter-sized patch and pinnacle reefs) have a variable development throughout the sequences, mostly in the foreshoal and oVshore-proximal environments. The preferential occurrence and down-dip gradation of non-skeletal carbonate grains has been evaluated across the three models: low-energy peloidal-dominated, intermittent high-energy oolitic-dominated and highenergy oolitic–oncolitic dominated. The predominance of these non-skeletal grains in the shoal facies was mainly controlled by the hydrodynamic conditions and spatial heterogeneity of terrigenous input. The models illustrate particular cases of down-dip size-decrease of the resedimented grains (ooids, peloids, oncoids) due to storm-induced density Xows. OVshore coarsening of certain particles (intraclasts, oncoids) is locally observed in the mid-ramp areas favorable for microbial activity, involving coral-microbial reef and oncoid development. The observed facies variations can be applicable to carbonate platforms including

B. Bádenas (&) · M. Aurell Dpto. Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain e-mail: [email protected]

similar non-skeletal components, where outcrop conditions make the recognition of their three-dimensional distribution diYcult. Keywords Carbonate ramp · Carbonate grains · Sequences · Late Jurassic · Iberian basin

Introduction The reconstruction of facies distribution models on epeiric, tropical–subtropical carbonate ramps is complex, and the knowledge of the factors that controlled the sedimentary evolution is limited. A major diYculty is the large lateral extent of these types of sedimentary systems, the absence of recent analogues, and the diVerences between the climatic and oceanic parameters of icehouse and greenhouse intervals (e.g., Burchette and Wright 1992; Aurell et al. 1995; Wright and Burchette 1996). The knowledge of the geometry and lateral continuity of porous and permeable grain-supported facies is a key aspect for reservoir exploration and development strategies in ancient carbonate platforms (e.g., Borkhataria et al. 2005). A signiWcant diVerence between recent rimmed platforms and ancient epeiric carbonate ramps is the lateral development and extent of carbonate shoals. Recent platforms are limited in their progradation by the bordering deep ocean Xoor, whereas in epeiric ramps, the potential of progradation of the shoals over depositional slopes of a few degrees only, results in a much higher potential of preservation of grainsupported facies (Droste 2006). The Iberian basin was an intracratonic basin developed in the northeastern part of the Iberian plate during the Mesozoic extension (e.g., Salas and Casas 1993). During Late Jurassic times, wide carbonate ramps developed in this

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44° FRANCE

Valdecuenca SPAIN

Zaragoza Barcelona

AL

VA1

PaleozoicTriassic outcrop

BC

AR BD Jabaloyas

VI 8°

BH

0°

4°

Kimmeridgian outcrops Logged sections Reference villages Cross-sections

Tormón

MS

40° STUDY AREA Villel

BB

TO

CA

Madrid Teruel

PORTUG

VA2

Alobras Libros CU

El Cuervo

RP AC

Riodeva

Arroyo Cerezo

HO

RI

Hontanar TB Torre Baja 0 1

5

10 km

Fig. 1 Extent of the Kimmeridgian outcrops (gray areas) and location of the studied logs south of Teruel (northeast Spain); dashed lines indicate the cross sections shown in Figs. 6, 7, 8, and 9. AC Arroyo Cerezo, AR Arroyofrío, BB Barranco de las Balsillas, BC Barranco Canaleja,

BD Barranco del Diablo, BH Barranco de la Hoz, CA El Cañigral, CU El Cuervo, HO Hontanar, MS Masegarejo, RI Riodeva, RP Rambla Palomareja, TB Torre Baja, TO Tormón, VA Valdecuenca, VI Villel

basin, which was located around 33°N of palaeolatitude. In particular, the Kimmeridgian–Early Tithonian carbonate ramps had the more shallow sedimentary areas located to the west. These shallow domains include a wide range of grain-supported skeletal, oolitic, oncolitic, peloidal, intraclastic, and reefal facies, with intermittent siliciclastic intervals. OVshore, the relatively deep sedimentation areas (i.e., the outer-ramp settings) are characterized by the presence of monotonous successions of well-bedded lime mudstones. A signiWcant part of the carbonate mud accumulated in these outer-ramp domains was supplied from the shallow, high-productivity areas (Aurell et al. 1998; Bádenas and Aurell 2001a). The shallow facies of the Kimmeridgian Iberian carbonate ramps are widely exposed south of Teruel (northeast Spain). Of special relevance for sedimentological analysis

are the Kimmeridgian outcrops that form an almost continuous belt around the localities of Valdecuenca, Jabaloyas, Tormón, and Arroyo Cerezo (Fig. 1). The key aspect of these outcrops is that they allow the access to the facies deposited in the transition area between the relatively shallow and the deep carbonate ramp environment, with frequent interWngering between the grain- and mud-supported facies. Moreover, they include several levels with coralmicrobial reefs, locally displaying prominent pinnacle morphology (Fezer 1988; Leinfelder et al. 1993; Nose 1995; Bádenas and Aurell 2003; Aurell and Bádenas 2004). The main purpose of this work is to characterize the facies evolution of the Late Kimmeridgian Iberian carbonate ramp exposed in the outcrops south of Teruel. The data set includes the facies and the high-frequency sequences identiWed after a bed-by-bed logging. The correlation of

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logs provided a precise scheme showing the lateral and vertical facies distribution. This scheme is relevant for understanding some key sedimentary aspects of the carbonate ramps, such as the lateral distribution (from inner to midramp) of the more common non-skeletal components (peloids, oncoids, ooids, and intraclasts) or the preferential sites for coral-microbial reef development. Three sedimentary models with shoals dominated by diVerent proportions of peloids, ooids, and oncoids are deWned. These models have potential interest for further comparison and understanding of the facies heterogeneities observed in other less well exposed or buried carbonate platforms.

Geological setting and methodology The Kimmeridgian to Early Berriasian sedimentary units recorded in the Iberian basin (northeast Spain) are organized in four long-term depositional sequences (Kim1, Kim2, Ti1, and Ti2 sequences in Fig. 2). The observed overall facies evolution reXects the long-term regression operating at the end of the Jurassic in the Iberian basin (Aurell et al. 2003, 2009). This regressive trend is reXected by: (1) the long-term progradation and oZap of the shallow facies belt represented by the Pozuel, Torrecilla, and Higueruelas formations over the outer-ramp lime mudstones and marls of the Loriguilla Fm, (2) the existence of a stratigraphic gap (due to erosion and/or non-sedimentation), with an amplitude increasing towards the more western marginal areas, and (3) the variable age of the onset of the sedimentation of the coastal to continental siliciclastic dominated unit, represented by the Villar del Arzobispo Fm. The demise of the Kimmeridgian–Early Tithonian carbonate ramps has been related to the increasing tectonic activity starting around the Tithonian–Berriasian transition: the western marginal areas of the Iberian basin were uplifted, and some subsident furrows coevally developed eastwards were Wlled by coastal to continental, siliciclasticdominated successions of the Villar del Arzobispo Fm from the middle Tithonian onwards (Salas and Casas 1993; Aurell et al. 2003). The present study concentrates in the Kim2 sequence, in the outcrops located around Jabaloyas, Arroyo Cerezo, Villel and Riodeva, representing an area of 20 £ 25 km (Fig. 1). The studied sequence has an overall thickness ranging between 50 and 65 m and developed during most of the Late Kimmeridgian. It includes the Torrecilla Fm and the lateral oVshore Loriguilla Fm. The upper boundary of the Torrecilla Fm is considered to be an isochronous surface between Jabaloyas and Arroyo Cerezo and corresponds to a prominent discontinuity marked by the onset of the siliciclastic deposits of the Villar del Arzobispo Fm. This discontinuity was developed around the Kimmeridgian–

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Tithonian transition (determination based in larger benthic forams, see Fezer 1988) and corresponds to the boundary between the Kim2 and Ti1 sequences. The facies analysis is based on a bed-by-bed Weld description of 17 logs (see Fig. 1 for location), complemented by the analysis of more than 300 thin sections. The datum for correlation of the more proximal logs, found around Jabaloyas (BD, BC), Tormón (TO, MS) Arroyo Cerezo (AC), El Hontanar (HO), El Cuervo (CU), Villel (VI), Torre Baja (TB) and Riodeva (RI), is a 1 to 2-m-thick cross-bedded and graded sandstone interval that can be traced at regional scale. This interval was interpreted as deposited at the end of progradational stages of the Kim1 sequence (Aurell and Bádenas 2004). A widespread Xooding event involving the deposition of the shallow carbonate facies of the Kim2 sequence then covered these sandstones. In the more distal logs studied near Torre Baja (TB) and Riodeva (RI), this discontinuity is located below the Wrst appearance of thicker skeletal and oncolitic beds intercalated with the well-bedded dm-thick lime mudstones of the Loriguilla Fm. The studied Kim2 sequence is arranged in Wve deepening-shallowing higher-frequency sequences A–E that can be traced at regional scale (Aurell and Bádenas 2004). Some Weld views of these sequences are illustrated in Fig. 3. The bounding discontinuities are planar and wellcemented bedding surfaces, followed by sharp facies changes formed after Xooding events. Evidences of subaerial exposure are only locally recognized. Sequences A–E have ranges of duration and thickness equivalent to the fourth-order sequences of Einsele (1992) or to the mediumscale sequences of Colombíé and Strasser (2005). In many cases, they can be further subdivided into four to Wve higher-order sequences equivalent to the Wfth-order sequences of Einsele (1992) and the small-scale sequences of Colombíé and Strasser (2005). The total duration of the Late Kimmeridgian (i.e., around 2 Ma, Gradstein et al. 2004) suggests that sequences A–E have been controlled by eustatic oscillations in tune with orbital cycles (Aurell and Bádenas 2004). The inXuence of the short- and long-term eccentricity cycles on the sedimentation on the Late Kimmeridgian platforms has been previously suggested in the Iberian basin (Bádenas et al. 2005) and in the French and Swiss Jura Mountains (Colombíé and Strasser 2005; Strasser 2007).

Facies and environments Previous facies analyzed in the Late Kimmeridgian carbonate ramp between Jabaloyas and Arroyo Cerezo resulted in the deWnition of successive facies belts, showing a low gradient of depositional dip from inner-ramp domains (marsh,

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Fig. 2 Summary of the stratigraphy of the Late Jurassic in the marginal areas of the Iberian basin (around Teruel), locating the studied interval. The two lower maps show the palaeogeography at the Early

and Late Kimmeridgian (compiled from Aurell et al. 2003, 2009). Numbers 1–5 are reference localities in maps

sheltered lagoon, and shoreline-detached high-energy shoals) to mid-ramp areas, including high-energy and lowenergy oVshore environments with coral-microbial reefs (Aurell and Bádenas 2004). Siliciclastic facies (lutites and poorly bedded medium to coarse sandstones) are locally recorded and mainly associated with interior lagoon environments. The sedimentological information reported in Aurell and Bádenas (2004) has been enlarged with new data obtained in the present work. Six carbonate ramp environments are here deWned based on stratiWcation, sedimentary structures, texture, and types of carbonate particles (skeletal and nonskeletal grains). As explained in the next section, the occurrence and lateral relationships of the deWned facies belts

and the development of coral-microbial reefs are complex and variable throughout the evolution of the studied highfrequency sequences A–E. The inner area of the carbonate ramp is characterized by the presence of a low-energy protected environment (lagoon), which includes oncolitic rudstones (R) and Xoatstones (F) and bioclastic-peloidal wackestones–packstones (W–P). The backshoal environment includes packstones– grainstones (P–G) with diVerent proportions of peloids, bioclasts, ooids, and oncoids. The shoal environment is represented by grainstones (G) dominated by diVerent nonskeletal components (peloids, ooids, oncoids, and intraclasts). OVshore, the progressive decrease of wave energy in midramp areas is reXected by the decrease of hydrodynamic

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Fig. 3 Field views of the distribution of the high-frequency sequences A–E in two logs: Arroyo Cerezo (AC) and Hontanar (HO). Notice the presence of two pinnacle reefs in AC (sequence C)

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sedimentary structures and grain-size, and by the increase of mud-content and burrowing. The foreshoal environment is represented by packstone–grainstones (P–G) with varied non-skeletal components. These facies grade down-dip into the wackestones–packstones (W–P) facies of the oVshoreproximal environment and the mudstones–wackestones (M–W) typical of the oVshore-distal environment. The key aspects of the diVerent facies are summarized below and are also illustrated in Figs. 4 and 5.

Facies (2010) 56:89–110 Fig. 4 a Bioclastic tempestite with gastropods, bivalves and lituolids 䉴 (oVshore-distal facies). b Bioturbated peloidal tempestite (oVshoreproximal facies). c Intraclastic–oncolitic packstone showing type-I oncoids with poorly laminated micritic cortex (dashed arrow) and type-II oncoids with micritic and grumose laminations (white arrow). d Type-III oncoids showing thick cortex with micritic and grumose laminations and external organism-bearing encrustations with Bacinella and serpulids. e Peloidal shoal facies composed by poorly sorted peloids. f Intraclastic–bioclastic shoal facies with poorly sorted and poorly rounded micritic intraclasts. g, h Relatively well-sorted type-3 ooids showing thinly laminated Wne-radial cortices

Lagoon environment The lagoon environment includes Bacinella-oncoid F and R and bioclastic-peloidal W–P. These facies are generally arranged in 0.5–1.5-m-thick tabular beds or in irregular beds with intense burrowing (Thalassinoides and Planolites traces). Bivalve-encrusted top surfaces occur occasionally. The Bacinella-oncoids (up to 1.5 cm in diameter) have amoeboid or not sharply deWned contours and bioclastic cores (gastropods, bivalves, stromatoporoids, corals). They have a thick cortex mainly composed by organism-bearing encrustations (sensu Dahanayake 1977) with minor proportion of micritic discontinuous laminations. The encrustations are characterized by the predominance of sparitic patches of the cyanobacteria Bacinella irregularis (Fig. 5h) along with Lithocodium aggregatum, Cayeuxia, Thaumatoporella, and Marinella. The Bacinella-oncoid F and R facies also include variable proportions of poorly rounded bioclasts (mainly miliolids, gastropods and bivalves, and minor proportions of lituolids, textulariids, Thaumatoporella, echinoderms, and dasycladacean algae), poorly sorted peloids, micritic intraclasts, and micritized ooids. These Wner grains can be occasionally accumulated in mm-thick laminae. Stromatoporoids, hermatypic corals, and chaetetids are locally fragmented or in growth position. The bioclastic-peloidal W–P are composed of micritized bioclasts and peloids (Fig. 5f). Gastropods, bivalves, foraminifera (miliolids, textulariids, lituolids), echinoderms and algae (Marinella, Cayeuxia, dasycladaceans) are frequent. Ostracods and small fragments of stromatoporoids and corals are scarce. The peloids are irregular and poorly sorted showing gradation into micritic intraclasts. Also present are scattered Bacinella-oncoids (up to 1 cm in diameter) (Fig. 5g), micritized ooids and regular mm-size oncoids with discontinuous micritic laminations (type-I oncoids of Dahanayake 1977). The predominance of muddy textures, the frequent bioturbation and the skeletal content (especially the presence of miliolids and dasycladacean algae but also of openmarine fauna) reXect low-energy conditions in protected (not restricted) lagoon areas. This interpretation is consistent with the presence of the Bacinella-oncoids formed under calm conditions favoring bacterial growth, and the

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frequent micritization of skeletal grains and ooids. The presence of rudstones levels and peloidal and oolitic accumulations, reXect some episodic storm reworking in the lagoonal areas. Backshoal environment The backshoal environment is represented by bioturbated bioclastic–oolitic–oncolitic P–G and bioclastic–oolitic P–G. These facies are generally arranged in tabular and irregular levels up to 1 m-thick, with local planar cross-bedding. The bioclastic–oolitic–oncolitic P–G are composed of variable proportions of bioclasts, ooids, oncoids, and peloidsintraclasts. The more common skeletal grains are lituolids, bivalves, gastropods, and echinoderms; miliolids, textulariids, ostracods, and dasycladacean algae are also present in lower abundance (Fig. 5e). The dominant coated grains are type-1/3 ooids with alternating Wne-radial and micritic laminae (terminology after Strasser 1986) that appear partially micritized and frequently aggregated, and type-I and II oncoids with discontinuous micritic and grumose laminations (terminology after Dahanayake 1977). The Wner-grained carbonate grains are irregular and poorly sorted peloids showing gradation into micritic intraclasts. Intraclasts derived from the erosion of the reefal facies (corals and stromatoporoids covered by microbial crusts) and intraclasts of lagoonal bioclastic-peloidal W–P are also present. The bioclastic–oolitic P–G show micritized cm-size fragments of bivalves, Marinella and gastropods. In lower proportion are found foraminifera (miliolids, lituolids, and textulariids), corals, chaetetids, echinoderms, and Cayeuxia. The ooids (up to 3 mm in diameter) display variable cores (quartz grains, peloids, bioclasts) and are frequently micritized. Type-1/3 ooids and ooids with cortices composed by few Wne-radial laminae (type-4 ooids; Strasser 1986) have been identiWed. Micritic and oolitic intraclasts, peloids, oncoids and quartz grains are occasionally found. The two described facies show a mixture of skeletal and non-skeletal grains (mainly ooids and oncoids) partly derived from the interior lagoonal areas and from the active shoal facies belt. Compared to the lagoon areas, the bioclastic content indicates a more open-marine condition, with

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Facies (2010) 56:89–110 䉳 Fig. 5 a, b Relatively poorly sorted type-1/3 ooids with alternating Wne radial and micritic laminae; the arrow in a indicates a type-I oncoid with oolitic core. c, d Type-1/3 ooids and type-I oncoids (dashed arrow). e Backshoal facies with resedimented grains (gastropods, dasycladacean algae: white arrows) and resedimented type-1/3 ooids (dashed arrow). f, g Lagoon facies with poorly sorted peloids, bioclasts (gastropods, dasycladacean algae: white arrow in f) and sparse Bacinella-oncoids (dashed arrow in g). h Bacinella-oncoids (arrow) with irregular contour and poorly deWned micritic laminations (dashed arrow)

lower proportion of the bioclasts typical of the lagoon environment (i.e., miliolids, textulariids, ostracods, and dasycladacean algae). The common bioturbation and the micritization and aggregation of the skeletal and coated grains reXect shoal stabilization in the backshoal environment. Shoal environment The shoal environment includes Wve grainstone (G) facies, each one characterized by diverse dominant non-skeletal components: peloids, type-3 ooids, type-1/3 ooids, type-I and II oncoids and intraclasts-bioclasts. At the outcrop scale, these facies types form thick cemented successions of dm to m-thick tabular beds, showing frequent graded intervals, parallel lamination, planar cross-bedding, and local Thalassinoides traces. The peloidal G are formed almost exclusively by irregular poorly sorted peloids, up to 0.1 mm in diameter, with sharply deWned contours (Fig. 4e). The skeletal content (less that 10%) consists of lituolids (frequently accumulated in mm-thick laminae) and fragments of echinoderms and bivalves. Also present are gastropods, miliolids, textulariids, brachiopods, and small coral fragments. Fine quartz sand, plant remains, and micritic intraclasts are found in lower proportion. The peloidal G locally form levels with channel geometry with accumulations of micritic intraclasts at the base and dm-scale ripples on top. The two types of ooidal G (dominated either by type-3 or type-1/3 ooids) are frequently interbedded and may even show gradation at the bed scale. Type-3 ooids (up to 1 mm in diameter) show thinly laminated Wne-radial cortices and bioclasts, peloids, and quartz grains in the cores (Fig. 4g– h). Type-1/3 ooids (up to 3 mm in diameter) show peloidal and bioclastic cores and thick mixed cortices with alternating thinly micritic type-1 laminae and Wne-radial type-3 laminae (Fig. 5a–b). In general, type-3 ooid G are Wnergrained and better sorted than type-1/3 ooid G. These two facies may also show a variable proportion of irregular and poorly sorted peloids and bioclasts. In type-3 ooid G, bivalves, echinoderms, and lituolids are more abundant, whereas gastropods, brachiopods, miliolids, lituolids, textulariids, Marinella and Cayeuxia are scarce. In the areas

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close to coral-microbial reefs the skeletal content is higher, mainly with cm-size debris of corals and chaetetids, and poorly rounded fragments of reefal microbial crusts. In type-1/3 ooid G, bioclasts can be locally abundant (up to 25%) and are frequently accumulated in cm-thick laminae. The more common skeletal grains are bivalves, echinoderms and gastropods. Lituolids, textulariids, brachiopods, Cayeuxia, and cm-size fragments of corals, chatetids, stromatoporoids, and bryozoans are also present. This facies also shows scarce type-I and II oncoids, mudclasts, fragments of reefal microbial crusts and Wne quartz sand. The type-I and II oncoid G show gradation at bed-scale with type-1/3 ooid G. The dominant carbonate grains are type-1/3 ooids and up to 25% of oncoids; in lower proportion are found peloids, intraclasts, and bioclasts similar to those found in the type-1/3 ooid G (up to 20% of the grains). The oncoids have variable diameters (up to 1 cm) and diVerent types of cortices. Small and regular oncoids with more or less continuous micritic and grumose laminations are dominant (type-I and II oncoids, Fig. 5c–d). The larger the oncoids are the more irregular they are in shape, showing external organism-bearing encrustations (serpulids, bryozoans, Lithocodium, Bullopora, Bacinella), similar to type-III oncoids. The nuclei correspond to aggregate type-1/3 ooids, bioclasts (mainly echinoderms, bivalves, gastropods, corals), and intraclasts. The intraclastic–bioclastic G are formed by a similar proportion of poorly rounded intraclasts-peloids and bioclasts. The intraclasts are irregular (up to 4 mm in diameter) and grade into poorly sorted peloids (Fig. 4f). They mainly correspond to fragments of reefal microbial crusts and mudclasts. The bioclasts are variable in size (mm– cm) and include bivalves, echinoderms, lituolids, and corals. In lower proportion there are chaetetids, Cayeuxia, stromatoporoids, Solenopora, gastropods, bryozoans, serpulids, textulariids and miliolids. Also scattered are type3 ooids. StratiWcation, hydrodynamic sedimentary structures (cross-bedding, parallel lamination, channel morphologies, ripples), dominant grainstone textures, scarce bioturbation and the variety of skeletal grains indicate active shoals developed in open-marine high-energy areas, located above or around the fair-weather wave base. The occurrence and lateral relationships of the diVerentiated peloidal, oolitic, oncolitic, and intraclastic–bioclastic shoal facies were variable throughout the formation of sequences A–E. Foreshoal environment The foreshoal environment includes four diVerent types of grain-supported facies located either at the base of the shoal facies successions or as isolated levels intercalated with the mud-dominated facies of the oVshore environment.

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The peloidal P–G appear as isolated dm-thick tabular beds, with frequent planar cross-bedding and lamination and local development of hummocky structures and ripples. Planolites and Chondrites traces are also common. The components are similar to those found in the peloidal shoal facies, with poorly sorted and irregular peloids and bioclasts (less that 15%), including echinoderms, lituolids and bivalves, and scarce miliolids, corals, and gastropods. Micritic intraclasts, fragments of reefal microbial crusts and Wne quartz sand are also recognized. The oolitic-peloidal P–G are arranged in dm-thick tabular beds showing frequent bioturbation, Planolites traces, and parallel lamination. This facies has components similar to those of the type-3 ooid shoal facies, although the dominant type-3 ooids and incipient ooids are smaller in size (i.e., 0.5 mm in mean diameter). Dominant skeletal grains (up to 15%) are small fragments of bivalves, lituolids, and echinoderms; gastropods, brachiopods, textulariids, and miliolids are in lower proportion. Bioclastic grains, micritic intraclasts, and fragments of reefal microbial crusts can be accumulated in mm-thick laminae. Also present are type-I oncoids and Wne quartz sand. The intraclastic–bioclastic P–G correspond to dm-thick irregular beds with frequent bioturbation and parallel lamination, with components similar to those of the intraclastic– bioclastic shoal facies. Dominant grains are poorly sorted and poorly rounded mm to cm-size intraclasts (mudclasts and fragments of reefal microbial crusts) grading into poorly sorted peloids. The skeletal content (up to 25%) mainly consists of echinoderms, lituolids, bivalves (frequently accumulated in mm-thick laminae), with lower proportions of gastropods, brachiopods, corals, stromatoporoids, bryozoans, Cayeuxia, textulariids, miliolids, and serpulids. The diameters and proportions of metazoan debris and intraclasts of microbial crusts are larger in the levels occurring laterally to the reefal facies. Also present are type-I and II oncoids, type-3 ooids and Wne quartz sand. The type III-oncoids R–F are arranged in bioturbated irregular dm to m-thick beds, with occasional planar cross-bedding. The grains show two size fractions: oncoids and a Wne-grained intraclastic-peloidal matrix with diVerent proportions of bioclasts, similar to those of the intraclastic–bioclastic P–G. Regular type-III oncoids (up to 1 cm in diameter) showing thick cortices with grumose laminations and organism-bearing encrustations (serpulids, bryozoans, Lithocodium, Bacinella) predominate (Fig. 4d). The cores are aggregated smaller oncoids, intraclasts (mudclasts and fragments of reefal microbial crusts) and bioclasts (bivalves, gastropods, corals, serpulids, stromatoporoids, echinoderms, lituolids). Whole or fragmented type-I and II oncoids are also present in lower proportion.

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The stratigraphic location of the facies (at the base of shoal facies or intercalated with oVshore mud-dominated successions), the sedimentary structures (parallel lamination, local planar cross-bedding, hummocky, bioturbation), the nature of the carbonate grains (composition analogous to that of the grains found in the coeval shoal facies) and other textural aspects (i.e., grain-supported, poorly sorted, and poorly rounded intraclasts and open-marine bioclasts) indicate that they correspond to sediments deposited oVshore of the active shoals and underwent episodic storm reworking. Foreshoal facies include not only grains derived from the shoal areas (ooids, peloids, oncoids, intraclasts), but also in situ coated grains (type-III oncoids) indicating the existence of areas favourable to microbial activity. OVshore-proximal environment The oVshore-proximal environment is represented by peloidal–bioclastic and intraclastic–oncolitic facies, arranged in dm-thick irregular beds, showing a mixture of grain and mud-supported textures due to the ubiquitous bioturbation with Chondrites, Planolites, and Rhizocorallium traces. Millimeter to cm-thick grain-supported tempestites with parallel lamination are locally preserved. The peloidal–bioclastic W–P are mainly composed of variable proportions of well-rounded but poorly sorted and occasionally ferruginized peloids (up to 0.1 mm in diameter; Fig. 4b). They correspond to small micritized bioclasts, fecal pellets, and rounded intraclasts (mudclasts and fragments of reefal microbial crusts up to 3 mm in diameter are locally present). Skeletal grains (up to 25%) are variable in size (up to 1 cm, but mainly Wne-grained). Micritized or ferruginized lituolids, echinoderms, and fragments of or whole bivalves and gastropods are abundant and appear accumulated in mm to cm-thick laminae. Brachiopods, serpulids, hermatypic and solitary corals, stromatoporoids, bryozoans, Cayeuxia, Solenopora, miliolids, and textulariids are less abundant. The skeletal debris of metazoans, algae and fragments of microbial crusts have larger abundance and sizes in the areas located close to the coral-microbial reefs. Also present are quartz grains (Wne sand, up to 10%), fragmented and whole type-I and II oncoids and plant remains. The intraclastic–oncolitic W–P show peloids and skeletal debris similar to those of the peloidal–bioclastic W–P, but they have a larger proportion of intraclasts and/or oncoids. These two components can be accumulated in dmthick levels, with local channel geometry; in other cases, oncoids may form dm-thick F–R levels with mud- or grainsupported Wne-grained matrix (bioclasts, peloids, and micro-peloids with no sharply deWned rims). The oncoids are variable in size (up to 1 cm in diameter). In general, type-I and II oncoids predominate (micritic and grumose lamination in the external laminae; Fig. 4c). Also present

Facies (2010) 56:89–110

are irregular type-III oncoids with initial micritic and grumose laminations and external organism-bearing encrustations (serpulids, Lithocodium, Bacinella, and bryozoans). The cores are intraclasts (fragments of reefal microbial crusts, and mudclasts), bioclasts (bivalves, corals, gastropods, stromatoporoids, serpulids, lituolids) or aggregated smaller oncoids. Also present are fragmented, aggregated, and ferruginized type-I and II oncoids and aggregate typeIII oncoids occasionally bored by bivalves. The described facies represent a mixture of resedimented and in situ or slightly reworked non-skeletal grains accumulated in the transition area between the more proximal (high-energy) and the distal (low-energy) mid-ramp environments. Episodic storm-Xows resulted in the formation of the dm-thick (peloidal–bioclastic and intraclastic–oncolitic) tempestites intercalated with the lime-mudstones successions. Accumulation of lime mud and bioturbation during quiet periods led to the observed mixture of wackestone and packstone textures.

99

encrusters (e.g., Fezer 1988; Leinfelder 1994; Nose 1995). According to Nose (1995), the dominant coral taxa in the pinnacle reefs are Thamnasteria and Microsolena. Other coral groups, stromatoporoids (Actinostromaria, Disparistromaria, Dehornella, Milleporidium, Cladocoropsis), chaetetids (Chaetetes, Ptychochaetetes) and Solenopora are less common. Lithophagid bivalves, gastropods, echinoids, and lithistid demosponges are also present. A dense micritic to peloidal microbial crust is found around the colonial forms and contain a rich association of encrusting organisms (serpulids, bryozoans, Tubiphytes, Terebella, Koskinobullina, Lithocodium, Placopsilina, Cayeuxia, Bacinella and Thaumatoporella). However, a microbial crust with lower diversity of micro-encrusters (high abundance of Tubiphytes and Terebella) dominates the reef fabric at the initial stages of growth (i.e., in coral-bearing thrombolites).

Facies distribution in the high-frequency sequences OVshore-distal environment The oVshore distal environment is represented by bioturbated bioclastic M–W. The facies is arranged in tabular to irregular beds (0.5 m mean thickness) intercalated with marly limestones and marls. Disarticulated or whole gastropods, bivalves, lituolids, brachiopods, echinoderms, serpulids, and solitary corals are the main skeletal components. Poorly sorted and ferruginized peloids and bioclasts forming mm-thick laminae disrupted by Planolites and Chondrites traces are frequent and are interpreted as distal tempestites (Fig. 4a). Poorly sorted peloids, fecal pellets and micro-peloids with no sharply deWned rims are recognized in the matrix. Also scattered plant remains and quartz grains (Wne sand) occur. Coral-microbial reefs Coral-microbial reefs of diVerent size and morphology occur dispersed mostly in the foreshoal and oVshore-proximal environments described above. Most of the reefs are patches around 1–3 m high, but they may also form pinnacles with very steep slopes (i.e., conical to cylindrical shape, up to 15 m high). Most of the growth of these pinnacles occurred during the early stages of rapid gain of accommodation represented by the lower deepening interval of the high-frequency sequences C and E (Bádenas and Aurell 2003; Aurell and Bádenas 2004). Corals, chaetetids, and stromatoporoids also colonized the lagoon environment but, in this case, did not construct positive-relief reefs. The reef fabric consists of framestones with variable proportions of colonial organisms (mainly corals) and microbial crusts with associated encrusters and micro-

The vertical facies trends observed in the diVerent logs, combined to the analysis of the discontinuity surfaces, allowed the deWnition of the Wve high-frequency sequences A–E that can be correlated across the studied logs. This correlation is based in the assumption of the age equivalence of the sequence boundaries across the studied ramp area, which is supported by several observations: (1) the equivalent number of high-frequency sequences in individual logs, (2) the facies distribution within the sequences that are thought to be coeval is coherent with the overall orientation of the facies belts on the studied carbonate ramp (i.e., a progressive deepening towards the east-southeast), (3) the lateral continuity of the cemented surfaces interpreted as sequence boundaries, which have been walked out over long distances (e.g., 3–5 km in the continuous outcrops around Jabaloyas and Arroyo Cerezo: see Fig. 1). The distribution and correlation of the facies types across sequences A–E is shown in Figs. 6–9. We have also included successive maps illustrating a possible distribution of facies belts during certain stages of sequence development. The correlation between the logs located in the western part of the study area is supported by the continuity of the Kimmeridgian outcrops (between Valdecuenca and Jabaloyas, see Fig. 1); however, the correlation with the isolated outcrops of TB, RI, and VI is more open to discussion. In the correlation maps, we have left a gap in the north-central area, which today is occupied by a large Paleozoic–Triassic outcrop. The proposed correlations allow us to understand the evolution over time and space of the six environments deWned by the diVerent facies belts, the lateral relationship between the facies types included in the successive

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SEQUENCE A 5

0 BC mfs 5

BD

No outcrop control

No outcrop control

MS

BC

BD

VI

CU

No outcrop control

Ml MW PG

RI AC

HO

?

5

N

VI

TO

mfs 0

10 km

TB

mfs

Facies distribution: Late highstand

TO 0

mfs

MS CU

5

mfs

SHALLOWING

5m

Covered RI

mfs: maximumflooding surface

0

AC

DEEPENING HO

1

0

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FACIES AND ENVIRONMENTS Backshoal

Lagoon Bacinellaoncoid F Bacinellaoncoid R

R

Bioclasticpeloidal W-P

Covered TB

10 km

5

Shoal

Foreshoal Peloidal G Type-3 ooid G

Bioclasticoolitic P-G

Type-1/3 ooid G Type-I and II oncoid G Intraclasticbioclastic G

Bioclastic-oolitic oncolitic P-G

Offshore-proximal Offshore-distal

Peloidal P-G Oolitic-peloidal P-G Intraclasticbioclastic P-G Type-III oncoid R-F

Peloidalbioclastic W-P Intraclasticoncolitic W-P

Bioclastic M-W and marly limestones

Ml: marls M: lime mudstones W: wackestones P: packstones G: grainstones F: floatstones R: rudstones

Coral-microbial reef

Siliciclastic facies

Coral reefs

Coral-bearing thrombolite

SEQUENCE B No outcrop control

Ml MW PG

BD

?

2

BC No outcrop control

?

mfs 0

No outcrop control

BC

BD

10 km

N

VI

VI MS

TO CU

5

mfs

RI

SHALLOWING

AC

mfs: maximumflooding surface

TO 0

HO TB

MS


DEEPENING CU

5

mfs 0 5m

RI AC HO

0

5

0

0

1

5

10 km

Fig. 6 Facies distribution in sequences A and B

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?

TB

Facies (2010) 56:89–110

sequences, and the location and distribution of the diVerent non-skeletal grains across the carbonate ramp. Sequence A Sequence A (5–8 m thick) shows a deepening-shallowing upward trend and is composed entirely of subtidal facies, with no subaerial exposure surface on top (Fig. 6). It corresponds to a subtidal cycle (Osleger 1991) equivalent to the give-up sequence of Hillgärtner and Strasser (2003). The lower deepening trend is reXected by the retrogradation of the oVshore facies over siliciclastic facies in the proximal logs. The maximum-Xooding surface (mfs) has been located in a cemented surface found at the top of a lower thickening-upward interval, representing the maximum extent of the oVshore facies. Low sedimentary rates around this maximum-Xooding interval favored the microbial crust development: the stabilization and hardening of the substrate allowed the local growth of coral-microbial reefs up to 2 m thick around AC. Above the mfs there is a widespread progradation of foreshoal and oVshore-proximal facies. The reconstruction of the facies belts at the late highstand shows a down-dip (northwest-to-southeast) gradation of peloidal and bioclastic sediments: from peloidal shoal and foreshoal facies, to peloidal–bioclastic and bioclastic oVshore facies. However, the northern area around VI is dominated by irregular foreshoal type-III oncoids formed in situ, reXecting low-energy conditions favorable for microbial activity. Most of the peloids found in sequence A (with sharply deWned contours and poorly sorted) correspond to small intraclasts. In the southern areas around HO and CU there are foreshoal coarser-grained facies (intraclastic–bioclastic) instead of peloidal. Most of the included intraclasts consist of mm to cm-size micritic and reefal fragments. These components reXect the destruction and reworking of the coral reef facies located nearby (e.g., AC) and/or from a possibly shallower intraclastic shoal facies belt developed southeast of the study area. The oVshore counterparts (i.e., intraclastic–oncolitic facies) also contain this type of intraclastic and peloidal grains along with in situ or slightly resedimented type-III oncoids. Sequence B The onset of sequence B is marked by a widespread deepening event, involving the setting of the oVshore-distal facies over large domains of the carbonate ramp. The sequence (thickness ranging from 5 to 10 m) is a subtidal cycle with a general shallowing-upward trend, and a lower deepening interval irregularly recorded across the studied logs. In VI, the maximum Xooding is reXected by the

101

deposition of a thick succession of oVshore-distal facies. In MS, TO, AC, HO and CU the maximum Xooding is located in a cemented surface at the top of a thickening and coarsening-upward basal interval. Decrease of carbonate production can be related to siliciclastic input. Increase of terrigenous components is observed in the middle part of the BD, HO and CU logs around the mfs. The sequence includes the development of coral-microbial reefs at the late highstand, coeval to the foreshoal facies (BC) and to the oVshore-proximal facies (VI). During the highstand, the shallow areas of the ramp were covered by oolitic-peloidal and intraclastic–bioclastic foreshoal facies, the later with abundant grains derived from the coevally developed coral reefs. These foreshoal facies grade oVshore to Wner-grained peloidal–bioclastic facies. Further oVshore, there is a north-to-south oriented facies belt formed by in situ or slightly reworked intraclastic– oncolitic W–P and, eastwards, the oVshore-distal bioclastic M–W. As in sequence A, there are coarser-grained facies (intraclastic–bioclastic) in the southern sectors (around HO), which could be related to the existence of intraclastic shoal facies to the south and/or to the reworking of the in situ oncolitic sediments (type-III oncoid R–F) developed at TO and CU. The widespread development of these distal oncolitic facies indicates general low-energy conditions favourable for oncoid growing. The conditions favoring microbial activity could be related to the long-term relative sea-level rise developed during the lower part of the Kim2 sequence (Aurell and Bádenas 2004). Sequence C Sequence C has variable thickness (12–18 m) and is characterized by the widespread development of coral pinnacle reefs in shallow areas (Fig. 7). In these shallow areas, the sequence has a general deepening-shallowing facies trend. The mfs is an encrusted surface involving a sharp facies change in the shallow ramp area (e.g., BD). In distal areas, the mfs cannot be identiWed and sequence C is formed by Wve shallowing-upward higher-order sequences (see dashed lines in Fig. 7). In shallower areas, the upper boundary of sequence C is a planar and erosive surface formed after local subaerial exposure, with a signiWcant erosive gap (e.g., AC, where the sequence ends with shoal facies with erosion down to the top of some of the pinnacle reefs: Fig. 3). Sequence C is interpreted to correspond to a catchdown type sequence (sensu Hillgärtner and Strasser 2003). During the early stage of the transgressive episode and around the maximum Xooding (late transgressive, Fig. 7), type-3 ooid and intraclastic shoals and intraclastic foreshoals covered the shallow ramp areas located to the northwest. These shallow facies grade oVshore to peloidal–bioclastic

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Facies (2010) 56:89–110 SEQUENCE C

15 5

0

BD mfs

BC

N

VI

10

No outcrop control

No outcrop control

?

TO

MS

10 km

?

5

CU

0

AC

HO

BC

BD

No outcrop control

RI

?

?

TB

VI


Ml MW PG

5

0 10

BD

BC No outcrop control

N

VI

? TO

5

mfs

?

10 km

MS

TO

MS CU RI

0

AC

CU

HO TB

Facies distribution: Late transgressive RI AC SHALLOWING

HO

10

TB mfs: maximumflooding surface

5

DEEPENING 0

5m

0

0

1

5

FACIES AND ENVIRONMENTS Lagoon

R

Backshoal

Bacinellaoncoid F Bacinellaoncoid R Bioclasticpeloidal W-P

Bioclasticoolitic P-G Bioclastic-oolitic oncolitic P-G


Fig. 7 Facies distribution in sequence C

123

10 km

Shoal




Offshore-proximal Offshore-distal Peloidalbioclastic W-P Intraclasticoncolitic W-P



Coral reefs



Facies (2010) 56:89–110

W–P and, more to the east, to bioclastic M–W. Coral reefs were coevally developed to the shoal and foreshoal facies. During the early deepening episode, these coral reefs show thrombolitic fabric with predominance of microbial crusts with Tubiphytes and Terebella, adapted to low oxygen levels and low sediment supply (e.g., Leinfelder et al. 1993; Dupraz and Strasser 2002). Most of the vertical growing of the pinnacle reefs (with coral-microbial reef fabric) took place during the late transgressive episode. The reef growth was interrupted at the stage of the maximum Xooding (see S2 surface in Fig. 7). At the early highstand, the lowering of the rates of creation of accommodation allowed the recovery of the carbonate production. The accommodation available in inter-pinnacle areas became progressively Wlled up by the onlapping of the oVshore-proximal peloidal– bioclastic facies, and the growth of the pinnacles continued up to the earliest stages of the late highstand (Aurell and Bádenas 2004). The highstand is characterized by the rapid progradation of the shallow facies over the oVshore-proximal peloidal– bioclastic facies (Fig. 7). Most of the western ramp areas were dominated by type-3 ooid shoals, passing eastwards to the type-1/3 ooid and peloidal shoals (TO, VI). The observed facies distribution supports the idea that the type3 ooid shoals may represent more interior areas compared to the type-1/3 ooid and peloidal shoals. Inshore, there is the local record of the backshoal bioclastic–oolitic facies (with abundant micritized ooids) around BC. In southern areas, there is a clear facies gradation of the non-skeletal grains (ooids, peloids) from foreshoal to oVshore areas: type-3 ooid shoals grade oVshore into oolitic-peloidal and peloidal foreshoal facies, and to oVshore-proximal peloidal–bioclastic facies. However, as in sequence B, in the central sector around TO and CU there was a foreshoal area favorable for the deposition of type-III oncoids. Further oVshore (RI), there was also an area favorable for the growing of these oncoids, dominated by the intraclastic–oncolitic oVshore-proximal facies. Sequence D Sequence D has variable thickness (Fig. 8), increasing from proximal western areas (around 8–14 m) to distal eastern localities (from 16 to 26 m). The lower boundary represents a deepening event, reXected in proximal areas by the sharp retrogradation of the oVshore-proximal facies. The sequence has a general shallowing-upward facies trend and is formed by Wve thickening and coarsening shallowingupward higher-order sequences. A possible lower deepening interval is recorded in HO, CU, and TB. The upper boundary of sequence D is a Xat and cemented surface, followed by a sharp retrogradation of oVshore-proximal facies at the onset of sequence E.

103

In northern areas, the sequence is dominated by marsh to interior lagoon environments (between BD and VI) and by carbonate lagoonal and shoal facies. However, the central sector (around CU) is characterized by the deposition of thick successions of oVshore-proximal facies. As in previous sequences, this sector includes facies indicating deeper and/or low-energy conditions than those located in southern and northern sectors. Compared to the previous sequences, sequence D is characterized by a widespread development of the oncolitic facies from shallow to relatively deep areas. In turn, the coral reefs widely developed in the previous sequence C are only locally recorded around CU (metersize coral-microbial patch reefs). During the early highstand (Fig. 8), type-3 ooid shoals and/or siliciclastic sediments covered the shallower areas of the ramp. As in sequence C, type-3 ooid shoals grade oVshore to type -1/3 ooid shoals. The-1/3 ooids form the bulk of a wide facies belt developed in the southern area, which progressively grades into intraclastic–bioclastic foreshoal facies and to oVshore-proximal (peloidal–bioclastic) facies. Further oVshore, intraclastic–oncolitic and bioclastic facies were deposited. During the late highstand, type-I and II oncoids deWne a wide shoal belt around HO. The backshore facies found around AC contains type-1/3 ooids and type-I and II oncoids probably resedimented from these shoals. The central area (around CU) is represented by intraclastic–bioclastic shoals, with local growth of coral reefs. Sequence E Sequence E has a homogeneous thickness around 15 m (Fig. 9). Facies development involves a major change across the ramp with respect to the previous sequence: dominance of peloids instead of ooids and oncoids in the shoals; presence of coral-microbial reefs in the mid-ramp area; widespread development of Bacinella-oncoids in the lagoon and loss of the siliciclastic input in the marginal areas. In western shallow areas, sequence E shows a deepening-shallowing trend. OVshore, the facies trend is more complex due to the existence of four higher-order shallowing-upward sequences. The lower deepening episode allowed the local pinnacle reef development and retrogradation of the oVshore-proximal facies over the entire study area. The initial stage of growth corresponds to thrombolitic fabrics developed during the Xooding event at the onset of the sequence (Bádenas and Aurell 2003). The upper shallowing episode is reXected by the sharp progradation of inner-ramp lagoonal facies, which covered most of the study area at the end of the sequence. During the early highstand (Fig. 9), bioclastic-peloidal lagoon facies formed a northeast–southwest oriented belt.

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Facies (2010) 56:89–110 0

SEQUENCE D

1

10 km

5

5m 5

0

BD

BC

Eroded

10

TO

N

VI

No outcrop control

0

Cretaceous

?

MS

? CU

5

No outcrop control

10 km

? RI

? AC HO TB

0

BC

BD


BD

BC ?

MS

No outcrop control

TO

Cretaceous

TO

?

10 km

N

VI No outcrop control

? Ml MW PG

5

0

VI

?

CU

RI

MS AC HO TB CU

Facies distribution: Early highstand

RI

AC SHALLOWING

HO

5

mfs: maximumflooding surface DEEPENING

? TB

0

? ?


R

Backshoal




Fig. 8 Facies distribution in sequence D

123

Shoal







Coral reefs



Facies (2010) 56:89–110

105 5

0

SEQUENCE E

BD BC

0

1

10 km

5

No outcrop control

R

Eroded

5m

Ml MW PG

R R

Eroded

BC

BD

10

R

R

? ?

CU

0

?

AC

VI

N

VI

TO

MS

Eroded

10 km

RI

HO

R

TB mfs 5

Facies distribution: Late highstand 5

0

mfs

BD BC

?

0

TO

No outcrop control

Eroded

Eroded

MS

MS

10 km

N

VI ?

TO CU RI

CU AC HO TB

Facies distribution: Early highstand RI

AC 15

R

HO ?

SHALLOWING 10 mfs: maximumflooding surface

TB

5

mfs

DEEPENING 0

?


R

Backshoal



Shoal


Type-1/3 ooid G Type-I and II oncoids G Intraclasticbioclastic G







Coral reefs


Fig. 9 Facies distribution in sequence E

Bioclastic–oolitic–oncolitic backshoal and peloidal shoals are locally recorded. Foreshoal facies (peloidal and intraclastic–bioclastic) covered a wide area between AC and TB. They contain abundant intraclasts and reefal debris in the area located close to the coral-microbial

reefs. The intraclastic foreshoal facies grades into peloidal–bioclastic oVshore-proximal facies with local patch reefs (CU). Towards the end of the sequence (late highstand), the Bacinella-oncoid R–F covered the lagoon developed in the

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western and southern areas of the ramp. The distal portion of the lagoon is dominated by bioclastic-peloidal facies. The foreshoal environment (RI) was also an area favorable for microbial activity and development of type-III oncoids. The presence of the backshoal and peloidal shoal belts between the lagoonal and the foreshore environments is interpreted based on the vertical facies association observed in diVerent logs.

Overall distribution of facies belts The distribution of facies belts throughout the studied Wve high-frequency sequences indicates a progressive eastward increase of the depositional dip of the ramp, which is coherent with the basin-wide palaeogeographic reconstruction of the Iberian basin (Bádenas and Aurell 2001a; Aurell et al. 2009). The lateral facies relationships conWrm the stormdominated character of the Kimmeridgian ramp, which was related to the windward orientation of the basin respect to hurricanes and winter winds. The reported data permit to assign approximate widths of the six facies belts, distributed from inner to mid-ramp environments (Fig. 10). The inner-ramp lagoon was at least 10 km wide and was mainly covered by low-energy mud-supported sediments including variable proportion of Bacinella-oncoids, bioclasts, and peloids. Grain-supported sediments are dominant in the backshoal, shoal, and foreshoal environments. This higher-energy area located around the fair-weather wave base deWnes the boundary between the inner and mid-ramp areas (Burchette and Wright 1992). The backshoal environment reached around 3 km of maximum extent. The width of the related shoal environment was variable (3–10 km). The foreshoal environment contains sediments mainly deposited by storm reworking and has a probable maximum extent of 10 km. The whole width of these high-energy backshoal-shoalforeshoal areas is larger during the stages of highstand progradation. The oVshore environment shows progressively decreasing low-energy conditions, resulting in the deposition of mud-dominated sediments. The oVshore-proximal belt reached a variable extent from 3–20 km and was characterized by the abundant intercalation of coarse-grained graded tempestites, mainly transported from shallower areas by storm-generated density currents. This range of widths Wts well the value of 8 km for the facies belt with frequent storm-related deposits measured in age-equivalent Kimmeridgian outcrops located in the northern Iberian basin (Aurell et al. 1998; Bádenas and Aurell 2001b). The input of resedimented coarse grains decreases to the oVshore-distal areas, dominated by lime muds with distal tempestites.

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Facies (2010) 56:89–110 Fig. 10 Summary of the facies and non-skeletal component distribu- 䉴 tion for the three proposed sedimentary models. Black horizontal bars indicate the relative abundance of non-skeletal grains; grey horizontal bars indicate the relative abundance of some speciWc non-skeletal grains in areas where coral reef and oncoid grow

Facies models SpeciWc facies developed from inner to mid-ramp areas across the diVerent stages of evolution. In particular, there was a preferential accumulation of either peloidal, oolitic, or oncolitic shoals. Based on the relative abundances of these three types of non-skeletal grains, three facies models are proposed (Fig. 10). The down-dip gradation of the diVerent non-skeletal grains and the factors controlling the observed facies distribution in space and time are discussed. The variable extent of the coral-microbial reefs across the ramp and their vertical growth is also analyzed. Peloidal-dominated ramp Relatively low-energy peloidal shoals dominated during sequences A and E (Figs. 6, 9). The facies distributions in these sequences are used to propose the sedimentary model of the peloidal-dominated ramp (Fig. 10), which is mainly characterized by: (1) the development of a low-energy peloidal or oncolitic lagoon, (2) the existence of peloidal shoals with a progressive oVshore gradation of the peloidal grains, and (3) the growing of coral-microbial reefs from foreshoal to oVshore-proximal areas during the stages of rapid gain of accommodation. The peloidal shoal that characterizes this ramp-type is composed of poorly sorted peloids mainly originated from the reworking of the muddy lagoonal sediments (small mudclasts) but also from laterally related intraclastic and coral-microbial reefs (i.e., fragments of microbial crusts). The backshoal environment includes peloids grading into micritic intraclasts and micritized and aggregate coated grains (type-1/3 ooids, type-I and II oncoids). Some peloids probably correspond to micritized ooids. The abundance of micritized bioclasts points to the possibility that peloids may also have resulted from alteration and breakdown of skeletal components (e.g., Samankassou et al. 2005). Bacinella-oncoids were widely developed in the interior lagoon environment (upper part of sequence E), with lowenergy conditions favorable for the bacterial growth. Similar Bacinella-oncoids have been described and interpreted as generated in very low-energy lagoon areas in the Late Oxfordian of the Swiss Jura (type-4 oncoids of Védrine et al. 2007). The extensive deposition of oncoids is also related to the absence of siliciclastic input (and reduced nutrient input), which contributed to the growing of oncoids

Facies (2010) 56:89–110

107

INNER-RAMP FACIES AND ENVIRONMENTS

Lagoon (10 km)

MID-RAMP

Back shoal Shoal (3 km) (3-10 km)

Dominant texture

Offshore-proximal (3-20 km)

Foreshoal (3-10 km)

grain-supported

Offshore-distal

mud-supported

Peloidal-dominated ramp (Sequences A and E) Peloids Intraclasts Bacinellaoncoids Type-III oncoids Type-I and II oncoids Type-1/3 ooids

sea level

R

R

Bacinellaoncoid F Bacinellaoncoid R

BioclasticBioclasticPeloidal G Peloidal P-G peloidal W-P oolitic-oncolitic P-G Coral reefs Laretal variations in areas where coral reefs and oncoids grow Intraclasticbioclastic P-G

Peloidalbioclastic W-P Type-III oncoid R-F


Intraclasticoncolitic W-P

Oolitic-dominated ramp (Sequences B and C) Peloids Intraclasts Type-III oncoids Type-I and II oncoids Type-1/3 ooids Type-3 ooids

sea level

Bioclasticpeloidal W-P Laretal variations in areas where coral reefs and oncoids grow

BioclasticType-3 ooid G ooliticP-G

Oolitic-peloidal Peloidal P-G P-G Coral reefs

Intraclasticbioclastic G

Peloidalbioclastic W-P



Intraclasticbioclastic P-G

Oolitic-oncolitic-dominated ramp (Sequences C and D) Peloids Intraclasts Type-III oncoids Type-I and II oncoids Type-1/3 ooids Type-3 ooids

sea level

Bioclasticoolitic P-G

Type-3 ooid G Type-1/3 ooid G

BioclasticLateral variations in areas where oolitic-oncolitic P-G oncoids grow

Type-III oncoids PeloidalR-F bioclastic W-P Type-I and II oncoid G Intraclasticbioclastic P-G



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with light-dependant and oligotrophic micro-encrusters (e.g., Leinfelder et al. 1993; Dupraz and Strasser 1999). In the Iberian case, the local presence of isolated stromatoporoids, chaetetids, and corals in the lagoon indicates also good water transparency and oligotrophic conditions. The peloids and intraclasts found in the shoal-foreshoal high-energy belt were resedimented forming the peloidal– bioclastic tempestites common in oVshore-proximal areas. In oVshore-distal areas, well-sorted peloids (fecal pellets) and micro-peloids (bacterial in origin?) are also present in low proportion. This down-dip gradation reXects the decreasing energy of the storm-related density currents. Type-III oncoids are present in the foreshoal areas coevally to coral-microbial reefs and in the oVshore-proximal areas lateral to the peloidal–bioclastic sediments (see also Figs. 6, 9). These oncoids show grumose laminations and organism-bearing encrustations of Lithocodium, Bacinella, and serpulids. They are similar to type-3 oncoids of Védrine et al. (2007), which were interpreted to represent relatively low-energy conditions and clear waters in lagoonal areas. However, in the Iberian case, these oncoids are found in open mid-ramp areas, with low-energy and clear waters favorable for the microbial activity. Oolitic-dominated ramp The oolitic-dominated ramp model characterizes the facies distribution observed in sequences B and C (Fig. 10). The key aspects of this model are the widespread development of relatively high-energy type-3 ooid shoals and the presence of particular facies types in the related backshoal and foreshoal environments. However, the distal portion of the lagoon environment (i.e., bioclastic-peloidal facies) and the oVshore facies are similar to the peloidal-dominated ramp described above. The shoals are mainly formed by ooids with thinly laminated Wne-radial cortices (type-3 ooids), with variable proportion of peloids and ooids with alternating micritic and sparitic laminae (type-1/3 ooids). Type-3 ooids are indicative of normal-marine shallow waters and intermittent highenergy conditions (Strasser 1986). The backshoal is characterized by bioclastic facies with variable amount of micritized type-1/3 ooids (probably resedimented) and ooids with few Wne-radial laminae (type-4 ooids). Type-4 ooids may be formed either in situ or resedimented from interior lagoon areas, because they are interpreted to preferentially formed in restricted lagoonal environments (Strasser 1986). OVshore to the oolitic shoal, a gradation of sediments composed by ooids and peloids is observed: foreshoal oolitic-peloidal, oVshore-proximal peloidal–bioclastic and oVshore-distal bioclastic. The observed gradation is related to the down-dip decreasing energy of the storm-related density currents.

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Facies (2010) 56:89–110

Similar to the peloidal-ramp model, the open-marine areas were favorable for coral-microbial reef growth and for low-energy oncoid generation. This reXects general water transparency and low nutrient levels (oligotrophic conditions), which is coherent with the low inXux of terrigenous sediments during this stage of ramp development (e.g., Védrine et al. 2007). Coral reefs grew widely from shoal to oVshore distal environments during the transgressive phase of sequence C. However, the initial growth of thrombolitic fabrics may reXect low sediment supply and low oxygen levels during the initial stages of rapid accommodation gain (Aurell and Bádenas 2004). The coeval inter-reef facies have a large proportion of intraclasts derived from the physical destruction of reefal fabric. Oolitic–oncolitic-dominated ramp The oolitic–oncolitic-dominated ramp is characterized by the widespread occurrence of type-1/3 ooids and type-I and II oncoids in the shoal facies (Fig. 10). The development of this particular type of oolitic and oncolitic shoals during the highstand episode of sequence C and in sequence D (see Figs. 7, 8) was mainly controlled by hydrodynamic conditions. The backshoal environment consists of bioclastic grains mixed with micritized and aggregated type-1/3 ooids and type-I and II oncoids, probably resedimented from the shoal facies. The foreshoal and oVshore environment are similar to those of the peloidal-dominated ramp. However, coralmicrobial reefs are almost completely absent: the only exception are small patch reefs located in CU (sequence D), which could explain the local record of the related foreshoal intraclastic–bioclastic facies. Type-3 ooid and type-1/3 ooid shoals coexisted during the highstand episode of sequence C and during the initial stages of sequence D. This coexistence is observed at outcrop-scale (interWngering and grading) and also in a broader scale. However, type-3 ooid shoals preferentially developed in the interior portions of the shoal belt respect to the type-1/3 ooids, developed in the more open areas of the shoals. These observations are coherent with the interpretation of Strasser (1986): type-1 ooids with micritic laminae formed under continuous agitation, whereas sparitic type-3 ooids reXect intermittent high-energy. In the studied case, continuous agitation could control the preferential formation of type-1/3 ooids in the seaward or storm-facing side of the shoal belt, whereas slightly minor agitation in the interior area of the shoals would result in the formation of type-3 ooids. Microbial activity could also have some inXuence on the preferential precipitation of micritic ooids (Strasser 1986), as suggested by the presence of type-I and II oncoids in the type-1/3 ooid shoals facies.

Facies (2010) 56:89–110

Type-I and II oncoids reached a maximum extent in the late highstand of sequence D, replacing the oolitic shoals in some speciWc areas of the ramp (see Figs. 8, 10). These oncoids show more or less continuous micritic and grumose laminations and are similar to the type-1 and 2 oncoids of Védrine et al. (2007). They were formed by sediment trapping by micro-organisms under relatively high-energy conditions to permit rolling of the particles. The variety of skeletal components and the micro-encrusters recorded in the oncolitic shoals indicates good water transparency and low nutrient levels, which are related to areas with low inXux of terrigenous sediment. The proliferation of oncolitic facies in sequence D indicates an increase of the microbial activity in the inner-ramp, which also continued in sequence E, when Bacinella-oncolitic facies widely developed in the low-energy lagoon environment. The oncolitic shoals deposited preferentially far away of the areas with high siliciclastic input, which are in turn dominated by the oolitic shoals (i.e., in the northern areas, see Fig. 8). This fact indicates that the patchy distribution of oncolitic shoals could be attributed to a spatial heterogeneity of terrigenous input (e.g., Hallock 1988; Védrine et al. 2007).

Conclusion Facies analysis and correlation of Wve high-frequency (medium-scale) sequences over the Kimmeridgian outcrops exposed south of Teruel (northeast Spain) resulted in the characterization of the down-dip and vertical evolution of successive facies belts, which represented diVerent environments on a low-angle carbonate ramp. These facies belts occurred in the shallow portion of the ramp, located above and around the fair-weather wave base. Protected (but not restricted) lagoons (10 km of minimum lateral extent) and high-energy backshoal and shoal environments (3 and 3–10 km, respectively) developed in inner-ramp areas. The mid-ramp domain is represented by a high-energy foreshoal environment (3–10 km) and lowenergy, oVshore-proximal (3–20 km) and oVshore-distal environments. Meter-size coral-microbial reefs of variable morphology (from patch reefs to pinnacles) have an irregular development across the foreshoal and oVshore environments. There are signiWcant vertical changes (i.e., across the diVerent high-frequency sequences) concerning the dominant non-skeletal grains accumulated in the shorelinedetached high-energy shoals. The observed changes are summarized in three diVerent sedimentary models: peloidal-dominated, oolitic-dominated, and oolitic–oncoliticdominated carbonate ramps. These models also reXect a preferential spatial distribution of non-skeletal carbonate

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grains, which are common in the shallow portions of the carbonate platforms. The dominance of one or another type of non-skeletal grains in the shoal facies was mainly controlled by the hydrodynamic conditions: (1) relatively low-energy conditions favor the development of shoals dominated by peloids, mainly derived from the reworking of inner muddy lagoon sediments and from the erosion of mid-ramp coralmicrobial reefs. (2) Shoals dominated by ooids with thinly laminated Wne-radial cortices (type-3 ooids) developed in the proximal portion of the shoal belt under intermittent high-energy conditions, whereas ooids with alternating Wne-radial and micritic laminae (type-1/3 ooids) formed in the higher energy seaward side of the shoal belt. (3) Small and regular oncoids with more or less continuous micritic and grumose laminations (type-I and II oncoids) are dominant in areas of minor-energy located away from the point sources of siliciclastics. The storm-facing exposure of the carbonate ramp controlled the oVshore resedimentation distance of the nonskeletal components by the storm-related density currents. As a consequence, oVshore of the shoals there was a downdip gradation of the sediments (progressively Wner-grained, thinner beds and mud-dominated), including mainly resedimented peloids, ooids, and oncoids. In contrast, in situ or slightly reworked grains were dominant in the lagoon environment (Bacinella-oncoids, skeletal grains, peloids) and in the backshoal environment (bioclastic, oolitic, and oncolitic sediments). The models show local facies heterogeneities in the midramp areas. In particular, (1) the local growth of patch reefs and pinnacles results in an increasing amount of the intraclastic–bioclastic grains, (2) the facies can be dominated by in situ generated oncoids, characterized by irregular shapes and thick cortices with grumose laminations and organismbearing encrustations (i.e., type-III oncoids). Coral reef growth took place mainly during the stages of accommodation gain (i.e., transgressive episodes) and stages of relatively low siliciclastic input (i.e., peloidal-dominated and oolític-dominated ramps). The facies distribution and down-dip heterogeneities summarized in the three proposed carbonate-ramp models can be applied to the interpretation of shallow carbonate platforms including similar non-skeletal components, specially when outcrops conditions do not allow a direct access to check the lateral and vertical facies relationship (i.e., widely spaced 1-D logs or wells). In particular, the reported data point to a preferential distribution and lateral extent of the diVerent shoals and coral-microbial reefs that can be useful for reservoir characterization. Acknowledgments Financial support was provided by the research Spanish government projects CGL2007-62469/BTE, CGL2008-01237/

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110 BTE and CGL2008-04916/BTE, and by the Aragón government (Grupo “Reconstrucciones Paleoambientales”). We are grateful to André Strasser and André Freiwald for their constructive comments, which improved the original version of the manuscript.

References Aurell M, Bádenas B (2004) Facies and depositional sequence evolution controlled by high-frequency sea-level changes in a shallowwater carbonate ramp (Late Kimmeridgian, NE Spain). Geol Mag 141:717–733 Aurell M, Bosence D, Waltham DA (1995) Carbonate ramp depositional systems from a Late Jurassic epeiric platform (Iberian basin, Spain): a combined computer modelling and outcrop analysis. Sedimentology 42:75–94 Aurell M, Bádenas B, Bosence D, Waltham DA (1998) Carbonate production and oVshore transport on a Late Jurassic carbonate ramp (Kimmeridgian, Iberian basin, NE Spain): evidence from outcrops and computer modeling. In: Wright VP, Burchette TP (eds) Carbonate ramps. Geol Soc Lond Spec Publ 149, pp 137–161 Aurell M, Robles S, Bádenas B, Quesada S, Rosales I, Meléndez G, García-Ramos JC (2003) Transgressive/regressive cycles and Jurassic palaeogeography of northeast Iberia. Sediment Geol 162:239–271 Aurell M, Bádenas B, Ipas J, Ramajo J (2009) Sedimentary evolution of an Upper Jurassic carbonate ramp (Iberian Basin, NE Spain). In: van Buchem F, Gerdes FK, Esteban M (eds) Reference models of Mesozoic and Cenozoic carbonate systems in Europe and the Middle East—stratigraphy and diagenesis. Geol Soc Lond Spec Publ (in press) Bádenas B, Aurell M (2001a) Kimmeridgian palaeogeography and basin evolution of northeastern Iberia. Palaeogeogr Palaeoclimatol Palaeoecol 168:291–310 Bádenas B, Aurell M (2001b) Proximal–distal facies relationship and sedimentary processes in a storm dominated carbonate ramp (Kimmeridgian, northwest of the Iberian Ranges, Spain). Sediment Geol 139:319–342 Bádenas B, Aurell M (2003) Análisis comparado y controles en la sedimentación de dos arrecifes de la zona media de una rampa carbonatada del Jurásico Superior de la Cordillera Ibérica. Revista Sociedad Geológica de España 16:151–166 Bádenas B, Aurell M, Gröcke DR (2005) Facies analysis and correlation of high-order sequences in middle-outer ramp successions: variations in exported carbonate in basin-wide 13Ccarb (Kimmeridgian, NE Spain). Sedimentology 52:1253–1276 Borkhataria R, Aigner T, Pöppelreiter MC, Pipping JCP (2005) Characterisation of epeiric “layer-cake” carbonate reservoirs: Upper Muschelkalk (Middle Triassic), The Netherlands. J Petroleum Geol 28:119–146 Burchette TP, Wright VP (1992) Carbonate ramp depositional systems. Sediment Geol 79:3–57

123

Facies (2010) 56:89–110 Colombíé C, Strasser A (2005) Facies, cycles and controls on the evolution of a keep-up carbonate platform (Kimmeridgian, Swiss Jura). Sedimentology 52:1207–1228 Dahanayake K (1977) ClassiWcation of oncoids from the Upper Jurassic carbonates of the French Jura. Sediment Geol 18:337–353 Droste H (2006) A new model for epeiric carbonate platforms. GEO 2006 Middle East Conference and Exhibition 27–29 March 2006. Manama, Bahrain Dupraz C, Strasser A (1999) Microbialites and micro-encrusters in shallow coral bioherms (Middle to Late Oxfordian, Swiss Jura Mountains). Facies 40:101–130 Dupraz C, Strasser A (2002) Nutritional modes in coral-microbialite reefs (Jurassic, Oxfordian, Switzerland): evolution of trophic structure as a response to environmental change. Palaios 17:446–471 Einsele G (1992) Sedimentary basins. Springer, Berlin Heidelberg New York, 627 pp Fezer R (1988) Die oberjurassische karbonatische Regressionsfazies im südwestlichen Keltiberikum zwischen Griegos und Aras de Alpuente (Prov. Teruel, Cuenca, Valencia, Spanien). Arb Institut fur Geologie und Paläontologie Universitat Stuttgart 84:1–119 Gradstein F, Ogg J, Smith A (2004) A geologic time scale 2004. Cambridge University Press, Cambridge, 589 pp Hallock P (1988) The role of nutrient availability in bioerosion: consequences to carbonate build-ups. Palaeogeogr Palaeoclimatol Palaeoecol 63:275–291 Hillgärtner H, Strasser A (2003) QuantiWcation of high-frequency sealevel Xuctuations in shallow-water carbonates: an example from the Berriasian–Valanginian (French Jura). Palaeogeogr Palaeoclimatol Palaeoecol 200:43–63 Leinfelder RR, Nose M, Schmid D, Werner W (1993) Microbial crusts of the Late Jurassic: composition, palaeoecological signiWcance and importance in reef construction. Facies 29:195–230 Nose M (1995) Vergleichende Faziesanalyse und Palökologie korallenreicher VerXachungsabfolgen des Iberischen Oberjura. ProWl 8:1–237 Osleger D (1991) Subtidal carbonate cycles: implications for allocyclic vs autocyclic controls. Geology 19:917–920 Salas R, Casas A (1993) Mesozoic extensional tectonics, stratigraphy and crustal evolution during the Alpine cycle of the eastern Iberian basin. Tectonophysics 228:33–55 Samankassou E, Tresch J, Strasser A (2005) Origin of peloids in Early Cretaceous deposits, Dorset, South England. Facies 51:264–273 Strasser A (1986) Ooids in Purbeck limestones (lowermost Cretaceous) of the Swiss and French Jura. Sedimentology 33:711–727 Strasser A (2007) Astronomical time scale for the Middle Oxfordian to Late Kimmeridgian in the Swiss and French Jura Mountains. Swiss J Geosci 100:407–429 Védrine S, Strasser A, Hug W (2007) Oncoid growth and distribution controlled by sea-level Xuctuations and climate (Late Oxfordian, Swiss Jura Mountains). Facies 53:532–535 Wright VP, Burchette T (1996) Shallow-water carbonate environments. In: Reading HG (ed) Sedimentary environments: processes facies and stratigraphy. Blackwell, London, pp 325–394