The pinnacle reefs ofJabaloyas (Late I{immeridg¿an, NE Spain): Vertical zona[ionand associatedfacies related [osea level changes
M. AUREIi. and 13. BÁ])ENAS Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50.009 Zaragoza, Spain
ABSTRACT Tite outcrops located near Jabaloyas (Northeast Spaln, Iberian basin) allow the reconstruction of tite sedimentary environments of a late Kimme- ridgian carbonate ramp. In tite middle ramp arcas, aboye storm wave base le- vel, grew a set of reefs which generally display a pinnacle geometry. The fa- brie of these reefs consists of different proportions of colonial forms (mainily corals), internal sediment and microbial crusts to associated encrusting orga- nisms. Four pinnacles have been sampled along a 6 Km proximal-distal sec- tion across thc ramp. Tite relative proportion of corals and microbial crusts evaluated in titese samples allows to diffcrcntiate between coral titrombolites and corál-mierobial ernst reefs fabrica. Changes in thesc fabrica allowto defi- ne some vertical and lateral zonation in the pinnacle recfs. Tite variation of tite fabrics in the pininacle reefs and tite transition between the different asso- ciated facies have been related to sea level changes. An iitial fast rise of sea level resulted in botit the drowning of the mid ramp grain-supported facies and in tite grow of scattered coral thrombolites. Tite aggradation of tite pin- nades, with increasing proportion of metazoan builders, was initiated and/or followed during the continuous riscr of sea level, and coeval carbonate sedi- mentation recovered in tite inner arcas of tite middle ramp. The total risc of sea level was between 12 to 15 m. During a subsequent stillstand of sea level, tite successive observation of aggradational and progradational stacking pat- teras in tite coevally developed inter-reef facies allows tite diflerentiation of an early and late highstand systems tract. Key wnrds: Late Jurassic, Iberian basin, carbonate ramp, reef, sea level changes
Cuadernos de Geología lb4ñca, mini. 22, 37-64. Servicio de Publicaciones. Universidad C<>rnplutense, Madrid, 1997. 38 Al. Áu,-clI y B. Bádenes
RESUMEN
Los afloramientos localizados en las proximidades de Jabaloyas (Cordi- llera Ibérica, Teruel) han permitido reconstruir los distintos amiñentes sedi- mentarios de la rampa carbonatada del Kimmeridgiense superior. En las par- Les medias de esta rampa, sobre cl nivel de base de oleaje de mal tiempo, tuvo lugar el crecimiento de una serie de arrecifes alsíados, que generalmente pre- sentan morfología de pináculo. La fábrica básica de estos arrecifes está for- mada por diferentes proporciones de formas coloniales (corales en mayor abundacia), sedimento interno y costras microbianas, que incluyen organis- mos encostrantes asociados. Se ha evaluado la proporción relativa entre estos componentes a partir de cuatro pináculos, localizados en los diferentes domi- nios de sedimentación. Los cambios en la fábrica arrecifal permiten definir cierta zonación vertical y lateral en los pináculos arrecifales. Se han relacio- nado las variaciones en las fábricas arrecifales y los diferentes cambios en las facies asociadas, con sucesivas variaciones del nivel del mar. Una etapa inicial de ascenso rápido del nivel del mar implicó ia estabilización (le las facies gra- nosostenidas interarrecifales, así como el crecimiento local de arrecifes donii- nados por costras microbianas. El crecimiento vertical de los pináculos, con un predominio de las formas coralinas, se inició o continnó durante esta eta- pa de ascenso Palabras clave: Jurásico, cuenca Ibérica, rampa carbonatada, arrecifes, caminos del nivel del mar. INTRODUCTION The growth of organisms that construct reefs is controlled by factors like xvave energy, 1)ackground sedimentation, nutrient supply or oxygen fluctua- tions. Because some of these factors may change with depth, tite internal va- riation of the composition and fabric of tite reefs may reflect variations in sea level. TIle interplay between reef and carbonate platforrn growth and sea le- ‘e’ vhdl lid.> uve’’ i epuí LW ni >evei di »luutc> ~ rWllUdIl dliii CUU1d~Ci 198i; James and Macintyre, 1985>. Tite resulting data have been applied to the geological record to define sea level cycles of d¡ffercnt order and magni- tude. To aclíjeve reliáble reconstructions of sea level cycles, a precise control Tite pinnacle reefl oflabaloyas GEOLOGICAL AND STRATIGRAPH1CAL SETTING Tite Iberian Citain, a montainous system located in the northeastern part of the Iberian Peninsula, contains well-preserved and continuous outcrops of Mesozoic sedimentary rocks. The Upper Jurassic outcrops of Jabaloyas are located Southeast of Teruel (Nortiteast Spain), in tite western-central part of the Iberian Chain (flg. 1). The reef studied were developed in marginal are- as of Ile so-called Iberian basin. Marine sedimentation in the lberian basin took place in shallow and extensive carbonate ramp settings (several hun- dreds of kilometres across) during Late Jurassic times. Titese ramps were open to the Tetlíys sea to thc East. 1 lowever, during major flooding episodes 40 M. Aurelí y 8. Bádenas N420 Fig. 1 —Location of Ihe studied aiea and distribution of tbe upper Jurassic outcrops between Frías and Jabaloyas localities. The lower inset locates thefive sections studied around Jabaloyas. Fig. 1.—Situación del área estudiada y distribución de los afloramientos del Jurásico superior entre Frías y Jabaloyas. La parte inferiormuestra la situación de los perfilesestudiados en torno a Jabaloyas. The pinnacle reefs ofJabaloyas (Late Kimmeridgian, NE Spain) 41 conneetion with the boreal realm was possible aeross the so-caiUed Soria Sea- way to tite Northwest (Aureil and Meléndez, 1993). The main lithologies and stratigrapliic distribution of tite Kimmeridgian sedimentary rocks of Ile Sierra tite Jabalón, betweentite Arroyofrío and Ja- baloyas localities, is shownin Fig. 2. The lower marly unit corresponds to tite Sot tite Chera Formation and spans from Late Oxfordian to Early Kinne- rid gian. This unit changes offshore to Ile rhythmic mudstone and marí al- ternations of tite Loriguilla Formation. The sandstones and ooliIlic gralnsto- nes of tite Pozuel Formation prograde aboye titese units (AureIl, 1990; Báde- nas and Aurelí, 1997). The topmost Kimmeridgian unit includes tite reefal unit studied in titis work. Based on titeir mieropalontological contení, Fezer (1988) dated Ile studied reefs and associated facies as Late Kimmeridgian. According to Nose (1995), they belong to tite the lowermost Late Kimmeridgian biozone (i.e. acantbicum biozone). Lititostratigraphically, they have traditionaily been as- signed to the Higueruelas Formation. 1lowever, according t() both its litho- logy, its fossil content and its lateral equivalence witit tite offshore micrites of the Loriguilla Formation we propose tite use of Ile term Torrecilla Forma- tion br Ibis reefal unit (Fig. 2>. Tite Torrecilla Formation is a Rlmmeridgian reefal unit, defined by Alonso and Mas (1990) in the north-western part of the basin. A sequence boundary below tite Torrecilla Fm. is indicated by a signifi- cant backstepping of facies (Aurelí, 1990; Fig. 2). In earlier works, we corre- lated this sequence boundary with the unconformity which is found offshore between the Loriguilla and Higueruelas Formations (Aurelí, 1990; Aurelí and Meléndez, 1993). This boundary was developed during tite Early Titho- man. However, Ile precise dating reported by Nose (1995) makes unlikely tbis assignment. Consequently, the studied reefs are located in Ile iower part of a depositional sequence witich spans from Late Kimmeridgian to Early Tititonian. This sequence would corrcspond to tite upper part of tite Kimme- ridgian Sequence used in our previous works, and is also recognized in noii- itern areas OVERALL FACIES DISTRíBUTION IN THE TORRECILLA FORMATION The Torrecilla Formation reacites a maximum tbickness of 72 m east- wards, ni Ile Barranco de las Balsillas section (see BB section in Fig. 2). To Ile West, the upper part of tite unit is partly eroded, and is unconformably overlain by Albian fluvial sandstones (i.e. Utrillas Formation). Tite lower 42 Al. Ani-oíl yB. Bádenas ¡‘u,> pe!pn4s E ca ca ÍD E e. 1 4 ‘4 D O >1 iro .0 u, ‘4 4 1 <0 o 1- fi o II Ii Fig. 2—Stratigraphy of the FQimmeridgian between Pie Arroyí>frftí iríd 4aL.>al >vis 1 IIEEFAL FACIES ‘111w n-iorphoiogy aud Lite fabrie of tite reefs of Jabaloyas has been descri- I)ed by Fezer (1988), Errenst (1990a,b), Leinfelder et al. (1993, 1994) and Nose (1995). Titese works include the identification and description of tite diffcrent fossils aud titeir distribution along Ile reefs. Below, we outline tite main features ol)scrved in the rectal facies. Moíwi I(IWC’ OF i-4vvl~S Tite studied parasequence includes seattcred patch reef with variable morphology. Most of t.bem have a írinnacle morphology and are distributed in a discrete hoí-izon, from the ED to tIic BE sections (Fig. 4). Wcstward. in Uhe FT section, tite pinnacles are absení and tliey laterally grade to a set of m.etric patcli recta The pinnacles have a it.eight/widtb ratio close to 1 and ‘¡el-y steep slopes, more Ihan 450 The local coalescence of Lhese pinnacles may result in reefs some tens of meter iii heigbt. Tite highness of dic pinna- cies iw.reases eastward, with maxhnum vertical development in tite 1313 site- tion, wííere they can reach 16 m. Aronud Litis outcrop, metrie patch reefs are also laLcrally found to tite top of tite pinnacles. l3etxveen the 1W and thc ED sections, me pinnaeles are generally up to 12-13 m high. Locally on some of 44 Al. Aurelí y 8. Bádenas V.g. 3.—Facies distribution iii the studied parasequence (see Fig. 1 fo>- location). ~g. 3.—í )istrib»íción de facies en Ea parasecuencia estudiad-a (situación en ]a Hg. 1 TIre pinnade reefs ofJabaloyas (Late Kimnmeridgian, NE Spain) 45 Fig. 4—Facies distribution in theBI 1 outcrop. The boundary between facies A asid C is an en- crusted asid bui-rowed surface tlhat can be traced np into tire pinnacle core (i.e. 52 surface). The distribufion of Pie samples in the Bit piimacle is also shown (tire topmost sample J is out of tibe scope of tire photograph). Seetext for facies explanation. Fig. 4—Distribución de facies en el perfil 1311. El limite entre las facies Ay C es una superficie bioturbada y encostrada que se puede prolongarhacia el interior del pináculo (superficie 52). Se muestra asimismo la distribución de las muestras analizadas (la muestra J queda fuera de la fo- tografía). 46 Al ..~ 1 ¿<‘vil y U. Badenes /v >‘~>V y, ~ 8- -— FACIES O ____ FACIES C FACIES A Fig. 5,—Facies aud sampie distributhirí in the BC outcrop. lSelo~v tlíc st,sd cd 1>innacle. a intelí ecl with a stratal niorj>hology is observed. See Lext br facies explana[i PÁg. 6—Facies mxl sample distribution in Wc UD outcníp. Two prominent disa>ndnuities (le. Sí and 82 surfaces) are found ja Wc pinnacle core. See text for facies explanation. Fig. 6—-Distribución dc facies y de muestras en el perfil UD. l)entro del núcleo del pináculo se reconocen dos superficies de discontinuidad (superficies SI y 52). Ver texto para la explicación de facies. 48 M. AureIly E. Bádenas these sections (cg., BC section, see Fig. 5>, small biostronws up to 3 ni thick are found below Ile pinnacles. Fíat and sharp surfaces occur in the core of tite pinnacles. An upper sur- face, located 8 to 9 m aboye tite bottom of Ile reef is recognized in boIl the BD, BH and BC pinnacles (see S2 in Figs. 4 and 6), whereas a lower surface, located sorne 5 ni aboye tite bottom is recognized lii Ile more western pinna- eles, located around Ile BO outcrop (see Sí in Fig. 6). Ti ni I4EEF FABIuC The basic reef fabrie consists of variable proportions of boIl colonial forms (mainly corals: 5-60%), microbial crusts and associated encrusters and microencrusters (10-80%) and internal sediment <15-40%), giving risc lo fra- mestonetextures (Hg. 7). Other orgainisms such us lithophagid bivalves, gas- tropods and echinoids are common throughout Ile reef. The different pro- portions between colonial forms and mierobial crusts allows to separate two reef types (basedin the classification of Leinfelder, 1993): (1) coral-microbial ernst reefs (refereed here as coral reefs), when tite proportion of colonial forms is larger titan tite proportion of microbial crusts, and (2) coral-bearing titrombolites y, -. - a, “ 4 .4 ‘ - Intsrnaj sdlment Nicrobial Type 1 cav>t es Encr,ntecs: Tb-K- KoskinobullhríaTublphytes Th- Thaurretoporelia Type 2 caví e> B- Bacinolís Sp- Serpulid Le- Lithocedlum A- Calcareous algae Fig. 7.—Example of tire reef fabric, showing tire distribution of different encrusting organisms (sample D inthe 131-1 pinnacle>. Fig. 7—Ejemplo de fábrica arrecifal, en el que se muestra la distribución de diversos orgarús- mos incrustantes (muestra D del Pináculo 21-1). 50 Al. Aurelí y Li Rádenas and larger encrusters like serpulids or bryozoans (Fig. 7). Thcy usually form less than 10% of tite total volume of the rock. However, witen tite fabrie 18 do- minated by microbial crusts, Iley can reacit up to 20%. In these instances, tite d iversitv of micro-encrusters is lower, being dominated by «Tubifhytes» mo- rronensis. Botb tite microbial crusts and tite metazoají builders are largely bo- red by lithophagid bivalves. 3. Infernal sedimení: Two types of internal cavities are distinguislíed (Fig. 7): (1) type 1 cavities correspond to tite holes lcft during tite growing of both colonial forms and microbial crusts; <2) type 2 cavities were origiriated 1w the biocrosion and boring of the metazoan builders or the microbial crusts. Tite cavities are generally filled by internal sediment. The internal sedimeuL mosth’ consists of silty biomicrites (mudstoncs to wackestones), wilb scntte- red debris of bivalves, echinoderms, gastropods, bentlíic forams, coralsand microbial crusts. These niicritic fillings may be interrupted by tibe growiríg of microbial crusts at several leveis. Grain-supported facies (i.e. peloidal aud noidal packstones-grainstones) may also occur as interna) sediment. Bot.h grain-supl)orted and micritie facies may be associated, formirig graded and 1 arninated structures in geopetal fillings. GENERAL. [REN[)S (IP VERTICAL ANO LA-rERAL. ZONATION ON REIEFS Four pinnacles regu.larly distributed in a proximal-distal ramp section have been sampled in order to evaluate tibe general trend of tite vertical aud lateral variation on tite proportion between colonial forms and ruicrobial crusts. 1. Rl) pinnacle: Tite distribution of tite studied samples mvi the location of tííe two planar surfaces along the core of the BD pinnacle is sbown in Fig. 6. Tite vertical variatiotí of the proportion of both colonial fornís aud mitro- bial crusts (cf/mc ratio) is reported iii Fig. 8. Tite reef shows an overail up- xvard increase of tite cf/mc ratio. Proportions of microbial crusts (45-75%) are larger than colonial forms be]oxv Sí. The cf/mc ratio ranges froní 1.5 Lo 4 l)etween Sí and 52. In Uds zone, an important volume of the internal sedi- ment contains ooidal particles, similar to LLe ones located in tite inter-reef arcas (facies B, see below). Aboye 52, tite internal sediment is micritie and Ile cf/mc ratio 15 larger titan 2.5. 2. 1311 pinnacle: ‘¡‘he distribution of tite studied samples in the BM puma- ele is shoxvn in Fig. 4. Tite results reponed in Fig. 8 sitows overalí volumes of colonial form between 40-70%, clearlylarger titan microbial crusís (generally below 30%). 1 loivever, Hiere al-e two arcas xxntit larger proporlion of mitro- bial crusts: tite bottnm of Uae pinnacle (sample A) and Ile zone located around tite 52 surface (sample G>. The cf/mc ratio is also differentbelow and aboye tite 52 surface. i.e fi-orn 1 .3 to 3.2 and larger titan 6 respcctively. Tlic pinnacle recj oJ jabaloyas (LateRhntneñdgan, NR Spain) 51 nioroblal c,usts ooi.io,mu/mIor.oruat - 100% ,1 A- ] 50 0’ 0 50 100% 10 -5, 2 e o ¡ FACIES A FACIES A 2 ~ •~‘1 [~Bo 50 100 ¡E - o 4 0 o ¡ 2 n, 1~ 0 A 1 Vi =~~Z~””’ =48 Ñtfr ti ji oit osí o rE [líe paipo 3. BC pinnacie: Like in tite previous pinnacles, titere is an overalí up- ward increase of tite cf/mc ratio, only interrupted by samples F aud H (52 and 39% of microbial crust respectively). tite latter located on 52 siírface. ‘rite biostrome located below tite BC pinnacle was also sampled (sample A, Figs. 5 and 8). Samples A and B show a close to 0.5 cf/mc ratio and tite- refore correspond to coral titrombolites. ‘lite coral reef samples located be- low S2 slíow ratios up to 2.8, whereas tite ones located aboye líave ratios down to 2.6. 4. BR pinnacle: Tite studied samples slíow a lower part (up te 12 m) do- minated by microbial crusts (60 to 80 %, witit less titan 20% of coráIs) and an upper part dominated by corals (less titan 20% of microbial crusts and 60- 70 tora» cora¡-bearlng o reela ihnniboii¡sS Fig. O Cor reí ttion of the four soimpled piunacles boised on the Si oi»¡d 82 strrfoíces. showiug tire latcral ‘s »nataju of te c»ulouial formns/microbiod críist raticx defining ctu-al-reef c,r coral throm- b»,lit ¡c f tcws (see right coltionns in Kg. 8>. Hg. 9 (u? reí >cio.r~ entre los cuatro pináculos muestreadts en base a las superfocíes Sí y 82, en la cjue sc mucstra la variación Literal de la proporción formas coloniales/costras niicrobioinas (ver 1 1)1 ulun is cíe la íu»rte derecha en la PÁg. 8) TIre pinnacle reefr ofjabaloyas (Late Kimmeridgian, NE Spain) 53 previously reported by Giner and Barnolas (1979> and Leinfelder el al. (1993). Stacked horizons wiIl similar cf/mc ratio separated by sharp surfa- ces are also recognized in tite studied pinnacles. On tite basis of tite interme- diate Sí and S2 surfaces, a correlation between Ile pinnacles can be estajÁis- taxi. Titree vertical zones are distinguished: (1> below Si, there are coral it- rombolites, with variable proportion of corals; <2) between Sí and S2 surface, Ilere is some lateral variation on tite pinnacles: tite proximal ones are dominated by colonial forms, whereas Ile distad ones are microbial crust- dominated; (3) aboye 82 the microbial crust become searce, with cf/mc ratio larger than 2. TI lE ASSOCIATED FACIES Tite vertical and lateral distriibution of Ile facies associations across tite studied cross-section is shown in Fig. 3. As a whole, tite facies distribution sitows a retrogradational stacking facies in tite lower part of tite parasequen- ce, followed by a rapid progradation of facies in tite upper part of tite para- sequence. Two man groups of inter-reef facies are found: grain supported fa- cies in tite lower pad (Facies A and B), followed by mud-dominated facies in tite upper part (Facies C). Facies O is found covering al! tite reef and inter-reef facies, and titerefore they correspond to tite post-reef facies. 1 lowever, sorne interfingering between Facies C and O also occur. Tite boundary between tite grain- and mud-supported inter-reef facies is located to tite lower part of tite pinnacles in tite offsitore seetions (BB section), and to tite top in tite insitore sections (BO section, see Fig. (3). In titese proxi- mal sections, tite líoundary is rnairked by a sitarp, burrowed (Thalassinoides) ornd pon-Uy encrusted surface. la sorne outcrops, titis sm-face display some de- positional siope towards tite flanks of tite pinnacles. tn tite BH outcrop (Fig. 4), tite boundary reaches a minimun higliness of 4 m aboye tite bottom of tite pinnacles in Ile inter-reef areas. Titis highness inereases to tite flank of tite pinnacle, reaching 8-9 ní. Moreover, titis surface has continuity in tite pinna- cíe core (le. 52 surface). FACIES A: IJF 0.1kM- ANO BIOCLASIIC l~’ACKSTONES TO GRAINSTONES Facies A occurs below and laterally to tite more western pinnacles. It is arranged both in massive and cross-laminatedtabular beds 0.5 to 0.7 m titiek and eross-beds up to 0.3 m thick. Tite peloids are variable in sitie and forní np to 35% of tite volume of tite facies. Titere are also micritic intraclasts 2-3 mm in diameter, whicit consists of debris of tite reef microbial crust, incín- díng encrusting organisms such as «Tubi~hytes» inorronensis, Koski nobu/lina, 54 Ml urdí y B. i3ádenas Bacinella, serpulids and bryozoans. Tite proportion of tite intraclasts ranges froní 1 0 to 25 %. Tite bioclasts forin np to 20% of tite total volume of tite facies and coiisists of debris of corals (roundcd clasits of np to 3 cm iii diameter), bivalves. eclíi- noids (Balanocidaris) and bentitic forains (lituolids). ln lower proportioii are found otiter fossils sucit as gastropods, 1kTautiloculina oolithica, Cayeuxia, br- yozoans. bracitiopods, clíaetetids, níiliolidae and solenoporacean algae. ltxcí vs 13: 00.11 )A.l ..AND BTOCJÁSÁ 1< l’ACKS’ItNR TO ORAJNS’rt)NRS Facies 13 is dic nsliore equival.ent of facies A. it is found below and late- ra!lv Lo tite more proximal pinnacle reefs. Facies 13 is arranged in tabular beds (1.3 to 0.5 ní thiek. Cross-bedded lcvels up to 0.3 m thick also occur. The ooíds forní np to 200/ti of tite total ‘solume of fixe facies. Titeir size is variable, dispL u-mg diamcters up to 1 mm. Tite core of tixe ooids consists of sUicidas- tic. gralos aud skeletaL partides Facíns (2: SKRI.JÚTAI. \VACKFSrONItS kiries C ocettrs latera.Lly to tite upper paut of tite pinnacles and its overalí Uhickness mercases offsitore. Althorigh. tíle top of tite FT section is cí-oded. ive Nave. ¡ ¡íi.erprctcd that Facies C pinches oui to tIie more proxinial sections, witere fíe pinnacie recis are also thougitt tobe absent (Fig. 3). Tite facies con- sísts of Lii rrowed tabular i)io.[nicrit.ic beds up Lo 0.3 m thick, alternatin.g witit both ni ¡rl’» Uveis and bioclastie levels incl.ud.ing debris of metazoan btíilders (¡e to¡als and citactcLids) np to vi cm in diameter. Tite bioinicritic beds are oní mping ox ti dic flanks of tite pinnacle rccfs. 11w skeleial debris ¡nay form up to 30 % of tite facies. CoráIs, (titaetetids and u hmnords are tite more abundant skeletal grains, wIiem-eas otiter fossils like hiv xli es líLuolids, gastropods, solenoptxracean algae,A. oolithica, miliolids, br- yozoans ‘md serpulids are more searce. Tite facies also contain sifl of both car- iton ite ‘md siuiciclastie grains. tntraelasts of microbial crasIs are also eommon. TIre júnnacle regft ofjabaloyas (Late Kimmeñdgían, XIS Spain) oía FACIES O: PELOIDAL, OOIOAL ANI) BiOCIASVI(.1 PALKSTONES AND CJRMNS’rONES Facies O is located on top of tite studied parasequence, aboye tite llorizon witich includes tite pinnacle reefs. Tite loiver boundary of facies O is generally a sitarp an even surface. Hoivever, in some outcrops (cg. BB and 13C see- tions), some interiayering between facies D aud dic underlying biomicrites (facies C) is observed (Hg. 3). Facies O includes a wide spectrum of facies, defined by variable amounts of peloids, ooids and skeletal grains. Tite facies domijíated by peloids corres- ponds lo peloidal aud bioclastie packstones aud peloidal grainstones. Tbey form 0.5 to 1 ní titick beds, witb occasional cross-liedding. Tite facies con- tains np to 40% of peloidsand 250/ti of skeletal grains, mainly debris of lituo- lids, miiiolids, coráIs, gastropods (occasionaliy forming accumulations in dis- ti-cte levels) and bivalves. ‘tite tíoid-dominated facies are ooidal and bioclastie packstones and grainstones. Titey are arranged in 0.3-1 m tbick beds, locally cross-bedded and eross-Iaminated. Tite ooids are mainly of type 3 (Strasser. 1986), are up to 1 mm iii diarneter and generally dispiay siliciclastie cores. Tite skeletal grains may forní up to 20% of Ile facies. Tite more abtindant fossils are bi- ralves, gastropocJs, solenoporttceaii algae, inñíolids and lituoiids. Type 1 mM II oncoids (Dalíanayake, 197’7) of 5 mm of mean diameter are occasionally found. Tite bioclastie facies are wackestones tú packstones and are arranged in tabular beds 0.3 Lo 015 m thick. Tite more abundant skeletal grains are gas- tropods and soleííoporacean algae. Bivalves, Cayeuxia, coráIs, echinoids. Ii- tuolids, níiliolids, brachiopods, dasycladacean algae (Acicularia) and N. oo- llíhica are fotiud in lower proportion. Most of titese bioclasts sitoív titin mi- critie coatings. Encrusted surfaces with oysters aud accumulations of bivalves givíng risc to a small patehes are occasionally found on titese facies. INTERPRETATION SEDíMEN’í’ARY REAl -MS IN Ti lE LATE KJ.MMERIDGIAN RAMP Tlíe nature and distribution of Lite facies in tite studied parasequence, allows tite reconstruction of tite sedimentary realms of tite Late Kimmerid- gian carbonate ramp in tite Jabaloyas area (Fig. tú). Facies D is considered to be deposited in inner ramp arcas (internal lagoon and marginal sand shoa]s), whereas tite pinnacle reef arid associated facies (A, B, C) would growttí in tite open and relatively deep mid ramp domains. Tite inner and mid ramp arcas are placed aboye aud below fair iveatiter wave base respectively. The mid 56 Al. Aurelí yB. Bádenas ramp areas are aboye storm wave base sea level, and titerefore periodieaily aif- fected by high energy events (Burcitette and Wright, 1992). Hg. lO.—Sedimentary model for [he Late Kimmeridgian carbonate rotmp in Pie Joibaloyas ares. Fig. 10—Modelo de sedimentación poro» la rampa carbonatada del Kiniuoeridgieusc superior en el sector de JabaJoyas Two basic types of facies are recognized in tite mid ramp areas. Tite more interna! domains are covered by grain-supported facies (facies A and 13), whereas tite outer realm of tite mid ramp is dominated by burroived, mud-dominated facies, witich are indicative of lower energy environment (facies C). Insitore, tite sediment is dominated by high energy ooids (type 3, Strasser, 1986) and by a wide spectrum of skeletal grains. which are indica- tive of sitallow aríd open marine conditions (facies B). Offshore, tite grain- supported sedimenis are peloidaL and skeletal, including also a diversified and open bentlíic community with forams, bivalves, solenoporacean algae and eclíinoids (facies A>. Scattered in tite mid ramp are found a set of patcit reefs. Tite elevation of tite reefs aboye l)ottom floor was variable botit in time and in space. Based on the BH section, where it is possible to examine tite relationsitip between coe- val inter-reef facies and intermediate stages of growing of the pinnacle reef (Hg. 4), tite maxiinum risc of the pinnacles aboye tite surrounding sediments can be estimated to be around 4 lo 5 m. Tite elevation of tite patch reefs is re- duced insitore. In tite more internal arcas of Ile mid ramp TI-lE PIMNACIÁ? [ Tite relationship between tite reefs and tite associated facies exposed abo- ve sitows that Ile growing of tite pinnacles took place in mid ramp areas. Giner and Barnolas (1979), Fezer (1988), Aurelí (1990), Nose (1995) and Baumgártner and Reyle (1995) have proposed a similar setting for Ile reef growing. The nature of tite organisms that constructed Ile reefs are also co- iterent tú titAs assignnient (see Nose (1995) for details). In addition, tite asso- ciated micro-encrusters found commonly in the microbial crusts, wiIl Ba4- nella, Lithocodium, Koskinobullina, «Tubiphylesx’ morronensis and serpulids, are considered by Leinfelder el al. (1993> as representative of shallow ranip areas. Titecolonial forms are preserved in Ile reefs as debris of different size and are only occasionallyfound in growth position. Tite breakageof tite skeletons was due tú botit storm reworking and biocrosion. Part of the debris origina- ted by these processes were accumulated in tite inter-reefs sediments or trans- ported insitore. Accordingly, tite proportion of tite preserved metazoan buil- ders in tite reef is lower titan the proportion during reef growing (Longman, 1981). l-Iowever, tite bulk of titese debris remains in the reefs, forming titeir frameworks along lo tite microbial crusts. Tite role of tite microbial crusts in Ile origin and development of Ile Late durassic reefs has been examined in detail by Leinfelder el al. (1993, 1994>. According to titese autitors, tite microbial crusts are of paramount importm- ce for Ile origin, stabiiitization and development of positive buildups. Tite microbial crusts are binding and bounding togetiter the debris of tite metazo- an builders, forming also variable proportions of Ile reef fabrie. Titese crusts were rapidly itardened, as indicated by tite presence of borings on tite ernst it- self. Tite development of tite microbial ernst is discontinuous, as it is shown by both tite irregular intergrowing between peloidal or micritic fabrics and tite presence of tite micro-encruster organisms. Tite internal cavities, either left during tite reef growing or originated by bioerosion, are rarely filled by marine or meteoric cements. Only some par- tially filled reef cavities (geopetais) have been later cemented by sparite. Most of tite cavities are occupied by muddy (occasionally peloidal or ooidal) inter- nal sediment. Titis mud may be originated cititer by bioerosion (Tueker and Wright, 1990) or by filtering and baffling tite fine grain sediment suspended in Ile surrounding marine waters. Arguments such as tite presence of ooids or siliciclastie silt in tite muddy intemal sediment or tite occasional lamina- 58 14. Aurelí y J3• Bádenes tion and gradatiori in tite peloidal fillings, demonstrate an external supply. 1 lowever, it is difficult to estimate itow mucit interna! sediment itas been ori- ginated cititer by bioerosion or by externa] supply. DiSCUSSION: REEF GRO\VTH AND SEA LIBVEL CHANCES Tite general trend on tlie vertical and latera! reef zonation described abo- ve and tite inLer-reef facies distribution, aflows to discuss tite rclationship bet- iveen ttíe growing of the pinnacles asid Ile changes of sea level. Tite evolution of tlíe studied parasequence titrougitout four successive sea level episodes is sitown irí Fig. 11. Episodes 1 and 2 are coeval to a continnoas sea level rise (Le. Lrarísgressive systems tract), witereas episodes 3 and 4 sliow tile facies distribulion during tite subsequent stillstand of sea leve] (i.e., higbstand sys- 11’ite evolutioíi in Fig. 11 itas been illustrated upwards from tite tenis tract) - ito.rizoií including tite reefs. Tite prexáous sandy, marly aud grain-supported sitalloiv earboííates present in tite lower parL of tite sttídied sections (see Fig. 3) would represent a continuous flooding of tite ramp, from trajísitional to sbailow marine environments. TRANSCORIVSSIVE SYSTEMS -rRÁCT A. first episode corresponds to a fast rise of sea level iviticlí involved tite initial flooding of tite carbonate ramp (Fig. 11.1). Tite top of this episode Co- rresponds to tite Sí surface. As a consequence of a rapid creation of accom- modation in tite basin, a sedimentary starvation in tite mid ramp occurred. Only tite fast vertical growing of some pinnacles is able Lo partly compensate for tite accommodation. Stratal biostromes, ivith variable latera! extension, also greív during titis episode. Tite local development of microbial crusts produced tite stabilisatiou and bardening of tite substrata, allowing tite gro- wing of tite coral forms in subsequent episodes (Leinfelder el al., 1993). Tite partial reworkíng of tite microbial ernst is indicated by tite common presen- ce of debris of tite ernst in tite coeval peloidal, oolithic and bioclastie facies A and 13. During Uds first episode tite reefs sitow widespread coral dírombolitie fa- bries. As indicated by Leinfelder e! al. (1993), tite main prerequisite for tite occurrence of microbial crust is a eessation of tite background sedimentation wtuch can be eommoniy tied to rises of sea level. 1 fowever, aecording to titis autitor, low sedimentation rate is aÑo favorable for coral groívtit. Tite low proporLion of corals and tite loív diversity of micro-encrusters during titis lo- iver epist)de are in(licativc of sorne restriction in tite manne envíronment. As The pininicle reeJs ¿flahaloyas (LateIúrníneridgian, PIESpain) 59 explained by Leinfelder <1993) and Leinfelder e! al. <1993) a rise of tite dy- saerobic waters due to lowering cireulation during sea level rises may exclu- de tite extensive growing of metazoans, witilst Ile euroxie microbes remxn. Tite overail vertical growing of tite reefs followed and/or initiated during tite continuing riser of sea level (Fig. 11.2). Tite inter-reef sedimentation re- covered in tite intemal arcas of Ile mid ramp. Tite deposition of grain-sup- ported facies A and 13 was coeval to tite reef development, as indicated by tite I)resence of ooids and peloids in tite internalreef cavities. Both tite mercase of tLíe background sedimentation aud tite recovery of Ile normal oxygenated environment alter tite initial flooding of tite ni-np in tite more proximal are- as, may explain tite rapid sitift from coral-titrombolitic to coral reefal fabries. Titerefore, tite shaw boundary locally observed betíveen both types of reef fa- brie in tite insitore pinnacles (e.g. Sí in ttíe BI) I)innacle) is likely to reflect some nutrient and/or oxygen fluctuaLion. Hoivever, titrombolitie fabries are stiiil dominant in tite offsitore reefs. Se- dimentary rates were lower in tite external arcas of tite mid ramp, as indica- ted by tlíe offshore titickness reduction of Llie inter-reef facies. Tite coeval de- velopment of coral titrombolites and coral reef at apparentiy similar bathy- metrie conditions, would refiect not only sorne latera! variation in Lhe oxygen and/or nutrient content, but aÑo tlíe off-slíore decrease of tite sedimentary ra- Les across tite inid ramp area. Wc líave placed Lite upper boundary of tite transgressive systems traet or níaiximurn flooding surface on tite so-called S2 surface. Titis is a burroived and encrusted surface covering tite grain supported facies A and 13 between tite 131) and BI 1 sections. Tlíis surface is coeval tú tite development of tite fiat surface witit mierobial crusts located some 9 m aboye tite bottom of tite more proxiínal pinnacles (i.e. 82 surface. see Figs. 4, 5 and 6). Tite biomicritie in- ter-reef facies located off-sitore (facies C) are intensively burrowed, indicating also some sedinientary condensation. Tite deerease of tite sedimentary rates iii relation to tite increasing accommodation rates is also indicated by a re- trogradational staeking pattern, ívitit tite progressive backsteeping of tite rnud-supporLed facies (2. 1 liclislANIí SYSTEMS 1RACT Tite rapid risc of tite sea level resumes at Ile onset of Ilis episode, domi- nated now by a sea level stabil¡sation, witicit aillows tite recovery of Ile car- bonate production. Tite successive observation of aggradational and progra- dational facies arrangement in tlíe sediments deposited during Uds sLillstand episode, allows to difícrentiate between early ¿md late highstand systems tract. At tite onset of a first episode or early itighstand systems tract (Fig. 11.3) 60 Al. Aurelí y B. Bádenas ¡So~ sc FÉÁZ -‘~¶2~-- e’ —1 4. LATE HIGHSTAND 3. EARLY HIE3HSTAND 2 2. MAXIMUM FLOODINS 1. INIT¡AL FLOODING - ¡ A sA~»~.O ¡ <~~wísr; - - 7éó~ Ó increasing rol>, ¡ — fac es :~ ¡ cl/m.c En Coral recia: 4m~ fac¡esA co»aI throsnbo¡ites 1000 ir, ¡ Fig. II —Evolution of tire pinnacle reefs ¿md associated facies relattd to sea level variation. Fig. 11 —Evolución de los pináculos arrecifales y facies asociados en relación con las variacio- nesdel nivel del mor. ¡ TIre pinnacle reefs ofjabaloyas FINAL REMARKS 1. Tlíe pinnacle reefs of tite Jabaloyas area sitow some vertical ¿md latera! variation in tite relative proportion of microbial crusts and metazoari buil- ders. Tite overalí pattern of reef zonation presented in our work is based on vertical logs across four separated pinnacles, aiong to ficíd observation in in- termediate reefs. However, titere are some lateral varibility in Ile reef fabrie wititin individual reefs. Titis shouid be d.ue to coral aggressivity and, particu- larly, tú intemal differences in sedimentation (Leinfeder, per. com.). There- fore, Ile ratios of cf/mc presented in Figs.8 and 9, witicit are based on verti- cal logs along tite piinnacles, should not be taken as exael ratios. Also, in or- der to acitieve a more realistie pattern of Ile lateral variation of tite reef fabric along to tite proximal-distal section, more intermediate reefs sitonid be eva- luated under tite seope of Ilis work. However, we believethat Ile preliminary results presented in titis work give a reliabie idea on Ile overall trending of tite vertical and latera! reef fabrie variation. BoIl, tite similarity between Ile vertical variation on alí tite sampled pinnacles and tite presence of correlata- ble horizons, which display comparable cf/mc ratios separated by discontí- nuity surfaces, give support to tIlis assumption. 2. Tite sedimentological analysis of tite reefs of Jabaloyas aud of titeir as- 62 Al. ¡1 u,-ell y .B. Bádenas sociated facies presented in our work, itas aliowed to explain several aspects related to titeir origin and deve]opment in the Late Kimmeridgian Iberian carbonate rainp. Questions addressed in our work, sucit us tite relations.hip betxveen reef and inter-reef facies or its evolution during successive sea level variation along to a proxirnal-distaL section, gives additional information aud support to tite results obtained in previous works, concerning tite fae- L.ors witieh controlled tite origin and evolution of Líle tiipper Jurassic reefs (see especiallv Leinfelder. 1993; Leinfelder el al., 1993, 1994; Baumgárt- ¡]er and. Revle, 1995 aud Nose, 1995). l-{esults reported in titese studies, sucb us tlíe intense development of microbial ernst dite to very low back- ground sediníentation rates amI to partial exelusion of corals by fiuctuating oxygen/nutrieíít !evels related to sea leve! rises. are fiílly supported ‘»vitit our data. 3. The studied sediments belong to a cyclic parasequence located in Lite lower part of a titird order depositional sequence, witicit sparis froní Late Kimrneridgian to Early Tititonian. Tite variation of aceominorlation deduced from facies ana!vsis sitows a rapid initial sea level risc at tite onset of tite pa- rasecínence, folloived by a later stillstand of sea level. Taking into account 1)otit tlíe nature of tite facies below aud abose tite pinnacles, tite mean tlíick- ness of tite stud ied parasequence and tite poonLy compactioií (>l)served in tIte reef fabrie, tite total accommodaiton (Teated in tite basin froní tite initial de- veloprnent cf tite reets to titeir late burial sitoií!d be around 20 rn. Titis ar- commodation is a combníation of both, loca!. subsidence a.nd custatie varia- tiolls lost of tiíis sea level lise was concerítrated during tite deposition of tite transgressive systems tract deposits, wbere it can be esti maled to be around 12-15 rn (see dashed arrows in Ng. 11, episodes Y and 2). Leinfelder (1993) and Nose <1995) itave suggested an stroííg regional or global custatie control on tUis risc of sea level. 1. Tite slíalioxv carbonate ramp developed at Jabalovas allows to anailyse tite response to tite carbonate production on a carbonate ramp during a rapid relative sea Jevel risc. Reduced carbonate production in tite studied Late Ju- rassic ramp during initial sea level risc resulted in a partly condensed section in mi(I ramp arcas, folloxved by a laíídward shifL (backstepping) of the deeper biomkritic facies. ¡Iowever, tite vertical aggradation of sorne reefs was able to compensate for rnost of tite acconímodation ereated during sea level rise in onter middle raffip arcas, resulting in a facies distribution similar to Llíe catcit np type platforms defined l~ Keiídall and Schlager (1981). Duriííg late sta- ges of rising sea level, carbonate production was recovered in sbal!ower are- as, resulting in an aggradational stacking pattern (see lateral transition bet- ween facies A and B in Fhg. Ii .2). 1 liglí carbonate productivitv- during tite ul- tenor slillstand of sea level resulted in tite facies agradation in tite iííter-reef facies foliowed by a fast progradational pattern (i.e.. earlv and itigitstand sys- tems tracis). TIre pinnacle ¡-cefi qfJabaloyas (Late Khnrneridgian, NT SPain) 63 ACKNOWLEI)GMENTS Finornciofl support was I4E)Uáed by fije project DOICYT PB 92-0862. Tbe work of 3. 8. was f¡.rnded br a grant of tire Institutt» de Estc,dios Turolenses. Ibis researcb has greatly benefited from disct,ssi.ons oiíwl revie’svs by 1. Nt. Martín, A. Meléndez otiíd R. R. Leinfeltíer. REFERENCES ALONSO, A. 5 MÁs, J. R. (1990): «El Jurásico superior en el sector Demanda-Cameros (La Rioja-Soda)»», Cuad. Geol. Ibérica, 14 173-198. A» uiú±,Xl. (1990): El! urásico superior en la Cordillera Ibérica Central <‘provincias de Zaragoza y Teruel). Análisis de cuenca, Tesis Doct., Opto. Geol., Ser’»’. Public. Unir. Zaragoza Ed. 389 m. & NXFr.¡tNouz, A. (1993): «Sedimentary evolution and sequence stratigrapity of tire Upper Jtn-assic in tite central Iberian Chain, nortiteast. Spain»». iii Sequence SÉratí- graphy and Facies Associations (Ed. be Posamentier, 11. XV. el al.), InI. Assoc. Se- dimen!.,Spec. Pub., 18, 343-368. 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