Late Cretaceous Carbonate Platfonns: Origin and

Chapter 24

Late Cretaceous Carbonate Platfonns: Origin and Evolution, Iberian Range, Spain Angela Alonso Departamento de cslratigrafti1 Universidad Complutense Mndríd, Spain Ramón Mas Deparltlmenw de Estratigrafía Universidad Complutense l'vladrúi, Spain

Mare Floquet Cenlre des Sciences de In Terre Université de Bourgogne Dijon, France

Alfonso Meléndez Departamento de Ceologra Universidad de Zaragoza ZaragoZil, Spain

SUMMARY Name: lberian seaway Authors: Angela Alonso, Marc Flaquet, Ramón Mas, and Alfonso Meléndez Locanon: Frem 39' to 43 • north latitude and O' to 5" 30' wes! longitude, IberianRange, Spain Geologic time interval: Late Cretaceous, middle AIbian to latest Masstrichtian Tectonic-sedirnentary selting: Iberian plate; stable cratonic areas between Bay of Biseay (Cantabrian) opening and Tethyan closing Basin type: Epeirlc platform Paleodimate: Albian to late Santonian, warm and humid; Campanian, warm and semíarid; Maastrichtian, warm and hurnid Platfonn type: Rarnps, shelf Platform geometry: Seaway oriented northwest-southeast, 500 km long, 250-350 km wide, and 500-1300 m thick Facies and fossíls: Mícrites, marls, fine and coarse carbonates, minor amounts of evaporltes and sandstones. Benthic and planktonic foraminifera, ammonites, rudists, molluscs, and algae Systems tracts: Best represented are shallow rarnp highstand system tracts; second are transgressive system trac!s; lowstand system tracts are no! represented Stacking patterns: Retrogradatíonal onlaping and progradational (sometimes sigmoidal) to aggradational parasequence sets

297

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INTRODUCTION The importan! Albian to Carnpanian global sea level rise (Vail et al., 1977; Hancock and Kauffman 1979),

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During development of this first megasequence, marine flooding was discontinuous, each of the transgressive impulses being progressively more expansive toward the most shallow, central areas of the seaway. Four depositional sequences are identified. The three first cycles (middle-Iate Albian, latest Albian-earliest Cenomanian, and early-middle Cenomanian) led to the formation of three successive ramps on the Atlantic side and three on the Tethyan. Progressive onlap toward the emerged areas of the lberian seaway is observed, culminating during the fourth depositional sequence, when the Atlantic and Tethyan realms were linked via the central part of the seaway (middle Cenomanian). From this moment on, a single platform (ramp) with double polarity developed (Figure 5a), Alluvial sands, conglomerates, and clays of the Utrillas Formation are everywhere present at the base of the marine deposits. During the fust transgressive cycle (D5-1, middle-late Albian age), the fust marine sedirnents consisted of shallow ramp calcarenites and micrites in the Valmaseda Formation in the north, and calcarenites of similar origin in the Aras de Alpuente Formation (Estenas Member) in the south. During the second pulse (D5-2, latest Albian-earliest Cenomanian age), marginal areas of the lberian seaway were covered by the sea, 5hallow ramp facies (micrites and calcaren-

ites with clastic input and common rudists) of the Valmaseda and Dosante formations in the north and the Aras de Alpuente Formation (Estenas Member and Bicuerca Member) in the southeast appeared. 5ediments of the third transgressive pulse (D5-3, early Cenomanian age) overlie a type 2 unconformity and are more extensive than the preceding cycle. Those sediments consist of shallow ramp calcarenites (Dosante Formation) in the north and lagoon marls (Chera Formation) and shallow ramp micrites and calcarenites (Alatoz Formation) in the south. During this stage, terrestrial sediments of the Utrillas Formation were deposited in the central part of the lberian seaway, displaying a marked diachrony. During the fourth transgre,ssive pulse (D5-4, middle Cenomanian age), the Atlantic and Tethyan ramps joined, forming a single platform with double polarity in the Iberian seaway, Two ramps opened to the northwest and southeast, respectively. From north to south, the lateral equivalents of the Dosante Formation (rudist-bearing calcarenites) can be observed, representing shallow platform ramp and marginallagoon deposits: Sta Maria de la Hoyas Formation (sandy lirnestones with oysters), Nuévalos Formation (laminated mudstones), and Villa de Ves Formation (shallowing upward sequences with dolostones and stromatolites),

24. Late Cretaceous Carbonate Platjonns: Origin and Evolutíon Iberian Range, Spain

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Late Cenomanian-Earliest Coniacian Megasequence Th" second megasequence (late Cenomanian-1?arliest Coníacian) indicates a totally different configuration oí the Iberían seaway (Figures 5a and 8). At its base, a firsl-order unconformity formed al the end of lhe previous cyc1e, during generallzed tilting to !he norlh and fracturing of !he platforrn. As a result, the platform was open to the Atlantic, with its southeastern edge emerged during most of the time of deposition of !hi, cycle. Three punctuated marine flooding events tha! advanced from the Atlantic are identified in this megasequence. These flooding évents deposited their deepest facies to the north. Afler each marine flooding even!, progradation of shallow ramp facies southward over the deep ramp facies is well docurnented. The final consequence is a laterally acretionary geometry (Figure 8). The observed relationships of !he three depositional sequences ls an overall offlap. Indeed, marine sediments of the first sequence are found covering all !he platform, whereas the two upper are only represented in !he central and northem parts of!he platform. At the onse! of the second episode, !he southem areas were exposed, and during the third episade, the central part was also partially emerged. The distribution of sedimentary umts during the first depositional sequence (05-5, late Cenomaman age) is as follows. Deepest marine facies of the Arceniega Formation (planktonic foraminifera marls) grade

sou!hward into nodular rnicritic limestones and marls of the Cabrejas del Pinar Formation (renamed from Abejar Formation of Hoque!, 1991) in the central areas and the echinoid-bearing marls of the Casa Medina Formation in !he southem areas. Prograding over these outer ramp facies are micrites and calcarenites wi!h rudists of the Ciudad Encantada Formanon. Mierites and marl, deposíted in lagoonal environments and corresponding to the Alarcon Formation in turn prograde over the timestones of the Ciudad Encantada Formation The second marine flooding (DS-6, latest Ceno· manian~middle Turonían age) is represented in northern areas by outer ramp facies conslsting of marIs bearing echinoids and ammonites (Puentedey and Homillalatorre fonnations). Outer ramp facies are also recorded in central arcas (Picofrentes and Monterde formations). Over these outer ramp facies are pro· grading shallow to proximal rinnp facies tha! consist oí calcaremtes containing scattered rudist patches (Taraba Formation). The third marine flooding (DS-7, late Turonianearliest Comacian age) covered onIy the northern and central areas of the platfOlm. Outer ramp facies (Homillalatorre Formation) consiat of limestones and marls bearing echinoids and planktomc foraminifera. Shallow ramp facies prograding on the outer ramp consls! of coral reefs and skeletal calcarenítes of the Cueva Formation and tidalites and lagoonal micrites of the Pantano de la Tranquera Formation.

306

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309

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24. Late Cretac1!ous Carbonate Platforms: Drígin ¡¡nd Evo/ulion, Iberian Range, Spain tectonic trend played Ihe most important role at thal time. These eombined factors created a wide ramp inelined toward the north, which developed in three sueeessive slages; each one evolved from a drowned platform lo a relative1y deep ramp (Figures 8 and lOa). During the late Cenomanian, the fust nel AUanlle influx occurred, with eorresponding open marine facies (nectonic and planktonie organisms) dominating in the North Meseta and shal!ower, more proximal envrronments characterizing the southeaslern par! of lhe basin. Indeed, the filling oí the ramps shows a progradation from south to north, which had already started in lhe late Cenomanian (Garda el al., 1985, 1987; Alonso and Mas, 1985). From lhe latesl Cenomanlan to the middIe Turonían, a similar evolution occurred on the platform. First, drowning during latest Cenomanian and earliest Turonian (maximum flooding during the Nodosoides zone) led to developmen! of a new ramp open toward the north under Atlantic influx (D5-6 in Figure lOa). During earIy-middle Turonial4 the ramp was infilled by means of progradation from south lo north. The shallower environments in Ihe cenlral part emerged, and finally, more than half of the ramp was exposed. During the late Turonian and earliesl Coniacian, the platform presented a similar configuration. The facies dIstribution shows a shallowing trend in almost the entire area, with a reef barrier growing on the northern margin of the platform (Floquet et al., 1982; Alonso and Ploquet, 1982; Ploque!, 1991). Low energy lagoonal facies dominated lhe central parl oi Ihe seaway resulting in a general shallowing upward sequenee. Eustasy continued; sedimentation attempting to keep pace with !he continuous riBe of sea leve!. Ouring the earHest Coniacirul, the shoreline relreated norlhward, Praetically the entire area was exposed, except for the northern part of Ihe seaway (05-7 in Figure 10b). Tectonic uplift is invoked to explain Ihis regressive episade, which was far more importan! in the southem half of the seaway. The dIscontinuity has been dated as earliest Coniacian in the north (Aoquet et al., 1982). In the southeast, !his discontinuity is added to a hiatus, with the Turonian and perhaps part of !he Coniacian missing (Gimenez, 1987; Calonge, 1989; Carenas, 1987). During the early~middIe Coniacian, subsidence was renewed and a second transgressive pulse star!ed from north to south causing progressive drowning of the seaway (DS-8 in Figure 10b). The new platform was a ramp, inclined toward the north, which had outer facies to the north and an inner platfonn and a wide, shallow, tidally influenced area to the southeast. During the early 5antonian, a gradual progradation oí the shoreline occurred toward !he north.

311

During the middle 5antonian, lhe situatíon was again much like the late Cenomanian, The transgression continued lo produce an uniform and extensive envíronment, with two carbonate ramps dipping toward lhe north and southeast. Hígh energy fades developed in most of the seaway, except for the northern margil4 where open deep marine facies are observed. Although the Atlantic int1uence was more important, connecllon with the Tethys is certain (D5-9). Ouring the late Santonian, a new major sedirnentary infilling resulted in exposure of nearly the whole area. During the latest Santonian, another transgressive pulse occurred (D5-10 in Figure lOe), fol!owed during fue Campanian by a gradual and clearly diachronous re!rea! oí the coastlíne toward hoth the AtIantic and Tethyan oceans. Shallow water carbonates and evaporites and continental facies developed over most of the seaway. The old seaway was broken up during the Maastrichtian into a series of smal! sedímentary basins in response to an early compressive teetonic event which gave rise lo gentle folding (Alonso et al., 1987b). Such basln.s were infilled with continental deposits !hat indicate a climatic change, wilh conditions becoming more humid. 'Ihe sedirnents were mainly fluviatile and lacustrine, and in a few basins are evaporitic fades, which are always at the base of the sequenee, Marine sedimenlation in apparenl eontinuity occurred in the Northern Meseta during the Maastrichtian (D5-11 and 05-12 in Figure Be) (Ploquet, 1991) and Paleocene. In the remainder of the basin, hiatu5es and progress!ve dIscontinuities are clearly marked in continental deposits (Iatest Cretaceous and Paleocene).

Acknowledgments This work has been supported by lhe DIGCYT PE 88-0071. Our thanks lo an anonymous rejeree whose camments ami suggestíons have notably imprm;ed the texto We are also grateful lo Drs. c. Evans and M. Aurell who revised the translalion and provided sorne useful

camments.

References Cited ~~~~~~~~~Alonso, A., 1981, El Cretádco de la provincia de Segovla borde norte del Sistema Central: Editorial de la Universidad Complutense, Madrid, Seminarios de Estratigrafía. Serie Monografias 7, p. 271. Alonso, A., and J. R Mas, 1982, Correlación y evolución paleogeográfica del Cretácico al norte y al sur del Sistema Central: Cuadernos de Geologia Ibérica, Madrid, v 8. p.

151-172.

312

Awnso et al.

Alonso, A., and J. R. Mas, 1985, Estratigrafía, sedimentologí. y paleogeograffa del Jurásico terminal y Cretácico de la Hoja a escala 1:200.000 de Valencia (56), IGME: Servicio de publicaciones del Ministerio de Industria y Energía, Nueva Serie, Madrid, p. 43-44. Alonso, A., and J. R. Mas, in presE, Control tectónico e influencia del euslalismo en la sedimentación del Cretácico inferior de la Cuenca de Los Cameros, Espafla: Cuadernos de Geología Ibérica, Madrid. Alonso, A., and M. Floquet, 1982, Sedimentation et environnements .u Turonien en Vieille Castille (Espagne): Un lIlodéle d' évolution en domaine de plote-forme: Mémoires du Muséum N.tianal d'Histoire Natorelle, Nouvelle Série, Serie C, Sciences de la Terre, París, Tome XLIX, p. 113-128. Alonso, A., M. P1oque!, A. Meléndez, .nd J. Saloman, 1982, Capítolo 7, Cameros.-Castílla, in El Cretácico de Espaf.a: Editorial de la Cniversidad Complutense, Madrid,

1'.345-456.

Alonso, A., M. P1oquel, J. R. Mas, and A. Meléndez, 1983, Evolution paléogéogr.phique des plates-forrnes de la Meseta Nord-Casiillane el de la Cordillére lbérique (Espagne) au Sénonien. Géologíe lvléditerranéerme: Editions de rUniversité de Provence, t. X, n. ~ p. 361-367. Alonso, A., M. P1oque!, J. R Mas, and A. Meléndez, 19873, Origine et évolution du détroít ibérique au Crétacé supérieur: Mémoires Géologíques de rUniversité de Dijo!\, v. 11. p. 79-130. Alonso, A., M. P1oque!, J. R Mas, A. Meléndez, N. Meléndez, J. Salomon, and J. P. Vadot, 1987b, Modalités de la régression sur le dé!roit ibérique (Espagne) á la fin du Cretacé: Mémoíres Géologíques de l'Université de DijO!\, v. 11. p. 91-102. Alonso, A., M. FIoquet, J. R Mas, and A. Meléndez, 1989, Origln and evolution of an epeiric caroonate platforrn, Upper Cretaceous, Spain: Volumen de Publicaciones Xl1 Congreso Español de Sedimentologia,. Simposios, Bilbao,

p.21-32. Alvarado, M. 1980, Introducción a la Geología general de España: Boletín dellnstiluto Geológico y Minero de España, Madrid, T. XCLl, P 1-