Western Cameros Basin (North Spain)
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SANDSTONE PETROGRAPHY OF CONTINENTAL DEPOSITIONAL SEQUENCES OF AN INTRAPLATE RIFT BASIN: WESTERN CAMEROS BASIN (NORTH SPAIN) JOSE ARRIBAS,l ANGELA ALONSO,2 RAMON MAS,3 AMPARO TORTOSA,l MAGDALENA RODAS,4 JOSE F. BARRENECHEA,4 4 JACINTO ALONSO-AZCAAATE,5 AND ROSANA ARTIGAS 1 Departamento de Petrologiay Ge(Xjuimica, Facultad de Ciencias Geol6gicas, Universidad Complutense de Madrid, 28040-Madrid, Spain e-mail: [email protected] 2 Laboratorio de Geologia, Universidad de A Coruiia, Spain 3 Departamento de Estratigrafia, Facultadde Ciencias Geol6gicas, UniversidadComplutens e de Madrid, 28040-Madrid, Spain 4 Departamento de Cristalografiay Mineralogl'a, Facultad de Ciencias Geo16gicas, Universidad Complutense de Madrid, 28040-Madrid, Spain 5 Departamento de Fisica-Quimica, Facultadde Ciencias del MEdioAmhiente, Universidad de Castilla-La Mancha, 45004-Toledo, Spain ABSTRACT: The Cameros Basin in Central Spain is an intraplate rift INTRODUCIION basin that developed from Late Jurassic to lVIiddle Albian time along The Cameros Basin, located in the northern part of the Iberian Range, NW-SE trending troughs. The sedimentary basin fill was deposited is one of the basins forming part of the Mesozoic Iberian RiftSystem (Mas predominantly in continental environments and comprises several de et al. 1993; Guimera et al. 1995; Salas et al. 2001). The IberianRift System positional sequences. These sequences consist of fluvial sandstones that was inverted during the Paleogene and today corresponds to the Iberian commonly pass upward into lacustrine deposits at the top, producing Range (Fig. 1). The Cameros Basin was formed duimg intraplale rifling considerable repetition of facies. This study focused on the western which took place from Late Jurassic to the Early Albian time, when Iberia sector of the basin, where a total of seven depositional sequences (DS- 1 was separated fromEurope, in conjunction -withthe opening of the oceanic to DS-7) have been identified. Bay of Biscay Basin. At this time several basins were formed along the The composition of sandstones permits the characterization of each NW-SE trending Iberian trough. The Cameros Basin is the most north sequence in terms of both clastic constituents and provenance. In ad westernbasin in the Mesozoic IberianRift System (Salas et al. 2001). This dition, four main petrofacies are identified. Petrofacies A is quartzo inboard position resulted from a minor marine influence and a delaying of sedimentolithic (mean of QmSSF2Lt13) and records erosion of marine the processes of diastrophism, because the rifting started first in the south Jurassic pre-rift cover during deposition of fluvial deposits of DS-l easternpart of the trough and then propagated towards the northwest (Salas (Brezales Formation). Petrofacies B is quartzofeldspathic (mean of et al. 2001). However, in spite of its interior position, the Cameros Basin > 1 QmslF14L�) with P/F at the base. This petrofacies was derived experienced the most subsidence of any basin in the Iberian Rift System, from the erosion of low- to medium-grade metamorphic terranes of accumulating a thick pile of clastic sediments (up to 9000 m in the depo the West Asturian--Leonese Zone of the Hesperian Massif during de center area). These sediments were derived from erosion of the Hercynian position of DS-2 (Jaramillo Formation) and DS-3 (Salcedal Formation). basement (metamorphic and crystalline rocks) and the Mesozoic sedimen Quartzose sands tones characterize the top of DS-3 (mean of tarycover (Triassic and Jurassic). This sedimentaryinfill comprisesseveral QmnF4LtJ. Petrofacies C is quartzarenitic (mean of Qm9SF3Liz) with sequences consisting mainly of fluvial sandstones and lesser amounts of P/F > 1 and was produced by recycling of sedimentary cover (Iriassic conglomerates that commonly pass upward into lacustrine carlxmates and arkoses and carbonate rocks) in the SW part of the basin (DS-4, Peii marls at the top of each sequence. The repetition of facies makes differ acoba Formation). Finally, depositional sequences 5, 6, and 7 (Pinilla entiation of the clastic units difficult, especially so because biostratigraphic de los Moros--Hortigiiela, Pantano, and Abejar-Castrillo de la Reina data are scarce. formations, respectively) contain petrofacies D. This petrofacies is Sandstone petrography is -widely considered to be a powerful tool for quartzofeldspathic with P/F near zero and a very low concentration of determining the origin and tectonic reconstructions of ancient teni.genous metamorphic rock fragments (from QmSSFllLt4 in Pantano Formation deposits (e.g., Blalt 1967; Dickinson 1970; Pettijohn et al. 1972). Varialions in clay-mineral assemblages -within shaly and marly beds also may be use to Qm73F 26Ltl in Castrillo de la Reina Formation). Petrofacies D was ful for detecting changes in the source areas in sedimentologically homo generated by erosion of coarse crystalline plutonics located in the Cen geneous materials (Alonso-Azcarate et al. 1997). Sandstone and clay min tral Iberian Zone of the Hesperian :Massif. In addition to sandstone eralogical characterization of basin fill is critical to any basin analysis, and petrography, these provenance interpretations are supported by clay many studies have pointed to an intimate relationship between detrital sand mineralogy of interbedded shales. Thus, shales related to petrofacies composition (i.e., bedrock composition of the sources) and tectonic setting A and C have a variegated composition (illite, kaolinite, and randomly (e.g., Ingersoll 1978; Dickinson and Suczek 1979; Dickinson et al. 1983; interlayered illite-smectite mixed-layer clays); the presence of chlorite Dickinson 1985; Valloin 1985; Schwab 1986; DeCelles and Hertel 1989; characterizes interbedded shales from petrofacies B; and Illite and ka Critelli1999). Sand composition also is sensitive to a complex set offactors olinite are the dominant clays associated with petrofacies D. involved in the clastic sediment system (climate, relief, transport, diagen These petrofacies are consistent with the depositional sequences and esis), which provides valuable information for paleogeologic reconstruc their hierarchy. An early megacycle, consisting of petrofacies A and B tions (e.g., Jobnsson 1993). The clay-mineral assemblage also is affected (DS-l to DS-3) was deposited during the initial stage of ritting, when by such factors, although data must be regarded cautiously because post troughs developed in the West Asturian-Leonese Zone. A second stage depositional processes may produce significant variations from original of ritting resulted in propagation of trough-bounding faults to the SW, compositions. Therefore, sand composition can supplement in sequence involving the Central Iberian Zone as a source terrane and producing stratigraphic analysis in deciphering stratigraphic boundary surfaces and a second megacycle consisting of petrofacies C and D (DS-4, DS-5, DS- the internal anatomy of unconformity-lxmnded units of basin fill (Fontana 6, and DS-7). Sandstone composition has proven to be a powerful tool et al. 1989; Zuffa et al. 1995). in basin analysis and related tectonic inferences on intraplate rift ba The purpose of this study \Vasto analyze the sandstone composition and sins because of the close correlation that exists between depositional clay-mineral assemblages of the sedimentary infill in the western sector of sequences and petrofacies. the Cameros Basin. These data throw light on the evolution of source areas 6° 4° 2° 0° 2° GIJ6N ����!lt€�����SANTANDER D TERTIARY 0 0 0 0 0 0 lo o 3° BASINS 4 (clastics, carbonates & gypsum) DUERO BASIN 42° El • MESOZOIC VALLADOLlD BASINS (sandstones, carbonates & gypsum) 41° •••. N HERCYNIAN 40° BASINS (metasediments, schists, A gneisses & granitoids) Tertiary ° 0 Upper Cretaceous West Cameros Basin infill Triassic and N Marine Jurassic S. Leonardo t Paleozoic location of stratigraphic sections o A stratigraphic transects o 20 Km 10 FIG. I.-Simplified geologic map showing study area and location of stratigraphic transects A and B. These transects are shown in Fignres 3 and 4, respectively. "-_. ._------- ------------------ ---, ,--- --- 1 CfJ IBERIAN CfJ ! FORMATIONS W BASIN VVEST CAMEROS Z UPPER I<: GENERAL DEPOSITIONAL � SEQUENCE CRETACEOU S I SEQUENCES t-- (Salas et aI., 20 MEGACYCLE Utrillas Fm Castrillo de la Reina FIll_ E - -- 0 -�., .. - APTIAN .. ,� . 0 K1.B - - 0 � , 7 Abejar Fm 0 BARREMIAN 0 K1.7 (') E 0 Pantano de la Cuerda 0 K1.6 BARREMIAN co 6 del Pozo Fm , 0 H E ortiguela Fm 0 K1.S i BARREMIAN 0 v HAUTERIVIAN 5 Pinilla de los Moros Fm � K1.4 E K1.3 HAUTERIVIAN 0 L() 4 Penacoba Fm , K1.2 VALANGINIAN 0 K1.1 E S. Marcos Fm 0 ------- 0 v J10.3 z , « 3 Rio del Salcedal Fm 0 en « a:: c::: Campolara Fm w .... _----- aJ E 0 L() v J10.2 2 Jaramillo de la Fuente Fm , z 0 � z o J: I E Boleras Fm 0 ;:: ----�-- (') � J10.1 , 1 Ntra. Sra. De Brezales Fm 0 � � CALLOVIAN - MARINE JURA SSIC (Dogger or Maim) KIMMERIDGIAN LEGEND: f0"':�� Conglomerates (matrix-support) Unconformities Conglomerates (clast-support) Plane beds �(::·.::<"':'.:l p Plant material - E5> Ostracodes -e Trough cross bedding . Sands & sandstones : ... .. '. :'.1 � I: 0 Charofites Planar cross bedding ::: ::3 Shales .i Bones (terrestrial vertebrates) "-"-" - Epsilon cross bedding F= '" _ - ee Oncolites r-�- __ Marls ..-«C'. Current ripples j A\ Roots FIG. 2.-Uppennost Jurassic to Lower Lenticular bedding Limestones mudstone-wakestone Cretaceous stratigraphic units and depositional � Logs [Cl: ;�j sequences