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Contribución de la mineralogía de arcillas a la interpretación de la evolución paleogeografica del sector occidental de la Cuenca del Guadalquivir

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Author(s): Galán, E. | González, I.

Journal: Estudios Geologicos
ISSN 0367-0449

Volume: 49;
Issue: 5-6;
Start page: 261;
Date: 1993;
Original page

Keywords: Clay minerals | paleogeographic evolution | Guadalquivir Basin | South Spain | Clay minerals | paleogeographic evolution | Guadalquivir Basin | South Spain

ABSTRACT
Marine tertiary materials of the Guadalquivir basin consist of four mayor depositional sequences of great continuity in the whole basin which are separate by unconformities. The lower outcroping unit (unit 2) ineludes glauconite-rich sandstones and marly limestones (Fm. Calcarenitas de Niebla, Tortonian-Messinian) and Olisthostromic materials. This unit lies discordantly over the Paleozoic, and was sedimented in a shaUow marine platform. Olisthostromic materials (Mesozoic and Miocene), composed of sand and elayey sand, were deposited during Tortonian-Messinian times. As a consequence of a transgressive pulse, the sedimentation of a thick marly series (Fm. Arcillas de Gibraleón) ofthe Messinian-Low Pliocene age took place. In the last stages of the filling of the basin (Pliocene) a regression began, and sands and silts were deposited (Fm. Arenas de Huelva and Fm. Arenas de Bonares). Also, and as a final consequence of the regression stage, lacustrine sedimentary deposits (Upper Pliocene) occur at the south of the basin, which are composed of marly limestone and greenish palygorskite and sepiolite marls. From a mineralogical point of view, autochthonous materials from this marine detritalcarbonate series, are mainly composed of calcite, quartz and phyUosilicates with minor dolomite and feldspars, and secondary gypsum. The elay minerals present are illite and smectite with minor kaolinite and chlorite. The evolution of the elay minerals associations varies from bottom to top as foUows: Illite or Clauconite >> Smectite > Chlorite/Kaolinite (Fm. Calcarenitas de Niebla); Smectite â&#137;¥ Illite > Kaolinite (Lower Fm. Arcillas de Gibraleón); Illite > Smectite â&#137;¥ Kaolinite/Chlorite) (Upper Fm. Arcillas de Gibraleón), and Smectite > Illite > Kaolinite (Fm. Arenas de Huelva y Fm. Arenas de Bonares). This vertical variation confirms a stratigraphical discontinuity (paraconformity) into the Fm. Arcillas de Gibraleón, which was observed by others from stratigraphical and paleontological data, and supports a new mineralogical change between the Fm. Arcillas de Gibraleón y Fm. Arenas de Huelva. Sedimentation of those materials above described took place in a shallow marine environment which was more superficial upward, according to palaeontological data. The illite crystal-chemistry characteristics, suggest that metamorphic and igneous rocks from the South Iberian Massif should be the source area for these sediments. The mineralogical composition of allochthonous materials are quartz, opal-A and opalCT, phyllosilicates, and calcite. The clayminerals are predominantly smectites and minor amounts of illite and kaolinite. The microfauna associations together with the absence of detrital minerals, may support that sedimentation of these materials took place in a rather shallow marine basin (< 150 m deepth). The presence of opal A and CT, seem to indicate that sediments have only undergone an early diagenesis. The source area for these materials could be the Triassic materials of the Betic Cordillera.Los minerales de la arcilla presentes en los materiales terciarios del SO de la Cuenca del Guadalquivir son illita, esmectitas, con elorita y caolinita en menores proporciones. El estudio de la variación vertical y lateral de las asociaciones mineralógicas ha permitido aportar datos que complementan los ya existentes de tipo estratigráfico o paleontológico. En concreto se han correlacionado espacialmente los distintos materiales, y se confirma por mineralogía de arcillas la ruptura sedimentaria propuesta por otros autores dentro de la Formación Arcillas de Gibraleón, también se observa un cambio mineralógico no detectado anteriormente en el paso de la Formación ArciUas de Gibraleón a la Serie de Transición o la Formación Arenas de Huelva. Se da una interpretación sobre el medio y condiciones de depósito para los materiales autóctonos y parautóctonos y se propone como área fuente de estos materiales las pizarras alumínicas y ferromagnesianas del Macizo Ibérico y los materiales triásicos de la Cordillera Bética. Por último, se propone un modelo de evolución paleogeográfica de la cuenca.

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