Variations in the isotopic carbon record from two lower Aptian sections belonging to the External –Middle Subbetic transition (Betic Cordillera, Jaén Province)

The lower Aptian pelagic and hemipelagic sediments of the Carbonero Fm were deposited in the Southern Iberian Palaeomargin, within the transition between the External to Middle Subbetic palaeogeographic domains. The concrete area of deposition was a subsiding sector bounded by faults. A stratigraphic and sedimentological study of two nearby sections from this area (Solana de Morales and La Frontera) has revealed the existence of notable differences in their stratigraphic record, which are interpreted in terms of a different sedimentary context. Both sections include a lower Aptian episode of black shales, which is interpreted to represent the local record of the Oceanic Anoxic Event 1a (OAE1a). The d13Ccarb curves from both sections can be easily correlated, and also a good correlation is observed with respect to curves from other areas, which record the global carbon cycle perturbation related with the OAE1a. The discrepancies in the isotopic d13Ccarb record between the two sections are interpreted in terms of local differences in the sedimentary environmen

Record of the oceanic anoxic event OAE1a (Lower Aptian) in a platform setting. Prebetic (Alicante province)

The Early Aptian was a time of major global events, being probably the most notable the Oceanic Anoxic Event 1a. In this paper, we present the study of the record of the OAE1a in a platform setting, the Prebetic Zone of the Betic Cordillera, which represents the shallow platform environments of the Southern Iberian Palaeomargin during the Mesozoic. In this context, several events of global and regional character are recorded, whose timing and relationships are extremely interesting to be clarified. The correlation between the studied sections has permitted the establishment of the timing of the main sedimentary events. The transgressive general context recorded in the studied units, linked to the tectonic subsidence, resulted in several retrogradational pulses, leading finally to the drowning of the shallow platform, which was postdated by the OAE1a event. The record of the OAE1a in a platform setting is explained as related to a local combination of factors, as a transgressive general context, strong local subsidence rate, and important input of terrestrial organic matter in the platform, as has been supported by the data provided from the analysis of the organic matter contained in the sediment

Tracking magmatism and oceanic change through the early Aptian Anoxic Event (OAE 1a) to the late Aptian: Insights from osmium isotopes from the westernmost Tethys (SE Spain) Cau Core

Some of the major Carbon cycle perturbations of the Phanerozoic occurred during the Aptian, in relation to magmatism. The highest temperatures reconstructed for the Cretaceous Period correspond to the Oceanic Anoxic Event of the early Aptian (OAE 1a), an episode of accelerated global change. Here we present a chemostratigraphic study based on osmium isotopes integrated with high-resolution Carbon-Oxygen stable isotope data from the Cau Core (Western Tethys, SE Spain), including a 6.4 Ma record from the early to the late Aptian. This high-resolution study of the continuous and expanded Cau section permits a thorough understanding of the duration of the Aptian events, as well as an evaluation of the mechanisms triggering the abrupt changes of the global carbon and osmium cycles and their interdependence. Here we show that the Large Igneous Province (LIP) Aptian magmatism initiated 550–750 kyr prior to the OAE 1a, and persisted for 1.4 Myr after the event, influencing the composition of seawater for 2.8 Myr. We show a continuous Os isotope record encompassing the OAE 1a and the late Aptian for the first time, and demonstrate that the recovery from the exceptionally unradiogenic composition of seawater Os produced by the dominance of the Ontong Java Plateau volcanism, was slow. Our results demonstrate the different time duration of some events, and the asynchronous relationship between the carbon and osmium cycles

The upper Valanginian of the Oliva section (Prebetic Zone, Valencia): facies analysis, biostratigraphy, C-isotope stratigraphy and organic geochemistry

The Upper Valanginian stratigraphic section of the sierra de la Oliva (Prebetic, Valencia province) records a significant sedimentary episode which has been named as ”Weissert Event”.This event is characterized by a positive excursion in the δ13C profile, which have been considered to be linked to a global perturbation in the carbon cycle, with environmental consequences that have been the object of debate, especially the degree of oxygenation of the sea bottom waters.We studied the sedimentary evolution during the late Valanginian in a shallow platform setting, beginning with the drowning of the early Valanginian carbonate platform, followed by a succession of shallowing- upwards sequences, which define a general deepening-upward evolution. The δ13C profile records a positive excursion during the late Valanginian, and the biomarker study has revealed the episodic development of anoxia, coeval to the deposition of organic rich facies, occurred during the episode of maximum deepening of the platform.This study has demonstrated that the “Weissert Event” has been recorded in the Prebetic platform, and that the environmental perturbations gave place to the occasional development of anoxia in a context of high organic productivityLa sección estratigráfica del Valanginiense superior de la sierra de la Oliva (Prebético, provincia de Valencia) registra un interesante episodio sedimentario que ha sido denominado “Evento Weissert”. Este evento está caracterizado por una excursión positiva en los valores del δ13C, que se considera ligada a una perturbación global en el ciclo del carbono, cuyas consecuencias ambientales son objeto de discusión, especialmente las condiciones de oxigenación en los fondos marinos. El estudio presentado aquí muestra la evolución sedimentaria del Valanginiense superior en un ámbito de plataforma somera, que comienza con el drowning de la plataforma carbonatada del Valanginiense inferior, y continúa con una sucesión de secuencias de somerización, que en conjunto definen una evolución general de profundización. El perfil de δ13C registra una excursión positiva durante el Valanginiense superior, y el estudio de los biomarcadores ha puesto de manifiesto el desarrollo puntual de anoxia, simultáneo al depósito de facies ricas en materia orgánica, ocurrido en el momento de mayor profundización de la plataforma. Este estudio demuestra que el denominado “EventoWeissert” quedó reflejado en la plataforma Prebética, y que las perturbaciones ambientales locales dieron lugar al desarrollo puntual de anoxia en un contexto de elevada productividad orgánic

Progradation of a shallow carbonate platform developed on a fault-block in the Western Tethys (lower Aptian, Sierra de Bedmar-Jódar, Prebetic of Jaén, Spain).

The Middle Member of the Llopis Fm in the Sierra de Bedmar-Jódar Unit of the Prebetic Zone of Jaén (southern Spain) was deposited on a shallow-marine platform of the Southern Iberian Continental Margin during the earliest Aptian. Detailed field logging of nine stratigraphic sections and facies mapping have allowed seven lithofacies associations (L1–L6) to be distinguished, one siliciclastic (L1) and five carbonate facies (L2–6). The succession is composed of eight consecutive elemental sequences of lithofacies associations L1–L6. Each elemental sequence is interpreted as representing one episode of shallowing-upwards carbonate deposition in a very shallow platform-lagoon that was bounded shoreward by clastic/ooid bars and passed seaward either to stromatoporoid bioconstructions (bioherms and biostromes) or rudist biostromes. The successive elemental sequences show north-eastward progradational geometries. Three phases of platform development are identified: (1) installation of the shallow platform; (2) development of a lagoon bounded by a stromatoporoid barrier and (3) development of an Urgonian-type platform dominated by rudists. During the early Aptian, the Bedmar-Jódar platform was partially isolated from the rest of the Prebetic platform and showed overall progradation towards the NE, in contrast to the general south-eastward progradational trend of the Prebetic platform. Sedimentation was controlled by rift-generated extensional tectonics that resulted in tilting of the platform block, causing the deviation of progradation from the general trends of the Prebetic Platform. In addition, climatic influence is inferred from the presence of siliciclastic sediments derived from weathering of the hinterland, which restricted the carbonate factory.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEUniversidad de JaénSecretaría de Estado de I + D + iJunta de Andalucíapu

Stratigraphy and chemostratigraphy of the Valanginian (pro parte) from Loma Solana, Sierra de Quípar (External Subbetic, Cehegín, Murcia)

The stratigraphy, biostratigraphy and geochemistry (C stable isotopes and RSTE trace elements) of a succession of Valanginian age outcropping in Loma Solana (External Subbetic) is presented. The succession is composed of two local sections, one cropping out to the west of Cehegín (Murcia) and another in the Garranchal gorge, to the SSW of this locality. The lithology consists of marl and marlstone rhythmically interbedded, which is typical of the Carretero Fm of the Subbetic. The ammonite zones and subzones of the middle- late early Valanginian and the complete late Valanginian, except for the lattermost part, have been identified, without any evidence of stratigraphic discontinuity between the two local sections. The δ13C curve show a similar shape to those of the same age obtained in other basins and the positive excursion of the δ13C characterizing the Weissert episode of environmental change (EECWeissert) has been identified. The RSTE, redox sensitive trace elements, analyzed do not show any particular increase as is typical of anoxic events and consequently conclude that anoxia due not exist in this part of the Subbetic basin during this EECSe presenta el estudio estratigráfico, bioestratigráfico y geoquímico de una sucesión del Valanginiense que aflora en Loma Solana (Subbético Externo). Se trata de una sección compuesta de dos secciones parciales, una de ellas levantada al oeste de Cehegín (Murcia) y la otra en el barranco del Garranchal, al SSO de dicha localidad. La litología,margas y margocalizas en alternancia rítmica, es la típica de la Fm. Carretero, a la que corresponde. Se identifican las zonas y subzonas de ammonites de la parte media-alta del Valanginiense inferior y de todo el Valanginiense superior, excepto la parte más terminal del mismo, sin que se haya denotado discontinuidad alguna entre una sección y otra. La curva de valores de δ13C muestra una forma similar a la obtenida en otras cuencas para la misma edad y en ella se puede identificar la excursión positiva del δ13C que caracteriza el episodioWeissert de cambio ambiental. Los elementos traza analizados, sensibles a cambios en las condiciones redox del medio sedimentario (elementos RSTE), no indican que hubiera condiciones anóxicas en el mismo durante este episodio de cambio ambienta

Dificultades en la enseñanza de mapas geológicos: Causas, propuestas de solución y desarrollo de material didáctico

Las prácticas de identificación e interpretación cartográfica de estructuras geológicas y la elaboración de perfiles geológicos están presentes en numerosas asignaturas de Geología de titulaciones de la Universidad de Jaén. Básicamente, su dificultad radica en los problemas de comprensión y visualización tridimensional de estructuras geológicas (estratificación, fallas, pliegues…) a partir de la información de superficie que proporcionan los mapas geológicos (Fig. 1). Esto se halla muy relacionado con la falta de conocimiento sobre sistemas de proyección.Fuera del ámbito universitario de la licenciatura en Ciencias Geológicas, situación en la que nos encontramos en la Universidad de Jaén, el problema se agrava, ya que el diseño de los planes de estudios determina una disponibilidad muy limitada de tiempo para su impartición. Esto lleva a los alumnos a que interpreten, erróneamente, que se trata de conocimientos accesorios sin relación directa con su futuro desarrollo profesional generando una desmotivación generalizada, que se traduce en un problema adicional para el desarrollo de las prácticas

Calcite-cemented concretions as a field outcrop criterion to identify forced-regressions. A field outcrop example in Lower Cretaceous sandstone of the Cerrajón Formation (External Zones, Betic Cordillera)

Calcite-cemented concretions were studied from Lower Cretaceous forced-regressive shoreface sandstones (Cerrajón Fm, External Zones, Betic Cordillera). During early diagenetic, patchy calcite cement consolidates clean and well-sorted sand in the form of concretions of spheroidal to oval shape within host sand uncemented. Then a new relative sea level fall characterised by incised valleys cutting the overlying TST and HST pelagic marls and also cutting shoreface sandstones (concretions host) is reported. Coastal and presumably subaerial reworking of exposed sandstone concretions by relative sea-level fall erosion (intensively bored by lithophaga, Fe-oxidized surface, oysters and corals attached) fill the incised valleys in proximal areas and they are also found isolated into distal marl