Sedimentology and cyclostratigrahy of three Jurasic shallow platforms (Central Iberian Basin): the interplay of internal and external factors
| Autor: | Val Muñoz, Jorge, Badenas Lago, Beatriz, Aurell Cardona, Marcos |
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| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: | |
| Zdroj: | Zaguán. Repositorio Digital de la Universidad de Zaragoza instname |
| Popis: | This PhD Thesis presents the sedimentological and cyclostratigraphic analyses performed on three selected shallow marine platform areas with deposition of both carbonate and siliciclastic sediments, which developed in the central areas of the Iberian Basin during Jurassic times. The main objectives are: 1) to comprehend the depositional environments and the relative contribution of different internal and external factors controlling the sequence architecture in each case; 2) to establish a comparison in order to discuss the interplay of these internal and external factors determining the sequence architecture under different sedimentary contexts of shallow marine ramps.The bulk of data required for reconstructing the depositional models have been obtained by extensive fieldwork including logging, sampling and analysis of sedimentary bodies by physical tracing, also supported with drone-made videos, satellite images and high-resolution photomosaics. The cyclostratigraphic analysis has been assessed by the means of the identification of high-frequency sequences of different scale. Assigning them to the imprint of orbitally-driven climate cycles has required getting accurate age calibrations on the basis of biostratigraphic data (i.e., ammonite zones, benthic foraminifera), and chemostratigraphic data (strontium stable isotopes). The three selected examples are outcropping in the Iberian Ranges and hold common features, since they represent depositional environments dominated by wave-related sediment flows, under general greenhouse climate conditions and basin-scale long-term regressive stages. They correspond to: 1) late Pliensbachian bioclastic mid to proximal outer ramp (Barahona Formation), 2) early Kimmeridgian oolitic-siliciclastic inner to distal mid ramp including an infralittoral prograding wedge (Ricla Member), 3) latest Kimmeridgian–early Tithonian carbonate-siliciclastic coastal to shallow marine domains (Villar del Arzobispo Formation).Orbitally-driven climate cycles translated in high-frequency sequences of different scale, depending on the type of depositional system. In the late Pliensbachian mid to outer ramp areas, long eccentricity-relate sequences (4–5 m-thick) and short eccentricity-related sequences (1 m-thick) are recorded, being the link of dm-scale individual beds to precession cycles open to discussion. The infralittoral prograding wedge hosted by the early Kimmeridgian inner to mid ramp areas could correspond itself to a short eccentricity-related sequence formed by precession-related sequences (4.5–17.5 m of maximum vertical thickness), in turn formed by possible sub-Milankovitch-related sequences. The latest Kimmeridgian–early Tithonian coastal to shallow marine platform records long eccentricity-related sequences (40–60 m-thick in average) and some preserved short eccentricity-related sequences (15–20 m-thick).Orbitally-induced fluctuations in sea level and hydrodynamic levels (i.e. fair-weather wave base and storm wave base) have been recognized in the late Pliensbachian and early Kimmeridgian platforms, controlling changes in re-sedimentation of carbonate and siliciclastic grains (ooids, quartz grains, skeletal grains) and muds. The controlling mechanism has been tentatively related to a dominant aquifer-eustasy in the early Kimmeridgian platform (greenhouse warm climate conditions), generating wave base changes by the means of arid-humid alternations inducing water storing and release from continental aquifers to the ocean. In the late Pliensbachian platform both glacio-eustasy and aquifer-eustasy were probably interplaying, since greenhouse cold climate conditions (with possible development of polar ice caps) were acting. In the latest Kimmeridgian–early Tithonian coastal-shallow platform, orbitally-controlled climate cycles caused variations in pluviometry, and therefore in siliciclastic input, but not significant sea level fluctuations, since the prevalent humid climate conditions kept groundwater saturation and avoided the aquifer-eustasy.The distribution of the hydrodynamic levels and the dominance of different sedimentary processes determined the sedimentological response to the allocyclic signal and their imprint through the platform. In particular, the preservation potential of orbitally-related high-frequency sequences results from the interaction between internal processes and accommodation changes, controlling sediment production/input, re-sedimentation and accumulation. In that sense, shallow areas of the platform are more likely to record lower-frequency sequences (i.e. eccentricity-related sequences), whilst the mid ramp–proximal outer ramp areas are more favourable to preserve higher-frequency sequences, so its sequence architecture can reflect precession and/or eccentricity sequences. The three studied shallow marine platforms show storm-related autocyclic signal concurring and interplaying with the allocyclic climate signal. There have been identified different types of storm-related deposits, whose distribution reflects the fluctuation of hydrodynamic levels associated to sea level changes. |
| Databáze: | OpenAIRE |
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