Sedimentary processes and resulting continental margin configuration during large-scale sea-level drawdown: The Messinian Salinity Crisis in the Western Mediterranean Sea

Autor: Lago Cameselle, Alejandra
Jazyk: angličtina
Rok vydání: 2015
Předmět:
Zdroj: TDX (Tesis Doctorals en Xarxa).
Druh dokumentu: Doctoral Thesis
Popis: Tesi realitzada a l'Institut de Ciències del Mar (ICM-CSIC)
At the end of the Miocene (5.97-5.33 Ma), the Mediterranean basins underwent deep morphological and sedimentological changes as a result of the large-scale sea-level fall during the so-called Messinian Salinity Crisis (MSC) and subsequent fast sea-level rise in the 3 Zanclean. Whereas deep basins accumulated more than 1 million km of evaporites, continental margins recorded several erosion surfaces. Through the analysis of 2D and 3D seismic reflection data and 2D numerical modelling, this Thesis attempts to contribute to better understand the sedimentary processes and resulting continental margin configuration during the large-scale Messinian sea-level drawdown. Detailed mapping of the seismic stratigraphy from the continental margin to the deepwater basin of the Valencia Trough (Western Mediterranean) has revealed two Messinian depositional units (Complex and Upper Units) and four erosional surfaces (Margin Erosion Surface, and Bottom, Top and Intermediate Surfaces). The stratigraphic relationship and margin configuration of these ‘Messinian seismic markers’ suggest that during the Miocene and until late Tortonian, the Mediterranean passive margins were characterized by prograding depositional sequences in the context of a Highstand System Tract. At that time, a sedimentary- active continental slope and delta progradation developed in a normal regressive in the Ebro margin, suggesting context associated to a pre-Messinian Ebro River. During late Messinian, the large-scale sea-level drawdown resulted in the initial development of a Falling Stage System Tract. The subaerial exposure of the shelf and upper slope of the Valencia continental margin at the beginning of the sea-level drawdown – probably in combination with local factors – induced destabilization of the continental slope and deposition of major Mass-transport Deposits (MTD). Results obtained from 2D numerical modeling of coupled transient seepage and deformation analysis and stability analysis suggest a decrease in hydrostatic pore pressures and development of seepage and stress-induced excess pore pressures. As the sea-level dropped, depocenters displaced offshore, major Mediterranean rivers incise to adapt to the base level, and high sediment supply contributed to the development of submarine channels. Concurrently, a submarine paleo-Valencia channel formed in the deepwater Valencia Trough. The gradually slow-down of the sea-level fall allowed the development of a smooth surface at the top of the Lowstand System Tract, whereas the long- time exposure of the proximal shelf and upper slope resulted in a rough erosional surface deeply carved by drainage networks. The Margin Erosion Surface (MES) attained full development on the margins and the MTDs were partially eroded. The development attained by the Messinian Ebro network during the MSC corroborates that the capture of the Ebro Basin occurred prior to the MSC. A slow transgressive phase before the final rapid re-flooding, together with high evaporation rate, favored aggradational deposition of the Upper Unit in a shallow-water basin. At the end of the MSC, the reestablishment of the Mediterranean-Atlantic connection triggered the rapid sea-level rise and the return marine conditions, supported by the outstanding preservation of the fluvial deposits on the main valleys of the MES.
Ó final do Mioceno (5.97-5.33 Ma) a Cuenca Mediterránea sufriu importantes cambios morfolóxicos e sedimentarios como consecuencia dunha baixada do nivel do mar duns 1500 m durante o evento coriecido coma Crise Salina Messiniense. A través da análise de datos de sísmica de reflexión 2D e 3D e do modelado numérico, esta Tese quere contribuír a un mellor entendemento dos procesos sedimentarios e a configuración resultante da marxe continental durante unha Baixada do nivel do mar a gran escala. A mostraxe detallada da estratigafía sísmica do Surco de Valencia (Mediterráneo Occidental) revelou a existencia de dúas unidades deposicionais (Complex and Upper Units) e catro superficies limitantes (Margin Erosion Surface, and Bottom, Top and Intermediate Surfaces). Ás relación estratigráficas suxiren que durante o Mioceno e ata o Tortoniense, a marxe estivo caracterizada por un Sistema deposicional progradante asociado ós aportes dun proto-rio Ebro. Ó final do Messiniense, unha Baixada do mar a gran escala provocou a exposición subaérea das marxes continentais e a desestabilización dos taludes da marxe de Valencia que, posiblemente en combinación con factores locais, ocasionou desprendementos submarinos que depositáronse ó pé do talude. A medida que o nivel do mar descendía, a sedimentación desprazouse cara o mar e os grandes ríos Mediterráneos incidíronse nas plataformas continentais para adaptarse ó novo nivel de base do mar. Ó mesmo tempo, o gran transporte de sedimentos xerado facilitou o desenvolvemento de canóns e sistemas de canles submarinas como o paleo-Canle de Valencia. Unha diminución da taxa de baixada do mar facilitou a formación dunha plataforma de erosión no teito do Lowstand System Tract, mentras a zona proximal da marxe – moito máis tempo exposta á erosión – transformouse nunha superficie moi irregular e amplamente escarvada por sistemas fluviais.. O nivel de madurez que caracteriza ó proto-rio Ebro suxire que a súa captura foi previa á Crise Salina Messiniense. Unha fase transgresiva lenta, previa á inundación, unida cunha alta taxa de evaporación, favoreceu a deposición das evaporitas na conca profunda. Ó final da Crise Salina Messiniense, o restablecemento da conexión do Mar Mediterráneo có Océano Atlántico permitiu á volta as condicións mariñas normais.
Databáze: Networked Digital Library of Theses & Dissertations
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