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Exploration Gulf of Caiz

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Carlos Giraldo Ceballos
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The studied area is located along the Atlantic continental slope (Moroccan–Iberian margin) to the Wof the Gibraltar Straits. Preliminary resultsobtained from interpretation of 2d reflexion seismic lines and compilation of different public sources ( Scientific Projects , regional geology ) would indicate that there is some relationships between the absence of mud volcanoesphenomena along the slope and the presence of geological structures associated to gravitationalinstability processes.In this first evaluation it can be considered that these gravity-driven structures would act as barriers for the growth and development of mud volcanoesthat controlfluids migration pathways related withthe mud mobilization through seaflooralong the slope. The gravity-driven structures here described seem to have been developed during Quaternary times. Along the area different structural styles can be interpreted from 2d seismic lines: normal faulting (extensional) and reverse faulting/toe-thrust type (compressive)
Resumen: El área de estudio se encuentra localizada a lo largo del talud continental Atlántico (sector Íbero–Marroquí) al O del Estrecho de Gibraltar. A partir de la interpretación de líneas sísmicas de reflexión (2D) y análisis de datos procedentes de diferentes fuentes públicas (proyectos de investigación, geología regional) se pueden establecer relaciones genéticas entre la ausencia de volcanes de lodo y la presencia de estructuras geológicas asociadas a fenómenos de inestabilidad gravitacional. En esta primera evaluación se postula que dichas estructuras podrían actuar como barreras que impiden el crecimiento y desarrollo de volcanes de lodo ya que podrían controlar las vías de migración de los fluidos relacionados con la expulsión de material arcilloso hacia el fondo marino. Estas estructuras geológicas gravitacionales ham podido producirse durante el Cuaternario y a lo largo de ellas se pueden interpretar, a partir de líneas sísmicas, sectores en extensión (fallas normales) como sectores en compresión (fallas inversas tipo toe-thrust). Abstract: The studied area is located along the Atlantic continental slope (Moroccan–Iberian margin) to the W of the Gibraltar Straits. Preliminary results obtained from interpretation of 2d reflexion seismic lines and compilation of different public sources (Scientific Projects , regional geology) would indicate that there is some relationships between the absence of mud volcanoes phenomena along the slope and the presence of geological structures associated to gravitational instability processes. In this first evaluation it can be considered that these gravity-driven structures would act as barriers for the growth and development of mud volcanoes that control fluids migration pathways related with the mud mobilization through sea floor along the slope. The gravity-driven structures here described seem to have been developed during Quaternary times. Along the area different structural styles can be interpreted from 2d seismic lines: normal faulting (extensional) and reverse faulting/toe-thrust type (compressive).
The objective of this study is to evaluate deformation styles prior to the Messinian Salinity Crises (MSC) west and east of the Gibraltar Arch and to understand possible relationships between geodynamic setting, deformation styles and isostatic rebound of the Betic-Rif ranges. Regionally, the Gibraltar Arch is part of the Betic-Rif arcuate fold-thrust belt that resulted from collision between the Alborán, Iberian, and African plates during the early Neogene. The Gibraltar Arch isostatic rebound, in contrast to tectonic uplift, occurred prior to the Pliocene and is considered to be the main cause of disconnection between the Atlantic Ocean and the Mediterranean that led to the MSC (5.96 Ma-5.33 Ma). 2D and 3D seismic interpretation in the Gulf of Cádiz and west Alborán Sea suggest that dominant deformation styles of Neogene sediments prior to the MSC are associated with gravitational-gliding processes resulting in toe-thrusts and extensional rollovers. This gravitational deformation is related to the isostatic uplift of the Gibraltar Arch, which occurred during the Middle-Late Miocene and is sealed by Pliocene strata. At least two episodes of gravity gliding processes occurred on the west Alborán side: Middle Miocene (c. 13-15 Ma) and Late Miocene (c. 7-10 Ma). In the Gulf of Cádiz a very large gravity-gliding feature known as the “Olistostrome” event is sealed by Upper Miocene sediments (c. 7-10 Ma). Active mud volcanism, triggered from Miocene overpressured shales, post-dates the MSC west and east of the Gibraltar Arch. In the west Alborán domain the Neogene basin lies directly above the igneous-metamorphic complex known as the Alborán allochthonous. However, in the Gulf of Cádiz area the contemporaneous Neogene sediments have been deposited above the northernmost extension of the Mesozoic-Tertiary passive margin of the West African plate.