Estratigrafía sísmica de alta resolución en márgenes continentales pasivos: factores de control durante el Cuaternario
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[1] Instituto de Ciencias del Mar
Instituto de Ciencias del Mar
Barcelona, España
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- Localización: Revista de la Sociedad Geológica de España, ISSN 0214-2708, Vol. 2, Nº. 3-4, 1989, págs. 269-289
- Idioma: español
- Enlaces
- Dialnet Métricas: 2 Citas
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Resumen
- español
La estratigrafía sísmica aplicada a perfiles sísmicos de alta resolución muestra que las secuencias deposicionales del Cuaternario presentan características diferentes a los modelos establecidos a partir de sísmica de multicanal. Así, el desarrollo de sistemas turbidíticos puede estar asociado, no sólo a una primera fase de descenso hasta el borde de la plataforma (tipo 1), sino también a los últimos estadios evolutivos del cortejo de borde de plataforma en los descensos de tipo 2. El desarrollo de cortejos de borde de plataforma está relacionado con descensos de tipo 2 y se manifiesta por la formación de depósitos deltaicos que aparecen con clinoformas oblicuo-tangenciales en sísmica de alta resolución, mientras que en la sísmica de multicanal predominan las configuraciones sigmoidales por superposición de sucesivos sistemas deltaicos. Los cortejos transgresivos están representados por facies litorales con escaso desarrollo vertical, mientras que los cortejos de alto nivel del mar están representados por facies prodeltaicas o litorales.
El desarrollo de secuencias deposicionales en márgenes continentales durante el Cuaternario es fundamentalmente el resultado de la interacción de dos factores de ámbito global: el clima y las oscilaciones del nivel del mar. Otros factores, como son la tectónica, subsidencia, fisiografía, y aporte sedimentario, sólo modifican los anteriores a nivel de cuenca o de ambiente deposicional. La interacción entre estos factores queda registrada en las diferencias que presentan las secuencias deposicionales en los distintos tipos de márgenes continentales. Además, las oscilaciones del nivel del mar y el aporte sedimentario, que actuan sincrónicamente, condicionan el volumen relativo de los distintos cortejos.
La sísmica de alta resolución permite la identificación de ciclos de variación del nivel del mar de alta frecuencia que están por debajo del límite de resolución de las técnicas de multicanal, que puede condicionar el replanteamiento de la correlación precisa de los depósitos con los ciclos globales de cambio relativo del nivel del mar y el desarrollo conceptual de la estratigrafía sísmica.
- English
The stratigraphy and growth patterns of high-terrigenous-influx progradational continental margins are analysed on the basis of high resolution seismic profiles with the concepts of depositional sequences analysis. The available models are largely based on multichannel seismic records, but significant insights into the conceptual models may be gained by examination of modern marine environments and the Plio-Quaternary sequences by high resolution seismic techniques. We propose a more precise evolutionary model for continental margin development that can be summarized in the following conclusions.
The base of turbidite deposits corresponding to the lowstand systems tract has ben defined by type 1 sequence boundary. The turbidite systems can overly, however, type 2 sequence boundary as shwon by the Quaternary turbidite systems of the northwestern Mediterranean. Mass-movements occur during both type 1 and type 2 sea level falls. These processes are controlled by important sediment input off the shelf-break and mass-unstability on the upper slopes is due to the high gradients. The development of lowstand wedge are related to prodeltaic deposits on the upper slope/shelf edge. The are characterized in sparker, seismic profiles, by sigmoidal configuration. The transgressive systems tract in the continental shelf is represented by reduced coastal facies development (0-10 m thick) and large lateral variability of facies as result of the complexity of nearshore environments. The highstand systems tract is represented by the Holocene prodeltaic facies or coastal facies located in the inner shelf. They are commonly sedimentary wedges with parallel reflectors and locally opaque facies due to gas accumulation.
Two main global factors have controlled the development of depositional sequences in the continental margin during the Quaternary: climate fluctuations and sea level changes. Second order global cycles of sea level (more than 10 m.a.) can be be well stablished by the interpretation of multichannel profiles, whereas those of third order (less than 10 m.a.) are better defined on the basis of high resolution seismic profiles. Third order global cycles of sea level (high frequency) are developed by climatic events, that control both sea level fluctuations and sediment input. The interplay of these two factors result in the differences of the geometry of systems tract, as revealed by the great thicknees of Iowstand systems tract in comparison to transgressive systems tract. Moreover, the influence of climate and sea level fluctuations can be modified by local factors such as tectonic, subsidence, physiography and river input. As result of the interplay between these factors, third order cycles may have different expression in the continental margins around the world.
We conclude that the analysis of depositional sequences, for high resolution seismic techniques allow the identification of high frequency sea level cycles that can not be detected with the resolution Iimit of most multichannel seismic techniques. The interpretations and evolutionary models developed from high resolution profiles improve some restrictions to the previous interpretations and several of the concepts of seismic stratigraphy need to be reviewed, mainly those related to correlation between third order global cycles and the development of depositional sequences.
- español
