Spectral analysis and gravity modelling of the Almazán Basin (Central Spain)

Resumo

A study concerning the deep structure of the Almazán basin has been carried out by using seismic, gravity and geological data. A new interpretation of previous seismic reflection lines has provided an isopach map for the top Albian unit showing an overall simple flat-bottomed syncline geometry with a 4500 m thickness depocenter placed near the northeastern boundary of the basin. A gravity survey provided a gravity map of the basin and surrounding areas, depicting relative gravity highs and lows linked to sedimentary infill variations and lithological changes in the basement. A map for the theoretical gravity due to the sedimentary infill has been done by integrating the data derived from the isopach map with the function which describes the density increasing with depth. Substracting this map to the observed gravity map, a new one depicting the gravity response for the basement has been obtained. Spectral analysis of this new map shows the occurrence of a regional source located at 11 km. Integrating all the aforementioned data, three 2+1/2 D gravity models have been obtained. These models display an acceptable fitting linking surface geological structure with bottom basin geometry, as well as different basement bodies and the geometry of the boundary between the basement and middle crust.