Tesis de licenciatura: Magnetología de las sucesiones cenozoicas de la cuenca de As Pontes (La Coruña, NW de España

Abstract

The Tertiary basin of As Pontes (NW Spain) is associated to a NWSE dextral strike-slip fault system. The basin infill is composed by alternating beds of lignite and terrigenous facies deposited on alluvial and in lacustrine-palustrine systems. Several tectonic structures (thrusts, folds and normal faults), linked to the evolution of the strike-slip fault system, controlled the basin evolution and in the early stages resulted in the generation of two sub-basins which laer coalesced and resulted in a single depositional zone. Syntectonic Cenozoic infills was dated by means of magnetostratigraphy. A total of four local magnetostratigraphic successions has been constructed. In the four succesions more than 500 sites were sampled at an average spacing of approximately 2 m. The studied litology were mainly mudstones with low content of organic matter. In total there is been demagnetizated about 900 samples, through thermal demagnetization and through alternate fields. The minerals that carry the magnetisation in the studied sediments are magnetite and iron sulphides. The magnetochronological correlation of the different successions of the basin has allowed to establish a highly precise chronological correlation of the two sub-basins and the isochrony or nearly isochrony for the different lignite seams and for the lithostratigraphical units of the basin. Correlation to GPTS shows that sedimentation in the basin began some time before the end of the Chron 10r (28.7 My) and it lasted, at least, until the end of the subchron 6AAr.2n (22.5 My). The minimal diiration of the sedimentation in the basin was about 6.2 My, and it comprises from the uppermost Early Oligocene (upper part of the Stampian) to the Early Miocene (upper Aquitanian). The magnetochronology of the syntectonic sedimentary infilling of the Tertiary Basin of As Pontes has allowed to determine that the activity of the NW-SE dextral strike-slip faults systems of NW Spain affecting the NW margin of the Iberian Plate was from the upper most Early Oligocene to the Early Miocene. The end of the movement of these fault systems coincides with the end of activity of the NW Iberian plate boundary according to the sea-floor magnetic anomalies (AM 6). Thus the end of the main offshore tectonic activity coincides with its end in the NW Spanish onshore.