Geomorfologia e geologia regional do sector de Porto-Espinho (W de Portugal): implicações morfoestruturais na cobertura sedimentar cenozóica Regional geomorphology and geology from the Porto-Espinho sector (W Portugal): morphostructural implications to Cenozoic sedimentary cover

One of the most common characteristics of the Portuguese littoral is the existence of a planed surface (the so-called “littoral platform”), situated at different altitudes and bordered from the inland by a straight relief, strongly contrasting with that planed surface. This one is generally covered with several outcrops of the so-called Plio-Pleistocene deposits. Till the eighties this platform has been interpretated as stable staircase of old marine levels, registering in a passive way the eustatic variations. The rigid step bordering it easterly should be a fossil cliff. However, our study has proved that many of these deposits have a continental origin. These continental deposits have fluvial or alluvial fan facies and they are lying above 40 meters. Marine deposition seems to be quite rare and it only occurs on a small western area, beneath the altitude of 40 meters, and developing into three different marine levels. There is a rigid step between the two kinds of deposits. We think that the clear geometric separation between these deposits together with this rigid step, indicates the results from tectonic activity. It seems that the sea must have touched only the western part of this surface, when neotectonic movements lowered it down. There are more evidences for neotectonic movements: a) there are faults (mainly inverse faults) affecting the higher deposits of this littoral platform; b) the same marine level seems to appear at different altitudes, developing an irregular pattern with a general trend dipping from the North to the South.