El eóceno de la cuenca de Pamplona: estratigrafía, facies y evolución paleogeográfica. (The Eocene of the Pamplona basin: stratigraphy, facies and paleogeographic evolution)

This project has focused on the Early and Middle Eocene sediments of the Pamplona Basin, an area which had seldom been previously studied. However, the Eocene Pamplona Basin has turned out to be of considerable interest, first because it is one of the few areas in the pyrenean domain that allows for the reconstruction of a complete shallow- to deep-water transect (i.e., from the Northiberian Platform to the Southpyrenean Trough), and also because of its strategic position between the Central Southpyrenean Zone and the Basque-Cantabrian Region. In addition to an improvement of existing geological maps, this study has produced the following results: (a) new lithostratigraphic and sequence stratigraphic schemes of succession, (b) the biostratigraphic age dating of the different units of both schemes, (c) a better understanding of the sedimentological and tectonic processes which control the development of the succession, and (d) the determination of the paleogeographic evolution.

Three main stratigraphic units have been defined, all of the them bounded by important sedimentological breaks (RSBE, RSiY, RSiL and RSiB). Unit 1 (early-middle Ypresian) represents a stage of gentle regression and incipient tectonic activity. Unit 2 (late Ypresian/middle Lutetian-I) records the enhancement of the regression and the amplification of the tectonic activity, with important right lateral movements along the Pamplona fault zone. Unit 3 (middle Lutetian-II/early Bartonian) has a transgressive trend developed during a period of attenuated tectonism. Units 1 to 3 are parts of two 2ndorder transgressive-regressive facies cycles (CTR-1 and 2). Thus, Units 1 and 2 form the regressive hemicycle of CTR-1, the former representing a depositional regression, the latter a forced one. Unit 3, on the other hand, represents the transgressive hemicycle of CTR-2 (the Upper Maastrichtian-Paleocene transgressive hemicycle of CTR-1 and the latest Eocene regressive hemicycle of CTR-2 have not been studied in this Thesis). The genesis of both CTRs was determined by changes in the second-order tectonic subsidence rate. Thus, the regressive hemicycle of CTR-1 (Units 1 and 2) record the tectonic uplift of the shallow-water domain, a process probably linked to the initial development of a forebulge in the western part of the southpyrenean foreland basin. Likewise, the transgressive hemicycle of the CTR-2 (Unit 3) was driven either by the disappearance of the forebulge or by its southwards migration. Climate was an additional control of the sedimentation during the studied interval, the earliest Eocene climatic maximum being particularly important.

Thirteen depositional sequences (SD-E1 to SD-E13) have also been recognised. Their genesis responds to 3rd-order relative changes of sea level that, at least in certain cases, were undoubtedly caused by tectonics. Internal organisation of these depositional sequences varies depending on their position within the CTRs, probably due to the interference of the 2nd-order subsidence curve. Highorder sequence stratigraphic units and a variety of event deposits have finally been identified. The most interesting examples of the latter are carbonate megabeds redeposited within the deep-water deposits, that represent important tectonic tilting episodes of the platform domain. The temporal restriction of such megabeds to the late Ypresian/middle Lutetian-I reinforces the strong tectonic activity deducted for this particular interval.

The CTRs of the Pamplona Basin and some of their depositional sequences seem to occur in other pyrenean zones. Also, the major sedimentary breaks of the Pamplona Basin can be correlated with specific discontinuities of other euro-atlantic zones, and seem to be contemporaneous with periods of readjustment of lithospheric plates. Such coincidences suggest that the main controls of the tectonosedimentary evolution of the Eocene Pamplona Basin were the interactions in both the north-Atlantic ridge and the Iberian-European plate boundary