Stratigraphy and foraminifera of the neogene of the Eastern Guadalquivir basin (Southern Spain)

The Neogene succession of the eastern part of the Guadalquivir basin was found to consist from bottom to top of turbidites, fine marly and clayey sedi,- ments and again turbidites. Five formations and one member could be distinguished. In the southern part of the basin sediments appear to be allochthonous; their area of deposition must have been farther south. In the North there is possibly a gradual change in upward direction into autochthonous sediments of the Upper Miocene. In studying the planktonic foraminifera attention has been paid to their horizontal and vertical variation. It appeared necessary to extend the concept of some species, like that of Globigerina pseudobesa and Globigerinoides bulloideus. Several new forms have been described; partly they may be considered as local variants of known species, like Globorotalia d. mayeri, Globigerina aff. pachy.,. derma, Globigerina sp., Globigerinoides d. conglobatus. Other {orms seem to be less close to known species, like Globorotalia sp., Globigerino£des afL Tuber and sphaeroidinellopsis sp. As their stratigraphical occurrence was not studied outside the field area and phylogenetic relationships to other species remained undear,;it seemed not justified to erect them as new species. Study of pre-adult stages was done by removing the final chambers of adult specimens. It proved to be a help in disentangling homeomorphic species. Investigation on several members of the Globigerinoides trilobus - Orbulina universa lineage, indicates that together with a change in relative size and shape of the final chamber also oachange in the earlier stage has taken place. In sections considered to be Middle Tortonian representatives of the Globigerinoides bulloideus group occur in great abundance and with an extremely wide variation. In these strata transition between the genera Globigerina and Globigerinoides is constantly present. For most variants the stratigraphic range is very short, however. For the Globorotalia menardii group a general trend from unkeeled to keeled was found throughout the stratigraphic column. The outline of the chambers in spiral view also underwent a gradual change. As these trends seem to be of local importance only, no names were given to the distinctive forms. Coiling direction of this group changes from left to right in strata which are considered to be Middle Tortonian. On the basis of their content of planktonic foraminifera separate sections could be arranged in biostratigraphic order. Moreover in most cases correlation with the biozonation of BLOW (1969) appeared to be possible, indicating that the sediments range from zone N. 4 toN.-16/N. 17. According to the current literature this should be from Aquitanian to Upper Tortonian/Messinian (?). Miogypsinids found in the oldest sections suggest a Chattian to Aquitanian Age. Uvigerinids belonging to the U. cretensis lineage are present in the younger formations. They allow correlation with the upper part of the Tortonian stratotype, which is in fairly good agreement with the planktonic foraminifera. Some speculations have been made about the factors affecting the deposition of the laminated and non-laminated siliceous marl (moronitas) in the southern part of areas with and without burrowing activities, which might explained by an tion might have been caused by a combination of high and fairly constant production of phytoplankton and zooplankton (as a result of upwelling water) together with a seasonal peak in the influx of terrigenous material from rivers. Absence of burrowing organisms as a consequence of a zone of low concentration of dissolved oxygen might account for the fact that lamination remained preserved. The cooccurrence of laminated and non-laminated sediments of the same age is in favor of areas with and without burrowing activities, which might be explained by an irregular bottom topography. Northward moving slipped masses might account for such sea floor relief. The presence of turbidites as topmost sediment indicates a still rather deep basin at that time. Unless later sediments have been completely eroded away, it suggests that the eastern part of the Guadalquivir basin rather suddenly emerged at the end of the Miocene. In the western part of the basin (Carmona area) sedimentation lingered on, but of a more shallow character. The larger part of the section at Carmona does not seem to have equivalents in time in the eastern part of the basin