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

• Main Author: Tjalsma, R.C.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 1971
• Subjects: Earth Sciences; Planktonic foraminifera
• Online Access: https://dspace.library.uu.nl/handle/1874/205787

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 ...