Marine Micropaleontology, 21 (1993) 143-168 143 Elsevier Science Publishers B.V., Amsterdam Late Miocene globorotaliid event-stratigraphy and biogeography in the NE-Atlantic and Mediterranean F.J. Sierro, J.A. Flores, J. Civis, J.A. Gonz~ilez Delgado and G. Francrs Departamento de Geologia, Facultad de Ciencias, Universidad de Salamanca, 37008 Salamanca, Spain (Received March 28, 1991; revision accepted October 5, 1992 ) ABSTRACT Sierro, F.J., Flores, J.A., Civis, J., Gonz~ilez Delgado, J.A. and Francrs, G., 1993. Late Miocene globorotaliid event-stratig- raphy and biogeography in the NE-Atlantic and Mediterranean. Mar. Micropaleontol., 21: 143-168. The quantitative study of keeled and unkeeled globorotaliids in several Late Miocene sites of the NE Atlantic, the North Betic and South Rifian Gateways and the Western Mediterranean enabled us to recognize a sequence of planktic forami- niferal (PF) events useful for a high resolution correlation of the Mediterranean with the global ocean for the time interval immediately prior to the salinity crisis. P F-Event 1 (6.7 Ma, end of Subchron 7n 1 ) is defined by the sudden disappearance or reduction of Globorotalia men- ardii group I (sinistral) in most of the NE Atlantic and Mediterranean. This is probably due to a southward migration of these forms to more subtropical latitudes. PF-Event 2 (6.56 Ma; Subchron 6r2 ) is defined by the abundant occurrence of Globorotalia menardii group II (dextral). Between PF-Events 1 and 2, the temperate waters of the NE Atlantic Ocean and Mediterranean Sea were almost completely lacking in keeled globorotaliids. The most prominent change in the assem- blages, the replacement of the Globorotalia menardii group II by the Globorotalia miotumida group (PF-Event 3; 6.4 Ma, Subchron 6n) may be correlated with the Tortonian/Messinian boundary and is related to a widespread second southward migration of northern temperate faunas replacing the subtropical ones as the North Atlantic latitudinal thermal gradients increased. This event also coincides with the beginning of the Mediterranean crisis recorded by isotope fluctuations in surface waters and immediately followed by the development of widespread anoxic conditions in the deep and intermedi- ate waters during the deposition of the Tripoli Formation. PF-Event 4 (first abundant occurrence of dextral specimens in the Neogloboquadrina acostaensis group; approximately between 5.6 and 5.5 Ma, Subchron 5rl ) and PF-Event 5 (reduc- tion or disappearance of the Globorotalia miotumida group; approximately between 5.6 and 5.5 Ma, Subchron 5rl ) pre- date the Lower Evaporites and PF-Event 6 (First abundant occurrence of Globorotalia margaritae s.s.; Subchron 5n 1 ) is contemporary to their deposition. The coiling direction of unkeeled globorotaliids, highly variable in the first part of the Late Tortonian, became almost 100% dextral (PF-Event A) a short time after PF-Event 2. This group maintained this pattern until the Late Messinian with the exception of a short interval with a peak of sinistral forms just at the Tortonian/Messinian boundary. On comparing these events with the carbon isotope records of different sites of the Atlantic Ocean we recognized similar trends between the events. Maximum ~l~c values in planktic and benthic foraminifera coincide with PF-Event 1, they decrease between PF-Events 1 and 2 and increase again immediately after PF-Event 2. PF-Event 3 coincides with the beginning of the global Late Miocene carbon shift. Introduction Previous contributions (Sierro, 1985; Sierro et at., 1987) recognized a series of changes in the assemblages of keeled globorotaliids in some sections of the Guadalquivir basin (Spain). Based on these studies, the present work mainly focuses on the investigation of the geographic and stratigraphic distribution of several groups of Globorotalia in the NE Atlan- tic and the Mediterranean throughout the Late Miocene. At present, the Globorotalia menardii group lives exclusively in waters from the tropical and 0377-8398/93/$06.00 © 1993 Elsevier Science Publishers B.V. All rights reserved.