Late Miocene globorotaliid event-stratigraphy and biogeography in the NE-Atlantic and Mediterranean

Author(s): Sierro, F. J.; Flores, J. A.; Civis, J.; González Delgado, J. A.; Francés, G.
Author Affiliation(s): Primary:
Universidad de Salamanca, Departamento de Geología, Salamanca, Spain
Volume Title: Marine Micropaleontology
Source: Marine Micropaleontology, 21(1-3), p.143-168. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-8398 CODEN: MAMIDH
Note: In English. 84 refs.; illus. incl. strat. cols., sketch maps
Summary: 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 foraminiferal (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. PF-Event 1 (6.7 Ma, end of Subchron 7n1) is defined by the sudden disappearance or reduction of Globorotalia menardii 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 assemblages, 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 intermediate 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 5r1) and PF-Event 5 (reduction or disappearance of the Globorotalia miotumida group; approximately between 5.6 and 5.5 Ma, Subchron 5r1) predate the Lower Evaporites and PF-Event 6 (First abundant occurrence of Globorotalia margaritae s.s.; Subchron 5n1) 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 δ13C 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.
Year of Publication: 1993
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Africa; Atlantic Ocean; Biogeography; Biostratigraphy; C-13/C-12; Cape Bojador; Cape Verde Atlantic; Carbon; Cenozoic; DSDP Site 135; DSDP Site 334; DSDP Site 397; DSDP Site 410; DSDP Site 415; DSDP Site 416; DSDP Site 544; Deep Sea Drilling Project; Foraminifera; Globorotaliids; IPOD; Invertebrata; Isotope ratios; Isotopes; Leg 107; Leg 14; Leg 37; Leg 47; Leg 49; Leg 50; Leg 79; Mazagan Plateau; Mediterranean Sea; Microfossils; Mid-Atlantic Ridge; Miocene; Morocco; Neogene; North Africa; North Atlantic; Northeast Atlantic; ODP Site 654; Ocean Drilling Program; Paleoclimatology; Protista; Stable isotopes; Tertiary; Tyrrhenian Sea; Upper Miocene; West Mediterranean
Coordinates: N453030 N453030 W0292830 W0292830
N370206 N370206 W0342454 W0342454
N334600 N334600 W0092418 W0092418
N453030 N453030 W0292830 W0292830
N310142 N310142 W0390600 W0390600
N325012 N325012 W0104806 W0104806
Record ID: 1993010304
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands