Mid-Miocene invasion of ecological niches by planktonic Foraminifera of the Kerguelen Plateau, Antarctica

Author(s): Majewski, Wojciech
Author Affiliation(s): Primary:
Polish Academy of Sciences, Institute of Paleobiology, Warsaw, Poland
Volume Title: Marine Micropaleontology
Source: Marine Micropaleontology, 46(1-2), p.59-81. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-8398 CODEN: MAMIDH
Note: In English. Includes appendices. 52 refs.; illus., incl. 3 tables
Summary: Miocene deep-sea sediments from ODP Site 744 (Kerguelen Plateau, southern Indian Ocean) contain abundant and diverse planktonic foraminiferal assemblages. Their analysis led to the identification of the interval between 17.0 and 14.2 Ma as a time of mid-Miocene warmth, which is investigated here in detail. This investigation includes reconstruction of trends in foraminiferal faunal composition and diversity through time, as well as in morphology and coiling direction within Globorotalia praescitula and Globorotalia zealandica plexi. These two large-globorotaliid plexi constitute the most characteristic component of the mid-Miocene foraminiferal faunas at ODP Site 744. Selected benthic (Cibicidoides sp.) and planktonic foraminifera were also analyzed for δ18O and δ13C ratios. Distinctive planktonic assemblages were the basis for identification of three foraminiferal biofacies between 17.0 and 14.2 Ma. The most prominent faunal changes took place between Biofacies 2 and 3 (15.5-15.0 Ma). Six of 11 macroperforate planktonic foraminifera from the >150-µm size fraction occur principally within Biofacies 3. Three other taxa are present throughout the interval analyzed. Moreover, both aforementioned globorotaliid plexi exhibit an increase in morphological diversity between Biofacies 2 and 3. Within the same interval, the G. zealandica plexus shows a switch from random coiling (50% sinistral) to clearly sinistral-dominated coiling. The faunal changes recognized are interpreted as the result of foraminiferal immigrations (increase in faunal diversity) and evolutionary trends (increase in morphological variability and change in coiling mode among the globorotaliid plexi). The stable isotopic results allow paleoenvironmental interpretation of these faunal changes. According to the δ18O values, no significant change in sea-surface temperature occurred between 17.0 and 14.2 Ma. However, the same data suggest an increase in ecological distance between various niches, which is expressed by a rising δ18O gradient recorded between various planktonic taxa upward within the section. This trend suggests niche-space availability as a likely factor responsible for the faunal changes recognized. Changes in the shape and depth of the thermocline, as well as in seasonality and eutrophication are considered as possible causes. Among these an increase in seasonality appears to have been responsible for the increase in species and morphological diversities between 15.5 and 15.0 Ma. The proposed scenario suggests that changes in seasonality may be an important factor driving faunal migrations and evolution. Variable seasonality may also affect the oxygen isotopic record of planktonic foraminiferal taxa. Abstract Copyright (2002) Elsevier, B.V.
Year of Publication: 2002
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Anomalinidae; Antarctic Ocean; Assemblages; Biochemistry; Biodiversity; Biofacies; Biogeography; C-13/C-12; Carbon; Cassidulinacea; Cenozoic; Cibicidoides; Coiling; Faunal list; Foraminifera; Globigerinacea; Globorotalia; Globorotalia praescitula; Globorotalia zealandica; Globorotaliidae; Invertebrata; Isotope ratios; Isotopes; Kerguelen Plateau; Leg 119; Marine environment; Microfossils; Middle Miocene; Migration; Miocene; Morphology; Neogene; Niches; O-18/O-16; ODP Site 744; Ocean Drilling Program; Oxygen; Paleo-oceanography; Paleoclimatology; Paleoecology; Paleotemperature; Planktonic taxa; Protista; Rotaliina; Seasonal variations; Stable isotopes; Statistical analysis; Tertiary; Thermocline
Coordinates: S613440 S613439 E0803528 E0803527
Record ID: 2002075056
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands