Climatic change and the planktonic foraminiferal species - coincidences in some Late Neogene clades
Planktonic foraminifera adjust their position in the water column through modifications in size, shape, and external ornamention (keel, costae, etc.); this is useful in exploiting new ecologic niches. Evolutionary change may be triggered by paleoceanographic change, for example, low sea level, often associated with cool climate, may result in enhanced vertical mixing in the upper water column, decrease in density stratification and available niches. Phyletic evolution is well documented in several clades of Late Neogene planktonic foraminifera. Accelerated or decelerated evolutionary rates in these clades may be due to change in selection pressure in response to changing paleoceanographic conditions. The latest Miocene was marked by low sea level and cool climate; the earliest Pliocene by higher sea level and warmer, more stable climate. In response, size (cross-sectional area) in the Globorotalia tumida clade trebled, test acquired thicker encrustation, ventral/dorsal height proportions changed; the keel was lost in the Globorotalia inflata clade, and chambers became rounded rather than conical; and supplementary apertures appeared in the Sphaeroidinellopsis-Sphaeroidinella clade. The beginning of gradually increasing conicality in the G. inflata clade, which continued to the Miocene-Pliocene boundary, coincided with falling sea level and depletion of delta/sup 13/C in sea water at about 6 ma. Lowered sea level and cooler climate in the middle Pliocene (3.2 Ma) may be responsible for a relatively rapid increase in frequency of supplementary apertures (from 20 to 100 %) in the Sphaeroidinellopsis-Sphaeroidinella clade. This event also coincided with a stepwise increase in benthonic delta/sup 18/O and a brief interval of increased planktonic delta/sup 18/O.
- Research Organization:
- Univ. of Uppsala (Sweden)
- OSTI ID:
- 6457023
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 17; ISSN GAAPB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580100* -- Geology & Hydrology-- (-1989)
ANIMALS
BIOLOGICAL EVOLUTION
CENOZOIC ERA
ECOLOGY
FORAMINIFERA
GEOLOGIC AGES
GLOBAL ASPECTS
INVERTEBRATES
LEVELS
MICROORGANISMS
MORPHOLOGICAL CHANGES
PALEOCLIMATOLOGY
PALEONTOLOGY
PROTOZOA
SARCODINA
SEA LEVEL
SEAS
SURFACE WATERS
TERTIARY PERIOD
VARIATIONS