Coiling preferences and evolution in the middle Miocene Fohsella chronocline

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doi: 10.1016/j.marmicro.2006.05.001
Author(s): Eisenach, Adam R.; Kelly, D. Clay
Author Affiliation(s): Primary:
University of Wisconsin, Department of Geology and Geophysics, Madison, WI, United States
Volume Title: Marine Micropaleontology
Source: Marine Micropaleontology, 60(4), p.243-257. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-8398 CODEN: MAMIDH
Note: In English. Includes appendix. 43 refs.; illus., incl. 2 plates, 3 tables, sketch map
Summary: Micropaleontologists have traditionally recognized the mid-Miocene Fohsella lineage as a flagship for phyletic gradualism within the planktic foraminifera. However, study of a deep-sea record from the western equatorial Pacific (ODP Site 806) reveals that coiling ratios within this clade suddenly (<5 kyr) shift after a prolonged, ancestral state of near randomness (∼50%) to a transient phase (13.42-13.43 Ma) of dextral dominance (∼75%) immediately following the first common occurrence of keeled fohsellids. This brief period of dextral dominance was abruptly (<5 kyr) succeeded by an irreversible change to sinistral dominance (∼96%). Fohsellid abundances decline markedly through the interval in which the sinistral preference is established. The shift to sinistrality (13.42 Ma) predated the deepening of fohsellid depth ecology by ∼240-488 kyr, indicating that these two events were unrelated. This view is supported by a lack of δ18O evidence for depth-habitat differences between the two chiral forms, which refutes the notion that sinistral fohsellids were "pre-adapted" for ensuing hydrographic change because they occupied a deeper depth habitat than their dextral counterparts. Planktic foraminiferal assemblages become strongly oligotrophic in character through the interval in which the fohsellid δ18O increase is recorded, indicating that the migration to deeper depths was fostered by an expansion of the mixed layer in the western equatorial Pacific. Salient aspects of this brief, but conspicuous faunal change are a marked increase in the abundance of symbiont-bearing globigerinoidids, a concomitant collapse of local Jenkinsella mayeri/siakensis populations, and reduced fohsellid abundances. The rapid and permanent nature of the Fohsella sinistral shift provides a distinct, unequivocal datum that may prove useful for correlating mid-Miocene sections throughout the Caribbean Sea and tropical regions in the western sectors of the Pacific and Atlantic. The coiling ratio changes that occurred during the evolution of the Fohsella chronocline probably reflect changing population dynamics between cryptic genotypes with different coiling preferences. Abstract Copyright (2006) Elsevier, B.V.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 10 Paleontology, Invertebrate; Biologic evolution; C-13/C-12; Carbon; Cenozoic; Coiling; Deep-sea environment; Equatorial Pacific; Fohsella; Foraminifera; Habitat; Invertebrata; Isotope ratios; Isotopes; Leg 130; Marine environment; Microfossils; Middle Miocene; Miocene; Morphology; Neogene; O-18/O-16; ODP Site 806; Ocean Drilling Program; Ontong Java Plateau; Oxygen; Pacific Ocean; Paleoenvironment; Planktonic taxa; Protista; SEM data; Stable isotopes; Tertiary; West Pacific
Coordinates: N001906 N001907 E1592142 E1592140
Record ID: 2007046292
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands