Early pliocene evolution of coccolithophores in the Caribbean Sea : taxonomy, biostratigraphy, paleoecology and paleoceanography

Content Provider	Semantic Scholar
Author	Crudeli, Daniela
Copyright Year	2006
Abstract	The early Pliocene was a period of significant turnover among reticulofenestrid coccolithophores (Young, 1989) including the first consistent occurrence (FCO) of small Gephyrocapsa and the first occurrence (FO) of Pseudoemiliania. These bioevents have been widely recognised by light microscopy (LM), and precede by a few hundred thousand years the last occurrence of other important Neogene calcareous nannofossils (Perch-Nielsen, 1985; Young, 1998). The evolutionary development of these coccolithophores in relation to environmental and paleoceanographic changes is, however, poorly understood (Bown et al., 2004). In order to get an insight into the tempi and modes of their evolutionary radiation, we conducted a high-resolution scanning electron microscopy (SEM) study of calcareous nannofossils from cores from the South Caribbean Sea (ODP Hole 1000A) which include the FCO of small Gephyrocapsa (Kameo and Sato, 2000). The interval on which the thesis focuses corresponds to 4.5-3.8 Ma (Steph et al., in revision), an interval where the gradual shoaling of the Isthmus of Panama led to significant changes in the surface water circulation patterns and hydrography in the Caribbean Sea (Haug et al., 2001). The investigated sediments are exceptionally well-preserved and contain a number of previously undescribed morphotypes. Several new, very small to small (<3μm, 3-5μm) reticulofenestrid species Reticulofenestra calicis n. sp., R. alis n. sp., R. pujosiae n. sp. and R. premoliae n. sp. were recognised from these sediments and accurately described. These new species proved to be key-species for the reconstruction of the phylogeny of Gephyrocapsa theyeri, arguably the first evolved species of the Gephyrocapsa plexus. The FO of the species could be defined and dated at 4.45Ma by high-resolution stable isotope stratigraphy (Steph et al., in revision). The evolutionary development of Gephyrocapsa, from the FO of G. theyeri on has been investigated in detail by SEM observations and high-resolution morphometry. Five new Gephyrocapsa species were recognised and described G. drieveri n. sp., G. samtlebenii n. sp., G. bollmannii n. sp., G. matsuokae n. sp. and G. jerkovicii n. sp. and, G. sp. cf. theyeri, are present. The occurrence of the new species is traced in the cores. A pattern of initial radiation among the plexus is recognised which is followed by successive speciation events. The detailed study of the evolutionary origin of the group provides a perspective for the investigation of their radiation in the Quaternary. The hitherto unrecognised biodiversity of coccolithophores indicates that the early Pliocene reticulofenestrid turnover is more complex than previously thought and provides a new insight into the evolution of the group. The here presented high-resolution taxonomic study shows, that the complexity recently discovered by molecular genetics among planktonic organisms can also be traced in the fossil record. The abundance of the deep dwelling species Florispharea profunda, a species not considered in previous studies of the cores (Kameo and Sato, 2000), is quantified by SEM. The relative abundance of F. profunda, a proxy for surface water productivity (Kinkel et al., 2000), provided significant information for understanding the “anomalous” high sea surface temperature obtained by Mg/Ca-ratios in planktic foraminifera.
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Ending Page	76
Page Count	76
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Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article