Calcareous Nannofossils in Pleistocene Sediment Cores From the South African Continental Slope

Siesser, William G.

doi:10.1080/00359197609519905

Cited by 5 publications

(4 citation statements)

References 35 publications

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“…Although the conventional view is that coccolithophores secrete low-Mg calcite in modern seawater (Siesser, 1977), Coccolithus neohelis was the only one of our experimental species to secrete low-Mg calcite in all seawater treatments (Fig. 1A).…”

Section: Changes In Mineralogy With Changes In Seawater Chemistrymentioning

confidence: 85%

Seawater chemistry, coccolithophore population growth, and the origin of Cretaceous chalk

Stanley

Ries

Hardie

2005

Geol

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The magnesium/calcium ratio (Mg/Ca) and calcium (Ca) concentration of seawater have oscillated throughout geologic time; our experiments indicate that these variables have strongly influenced biomineralization and chalk production by coccolithophores. The high Mg/Ca ratio of modern seawater favors precipitation of high-Mg calcite and/or aragonite. In contrast, the low Mg/Ca ratio of imputed Cretaceous seawater favored precipitation of low-Mg calcite. We have discovered that some coccolithophore species today secrete skeletal elements of high-Mg calcite, rather than low-Mg calcite, as conventionally believed. These species incorporated less Mg when the ambient Mg/Ca ratio was lowered, secreting low-Mg calcite in imputed Cretaceous seawater. Calcification stimulates coccolithophore population growth by contributing CO 2 to photosynthesis. Three extant coccolithophore species multiplied much faster as the composition of ambient seawater was shifted toward that estimated for Cretaceous seas. Two of these species secreted high-Mg calcite in ambient seawater having Mg/Ca Ͼ 1, and incorporation of Mg in a calcite crystal inhibits growth. Calcification of the third species, which secreted low-Mg calcite at all ambient Mg/Ca ratios, is hindered by the high Mg/Ca ratio and low absolute concentration of Ca of modern seawater. We conclude that the ionic composition of Cretaceous seawater enabled coccolithophores to produce massive chalk deposits, and conversely, that the ionic composition of modern seawater inhibits population growth for most extant coccolithophore species, which occupy nutrient-poor waters and fail to respond to fertilization by nitrate, phosphate, or iron.

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Section: Changes In Mineralogy With Changes In Seawater Chemistrymentioning

confidence: 85%

Seawater chemistry, coccolithophore population growth, and the origin of Cretaceous chalk

Stanley

Ries

Hardie

2005

Geol

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“…Coccolithus pelagicus prefers cool waters, whereas Discoaster brouweri thrived in warmer waters (Mclntyre et al, 1970;Bukry, 1971Siesser, 1975;Haq, 1980). The abundance ratio of Coccolithus pelagicus abundance to that of D. brouweri may therefore provide an estimate of the relative paleotemperature changes of the surface water.…”

Section: Coccolithus Pelagicus/discoaster Brouweri Ratios and Their Imentioning

confidence: 99%

Cenozoic Calcareous Nannofossils from the Galicia Margin, Ocean Drilling Program Leg 103

Wei¹,

Bergen²,

Applegate³

1988

Proceedings of the Ocean Drilling Program

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Ocean Drilling Program Leg 103 occupied five sites on the Galicia margin, northwest of the Iberian Peninsula. Two holes (Holes 637A and 638B) yielded significant Cenozoic sedimentary sections ranging from late Miocene to late Pleis tocene in age. From the nannofossil stratigraphy, one hiatus is recognized in Hole 637A (2.35-2.4 Ma), whereas two hia tuses (one at 1.9-2.6 Ma and another at 3.5-3.7 Ma) are recognized in Hole 638B. Sediment-accumulation rates for the Cenozoic portions of these two holes have been calculated based on the nannofossil datums. The abundance ratios of Coccolithus pelagicus to Discoaster brouweri for Hole 637A show relatively low values and small fluctuations from 2.5 to 6.5 Ma but sharply increase and then widely fluctuate beginning at about 2.5 Ma. This may indicate relatively warmer, more stable surface-water temperatures from 2.5 to 6.5 Ma and cooler, variable surface-water temperatures af ter 2.5 Ma at Site 637. C. pelagicus/D. brouweri ratios from Hole 638B also show a trend of increasing values with time from late Miocene to late Pliocene, but with more fluctuations and a different pattern from that of Hole 637A.

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“…Bukry (1971b) proposed that Coccolith assemblages with a limited diversity or small size and shape are typical of cooler water. Siesser (1975) believes this may also apply to assemblages of discoasters, which are associated with warmer surface water temperatures because of their abundance in lowlatitude sediments. Increased numbers of chiasmoliths in high-latitude sediments suggest an affinity for cool surface water temperatures.…”

Section: Paleoecologymentioning

confidence: 99%

“…The following list of "cool-water" and "warm-water" species was compiled by Siesser (1975) from data presented by Martini (1970), Bukry (1971aBukry ( , 1973b, Edwards (1973), Wise (1973), andThierstein (1974) (Haq and Lohmann, 1976). The Paleogene was subsequently divided into 23 latitudinaltemperature assemblages.…”

Section: Paleoecologymentioning

confidence: 99%

Paleocene and Eocene Calcareous Nannofossils from Deep Sea Drilling Project Legs 25 and 40, South and East of Africa

Mackenzie¹,

S.W.²

1983

Initial Reports of the Deep Sea Drilling Project

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Paleocene and Eocene nannofossil flora from Deep Sea Drilling Project Legs 25 and 40 were analyzed in order to provide a basis of comparison with DSDP Legs 36 and 71 and with other South Atlantic assemblages. A mid-latitude biostratigraphic zonation, using previously described zonal markers, was adopted for the southwest Indian Ocean. Various diagenetic effects were noted in the sedimentary sequences. Some of these mask to some extent paleoecologic signals, particularly those generated by the Discoaster/Chiasmolithus ratio.

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Calcareous Nannofossils in Pleistocene Sediment Cores From the South African Continental Slope

Cited by 5 publications

References 35 publications

Seawater chemistry, coccolithophore population growth, and the origin of Cretaceous chalk

Seawater chemistry, coccolithophore population growth, and the origin of Cretaceous chalk

Cenozoic Calcareous Nannofossils from the Galicia Margin, Ocean Drilling Program Leg 103

Paleocene and Eocene Calcareous Nannofossils from Deep Sea Drilling Project Legs 25 and 40, South and East of Africa

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