Globorotaloides variabilis Bolli 1957 from: Spezzaferri, S.Silva, I.S.. (1990): Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico . Palaeogeography, Palaeoclimatology, Palaeoecology Vol. 83 p. 217-263 | . |
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Species Globorotaloides variabilis Bolli 1957 |
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| Diagnosis / Definition: |
Kennett & Srinivasan (1983):
Test low, trochospiral, spiral side almost flat, equatorial periphery lobulate, axial periphery subacute to subrounded; chambers subangular to ovate, five to six rapidly
enlarging chambers in the final whorl; sutures on both spiral and umbilical sides distinctly curved in early stage, later becoming radial, depressed; surface distinctly cancellate ; umbilicus fairly wide; aperture a very low arch or slit interiomarginal, umbilical-extraumbilical in early stage, later becoming umbilical.
Bolli (1957):
Shape of test low trochospiral, biconvex; equatorial periphery lobate, in small specimens somewhat elongate; axial periphery subacute in immature specimens, rounded in mature specimens. Wall calcareous, perforate, surface very finely cancellate. Chambers subangular to ovate in early stage, later becoming ovate to spherical; about 1-18, arranged in 2-2 1/2 whorls; the 5-7 chambers of the last whorl increase fairly rapidly in size. Sutures on spiral side distinctly curved in early stage, later becoming more radial, depressed; on umbilical side slightly curved in early stage, later becoming radial, depressed. Umbilicus fairly wide, open in immature specimens, in mature specimens partly or completely covered by a bulla like chamber. Aperture a slit or low arch; interiomarginal, umbilical extraumbilical in early stage, later becoming umbilical, which in the mature stage becomes covered by a bullalike chamber with one infralaminal aperture. Coiling random. Largest diameter of holotype 0.45 mm. |
| Discussion / Comments: |
Kennett & Srinivasan (1983):
This species is distinguished from Gd. suteri by having more compressed early chambers, more curved sutures, and a greater
number of chambers in the final whorl.
Bolli & Saunders (1985):
G. variabilis is distinguished from G. suteri by its generally larger size and particularly by the more numerous and less inflated chambers of the early stage with their distinctly curved sutures and by the more rapidly increasing size of the last chambers.
Bolli (1957):
Globorotaloides variabilis, new species, is distinguished from G. suteri, new species, by having more compressed early chambers, more curved sutures and a greater number of chambers. It is likely that G. suteri, which is restricted to the lower and middle part of the Cipero formation, is the ancestor of G. variabilis, new species.
Chaisson & Leckie (1993):
Similar species: Globorotaloides variabilis can resemble juvenile specimens
of Globoquadrina venezuelana and G. conglomerata, but it can be
distinguished from these taxa by its distinctive subacute margin on the early
chambers of the final whorl and the lack of an apertural tooth-plate. The chambers
of G. variabilis are more embracing than those of G. hexagona. The subacute
peripheral margin of G. variabilis also serves to distinguish these two taxa. |
| Systematics: |
3
Classis Foraminifera
Genus Globorotaloides
Species Globorotaloides variabilis
22
Genus Globorotaloides
Species Globorotaloides variabilis
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| Synonym list: |
Kennett & Srinivasan (1983):
Bolli & Saunders (1985):
Chaisson & Pearson (1997):
Bolli (1957):
Vincent & Toumarkine (1990):
Spezzaferri & Silva (1990):
Chaisson & Leckie (1993):
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| References: |
Bolli,H.M. (1957):
Planktonic foraminifera from the Oligocene-Miocene Cipero and Lengua formations of Trinidad, B.W.I..
In: Studies in Foraminifery, Bulletin of the U.S. National Museum Vol. 215 Eds: Loeblich, A.R.Tappan, H.Beckmann, J.P.Bolli, H.M.Gallitelli, E.M.Troelsen, J.C. p. 97-123
Kennett,J. and Srinivasan,M.S. (1983):
Neogene Planktonic Foraminifera - A Phylogenetic Atlas.
Bolli,H.M. and Saunders,J.B. (1985):
Oligocene to Holocene low latitude planktic foraminifers.
In: Plankton Stratigraphy Eds: Bolli, H.M.Saunders, J.B. p. 155-262
Spezzaferri,S. and Silva,I.S.. (1990):
Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico . Palaeogeography, Palaeoclimatology, Palaeoecology Vol. 83 p. 217-263
Vincent,E. and Toumarkine,M. (1990):
Neogene planktonic foraminifers from the Western Tropical Indian Ocean, Leg 115.
In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 115 Eds: Duncan, R.A..Backman, J.Peterson, L.C. p. 795-836
Chaisson,W.P. and Leckie,R.M. (1993):
High-Resolution Planktonic Foraminifer Biostratigraphy of Site 806, Ontong Java Plateau (Western Equatorial Pacific).
In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 130 Eds: Berger, W.H.Kroenke, L.W..Mayer, L.A..et al. p. 137-178
Chaisson,W.P. and Pearson,P.N. (1997):
Planktonic foraminifer biostratigraphy at Site 925: middle Miocene–Pleistocene.
In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 154 Eds: Shackleton, N.J.Curry, W.B.Richter, C.Bralower, T.J.
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