Globorotalia continuosa Blow 1959 from: Bolli, H.M.Saunders, J.B. (1985): Oligocene to Holocene low latitude planktic foraminifers. In: Plankton Stratigraphy Eds: Bolli, H.M.Saunders, J.B. p. 155-262 | . |
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Species Globorotalia continuosa Blow 1959 |
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| Discussion / Comments: |
Bolli & Saunders (1985):
This small, 4-chambered species was regarded by its author as closely related to the ancestral G. opima nana and to be itself the ancestor of G. acostaensis, which appears at the base of the Late Miocene. Origin, relations and range of G. continuosa were re investigated by Bolli & Saunders (1982a) in conjunction with their study on G. mayeri. Here also their observations are based on a sequence of specimens throughout the range of the species. G. continuosa appears to have developed gradually from the G. opima nana stock through the Globigerina ciperoensis ciperoensis Zone to the Globigerinatella insueta Zone, becoming more lobate and gradually acquiring a higher arched aperture (Bolli & Saunders, 1982a, pl. 4). From G. mayeri the species is distinguished by its smaller size and by possessing only 4 instead of 5-6 chambers in the last whorl. Identical with G. mayeri is the overall morphology, the range and the coiling pattern. We do not agree with Blow that G. continuosa is the ancestor of G. acostaensis for the following reasons: In Trinidad and Java G. continuosa became extinct together with G. mayeri at the top of the G. mayeri Zone. G. acostaensis appeared on the other hand only at the base of the zone of the same name. Both species are therefore absent in the intermediate Globorotalia menardii Zone. This interval lacking both G. continuosa (and also G. mayeri) and G. acostaensis is particularly well documented in the continuously cored section of well Bodjonegoro 1 in Java (Bolli, 1966b), where the Globorotalia menardii Zone is 214 metres thick. In addition, the aperture of G. continuosa is a high, comma shaped arch while that of G. acostaensis is, in contrast, a low slit. From the above cited observations it is therefore concluded that G. continuosa is in its overall morphology and range closely related to G. mayeri and that the species is not the ancestor of the G. acostaensis G. humerosa G. dutertrei plexus, which first appears with G. acostaensis only sometime after the extinction of G. continuosa. From the stratigraphic point of view it is considered that there is little value in separating G. continuosa from G. mayeri. |
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Bolli & Saunders (1985):
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| References: |
Blow,W.H. (1959):
Age, correlation and biostratigraphy of the upper Tocuyo (San Lorenzo) and Pozón Formations, eastern Falcon, Venezuela . Bull. Am. Paleontol. Vol. 39(178) p. 67-252
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
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