Chiloguembelina Loeblich and Tappan and Related 



Foraminifera from the Lower Tertiary 



of Trinidad, B. W. I. 



By J. P. Beckmann ' 

 Introduction 



RECENT STUDIES BY Montaiiaro Gallitelli (1955) indi- 

 cate that Guembelina Egger, 1899, is a junior 

 synonym of Heterohelix Ehrenberg, 1843, and therefore 

 invalid. Loeblich and Tappan (1956) have erected 

 the genus Chiloguembelina, to include some Tertiary 

 species previously referred to Guembelina. Chiloguem- 

 belina is distinguished from the Cretaceous genus 

 Heterohelix by the absence of an early coiled stage, 

 the presence of necklike apertural extensions, and the 

 tendency to develop a twisted test and asymmetrical 

 aperture. 



In Trinidad, ChUoguembelina is present in a great 

 number of planktonic faunas of Paleocene, Eocene, and 

 Oligocene age. The specimens are usually well pre- 

 served and the morphological details are easily seen, 

 except in some middle Eocene samples, where the 

 number of good specimens is sometimes insufficient. 



It is the purpose of this paper to describe the species 

 of ChUoguembelina from the lower Tertiary of Trinidad, 

 to establish their stratigraphic ranges, and to discuss 

 their relationships to the Heterohelicidae and Buli- 

 minidae. 



Acknowledgments 



The author wishes to express his appreciation to the 

 management of The Trinidad Oil Company for allowing 

 him to use the facilities of the Geological Laboratory 

 at Pointe-a-Pierre and for permission to publish this 

 paper. Special thanks are due to Dr. H. M. BoUi 

 (Pointe-a-Pierre, Trinidad, B.W.I.) for encouraging and 

 assisting the writer in his investigations and to Dr. A. 

 R. Loeblich (U. S. National Museum) and Mrs. Helen 

 Tappan LoebHch for assistance with the manuscript. 

 The illustrations were drawn by Lawrence and Patricia 

 Isham, scientific illustrators, U. S. National Museum, 

 under the grant to Dr. Loeblich for planktonic Fora- 

 minifera studies, administered by the Smithsonian 

 Institution, for which fimds were supplied by the 

 California Research Corporation, the Carter Oil Com- 

 pany, the Gulf Oil Corporation, and the Humble Oil 

 and Refining Company. The author wishes to express 

 his sincere thanks also to Dr. P. J. Bermudez (Jusepin, 



Trinidad Oil Company, Ltd., Polnte-&-Plerre, Trinidad, B. W. I. 



Venezuela), Prof. Rutten (Utrecht, Netherlands) and 

 Dr. J. Hofker (Den Haag) for furnishing valuable 

 information, and to his colleague J. B. Saunders for 

 reading the manuscript. 



Stratigraphy 



The species of ChUoguembelina, Guembelitria and 

 Zeauvigerina described in this paper were obtained from 

 samples from the following formations: 



Cipero formation, lower part (Oligocene) 



San Fernando formation (uppermost Eocene) 



Navet formation (middle Eocene to lower part of upper 



Eocene) 

 Lizard Springs formation (Paleocene to lower Eocene). 



Details of the further subdivision of these formations 

 are given in the range chart (text-fig. 16). The com- 

 plete data, with descriptions of the planktonic Fora- 

 minifera, have been published by Bolli (1957a, 1957b, 

 1957c). 



The generic names of the zonal markers used in this 

 paper are in accordance with the recent classification 

 of planktonic Foraminifera by Bolli, Loeblich, and 

 Tappan (1957). 



General Morphology 



The chamber arrangement of the Tertiary species of 

 Chiloguembelina is biserial throughout. None of the 

 species investigated by the author show the early coil 

 described from the Cretaceous Heterohelicidae (Loeb- 

 lich, 1951; Montanaro GaUiteUi, 1955). The presence 

 of a triserial stage in Guembelina venezuelana Nuttall, 

 recorded by Hofker (1954), could not be confirmed. 

 The diameter of the proloculum is from 0.005 to 0.02 

 mm. Its size varies from species to species, as well as 

 within one species. In the latter case, this seems to 

 indicate the existence of megalospheric and micro- 

 spheric generations. 



The characteristics fairly constant within one 

 species, and therefore most useful for systematic 

 purposes, are: The aperture — its shape and position 

 (eccentric or in the center of the apertural face), and 

 the presence or absence of transparent collars or 



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