Planktonic Foraminif era from the Oligocene-Miocene Cipero and 

 Lengua Formations of Trinidad, B.W.I. 



By Hans M. BoUi ' 

 Introduction 



THIS PAPER DISCUSSES the planktonic Foraminif era of 

 the Oligocene-Miocene Cipero and Lengua forma- 

 tions and their stratigraphic distribution. Planktonic 

 Foraminifera have been chosen as a basis for the sub- 

 division of the Cipero and Lengua formations because 

 of their abundance and the short time ranges of many 

 species. By their nature, they are independant of 

 bottom conditions and therefore have a wider lateral 

 distribution than many benthonic Foraminifera, making 

 them very valuable for both local and interregional 

 correlation. 



Cushman and Stainforth (1945) were the first to 

 realize the stratigraphic importance of the strongly 

 dominant planktonic Foraminifera in the Cipero forma- 

 tion. They described 16 planktonic species and sub- 

 divided the formation into three zones with Globigerina 

 concinna (now known as Glohigerina ciperoensis) diag- 

 nostic for Zone I, Glohigerinatella insueta for Zone II 

 and Glohorotalia fohsi for Zone III. 



The need for a closer zonation of the Cipero forma- 

 tion, in particular its upper part where the oil-bearing 

 Herrera sands occur, later led to the subdivision of the 

 Glohorotalia fohsi zone into four additional zones. This 

 subdivision was based on evolutionary changes of 

 Glohorotalia fohsi (Bolli, 1951). In addition, the Glohi- 

 gerina dissimilis zone (now Catapsydrax dissimilis zone) 

 lying between Cushman and Stainforth's Zones I and 

 II and the Glohigerina apertura zone (now Glohigerina 

 ampliapertura zone) were introduced (Cushman and 

 Renz, 1947; Suter, 1951). The last mentioned zone 

 represents the basal Cipero. 



Detailed surface and subsurface exploration during 

 recent years made it necessary to further subdivide the 

 lower part of the Cipero formation. It is now possible 

 to separate a Glohorotalia opima opima zone from the 

 Glohigerina ciperoensis ciperoensis zone, a Glohorotalia 

 kugleri zone from the Catapsydrax dissimilis zone, and 

 a Catapsydrax stainforthi zone from the Glohigerinatella 

 insueta zone. Thus, the Cipero formation can be 

 clearly divided into 11 biozones, based on the distribu- 

 tion of planktonic Foraminifera. 



The Lengua formation is divided into two zones, a 

 lower Glohorotalia mayeri and an upper Glohorotalia 

 menardii zone (Bronnimann, 1951a). 



' Trinidad OU Company, Ltd. (formerly Trinidad Leaseholds, Ltd.), Polnte-a- 

 Plene, Trinidad, B.W.I. 



The detailed zonation of the Cipero and Lengua 

 formations finds its practical appUcation in the geolog- 

 ical surface and subsurface exploration for oU in the 

 Oligocene and Miocene of south Trinidad. Forami- 

 nifera provide the safest means of subdividing and 

 correlating the marl and calcareous clay sequences of 

 these formations. 



Several papers on individual genera and species of 

 planktonic Forammifera from the Cipero and Lengua 

 formations have been published recently. Bronnimann 

 (1950) gave a detailed account of the genus Glohigerina- 

 tella from the Cipero formation. The same author 

 (1951a, 1952) described the genera Glohigerinita, and 

 Glohigerinoita from the Lengua formation. Bronnimann 

 (1951b) and Blow (1956) discussed the genus Orbulina 

 and its evolutionary trends in the Cipero and Lengua 

 formations. The present author followed his earlier 

 investigations on coiling ratios of some Cipero-Lengua 

 Globorotalias (1950) with a study on a number of species 

 of other planktonic genera (1951). 



Herein are figured and described, or discussed, 60 

 planktonic species and subspecies, belonging to 15 

 genera; of these, 1 genus and 21 species or subspecies 

 are new. The age of the Cipero and Lengua forma- 

 tions is discussed, and a correlation with other forma- 

 tions in Trinidad and the Caribbean and the Gulf Coast 

 region is presented. A re-interpretation of the Cipero 

 type section is also presented. 



For details on the lithostratigraphy, earUer strati- 

 graphic subdivisions, and environmental conditions of 

 the Cipero formation, reference is made to Stainforth 

 (1948b). 



Acknowledgments 



The publication of this paper has been made possible 

 through a grant of the Geological Society of America 

 (R. A. F. Penrose, Jr., bequest) for preparation of 

 illustrations, for which the writer wishes to express his 

 sincere gratitude. He is indebted to The Trinidad 

 Oil Company for permission to publish this study and 

 for use of the Company's laboratory and drafting 

 facilities at Pointe-a-Pierre. 



The author wishes to thank Dr. H. G. Kugler, Con- 

 sulting Geologist to Central Mining Investment Cor- 

 poration, and Mr. J. B. Saunders, Paleontologist of 



