98 



UNITED STATES NATIONAL MUSEUM BXJLLETIN 215 



The Trinidad OU Company, for many suggestions 

 during the preparation of the paper and for reading and 

 discussing the manuscript. Dr. K. Kohr of The 

 Trinidad Oil Company is largely responsible for the 

 map showing the type section of the Cipero formation. 

 Through discussions and exchange of material Mr. 

 W. H. Akers of the California Company and Dr. P. J. 

 Bermudez of the Creole Petroleum Corporation have 

 kindly helped the author in the determination of 

 numerous species. Thanks are due to Dr. A. R. 

 Loeblich, Jr., of the U. S. National Museum, and to 

 Dr. Helen Tappan Loeblich, Eesearch Associate, 

 Smithsonian Institution, for their help extended during 

 the preparation of this paper. A part of the illustra- 

 tions for the present paper were prepared under the 

 grant to Dr. Loeblich for planktonic studies, admini- 

 stered by the Smithsonian Institution, for which funds 

 were supplied by the California Research Corporation, 

 the Carter OU Company, the Gulf Oil Corporation, 

 and the Humble Oil and Refining Company. 



Mr. R. A. Pallant, Senior Draftsman of The Trinidad 

 on Company, supervised the preparation of the tables. 

 The plate illustrations are camera lucida drawings by 

 Patricia and Lawrence Isham, scientific illustrators, 

 U. S. National Museum. The plates were arranged 

 and mounted by Drs. Alfred and Helen Loeblich. 



Stratigraphy 



Unlike the Upper Cretaceous and lower Tertiary 

 formations, the Cipero and Lengua formations are well 

 exposed over wide areas of south Trinidad. The best 

 exposed section of the Cipero formation, the type 

 section along the Cipero coast south of San Fernando, 

 has previously been described in detail by Stainforth 

 (1948b). Although none of the known surface sections 

 presents a complete and tectonically undisturbed 

 sequence, it would nevertheless be possible to compile 

 the present-day stratigraphic subdivision of the Cipero 

 formation from these sources alone. However, the 

 subdivision of the Cipero and Lengua formations, as 

 herein presented, has been developed almost entirely 

 from subsurface information. Over one hundred wells, 

 mainly situated in the oilfields of the Barrackpore- 

 Penal area, have penetrated the Lengua and upper part 

 of the Cipero formation, and numerous exploration 

 wells have penetrated the lower part of the Cipero 

 formation. Many of these subsurface sections, often 

 closely cored, are stratigraphically more complete and 

 tectonically less disturbed than any of the known 

 surface sections. 



Text-figure 17 shows the calcium carbonate content 

 and the percentages by weight of Foraminifera in sam- 

 ples taken at the type localities of the Cipero and 

 Lengua zones. In addition, the number of planktonic 

 species and subspecies occurring in each zone is shown. 

 These figures show a marked increase in species from 

 the Globorotalia kugleri zone to the Catapsydrax dissimilis 

 zone. It is here that the Oligocene-Miocene boundary 



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Figure 17. — ^Weight percentage of Foraminifera (^0.06 mm.), calcium 

 carbonate content, and number of planktonic Foraminifera species 

 and subspecies in samples from the type localities of the Cipero and 

 Lengua formations. 



is tentatively placed. The stratigraphic ranges of aU 

 species and subspecies discussed are given in text- 

 figure 18. 



The Cipero Formation 



The Cipero formation of south Trinidad consists 

 predominantly of marls and highly calcareous clays 

 which, in the upper and middle part, may be replaced 

 by turbidity flow conglomerates and sands of the 

 Herrera and Retrench members. Part of the upper- 

 most Cipero foiination {Globorotalia Johsi robusta zone) 

 and the lower Lengua formation {Globorotalia mayeri 

 zone) may be replaced by the widespread Karamat 

 formation in which planktonic Foraminifera are vir- 

 tually absent. Along the southern edge of the Central 

 Range, a part of the Cipero formation {Globorotalia 

 kugleri to Catapsydrax stainforthi zones) is replaced 

 towards the North by the Nariva formation in which 

 planktonic Foraminifera are also absent. The part of 

 the Cipero formation which is above the Catapsydrax 

 stainforthi zone changes northwards into the neritic 

 facies of the Brasso formation. 



Small reefal limestone developments with orbitoidal 

 faunas are occasionally found in the Cipero formation 

 (e. g., Morne Diablo limestone, Mejias limestone; vide 

 Kugler, 1953). The coralliferous limestone of the Ste. 

 Croix member seemingly belongs to the base of the 

 Brasso formation. 



The basal part of the Cipero formation {Globigerina 

 ampliapertura zone) often appears as a dark silt. 

 Lithologically it then becomes almost indistinguishable 



