The Genera Praeglobotruncana, Rotalipora, Globotruncana, and 

 Abathomphalus in the Upper Cretaceous of Trinidad, B. W. I. 



By Hans M. Bolli' 



Introduction 



SINCE THE PUBLICATION of the author's papers on the 

 genus Globotruncana and on the Upper Cretaceous 

 stratigraphy of Trinidad (BoIU, 1951, 1952), much new 

 paleontologic and stratigraphic information has been 

 gained. It is the purpose of the present paper to 

 describe those species of the genera Praeglobotruncana, 

 Rotalipora, Globotruncana and Abathomphalus that were 

 not known before, to discuss some changes in the pre- 

 vious results, and to show the stratigraphic distribution 

 in Trinidad of all recorded species of these genera. 



The highly complex geology of central and southern 

 Trinidad, with its strongly distorted and incomplete 

 surface sections, is not an inviting ground for detailed 

 biostratigraphic studies. This applies in particular to 

 the Upper Cretaceous sediments. The few, widely 

 scattered outcrops are small, isolated slipmasses that do 

 not offer continuous stratigraphic sections. It is only 

 in recent years, during exploration activities in search 

 of Cretaceous oil, that valuable paleontologic and 

 stratigraphic information has come to light.^ Wells 

 drilled into and through the Upper Cretaceous have 

 made available a number of sections which, combined, 

 represent a fairly continuous succession of sediments. 

 Although this combined sequence is not regarded as 

 truly comprehensive— several stratigraphic gaps ap- 

 parently still exist — it may now be said that its com- 

 pleteness is at least equal to many of the best known 

 Upper Cretaceous sections in Central and South 

 America. 



The faunistic content of Trinidad's Upper Cretaceous 

 sediments is variable, but more often than not the 

 sediments contain rich fossU assemblages. Foramini- 

 fera are predominant in all formations. Only occa- 

 sionally are they out-numbered by Radiolaria (in parts 

 of the Naparuna Hill formation). Mollusks may be 

 numerous in the lower part of the Naparima HiU for- 

 mation where they become valuable markers. The 

 stratigraphic usefulness of certain species of Didymotis 

 and some ammonites in these beds has been noted 

 recently (Imlay, 1955). 



> Trinidad OU Company, Ltd., Polnte-S-Pierre, Trinidad, B. W. I. 



• Credit for this goes In the first place to Trinidad Oil Company, Ltd. (formerly 

 Trinidad Leaseholds, Ltd.), and to Trinidad Petroleum Development, Ltd., the 

 two Companies roost active In exploring the Upper Cretaceous oil prospects. 



About 450 different species and subspecies of Fora- 

 minifera are recognized today in Trinidad's Upper 

 Cretaceous. Of these, about 380 belong to calcareous 

 and arenaceous benthonic genera and the remaining 70 

 odd to planktonic genera. Of the latter, about 15 are 

 classified under the various genera of the family 

 Hantkeninidae and the genus Rugoglobigerina; another 

 20 under the genera Guembelina, Pseudotextvlaria, and 

 Ventilabrella; and the remaining 35 under Praeglobo- 

 truncana, Rotalipora, Globotruncana, and Abathom- 

 phalus. Benthonic and planktonic Foraminifera are 

 often present in equal numbers, though in the Guaya- 

 guayare and Gautier formations the latter predominate. 

 The abundance and short range of many of the plank- 

 tonic species make them ideally suited as markers for 

 stratigraphic work in the Upper Cretaceous of Trinidad. 



The generic position of several species discussed in 

 this paper had to be changed according to the classifi- 

 cation of planktonic Foraminifera proposed recently by 

 Bolli, Loeblich, and Tappan (1957). Globorotalia del- 

 rioensis Plummer and Globotruncana citae BoUi are now 

 included in Praeglobotruncana. Globotruncana inter- 

 media BoUi and G. mayaroensis BoUi belong to Abathom- 

 phalus. Several Upper Cretaceous species published 

 as Globigerina (e. g., Globigerina gautierensis Bronni- 

 mann) have been removed to the genus Praeglobo- 

 truncana since completion of this paper and are there- 

 fore omitted. 



Stratigraphy 



The Upper Cretaceous sediments of Trinidad are at 

 present grouped into the Gautier, Naparima HUl, and 

 Guayaguayare formations. Because of non-deposition 

 or subsequent erosion these formations show a very 

 irregular pattern of distribution in central and south 

 Trinidad. Strong tectonic movements in which they 

 were involved have further complicated the study of 

 the original sequence of the sediments. 



Most outcrops are small isolated masses, each repre- 

 senting not more than one zone. The only exception 

 is found in the Gautier River of the eastern Central 

 Range (for detailed locahty description, see p. 52). 

 There, the black Gautier shales (Rotalipora appenninica 

 appenninica zone) are seen in contact with strongly 

 silicified beds of the Naparima Hill formation. Higher 



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