156 



UNITED STATES NATIONAL MUSETJM BULLETIN 216 



Stratigraphy 



Navet Formation 



The term Navet formation was introduced by Renz 

 (1942) for the characteristic light grey to greenish-grey, 

 khaki-weathering, nodular marls occurring between the 

 Paleocene-lower Eocene Lizard Springs formation and 

 the upper Eocene San Fernando formation. They 

 contain a very rich fauna of smaller Foraminifera, 

 especially planktonic forms, and at some levels are 

 also rich in Radiolaria. 



In their paper on the Eocene Foraminifera of the 

 Navet and Hospital HiU formations of Trinidad, 

 Cushman and Renz (1948) described the fauna from 

 seven isolated localities. Tentative stratigraphic posi- 

 tions based on faunistic evidence for these localities 

 were given from top to bottom as follows : 



Penitence Hill marl 



Fitt Trace — Navet River — Nariva River marls 

 Friendship Quarry — Dunmore Hill marls 

 Ramdat marl 



For faunistic and lithologic reasons the Ramdat 

 marl has been moved to the Lizard Springs formation 

 (BoUi, 1957a, p. 64). No clear break has been recog- 

 nized between the Lizard Springs and Navet forma- 

 tions. The Globorotalia palmerae zone, here placed 

 in the basal Navet, occupies a somewhat transitional 

 position between the two formations. The calcium 

 carbonate content as measured at the type localities 

 does not exceed 10 to 15 percent in the lower Lizard 

 Springs and 25 percent in the upper Lizard Springs 

 but increases to 36 percent in the Globorotalia palmerae 

 zone and between 50 and 70 percent in the higher 

 Navet beds. 



The Hospital HiU marl was treated by Cushman 

 and Renz as a separate formation. However, it is 

 lithologicaUy so similar to the Navet formation that 

 it is here considered to represent its topmost zone. 

 To the author's knowledge, no contacts are exposed 

 between the marls of the Navet formation and the clays, 

 sUts, sands, and boulder beds of the younger San Fer- 

 nando formation. The Navet formation is here 

 regarded as comprising the uppermost part of the lower 

 Eocene, the middle Eocene, and the lower part of the 

 upper Eocene. 



The complete absence of continuous sections ia the 

 Navet formation and the difficulty in establishing 

 biostratigraphic sequences from isolated, small outcrops 

 and subsurface occurrences has already been pointed 

 out in the introduction. The large number of samples 

 studied has counterbalanced these unfavourable condi- 

 tions to some degree. The additional material studied 

 has enabled the erection of two more zones to the 

 subdivisions suggested by Cushman and Renz (1948): 



The Globorotalia palmerae zone: This zone shows 

 affinities to the Globorotalia aragonensis zone of the 

 uppermost Lizard Springs but contains in addition 

 Globorotalia aspensis (Colom) and the short-lived 

 Globorotalia palmerae Cushman and Bermudez. The 

 genera Hantkenina and Clavigerinella, both restricted 



to the middle and upper Eocene are not found here. 

 It is regarded as uppei-most lower Eocene (basal Navet). 



The Truncorotaloides rohri zone: This zone stiU 

 contatas the spinose forms of the Truncorotaloides rohri 

 Bronnimann and Bermudez group and small specimens 

 of Globorotalia lehneri Cushman and Jarvis but no 

 longer Globigerapsis kugleri Bolli, Loeblich, and Tappan 

 and the zonal marker of the Porticulasphaera mexicana 

 zone. Some species known in the upper Eocene and 

 lower Oligocene begin to appear, but the zonal marker 

 of the Globigerapsis semiinvoluta zone (Hospital HiU 

 marl) is not yet present. It is considered to be of 

 uppermost middle Eocene age. 



Seven zones, based on the distribution of planktonic 

 Foraminifera, are distinguished in the proposed bio- 

 stratigraphic subdivision of the Navet formation. The 

 foUowing tabulation (see also text-figures 25 and 26) 

 shows the Navet marl localities described by Cushman 

 and Renz in relation to the new zonation. They are 

 from top to bottom: 



Hospital Hill formation 



Penitence HiU marl 



Fitt Trace marl- Navet 



River marl 

 Dunmore HiU marl- 



Nariva River marl 

 Friendship Quarry marl 



semiinvoluta zone 

 Truncorotaloides rohri zone 

 Porticulasphaera mexicana 



zone 

 Globorotalia lehneri zone 



Globigerapsis kugleri zone 



Hantkenina aragonensis 



zone 

 Globorotalia palmerae zone 



Some of the Navet marl localities given by Cushman 

 and Renz contain poorly preserved faunas, this is 

 especiaUy true for the Friendship Quarry marl. One 

 of them, the Penitence HUl marl locality, is no longer 

 accessible. Therefore, in addition to the Cushman and 

 Renz localities which are here maintained as type 

 localities, a number of outcrops which contain better 

 preserved faunas are proposed as cotype localities. A 

 very suitable area for such outcrops is found between 

 mUeposts 12 and 12% of the Brasso-Tamana Road and 

 the Navet River in the Central Range (see text-fig. 25). 

 AU but one zone of the Navet formation, including a 

 new type locality, are here exposed in a very restricted 

 and comparatively easUy accessible area. Most of the 

 outcrops lie in two smaU ravines leading into the Navet 

 River. A few are found along the Navet River and 

 two more are situated further north, one on the Brasso- 

 Tamana Road, near mUepost 12%, the other west of 

 the road, on the slope of a small marl hiU. Although 

 almost every zone is represented in this area, they are 

 not in any normal stratigraphic sequence, the Navet 

 being present as slip-masses in the upper Oligocene- 

 lower Miocene Nariva formation. 



Globorotalia palmerae Zone 



Type locality: Trinidad Petroleum Development 

 weU Esmeralda 1, eastern Central Range, Trinidad 

 (coordinates N:270297 links; E:415893 links), type 

 sample: core 9,386-9,405 feet (TTOC 228911). 



