160 



UNITED STATES NATIONAL IVTUSEUM BULLETIN 215 



Lithology: Yellowish-grey, nodular marl. 



Remabks: The Globigerapsis semiinvoluta zone is char- 

 acterized by the zonal marker, and by the absence of 

 the middle Eocene spinose Truncorotaloides rohri Bron- 

 nimann and Bermudez group and the strongly com- 

 pressed Globorotalia lehneri Cushman and Jarvis. 



San Fernando Formation 



The term San Fernando beds was introduced by 

 Guppy (1866). These beds, later elevated to forma- 

 tion rank, are best exposed in the San Fernando area, 

 south Trinidad, where they are developed as glauconi- 

 tic calcareous clays, clays, silts, sands, boulder beds, 

 and small complexes of reefal limestone. As might be 

 expected, these varied lithologic units, together com- 

 prising a thickness of up to 800 feet, carry equally 

 varied foraminiferal faunas including completely are- 

 naceous, predominantly planktonic, and shallow reefal 

 assemblages. The larger Foraminifera of the limestones 

 have been described by Vaughan and Cole (1941). 

 Reworked Foraminifera, especially from the Navet for- 

 mation, occur almost throughout the formation. 



The Mount Moriah formation is considered synony- 

 mous with Guppy 's San Fernando formation. The 

 term "Mount Moriah" is today only used in member 

 status for the silts, sands, and boulder beds of the San 

 Fernando formation. 



In some sections in the San Fernando area (see Bolli, 

 1957b, p. 98) the calcareous clays of the San Fernando 

 formation are overlain, apparently without a distinct 

 lithologic break, by calcareous clays and marls of the 

 Olobigerina ampliapertura zone, Cipero formation. 

 Faunistically, the separation is clearly shown by the 

 disappearance of the typical Eocene planktonic and 

 benthonic marker Foraminifera such as Hantkenina, 

 Globorotalia cocoaensis Cushman, Globorotalia centralis 

 Cushman and Bermudez, Bulimina jacksonensis Cush- 

 man etc. The only planktonic species which appear 

 for the first time in the basal Cipero are Olobigerina 

 ciperoensis ciperoensis BoUi and Cassigerinella chipolen- 

 sis (Cushman and Ponton) . 



In the San Fernando area the San Fernando forma- 

 tion rests imconformably on the lower part of the Navet 

 formation or on the Lizard Springs formation. 



Because of the varied foraminiferal assemblages in 

 the San Fernando formation and the strong reworking 

 of Foraminifera from older formations, no subdivision 

 into biozones is possible with the sections available at 

 the present time. 



Globorotalia cocoaenBis Zone 



Type locality: Steep bank on east (waiting rooms) 

 side of San Fernando Railway Station (coordinates 

 N:237060 links; E:356425 links), type sample KR25684 

 (TTOC 238769). 



Lithology: Dark grey-brown calcareous silt. 



Remarks: The zone is characterized by the presence 

 of Globorotalia cocoaensis Cushman, Hantkenina primi- 



tiva Cushman and Jarvis and Cribrohantkenina ber- 

 mudezi (Thalmann) and the absence of Globigerapsis 

 semiinvoluta (Keijzer). 



Evolutionary Trends and Direction of Coiling 



More complete sections than those available in 

 Trinidad would be necessary to study in detail the 

 evolutionary trends and patterns of coiling in the middle 

 and upper Eocene. However, the following condensed 

 remarlss on observation made on the Trinidad material 

 wiU sufl&ce to show that the rapid tempo in evolution 

 and distinct patterns in preferred coiling directions 

 as shown for many planktonic species in the upper 

 Paleocene and lower Eocene (Bolli, 1957a) also persist 

 through the middle and upper Eocene. The same 

 trends were found again in the Oligocene and Miocene 

 (Bolli, 1950, 1951). 



The species of the genera Globigerapsis, Globiger- 

 inatheka, and Porticulasphaera obviously represent a 

 related group. Transitional specimens indicate that 

 Globigerapsis kugleri Bolli, Loeblich, and Tappan 

 branched off from the long-ranging Globigerapsis index 

 (Finlay) and later developed into Porticulasphaera 

 mexicana (Cushman). Globigerinatheka barri Bron- 

 nimann is closely related to Globigerapsis kugleri, 

 differing only in the possession of sutural bullae. Al- 

 though no transitional specimens were observed in 

 Trinidad between Globigerapsis index (Finlay) and 

 Globigerapsis semiinvoluta (Keijzer) it is likely that the 

 latter branched off from the former in early upper 

 Eocene time. 



The fact that over 90 percent of the specimens of 

 the species belonging to the genera Globigerapsis, 

 Globigerinatheka, and Porticulasphaera coil dextrally is 

 further proof for close genetic relationship. 



The earliest recorded species of Truncorotaloides in 

 the upper Paleocene coil almost exclusively dextrally. 

 This trend seems to persist throughout the lower 

 Eocene. The lower middle Eocene Globorotalia bvll- 

 brooki Bolli, new species, (probably a Truncorotaloides) 

 stiQ shows a preference for dextral coiling, although 

 this is much less pronounced than in the older Trun- 

 corotaloides. A rapid change towards sinistral coiling 

 in Truncorotaloides apparently occurs at the end of the 

 Hantkenina aragonensis zone. The ratio of sinistral 

 to dextral coiling of T. rohri Bronnimann and Bermudez 

 and T. topilensis (Cushman) in the Globigerapsis 

 kugleri to Truncorotaloides rohri zones is over 90 percent. 



The strong preference for suiistral coiling (over 90 

 percent) shown by Globorotalia aragonensis Nuttall 

 and Globorotalia broedermanni Cushman and Bermudez 

 in the uppermost Lizard Springs (Bolli, 1957a) is found 

 to continue in the Navet formation until the two species 

 become extinct at the top of the Globigerapsis kugleri 

 zone. Of approximately 100 specimens of Globorotalia 

 renzi Bolli, new species, counted in samples throughout 

 the recorded range, all were found to coil dextraUy. 



