On Saturday 5th March 1988, 30 members of the Geological Society of Trinidad and Tobago set out by two pirogues from Staubles Bay on a field trip to Gaspar Grande Island, off the northwest peninsula of Trinidad (Fig. 1).The objectives of this field trip were to afford our members yet another opportunity of becoming professionally knowledgeable of our surroundings, in keeping with one of the aims of our Society, and to enhance the social and professional camaraderie among our members.
The opportunity was also taken to visit Cronstadt Island while en route to Gaspar Grande in order to acquaint ourselves, first hand, with the activities which are pursued on that island relative to the petroleum industry.

Stop I - Cronstadt Island:
At Cronstadt Island we were welcomed by Mr. Max Edgehill, Manager of Baroid (Trinidad) Ltd. and shown around and briefed on the activities of that company. Contrary to popular belief there is no deposit of naturally occurring barytes on that island or in any part of Trinidad and Tobago. Previously, barytes for the operations at Cronstadt Island was imported from Brazil, but today that commodity is imported from Morocco, calcined and crushed to specification (Plate 1), then bagged for use in the petroleum industry as one of the components of drilling muds. Bentonite imported from Wyoming, USA is also handled at Cronstadt Island. Like barytes, the bentonite is dried properly, mixed to specification and bagged for use as an additive to drilling muds because of its peculiar property of gelling and of increasing the viscosity of the muds.
It is interesting to note that although there are excellent deposits of limestone of the Laventille Formation of Lower Cretaceous, possibly Jurassic age on Cronstadt Island, no active quarrying is being conducted there at this time. In the recent past, however, limestone was quarried there, and taken to Point Lisas by barge for the construction of its deep water mooring facility.

Stop 2 - Winn's Bay:
Our next stop was at Winn's Bay, Gaspar Grande (Fig. I) where examined the excellent exposures of the outcrops along the beach before starting our climb uphill. The outcrops afforded us the opportunity of observing Lower Laventille sequence of phyllites and limestones - the latter being dense, grey and intensely fractured (Plate 2).The ascent to the fluorspar deposit was steep and the absence of a beaten track, the presence of a thicket of thorny shrubs and the sweltering heat made the climb a bit uncomfortable. We reached a strategic part of the ridge from where we descended to the area of the fluorspar deposits.
There we found 3 of the trenches dug several years ago by the then Ministry of Petroleum and Mines, and left open to facilitate further studies of the fluorspar deposits. No definite lens or bed was observed but the attitude of the blocks encountered suggests that the deposits" are in the phyllites which are most probably part of the sequence encountered at lower level along the beach. It is also suggested that faulting may account for the presence of the fluorspar. However, while there have been several suggestions as to its origin
- including a 1964 Ministerial report by F. Joubin - a systematic mapping exercise would be necessary in order to place that deposit in its proper stratigraphic position.
From the section traversed a lithological and stratigraphic relationship is postulated as follows:

Stops 3 and 4 - Calypso Beach and Gaspar Grande Caves:
leaving Winn's Bay the party headed back east and north into Calypso Beach where an attempt was made to land in order to undertake another steep climb the Gaspar Grande ironstones (hematite or goethite) being the target. Unfortunately we were not permitted to disembark there unless each member of the trip paid a compromised figure of $5.00. This not being considered acceptable, we decided to forego that stop and to make proper arrangements at a future date to get to those deposits via Bombshell Bay instead. As a result the party proceeded to Stop 4, Pointe Baleine and the Gaspar Grande Caves, also known as the Blue Grotto.

After wending our way down approximately 35 meters of sinuous steps we reached the floor of the main cave. A turquoise pond of cold sea water about 25 meters in diameter and more than 10 meters at its deepest point with three inlets connected to the sea was located in the floor of the main cave. Giant stalagmites of various forms, huge stalactites hanging from the dome-shaped basilica, and several solution cavities were observed. The writer suggests that the G.S.T.T. undertake a professional study of these caves for posterity.


Stop 5 - Scotland Bay:
leaving Pointe Baleine we headed for the western extremity of the northwest peninsula where we swam to our hearts' delight in the clear blue and warm waters of Scotland Bay before returning to Staubles Bay. Thus concluded a most enjoyable day of geology cum pleasure.

2. SOLOMON HOCHOY HIGHWAY AND NEARBY OUTCROPS FIELD TRIP

N. Payne (TR IN TOC)

The Solomon Hochoy Highway between Gasparillo and the Couva Main Road transects a stratigraphic section ranging from Paleocene to Upper Pliocene in age. Exposures within this section and in some nearby outcrops are easily accessible in the dry season. A reconnaissance field trip to the area was organised by J. Frampton and N. Payne on Sunday 24th April, 1988, after a series of bush fires had exposed much of the geological section.
The trip was held in two parts: a morning traverse to view and discuss the general stratigraphic section (Stops 1 to 8) and an afternoon session which concentrated mainly on observations of Brasso/Tamana relationships along a well exposed, east-west trending structure (Stops 9 to 11). The locations examined are plotted on Kugler's 1:50,000 geological map (Fig. 2) and reference was made in the field to descriptions by Saunders of samples collected by Higgins during the construction of the Highway.

STOP 1: Approximately l00m of Paleocene to Oligocene shales, siltstones and sandstones were examined in this location. Samples taken by Higgins in 1971 indicated these rocks belong to the Pointe-a-Pierre, Chaudiere and Nariva Formations. No good bedding is preserved but conspicuous chaotic sandstone blocks were common. The moderately soft bedrock shales resemble those of the Nariva Formation (Oligocene).

STOP 2: Light grey fossiliferous, calcareous silts of the Concord member of the Tamana Formation (Middle Miocene) are exposed at this stop. This outcrop is weathered and no bedding is visible.

STOP 3: This stop involved a short walk to the Plaisance conglomerate (Plate 3). a very heterogeneous rock consisting of boulder to pebble sized clasts of Cretaceous and lower Tertiary lithologies. It is interpreted as belonging to the San Fernando Formation (Upper Eocene). Clasts range from shallow water, fossiliferous limestones to quartz conglomerates with graded beds. According to Kugler's maps the outcrop lies within the Nariva Formation.

STOP 4: This location is just north of the Warm Springs Fault as mapped by Kugler. Well bedded, light yellow, fine grained sandstones with iron-rich concretions outcrop here and are probably the Telemaque member of the Manzanilla Formation. A glauconitic, greenish grey, calcareous siltstone, probably a lower Manzanilla member, outcrops to the south.

STOP 5: In the Springvale Quarry, west of the highway. Thick-bedded sands of the Telemaque member dip to the northwest. Dips average 300 to 400 and Callianassa burrows and cross bedding are visible in some beds.

STOP 6: The multicoloured clays of the Caparo member of the Talparo Formation outcrop between the Couva Main Road and Rivulet Road. Grey is the dominant colour but bright yellow and reddish brown varieties are common. Plant remains are present and probably indicate a brackish to continental environment of deposition.
STOP 7 and 8: Springvale Quarry Eastern Section; stop 7 is Kugler co-type locality of the Savaneta glauconitic sandstone member of the Springvale Formation. It is an extremely fossiliferous outcrop with numerous large bivalves and gastropods (Plate 4). Common genera include Ostrea, Pecten and Dosina. The massive Telemaque sands of stop 5 are exposed at stop 8 the southern end of the quarry, together with thin interbedded lignite Secondary gypsum and Callianasa burrows are common.


STOP 9: A near vertical bed of Tamana limestone lies in fault contact (trending ENE) with Brasso shale at the outcrop (Plate 5). Good evidence horizontal slickensides was observed.

STOP 10: The Guaracara limestone of the Tamana Formation was mined this quarry. Again the Brasso shale is fault contact with the limestones. Cora and other reef builders are visible.


STOP 11: West Quarry; this is spectacular outcrop of near vertical limestone beds cut by a series of hit angle faults, some of which converge while others appear to jump across bedding planes (Plate 6). Corals and other reef building organisms are common as are darker organic rich limestone beds. Once again slickensided and squeezed Brasso shales can be observed along fault contacts, which trend in the same ENE direction.

STOP 12: An additional stop at the Pointe-a-Pierre grits was included on the trip due to its proximity. This outcrop, an abandoned quarry, comprises massive, coarse grained, red weathering sandstone beds with thin shale intercalations dipping approximately 800 to the northwest. The fining upwards character of some beds, and the presence of incomplete Bouma and Mutti-Ricci Lucchi "A" sequences, suggest a proximal turbidite channel.

CONCLUSIONS: Due to the reconnaissance nature of the trip, no detailed examinations were carried out. However, enough was seen to justify a critical review of both the stratigraphic and structural interpretations of this area, and by extension of the Trinidad area as a whole. A recently appointed GSTT stratigraphic sub-committee has already begun work on the former. Specific areas of concern which were evident on this field trip include: currently used stratigraphic terminology, e.g. the "Tamana Formation", an apparent rock-biofacies unit with reefal limestone members, and the Nariva shale, a litho- or a chrono-stratigraphic unit? We also saw faulted contacts in the Central Range which have been previously mapped as unconformities. Are these thrust or strike-slip faults?

It is obvious that there is much fieldwork yet to be done in Trinidad. The numerous unrecorded outcrops and other exposures that exist should be examined, and the results integrated into existing maps and models of the basin.

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