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MANZANILLA COAST FIELD TRIP

One of the many field trips planned by the Geological Society of Trinidad and Tobago, took us to the Manzanilla Coast on May 15, 1982. Many of the local oil companies were represented and we were pleased to have a member of the Geological Staff of Maraven, Venezuela. The party was lead by Dr. John Frampton of Texaco Trinidad, Inc.

The primary purpose of the trip was to examine Northern Basin sediments of Miocene and Pliocene age, which are well exposed on the East Coast of Trinidad.

The first stop was at Manzanilla Bay which is the type locality for the Manzanilla Formation. Here, the dark calcareous fossiliferous silts of the San Jose member were examined. Numerous specimens of the Manzanilla marker pelycypod
noetia trinitaria and other species, Chione walli and Corbula sp. as well as the bryozoan Cupuladria were identified. The environment of deposition for these silts is considered to be open marine - inner sub-littoral. The second stop was at Upper
Fishing Pond then a short walk through swamplands to the beach at Point Lobin. This was the start of the main part of the field trip which was intended to examine the section along the beach from Point Lobin to Point Paloma to the south.

The stratigraphic section forms the southern limb of the Fishing Pond Syncline as seen by well-defined northerly dips, and comprises the Talparo Formation (Pliocene Age) overlying the Springvale Formation (Pliocene Age) which in turn overlies the Manzanilla Formation (Miocene Age) to the south.

The Talparo Formation exposures at and just south of Point Lobin consist of interbedded fine to very fine sands, silts and silty clays with occasional lenses of lignite up to 5' thick. The presence of laterally persistent rhythmic beds, lignites, mangrove roots or possibly callianassa burrows, shell beds, and well-rounded quartz and chert pebbles suggest a swamp/beach environment of deposition. This is the same environment of deposition which exists in the area today.

The contact between the Talparo Formation and the underlying Springvale Formation occurs midway along the beach between Point Lobin and Point Paloma. Cliff exposures show the Springvale Formation to consist of interbedded fine sands, silts and clays with occasional lignite lenses up to 3' thick. Laterally persistent stratification, lignite beds, shell beds and ripple drift cross-laminations in sandstones suggest an environment of deposition similar to that of the overlying Talparo Formation.

Within the Springvale Formation, escaping gasses form the burning lignites were seen, with the surrounding clays being baked into porcellanite. A similar phenomenon presently exists at White Cliffs, Chatam, on the south coast of Trinidad. This is direct evidence for the theory that the widespread occurrence of porcellanite within the Erin Formation in the southwest part of Trinidad has resulted from the spontaneous combustion of organic matter in the subsurface.

Unfortunately, the trip remained unfinished as the encroachment of high tide prevented the party from examining the Manzanilla Formation, which is exposed along the cliffs at Point Paloma. Nevertheless, enough was seen to make the trip an interesting and unforgettable one.

FIELD TRIP TO GUAYAGUAYARE / Point Radix Area

In June 1981, Phillip Farfan led a well attended field trip to the Guayaguayare and Point Radix area of the Trinidad East Coast area.

The trip started off in the Texaco Trinidad Guayaguayare Beach Field area where massive Gros Morne sands (Pliocene Age) were seen in beautiful outcrops along the road leading to the Staff Club which lies on the Gros Morne anticline. Several features observed in these massive sandstone outcrops such as the northwest dip, the small scale cross bedding an the known fauna found in these beds, indicated they probably were deposited in shallow water marine environment and were sourced from the southeast. The Gros Morne sands provide the major oil production in the Guayaguayare Beach (Upper Gros Morne) and Navet Fields (Lower Gros Morne).

The second stop on the trip entailed a difficult walk along an overgrown track to one of the high points of the Gros Morne anticline from where a majestic view of the forested hills and steeply dissected valleys of the Southern Range was observed to the Northwest.

The next stop was along the road leading to the Goudron Field to see what is considered to be an exposure of the east-west trending Marcelle Valley wrench fault. The Gros Morne sands on the south side of the fault are complexly faulted into many small slivers and blocks with many minor thrust faults seen within the section. On the north side however, the Gros Morne beds were much less faulted and the massive nature of the beds was more or less retained.

A short distance to the north on the road to Navet Field, about a hundred yards from the bridge near well 29, the field party examined several outcrops of Upper Gros Morne sands which are cut by sedimentary dykes (between 6 inches and 3 feet wide) along tensional joints. It is believed that these dykes which are composed of silt and clay and some sand were formed during tectonism associated with formation of the Central Range. Analysis of the Foraminiferal faunas found in the samples taken in the dykes show species which are found in the Lizard Springs and Lower Cruse Formations of Pa1eocene and Upper Miocene Age respectively.

The fifth stop was along the Guayaguayare road where on the beach, the Mayaro Formation (Pliocene Age) outcrops, dipping about 30 to the north. It consists of massive sands with cross bedding showing cut and fill channel features with large clasts at the base and becoming finer upwards. The beds appeared to have been rapidly deposited in shallow marine conditions.

The starting point of the next and final stop was at the top of the hill at Pt. Radix from where a beautiful view of the Manzanilla coastline could be seen. This final stop required a one mile walk down the hill to the beach to examine outcrops of the Mayaro Formation which varied from massive sands to silts to all clay.

At the most seaward point of Point Radix were observed beautiful burrows of Callianasa Sp. which now form casts filled with iron (see photograph on cover) in the massive sandstone beds of the Mayaro Formation. These fossils indicate a shallow marine/ beach environment of deposition for the sandstone beds.

On a closing note, it was pleasing to see that the trip was well attended and the observations and discussion made in the field helped to make the trip a memorable one.

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