ANTILLEAN-CARIBBEAN REGION 



687 



sic and Cretaceous rocks crop out in Trinidad, giving insight into the 

 pre-Eocene history of the southern West Indian region. Jurassic rocks are 

 found only in the North Range. According to Senn ( 1940 ) , they consist 

 mainly of phyllites with abundant lenses and veins of quartz and inter- 

 bedded crystalline limestone. Presumably they are equivalent to the lower 

 Caribbean series of Waring (1926), which he describes as calcareous and 

 carbonaceous schists and quartzitic grits. Associated with the Jurassic 

 rocks is a younger system of less metamorphosed dark limestones, grits, 

 and slightly metamorphosed shales, from which Trechman ( 1935 ) col- 

 lected fossils of late Cretaceous age. The North Range schists have been 

 tightly folded, in general, showing axial-plane foliation (Waring, 1926). 

 They strike a few degrees north of east and are overturned toward the 

 north. 



In a small area near the village of San Souci, igneous rock identified as 

 "granophyr" intrudes dark, calcareous schists of the lower Caribbean 

 series (Waring, 1926). Both massive and pyroclastic igneous rocks are 

 present, and on Manantial hill, dark, calcareous schist seems to be in- 

 folded into the igneous mass. A fine-grained, holocrystalline augite andes- 

 ite with a diabasic texture occurs in the San Souci area. 



The North Range seems to have been involved in at least two periods of 

 folding, one in post-Jurassic and one in post-Late Cretaceous time. Igneous 

 rocks at San Souci were intruded and extruded between the periods of 

 deformation; otherwise there is no evidence of igneous activity. Quite 

 probably the earlier folding, involving Jurassic and possibly Lower Creta- 

 ceous sediments, took place in Late Cretaceous time, since this is a period 

 of major deformation in the Coast Range of Venezuela. A slight amount of 

 volcanic activity followed this deformation in Trinidad, then uppermost 

 Cretaceous sediments were laid down and subsequently folded, probably 

 during the strong middle Eocene deformation. 



The North Range schists of Trinidad resemble the Tobago North Coast 

 schists in degree of metamorphism, in the fact that both series are iso- 

 clinally folded and overturned to the north, and in that both have as- 

 sociated younger andesitic volcanics. On the other hand, Tobago lacks 

 the limestone, graphitic schists, and coarse grits of the North Range; and 

 Trinidad has no counterpart of the metavolcanics comprising a major part 



of the Tobago schists. The small amount of igneous activity in Trinidad 

 is likewise in marked contrast to the predominantly igneous character of 

 Tobago. The above review was taken from Maxwell, 1948. 



Northern Venezuela. Schists identical with those of the North Range 

 of Trinidad appear in the Serrania de la Costa Oriental of Venezuela. 

 East of Caracas, fossils of probable latest Jurassic age were found in the 

 older beds of the Serrania de la Costa Occidental (Wolcott, 1943). Pre- 

 sumably the overlying schists are of Cretaceous age, as in Trinidad. The 

 first great deformation in northern Venezuela occurred in the Cretaceous, 

 probably in pre-late Senonian and certainly in pre-Maestrichtian time. 

 The second deformation came about at the beginning of the upper Eo- 

 cene, at which time granitic rocks were intruded in the Coast Range, and 

 the Cretaceous and Tertiary sediments were metamorphosed (Hedber'i. 

 1937). In the Miocene-Pliocene deformation, the Serrania del Interior was 

 formed, involving Cretaceous and Tertiary beds in tight folding and 

 southward overthrusting. 



A belt of small seq^entine intrusives occurs in the Serrania de la Costa 

 near Caracas, and several larger peridotite bodies intrude Cretaceous 

 sedimentary rocks south of the Serrania del Interior. Hence the ultra - 

 mafics are late Mesozoic or younger in age. 



PUERTO RICO TRENCH AND GRAVITY ANOMALIES 



Submarine Topography 



North of Hispaniola, Puerto Rico, and the Virgin Islands bank is a nar- 

 row trough of great depth. Its bottom exceeds 24,000 feet from the west 

 end of Hispaniola eastward to a point off the island of Barbuda, a distance 

 of about 500 miles. For a distance of 200 miles north of Puerto Rico, the 

 trough is over 27,000 feet deep, with a greatest recorded depth of 2S.6S0 

 feet. Southward from a point off Barbuda, the trough follows the arc of 

 the volcanic Caribbees but begins to shallow, and finally it ends in the 

 Tobago trough, a fairly wide basin betwen the volcanic arc on the west 

 and the island of Barbados on the east. The Tobago trough has a greatest 

 known depth of 8220 feet. Refer to map of Fig. 42.1 and cross section of 

 Fig. 42.11. 



