686 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



Late Cretaceous age are folded into a syncline along the south coast. Up- 

 per Miocene sediments lie unconformably on the lower Tertiary-Creta- 

 ceous section. In Margarita, as in Tobago, the foliation in the schist strikes 

 slightly north of east and dips steeply to the southeast. Locally, the peri- 

 dotite shows relatively low-temperature hydrothermal alteration, prob- 

 ably related to the diorite intrusions, though this is the only evidence 

 bearing on the relative age of the peridotite and diorite. The diorite has 

 suffered strong shearing, as in Tobago. The period of major deformation 

 was post-Middle Cretaceous and pre-Maestrichtian. Detrital grains of 

 chromite and enstatite in Middle Eocene sands prove that the ultramafic 

 mass had been exposed to erosion by that time and hence is pre-Middle 

 Eocene in age. Sometime between the middle Eocene and upper Miocene, 

 a period of moderate deformation folded the Cretaceous and lower 

 Tertiary sediments into a syncline, with its axis approximately parallel 

 to the foliation in the schist. 



The Dutch Leeward Islands, Aruba, Curacao, and Ronaire, are vol- 

 canic in character, comparable with the Greater Antilles and the outer 

 islands of the Lesser Antilles. A deformed basement of intrusive and ex- 

 trusive gabbroic and dioritic rocks with intercalated radiolarian cherts, 

 limestone, and graywacke is present on all three islands. Quartz-augite 

 diorite in Curacao (G. J. H. Molengraaff, 1931) and quartz diorite in 

 Aruba ( Westermann, 1931) intrude the basement rocks. On Ronaire, 

 limestone of latest Cretaceous age unconformably overlies the basement 

 rocks, which likewise are believed to belong to the Upper Cretaceous 

 (Pijpers, 1933). On Curacao, a series of coarse detrital sediments overlies 

 the limestone and is folded with it. Upper Eocene limestone is not in- 

 volved in the folding. In the Dutch Leeward Islands then, a basement 

 of volcanic rocks was deformed in pre-latest Cretaceous time, uncon- 

 formably overlain by Upper Cretaceous-Eocene ( ? ) sediments, and again 

 folded prior to late Eocene. 



Barbados-Trinidad Belt 



Barbados. The geology of Rarbados has been discussed in detail by 

 Senn (1940). Clastics of early and middle Eocene age are the oldest beds 

 exposed. These beds were uplifted, strongly folded and thrust-faulted and 



eroded, then covered by a thick series of mud flows. Upon the strongly 

 folded clastic sediments and mud flows were deposited the Oceanic beds, 

 a considerable thickness of upper Eocene chalk, radiolarian earth, and 

 tuff, which Senn and earlier writers interpret as a deep-sea deposit. Senn 

 shows that the area moved down very suddenly into a region of deeper- 

 water sedimentation, a circumstance explained by great downbuckling, 

 to be considered later in this chapter. Senn also points out that radio- 

 larian earth similar to that of the Oceanic formation occurs in the upper 

 Eocene of northern Cuba, and that the radiolarian earths of Rarbados and 

 Cuba probably were deposited in a late Eocene equivalent of the Puerto 

 Rico trench. See Fig. 42.4, bottom section. 



Deformation apparently continued in Rarbados during the deposition 

 of the Oceanics, for these beds are also folded and faulted, though much 

 less so than the older formations. The Oceanic beds, in turn, were uplifted 

 and eroded, then submerged and covered by upper Oligocene-Miocene 

 marls. There is evidence of Miocene-Pliocene folding and post-Pleisto- 

 cene uplift and fracturing. The above review was taken from Maxwell, 

 1948. 



Tobago. The northern part of Tobago Island is made up of isoclinally 

 folded schists, phyllites, predominantly metavolcanic in origin. South of 

 the schists lies a belt of igneous rocks, including ultramafic and dioritic 

 intrusives and andesitic and basaltic volcanics. A low, coral-covered plain 

 forms the southwest tip of the island. 



At least two periods of diastrophism are indicated. The earliest, prob- 

 ably of Late Cretaceous age, produced the schists. Intense igneous activity 

 followed this diastrophic period; then the igneous rocks were themselves 

 strongly sheared by diastrophic movements considered to be of late Eo- 

 cene age. 



Undeformed, fossiliferous upper Miocene-Pliocene sands and clays lie 

 unconformably on volcanic rocks near the present coast line, and Quater- 

 nary coral limestone overlaps both igneous rocks and late Tertiary sedi- 

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



Trinidad. The middle Eocene clastic sedimentation, the late Eocene 

 deformation, and the Miocene-Pliocene period of folding of Barbados are 

 paralleled by a similar sequence of events in Trinidad. In addition, Juras- 



