ABSTRACT We interpret that the thick Cunapo conglomerate blanket overlying a significant forebulge(?) unconformity on the floor of the Northern Basin, Trinidad, represents part of a relict foreland basin that was filled in with syncontractile or syntranspressional sediments, chiefly in the Miocene–Pliocene. These deposits were subsequently modified (tilted, bent, faulted) and buried by late postcontractile transform tectonics and related sedimentation. We studied five outcrops of distal Northern Basin Oligocene–Pliocene Cunapo conglomerate from upturned Nariva, Tamana (Guaracara Limestone), and Manzanilla formations outcrops along the north flank of the Central Range. We measured pebble clast size (range = 12–46 mm), roundness (sub-angular to rounded), projected sphericity (average = 0.7), clast shape (~equant), and used sedimentologic, map, and well control to determine that the Cunapo clasts were derived from a proximal provenance north of the outcrop belt. The clasts lithotypes are predominantly similar to the unmetamorphosed Mesozoic–Paleogene precontractile stratal succession, exposed today in central Trinidad that include brittlely deformed black chert and white argillite of the Naparima Formation or a lithically similar unit, black coarse- to fine-grained sandstone that may have been derived from Cretaceous Cuche or Gautier formations, and white-brown sandstones similar to the Eocene sandstones of the Pointe-a-Pierre and Chaudiere formations. The magnitude of brittle strain recorded in quartz veins in the pebbles (17%–48%, average = 26%) indicates significant strain in the clasts’ provenance area. We interpret that the clasts were eroded off a mostly now-missing, brittlely deformed, upper crustal “lid” of the proto-Northern Range.

ABSTRACT We measured stratigraphic sections and collected samples from Oceanic suite outcrops at Gay’s Cove and Bath Cliffs, Barbados, in order to restudy the late Eocene microtektite layer(s) and provide new geological context. We disaggregated and processed samples into separates of microfossils, microtektites, and heavy minerals, and we present up-to-date glass geochemistry, biostratigraphic analysis, and detrital zircon U-Pb analysis. Results from the new Barbadian microtektite glass chemistry analysis (Gay’s Cove) compare well with those from other published microtektite analyses, as well as those from the correlative North American strewn field. Micropaleontology confirms a late Eocene age for the Oceanic microtektite horizon at Gay’s Cove. Using U-Pb, we dated 24 Tertiary zircon grains, probably from volcanic ash-fall events, which at Gay’s Cove yielded a preliminary, poorly defined, and incorrect depositional age for the microtektite layer (≤31.84 ± 0.85 Ma; weighted mean of only three grains). Three additional new U-Pb depositional ages (≤38.52 ± 1.0 Ma, ≤39.23 ± 0.3 Ma, ≤35.25 ± 0.82 Ma) were obtained from bottom to top in the 24 m section at Bath Cliffs. We also dated 46 Paleozoic–Proterozoic zircon grains using U-Pb and discuss whether these “old” grains represent recycled (subducted and extruded) volcanic grains or windblown silt/sand from Africa.

The Paria Península in eastern Venezuela exposes an E-W–oriented mountain belt composed of deformed and metamorphosed sediments that were deposited on the northern South American passive margin in early Mesozoic time. The metamorphic grade, mostly greenschist facies, decreases from north to south in a direction perpendicular to the trend of the metamorphic belt. Foliation (S 1 ) dips steeply to the south along the southern coast and progressively gentler to the north to 25–30°. S 1 strikes ∼ 060–075° subparallel to oblique to the general trend of the metamorphic belts. Stretching lineation (L 1 ) plunges variably to the SW. The pattern of crystallographic preferred orientation (CPO) of quartz c -axes indicates a transition from symmetric coaxial strain to weak top-to-SW or oblique-normal sense of shear. The fabric patterns suggest activation of the basal <a>, prism <a>, and rhomb <a> slip systems under relative low-temperature (300–400 °C). Apatite fission-track ages range from 29 Ma in the south to 5 Ma in the north. Similarly, samples in the northern and central zone yielded the youngest zircon fission track (FT) ages, ranging from 5 Ma to 9 Ma, and the southern zone yielded slightly older ages ca. 13 Ma. From the FT ages we estimate a diachronous cooling from south to north and a cooling rate in the range of 16–56 °C/m.y. (∼1–2 mm/yr of exhumation). That many of the cooling ages postdate pre–10 Ma transpression suggests that tectonically driven vertical extrusion alone cannot account for the observed exhumation. The topography of the Paria Península and its current precipitation pattern are both asymmetric. Exhumation, deformation, topography, erosion, and precipitation patterns from the transpressional orogen of the Paria Península are comparable to those described in the Southern Alps of New Zealand. A general model for these two-sided transpressional wedges is proposed based on geologic observations. Obliquity of the compression and erosion seems to play an important role in the evolution, exhumation, and deformation of these two naturally deformed orogens.