VARIABLE SCALES OF LANDSCAPE RESPONSE TO TECTONIC FORCING ADJACENT THE GULF OF PARIA, TRINIDAD AND VENEZUELA

The pattern and history of tectonic deformation associated with oblique convergence between the Caribbean and South American plates from 59 Ma to 10 Ma and dextral wrenching since 10 Ma are expressed in the geomorphology of drainage basins, piedmont deposits, and coastlines of northern Trinidad and the Paria Peninsula of Venezuela. The skeletal framework for drainage basins in the E-W trending Northern Range of Trinidad and the Paria Peninsula range was established during the period of oblique convergence. In the western and central Northern Range, S1 dips consistently southward, producing asymmetric ranges with elongated drainage basins on their southern flanks. Whereas stream length is adjusted to basin area according to Hack's Law, drainage spacing on the southern flank is 2-3 times greater than established relations. Basin morphometry, distribution of piedmont deposits, and coastal morphology result from more recent vertical motion associated with the development of the Gulf of Paria, a pull-apart basin resulting from dextral wrenching along the El Pilar Fault in Venezuela stepping across the gulf to the Central Range Fault in Trinidad. North of the Central Range Fault in Trinidad, the Northern Range, the range-bounding Arima Fault, and the Northern Basin form a quasi-rigid block sinking westward into the Gulf of Paria pull-apart basin and rebounding upward toward the east. The Paria Peninsula is its mirrored western counterpart, sinking eastward into the Gulf. Trends in mean basin elevation, relief, slope, and basin shape and asymmetry, are generally symmetrical about the Gulf of Paria and reflect subsidence towards the Gulf in proximal areas and relative uplift away from the Gulf. Bedrock valley bottoms in drainage basins nearest the Gulf on Trinidad are buried by as much as 110 m of sediment, with wide, flat valley floors, and the basin outlets on both sides nearest the Gulf are drowned as evidenced by their embayed nature. With increasing distance from the Gulf and resulting from flexure and uplift, valleys are more constricted, dominated by bedrock, and v-shaped, and alluvial fans are segmented and dissected along the mountainfront. Marine terrace deposits on the northeast coast of Trinidad, currently 10-15 m above sea level, yielded an OSL age of 70,670 +/- 4990 yr (UIC1912).