Abstract

In April and May 1971, the R/V Alaminos (cruise 71-A-4, leg 5) recorded a 710-km-long seismic profile in the central Caribbean Sea. This southeast-northwest profile began on the lower Colombian-Venezuelan continental margin, crossed the Aruba Gap, Beata Ridge, and Colombian Basin, and ended on the southern flank of the Nicaraguan Rise. Our principal purpose was to tie three significant Deep Sea Drilling Project (DSDP) sites on one continuous profile. Within the accuracy of our satellite navigation, we tied Sites 153, 151, and 152, respectively, on the north edge of the Aruba Gap, crest of the Beata Ridge, and lower southern flank of the Nicaraguan Rise.

Two seismic reflectors, designated Horizons A″ and B″, have been identified and traced through much of the southern Caribbean Sea. The former is a lower Paleogene siliceous or cherty chalk or limestone; the latter is basalt or a coarser grained mafic equivalent, overlain directly by Upper Cretaceous sedimentary rocks. Overlying Horizon A″ is an upper Paleogene and Neogene unit of acoustically transparent and pelagic fossiliferous chalk, ooze, and marl. The pelagic section between the reflectors is similar but more indurated and siliceous than the unit above.

Horizon A″ is somewhat more restricted in area than Horizon B″. Along this profile it is absent from the crest and steep flanks of the Beata Ridge and from local promontories on the lower flanks of the Beata Ridge and Nicaraguan Rise, and it is masked through the central Colombian Basin by a prominent set of reflectors. DSDP results at Site 152, where Horizon A″ is absent, indicate uplift of the ridge and erosion prior to deposition of the upper pelagic unit.

Excellent correlation between this profile and the DSDP results permits reconstruction and interpretation of the complete stratigraphic history along this section. We believe that with the stratigraphic data available and with the gift of hindsight, scientists can now program seismic lines that will be extremely useful in illustrating stratigraphic patterns and solving problems. Tying a series of selected DSDP sites into a continuous profile or a network of lines will permit the study of regional and three-dimensional stratigraphic patterns, sedimentational processes, and tectonics. This is another method of further utilizing these drilling results.

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