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Structure and Petroleum Potential of the South Caribbean Deformed Belt and Tayrona Basin, Offshore Northern Colombia


A 250-km-long segment of the Southern Caribbean Deformed Belt (SCDB) offshore Northern Colombia, in waters 2 to 4 km deep, is imaged on 18 high quality 2D seismic reflection profiles (2,200 line km) provided by Spectrum Geophysical. The seismic data tie DSDP site 153, providing age control on the Cretaceous to recent sediments that make up the SCDB. The SCDB is an accretionary prism, formed by active oblique subduction of the Caribbean plate beneath South America, with partitioned right-lateral strike slip motion on more landward fault systems. The Tayrona Basin is a 130-km-long by 50-km-wide forearc basin with its seaward margin formed by the uplifted accretionary prism of the SCDB and its landward margin formed by domed igneous and metamorphic rocks of the now extinct Great Arc of the Caribbean. The Tayrona Basin contains up to 5 km of Cretaceous to recent sediments. We identify several large and prospective structures (>200 km2) within the SCDB and Tayrona basin that have structurally conformable amplitude anomalies that presently remain undrilled. These structures include thrusted anticlines with the SCDB prism and turtle structures related to shale withdrawal within the Tayrona Basin. The long axes of these anticlines trend Northeast/Southwest in water depths ranging from 2700 to 3900 m, with depths below mudline from 1000 to 2200 m. We present 2D basin models for the burial and maturation of deep, oil-prone, late Cretaceous age source rocks as well as organic-rich, gas-prone sediments from Mio-Pliocene deposition. We propose numerous faults throughout the area as hydrocarbon migration routes from underlying Cretaceous source rocks and image major thrust faults breaching the seafloor with associated mud volcanoes. We suggest reservoir intervals include distal deep-water Mio-Pliocene turbidites and associated basin floor fans from the Magdalena River slope and submarine fan, or, in the case of the Tayrona Basin, coarser-grained sediments from smaller rivers draining the Santa Marta Massif. We propose that hemi-pelagic marine shale, imaged as widespread, contiguous, and low-amplitude layers act as seals. The simplest and largest structural closures exist within the frontal thrusts of the SCDB prism at depths of 4800 to 6000 mbsl, are associated with extensive bright spots, and may harbor large (>5 Tcf), commercially viable hydrocarbon accumulations.