资源环境科技发展态势分析平台

We used geothermochronologic data from sedimentary rocks, coupled with strati-graphic analyses, to unravel the late Paleogene to early Neogene exhumation of the Sierra Nevada de Santa Marta massif. This fault-bounded triangular northernmost promontory of the Northern Andes exposes Precambrian to Paleozoic metamorphic rocks and a Triassic to Jurassic magmatic arc. We examined the Neogene basin fills of two marginal basins, a western one located along the Santa Marta-Bucaramanga fault, and a northern one occupying the southern hanging-wall block of the Oca fault. The western sequence consists of similar to 1200- m-thick conglomeratic gravity deposits that define a progradational Gilbert-type delta emanating from a scarp coinciding with the present Santa Marta-Bucaramanga fault. By its stratigraphic and structural position, this sequence is similar to the northern sequence, which reveals a retrogradational stacking pattern. In order to reconcile these different architectural styles, we propose a regional-scale tilting of the Sierra Nevada de Santa Marta massif toward the NE during the late Paleogene-early Neogene. This model presumes a concomitant evolution of the two sedimentary sequences. Provenance analyses performed on representative units of these sedimentary sections yielded U-Pb age spectra of zircons that correlate with known age data of the underlying basement. Particularly, they lack pre-Grenvillian and Ordovician signals common to Neogene sediments of the wider Miocene Magdalena basin. These marginal basins thus evolved disconnected from the trunk system of the proto-Magdalena River, and they record an initial stage of Oligocene-Miocene segmentation of the South American plate margin. These new findings help to better constrain the paleogeographic setting of the Sierra Nevada de Santa Marta massif and its marginal basins for the late Oligocene-early Neogene during initial breakup of the Caribbean margin. Their sedimentary record depicts an early stage of fault-controlled subsidence of the western margin and a presumably tilt-related transgression of the northern margin that preceded the Miocene expansion of local depocenters and their merging into a wider embayment of the Neogene Lower Magdalena basin.