An integrated analysis of an orogen-sedimentary basin pair: Latest Cretaceous-Cenozoic evolution of the linked Eastern Cordillera orogen and the Llanos foreland basin of Colombia

Abstract

The integration of restored basin geometry and internal features of syntectonic units (e.g., stratal architecture, thickness, sandstone composition) with fl exural modeling of the lithosphere constrains the evolution of a basin and its fl exural history related to orogenic growth (spatial/temporal loading confi guration). Using this approach, we determined the Maastrichtian-Cenozoic polyphase growth of the Eastern Cordillera of Colombia, an inverted Mesozoic extensional basin. The record of this growth occurs in an Andean (post‐middle Miocene) thrust belt (the Eastern Cordillera) and in adjacent foreland basins, such as the Llanos Basin to the east. This approach permitted the identifi cation of fitectono-stratigraphic sequences in the foreland basin and fi ve phases of shortening for the Eastern Cordillera. Thermochronological and geochronological data support the spatial and temporal evolution of the orogen‐foreland basin pair. Tectono-stratigraphic sequences were identifi ed in two restored cross sections, one located at a salient and the other in a recess on the eastern fl ank of the Eastern Cordillera. The lower two sequences correspond to late Maastrichtian‐Paleocene fl exural events and record the eastward migration of both tectonic loading and depositional zero in the Llanos Basin. These sequences consist of amalgamated quartzarenites that abruptly grade upward to organic-rich fi ne-grained beds and, to the top, light-colored mudstones interbedded with litharenites in isolated channels. Amalgamated conglomeratic quartzose sandstones of the third sequence record ~15 m.y. of slow subsidence in the Llanos Basin and Llanos foothills during early to middle Eocene time, while shortening was taking place farther west in the Magdalena Valley. The fourth sequence, of late Eocene‐ middle Miocene age, records a new episode of eastward migration of tectonic loads and depositional zero in the Llanos Basin. This sequence begins with deposition of thick fi ne-grained strata to the west, whereas to the east, in the Llanos basin, amalgamated quartzarenites unconformably overlie Cretaceous and older rocks (former forebulge). Apatite fi ssion tracks in the axial zone of the Eastern Cordillera, growth strata in the