Andrés Reyes-Harker

Linking sedimentation in the northern Andes to basement configuration, Mesozoic extension, and Cenozoic shortening: Evidence from detrital zircon U-Pb ages, Eastern Cordillera, Colombia

Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analyses of 29 samples from the Eastern Cordillera of Colombia reveal the origin of northern Andean basement and patterns of sedimentation during Paleozoic subsidence, Jurassic–Early Cretaceous extension, Late Cretaceous postrift subsidence, and Cenozoic shortening and foreland-basin evolution. U-Pb geochronological results indicate that presumed Precambrian basement is mainly a product of early Paleozoic magmatism (520–420 Ma) potentially linked to subduction and possible collision. Inherited zircons provide evidence for Mesoproterozoic tectonomagmatic events at 1200–1000 Ma during Grenville-age orogenesis. Detrital zircon U-Pb ages for Paleozoic strata show derivation from Andean basement, syn depositional magmatic sources (420–380 Ma), and distal sources of chiefl y Mesoproterozoic basement (1650–900 Ma) in the Amazonian craton (Guyana shield) to the east or in possible continental terranes along the western margin of South America. Sedimentation during Jurassic–Early Cretaceous rifting is expressed in detrital zircon age spectra as Andean basement sources, recycled Paleozoic contributions, and igneous sources of Carboniferous–Permian (310–250 Ma) and Late Triassic–Early Jurassic (220–180 Ma) origin. Detrital zircon provenance during continued Cretaceous extension and postrift thermal subsidence recorded the elimination of Andean basement sources and increased infl uence of craton-derived drainage systems providing mainly Paleoproterozoic and Mesoproterozoic (2050–950 Ma) grains. By Eocene time, zircons from the Guyana shield (1850–1350 Ma) dominated the detrital signal in the easternmost Eastern Cordillera. In contrast, coeval Eocene deposits in the axial Eastern Cordillera contain Late Cretaceous–Paleocene (90–55 Ma), Jurassic (190–150 Ma), and limited Permian–Triassic (280–220 Ma) zircons recording initial uplift and exhumation of principally Mesozoic magmatic-arc rocks to the west in the Central Cordillera. Oligocene–Miocene sandstones of the proximal Llanos foreland basin document uplift-induced exhumation of the Eastern Cordillera fold-thrust belt and recycling of the Paleogene cover succession rich in both arc-derived detritus (dominantly 180– 40 Ma) and shield-derived sediments (mostly 1850–950 Ma). Late Miocene–Pliocene erosion into the underlying Cretaceous section is evidenced by elimination of Mesozoic– Cenozoic zircons and increased proportions of 1650–900 Ma zircons emblematic of Cretaceous strata.

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

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

Inversion tectonics under increasing rates of shortening and sedimentation: Cenozoic example from the Eastern Cordillera of Colombia

Abstract The Northern Andes of Colombia is a key locality for understanding tectonic inversion of symmetric rifts. A review of available data on structural geometry and deformation timing, and new thermochronology and provenance data from selected localities, enable the construction of balanced cross-sections and shortening budgets. During early deformation in the Palaeocene, most shortening was focused in the western sector of the orogen, in the Central Cordillera and the Magdallena Valley, although widely spaced and mild inversion occur in areas as far to the east as the Llanos Basin. After a period of tectonic quiescence in the Middle Eocene, deformation resumed across a former early Mesozoic graben in the Eastern Cordillera. Peak shortening rates and out-of-sequence reactivation of the main inversion faults were in place in latest Miocene time, during a phase of topographical growth. Our results indicate that coeval activation of basement highs and adjacent slower-slip shortcuts appear to be characteristic of inverted symmetric grabens. However, before reactivation and brittle faulting occur, strain hardening is required. Deformation rates in the Eastern Cordillera correlate with the westwards velocity of the South American Plate. A threshold convergence rate of approximately 2 cm year−1 seems to be necessary to activate shortening in the upper plate.

Cenozoic paleogeography of the Andean foreland and retroarc hinterland of Colombia

New biostratigraphic zonations, core descriptions, sandstone petrography, facies analysis, and seismic information are compared with published detrital and bedrock geo- and thermochronology to build a Cenozoic paleogeographic reconstruction of the Andean retroarc region of Colombia, encompassing the ancestral Central Cordillera, Middle Magdalena Valley, Eastern Cordillera, and Llanos basin. We identify uplifted sediment source areas, provenance domains, depositional environments, and thickness changes to propose a refined paleogeographic evolution of eastern Colombia. We conclude that Cenozoic evolution of the northernmost Andes includes (1) a period of contractional deformation focused in the Central Cordillera and Middle Magdalena Valley that may have started by the Late Cretaceous, although thermochronological data points to maximum shortening and exhumation during the late Paleocene; (2) a period of slower deformation rates or even tectonic quiescence during the middle Eocene; and (3) a renewed phase of contractional deformation from the late Eocene to the Pleistocene/Holocene expressed in provenance, bedrock thermochronology, and increased subsidence rates in the Llanos foreland. The sedimentary response in the Llanos foreland basin is controlled by source area proximity, exhumation and shortening rates, relationships between accommodation and sediment supply, as well as potential paleoclimate forcing. This new reconstruction changes the picture of Cenozoic basin evolution offered by previous reconstructions, providing an updated chronology of deformation, which is tied to a more precise understanding of basin evolution.

Hyperspectral imaging for the determination of bitumen content in Athabasca oil sands core samples

New biostratigraphic zonations, core descriptions, sandstone petrography, facies analysis, and seismic information are compared with published detrital and bedrock geo- and thermochronology to build a Cenozoic paleogeographic reconstruction of the Andean retroarc region of Colombia, encompassing the ancestral Central Cordillera, Middle Magdalena Valley, Eastern Cordillera, and Llanos basin. We identify uplifted sediment source areas, provenance domains, depositional environments, and thickness changes to propose a refined paleogeographic evolution of eastern Colombia. We conclude that Cenozoic evolution of the northernmost Andes includes (1) a period of contractional deformation focused in the Central Cordillera and Middle Magdalena Valley that may have started by the Late Cretaceous, although thermochronological data points to maximum shortening and exhumation during the late Paleocene; (2) a period of slower deformation rates or even tectonic quiescence during the middle Eocene; and (3) a renewed phase of contractional deformation from the late Eocene to the Pleistocene/Holocene expressed in provenance, bedrock thermochronology, and increased subsidence rates in the Llanos foreland. The sedimentary response in the Llanos foreland basin is controlled by source area proximity, exhumation and shortening rates, relationships between accommodation and sediment supply, as well as potential paleoclimate forcing. This new reconstruction changes the picture of Cenozoic basin evolution offered by previous reconstructions, providing an updated chronology of deformation, which is tied to a more precise understanding of basin evolution.

Cenozoic paleogeography of the Andean foreland and retroarc hinterland of ColombiaPaleogeography of the Northern Andes

New biostratigraphic zonations, core descriptions, sandstone petrography, facies analysis, and seismic information are compared with published detrital and bedrock geo- and thermochronology to build a Cenozoic paleogeographic reconstruction of the Andean retroarc region of Colombia, encompassing the ancestral Central Cordillera, Middle Magdalena Valley, Eastern Cordillera, and Llanos basin. We identify uplifted sediment source areas, provenance domains, depositional environments, and thickness changes to propose a refined paleogeographic evolution of eastern Colombia. We conclude that Cenozoic evolution of the northernmost Andes includes (1) a period of contractional deformation focused in the Central Cordillera and Middle Magdalena Valley that may have started by the Late Cretaceous, although thermochronological data points to maximum shortening and exhumation during the late Paleocene; (2) a period of slower deformation rates or even tectonic quiescence during the middle Eocene; and (3) a renewed phase of contractional deformation from the late Eocene to the Pleistocene/Holocene expressed in provenance, bedrock thermochronology, and increased subsidence rates in the Llanos foreland. The sedimentary response in the Llanos foreland basin is controlled by source area proximity, exhumation and shortening rates, relationships between accommodation and sediment supply, as well as potential paleoclimate forcing. This new reconstruction changes the picture of Cenozoic basin evolution offered by previous reconstructions, providing an updated chronology of deformation, which is tied to a more precise understanding of basin evolution.