− | The crystalline basement of the Llanos is covered by [[Paleozoic]] series that consist of siliciclastic [[Silurian|Siluro]]-[[Devonian]] [[deposit]]s; a strong unconformity separates these, locally highly deformed, series from the [[Mesozoic]] and [[Tertiary]] deposits. The Mesozoic [[tectonic]] context was mainly extensive in Colombia, but the [[depocenter]] was located westward of the LBC (Villamil, 1999<ref name=Villamil1999>Villamil, T., 1999, Campanian-Miocene tectonostratigraphy, depocenter evolution and basin development of Colombia and western Venezuela: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 153, no. 1–4, p. 239–275, [https://www.sciencedirect.com/science/article/pii/S0031018299000759 DOI: 10.1016/S0031-0182(99)00075-9].</ref>). The Lower [[Cretaceous]] series, known in the Eastern Cordillera (Campos Alvarez et al., 2007<ref name=Camposalvarezetal2007>Campos Alvarez, N. O., and B. P. Roser, 2007, Geochemistry of black shales from the Lower Cretaceous Paja Formation, Eastern Cordillera, Colombia: Source weathering, provenance, and tectonic setting: Journal of South American Earth Sciences, v. 23, p. 271–289.</ref>), are restricted to the western side of the [[Guaicaramo fault]] and are so absent in the Llanos [[foreland]]. In the west of Colombia the compression that leads to the [[Andes]] formation began during the [[Cretaceous]] times; the first [[accretion]] started during the [[Aptian]], whereas subsidence continued eastward with the deposition of the [[Une formation|Une]], [[Gacheta formation|Gacheta]], and [[Guadalupe formation]]s in the Llanos (Sarmiento, 2001<ref name=Sarmiento2001>Sarmiento, L. F., 2001, Mesozoic rifting and Cenozoic basin inversion history of the Eastern Cordillera, Colombian Andes. Inferences from tectonic models: Ph.D. Thesis Vrije Universiteit, Amsterdam, The Netherlands, 297 p.</ref>). Subsequent accretion took place westward at the end of the [[Maastrichtian]], resulting in the beginning of [[uplift]] of the Central Cordillera and the first [[inversion]] in the now Magdalena Valley (Casero et al., 1997; Sarmiento, 2001). In the Llanos, [[subsidence]] continued in a very poorly deformed basin during the [[Paleocene]], with the [[deposition]] of the [[Barco formation|Barco]], [[Los Cuervos formation|Los Cuervos]], and [[Mirador formation]]s (Cooper et al., 1995<ref name=Cooperetal1995>Cooper, M. A., F. T. Addison, R. Alvarez, A. B. Hayward, S. Howe, A. J. Pulham, et al., 1995, [http://archives.datapages.com/data/specpubs/memoir62/35cooper/0659.htm Basin development and tectonic history of the Llanos Basin, Colombia]], in Petroleum Basins of South America: [http://store.aapg.org/detail.aspx?id=476 AAPG Memoir 62], p. 659–665.</ref>; Bayona et al., 2008<ref name=Bayonaetal2008>Bayona, G., M. Cortés, C. Jaramillo, G. Ojeda, J. J. Aristizabal, and A. Reyes-Harker, 2008, 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: GSA Bulletin, v. 120, no. 9/10, p. 1171–1197.</ref>; Reyes-Harker et al., 2015<ref name=Reyesharkeretal2015>Reyes-Harker, A., C. F. Ruiz-Valdivieso, A. Mora, J. C. Ramirez-Arias, G. Rodriguez, F. de la Parra, et al., 2015, Cenozoic paleogeography of the Andean Foreland and retroact hinterland of Colombia: [http://archives.datapages.com/data/bulletns/2015/08aug/BLTN11110/BLTN11110.html AAPG Bulletin], v. 99, no. 8, p. 1407–1454, DOI: 10.1306/06181411110.</ref>). A compressive context predominates in the Eastern Cordillera since the [[Eocene]]. After the inversions of the Mesozoic extensional [[graben]]s, a thrust regime developed, and the [[Llanos Orientales]] became a classical, but rather external, [[foreland]] during the [[deposition]] of the [[Carbonera formation|Carbonera]] and [[Leon formation]]s (Moretti et al., 2009<ref name=Morettietal2009a>Moretti, I., J. C. Mondragon, J. C. Garzon, G. Bosio, and J. M. Daniel, 2009a, Structural style and decollement levels in the Llanos Orientales Basin (Colombia). X Congress Bolivariano, Conference Proceedings.</ref>; Mora et al., 2015<ref name=Moraetal2015>Mora, A., W. Casallas, R. Ketcham, D. Gomez, M. Parra, J. Manson, et al., 2015, Kinematic restoration of contractional basement structures using thermokinematic models: A key tool for petroleum system modeling: [http://archives.datapages.com/data/bulletns/2015/08aug/BLTN11108/BLTN11108.html AAPG Bulletin]], v. 99, no. 8, p. 1575–1598, DOI: 10.1306/04281411108.</ref>). The Eastern Cordillera is a double verging mountain belt: the western flank in the Magdalena Valley was initially the more active one but the active [[compression|compressive]] front has now shifted to the Llanos where the [[Miocene]] [[foreland]] is currently affected by the compression that propagates eastward. The structure that corresponds to the former Early [[Cretaceous]] basin edge is the [[Guaicaramo fault]] (Bayona et al., 2008<ref name=Bayonaetal2008 />), but some [[thrust]]s and blind thrusts exist eastward of it (called compressive front in the figures). | + | The crystalline basement of the Llanos is covered by [[Paleozoic]] series that consist of siliciclastic [[Silurian|Siluro]]-[[Devonian]] [[deposit]]s; a strong unconformity separates these, locally highly deformed, series from the [[Mesozoic]] and [[Tertiary]] deposits. The Mesozoic [[tectonic]] context was mainly extensive in Colombia, but the [[depocenter]] was located westward of the LBC (Villamil, 1999<ref name=Villamil1999>Villamil, T., 1999, Campanian-Miocene tectonostratigraphy, depocenter evolution and basin development of Colombia and western Venezuela: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 153, no. 1–4, p. 239–275, [https://www.sciencedirect.com/science/article/pii/S0031018299000759 DOI: 10.1016/S0031-0182(99)00075-9].</ref>). The Lower [[Cretaceous]] series, known in the [[Eastern Cordillera]] (Campos Alvarez et al., 2007<ref name=Camposalvarezetal2007>Campos Alvarez, N. O., and B. P. Roser, 2007, Geochemistry of black shales from the Lower Cretaceous Paja Formation, Eastern Cordillera, Colombia: Source weathering, provenance, and tectonic setting: Journal of South American Earth Sciences, v. 23, p. 271–289.</ref>), are restricted to the western side of the [[Guaicaramo fault]] and are so absent in the Llanos [[foreland]]. In the west of Colombia the compression that leads to the [[Andes]] formation began during the [[Cretaceous]] times; the first [[accretion]] started during the [[Aptian]], whereas subsidence continued eastward with the deposition of the [[Une formation|Une]], [[Gacheta formation|Gacheta]], and [[Guadalupe formation]]s in the Llanos (Sarmiento, 2001<ref name=Sarmiento2001>Sarmiento, L. F., 2001, Mesozoic rifting and Cenozoic basin inversion history of the Eastern Cordillera, Colombian Andes. Inferences from tectonic models: Ph.D. Thesis Vrije Universiteit, Amsterdam, The Netherlands, 297 p.</ref>). Subsequent accretion took place westward at the end of the [[Maastrichtian]], resulting in the beginning of [[uplift]] of the Central Cordillera and the first [[inversion]] in the now Magdalena Valley (Casero et al., 1997; Sarmiento, 2001). In the Llanos, [[subsidence]] continued in a very poorly deformed basin during the [[Paleocene]], with the [[deposition]] of the [[Barco formation|Barco]], [[Los Cuervos formation|Los Cuervos]], and [[Mirador formation]]s (Cooper et al., 1995<ref name=Cooperetal1995>Cooper, M. A., F. T. Addison, R. Alvarez, A. B. Hayward, S. Howe, A. J. Pulham, et al., 1995, [http://archives.datapages.com/data/specpubs/memoir62/35cooper/0659.htm Basin development and tectonic history of the Llanos Basin, Colombia]], in Petroleum Basins of South America: [http://store.aapg.org/detail.aspx?id=476 AAPG Memoir 62], p. 659–665.</ref>; Bayona et al., 2008<ref name=Bayonaetal2008>Bayona, G., M. Cortés, C. Jaramillo, G. Ojeda, J. J. Aristizabal, and A. Reyes-Harker, 2008, 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: GSA Bulletin, v. 120, no. 9/10, p. 1171–1197.</ref>; Reyes-Harker et al., 2015<ref name=Reyesharkeretal2015>Reyes-Harker, A., C. F. Ruiz-Valdivieso, A. Mora, J. C. Ramirez-Arias, G. Rodriguez, F. de la Parra, et al., 2015, Cenozoic paleogeography of the Andean Foreland and retroact hinterland of Colombia: [http://archives.datapages.com/data/bulletns/2015/08aug/BLTN11110/BLTN11110.html AAPG Bulletin], v. 99, no. 8, p. 1407–1454, DOI: 10.1306/06181411110.</ref>). A compressive context predominates in the Eastern Cordillera since the [[Eocene]]. After the inversions of the Mesozoic extensional [[graben]]s, a thrust regime developed, and the [[Llanos Orientales]] became a classical, but rather external, [[foreland]] during the [[deposition]] of the [[Carbonera formation|Carbonera]] and [[Leon formation]]s (Moretti et al., 2009<ref name=Morettietal2009a>Moretti, I., J. C. Mondragon, J. C. Garzon, G. Bosio, and J. M. Daniel, 2009a, Structural style and decollement levels in the Llanos Orientales Basin (Colombia). X Congress Bolivariano, Conference Proceedings.</ref>; Mora et al., 2015<ref name=Moraetal2015>Mora, A., W. Casallas, R. Ketcham, D. Gomez, M. Parra, J. Manson, et al., 2015, Kinematic restoration of contractional basement structures using thermokinematic models: A key tool for petroleum system modeling: [http://archives.datapages.com/data/bulletns/2015/08aug/BLTN11108/BLTN11108.html AAPG Bulletin]], v. 99, no. 8, p. 1575–1598, DOI: 10.1306/04281411108.</ref>). The Eastern Cordillera is a double verging mountain belt: the western flank in the Magdalena Valley was initially the more active one but the active [[compression|compressive]] front has now shifted to the Llanos where the [[Miocene]] [[foreland]] is currently affected by the compression that propagates eastward. The structure that corresponds to the former Early [[Cretaceous]] basin edge is the [[Guaicaramo fault]] (Bayona et al., 2008<ref name=Bayonaetal2008 />), but some [[thrust]]s and blind thrusts exist eastward of it (called compressive front in the figures). |
− | Numerous studies of the petroleum system have been published; they allow us having a good knowledge of the foreland geometry and temperature evolution through time. The precise analysis of hydrocarbon charge in the LCB is out of the scope of this study but since water and hydrocarbons are migrating together in the foreland, the main features of this system in terms of fluid circulation have to be summarized. More details could be found in Villegas et al. (1994), Moretti et al. (2009b), Mora et al. (2010), Person et al. (2012), and Vayssaire et al. (2013). | + | Numerous studies of the [[petroleum system]] have been published; they allow us having a good knowledge of the foreland geometry and temperature evolution through time. The precise analysis of [[hydrocarbon]] charge in the LCB is out of the scope of this study but since water and hydrocarbons are migrating together in the [[foreland]], the main features of this system in terms of [[fluid]] circulation have to be summarized. More details could be found in Villegas et al. (1994<ref name=Villegasetal1994 />), Moretti et al. (2009<ref name=Morettietal2009b>Moretti, I., C. Mora, W. Zamora, M. Valendia, G. Rodriguez, and M. Mayorga, 2009b, Petroleum system variations in the Llanos Basin (Colombia). X Congress Bolivariano, Conference Proceedings.</ref>), Mora et al. (2010<ref name=Moraetal2010>Mora, A., B. K. Horton, A. Mesa, J. Rubiano, R. A. Ketcham, M. Parra, et al., 2010, Migration of Cenozoic deformation in the Eastern Cordillera of Colombia interpreted from fission track results and structural relationships: Implications for petroleum systems: [http://archives.datapages.com/data/bulletns/2010/10oct/BLTN09111/BLTN09111.HTM AAPG Bulletin], v. 91, no. 10, p. 1543–1580.</ref>), Person et al. (2012<ref name=Personetal2012>Person, M., D. Butler, C. W. Gable, T. Villamil, D. Wavrek, and D. Schelling, 2012, Hydrodynamic stagnation zones: A new play concept for the Llanos Basin, Colombia: [http://archives.datapages.com/data/bulletns/2012/01jan/BLTN11019/BLTN11019.HTM AAPG Bulletin], v. 96, no. 1, p. 23–41, DOI: 10.1306/08101111019.</ref>), and Vayssaire et al. (2013<ref name=Vayssaireetal2013>Vayssaire, A., H. Abdallah, W. Hermoza, and E. Figari Negri, 2013, Regional study and petroleum system modeling of the Eastern Llanos, Search and Discovery Article 10564, accessed May 31, 2017, http://www.searchanddiscovery.com/pdfz/documents/2014/10564vayssaire/ndx_vayssaire.pdf.html.</ref>). |
− | Eastward the reservoirs are shallow, and so at temperatures lower than 80°C (176°F), biodegradation occurs, resulting in heavy oil reserves. Westward the first flow of hydrocarbons reached shallow reservoirs and has also been biodegraded, but the current charge of hydrocarbons that refreshes these reservoirs may consist of high API light oils (Dzou et al., 1999; Ramón et al., 2001). An alternative interpretation of these data has been proposed recently: the mixture between low-gravity and high-gravity HC in the western field could also be due to the mélange between a first charge of only early-mature HC and a more recent charge pulse of late-mature HC (Gonzalez-Penagos et al., 2015). In addition to the fact that there are numerous source rocks, this mixture of different oil at different maturity levels makes it difficult to predict the characteristics of the hydrocarbons (Figure 2). | + | Eastward the reservoirs are shallow, and so at temperatures lower than 80°C (176°F), [[biodegradation]] occurs, resulting in heavy [[oil]] [[reserves]]. Westward the first flow of [[hydrocarbon]]s reached shallow [[reservoir]]s and has also been biodegraded, but the current charge of hydrocarbons that refreshes these reservoirs may consist of high API light oils (Dzou et al., 1999<ref name=Dzouetal1999>Dzou, L. I., A. G. Holba, J. C. Ramón, J. M. Moldowan, and D. Zinniker, 1999, Application of new diterpane biomarkers to source, biodegradation and mixing effects on Central Llanos Basin oils, Colombia: Organic Geochemistry, v. 30, no. 7, p. 515–534, [https://www.sciencedirect.com/science/article/pii/S014663809900039X DOI: 10.1016/S0146-6380(99)00039-X].</ref>; Ramón et al., 2001<ref name=Ramonetal2001>Ramón, J. C., L. I. Dzou, W. B. Hughes, and A. G. Holba, 2001, Evolution of the Cretaceous organic facies in Colombia: Implications for oil composition: Journal of South American Earth Sciences, v. 14, no. 1, p. 31–50, [https://www.sciencedirect.com/science/article/pii/S0895981101000104 DOI: 10.1016/S0895-9811(01)00010-4].</ref>). An alternative interpretation of these data has been proposed recently: the mixture between low-[[gravity]] and high-gravity hydrocarbons in the western field could also be due to the mélange between a first charge of only early-mature hydrocarbon and a more recent charge pulse of late-mature hydrocarbon (Gonzalez-Penagos et al., 2015<ref name=Gonzalezpenagosetal2015 />). In addition to the fact that there are numerous [[source rock]]s, this mixture of different oil at different maturity levels makes it difficult to predict the characteristics of the hydrocarbons ([[:file:M114CH08FG02.jpg|Figure 2]]). |