Stratigraphy of the Chubut Group (Cretaceous, Golfo San Jorge Basin, Argentina): impacts of allogenic controls on the alluvial macro-architecture

José Matildo Paredes; Nicolás Foix; José O. Allard; Sabrina Lizzoli; Sabrina X. Olazábal; Maisa A.  Tunik

Authors

José Matildo Paredes Departamento de Geología, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia, Chubut, Argentina https://orcid.org/0000-0002-9942-4908
Nicolás Foix Departamento de Geología, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia, Chubut, Argentina https://orcid.org/0009-0000-1792-0397
José O. Allard Departamento de Geología, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia, Chubut, Argentina https://orcid.org/0000-0002-4004-7415
Sabrina Lizzoli Centro de Investigaciones Geológicas, CONICET-UNLP https://orcid.org/0000-0003-3317-2901
Sabrina X. Olazábal Departamento de Geología, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia, Chubut, Argentina
Maisa A. Tunik Instituto de Investigación en Paleobiología y Geología (IIPG), Universidad Nacional de Río Negro (UNR)-CONICET, General Roca, Río Negro, Argentina https://orcid.org/0000-0002-4593-6991

Keywords:

endorheic basin, Cretaceous fluvial systems, alluvial architecture, allogenic controls, Patagonia

Abstract

The Chubut Group (Cretaceous, Golfo San Jorge Basin) is a continental succession up to 6,000 meters thick, preserved in an endorheic basin. Its basal depositional system includes the fluvial Matasiete Formation and the lacustrine Pozo D-129 Formation, the main source rock for the hydrocarbons of the basin. The Matasiete Formation (Aptian) represents a high-accommodation, exotic fluvial system with headwaters in the present-day Cañadón Asfalto Basin (CAB), referred to as the Los Adobes Formation. Sediment was transported southward to a saline-alkaline lake (Pozo D-129 Formation) through N–S sedimentary corridors in an extensional setting. The overlying depositional system is integrated by the Castillo and Mina del Carmen formations (Albian), and it consists of reworked volcaniclastic particles in drainage catchments within a W–E elongated extensional basin, disconnected from the CAB. The subsequent depositional system includes the Bajo Barreal Formation (Cenomanian–Turonian?), containing the main hydrocarbon reservoirs. It shows varied stacking density in hundreds of meters thick cycles, linked to climatic cycles. Low net-to-gross fluvial stratigraphy featuring small-scale channel belts and paleosols indicates a temperate, subhumid/humid climate with seasonal rainfall. High net-to-gross fluvial stratigraphy records larger-scale channel belts interbedded with paleosols developed in a warmer, humid climate with perennial rainfall. The uppermost depositional system includes the paleosol-rich Laguna Palacios Formation at basin margins, with maximum thicknesses along syncline axes, and the red-colored, anastomosing fluvial systems of the Maastrichtian Colhué Huapi Formation that fill incised valleys. Both units are equivalent to the upper strata of Meseta Espinosa and El Trébol formations in the subsurface, showing degradational features marking the onset of surface uplift in the San Bernardo Fold Belt.

References

Allard, J. O., Paredes, J.M., Foix, N., and Giacosa, R. E. (2015). Conexión cretácica entre las cuencas del Golfo San Jorge y Cañadón Asfalto (Patagonia): paleogeografía, implicancias tectonoestratigráficas y su potencial en la exploración de hidrocarburos. Revista de la Asociación Geológica Argentina, 72(1), 25–41.

Allard, J. O., Foix, N., Bueti, S. A., Sánchez, F. M., Ferreira, L., and Atencio, M. (2020). Comparative structural analysis of inverted structures in the San Bernardo fold belt (Golfo San Jorge basin, Argentina): inversion controls and tecto-sedimentary context of the Chubut Group. Journal of South American Earth Sciences, 97, 102405. https://doi.org/10.1016/j.jsames.2019.102405

Allard, J. O., Paredes, J. M., Foix, N., Giacosa, R. E., Bueti, S. A., and Sánchez, F. M. (2021). Estratigrafía de la cuenca de Cañadón Asfalto. In R. E. Giacosa (Ed.), Geología y Recursos Naturales de la Provincia del Chubut (pp. 187–266). Relatorio 21° Congreso Geológico Argentino.

Allard, J. O., Foix, N., Urrez, N., and Cuello, M. J. (2022). Edades U-Pb del Grupo Chubut en el Codo del Río Senguerr, cuenca del Golfo San Jorge (Patagonia extraandina): calibración cronoestratigráfica e impacto en el análisis del sistema petrolero. 11° Congreso de Exploración y Desarrollo de Hidrocarburos (pp. 215–243).

Bridge, J. S., Jalfin, G. A., and Georgieff, S. M. (2000). Geometry, lithofacies, and spatial distribution of Cretaceous fluvial sandstone bodies, San Jorge Basin, Argentina: outcrops analog for the hydrocarbon-bearing Chubut Group. Journal of Sedimentary Research, 70, 319–337. https://doi.org/10.1306/2DC40915-0E47-11D7-8643000102C1865D

Casal, G. A., Allard, J. O., and Foix, N. (2015). Análisis estratigráfico y paleontológico del Cretácico Superior en la Cuenca del Golfo San Jorge: nueva unidad litoestratigráfica para el Grupo Chubut. Revista Asociación Geológica Argentina, 72, 81–99.

Ferreira, M. L., Martínez Cal, V., Mussel, F., Utge, S., and Basile, Y. A. (2018). Los reservorios de la Formación Pozo D-129. In M. Schiuma, G. Hinterwimmer, and G. Vergani (Eds.), Rocas Reservorio de las cuencas productivas de la Argentina (2nd ed., pp. 175–196). Instituto Argentino del Petróleo y del Gas (IAPG).

Figari, E. G., Stelkov, E. E., Laffitte, G., Cid de la Paz, M., Courtade, S., Celaya, J., Vottero, A., Lafourcade, P., Martinez, R., and Villar, H. J. (1999). Los sistemas petroleros de la Cuenca del Golfo San Jorge: Síntesis estructural, estratigráfica y geoquímica. 4° Congreso de Exploración y Desarrollo de Hidrocarburos (pp. 197–237).

Figari, E. G., and García, D. (2018). Modelos analógicos superficie subsuelo para el Chubutiano Inferior de las cuencas de Cañadón Asfalto y del Golfo San Jorge, Argentina. 10° Congreso de Exploración y Desarrollo de Hidrocarburos (pp. 669–688).

Fitzgerald, M. G., Mitchum, R. M., Uliana, M. A., and Biddle, K. T. (1990). Evolution of the San Jorge Basin, Argentina. American Association of Petroleum Geologists Bulletin, 74, 879–920. https://doi.org/10.1306/0C9B23C1-1710-11D7-8645000102C1865D

Foix, N., Allard, J. O., Ferreira, M. L., and Atencio, M. (2018). Aportes a la arquitectura estratigráfica del Grupo Chubut en el Flanco Norte, Centro de Cuenca y Offshore de la cuenca del Golfo San Jorge, Argentina. 10° Congreso de Exploración y Desarrollo de Hidrocarburos (pp. 779–795).

Genise, J. F., Sciutto, J. C., Laza, J. H., González, M. G., and Bellosi, E. S. (2002). Fossil bee nests, coleopteran pupal chambers and tuffaceous paleosols from the Late Cretaceous Laguna Palacios Formation, Central Patagonia (Argentina). Palaeogeography, Palaeoclimatology, Palaeoecology, 177, 215–235. https://doi.org/10.1016/S0031-0182(01)00333-9

Genise, J. F., Bellosi, E. S., Sarzetti, L. C., Krause, J. M., Dinghi, P. A., Sánchez, M. V., Umazano, A. M., Puerta, P., Cantil, L. F., and Jicha, B. R. (2020). 100 Ma sweat bee nests: Early and rapid co-diversification of crown bees and flowering plants. PLOS ONE, 15(1), e0227789. https://doi.org/10.1371/journal.pone.0227789

Giampaoli, P. (2019). Cretaceous extensional systems of the Golfo San Jorge basin: insights from the analysis of fault length and displacement data. Journal of South American Earth Sciences, 92, 298–309. https://doi.org/10.1016/j.jsames.2019.03.021

Gianni, G., Navarrete, C., Orts, D., Tobal, J., Folguera, A., and Giménez, M. (2015). Patagonian broken foreland and related synorogenic rifting: the origin of the Chubut Group Basin. Tectonophysics, 649, 81–99. https://doi.org/10.1016/j.tecto.2015.03.006

Hartley, A. J., Weissmann, G. S., Nichols, G. J., and Warwick, G. L. (2010). Large distributive fluvial systems: characteristics, distribution, and controls on development. Journal of Sedimentary Research, 80, 167–183. https://doi.org/10.2110/jsr.2010.016

Hechem J. J., and Strelkov, E. E. (2002). Secuencia sedimentaria mesozoica del Golfo San Jorge. In J. M. Haller (Ed.), Geología y Recursos Naturales de Santa Cruz. Relatorio 15° Congreso Geológico Argentino, (pp. 129–147).

Hechem, J. J., Homovc, J. F., and Figari, E. G. (1990). Estratigrafía del Chubutiano (Cretácico) en la Sierra de San Bernardo, cuenca del Golfo San Jorge, Argentina. Relatorio 11° Congreso Geológico Argentino (pp. 173–176).

Lizzoli, S., Raigemborn, M. S., Varela, A. N., and Paredes, J. M. (2025). Paleosols as paleoclimate proxies to reconstruct mid-cretaceous paleoclimate conditions in Central Patagonia, Argentina. Sedimentary Geology, 478, 106836. https://doi.org/10.1016/j.sedgeo.2025.106836

López-Angriman, A., Zarpellón, C., Mussel, F., and Cohen, M. (2014). Modelo Paleogeográfico de la Sección Superior de la Formación Pozo D-129. Su aplicación al desarrollo de reservas en la cuenca del Golfo San Jorge, Argentina. 9° Congreso de Exploración y Desarrollo de Hidrocarburos (pp. 489–510).

Nichols, G. J. (2012). Endorheic basins. In: C. Busby and A. Azor (Eds.), Tectonics of Sedimentary Basins: Recent Advances (1st ed., pp. 621–631). Blackwell Publishing Ltd. https://doi.org/10.1002/9781444347166.ch31

North, C. P., and Warwick, G. L. (2007). Fluvial fans, myths, conceptions, and the end of the terminal fan model. Journal of Sedimentary Research, 77(9), 693–701. https://doi.org/10.2110/jsr.2007.072

Olazábal, S. X., Tunik, M. A., and Paredes, J. M. (2020). Sandstone petrography and provenance of the Chubut Group (Cretaceous) in the Matasiete Canyon (Golfo San Jorge Basin, central Patagonia): implication for basin evolution and alluvial organization. Journal of South American Earth Sciences, 98, 102463. https://doi.org/10.1016/j.jsames.2019.102463

Paredes, J. M. (2023). Analogs in the study of fluvial successions: conceptual framework and examples from the Chubut Group (Cretaceous) of Argentina. Journal of South American Earth Sciences, 123, 104202. https://doi.org/10.1016/j.jsames.2023.104202

Paredes, J. M., Plazibat, S., Crovetto, C., Stein, J., Cayo, E., and Schiuma, A. (2013). Fault kinematics and depocenter evolution of oil-bearing, continental successions of Mina del Carmen Formation (Albian) in the Golfo San Jorge basin, Argentina. Journal of South American Earth Sciences, 46, 63–79. https://doi.org/10.1016/j.jsames.2013.05.002

Paredes, J. M., Allard, J. O., Foix, N., Álvarez, B., and Olazábal, S. X. (2014). Sedimentología y perfiles de rayos gamma de la Formación Pozo D-129 en la Sierra de San Bernardo, Chubut. 9° Congreso de Exploración y Desarrollo de Hidrocarburos (pp. 455-479).

Paredes, J. M., Foix, N., Allard, J. O., Colombo, F., Tunik, M. A. (2015). Alluvial architecture of reworked pyroclastic deposits in peri-volcanic basins: Castillo Formation (Albian) of the Golfo San Jorge Basin, Argentina. Revista de la Asociación Geológica Argentina, 72(1), 42–62.

Paredes, J. M., Foix, N., Allard, J. O. (2016). Sedimentology and alluvial architecture of the Bajo Barreal Formation (Upper Cretaceous) in the Golfo San Jorge Basin: outcrop analogues of the richest oil-bearing fluvial succession in Argentina. Marine and Petroleum Geology, 72, 317–335. https://doi.org/10.1016/j.marpetgeo.2016.02.013

Paredes, J. M., Aguiar, M., Ansa, A., Giordano, S. R., Ledesma, M., and Tejada, S. (2018a). Inherited discontinuities and fault kinematics of a multiphase, non-colinear extensional setting: Subsurface observations from the South Flank of the Golfo San Jorge Basin, Patagonia. Journal of South American Earth Sciences, 81, 87–107. https://doi.org/10.1016/j.jsames.2017.11.010

Paredes, J. M., Foix, N., Allard J. O., Valle, M. N., and Giordano, S. R. (2018b). Complex alluvial architecture, paleohydraulics and controls of a multichannel fluvial system, Bajo Barreal Formation (Upper Cretaceous) in the cerro Ballena anticline, Golfo San Jorge basin, Patagonia. Journal of South American Earth Sciences, 85, 168–190. https://doi.org/10.1016/j.jsames.2018.05.007

Paredes, J. M., Giordano, S. R., Valle, M. N., Olazábal, S. X., Allard, J. O., Foix, N., and Tunik, M. A. (2020). Climatic control on stacking density of fluvial successions: Upper Cretaceous Bajo Barreal Formation of the Golfo San Jorge Basin, Patagonia. Marine and Petroleum Geology, 113, 104116. https://doi.org/10.1016/j.marpetgeo.2019.104116

Paredes, J. M., Foix, N., and Allard, J. O. (2021). Estratigrafía cretácica de la cuenca del Golfo San Jorge. In R. E. Giacosa (Ed.), Geología y Recursos Naturales de la Provincia del Chubut (pp. 142–186). Relatorio 21° Congreso Geológico Argentino.

Paredes, J. M., Allard, J. O., Foix, N., Olazábal, S. X., Valle, M. N., and Tunik, M. A. (2024). Drainage reorganization and alluvial architecture of endorheic basins: The Lower Cretaceous record of the Chubut Group in the Golfo San Jorge Basin (Patagonia, Argentina). Journal of South American Earth Sciences, 144, 105031. https://doi.org/10.1016/j.jsames.2024.105031

Pérez Loinaze, V. S., Césari, S. N., Giordano, S. R., Stach, N. H., and Ansa, A. (2019). Palynological analysis of a Lower Cretaceous subsurface succession from the south flank of the Golfo San Jorge Basin, Argentina. Cretaceous Research, 97, 94–106. https://doi.org/10.1016/j.cretres.2019.01.008

Pérez Loinaze, V. S., Giordano, S. R., and Limarino, C. O. (2021). Late Cretaceous palynomorphs from the Golfo San Jorge Basin, Argentina. Journal of South American Earth Sciences, 107, 103151. https://doi.org/10.1016/j.jsames.2020.103151

Sciutto, J. C., 1981. Geología del Codo del Río Senguerr, Chubut, Argentina. Relatorio 8° Congreso Geológico Argentino (pp. 203–219).

Sylwan, C., Droeven, C., Iñigo, J., Mussel, F., and Padva, D. (2011). Cuenca del Golfo San Jorge. In Simposio Cuencas Argentinas: visión actual (pp. 139–183). 8° Congreso de Exploración y Desarrollo de Hidrocarburos.

Suárez, M., Márquez, M., De La Cruz, R., Navarrete, C., and Fanning, M. (2014). Cenomanian? early Turonian minimum age of the Chubut Group, Argentina: SHRIMP U-Pb geochronology. Journal of South American Earth Sciences, 50, 67–74. https://doi.org/10.1016/j.jsames.2013.10.008

Tunik, M. A., Paredes, J. M., Fernández, M. I., Foix, N., and Allard, J. O. (2015). Análisis petrográfico de areniscas de la Formación Castillo (Albiano) en la Faja Plegada de San Bernardo, cuenca Golfo San Jorge, Argentina. Revista de la Asociación Geológica Argentina, 72, 63–80.

Umazano, A. M., Bellosi, E. S., Visconti, G., and Melchor, R. N. (2008). Mechanism of aggradation in fluvial systems influenced by explosive volcanism: an example from the Upper Cretaceous Bajo Barreal Formation, San Jorge Basin, Argentina. Sedimentary Geology, 203, 213–228. https://doi.org/10.1016/j.sedgeo.2007.12.001

Vallati, P., De Sosa Tomas, A., and Casal, G. (2019). A Maastrichtian terrestrial palaeoenvironment close to the K/Pg boundary in the Golfo San Jorge basin, Patagonia, Argentina. Journal of South American Earth Sciences, 97, 102401. https://doi.org/10.1016/j.jsames.2019.102401