See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/324183210 The Late Oligocene–Early Miocene Marine Transgression of Patagonia Chapter · April 2018 DOI: 10.1007/978-3-319-67774-3_18 CITATIONS READS 15 762 17 authors, including: Alfonso Encinas Andres Folguera University of Concepción National Scientific and Technical Research Council-Facultad de Ciencis Exactas y Na… 95 PUBLICATIONS 1,334 CITATIONS 342 PUBLICATIONS 5,568 CITATIONS SEE PROFILE SEE PROFILE Florencia Bechis Kenneth L. Finger National Scientific and Technical Research Council University of California, Berkeley 68 PUBLICATIONS 1,336 CITATIONS 72 PUBLICATIONS 825 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Bioturbation and Its Effects on Porosity and Permeability in Carbonate Rocks View project Ichnology, sedimentary environments and sequence stratigraphy of the Ordovician Stony Mountain Formation in the Williston Basin View project All content following this page was uploaded by Andres Folguera on 11 April 2018. The user has requested enhancement of the downloaded file. Layout: T1 Standard Book ID: 385154_1_En Book ISBN: 978-3-319-67773-6 Chapter No.: 18 Date: 23-11-2017 Time: 1:10 pm Page: 431/462 1 The Late Oligocene–Early Miocene 2 Marine Transgression of Patagonia 3 Alfonso Encinas, Andrés Folguera, Florencia Bechis, Kenneth 4 L. Finger, Patricio Zambrano, Felipe Pérez, Pablo Bernabé, 5 Francisca Tapia, Ricardo Riffo, Luis Buatois, Darío Orts, Sven 6 N. Nielsen, Victor Valencia, José Cuitiño, Verónica Oliveros, Lizet De 7 Girolamo Del Mauro and Victor A. Ramos 8 Abstract The most important Cenozoic marine transgression in Patagonia occur- 9 red during the late Oligocene–early Miocene when marine waters of Pacific and 10 Atlantic origin flooded most of southern South America including the present * 11 Patagonian Andes between 41° and 47° S. The age, correlation,PROOF and tectonic 12 setting of the different marine formations deposited during this period are debated. 13 However, recent studies based principally on U–Pb geochronology and Sr isotope 14 stratigraphy, indicate that all of these units had accumulated during the late 15 Oligocene–early Miocene. The marine transgression flooded a vast part of southern 16 South America and, according to paleontological data, probably allowed for the first 17 time in the history of this area a transient connection between the Pacific and 18 Atlantic oceans. Marine deposition started in theED late Oligocene–earliest Miocene 19 (*26–23 Ma) and was probably caused by a regional event of extension related to 20 major plate reorganization in the Southeast Pacific. Progressive extension and Editor Proof A. Encinas (&) Á F. Pérez Á P. Bernabé Á F. Tapia Á R. Riffo V. Oliveros Á L. De Girolamo Del Mauro Departamento de Ciencias de la Tierra, Universidad de Concepción, Concepción, Chile e-mail: [email protected] A. Folguera Á Victor A. Ramos Instituto de Estudios Andinos “Don Pablo Groeber,” Departamento de Ciencias Geológicas, FCEN, Universidad de Buenos Aires–CONICET, Buenos Aires, Argentina F. Bechis Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio (IIDyPCa), CONICET - Universidad Nacional de Río Negro, San Carlos de Bariloche, Argentina K. L. Finger University of California Museum of Paleontology, Berkeley, California, USA P. Zambrano Universidad Andres Bello, Facultad de Ingeniería, Geología, Concepción, Chile L. Buatois Department of Geological Sciences, University of Saskatchewan, Saskatoon, Canada D. Orts Instituto de InvestigaciNCORRECTón en Paleobiología y Geología, Universidad Nacional de Río Negro–CONICET, General Roca, Argentina © SpringerU International Publishing AG 2018 431 A. Folguera et al. (eds.), The Evolution of the Chilean-Argentinean Andes, Springer Earth System Sciences, https://doi.org/10.1007/978-3-319-67774-3_18 Layout: T1 Standard Book ID: 385154_1_En Book ISBN: 978-3-319-67773-6 Chapter No.: 18 Date: 23-11-2017 Time: 1:10 pm Page: 432/462 432 A. Encinas et al. 21 crustal thinning allowed a generalized marine flooding of Patagonia that reached its 22 maximum extension at *20 Ma. It was followed by a phase of compressive tec- 23 tonics that started around 19–16 Ma and led to the growth of the Patagonian Andes. 24 The youngest (*19–15 Ma) marine deposits that accumulated in the eastern 25 Andean Cordillera and the extra-Andean regions are coeval with fluvial synoro- 26 genic deposits and probably had accumulated under a compressive regime. 2927 Keywords Oligocene–Miocene transgression Á Patagonia Á Patagonian andes 28 Extension Á Orogenesis 30 1 Introduction 31 The Patagonia region in southern South America has been flooded by several marine 32 transgressions throughout its history. During most of the Mesozoic,PROOF this area was 33 characterized by a convergent margin dominated by extensional tectonics, which led to 34 a low-relief volcanic arc and a series of interconnected back-arc basins that were 35 periodically covered by marine transgressions of Pacific origin (Mpodozis and Ramos 36 1990) (see Chaps. “Lower Jurassic to Early Paleogene Intraplate Contraction in Central 37 Patagonia” and “Cretaceous Orogeny and Marine Transgression in the Southern 38 Central and Northern Patagonian Andes: Aftermath of a Large-Scale Flat-Subduction 39 Event?”). By the late Early Cretaceous, a shift to aED contractional tectonic regime was 40 caused by the accelerated westward drift of South America that triggered the inversion 41 of the Mesozoic back-arc basins and the initial uplift of the Andes (Mpodozis and 42 Ramos 1990). From the latest Cretaceous onwards, a series of marine transgressions Editor Proof 43 periodically covered part of Patagonia (Malumián 1999). Most of those transgressions 44 had an Atlantic origin, as the orographic barrier imposed by a growing Andean 45 Cordillera prevented the ingression of Pacific waters (Mpodozis and Ramos 1990). 46 The most extensive Cenozoic marine transgression in Patagonia occurred during 47 the late Oligocene–early Miocene. During that period, marine waters of Pacific and 48 Atlantic origin flooded most of southern South America and reached the present 49 Patagonian Andes (Ramos 1982a, b; Elgueta et al. 2000; Malumián and Náñez 50 2011; Bechis et al. 2014; Encinas et al. 2016) (Fig. 1). Correlation of the marine 51 deposits that accumulated during this period is difficult because they occur as small 52 and discontinuous outcrops, principally in the Andean Cordillera (Fig. 1). This is 53 due to several factors: (1) the dense vegetation that covers this area; (2) the high 54 exhumation rates that affected the Patagonian Andes during the Late Cenozoic and 55 caused the erosion of most of the Meso-Cenozoic volcano-sedimentary sequence S. N. Nielsen Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile V. Valencia NCORRECT School of the Environment, Washington State University, Pullman, Washington, USA J. Cuitiño InstitutoU Patagónico de Geología y Paleontología, CCT CENPAT-CONICET, Puerto Madryn, Chubut, Argentina Layout: T1 Standard Book ID: 385154_1_En Book ISBN: 978-3-319-67773-6 Chapter No.: 18 Date: 23-11-2017 Time: 1:10 pm Page: 433/462 The Late Oligocene–Early Miocene Marine Transgression … 433 PROOF ED Editor Proof Fig. 1 DistributionNCORRECT of upper Oligocene–lower Miocene marine deposits in central and southern Chile andU Argentina. Modified from Encinas et al. (2014) Layout: T1 Standard Book ID: 385154_1_En Book ISBN: 978-3-319-67773-6 Chapter No.: 18 Date: 23-11-2017 Time: 1:10 pm Page: 434/462 434 A. Encinas et al. 56 (Thomson 2002; Adriasola et al. 2006); and (3) fossils from marine deposits of the 57 Andean range are poorly preserved, which hinders their recognition at the species 58 level. As a consequence, the age, tectonic setting, and possible connections with the 59 Pacific or Atlantic oceans during the accumulation of these strata have been largely 60 debated (see Encinas et al. 2016 and references therein). In this contribution, we 61 analyze the most important antecedents on the late Oligocene–early Miocene 62 marine deposits of Patagonia and discuss their tectono-sedimentary evolution and 63 paleogeography. 64 2 Geologic Setting 65 The Patagonian Andes are located between *38° and 47° S. Compared to the 66 Central Andes to the north, this segment is characterized by lower elevation 67 (1–2 km), narrower width (*300 km), reduced crustal thicknessPROOF (*40 km), and 68 less shortening (12–25 km) (Mpodozis and Ramos 1990; Hervé 1994; Orts et al. 69 2012). An active spreading center, the Chile Rise, is currently subducting at the 70 latitude of the Taitao Peninsula (*46° S) and defines the Chile triple junction 71 between the Nazca, South American, and Antarctic plates (Cande and Leslie 1986) 72 (see Chap. Mantle Influence on Andean and Pre-Andean Topography). Also dis- 73 tinctive of the Patagonian Andes is the LiquiEDñe-Ofqui Fault Zone (LOFZ), 74 a *1000-km trench-parallel dextral strike-slip fault system (Hervé 1994). Five N– 75 S-trending physiographic units characterize the Chilean margin at these latitudes. 76 From west to east these are: (1) the offshore continental shelf; (2) the Coastal 77 * Editor Proof Cordillera; (3) the Central Depression, which is submerged south of 42° S and 78 gradually disappears toward the south; (4) the Main Andean Cordillera, which 79 includes the highest peaks; and (5) the extra-Andean region, a mostly flat low-lying 80 area that extends between the Main Andean Cordillera and the Atlantic coast. 81 The most extensive rocks in the study area are: (1) Paleozoic–Triassic meta- 82 morphic rocks, which crop out principally on the forearc (Hervé et al. 2003) but also 83 in some parts of the Andean Cordillera and the western extra-Andean region 84 (Ramos and Ghiglione 2008 and references therein); (2) Jurassic, Cretaceous, 85 Eocene, and Miocene plutonic rocks of the Patagonian batholith (Hervé et al. 1985; 86 Pankhurst et al.