This manuscript is a preprint and has been submitted to Basin Research for peer review. Please note that, this manuscript has to be formally accepted for publication. Subsequent versions may have slight differences in content according to the peer review process. If accepted, the final version of this manuscript will be available via the ‘Peer-reviewed Publication DOI’ link on the right information panel of this website. We welcome feedback on the content of this manuscript. Please feel free to contact any of the authors. EVALUATING THE ROLE OF TECTONICS, EUSTASY, AND CLIMATE ON THE MAASTRICHTIAN-DANIAN TRANSGRESSION IN THE MAGALLANES- AUSTRAL BASIN (CHILEAN PATAGONIA) Huber A. Rivera1, 2, *, Jacobus P. Le Roux1, Marcelo Farías1, Néstor M. Gutiérrez1, Alejandro Sánchez3, Sylvia Palma-Heldt4, Lissett Celle1 1Departamento de Geología, FCFM, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile 2Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France 3Departamento de Ingeniería en Minas, Universidad de Santiago de Chile, Av. O'Higgins 3363, Estación Central, Santiago, Chile 4Departamento de Ciencias de la Tierra, Universidad de Concepción, Barrio Universitario S/N°, Concepción, Chile *Corresponding author: [email protected]; [email protected] Page 1 of 65 Basin Research 1 2 3 Evaluating the role of tectonics, eustasy, and climate on the Maastrichtian-Danian 4 5 6 transgression in the Magallanes-Austral Basin (Chilean Patagonia) 7 8 9 Huber A. Rivera1, 2, *, Jacobus P. Le Roux1, Marcelo Farías1, Néstor M. Gutiérrez1, 10 3 4 1 11 Alejandro Sánchez , Sylvia Palma-Heldt , Lissett Celle 12 13 1Departamento de Geología, FCFM, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile 14 15 2Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France 16 3 17 Departamento de Ingeniería en Minas, Universidad de Santiago de Chile, Av. O'Higgins 3363, Estación Central, 18 Santiago, Chile 19 20 4Departamento de Ciencias de la Tierra, Universidad de Concepción, Barrio Universitario S/N°, Concepción, Chile 21 *Corresponding author: [email protected]; [email protected] 22 23 24 ABSTRACT 25 26 The Maastrichtian-Danian transgression was the first and most extended Atlantic-derived marine 27 28 29 incursion in Patagonia, and the detailed study of its stratigraphic record and causative mechanism 30 31 in the Magallanes-Austral Basin reveals the interplay of sedimentation, tectonism, and base-level 32 33 changes. This contributes to our understanding of the foreland basin dynamics. We present a multi- 34 35 36 faceted approach including sedimentology, palynology, sequence stratigraphy, and 37 38 geochronology, to evaluate the role of climate, tectonics, and eustasy on the transgression. Two 39 40 stratigraphic sequences are recognized: (1) from the late Campanian to Maastrichtian, when a 41 42 43 normal regression occurred that shifted shelf and upper slope deposits (Fuentes Formation) to 44 45 shoreface and deltaic environments (Rocallosa-Dorotea Formations) favoured by high erosion 46 47 rates in the fold-thrust belt and a sea-level drop during a prevailing cool, rainy, and humid climate; 48 49 (2) from late Maastrichtian to Paleocene when the transgression took place, manifested by 50 51 52 estuarine deposits (upper Dorotea Formation) in an incised valley system and by deep-water 53 54 turbidites (Chorrillo Chico Formation and Cabo Naríz beds). The development of the stratigraphic 55 56 57 58 1 59 60 FOR REVIEW PURPOSES ONLY Basin Research Page 2 of 65 1 2 3 sequences was mainly tectonic-driven where the interplay of flexural loading and sediment supply 4 5 6 sourced from the uplifted Patagonian Andes shape the evolution of the accommodation space. This 7 8 study highlights the significance of a major thrusting event at ca. 67 Ma that generated flexural 9 10 subsidence causing the transgression, as well as two phases of Patagonian orogenic building and 11 12 long-term detritus input from the Southern Patagonian Batholith, mafic Rocas Verdes Basin 13 14 15 remnants, and Andean metamorphic terranes exposed in the hinterland. Moreover, point-out the 16 17 importance of the preceding basin configuration to the formation whether of subaerial 18 19 unconformities or correlative conformities. 20 21 22 Keywords: Incised valley; Transgression; Patagonian Andes; Cretaceous paleoclimate; sequence 23 24 stratigraphy. 25 26 27 1. INTRODUCTION 28 29 30 The study and understanding of transgressions have become of vital importance in almost 31 32 all basins that are of interest for petroleum exploration. In addition, transgressions have significant 33 34 implications in active foreland basins since they not only reflect the interplay of dynamic and 35 36 37 flexural subsidence in deepening the basin (e.g., Mitrovica et al., 1989; Sinclair et al., 1998) but 38 39 also allow a better understanding of the balance of tectonic loading-unloading, sedimentation, and 40 41 sea-level changes within their complex and dynamic evolution (e.g., Catuneanu, 2004; Yang & 42 43 44 Miall, 2008; Rodazz et al., 2010). 45 46 In Patagonia, the Maastrichtian-Danian transgression is considered to have been the first, 47 48 deep and extended Atlantic marine ingression (Malumián & Náñez, 2011). Contrary to most other 49 50 Cenozoic transgressions, the first Atlantic transgression was not related to relative climatic optima 51 52 53 and appears to have been linked to significant cooling conditions, accompanied by a gradual sea- 54 55 level decline between the Maastrichtian and Danian (Barrera & Savin, 1999; Haq, 2014; Huber, 56 57 58 2 59 60 FOR REVIEW PURPOSES ONLY Page 3 of 65 Basin Research 1 2 3 2018), which raises interesting questions about the role of eustatic versus tectonic processes during 4 5 6 the transgression. 7 8 To date, the best indicator of this transgression lies in the foraminifera assemblage recorded 9 10 in all the Patagonian basins except for the Península Valdes and Rawson Basins (Náñez & 11 12 Malumián, 2009; Malumián & Náñez, 2011). A good sedimentological record being present only 13 14 15 in the northernmost basins (Aguirre-Urreta et al., 2011 and references therein). The stratigraphic 16 17 record of this transgression is unknown throughout the Magallanes-Austral Basin because (1) the 18 19 K-Pg boundary has been hardly recognized (Charrier & Lahsen, 1969; Malumián & Caramés, 20 21 22 1997; Malumián & Náñez, 2011), and (2) there is a lack of sequence-stratigraphic and 23 24 sedimentological studies on the K-Pg transition. On the other hand, the continuous history of 25 26 marine sedimentation in the Magallanes-Austral Basin (Fig. 1a) since its formation, imposes an 27 28 29 even greater complexity to decipher the relative control between the processes that intervene in 30 31 the transgression. 32 33 The aim of our work is to broaden current knowledge of the stratigraphic record of the first 34 35 Atlantic transgression and its causative mechanism in the Magallanes-Austral Basin (Fig. 1a) by a 36 37 38 multidisciplinary approach, including sedimentological, sequence stratigraphic, palynological, and 39 40 geochronological studies. Our study examines to what extent the climate, eustasy and tectonics 41 42 controlled the marine incursion and provides a sequence stratigraphic framework that facilitates 43 44 45 the understanding of the juxtaposition, evolution, and inter-basin correlation of the depositional 46 47 units (from Campanian-Maastrichtian to Paleocene). In addition, the results of this study allow us 48 49 to constrain the timing of the latest Cretaceous-early Cenozoic tectonic events and establish an 50 51 52 accurate delineation of sea-level changes at the K-Pg transition, which have significant 53 54 55 56 57 58 3 59 60 FOR REVIEW PURPOSES ONLY Basin Research Page 4 of 65 1 2 3 implications for our understanding of the palaeofaunistic and palaeofloristic interchange dynamics 4 5 6 between South America and the Antarctic Peninsula. 7 8 9 10 2. TECTONIC AND STRATIGRAPHIC SETTING 11 12 2.1 Stratigraphic synthesis of the study area 13 14 15 Our study encompasses the uppermost Fuentes, Rocallosa-Dorotea, and Chorrillo Chico 16 17 Formations (Fig. 1b). The locations of stratigraphic sections are primarily on the Brunswick 18 19 Peninsula, the northern coast of the Skyring Sound and Riesco Island, belonging to the Magallanes 20 21 22 Province (MP; Fig. 2); the Cerro Pelario, Demaistre area, and the southern extension of Sierra 23 24 Dorotea, belonging to the Última Esperanza Province (UEP; Fig. 2). Additionally, we present 25 26 petrological data of the Cabo Naríz strata (equivalent to the Chorrillo Chico Formation) studied 27 28 29 previously by Sánchez et al. (2010) in the west coast of Tierra del Fuego (Fig. 1a). This strategic 30 31 distribution of stratigraphic sections (Table 1; Fig. 2) allows us to study in greater detail the facies 32 33 changes and depositional evolution along the axis of the basin. 34 35 The K-Pg stratigraphic nomenclature between Argentina and Chile (and within Chile itself) 36 37 38 is particularly confusing as many units are referred to by different names (Fig. 1b). Moreover, the 39 40 Maastrichtian-Danian transgression and subsequent regressive deposits have been unevenly 41 42 studied on both sides of the international boundary. In the Río Turbio area (Argentina) (Fig. 1a), 43 44 45 the massive, glauconitic sandstones with intercalations of mudstones, and conglomerates of the 46 47 Monte Chico Formation (Maastrichtian-Danian; Fig. 1b) followed by the fine-to-coarse-grained 48 49 sandstone- and conglomerate-bearing coal seams of the Cerro Dorotea Formation (Danian- 50 51 52 Selandian; Fig. 1b) are often thought to represent a transgressive-regressive (T-R) cycle 53 54 (Malumián & Caramés, 1997; Álvarez et al., 2006; Mpodozis et al., 2011; Fosdick et al., 2015) 55 56 57 58 4 59 60 FOR REVIEW PURPOSES ONLY Page 5 of 65 Basin Research 1 2 3 and it can only be assumed (indirectly) that the Maastrichtian-Danian Atlantic transgression is 4 5 6 equivalent to the T hemicycle.