Sedimentary record of terminal Cretaceous accretions in Ecuador: The Yunguilla Group in the Cuenca area

Abstract

A reappraisal of the ''Late Cretaceous Yunguilla Formation'' of the Cuenca area enables the definition of four distinct formations, correlatable with those of southwestern Ecuador. A mid-to late-Campanian marine transgression (Jadán Formation) is overlain by quartz-rich conglomerates of fan-delta to turbiditic fan environment (Quimas Formation) of latest Campanian-earliest Maastrichtian age, which are interpreted as evidence of the accretion of a first oceanic terrane (San Juan). Disconformable, arkosic turbidites and cherts (Tabacay Formation) of early Maastrichtian age are thought to represent the erosion of the newly accreted oceanic terrane. A major unconformity of late Maastrichtian age, caused by the accretion of a second oceanic terrane (Guaranda), is followed by the deposition of quartz-rich micaceous shelf sandstones (Saquisilí Formation) of Paleocene age. A third accretion event (late Paleocene) is recorded in coastal Ecuador. Each accretion event correlates with the uplift and erosion of the Eastern Cordillera and with a sedimentary hiatus in the eastern areas. In Ecuador, accretion of oceanic terranes contributed to the build up of the Andes through tectonic underplating of low-density material, and the eastern areas did not behave as flexural foreland basins during late Cretaceous-Paleogene times.

Across‐arc versus along‐arc Sr‐Nd‐Pb isotope variations in the Ecuadorian volcanic arc

“…We chose samples to fill local gaps in Figure 2. Schematic map of the main geological zones in Ecuador (modified from Jaillard et al [2008]). Volcanic centers are displayed and sorted according to their geographical location (Western Cordillera, Inter-Andean Valley, Eastern Cordillera, and back arc).…”

“…The composition and age of the crustal basement beneath these volcanic alignments varies. The Western Cordillera basement consists of oceanic MORB‐like basalts and overlying sedimentary rocks, which were accreted onto the ancient Ecuadorian margin during Late Cretaceous and Cenozoic times [ Hughes and Pilatasig , ; Luzieux et al ., ; Jaillard et al ., ]. In contrast, the Eastern Cordillera basement consists of older continental formations, made up of Palaeozoic to late Mesozoic felsic and mafic igneous and metamorphic rocks [ Aspden and Litherland , ; Chiaradia et al ., ].…”

Partitioning of oblique convergence in the Northern Andes subduction zone: Migration history and the present‐day boundary of the North Andean Sliver in Ecuador

“…The history of the large-scale deformation in Ecuador involves a succession of discrete and intense tectonic events rather than deformation continuous through time. Accretion of oceanic terranes to the Ecuadorian continental margin occurred between 75 and 58 Ma [Reynaud et al, 1999;Spikings et al, 2001;Jaillard et al, 2004Jaillard et al, , 2008Jaillard et al, , 2009]. Since then, NE-ward oceanic convergence led to the activation of the former sutures bounding the oceanic terranes as dextral strike-slip faults and flower structures [Jaillard et al, 2004[Jaillard et al, , 2009Amortegui et al, 2011], according to a sequence of events.…”

“…This plate interaction led to large‐scale lithospheric deformation of northern South America involving several individualized continental blocks (Figure ) [ Audemard and Audemard , ; Pindell and Kennan , ]. Furthermore, between 75 and 58 Ma, oceanic terranes have been accreted to the Ecuadorian continental margin through successive episodes [ Reynaud et al ., ; Spikings et al ., ; Jaillard et al ., , , ], before the main orogeny phase started 23 Ma ago [ Hey , ; Audemard and Audemard , ]. In the latest stage of the Northern Andes evolution, an upper plate “sliver” in Ecuador and Colombia, trapped between the trench and the South American craton (i.e., the Guyanese Shield) is “escaping” NE‐ward since the Mio‐Pliocene [ Pennington , ; Costa et al ., ; Egbue and Kellogg , ; Nocquet et al ., ].…”

The contribution of the young Cretaceous Caribbean Oceanic Plateau to the genesis of late Cretaceous arc magmatism in the Cordillera Occidental of Ecuador

“…The oldest, the San Juan oceanic plateau, is thought to be 123 Ma-old and accreted to the margin 75 Ma ago (Late Campanian, Lapierre et al, 2000;Jaillard et al, 2008), its existence is debated by many authors who suggest an age of 88.1 ± 1.6 Ma (Kerr and Tarney, 2005;Luzieux et al, 2006). The second oceanic plateau, the Guaranda plateau, is interpreted as part of the Caribbean-Colombian Oceanic Plateau (CCOP, Kerr et al, 1997a,b;Reynaud et al, 1999), dated to 92-88 Ma (Turonian-Coniacian, Sinton et al, 1998), and its age of accretion is said to be 68 Ma (Mid Maastrichtian, Jaillard et al, 2004).…”