Basin Development in an Accretionary, Oceanic-Floored Fore-Arc Setting; Southern Coastal Ecuador During Late Cretaceous-Late Eocene Time

Comment on “The Chongón/Colonche orocline transrotational bending and the coeval opening of the Progreso basin in southwestern Ecuador” by Alemán et al

“…It seems to exist a misunderstanding by Alemán et al, [2021] when affirming that our interpretation of the Azúcar Formation is related only to the recording of an early trench-slope basin. This is the assertion presented by Benitez [1995] and Jaillard et al, [1995], cited in Aizprua et al, [2019] within the Geodynamic and Geological settings section. Herein, we present a unified tectonostratigraphic view of the Azúcar Formation for clarification, given the recurrent referral by Alemán et al, [2021] to the work presented by Aizprua et al, [2019] and Witt et al, [2019b].…”

“…A recurrent discrepancy between researchers working with the geology of the Northern Andes is related to the number of oceanic plateaus and accretionary episodes that have taken place since the Late Cretaceous. In this context, Alemán et al, [2021] support the premise of two distinctive intra-oceanic arcs and two episodes of accretion by concurring with Jaillard et al, [1995]. However, Alemán et al, [2021] overlooked the model updates presented by the same authors in Van Melle et al, [2008] and Jaillard et al, [2009].…”

“…Seyler et al, [2021] suggest that the Pascuales felsic intrusives are associated with a process of partial melting of mafic-ultramafic cumulates, probably related to the initial stage of subduction leading to the San Lorenzo and Rio Cala arcs. Alemán et al, [2021] propose the development of a foredeep basin (hosting the Azúcar Formation and Ancón Group) controlled by a Late Paleocene collision of the "Cayo remnant arc" against the Andean margin, based on a model proposed by Jaillard et al, [1995]. However, we found an inconsistency in this proposal, as it is difficult to reconcile the current location of the proposed suture (Chongón-Jipijapa-Jama), ~150 km west of the collision front with the Andean margin.…”

Significance of Northern Andes Terrane Extrusion and Genesis of the Interandean Valley: Paleomagnetic Evidence From the “Ecuadorian Orocline”

“…From a tectonostratigraphic and geomorphologic point of view, the Ecuadorian Andes can be subdivided into five trench-parallel domains bounded by major faults (Figure 1). From West to East, the Coastal zone represents the fore-arc domain and is composed of upper Cretaceous mafic plume-related basement overlain by upper Cretaceous, and Paleocene to Miocene volcanoclastic sequences (e.g., Benitez, 1995;Gansser, 1973;Goossens & Rose, 1973;Jaillard et al, 1995Jaillard et al, , 1999. The Pallatanga fault marks the boundary between the Coastal fore-arc zone and the Cordillera Occidental, which consists of upper Cretaceous island arc volcanic rocks, oceanic-related fragments, plutons, and unconformable upper Cretaceous to Eocene turbidites.…”

“…In Ecuador, the Dolores‐Guayaquil megashear and the Peltectec faults are NE‐trending dextral strike‐slip fault systems that have been related to two distinct collisional events: the first spanning from Santonian‐early Campanian (85–80 Ma) (Aspden et al., 1992; Kerr et al., 2002; Lebras et al., 1987; Spikings et al., 2005) to late Campanian‐Maastrichtian (75–65 Ma) (Jaillard et al., 2004; Luzieux et al., 2006; Spikings et al., 2001, 2010), the second between Late Paleocene (Jaillard et al., 1995), or Eocene (Kerr & Tarney, 2005; Kerr et al., 2002) to Late Eocene‐Oligocene (Spikings et al., 2005). Conversely, other works (e.g., Aizprua et al., 2019) suggested that a single west Ecuadorian Andes terrane existed prior to accretion to South America that broke up and rotated CW during and after collision (Luzieux et al., 2006; Vallejo et al., 2009, 2019; Spikings et al., 2010) and that the Nazca subduction trench was reestablished after the accretionary tectonic phase in the Early Eocene (Aizprua et al., 2019).…”