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

Etienne Jaillard 1, 2, Peter Bengtson 3, Martha Ordoñez 4, Wilmer Vaca 5, Annie V. Dhondt, Johnny Suárez 4, Jorge Toro Álava 6

For the Convention IRD - Petroproducción collaboration(s)

(2005)

A reappraisal of the “Late Cretaceous Yunguilla Formation” of the Cuenca area made it possible to define four distinct formations, correlatable with those of southwestern Ecuador. A mid to late Campanian marine transgression (Jadán Fm) is overlain by quartz-rich conglomerates of fan-delta to turbiditic fan environment (Quimas Fm) 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 Fm) 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 Fm) 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. This suggests that in Ecuador, accretion of oceanic terranes contributed to the build-up of the Andes through tectonic underplating of low-density material, and that the eastern areas did not behave as a flexural foreland basins during late Cretaceous-Paleogene times.

1:	Laboratoire de géodynamique des chaines alpines (LGCA)
	CNRS : UMR5025 – OSUG – INSU – Université de Savoie – Université Joseph Fourier - Grenoble I
2:	Laboratoire des Mécanismes et Transfert en Géologie (LMTG)
	CNRS : UMR5563 – Observatoire Midi-Pyrénées – Université Paul Sabatier [UPS] - Toulouse III – Institut de recherche pour le développement [IRD] : UMR154
3:	Geologisch-Paläontologisches Institut
	Universität Heidelberg
4:	Centro de Investigación Geológica- Guayaquil (CIGG)
	Petroproducción
5:	Escuela Politécnica Nacional (EPN)
	Escuela Politécnica Nacional
6:	Petroproducción
	Petroproducción

Subject

:

Sciences of the Universe/Earth Sciences/Stratigraphy

Keyword(s): Ecuador – accretions – syntectonic sedimentation – stratigraphy – ammonites

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From: Etienne Jaillard <>

Submitted on: Monday, 5 February 2007 16:44:52

Updated on: Monday, 5 February 2007 19:38:56