T109 Lakes through Space and Time (Posters)

Monday, 5 November 2018
9:00 AM - 6:30 PM
Halls J-K

NEW INSIGHTS ON THE STRATIGRAPHY, SEDIMENTOLOGY AND DEFORMATIONAL EVOLUTION OF AN ANDEAN INTERMONTANE QUATERNARY PALEOLAKE

Paper number: T109-6
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

We present new results about the stratigraphy, sedimentology and syn-sedimentary deformation of a Pleistocene lacustrine sequence developed within an intermontane basin in the core of northern Andes orogen. We carried out a detailed facies analysis of the ~100 m-thick lacustrine succession, known as the San Miguel Fm. The lower part of the lacustrine deposits is characterized by a regressive sequence formed by volcanoclastic conglomerates and sandy deltaic progradational sequences. These coarse-grained sediments pass gradually to a transgressive sequence constituted by massive claystones and tuffs, contoured bedding, gullies and thick sandy debris flows. The upper part is mainly characterized by millimetre rhythmic laminated sediments composed of light-grey claystone–siltstone laminates alternating with light diatomite laminates. These fine sediments are interbedded with mass-transport volcanoclastic sandstones beds. The San Miguel Fm. was deposited in a tectonically and volcanically active strike-slip basin associated to a crustal-scale N–S dextral restraining-bend megashear. This megashear controlled the orogenic uplift and volcanic activity of the sector during the last ~5.5 Ma. The tectonic evolution of the basin was locally driven by the active NW–SE Quito faults’ system located in the south-western part of the basin and linked to the N–S megashear. The tectonic evolution of the basin can be divided into two stages: 1) normal movements of these faults system, which promoted the deepening of the lake to south-westward and 2) inverse movements related to the end of the lake, as well as soft-sediment deformation characterized by NE-verging folds, shallow thrusts and abundant sandy dikes and sills intrusion. The interandean San Miguel Fm. allows us to relate the tectonic evolution of the N–S trend strike-slip faults systems to the last Andean uplift pulse. Moreover, the volcanic, volcanoclastic and fine laminated sediments constitute an excellent record for the volcanic and paleoclimatic history of this region.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-319388

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