Paleoenvironmental reconstruction of Cretaceous rocks of the Amazonas Basin: preliminary researches MSc. Anderson Mendes Programa de Pós Graduação em Geologia e Geoquímica - IG - UFPA Grupo de Análise de Bacias Sedimentares da Amazônia

When did the Amazon River? 1. Middle to Upper Miocene (Hoorn et al, 1995;. Gingras et al, 2002;. Rodaz et al, 2005;. Potter, 1997;. Figueiredo et al, 2009) ou, 2. Plio-Pleistocene (Campbell et al, 2006; Nogueira, 2008).

As it was before the onset of the Amazon River? "Sanozama River? 1. Almeida, 1974 Called the upper portion of Solimões Formation of "Sanozama Formation" and positioned in the Late Pliocene-Pleistocene. 2. Potter, 1997 Uplift the Northeast due to the breakdown of Pangea.

Introduction New information about the Cretaceous Economic importance (HC's) Scientific importance Alter do Chão Formation (Cretaceous?) Attributed to a river system, but new interpretations, attributed the formation system with wave-dominated deltaic marine influence (Rossetti & Neto, 2006), and a meandering fluvial system mixed load (Mendes et al 2012).

Objectives Reconstructions of ancient environments of the late Cretaceous deposits of the Amazonas basin; Trying to demonstrate the reversal of drainage through data Paleocurrent; Integrate data from facies, stratigraphy, provenance, and paleocurrent for proposition model(s) paleoenvironmental and paleogeographic to the central portion of the Amazon basin.

Localization

Fluvial-deltaic deposits of Alter do Chão Formation (Cretaceous), central part of the Amazonas Basin, Brazil Observed in two areas: a) Óbidos e Parintins e b) Manaus. 1. Óbidos e Parintins 9 Lithofacies Conglomerates massive Mudstones Sandstones Massive Deformed bedding Bioturbated Trough cross-bedding Tabular cross-stratification Plane parallel-stratification Bioturbated Massive

Columnar sections (profiles) of areas. Alter do Chão Fm., Óbidos and Parintins

Óbidos-PA Colocar foto de campo ampla

Óbidos-PA Colocar foto de campo ampla

A) Massive Conglomerate; B) Contact Sandtone/Mudstone; C and D) Trough cross-stratification Sandstone.

E, F) Sandstone Tabular cross-stratification; E) Mudstone Massive and (F) Deformed bedding.

Depositional model (Óbidos and Parintins)

Fluvial-deltaic deposits of Alter do Chão Formation (Cretaceous), central part of the Amazonas Basin, Brazil 2. Manaus 10 Lithofácies Sandtones Trough cross. bedding and bioturbated Tabular cross. bedding and bioturbated Estr. cruz. sigmoidal, bioturbado low-angle stratification Swaley cross. bedding Deformated (covolutions e Ball-and-pillow). Massive Siltstones Plane parallel lamination Mudstones cross lamination thrusting

Columnar sections (profiles) of Alter do Chão Fm., Manaus area.

Manaus

Manaus

Manaus

a) Meniscus tube Taenidium, facies St and Ac; B) Bioturbated sandstone; c) Taenidium tubes endicniais ; d) Thalassinoides tubes.

A) Deformated sandstone/mudstone, covolution laminations (arrow); B) Ball-and-pillow deformations arrow; C-D) Mudstone laminate.

Some conclusions... In Obidos (PA) and Parintins (AM) region were recognized nine lithofacies organized in fining-upward cycles and grouped into two facies associations: 1. Channel Fill 2. Overbank Deposits Mendes et al 2012 In Manaus (AM) region were recognized ten lithofacies organized. (Mendes et al 2013, no prelo). System deltaic with wave-dominated and marine influence (Rossetti & Neto, 2006)?.

Some conclusions... The paleocurrent measures indicate paleofluxos preferred to S/SW suggesting sources in the N/NE area. Was proposed to Alter do Chão Formation up the Amazon River meandering fluvial system with varying sinuosity (high, base and low profiles, top) with mixed load (Obidos-PA), which changed river system for interlaced (braidad).

Alter do Chão Formation - fluvial deposits of the Cretaceous-Paleogene?

Petrography and diagenesis of sandstones, Alter do Chão Formation, central part of the Amazonas basin. Kaolinitic sandstone matrix, cement and silica overgrowth; Quartz grains mono and polycrystalline; Embayment and bipiramidal. Feldspar kaolinite Lithic fragments fragments and pebbles of gneisses and mudstones

Provenience of Alter do Chão Formation: an integrated study of facies, heavy minerals, paleocurrent and U-Pb zircon geochronology System Identification: 1. Meandering fluvial to braided. Paleocurrent preferred to S/SW Quartz sandstones with open framework Heavy Minerals 60 samples

Heavy Minerals

A) Geological map and paleocurrent measurements along the Amazonas River. B) Schematic map of the geochronological provinces of the Amazonian Craton. C) U-Pb ages of detrital zircons from the Alter do Chão Formation, near Obidos-PA.

Support 159509/2010 2009: Unidades cretáceo-cenozóicas no Amazonas: estratigrafia e potencialidade para bauxita. Adriana Horbe - Coordenador IG PPGG

Thank you! acmendes@ufpa.br