Movimentos de massa multiescala na bacia da foz do Amazonas - margem equatorial brasileira

Abstract

ABSTRACT. Analysis of 2D multi-channel seismic data provided evidences that sediment slides are recurrent elements in the sedimentary succession of the Foz do Amazonas Basin. In the Amazon Fan, a linked extensional-contractional system glides along weak levels, forming gravitational fold-and-thrust belts of regional scale. Gravity-related fault scarps and sea-floor uplifts (up to 500 m high) induced surficial sediment slides along thrust-faults (average thickness between 200-300 m), resulting in structurally-driven mass movement deposits, as large as 10 4 km 2 . We document, as well, the occurrence of two thick large-scale megaslides along the steep margin to the NW and to the SE of the fan. Megaslides can remobilize siliciclastic series downslope as allochthonous masses over areas as large as thousands of km 2 :the Pará-Maranhão Megaslide (up to 1000 m thick) extends downslope to the Pará-Maranhão Basin over an area of about 90,000 km 2 . To the Northwest of the fan, the Amapá Megaslide Complex consists of a series of recurrent megaslides (each one as thick as 300-700 m), forming a thick stratigraphic succession related to mass transport processes, across an area of about 80,000 km 2 . The instability that triggers megaslides is most likely created by pore overpressure as indicated by the seismic attributes of their respective base of slides, characterized by seismic signals of negative polarity.

Deposition and deformation in the deepwater sediment of the offshore Barreirinhas Basin, Brazil

“…The postrift structural evolution of this part of the Barreirinhas Basin is dominated by a series of collapse systems involving detachment surfaces within shale units. Other fold structures comparable to those analyzed have been mapped in the Barreirinhas and Pará-Maranhão basins (Zalan, 2011) and in the Foz do Amazonas (Cobbold et al, 2004;Araujo et al, 2009;Perovano et al, 2009), and each is a highly complex three-dimensional system. Variations in the exact timing of fault movements within the basin seem likely.…”

“…4) (Figueiredo et al, 2009). That may also be the case for other large deepwater fold and thrust structures developed on the Brazilian Equatorial margin from the Amazon Cone (Araujo et al, 2009;Perovano et al, 2009) to the Barreirinhas Basin (Zalan, 1998(Zalan, , 2004(Zalan, , 2005(Zalan, , 2011Gilbert, 2006Krueger and Gilbert, 2009;Krueger et al, 2011).…”

“…In areas of very thick sediment accumulation such as the Amazon Cone (Araujo et al, 2009;Perovano et al, 2009) and Niger Delta (Corredor et al, 2005;Billotti and Shaw, 2005;Cobbold et al, 2009), the sediment weight depress the lithosphere (Morley et al, 2011) causing the slope of the basal contact of the sedimentary pile to dip landward, which is also observed to a lesser extent in the Barreirinhas Basin (Zalan, 2011).…”

Identification and analysis of bottom simulating reflectors in the Foz do Amazonas Basin, Northern Brazil

“…The extreme sediment load drives the gravitational collapse of the fan, creating a proximal extensional domain with normal faults on the outer continental shelf and upper slope, and an outer compressional domain with thrust faults and folds, in the upper-fan (Reis et al 2010(Reis et al , 2016. Extensive mass-transport deposits (MTD) prevails across the fan, interlayered with channel-levee systems, representing the Neogene stratigraphic succession (Araújo et al 2009, Reis et al 2010. Additionally, voluminous MTD complexes occur on the northwestern and southeastern flanks of the submarine fan.…”

Morphodynamics and spatial distribution of regional slope failures in the Offshore Amazon Basin, Brazilian Equatorial Margin

“…These authors recognized the occurrence of near-surface quaternary MTDs (Figure 1A) and associated failure features on the central basin (~Amazon fan area), occurring interbedded with welldeveloped channel-levee systems, on subsurface. More recently works, based on regional 2D seismic lines, showed the existence of vertical stacked failure masses, Middle Pliocene-Quaternary in age, with individual thicknesses up to 1000m thick (Araújo et al, 2009;Reis et al, 2016;Silva et al, 2016). Those MTDs constitute megaslides complexes (MCs), notably distributed on the NW and SE sectors of the Offshore Amazon basin, but also interbedded within the Amazon fan series (Figure 1A).…”