Page 634 - Economia Azul - versão: inglês

Figure Z1
The Rio Grande Cone Gas Hydrates Province

The Rio Grande Cone (RGC) is located that accommodate the movement in a set
in the southern portion of the Pelotas Basin of horsts and grabens. In the compressional

and has an approximate area of 35,000 km², domain (red rectangle in Figure Z1) there are
at water depths between 200 and 3,000 m, thrust faults with thrusting and folding of
200 km from the city of Rio Grande. The the sedimentary layers, folds with a high an-
maximum thickness of sediments reaches gle of closure that form gaps of the order of 30 o 0’0’’S
about 5,000 m (FONTANA, 1996), deposited 200 m in the seabed (SILVEIRA and MACH-
since the lower Miocene, about 23 M.a. The ADO, 2004; CASTILLO et al., 2009).
RGC is mainly composed of fine siliciclastic Unlike the Foz do Amazonas Fan region,
sediments, whose construction is attributed the BSR reflector presents itself continuously Legend
Pelotas Basin
to inputs from three different drainages, the in the seismic lines, from 520 m to approxi- BSR
La Plata (MARTINS et al., 1972; CONTRE- mately 3,500 m in water depth, extrapolat-
RAS et al., 2010), Camaquã and Jacuí rivers ing the eastern limit of the Cone. Its area

(BUENO, 2021), although today there is no of occurrence reaches 35,000 km² (Figure
large-scale drainage flowing there. Z1), with an average thickness of around 35 o 0’0’’S
As in the Foz do Amazonas Fan, the RGC 200-300 m (SAD et al., 1998; OLIVEIRA et
is in the process of gravitational collapse, al., 2010). Sad et al. (1998), assuming these 50 o 0’0’’’W 45 o 0’0’W
where the upper portion slides over the de- volumetric parameters and estimating a Distensional Domain Compressional Domain
tachment surface at the base of the Miocene 1.5% saturation of gas hydrates, conclude 1.000
sequence. The structures formed in the RGC that there is a possible volume of 780 tcf 2.000
3.000
region have their genesis related to the rapid (~22 trillion m³) of methane in the region. It 4.000
TWTs
accumulation of sediments coming from the should be noted that these numbers were 5.000
west-southwest, from the Miocene, associat- based on volumes extrapolated from the 6.000
6.500
ed with mega mass wasting events (MTDs) to seismic data.
3.000
the east-northeast, forming a zone of over- Figure Z1: Bathymetric map highligh-
pressure, substrate for tectonic movement ting the BSR occurrence area in the Rio 4.000
(detachment zone). This detachment surface Grande Cone, in blue. (A) – Seismic line TWTs
caused all the layers above it to move, form- A-A’ showing the detachment surface, in 5.000
ing two tectonic domains with distinct struc- yellow, and the extensional and compres- 6.000
tural characteristics, the extensional domain, sional domains; in the extensional domain,
and the compressional domain (MILLER et al., listric normal faults (black) and flat, syn- 3.500
2015 – Figure Z1). thetic, and antithetic normal faults (green)
In the extensional domain, near the are recognized. The compressional domain
TWTs
western limit of the RGC, normal and listric is characterized by thrust faults (red). The 4.000
blue dashed line corresponds to the BSR.
faults favored the migration of gas at the de- (B) – Red rectangle corresponding to the
pocenter position, and the increase in sedi- detail of the folds. C – Note the thrusting 4.500
ment pressure caused the formation of mud of the NW-SE layers.
diapirs, residual anticlines and fault swarms Source: Miller et al., (2015)

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632 BLUE ECONOMY State of the Art of Gas Hydrate Occurrences 633