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The region where the Martian carbonate material was discovered is located
within a system of small canyons known as Nili Fossae, at the northern hemisphere
of Mars. The carbonates were discovered by NASA's Mars Reconnaissance Orbiter
robotic spacecraft, in December 2008.
Plumes of CH 4 above that location was also discovered. The diagenetic alteration
of the subsurface rocks was probably due to hydrothermal activity which might have
existed in that region.
So I make specific comparisons among such diagenetic processes on Earth and
on Mars to give a contribution - via the use of biased techniques and gained
experience - for future exploration and understanding of that planet. By repeatedly
studying geophysical-chemical properties of carbonate diagenetic deposits, it is
possible to characterize their minerals each time better and, with that, to better
determine the geological evolution of deposits of sediments, gradually altered by
physicochemical-biological processes after their deposition (diagenesis), as, for
example, the carbonates - the subject of this work (Leinz and Amaral 2003 ;Teixeira
et al. 2008 ).
These practical carbonate sedimentology analysis and comparisons can be
applied to more focused robotic and manned in situ search for biogeochemical
signatures at past Earth and present Mars. The study of the arenites of the carbonate
diagenetic deposits present at the Bauru Group shows evidence of sedimentary
homogeneity at different depths of soundings and at different areas. The detritic
properties of these arenites are constituted essentially by quartz and feldspars and, at
smaller quantity, by lithic fragments and accessory minerals with great intergranular
porosity. This is a good indicator of shallow eodiagenetic processes with low
mechanical pressure, indicating past presence of subsurface waters in that location.
The principal diagenetic processes observed were dissolution of heavy minerals,
lithic fragments, and aluminosilicates and cementing by microcrystalline calcite
(Stradioto et al. 2008 ). I observed negative biaxial refringe and formation of clay
minerals as montmorillonite and kaolinite.
Infrared images of Nili Fossae by CRISM-MRO show bedrock containing clays
(principally smectites), exposed olivine, and carbonates at the same stratigraphic
level. Much probably, the olivine was altered by hydrothermal action, possibly
present at that location 3.6 Gyrs ago, transformed into the found carbonates. It
is known that carbonates are formed in neutral or basic waters (pH> 7), which
indicates that dissolution of the minerals was not only in acid environment, showing
a great pH variation of the waters, interesting to the diagenetic evolution of
hydrothermal, volcanic, and sedimentary regions on planet Mars, as this carbonatic
one being studied here on planet Earth (Fig. 8.30 ).
Other minerals found by CRISM-MRO were aluminosmectite, iron/magnesium-
smectite, hydrated silicates, minerals of the kaolinite group, and iron oxides. In
2004, the NASA's robotic rover Opportunity discovered the minerals hematite [iron
(III) oxide (Fe 2 O 3 )] and jarosite [KFe 3C 3 (OH) 6 (SO 4 ) 2 ] in the Martian surface.
Jarosite is formed by the oxidation of iron sulfides in the presence of liquid acid
water, which shows (aside from several evidences, geomorphic and geologic ones by
remote sensing) that Mars much probably had liquid water with relative abundance
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