The hydrochemical evolution of alkaline volcanic lakes: a model to understand the South Atlantic Pre-salt mineral assemblages

Mercedes‐Martín, Ramon; Ayora, Carlos; Tritlla, J.; Sánchez‐Román, Mónica

doi:10.1016/j.earscirev.2019.102938

Cited by 40 publications

(11 citation statements)

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“…enabling natural alkaline, saline waterbodies to chemically behave, at least in part, as anthropogenic spherulite-producing sites (Mercedes-Martín et al, 2019).…”

Section: Comparing Natural Alkaline Saline Lakes With Anthropogenic mentioning

confidence: 99%

What Causes Carbonates to Form “Shrubby” Morphologies? An Anthropocene Limestone Case Study

et al. 2019

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“…enabling natural alkaline, saline waterbodies to chemically behave, at least in part, as anthropogenic spherulite-producing sites (Mercedes-Martín et al, 2019).…”

Section: Comparing Natural Alkaline Saline Lakes With Anthropogenic mentioning

confidence: 99%

What Causes Carbonates to Form “Shrubby” Morphologies? An Anthropocene Limestone Case Study

et al. 2019

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“…The balance between the solutes coming from run‐off versus groundwater will also be affected by changes in evaporation–precipitation and climate (e.g. Mercedes‐Martín et al ., 2019).…”

Section: Introductionmentioning

confidence: 99%

The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

Wright

2020

Sedimentology

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During the Aptian (Cretaceous), in what is now the South Atlantic, the largest chemogenic (abiotic) carbonate factory so far identified in the Phanerozoic geological record developed as a vast hyper‐alkaline lake system. This covered at least 330 000 km2, producing carbonates, locally over 500 m thick, in what are now the offshore Santos and Campos basins (Brazil), and Kwanza Basin (Angola). Current evidence supports the view that almost all of this carbonate was chemogenic in origin, precipitated from hyper‐alkaline, shallow lake waters, probably by evaporation. This unit, best documented from offshore Brazil and known as the Barra Velha Formation (Santos Basin) and the Macabu Formation (Campos Basin), consists of just two basic carbonate components, millimetre to centimetre sized crystal shrubs and spherulites. These are commonly in situ but can also be reworked into a range of detrital facies. Demonstrable microbialites are generally rare. These carbonates are associated with Mg silicates (as clays) which had a profound influence not only on the textural development of the in situ carbonates, but also on their diagenesis. The dissolution of the clays produced much of the porosity in these limestones, which are the hosts for multi‐billion barrel oil fields. The source of the carbonate was most likely from metasomatic alteration of mafic rocks, such as continental flood basalts related to Atlantic opening, with some contribution from much older continental basement. Clear evidence that serpentinization of possible exhumed mantle is lacking but mantle CO2 is likely to have been a critical factor in determining the composition of the fluids from which the carbonates formed and the high alkalinities of the lake waters.

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“…On the other hand, the identification of mineralogical sequences (Figures 5 and 6) shows a greater dependence on the hydrochemical conditions of the lake, since the formation of magnesian clays is mainly controlled by alkalinity (pH), salinity and p(CO 2 ) [61]. The stability relationships of hydrated Mg-silicates in relation to solute activities indicates that the equilibria between sepiolite, stevensite and kerolite depend on salinity (Na + concentration), pH and Mg 2+ concentration [18,51]. High salinity favors the formation of stevensite while sepiolite and kerolite form under lower salinity conditions, where sepiolite formation is favored when the Si 4+ /Mg 2+ ratio is higher.…”

Section: Discussionmentioning

confidence: 99%

“…The causes, however, are still controversial. Some hypotheses have been invoked to explain a persistent high pH in a lake system: (i) input of mantle CO 2 into the lake waters [27,28,64], or (ii) reduced infiltration rates of lake waters into ground water aquifers [18]. In addition, it is suggested that the sources of Ca 2+ , Mg 2+ and SiO 2 , among others would come from the leaching and chemical weathering of basalts by phreatic and hydrothermal waters [65], and felsic rocks in a very extensive, shallow and endorheic lake [21].…”

Section: Discussionmentioning

confidence: 99%

“…Papers concerning the influence of diagenetic and hydrothermal processes on reservoir quality and lithofacies classification, also recognized the presence of magnesian clays, identifying kerolite and magnesian smectite as the most common clay minerals in their study areas [15][16][17]. Recent studies such as that reported by Mercedes-Martín [18] have proposed a thermodynamic conceptual model to evaluate the role of the hydrological budgets in clay-silica-carbonate alkaline lacustrine precipitation, and its application to the Aptian pre-salt case study.…”

Section: Introductionmentioning

confidence: 99%

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Paleoenvironmental Implications of Authigenic Magnesian Clay Formation Sequences in the Barra Velha Formation (Santos Basin, Brazil)

et al. 2022

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The characterization of Mg-clays in rock samples (well P1) from the Barra Velha Formation (Early Cretaceous) allowed the establishment of mineral assemblages on the basis of their kerolite and Mg-smectite (stevensite and saponite) content. Kerolite-rich assemblages (A and B) rarely contain saponite. Assemblage B is composed of kerolite-stevensite mixed layers, while assemblage A consists of more than 95% kerolite. Mg-smectite-rich assemblages (C and CB) are made up of both Mg-smectites. The predominance of stevensite in the lower interval of the stratigraphic succession suggests evaporative conditions, higher salinity and pH, which would favor its authigenesis by neoformation. In the upper portion, the occurrence of thick kerolite-rich intervals suggests regular water inputs, contributing with a decreasing in salinity and pH, favoring the neoformation of kerolite and later kerolite-stevensite mixed layering. The saponite would be the result of the transformation from Al-smectite into Mg-smectite in a Mg2+ rich medium. The results indicate that lake hydrochemical processes would have allowed the establishment of a basic depositional sequence, from base to top, as follows: (i) initial lake expansion stage marked by the occurrence of saponite, (ii) later kerolite neoformation, (iii) formation of kerolite-stevensite mixed layer with increasing salinity, and (iv) neoformation of stevensite, marking a final stage of maximum salinity (evaporation) and alkalinity of the lake.

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The hydrochemical evolution of alkaline volcanic lakes: a model to understand the South Atlantic Pre-salt mineral assemblages

Cited by 40 publications

References 91 publications

What Causes Carbonates to Form “Shrubby” Morphologies? An Anthropocene Limestone Case Study

What Causes Carbonates to Form “Shrubby” Morphologies? An Anthropocene Limestone Case Study

The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

Paleoenvironmental Implications of Authigenic Magnesian Clay Formation Sequences in the Barra Velha Formation (Santos Basin, Brazil)

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The hydrochemical evolution of alkaline volcanic lakes: a model to understand the South Atlantic Pre-salt mineral assemblages

Cited by 40 publications

References 91 publications

What Causes Carbonates to Form “Shrubby” Morphologies? An Anthropocene Limestone Case Study

What Causes Carbonates to Form “Shrubby” Morphologies? An Anthropocene Limestone Case Study

The mantle, CO2and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

Paleoenvironmental Implications of Authigenic Magnesian Clay Formation Sequences in the Barra Velha Formation (Santos Basin, Brazil)

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The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born