Calcium‐poor dolomite from the sabkhas of Kuwait

Gunatilaka, Ananda; Saleh, A.; Al-Temeemi, A.; Nassar, Nashaat N.

doi:10.1111/j.1365-3091.1987.tb00589.x

Cited by 22 publications

(8 citation statements)

References 9 publications

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“…The first lacustrine stage was characterised by the development of a perennial to semiperennial brackish lake and the second, and recent, stage corresponds to a shallow saline lake. The sedimentological and chemical features of the recent lake are similar to most modern Ca-Mg-carbonates-bearing lacustrine environments: shallow playas with saline waters and high Mg/Ca ratios and sulphate content (McKenzie 1981;Gunatilaka 1987;Gunatilaka et al 1987;Last 1990;Vasconcelos and McKenzie 1997;Chafetz et al 1999;Wright 1999;van Lith et al 2002). In fact, various studies in the lake (Comín et al 1990;Queralt et al 1997;Rodó et al 2002;Mayayo et al 2003;Corzo et al 2005) reveal that different carbonates are currently forming, even though, due to the scarcity of works documenting the genesis of these minerals in recent environments, the authigenesis of the CaMg carbonates (dolomite and magnesite) is of special interest.…”

Section: Introductionmentioning

confidence: 91%

Stable isotope characterisation of co-existing carbonates from the Holocene Gallocanta lake (NE Spain): palaeolimnological implications

Luzón

Mayayo

Pérez

2008

Int J Earth Sci (Geol Rundsch)

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The sedimentary succession of Gallocanta lake, a closed saline lake located in the Iberian Range (NE Spain), documents two successive lacustrine stages: (1) brackish lake stage and (2) shallow saline lake stage. The saline stage corresponds to the present-day situation in which the lake water properties are mainly controlled by a strongly negative annual water balance. The carbonates of the brackish lake stage have relatively constant d 18 O values, however, they are rather high (d 18 O Do = 2.4% and d 18 O Cc = 4.5% mean values) suggesting a hydrologically closed lake with a long residence time of the waters. d 18 O values of carbonates from the saline stage vary greatly, and are lighter than in the previous stage (d 18 O Do = 0.5%, d 18 O Cc = -0.7%, d 18 O Mgs = -2.3% mean values).These carbonates also precipitated in a hydrologically closed lake, but in equilibrium with a lake water of more variable isotopic composition. The d 13 C values for carbonates of both stages reflect a mixing of different pools of carbon, but during saline stage d 13 C values have been more controlled by the equilibrium of the lake waters with atmospheric CO 2 . During the current stage, calcite and dolomite precipitate in Gallocanta lake mainly during spring and summer, although dolomite precipitation is more favoured towards the summer. Magnesite precipitates at the beginning of autumn, when the first rainfall re-dissolves the saline surface crust, producing saline waters with a high Mg 2+ content. The isotopic composition of lake waters sampled in 2005 are far higher than those calculated from the carbonates. It is considered that this could be due to two factors: either because there have not been many extremely dry years (like the year 2005) during the development of the lake, or because the physical and chemical characteristics of the lake waters in such conditions are not appropriate for the development of these minerals.

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Section: Introductionmentioning

confidence: 91%

Stable isotope characterisation of co-existing carbonates from the Holocene Gallocanta lake (NE Spain): palaeolimnological implications

Luzón

Mayayo

Pérez

2008

Int J Earth Sci (Geol Rundsch)

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“…Holocene dolomites are generally characterized by submicrometre to decimicrometre crystal sizes, poor cation ordering and high Ca/Mg ratios (e.g. Illing et at., 1965;Shinn et al, 1965;Gebelein et af., 1980;McKenzie, 1981 ;Carballo et al, 1987;Gunatilaka et al, 1987;Mazzullo et al, 1987; and many others). Although it is recognized that poorly ordered and non-J .…”

Section: Introductionmentioning

confidence: 97%

Early diagenetic recrystallization of Holocene (<3000 years old) peritidal dolomites, Ambergris Cay, Belize

1992

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Three peritidal carbonate crusts and associated intercrust sediments (total thickness of ∼30cm; aged <3000 years BP) on Ambergris Cay, Belize, contain 32–100% calcian dolomite (δx=72·5% dolomite) ranging in composition from 40 to 46 mol% MgCO3 (δx=43·3). Dolomite replaced high Mg calcite foraminiferal muds penecontemporaneously with sedimentation, forming partially dolomitized sediments and lithified crusts. Dolomitization probably occurred in normal to moderately evaporated seawater and is apparently continuing at the present. Detailed scanning electron microscope analysis shows a linear increase in mean dolomite crystal size with depth; 0·4 μm near the top of the section to 1·0 μm near the base of the dolomitized section. This size increase is not accompanied by any significant decrease in porosity. Crystal size distributions appear to be log‐normal and become increasingly broad and flat with depth. Rietveld X‐ray pattern‐fitting structure refinements indicate increasing Ca and Mg concentrations on their respective sites (cation ordering) as a function of increasing depth. Most of the ordering occurs within the first 15 cm of the surface. Stoichiometry does not increase with depth indicating no relationship between the Ca/Mg ratio and cation ordering. Strong geochemical trends were observed down‐section in the dolomite, including: (1) increasing Mn content (44 to 274 ppm), and (2) decreasing δ13C values (−0·9 to −5·5‰ PDB). Oxygen isotope values range from δ18O = 1·3‰ PDB in the upper part of the section to 2·6‰ PDB in the lower part of the section and are interpreted to represent two distinct groups of values rather than a continuous trend. Down‐section dolomite crystal size increase and shapes of crystal size distributions are consistent with recrystallization via a surface energy‐driven dissolution‐reprecipitation process (Ostwald ripening). The observed trends in carbon isotopes and Mn content probably result from geochemical re‐equilibration during recrystallization and reflect reducing conditions and an isotopically light, organically derived, carbon source. Oxygen isotope compositions probably reflect relict original dolomite values and are a result of decreasing evaporation due to rising sea level.

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“…Such conditions are favorable for the dolomitization of the aragonitic mud and also continuation of dolomite crystallization on the dolomitized aragonite nuclei. A similar mechanism was suggested by Gunatilaka et al (1984) for the occurrence of recent subtidal dolomites in a hypersaline lagoon in Kuwait.…”

Section: Genesis Of the Host Biodolomicritesmentioning

confidence: 50%

Occurrence of diagenetic pseudobreccias within the paleokarst zone of the upper Dammam Formation in Kuwait, Arabian Gulf

Khalaf

2009

Arab J Geosci

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A paleokarstic zone capping the Middle Eocene dolomitic Dammam Formation delineates a regional disconformity with the overlying Mio-Pleistocene fluvial deposits in Kuwait. This formation outcrops in a quarry located in the southeast of Kuwait and occurs in the subsurface of Umm Ghudair water field, west Kuwait. Karstification has affected the upper member of the Dammam Formation, which is formed of extensively chertified, vuggy chalky biodolomicrite. Karstification is manifested by two phases: a dissolution phase that was responsible for the occurrence of surface and near surface karst features and a precipitation phase during which a karst carapace and dolocretic and calcitic pseudobreccias were developed. Petrographic investigations of both the biodolomicrites host rock and the karst lithotypes revealed a complex diagenetic history that encompasses the following diagenetic events, arranged in a chronological order: (a) replacive dolomitization, (b) precipitative dolomitization, (c) precipitative silica, (d) replacive silica, (e) karstification, (f) development of karst carapace [calcretization and calcitization (development of calcitic psuedobreccia)], (g) dolocretization (development of dolocretic psuedobreccia), (h) mild karstification, (i) calcite precipitation, and (j) silica precipitation. The development of the karst carapace at the unconformity surface between the Eocene Dammam Formation dolomicrites and the overlying Mio-Pleistocene Kuwait Group clastics has played a significant role in the hydrological characteristics of Kuwait usable groundwater resources. It is recommended that the occurrence of similar diagenetic processes within the Arabian carbonate shelf deposits be investigated.

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Calcium‐poor dolomite from the sabkhas of Kuwait

Cited by 22 publications

References 9 publications

Stable isotope characterisation of co-existing carbonates from the Holocene Gallocanta lake (NE Spain): palaeolimnological implications

Stable isotope characterisation of co-existing carbonates from the Holocene Gallocanta lake (NE Spain): palaeolimnological implications

Early diagenetic recrystallization of Holocene (<3000 years old) peritidal dolomites, Ambergris Cay, Belize

Occurrence of diagenetic pseudobreccias within the paleokarst zone of the upper Dammam Formation in Kuwait, Arabian Gulf

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