Integration of stable isotopes, radiometric dating and microthermometry of saddle dolomite and host dolostones (Cretaceous carbonates, Kurdistan, Iraq): New insights into hydrothermal dolomitization

Mansurbeg, Howri; Alsuwaidi, Mohammad; Salih, Namam; Shahrokhi, Salahadin; Morad, S.

doi:10.1016/j.marpetgeo.2021.104989

Cited by 20 publications

(14 citation statements)

References 61 publications

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“…Constraining the depths at which the flux of hot dolomitizing basinal brines occurred is difficult without radiometric dating of dolomite [54,55]. However, the cross-cutting relationship between the stylolites and dolomite cement suggests that dolomitization took place at shallow depths [36].…”

Section: Discussionmentioning

confidence: 99%

Origin of Drusy Dolomite Cement in Permo-Triassic Dolostones, Northern United Arab Emirates

Mansurbeg

Alsuwaidi

Dong

et al. 2021

Water

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While the characteristics and origin of drusy calcite cement in carbonate deposits is well constrained in the literature, little attention is paid to drusy dolomite cement. Petrographic observations, stable isotopes, and fluid-inclusion microthermometry suggest that drusy dolomite cement in Permo-Triassic conglomerate/breccia dolostone beds in northern United Arab Emirates has precipitated as cement and not by dolomitization of drusy calcite cement. The low δ18OVPDB (−9.4‰ to −6.2‰) and high homogenization temperatures of fluid inclusions in drusy dolomite (Th = 73–233 °C) suggest that dolomitization was caused by hot basinal brines (salinity = 23.4 wt% NaCl eq.). The δ13CVPDB values (+0.18‰ to +1.6‰) and 87Sr/86Sr ratio (0.708106 to 0.708147) indicate that carbon and strontium were derived from the host marine Permo-Triassic carbonates. Following this dolomitization event, blocky calcite (Th = 148 °C; salinity = 20.8 wt% NaCl eq.) precipitated from the hot basinal brines. Unravelling the origin of drusy dolomite cement has important implications for accurate construction of paragenetic sequences in carbonate rocks and decipher the origin and chemistry of diagenetic waters in sedimentary basins.

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Section: Discussionmentioning

confidence: 99%

Origin of Drusy Dolomite Cement in Permo-Triassic Dolostones, Northern United Arab Emirates

Mansurbeg

Alsuwaidi

Dong

et al. 2021

Water

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“…We found only three carbonate phases that may be considered "late-stage" or that at the very least indicate higher precipitation temperatures. The first corresponds to saddle dolomite, characteristically formed under high temperature conditions under burial or hydrothermal conditions [49,[139][140][141][142][143] (Figure 16A,B). The second is dawsonite (NaAl(OH) 2 CO 3 ) (Figure 16C), originally identified in the Pre-salt by Farias et al [15] and by Lima and De Ros [16].…”

Section: Mesodiagenetic/hydrothermal Interactionsmentioning

confidence: 99%

“…dolomite, characteristically formed under high temperature conditions under burial or hydrothermal conditions [49,[139][140][141][142][143] (Figure 16A,B). The second is dawsonite (NaAl(OH)2CO3) (Figure 16C), originally identified in the Pre-salt by Farias et al [15] and by Lima and De Ros [16].…”

Section: Mesodiagenetic/hydrothermal Interactionsmentioning

confidence: 99%

“…An alternative origin for saddle dolomite is from basinal brines under burial ( [146] and references therein [113,[149][150][151][152]). These fluids are highly saline and concentrated waters with varied origins, such as modified seawater (e.g., [102,143,153]), post-evaporite brines ( [146] and references therein), deeply buried mudstones [143], or alteration of mafic/ultramafic rocks [143].…”

Section: Mesodiagenetic/hydrothermal Interactionsmentioning

confidence: 99%

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Interactions between Clays and Carbonates in the Aptian Pre-Salt Reservoirs of Santos Basin, Eastern Brazilian Margin

Schrank,

Dos Santos,

Altenhofen

et al. 2024

Minerals

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The giant Pre-salt reservoirs represent most of the oil production in Brazil. The main Aptian sag reservoirs were deposited in a unique and highly complex hyper-alkaline lacustrine setting. These deposits are essentially constituted by fascicular and spherulitic calcite precipitated in a magnesian clay matrix (stevensite, kerolite, and saponite/hectorite). Although vital for understanding the origin and main reservoir quality control, the genesis and interactions of clays and carbonates are still poorly constrained. The detailed petrographic description was focused on 812 thin sections from five wells drilled in the Santos Basin Aptian Barra Velha Formation, combined with cathodoluminescence, UV epifluorescence, and X-ray diffraction analyses. The main syngenetic processes were the deposition of finely laminated peloidal and ooidal Mg-clays, the formation of fascicular calcite crusts on the sediment–water interface, and the redeposition of these materials as intraclasts. Abundant clay peloids engulfed in syngenetic shrubs indicate that calcite and clay precipitation was concomitant, though with highly variable rates. Eodiagenetic phases include matrix-replacive and -displacive spherulites and fascicular shrubs; matrix-replacive blocky calcite and dolomite; lamellar carbonates filling matrix shrinkage pores; and microcrystalline calcite, dolomite, and silica replacing the Mg-clay matrix. The preferential dolomitization and calcitization of peloidal layers were most likely due to their higher permeability and larger specific surface. Matrix-replacive saddle dolomite, macrocrystalline calcite, and dawsonite are interpreted as mesodiagenetic or hydrothermal phases after significant matrix dissolution. Unraveling the processes of the formation and alteration of the carbonates and clays and their interactions in the Pre-salt deposits is essential for constraining the depositional and diagenetic conditions in their unique environments and their diagenetic overprinting and for decreasing the exploration risks and increasing the production of those extraordinary reservoirs.

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“…However, the δ 13 C values for some MCD and SD are significantly positive, essentially above 2.0-2.5‰ (Figure 8; Supplementary Appendix S4). This is because high-temperature hydrothermal fluids could cause low oxygen contents in seawater, leading to increased carbon burial rates and consequently high δ 13 C values (Ahmad et al, 2021;Mansurbeg et al, 2021).…”

Section: Carbon and Oxygen Isotopic Analysesmentioning

confidence: 99%

Multiphase dolomitization mechanisms of the Cambrian upper Changping Formation, North China Platform, China

Ying

Zhao²,

Gao³

2023

Front. Earth Sci.

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The Cambrian dolomite reservoirs of the North China Platform offer good exploration prospects, but their occurrence and the impacts of dolomitization on reservoir quality are not yet clearly understood. The study herein assesses outcrop samples in the Cambrian upper Changping Formation, Dingjiatan area, and highlights the important role of multiphase dolomitization in the formation of paleo-reservoirs of acceptable porosity, where oil pools and fields may be discovered. A combination of petrology, fluid inclusion microthermometry, isotopes, and trace element compositions has been used to explain multiphase dolomitization mechanisms and their impacts on dolomite reservoirs. Five types of dolomites are identified through outcrop observation, thin section identification via transmitted light, and cathodoluminescence. The following geochemical analyses reveal various dolomitization mechanisms. In the (pene) contemporaneous stage, microbial dolomite is commonly related to microbial metabolic activities with significant carbon isotopic depletion compared to the Cambrian seawater values. With the influence of microbial dolomitization, dolomicrite corresponds to the sabkha dolomitization mode in a low-salinity seawater environment and early-stage dolomitization. The structureless dolomite (ssD) in the early highstand systems tract (EHST), characterized by elevated 87Sr/88Sr ratios and low oxygen isotopic values, forms from stratum brine water in the shallow-middle burial stage rather than in the (pene) contemporaneous stage. In contrast, ssD in the late highstand systems tract (LHST) undergoes (pene) contemporaneous dolomitization at salinities between 6% and 28% before later pore water transformation, with the participation of atmospheric freshwater through faults and unconformities exhibiting the lowest inclusion temperature and salinity values. The medium to coarse crystalline dolomite (MCD) in the LHST and the saddle dolomite (SD) in the EHST with low REE values are atypical hydrothermal dolomites caused by a combined superposition of middle-deep burial hydrothermal fluids at temperatures >150°C and stratigraphic brines. The MCD is also influenced by terrigenous water characterized by relatively low Eu anomaly values. Finally, the mechanisms of porosity increase are investigated, and it is concluded that the pore increase caused by the (pene) contemporaneous reflux interaction and the later pore retention both lead to better ssD reservoirs in the LHST than in the EHST.

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Integration of stable isotopes, radiometric dating and microthermometry of saddle dolomite and host dolostones (Cretaceous carbonates, Kurdistan, Iraq): New insights into hydrothermal dolomitization

Cited by 20 publications

References 61 publications

Origin of Drusy Dolomite Cement in Permo-Triassic Dolostones, Northern United Arab Emirates

Origin of Drusy Dolomite Cement in Permo-Triassic Dolostones, Northern United Arab Emirates

Interactions between Clays and Carbonates in the Aptian Pre-Salt Reservoirs of Santos Basin, Eastern Brazilian Margin

Multiphase dolomitization mechanisms of the Cambrian upper Changping Formation, North China Platform, China

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