Petroleum Science >2016,??Issue 3:??434-449 DOI: https://doi.org/10.1007/s12182-016-0114-5
Origin of dolomite in the Middle Ordovician peritidal platformcarbonates in the northern Ordos Basin, western China Open?Access
文章信息
1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Sichuan, China 2 School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, Sichuan, China;1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Sichuan, China 2 School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, Sichuan, China;3 Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China;4 College of Energy, Chengdu University of Technology, Chengdu 610059, Sichuan, China;5 Department of Geology, University of Regina, Regina, SK S4S 0A2, Canada
文章摘要
submember of the Majiagou Formation in the northern
Ordos Basin are partially to completely dolomitized. Two
types of replacive dolomite are distinguished: (1) type 1
dolomite, which is primarily characterized by microcrystalline
(\30 lm), euhedral to subhedral dolomite crystals,
and is generally laminated and associated with gypsumbearing
microcrystalline dolomite, and (2) type 2 dolomite,
which is composed primarily of finely crystalline
(30–100 lm), regular crystal plane, euhedral to subhedral
dolomite. The type 2 dolomite crystals are truncated by
stylolites, indicating that the type 2 dolomite most likely
predated or developed simultaneously with the formation
of the stylolites. Stratigraphic, petrographic, and geochemical
data indicate that the type 1 dolomite formed
from near-surface, low-temperature, and slightly evaporated
seawater and that the dolomitizing fluids may have
been driven by density differences and elevation-related
hydraulic head. The absence of massive depositional
evaporites in the dolomitized intervals indicates that
dolomitization was driven by the reflux of slightly evaporated
seawater. The d18O values (-7.5 to -6.1 %) of type
1 dolomite are slightly lower than those of seawaterderived
dolomite, suggesting that the dolomite may be
related to the recrystallization of dolomite at higher temperatures
during burial. The type 2 dolomite has lower
d18O values (-8.5 to -6.7 %) and Sr2? concentration and
slightly higher Na?, Fe2?, and Mn2? concentrations and
87Sr/86Sr ratios (0.709188–0.709485) than type 1 dolomite,
suggesting that the type 2 dolomite precipitated from
modified seawater and dolomitic fluids in pore water and
that it developed at slightly higher temperatures as a result
of shallow burial.
關(guān)鍵詞
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Carbonate platform Dolomitization Dolomite Middle Ordovician Ma5 5 submember Dolomitizing fluids