Tracking the Origin and Evolution of Diagenetic Fluids of Upper Jurassic Carbonate Rocks in the Zagros Thrust Fold Belt, NE-Iraq

Abstract

Utilizing sophisticated tools in carbonate rocks is crucial to interpretating the origin and evolution of diagenetic fluids from the Upper Jurassic carbonate rocks along the Zagros thrust-fold Belt. The origin and evolution of the paleofluids utilizing in-situ strontium isotope ratios by high resolution laser ablation ICP-MS, integrated with stable isotopes, petrography and fieldwork are constrained. Due to the lack of information on the origin of the chemistry of the fluids, the cements that filled the Jurassic carbonate rocks were analysed from the fractures and pores. This allowed us to trace the origin of fluids along a diagenetic sequence, which is defined at the beginning from the sediment deposition (pristine facies). Based on petrography and geochemistry (oxygen-, carbon- and strontium-isotope compositions) two major diagenetic stages involving the fluids were identified. The initial stage, characterized by negative δ13CVPDB values (reaching −10.67‰), involved evaporated seawater deposited with the sediments, mixed with the input of freshwater. The second stage involved a mixture of meteoric water and hot fluids that precipitated as late diagenetic cements. The late diagenetic cements have higher depleted O–C isotope compositions compared to seawater. The diagenetic cements display a positive covariance and were associated with extra- δ13CVPDB and δ18OVPDB values (−12.87‰ to −0.82‰ for δ18OVPDB and −11.66‰ to −1.40‰ for δ13CVPDB respectively). The distinction between seawater and the secondary fluids is also evident in the 87Sr/86Sr of the host limestone versus cements. The limestones have 87Sr/86Sr up to 0.72859, indicative of riverine input, while the cements have 87Sr/86Sr of (0.70772), indicative of hot fluid circulation interacting with meteoric water during late diagenesis.

Paleoenvironmental Evaluation Using an Integrated Microfacies Evidence and Triangle Model Diagram: A Case Study from Khurmala Formation, Northeastern Iraq

“…This analysis is based on the diversity in bio-contents, fluctuating in microfacies and lithology (cf. [17][18][19]); from the fore-reef environment, the flooding encrustation of calcareous red algae is absent, which represents the major components of organic reef that occasionally occurs in this study, and this probably suggests a sub-environment close to the main body of the reefal crest in the back-reef area. Based on the percentage of each group (I, II, III) (See Figures 7 and 9; Table 1) from the coralligenous-algal wackestone microfacies, the upper part characterizes a lagoonal environment equivalent to standard microfacies type (SMF) 8, which reflects a tropical lagoon surrounded by coral reefs (FZ8).…”

“…This interpretation gives the impression that the coral reef body represents a frame reef sensu Riding [16] with skeletons in contact. Moreover, a rimmed carbonate platform with a barrier reef and a steep slope surrounding the Intisar embayment was interpreted [17,18] as frame reef sensu Riding [16] with significant topographic relief. Fieldwork integrated with microfacies analysis enabled the recognition of three microfacies from the Tertiary carbonate rocks in the Khurmala Formation.…”

X-ray Computed Tomography (CT) to Scan the Structure and Characterize the Mud Cake Incorporated with Various Magnetic NPs Concentration: An Application to Evaluate the Wellbore Stability and Formation Damage

“…( Figure 3 c). The uniform thin layer, evidenced by CTN as compacted mud cake structure, probably formed by precipitation or exchanging elemental/mineral composition during fluid-particle interactions [ 30 , 31 ]. Consequently, the dense and compacted mud cake probably prevented the formation damage, driving away drilling fluid from the formation.…”

Petroleum System Analysis and Burial History of Middle Permian Source Rock in Turpan–Hami Basin, NW China

“…The generation of heavy oil has been investigated extensively. It is related to the uplift and exposure of the reservoir subject to meteoric weathering and leaching [81][82][83]. By far, the discovered heavy oil reservoirs mostly occur in the Wutonggou Formation and Karamay Formation, and the oil source correlation shows that such heavy oil is sourced from the Taodonggou Group source rocks in the Taibei Sag [84,85].…”