The identification of structural diagenesis and the reconstruction of diagenetic paragenesis in fault damage zones is important for understanding fault mechanisms and fluid flow in the subsurface. Based on the examination of core and sample thin section data, we deciphered the diagenetic parasequence and their fault controls for Ordovician carbonates in the northern Tarim intracratonic basin in NW China (Halahatang area). In contrast to the uniform nature of diagenesis observed in country rocks, there is a relatively complicated style of compaction and pressure solution, multiple fracturing, and cementation and dissolution history along the carbonate fault damage zones. The relative paragenetic sequence of the structure related diagenesis suggests three cycles of fracture activities, following varied fracture enlargement and dissolution, and progressively weaker calcite cementation. These processes of structure related diagenesis are constrained to the fault damage zones, and their variation is affected by the fault activities. The results of this study suggest that the carbonate reservoir and productivity could be impacted by the structure related diagenesis locally along the fault damage zones.

Reservoir spaces, such as vesicles, ‘secondary’ amygdales, dissolution caverns and geodes, are widely developed in the Emeishan basaltic lavas in the Zhoudaping section, Leshan, west Sichuan, China. The dissolution characteristics, cementation sequences, hydrothermal activity stages, as well as fluid types, and their effects on the reservoir capacity were investigated for each stage. Macroscopically, the dissolution features present as irregular dissolution zones, which are characterised by a light red colour. Microscopically, in the dissolved zone, the cementation-filling minerals are associated with complex fill sequences, such as quartz/laumontite/chlorite–chlorite/saponite–epidote/celadonite–cryptocrystalline chlorite–laumontite/calcite/quartz. The U–Pb geochronology shows that the age of chlorite fill in amygdales is 235.3 ± 19.6 Ma; the coarse-crystalline quartz inside dissolution caverns/geodes, 124.47 ± 5.63 to 123.84 ± 5.63 Ma; and the siliceous mineral-filled amygdales, 118.34 ± 3.70 to 114.08 ± 3.76 Ma, which correspond to the early Late Triassic and the mid–late Early Cretaceous, respectively. Combined with geochemical characteristics of post-dissolution fill, the amygdales are affected by two stages of hydrothermal activity: chlorite filling of the amygdales corresponds to post-magma hydrothermal fluids during the early Late Triassic, and the siliceous mineral-fill in amygdales corresponds to deep-sourced hydrothermal fluids during the mid–late Early Cretaceous. The geodes/dissolution caverns result from a single stage of hydrothermal activity related to the mid–late Early Cretaceous deep-source low-temperature hydrothermal fluid. The Late Triassic post-magma hydrothermal fluids are generally destructive to pores, and tectonic-related dissolution of deep-sourced hydrothermal fluids has a positive effect on the formation of reservoir spaces, greatly enhancing fluid storage and flow capacities of the volcanic lavas. We recommend the multi-stage hydrothermal dissolution during Late Triassic–Early Cretaceous and faults, fractures and columnar joints be the focus of hydrocarbon exploration.

The Permian Qixia dolostone in the Central Sichuan Basin is a significant hydrocarbon reservoir of hydrothermal origin, linked to the Emeishan Large Igneous Province and structurally controlled by E–W strike–slip faults. However, how this process controls reservoir quality remains poorly understood. To address this, we integrate core observation, thin-section petrography, XRD analysis, thickness mapping, MICP, and μ-CT to characterize the lithofacies and pore structures of the Qixia Formation in the study area. Six lithofacies are recognized, including mudstone (F1), wackestone (F2), packstone (F3), grainstone (F4), rudstone (F5), and dolostone (F6), and F6 is further divided into three subtypes (F6-1, F6-2, F6-3). Dolostones exhibit superior reservoir quality relative to limestones, and among the dolostone, reservoir quality improves progressively from F6-1 to F6-3 with increasing crystal size and dolomite content. Dolostone distribution is spatially tied to E–W strike–slip faults, and its formation age coincides with documented fault activity, implicating these faults as the primary fluid conduits. Quantitative pore structure analyses further indicates that dolomitization enhanced permeability by enlarging pore–throat radii and improving macropore connectivity, with associated dissolution contributing additional secondary porosity.

The stratigraphic evolution of low-latitude carbonate platforms, highly sensitive to sea-level changes, is often poorly constrained due to limited core data and discontinuous depositional records. This study elucidates the evolution of the Meiji Atoll, a representative low-latitude platform in the southern South China Sea (SCS), since the late Miocene, using the reef-penetrating core (Well NK1) from Nansha Island. By integrating facies analysis, sequence stratigraphy, and geochemical proxies, we identified two third-order sequences (SQ1 and SQ2), each comprising transgressive (TST) and highstand (HST) systems tracts. Geochemical data indicate that TSTs were associated with enhanced upwelling and nutrient availability, fostering algal productivity, while HSTs were marked by subaerial exposure. The overall retrogradational stacking pattern of the atoll reflects a dominant control by long-term sea-level rise, superimposed by eustatic fluctuations. Our findings confirm that eustatic sea-level variations were a primary factor controlling the stratigraphic architecture and development of Cenozoic low-latitude carbonate systems.