Fig.1 Overview of the Emeishan Large Igneous Province (ELIP) a—Geographic distribution of the ELIP outcrop area (depicted in brown shades), its zonation delineated by black dashed circles, and the specific study area highlighted within a light yellow rectangle. b—Detailed depiction of the study area within the Sichuan Basin, with well sites denoted by yellow dots. Yellow dots represent well sites.

Fig.2 Fundamentals of mafic volcaniclastic rock classification: a—Compositional classification of volcaniclasts; b—Size-based classification of volcaniclasts; c—Size-based classification of mafic volcaniclastic rocks(adapted from [25]); d—Genetic terminology for mafic volcaniclastic rocks.

Fig.3 (a) Well log of the sections of well-developed volcanic reservoir; (b-f) Image logging with corresponding depth

Fig.4 Observations of ignimbrites YT1 ignimbrites: a,b—Display darker green fiammes; c,d—Microscopic view shows eutaxitic texture. TF1 ignimbrites: e—Contain recrystallized limestone blocks mixed with fiammes and tephra matrix; f—Microscopic view reveals plagioclase crystal shards sticking together due to welding magma shards. Cement generations in dissolved vugs: g—Progress from albite to bitumen to calcite. TF2 ignimbrites: h—Observed. Microscopic view of TF2 ignimbrites: i,j—Depicts dissolving molds of juvenile clasts (blue colored), with limestone lithic blocks and micrite matrix showing no interference. TF102 ignimbrites: k—Observed. Development of significant vugs filled with bitumen and calcite in TF102 ignimbrites: l—A huge dissolved vug developed in the ignimbrite in TF102, filling with earlier-stage bitumen and later-stage calcite crystals.

Fig.5 Plate of autoclastic breccia a,b—Autoclastic breccia in TF8. Note the distinctive features of autoclastic breccia compared to ignimbrites: the clastic-supporting framework with jigsaw-fitted boundaries, unwelded texture, and absence of epiclastic blocks. c,d—Microscopic views of autoclastic breccia in TF8 corresponding to (a) and (b), respectively. Please observe the location where pore spaces are developed within the clasts, while the initial inter-clastic spaces are completely filled. e,f—Autoclastic breccia in TF102.

Fig.6 Plate of spattering agglomerates a,b—Spattering agglomerates in TF1, featuring white lithic blocks composed of recrystallized limestones. b—Section of a fusiform bomb. c,d—Microscopic views of spattering agglomerates, showing inter-clast spaces filled with albite, bitumen, and calcite.

Fig.7 Schematic diagram of the eruptive genesis mechanisms of three types of lithological series a—Eruption by on-land gas overflowing generates volcanic pyroclastic flows, leading to the formation of welded tuff. The white circles in the magma chamber represent overflowing volatile components, the light gray blocks are country rock (limestone) fragments, and the dark blocks are early volcanic materials. The fine dots represent ash clouds accompanying the eruption of volcanic pyroclastic flows. b—Eruption through fissures results in the overflow of molten lava and its fracturing process. If the magma core eventually stops moving, the core often forms dense basalt, transitioning to fissure-rich basalt at the front, and eventually to angular breccia. c—During the magma upwelling process, if the amount of overflowing volatile components is low and magma fragmentation is not significant, the erupted magma clasts can be very large, often appearing as volcanic bombs. These volcanic bombs are ejected with low energy along the crater at short distances, forming proximal deposits and creating layers of volcanic bomb accumulations.

Fig.8 Major pore spaces in the Chengdu-Jianyang volcanics a,b—Intraclastic dissolving pores. c,d—Intercrystalline pores in altered chlorites.