Micritization and development of microporosity in miocene platform carbonates from NE Iberia: diagenetic processes and controls

Microporous limestones formed by micritization are widespread in Mesozoic and Cenozoic carbonate successions and constitute major hydrocarbon reservoirs worldwide. Despite the strong control of microporosity on petrophysical behavior, uncertainties surrounding its origin and evolution hinder accurate diagenetic modeling and subsurface heterogeneity interpretations. This study characterizes micritized carbonates from the Neogene Penedès Basin (NE Spain), which represents the onshore analogue of the offshore hydrocarbon-bearing Amposta Limestone. Integrating field mapping, petrographic analyses, and stable isotope and trace element geochemistry, we link measured porosity (30–40%) and permeability (< 200 mD) directly to carbonate microfabrics. Four distinct stages of micritization are identified: (1) a coalescent micritic matrix with low porosity (8%) and permeability (< 0.5 mD); (2) a slightly micritized mesh-like matrix exhibiting higher porosity (~ 30%) and permeability (~ 180 mD); (3) a moderately micritized serrate matrix with no significant further increase in petrophysical values (32–34%; 20–181 mD); and (4) highly micritized textures with punctic crystal contacts exhibiting the highest porosity values (~ 40%) but reduced permeability (~ 50 mD). Micropore-throat diameters are predominantly <0.44 µm, bounded by low-Mg calcite crystals between 1 and 4 µm. Isotopic compositions δ 18 O and δ 13 C cluster along the meteoric calcite line (δ 18 O~ −5‰). Furthermore, samples displaying punctic microfabrics exhibit the strongest trace element depletion, reflecting advanced micritization. The results suggest that early, most probably during Serravallian times, and sustained meteoric water influx was the primary driver of diagenetic alteration, leaching, and microporosity development in the studied basin.