Dedolomitization and other early diagenetic processes in Miocene lacustrine deposits, Ebro Basin (Spain)

摘要: Abstract A variety of meteoric diagenetic features reveal the development a syngenetic karst on lacustrine deposits Ebro Basin. Diagenetic processes that operated laminated and stromatolitic carbonates include following. (1) first syndepositional stage with such as dolomitization, desiccation related breccia formation sulphate precipitation, either lenticular gypsum crystals or nodules. This took place under progressive evaporation due to lake level fall, when previous carbonate became exposed supra-littoral fringe surrounding saline mud flats adjacent depositional environments. (2) second early in which dissolution collapse brecciation, dedolomitization, calcite spar cementation silicification occurred result water input caused rise level. Light isotopic compositions (δ 13 C δ 18 O) calcites, versus heavier primary limestones, confirm influence. The is best developed at boundary between two allostratigraphic units coincided one extensive stages deposition end Early Miocene. facies an area was low-relief barrier separated sites during low levels. indicates controlled by topographic changes within basin record shift from arid wetter climatic conditions, suggested overlying freshwater deposits. presence those described central Basin affecting relevant because they can be used indicators subaerial exposure periods terrestrial environments also important palaeogeographic palaeoclimatic events basinal extent.