Contribution to petrology and diagenesis of the hyaloclastites of Macau Formation, Potiguar Basin, RN, Brazil

Abstract

Based on the study of 40 subsurface rock samples from bore holes of the Macau Formation, Potiguar Basin in Brazil, it was possible to set up a petrographic characterization of the rocks and to establish a diagenetic pathway for the unit. The lithologic types investigated here have been c/assified as hyaloc/astites, whose origin is related to the interaction of mafic lava flows with sea water. The mixture of terrigenous and bioclastic fragments suggests a shallow water depositional environment. Based on thin section descriptions, X-ray diffractometry, infrared spectrometry, REM determination and fluid inclusions studies, six diagenetic events were recognized, and they probably affected the rocks in they following chronological sequence: pyritization, palagonitization, authigenic c/ay formation, authigenic zeolite formation, carbonate cementation and carbonate dissolution. The last diagenetic event ls responsible for they secondary porosity (up to 20%) observed in some samples. This porosity was estimated by point counting in thin sections and belongs mainly to the intergranular and moldic types.