Clay mineral mixtures as alteration products in pillow basalts from the eastern flank of Juan de Fuca Ridge: a TEM-AEM study

Transmission electron microscope-analytical electron microscope analyses have been carried out on secondary minerals from pillow basalts with various degrees of alteration from the Juan de Fuca Ridge (ODP Leg 168). The electron microscopic data indicate that the alteration products consist mainly of phyllosilicate mixtures. The least altered sample shows poorly crystalline phyllosilicates occurrring as flakes with 10 Å -spaced lattice fringes. They have compositions of celadonite mixed with smectite and/or Fe oxyhydroxides and Mg-rich smectite. Proceeding towards older, more altered basalts, the alteration products consist of: (1) poorly crystalline celadonite mixtures and Mg-rich smectite; and (2) phyllosilicates with a higher degree of crystallinity, showing lattice fringes with 9.1 Å -spacing and with a talc-like composition. Changes in phyllosilicate association occur as the type of alteration changes from an oxidizing, water-dominated system (occurrence of celadonite mixtures with Fe hydroxides) to a reducing, rock-dominated system (occurrence of Fe-smectite and talc-like mixtures).

Caracterização da Matéria Orgânica Dispersa através da técnica de Pirólise "Rock-Eval II" Vantagens e Limitações para a Geologia

The development of Rock-Eval II pyrolysis technique in the end of 70's, offered a very important tool for disperse organic matter study. Rock-Eval II pirolysis of whole rock has been used by geologist to identify the type, quantity and thermal maturity of organic mailer associated with sedimentary rocks. It is fast and inexpensive method to evaluate petroleum-generation potential and organic metamorphism of rocks. This technique allows obtention of repeatable data, very important determining stratigraphic and geographic extent of occurrence of source rock. However pyrolysis is results must be carefully analised to avoid misunderstanding, regarding, for example, altered sample. interference of clay-minerals associated with organic matter, the kerogen type, imature sediments etc., can lead to mistaken interpretation.