Clay Mineral diagenesis of a Pleistocene volcanogenic sequence, Mexican Basin

摘要

Diagenesis of the Pleistocene volcanogenic depositional sequence of the Mexican Basin transformed volcanic ash to dioctahedral smectite, a 7A-phyllite and mixed-layers of this 7A-phyllite and smectite when high permeability and low retention of fluids prevailed. The predominant interstratifications are R1 and R3 7A-phyllite(0.80)/2H_2O-smectite. In the mud underlying the coarse ash diagenetic alteration was to dioctahedral smectite. The ?A-phyllite corresponds with (Si_(1.87)Al_(0.13))(Al_(1.65)Fe~(3+)_(0.36)Mg_(0.03)Ti_(0.04))O_5(OH)_4. The smectites are aluminian with layer charges from 0.43 to 0.57 when replacement was in the octahedral sheet and of 0.25-0.42 when replacement was in the tetrahedral and octahedral sheets. The hydroxyl complexes are characterized by (Al_(1.57)Fe~(3+)_(0.26)Ti_(0.03)Mg_(0.16))(OH)_6.