POROSITY CORRECTIONS FOR SMECTITE-RICH SEDIMENTS - IMPACT ON STUDIES OF COMPACTION, FLUID GENERATION, AND TECTONIC HISTORY

Porosity is a fundamental parameter that must be correctly determined in order to relate physical property, hydrologic, and chemical flux st udies to natural systems. Traditional porosity determinations generate d from physical property or seismic data can greatly overestimate the true porosity of sediments in which hydrated minerals such as smectite are abundant. To produce a true porosity distribution such data must be corrected to account for the H2O residing in smectite interlayers w hich can make up to 25% of the total hydrated mineral mass. Such H2O i s easily removed from the mineral by oven drying and/or exposure to lo w humidities. Standard physical property measurements can be corrected , provided the weight percent smectite in the sediment is known and th e interlayer H2O content of the mineral can be estimated, We illustrat e the significant consequences of this correction by comparing profile s of reported and corrected porosities for smectite-rich Barbados abys sal plain and accretionary wedge sediments from Ocean Drilling Program Leg 110, Sites 671 and 672.