Modeling
Near-surface Porosity Evolution in Isolated Carbonate Platforms: a New
Diagenetic Scheme for the CARB3D+ Forward Simulation Model
Smart, Peter L.1, Fiona
Whitaker2, Richard Paterson3, David Oldham1
(1) University of Bristol, Bristol, England (2) University of Bristol, Bristol,
United Kingdom (3) Bristol University, Bristol, United Kingdom
We have developed a 3-dimensional forward
model for the sedimentology of carbonate platforms (CARB3D+) which incorporates
near-surface diagenesis (Patterson et al, Journ. Sed. Res. 76). This provides a
useful tool to aid understanding of the complex relationships between sequence
stratigraphy and the extent of diagenetic modification. A depth-averaged
freshwater lens model is used to predict the distribution of vadose,
freshwater, mixing and saline zones in exposed carbonate sediments. Processes
and uniform rates of diagenesis are than defined for these zones, allowing the
progressive changes in fabric selective porosity, cement volume and mineralogy
to be tracked through time. Secondary porosity is used to up-scale to
island-scale permeability, permitting critical feedbacks between the evolving
poro-perm characteristics and distribution of the hydrological-zones to be
included. A revised diagenetic scheme is currently under development which
reduces the extent of user-defined model parameterisation, being based on the
nature of the regional climate (temperature, rainfall and potential
evapotranspiration) and nature and thickness of the soil cover. It is conceptually
based on hydrological flow paths, and considers the progressive changes which
occur in the geochemistry of waters along these paths. It is therefore
incorporates 2 key aspects of diagenesis recognised from hydrochemical and
geological studies of modern carbonate platforms; the strong depth dependence
of both dissolution and cementation in any specific hydro-zone, and the
dependence of diagenesis rates on the extent of diagenesis in the overlying
hydro-zone. Preliminary 1D modelling results will be presented to explore the
implications of different model schemes for meteoric dissolution and
cementation.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California