Abstract: Simultaneous, Multi-Parameter Stratigraphic Inversion of the Mesaverde Clastic Wedge, San Juan Basin
CROSS
, TIMOTHY A., and MARGARET A. LESSENGER, Colorado School
of Mines
Simultaneous, multi-parameter stratigraphic inversion is a quantitative method of extracting values of process parameters (e.g., sea level, tectonic movement, lithosphere rigidity, sediment supply rate, topography) directly from stratigraphic data (e.g., facies, thicknesses, inferred bathymetry, grain size, ages, stratigraphic cycles). Tests with synthetic data demonstrated that the correct values of process parameters were recovered by stratigraphic inversion of limited data, and the solutions were uniquely bounded with very small uncertainties. Encouraged by these results, we performed similar experiments with well log, core and outcrop data from the Mesaverde clastic wedge of the San Juan basin, SW Colorado.
A basin-scale, dip-oriented stratigraphic cross
section
containing 62 closely-spaced wells along the northwest side of the
San Juan Basin was the data base for the stratigraphic inverse
modeling. Fifteen progradational/aggradational stratigraphic units
are recognized, nine in the seaward-stepping lower Mesa Verde and
six in the landward-stepping upper Mesa Verde. Each unit contains
continental, shoreface and marine shelf strata. Data from 5 of the
62 wells were inverted, and the inversion results were tested
against measurements from the other wells not used in the
inversion.
The cross
section
shows that the shoreface sandstones in the
lower half of the Mesa Verde have a stepped geometry of
stratigraphic rise during progradation. The model shows the same
style of progradation. The depositional limit of the shoreface, or
the turnaround position from seaward- to landward-stepping
divisions of the clastic wedge is predicted exactly by the model.
Shorefaces of the upper half of the Mesa Verde form 8 to 15 km
broad benches which step progressively landward. The model matches
the number, position and dimensions of these benches. One of the
most surprising results was that the model recreated the 55 km
shift of the shoreface facies tract from the turnaround position to
the position of the lowest landward-stepping bench.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah