Description
PERMIAN BASIN SECTION SEPM FALL FIELD TRIP
November 11th– 13th, 2011
Registrations must be received by October 28th, 2011, 5:00 p.m. in PBS-SEPM office
Paleozoic mounds stratigraphic architecture in the Sacramento Mountains:
implication for reservoir characterizations
Dr. Xavier Janson
Reservoir Characterization Research Laboratory
Bureau of Economic Geology
University Of Texas at Austin
This two day trip will use the unique suite of carbonate outcrops in Sacramento Mountains to illustrate reservoir-scale stratalarchitecture and methodologies for interpreting these carbonate mounds geometries from contained facies. Two different platform style of mounds development will be visited. The Mississippian mounds grew on a wide low angle ramp below wave base and are dominated by aphotic to oligophoticbiota, whereas the Virgilian algal mounds are dominated by euphotic biota that depends on light to grow and has a result are controlled not only by the hydrodynamic regime but also the water depth (accommodation). We will draw comparison with the subsurface data from the Horseshoe Atoll and in the Fort Worth Basin where these two types of mounds are present or at least suspected whenever possible. We will contrast the two stratigraphic architectures and discuss the applicability of these outcrop and outcrop-derived conceptual model to the isolated platform case in Horseshoe Atoll and Forth Worth Basin.
Day 1: Mississippian outer-ramp deposits and associated mud mounds: Mississippian Lake Valley mid- and outer-ramp deposits and buildups are well displayed across the west-facing wall of the Sacramento Mountains for some 12 miles in an approximate dip orientation. We will examine mound geometries, flank beds, and crinoidalgravity flows at three locations along the Lake Valley ramp. The most updiplocality will consist of small mound complexes, followed by larger mounds complexes and large lobatecrinoidalrudstonedeposits in Alamo Canyon downdip. Finally, we will then examine the famous Muleshoe mud mound in a more downdipposition along the ramp profile. These exposures will give us the opportunity to compare stages of mound growth—including lenticular, aggradational, and laterally accreting along the updipto downdipaccommodation profile of the Lake Valley ramp—with the phylloid-algal mound we‘ll see the next day in the Pennsylvanian. We will also examine the stratalgeometries of outer-ramp crinoidalturbiditelobes. We will discuss similarities and differences between phylloid-algal and crinoid mounds and try to make some generalization about other skeletal-mound systems, such as Cretaceous rudistmounds.
Day 2: Mixed siliciclasticUpper Carboniferous shelf in Dry Canyon: icehouse cyclicityand mound-dominated margin architecture The Dry Canyon area of the Sacramento Mountains is a classic exposure of complex icehouse-mixed-siliciclastic-carbonate strata deposited in shallow-water-shelf, shelf-margin, and slope settings. The narrow shelf exposed in Dry Canyon will allow us to contrast faciesdistribution and proportion, stratalgeometries, and cycle architecture between the shelf interior and the shelf margin. We will examine stratalgeometries and cycle boundaries typical of high-amplitude, sea-level changes found in icehouse conditions. We will observe variations of phylloid-algal mound size, shape, and distribution in three dimensions and between two distinct stratigraphic intervals. We will examine and discuss the influence of antecedent topography and differential compaction on facies/cycle architecture and, ultimately, reservoir quality.