Thin-Bedded Reservoir Architecture of a Storm-Dominated Delta Front and Prodelta Facies, Cretaceous Ferron Notom Delta, Utah

This study examines thin-bedded facies within shelf and prodelta deposits of the Cretaceous Ferron Notom Delta, in central Utah. Thin beds may be the result of storms (tempestites), ignitive turbidity currents or hyperpycnites. Ignitive turbidites show normally graded Bouma sequence; whereas hyperpycnites can show either inverse grading followed by normal grading, or repeated Bouma sequence units indicating a more sustained flow. Tempestites are typically normally graded with gutter casts, hummocky cross stratification (HCS), wave-ripples. Wave-dominated parasequences show higher amounts of bioturbation. This study quantitatively evaluates the proportion of each facies types within heterolithic strata at the base of the sandier lithofacies to better characterize the relative proportion of formative processes. Primary data was derived from well-exposed outcrops of parasequences 5a, 5b, 6, and 16, within the Notom deltaic wedge, which represent a spectrum of wave-dominated shorefaces to river-dominated deltas.

Parasequence 5a and 5b comprise over 50% HCS beds with subordinate wave ripples and a high Bioturbation index (BI) of 3-6. A greater proportion of massive to planar interbeds in Parasequence 5b suggests fluvial and wave mixing. Parasequence 6 shows river dominance. It is predominantly normal and inverse graded units with numerous Bouma sequences and starved ripples. BI is usually low (1-2) with local high BI on bedding surfaces. Parasequence 16 is dominated by massive units, along with graded beds, Bouma sequences, and rare HCS. Bioturbation is minimal, but locally high (BI = 6) on bedding planes Parasequence 5a represents a high energy wave environment. Locally high BI occurs between storm events. Parasequence 5b also reflects a wave dominated environment, with a greater proportion of river-flood derived turbidite deposits. Parasequence 6 is river flood dominated, containing both ignitive turbidites, as well as hyperpycnites. Parasequence 16 shows evidence of all three processes, although ignitive turbidite deposits seem to dominate.

Tempestites, Ignitive turbidites, and hyperpycnites are likely to occur within the same system. They interact with each other producing deposits having remnant signatures of each. Results show that it is possible to document the relative proportion of formative processes within heterolithic sequences.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California