Sequential Evolution and Stratigraphic Architecture of a Mixed River and Wave-Dominated Delta, Iles Formation, Colorado

Abstract

Ancient river-dominated deltas host significant accumulations of hydrocarbons. The influence of wave energy is common, and adds architectural complexity to the stratigraphic record. While facies models for wave-influenced deltas exist, they are under-represented among the suite of deltaic outcrop analogs. The Campanian Upper Sego Member of the Iles Formation is composed of prograding deltaic parasequences. This study focuses on one parasequence, located around Hunter Canyon, Colorado, that is exceptionally well exposed in three dimensions and contains evidence of mixed fluvial and wave influence. During deposition the parasequence evolved from a fluvial-dominated delta, then to a wave-dominated delta, and finally back to a fluvial-dominated delta. This study documents the imprint of these process regimes on stratigraphic architecture. Data collected in this study include high-resolution interpreted photo panels, detailed measured sections at decimeter resolution, and paleocurrent data to document the 3D stratigraphic architecture and facies distribution of one delta lobe. Fluvial dominated components of the delta contain distributary channels, clinoforming mouth bars, and significant bottomset (i.e. prodelta mudstone) aggradation. In contrast, wave dominated components are erosional into underlying strata, composed primarily of swaley cross stratification, have relatively low-angle foresets, and contain a large proportion of soft-sediment deformational features.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015