--> Analysis of Fluvial Facies Variations of the Price River Formation, Mesaverde Group, Book Cliffs, Utah, U.S.A.

AAPG ACE 2018

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Analysis of Fluvial Facies Variations of the Price River Formation, Mesaverde Group, Book Cliffs, Utah, U.S.A.

Abstract

Understanding facies variations is important in characterising the style of fluvial systems for subsurface application. This study focusses on fluvial facies distribution within the Campanian Price River Formation east-central Utah. The aim of the study is to determine downstream facies trends and to assess if vertical and/or spatial change can define the formation within a distributive fluvial system (DFS) context.

A total of 12 log sections (total thickness of 1675 m) were described. Paleo-flow directions measured from cross-strata indicate north-easterly directed transport. Interpretation of LiDAR data provided additional high-resolution architectural panels from which 8 virtual outcrop logs were generated for statistical data collection. These datasets were integrated with well data from coal-bed methane wells drilled throughout the study area and calibrated against outcrop data in adjacent areas to define vertical and lateral trends.

Channel and floodplain deposits are the main facies observed within the study area. In-channel deposits include cross-stratified sandstone (trough, planar and low angle), massive sandstone and horizontally laminated/bedded sandstone. Chanel facies are interpreted to represent amalgamated and isolated meander-belt deposits. Floodplain deposits include thin beds of very fine sandstone/siltstone and contain scattered nodules and may display mottled surfaces indicative of paleosol development. Up-section trends show an increase in floodplain facies from approximately 32% to 61%. For simple data descriptions, the formation was divided into three portions based on percentage of channel and floodplain deposits. Statistical data from virtual outcrop logs recorded 74% of channel deposit in the lower portion, whereby, 40% and 21% were recorded for middle and upper portions respectively.

The documented trends indicate the Price River Formation is a backstepping (retrograding) fluvial system. The higher percentage of channel deposits in the lower portion is considered to represent the proximal section of a DFS. Middle and upper portions recording medial and distal DFS deposits respectively as indicated by a decrease in channel facies and increased floodplain preservation. Possible controls are discussed as to what the possible causes of retrogradation are, including changes in the relationship between basin accommodation space and sediment supply.