Lithofacies Characterization of Mixed-Aeolian-Fluvial Deposits: Example from the Permo-Triassic of the Cheshire Basin, NE United Kingdom

Abstract

In order to improve prediction of accurate facies definitions (which has implications for fluid flow properties) in Triassic red-bed mixed fluvial and aeolian deposits, a study has been undertaken to assess the variability in lithofacies at outcrop scale from Burton Point and Helsby Forest Farm in the Cheshire Basin, England. Outcrop studies using the concept of Discrete Genetic Intervals from the fluvial Chester Pebble Beds at Burton Point demonstrated that the fluvial facies consists of amalgamated channel bars deposited within braided stream system. Reservoir heterogeneity is expected to results from decrease in bed thickness and fining upwards within beds, to fining upwards within cross strata. The Kinnerton Formation exposed at Burton Point and Helsby Forest Farm show that the Aeolian facies could be divided into moderate to high angle planar crossed stratified aeolian dune slip-face deposits (A1), horizontal to near horizontal dune base and dry interdune sub-facies (A2, B1), wavy laminated horizontal to near horizontal wet interdune deposits (B2) and interdune hollow fill mudstones (B3). Based on the grain size and sorting, the lithofacies A1 is expected to have the best reservoir quality sandstones while the B3 lithofacies may prevent vertical flow of fluid especially at well-scale. This study suggests that detailed outcrop studies is essential for more accurate definition of the lithofacies type, which is particularly important in interpreting depositional environments as well as reservoir studies.