ON THE ROLE OF SECONDARY FLOW ON FACIES ASSOCIATIONS AND STRATIGRAPHIC ARCHITECTURE IN SINUOUS SLOPE CHANNELS: CONCEPTS LEARNED FROM A 3D EXPOSURE OF A SINUOUS SLOPE CHANNEL, BRUSHY CANYON FORMATION, WEST TEXAS

The Beacon Channel of the Brushy Canyon Formation, west Texas is a rare example of a 3D outcrop of a sinuous slope channel. The channel is 20m thick and 250m wide, with a sinuosity of 1.20. It is exposed on five cliff faces in an area of one square kilometer. LiDAR, paleocurrent measurements, stratigraphic columns, and photopanels were used to document the 3D stratigraphy of the channel. Data reveal concepts related to secondary flow trends in the channel and their impact on architecture and facies.

In the Beacon Channel, river-like, sigmoid-shaped point bars record a time of increasing sinuosity and channel down cutting. However, unlike in rivers, point bars in the Beacon Channel contain fine-grained strata partitioned to their lower and upper parts, and coarse-grained, cross-bedded strata are partitioned to their middle part. These strata contain greater facies and grain-size diversity than the rest of the strata in the channel. Paleocurrent data in the point bars provide evidence that the turbidity currents associated with them had a secondary component to flow that rotated opposite that of water in bank-full rivers. In contrast to Beacon Channel point bars, younger strata related to the filling of the channel are flat-lying, homogeneous, amalgamated sandstones that progressively onlap the margins of the channel and contain a fining-upward association. Paleocurrent data in these strata provide no evidence for a secondary component to flow.

These observations illustrate that turbidity currents and strata associated with increasing the sinuosity and depth of sinuous slope channels are distinctly different than turbidity currents and strata associated with their fill.