Devonian lake margin environments and processes, SE Shetland, Scotland

Abstract

The Devonian lake or lakes of SE Shetland were characterized by 4 environments: (1)a marginal environment dominated by the high energies of the surf zone and just lakeward of the breaker zone; (2) an additional marginal environment consisting of small, shallow, oxidizing lakes on a low-gradient coastal flood plain over which waters from the main body of the lake fluctuated; (3) an intermediate environment characterized by continuous to intermittent wave agitation, in water depths of probably <5 m; and (4) an offshore environment characterized by a lack of evidence for current or wave action, at depths of >5–10m. The marginal environment was influenced by both wave and current processes. A friction dominated outflow produced sedimentary structures that indicate a south-easterly flow and depositional slope. Outflow competed with shoaling waves which advanced from E to W onto the lake shoreline. Where outflow was weakest, wave processes dominated. Longshore drift was an additional component in the movement of the nearshore waters. The Devonian lake or lakes of SE Shetland possessed rather shallow shoaling margins.