Palaeontology: early Jurassic fossil-Lagerstatten in central England

摘要

Jon Radley (Warwickshire Museum and University of Portsmouth) and Mike Barker (University of Portsmouth) write Shells and other skeletal particles within shallow-marine environments often undergo concentration by waves and currents, giving rise to shell and bone beds. Some of the richest fossil concentrations in the rock record formed in this way. The onshore British Jurassic is made up largely of marine sediments. Shallow, nearshore environments are indicated by richly fossiliferous coarse sediments such as sandstones, ironstones and limestones showing much evidence for wave and current disturbance (e.g. ooids, broken shells and cross-bedding). However, ammonite-rich mudstones probably represent the deepest water deposits. In recent years, it has become apparent that major storms affected the deep-water sediments of the Jurassic seas. Silt-filled scours, ripped up mud-chips and layers of broken shells within the Jurassic mudstones demonstrate that powerful storm currents periodically disturbed the peace even though much of their destructive force had been dissipated with increasing depths.