Chapter 11 - Changes in the Shape of Breccia Lenses Sliding From Source to Sink in the Cambrian Epeiric Sea of the North China Platform

Abstract

A series of lenses of limestone breccia that slid down over the gently inclined bottom of an epeiric sea came to rest within an oolite layer that forms part of the Late Cambrian (Furongian) Chaomidian Formation in Shandong Province, China. The lenses, which are exposed closely together at the same level in one single section, have different sizes (centimeters to decimeters thick and decimeters to more than 10m long). They are interpreted as fragments of a broken-up breccia layer. The shapes of some of the (almost) unaffected lenses (with a meter-scale size) are remarkable: they show a tear-like front part with a tail behind them. This is interpreted to result from the sliding of a semiconsolidated breccia mass through water that provided sufficient resistance to affect the shape of the sliding semiconsolidated fragment. The top parts of the larger lenses were postdepositionally abraded, so that their original shape cannot be determined anymore. The abrasion is interpreted to be due to wave action. Wave action also affected some smaller lenses, giving them a convex upper surface. The overall shape, however, is determined by the sliding of a fragmented breccia layer from the parent layer (the source) to its depositional site (the sink).