Dendroid morphology and growth patterns: 3-D computed tomographic reconstruction

Abstract

This paper analyzes the growth patterns of dendrolite in the Zhangxia Formation (Middle Cambrian), Shandong Province, China, using the technique of 3-D computed tomographic reconstruction. Dendroids are classified into V-dendroids, columnar dendroids, and arborescent dendroids, based on morphological characteristics. The means of interconnection between dendroids are classified into trunks, nodules, shoots, and fingers. Stacking and tiering control the gross morphology and structural framework of dendrolite. Stacking is a process of vertical growth, in which V-dendroids create a staircase-like structure. Tiering occurs when a layer of dendroids is covered by sediment, and then partially eroded, allowing a new layer of dendroids to form. A comprehensive blueprint of the structural divisions of dendrolite is presented, according to scale, being divided into micro-, meso-, macro-, and megastructures. The mesostructure, which includes individual dendroids and their combined structures, is subsequently divided into primary (V-dendroid), secondary (columnar and arborescent dendroid), and tertiary (stair and tier) structures and a basic growth model is provided for V-dendroids. The stages of V-dendroid growth are: 1) trunk extension and base expansion, 2) divergence, 3) expansion and convergence, followed by repetition of stages 2 and 3, until 4) growth completion, followed by the subsequent emergence of a new dendroid by either stacking or tiering. This development of systematically ordered structures is suggestive of the reaction of microbial colonies to external environmental conditions.