Fig. 6

Macro- and microscopic characteristics of the columnar stromatolites. a Vertical section of columnar stromatolites on the core surface, where column diameters are 2–5 cm and increase upward. The arching degree and laminae thickness decreased but the alternation frequency increased from down toward the top; b Vertical section showing pillared laminae are composed of micro-branched stromatolites and dendrolites with widths of 60–170 μm and heights of 180–800 μm. The brighter laminae formed when the micro-stromatolite growth density decreased; c Micro-oncolites between the micro-stromatolite columns; d Pillared laminae composed of micro-columnar stromatolites, which exhibit passive branching structures, and the branches have steeply convex laminar shapes. The tussocky laminae are also composed of micro-columnar stromatolites; e Line drawing of (d)