Paleoenvironmental analysis of Cretaceous non-marine stromatolites from Namhae Island, Korea

The sedimentary sequence of the non-marine Cretaceous Jinju Formation from Namhae, Korea contains a great number of rod-shaped stromatolites (RSS) characterized by concentric lamination, together with stratiform, domal and columnar stromatolites. The original, branched gross morphology of the ancient plant twigs is often preserved, and remains of plant tissues are well preserved in the central parts of the RSS, which are now filled with siliciclastic sediments following degradation of the original plant materials. They are, therefore, interpreted as stromatolitic algal and microbial encrustations over dead or living plant twigs, which formed through concentric carbonate precipitation by epiphytic algal photosynthesis. Varied filamentous fossils were found in the organic-rich layers, which are calcified tiny tubes characterized by brown micritic walls and light central parts composed of sparite. Size of filament diameter ranges from 1 to 44". Based on size of diameter, absence or presence of branching pattern, and/or their ecological roles in the formation of stromatolites, the filaments were classified into two groups: cyanobacteria (6"-8") and green algae (26"-29"). The cyanobacterial fossils played a key role in the formation of rod-shaped stromatolites, while green algal filaments were auxiliary stromatolite-builders.