TUBULAR FOSSILS IN THE PALAEOPROTEROZOIC LOWER VINDHYAN OF INDIA

The phosphoritic stromatolites of the ca 1.6 Ga Lower Vindhyan Tirohan Dolomite in central India are characterized by extensive cyanobacterial biomats. Within these mats there occur rare tubular fossils 100–180 µm in diameter and up to at least 2 mm in length. Some of the tubes have annular grooves, 60–140 µm apart, which correspond to internal segmentation produced by complete cross-walls. Synchrotron-based X-ray tomographic microscopy (SRXTM) reveals the internal structure of the tubes, showing that the segmentation is cellular in nature. The large cytoplasm volume and the presence of subcellular structures suggest that these segmented tubes are eukaryotic filamentous algae. Other tubular fossils in the same deposits, however, may belong to bacteria.