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The emergence of multicellular organisms (metaphytes and metazoans) is an important event in the evolutionary history of Precambrian life since the emergence of unicellular eukaryotes. The oldest remains of multicellular organisms are therefore one of the keys to the early evolution of life on Earth. A few megascopic carbonaceous films of Tyrasotaenia from the 1700-million-year-old Tuanshanzi Formation of the Changcheng Group in the Jixian area, north China, have been reported (1) but have not been widely accepted as multicellular organisms (2, 3).
In addition to a few samples of ribbonlike and sausagelike megafossils resembling the vendotaenids and tawuids, respectively, we have recently found more than 300 specimens of megascopic carbonaceous fossils shaped like leaves from the locality and horizon close to that described in (1). These leaflike megafossils have obvious characteristics of multicellular algae. The megascopic carbonaceous remains were found near Tuanshanzi Village and its adjacent area (40deg10'N, 117deg27'E), about 20 km northeast of Jixian Town (Fig. 1). (Figure 1 omitted) The best-preserved specimens came from the lower part (first member) of the Tuanshanzi Formation, ==44 to 47 m above its base (Fig. 2). (Figure 2 omitted) The Tuanshanzi Formation belongs to the Paleoproterozoic Changcheng Group. The group includes the Changzhougou (conglomerate, sandstone), Chuanlinggou (silty and illitic shale), Tuanshanzi (muddy and silty dolomicrite), and Dahongyu (sandstone, volcanic rocks, cherty dolomicrite) formations in ascending order, and has a total thickness of 2629 m. These rocks were deposited from ==1850 to 1600 million years ago (Ma) (4). The type section of this group is at Tuanshanzi Village and surroundings.
The Tuanshanzi Formation is mainly composed muddy and silty dolomicrite with a total thickness of 518 m (5). The lower member of this formation is rich in muddy, silty, and carbonaceous lithologies, and has pyrite impregnations and black carbonaceous films on the bedding planes. In the upper member, the content of clastics increases markedly upward and dolomitic sandstone, sandy dolostone, thin-bedded sandstone, and small stromatolite bioherms are common. The lower member of the Tuanshanzi Formation is characterized by even bedding with local slumps. In the upper member, flute casts, furrow casts, ripple marks, mud cracks, and salt pseudomorphs are common. The Tuanshanzi Formation represents an upward shallowing sequence; its lower part was mainly formed in a relatively quiet,...