Links between Palaeoproterozoic palaeogeography and rise and decline of stromatolites: Fennoscandian Shield

Abstract

Through a review of literature and new data we have documented two major events in the Palaeoproterozoic history of stromatolites as indicated by palaeontological and palaeoenvironmental studies. With a time resolution of between 40 and 200 Ma we confirm Semikhatov and Raaben's, and Awramik's (albeit approximately) maximum in diversity and abundance of stromatolites between 2330 and 2060 Ma ago (Jatulian diversification). We suggest that this taxonomic diversity was driven by a major phase of cratonisation, formation of the Karelian carbonate platform and numerous rift-related shallow-water carbonate basins supersaturated with Ca +2, Mg +2 and CO 2. The Jatulian stromatolite explosion is synchronised with a positive δ 13C carb shift of Jatulian age carbonates. We also document stromatolite decline which occurred on the Fennoscandian Shield somewhere between 2060 and 1900 Ma ago. This decline, both in abundance and in taxonomic diversity, is interpreted as having been caused by the first phase of ‘oceanisation’. The oceanisation led to the considerable reduction in ecological niches that could be utilised by cyanobacteria. The post-Jatulian decline of stromatolites coincides with an abrupt, downward δ 13C org shift from −19%. to −38% and is roughly coeval with the appearance of the first eukaryotic algae documented elsewhere. The systematics of the Fennoscandian diversity of Palaeoproterozoic stromatolites is identical to that reported from India and China and reveals a dissimilarity with abundance and diversity patterns in Australia and Northern America.