GLOBAL COAL GAP BETWEEN PERMIAN-TRIASSIC EXTINCTION AND MIDDLE TRIASSIC RECOVERY OF PEAT-FORMING PLANTS

Early Triassic coals are unknown, and Middle Triassic coals are rare a nd thin. The Early Triassic coal gap began with extinction of peat for ming plants at the end of the Permian (ca. 250 Ma), with no coal known anywhere until Middle Triassic (243 Ma). Permian levels of plant dive rsity and peat thickness were not recovered until Late Triassic (230 M a). Tectonic and climatic explanations for the coal gap fail because d eposits of fluctuating sea levels and sedimentary facies and paleosols commonly found in coal-bearing sequences are present also in Early Tr iassic rocks. Nor do we favor explanations involving evolutionary adva nces in the effectiveness of fungal decomposers, insects or tetrapod h erbivores, which became cosmopolitan and much reduced in diversity acr oss the Permian-Triassic boundary, Instead, we favor explanations invo lving extinction of peat-forming plants at the Permian-Triassic bounda ry, followed by a hiatus of some 10 m.y. until newly evolved peat-form ing plants developed tolerance to the acidic dysaerobic conditions of wetlands. This view is compatible not only with the paleobotanical rec ord of extinction of swamp plants, but also with indications of a term inal Permian productivity crash from delta(13)C(org) and total organic carbon of both nonmarine and shallow marine shales.