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GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Geological Society of America Special Paper 399 2006 Carbon isotopic evidence for terminal-Permian methane outbursts and their role in extinctions of animals, plants, coral reefs, and peat swamps Gregory J. Retallack* Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272, USA Evelyn S. Krull* CSIRO Land and Water, Adelaide Laboratories, PMB2, Glen Osmond, South Australia 5064, Australia Dedicated to the memory of William T. Holser, colleague and friend. ABSTRACT A gap in the fossil record of coals and coral reefs during the Early Triassic follows the greatest of mass extinctions at the Permian-Triassic boundary. Catastrophic meth- ane outbursts during terminal Permian global mass extinction are indicated by organic δ13 13 carbon isotopic ( Corg) values of less than –37‰, and preferential sequestration of C- depleted carbon at high latitudes and on land, relative to low latitudes and deep ocean. Methane outbursts massive enough to account for observed carbon isotopic anomalies require unusually effi cient release from thermal alteration of coal measures or from methane-bearing permafrost or marine methane-hydrate reservoirs due to bolide impact, volcanic eruption, submarine landslides, or global warming. The terminal Permian carbon isotopic anomaly has been regarded as a consequence of mass extinc- tion, but atmospheric injections of methane and its oxidation to carbon dioxide could have been a cause of extinction for animals, plants, coral reefs and peat swamps, killing by hypoxia, hypercapnia, acidosis, and pulmonary edema. Extinction by hydrocarbon pollution of the atmosphere is compatible with many details of the marine and terres- trial fossil records, and with observed marine and nonmarine facies changes. Multiple methane releases explain not only erratic early Triassic carbon isotopic values, but also protracted (~6 m.y.) global suppression of coral reefs and peat swamps. Keywords: Permian, Triassic, boundary, methane, mass extinction, coal, reef INTRODUCTION the longest temporal gap in the fossil record of coals since their Late Devonian appearance (Retallack, et al., 1996) and of coral Mass extinctions of the past, like a good murder mystery, reefs since their Ordovician appearance (Weidlich et al., 2003). can be instructive for the living. The Permian-Triassic bound- No coals or coral reefs are known for the entire Early Triassic ary, for example, not only was the greatest biodiversity crisis (Fig. 1), which has a currently dated duration of ~6 m.y. (Mundil of the past 500 m.y. (Erwin, 1993), but it also was followed by et al., 2004; Gradstein et al., 2005). The causes of this global eco- logical crisis are potentially relevant to modern anthropogenic *E-mails: [email protected]; [email protected]. extinctions, wetland pollution (Whiting and Chanton, 2001), and Retallack, G.J., and Krull, E.S., 2006, Carbon isotopic evidence for terminal-Permian methane outbursts and their role in extinctions of animals, plants, coral reefs, and peat swamps, in Greb, S.F., and DiMichele, W.A., Wetlands through time: Geological Society of America Special Paper 399, p. 249–268, doi: 10.1130/2006. 2399(12). For permission to copy, contact [email protected]. ©2006 Geological Society of America. All rights reserved. 249 250 G.R. Retallack and E.S. Krull coral reef predation and bleaching (Pandolfi , 1992; Marshall and are common to most carbon isotopic records across the Permian- McCulloch, 2002). Triassic boundary. Here we consider the magnitude, shape, and A diagnostic clue to the life-crisis at the Permian-Triassic paleogeographic distribution of numerous Permian-Triassic car- boundary is a marked carbon isotopic anomaly (negative δ13C bon isotopic spikes as evidence for the nature of the carbon-cycle spike) in both carbonate and organic matter (Magaritz et al., crisis some 251 m.y. ago. 1992; Morante, 1996), which has been instrumental for recogni- The negative carbon isotopic anomaly at the Permian-Trias- tion of this mass extinction at many localities worldwide (Fig. 2). sic boundary has been variously attributed to curtailed biologi- When comprehensively sampled and well preserved, the isotopic cal productivity in the ocean (Kump, 1991; Wang et al., 1994), anomaly has a characteristic shape of rapid but steady decline curtailed biological productivity on land (Broecker and Peacock, to a very low value, then rebound followed by one or more low 1999), change from woody to herbaceous vegetation (Gorter et spikes, before settling on Early Triassic values often a little lower al., 1995; Foster et al., 1998), erosion of coals exposed during than during the Late Permian (Figs. 3–5). Other abrupt or erratic low sea level (Holser and Magaritz, 1987; Magaritz et al., 1992), carbon isotopic excursions at the Permian-Triassic boundary may overturn of a stratifi ed ocean carbonated with dissolved CO2 refl ect local disconformities and inadequately dense sampling, (Hoffman et al., 1991; Kajiwara et al., 1994; Knoll et al., 1996), but one or more negative spikes and later persistent lower values introduction of extraterrestrial carbon from comet or asteroid Helongshan Formation Fremouw COAL GAP Formation Figure 1. Permian-Triassic boundary - Permian-Triassic boundary REEF GAP sections showing strata (A) within the global coal gap in nonmarine strata of Graphite Peak, Antarctica and (B) with- in the global reef gap in marine strata of Meishan, China. For scale: at Graphite Yinkeng Peak, small triangular tents; at Meishan, Buckley Formation -Kaiho Formation Permian-Triassic boundary- Kunio Kaiho collecting samples. -tents Changsing Limestone EARLIEST TRIASSIC SIBERIAN TRAP LAVAS RECONSTRUCTION Spitzbergen Sasayama Taho Schuchert Dal Kamura Gartnerkofel SUBDUCTION ZONE Val Badia Siusi Williston Lake Idrijca Kemer Gorge Shangsi MOUNTAINS Curuk Dag Meishan Emarat Heping Figure 2. World paleogeographic map at Kaki Vigla Vedi Abadeh Taiping the Permian-Triassic boundary (251 Ma, Sovetashan Guryul Ravine from Scotese 1994) showing sites ana- LOWLANDS Kuh-e-Ali Bashi Morondava Palgham lyzed for carbon isotopic anomalies. Wardha Nammal Gorge BEDOUT CRATER Godhavari Fishburn Bethulie Paradise Tern Denison Lootsberg Carleton Heights Talcher Eddystone Tweefontein Wybung Head Wapadsburg Murrays Run Graphite Peak Banspetali Raniganj Coalsack Bluff Portal Mountain Wairoa Gorge Mount Crean Shapeless Mountain Grain size TerminalCarbonate Permian carbon methane isotopic value 251 (δ13Ccarb. %o) - - - - - cm - - - - - - - - - - -4 -2 0 - clay coal -6 2 silt sand gravel 250 - Yin et al., 1996 bluish gray (5B5/1) - light bluish gray (5B6/1) - - bluish gray (5B5/1) light greenihs gray (5G7/1) s - 200 - bluish gray (5B5/1) - Figure 3. Stratigraphic section at the - light bluish gray (5B6/1) Hindeodus parvus global Permian-Triassic stratotype in - gray (5Y6/1) Hindeodus typicalis Xu and Yan 1993 TRIASSIC Meishan quarry D, China, measured by - Isarcicella isarcica 150 light yellowish brown - Retallack, with conodont ranges from (2.5Y6/4) - Yin et al. (1996) and carbonate carbon - light yellowish brown isotopic data after Xu and Yan (1993) - Clarkina changsingensi YINKENG FORMATION (2.5Y6/3) and Baud et al. (1989). Additional iso- - dark gray (5Y4/1) 100 topic data of d’Hondt et al. (2000) show - light gray (5Y7/1) - gray (5Y6/1) a shift comparable to that in the data of - dark gray (5Y4/1) Baud et al. (1989), which were preferred - for our compilation (Table 1). gray (5Y6/1) - Baud et al. 1989 50 dark gray (5Y4/1) - PERMIAN - gray (5Y5/1) - gray (5Y6/1) - gray (5Y5/1) CHANGSING LS CHANGSING - - - - - 0 - limestone dolostone sandstone shale planar bedding Grain size Paleosol organic carbon isotopic value Development (δ13Corg. %o) - - - - - strong - - - - weak - - - - - -40 -35 -25 silt - -30 -20 clay coal sand gravel m - - WILLIAM 280 - MICHAEL first appearance of - Lystrosaurus - - EDWIN - - - - - - WILLIAM 270 - DOLORES Figure 4. Stratigraphic section of the - MICHAEL Permian-Triassic boundary at Graphite - Peak, with stratigraphic and fossil range TRIASSIC WILLIAM - DOLORES data from Retallack and Krull (1999) - MICHAEL and carbonaceous carbon isotopic data - WILLIAM - from Krull and Retallack (2000) and MICHAEL - Retallack et al. (2005). FREMOUW FORMATION - MICHAEL - 260 - - claystone breccia - - DOLORES - EVELYN - EVELYN - last appearance of - Vertebraria - EVELYN PERMIAN BUCKLEY - - - - - 250 - claystone sandstone shale,