R EPORTS date, the only complete Early and Middle Triassic carbon isotopic data set previously Large Perturbations of the compiled from a single stratigraphic section is in an unpublished dissertation (23). Carbon Cycle During Recovery We sampled the Great Bank of Guizhou (GBG), an isolated Late Permian to Late from the End-Permian Extinction Triassic carbonate platform in the Nanpan- jiang Basin of Guizhou Province, southern Jonathan L. Payne,1* Daniel J. Lehrmann,2 Jiayong Wei,3 China (Fig. 1A), to obtain high-resolution 4 1 1 ␦13 Michael J. Orchard, Daniel P. Schrag, Andrew H. Knoll profiles of Ccarb from the Late Permian through the Middle Triassic. The exposure of High-resolution carbon isotope measurements of multiple stratigraphic sections in sections in both platform interior and basin south China demonstrate that the pronounced carbon isotopic excursion at the margin settings further allows us to compare Permian-Triassic boundary was not an isolated event but the first in a series of large data across a range of depositional environ- fluctuations that continued throughout the Early Triassic before ending abruptly ments (Fig. 1B). A detailed stratigraphic early in the Middle Triassic.The unusual behavior of the carbon cycle coincides with framework for the platform has been developed the delayed recovery from end-Permian extinction recorded by fossils, suggesting from sequence stratigraphic (26), biostrati- a direct relationship between Earth system function and biological rediversification graphic, and geochronologic studies (27). in the aftermath of Earth’s most devastating mass extinction. Our results show that the P-Tr boundary carbon isotope excursion was not an isolated The most severe extinction since the advent Aside from the extinction itself, the stron- event. Rather, it was the first in a series of of animal life on Earth occurred at the end gest evidence for environmental disturbance (mostly larger) excursions that continued of the Permian Period, 251 million years at the Permian-Triassic (P-Tr) boundary is a throughout the Early Triassic and into the ago (Ma) (1–3), with global loss of marine sharp negative excursion of 2 to 4 per mil early part of the Middle Triassic Period (Fig. species estimated near 90% (4, 5). Organ- (‰) in the carbon isotopic composition 2). The excursions ended early in the Anisian ␦13 ␦13 isms with heavy calcification and limited ( C) of marine carbonate ( Ccarb)(17, (Bithynian) and were followed by an extend- elaboration of circulatory and respiratory 18) and one or more similar excursions in the ed interval of stable values around 2‰. The ␦13 ␦13 systems were most severely affected, C of organic matter ( Corg)(19–21). interval of carbon-isotopic stability continued whereas those with more active control of Although the apparent stabilization of through the remainder of the Middle Triassic ␦13 circulation, elaborated structures for gas Ccarb above the boundary interval (17) has and into the Carnian (Fig. 3), demonstrating ␦13 exchange, and lightly calcified or uncalci- been used to suggest a stable but reduced that the large fluctuations in Ccarb are fied skeletons survived in much higher pro- fraction of organic carbon burial in the Early confined to Early Triassic strata. portions (6). The ensuing Early Triassic Triassic (22), the carbon isotopic record of Absolute ages of 251.4 Ϯ 0.3 Ma (1) was an interval of delayed biotic recovery Early and Middle Triassic rocks has received or ϳ253 Ma (2) for the P-Tr boundary and characterized by continued low diversity relatively little study. Positive carbon isoto- ϳ247 Ma for the Early-Middle Triassic (5); the persistence of a cosmopolitan fauna pic excursions have been noted at the Diene- boundary (27) constrain the entire Early Tri- in the oceans (7); the absence of metazoan rian-Smithian (23), Smithian-Spathian (24), assic to ϳ4.5 to 6 Ma and individual isotopic reefs (8), calcareous algae (9), calcareous and Spathian-Anisian boundaries (25), but, to excursions to less than 1 million years in each sponges (10), and corals (11); the apparent absence of marine taxa recorded in both Permian and Middle Triassic rocks (12); a reduction in the size of invertebrates (13); and, on land, a hiatus in coal deposition (14). Sustained recovery of marine diversi- ty and ecology began primarily in the early Fig. 1. (A) Early Triassic paleo- part of the Middle Triassic, some 4 to 8 geographic map, modified from million years after the extinction itself. The (26). Inset: Hash pattern indi- apparent delay of biological renewal could cates the NanpanjiangBasin reflect the time scale necessary for reinte- and brick pattern indicates the gration of ecosystems (5, 12) or poor Early Yangtze. (B) Schematic cross Triassic fossil preservation (12), but it has section of the GBG, illustrating the locations of stratigraphic also been widely interpreted as a conse- sections within the platform quence of persistently unfavorable environ- architecture. mental conditions through part or all of the Early Triassic (5, 15, 16). 1Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA. 2Department of Geology, University of Wisconsin– Oshkosh, 800 Algoma Boulevard, Oshkosh, WI 54901, USA. 3Guizhou Bureau of Geology and Mineral Resourc- es, Bagongli, Guiyang 550011, Guizhou, People’s Repub- lic of China. 4Geological Survey of Canada, 101-605 Robson Street, Vancouver, BC V6B 5J3, Canada. *To whom correspondence should be addressed. E- mail: [email protected] 506 23 JULY 2004 VOL 305 SCIENCE www.sciencemag.org R EPORTS ␦13 case. The drops in Ccarb at the P-Tr bound- records on the GBG, and the consistency of (36), however, the more gradual and roughly ␦13 ary and at the base of the overlying cyclic the platform interior and basin margin symmetric increases and decreases in Ccarb interval in the platform interior (Fig. 2) occur records indicate that these data reflect global during the later part of the Early Triassic would within 10 m of section, suggesting a very instability of the Early Triassic carbon cycle require extended, alternating intervals of meth- short time scale for these events, whereas the rather than local, diagenetic, or facies-specif- ane storage and release. The long time scale positive and negative excursions observed in ic effects. Confirmation of the global nature [Ͼ100 thousand years (ky), assuming constant the upper part of the platform interior and on of the signal will depend upon additional sedimentation rates] of the negative shifts is the basin margin occur over longer strati- high-resolution studies at other localities. difficult to account for under the scenario of graphic intervals (Ͼ50 m), implying that they What physical mechanisms could have gen- methane release, because as the time scale of developed more slowly, although still in less erated positive and negative isotopic shifts in the isotopic shift increases, so too does the ␦13 than 1 million years. The symmetry of the Ccarb of up to 8‰ in marine carbonates over amount of methane needed to produce the same positive and negative excursions indicates time scales of tens to hundreds of thousands of excursion. The ϳ8‰ drop from the late Die- that the time scales of increases and decreases years? Although the rapidity of the extinction nerian to Smithian (Fig. 2) over 100 to 500 ky ␦13 in Ccarb were similar. (31) and isotopic excursion at the P-Tr bound- would require the release of much more than Our data (28) reproduce both the gradual ary is compatible with emerging evidence of 10,000 Gt of methane (1 Gt ϭ 107 kg) (37), carbon-isotopic drop in Late Permian oceans bolide impact (32, 33), the longer time scale of more than five times the amount suggested to and the rapid negative excursion at the P-Tr the subsequent excursions suggests another account for the Late Paleocene thermal maxi- boundary (17). The negative excursion at the cause. Eruption of the Siberian Traps provides mum (36). Furthermore, the dependence of base of the platform interior cyclic interval another possible explanation for prolonged in- methane production on organic carbon burial and the subsequent positive excursion are stability in the carbon cycle. Available radio- precludes rapid (i.e., Ͻ1 million years) replen- ␦13 hinted at by basal Triassic Corg profiles for metric dates restrict Siberian trap basalts to the ishment of the methane hydrate reservoir in the nonmarine successions (19), and they appear boundary interval itself (34), but the limited absence of extraordinarily high rates of organic to correlate with data from the Italian Dolo- geographic scope of dated sections relative to carbon burial (38). Methane release is an attrac- mites reported in an abstract (29). Our data the known area of the volcanic flows and the tive hypothesis for the P-Tr carbon-isotopic also corroborate previous reports of positive presence of Ͼ1000 m of flows above the event viewed in isolation, but the full Early excursions at the Smithian-Spathian (24) and youngest dated horizon (34) leave open the Triassic record is not easily reconciled with a Spathian-Anisian (25) boundaries, as well as possibility that episodic eruption occurred methane-driven scenario. the general shape of composite isotopic pro- through much of the Early Triassic. More age Another explanation for the positive and files developed from sections in Anhui Prov- data are needed to test this scenario. negative excursions is that there were mas- ince, China (30), and multiple profiles report- Massive methane release from sea-floor gas sive changes in the burial of organic carbon ed from across the Tethys (23). The consis- hydrate reservoirs has also been suggested as an relative to carbonate carbon ( forg). Such an tency of our findings with the more limited explanation for the P-Tr boundary excursion (5, explanation requires periodic episodes of results from other areas, the sharp contrast 19, 21, 35).