Terrestrial Permian Triassic Boundary Research Articles

Occurrence of anatase in reworking altered ash beds (K-bentonites and tonsteins) and discrimination of source magmas: a case study of terrestrial Permian–Triassic boundary successions in China

AbstractPotential secondary influences on titanium distribution should be evaluated when using ash beds as volcanic source indicators and for correlation purposes. In this study, well-correlated altered ash beds in Permian–Triassic boundary (PTB) successions of various facies in South China were investigated to better understand their use in source discrimination and stratigraphic correlation. The ash beds deposited in lacustrine and paludal facies contain significantly more Ti relative to deposits in marine facies. Neoformed anatase grains nanometres to micrometres in size are associated closely with clay minerals, whereas detrital anatase was observed in the remnants of altered ash beds of terrestrial facies. Extraction of the clay fraction of altered ash beds may exclude significantly detrital accessory minerals such as anatase and rutile added during sediment reworking, and the concentrations of immobile elements in the clay fraction may therefore be used to interpret more effectively their source igneous rocks.

Intensifying aeolian activity following the end‐Permian mass extinction: Evidence from the Late Permian–Early Triassic terrestrial sedimentary record of the Ordos Basin, North China

AbstractSedimentary successions provide direct evidence of climate and tectonics, and these give clues about the causes of the mass extinction around the Permian–Triassic boundary. Terrestrial Permian–Triassic boundary strata in the eastern Ordos Basin, North China, include the Late Permian Sunjiagou, Early Triassic Liujiagou and late Early Triassic Heshanggou formations in ascending order. The Sunjiagou Formation comprises cross‐bedded sandstones overlaid by mudstones, indicating meandering rivers with channel, point bar and floodplain deposits. The Liujiagou Formation was formed in braided rivers of arid sand bars interacting with some aeolian dune deposits, distinguished by abundant sandstones where diverse trough and planar cross‐bedding and aeolian structures (for example, inverse climbing‐ripple, translatent‐ripple lamination, grainfall and grainflow laminations) interchange vertically and laterally. The Heshanggou Formation is a rhythmic succession of mudstones interbedded with thin medium‐grained sandstones mainly deposited in a shallow lacustrine environment. Overall, the sharp meandering to braided to shallow lake sedimentary transition documents palaeoenvironmental changes from semi‐arid to arid and then to semi‐humid conditions across the Permian–Triassic boundary. The die‐off of tetrapods and plants, decreased bioturbation levels in the uppermost Sunjiagou Formation, and the bloom of microbially‐induced sedimentary structures in the Liujiagou Formation marks the mass extinction around the Permian–Triassic boundary. The disappearance of microbially‐induced sedimentary structures, increasingly intense bioturbation from bottom to top and the reoccurrence of reptile footprints in the Heshanggou Formation reveal gradual recovery of the ecosystem after the Permian–Triassic boundary extinction. This study is the first to identify the intensification of aeolian activity following the end‐Permian mass extinction in North China. Moreover, while northern North China continued to be uplifted tectonically from the Late Palaeozoic to Late Mesozoic, the switch of sedimentary patterns across the Permian–Triassic boundary in Shanxi is largely linked to the development of an arid and subsequently semi‐humid climate condition, which probably directly affected the collapse and delayed recovery in palaeoecosystems.

New geochemical and palaeontological data from the Permian-Triassic boundary in the South African Karoo Basin test the synchronicity of terrestrial and marine extinctions

The end-Permian mass extinction (EPME) is widely recognised as the largest mass extinction in Phanerozoic history. In marine strata the main extinction event is well constrained, and has been radiometrically-dated to an interval of some 60 kyr, approximately 251.9 million years ago. However, the age and duration of the EPME in the terrestrial realm, as well as its possible synchronicity with that of the marine realm, is debated. Here, we shed light on issues pertaining to the identification and position of the terrestrial EPME in southern Africa. Using recently collected sedimentological (facies sequences), palaeontological (biostratigraphic ranges), geochemical (stable isotope analyses) and detrital zircon (ID-TIMS) data from a new site in the Xhariep District of the South African Karoo Basin, we demonstrate that the Permian-Triassic boundary sequence containing evidence for phased tetrapod extinctions is time equivalent with the marine extinction. We conclude that the terrestrial EPME recorded in the Karoo may be regarded as essentially synchronous with the EPME currently defined in the marine realm, and was likely the result of the same volcanically-induced atmospheric disturbances. This study describes the first single, vertical succession of vertebrate and plant fossils that span the terrestrial Permian-Triassic boundary that are also well-constrained both by relative (stable isotopes) and absolute (detrital zircon geochronology) dating methods.

Mercury evidence of intense volcanic effects on land during the Permian-Triassic transition

Abstract The Siberian Traps large igneous province (STLIP) was the likely trigger for the ca. 252 Ma latest Permian mass extinction (LPME), but direct evidence for global volcanic effects on land remains rare. Here, we used mercury (Hg) enrichments, a proxy for ancient volcanic activity, to assess volcanic inputs to two terrestrial Permian-Triassic boundary (PTB) sections that were separated by thousands of kilometers and represent different latitudinal zones—the peri-equatorial Lubei section (South China craton) and the high-latitude (40–60°N) Dalongkou section (Junggar terrane). Both sections exhibit strong Hg enrichment within a discrete (≤40 m) stratigraphic window representing the LPME. At Lubei, this interval is also characterized by negative mass-independent fractionation (MIF) of odd Hg isotopes, consistent with massive volcanogenic and/or terrestrial Hg inputs. These findings are significant in documenting Hg spikes and negative MIF excursions near the PTB in terrestrial sections for the first time, providing evidence of the global influence of the STLIP, as well as in demonstrating at high stratigraphic resolution its synchronicity with the PTB negative carbon-isotope excursion (CIE), supporting a common global cause for these anomalies.

Discussion of “Permian—Triassic vertebrate footprints from South Africa: Ichnotaxonomy, producers and biostratigraphy through two major faunal crises” by Marchetti, L., Klein, H., Buchwitz, M., Ronchi, A., Smith, R.M.H., DeKlerk, W.J., Sciscio, L., and Groenewald, G.H. (2019)

A newly devised tripartite subdivision of the Karoo Basin, South Africa, is based on a number of vertebrate-trackways spanning the Middle Permian (Wordian/Capitanian) to Lower Triassic (reportedly Induan) rocks of the Beaufort Formation. The youngest Footprint Assemblage (FA III) is reported to occur in the lowermost Triassic rocks of the Palingkloof Member. One collection site from which seven trackways are reported, Bethel farm, is a classic South African locality where some authors place the end-Permian extinction event and, coincidentally, the vertebrate-based terrestrial Permian—Triassic Boundary. Published GPS coordinates for the Bethel farm site, though, indicate that these trackways originate from exposures of the Burgersdorp Formation near the town of Aliwal North. Outcrops here are assigned to the Cynognathus Assemblage Zone, and indicate a Middle Triassic age assignment. In addition, we caution the use of any small temporally or spatially restricted dataset, which is of severely limited utility, in making broad generalizations about paleoenvironmental or paleoecological interpretations.

Reply to the comment on “Terrestrial Permian-Triassic boundary in southern China: New stratigraphic, structural and palaeoenvironment considerations” by H. Zhang, Z. Feng, J. Ramezanik, S-Z Shen

In their comment, Zhang et al. (2018) question the existence of the deformation structures that we report for the upper part of the Chahe Permian-Triassic Boundary reference section. These authors further suggest that this deformation contradicts the regional litho, bio- and chemostratigraphic results. Here again, and based on the outcrop picture provided by Zhang et al. (2018), we present new arguments attesting for a major tectonic deformation in the upper part of the Chahe section. We argue that the color pattern of the outcrop, the flora description, the δ13Corg isotope profile showing a negative excursion and the lack of coal bed in the upper part of series cannot be used as definitive arguments for a continuous succession. In consequence, we maintain that, above Bed 66, the succession is affected by numerous fold-accommodation faults, preventing any continuous logging and coherent stratigraphic analysis in the Kayitou and Dongchuan formations along that section.

Comments on “Terrestrial Permian–Triassic boundary in southern China: New stratigraphic, structural and palaeoenvironment considerations” by Bourquin et al. (2018)

The terrestrial Permian-Triassic transitional section at Chahe in western Guizhou Province, South China has served as a key reference section for the study of terrestrial PTB, as well as the end-Permian mass extinction on land in South China. However, Bourquin et al. (2018) recently reported that the PTB interval at Chahe has undergone serious tectonic deformation and thus is not suitable for studying the PTB transition or the terrestrial end-Permian extinction due to an unknown amount of stratigraphy removed/displaced by faulting. In order to clarify the observations of Bourquin et al. (2018), we re-surveyed the Chahe section in further detail recently and our observations suggest that the interpreted deformation by Bourquin et al. (2018) cannot be verified and it also contradicts the regional litho- and bio-stratigraphic and chemostratigraphic results. We provide detailed outcrop imagery and data for all colleagues who are interested in this section to check our observations.

Volcanic sources and diagenetic alteration of Permian–Triassic boundary K-bentonites in Guizhou Province, South China

Terrestrial Permian–Triassic boundary (PTB) sequences in South China usually contain one to three ash beds (K-bentonites), which provide evidence of a possible trigger for the terrestrial mass extinction and are useful as a distinct marker for correlation of the PTB boundary interval from terrestrial to marine areas. Here, we investigate the clay mineralogy and geochemistry of ash beds in the Zhejue and Jiucaichong sections, representing paludal and lacustrine environments, respectively, in order to better understand the source(s) and preservation of these ash beds. The two Zhejue K-bentonites exhibit similar compositions that are distinctly different from that of the Jiucaichong K-bentonite. The former contain mainly clay minerals with minor quartz, anatase, and lepidocrocite, and the clay minerals in these layers are mainly R1 and R3 mixed-layer illite/smectite (I/S) and well-crystallized to poorly-crystallized kaolinite, whereas the latter consists mainly of R3 I/S with minor quartz, feldspars, and anatase. The former have higher CIA values (92.2 and 93.8) than the latter (79.4), indicating more intense chemical weathering that may have been related to deposition in a paludal setting with high organic acid concentrations in pore fluids. These K-bentonites also exhibit differences in major-element chemistry (MgO and K2O contents are higher at Jiucaichong due to lesser weathering intensity and, possibly, early diagenetic uptake from pore fluids), REE chemistry (Jiucaichong exhibits a larger Eu anomaly), and Nd isotopic compositions (Zhejue K-bentonites have 143Nd/144Nd ratios of 0.512436 and 0.512400, higher than the 0.512190 ratio for Jiucaichong). Although some of these compositional differences may be related to the dissimilar chemical environments in which diagenesis occurred (i.e., paludal vs lacustrine), the differences in Eu anomalies and Nd isotopic compositions imply heterogeneous volcanic ash sources. The source of these K-bentonites was probably a continental volcanic arc located on the paleo-southern margin of the South China Craton, within which multiple volcanic vents may have been active concurrently.

Terrestrial Permian–Triassic boundary in southern China: New stratigraphic, structural and palaeoenvironment considerations

The Permian–Triassic boundary is located above the main Phanerozoic terrestrial and marine biotic crisis. Southwest China (eastern Yunnan and western Guizhou) is considered as an ideal place in Asia to study the terrestrial Permian–Triassic boundary, its correlation with the stratigraphically equivalent marine deposits, and to discuss the contemporaneity between the marine and terrestrial extinctions. The Chahe and Zhejue sections, which have already been studied in detail, especially using δ13C isotopic analyses for both sections and geochronology for the Chahe section, are considered to be the reference terrestrial sections to discuss changes (both through time and space) in macroflora, pollen diversity and paleoenvironment. Based on new structural analyses of these sections, we demonstrate that they have been strongly affected by polyphase deformations and are, therefore, not suitable to discuss the vertical and/or lateral evolutions of the depositional environments within the Permian–Triassic succession. The use of the Chahe and Zhejue sections to study the contemporaneity between marine and terrestrial extinction events at the end of the Permian in southern China, as well as the stratigraphic correlations and the palaeoenvironment reconstitution of western Guizhou and eastern Yunnan, therefore, must be reconsidered.

Carbon cycle perturbation expressed in terrestrial Permian–Triassic boundary sections in South China

Stable isotopes of inorganic and organic carbon are commonly used in chemostratigraphy to correlate marine and terrestrial sedimentary sequences based on the assumption that the carbon isotopic signature of the exogenic carbon pool dominates other sources of variability. Here, sediment samples from four Permian–Triassic boundary (PTB) sections of western Guizhou and eastern Yunnan provinces in South China, representing a terrestrial to marine transitional setting, were analyzed for δ13C of organic matter (δ13Corg). These values were subsequently compared to published δ13C values of carbonates (δ13Ccarb) from the Global Stratotype Section and Point at Meishan and many other marine and terrestrial sections. A similar isotopic trend evident through all four sections is characterized by a negative shift of 2–3‰ at the top of the Xuanwei Formation, where we tentatively place the PTB. This negative shift also corresponds to a turnover in the vegetation and the occurrence of fungal spores, which is generally interpreted as a proliferation of decomposers and collapse of complex ecosystems during the end-Permian mass extinction event. Moreover, the absolute values of δ13Corg are more extreme in the more distal (marine) deposits. The δ13Corg values for the studied sediments are more variable compared to coeval δ13Ccarb records from marine records especially in the interval below the extinction horizon. We contend that the depositional environment influenced the δ13Corg values, but that the persisting geographic δ13Corg pattern through the extinction event across the four independent sections is an indication that the atmospheric δ13C signal left an indelible imprint on the geologic record related to the profound ecosystem change during the end-Permian extinction event.

Early Triassic Conchostracans (Crustacea: Branchiopoda) from the terrestrial Permian–Triassic boundary sections in the Moscow syncline

Abstract The Permian–Triassic boundary marks the greatest mass extinction in Earth's history. In order to understand the real causes of this severe extinction event, multidisciplinary investigations around the globe are required. Here, the terrestrial Permian–Triassic boundary sections in the Vladimir region, Central Russia, were sampled bed-by-bed for conchostracan study. In the Early Triassic intervals the following taxa were recognized for the first time: Cornia germari (Beyrich, 1857), Euestheria gutta (Lutkevitch, 1937), Magniestheria mangaliensis (Jones, 1862), Palaeolimnadiopsis vilujensis Varentsov, 1955, and Rossolimnadiopsis Novozhilov, 1958. The wide distribution of C. germari demonstrates their high value for biostratigraphy, since this species was also reported from the Lower Buntsandstein Subgroup in the Germanic Basin as well as from Early Triassic deposits in Hungary, Greenland and Siberia. The assumption of an Early Triassic age of the studied sections is also supported by associated Tupilakosaurus bone fragments, which point to the Tupilakosaurus wetlugensis Zone in the earliest Triassic.

The terrestrial Permian–Triassic boundary event bed is a nonevent: COMMENT

We welcome the fact that [Gastaldo et al. (2009)][1] have been continuing research in the Karoo of South Africa; those of us who have worked there know how important new research in this area is if we are to ever understand the causes of the Permian–Triassic mass extinction on land. However, here

The terrestrial Permian–Triassic boundary event is a nonevent: REPLY

We are pleased to reply to [Ward et al. (2012)][1] about the stratigraphic record of the Karoo Basin where the terrestrial ecosystem response to the End-Permian extinction is recorded. The present extinction model envisions a marine and terrestrial response coupling. The Permian–Triassic boundary

The terrestrial Permian-Triassic boundary event bed is a nonevent

Research Article| March 01, 2009 The terrestrial Permian-Triassic boundary event bed is a nonevent Robert A. Gastaldo; Robert A. Gastaldo 11Department of Geology, Colby College, Waterville, Maine 04901, USA Search for other works by this author on: GSW Google Scholar Johann Neveling; Johann Neveling 22Council for Geosciences, Private Bag x112, Silverton, Pretoria 0001, South Africa Search for other works by this author on: GSW Google Scholar C. Kittinger Clark; C. Kittinger Clark 11Department of Geology, Colby College, Waterville, Maine 04901, USA Search for other works by this author on: GSW Google Scholar Sophia S. Newbury Sophia S. Newbury 11Department of Geology, Colby College, Waterville, Maine 04901, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Robert A. Gastaldo 11Department of Geology, Colby College, Waterville, Maine 04901, USA Johann Neveling 22Council for Geosciences, Private Bag x112, Silverton, Pretoria 0001, South Africa C. Kittinger Clark 11Department of Geology, Colby College, Waterville, Maine 04901, USA Sophia S. Newbury 11Department of Geology, Colby College, Waterville, Maine 04901, USA Publisher: Geological Society of America Received: 13 Jun 2008 Revision Received: 15 Oct 2008 Accepted: 16 Oct 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2009 Geological Society of America Geology (2009) 37 (3): 199–202. https://doi.org/10.1130/G25255A.1 Article history Received: 13 Jun 2008 Revision Received: 15 Oct 2008 Accepted: 16 Oct 2008 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Robert A. Gastaldo, Johann Neveling, C. Kittinger Clark, Sophia S. Newbury; The terrestrial Permian-Triassic boundary event bed is a nonevent. Geology 2009;; 37 (3): 199–202. doi: https://doi.org/10.1130/G25255A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A unique isochronous interval in the Karoo Basin, South Africa, previously has been interpreted to postdate vertebrate extinction at the Permian-Triassic boundary in the Bethulie area, Lootsberg Pass, and elsewhere. It is demonstrated that the laminated beds, or laminites, in the Bethulie region are stratigraphically indistinct. The heterolithic interval exposed on the Heldenmoed farm is ~8 m below the Bethel farm section, <1 km away. At Lootsberg Pass, the laminated interval is below the Permian-Triassic boundary as defined by vertebrate biostratigraphy, rather than overlying it. Hence, this interval, critical to models of end-Permian mass extinction, is neither isochronous across the basin nor unique. Rather, the lithofacies represents avulsion channel-fill deposits within aggradational landscapes. South African models for the response of terrestrial ecosystems to the perturbation in the marine realm require critical reevaluation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Timing of the terrestrial Permian-Triassic boundary biotic crisis: Implications from U-Pb dating of authigenic zircons

The Late Permian to Early Triassic transition represents one of the most important Phanerozoic mass extinction episodes. The cause of this event is still in debate between catastrophic and gradual mechanisms. This study uses the U-Pb method on zircons from the uppermost Permian/lowermost Triassic clay deposits at Chahe (Guizhou Province, SW China) to examine time constraints for this event. The results of both this and previous studies show that the ages of Bed 68a and 68c (the upper clay bed of the terrestrial Permian-Triassic boundary (PTB)) respectively are 252.6±2.8 and 247.5±2.8 Ma. This age (within the margin of error) almost accords with the upper clay bed (Bed 28) age of Meishan and the eruption age of Tunguss Basalt, and is so far the most accurate age obtained from terrestrial PTB. The claystone of Bed 68 was formed in the earliest Triassic. The biotic crisis occurred at nearly the same time in terrestrial and marine environments during Permian-Triassic interval; however the extinction patterns and processes are different. The extinction pattern of the terrestrial plants shows a major decline at the PTB after long-term evolution, followed by a retarded extinction of the relicts in the earliest Triassic.

Palynological assemblages of non-marine rocks at the Permian–Triassic boundary, western Guizhou and eastern Yunnan, South China

Marine and non-marine facies of the Permian–Triassic boundary stratigraphic set (PTBST) are well developed in South China. Palynological assemblages enable subdivision and correlation of the Permian–Triassic boundary (PTB) rocks. Three palynological assemblages are recognized across the PTBST in two terrestrial PTB sections in western Guizhou and eastern Yunnan, South China. Assemblage 1 (Xuanwei Formation) is a Late Permian palynological assemblage dominated by ferns and pteridosperms, with minor gymnosperms. Most taxa are typical long-ranging Paleozoic forms, but the appearance of Lueckisporites confirms a Late Permian age for this assemblage. Assemblage 2 (PTBST) is marked by an abrupt decrease in palynomorph abundance and diversity, and thriving fungal/algal(?) spores. Assemblage 2 is still dominated by ferns and pteridosperms, with a few gymnosperms, but is characterized by a mixed palynoflora containing both Late Permian and Early Triassic elements. Most taxa are typical Late Permian ones also found in Assemblage 1, however, some taxa of Early Triassic aspect, e.g. Lundbladispora and Taeniaesporites, appeared for the first time. In Assemblage 3 (top Xuanwei Formation and Kayitou Formation), the proportion of gymnosperm pollen increases rapidly, exceeding that of ferns and pteridosperms, but the abundance of palynomorphs is still low. Typical Early Triassic taxa (such as Lundbladispora, Aratrisporites and Taeniaesporites) are present in greater abundance and confirms an Early Triassic age for this assemblage.

Characteristics of claystones across the terrestrial Permian-Triassic boundary: Evidence from the Chahe section, western Guizhou, South China

X-ray diffraction (XRD), scanning electronic microscopy (SEM) and X-ray fluorescence spectroscopy (XFS) studies were undertaken for claystones and/or mudstones from the Chahe section—a terrestrial Permian-Triassic boundary (TPTB) section. Our results indicate that the compositions of claystones in the Permian-Triassic boundary (PTB) interval (Beds 66f–68) outlined by biostratigraphy are different from claystones and/or mudstones found either below or above the interval of the same section. The clay minerals in the claystones of the PTB interval are mainly composed of illite–montmorillonite interlayers, with a few montmorillonites and chlorites. The other claystones and/or mudstones underlying and overlying the PTB consist of chlorites and/or kaolinites. Some authigenic clastic minerals, such as hexagonal dipyramid quartz and zircons, are only found in claystones in the PTB interval from the Chahe section and some marine PTB sections in western Guizhou and eastern Yunnan, southwestern China. In addition, some elements are present in abnormal concentrations in the claystones of the PTB interval as well. Most important is that we found no spherules in all the claystones studied, indicating no evidence of an extraterrestrial impact during the Permian-Triassic transition. The particular characteristics of the TPTB claystones at the Chahe section indicate their volcanic origin and thus provide a reliable auxiliary event marker for high-resolution demarcation of the TPTB in South China. They are also indicative in the marine PTB claystones in South China. Thus, the PTB claystones can be used as auxiliary markers for high-resolution correlation of the PTB from marine facies to land in South China when direct fossil evidence in the PTB sequence is lacking.

High-resolution terrestrial Permian–Triassic eventostratigraphic boundary in western Guizhou and eastern Yunnan, southwestern China

The adjoining area of western Guizhou and eastern Yunnan Provinces in southwest China is an ideal place to investigate the feasibility of correlating marine and nonmarine Permian–Triassic boundary (PTB) sequences, as it contains outcrop sections of shallow marine, marginal marine (or paralic), and terrestrial PTB sections, all in close geographic proximity. This paper documents for the first time multiple stratigraphic data from several well-preserved terrestrial PTB sections in the area and attempts to use these data to define, locate, and correlate the PTB in the area. A study of the spores and pollen and vegetation types across the terrestrial PTB sections in the study area suggests three distinct evolutionary stages across the boundary: Stage 1 (Xuanwei Formation) is characterised by Late Permian or Paleozoic-type ferns and pteridosperms (85.0%), with a few gymnosperms (15.0%); stage 2 is marked by an abrupt drop of sporopollen elements of Late Permian aspects, coupled with the appearance of fungal spores and limited Early Triassic palynomorphs; stage 3 (top Xuanwei Formation and Kayitou Formation) is dominated by gymnosperm pollen (58.8%) of clearly Early Triassic aspect, although still retaining limited ferns and pteridosperms. The three biotic stages seem to well correspond with the changing trend of the δ 13C org curves from the same sections, which is characterized by a sharp drop just before the PTB, followed by a short term partial recovery across the boundary, and then succeeded by a gradual decline after the PTB in the Early Triassic. Combining evidence from eventostratigraphic (i.e., the succession of boundary clay beds), biostratigraphic (using both macroplants and palynomorphs), and chemostratigraphic (i.e., organic carbon isotope excursion signals), we propose that a high-resolution PTB succession, closely correlatable to its marine counterpart at the Meishan section in eastern China, is recognisable at the terrestrial PTB sections in the western Guizhou–eastern Yunnan area in southwest China.

Sulfur geochemistry across a terrestrial Permian–Triassic boundary section in the Karoo Basin, South Africa

Concentrations of sulfur and carbon, and isotopic compositions of sulfur were determined in sedimentary rocks from a section across the terrestrial Permian–Triassic (P–Tr) boundary in the northern Karoo Basin, South Africa. High concentrations of sulfide produced by sulfate-reducing bacteria were found in the sedimentary rocks at and just below the perceived P–Tr boundary. The ratios of organic carbon to sulfide of the sedimentary rocks with high concentrations of sulfide are relatively constant and similar to those of marine environments. This means that the enhanced accumulation of sulfide is a result of the enrichment of sulfate in the water. As the sulfide concentrations do not correlate with concentrations of any major elements indicative of weathering intensity, the supply of sulfate was independent of environmental factors, such as temperature and CO2 concentrations in the atmosphere, which control weathering intensity. Therefore, it is reasonable to consider that the sulfate might have been supplied to the freshwater directly as acid rain by an event such as a bolide impact or a volcanic eruption. The absence of evidence for an impact event in the geological record, though, favors volcanic input as the cause of the acid rain.