Smithian-Spathian Boundary Research Articles

Large nitrogen cycle perturbations during the Early Triassic hyperthermal

Ocean temperature, redox state, circulation, and nutrient levels regulate the marine nitrogen (N) cycle, yet their specific impacts during greenhouse intervals remain poorly understood. Here, we examined the Smithian–Spathian hyperthermal event (∼250.5 Ma) during the Early Triassic greenhouse using stable N isotopes (δ15N) from sedimentary records in the Nanpanjiang Basin and Northern Yangtze Basin of South China. The δ15N profiles in both basins reveal consistent trends that correspond to fluctuations in temperature across the Smithian–Spathian transition. The Smithian hyperthermal interval exhibited low δ15N values (mostly <+2‰), indicating N deficiency and enhanced biological N2 fixation. Bacterial blooms and the release of the potent greenhouse gas N2O, enhanced by high temperatures, may have triggered positive feedback mechanisms that sustained the warming and contributed to the late Smithian extinction. During subsequent cooling across the Smithian–Spathian transition, δ15N increased to a range of +3‰ to +7‰, likely reflecting signals of partial denitrification based on reconstruction of the NO3− inventory associated with oceanic cooling and oxygenation. The prevailing increases in sedimentary TOC/TN ratios signify heightened deamination (removal of amino groups) and N recycling across the Smithian–Spathian boundary. This transition is likely attributed to cooling-driven amelioration of seawater stratification and anoxia from the Smithian to the Spathian, which resulted in increased nitrate availability in the photic zone. Eukaryotic algae thrived while prokaryotes declined during the Spathian, evidenced by elevated δ15N and Δ13Ccarb-org (the difference between carbonate and organic carbon isotopes). The proliferation of eukaryotic algae had a positive impact on environmental conditions and facilitated biotic recovery due to more efficient burial of organic particles. A notable latitudinal gradient in the N cycle response was observed, with low-latitude regions showing a more pronounced response to cooling compared to mid-latitude areas. This significant gradient may suggest that the rapid recovery of nutrient cycles, despite relatively small decline in high temperature, was a key factor in the amelioration of climate and recovery of life in low latitudes. These findings highlight that the marine N cycle is highly sensitive to temperature changes, particularly in low-latitude regions, and that changes in N cycle under high-temperature conditions may be a critical life-limiting factor.

Evidence for variable provenance of Mercury anomalies during the Smithian–Spathian (Olenekian)

Mercury (Hg) enrichment recorded in Smithian to Spathian (Olenekian) marine sedimentary successions has been used to link putative renewed Siberian Traps Large Igneous Province (STLIP) magmatism to climatic and environmental perturbations during this interval. To assess the potential for massive volcanism as a trigger for marine environmental disturbances across the Smithian – Spathian boundary (SSB), the patterns and provenance of Hg sequestration in four Tethyan marine sedimentary successions are investigated in the current study. We present a diverse array of new, temporally calibrated geochemical data including Hg concentrations and isotopic compositions, strontium, and neodymium isotope records, as well as major and trace element concentrations from carbonate-poor and -rich strata alike, including volcanic ashes. Results indicate that Hg anomalies in middle to late Smithian strata vary in magnitude and age. Based on several lines of evidence, the Hg anomalies recorded for the investigated PaleoTethyan successions are interpreted to have been sourced from subduction-related arc volcanism, with potential contributions from terrestrial Hg reservoirs. In contrast, a low-magnitude mercury enrichment interval recorded for NeoTethyan late Smithian strata is attributed to hydrothermal fluid or submarine volcanic activity. These results, together with previously published Smithian to Spathian Hg records, provide evidence that Smithian Hg anomalies cannot be attributed to a singular source such as renewed STLIP activity. Instead, the stratigraphically variable mercury anomalies reflect local patterns of enhanced mercury sequestration from various sources during the middle Smithian to SSB. Consequently, evidence for STLIP magmatism during the Smithian – Spathian transition is still lacking, and regional volcanic activity may have been influential in causing marine environmental upheavals in the Tethys region across the SSB.

Lower to Middle Triassic conodont biostratigraphy and carbonate carbon isotope chemostratigraphy of the Zuodeng area, Guangxi, South China, and its relevance for stratigraphic correlation from the Induan to the Anisian

The Nanpanjiang Basin in South China is a vital area for studying the Early Triassic marine ecosystem recovery in the aftermath of the end-Permian mass extinction (EPME). The Zuodeng sections (A, B, and C) are located on the Debao platform, one of the isolated shallow-water platforms within the Nanpanjiang Basin. This area preserves a relatively complete conodont succession from the Lower Triassic to the lower Middle Triassic. Here, a total of 12 conodont zones and 4 subzones are established, namely, the Hindeodus postparvus Zone, the Hindeodus sosioensis Zone, the Neoclarkina krystyni Zone, the Neoclarkina discreta Zone, the Neospathodus dieneri Zone (including the Neospathodus dieneri M1 and Neospathodus dieneri M3 subzones), the Neospathodus cristagalli Zone, the Neospathodus pakistanensis Zone, the Novispathodus waageni eowaageni Subzone, the Novispathodus waageni waageni Subzone, the Neospathodus yangtzeensis-Novispathodus shani Zone, the Novispathodus pingdingshanensis Zone, the Triassospathodus homeri Zone, the Neospathodus triangularis Zone and the Chiosella timorensis Zone.The Permian-Triassic boundary is placed at the base of Bed 48 in the Zuodeng A section, coinciding with the base of the widespread microbialite beds and the carbon isotope excursion. The Induan-Olenekian boundary is placed at the bases of Bed 86 and Bed 21 in the Zuodeng A and Zuodeng B sections, respectively, where Nv. ex gr. waageni occurs at or slightly below the peak of the positive δ13Ccarb excursion. The Smithian-Spathian boundary is recognized at the bases of Bed 92 and Bed 33 in the Zuodeng A and Zuodeng B sections, respectively, based on the first occurrence (FO) of Nv. pingdingshanensis near the middle point of the positive δ13Ccarb excursion. The Olenekian-Anisian boundary is drawn at the top of Bed 5 in the Zuodeng C section based on the FO of Ch. timorensis. The conodont zones recognized in the Zuodeng area correlate well with sections in South China and elsewhere worldwide. The Ns. yangtzeensis-Nv. shani Zone is newly established, and the recognition of this zone in several sections significantly improves the accuracy of stratigraphic subdivision and correlation of the Smithian. The conodont zones in the Zuodeng area thus provide a high-precision time scale for future studies on marine ecosystem recovery in the aftermath of the EPME and environmental events during the Early Triassic.

Calcium isotopes reveal shelf acidification on southern Neotethyan margin during the Smithian-Spathian boundary cooling event

The Smithian-Spathian transition of the late Early Triassic was a critical period of environmental and biological upheavals, following the end-Permian mass extinction. Changes in carbonate deposition during this period have been attributed to intensified upwelling along shelf margins, but relevant studies are scarce. Here, we present calcium isotopes of bulk marine carbonate (δ44/40Cacarb) from a Smithian–Spathian boundary (SSB) succession (Guryul Ravine section, Kashmir) on the southern margin of the Neo-Tethys. Our smoothed δ44/40Cacarb curve reveals a ∼ 0.2‰ negative shift (from ∼ − 1.1‰ to ∼ − 1.3‰) across the SSB, concurrent with a ∼ +10‰ shift in δ13Ccarb. While increased Ca isotopic fractionation could play a role, we specifically examine potential impacts due to changes in marine Ca fluxes. Using a Ca-cycle mass balance model, we explore scenarios of decreased carbonate burial flux (Fcarb), decreased riverine flux (Friv), and a combination of these processes. The modeling suggest that a pulse decrease in Fcarb by 40% over ∼0.06 Myr match the negative shift in δ44/40Cacarb at Guryul Ravine. We infer that this decrease was likely related to intensified upwelling of acidic deep seawater due to invigorated global-oceanic circulation during the SSB cooling event. We suggest that the regionally diverse excursions in δ44/40Cacarb in the Tethyan region could be attributed to spatially varied upwellings in the shelf margin. The upwelling of acidic and anoxic deep seawater may have driven the second-order extinction of ammonoids and conodonts at the beginning of the SSB cooling event.

Upper Changhsingian to lower Anisian conodont biostratigraphy of the Datuguan section, Nanpanjiang Basin, South China

The Great Bank of Guizhou (GBG) of South China is an important area for the study of Lower Triassic conodont biostratigraphy, but few studies have concerned the clastic facies of this region. The Datuguan section in Luodian County, southern Guizhou Province, is a typical clastic ramp section, preserving a relatively complete conodont succession from the uppermost Permian to lower Middle Triassic. A total of nearly 4000 P1 elements were obtained from this section, and 48 conodont species belonging to 16 genera have been identified, including a new species, Gladigondolella luodianensis sp. nov. 12 conodont biozones have been recognized, namely, the Clarkina yini Zone, the C. meishanensis Zone, the Hindeodus postparvus Zone, the Novispathodus waageni Zone, the Discretella discreta Zone, the Nv. pingdingshanensis Zone, the Icriospathodus collinsoni Zone, the Triassospathodus homeri Zone, the Tr. symmetricus Zone, the Tr. triangularis Zone, the Tr. sosioensis Zone, and the Chiosella timorensis Zone in ascending order. These conodont zones improve the resolution of correlation with other sections in this region, as well as globally. Based on the conodont successions and correlation of lithology, the Permian–Triassic boundary (PTB) and the Griesbachian–Dienerian boundary (GDB) are temporarily placed at the middle of Bed 8, 7 m below the top of the Linghao Formation, and the top of Bed 12, 15 m above the bottom of the Luolou Formation, respectively. The Induan–Olenekian boundary (IOB), the Smithian–Spathian boundary (SSB), and the Olenekian–Anisian boundary (OAB) are drawn at Bed 15–1, Bed 27–1, and Bed 42–2, in terms of the first occurrences (FOs) of Nv. waageni sensu lato, Nv. pingdingshanensis, and Ch. timorensis sensu stricto respectively. The conodonts and ammonoids from the Datuguan section supplement the materials of the Guandao section, which is an important reference section for the definition of OAB. In addition, the distribution of segminiplanate conodonts from the platform margin to the basin center has been determined in the Nanpanjiang Basin, revealing that segminiplanates migrated to equatorial region four times and preferred a narrow mid-depth setting during relatively cooler periods of the Early Triassic, in addition to occupying the more oxygenated deep-water basin at other time.

An expanded Smithian–Spathian (Lower Triassic) boundary from a reefal build‐up record in Oman: implications for conodont taxonomy, high‐resolution biochronology and the carbon isotope record

AbstractSome 2.7 myr after the Permian–Triassic boundary mass extinction, a stepwise extinction of the nekton (ammonoids and conodonts) ended at the Smithian–Spathian boundary (SSB) during an episode of climate cooling. SSB records from continental shelves are usually affected by an unconformity, suggesting a forced regression of glacio‐eustatic origin. Here, we document a new 30‐m‐thick SSB section from Jebel Aweri (Batain Plain, Oman) that provides an exceptionally complete and expanded record preserved in an exotic block. Most of this SSB section consists of microbial boundstone build‐ups with a framework of metazoan bioclasts that formed in shallow water on an offshore seamount. In Wadi Musjah (Hawasina nappes, Oman), another exotic block records the SSB in a deeper water setting represented by Hallstatt‐type facies. These two sections provide a unique perspective on the early Spathian rapid re‐diversification of conodonts. They led to a thorough revision of conodont taxonomy around the SSB and to the construction of the highest resolution biochronological scheme for this time interval in the Tethys. A total of five SSB sections from Oman representing both offshore seamounts and lower slope deposits were included in a high‐resolution, quantitative unitary associations (UA) analysis. The resulting 8 conodont biozones are intercalibrated with ammonoid zones and with the carbonate carbon isotope record ultimately placing the SSB in the interval of separation between UAZ3and UAZ4. Only the association ofNovispathodus pingdingshanensiswithIcriospathodus crassatuscan be used to unambiguously characterize the base of the Spathian.

A Unitary Association-based conodont biozonation of the Smithian–Spathian boundary (Early Triassic) and associated biotic crisis from South China

The Smithian–Spathian boundary (SSB) crisis played a prominent role in resetting the evolution and diversity of the nekton (ammonoids and conodonts) during the Early Triassic recovery. The late Smithian nektonic crisis culminated at the SSB, ca. 2.7 Myr after the Permian–Triassic boundary mass extinction. An accurate and high-resolution biochronological frame is needed for establishing patterns of extinction and re-diversification of this crisis. Here, we propose a new biochronological frame for conodonts that is based on the Unitary Associations Method (UAM). In this new time frame, the SSB can thus be placed between the climax of the extinction and the onset of the re-diversification. Based on the study of new and rich conodont collections obtained from five sections (of which four are newly described here) in the Nanpanjiang Basin, South China, we have performed a thorough taxonomical revision and described one new genus and 21 new species. Additionally, we have critically reassessed the published conodont data from 16 other sections from South China, and we have used this new, standardized dataset to construct the most accurate, highly resolved, and laterally reproducible biozonation of the Smithian to early Spathian interval for South China. The resulting 11 Unitary Association Zones (UAZ) are intercalibrated with lithological and chemostratigraphical (δ13Ccarb) markers, as well as with ammonoid zones, thus providing a firm basis for an evolutionary meaningful and laterally consistent definition of the SSB. Our UAZ8, which is characterized by the occurrence of Icriospathodus ex gr. crassatus, Triassospathodus symmetricus and Novispathodus brevissimus, is marked by a new evolutionary radiation of both conodonts and ammonoids and is within a positive peak in the carbon isotope record. Consequently, we propose to place the SSB within the separation interval intercalated between UAZ7 and UAZ8 thus leaving some flexibility for future refinement and updating.

New Early Triassic marine δ13C record from the northeastern Yangtze Platform: Implications for contemporaneous temperature changes and volcanic eruptions

The Early Triassic records the largest inorganic carbon isotope excursions of the Phanerozoic. The causes of these enormous δ13C shifts remain unclear. Here, we present a new high-resolution marine carbonates δ13C record from the Yashan section in the northeastern Yangtze Platform of South China. The δ13C profile shows two significant positive excursions (with maximum δ13C values of ∼ +6‰ and ∼ +9‰, respectively) at the Induan–Olenekian boundary and Smithian–Spathian boundary, which is similar to what is recorded in the shallow platform in Nanpanjiang Basin and in the upper Yangtze Platform area. Negative δ13C excursions during the Griesbachian–early Dienerian, Smithian and middle Spathian, are coincident with warming intervals and accounted for by coeval peaks of volcanic activity (e.g., the release of CO2 from the Siberian Traps and arc volcanism). Enhanced marine primary productivity, as a final effect of massive carbon release, could account for the two positive δ13C excursions, with minor influence of local effects on the magnitude of the shifts. Although the age of volcanism after the Permian–Triassic mass extinction is still not constrained, more lines of evidence support a volcanism-temperature-weathering-productivity mechanism of δ13C perturbations during the Early Triassic.

A massive magmatic degassing event drove the Late Smithian Thermal Maximum and Smithian–Spathian boundary mass extinction

The role of volcanism as a driver of climate change remains widely debated. Following the end-Permian mass extinction, the protracted Early Triassic recovery interval was characterized by extreme climatic and environmental perturbations (hyperwarming, intense subaerial weathering, and extensive marine euxinia) and large carbon- and sulfur-cycle perturbations. Although a magmatic trigger is widely accepted, details regarding the timing and magnitude of degassing and its relationship to contemporaneous climate changes remain poorly understood. In this study, we present new paired carbonate δ13C and carbonate-associated-sulfate δ34S data from deep-water settings in the Lower Triassic of South China to evaluate these issues. Our dataset reveals large positive shifts of both proxies across the Smithian/Spathian boundary (SSB), recording globally synchronous changes in the C and S cycles linked to co-burial of large quantities of organic matter and pyrite. Biogeochemical modeling of the C-S cycles shows that massive carbon release linked to increased magmatic degassing can account for observations of concurrent positive shifts of δ34S and δ13C, enhanced weathering, expanded marine euxinia, and the Late Smithian Thermal Maximum (LSTM). Measured increases in δ13C (+3.2 ± 1.6‰) and δ34S (+7.3 ± 2.3‰) across the SSB relative to their baseline values are consistent with a major magmatic degassing event during the Early to Middle Smithian, whose magnitude and rate we estimate at ~78,000 ± 13,000 Gt C and 0.26 Gt C yr−1, respectively. Our results provide evidence that Early–Middle Smithian degassing was the primary trigger of the LSTM and concurrent biotic crisis.

Depositional framework and trace fossil assemblages of the Lower Triassic Montney Formation, northeastern British Columbia, Western Canada Sedimentary Basin

Hydrocarbon production from the Lower Triassic Montney Formation in northeastern British Columbia, occurs primarily from unconventional reservoirs consisting predominantly of fine-to coarse-grained siltstone beds. In this area, the lithostratigraphy of the formation is difficult to characterize due to the complexities associated with subtle grain-size variation, diminutive biogenic structures, lateral facies variability, and distribution of local discontinuities. Detailed sedimentologic and stratigraphic analyses are essential for understanding and refining the depositional models and stratigraphic framework of the Montney Formation. Based on detailed core examination focused on sedimentological, paleontological and ichnological characteristics, eleven lithofacies and three recurring facies associations are identified within the Lower Triassic Montney Formation in northeastern British Columbia. The lithofacies identified are interpreted to have been deposited in offshore, offshore transition and lower shoreface settings, along a storm-dominated mixed siliciclastic-carbonate ramp. Facies associations include FA(A): siliciclastic distal offshore transition to distal offshore; FA(B): mixed siliciclastic carbonate, storm-influenced offshore to offshore transition; and FA(C): storm-dominated siliciclastic offshore transition to lower shoreface. Trace fossil assemblages correspond to a stressed Cruziana Ichnofacies, and are overall characterized by low diversity (1–6 ichnogenera), small size trace fossils (1–12 mm in diameter), and variable bioturbation intensity (0–6). The vertical variation in SDI values reflect changes in physico-chemical conditions during deposition of the Montney Formation, particularly across the Smithian-Spathian boundary. Understanding the lateral-facies variability and overall stratigraphic architecture of the Montney Formation in northeastern BC, constitute key elements in defining and correlating existing and new potential hydrocarbon reservoirs in the area.

Biomarker evidence for the prolongation of multiple phytoplankton blooms in the aftermath of the end-Permian mass extinction

The end-Permian mass extinction was the most catastrophic event for life in the Phanerozoic eon because it impacted numerous organisms, from micro-sized photosynthetic organisms to large (meter-long) animals and fundamentally altered marine and terrestrial ecosystems. C33n-alkyl cyclohexane (C33-ACH), an angstrom-size molecular fossil of phytoplankton, has been widely found in Permian–Triassic (P-Tr) marine sediments, associated with the collapse of the marine ecosystems at the end-Permian mass extinction. Here, we describe multiple C33-ACH spikes in the Lower Triassic succession at the Chaohu section of the South China Block, which imply that phytoplankton blooms occurred repeatedly during the early–middle Early Triassic. Comparison with previous studies shows that C33-ACH was not only globally enriched at the P-Tr boundary, but also abundant at the Induan–Olenekian boundary and middle Smithian in both the South China and Boreal seas. In addition, the Chaohu section record reveals a C33-ACH peak at the Smithian–Spathian boundary. Moreover, the C33-ACH spikes were synchronous with the peaks of mercury and the pristane/phytane (Pr/Ph) ratio. Since the peaks in mercury and the Pr/Ph ratio indicate increased volcanic activity and large influxes of terrestrial source material into the ocean, the correspondence between the high abundance of C33-ACH with mercury and Pr/Ph ratio peaks implies that volcanism and riverine nutrient input fertilized the surface phytoplankton, which triggered the expansion of anoxia that in turn delayed the benthic metazoan recovery.

Late Permian–Middle Triassic magnetostratigraphy in North China and its implications for terrestrial-marine correlations

A detailed magnetostratigraphic study, linked to a new latest Permian U–Pb ID-TIMS age, was undertaken on the continental Shichuanhe section (SCH) in North China in order to provide a magnetic polarity scale for the Late Permian–early Middle Triassic interval. Tilt-corrected mean directions of the characteristic remanent magnetization pass the reversal test and correspond to a site paleolatitude of 18.1°N during the Early Triassic, consistent with previous results from the North China Block. The magnetostratigraphy shows close similarity with previous studies, allowing interregional correlations with both marine and non-marine records. Normal magnetozone SCH3n, constrained by an absolute age of 252.21±0.15 Ma from an ash bed 3.5 m below its base, is unambiguously correlated to the earliest Triassic normal magnetochron LT1n. Our newly established magnetostratigraphic framework and published carbon-isotope chemostratigraphy, indicate that the Permian–Triassic Boundary is ca. 8 m above the base of SCH3n (within the middle part of the Sunjiagou Formation) at SCH. The overlying reverse polarity dominated interval (SCH3r–SCH5r) ranges to the middle Liujiagou Formation, and straddles an interval from the mid-Griesbachian to mid-Smithian. The base of the Olenekian is provisionally located in the lower part of the Liujiagou Formation, near the base of magnetozone SCH5n. The succeeding thick normal magnetozone SCH6n persists into the upper Heshanggou Formation, with the inferred Smithian–Spathian boundary located in the upper part of the Liujiagou Formation. The transition from reverse magnetozone SCH6r to the overlying normal magnetozone SCH7n, coincides with a clear erosional contact with the base of the Ermaying Formation. Consequently, magnetozone SCH7n is matched to the Early Anisian magnetochron MT3n, with the Olenekian–Anisian boundary interval missing. Our new timescale provides additional magnetostratigraphic constraints on the timing of the terrestrial ecological crisis in North China, which is found to lie within reverse magnetozone SCH2r (equivalent with reverse magnetochron LP3r), a level some 270±150 kyrs before the main marine extinction, that falls in the overlying normal magnetochron LT1n.

Lower Triassic conodont biostratigraphy of the Guryul Ravine section, Kashmir

The Guryul Ravine section in Kashmir, northern India is an important reference section for global Lower Triassic stratigraphy. Once a candidate Global Stratotype Section and Point (GSSP) for the Permian-Triassic Boundary (PTB), the section has attracted intense attention for the PTB beds, but few studies have concerned the entire Lower Triassic stratigraphy. As one of the most continuous marine Lower Triassic successions on the northern margins of Gondwana, the Guryul Ravine section provides an important conodont biostratigraphic yardstick for worldwide correlations. This study presents recent results of the Lower Triassic conodont zonation from the Guryul Ravine section. A total of 6500 elements including 1600 P1 elements were recovered. Ten conodont zones were recognized from the Griesbachian to Spathian: Hindeodus parvus, Isarcicella staeschei, Clarkina planata, Neoclarkina krystyni, Neospathodus dieneri, Ns. pakistanensis, Novispathodus waageni, Scythogondolella mosheri, Nv. pingdingshanensis, and Nv. abruptus – Nv. brevissimus zones. The PTB is placed within Bed 52 in Unit E2, 80 cm above the base of Unit E2, based on the first occurrence (FO) of H. parvus. The Induan–Olenekian boundary (IOB) is tentatively placed at the base of Member G according to the positive maximum δ13Ccarb values, but it could be slightly higher based on conodonts. The Smithian-Spathian boundary (SSB) is drawn at the top of Member H based on the FO of Nv. pingdingshanensis and the carbon mdpt(N3-P3). Several conodont taxa are newly recognized near the top of the study section where the conodont fauna is dominated by segminiplanate elements of the Neogondolellinae. Many of these age-diagnostic species have been identified in other sections around the world, and their occurrence in Guryul Ravine supports their potential for worldwide correlation. The conodont sequence erected from the study section corresponds well to those of South China (e.g. Meishan) and elsewhere worldwide. The newly established conodont zonation from Kashmir provides a high precision time-frame to consider biotic evolution and environmental change during the Early Triassic, a crucial period of Earth history.

Marine productivity variations and environmental perturbations across the early Triassic Smithian-Spathian boundary: Insights from zinc and carbon isotopes

The biotic recovery following the end Permian mass extinction (EPME) was unstable with repeated environmental crises, each of which was followed by a comparably more hospitable interval for life. The early Triassic Smithian-Spathian boundary (SSB) event represents a conspicuous turnover in the environment, climate, and biotic communities. To explore the causes and consequences of this event we measured zinc and carbon isotopes along with elemental paleoenvironment proxies through the West Pingdingshan section, Chaohu, South China. An abrupt decrease of δ66Zn values, along with the highly negative δ13C values occur in the latest Smithian in Beds 47–50 of the section, are coincident with the bio-crisis, and are ascribed to weak marine productivity and extremely hot climatic conditions. Rapid positive shifts in δ13Corg and δ13Ccarb values and high contents of TOC in Beds 51–52, demonstrate elevated marine productivity associated with a surface seawater cooling event, but also resulted in oxygen-starved conditions lethal to organisms. Marine and terrestrial ecosystems recovered in the early Spathian in Beds 53–57, as evidenced by high values of δ66Zn, δ13C and the absence of framboid pyrite, and low Al content. These characteristics indicate a return to normal marine productivity and oxygenated seawater, and decreased terrestrial sediment input. Our findings propose that marine productivity played an important role in affecting the marine Zn cycling across the SSB and provide a scenario of environmental perturbations in response to temperature changes during the SSB transition.

Abundant conodont faunas from the Olenekian (Early Triassic) of subsurface British Columbia, Canada and diversification of the Neogondolellinae around the Smithian–Spathian boundary

Abundant conodont faunas from the subsurface of British Columbia, Canada, allow the correlation of Lower and Middle Triassic strata with outcrop sections in British Columbia, the Canadian Arctic and the western USA, as well as recording the previously recognized radiation of neogondolellin conodonts in the early Spathian. Twenty-eight samples collected from the Progress Hz Caribou D-040-H/094-G-07 and Progress Hz Laprise A-082-I/094-G-01 wells yielded more than 1100 conodont specimens, representing twenty-nine pectiniform species belonging to fourteen genera. These faunas enable the recognition of the Dienerian–Smithian, Smithian–Spathian, and Spathian–Anisian boundaries in these wells. Five of the conodont species recognized in the Smithian and Spathian samples are new: Neogondolella n. sp. A, Borinella n. sp. A, Magnigondolella. n. sp. A, Columbitella n. sp. A, and Co. talpa sp. nov. Together with these new segminiplanate species, several other neogondolellin conodonts occur. These faunas are the manifestation in British Columbia of the previously recognized increase in abundance of neogondolellin conodonts in the early Spathian, and they are consistent with hypotheses in which the earliest species of Magnigondolella evolved from Borinella by a progressive fusion of the denticles of the carina. These conodonts help to characterize the events around the globally significant Smithian–Spathian boundary, and to correlate this boundary in North America.

Smithian (Olenekian, Early Triassic) Conodonts from Ammonoid-Bearing Limestone Blocks at Crittenden Springs, Elko County, Nevada, USA

The ammonoid-bearing limestone blocks at the classic Crittenden Springs ammonoid site belong to the lower part of the Lower Triassic Thaynes Group. These 0.5–1.2 m thick blocks, consisting mainly of bioclastic floatstone and rudstone, contain abundant macro- and micro-fossils such as ammonoids, gastropods, bivalves and scaphopod shells, as well as conodont elements, fish and echinoid remains. Ammonoid and conodont assemblages obtained from three blocks are utilized for biostratigraphical analysis. Twelve informal Smithian ammonoid biostratigraphic intervals from a previous study are condensed into four ammonoid beds, based on the range of age-diagnostic taxa, in ascending order: Meekoceras millardense-M. aff. olivieri beds, Owenites koeneni beds, Anasibirites multiformis bed, and Condensoceras youngi bed. Conodonts recovered from the three blocks consist of 30 species distributed among 15 genera, including one newly described taxon, i.e., Guangxidella minuta Maekawa and Jenks sp. nov. The blocks are divided into two conodont interval zones, i.e., the Novispathodus ex gr. waageni Interval Zone and Nv. pingdingshanensis Interval Zone, based on the first occurrences of their eponymous taxa. Additionally, four conodont range zones, i.e., the Paullella meeki Range Zone, Guangxidella bransoni Range Zone, Scythogondolella milleri Range Zone, and Borinella buurensis Range Zone are recognized, based on the ranges of these four index species. Conodonts within these interval and range zones vary in age from middle Smithian to latest Smithian. The presence of key ammonoid and conodont taxa regarding the Smithian-Spathian boundary (SSB) such as the AW (Anasibirites and Wasatchites) and GXP (Glyptophiceras, Xenoceltites and Pseudosageceras) ammonoid assemblages and the conodonts B. buurensis, Nv. pingdingshanensis and S. milleri demonstrate that the study area is an important reference site for the SSB in the eastern Panthalassa area.

Triassic Foraminifera from the Great Bank of Guizhou, Nanpanjiang Basin, south China: taxonomic account, biostratigraphy, and implications for recovery from end-Permian mass extinction

AbstractForaminifera are important components of tropical marine benthic ecosystems and their recovery pattern from the end-Permian mass extinction can yield insights into the Mesozoic history of this group. Here we report the calcareous and agglutinated foraminifera recovered from five measured stratigraphic sections on the Great Bank of Guizhou, an uppermost Permian to Upper Triassic isolated carbonate platform in the Nanpanjiang Basin, south China. The material contains &gt;100 Triassic species, including three that are newly described (Arenovidalina weiin. sp.,Meandrospira?enosin. sp., andSpinoendotebanella lehrmannin. gen., n. sp.), ranging from Griesbachian (Induan) to Cordevolian (Carnian) age. The species belong to the classes Miliolata, Textulariata, Fusulinata, Nodosariata, and to an unknown class housing all aragonitic forms of the orders Involutinida and Robertinida. Based on previously established conodont zones and carbon isotope chemostratigraphy, the Griesbachian (early Induan) through Illyrian (late Anisian) interval has been subdivided into 12 foraminiferal zones and two unnamed intervals devoid of foraminifera. Following the extinction at the Permian-Triassic boundary, habitable ecological niches of Griesbachian age were invaded by disaster taxa that subsequently became extinct during the Dienerian (late Induan) and left no younger descendants. The disaster taxa were replaced by Lazarus taxa with Permian origins, which were then decimated by the Smithian-Spathian (mid-Olenekian) boundary crisis. The tempo of recovery appears to have been modulated by environmental changes during the Griesbachian through Smithian that involved both climate change and expansion of anoxic ocean bottom waters. Uninterrupted and lasting recovery of benthic foraminifera did not begin until the Spathian.UUID:http://zoobank.org/2a6e9061-b163-402a-9098-8765a80576b3

A Hiatus Obscures the Early Evolution of Modern Lineages of Bony Fishes

About half of all vertebrate species today are ray-finned fishes (Actinopterygii), and nearly all of them belong to the Neopterygii (modern ray-fins). The oldest unequivocal neopterygian fossils are known from the Early Triassic. They appear during a time when global fish faunas consisted of mostly cosmopolitan taxa, and contemporary bony fishes belonged mainly to non-neopterygian (“paleopterygian”) lineages. In the Middle Triassic (Pelsonian substage and later), less than 10 myrs (million years) after the Permian-Triassic boundary mass extinction event (PTBME), neopterygians were already species-rich and trophically diverse, and bony fish faunas were more regionally differentiated compared to the Early Triassic. Still little is known about the early evolution of neopterygians leading up to this first diversity peak. A major factor limiting our understanding of this “Triassic revolution” is an interval marked by a very poor fossil record, overlapping with the Spathian (late Olenekian, Early Triassic), Aegean (Early Anisian, Middle Triassic), and Bithynian (early Middle Anisian) substages. Here, I review the fossil record of Early and Middle Triassic marine bony fishes (Actinistia and Actinopterygii) at the substage-level in order to evaluate the impact of this hiatus–named herein the Spathian–Bithynian gap (SBG)–on our understanding of their diversification after the largest mass extinction event of the past. I propose three hypotheses: 1) the SSBE hypothesis, suggesting that most of the Middle Triassic diversity appeared in the aftermath of the Smithian-Spathian boundary extinction (SSBE; ∼2 myrs after the PTBME), 2) the Pelsonian explosion hypothesis, which states that most of the Middle Triassic ichthyodiversity is the result of a radiation event in the Pelsonian, and 3) the gradual replacement hypothesis, i.e. that the faunal turnover during the SBG was steady and bony fishes were not affected by extinction events subsequent to the PTBME. Based on current knowledge, hypothesis three is favored herein, but further studies are necessary to test alternative hypotheses. In light of the SBG, claims of a protracted diversification of bony fishes after the PTBME should be treated with caution.

Integrated bio-chemostratigraphy of Lower and Middle Triassic marine successions at Spiti in the Indian Himalaya: Implications for the Early Triassic nutrient crisis

In this paper we study the Lilang Super Group in the Spiti area, Indian Himalaya to understand environmental changes in the aftermath of the end-Permian mass extinction. We focus on the Mikin and Kaga Formations, which span the Induan to Ladinian stages of the Lower and Middle Triassic. These strata formed on the southern mid-palaeolatitude margin of East Gondwana and are interpreted as condensed, mixed carbonate – siliciclastic ramp deposits that deepened distally. Carbon isotope ratios of carbonate (δ13Ccarb) show an increase from −2.6 to 0‰ from the Griesbachian substage to the Dienerian-Smithian transition, followed by a negative shift to −3‰ in the Smithian substage and a large positive excursion from −3.0 to 3.5‰ across the Smithian-Spathian boundary. A short negative shift to −1.0‰ occurred in the early Spathian substage, and is followed by a positive trend from ~−1.0 to 1.0‰ in the Middle Triassic, with several minor excursions occurring during the Aegean substage. Carbon isotope ratios of total organic carbon (δ13Corg) co-vary with δ13Ccarb, suggesting that both proxies represent the original isotopic signatures. Sedimentary and palaeontological evidence, as well as trace metal geochemistry (Mo/Al ratio), indicate anoxic conditions developed from the late Griesbachian to the Dienerian substages, and dysoxic to probably fully oxic conditions from the late Dienerian substage onward. Anoxic conditions only very briefly reoccurred in the late Smithian substage. Ti/Ca and Zr/Al ratios suggest a consistently high terrestrial input in the first three substages of the Early Triassic, followed by a decrease across the Smithian–Spathian boundary. Thus, in the Spiti area, the positive δ13Ccarb excursion across the Smithian–Spathian boundary is recorded in generally well‑oxygenated sediments and coincides with a decrease in terrestrial input. While evidence for enhanced weathering is lacking, observations are strongly at odds with studies postulating eutrophication as a universal kill mechanism for the Smithian–Spathian crisis. The strata in the Spiti area contain an Early Triassic gap in phosphorite deposition indicating a ~ 5 Myr waning of coastal upwelling in an otherwise persistent (>100 Myr) upwelling zone of the East Gondwana margin. The phosphorite gap suggests low P availability, low rates of organic matter degradation, and a reduction in nutrient exchange between deep and surface water masses. Altogether, the phosphorite gap, the paucity of sessile and filtering fauna in oxygenated waters, and low organic carbon burial rates indicate a collapse in marine productivity in the aftermath of the end-Permian mass extinction.

Carbon isotope chemostratigraphy and conodont biostratigraphy around the Smithian–Spathian boundary in the Panthalassan carbonate succession (SW Japan)

Abstract The Tahogawa Member of the Triassic Taho Formation in Southwest Japan consists predominantly of light, dark, and brownish gray bedded limestones and contains abundant Lower to Middle Triassic conodonts. The late Smithian to early Spathian sequence of the Tahogawa Member is divided into five conodont zones, in ascending order: Novispathodus ex gr. waageni, Nv. pingdingshanensis, Nv. brevissimus, Triassospathodus symmetricus, and Tr. homeri. The Scythogondolella milleri Subzone of the Nv. ex gr. waageni Zone contains a late Smithian Anasibirites bearing ammonoid bed. The carbon isotope (δ13Ccarb) curve for the late Smithian to early Spathian shows a rapid excursion with values increasing from ~0.11‰ to ~5.88‰ (VPDB). The rise in δ13Ccarb starts in the upper part of the Nv. ex gr. waageni Zone and continues into the overlying Nv. pingdingshanensis Zone. The δ13Ccarb values peak in the Nv. pingdingshanensis Zone at 5.88‰, and subsequently decrease to 1.13‰ in the Tr. symmetricus Zone. The carbon cycle perturbation recorded in the Tahogawa Member corresponds to the late Smithian to early Spathian global carbon isotope positive and following negative excursions reported from the Tethyan, Panthalassan, and Boreal regions. The Smithian–Spathian boundary is probably located within the Nv. pingdingshanensis Zone of the Tahogawa Member, coincident with the decreasing limb of the carbon isotope perturbation. The combination of δ13Ccarb and conodont stratigraphic data enable us to correlate between the eastern Tethys and Panthalassan regions.