Global warming is widely regarded to have played a contributing role in numerous past biotic crises. Here, we show that the end-Permian mass extinction coincided with a rapid temperature rise to exceptionally high values in the Early Triassic that were inimical to life in equatorial latitudes and suppressed ecosystem recovery. This was manifested in the loss of calcareous algae, the near-absence of fish in equatorial Tethys, and the dominance of small taxa of invertebrates during the thermal maxima. High temperatures drove most Early Triassic plants and animals out of equatorial terrestrial ecosystems and probably were a major cause of the end-Smithian crisis.

https://science.sciencemag.org/content/sci/338/6105/366.full.pdf

Lethally Hot Temperatures During the Early Triassic Greenhouse

The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ13C over 90,000 years, and coincided with a δ13C excursion of −5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

https://science.sciencemag.org/content/sci/334/6061/1367.full.pdf

Calibrating the End-Permian Mass Extinction

Stable carbon and oxygen isotopes (δ18O and δ13C values) and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years. As valuable as these insights have been, many problems regarding the interpretation of geochemical signals within mature rocks remain. For example, while the δ18O values of carbonate rocks are dependent both upon the temperature and the δ18O value of the fluid, and additional information including trace element composition aids in interpreting such signals, direct evidence of either the temperature or the composition of the fluids is required. Such information can be obtained by analysing the δ18O value of any fluid inclusions or by measuring the temperature using a method such as the ‘clumped’ isotope technique. Such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well-known tendency for δ18O values of carbonate rocks to decrease with increasing age. Unlike the δ18O, δ13C values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time. However, many studies have not sufficiently emphasized the effects of diagenesis and other post-depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored. Finally, many additional proxies are poised to contribute to the interpretation of carbonate diagenesis. Although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods, care should be taken to understand both old and new proxies before applying them to the ancient record.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/sed.12205

The geochemistry of carbonate diagenesis: The past, present and future

The Dutch ethologist Niko Tinbergen famously distinguished between proximal and ultimate explanations in biology. Proximally, biologists seek a mechanistic understanding of how organisms function; most of this volume addresses the molecular and physiological bases of biomineralization. But while much of biology might be viewed as a particularly interesting form of chemistry, it is more than that. Biology is chemistry with a history, requiring that proximal explanations be grounded in ultimate, or evolutionary, understanding. The physiological pathways by which organisms precipitate skeletal minerals and the forms and functions of the skeletons they fashion have been shaped by natural selection through geologic time, and all have constrained continuing evolution in skeleton-forming clades. In this chapter, I outline some major patterns of skeletal evolution inferred from phylogeny and fossils (Figure 1⇓), highlighting ways that our improving mechanistic knowledge of biomineralization can help us to understand this evolutionary record (see Leadbetter and Riding 1986; Lowenstam and Weiner 1989; Carter 1990; and Simkiss and Wilbur 1989 for earlier reviews).



 Figure 1. 
A geologic time scale for the past 1000 million years, showing the principal time divisions used in Earth science and the timing of major evolutionary events discussed in this chapter. Earlier intervals of time—the Mesoproterozoic (1600–1000 million years ago) and Paleoproterozoic (2500–1600 million years ago) eras of the Proterozoic Eon and the Archean Eon (> 2500 million years ago)—are not shown. Time scale after Remane (2000).



My discussion proceeds from two simple observations:



1. Skeletal biomineralization requires energy and so imposes a metabolic cost on skeleton-forming organisms.

2. Mineralized skeletons have evolved in many clades of protists, plants and animals.



If both statements are true, then clearly for many but not all eukaryotic organisms the biological benefits of biomineralization must outweigh its costs. But cost-benefit ratio is not static. It will change through …

Biomineralization and Evolutionary History

Recent analyses of Sepkoski’s genus-level compendium show that only three events form a statistically separate class of high extinction intensities when only post-Early Ordovician intervals are considered, but geologists have called numerous events mass extinctions. Is this a conflict? A review of different methods of tabulating data from the Sepkoski database reveals 18 intervals during the Phanerozoic have peaks of both magnitude and rate of extinction that appear in each tabulating scheme. These intervals all fit Sepkoski’s definition of mass extinction. However, they vary widely in timing and effect of extinction, demonstrating that mass extinctions are not a homogeneous group of events. No consensus has been reached on the kill mechanism for any marine mass extinction. In fact, adequate data on timing in ecologic, rather than geologic, time and on geographic and environmental distribution of extinction have not yet been systematically compiled for any extinction event.

Phanerozoic biodiversity mass extinctions

Permian-Triassic boundary (PTB) sections from isolated carbonate platforms in the Nanpanjiang Basin of south China contain Upper Permian skeletal packstones with diverse open-marine fossils overlain by a 7–15 m thick boundary horizon composed of calcimicrobial framestone constructed by globular to tufted, calcified cyanobacteria similar to Renalcis. The framestone contains interbeds of lime-grainstone with abundant thin-shelled bivalves and brachiopods. The overlying Lower Triassic strata contain microgastropod lime-packstones followed by a thick succession of thin-bedded lime-mudstones. The PTB event horizon is interpreted to occur at the top of the packstone containing diverse, open-marine fauna and Palaeofusulina and coincident with the abrupt change to calcimicrobial framestone lacking Permian macrofossils. The conformable biostratigraphic boundary occurs at the first appearance of Hindeodus parvus within the basal meter of the calcimicrobial framestone. Intensively studied PTB sections in so...

Permian–Triassic Boundary Sections from Shallow-Marine Carbonate Platforms of the Nanpanjiang Basin, South China: Implications for Oceanic Conditions Associated with the End-Permian Extinction and Its Aftermath

Stable carbon isotope stratigraphy across the Permian-Triassic boundary in shallow marine carbonate platforms, Nanpanjiang Basin, south China

Lower Triassic peritidal cyclic limestone: an example of anachronistic carbonate facies from the Great Bank of Guizhou, Nanpanjiang Basin, Guizhou province, South China

The Nanpanjiang basin occurs in the southern margin of the south China plate. Marine sedimentation dominated from the Late Proterozoic to the Late Triassic when siliciclastic turbidites filled the basin and sedimentation regionally shifted to fluvial deposition. Permian and Triassic carbonate strata record a long history of platform evolution and include diverse architectures and evolutionary histories that reflect the impact of local depositional environments, rates of siliciclastic flux and accelerating tectonic subsidence as the basin experienced tectonic convergence and foreland basin development in the Triassic. The Triassic margin of Yangtze platform that rims the basin extends in a sigmoidal SW/NE trend fromYunnan through Guizhou. Several isolated platforms, including the Great Bank of Guizhou (GBG) and Chongzuo-Pingguo platform, occur within the basin in southern Guizhou and Guangxi. The basin expanded in the Late Permian during a regional transgression. The Yangtze platform and isolated platforms evolved from low-angle ramps with oolite margins in the Early Triassic to steepening Tubiphytes reef margins in the Middle Triassic (Anisian). Basin-wide shift from ramp to steepening-margins was stimulated by the evolution of Tubiphytes and other organisms that stabilized platform margins. The western Yangtze platform (Guanling and Zhenfeng) and northernmost isolated platform (GBG) aggraded and developed steep reef rimmed margins in the Anisian. During the Ladinian the Yangtze platform at Guanling aggraded and intertongued with basin filling clastics, while the margin at Zhenfeng developed a tectonically backstepped morphology controlled by faults. At the same time the eastern sector of the Yangtze platform (Guiyang) evolved from an erosionally collapsed margin to a progradational margin that advanced basinward at least 600 m over basin filling clastics. Unlike the Yangtze platform the northernmost isolated platform (GBG) evolved during the Ladinian from an aggradational reef rim to a high-relief erosional escarpment with a starved basin margin. The western Yangtze platform was drowned and buried by turbidites in the Late Triassic (Carnian) whereas shallow-water carbonate sedimentation continued until burial by siliciclastics in the eastern sector. The isolated platforms exhibit a south to north pattern of step-backed margins and pinnacle development and earlier drowning and burial by siliciclastics in the south versus greater longevity and later drowning in the north. Like the western sector of Yangtze platform, the northernmost isolated platform (GBG) drowned and was buried by clastic sediments in the Later Triassic (Carnian). These differences resulted from faster subsidence rates in the southern part of the basin caused by tectonic convergence along the southern margin of the south China plate. GBG has the longest history of isolated carbonate platforms in the basin. A faulted syncline exposes a continuous two-dimensional cross section through the platform interior and margins, thus facilitating a detailed assessment of its architecture and depositional history. Conformable Permian-Triassic boundary sections, and thick, continuously exposed sections through the Early to Middle Triassic biotic recovery interval make this platform an ideal area for evaluating the marine environments and biotic conditions that operated during the end-Permian extinction and its aftermath.

Youyi Yu

Papers

Permian–Triassic Boundary Sections from Shallow-Marine Carbonate Platforms of the Nanpanjiang Basin, South China: Implications for Oceanic Conditions Associated with the End-Permian Extinction and Its Aftermath

Stable carbon isotope stratigraphy across the Permian-Triassic boundary in shallow marine carbonate platforms, Nanpanjiang Basin, south China

Lower Triassic peritidal cyclic limestone: an example of anachronistic carbonate facies from the Great Bank of Guizhou, Nanpanjiang Basin, Guizhou province, South China

Triassic Depositional History of the Yangtze Platform and Great Bank of Guizhou in the Nanpanjiang Basin of South China