On the causes of mass extinctions

The temporal link between mass extinctions and large igneous provinces is well known. Here, we examine this link by focusing on the potential climatic effects of large igneous province eruptions during several extinction crises that show the best correlation with mass volcanism: the Frasnian-Famennian (Late Devonian), Capitanian (Middle Permian), end-Permian, end-Triassic, and Toarcian (Early Jurassic) extinctions. It is clear that there is no direct correlation between total volume of lava and extinction magnitude because there is always suffi cient recovery time between individual eruptions to negate any cumulative effect of successive fl ood basalt eruptions. Instead, the environmental and climatic damage must be attributed to singlepulse gas effusions. It is notable that the best-constrained examples of death-byvolcanism record the main extinction pulse at the onset of (often explosive) volcanism (e.g., the Capitanian, end-Permian, and end-Triassic examples), suggesting that the rapid injection of vast quantities of volcanic gas (CO 2 and SO 2 ) is the trigger for a truly major biotic catastrophe. Warming and marine anoxia feature in many extinction scenarios, indicating that the ability of a large igneous province to induce these proximal killers (from CO 2 emissions and thermogenic greenhouse gases) is the single most important factor governing its lethality. Intriguingly, many voluminous large igneous province eruptions, especially those of the Cretaceous oceanic plateaus, are not associated with signifi cant extinction losses. This suggests that the link between the two phenomena may be controlled by a range of factors, including continental confi guration, the latitude, volume, rate, and duration of eruption, its style and setting (continental vs. oceanic), the preexisting climate state, and the resilience of the extant biota to change.

Large igneous provinces and mass extinctions: An update

The Mesozoic stratigraphic record of the southern Qiangtang basin in central Tibet records the evolution and closure of the Bangong-Nujiang ocean to the south. The Jurassic succession includes Toarcian-Aalenian shallow-marine limestones (Quse Formation), Aalenian-Bajocian feldspatho-litho-quartzose to feldspatho-quartzo-lithic sandstones (shallow-marine Sewa Formation and deep-sea Gaaco Formation) and Bathonian outer platform to shoal limestones (Buqu Formation). This succession is truncated by an angular unconformity, overlain by upper Bathonian to lower Callovian fan-delta conglomerates and litho-quartzose to quartzo-lithic sandstones (Biluoco Formation) and Callovian shoal to outer-platform limestones (Suowa Formation). Sandstone petrography coupled with detrital-zircon U-Pb and Hf isotope analysis indicate that the Sewa and Gaaco formations contain intermediate to felsic volcanic detritus and youngest detrital zircons (183-170 Ma) with eHf(t) ranging widely from +13 to -25, pointing to continental-arc provenance from igneous rocks with mixed mantle and continental-crust contributions. An arc-trench system thus developed towards the end of the Early Jurassic, with the southern Qiangtang basin representing the forearc basin. Above the angular unconformity, the Biluoco Formation documents a change to dominant sedimentary detritus including old detrital zircons (mainly > 500 Ma ages in the lower part of the unit) with age spectra similar to those from Paleozoic strata in the central Qiangtang area. A major tectonic event with intense folding and thrusting thus took place in late Bathonian time (166 ± 1 Ma), when the Qiangtang block collided with another microcontinental block possibly the Lhasa block.

Sedimentary and tectonic evolution of the southern Qiangtang basin: Implications for the Lhasa-Qiangtang collision timing

https://hera.ugr.es/doi/16656192.pdf?origin=publication_detail

Carbon–isotope stratigraphy and ammonite faunal turnover for the Middle Jurassic in the Southern Iberian palaeomargin

An analysis is presented of the diversity and faunal turnover of Jurassic ammonites related to transgressive/regressive events. The data set contained 400 genera and 1548 species belonging to 67 ammonite zones covering the entire Jurassic System. These data were used in the construction of faunal turnover curves and ammonite diversities, that correlate with sea-level fluctuation curves. Twenty-four events of ammonite faunal turnover are analyzed throughout the Jurassic. The most important took place at the Sinemurian-Carixian boundary, latest Carixian-Middle Domerian, Domerian-Toarcian boundary, latest Middle Toarcian-Late Toarcian, Toarcian-Aalenian boundary, latest Aalenian-earliest Bajocian, latest Early Bajocian-earliest Late Bajocian, Early Bathonian-Middle Bathonian boundary, latest Middle Bathonian-earliest Late Bathonian, latest Bathonian-Early Callovian, earliest Early Oxfordian-Middle Oxfordian, earliest Late Oxfordian-latest Oxfordian, latest Early Kimmeridgian, Late Kimmeridgian, middle Early Tithonian and Early Tithonian-Late Tithonian boundary. More than 75 percent of these turnovers correlate with regressive-transgressive cycles in the Exxon, and/or Hallam′s sea-level curves. In most cases, the extinction events coincide with regressive intervals, whereas origination and radiation events are related to transgressive cycles. The turnovers frequently coincide with major or minor discontinuities in the Subbetic basin (Betic Cordillera).

Evolutionary Rates of Jurassic Ammonites in Relation to Sea-level Fluctuations

A biostratigraphical and taxonomic revision of the genus Euhoploceras is presented using new material collected from the Upper Aalenian–Lower Bajocian of south-west England and the Betic Cordillera (Spain). Euhoploceras is shown to range from the uppermost Aalenian (Concavum Zone, Limitatum Subzone) to the Lower Bajocian (Laeviuscula Zone). S. S. Buckman's 69 species of Sonninia are grouped into three macroconch morphospecies: Euhoploceras acanthodes (Buckman), strongly ornamented, with tubercles and strong ribs throughout ontogeny; Euhoploceras marginatum (Buckman) with tuberculate inner whorls and relatively strong ribs persisting to the outer whorls, and Euhoploceras modestum (Buckman) with ribbed, sometimes slightly tuberculate inner whorls, becoming smooth or only slightly ornamented in later stages of coiling. Euhoploceras adicrum (Waagen) is a younger species with a type horizon in the Laeviuscula Zone. Dimorphism and possible polymorphism are present in both English and Spanish faunas. Euhoploceras subspinosum (Buckman) probably represents dwarf forms of E. acanthodes[M] and is included as a junior synonym of the latter; likewise, E. subdecoratum (Buckman) may belong with E. marginatum[M], although they are described separately herein. Some of the microconchs of Euhoploceras[M] are probably represented by Nannoceras. Similarities between English and Betic Euhoploceras confirm that during late Aalenian–earliest Bajocian times, the English and Spanish palaeobiogeographical regions were connected. The ammonite assemblages revised here come from the Concavum to Ovalis zones.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.0031-0239.2000.00137.x

The sonniniid ammonite Euhoploceras from the Middle Jurassic of south-west England and southern Spain

We present a modern revision of the dimorphic ammonite pair Strigoceras QUENSTEDT, 1886/Cadomoceras MUNIER-CHALMAS, 1892 from the Middle Jurassic. The stratigraphically oldest hitherto known chronospecies of Strigoceras, S. praenuntium (BUCKMAN) appears in the Middle Aalenian as an extreme rarity. Records of the microconch genus Cadomoceras remain unknown from strata older than Early Bajocian, but otherwise its stratigraphical range corresponds well with that of the macroconchs. The genus probably became extinct in the Early Bathonian (Zigzag Zone). The youngest known Strigoceras is S. callomoni n. sp. described here from the Macrescens Subzone of the Early Bathonian. Another new strigoceratid species, Granulochetoceras oppeliisculptum n. sp., is recorded by a single specimen from the early Garantiana Zone of eastern Spain, representing an interesting phyletic link between Strigoceras QUENSTEDT, 1886 and Granulochetoceras GEYER, 1960. We include a brief review of the latter genus. By including Granulochetoceras in the Strigoceratidae the family would extend to the Late Kimmeridgian of the Late Jurassic. The palaeogeographic distribution of Strigoceras/Cadomoceras is focussed on the western Tethyan Province, but some species also occur in the northern Pacific and its adjacent shelves. A benefit of this large area of distribution is that strigoceratids may be used to correlate distant locations, but this is partly hampered by the relatively wide range of variability within succeeding chronospecies and remarkably large variation in size of adult macroconchs.

Revision of the Middle Jurassic dimorphic ammonite genera Strigoceras/Cadomoceras (Strigoceratidae) and related forms

Latest Toarcian-earliest Bajocian (Jurassic) Grammoceratinae (Hildoceratidae, Ammonitina) of the western Tethys: Their palaeobiogeographic and phylogenetic significance

Aalenian and Bajocian ammonites from the Qiangtang block (North Tibet) are described. Comparisons with successions of similar age in Europe allow the establishment of a correlation at zonal level. The relationship between early stephanoceratids and the otoitid Emileites is discussed. Emileites callomoni sp. nov. is erected. Haplopleuroceras , Fontannesia , Witchellia and Sonninia also occur and their significance highlighted. A lectotype for Haplopleuroceras mundum Buckman is designated.

Aalenian to Lower Bajocian ammonites from the Qiangtang block (North Tibet)

Two new species of stephanoceratid ammonites are erected: Stephanoceras (Riccardiceras) eoeteosum sp. nov. and Stephanoceras (Skirroceras) englandi sp. nov. from the Inferior Oolite Formation of Dorset, UK. They represent the first and last members of a chronocline of serpenticonic morphospecies. The stratigraphical position of Rhytostephanus rhytus Buckman is reviewed, necessitating a change in the faunal horizon scheme. The term mesoconch is proposed for use in describing microsomic macroconchs, the function of which is considered. Names applied to morphospecies and their uses are reviewed. The role of conservation is discussed in respect of preserving Dorset Inferior Oolite exposures.

Robert B. Chandler

Papers

The sonniniid ammonite Euhoploceras from the Middle Jurassic of south-west England and southern Spain

Revision of the Middle Jurassic dimorphic ammonite genera Strigoceras/Cadomoceras (Strigoceratidae) and related forms

Latest Toarcian-earliest Bajocian (Jurassic) Grammoceratinae (Hildoceratidae, Ammonitina) of the western Tethys: Their palaeobiogeographic and phylogenetic significance

Aalenian to Lower Bajocian ammonites from the Qiangtang block (North Tibet)

Two new stephanoceratid ammonites from the Aalenian-Lower Bajocian (Middle Jurassic, Dorset, UK) and their phylogenetic significance