ONE PULSE OR TWO? COMBINING SIMULATIONS OF SEQUENCE-STRATIGRAPHIC ARCHITECTURE AND DIVERSIFICATION PROCESSES TO MODEL THE EXPRESSION OF THE LATE ORDOVICIAN MASS EXTINCTION

Interpretations of the tempo of mass extinctions and recoveries often rely on the distribution of fossils in a stratigraphic column. These interpretations are generally compromised when they are not based on a knowledge of marine ecological gradients and sequence-stratigraphic architecture. Crucially, last and first occurrences of species do not record times of extinction and origination. A face-value interpretation of the stratigraphic record leads to incorrect inferences of pulsed extinction, underestimates of the duration of mass extinction, and overestimates of local recovery times. An understanding of the processes of extinction and recovery is substantially improved by knowledge of the distribution of species along marine environmental gradients, interpreting sequence-stratigraphic architecture to show how those gradients are sampled through time, and sampling along regional transects along depositional dip. Doing so suggests that most ancient mass extinctions were substantially longer and local recoveries substantially shorter than generally thought. ▪ The concepts that let geologists find petroleum allow paleontologists to reinterpret ancient mass extinctions and their recoveries. ▪ Most ancient mass extinctions were longer than the fossil record suggests, lasting hundreds of thousands of years to a few million years. ▪ Ancient recoveries from mass extinctions were shorter than thought and likely overlapped with extinction during a period of turnover.

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Palaeoecological analysis of maximum flooding zones from the Tithonian (Upper Jurassic) of the Kachchh Basin, western India

Facies ◽

10.1007/s10347-020-00617-6 ◽

2020 ◽

Vol 67 (1) ◽

Author(s):

Franz T. Fürsich ◽

Matthias Alberti ◽

Dhirendra K. Pandey

Keyword(s):

Upper Jurassic ◽

Carbonate Content ◽

Western India ◽

Rift Basin ◽

Benthic Assemblages ◽

Depositional Sequence ◽

Sequence Stratigraphic ◽

Stratigraphic Architecture ◽

Kachchh Basin ◽

Rich Fauna

AbstractThe siliciclastic Jhuran Formation of the Kachchh Basin, a rift basin bordering the Malagasy Seaway, documents the filling of the basin during the late syn-rift stage. The marine, more than 700-m-thick Tithonian part of the succession in the western part of the basin is composed of highly asymmetric transgressive–regressive cycles and is nearly unfossiliferous except for two intervals, the Lower Tithonian Hildoglochiceras Bed (HB) and the upper Lower Tithonian to lowermost Cretaceous Green Ammonite Beds (GAB). Both horizons represent maximum flooding zones (MFZ) and contain a rich fauna composed of ammonites and benthic macroinvertebrates. Within the HB the benthic assemblages change, concomitant with an increase in the carbonate content, from the predominantly infaunal “Lucina” rotundata to the epifaunal Actinostreon marshii and finally to the partly epifaunal, partly infaunal Eoseebachia sowerbyana assemblage. The Green Ammonite Beds are composed of three highly ferruginous beds, which are the MFZ of transgressive–regressive cycles forming the MFZ of a 3rd-order depositional sequence. The GAB are highly ferruginous, containing berthieroid ooids and grains. GAB I is characterized by the reworked Gryphaea moondanensis assemblage, GAB II by an autochthonous high-diversity assemblage dominated by the brachiopods Acanthorhynchia multistriata and Somalithyris lakhaparensis, whereas GAB III is devoid of fossils except for scarce ammonites. The GAB are interpreted to occupy different positions along an onshore–offshore transect with increasing condensation offshore. Integrated analyses of sedimentological, taphonomic, and palaeoecological data allow to reconstruct, in detail, the sequence stratigraphic architecture of sedimentary successions and to evaluate their degree of faunal condensation.

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Hirnantia Fauna from the Condroz Inlier, Belgium: another case of a relict Ordovician shelly fauna in the Silurian?

Journal of Paleontology ◽

10.1017/jpa.2021.74 ◽

2021 ◽

pp. 1-27

Author(s):

Sofia Pereira ◽

Jorge Colmenar ◽

Jan Mortier ◽

Jan Vanmeirhaeghe ◽

Jacques Verniers ◽

...

Keyword(s):

Sea Level ◽

Mass Extinction ◽

Late Ordovician ◽

Lake District ◽

Low Diversity ◽

Hirnantia Fauna ◽

And Sea Level

Abstract The end-Ordovician mass extinction, linked to a major glaciation, led to deep changes in Hirnantian–Rhuddanian biotas. The Hirnantia Fauna, the first of two Hirnantian survival brachiopod-dominated communities, characterizes the lower–mid Hirnantian deposits globally, and its distribution is essential to understand how the extinction took place. In this paper, we describe, illustrate, and discuss the first macrofossiliferous Hirnantia Fauna assemblage from Belgium, occurring in the Tihange Member of the Fosses Formation at Tihange (Huy), within the Central Condroz Inlier. Six fossiliferous beds have yielded a low-diversity, brachiopod-dominated association. In addition to the brachiopods (Eostropheodonta hirnantensis, Plectothyrella crassicosta, Hirnantia sp., and Trucizetina? sp.), one trilobite (Mucronaspis sp.), four pelmatozoans (Xenocrinus sp., Cyclocharax [col.] paucicrenulatus, Conspectocrinus [col.] celticus, and Pentagonocyclicus [col.] sp.), three graptolites (Cystograptus ancestralis, Normalograptus normalis, and ?Metabolograptus sp.), together with indeterminate machaeridians and bryozoans were identified. The graptolite assemblage, from the Akidograptus ascensus-Parakidograptus acuminatus Biozone, indicates an early Rhuddanian (Silurian) age, and thus, an unexpectedly late occurrence of a typical Hirnantia Fauna. This Belgian association may represent an additional example of relict Hirnantia Fauna in the Silurian, sharing characteristics with the only other known from Rhuddanian rocks at Yewdale Beck (Lake District, England), although reworking has not been completely ruled out. The survival of these Hirnantian taxa into the Silurian might be linked to delayed post-glacial effects of rising temperature and sea-level, which may have favored the establishment of refugia in these two particular regions that were paleogeographically close during the Late Ordovician–early Silurian.

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Long-lived glaciation in the Late Ordovician? Isotopic and sequence-stratigraphic evidence from western Laurentia

Geology ◽

10.1130/g21219.1 ◽

2005 ◽

Vol 33 (2) ◽

pp. 109 ◽

Cited By ~ 184

Author(s):

Matthew R. Saltzman ◽

Seth A. Young

Keyword(s):

Late Ordovician ◽

Sequence Stratigraphic

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Llandovery (early Silurian) crinoids from Hiiumaa Island, western Estonia

Journal of Paleontology ◽

10.1017/jpa.2016.120 ◽

2016 ◽

Vol 90 (6) ◽

pp. 1138-1147 ◽

Cited By ~ 6

Author(s):

William I. Ausich ◽

Mark A. Wilson

Keyword(s):

Mass Extinction ◽

Late Ordovician

AbstractRhuddanian crinoid faunas are poorly known globally, making this new fauna from the Hilliste Formation of western Estonian especially significant. The Hilliste fauna is the oldest Silurian fauna known from the Baltica paleocontinent, thus this is the first example of the crinoid recovery fauna after the Late Ordovician mass extinction. Hiiumaacrinus vinni n. gen. n. sp., Protaxocrinus estoniensis n. sp., Eomyelodactylus sp., calceocrinids, and five holdfast types are reported here. Although the fauna has relatively few taxa, it is among the most diverse Rhuddanian faunas known. Similar to other Rhuddanian crinoid faunas elsewhere, the Hilliste crinoid fauna contains crinoids belonging the Dimerocrinitidae, Taxocrinidae, Calceocrinidae, and Myelodactylidae; most elements of the new fauna are quite small, perhaps indicative of the Lilliput Effect.

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