Influence of changes in climate, sea level, and depositional systems on the fossil record of the Neoproterozoic-Early Cambrian metazoan radiation, Australia

Geology ◽  
1992 ◽  
Vol 20 (11) ◽  
pp. 1031 ◽  
Author(s):  
Jeffrey F. Mount ◽  
Catherine McDonald
Keyword(s):  
Sea Level ◽  
Fossil Record ◽  
Early Cambrian ◽  
Depositional Systems

scholarly journals Completeness metrics and the quality of the sauropodomorph fossil record through geological and historical time

Paleobiology ◽  
2010 ◽  
Vol 36 (2) ◽  
pp. 283-302 ◽  
Author(s):  
Philip D. Mannion ◽  
Paul Upchurch
Keyword(s):  
Sea Level ◽  
Fossil Record ◽  
Quantitative Methods ◽  
Phylogenetic Analyses ◽  
Type Specimen ◽  
Time Interval ◽  
Historical Time ◽  
Rock Outcrop ◽  
Type Specimens ◽  
Fossil Remains

Despite increasing concerns about the effect of sampling biases on our reading of the fossil record, few studies have considered the completeness of the fossil remains themselves, and those that have tend to apply non-quantitative measures of preservation quality. Here we outline two new types of metric for quantifying the completeness of the fossil remains of taxa through time, using sauropodomorph dinosaurs as a case study. The “Skeletal Completeness Metric” divides the skeleton up into percentages based on the amount of bone for each region, whereas the “Character Completeness Metric” is based on the number of characters that can be scored for each skeletal element in phylogenetic analyses. For both metrics we calculated the completeness of the most complete individual and of the type specimen. We also calculated how well the taxon as a whole is known from its remains. We then plotted these results against both geological and historical time, and compared curves of the former with fluctuations in sauropodomorph diversity, sea level, and sedimentary rock outcrop area. Completeness through the Mesozoic shows a number of peaks and troughs; the Early Jurassic (Hettangian–Sinemurian) is the interval with highest completeness, whereas the mid-to-Late Cretaceous has completeness levels that are consistently lower than the rest of the Mesozoic. Completeness shows no relationship to rock outcrop area, but it is negatively correlated with sea level during the Jurassic–Early Cretaceous and correlated with diversity in the Cretaceous. Completeness of sauropodomorph type specimens has improved from 1830 to the present, supporting the conclusions of other recent studies. However, when this time interval is partitioned, we find no trend for an increase in completeness from the 1990s onward. Moreover, the 2000s represent one of the poorest decades in terms of average type specimen completeness. These results highlight the need for quantitative methods when assessing fossil record quality through geological time or when drawing conclusions about historical trends in the completeness of taxa. The new metrics may also prove useful as sampling proxies in diversity studies.

Latest Early Cambrian small shelly fossils, trilobites, and Hatch Hill dysaerobic interval on the Québec continental slope

2002 ◽  
Vol 76 (2) ◽  
pp. 287-305 ◽  
Author(s):  
Ed Landing ◽  
Gerd Geyer ◽  
Kenneth E. Bartowski
Keyword(s):  
New York ◽  
Sea Level ◽  
Continental Slope ◽  
Sea Level Change ◽  
Early Cambrian ◽  
The West ◽  
Fossil Assemblage ◽  
Level Change ◽  
New Name ◽  
Small Shelly Fossils

Latest Early Cambrian continental slope deposition of the early Hatch Hill dysaerobic interval (new name, latest Early Cambrian—earliest Ordovician) is recorded by dark grey shales and turbidite limestones in the Bacchus slice at Ville Guay, Québec. Platform-derived microfaunas of the Bicella bicensis trilobite assemblage were transported into a dysoxic environment of the upper “Anse Maranda Formation,” and many organisms were buried alive. Phosphatization preserved a diverse skeletal fossil assemblage that includes four agnostid trilobites, echinoderm debris, and twenty small shelly fossil taxa. The latter include five helcionellids; Pelagiella Matthew, 1895b, classified herein as a gastropod; a bivalve (Fordilla Barrande, 1881); the brachiopod Linnarssonia taconica Walcott, 1887; two conodontomorphs; four hyoliths; and such phosphatic and calcareous problematica as Coleoloides Walcott, 1889, emend. Most small shelly fossil taxa, including Discinella micans Billings, 1872, range through much of the Olenellus Zone and Elliptocephala asaphoides assemblage interval. Trilobites allow a more resolved correlation into the uppermost Olenellus Zone. A comparable stratigraphy occurs in Cambrian—Ordovician slope facies of the Bacchus slice and the Giddings Brook slice in eastern New York. The “Anse Maranda Formation” correlates with the West Granville—Browns Pond—lower Hatch Hill formations in eastern New York and brackets two dysaerobic intervals (Browns Pond and early Hatch Hill). Sea-level change associated with the Hawke Bay regression between the Browns Pond and Hatch Hill onlap/dysaerobic intervals led to the longest period of oxygenated green shale and sandstone deposition on the east Laurentian slope in the late Early Cambrian-earliest Ordovician.

Occurrence of the siliceous sponge spicule Konyrium (Hexactinellida) in the upper Cambrian of the Mackenzie Mountains, northwestern Canada

2002 ◽  
Vol 76 (3) ◽  
pp. 565-569 ◽  
Author(s):  
Brian R. Pratt
Keyword(s):  
Fossil Record ◽  
Southern China ◽  
South Australia ◽  
Early Cambrian ◽  
Siliceous Sponge ◽  
Sponge Spicule ◽  
Animal Phyla ◽  
Sponge Diversity ◽  
Siliceous Sponges ◽  
Late Neoproterozoic

The fossil record of siliceous sponges—Hexactinellida and demosponge “Lithistida”—hinges upon both body fossils plus isolated spicules mostly recovered from limestones by acid digestion. The earliest record of siliceous sponge spicules extends back to the late Neoproterozoic of Hubei, southern China (Steiner et al., 1993) and Mongolia (Brasier et al., 1997), and body fossils attributed to the hexactinellids have been described from the Ediacaran of South Australia (Gehling and Rigby, 1996); thus they are the oldest-known definite representatives of extant animal phyla. The Early Cambrian saw a remarkable diversification in spicule morphology, with the appearance of an essentially “modern” array of forms (Zhang and Pratt, 1994). While a diversity decline may have occurred with the late Early Cambrian extinction(s), the subsequent Paleozoic and Mesozoic fossil record of spicules shows a relatively consistent range of morphologies (e.g., Mostler, 1986; Bengtson et al., 1990; Webby and Trotter, 1993; Kozur et al., 1996; Zhang and Pratt, 2000). However, because spicule form is not restricted to individual taxa and many sponge species secrete a variety of spicule shapes, it is difficult to gauge true siliceous sponge diversity and to explore their biostratigraphic utility using only isolated spicules.

scholarly journals A unique fossil record from neptunian sills: the world’s most extreme example of stratigraphic condensation (Jurassic, western Sicily)

2017 ◽  
Vol 67 (2) ◽  
pp. 163-200 ◽  
Author(s):  
Jobst Wendt
Keyword(s):  
Sea Level ◽  
Host Rock ◽  
Fossil Record ◽  
Unique Feature ◽  
Extreme Case ◽  
Sea Floor ◽  
Western Tethys ◽  
Earth History ◽  
Sea Level Oscillations ◽  
Western Sicily

AbstractNeptunian sills at Rocca Busambra, a fragment of the Trapanese/Saccense Domain in western Sicily, host the most abundant ammonite and gastropod fauna which has ever been recorded from the Jurassic of the western Tethys. The fauna is dominated by parautochthonous organisms which were swept into the sills by gentle transport. Ammonites are characterized by perfect preservation and small size, a feature which is due to the predominance of microconchs but also of stunting. The most complete sill is 0.7 m thick and could be separated into 17 levels which range in age from the early Toarcian into the late Kimmeridgian, thus representing the most extreme case of palaeontologically and depositionally documented stratigraphic condensation in Earth history. The unique feature of the Rocca Busambra sills is due to the interaction of three processes: extreme stratigraphic condensation on the sea floor, weak tectonic fracturing of the host rock and repeated reopening on top of already existing sills. Contrasting percentages of gastropods in individual levels reflect sea-level oscillations which correspond to long known low- and highstands during the Jurassic of the western Tethys. Comparisons with other ammonite-bearing sill faunas reveal several similarities, but represent only short-timed phases of tectonic pulses and deposition.

Faunas and Cambrian volcanism on the Avalonian marginal platform, southern New Brunswick

2008 ◽  
Vol 82 (5) ◽  
pp. 884-905 ◽  
Author(s):  
Ed Landing ◽  
Susan C. Johnson ◽  
Gerd Geyer
Keyword(s):  
New Brunswick ◽  
Sea Level ◽  
Lower Cambrian ◽  
Volcanic Edifice ◽  
Early Cambrian ◽  
Early Paleozoic ◽  
Middle Cambrian ◽  
Cool Water ◽  
Senior Synonym ◽  
Lane Formation

The Cambrian inlier at Beaver Harbour, southern New Brunswick, is now confidently referred to the marginal platform of the late Proterozoic–Early Paleozoic Avalon microcontinent. The sub-trilobitic Lower Cambrian Chapel Island and Random Formations are unconformably overlain by the mafic volcanic-dominated Wade's Lane Formation (new). Late Early Cambrian trilobites and small shelly taxa in the lowest Wade's Lane demonstrate a long Random–Wade's Lane hiatus (middle Terreneuvian–early Branchian). Latest Early–middle Middle Cambrian pyroclastic volcanism produced a volcanic edifice at Beaver Harbour that is one of three known volcanic centers that extended 550 km along the northwest margin of Avalon. Middle Middle Cambrian sea-level rise, probably in theParadoxides eteminicusChron, mantled the extinct volcanics with gray-green mudstone and limestone of the Fossil Brook Member. Black, dysoxic mudstone of the upper Manuels River Formation (upper Middle Cambrian,P. davidisZone) is the youngest Cambrian unit in the Beaver Harbour inlier.Lapworthella cornu(Wiman, 1903) emend., a senior synonym of the genotypeL. nigra(Cobbold, 1921),Hyolithellus sinuosusCobbold, 1921, and probablyAcrothyra seraMatthew, 1902a, range through the ca. 8 m.y. of the trilobite-bearing upper Lower Cambrian, andH. sinuosusandA. serapersist into the middle Middle Cambrian.Lapworthella cornuandH. sinuosusreplaced the tropical taxaL. schodackensis(Lochman, 1956) andH. micansBillings, 1872, in cool-water Avalon.

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