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Trace fossils and correlation of late Precambrian and early Cambrian strata
- T. Peter Crimes
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- Journal:
- Geological Magazine / Volume 124 / Issue 2 / March 1987
- Published online by Cambridge University Press:
- 01 May 2009, pp. 97-119
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Trace fossils are abundant and diverse in many clastic sequences spanning the Precambrian-Cambrian boundary and may prove to be the most useful palaeontological method for global correlation in this stratigraphic interval. The ichnofaunas of the latest Precambrian (Vendian) rocks include some forms whose range does not extend into the Cambrian (e.g. Bilinichnus, Intrites, Palaeopascichnus, Vendichnus, Vimenites) and others which continue throughout most or all of the Phanerozoic (e.g. Arenicolites, Aulichnites, Cochlichnus, Didymaulichnus, Gordia, Neonereites, Planolites, Skolithos). At least 50 ichnogenera make their first appearance below the lowest trilobites in sections with broad geographic spread. A few of these appear to have a short time range, extending to about the incoming of the trilobites (e.g. Astropolichnus, Didymaulichnus miettensis, Plagiogmus, Taphrhelminthopsis circularis), but the majority continue through most or all of the Phanerozoic.
For correlation of Precambrian-Cambrian boundary sequences it is therefore possible to use both the occurrence of those ichnogenera with a short time range and the incoming of those with an extended range. Three stratigraphical zones can be recognized with respect to the incoming of trace fossils. Zone I is of Upper Vendian age and includes Arenicolites, Bilinichnus, Cochlichnus, Didymaulichnus, Gordia, Harlaniella, Intrites, Nenoxites, Neonereites, Palaeopascichnus, Skolithos, Vendichnus and Vimenites. In Zone II, of Lower Tommotian age, the earliest examples of Bergaueria, Phycodes, Teichichnus and Treptichnus are encountered. Many trace fossils appear in Zone III, which extends from Upper Tommotian to Lower Atdabanian, but the most important are: Astropolichnus, Cruziana, Diplichnites, Diplocraterion, Dimorphichnus, Plagiogmus, Rusophycus and Taphrhelminthopsis circularis.
This vertical zonation of trace fossils allows an attempt at world-wide correlation, from which the most significant conclusions are that the Vendian/Tommotian boundary can probably be placed: (i) near the middle of the McNaughton Formation in the Rocky Mountains, Canada; (ii) at the base of the Deep Spring Formation or in the underlying Reed Dolomite in the White Inyo Mountains, California, U.S.A.; (iii) low in the Chapel Island Formation in the Burin Peninsula, Newfoundland, Canada; (iv) at or close to the base of the Candana Quartzite in North Spain; (v) at or below the base of the Breivik Member in Finnmark, Norway; and (vi) near or below the base of the Zhongyicun Member at Meischucun, China.
The sections in the Burin Peninsula, Newfoundland and Meischucun, China are favoured candidates for the global stratotype for the Precambrian-Cambrian boundary. In the Burin Peninsula, the trace fossils suggest that the Tommotian/Atdabanian boundary may be within or at the base of the Random Formation, thereby implying that the Tommotian may include a thickness of 500 m of sediment comprising at least most of the Chapel Island Formation. At Meishucun, the ichnofaunal evidence implies that the Tommotian/Atdabanian boundary is probably no higher than the top of the Zhongyicun Member. The thickness of the Tommotian is therefore possibly only about 20 m here, implying a very condensed sequence, a conclusion consistent with an abundance of phosphorites. Two stratotype reference points for the Precambrian-Cambrian boundary have been suggested in this section. The lower point (0.8 m above the base of the Xiawaitoushan Member) may be near the Vendian/Tommotian boundary or younger, while the higher point (base of Unit 7 of the Zhongyicun Member) is probably Upper Tommotian or even Lower Atdabanian. The higher point would place the boundary above the world-wide dramatic increase in trace fossil abundance and diversity but probably before the first trilobites. This would almost certainly have advantages for correlation. The inference that the Meishucun section is younger than most Chinese work suggests should not therefore, by itself, prejudice its adoption as global stratotype.
In general, where comparative data are available, the trace fossil correlations agree well with pre-existing proposals based on small shelly fossils. The degree of resolution of the two methods would appear at present to be similar but trace fossils, being found mainly in clastic facies, may benefit from more frequent occurrence.
Fossils and matgrounds from the Neoproterozoic Longmyndian Supergroup, Shropshire, UK
- DUNCAN MCILROY, T. PETER CRIMES, JOHN C. PAULEY
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- Journal:
- Geological Magazine / Volume 142 / Issue 4 / July 2005
- Published online by Cambridge University Press:
- 18 July 2005, pp. 441-455
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Body and trace fossils of Ediacaran affinity are described from strata of the late Neoproterozoic Longmyndian Supergroup exposed near Church Stretton, Shropshire, UK. The almost spherical soft-bodied Ediacaran fossil Beltanelliformis brunsae Menner occurs rarely in the Burway Formation, but much smaller, simpler, discoidal structures are common in both the Burway and Synalds formations and are referred to Beltanelliformis minutae sp. nov. Similar discoidal structures, but with a distinct central depression, are included in Intrites punctatus Fedonkin and are common at several horizons. Two blocks with numerous examples of Medusinites aff. asteroides (Sprigg) Glaessner & Wade were recovered from the Burway Formation. The purported Ediacaran body fossil ‘Arumberia’ Glaessner & Walter is common at several horizons but its biogenicity is not accepted herein. ‘Arumberia’ is thus treated along with evidence for microbially bound sediment surfaces or matgrounds that have been suggested by several authors to be necessary for some types of Ediacaran preservation. The assemblage of simple trace and body fossils along with matgrounds is typical of latest Neoproterozoic time, though some elements range into the Phanerozoic.
Onshore-offshore patterns in Late PreCambrian and Lower Palaeozoic trace fossils
- T. Peter Crimes, N. Chris Hunt
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- Journal:
- The Paleontological Society Special Publications / Volume 6 / 1992
- Published online by Cambridge University Press:
- 26 July 2017, p. 77
- Print publication:
- 1992
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There was a dramatic increase in abundance and diversity of trace fossils in Upper Precambrian and Lower Cambrian shallow water seas. The trace-producing animals rapidly filled all the available niches and in low energy, muddy, environments they evolved winding, meandering and patterned habits. Traces such as Taphrhelminthopsis, Helminthoida, Nereites, Paleodictyon and Squamodictyon had all evolved in clastic shelf seas during the pre-trilobite Lower Cambrian.
Significant colonisation of the deep oceans seems to have mostly been delayed until the Ordovician. A recently described suite of trace fossils from a flysch sequence in Eire includes such deep water types as: Glockerichnus, Helminthopsis, Lorenzinia, Paleodictyon and Taphrhelminthopsis. This migration into the deep sea is accompanied by a virtual absence of such traces from shallow water sequences after the Cambrian.
Deep water trace fossils therefore seem to have evolved initially in shallow water clastic seas and then migrated in to the deep ocean, thereby providing an exciting example of an onshore-offshore pattern. This may be of particular significance in that it is presumably mimicked by body fossil migrations in these early seas.
Evolution, dispersal and habitat preference of deep-sea trace fossils
- T. Peter Crimes
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- Journal:
- The Paleontological Society Special Publications / Volume 6 / 1992
- Published online by Cambridge University Press:
- 26 July 2017, p. 76
- Print publication:
- 1992
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Cambrian deep-sea sediments have yielded few trace fossils. The first moderately diverse suite is found in an Arenig flysch sequence in Eire. There followed a gradual increase in diversity and abundance of trace fossils in deep-sea niches in the Palaeozoic and early Mesozoic. A major burst of behaviourial evolution appears to have taken place during the Cretaceous and, from then through the Tertiary, high levels of trace fossil abundance and diversity were maintained. This is confirmed by recent work on Miocene deep-sea sequences and from a superbly preserved, diverse, ichnofauna recently discovered in strata of Oligocene and Miocene age in the Makran Range of Iran.
In the past, it has been inferred that there was a gradual improvement in behavioral programming in deep-sea traces, with a trend towards economy of effort and perfection. However, Lower Palaeozoic deep water traces show careful, complex, behavioral programming which was to change little through the rest of the Phanerozoic.
Within the deep-sea, there are, however, significant variations in the ichnospectrum in different niches. For example, the inner parts of seep-sea sand fans, particularly the channelled areas, have a mixture of “deep” and “shallow” water traces, whereas the outer fan normally has only deep water forms.