Burgess Shale-type preservation

Last updated

The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 69 [1] other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion. Additional sites with a similar form of preservation are known from the Ediacaran [2] and Ordovician periods. [3]

Contents

These various shales are of great importance in the reconstruction of the ecosystems immediately after the Cambrian explosion. The taphonomic regime results in soft tissue being preserved, meaning that organisms without conventionally fossilized hard parts can be seen. This provides further insight into the organs of more familiar organisms such as the trilobites.

The most famous localities preserving organisms in this fashion are the Canadian Burgess Shale, the Chinese Chengjiang fauna, and the more remote Sirius Passet in north Greenland. However, a number of other localities also exist.

Distribution

Burgess Shale-type biotas are found principally in the early and middle Cambrian, [4] but the preservational mode is also present before the Cambrian (e.g. Lantian biota) and through into the Ordovician (e.g. Fezouata). It is surprisingly common during the Cambrian period; over 40 sites are known from across the globe, [5] and soft-bodied fossils occur in abundance at nine of these. [1]

Preservational regime

A Burgess Shale trilobite showing soft-part preservation Olenoides serratus oblique with antennas.jpg
A Burgess Shale trilobite showing soft-part preservation

Burgess Shale-type deposits occur either on the continental slope or in a sedimentary basin. They are known in sediments deposited at all water depths during the Precambrian (Riphean stage onwards), with a notable gap in the last 150 million years of the Proterozoic. [6] They become increasingly restricted to deep waters in the Cambrian. [7]

In order for soft tissue to be preserved, its volatile carbon framework must be replaced by something able to survive the rigours of time and burial.

Charles Walcott, who discovered the Burgess Shale on 30 August 1909, [8] hypothesised that the organic material was preserved by silicification. [1] When the shale was redescribed in the 1970s, it was possible to take a more experimental approach to determining the nature of the fossils, which turned out to be mainly composed of carbon or clay minerals. [1] In many cases, both were present, suggesting that the original carbon was preserved, and the process of its preservation caused clay minerals to form in a predictable fashion. [1]

When carbon is preserved it usually forms films of the highly cross-linked and essentially inert compound kerogen, with kerogen formation from organic precursors likely to happen as the host rock is exposed to high pressures. [9] In addition, films of phyllicate (clay) minerals can grow in situ , overprinting the biological tissue. [10] The decay process creates chemical gradients that are essential for mineral growth to continue long enough for the tissue to be preserved. [7] Oxygen in the sediment allows decomposition to occur at a much faster rate, which decreases the quality of the preservation, but does not prevent it entirely. The conventional, exceptionally preserved fossils of the Burgess Shale are supplemented by the shells of organisms which lived on, and burrowed into, the sediment before the exceptional preservation pathway was complete. The organisms' presence shows that oxygen was present, but at worst this "paused" the mineralisation process. [7] It seems that whilst anoxia improves Burgess Shale-type preservation, it is not essential to the process. [11]

In addition to the organic films, parts of many Burgess Shale creatures are preserved by phosphatisation: The mid-gut glands of arthropods often host a concentration of high reactivity phosphates, making them the first structures to be preserved; they may be preserved in three dimensions, having been solidified before they could be flattened. [12] As these structures are unique to predatory and scavenging arthropods, this form of preservation is limited to—and diagnostic of—such creatures. [12]

Another type of mineralisation that is common in Chengjiang deposits is pyritisation; pyrite is deposited as a result of the activity of sulfate-reducing bacteria organisms soon after their burial. [1]

With the exception of phosphatic preservation, individual cells are never preserved; only structures such as chitinous exoskeleton, or scales and jaws, survive. This poses little problem for most invertebrate groups, whose outline is defined by a resistant exoskeleton. [6] Pyrite and phosphate are exceptional additions to Burgess Shale-type preservation, and are certainly not found in all localities. The defining preservation process is that which preserves organic film plus phyllosilicate. For this preservation to occur, the organisms must be protected from decay. [1] There are a few ways that this can happen; for instance they can be chemically protected within the sediment by phyllosilicates or biopolymers, which inhibit the action of decay related enzymes. [1] Alternatively the sediment could be "sealed" soon after the organisms were buried within it, with a reduction in porosity preventing oxygen from reaching the organic material. [1]

What is preserved

Carbon

The fossils usually comprise a reflective film; when the part bears an opaque, silvery film composed of organic carbon (kerogen), the counterpart's film is blue, less reflective, and more translucent. [10] A carbon film seems to be common to all BST deposits, although the carbon may 'evaporate' as rocks are heated, potentially to be replaced with other minerals. [13]

Phyllosilicates

Butterfield sees carbonaceous compressions as the main pathway of Burgess Shale-type preservation, [14] but an alternative has been proposed. The fossils actually comprise aluminosilicate films (except for some localized carbonaceous regions, such as the sclerites of Wiwaxia ), and Towe, followed by others, suggested that these may represent the mechanism of exceptional preservation. [15] Orr et al. emphasize the importance of clay minerals, whose composition seems to reflect the chemistry of the underlying, decaying, tissue. [16]

It seems that the original carbon film formed a template on which aluminosilicates precipitated. [1] [17]

Different phyllosilicates are associated with different anatomical regions. [18] This seems to be a result of when they formed. Phyllosilicates primarily form by filling voids. Voids formed in the fossils as the carbon films were heated and released volatile components. Different types of kerogen—reflecting different initial conditions—mature (i.e. volatilize) at different temperatures and pressures. The first kerogens to mature are those that replace labile tissue such as guts and organs; cuticular regions produce more robust kerogens that mature later. Kaolinite (rich in Al/Si, low in Mg) is the first phyllosilicate to form, once the rock is metamorphosed to the oil window, and thus replicates the most labile regions of the fossil. Once the rock is heated and compressed further, to the gas window, illite (rich in K/Al) and chlorite (rich in Fe/Mg) start to form; once all the available K is used up, no further illite forms, so the last tissues to mature are replicated exclusively in chlorite. [18] The precise mineral formation depends on the porewater (and thus rock) chemistry; the thickness of the films increases as metamorphism continues; and the minerals align with the prevailing strain. They are not present in comparable deposits with very little metamorphism. [18]

Calcium carbonate was originally present in the carapaces of trilobites, and may have crystallized early in diagenesis in (for example) the guts of Burgessia . It may also have filled late-stage veins in the rock. The carbonate was apparently leached away [18] and the resultant voids filled with phyllosilicates. [10]

Pyrite

Pyrite takes the place of phyllosilicates in some BST deposits. Labile tissues are associated with framboids, as they produced many nucleation sites due to the rapid production of sulfides (perhaps by sulfur-reducing bacteria); recalcitrant tissues are associated with euhedra. [19] It's not entirely clear whether pyrite is involved in the preservation of the anatomy, or whether they simply replace carbon films later in diagenesis (in the same fashion as phyllosilicates). [2]

Other preservational pathways

Some specimens bear a dark stain representing decay fluids injected into the surrounding wet sediment.

Muscle can in very rare cases survive by silicification, [20] or by authigenic mineralization by any of a range of other minerals. [21] However, predominately soft tissues, such as muscles and gonads, are never preserved by the carbonaceous-compression preservational pathway. [22] Phosphatisation and the presence of other enzymes means that guts and mid-gut glands are often preserved. Some bilaterally-symmetrical entities in the heads of arthropods have been interpreted as representing nervous tissue—a brain. [23] [24]

Otherwise it is cuticle that is most consistently present. Butterfield argues that only recalcitrant tissue (e.g. cuticle) can be preserved as a carbonaceous compression, [25] and cellular material has no preservation potential. [22] However, Conway Morris and others disagree, [26] and non-cuticular organs and organisms have been described, including the setae of brachiopods [27] and the jellyfish ctenophores (comb jellies). [28]

The mineralogy and geochemistry of the Burgess Shale is completely typical of any other Palaeozoic mudstone. [29]

Variation between BST sites

Preservation in the Chengjiang is similar, but with the addition of a pyritization mechanism, which seems to be the primary way in which soft tissue was preserved. [19]

Different BST deposits display different taphonomic potentials; in particular, the propensity of entirely soft-bodied organisms (i.e. those without shells or tough carapaces) to preserve is highest in the Burgess Shale, lower in the Chengjiang, and lower still in other sites. [30]

How it is preserved

Normally, organic carbon is decayed before it is rotted. Anoxia can prevent decay, but the prevalence of bioturbation associated with body fossils indicates that many BS sites were oxygenated when the fossils were deposited. It seems that the reduced permeability associated with the clay particles that make up the sediment restricted oxygen flow; furthermore, some beds may have been 'sealed' by the deposition of a carbonate cement. [31] The chemistry of the clay particles that buried the organisms seems to have played an important role in preservation. [32]

The carbon isn't preserved in its original state, which is often chitin or collagen. Rather, it is kerogenized. This process seems to involve the incorporation of aliphatic lipid molecules. [33]

Elemental distribution

Elemental distribution is unevenly spread through the organic remains, allowing the original nature of the remnant film to be predicted. For example:

Because the fossiliferous layer is so thin, it is effectively transparent to electrons at high-accelerating (>15V) voltages. [36]

Sedimentary setting

In the Wheeler Formation, lagerstätte occur predictably at periodic sea-level high-stands. [37] They formed on an oxygenated sea floor, and are associated with mud-slides or turbidity current events. [37]

Brine seeps

One hypothesis for exceptional preservation is that brine seeps—inputs of water with a high ion content, probably associated with fluid flow along faults—altered the sedimentary environment. They would enrich the area with nutrients, allowing life to prosper; the high salinity of the sea floor would deter burrowing and scavenging; and the unusual cocktail of chemicals may have enhanced preservation. [38]

Pikaia gracilens trying to escape a brine seep at the bottom of the Cathedral Escarpment Pikaia in Brine Seep.png
Pikaia gracilens trying to escape a brine seep at the bottom of the Cathedral Escarpment

Before burial

The majority of the decay process occurred before the organisms were buried. [39]

While the Chengjiang fauna underwent a similar preservational pathway to the Burgess Shale, the majority of organisms there are fossilised on their flattest side, suggesting that they were swept to their final resting place by turbidity currents. [40] The location at which an organism ultimately comes to rest may depend on how readily it floats, a function of its size and density. [40] Organisms are much more randomly arranged in the Burgess Shale itself. [40]

Turbidity currents have also been posited as the depositional system for the Burgess Shale, but mud-silt flows seem more consistent with the available evidence. Such "slurry flows" were somewhere between a turbidity current and a debris flow. [41] Any such flows must have enveloped free-swimming as well as bottom-dwelling organisms. [42] In either case, additional processes must have been responsible for the exceptional preservation. [41] One possibility is that the absence of bioturbation permitted the fossilisation, [41] but some Burgess Shale fossils contain internal burrows, so that can't be the whole story. [43] It is possible that certain clay minerals played a role in this process by inhibiting bacterial decay. [41] Alternatively, reduced sediment permeability (a result of lower bioturbation rates and abundant clays) may have played a role by limiting the diffusion of oxygen. [41]

During burial

The mineralisation process began to affect the organisms soon after they had been buried. [39] Organisms' cells rapidly decayed and collapsed, meaning that a flattened two-dimensional outline of the three-dimensional organisms is all that is preserved. [6] Pyrite began to precipitate from seawater trapped within the sediment forming lenses of framboidal (raspberry-shaped under magnification) crystals. [41]

Post burial

Organisms may have been shielded from oxygen in the ocean by a microbial mat, which could have formed an impermeable layer between the sediment and the oxic water column. [39] [44] There is no evidence for these mats in the higher stratigraphic units of the Burgess Shale Formation, so they cannot be the whole story. [41] However, cyanobacteria do appear to be associated with the preservation of the Emu Bay Shale, which was deposited beneath an oxygen-rich water column; by growing over carcasses, microbial mats held their soft tissue in place and allowed its preservation. [44] It is possible that the sediments were not always anoxic, but that burrowing was prevented in oxic intervals by a high deposition rate, with new material provided faster than burrowers could keep up with. [41] Indeed, a growing body of research indicates that sediment oxygenation is not related to preservation quality; the Burgess Shale itself appears to have been consistently oxic [38] and trace fossils are sometimes found within body fossils. [45]

Because of the great age of Cambrian sediments, most localities displaying Burgess Shale-type preservation have been affected by some form of degradation in the following 500+ million years. [1] For instance, the Burgess Shale itself endured cooking at greenschist-level temperatures and pressures (250–300 °C, ~10 km depth [10] / 482-572 F, ~6.2 miles), while the Chengjiang rocks have been deeply affected by weathering. [1] The Burgess Shale has been vertically compressed by at least a factor of eight. [46]

Closing the taphonomic window[ clarification needed ]

Burgess Shale-type preservation is known from the "pre-snowball" earth, and from the early to middle Cambrian; reports during the interlying Ediacaran period are rare, [6] although such deposits are now being found. [47] Burgess Shale-type Konzervat-lagerstätten are statistically overabundant during the Cambrian compared to later time periods, which represents a global megabias. [7] The mode of preservation is more abundant before the Cambrian substrate revolution, a development in which burrowing organisms established a foothold, permanently changing the nature of the sediment in a fashion that made soft-part preservation almost impossible. Consequently, the quantity of post-Cambrian Burgess Shale-type assemblages is very low. [7] Although burrowing reduced the number of environments that could support Burgess Shale-type deposits, it alone cannot explain their demise, and changing ocean chemistry—in particular the oxygenation of ocean sediments—also contributed to the disappearance of Burgess Shale-type preservation. [48] The number of pre-Cambrian assemblages is limited primarily by the rarity of soft-bodied organisms large enough to be preserved; however, as more and more Ediacaran sediments are examined, Burgess Shale-type preservation is becoming increasingly well known in this time period.

While the post-revolution world was full of scavenging and predatory organisms, the contribution of direct consumption of carcasses to the rarity of post-Cambrian Burgess Shale-type lagerstätten was relatively minor, compared to the changes brought about in sediments' chemistry, porosity, and microbiology, which made it difficult for the chemical gradients necessary for soft-tissue mineralisation to develop. [7] Just like microbial mats, environments which could produce this mode of fossilisation became increasingly restricted to harsher and deeper areas, where burrowers could not establish a foothold; as time progressed, the extent of burrowing increased sufficiently to effectively make this mode of preservation impossible. [7]

However, Burgess Shale-type biotas do in fact exist after the Cambrian (albeit somewhat more rarely).[ citation needed ] Other factors may have contributed to the closure of the window at the end of the Amgan (middle Mid-Cambrian), with many factors changing around this time. A transition from an icehouse to a greenhouse world has been associated with an increase in storm intensity, which may have hindered exceptional preservation. [49] Other environmental factors change around this time: Phosphatic units disappear, and there is a stem change in organisms' shell thickness. [49]

Faunas

The mode of preservation preserves a number of different faunas; most famously, the Cambrian "Burgess Shale-type fauna" of the Burgess Shale itself, Chengjiang, Sirius Passet, and Wheeler Formation. However, different faunal assemblages are also preserved, such as the microfossils of Riphean (Tonian-Cryogenian age) lagerstätten. [14]

Related Research Articles

<span class="mw-page-title-main">Burgess Shale</span> Fossil-bearing rock formation in the Canadian Rockies

The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years old, it is one of the earliest fossil beds containing soft-part imprints.

<span class="mw-page-title-main">Maotianshan Shales</span> Series of Early Cambrian deposits in the Chiungchussu Formation

The Maotianshan Shales (帽天山页岩) are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation, famous for their Konservat Lagerstätten, deposits known for the exceptional preservation of fossilized organisms or traces. The Maotianshan Shales form one of some forty Cambrian fossil locations worldwide exhibiting exquisite preservation of rarely preserved, non-mineralized soft tissue, comparable to the fossils of the Burgess Shale of British Columbia, Canada. They take their name from Maotianshan Hill in Chengjiang County, Yunnan Province, China.

<span class="mw-page-title-main">Taphonomy</span> Study of decomposition and fossilization of organisms

Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term taphonomy was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms from the biosphere to the lithosphere.

<span class="mw-page-title-main">Phosphatization</span>

Phosphatization, or phosphatic fossilization, refers to the process of fossilization where organic matter is replaced by abundant calcium-phosphate minerals. It has occurred in unusual circumstances to preserve some extremely high-resolution microfossils in which careful preparation can even reveal preserved cellular structures. Such microscopic fossils are only visible under the scanning electron microscope.

<i>Wiwaxia</i> Genus of Cambrian animals

Wiwaxia is a genus of soft-bodied animals that were covered in carbonaceous scales and spines that protected it from predators. Wiwaxia fossils—mainly isolated scales, but sometimes complete, articulated fossils—are known from early Cambrian and middle Cambrian fossil deposits across the globe. The living animal would have measured up to 5 centimetres (2 in) when fully grown, although a range of juvenile specimens are known, the smallest being 2 millimetres (0.08 in) long.

Derek Ernest Gilmor Briggs is an Irish palaeontologist and taphonomist based at Yale University. Briggs is one of three palaeontologists, along with Harry Blackmore Whittington and Simon Conway Morris, who were key in the reinterpretation of the fossils of the Burgess Shale. He is the Yale University G. Evelyn Hutchinson Professor of Geology and Geophysics, Curator of Invertebrate Paleontology at Yale's Peabody Museum of Natural History, and former Director of the Peabody Museum.

<i>Leanchoilia</i> Extinct genus of arthropods

Leanchoilia is a megacheiran arthropod known from Cambrian deposits of the Burgess Shale in Canada and the Chengjiang biota of China.

A number of assemblages bear fossil assemblages similar in character to that of the Burgess Shale. While many are also preserved in a similar fashion to the Burgess Shale, the term "Burgess Shale-type fauna" covers assemblages based on taxonomic criteria only.

<span class="mw-page-title-main">Beecher's Trilobite type preservation</span> Replacement of soft tissues of a fossil with pyrite

The preservational regime of Beecher's Trilobite Bed and other similar localities involves the replacement of soft tissues with pyrite, producing a three-dimensional fossil replicating the anatomy of the original organism. Only gross morphological information is preserved, although the fossils are compressed some relief is preserved.

Ediacaran type preservation relates to the dominant preservational mode in the Ediacaran period, where Ediacaran organisms were preserved as casts on the surface of microbial mats.

<i>Paucipodia</i> Extinct genus of panarthropods

Paucipodia inermis is a lobopod known from the Lower Cambrian Chengjiang lagerstätte. Its gut is puzzling; in some places, it is preserved in three dimensions, infilled with sediment; whereas in others it may be flat. These cannot result from phosphatisation, which is usually responsible for three-dimensional gut preservation, for the phosphate content of the guts is under 1% – the contents comprise quartz and muscovite. Its fossils do not suggest it had any sclerites, especially when compared with the related Hallucigenia.

The fossils of the Burgess Shale, like the Burgess Shale itself, are fossils that formed around 505 million years ago in the mid-Cambrian period. They were discovered in Canada in 1886, and Charles Doolittle Walcott collected over 65,000 specimens in a series of field trips up to the alpine site from 1909 to 1924. After a period of neglect from the 1930s to the early 1960s, new excavations and re-examinations of Walcott's collection continue to reveal new species, and statistical analysis suggests that additional discoveries will continue for the foreseeable future. Stephen Jay Gould's 1989 book Wonderful Life describes the history of discovery up to the early 1980s, although his analysis of the implications for evolution has been contested.

<span class="mw-page-title-main">Archaeopriapulida</span> Class of marine worms

Archaeopriapulida is a group of priapulid worms known from Cambrian lagerstätte. The group is closely related to, and very similar to, the modern Priapulids. It is unclear whether it is mono- or polyphyletic. Despite a remarkable morphological similarity to their modern cousins, they fall outside of the priapulid crown group, which is not unambiguously represented in the fossil record until the Carboniferous. In addition to well-preserved body fossils, remains of several archaeopriapulid taxa are known to have been preserved primarily as organic microfossils, such as isolated scalids and pharyngeal teeth. They are probably closely related or paraphyletic to the palaeoscolecids; the relationship between these basal worms is somewhat unresolved.

The Phyllopod bed, designated by USNM locality number 35k, is the most famous fossil-bearing member of the Burgess Shale fossil Lagerstätte. It was quarried by Charles Walcott from 1911–1917, and was the source of 95% of the fossils he collected during this time; tens of thousands of soft-bodied fossils representing over 150 genera have been recovered from the Phyllopod bed alone.

The Mount Cap Formation is a geologic formation exposed in the Mackenzie Mountains, northern Canada. It was deposited in a shallow shelf setting in the late Early Cambrian, and contains an array of Burgess Shale-type microfossils that have been recovered by acid maceration.

<span class="mw-page-title-main">Fezouata Formation</span> Burgess shale-type deposits

The Fezouata Formation or Fezouata Shale is a geological formation in Morocco which dates to the Early Ordovician. It was deposited in a marine environment, and is known for its exceptionally preserved fossils, filling an important preservational window beyond the earlier and more common Cambrian Burgess shale-type deposits.

<span class="mw-page-title-main">Small carbonaceous fossil</span>

Small carbonaceous fossils (SCFs) are sub-millimetric organic remains of organisms preserved in sedimentary strata.

Most fossils represent mineralized material such as bone or shells. However, biopolymers such as chitin and collagen can sometimes leave fossils – most famously in Burgess Shale type preservation and palynomorphs. The preservation of soft tissue is not as rare as sometimes thought.

<span class="mw-page-title-main">Waukesha Biota</span> Lagerstätte Fossil site in Waukesha County, Wisconsin, U.S.

The Waukesha Biota is an important fossil site located in Waukesha County and Franklin, Milwaukee County within the state of Wisconsin. This biota is preserved in certain strata within the Brandon Bridge Formation, which dates to the early Silurian period. It is known for the exceptional preservation of soft-bodied organisms, including many species found nowhere else in rocks of similar age. The site's discovery was announced in 1985, leading to a plethora of discoveries. This biota is one of the few well studied Lagerstätten from the Silurian, making it important in our understanding of the period's biodiversity. Some of the species are not easily classified into known animal groups, showing that much research remains to be done on this site. Other taxa that are normally common in Silurian deposits are rare here, but trilobites are quite common.

<i>Lenisambulatrix</i> Extinct genus of Lobopodian

Lenisambulatrix is a genus of extinct worm belonging to the group Lobopodia and known from the Lower Cambrian Maotianshan shale of China. It is represented by a single species L. humboldti. The incomplete fossil was discovered and described by Qiang Ou and Georg Mayer in 2018. Due to its missing parts, its relationship with other lobopodians is not clear. It shares many structural features with another Cambrian lobopodian Diania cactiformis, a fossil of which was found alongside it.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 Gaines, Robert R.; Briggs, Derek E.G.; Yuanlong, Zhao (2008). "Cambrian Burgess Shale–type deposits share a common mode of fossilization". Geology. 36 (10): 755–758. Bibcode:2008Geo....36..755G. doi:10.1130/G24961A.1.
  2. 1 2 Cai, Y.; Schiffbauer, J. D.; Hua, H.; Xiao, S. (2012). "Preservational modes in the Ediacaran Gaojiashan Lagerstätte: Pyritization, aluminosilicification, and carbonaceous compression". Palaeogeography, Palaeoclimatology, Palaeoecology. 326–328: 109–117. Bibcode:2012PPP...326..109C. doi:10.1016/j.palaeo.2012.02.009.
  3. ↑ Van Roy, P.; Orr, P. J.; Botting, J. P.; Muir, L. A.; Vinther, J.; Lefebvre, B.; Hariri, K. E.; Briggs, D. E. G. (2010). "Ordovician faunas of Burgess Shale type". Nature. 465 (7295): 215–8. Bibcode:2010Natur.465..215V. doi:10.1038/nature09038. PMID   20463737. S2CID   4313285.
  4. ↑ Butterfield, N. J. (2000). "The oldest(?) and the youngest(?) Burgess Shale-type biotas in North America, Jasper National Park, Alberta.". Geological Society of America, Abstracts with Programs, 32, A301. 2000 GSA Annual Meeting -- Reno, Nevada. GSA. Archived from the original on 2012-03-18.
  5. ↑ e.g. Norway, Høyberget, Magne; Ebbestad, Jan Ove R.; Funke, Bjørn; Funke, May-Liss K.; Nakrem, Hans Arne (2023). "The Skyberg Lagerstätte from the Mjøsa area, Norway: A rare window into the late early Cambrian biodiversityof Scandinavia". Lethaia. 56 (2): 1–28. doi:10.18261/let.56.2.4. S2CID   258469759., ...
  6. 1 2 3 4 Butterfield, N.J. (2003). "Exceptional fossil preservation and the Cambrian explosion" (PDF). Integrative and Comparative Biology. 43 (1): 166–177. doi: 10.1093/icb/43.1.166 . PMID   21680421.
  7. 1 2 3 4 5 6 7 Orr, P.J.; Benton, M.J.; Briggs, D.E.G. (2003). "Post-Cambrian closure of the deep-water slope-basin taphonomic window". Geology. 31 (9): 769–772. Bibcode:2003Geo....31..769O. doi:10.1130/G19193.1.
  8. ↑ "Charles Walcott". Royal Ontario Museum. 10 June 2011. Archived from the original on 6 June 2013. Retrieved 29 August 2013.
  9. ↑ Gaines, R.; Kennedy, M.; Droser, M. (2005). "A new hypothesis for organic preservation of Burgess shale taxa in the middle Cambrian Wheeler formation, House Range, Utah". Palaeogeography, Palaeoclimatology, Palaeoecology. 220 (1–2): 193–205. Bibcode:2005PPP...220..193G. doi:10.1016/j.palaeo.2004.07.034.
  10. 1 2 3 4 Butterfield, Nicholas J.; Balthasar, Uwe; Wilson, Lucy A. (2007). "Fossil Diagenesis in the Burgess Shale". Palaeontology. 50 (3): 537–543. Bibcode:2007Palgy..50..537B. doi: 10.1111/j.1475-4983.2007.00656.x .
  11. ↑ Garson, D.E.; Gaines, R.R.; Droser, M.L.; Liddell, W.D.; Sappenfield, A. (2011). "Dynamic palaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah". Lethaia. 45 (2): 164–177. doi:10.1111/j.1502-3931.2011.00266.x.
  12. 1 2 Butterfield, N.J. (2002). "Leanchoilia guts and the interpretation of three-dimensional structures in Burgess Shale-type fossils" . Paleobiology. 28 (1): 155–171. doi:10.1666/0094-8373(2002)028<0155:LGATIO>2.0.CO;2. S2CID   85606166 . Retrieved 1 July 2008.
  13. ↑ Gaines, R. R.; Briggs, D. E. G.; Yuanlong, Z. (2008). "Cambrian Burgess Shale–type deposits share a common mode of fossilization". Geology. 36 (10): 755. Bibcode:2008Geo....36..755G. doi:10.1130/G24961A.1.
  14. 1 2 Butterfield, N. J. (1995). "Secular distribution of Burgess-Shale-type preservation". Lethaia. 28 (1): 1–9. doi:10.1111/j.1502-3931.1995.tb01587.x.
  15. ↑ We, K. M. T. O. (1996). "Fossil preservation in the Burgess Shale". Lethaia. 29 (1): 107–108. doi:10.1111/j.1502-3931.1996.tb01844.x.
  16. ↑ Orr, P. J.; Briggs, D. E. G.; Kearns, S. L. (1998). "Cambrian Burgess Shale Animals Replicated in Clay Minerals". Science. 281 (5380): 1173–1175. Bibcode:1998Sci...281.1173O. doi:10.1126/science.281.5380.1173. PMID   9712577.
  17. ↑ Butterfield, N. J.; Balthasar, U. W. E.; Wilson, L. A. (2007). "Fossil Diagenesis in the Burgess Shale". Palaeontology. 50 (3): 537. Bibcode:2007Palgy..50..537B. doi: 10.1111/j.1475-4983.2007.00656.x .
  18. 1 2 3 4 Page, A.; Gabbott, S. E.; Wilby, P. R.; Zalasiewicz, J. A. (2008). "Ubiquitous Burgess Shale–style "clay templates" in low-grade metamorphic mudrocks". Geology. 36 (11): 855. Bibcode:2008Geo....36..855P. doi:10.1130/G24991A.1.
  19. 1 2 Gabbott, S. E.; Xian-Guang, H.; Norry, M. J.; Siveter, D. J. (2004). "Preservation of Early Cambrian animals of the Chengjiang biota". Geology. 32 (10): 901. Bibcode:2004Geo....32..901G. doi:10.1130/G20640.1.
  20. ↑ Budd, G. E. (2007). "Arthropod body-plan evolution in the Cambrian with an example from anomalocaridid muscle". Lethaia. 31 (3): 197–210. doi:10.1111/j.1502-3931.1998.tb00508.x.
  21. ↑ Patrick J. Orr; Stuart L. Kearns; Derek E. G. Briggs (February 2002). "Backscattered electron imaging of fossils exceptionally-preserved as organic compressions". PALAIOS. 17 (1): 110–117. Bibcode:2002Palai..17..110O. doi:10.1669/0883-1351(2002)017<0110:BEIOFE>2.0.CO;2. JSTOR   3515673. S2CID   130719571.
  22. 1 2 Butterfield, N. J. (Dec 2006). "Hooking some stem-group "worms": fossil lophotrochozoans in the Burgess Shale". BioEssays. 28 (12): 1161–1166. doi:10.1002/bies.20507. ISSN   0265-9247. PMID   17120226. S2CID   29130876.
  23. ↑ Ma, X.; Hou, X.; Edgecombe, G. D.; Strausfeld, N. J. (2012). "Complex brain and optic lobes in an early Cambrian arthropod". Nature. 490 (7419): 258–261. Bibcode:2012Natur.490..258M. doi:10.1038/nature11495. PMID   23060195. S2CID   4408369.
  24. ↑ Strausfeld, Nicholas J. (2011). "Some observations on the sensory organization of the crustaceamorph Waptia fieldensis (Walcott)". Palaeontogr. Canadiana. 31: 157–169.
  25. ↑ Butterfield, N. J. (1 July 1990). "Organic Preservation of Non-Mineralizing Organisms and the Taphonomy of the Burgess Shale". Paleobiology. 16 (3): 247–399. Bibcode:1990Pbio...16..272B. doi:10.1017/S0094837300009994. ISSN   0094-8373. JSTOR   2400788. S2CID   133486523.
  26. ↑ Conway Morris, S. (2008). "A Redescription of a Rare Chordate, Metaspriggina walcotti Simonetta and Insom, from the Burgess Shale (Middle Cambrian), British Columbia, Canada". Journal of Paleontology. 82 (2): 424–430. Bibcode:2008JPal...82..424M. doi:10.1666/06-130.1. S2CID   85619898.
  27. ↑ Conway Morris, S. (1979). "The Burgess Shale (Middle Cambrian) Fauna". Annual Review of Ecology and Systematics. 10: 327–349. doi:10.1146/annurev.es.10.110179.001551.
  28. ↑ Conway Morris, S.; Collins, D. H. (1996). "Middle Cambrian Ctenophores from the Stephen Formation, British Columbia, Canada". Philosophical Transactions: Biological Sciences (Free full text). 351 (1337): 243–360. Bibcode:1996RSPTB.351..279C. JSTOR   56388.
  29. ↑ Page, Alex; Gabbott, Sarah; Wilby, Phillip R.; Zalasiewicz, Jan A (2008). "Ubiquitous Burgess Shale–style "clay templates" in low-grade metamorphic mudrocks". Geology. 36 (11): 855–858. Bibcode:2008Geo....36..855P. doi:10.1130/G24991A.1.
  30. ↑ Saleh, Farid; Antcliffe, Jonathan B.; Lefebvre, Bertrand; Pittet, Bernard; Laibl, Lukáš; Perez Peris, Francesc; Lustri, Lorenzo; Gueriau, Pierre; Daley, Allison C. (2020). "Taphonomic bias in exceptionally preserved biotas" (PDF). Earth and Planetary Science Letters. 529: 115873. Bibcode:2020E&PSL.52915873S. doi: 10.1016/j.epsl.2019.115873 .
  31. ↑ Gaines, R. R.; Hammarlund, E. U.; Hou, X.; Qi, C.; Gabbott, S. E.; Zhao, Y.; Peng, J.; Canfield, D. E. (2012). "Mechanism for Burgess Shale-type preservation". Proceedings of the National Academy of Sciences. 109 (14): 5180–4. Bibcode:2012PNAS..109.5180G. doi: 10.1073/pnas.1111784109 . PMC   3325652 . PMID   22392974.
  32. ↑ Forchielli, A.; Steiner, M.; Kasbohm, J. R.; Hu, S.; Keupp, H.; Forchielli, A.; Steiner, M.; Keupp, H.; Kasbohm, J. R.; Hu, S. (2013). "Taphonomic traits of clay-hosted early Cambrian Burgess Shale-type fossil Lagerstätten in South China". Palaeogeography, Palaeoclimatology, Palaeoecology. 398: 59–85. doi:10.1016/j.palaeo.2013.08.001.
  33. ↑ Gupta, N. S.; Briggs, D. E. G.; Pancost, R. D. (2006). "Molecular taphonomy of graptolites". Journal of the Geological Society. 163 (6): 897. Bibcode:2006JGSoc.163..897G. doi:10.1144/0016-76492006-070. S2CID   129853676.
  34. 1 2 3 Zhang, Xingliang; Briggs, Derek E. G. (2007). "The nature and significance of the appendages of Opabinia from the Middle Cambrian Burgess Shale". Lethaia. 40 (2): 161–173. doi:10.1111/j.1502-3931.2007.00013.x.
  35. ↑ Budd, G. E.; Daley, A. C. (2011). "The lobes and lobopods of Opabinia regalis from the middle Cambrian Burgess Shale". Lethaia. 45: 83–95. doi:10.1111/j.1502-3931.2011.00264.x.
  36. ↑ Orr, P. J.; Kearns, S. L.; Briggs, D. E. G. (2009). "Elemental mapping of exceptionally preserved 'carbonaceous compression' fossils". Palaeogeography, Palaeoclimatology, Palaeoecology. 277 (1–2): 1–8. Bibcode:2009PPP...277....1O. doi:10.1016/j.palaeo.2009.02.009.
  37. 1 2 Brett, C. E.; Allison, P. A.; Desantis, M. K.; Liddell, W. D.; Kramer, A. (2009). "Sequence stratigraphy, cyclic facies, and lagerstätten in the Middle Cambrian Wheeler and Marjum Formations, Great Basin, Utah". Palaeogeography, Palaeoclimatology, Palaeoecology. 277 (1–2): 9–33. Bibcode:2009PPP...277....9B. doi:10.1016/j.palaeo.2009.02.010.
  38. 1 2 Powell, W. (2009). "Comparison of Geochemical and Distinctive Mineralogical Features Associated with the Kinzers and Burgess Shale Formations and their Associated Units". Palaeogeography, Palaeoclimatology, Palaeoecology. 277 (1–2): 127–140. Bibcode:2009PPP...277..127P. doi:10.1016/j.palaeo.2009.02.016.
  39. 1 2 3 Caron, Jean-Bernard; Jackson, Donald A. (2006). "Taphonomy Of The Greater Phyllopod Bed Community, Burgess Shale". PALAIOS. 21 (5): 451–465. Bibcode:2006Palai..21..451C. doi:10.2110/palo.2003.P05-070R. S2CID   53646959.
  40. 1 2 3 Zhang, Xi-Guang; Hou, Xian-Guang (2007). "Gravitational Constraints on the Burial of Chengjiang Fossils". PALAIOS. 22 (4): 448–453. Bibcode:2007Palai..22..448Z. doi:10.2110/palo.2006.p06-085r. S2CID   128830203.
  41. 1 2 3 4 5 6 7 8 Gabbott, S.E.; Zalasiewicz, J.; Collins, D. (2008). "Sedimentation of the Phyllopod Bed within the Cambrian Burgess Shale Formation of British Columbia" . Journal of the Geological Society. 165 (1): 307. Bibcode:2008JGSoc.165..307G. doi:10.1144/0016-76492007-023. S2CID   128685811.
  42. ↑ Vannier, J.; Garcia-Bellido, C.; Hu, X.; Chen, L. (Jul 2009). "Arthropod visual predators in the early pelagic ecosystem: evidence from the Burgess Shale and Chengjiang biotas". Proceedings: Biological Sciences. 276 (1667): 2567–2574. doi:10.1098/rspb.2009.0361. ISSN   0962-8452. PMC   2686666 . PMID   19403536.
  43. ↑ Briggs, D. E. G.; Erwin, D. H.; Collier, F. J. (1995), Fossils of the Burgess Shale , Washington: Smithsonian Inst Press, ISBN   1-56098-659-X, OCLC   231793738
  44. 1 2 Hall, P. A.; McKirdy, D. M.; Halverson, G. P.; Jago, J. B.; Gehling, J. G. (2011). "Biomarker and isotopic signatures of an early Cambrian Lagerstätte in the Stansbury Basin, South Australia". Organic Geochemistry. 42 (11): 1324–1330. Bibcode:2011OrGeo..42.1324A. doi:10.1016/j.orggeochem.2011.09.003.
  45. ↑ Lin, J. P.; Zhao, Y. L.; Rahman, I. A.; Xiao, S.; Wang, Y. (2010). "Bioturbation in Burgess Shale-type Lagerstätten – Case study of trace fossil-body fossil association from the Kaili Biota (Cambrian Series 3), Guizhou, China". Palaeogeography, Palaeoclimatology, Palaeoecology. 292 (1–2): 245–256. Bibcode:2010PPP...292..245L. doi:10.1016/j.palaeo.2010.03.048.
  46. ↑ Whittington, H.B. (1975). "Trilobites with Appendages from the Middle Cambrian, Burgess Shale, British Columbia". Fossils Strata. Fossils and Strata. 4: 97–136. doi:10.18261/8200049639-1975-06. ISBN   8200049639.
  47. ↑ Xiao, Shuhai; Steiner, M.; Knoll, A. H.; Knoll, Andrew H. (2002). "A reassessment of the Neoproterozoic Miaohe carbonaceous biota in south China". Journal of Paleontology. 76 (2): 345–374. doi:10.1666/0022-3360(2002)076<0347:MCCIAT>2.0.CO;2.
  48. ↑ Gaines, R.R.; Droser, M.L.; Orr, P.J.; Garson, D.; Hammarlund, E.; Qi, C.; Canfield, D.E. (2012). "Burgess shale-type biotas were not entirely burrowed away". Geology. 40 (3): 283. Bibcode:2012Geo....40..283G. doi:10.1130/G32555.1.
  49. 1 2 Zhuravlev, A.Y.; Wood, R.A. (2008). "Eve of biomineralization: Controls on skeletal mineralogy" (PDF). Geology. 36 (12): 923. Bibcode:2008Geo....36..923Z. doi:10.1130/G25094A.1. Archived from the original (PDF) on 2016-03-04. Retrieved 2015-08-29.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.