摘要:

Burgess‐Shale‐type preservation is defined as a taphonomic pathway involving the exceptionalorganicpreservation of non‐mineralizing organisms in fully marine siliciclastic sediments. In the Phanerozoic it occurs widely in Lower and Middle Cambrian sequences but subsequently disappears as a significant taphonomic mode. The hypothesis that this distribution derives solely from a secular increase in the depth of bioturbation is falsified: low bioturbation indices do not prevent the rapid enzymatic degradation of organic structure, nor do they account for the conspicuous absence of comparable preservation during the Vendian. An earlier, Late Riphean (ca. 750–850 Ma), interval of enhanced organic‐walled fossil preservation suggests a long‐term recurrence in Burgess‐Shale‐type taphonomy that is independent of metazoan activity. A model based on the potentially powerful anti‐enzymatic and/or stabilizing effects of clay minerals on organic molecules is proposed to account for Burgess‐Shale‐type preservation. Long‐term changes in average clay mineralogies and the ocean chemistry that determines their interaction with organic molecules are likely to have induced the pronounced secular distribution of these fossil biotas, while regional variations in tectonism, weathering, etc., explain their non‐uniform geographic distribution; the close correlation between exceptional, organic‐walled fossil preservation and volcano‐genic sedimentation in Tertiary lake deposits provides a compelling analogue. Recognition of a temporal control on Burgess‐Shale‐type preservation constrains the evolutionary scenarios that can be drawn from such biotas; significantly, neither the initial rate of appearance, nor the ultimate fate of Burgess‐Shale‐type taxa can be directly assessed. □Taphonomy, exceptional preservation, organic preservation, fossil Lagerstätten, Burgess Shale, clay mineralogy, clay‐organic interacti

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01587.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01588.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Although the graptolites lacked biomineralised tissue, their skeletons are abundantly preserved in deeper‐water mudstones. Decay experiments and observations on the closely related living hemichordateRhabdopleurademonstrate that the periderm and stolon are highly resistant to decay, remaining intact for months, whereas the zooids are unrecognizable within days. The extreme rarity of the preservation of traces of the zooids in graptoloids reflects their planktic lifestyle; the zooids had normally decayed before burial. Curie‐point‐gas‐chromatography (Py‐GC) and Curie‐point‐gas‐chromatography‐mass spectrometry (Py‐GC‐MS) of the periderm ofRhabdopleuraconfirms that proteinaceous organic matter is a major constituent. Ultrastructurally preserved graptolite periderm (Ordovician, Oklahoma; Silurian, Arctic Canada), on the other hand, is a highly altered kerogen‐like substance rich in aliphatic biomacromolecules. The composition of the preserved graptolite periderm reflects diagenetic replacement by components probably mainly derive

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01589.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01590.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The calcichordate scenario of Jefferies and colleagues purports to explain the origin and early evolution of the phyla Echinodermata and Chordata. Calcichordate proponents have argued that echinoderms are the sister group of the chordates and urochordates are the sister group of the craniates. These phylogenetic hypotheses, which differ from the traditional groupings, are derived primarily from morphological interpretations of carpoids (solutes, cornutes, and mitrates), an enigmatic fossil group usually held to be primitive stem‐group echinoderms. Although the scenario has received only limited support, it has yet to be falsified. The difficulty with falsifying the calcichordate scenario is proving that the morphological interpretations, for example, that carpoids possessed notochords, dorsal hollow nerve cords, and other typical chordate or craniate characters, are incorrect. Here, rather than argue over the interpretation of fossils, the phylogenetic hypotheses embedded within the scenario are tested. It is found that the calcichordate scenario fails such a test, even if both the Recent and fossils forms are coded according to the calcichordate scenario. It is argued that: (1) the erection of scenarios must follow the construction of a cladogram; and (2) fossils are unable to dictate the relationships among phyla. □Calcichordate scenario, Carpoidea, Deuterostomia, Echinodermata, Chordata, phylogeny, cladist

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01591.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Shallow water benthic marine invertebrates (such as brachiopods from Benthic Assemblages [BA] 1–3) have usually played a much more important role than deeper ones (BA 4–5 or even deeper) in evaluating biogeographical provincialism in geological history. The Silurian brachiopodRetziellaFauna, characterized by the common presence ofRetziellain association with various provincial taxa and many common North Silurian Realm genera, is known from southwest Tienshan, North China, South China, North Vietnam, and East Australia. It is possibly also present in North Korea, the central Pamirs, Afghanistan, and New Zealand. The coevalTuvaellaFauna occurs only in the southern marginal belt of the Siberian Plate. Synecologically, both faunas inhabited a normal, shallow‐water, level‐bottom environment, usually with a low‐diversity community (commonly 3–8 genera); assignment to BA 2–3 is indicated. Their mutual exclusiveness is of biogeographical significance: subdivisions of the Uralian‐Cordilleran Region can be based on them, with theTuvaellaFauna being included in a redefined Mongolo‐Okhotsk Province. A Sino‐Australian Province is established and defined herein for the area occupied by theRetziellaFauna during the Ludlow‐Pridoli and probably the Wenlock. Two subdivisions of the province can be recognized, a Sino‐Central‐Asian Subprovince and an Australian Subprovince, based on different endemic brachiopods and separate geographical positions. The presence of a number of more cosmopolitan genera in both the tropical‐subtropical Sino‐Australian and subtropical‐temperate Mongolo‐Okhotsk Provinces during the Late Silurian testifies to oceanic surface current circulation patterns adequate for the distribution of planktic larvae capable of long‐distance dispersal while maintaining reproductive communication. This contrasts with the dispersal potential of endemic components of the newly defined Silurian biogeographical units. □ Late Silurian, Brachiopoda, Retziella, Fauna, TuvaellaFauna, Syn

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01592.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Oxygen and carbon isotopic profiles across the shells of well‐preserved bivalves and gastropods from the Pliocene Pinecrest Beds near Sarasota, Florida, provide detailed records of the paleoen‐vironmental and paleoclimatic conditions under which these high‐density shell beds accumulated, as well as offer insight into shell‐growth rates and longevity. Eight turritellid gastropods were analyzed from within and surrounding twoTurritella‐rich beds, an upper bed within unit 2(2.5‐2.0 Ma) and a lower bed situated near the top of the main shell bed, unit 6/7(3.5‐2.5 Ma). Three bivalves plus another turritellid specimen from a lower horizon (middle of unit 6/7), considered to represent offshore, normal‐marine conditions, were also analyzed. The isotopic profiles of all shells reflect year‐round shell growth in a seasonal, subtropical to warm‐temperate paleoenvironment. Cyclical patterns in δ18O reflect annual variations in water temperature which on average ranged from 15 to 24d̀C; minimum paleoseasonality contrasts varied from 7 to 9d̀C. Summer paleo‐temperatures compare favorably with those detemined from ostracodes, whereas winter temperatures appear slightly cooler. Except for one pectinid specimen, temperature differences between horizons and specimens are small. Annual δ18O cycles indicate:Turritella apicalislived longer and grew slightly faster thanTurritella gladeensis;and, shell growth rates and increment formation inMercenaria campechiensisare comparable to modern Florida populations. Coincident episodes of heavy δ18O and light δ18C in both turritellids and bivalves suggest a pattern of seasonal upwelling. This cool, nutrient‐rich, upwelled water may be partially responsible for the great abundance of Pinecrest fossils. □Stable isotopes, Pliocene, Pinecrest Beds, Florida, upwelling, paleot

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01593.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Two beds containing large numbers of turritellid gastropods (Family Turritellidae) occurring in the densely fossiliferous Upper Pliocene Pinecrest Sand of Florida formed as a result of upwelling and consequent high biological productivity, together with some degree of physically mediated time averaging. Analyses of size‐frequency distribution and shell surface condition, combined with isotopic data on chronological age of individual shells, water temperature and upwelling intensity, suggest that both beds formed relatively quickly, probably in less than 100–200 years. The upper bed, occurring within Petuch's (1982) unit 2 (2.5‐2.0 Ma) and containing abundantTurritella apicalisHeilprin, appears to have formed largely as a result of upwelling; the lower bed, occurring in upper unit 6/7 (3.5‐2.5 Ma) and containing abundantTurritella gladeensisMansfield, appears to have formed over a longer period, as a result of upwelling, increased time‐averaging, and perhaps cooler overall water temperatures. This study highlights the potential to isolate and examine separately some of the biological and physical factors affecting shell bed formation, and especially to address the role of biological productivity in this process. □Pinecrest Beds, Pliocene, upwelling, turritellid gastropods

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01594.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01595.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A low, rocky shoreline and attached abrasion platform of Late Pleistocene age are marked by a sharp disconformity within the Tamala Limestone Formation, exposed at Cape Burney facing the Indian Ocean near Geraldton, Western Australia. Colonization by an intertidal to shallow subtidal biota dominated by encrusting coralline red algae, oysters, and tube‐dwelling worms occurs on a sandstone surface with a channeled topographic relief of 20–30 cm. The encrusting cup coralRhizotrochus tuberculatusalso is present, and this report details what is probably the first fossil occurrence of that species. The ancient rocky shore above this level retains trace fossils characteristic of a boring barnacle, probably belonging toLithotrya.Herein named the Cape Burney sandstone, the distinctive unit on which the disconformity sits is assigned member status within the Tamala Limestone. Shell beds with a diversity of 35 species, dominated in volume by robust gastropods such asTurbo intercostalisandT. torquatus, thinly drape portions of the disconformity surface. Succeeding the shell drapes is a reef limestone with a maximum thickness of more than 2 m. The limestone is a massive accumulation of collapsed but otherwise mostly undisturbed coral fronds belonging primarily to a robust species ofAcropora.Herein named the Bootenall limestone, this unit is assigned member status within the Tamala Limestone. Based on an analysis of electron spin resonance (ESR) fromAcroporasamples, the fringing reef developed between 120 ka and 132 ka, in the terminal stage of coastal transgression during the last interglacial period (Oxygen Isotope Substage 5e). □Ancient rocky shores, intertidal abrasion platform, hard‐substrate colonization, reef suc

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1995.tb01596.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY