ABRASION

Volumen 1 Issue 3 Year 2003

2020-03-27T20:44:09+02:00October 26th, 2019|Volumen 1. Issue 3. Year 2003.|

VOLUME 1. NUMBER 3. 2003

Experimental Effects of Water Abrasion on Bone Fragments.

Yolanda Fernández-Jalvo

Keywords: TRANSPORT, SEDIMENT, WATER STREAM, EXPERIMENT, ABRASION, ROUNDING

[+info] VOLUME 1. ISSUE 3. 2003 (1 issue)

Water transport is a frequent taphonomic agent in continental environments that may affect and disturb original bone associations. Fossil allochthony occurs as a result of resedimentation (before burial) and/or secondary deposition (after initial burial) altering palaeoenvironmental and palaeoecological indications provided by fossils. Skeletal element sorting or preferred orientations of fossils are evidence of fluvial transport as studied by several authors. Bone surface abrasion is another trait recorded on fossils that may provide evidence of water transport in a fossil association. Results of a preliminary experiment on the effects of abrasion have shown characteristic differences relating to the type of sediment (coarse to fine) and the type of bone involved (fresh, dry, weathered or fossil). This indicates that the effects and consequences of water transport on bone associations can be identified from traits of abrasion. This paper also considers other experiments involving abrasion on large and small mammal bones and owl pellets.

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Some Middle Paleozoic Conulariids (Cnidaria) as Possible Examples of Taphonomic Artifacts.

Marcello Guimarães Simões*, Sabrina Coelho Rodrigues, Juliana de Moraes Leme, Heyo Van Iten.

Keywords: TAPHONOMY, TAPHONOMIC ARTIFACTS, CONULARIIDS, CNIDARIA, DEVONIAN

[+info] VOLUME 1. ISSUE 3. 2003 (2 issue)

Conulariids provide good examples of how biometric and other characters that have been used to diagnose fossil species can be affected by taphonomic processes, possibly leading to the erection of taphonomic taxa, or taphonomic artifacts. Based on analysis of the taphonomy of Conularia quichua Ulrich from the Devonian Ponta Grossa of southern Brazil, we argue that caution must be exercised when using biometric and other characters to diagnose conulariid species. For example, measurements of the spacing of the transverse ribs must be corrected for compaction of the theca parallel to its long axis. C. quichua oriented at high angles to bedding almost always exhibit this kind of deformation, which if not corrected for results in substantial additional measurement error. Similarly, the value of the apical angle of C. quichua differs between compressed and uncompressed specimens, making it difficult to measure this character with a high degree of consistency and reproducibility. Other characters (geometry of the transverse ribs, presence or absence of interspace ridges and nodes) used to diagnose conulariids are susceptible to modification and information loss through weathering. In reviewing published descriptions of other conulariids, we have found that certain species may be taphotaxa. Future descriptions of new species should be based on collections encompassing the known spectrum of preservational patterns. Also, the erection of new conulariid taxa should be based as much as possible on complete or nearly complete specimens, and morphometric comparisons should be made using specimens showing similar patterns of preservation.

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Smothered Scampi: Taphonomy of Lobsters in the Upper Cretaceous Bearpaw Formation, Southern Alberta.

Cameron J. Tsujita.

Keywords: BURROWS, CONCRETIONS, CRETACEOUS, CRUSTACEANS, DECAPODS, DIAGENESIS, PHOSPHATE, TAPHONOMY

[+info] VOLUME 1. ISSUE 3. 2003 (3 issue)

Phosphatic concretions, containing remains of the lobster Palaeonephrops browni (Whitfield), are described from the Upper Cretaceous Bearpaw Formation of southern Alberta. Two modes of burial are interpreted to have enhanced the preservation potential of the lobsters: (1) burial of remains by volcanic ash, and (2) burial of remains within burrows due to sediment injection during storms. The latter mode of burial is indicated for the majority of the specimens studied, suggesting that the exceptional preservation of Palaeonephrops, and probably some other fossil decapod taxa may have been more strongly influenced by their life-habits than previously assumed. Within-burrow preservation of lobster specimens also demonstrates that obrution is not only important for the preservation of faunal elements residing on the sea-floor, but can also bias the preservation of some deep infaunal taxa. Following rapid burial, the preservation potential of the lobster remains was further enhanced by virtue of its phosphate-bearing cuticle, upon which, early diagenetic phosphate cements were preferentially precipitated. Further phosphate precipitation resulted in the entombment of the remains within phosphatic concretions, further protecting them from destructive taphonomic processes.

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Volumen 5. Issue 4. Year 2007.

2020-03-28T19:19:04+02:00October 26th, 2019|Volumen 5. Issue 4. Year 2007.|

VOLUME 5. NUMBER 4. 2007

Criteria for the Identification of Formation Processes in Guanaco (Lama guanicoe) Bone Assemblages in Fluvial-Lacustrine Environments.

María A. Gutierrez, Cristian A. Kaufmann.

Keywords: SITE FORMATION PROCESSES, GUANACO (Lama guanicoe), BONE DISPERSION POTENTIAL, ONTOGENETIC DEVELOPMENT, FLUVIAL AND LACUSTRINE ENVIRONMENTS, ARGENTINA

[+info] VOLUME 5. ISSUE 4. 2007 (1 issue)

The aim of this paper is to present and discuss methodological criteria that may be of use in exploring the role of water in the formation of the faunal record in fluvial and lacustrine environments. As such, the dispersion potential of the bones of adult and neonate guanaco (Lama guanicoe) skeletons in an aquatic environment with very low hydraulic energy is evaluated through experimentation. Results of the experiments are integrated with other, complementary criteria and applied to the bone assemblage recovered at Paso Otero 1 site, situated on the margin of the ancient flood plain of the Quequén Grande River (Buenos Aires Province, Argentina). The results of this study indicate that water was the main agent responsible for guanaco bone accumulation at the site. It is proposed that some of the skeletal parts, which belong to guanaco carcasses that were processed and exploited by hunter-gatherers in areas close to the site, were added to those from animals that died naturally. This resulted in a mixture of material of both natural and anthropic origin.

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Taphonomy in Present Day Desertic Environment: The Case of the Djourab (Chad) Plio-Pleistocene Deposits.

Denys, Christiane, Schuster M., Guy F., Mouchelin G.,Vignaud P., Viriot L., Brunet M, Duringer P., Fanoné F., Djimdoumalbaye A, Likius A, Mackaye H.T., Sudre J.

Keywords: DJOURAB DESERT, CHAD, HOMINIDS, WIND ABRASION, REWORKING

[+info] VOLUME 5. ISSUE 4. 2007 (2 issue)

Preliminary taphonomic studies were conducted on three different early hominid Chadian sites aged between 5 Ma and 3 Ma (KB, KL, KT fossil areas). Specific excavations and taphonomic sampling protocols were established. Research of the various alterations and the origins of bone modifications were carried out. All fossil assemblages bear traces of carnivore tooth marks as well as weathering and wind/water polishing. Digestion is present on bones from the KB & KL sites. Rootmark traces were found only on bones from the KB and KT sites. All three sites display various polishing patterns among which much of the abrasion results from wind polishing on the top surface, on the exposed face of large flat bones difficult to move. By contrast water action works on all faces of polished bones. KL seems to show more water transport influence than the two other sites. Weathering stages are light to heavy (stages 2-4) and the presence of gnawing, and traces of roots plus tooth marks indicates that bones stayed sometimes on the soil surface and that the assemblages may be of attritional origin. But the low density of bones and the presence of a very thin fossil layer are very exceptional and it is not clear weather the fossil sites have been condensed during the past or if this is the result of present day extreme desert conditions. More detailed work on other Djourab sites should allow to refine the taphonomic history concerning these early hominid accumulations and formation.

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Brachiopod Shells on the Beach: Taphonomic Overprinting in a Fair-Weather Shell Accumulation.

Marcello Guimarães Simões, Sabrina Coelho Rodrigues, Juliana de Moraes Leme, Ricardo Angelim Pires-Domingues.

Keywords: BRACHIOPOD SHELLS, TAPHONOMIC OVERPRINTING, ABRASION, SHELL SURFACE TEXTURE, SPATIAL FIDELITY, BEACH ENVIRONMENT, LATE HOLOCENE

[+info] VOLUME 5. ISSUE 4. 2007 (3 issue)

This study documents the occurrence of brachiopod shells (Bouchardia rosea) in wrack-lines from backshore deposits of a tropical beach (Itamambuca beach), in the northern coast (Ubatuba County) of the state of São Paulo, Brazil. The main goals are: (a) to analyze the provenance and sorting of the brachiopod shells; (b) to provide the taphonomic signatures of the shells, which may favor the recognizance, description and diagnoses of similar shell concentrations in ancient rocks, and (c) to discuss the taphonomic meaning of these detrital accumulations. Sampling transects were done at the reflective and dissipative sectors of the Itamambuca beach. For this project, two thousand brachiopod shells were collected and examined. In general, shells are minute, pale in color, and extremely rounded with reduced shell micro-relieves. Abrasion is the main taphonomic signature recorded. Abraded shells are characterized by V-shaped scars on the external surface, exposing the secondary fibrous layer of the shell microstructure. In some cases, holes produced by abrasion (facets) are recorded in the most convex portion of the shells. A pronounced bias in favor of ventral valve is also noted, and the size frequency distribution of shells is shaped by taphonomy. Finally, shells show intense taphonomic overprinting, but the taphonomic signatures recorded on those shells are worth to provide valuable clues about the taphonomic pathways and spatial transportation of each bioclast.

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The Taphonomist´s Corner: Taphonomy and praxis.

Mariano Padilla Cano

Keywords

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