Abrasion surfaces on internal moulds of ammonites as palaeobathymetric indicators

Fernández-López, Sixto R.; Meléndez, Guillermo

doi:10.1016/0031-0182(94)90108-2

Cited by 32 publications

(5 citation statements)

References 12 publications

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“…Abraded internal molds of ammonoid shells, showing truncational facets, are good indexes of reworking in the Jurassic condensed section of the Iberian Range of Spain (Fernandez-L6pez, 1984(Fernandez-L6pez, , 1991Fernandez-Lopez and Melendez, 1994;Gomez and Fernandez-L6pez, 1994). Being sediment-filled, these shells probably behaved somewhat differently than waterlogged ones.…”

Section: Reworking Of Ammonoid Shellsmentioning

confidence: 99%

Ammonoid Taphonomy

Maeda

Seilacher

1996

Topics in Geobiology

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Section: Reworking Of Ammonoid Shellsmentioning

confidence: 99%

Ammonoid Taphonomy

Maeda

Seilacher

1996

Topics in Geobiology

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“…Such reworked shells in fossil cephalopods could be recognized by the difference in sediments between outside and inside the body chamber, and by shell abrasion and fragmentation (e.g. Seilacher 1963, 1966, 1971; Fernández‐López & Meléndez 1994; Wani 2001, 2004).…”

Section: Discussionmentioning

confidence: 99%

How to recognize in situ fossil cephalopods: evidence from experiments with modern Nautilus

Wani

2007

LET

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Field and flume experiments with modern Nautilus pompilius establish two prerequisites to recognize in situ preservation of fossil cephalopod shells (soft parts were within body chamber in situ at the time of fossilization): occurrence of the upper jaw within the body chamber and the position of jaws within the body chamber. Morphology of shells and jaws in modern and fossil nautiloids is so similar that these prerequisites can be applied for fossil nautiloids and provide implications for ammonoids. The upper jaws of Nautilus start to move at a water velocity of > 0.2 m/s, when the shells are reoriented with the aperture downstream; jaws are therefore unlikely to be secondarily deposited near the shell aperture by bottom currents. The lower jaws, moved at the velocity of > 0.1 m/s, can be deposited around the shell aperture by weak current (0.1–0.2 m/s in velocity), but never enter the inside of body chamber. Neither jaw is likely to be separately and selectively displaced from the inside of the body chamber through scavenging of the soft parts by burrowing infaunal animals. An upper jaw preserved inside the body chamber, together with a lower jaw, is thus a reliable indicator of in situ preservation; a sole lower jaw preserved around the shell aperture is likely to be secondarily deposited. Sedimentary structures inferring rapid burial events and jaw size are useful as additional evidence. Smaller jaws were more likely to be displaced from the body chamber by scavenging by infaunal animals after in situ burial, so that smaller jaws preserved within the body chamber suggest less scavenging. These findings are crucial to interpreting the taphonomic history and palaeo‐ecology of fossil cephalopods.

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“…12), it could be interpreted that the age of the belemnite providing the 87 Sr/ 86 Sr value is older than that deduced by biostratigraphy or by stratigraphic correlation. Older material (belemnites) might be found within a more recent deposit due to reworking ( sensu Fernández‐López, 1984, 1997; Fernández‐López & Meléndez, 1994; Wani, 2001). Thus, for example, sample 34 (section 12, Fig.…”

Section: Discussionmentioning

confidence: 99%

“…As these condensed levels contain organisms from distinct biozones and with different Sr‐isotope ratios, it is necessary to first determine whether the fossils used for dating had been reworked before attempting to further constrain the age of the levels. Fernández‐López (1984, 1997) and Fernández‐López & Meléndez (1994) have proposed several diagnostic criteria of taphonomic reworking, which are not always straightforward to apply.…”

Section: Introductionmentioning

confidence: 99%

Strontium‐isotope stratigraphy as a constraint on the age of condensed levels: examples from the Jurassic of the Subbetic Zone (southern Spain)

et al. 2007

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Condensed levels are often characterized by reworked fossils that may lead to incorrect age assessments. Strontium‐isotope stratigraphy is an important chronostratigraphic tool that can be used to verify the biostratigraphic information from condensed beds. This paper describes a study of the 87Sr/86Sr isotope ratios of 56 belemnite samples collected from 28 stratigraphic sections of the boundary between the Upper Member of the Gavilán Formation and the Zegrí Formation (Pliensbachian, Subbetic Zone). The petrographic and geochemical data (δ18O, δ13C, concentrations of Fe, Mn and Mg, and the Sr/Mn ratio) suggest that the belemnites have preserved their original marine geochemical composition. After plotting the samples in diagrams of 87Sr/86Sr values against time according to their biostratigraphic age, four different groups (A, B, C and D) were obtained with respect to the reference curve. In groups A and B, the age deduced from the Sr‐isotope ratio is in total or partial agreement, respectively, with the biostratigraphic age; therefore the 87Sr/86Sr ratio is a good method for the dating, correlation and assessment of biostratigraphic results. In groups C and D, the SIS age and the biostratigraphic age do not coincide. A graphic procedure is presented as a suitable methodology to constrain the age of the samples showing an SIS age that differs from the relative age deduced (by biostratigraphy or stratigraphic correlation) for the bed they were collected in. These situations are interpreted as being the result of reworking of the belemnites (group C) or ammonites (group D) that are included in condensed levels. These condensed levels formed during the maximum flooding event that led to the drowning of the Gavilán carbonate platform. The methodology supplied in this paper represents a valuable tool in identifying reworking processes, improving correlation and constraining biochronostratigraphic results. The values of 87Sr/86Sr represent a new contribution to the data set of 87Sr/86Sr ratios for the Pliensbachian.

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Abrasion surfaces on internal moulds of ammonites as palaeobathymetric indicators

Cited by 32 publications

References 12 publications

Ammonoid Taphonomy

Ammonoid Taphonomy

How to recognize in situ fossil cephalopods: evidence from experiments with modern Nautilus

Strontium‐isotope stratigraphy as a constraint on the age of condensed levels: examples from the Jurassic of the Subbetic Zone (southern Spain)

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