Molluscan shell condition after eight years on the seafloor – taphonomy in the Gulf of Mexico and Bahamas

Title:
Molluscan shell condition after eight years on the seafloor – taphonomy in the Gulf of Mexico and Bahamas
Authors:
Powell, Eric N.; Brett, Carlton E.; Parsons-Hubbard, Karla; Callender, W. Russell; Staff, George M.; Walker, Sally E.; Raymond, Anne L.; Ashton-Alcox, Kathryn A.
Abstract:
In 1993 and 1994, the shelf and slope experimental taphonomy initiative (SSETI) deployed shells of a suite of molluscan species in a range of environments of deposition (EODs) representing a range of depths, sediment types, and environmental conditions with the goal of measuring taphonomic rates over an extended period of time. In 1999 and 2001, SSETI retrieved skeletal remains from 41 locations in the Bahamas and on the Gulf of Mexico continental shelf and upper slope that had been on the seafloor for eight years. Here, we compare taphonomic processes in two different ocean basins, across 24 environments of preservation (EOP) to evaluate the influence of species, sedimentary environment, degree of burial, and water depth on the preservational process. Taphonomic signature after eight years was almost exclusively a function of location of deployment and, frequently, taphonomically-distinctive locations of deployment were subsumed within distinctive EODs. EOD-level characteristics were insufficiently discriminative to delineate environments of preservation. EOPs and EODs are not synonymous concepts. Across all sites and species, the dominant taphonomic process was discoloration. Dissolution was of penultimate importance; nevertheless the cumulative impact over eight years was insufficient to produce a significant loss in shell weight in any EOP. Maximum dissolution intensity was normally observed on the outer shell surface; the inner and outer shell surfaces are inherently different in their time course of shell deterioration. Principal components analysis (PCA) demonstrated limited co-occurrence of discrete taphonomic processes among the 24 EOPs. Breakage and edge rounding fell on the same PCA axis, but these two processes were independent of all others. PCA divided dissolution into three independent components that discriminated the inner and outer shell surface of bivalves (and spire and body whorl of gastropods) and pitting from the development of a chalky surface. Discoloration was dissembled into five distinctive discoloring processes: fading without subsequent discoloration, the development of a brown-to-red coloration, orange/orange mottled discoloration, development of a green/green mottled color, and gray-to-black discoloration. The only concordance of ostensibly distinctive taphonomic processes was the association of small pits on the shell surface with orange discoloration on the shell. Depth did not exert a single significant effect on any of the eight primary taphonomic factors resolved by PCA, likely because of burial processes. The trends in taphonomic signature cannot be explained by any simple combination of sediment type and degree of exposure. A comparison between two-year and eight-year deployments suggests that important revelations can be gleaned from short-term experimental deployments, yet the same comparison discloses the spuriousness of other inferences. Thus, long-term experiments are essential to understand the time course of preservation. The taphonomic process is, in general, slow, and nonlinearity in rates over time constrains the subset of inferences that can be deduced accurately from short deployment periods.
Citation:
Powell, Eric N., Carlton E. Brett, Karla M. Parsons-Hubbard, et al. 2008. "Molluscan shell condition after eight years on the seafloor – taphonomy in the Gulf of Mexico and Bahamas." Journal Of Shellfish Research 27: 191-225.
Publisher:
National Shellfisheries Association
DATE ISSUED:
2008
Department:
Geology
Type:
article
PUBLISHED VERSION:
10.2983/0730-8000(2008)27[191:MSCAEY]2.0.CO;2
PERMANENT LINK:
http://hdl.handle.net/11282/309526

Full metadata record

DC FieldValue Language
dc.contributor.authorPowell, Eric N.en_US
dc.contributor.authorBrett, Carlton E.en_US
dc.contributor.authorParsons-Hubbard, Karlaen_US
dc.contributor.authorCallender, W. Russellen_US
dc.contributor.authorStaff, George M.en_US
dc.contributor.authorWalker, Sally E.en_US
dc.contributor.authorRaymond, Anne L.en_US
dc.contributor.authorAshton-Alcox, Kathryn A.en_US
dc.date.accessioned2013-12-23T16:11:28Zen
dc.date.available2013-12-23T16:11:28Zen
dc.date.issued2008en
dc.identifier.citationPowell, Eric N., Carlton E. Brett, Karla M. Parsons-Hubbard, et al. 2008. "Molluscan shell condition after eight years on the seafloor – taphonomy in the Gulf of Mexico and Bahamas." Journal Of Shellfish Research 27: 191-225.en_US
dc.identifier.issn0730-8000en_US
dc.identifier.urihttp://hdl.handle.net/11282/309526en
dc.description.abstractIn 1993 and 1994, the shelf and slope experimental taphonomy initiative (SSETI) deployed shells of a suite of molluscan species in a range of environments of deposition (EODs) representing a range of depths, sediment types, and environmental conditions with the goal of measuring taphonomic rates over an extended period of time. In 1999 and 2001, SSETI retrieved skeletal remains from 41 locations in the Bahamas and on the Gulf of Mexico continental shelf and upper slope that had been on the seafloor for eight years. Here, we compare taphonomic processes in two different ocean basins, across 24 environments of preservation (EOP) to evaluate the influence of species, sedimentary environment, degree of burial, and water depth on the preservational process. Taphonomic signature after eight years was almost exclusively a function of location of deployment and, frequently, taphonomically-distinctive locations of deployment were subsumed within distinctive EODs. EOD-level characteristics were insufficiently discriminative to delineate environments of preservation. EOPs and EODs are not synonymous concepts. Across all sites and species, the dominant taphonomic process was discoloration. Dissolution was of penultimate importance; nevertheless the cumulative impact over eight years was insufficient to produce a significant loss in shell weight in any EOP. Maximum dissolution intensity was normally observed on the outer shell surface; the inner and outer shell surfaces are inherently different in their time course of shell deterioration. Principal components analysis (PCA) demonstrated limited co-occurrence of discrete taphonomic processes among the 24 EOPs. Breakage and edge rounding fell on the same PCA axis, but these two processes were independent of all others. PCA divided dissolution into three independent components that discriminated the inner and outer shell surface of bivalves (and spire and body whorl of gastropods) and pitting from the development of a chalky surface. Discoloration was dissembled into five distinctive discoloring processes: fading without subsequent discoloration, the development of a brown-to-red coloration, orange/orange mottled discoloration, development of a green/green mottled color, and gray-to-black discoloration. The only concordance of ostensibly distinctive taphonomic processes was the association of small pits on the shell surface with orange discoloration on the shell. Depth did not exert a single significant effect on any of the eight primary taphonomic factors resolved by PCA, likely because of burial processes. The trends in taphonomic signature cannot be explained by any simple combination of sediment type and degree of exposure. A comparison between two-year and eight-year deployments suggests that important revelations can be gleaned from short-term experimental deployments, yet the same comparison discloses the spuriousness of other inferences. Thus, long-term experiments are essential to understand the time course of preservation. The taphonomic process is, in general, slow, and nonlinearity in rates over time constrains the subset of inferences that can be deduced accurately from short deployment periods.en_US
dc.publisherNational Shellfisheries Associationen_US
dc.identifier.doi10.2983/0730-8000(2008)27[191:MSCAEY]2.0.CO;2en
dc.subject.departmentGeologyen_US
dc.titleMolluscan shell condition after eight years on the seafloor – taphonomy in the Gulf of Mexico and Bahamasen_US
dc.typearticleen_US
dc.identifier.journalJournal Of Shellfish Researchen_US
dc.subject.keywordTaphonomyen_US
dc.subject.keywordPreservationen_US
dc.subject.keywordEnvironment of preservationen_US
dc.subject.keywordDissolutionen_US
dc.subject.keywordShell carbonateen_US
dc.subject.keywordBurialen_US
dc.subject.keywordDiscolorationen_US
dc.subject.keywordMolluscen_US
dc.identifier.volume27en_US
dc.identifier.startpage191en_US
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