TY - JOUR
T1 - Spatial variation in the temporal resolution of subtropical shallow-water molluscan death assemblages
AU - Ritter, Matias Do Nascimento
AU - Erthal, Fernando
AU - Kosnik, Matthewa
AU - Coimbra, João Carlos
AU - Kaufman, Darrell S.
N1 - Funding Information:
This study was supported mainly by the FAPERGS (grant 1982-2551/13-7). Additional funds were covered by the CNPq (140568/2014-0 to MNR, and 140927/2008-5 to FE), and by the International Ocean Discovery Program (CAPES 0195/2016-02-BEX to MNR). We also thankful Felipe Caron, who shared the samples from site 1, as well as Iran C.S. Corrêa, Maribel S. Nunes, and Jair Weschenfelder who allowed access to the samples from the sites 2 and 3. We are grateful to Katherine Whitacre for valuable help with AAR analyses at NAU, and John Southon for the AMS analyses at UCI. Fabrizio Scarabino is acknowledged for his taxonomic assistance. We would also like to thank Claudio G. De Francesco, María A.G. Pivel, and Michał Kowalewski for their valuable comments on earlier drafts of this report. The authors also thank José Ortiz and an anonymous reviewer, as well as the Associate Editor Adam Tomasˇovy´ch, for their helpful comments and constructive criticism that considerably improved the manuscript.
Publisher Copyright:
Copyright © 2017, SEPM (Society for Sedimentary Geology).
PY - 2017/9/1
Y1 - 2017/9/1
N2 - Fossil assemblages are expected to be time-averaged as a result of biological and physical processes that mix skeletal remains. Our quantitative understanding of time-averaging derives primarily from actualistic studies, in which direct numerical dating of individual specimens is used to assess the scale and structure of age mixing in death assemblages (incipient fossil assemblages). Here we examine the age, and the time-averaging of Mactra shells (Bivalvia: Mollusca) gathered from surface mixed siliciclastic-bioclastic sands at three sites on a passive-margin subtropical shelf (the Southern Brazilian Shelf; ∼ 33°S). Sixty Mactra specimens were individually dated using amino acid racemization (AAR) calibrated using radiocarbon ages (n=15). The time-averaging and the total age variability was based on a Bayesian approach that integrates the estimation errors and uncertainties derived from the posterior distribution associated with the AAR calibration average model. The 14C-calibrated AAR ages, pooled across all three sites, are strongly right-skewed with 97% of the individual mollusk shell age estimates ranging from 0 to 6 cal kyr BP. The magnitude of time-averaging varied inversely with the water depth, from < 15 yr at the deepest site (21 m) up to 1020-1250 yr at the shallowest site (7 m). The substantial variation in the temporal resolution across nearby sites, which are located in a seemingly homogenous depositional setting, indicates the presence of notable (if cryptic) spatial heterogeneities in local sedimentation, production, and exhumation, all increasing with water depth.
AB - Fossil assemblages are expected to be time-averaged as a result of biological and physical processes that mix skeletal remains. Our quantitative understanding of time-averaging derives primarily from actualistic studies, in which direct numerical dating of individual specimens is used to assess the scale and structure of age mixing in death assemblages (incipient fossil assemblages). Here we examine the age, and the time-averaging of Mactra shells (Bivalvia: Mollusca) gathered from surface mixed siliciclastic-bioclastic sands at three sites on a passive-margin subtropical shelf (the Southern Brazilian Shelf; ∼ 33°S). Sixty Mactra specimens were individually dated using amino acid racemization (AAR) calibrated using radiocarbon ages (n=15). The time-averaging and the total age variability was based on a Bayesian approach that integrates the estimation errors and uncertainties derived from the posterior distribution associated with the AAR calibration average model. The 14C-calibrated AAR ages, pooled across all three sites, are strongly right-skewed with 97% of the individual mollusk shell age estimates ranging from 0 to 6 cal kyr BP. The magnitude of time-averaging varied inversely with the water depth, from < 15 yr at the deepest site (21 m) up to 1020-1250 yr at the shallowest site (7 m). The substantial variation in the temporal resolution across nearby sites, which are located in a seemingly homogenous depositional setting, indicates the presence of notable (if cryptic) spatial heterogeneities in local sedimentation, production, and exhumation, all increasing with water depth.
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U2 - 10.2110/palo.2017.003
DO - 10.2110/palo.2017.003
M3 - Article
AN - SCOPUS:85029457567
SN - 0883-1351
VL - 32
SP - 572
EP - 583
JO - Palaios
JF - Palaios
IS - 9
ER -