TY - JOUR
T1 - Improving the detection of shell alteration
T2 - Implications for sclerochronology
AU - Coimbra, Rute
AU - Huck, Stefan
AU - de Winter, Niels J.
AU - Heimhofer, Ulrich
AU - Claeys, Philippe
PY - 2020/12/1
Y1 - 2020/12/1
N2 - Sclerochronology makes use of (fossil) shell-archives to establish records allowing for investigation of high-resolution environmental dynamics. Nevertheless, this potential can often not be fully exploited due to the interplay between paleoenvironmental variability, vital effects and the potential diagenetic modification of skeletal materials, which often results in highly complex records. A novel dynamic approach, aiming to separate pristine from altered shell material for paleoclimate and paleoenvironmental reconstructions is proposed. Seventeen fossil bivalve shells (requieniid rudists, pectinids and chondrodonts) from two neighbouring Lower Cretaceous (Albian) shallow-water sections (Lusitanian Basin, western Portugal) were analysed for their major and trace elemental compositions using high-resolution quantitative μXRF line scans. Their complex records were subject to a novel statistical analysis protocol, which tested mono- and multi-species datasets, as well as comparing shells from both locations. Characteristic elemental associations reveal the differential impact of early and late diagenetic alteration processes. The incorporation of elements associated with detrital contribution (Fe, Si, Al) is attributed to syn-depositional bioerosion (shell-boring). In clear contrast, shell-portions showing a strong correlation between Fe and Mn are indicative of later diagenetic alteration. The influence of each process is different at each site, revealing local differential alteration pathways. Mono-specific comparisons provides identical geochemical responses, suggesting that intra-specific differences do not control the observed elemental patterns. In contrast, inter-species tests rendered a clear separation in the way elements are incorporated in the shells of pectinids and requieniids (e.g., as evidenced by differences in Mg or Sr content). Such differences can be linked to differential biomineralization pathways, easily detected by the applied method. We present a new, dynamic method for distinguishing pristine from altered shell material, not relying on arbitrary diagenetic thresholds for trace element content. By clearly identifying shell-alteration pathways, syn- to post-depositional processes are recognized. A progressive cleaning of the elemental dataset allows paleoenvironmental studies to be based on the most pristine data, contributing to unravelling the complex interplay between climate, environmental dynamics and their impact on biomineralization processes and sclerochronological archives.
AB - Sclerochronology makes use of (fossil) shell-archives to establish records allowing for investigation of high-resolution environmental dynamics. Nevertheless, this potential can often not be fully exploited due to the interplay between paleoenvironmental variability, vital effects and the potential diagenetic modification of skeletal materials, which often results in highly complex records. A novel dynamic approach, aiming to separate pristine from altered shell material for paleoclimate and paleoenvironmental reconstructions is proposed. Seventeen fossil bivalve shells (requieniid rudists, pectinids and chondrodonts) from two neighbouring Lower Cretaceous (Albian) shallow-water sections (Lusitanian Basin, western Portugal) were analysed for their major and trace elemental compositions using high-resolution quantitative μXRF line scans. Their complex records were subject to a novel statistical analysis protocol, which tested mono- and multi-species datasets, as well as comparing shells from both locations. Characteristic elemental associations reveal the differential impact of early and late diagenetic alteration processes. The incorporation of elements associated with detrital contribution (Fe, Si, Al) is attributed to syn-depositional bioerosion (shell-boring). In clear contrast, shell-portions showing a strong correlation between Fe and Mn are indicative of later diagenetic alteration. The influence of each process is different at each site, revealing local differential alteration pathways. Mono-specific comparisons provides identical geochemical responses, suggesting that intra-specific differences do not control the observed elemental patterns. In contrast, inter-species tests rendered a clear separation in the way elements are incorporated in the shells of pectinids and requieniids (e.g., as evidenced by differences in Mg or Sr content). Such differences can be linked to differential biomineralization pathways, easily detected by the applied method. We present a new, dynamic method for distinguishing pristine from altered shell material, not relying on arbitrary diagenetic thresholds for trace element content. By clearly identifying shell-alteration pathways, syn- to post-depositional processes are recognized. A progressive cleaning of the elemental dataset allows paleoenvironmental studies to be based on the most pristine data, contributing to unravelling the complex interplay between climate, environmental dynamics and their impact on biomineralization processes and sclerochronological archives.
KW - Diagenesis
KW - Geochemistry
KW - Paleoenvironment
KW - Shells
KW - Statistical analysis
UR - http://www.scopus.com/inward/record.url?scp=85089842671&partnerID=8YFLogxK
U2 - 10.1016/j.palaeo.2020.109968
DO - 10.1016/j.palaeo.2020.109968
M3 - Article
AN - SCOPUS:85089842671
SN - 0031-0182
VL - 559
JO - Palaeogeography, Palaeoclimatology, Palaeoecology
JF - Palaeogeography, Palaeoclimatology, Palaeoecology
M1 - 109968
ER -