A New Analytical Procedure to Graphically Characterize the Taphonomic Properties of Skeletal Carbonates. An Example From Miocene Limestones of New Zealand

Abstract

A new graphical representation of the taphonomy of skeletal carbonates observed at the thin-section scale is proposed, demonstrating their utility in drawing information about the effects of early sea-floor processes on the post-mortem fate of fossil hard parts. The graphical representations consist of two-axis diagrams, which integrate the degree of fragmentation, abrasion, bioerosion, and encrustation as primary descriptors of the average state of fossil remains in a Miocene limestone section from southeastern North Island of New Zealand. Numerical values are expressed as percentages that represent the contribution of each factor to alteration (i.e., the four factors represent up to 25% each of the total alteration), the sum of values quantifying the amount of departure from pristine condition. Data are plotted in a cumulative form that reflects synergistic action of sea-floor processes towards hard parts destruction. One important virtue of this graphical representation is that the nature, degree, and variability of taphonomic alteration can be visualized and compared in a single diagram for several grain categories within a sample, and between samples. The proposed scheme is particularly flexible because more than four taphonomic categories can be integrated, independently from the number of alteration classes specific to each category, provided conversion of scores obtained in each taphonomic categories into percentages. Compiled results of such taphonomic analyses could be used in the future to identify specific depositional conditions, such as hydraulic regime, transportation, and residence time on the sea floor (a potential proxy to net accumulation rates).

Shelf-derived mass-transport deposits: origin and significance in the stratigraphic development of trench-slope basins

“…The nature of the clasts implies that this substratum mostly comprised the pre-subduction series (e.g., Cretaceous up to Oligocene) (Chanier 1991;Chanier and Ferrière 1991). Yet, the few occurrences of Miocene shell bed clasts indicate that it also comprised some syn-subduction sedimentary rocks previously deposited in shallow-marine, mixed siliciclastic-carbonate environments (Chanier 1991;Bailleul et al 2007;Bailleul et al 2013;Caron et al 2019 occurred at lower bathyal depths (>1000 metres), with a planktic abundance varying from >80 to >95%, thus indicating deposition in a sub-oceanic to fully oceanic setting.…”

“…Even though deep marine sedimentation dominated at the time, several contemporaneously developing and older (Figure 4) shallow-marine, mixed siliciclastic-carbonate shelves were also reported in the area (Figure 3, sections f, i, m, ms, o, p, t, w) (Crundwell 1987;Chanier 1991;Bailleul et al 2007;Caron et al 2019;Bailleul et al Submitted;Caron et al Accepted). Bailleul et al (2013) and Bailleul et al (Submitted) demonstrated that whether attached to the continent or not, these shelfal systems preferentially formed above trench-slope basin-bounding structures that were affected by activemargin tectonic activity, such as uplift events.…”

“…It was restricted to the coarsest fraction of death assemblages contained in the MTDs, i.e., on fossil remains larger than five millimetres allowing assignment to a taxonomic group (from, at best, Species to Class level). In this study, three categories of skeleton damage, namely fragmentation, abrasion and bioerosion, were described visually using the graded classification scale presented in Appendix 3, complemented by those proposed by Caron (2011) and Caron et al (2019). Encrustation of skeletons was also evaluated but was found to be virtually absent.…”

Sclerobiosis: A Term for Colonization of Marine Hard Substrates

“…This approach enriches the study of the ecological structure of hard bottom assemblages. Sclerobiosis can also be applied in research focused on taphonomic analysis of bioclasts that include: 'bioerosion' and 'encrustation' signatures considered to be the result of particular biological processes (e.g., Caron et al, 2019); comparisons of encrustation patterns, abundance and diversity, and taphonomic pathways in past and present assemblages (e.g., Lescinsky et al, 2002;Rodland et al, 2004;; and studies of taphonomic feedback and time-averaging in which the accumulation of skeletal debris on the seabed favors the associations of colonizers on living and dead shells (e.g., Freeman et al, 2013;Kidwell, 2013).…”