Elsevier

Tectonophysics

Volume 721, 28 November 2017, Pages 501-512
Tectonophysics

Reply to the comment on “First records of syn-diagenetic non-tectonic folding in Quaternary thermogene travertines caused by hydrothermal incremental veining” by Billi et alii

https://doi.org/10.1016/j.tecto.2017.09.005Get rights and content

Highlights

  • CaCO3 mineralization and veins can develop within travertine after its formation.

  • It follows that the stratigraphic superposition law is not always valid in travertine.

  • The post-depositional process can modify the rock fabric and petrophysical attributes too.

Abstract

In our previous paper (Billi et al., 2017), using field geological observations, U-Th dating, and stable isotope analyses, we studied two deposits of Pleistocene thermogene travertines from Tuscany in central Italy. We concluded our study (1) warning that the common stratigraphic concept of travertine being a sedimentary succession with age younging from bottom to top is not always correct, (2) demonstrating that CaCO3 mineralization and veins can develop within the travertines after their formation with this syn-diagenetic process being able to modify the continuous bottom-up age evolution, and (3) showing that this post-depositional mineralization-veining process can not only modify the temporal succession but also deform and change the initial depositional travertine structure and its petrophysical properties. These conclusions could potentially make the interpretation of a travertine series more difficult than commonly thought. Alcicek et alii questioned our conclusions claiming that the travertine structures that we observed in Tuscany and interpreted as post-depositional features should have been interpreted, in analogy to similar structures from travertines elsewhere, as primary structures. Although we recognize, as already thoroughly stated in Billi et al. (2017), that the travertine depositional/post-depositional processes generally require further studies, we reaffirm the validity of our original interpretation at least for the structures analyzed in our previous paper. We, therefore, counter all criticisms by Alcicek et alii and conclude by indicating the way forward to further explore the depositional and post-depositional processes of thermogene travertines.

Introduction

We thank Alcicek et alii for bringing their opinion to our attention and welcome their comments that allow us to further detail our arguments. We begin our reply by synthesizing and better explaining our main results together with some instructive additions. We then reply to the main comments raised by Alcicek et alii and finally conclude with some general inferences.

The travertine exposures addressed in this paper belong to the Pleistocene Pianetti and Pian di Palma deposits, which are located in Tuscany, central Italy, at 42° 38′ 00.52″N and 11° 30′ 40.43″E, and 42° 41′ 21.15″N and 11° 29′ 52.79″E, respectively. The geological setting of these deposits is described in Carmignani et al. (2013), Berardi et al. (2016), Vignaroli et al. (2016), and Billi et al. (2017), whereas the origin and genetic context of Quaternary travertines from central Italy are described in Chiodini et al. (1995), Minissale et al. (2002), and Minissale (2004).

Section snippets

Rationale

Since thermogene travertines are more and more often used as (temporal) indicators of climate change, active faulting, and other environmental processes (Rihs et al., 2000, Minissale et al., 2002, Pentecost, 2005, Crossey et al., 2006, Crossey et al., 2009, Uysal et al., 2007, Uysal et al., 2009, Dockrill and Shipton, 2010, De Filippis and Billi, 2012, De Filippis et al., 2013, Kampman et al., 2012, Burnside et al., 2013, Sinisi et al., 2016), in our previous paper (Billi et al., 2017):

  • (1)

    We

Organization

In this section, we summarize some of Alcicek et alii's main comments and briefly reply, with the aid of a few figures, to each of them under three main thematic sub-sections.

Primary crystalline crusts vs. secondary mineralizations

Alcicek et alii stated that we did not recognize primary crystalline crusts, thus erroneously interpreting them as secondary mineralizations. We are aware of and did not challenge at all the fact that fan-shaped calcite crystals in thermogene travertines can be primary features (crystalline crusts in Guo and Riding, 1998).

Conclusions

The comments by Alcicek et alii, although welcome, do not alter our previous conclusions (Billi et al., 2017), which we synthetically re-propose here.

Since thermogene travertines are more and more often used as (temporal) indicators of climate change, active faulting, and further environmental processes, in Billi et al. (2017):

  • (1)

    We warned that the common stratigraphic concept of travertine registering sedimentary succession with age younging from bottom to top is not always correct.

  • (2)

    We then

Acknowledgments

Institutional funding from Roma Tre University, CNR-IGAG, Hungarian Academy of Sciences (János Bolyai scholarship to S.K.), Hungarian Scientific Research Fund (OTKA 101664), ETH Zürich, and ISTerre Grenoble are acknowledged. Dating at the HISPEC was supported by the Taiwan ROC MOST grants (105-2119-M-002-001 to CCS), and National Taiwan University (105R7625 to CCS). We acknowledge, in particular, no industrial funding for this study. We warmly thank P. Agard and an anonymous reviewer for

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