Tracing formation and durability of calcite in a Punic–Roman cistern mortar (Pantelleria Island, Italy)

Abstract

Ancient hydraulic lime mortar preserves chemical and isotopic signatures that provide important information about historical processing and its durability. The distribution and isotopic composition of calcite in a mortar of a well-preserved Punic-Roman cistern at Pantelleria Island (Italy) was used to trace the formation conditions, durability, and individual processing periods of the cistern mortar. The analyses of stable carbon and oxygen isotopes of calcite revealed four individual horizons, D, E, B-1 and B-2, of mortar from the top to the bottom of the cistern floor. Volcanic and ceramic aggregates were used for the production of the mortar of horizons E/D and B-1/B-2, respectively. All horizons comprise hydraulic lime mortar characterized by a mean cementation index of 1.5 ± 1, and a constant binder to aggregate ratio of 0.31 ± 0.01. This suggests standardized and highly effective processing of the cistern. The high durability of calcite formed during carbonation of slaked lime within the matrix of the ancient mortar, and thus the excellent resistance of the hydraulic lime mortar against water, was documented by (i) a distinct positive correlation of δ(18)Ocalcite and δ(13)Ccalcite; typical for carbonation through a mortar horizon, (ii) a characteristic evolution of δ(18)Ocalcite and δ(13)Ccalcite through each of the four mortar horizons; lighter follow heavier isotopic values from upper to lower part of the cistern floor, and (iii) δ(18)Ocalcite varying from -10 to -5 ‰ Vienna Pee Dee belemnite (VPDB). The range of δ(18)Ocalcite values rule out recrystallization and/or neoformation of calcite through chemical attack of water stored in cistern. The combined studies of the chemical composition of the binder and the isotopic composition of the calcite in an ancient mortar provide powerful tools for elucidating the ancient techniques and processing periods. This approach helps to evaluate the durability of primary calcite and demonstrates the importance of calcite as a proxy for chemical attack and quality of the ancient inorganic binder.

Exploring the impact of diagenesis on (isotope) geochemical and microstructural alteration features in biogenic aragonite

“…Replicate measurements of internal standards give standard deviations of 0·1‰ for oxygen and 0·04‰ for carbon isotopes. The δ values of the solids on the VPDB scale were transformed to the VSMOW scale using the expression δ 18 O VSMOW = 1·03091 * δ 18 O VPDB + 30·91 (Coplen et al ., ) for calculation of apparent oxygen isotope fractionation (Dietzel et al ., ).…”

Scale-fragment formation impairing geothermal energy production: interacting H2S corrosion and CaCO3 crystal growth

“…Additional samples from other fragments were recovered using a dentist drill. The stable carbon and oxygen isotopic compositions of the micromilled and drilled carbonate powders were subsequently measured by continuous-flow isotope ratio mass spectrometry (CF-IR-MS), i.e., a Thermo Fisher Scientific GasBench II connected to a Finnigan Delta plus XP mass spectrometer, following the procedure reported in Dietzel et al (2015). Measured isotope ratios are quoted relative to the VPDB standard and typical precision (2σ) is ±0.08 and ±0.1‰ for δ 13 C and δ…”

“…The scale-fragments themselves constitute a valuable chemical archive, i.e., their variable chemical composition and particular fabric (crystal growth) capture production-specific fluid-solid interaction. Applying high-resolution analytical techniques, the natural and man-made environmental conditions promoting unwanted carbonate scaling, corrosion, and fragmentation are evaluated comparable to scientific approaches in paleoenvironmental (paleoclimate) studies based on mineral precipitates (e.g., Boch et al 2011;Dietzel et al 2015). An increased process understanding of the particular carbonate scale growth dynamics and scale-fragment formation is targeted, i.e., elucidating the favorable versus unfavorable environmental and technical conditions that support scale-fragment evolution.…”

Aragonite–calcite veins of the ‘Erzberg’ iron ore deposit (Austria): Environmental implications from young fractures

“…Oxygen isotope data of siderite and ankerite were corrected for mineral specific phosphoric acid fractionation (Rosenbaum & Sheppard, ; Kim et al ., ). Measured isotope ratios are given relative to the Vienna Pee‐Dee Belemnite (VPDB) reference and typical analytical precision (2 σ ) is ±0·1 and ±0·08‰ for the δ 13 C and δ 18 O values, respectively (Dietzel et al ., ).…”