Hydrothermal history in the eastern margin of Tunisia: inferred magmatic rocks alterations, new paragenesis and associated gasoccurrences

This study documents the Cretaceous intraplatemagmatic-hydrothermal activity in the Eastern margin ofTunisia. The magmatic occurrences are believed to be directlylinked to deeply rooted faults, trending E–W, N–S andNW–SE,and which enabled basaltic magmas ascension. The settling ofthis magmatism was accompanied by circulation of hydrothermalfluids, generating a local abnormal geothermal gradient.Magmatic rocks suffered effects of hydrothermal alteration duringmagma cooling. Slightly deformed zones are characterisedby superimposed static paragenesis which began in green schistfacies (T=450–350 °C) and ended by analcime crystallization atrelatively low temperatures (T=180–130 °C). Temperature increaseand hydrothermal conditions led to the generation of anew mineral paragenesis around the enclosing sedimentary deposits.CO2, H2S, CH4 and N2 occurrences are also thought to bedriven by this magmatic repartition. In addition, it is most likelythat the gases, produced at deeper depth, migrated upwards alongthe highly permeable fault zones. The carbon isotopic signaturesof selected gas samples suggest a thermogenic origin for methaneand a crustal origin forCO2. The latter could have been generatedthrough thermal breakdown of carbonate rocks via contact metamorphismor through increasing burial depth and high heat flowinduced by the hydrothermal event in the studied area

Provenance and reference groups of African Red Slip ware based on statistical analysis of chemical data and REE

International audienceAfrican Red Slip (ARS) ware (sigillata africana) from three archaeological sites in northern (Oudhna, Sidi Khalifa) and central Tunisia (Henchir el Guellel) was studied by X-ray fluorescence and statistical treatment of chemical data in order to define homogeneous reference groups. The specimens from Henchir el Guellel are clearly different from those of the other two sites, which are compositionally more similar, due to their geographical vicinity. ARS ware from Sidi Khalifa is chemically very homogeneous, whereas that from Oudhna clusters into two distinct groups. The chemical correspondence with literature reference groups, based on both kiln wastes and sherds from archaeological surveys, defines new reference groups, statistically more numerous and representative. Comparisons of chemical data by neutron activation analysis on selected potsherds and clays from the surroundings of each site also identified the probable base-clays used to produce the ARS ware of Oudhna, Sidi Khalifa, and to advance some hypothesis on that used in Henchir el Guellel, thereby overcoming difficulties in assessing chemical contents of elements due to levigation processes