Thermal analysis of Cretaceous ambers from southern France
Résumé
Thermal properties of French Cretaceous ambers were investigated and compared with other ambers from various sites of the world. The amber samples came from 10 diff erent localities in southern France, in the Charentes, Languedoc, and Provence regions, ranging from Late Albian to Santonian in age. Thermogravimetric (TG) and Differential Thermogravimetric (DTG) profi les were obtained at heating rate of 10 K/min in air, starting from room temperature (20°C) and reaching a maximum temperature of 700°C. Elemental Analysis for total Carbon, Hydrogen, Nitrogen and Sulphur was also carried out. The TG combustion profile of the resins started after 200°C and complete combustion took place near 600°C. The DTG behaviour is characterized by a main exothermal peak situated between 394 and 420°C, accompanied by minor peaks and shoulders. The increasing value of the main exothermal peak correlates well to the increase of the age of the specimens, with a signifi cant correlation coeffi cient (r = 0.7721, p = 0.0089). A signifi cant correlation (r = 0.6728, p = 0.0004) is also found with other samples of diff erent age and origin. By considering the whole pattern of DTG peaks, a possible fi ngerprinting model of the French ambers is evaluated by multivariate analysis. Cluster Analysis and Principal Component Analysis show the presence of several clusters, according to the geological age and possibly to the palaeobotanical origin. Th e elemental analysis is consistent with that of other Cretaceous samples from diff erent sites of the world. Carbon and hydrogen are the main constituents (range 73-80% and 9.5-11.5% respectively). Sulphur is detected in small amounts (0.8-2.4%). Nitrogen is absent or appears as traces only (0-0.008%). Oxygen and other elements range from 4.6 to 16.8%. No successful clustering was possible according to the elemental composition. Thermal analysis, completed with multivariate statistics, is a useful source of information also for French ambers, as a help for identifi cation of the age, diagenetic processes and palaeobotanical origin.