Print this pageDiagenesis Related to Thrust-Sheet Emplacement: Tellian Atlas, Northern Algeria
MESSELLES, HADJ
The Tellian Atlas in northern Algeria consist of a complex east-west oriented thrust-sheet. The area went through an uplift and erosion episode between two major burial phases. The result is complex cementation by quartz and carbonate in the Albian and Tertiary sequences. These cements have been investigated systematically employing a number of techniques standard petrography (including CL), SEM, X-ray Diffraction, fluid inclusion analysis and geochemical techniques.
The relative importance of compaction/cementation process using the modal analysis data shows that the original porosity has been destroyed by a combined effect of compaction and cementation (locally cementation dominated process).
The average homogenisation temperatures measured in the Albian sequence in the fore land basin are slightly lower than the one measured in the nape zone. Quartz cementation occurred at temperature between 93 degrees C and 184 degrees C and from a wide range of salinities (3.39 - 11.7 wt percent NaCl equivalents). Dolomitisation was emplaced at temperature between 85 and 99 degrees C (lowest) in the fore land, whereas in the nape zone Th are between 153 and 162 degrees C. The petrography and fluid inclusion studies suggested that these dolomites are of burial origin and precipitate from a brine with a wide range of salinities. The carbon and oxygen stable isotope study constrain this figure. However, samples from Kef Gourine area exhibit more depleted values for the carbon (deltaC{13}= -2.618 and -3.672 percent),probably due to a contamination by meteoric water during the uplift erosion phase where the Albian has been exposed in that area.