Tectono-sedimentary environment of Upper Jurassic evaporite-carbonate deposits in the Ravar Zone, south of Tabas Block

The Ravar terrane, is situated at the south of the Tabas block. At the Ravar series Mesozoic strata, especially the Jurassic carbonate- evaporite deposits known as Pectinid limestone, Magu gypsum and Bido red evaporates are the most important parts of this deposits and have a variety of facies, distribution, and suitable exposure. Upper Jurassic Sequence stratigraphy of the mentioned deposits were messed up and even their position on the geological maps are not coherently elaborated. So investigation on the sedimentary environment and tectonic controller factors will be a great help in understanding the sequence stratigraphy position of these deposits. Thickness of mostly shale, interbedded Pectinid limestone, gypsiferous marl, red gypsum to white and finally red evaporates sequences were measured 470, 725, 50, more than 1450 (possibly contains Hojedk and Baghamshah Formations), and 1300 m, respectively. Eleven indicator facies were identified in the studied deposits which ended in tidal flat, lagoon, shoal and open marine belts. These facies illustrate environmental characteristics of carbonate-evaporite sequences. The facies changes, display the shallow carbonate homocline ramp setting.

After studying satellite images and field surveys in the Ravar region of Kerman, 5 sections of Lakarkuh-1 and 2, Horjond, Khorand and East of Bahabad were selected as the most suitable geological sections. Total of 68 thin sections from four sections of LakarKuh-1 and 2, Horjand and Khorand were examined by petrography. Of course, it is worth mentioning that no samples were taken from the Bahabad section and these were examined only to compare the thickness and lithological facies and especially evaporite deposits.

After extensive field surveys, five geological sections with the most complete outcrops were finally selected. The reason for the decrease in the thickness of evaporative deposits from 1450 m in the Khordand, 1300 m in the Bahabad, 725 m in the Horjond, 450 m in Lakarkuh-1 and 50 m in LakarKuh-2 can probably be due to the local changes in sea water levels and availability of more evaporative conditions. In order to identify and interpret gypsum and anhydrite facies and related fabrics, several sections have been selected in the Lakarkuh and Horjond areas. First, after introducing field photos, some of the important identified fabrics were examined. The microfacies investigation of 4 sections has led to the identification of 11 microfacies with the acronyms A, B, C and D, which belong to the 4 facies belts of intertidal, lagoon, shoal and open sea environments. Finally, according to the identified facies, a sedimentary environment model was presented.

The unusual and high thicknesses of gypsum in the Ravar region often have a tectonic origin and are mainly related to the formation of disharmonic folds. Evidence such as single nodules, enterolytic, and fenestral textures in evaporites show that these factories formed simultaneously with deposition or in the early stages of diagenesis. Three facies’ belts including intertidal zone facies (A1, A2 and A3 facies), high tidal zone facies (A4 and A5), and lagoon (B1) have been identified. The sedimentary model presented for the studied deposits in the shallow parts of a carbonate-evaporative system, which was probably a hemoclinical ramp. Examination of evaporitic facies in Lakarkuh and Horjond regions indicates that these facies are often deposited in sabkha and intertidal and lagoon environments.