The influence of compressive stresses on folding in the Middle Kura depression and the Turkmen shelf

Abstract

On the basis of the morphology of the folds, their three-dimensional position, the types of faults and the development of mud volcanism, the features of the spread of compres- sive stresses and their influence on the oil and gas bearing of the Kura and Gabirri interfluve, the Yevlakh-Agjabedi depression and the Godin massif were studied. For this purpose, maps of isomorphs and morphological schemes, positions of local folds on the plan of each of these structural elements were compiled. It has been established that within the depressions, the process of folding took place due to the mechanisms of longitudinal and latitudinal bending, which led to the formation of mostly linear and brachiform folds within them. The high intensity of compressive stresses with- in the Kura and Gabirri interfluve contributed to the development of mud volcanism here, and the increase in their intensity at the end of the Miocene led to the emergence of disharmony here in the structural plans between the Cretaceous-Eocene and Oligocene-Quater- nary complexes of sediments. For this purpose, the development of the Barda and Shirvanli structures located in the Yevlakh-Agjabedi depression along the section was investigated and it was determined that they had an uneven development. The Shirvanli fold, which is located in the southwestern zone of the region, had a height of 50-70 m according to the top of the Late Cretaceous. According to the top of the Paleocene, it reached a height of 150 m, and according to the top of the carbonate layer, which forms the lower part of the section of the Eocene, a fold developed and reached a height of 300 m. The Shirvanli fold, which began to form in the Eocene, developed more intensively in the Maikop age sediments. The reason for this was the high mobility of clay sediments along the section and the activation of compressive stress. The development of the Shirvanli structure in the Cretaceous proves its hereditary origin. The Barda fold, located in the northeast part of the Shirvanli fold, according to the top of the Eocene express itself as a structural terrace. It does not express itself as a structure by the bottom of Paleocene and the washed surface of the Cretaceous sediments complexes, but according to the top of the Maikop sedimentary complex, it is a local fold with a height greater than 300 m. It was determined that the thickness of Maikop sediments in the core of the Barda fold confirms that Maikop clays play a key role in the development of the fold. At the same time, the significant decrease in the thickness of the Sarmatian and Chokrak sediments in the crest part of the mentioned fold is indicative of its syn-depositional development in the same time interval. As it is clear from the morphological and developmental features of both mentioned folds , they are of diapiric origin, but due to the relatively weak development of compressive stresses, the low thickness of the sedimentary layer lying on the Maikop sediments, these folds did not have the necessary energy potential to fully realize diaprism. The latitudinal bending mechanism in the formation of these folds was relatively weak. The effusive massif in the Yevlakh-Agjabedi depression significantly limits the activity of compressional stress in this area. Compressive stresses have had their effect on the structures formed in the Oligocene-Miocene sediments on the northwestern slope of the Yevlakh-Agjabedi depression, but they were weakly expressed in the Neogene sediments due to the regional erosion that began in the second half of the Sarmatian age. It should be noted that the Barda and Shirvanli structures began their development period in the Cretaceous, and were faced with the compressive stresses in Maikop. Within the Godin massif, the morphology of the folds, their disordered three-dimensional position, testify to the absence of the influence of compressive stresses on the fold formation process.