Application of fractal methods to determine the Bouguer density in Charak Region (South of Iran)

Document Type : Original Article



A common method to determine the Bouguer density value as a random variable independent from topographic alternations has been introduced by Nettleton algorithm. During the correction processes, it may casually be accompanied by unexpected errors, for example in the folded region of Zagros, as a result of crustal thickening processes in the Southern regions of Iran. Sedimentary sequences in Charak-Namakin anticlines are known as important geological units which have been selected for prospecting oil related reservoirs by the National Iranian Oil Company. Gravimetric datasets have been acquired by this company through systematic land surveys in a total of 776 stations. The main target areas along Charak - Namakin salt domes are geographically located between 54.00 - 54.30 degrees of longitudes and 27.00 - 28.45 degrees of latitudes. Both Asmari (Oligocene) and Pabdeh - Gurpi formations (early Cenozoic) contain limestones with gray marls intercalations as a potentially valuable facies for hosting of hydrocarbore reservoirs under ascending movements of the Paleozoic formations in diapiric systems. Hormoz series (Cambrian) containing gypsum and other related evaporates play the main roles for oil trapping processes after arriving the emigrant volatiles to the permeable layers nearby brecciated structures. Determination of the optimum Bouguer density so that it is only related to Charak geological impressions is an important procedure which associates a number of gravimetric anomalies with probable oil trap locations. It means that Bouguer anomalies are comfortable geophysical quantities for density estimations according to statistical techniques. Although a linear method such as Nettleton correction can be used for density estimations, some abnormal thickening of the crust may increase in topographic disturbances and subsequently cause stochastic behaviors of the gravity values which cannot be interpreted by Euclidean geometry. Therefore, nonlinear analyses such as power law functions can be used to calculate the fractal dimensions as non-Euclid variables related to self similar peculiarities of the gravimetric values which are theoretically assumed to be spatially independent from crustal interactions with heavy masses of the lithosphere. According to Mark and Aronson, two fractal-based interpretations corresponding to gravimetric anomalous regions have been carried out by applying a variance – distance logarithmic equation in Free Air and Bouguer georeferred datasets, respectively. This research is an attempt to study the Brownian surfaces as unique area indicators to cumulative appearances of the gravimetric similarities above Charak sedimentary formations. Given the iteration processes on the log-log plots, some Bouguer anomalies have been recognized to be independent from topographic alternations in the ranges of 6.44-10.24 km distances from backgrounds. As a result, an averaged density value equal to 2.4 kgm-3 was calculated for Charak lithological occurrences by a stepwise fractal analysis of the total density assumptions (1.8-2.4 kgm-3). The fractal result was subsequently compared with the statistical result considered to be in a range of 2.3-2.4 kgm-3 as optimum density values for the Hormozgan Region after obtaining a new ratio of Bouguer regression versus the Bouguer Poisson coefficient (R2P) among estimation processes.     


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