Geophysics
Ata Eshaghzadeh; Alireza Hajian; Roghayeh Alsadat kalantari
Abstract
Potential field data is the assembled of effects of all underground sources. Computing regional-residual anomaly is a critical step in modeling and inversion in the gravity method. Existence quantitative noise in corrected gravity data is unavoidable. In this paper, we present a novel separation method ...
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Potential field data is the assembled of effects of all underground sources. Computing regional-residual anomaly is a critical step in modeling and inversion in the gravity method. Existence quantitative noise in corrected gravity data is unavoidable. In this paper, we present a novel separation method based on a Singular Value Decomposition (SVD) analysis of gravity dataset. With the SVD, a matrix of bouguer gravity data can be decomposed to a series of eigenimages. The number of required eigenimages or threshold for the reconstruction of the regional and residual (local) anomalies maps and noise distribution map from bouguer anomaly is determined based on the derived singular values by SVD. To reconstruct the data set by eigenimages may lose negligible information. We have considered which this value is equivalent with the mean of the variance of the resulted matrixes by eigenimages. The efficiency of the Singular Value Decomposition method was tested with the noisy synthetic gravity data of a hybrid model of the sphere as a local anomaly and deep-seated sloping plane as a regional anomaly. The separation results are satisfactory. The proposed method was applied on gravity field dataset of the Qom area, Iran.
N. Abbassi; A. Amini
Abstract
The Thalassinoides bearing calcareous sandstone and sandy limestones of Oligocene age unconformably overlay the Eocene volcaniclastic rocks and gradually pass into the lacustrine sediments (Miocene? in age) in the study area. These layers are dominated by Thalassinoides ...
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The Thalassinoides bearing calcareous sandstone and sandy limestones of Oligocene age unconformably overlay the Eocene volcaniclastic rocks and gradually pass into the lacustrine sediments (Miocene? in age) in the study area. These layers are dominated by Thalassinoides suevicus (Rieth 1932) in the Y shaped boxwork cylindrical and bifurcating burrows, which are mainly filled actively by trace maker(s). The bioturbations in the layers are categorized into five ichnofabric classes, which are equal to standard ichnofabric indexes of 1 to 5. Frequency of the ichnofabric classes are 40.37, 15.9, 8.85, 4.97 and 29.9 percents, respectively. Ichnofabric variations of the studied layers are arranged in seven bioturbated upward cycles, which are divided into two groups. The first group shows low ichnofabric fluctuations and a constancy in the bioturbation, where the second group shows high ichnofabrics fluctuations and variability in the bioturbation. Results from the study show that the Thalassinoides in the studied section formed in conditions similar to those of Cruziana and Glossifungites ichnofacies.
