Technique and results of complex analyses to study processes in sedimentary basin (in Estonia)

• Published in: Physics and chemistry of the earth Vol. 23; no. 3; pp. 327 - 337
• Main Authors: Shogenova, A., Bityukova, L., Götze, H.-J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1998
• ISSN: 0079-1946; 1879-3568
• DOI: 10.1016/S0079-1946(98)00032-9

The technique of multivariate statistical analyses was applied to the database including 25 petrophysical and geochemical parameters of 780 samples of rocks from early Paleozoic sedimentary basin in Estonia. Variations of magnetic, electrical, density and seismic properties of carbonate rocks studied together with their chemical composition were investigated by stratigraphical sequence, by Ordovician facial zones and in secondary altered fracture and fissure zones. Visualization of parameters variations and changes were performed by 2-D and 3-D models. R-mode factor analysis was applied to the six data sets including four different age rocks data sets (lower, middle, upper Ordovician and Silurian) and two ones with altered rocks from fracture and fissure zones. The first dominant factors which controlled the studied parameters were interpreted in the terms of processes. The most important groups of processes controlling the changes of petrophysical parameters were revealed: primary processes (sedimentation) and secondary alteration processes (dolomitization, fracturing, rock solution and leaching). Most of electrical, density and seismic properties of studied carbonate rocks depend on clay content, which is determined by sedimentation processes. The same properties in the fracture zone are changed with increase in secondary porosity. At least three geochemical types of dolomitization were revealed by factor analysis. In the most studied data sets dolomitization plays the second role in the parameters variations. Widespread lower Ordovician dolomitization and associated with vertical fracture zone dolomitization cause increase in magnetic properties in lower and middle Ordovician rocks.