THE CORRELATION POTENTIAL OF MAGNETIC SUSCEPTIBILITY AND OUTCROP GAMMA-RAY LOGS AT TOURNAISIAN-VISÉAN BOUNDARY SECTIONS IN WESTERN EUROPE

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Publikace nespadá pod Ekonomicko-správní fakultu, ale pod Přírodovědeckou fakultu. Oficiální stránka publikace je na webu muni.cz.
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BÁBEK Ondřej KALVODA Jiří ARETZ Maecus COSSEY Patrick DEVUYST Francois-Xavier HERBIG Hans-Georg SEVASTOPULO George

Rok publikování 2010
Druh Článek v odborném periodiku
Časopis / Zdroj Geologica Belgica
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Citace
Obor Geologie a mineralogie
Klíčová slova Outcrop logging techniques; foraminifer biostratigraphy; Carboniferous; deep-marine sediments; sealevel
Popis We have measured five deep-water carbonate and carbonate-siliciclastic sections at the Tournaisian-Viséan (Tn/V) boundary in western Europe, using petrophysical outcrop logging techniques (gamma-ray spectrometry /GRS/ and magnetic susceptibility /MS/). The aim was to trace correlatable log patterns across the flanks of the London-Brabant Massif from eastern Ireland to western Germany. Both GRS and MS logging proved useful for long-distance (up to ~1000 km) correlation. The log patterns can be interpreted in terms of sea-level fluctuations. A late Tournaisian regression, a sequence boundary at the Tn/V boundary, early Viséan lowstand systems tract and an overlying transgressive to regressive succession can be identified from the GRS and MS logs. The Tn/V sequence boundary can be correlated with exposure features and karstic surfaces in the up-dip shallow-water settings at the boundary between sequence 4 and 5 of Hance et al. (2001, 2002). This indicates that sea-level fluctuations around the Tn/V boundary were synchronous and traceable on the flanks of the London-Brabant Massif. The GRS-based logging has a greater correlation potential than MS as it can be applied in a broad spectrum of facies and depositional settings. In certain sections, the MS signal shows an increasing trend during transgression and a decreasing during regression, which is opposite to the MS paradigm from shallow-water carbonate platform settings. These trends are assumed to result from landward/basinward facies shifts of a low-productivity carbonate ramp system. Lowstand shedding of carbonate tempestites and turbidites results in low MS values while during sea-level rise the ramp systems backstep, developing a retrograding facies succession in its distal parts, which is associated with upward-increasing MS values.
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