Magnetic susceptibility evolution and sedimentary environments on carbonate platform sediments and atolls, comparison of the Frasnian from Belgium and Alberta, Canada

Abstract

a b s t r a c t a r t i c l e i n f oKeywords: Frasnian Magnetic susceptibility Correlations Platforms and atolls Magnetic susceptibility (MS) measurements on carbonate rocks are considered as a proxy for impurities delivered to the carbonate environments. In the absence of strong climatic or tectonic variations, bulk MS values have been linked to sea level variations, because sea-level fall increases clastic supply and therefore increases in magnetic mineral deposition. In this paper we explore the relationship between the average magnitude of bulk MS, with shallowing-up sequences and facies evolution in different Devonian carbonate complexes. Similarities and differences between these parameters have been scrutinized in carbonate attached platform and detached platforms (mounds and/or atolls) from Belgium and Canada. In the carbonate attached platforms from Belgium and Canada, the MS patterns are directly related to depositional environment. Mean MS values increase from the most distal towards the most proximal facies and towards the top of the majority of fourth-order shallowing-up sequences. These trends are in agreement with theoretical background (MS increases with regression). In the Belgian detached platform, the average MS pattern generally shows an opposite behaviour to that observed in the attached carbonate platforms. Average MS decreases towards the most proximal facies and towards the top of a majority of the fourth-order shallowing-up sequences. This behaviour can be explained by the influence of sedimentary rate and water agitation during deposition. A high sedimentary rate will dilute the magnetic minerals in the atoll facies and the high water agitation during deposition may be expected to have prevented the deposition of the magnetic grains. So, the combination of these two effects will result in the observed low values in the atoll crown and lagoonal facies. In the Canadian detached platform, MS is mainly negative. This means that the limestones are very pure. The technique does not appear to be appropriate in these rocks. The variations of average MS behaviour by platform type can imply difficulties in correlating carbonates from different settings. A comparison of time equivalent mound and platform deposits shows that after an important regressive surface, the MS values are increasing for the platform deposits and decreasing for the mound. So MS evolution can be in complete opposition (caused by highly different sedimentary rates) in different depositional settings. The MS signal preserved in carbonate rocks is probably mainly related to 1) varying clastic supplies; 2) varying carbonate accumulation rates (dilution of the magnetic minerals by high carbonate production) and 3) potentially diagenesis.

Magnetic Susceptibility Changes Correlated With Paleoenvironmental and Lithological Changes, Within Borehole Cores on Either Sides of the Kalamaki-Isthmia Fault in Corinth Canal

“…The magnetic susceptibility (MS) of sediments depends mostly on mineral composition and grain size. In general, iron bearing minerals lead to high values of MS (dimensionless SI units) (e.g., Mullins, 1997;Oldfield, 1991;Da Silva et al, 2009;Reicherter et al, 2010). Terrestrial deposits are often characterized by higher amounts of such minerals compared to marine sediments; therefore MS measurements can help to distinguish between different sedimentary environments.…”

Magnetic susceptibility application: a window onto ancient environments and climatic variations: foreword

“…This time period was selected because, for the Palaeozoic, it has a relatively robust biostratigraphic framework, allowing an essential control to frame the correlations through MS. Furthermore, an important amount of MS data had already been published on the Mid-Palaeozoic Ellwood et al 2001Ellwood et al , 2007Da Silva & Boulvain 2002, 2003, 2006Hladil 2002;Racki et al 2002;Hladil et al 2003Hladil et al , 2006Geršl & Hladil 2004;Whalen & Day 2008;Da Silva et al 2009b). This permitted insertion of the newly collected material (Devonian from the Czech Republic, China, Carnic Alps and Canada; see Da into an already extensive database.…”

Deposition within the vicinity of the Mid-Eifelian High: detailed sedimentological study and magnetic susceptibility of a mixed ramp-related system from the Eifelian Lauch and Nohn formations (Devonian; Ohlesberg, Eifel, Germany)

“…Moreover, MS measurements of Middle Devonian sections of Belgium recently showed that wave agitation is, in combination with terrigenous input, a main inXuencing parameter possibly responsible for non-deposition of MS carrying minerals Boulvain 2007a, b, 2008). The role of carbonate productivity and sedimentation rate has also been considered to lower MS signal by diluting MS carrying minerals (da Silva et al 2008). In order to track these inXuencing parameters within the Ohlesberg quarry, a combination of facies analysis of carbonated-dominated and siliciclastic-dominated facies and their magnetic properties is implemented here.…”

“…The inXuence of carbonate productivity favours lower MS values than expected by diluting the MS carrying minerals (Mabille and Boulvain 2007b;da Silva et al 2008). This is notably obvious for SD2 and SD3.…”