Combined controls of sedimentology and diagenesis on seismic properties in lacustrine and palustrine carbonates (Upper Miocene, Samos Island, Greece)

Abstract

SUMMARY For the subsurface characterization of carbonates, linking physical properties (e.g. porosity and seismic reflectors) with their geological significance (e.g. sedimentary facies and diagenesis) is of primary importance. To address this issue, we study the lacustrine and palustrine carbonates on Samos Island through a geological and geophysical characterization of a sedimentary succession. The microstructures of the samples are described, and the samples’ physical properties are measured (porosity, P-wave velocity and density). The results show that the identification of only the primary (i.e. sedimentary) microstructure is not sufficient for explaining the huge variations in porosity and P-wave velocity. Hence, we highlight two early diagenetic processes that strongly impact the microstructures and control the physical properties: (i) neomorphism occludes porosity and increases the P-wave velocity of mud- and grain-supported microstructures, which implies a mineralogical stabilization of the grains; (ii) conversely, the dissolution process creates porosity and decreases the P-wave velocity of grain-supported microstructures if the mineralogical composition of the grains is not previously stabilized. These two diagenetic processes thus depend on the primary microstructures and mineralogy of the sediments. This work aims to explain the variations in porosity and P-wave velocity for each defined primary microstructure. A 1-D seismogram is then built to highlight seismic reflectors with a metre-scale resolution. These reflectors are associated with several geological contrasts. Hard kicks (positive amplitude reflectors) match well with exposure surfaces related to palaeosols. They correspond to contrasts between non-modified primary microstructures and highly neomorphosed microstructures. Conversely, soft kicks (negative amplitude reflectors) are linked with diagenetic contrasts (e.g. neomorphosed microstructures versus non-modified primary microstructures) and sedimentary contrasts that can be overprinted by diagenesis (e.g. neomorphosed mud-supported microstructures versus dissolved grain-supported microstructures). This study highlights that high-resolution seismic reflectors of lacustrine and palustrine carbonates are strongly related to the spatial contrasts of primary microstructures overprinted by early diagenesis.

Upscaling of Elastic Properties in Carbonates: A Modeling Approach Based on a Multiscale Geophysical Data Set

“…The arrival times of P waves (first break) were directly measured on the oscillograph and divided by the length of samples to calculate P wave velocities. As indicated by Bailly, Adelinet, et al (), the error of this data set is mainly related to the first break picking (lower than 5%). Ultrasonic measurements provide millimetric wavelengths that are used to characterize the smaller scale (REV 1 of Figure ).…”

“…Then, the top of the sedimentary section highlights again grainy and muddy carbonates alternating with beds of marls (between 32 and 40 m). Note that Bailly, Adelinet, et al () give a more detailed description of the studied outcrop.…”

Petrophysics and sediment variability in a mixed alluvial to lacustrine carbonate system (Miocene, Madrid Basin, Central Spain)

“…Bailly et al (2019) in their study of a lacustrine–palustrine sedimentary system on Samos (Greece) highlighted that early diagenetic processes had a strong impact on the acoustic properties of the sediments. The Samos deposits showed large variations in porosity and associated P‐wave velocities.…”

“…The aim of this study is (a) to analyse the variations in petrophysical properties of lacustrine carbonates and (b) to resolve which factors determine the petrophysical characteristics of these continental deposits. Understanding the link between the actual sediments and their acoustic properties may help to determine to what extent petrophysical properties of these sediments differ from marine carbonates (Anselmetti & Eberli, 1993; Kenter & Ivanov, 1995; Kleipool et al, 2017; Verwer et al, 2008) and other continental carbonate deposits, for example, travertines and tufas (Bailly et al, 2019; García del Cura et al, 2012; Soete et al, 2015).…”

Upscaling of elastic properties in carbonates: A modeling approach based on a multiscale geophysical data set

“…The arrival times of P-waves (first break) were directly measured on the oscillograph and divided by the length of samples to calculate P-wave velocities. As indicated by Bailly et al (2019), the error of this dataset is mainly related to the first break picking (lower than 5 %). Ultrasonic measurements provide millimetric wavelengths that are used to characterize the smaller scale (REV 1 of Figure 3).…”