Diagenesis of the Marly-Gypsum Formations, Igoumenitsa Area, N.W. Greece

Abstract

The Igoumenitsa area, in northwestern Greece, is composed of organic-rich clay evaporitic formations, of the Ionian zone. They have undergone diagenetic processes, which effect the mineralogical transformations. The purpose of this paper is the study of the mineralogical diagenesis and the possible implications to the geotechnical behavior of these organic-rich clay evaporitic sedimentary rocks. The diagenetic minerals reported in this study are: A: The authigenic swelling clay minerals, smectite and mixed layers of smectite. B. The two characteristic minerals phases of the sulfate diagenesis: I. Bassanite (semi hydrated gypsum-Ca04.l/2H20) and 2. Celestite (SrS04) that can be considered as an indicator of bacterial sulphate reduction, fluid flow and recycling ofevaporites. The two authigenic minerals have derived from the evaporites, mostly by the dehydration of gypsum and by the action of pore water that is charged with the ions derived from the dissolution of preexistent sulfates, halite and carbonates. C. The neoformation of the carbonate minerals aragonite and dolomite, due to probably bacterial sulfate reduction. When organic-clay rich sediments, are associated to evaporites, the diagenetic processes become more complex and interacted. The diagenetic alterations of the gypsum/anhydrite rocks are related to the geotechnical behavior of the formation and may lead to possible karstiflcation. That may cause problems in roads and tunnels construction on or through these evaporitic series

Contrasting Styles of Salt‐Tectonic Processes in the Ionian Zone (Greece and Albania): Integrating Surface Geology, Subsurface Data, and Experimental Models

“…Other sources of information used to prepare this column are as follows: for the general chronostratigraphy of the Upper Triassic‐to‐Eocene carbonate section (Bega & Soto, 2017; Bourli et al., 2019; BP, 1971; IFP, 1966; Kamberis et al., 2022; Karakitsios, 2013; Meço et al., 2000; Papanikolaou, 2021; Rigakis & Karakitsios, 1998; Robertson & Shallo, 2000; Zelilidis et al., 2003, 2015; Zoumpoulis et al., 2022); and for the lithostratigraphy of the Oligocene and Miocene “flysches” and the most recent sedimentary sequences (Avramidis et al., 2002; Bellas, 1997; Bellas et al., 1995; Botziolis et al., 2021; Gjika et al., 2001; Kostopoulou et al., 2022; Makrodimitras et al., 2010; Maravelis et al., 2014; Papanikolaou et al., 2010; Papanikolaou & Lekkas, 2008; Sotiropoulos et al., 2008; Triantaphyllou, 2013). The positions of the different elements of the petroleum system, like possible source rocks (with TOC contents in wt.%) and reservoir and seal lithologies (with average porosity values in %) are from this study, averaging also determinations from previous works (Alexandridis et al., 2022; Bourli, Iliopoulos, Makrodimitras, et al., 2022; David et al., 2014; Kamberis et al., 2022; Karakitsios & Agiadi‐Katsiaouni, 2007; Karakitsios & Rigakis, 2007; Kontakiotis et al., 2020; Makri et al., 2021, 2023; Maravelis et al., 2014; Mavromatidis, 2009; Tsipoura‐Vlachou, 2007; Vilasi, 2009; Vilasi et al., 2009; Zelilidis et al., 2015, 2016). Porosity of the Cretaceous–Eocene limestones could be even larger than the values included in the column due to early karstification and secondary joining and fracturing during Alpine deformation (Karakitsios & Agiadi‐Katsiaouni, 2007; Van Geet et al., 2002; Vilasi et al., 2009).…”

“…The claystone and marl sequences usually have abundant intercalations of alabastrine gypsum and thin levels of black dolomites (Pomoni‐Papaioannou & Tsaila‐Monopolis, 1983), with local lenses of sub‐volcanic rocks (Dalipi et al., 1972). Some authors have interpreted that these gypsum layers, with massive and bedded micro‐fabrics, are transformed and recrystallized during burial into anhydrite (Bornovas, 1960; Pomoni‐Papaioannou & Tsaila‐Monopolis, 1983; Tsipoura‐Vlachou, 2007).…”

“…However, it is possible to find some continuous sections in which a thick section of reddish to green or grayish marls and clays grades downward to a gypsum‐rich series (Figure 5b). Levels of black oleaginous claystones (rich in kaolinite and illite, which may have up to 17% TOC and a porosity of up to 17%) may also be encountered toward the upper part of the evaporite sequence and within the lower part of the dolomites (Bornovas, 1960; Karakitsios & Rigakis, 1996; Renz, 1955; Tsipoura‐Vlachou, 2007). The claystone and marl sequences usually have abundant intercalations of alabastrine gypsum and thin levels of black dolomites (Pomoni‐Papaioannou & Tsaila‐Monopolis, 1983), with local lenses of sub‐volcanic rocks (Dalipi et al., 1972).…”