Implications of Salt Diapirism in Syn-Depositional Architecture of a Carbonate Margin-to-Edge Transition: An Example from Plataria Syncline, Ionian Zone, NW Greece

Abstract

The present study examines the imprint of salt tectonics on carbonate depositional patterns of the Ionian zone platform edge to slope transition. The study area is part of an overturned rim syncline adjacent to a salt diapir. The Ionian zone is made up of three distinct stratigraphic sequences (pre-, syn- and post-rift sequences) represented by evaporites and shallow water carbonates at the base that pass gradually to a sequence consisting of pelagic limestones with shale intervals. In the study area, six cross sections were constructed, mainly covering the edge-to-slope overturned succession of Early Cretaceous to Eocene carbonates (post-rift stage) in the northern limb of the syncline. In the measured sections, abrupt changes in sediment texture resulted in the formation of distinct, thick-bedded carbonate layers, identified as packstones to grainstones–floatstones, with abundant fossil fragments, indicating deposition by debrites in a platform slope or slope-toe environment. Planar and ripple cross-lamination also suggest the involvement of turbidity currents in the depositional process. In the upper levels of the Lower Cretaceous carbonates, chert bodies with irregular shapes indicate soft sediment deformation due to instability of the slope triggered by salt intrusion. Internal unconformities identified in the field and in the available seismic data combined with the vertical to overturned dipping of the strata correspond to a basal megaflap configuration. Syn-sedimentary deformation resulted in the accumulation of debritic and turbiditic layers, while the compressional regime established in the area from the Late Cretaceous to Early Eocene enhanced the fracture porosity of carbonates, which could eventually affect the reservoir properties.

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

“…Due to its position and deep structure, we interpret the Sqepuri as an imbricate of the Kurveleshi (Middle Ionian) sheet. Stratigraphic variations in the Mesozoic succession between these three thrust sheets have been described in previous studies of the IZ (Aliaj, 1974;Aubouin, 1958Aubouin, , 1959bBega & Soto, 2017;Bernoulli & Renz, 1970;BP, 1971;IFP, 1966;Karakitsios, 1995;Nikolaou, 1988;Plaku & Murataj, 1974;Prifti et al, 2013;Renz, 1955;Vakalas et al, 2023;Velaj, 2002;Velaj et al, 1999;Zoumpoulis et al, 2022). However, based on our field observations, we believe that these variations are thickness variations toward previous diapiric structures.…”

“…Thrusting of the IZ produces pluri‐kilometric tectonic repetitions of the evaporites (Figures 3, 7, and 8) (Jenkins, 1972; Kamberis et al., 2022; Mazzoli et al., 2022; Sadekaj et al., 1992; Sorel & Cushing, 1982; Sotiropoulos et al., 2022; Underhill, 1989; Vakalas et al., 2023; Velaj, 2001, 2015a, 2015b) and their ductile expulsion and flow feeding thick frontal plugs, like for example, in the Dumrë diapir (Figure 7) (Bega & Soto, 2017; Velaj et al., 1999). Our interpretation of the general structure of the IZ is given in the two regional cross sections in Figure 8 and is based on historical (from the 60's to the 90's) and recent borehole information and the interpretation of two large seismic line transects oriented parallel to the main shortening direction (NE–SW).…”

“…(1995), and Vakalas et al. (2023)), which has an upper part richer in shales (Karakitsios & Agiadi‐Katsiaouni, 2007; Karakitsios et al., 2007; Tsikos et al., 2004) and abundant breccia and slump intervals (Bourli et al., 2019, 2020, 2023). Above this formation are two limestone sequences of approximately uniform thickness, which are the Senonian (∼150 m) and Eocene (∼800–900 m) limestones, whose ages are Coniacian to Maastrichtian and Paleocene to upper Eocene (Priabonian), respectively (Bourli et al., 2019; Kontakiotis et al., 2020; Le Goff, 2015; Vilasi et al., 2009; Zoumpoulis et al., 2022).…”

“…Both marl intervals have high organic contents (up to 3.5% TOC according to our study) and constitute regionally the main source rocks of the IZ petroleum system. Overlying these discontinuous successions and with variable thickness and stratigraphic facies are limestones and white marly limestones with chert interbeds of variable thickness (up to ∼800 m) that are called the Vigla Limestone (Tithonian to Cenomanian; Danelian et al (2004), Getsos et al (2007), Skourtsis-Coroneou et al (1995), and Vakalas et al (2023), which has an upper part richer in shales (Karakitsios & Agiadi-Katsiaouni, 2007;Tsikos et al, 2004) and abundant breccia and slump intervals (Bourli et al, 2019(Bourli et al, , 2020(Bourli et al, , 2023. Above this formation are two limestone sequences of approximately uniform thickness, which are the Senonian (∼150 m) and Eocene (∼800-900 m) limestones, whose ages are Coniacian to Maastrichtian and Paleocene to upper Eocene (Priabonian), respectively (Bourli et al, 2019;Kontakiotis et al, 2020;Le Goff, 2015;Vilasi et al, 2009;Zoumpoulis et al, 2022).…”

“…In suprasalt successions such as those represented here by the carbonate sequence (Upper Triassic to Eocene), preorogenic structures such as those observed (Figure 20) may develop with progressive onlaps over the pillows (as in DP), truncations and important thickness variations around the diapirs (as in the NE edge of FSP), and condensed (or absent) successions over the higher-relief salt walls (as in BSW, FP, and FSW). Diapirs growth occurred during the Middle Jurassic to Lower Cretaceous (i.e., Lower Posidonia mudstones to the Vigla Formation), explaining the facies variations, the occurrence of syn-sedimentary faults, and the thickness variations observed in these sequences (e.g., Bourli et al, 2020Bourli et al, , 2023Karakitsios, 1991Karakitsios, -1992Karakitsios, , 1995Karakitsios, , 2007Vakalas et al, 2023;Zoumpoulis et al, 2022). Pre-existing diapirs could be originated by an initial stage of reactive diapirism related to extension or by lateral variations in the overburden loading (as was suggested, e.g., by Karakitsios (1995Karakitsios ( , 2013).…”