Microfacies and Depositional Conditions of Jurassic to Eocene Carbonates: Implication on Ionian Basin Evolution

Abstract

In order to decipher the paleo-depositional environments, during the Late Jurassic to Early Eocene syn-rift stage, at the margins of the Ionian basin, two different areas with exposed long sequences have been selected, Kastos Island (external margin) and Araxos peninsula (internal margin), and were examined by means of microfacies analysis and biostratigraphy. On Kastos Island, based on lithological and sedimentological features, the following depositional environments have been recognized: an open marine/restricted environment prevailed during the Early Jurassic (“Pantokrator” limestones), changing upwards into deep-sea and slope environments during the Late Jurassic and Early Cretaceous (Vigla limestones). The Upper Cretaceous (Senonian limestones) is characterized by a slope environment, whereas during the Paleogene, deep-sea and toe of slope conditions prevailed. In Araxos peninsula, Lower Cretaceous deposits (“Vigla” limestones) were accumulated in a deep-sea environment; Upper Cretaceous ones (Senonian limestones) were deposited in slope or toe of slope conditions. Paleocene limestones correspond to a deep-sea environment. In Araxos peninsula, changes occurred during the Cretaceous, whereas on Kastos Island, they occurred during the Paleocene/Eocene, related to different stages of tectonic activity in the Ionian basin from east to west.

Re-Evaluation of the Ionian Basin Evolution during the Late Cretaceous to Eocene (Aetoloakarnania Area, Western Greece)

“…From the Early Triassic to the middle Early Jurassic, the Ionian basin was part of an extensive shallow marine platform, during the pre-rift stage, which evolved into a vast basin bounded on both sides by shallow platforms, the Apulia platform on the west as well as the Gavrovo platform on the east [19,32]. The oldest rocks of the zone are Triassic evaporites and carbonates [11] and, more specifically, the lower evaporite layers are of Early to Middle Triassic age [2,3,9,16,19,33] (Figure 2).…”

“…They are overlain by the "Foustapidima" (Ladinian to Rhaetian) limestones and above them the "Pantokrator" Limestones (Hettangian to Sinemurian) occur [6,8,11] (Figure 2). From the late Early Jurassic (Pliensbachian) begins the syn-rift process when the initial shallow platform was submitted to extension, which caused a structural differentiation (shredding) into small sub-basins and started a general deepening, resulting in the formation of a deep basin [2,3,19,20]. At the base, the syn-rift sequence consists of the upper Lower Jurassic (Pliensbachian) pelagic "Siniais" limestones Formation and their lateral equivalent, the hemipelagic "Louros" limestones Formation which contain abundant ammonites, brachiopods, and foraminifera.…”

“…The main Ionian zone, in general, has been studied by Aubouin [7], IGRS-IFP [8], Bornovas [9], Bernoulli and Renz [10], BP [11], Karakitsios and Tsaila Monopolis [12], Karakitsios et al [13], Skourtsis-Coroneou et al [14] and Zelilidis et al [3,15]. Nevertheless, only a few studies have dealt with microfacies analysis combined with the overall architecture of the depositional system of the Ionian basin [16][17][18][19]. Specifically, according to Karakitsios [2,20] and Zelilidis et al [3] the depositional system of the Ionian basin was subdivided into three successions: the pre-rift succession, consisting of lower to middle Triassic evaporites and Upper Triassic to Lower Jurassic limestones, the syn-rift succession, consisting of Lower to uppermost Jurassic deposits and the post rift succession, consisting of Cretaceous to Eocene deposits, and which was further subdivided into two sub-stages, the Lower Cretaceous and the Upper Cretaceous to the lower Eocene sub-stage, respectively.…”

“…The studied section is located in south Aetoloakarnania, Western Greece. The succession is mainly composed of carbonate rocks of the Ionian zone, ranging in age from the Cretaceous to the Eocene [2,[19][20][21][22]. The more than 400 m thick Kato Retsina-Kato Mousoura stratigraphic succession has been studied in order to describe both the sedimentological characteristics and fossil assemblages of these Upper Cretaceous-Eocene carbonate deposits through microfacies analysis.…”

Comparison between Siliceous Concretions from the Ionian Basin and the Apulian Platform Margins (Pre-Apulian Zone), Western Greece: Implication of Differential Diagenesis on Nodules Evolution

“…According to [27][28][29], the Lower Cretaceous "Vigla" limestones in the external Ionian sub-basin consist of white, light-grey-to-yellowish micrites and radiolarian biomicrites, usually thin-bedded to platy with chert intercaltions and chert nodules. The middle sub-basin includes yellow-to-red marly limestones or shaly limestones and chert alternations, as well as clay layers that are usually green and red.…”