Meteoric diagenesis of Upper Cretaceous and Paleocene-Eocene shallow-water carbonates in the Kruja Platform (Albania): geochemical evidence

Abstract

Abstract:In the central part of the Kruja Platform (Albania) located in the Apulian passive margin, geochemical analyses (calcimetry, Sr, REE and isotopic, δ 13 C and δ 18 O) coupled with sedimentological and sequence stratigraphic study were carried out on Upper Cretaceous (CsB4, CsB5, CsB6 Biozones) and Paleocene to Middle Eocene shallowwater carbonates that crop out in the Kruje-Dajt massif (L'Escalier section) and Makareshi massif (La Route section).The lower values in Sr contents, the homogeneous δ18 O values in both sections and the covariance between δ 13 C and δ18 O values (La Route section) are attributed to diagenesis influence by a meteoric water-buffer system, supported by petrographic observations. Moreover, a new exposure surface during the Late Cretaceous time (between CsB5 and CsB6 Biozones) may be proposed according to the low or negative excursions of Sr values, the negative excursions of isotopic values in both sections and a positive peak of normalized REE values (La Route section). These variations correlate with the geochemical signal reported by the decreasing strontium isotope values of rudist shells in the Island of Brač carbonate platform (Apulia domain) during the late Middle Campanian (77.3 Ma). Also, this continental exposure is consistent with the global sea-level fall reported from the Boreal Realm, North Atlantic, and the southern Tethyan margin. This geochemical evidence is a complementary tool for the sedimentological analysis and suggests a maximum regression (a sea-level fall) at the transition between the CsB5 and CsB6 Biozones. The high values of Sr content in Middle Eocene carbonates (L'Escalier section) reflect changes in depositional environment from restricted to open marine conditions. REE values increase through transgressive systems tract, characterized by small increase of detrital input. However, anomalies of certain values in both sections suggest disturbances linked either to the changes in clay input and to diagenetic modifications. Peaks in dolomite content are linked with regressive episodes or tendencies, and dolomitic facies, as indicated by intertidal-supratidal depositional environments.

Diagenesis processes of the Gulneri Shale, Kometan, Mushorah formations within the upper Turonian - lower Campanian Supersequence from Bai Hassan area, North of Iraq

“…It is the process in which there is a change in the mineral and chemical composition of the sediments, including the process of dolomitization, which is the process of replacing the magnesium ion (Mg+ 2 ) with the calcium ion (Ca+ 2 ) in limestone rocks [19], and the limestone passes through several stages in order to turn into dolomite rocks, many limestone deposits contain dolomite mineral, but it is often secondary in origin and also exists as a cement material and is characterized by its rhombic crystals [20], and is considered one of the very important diagenesis processes because its rocks constitute more than 50% of the limestone rocks that store hydrocarbons in the world, and the increase in the intensity of the dolomitization leads to an increase in the percentage of porosity as the process of replacing the element magnesium with the element calcium leads to a decrease in the size of the crystals and thus increase porosity [21], Among the dolomite texture identified based on the classification [22] are both floating rhombic texture, which is characterized by its single rhombic crystals of large and small sizes scattered within the micrite or crystallized ground, and is characterized by incomplete to full-faceted crystals formed during the early stages of the dolomitization process [23], Fig ( 10/B), and contact rhombic texture, which is characterized by its adjacent crystals within the micrite or crystalline ground. Forms during the early and middle stages of the dolomitization process [24], Fig ( 10/C), While the authigenic minerals are minerals that are formed locally within the sedimentation basin as a chemical product, and the most important evidence of the locality of their origin is the limited appearance of these minerals to the gaps of structural and non-structural grains molded on the size and shape of the vacuum as well as the prevalence of these minerals and their spread in the form of colonies and clusters within the host facies negates the possibility of being transported [9], Among the most important authigenic minerals that have been diagnosed are pyrite (FeS 2 ), which is considered one of the important minerals in sedimentary rocks and the most common in the current study, and between [25] that most of the iron minerals associated with sedimentary rocks are formed by diagenesis processes and often early ones, and [26] pointed out that it is formed in reducing environmental conditions with high organic content, where anaerobic bacteria reduce dissolved sulfate ions, leading to the release of sulfur, which is in the form of (H 2 S) after its union with hydrogen Water and that (H 2 S) will combine with reduced iron compounds to form pyrite metal (FeS 2 ), Fig( 10/D), Glauconite, which is considered one of the clay minerals belonging to the mica group rich in silica, iron and aluminum, which is characterized by its bluish-green, yellowish-green or grayish-green colors and is easily identified in thin rock slides and in both ordinary and polarized lights [26], and its presence indicates unconformity surfaces and its chemical deposition in marine environments...…”

Metacuvillierinella sireli n. sp., a Campanian Rhapydioninidae (Foraminifera), from southeast Turkey. New considerations on the endoskeleton and particularities of the family, with a specialized lexicon

“…Two periods are particularized by emersive tendencies, marked by intertidal to supratidal deposition and frequent vadose diagenesis (BER-NIER & FLEURY, 1980); they are concomitant with presence of Sellialveolininae during Upper Albian-Cenomanian, Cuvillierinellinae and Rhapydionininae during the Campanian-Maastrichtian. Some periods of long term terrestrial emersion are even well characterized in Upper Cenomanian (POMONI-PAPAIOANNOU & ZAMBETAKIS-LEKKAS, 2009) and Maastrichtian (MAVRIKAS, 1993;LANDREIN et al, 2001) in Greece, as well as in Albania (HEBA et al, 2009). Among many others, some examples of foraminiferal tests modified by vadose diagenesis are published, i.e., Rhapydionina gr.…”

Rhapydioninidés du Campanien-Maastrichtien en région méditerranéenne : Les genres Murciella, Sigalveolina n. gen. et Cyclopseudedomia

“…Il est possible même que la zone CsB6a corresponde à une lacune de sédimentation ou à une ablation dans certaines régions : c'est ainsi que l'on peut tenter de rendre compte de l'absence des témoins de cette zone dans le massif de Pylos-Méthoni, où pourtant les carbonates campano-maastrichtiens affleurent largement (FLEURY et al, 1978). Une autre encore, envisagée par HEBA et al (2009) en Albanie, est possible entre les zones CsB5 et CsB6 ; celle-ci serait la cause de la disparition (au moins locale) des organismes présents sur la plate-forme depuis le Turonien-Coniacien, au profit des Rhapydioninidae. On notera encore que STEU-BER & SCHLÜTER (2012) dénombrent au cours du Campanien plusieurs discontinuités dans la distribution stratigraphique des rudistes, qui seraient corrélées à des périodes d'abaissement du niveau marin.…”