Upper Jurassic and Lower Cretaceous carbonate rocks of the Berdiga Limestone – Sedimentation on an onbound platform with volcanic and episodic siliciclastic influx. Biostratigraphy, facies and diagenesis (Kircaova, Kale-Gümüşhane area; NE-Turkey)

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Abstract:

The Berdiga Limestone (Oxfordian to Barremian; NE-Turkey) was analyzed by a profile of 320 m thickness consisting of well-bedded platform carbonates. The biostratigraphic subdivision is based on calcareous algae and benthic foraminifera. Oxfordian oncolitic, intraclastic packstones and grainstones (fragments of corals) are overlain by crystalline dolomite with ghost textures of intraclasts, ooids and biogenics. Micritic limestones with microbial laminae and gypsum pseudomorphs occur in the uppermost Oxfordian and Lower Kimmeridgian and are overlain by Middle Kimmeridgian diabase. Mudstones occur throughout the Upper Kimmeridgian and Tithonian. Marked changes of facies and fauna occur in the Cretaceous. Packstones and grainstones rich in foraminifera, fragments of molluscs, echinoids and micritic intraclasts (Valanginian) overlie dolomitic mudstones and packstones (Berriasian) just containing some foraminifera. Generally the development of limestones with high faunal diversity and numbers of individuals is continued up to the Barremian. Locally fine-crystalline dolomite, algal laminites with birds eyes and traces of gypsum pseudomorphs, a sandstone horizon (30 cm) and three conglomeratic, reddish, marker horizons with soil character are intercalated. Moreover, beds with higher terrestrial, siliciclastic input contain fragments of volcanic rocks and tuffs as well as grains of quartz, feldspar and minor pyroxenes indicating episodic erosion of a source area of intermediate to basic volcanic rocks. Roundness of some quartz grains points to deposits in higher energy coastal settings. Pores are predominantly closed by fine- to medium-granular clear calcite cements. Very locally relic-textures of marine-phreatic isopacheous Mg-calcite rim cements can be observed in packstones and grainstones. Four main types of dolomite/dedolomite can be distinguished: (1) Idiomorphic rhombohedra with cloudy inclusion-rich core and clear inclusion-free overgrowth, (2) rhombohedra in interparticle pores, (3) fine- to coarse-crystalline hypidiomorphic dolomite with relic textures, and (4) partly dedolomitized zoned dolomite crystals. Silica diagenesis is characterized by (1) partial replacement of fossil fragments under preservation or destruction of the primary shell structures, (2) chert sphaerulithes, (3) scattered tiny idiomorphic quartz crystals with well developed crystal outlines, and (4) initial growth of tiny quartz skeletons. Furthermore a complex diagenesis of overgrowth on detrital feldspars, partly dissolution, and subsequent calcitization can be recognized in Cretaceous limestones.
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