Multistage dolomitization in Late Jurassic-Early Cretaceous platform carbonates (Berdiga Formation), Basoba Yayla (Trabzon), NE Turkey: Implications of the generation of magmatic arc on dolomitization

KANDEMIR, RAIF/0000-0002-0344-9159; Ozyurt, Merve/0000-0003-1596-5916WOS: 000418971300001Late Jurassic-Early Cretaceous Berdiga Formation, which is widely distributed in an E-W trending belt in the Eastern Pontides (NE Turkey), is composed of platform carbonates. the formation shows varying lithofacies changing from supratidal to platform margin reef both laterally and vertically. the studied Baioba Yayla (Trabzon, NE Turkey) area comprises one of the typical exposures of formation in the northern zone of Eastern Pontides. in this area, the lower parts of the formation are pervasively dolomitized by fabric-destructive and fabric-preserving replacive dolomites that are Ca rich and nonstoichiometric (Ca56-60Mg40-44). Replacement dolomites (Rd) are represented by delta O-18 values of -15.3 to -4.2 (VPDB), delta C-13 values of -3.7-1.5 parts per thousand (VPDB), and Sr-87/Sr-86 ratios of 0.70675-0.70731. Petrographic and geochemical evidence implies that Rd dolomites are formed before compaction at shallow-moderate burial depths from Late Jurassic-Early Cretaceous seawater and/or partly modified seawater as a consequence of rock/water interaction, and they are recrystallized at elevated temperatures during subsequent burial. During subsequent Late Cretaceous diagenetic process when the region became a magmatic arc, Rd1a and Rd3 dolomite were recrystallized by hydrothermal fluids of marine origin. the dolomite cements (Cd) overlying the low-amplitude stylolites have similar geochemical charasteristics than Rd1a and Rd3 dolomite and are characterized by high homogenization temperatures (Th). This might indicate that Cd dolomite was precipitated from hydrothermal fluids of marine origin that recrystallized the Rd1a and Rd3 dolomite. the fact that Cd dolomite comprising the latest phase of dolomitization is overlain by coarsely crystalline mosaic calcite and silica cements may indicate that diagenetic fluids were undersaturated with respect to dolomite and oversaturated with respect to calcite and silica.Scientific Research Unit of the Karadeniz Technical University [8400]This study was financially supported by the Scientific Research Unit of the Karadeniz Technical University under contract no 8400. the appreciation is extended to Dr. Emin Ciftci (Istanbul Technical University) for his help for microscopic studies

REE Characteristics of Lower Cretaceous Limestone Succession in Gumushane, NE Turkey: Implications for Ocean Paleoredox Conditions and Diagenetic Alteration

TASLI, KEMAL/0000-0003-0160-6912; Al-Aasm, Ihsan/0000-0003-2166-0561; Hollis, Cathy/0000-0002-3980-2583WOS: 000565595400001Trace and rare earth elements (REEs) are considered to be reliable indicators of chemical processes for the evolution of carbonate systems. One of the best examples of ancient carbonate successions (Berdiga Formation) is widely exposed in NE Turkey. the Lower Cretaceous limestone succession of Berdiga Formation may provide a case study that reveals the effect of ocean paleoredox conditions on diagenetic alteration. Measurement of major, trace and REEs was carried out on the Lower Cretaceous limestones of the Berdiga Formation, to reveal proxies for paleoredox conditions and early diagenetic controls on their geochemistry. Studied micritic limestone microfacies (MF-1 to MF-3) indicate deposition in the inner platform to a deep shelf or continental slope paleoenvironment during the Hauterivian-Albian. the studied limestone samples mainly exhibit low Mg-calcite characteristics with the general chemical formula of Ca98.35-99.34Mg0.66-1.65(CO3). They are mostly represented by a diagnostic REE seawater signature including (1) slight LREE depletion relative to the HREEs (ave. 0.72 of Nd/Yb(N)and ave. 0.73 of Pr/Yb-N), (2) negative Ce anomalies (Ce/Ce* = 0.38-0.81; ave. 0.57), (3) positive La anomaly (La/La* = 0.21-3.02; ave. 1.75) and (4) superchondritic Y/Ho (ave. 46.26). Studied micritic limestones have predominantly low Hf (bdl to 0.5 mu g/g), Sc (bdl to 2 mu g/g) Th (bdl to 0.9 mu g/g) contents suggesting negligible to minor shale contamination. These findings imply that micritic limestones faithfully record chemical signals of their parental and diagenetic fluids. the succession also exhibits high ratios of Eu/Eu* (1.01-1.65; ave. 1.29 corresponding to the positive Eu anomalies), Sm/Yb (1.26-2.74; ave. 1.68) and La/Yb ratios (0.68-1.35; ave. 0.9) compared to modern seawater and wide range of Y/Ho ratios (29.33-70.00; ave. 46.26) which are between seawater and hydrogenetic Fe-Mn crusts. Several lines of geochemical evidence suggest water-rock interaction between parental seawater and basaltic rocks at elevated temperatures triggered by hydrothermal activity associated with Early Cretaceous basaltic magma generation. the range of Ce/Ce* values is suggestive of mostly oxic to dysoxic paleoceanographic conditions, with a sudden change to dysoxic conditions (Ce/Ce* = 0.71-0.81), in the uppermost part of the MF-1. This is followed by an abrupt deepening paleoenvironment with a relative increase in the oxic state of the seawater and deposition of deeper water sediments (MF-2 and MF-3) above a sharp transition. the differences in microfacies characteristics and foraminifera assemblage between MF-1 and overlying facies (MF-2 and MF-3) may also confirm the change in paleoceanographic conditions. Therefore, REEs data obtained from studied limestones have the potential to contribute important information as to regional paleoceanographic conditions of Tethys during an important period in Earth history.Scientific and Technological Research Council of Turkey (TUBITAK-CAYDAG)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [115Y005]; Karadeniz Technical University, Turkey (KTU BAP) [FBA-2015-5160, 7341-FBA-2018-7341]Funding for this study partly originated from Scientific and Technological Research Council of Turkey (TUBITAK-CAYDAG, Project no: 115Y005) and Karadeniz Technical University, Turkey (KTU BAP, Project no: FBA-2015-5160; and 7341-FBA-2018-7341)