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Open AccessArticle

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

1
Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey
2
School of Earth and Environmental Science, University of Manchester, Manchester M13 9PL, UK
3
School of the Environment, University of Windsor, Windsor, ON N9B 3P4, Canada
4
Department of Geological Engineering, Mersin University, 33343 Mersin, Turkey
5
Department of Geological Engineering, Recep Tayyip Erdoğan University, 53100 Rize, Turkey
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(8), 683; https://doi.org/10.3390/min10080683
Received: 2 July 2020 / Revised: 17 July 2020 / Accepted: 22 July 2020 / Published: 30 July 2020
Trace 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/YbN and ave. 0.73 of Pr/YbN), (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 µg/g), Sc (bdl to 2 µg/g) Th (bdl to 0.9 µg/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. View Full-Text
Keywords: platform carbonates; REE + Y chemistry; paleoceanographic proxies; diagenetic proxies; NE Turkey platform carbonates; REE + Y chemistry; paleoceanographic proxies; diagenetic proxies; NE Turkey
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MDPI and ACS Style

Özyurt, M.; Kırmacı, M.Z.; Al-Aasm, I.; Hollis, C.; Taslı, K.; Kandemir, R. REE Characteristics of Lower Cretaceous Limestone Succession in Gümüşhane, NE Turkey: Implications for Ocean Paleoredox Conditions and Diagenetic Alteration. Minerals 2020, 10, 683. https://doi.org/10.3390/min10080683

AMA Style

Özyurt M, Kırmacı MZ, Al-Aasm I, Hollis C, Taslı K, Kandemir R. REE Characteristics of Lower Cretaceous Limestone Succession in Gümüşhane, NE Turkey: Implications for Ocean Paleoredox Conditions and Diagenetic Alteration. Minerals. 2020; 10(8):683. https://doi.org/10.3390/min10080683

Chicago/Turabian Style

Özyurt, Merve; Kırmacı, M. Z.; Al-Aasm, Ihsan; Hollis, Cathy; Taslı, Kemal; Kandemir, Raif. 2020. "REE Characteristics of Lower Cretaceous Limestone Succession in Gümüşhane, NE Turkey: Implications for Ocean Paleoredox Conditions and Diagenetic Alteration" Minerals 10, no. 8: 683. https://doi.org/10.3390/min10080683

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