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Mineralogy and geochemistry of Upper Cretaceous Mazıdağı Phosphorite Deposits from the Northern Arabian Plate (Mardin, Turkey)

Tetiker Sema

Gospodarka Surowcami Mineralnymi

2023

T. 39, z. 2

37--69

In the Mardin-Mazıdağı region, which corresponds to the northern Arabian Plate, layers containing marine phosphorite rocks are found within the Karababa Formation (Upper Cretaceous). The Karataş member contains phosphorites and carbonate rocks with nodular chert geodes and fossils. The phosphorite and micritic limestones contain invertebrate fossil fragments and materials such as optical isotropic pelletic apatite minerals, angular/subangular and plated fish bone fragments, and brachiopod shells. SEM (scanning electron microscopy) results show that the apatite minerals are either spherical or ellipsoidal in shape and their size varies between 100-200 µm. According to X-ray diffraction (XRD) examinations, the rocks contain apatite (carbonate rich fluorapatite; CFA), carbonate (calcite, dolomite), silica (quartz and opal-CT), little feldspar, and clay (smectite, palygorskite/sepiolite, kaolinite, illite, chlorite, mixed layered chlorite-vermiculite (C-V) and illite-vermiculite (I-V). The average major and trace elements found in the phosphorite include P2O5 (35.41 wt.%), REEs (44.57 ppm), Y (52.85 ppm), and U (5.45 ppm). The Mazıdağı phosphorite analysis indicates that the conditions are slightly oxic, which is supported by their slightly negative Ceanom average values (–0.30), low Ce/La ratios (0.32), and a V/(V + Ni) mean of 0.93 ppm. All the recoded values of the average REE for the study area are considerably lower than those in Iraq (84.30 ppm), Tunisia (400.3 ppm), Morocco (571.75 ppm) and Jordan (187 ppm). It is inferred that mineral formation processes are affected by the biogenic and biogeochemical activities that occurred in conjunction with the changes in sea level driven by the tectonic conditions associated with the evolution of the Neotethys Ocean.

W regionie Mardin-Mazıdağı, który odpowiada północnej płycie arabskiej, w formacji Karababa (górna kreda) znajdują się warstwy zawierające morskie skały fosforytowe. Jednostka Karataş zawiera fosforyty i skały węglanowe ze sferoidalnymi geodami czertów (konkrekcji) i skamieniałościami. Wapienie fosforytowe i mikrytyczne zawierają skamieniałe fragmenty bezkręgowców i materiały takie jak: optycznie izotropowe granulowane minerały apatytowe, kanciaste/nieco kanciaste i blaszkowate fragmenty kości ryb oraz muszle ramienionogów. Wyniki SEM (skaningowej mikroskopii elektronowej) pokazują, że minerały apatytu mają kształt kulisty lub elipsoidalny, a ich wielkość waha się między 100-200 μm. Według badań dyfrakcji rentgenowskiej (XRD) skały zawierają apatyt (fluoroapatyt bogaty w węglany; CFA), węglan (kalcyt, dolomit), krzemionkę (kwarc i opal-CT), niewiele skalenia i glinę (smektyt, palygorskit/sepiolit), kaolinit, illit, chloryt, mieszany warstwowy chloryt-wermikulit (C-V) i illit-wermikulit (I-V). Główne i śladowe pierwiastki występujące w fosforynie zawierają średnio P2O5 (35,41% wag.), REE (44,57 ppm), Y (52,85 ppm) i U (5,45 ppm). Analiza fosforytów Mazıdağı wskazuje, że warunki są lekko tlenowe, co potwierdzają ich nieco ujemne średnie wartości Ceanom (–0,30), niski stosunek Ce/La (0,32) i średnia V/(V + Ni) wynosząca 0,93 ppm. Wszystkie zarejestrowane wartości średnie REE dla badanego obszaru są znacznie niższe niż w Iraku (84,30 ppm), Tunezji (400,3 ppm), Maroku (571,75 ppm) i Jordanii (187 ppm). Wywnioskowano, że na procesy formowania się minerałów mają wpływ działania biogenne i biogeochemiczne, które wystąpiły w połączeniu ze zmianami poziomu morza spowodowanymi warunkami tektonicznymi związanymi z ewolucją Oceanu Neotetydy.

Redox conditions, glacio-eustasy, and the status of the Cenomanian-Turonian Anoxic Event: new evidence from the Upper Cretaceous Chalk of England

Jeans Christopher V., Wray David S., Williams C. Terry, Bland David J., Wood Christopher J.

Acta Geologica Polonica

2021

Vol. 71, no. 2

103--152

The nature of the Cenomanian–Turonian Oceanic Anoxic Event (CTOAE) and its δ13 C Excursion is considered in the light of (1) the stratigraphical framework in which the CTOAE developed in the European shelf seas, (2) conclusions that can be drawn from new detailed investigations of the Chalk succession at three locations in England, at Melton Ross and Flixton in the Northern Province where organic-rich ‘black bands’ are present, and at Dover in the Southern Province (part of the Anglo-Paris Basin) where they are absent, and (3) how these conclusion fit in with the present understanding of the CTOAE. The application of the cerium anomaly method (German and Elderfield 1990) at Dover, Melton Ross and Flixton has allowed the varying palaeoredox conditions in the Chalk Sea and its sediments to be related to the acid insoluble residues, organic carbon, δ18O (calcite), δ13C (calcite), δ13C (organic matter), Fe 2+ and Mn2+ (calcite), and P/TiO2 (acid insoluble residue). This has provided evidence that the initial stages of the δ13C Excursion in England were related to (1) a drop of sea level estimated at between 45 and 85 metres, (2) influxes of terrestrial silicate and organic detritus from adjacent continental sources and the reworking of exposed marine sediments, and (3) the presence of three cold water phases (named the Wood, Jefferies and Black) associated with the appearance of the cold-water pulse fauna during the Plenus Cold Event. Conditions in the water column and in the chalk sediment were different in the two areas. In the Northern Province, cerium-enriched waters and anoxic conditions were widespread; the δ13C pattern reflects the interplay between the development of anoxia in the water column and the preservation of terrestrial and marine organic matter in the black bands; here the CTOAE was short-lived (~0.25 Ma) lasting only the length of the Upper Cenomanian Metoicoceras geslinianum Zone. In the Southern Province, water conditions were oxic and the δ13C Excursion lasted to the top of the Lower Turonian Watinoceras devonense Zone, much longer (~1.05 Ma) than in the Northern Province. These differences are discussed with respect to (1) the Cenomanian–Turonian Anoxic Event (CTAE) hypothesis when the ocean-continent-atmosphere systems were linked, (2) limitations of chemostratigraphic global correlation, and (3) the Cenomanian-Turonian Anoxic Event Recovery (CTOAER), a new term to define the varying lengths of time it took different oceans and seas to recover once the linked ocean-continent-atmosphere system was over. The possibility is considered that glacio-eustasy (the glacial control hypothesis of Jeans et al. 1991) with the waxing and waning of polar ice sheets, in association with the degassing of large igneous provinces, may have set the scene for the development of the Cenomanian-Turonian Anoxic Event (CTAE).