Major, trace, rare earth element, and stable isotope analyses of the Triassic carbonates along the northeastern Arabian Plate margin: a key to understanding paleotectonics and paleoenvironment of the Avroman (Biston) limestone formation from Kurdistan region, northeastern Iraq

Abstract

The Triassic carbonate rocks on the Avroman mountain, Halabja area, consist of massive gray-dark gray-colored detrital and biogenic limestones, that are stratigraphically represented by the Avroman formation in Iraq and Biston formation in Iran. This study focused on the tectonic setting and environmental conditions during the deposition of the formation using major and trace element and rare earth element (REE) analyses, along with their carbon and oxygen isotope data. The geochemical results are substantiated by field and petrographic studies, and extensive literature reviews. The study indicates that the limestones dominantly consist of CaO, followed by MgO, and minor quantities of SiO 2 and Al 2 O 3 , suggesting a predominantly calcite mineral phase and absence of dolomitization. The negligible amounts of the latter two oxides is possibly due to the lack of siliciclastic input during limestone depostion. Among the trace elements, strontium reported the highest concentrations while displaying a negative correlation with CaO due to the low terrigenous fraction content. Other trace elements such as Ni, Cr, V, Sc, Rb, Ba, Cu, Pb, Zn, U, and Th occur in minor concentrations. The low concentration of uranium (0.0-4.0) and authigenic uranium (average total U − Th/3 value = 0.39), along with a positive value of Mn* indicate depostion from normal seawaters under oxic conditions. The enrichment of heavy REE (HREE) over the light REE (LREE), with negative Ce anomaly and slightly positive Eu and Y anomalies further indicate their precipitation from the seawaters. The negative correlation of ΣREE with Al 2 O 3 FeO, TiO 2 , Cr Ni, and Sc, and a positive correlation with CaO and Y suggest extremely low contribution of terrigenous siliciclastic sediments and the absence of hydrothermal alterations during limestone precipitation. The δ 18 O and δ 13 C values for the four carbonate rocks from Avroman formation varied in the ranges − 3.53 to − 3.02‰ (average − 3.34‰) and 1.15-1.65 (average 1.39‰), respectively. The bivariate plot of δ 18 O and δ 13 C suggests that the majority of these carbonates are marine limestones. The Rb-Sr-Ba, La/Sc vs. Ti/Zr, and Sr/Rb vs. Sr/Ba plots categorize the Avroman limestones as carbonates of the continental margin with a tectonic setting relatively far away from igneous activities. Based on the above facts, a tectonic and paleogeographic model was constructed for the formation and was combined with the northeastern Arabian Plate margin, which bordered the Neo-Tethys ocean in the northwest during Triassic.

Geochemistry of the Devonian and Permo-Triassic Black Shales in Peninsular Malaysia: Insights into Provenance, Tectonic Setting, and Source Rock Weathering

“…Similarly, the Semantan black shales plot in the passive margin setting. Low-mobility trace elements represent the tectonic context more accurately during transport and deposition [65][66][67]. The La-Th-Sc plot adapted from [42] shows that all samples from BRSZ Unit 1 fall within the passive margin and the Gua Musang black shales show a chemical affinity to a passive margin and continental island arc, whereas the Semantan black shales point to a continental island arc (Figure 12).…”

Unconformity and Paleokarst in the Lower Part of the Qamchuqa Formation; An Example from the Arabian Carbonate Platform in the Zagros Belt NE Iraq

“…Daoud (2021) studied microfacies of the upper part of the Qamchuqa Formation and observed detrital limestone in the form of lithoclast and bioclasts packstonegrainstone with ooids as main facies. Karim (2020) and Mirza et al (2021) depicted the Platform as the western and southwestern boundary of the gigantic Neo-Tethys Ocean. Therefore, deposition, reef growth, and erosion were common processes on the platform while the erosion product mostly bypassed its attached slope and was deposited in the basin (Fig.…”

Petrography and Clay Mineral Variations Across the Cretaceous/Paleogene (K/Pg) Boundary, Sulaimani, Kurdistan Region, Iraq

“…Thus Qulqula group, carbonates of Bisotun block (Avroman Formation), and Zagros ophiolites were potential source rock lithostratigraphic units for sediments across K/Pg boundary in Dartw section. These units are mainly composed of radiolarian chert, limestones, mudstones, shale, peridotites, pyroxenites, and basalt (Mohammad, 2008;Baziany, 2014;Mirza et al, 2021).…”