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

Abstract

Late 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.