Whole-Rock, Clay Mineral Contents and Matrix Effect on the Cenomanian/Turonian Petroleum Source Rocks in the Lower Antalya Nappe, Western Taurus Region of Turkey

Abstract

Whole-rock analyses by x-ray powder diffraction and Rock-Eval pyrolysis studies were carried out on the Cenomanian/Turonian Dereköy formation shales from four sample sites in the Lower Antalya Nappe in the western Taurus region (SW Turkey) to determine rock-forming mineral assemblages, their abundance in bulk composition, and clay matrix effect on hydrocarbon yield during Rock-Eval pyrolysis. These studies indicate that the rock-forming minerals are mostly quartz (3–68%), clay minerals (32–81%) including smectite and illite, and rare to common calcite (0–39%), feldspar (0–5%) and mica (0–11%). High total organic carbon (TOC) contents (up to 42 wt%) and corrected hydrogen indices between 538 and 642 (mg HC/g TOC) correspond to marine organic matter (Type II kerogen) and excellent oil-prone hydrocarbon source rocks. Strong positive correlation (R ² = 0.84 to 0.96) between hydrocarbon yield (S ₂) and TOC content implies that the positive values of x and y-intercepts are relatively high, with values ranging between 1–13.117 mg pyrolysable hydrocarbon in 1 g of rock. These results mean that the clay matrix is the main agent of adsorbtion, and high amounts of hydrocarbon retention must be present.

Keywords:

• hydrocarbon yield vs. total organic carbon
• clay matrix effect
• hydrocarbon retention
• Rock-Eval pyrolysis
• Cenomanian/Turonian
• western Taurus region

ACKNOWLEDGMENTS

The study was supported in different phases by the Hacettepe University Research Fund and the Turkish Petroleum Corporation (TPAO). The author is grateful to Nehir Özgen Varol (Hacettepe University), Özgül Şen (Hacettepe University), and Tuğrul Şükrü Yurtsever (General Directorate of Mineral Research and Exploration, MTA) for their kind contributions.