Conditions of Formation and Hydrocarbon Potential of the Lower Pliocene Sediments of the Absheron–Balkhan Uplift Zone: Evidence from Geochemical Indicators

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Abstract—Conditions of formation of the Lower Pliocene sediments of the South Caspian Basin (SCB)—the Productive (PS) and Red-Colored (RS) sequences—were reconstructed by the example of the Absheron–Balkhan uplift zone using a complex of widely known geochemical criteria: major oxide and trace element ratios. The common and distinctive features of the conditions of formation of PS and RS are identified. It is established that PS sediments were formed under more oxidizing conditions than RS sediments and that the brownish–red coloration of RS is of diagenetic nature. The low hydrocarbon (HC) potential of PS–RS was confirmed by the pyrolysis method. It is shown that these sediments, being formed in deltaic and coastal–marine conditions, are characterized by the low quality of organic matter (OM), which is ascribed to the type 3 and consists of redeposited remains of wood plants with insignificant admixture of amorphous and algal organics. Results obtained for the Absheron–Balkhan zone are well consistent with the existing concepts on the conditions of formation of the Lower Pliocene sediments, which are the major reservoir of the SCB HC resources.