Aromatic hydrocarbons as parameters of oil formation conditions

Aromatic hydrocarbons in the oils of Absheron and Baku archipelago, as well as in coastal zones have been identified via the method of chromato-mass-spectrometry. Geochemical estimation of distribution character of main biomarkers and their correlations as well is presented. The similarity in the distribution of monoaromatic and triaromatic steroid hydrocarbons, as well as benzogopane and sekabenzogopans has been specified, which suggests that studied oils are associated with one source rock or organic facies. The varieties observed in the distribution of saturated steranes are most likely the result of differences in the values of thermal maturity or the processes of secondary alterations.

The Oceanic Anoxic Event 2 organic record in the South Iberian Paleomargin.

<p>The Cenomanian—Turonian boundary is marked by one of the warmest periods of the Mesozoic, associated with high <em>p</em>CO<sub>2</sub> levels and global sea-level highstands. Coupled to these extreme conditions is a massive magmatic episode, the establishment of worldwide marine anoxia, the deposition of organic-rich facies, and perturbations of the global carbon cycle, the so-called Oceanic Anoxic Event 2 (OAE2). In order to define the organic facies variability, this stratigraphic interval was analysed in the Baños de la Hedionda, a reference section positioned in the W part of the Internal Subbetic, representing the sedimentary record of a pelagic plateau located in the most distal part of the South Iberian Paleomargin. Regarding this goal, a high resolution study was developed on the Capas Blancas Formation (Capas Blancas, Black radiolaritic shales, and Boquerón members – Mb.), using organic petrographic and geochemical techniques. Carbon isotopic profile, for the isolated kerogen (δ<sup>13</sup>C<sub>kerogen</sub>), displays a positive excursion of ~2.5‰ observed in the Black radiolaritic shales Mb., which is in accordance with the worldwide recognized trend for the OAE2 isotopic record.</p><p>The pre-OAE2 is represented by the Capas Blancas Mb., with the majority of the samples of this unit showing no organic matter (OM) recovery (0.01—0.57 wt.% total organic carbon; TOC). Palynofacies analysis displayed an association co-dominated by the Amorphous and Palynomorph groups. The Amorphous Group is characterized mostly by marine phytoplankton-derived amorphous OM (AOM), while the Palynomorph Group is co-dominated by freshwater microplankton (Zygnemataceae and <em>Closteriu</em><span><em>m</em>) and choanoflagellates, with some specimens of marine microplankton, sporomorphs, and zoomorphs being also identified. The mixture of freshwater and marine components suggest deposition in a platform environment with shallow depths and oscillating oxygen regimen (oxic to dysoxic conditions). The freshwater components are most likely transported into the marine system due to the lower amorphization state, with the source area being in high proximity.</span></p><p>The OAE2, represented by the Black radiolaritic shales Mb., is characterized by a dominance of: (i) marine phytoplankton-derived AOM; (ii) plate-like bacterial AOM; and, (iii) sheet-like bacterial AOM with a cratered aspect (0.36—31.48 wt.% TOC). Choanoflagelates (with high degree of amorphization) at the base of the unit, zooclasts, sporomorphs, and solid bitumen are also present. The change in the organic facies suggests the occurrence of a transgressive phase. This organic facies is indicative of a relative sea level rise, with O<sub>2</sub> conditions deteriorating with the emplacement of reducing conditions, possibly related to an increase in primary productivity.</p><p>The post-OAE2, recognized in the Boquerón Mb., is characterized by a co-dominance of marine phytoplankton-derived AOM and palynomorphs, namely zoomorphs, and high percentages of opaque phytoclasts (below 0.25 wt.% TOC). Nevertheless, kerogen displays a reworked character and, therefore, data should be used with caution.</p><p>Furthermore, this study constitutes the first record of <em>Closterium</em> in sediments from the Cretaceous, and the first identification of choanoflagellates, the closest living relatives of Metazoa, in the fossil record.</p>

Preliminary investigation of the hydrocarbon generation potential from the post-rift Abbas shale Formation (Pliocene) in the Tihamah Basin, south-eastern Yemeni Red Sea

Pliocene shales included in the post-rift Abbas Formation were recovered from an exploratory well (Kathib-01) in the Tihamah Basin and geochemically analyzed. A preliminary evaluation of the organic facies of the Abbas shales and their petroleum generation potential was conducted based on basic organic geochemical results. Most Abbas shale samples had total organic carbon (TOC) contents < 1% and a fair source potential, while the remaining samples, with TOC contents > 1%, had a relatively good potential. Overall, the Rock–Eval hydrogen index values of the shales analyzed were between 96 and 234 mg of hydrocarbon per gram of TOC (mg HC/g TOC), indicating two dominant organic facies: types III and II/III kerogen, which indicate the presence of mainly gas- and oil-prone source rocks. We conclude that the Pliocene Abbas shales in the Tihamah Basin are still in a very early-mature stage (with respect to the oil window) and, hence, have not generated petroleum yet.