John Sanfilipo Paul C. Hackley 2016 <p><span>Organic geochemistry and petrology of Eocene Suzak bituminous marl outcrop samples from Madr village in north-central Afghanistan were characterized via an integrated analytical approach to evaluate depositional environment and source rock potential. Multiple proxies suggest the organic-rich (TOC ∼6&nbsp;wt.%) bituminous marls are ‘immature’ for oil generation (e.g., vitrinite R</span>_o<span>&nbsp;&lt;&nbsp;0.4%, T</span>_max<span>&nbsp;&lt;&nbsp;425&nbsp;°C, PI&nbsp;≤&nbsp;0.05, C</span>₂₉<span> ααα S/S&nbsp;+&nbsp;R&nbsp;≤&nbsp;0.12, C</span>₂₉<span> ββS/ββS+ααR&nbsp;≤&nbsp;0.10, others), yet oil seeps are present at outcrop and live oil and abundant solid bitumen were observed via optical microscopy. Whole rock sulfur content is ∼2.3&nbsp;wt.% whereas sulfur content is ∼5.0–5.6&nbsp;wt.% in whole rock extracts with high polar components, consistent with extraction from S-rich Type IIs organic matter which could generate hydrocarbons at low thermal maturity. Low Fe-sulfide mineral abundance and comparison of Pr/Ph ratios between saturate and whole extracts suggest limited Fe concentration resulted in sulfurization of organic matter during early diagenesis. From these observations, we infer that a Type IIs kerogen in ‘immature’ bituminous marl at Madr could be generating high sulfur viscous oil which is seeping from outcrop. However, oil-seep samples were not collected for correlation studies. Aluminum-normalized trace element concentrations indicate enrichment of redox sensitive trace elements Mo, U and V and suggest anoxic-euxinic conditions during sediment deposition. The bulk of organic matter observed via optical microscopy is strongly fluorescent amorphous bituminite grading to lamalginite, possibly representing microbial mat facies. Short chain </span><i>n-</i><span>alkanes peak at C</span>₁₄<span>–C</span>₁₆<span> (</span><i>n-</i><span>C</span>₁₇<span>/</span><i>n-</i><span>C</span>₂₉<span>&nbsp;&gt;&nbsp;1) indicating organic input from marine algae and/or bacterial biomass, and sterane/hopane ratios are low (0.12–0.14). Monoaromatic steroids are dominated by C</span>₂₈<span>clearly indicating a marine setting. High gammacerane index values (∼0.9) are consistent with anoxia stratification and may indicate intermittent saline-hypersaline conditions. Stable C isotope ratios also suggest a marine depositional scenario for the Suzak samples, consistent with the presence of marine foraminifera including abundant planktic </span><i>globigerinida</i><span>(?) and rare benthic </span><i>discocyclina</i><span>(?) and </span><i>nummulites</i><span>(?). Biomarker 2α-methylhopane for photosynthetic cyanobacteria implies shallow photic zone deposition of Madr marls and 3β-methylhopane indicates presence of methanotrophic archaea in the microbial consortium. The data presented herein are consistent with deposition of Suzak bituminous marls in shallow stratified waters of a restricted marine basin associated with the southeastern incipient or proto-Paratethys. Geochemical proxies from Suzak rock extracts (S content, high polar content, C isotopes, normal (αααR) C</span>_27–29<span> steranes, and C</span>₂₉<span>/C</span>₃₀<span> and C</span>₂₆<span>/C</span>₂₅<span> hopane ratios) are similar to extant data from Paleogene oils produced to the north in the Afghan-Tajik Basin. This observation may indicate laterally equivalent strata are effective source rocks as suggested by previous workers; however, further work is needed to strengthen oil-source correlations.</span></p> application/pdf 10.1016/j.marpetgeo.2016.02.029 en Elsevier Organic petrology and geochemistry of Eocene Suzak bituminous marl, north-central Afghanistan: Depositional environment and source rock potential article