Acta Geochimica最新文献

{"title":"Space weathering characteristics of lunar permanently shadowed regions soils: Evidence from experimental simulation","authors":"Zixuan Han,&nbsp;Yang Li,&nbsp;Chen Li,&nbsp;Ronghua Pang,&nbsp;Sizhe Zhao,&nbsp;Zhuang Guo,&nbsp;Kairui Tai,&nbsp;Rui Li,&nbsp;Zhenhao Hu,&nbsp;Li Liu","doi":"10.1007/s11631-024-00746-7","DOIUrl":"10.1007/s11631-024-00746-7","url":null,"abstract":"<div><p>Permanently shadowed regions (PSRs) on the Moon are potential reservoirs for water ice, making them hot spots for future lunar exploration. The water ice in PSRs would cause distinctive changes in space weathering there, in particular reduction-oxidation processes that differ from those in illuminated regions. To determine the characteristics of products formed during space weathering in PSRs, the lunar meteorite NWA 10203 with artificially added water was irradiated with a nanosecond laser to simulate a micrometeorite bombardment of lunar soil containing water ice. The TEM results of the water-incorporated sample showed distinct amorphous rims that exhibited irregular thickness, poor stratification, the appearance of bubbles, and a reduced number of npFe⁰. Additionally, EELS analysis showed the presence of ferric iron at the rim of the nanophase metallic iron particles (npFe⁰) in the amorphous rim with the involvement of water. The results suggest that water ice is another possible factor contributing to oxidation during micrometeorite bombardment on the lunar surface. In addition, it offers a reference for a new space weathering model that incorporates water in PSRs, which could be widespread on asteroids with volatiles.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 1","pages":"1 - 10"},"PeriodicalIF":1.4,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143362212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"First data on concentrations and composition of polycyclic aromatic hydrocarbons in soil, bottom sediments and suspended matter of water throughout the whole Fatala River Basin (Republic of Guinea)","authors":"Olga Victorovna Soloveva,&nbsp;Vladislav Yurievich Proskurnin,&nbsp;Ibrahima Keita,&nbsp;Alpha Issaga Palle Diallo,&nbsp;Elena Andreevna Tikhonova,&nbsp;Nataliya Yurievna Mirzoeva,&nbsp;Timofei Olegovich Barabashin,&nbsp;Abdoulaye Ibrahima Camara,&nbsp;Boubacar Bailo Sow,&nbsp;Maladho Barry","doi":"10.1007/s11631-024-00745-8","DOIUrl":"10.1007/s11631-024-00745-8","url":null,"abstract":"<div><p>The concentrations of polycyclic aromatic hydrocarbons (PAHs), their sources and toxic equivalent (TEQ) in soil, suspended matter and bottom sediments in the Fatala River Basin ecosystem were obtained for the first time to our knowledge. Determination of 14 PAHs (ΣPAHs) was carried out using high-performance liquid chromatography. The ΣPAH content in soil ranged from 13 to 50,920 (Me = 820) ng/g. The composition of PAHs (high proportion of low-molecular-weight compounds and values of individual PAHs ratios) reflected the significant oil pollution of soil. Contaminated soil was localated in the central part of the Fatala River Basin. The median benzo(a)pyrene toxic equivalent of soil at the study site was 1.08 (range, 0.05 to 53.16) ngTEQ/g, showing generally low soil toxicity. The ΣPAH content in suspended matter was in the range of 33 to 1316 (Me = 309) ng/L. The ΣPAH content in bottom sediments ranged from 36 to 6943 (Me = 478) ng/L, corresponding to clean and moderately contaminated sediments. The ΣPAH content in bottom sediments depended on the anthropogenic impact on the Fatala River Basin territory and the bottom sediment features. Bottom sediments and suspended matter had a low toxic equivalent.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 3","pages":"648 - 662"},"PeriodicalIF":1.3,"publicationDate":"2024-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145143957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chemical weathering in Manas River Basin: Driven by sulfuric acid or carbonic acid?","authors":"Jiaxin Zhang,&nbsp;Bingqi Zhu","doi":"10.1007/s11631-024-00737-8","DOIUrl":"10.1007/s11631-024-00737-8","url":null,"abstract":"<div><p>Carbonic acid produced by the dissolution of atmospheric and soil CO₂ in water is usually the most dominant catalyst for chemical weathering, but a sulfuric acid-driven phenomenon, different from usual, was found in the orogenic belt watersheds dominated by silicate bedrock. This study, rooted in comprehensive field investigations in the Manas River Basin (MRB) north of the Tianshan Mountains, delves into the mechanisms and impacts of sulfuric and carbonic acid as catalysts driving different types of chemical weathering in the Central Asian Orogenic Belt. Quantitative analyses elucidate that carbonate weathering constitutes 52.4% of the total chemical weathering, while silicate and evaporite account for 18.6% and 25.3%, respectively, with anthropogenic activities and atmospheric precipitation having little effect. The estimated total chemical weathering rate in MRB is approximately 0.075 × 10⁶ mol/km²/year. Quantitative findings further suggest that, preceding carbonate precipitation (&lt; 10⁴ year), chemical weathering can absorb CO₂. Subsequently, and following carbonate precipitation (10⁴–10⁷ year), it will release CO₂. The release significantly surpasses the global average CO₂ consumption, contributing to a noteworthy climate impact. This study underscores the distinctive weathering mechanisms, wherein sulfuric acid emerges as the predominant catalyst. The quantity of sulfuric acid as a catalyst is approximately three times that of carbonic acid. Sulfuric acid-driven carbonate rock weathering (SCW) is identified as the sole chemical weathering type with a net CO₂ release effect. SCW CO₂ release flux (5176 mol/km²/year) is roughly 2.5 times the CO₂ absorption by Ca–Mg silicate weathering, highlighting the pivotal role of chemical weathering in sourcing atmospheric CO₂ over the timescales of carbonate precipitation and sulfate reduction. Lastly, this study posits that catalyst and transport limitations are the most plausible critical factors in MRB. The interplay between sulfuric acid and dissolved CO₂ competitively shapes the types and rates of chemical weathering reactions.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 1","pages":"59 - 85"},"PeriodicalIF":1.4,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143362174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Depicting Permian to Triassic thickness variation of the Kunlun-Qaidam Continental Arc: Implication for tectonic evolution of the South Kunlun Ocean","authors":"Zhigang Wang,&nbsp;Jiaopeng Sun,&nbsp;Yukun Qi,&nbsp;Weidong He,&nbsp;Kai Ye,&nbsp;Zongli Li,&nbsp;Lei He,&nbsp;Junxiang Zhang,&nbsp;Teng Wang","doi":"10.1007/s11631-024-00744-9","DOIUrl":"10.1007/s11631-024-00744-9","url":null,"abstract":"<div><p>Determining the evolutionary history of the Permian-Triassic Kunlun-Qaidam Continental Arc is essential to understanding the subduction and closure processes of the South Kunlun Ocean. In this paper, we utilize (La/Yb)_N ratios collected from a filtered geochemical dataset on Permian to Triassic calc-alkaline rocks (55 wt%–68 wt% SiO₂) and plutonic rocks within the Kunlun-Qaidam Continental Arc to reconstruct the spatiotemporal variation of the relative crustal thickness. Combined with known geologic observations, we discuss the subduction-accretionary tectonics of the South Kunlun Ocean and the topographic evolution of the Kunlun-Qaidam Continental Arc. Two episodes of crustal thickening and thinning were revealed. The reconstructed thickness reveals two crustal thickening and thinning events for the Kunlun-Qaidam Continental Arc from ca. 270 to 210 Ma. The southern sector of the Kunlun-Qaidam Continental Arc is about 7 km thicker than the northern portion, with a maximum thickness of about 55 km at ca. 270 and 230 Ma. The ca. 270 and 230 Ma crustal thickening events coincide with renewed northward subduction of the South Kunlun Ocean plate and ocean closure, respectively, whereas the ca. 270‒240 Ma and ca. 230‒210 Ma crustal thinning events may reflect slab break-off of the oceanic plate and lithospheric collapse during the post-collision extension, respectively.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 3","pages":"599 - 608"},"PeriodicalIF":1.3,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145145098","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry, zircon U–Pb chronology and Hf isotope of the Weideshan high Ba–Sr granites in Jiaodong Peninsula of the North China Craton: Constraints on their petrogenesis and tectonic implications","authors":"Zhigang Zhang,&nbsp;Laiming Wang,&nbsp;Lijuan Wang,&nbsp;Bin Sun,&nbsp;Tianlong Ren,&nbsp;Youping Wang,&nbsp;Shipeng Yang,&nbsp;Jingjing Wang","doi":"10.1007/s11631-024-00739-6","DOIUrl":"10.1007/s11631-024-00739-6","url":null,"abstract":"<div><p>The lithospheric thinning and huge gold mineralization in the Jiaodong Peninsula is intensively studied, aiming to better understand the geodynamic setting of the magmatic petrogenesis and the relationship between magmatism and large-scale mineralization. Thus, we conducted detailed research on the Weideshan intrusions in the Jiaodong region, including field investigations, geochemical, geochronological and Hf isotope analysis, to reveal the tectonic implications for the destruction of the eastern North China Craton (NCC). The Weideshan intrusions consist of quartz monzodiorite, quartz monzonite and monzogranite. The SHRIMP zircon U-Pb dating results show that the Weideshan intrusions are emplaced at 115–112 Ma, namely, in the late Early Cretaceous period. Rocks of Weideshan intrusions are high-K calc-alkaline series and metaluminous granites. The trace elements are characterized by enrichment of Rb, Ba, Sr and LREE, with unobvious Eu anomalies and depletion of Nb, Ta, Zr, Hf and Ti. The contents of Ba and Sr are (913.00–1562.00)/1199.29 μg/g and (373.00–793.00)/536.71 μg/g, respectively, showing the features of high Ba–Sr granites (HBS). Development of numerous dark enclaves and negative εHf(<i>t</i>) values (− 17.93 to − 12.19) indicate that the Weideshan granites originate from the mixture of crustal-derived felsic magma from partial melting of the Paleoproterozoic crust and alkali-rich magma from the enriched mantle. The generation of the Weideshan granites was closely related to the asthenospheric upwelling during the lithosphere thinning of the NCC in the late Mesozoic.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 3","pages":"513 - 530"},"PeriodicalIF":1.3,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145145097","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evidence of a Cadomian arc in the northern margin of Gondwana: The Ediacaran-Cambrian Mahabad rhyolitic complex, NW Iran","authors":"Rana Noori Asl,&nbsp;Mohssen Moazzen","doi":"10.1007/s11631-024-00743-w","DOIUrl":"10.1007/s11631-024-00743-w","url":null,"abstract":"<div><p>The Mahabad rhyolitic complex, mostly composed of rhyolite but also including granite and granodiorite, is exposed in NW Iran as a part of the Central Iran Block. Porphyritic, hyalo-porphyritic and spheroidal are the main textures of the studied samples of rhyolite. U-Pb zircon chronology on three samples of Mahabad rhyolitic complex yielded Cambrian to Ediacaran ages of 537.6 ± 6.6 Ma, 547.4 ± 6.5 Ma and 556.2 ± 7.1 Ma. Based on geochemical analyses, the original magma was high potassium calc-alkaline to shoshonitic. The rocks are enriched in LREEs relative to HREEs. Trace element patterns of Mahabad rhyolite normalized to chondrites show negative anomalies of high-field-strength elements (Ti, Nb, Ta, Hf, Yb, Y and Zr) and high LREEs and large ion lithophile element contents (Rb, K, Th and Ba). ²⁰⁸Pb/²⁰⁴Pb (36.7219–39.0367), ²⁰⁷Pb/²⁰⁴Pb (15.4963–15.7669) and ²⁰⁶Pb/²⁰⁴Pb (16.9405–19.9567) ratios indicate an EM-II enriched mantle source for the rhyolite magma. Large variation of εHf(t) from −5.2 to + 4.5 points to a mantle source with crustal material contribution in the magma genesis. The rhyolitic magma erupted in an active continental margin. The formation of calc-alkaline high potassium magma was probably related to metasomatism of the mantle because of the north to south subduction of Proto-Tethys oceanic crust beneath the northern margin of Gondwana continental crust.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 3","pages":"609 - 630"},"PeriodicalIF":1.3,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145143960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The discovery of Late Triassic hypabyssal mafic dykes in the Huozhou complex and their geological significance: Evidence from petrology, geochemistry, and geochronology","authors":"Haiyan Liu,&nbsp;Chong Peng","doi":"10.1007/s11631-024-00741-y","DOIUrl":"10.1007/s11631-024-00741-y","url":null,"abstract":"<div><p>The Huozhou complex in the Trans-North China Orogen exhibits two events of mafic magmatism (separated by ca. 700 Ma): Neoproterozoic (920 ± 15 Ma) Shimenyu diabase and Late Triassic (217 ± 2.5 Ma) Xingtangsi diabase. Investigations have focused on systematic petrology, zircon U-Pb dating, Lu-Hf isotopes, and lithogeochemistry. The research findings indicate that the Late Triassic Xingtangsi diabase of the Huozhou complex can be classified as a transitional type between intermediate and mafic rocks based on their SiO₂ content. This classification is supported by an average SiO₂ content of 53.94%, ranging from 53.33% to 54.28%. In the Zr/TiO₂ vs. Ce diagram, all samples lie within the range of basalt. The zircons from the Late Triassic Xingtangsi diabase have low ε_Hf(t) values ranging from –12.7 to –8.7, with an average of –11.1. Additionally, the single-stage model age T_DM1 is estimated to be between 1207 and 1701 Ma. These findings suggest that the magma responsible for the dyke originated from either partial melting or an enriched mantle source inside the Meso-Proterozoic lithospheric mantle. The elevated concentrations of Th (thorium) and LREEs (light rare earth elements), as well as the Th/Yb and Th/Nb ratios, suggest the potential incorporation of subducted sediments within the magma source region. The rock displays negative Nb, Ta, Zr, Hf, and Ti anomalies. These geochemical attributes align with the distinctive traits observed in volcanic rocks found within island arcs. The formation of the Late Triassic Xingtangsi diabase is likely associated with the geological context of an arc setting, which arises from the collision between the Yangtze plate and the North China Craton.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 6","pages":"1013 - 1036"},"PeriodicalIF":1.4,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Late-Silurian intraplate basalts from the southwestern margin of the Ordos Basin: Implication for decompression melting of metasomatized evolved mantle in extension setting","authors":"Dongxu Wang,&nbsp;Hujun Gong,&nbsp;Jiangfeng Qin,&nbsp;Fenhong Luo","doi":"10.1007/s11631-024-00723-0","DOIUrl":"10.1007/s11631-024-00723-0","url":null,"abstract":"<div><p>The Longshan orogenic belt is located in the southwestern margin of Ordos Basin at the junction zone between the Western Qinling and Northern Qilian orogenic belt. Voluminous Early Paleozoic magmatism in this area is of key significance for determining the Early Paleozoic tectonic evolution and deep crust-mantle structure. Previous studies mainly focused on the Paleozoic granites; the coeval mafic rocks in this area are still poorly understood. A set of Late Silurian intraplate tholeiitic basalts has been discovered in Longshan area, providing key evidence for the mantle source and deep geodynamic background in this area. The Late Silurian Angou basalt has similar geochemical features as intraplate tholeiitic basalt, with high Na₂O/K₂O ratios (5.22–8.25), enriched in large ion lithophile elements and LREE. In combination with their relatively evolved Sr-Nd isotopic composition [⁸⁷Sr/⁸⁶Sr (i) = 0.7128–0.7140; <i>ε</i>_Nd (t) =  − 5.55 to − 3.40], it is suggested that it originated from decompression melting of metasomatized enriched mantle in extensional setting. These results indicate that the mantle source in the junction zone of the West Qinling-North Qilian orogenic belt evolved from depleted to enriched with the continuation of Proto-Tethys subduction from the Cambrian to the Silurian. These results are of great significance to understanding the genesis of contemporaneous granite and the crust-mantle interaction in the junction zone between the Western Qinling and Northern Qilian orogenic belt.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 2","pages":"260 - 277"},"PeriodicalIF":1.4,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143749236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study on natural gas-source correlation and hydrocarbon accumulation of the Lianggaoshan Formation in the east of Sichuan Basin, China","authors":"Xun Luo,&nbsp;Xuanbo Gao,&nbsp;Long Luo,&nbsp;Jianping Liu,&nbsp;Jia Wang,&nbsp;Huanhuan Zhou,&nbsp;Xin Yang,&nbsp;Xin Yu,&nbsp;Long Chen,&nbsp;Zhepei Gou,&nbsp;Yiting Gu,&nbsp;Shukui Zhu,&nbsp;Xianfeng Tan","doi":"10.1007/s11631-024-00740-z","DOIUrl":"10.1007/s11631-024-00740-z","url":null,"abstract":"<div><p>Uncertainties about natural gas source and hydrocarbon accumulation seriously restrict oil and gas exploration in the Lianggaoshan Formation (J₂l) in the Eastern Sichuan Basin, which has demonstrated great exploration potential in recent years. This study determines the origin of natural gas and the hydrocarbon accumulation model of J₂l in the Eastern Sichuan Basin. A new sample pretreatment method named gas purge-microsyringe extraction was employed and confirmed to be a practical and effective method for preparing condensate oil and collecting source rock extract samples. The source rocks of J₂l exhibited moderate to good qualities, characterized by high TOC values, dominance of type II₁ and II₂ kerogens, and high thermal maturities. Biomarker and aromatic characteristics revealed that the source rocks of J₂l were deposited in brackish water with weak anoxic conditions. The natural gas in J₂l was an organic thermogenic gas generated from the secondary cracking of crude oil, indicating that this natural gas was mainly derived from the source rocks of J₂l. The condensate oil-source rock correlation further confirmed the accuracy of the gas-source correlation results. Based on burial, thermal and hydrocarbon-generating histories, two hydrocarbon charging periods (141–133 Ma and 119–112 Ma) and four hydrocarbon accumulation periods of J₂l were determined. Combined with structural evolution, depositional histories and reservoir conditions, a simple gas reservoir accumulation model of J₂l was developed, which was identified as a “self-generating and self-storing” gas reservoir.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 3","pages":"547 - 572"},"PeriodicalIF":1.3,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145145008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Source rock potential of the Bajocian-Bathonian succession (Mtumbei Formation) in the Mandawa Basin, SE Tanzania","authors":"John William Gama,&nbsp;Emily Barnabas Kiswaka","doi":"10.1007/s11631-024-00738-7","DOIUrl":"10.1007/s11631-024-00738-7","url":null,"abstract":"<div><p>Over the past few decades, Middle Jurassic sediments in the Tanzanian Coastal Basin have gained attention on a regional palaeogeographical scale. These sediments, including thick black shales, were deposited following a widespread marine transgression initiated by the breakup of Gondwana supercontinent. Previous studies indicate that these shales possess good to excellent source potential, making them promising regional source rocks. However, no detailed geochemical studies have assessed them in the Mandawa Basin. In this study, geochemical assessment was caried out on cutting samples from two wells to: (i) constrain organic matter richness, type, quality, and: (ii) reconstruct thermal evolution and depositional conditions of the Bajocian-Bathonian black shales in the Mandawa Basin. Organic matter richness was measured using Total Organic Carbon (TOC) analysis, while the quality and thermal maturity of the organic matter were assessed through programmed pyrolysis. Paleo-redox conditions were determined from Th/U ratios derived from Spectra Gamma Ray Logs data. Geochemical data reveal that organic matter content (TOC) is generally low and varies spatially. The analysed TOC content fluctuates along stratigraphy with values ranging from 0.13 to 3.59 wt% with an average of 0.92 wt%. Whereas, Kerogen yield (S2) and Hydrogen Index (HI) are generally low; S2 and HI ranges from 0 to 1.95 (mg HC/g) with an average of 0.29 (mg HC/g), and 0‒92 (mg HC/g TOC) with an average of 24 (mg HC/g TOC), respectively. Organic matter is mainly composed of types III (gas prone) to IV (inert) that have been subjected to wide range of thermal alteration ranging from marginally mature to over mature. Comparison of TOC, Th/U and sediment composition data (clastics and carbonates) derived from cuttings samples suggests episodic deposition of organic matter under sub-oxic conditions. These were mainly controlled by fluctuation in sea level, tectonics and clastic dilution.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 3","pages":"531 - 546"},"PeriodicalIF":1.3,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145144565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}