Low Total Organic Content Research Articles

Factors controlling organic matter accumulation in the Longmaxi Formation shale, Changning area, South Sichuan Basin

Based on total organic content (TOC) tests and major-trace element test data, this study examined organic matter accumulation and controlling factors of the Longmaxi Formation shale in the Changning area, southern Sichuan Basin. The results showed that (1) TOC content of the Long11 submember (S1l11) shale was between 0.46% and 8.35%. Vertically, TOC revealed a ‘sandwich cake’ pattern with a high TOC content concentrated in the 1st layers of Long11 submember (S1l11–1) and 3rd layers of Long11 submember (S1l11–3) and a lower TOC content in the 2nd layers of Long11 submember (S1l11–2) and 4th layers of Long11 submember (S1l11–4). Spatial distribution of TOC showed variations and migration in S1l11. (2) S1l11 shale TOC showed a logarithmic correlation with sedimentary environment index, negative correlation with terrigenous influx, and complex correlation with paleoproductivity. (3) Factors controlling organic matter accumulation were mainly redox conditions, followed by paleoproductivity and terrigenous input in Changning area. When the paleoproductivity index (Babio) was less than 2200 μg/g, the redox conditions was the controlling factor of organic matter accumulation. On the contrary, it is ultrahigh paleoproductivity. Vertically, organic matter accumulation mode evolved from “preservation conditions” to “productivity–preservation conditions synergy mode” to “productivity mode”. (4) An anoxic condition was the basis of organic matter accumulation. Medium–high paleoproductivity was the key to organic matter accumulation. These study results are expected to contribute to shale gas exploration and development.

Hydrologic regulation of clay-mineral transformations in a redoximorphic soil of subtropical monsoonal China

Abstract Clay-mineral evolution in supergene environments is commonly a complex process subject to hydrologic influences on clay-mineral transformations, yet these influences remain insufficiently investigated to date. A quaternary red soil profile with evident redoximorphic features in subtropical monsoonal China was investigated with a focus on processes of secondary clay-mineral transformation. Evidence provided by soil physical and chemical descriptions, clay-mineral analysis, spectroscopic characterization, extractions of pedogenic Al and Fe species, and geochemical compositions reveals a complex relationship of clay minerals and iron phases to pedogenic weathering conditions as a function of depth in the studied soil profile. The soil profile can be divided into a homogenous horizon (HH; 0–2.0 m), a redoximorphic horizon (RH; 2.0–6.0 m), and a basal layer (BL; 6.0–7.2 m), and these three horizons are dominated by various intermediate clay phases. The HH is characterized by moderately acidic conditions (mean pH = 5.2) and low total organic content (TOC; TOC ≤2.1 g kg–1). More importantly, compared with the lower horizons, the HH contains significantly more active acid-forming cations, as reflected by a greater abundance of Al phases and higher aluminum saturation levels. We infer that the occurrence of hydroxy-interlayered vermiculite (HIV) in the HH is tightly coupled with the nature of the soil acidic pools, which include both H+ ions (i.e., pH) and active acid-forming cations (e.g., Al3+ and Fe3+). The reaction pathway from primary minerals to final weathering products appears to be highly sensitive to dynamic hydrological processes. HIV is favored in generally oxic, well-drained soil systems with adequate acidic cations to maintain acidic weathering. When soils are more waterlogged and the aqueous solution is dominated by base cations, primary minerals tend to transform to smectite group minerals. Therefore, discrete smectite, interstratified illite-smectite (I-S), and interstratified kaolinite-smectite (K-S) were observed only in the RH and BL. We present a novel framework that links clay-mineral transformation pathways to soil hydrological disturbances, providing new insights into understanding the kinetics of water-mineral interactions in natural soil systems.

Controls on the Organic Matter Accumulation of the Marine-Continental Transitional Shanxi Formation Shale in the Southeastern Ordos Basin.

The marine–continental transitional shale with favorable geological conditions for shale gas accumulation and broad resource prospects is widely distributed in China, which is also well developed in the Ordos Basin. The reservoir characteristic and gas-bearing properties of the transitional Shanxi Formation shale have been studied in previous studies. However, the factors influencing the organic matter (OM) accumulation have not been well studied, which restricts shale gas exploration and development of the Shanxi Formation in the Ordos Basin. According to analyses of organic geochemistry, mineral compositions, and major and trace elements, this paper has studied the paleoenvironment characteristic and its influence on the OM accumulation of the Shanxi Formation shale. The results indicate that the OM is characterized by the high mature stage and type III kerogen while the total organic content (TOC) of Member 1 is higher than that of Member 2. From Member 1 to Member 2, the paleowater depth gradually decreases, along with a gradually relative cold and dry climate, decreasing the terrestrial influx intensity and paleoproductivity and increasing the oxygen content in the water column. For Member 1, the OM accumulation is mainly controlled by the terrestrial influx intensity and paleowater depth, and other paleoenvironment factors have an unobvious contribution to the OM accumulation. For Member 2, the OM accumulation is commonly controlled by the weak terrestrial influx, low paleoproductivity, and oxic water column, resulting in the low TOC of Member 2. This study reveals the paleoenvironment characteristic and controls on the OM accumulation of the Shanxi Formation shale, which is beneficial to the reservoir selection of the Shanxi Formation in the southeastern Ordos Basin and the understanding of the OM accumulation in other transitional shales.

Multiscale storage and transport modeling in unconventional shale gas: A review

Several studies have been performed to model the storage and transport in organic matter present in shale gas. However, the unconventional formation does not only contain organic matter but also inorganic mineral matrix. The studies necessitated by this research gap showed that quartz pores contribute more to the amount of free gas present in shale while clay minerals play a significant role to the adsorbed gas storage capacity, especially in rocks containing low total organic content. Interestingly, methane and a small amount of carbon dioxide, ethane, propane, nitrogen, and water are trapped within the mineral pores and the interphase between two or more minerals. The gases present are stored in a sorbed and free state at different pore scales, which makes the modeling challenging. More so, the adsorbed gas layer influences gas transport through the pore structure. In this work, an extensive review of experimental and simulation outlook to these subjects was considered, with emphasis on key highlights and limitations to previous studies. Besides, there was a recap of commonly utilized field perspectives to compute the producible gas from shale reservoirs, and an insight into an experimental validation point of view. Analytical and numerical transport description methods were broadly debated. Furthermore, there was an overview of the widely availed relationship between heat with chemical and physical adsorption, including the process for evaluating the efficiency of CO 2 sequestration and enhanced gas recovery projects in shale reservoirs alongside the possible drawbacks in their application. • In addition to kerogen, bitumen and other semi-solids organics in shale impact on gas storage and transport. • Crushed samples with variable grain sizes are widely utilized for experimental adsorption and diffusion studies. • Clay has a complex mineralogy, microstructure and charged interlayer and external surface area. • The uncertainty in shale reserves can be reduced by integrating field and experimental approach. • Most existing volume models ignore capillary gas in shale confined pores.

Source rock evaluation in the central-western flank of the Tampico Misantla Basin, Mexico

Source rock evaluation is performed in a prospective block on the western-central flank of the Tampico Misantla Basin (TMB), Mexico, analyzing the Agua Nueva, Pimienta and Taman formations. The rock samples are drilling cores and cuttings obtained from legacy wells in an area delimited geographically on the west by the Sierra Madre Oriental. The area is located within the unconventional land region designated by Mexico's Ministry of Energy (SENER). Pyrolysis analyses on 167 samples were performed using the HAWK℠ instrument. The results of these source rock assessments indicate that most of the samples are classified in the oil to gas condensate window, with low Total Organic Content (TOC) -dominated by non-generative organic carbon- and low Hydrogen Index (HI). A few wells showing higher S1/TOC ratio are recommended for further investigation. There is a general trend of increasing thermal maturity from southern to central-western Tampico Misantla Basin. The geochemical results were integrated with previously published data, thus enhancing our interpretations and providing additional insight on the thermal maturity and the phase of hydrocarbons of the Jurassic–Cretaceous source rock intervals in the region.

Clay minerals trap hydrogen in the Earth's crust: Evidence from the Cigar Lake uranium deposit, Athabasca

Hydrogen (H2)-rich fluids are observed in a wide variety of geologic settings including gas seeps in serpentinized ultramafic rocks, sub-seafloor hydrothermal vents, fracture networks in crystalline rocks from continental and oceanic crust, and volcanic gases. Natural hydrogen sources can sustain deep microbial ecosystems, induce abiotic hydrocarbons synthesis and trigger the formation of prebiotic organic compounds. However, due to its extreme mobility and small size, hydrogen is not easily trapped in the crust. If not rapidly consumed by redox reactions mediated by bacteria or suitable mineral catalysts it diffuses through the rocks and migrates toward the surface. Therefore, H2 is not supposed to accumulate in the crust. We challenge this view by demonstrating that significant amount of H2 may be adsorbed by clay minerals and remain trapped beneath the surface. Here, we report for the first time H2 content in clay-rich rocks, mainly composed of illite, chlorite, and kaolinite from the Cigar Lake uranium ore deposit (northern Saskatchewan, Canada). Thermal desorption measurements reveal that H2 is enriched up to 500 ppm (i.e. 0.25 mol kg−1 of rock) in these water-saturated rocks having a very low total organic content (<0.5 wt%). Such hydrogen uptake is comparable and even exceeds adsorbed methane capacities reported elsewhere for pure clay minerals or shales. Sudoite (Al–Mg di-trioctahedral chlorite) is probably the main mineral responsible for H2 adsorption in the present case. The presence of multiple binding sites in interlinked nanopores between crystal layers of illite-chlorite particles offers the ideal conditions for hydrogen sorption. We demonstrate that 4 to 17% of H2 produced by water radiolysis over the 1.4-Ga-lifetime of the Cigar Lake uranium ore deposit has been trapped in the surrounding clay alteration haloes. As a result, sorption processes on layered silicates must not be overlooked as they may exert an important control on the fate and mobility of H2 in the crust. Furthermore, the high capacity of clay minerals to sorb molecular hydrogen may also open up new opportunities for exploration of unexpected energy resources and for H2 storage based on geo-inspired materials.

Gas reservoir characteristics of the Lower Gondwana Shales in Raniganj Basin of Eastern India

In India, Raniganj basin has become a prime target for shale gas exploration. Investigated shale core samples obtained from 9 boreholes during exploratory drilling with laterally varying depth from 11 to 1480m. A substantial amount of organic matter in shale beds having cumulative thickness of 86m, 327m and 126m are found in Raniganj, Barren Measures and Barakar Formations respectively. The total organic content (TOC) of shales signifies poor to excellent (1.01–12.73wt%), while the values of S1 and S2 revealed poor to good source rock generation potential, accentuating thermally immature to moderately mature shale reservoir. The various plots like HI vs. OI, HI vs. TOC, S2 vs. TOC, PI vs. S1 and S2, implies that studied shales are gas prone containing type II/III and type III kerogen except sample no 17, which has shown type IV kerogen owing to effects of nearby igneous intrusive. Comparatively less sorption in Raniganj shales reflecting low TOC content, whereas Barren Measures and Barakar shales has moderate sorption capacities controlled by organic matter and clay minerals. Low pressure N2 adsorption-desorption isotherms are used to categorise pore geometry such as cylindrical, slit-shaped and bottle neck pores in Raniganj, Barren Measures and Barakar shales respectively. Organic content have no significant influence over the surface area, because intensified thermal stress could have caused the destruction of thinner organic pores which reduced the involvement of organic pores in surface area. The pores are classified into four types using scanning electron microscopy (SEM) taking into account the origin, size and shape of pores, i) dissolved pores – developed due to the effect of groundwater or de-carbonic acid, ii) open pores associated with organic matter - formed during thermal cracking of kerogen, iii) Intergranular pores - formed due to incomplete cementation and iv) micro fractures - owed to tectonic movements or structural activities in the basin. The in-situ gas content obtained from canister test varies from 1.937 to 2.307m3/t, 0.378–3.035m3/t and 0.424–1.937m3/t for Raniganj, Barren Measures and Barakar shales respectively however, large cumulative thickness, high TOC, moderate sorption capacity, well developed pore geometry and significant surface area encourages the exploration and production development of shale gas in Raniganj basin. The estimated recoverable shale gas resource is 30.76 billion cubic meter (BCM) for Raniganj, 103.76 BCM for Barren Measures and 41.69 BCM for Barakar shales. This study would help the operators to fulfil the gap of lack of adequate knowledge to develop the shale gas play in this basin.

Effect of clay and organic matter on nitrogen adsorption specific surface area and cation exchange capacity in shales (mudrocks)

The resistivity log and its conventional application is one of the most important analysis used to find oil and gas saturated intervals. In unconventional oil and gas producing rocks, however, this tool and the consequent technique, is affected by many factors and not considered very reliable. Shale reservoir rocks usually have high total specific surface area (TSSA) due to high clay and total organic content (TOC) and nano-scale pores. Resistivity values are rather low and usually not indicative of reservoir zones in high TSSA rocks. Nitrogen adsorption and cation exchange capacity (CEC) are the common techniques to measure TSSA. Clays and organic matter (OM) affect the measured TSSA using either technique. This effect must be taken into account while calculating water saturation using conventional models. In this paper we investigate the mineralogical and geochemical associations of CEC and TSSA and their effects on resistivity in shale reservoirs.We studied samples from oil and gas producing reservoirs such as Bakken, Haynesville, European Silurian, Niobrara, and Monterey formations. CEC was measured using Co(III)-hexamine3+ with the spectrophotometric technique and the equivalent TSSA (CEC-TSSA) was calculated. We also measured the specific surface area using sub-critical Nitrogen gas adsorption technique (N2-SSA). Rock mineralogy, organic matter properties and scanning electron microscope (SEM) images were used to further analyze the data.We find that CEC values are directly correlated with the clay type and content regardless of the OM content or level of thermal maturity. Smectite and illite (when negligible smectite is present) dominate the CEC value in shales. N2-SSA correlates with clay content, especially smectite and illite, but is less sensitive to clay type as CEC. This correlation between N2-SSA and clay content was observed in Bakken (no organic matter), thermally mature (gas window) Haynesville, and low TOC (<2.67 wt%) Niobrara (oil window) samples. We also find that OM significantly affects N2-SSA in two different ways: (1) Blockage of pores and throats by bituminous kerogen, which limits the accessibility of nitrogen to clay surfaces. This effect was observed in thermally immature (oil window) Niobrara (TOC>2.6 wt%) and Monterey shales. (2) Development of nano-scale OM-hosted pores with high surface area mostly for thermally mature (gas window) shales as observed in high TOC (>1.5 wt%) Silurian shales. Correlation with N2-SSA and CEC values revealed that the average charge density for most of the shales in this study varies between 3 and 5 e/nm2 and for some high TOC Niobrara samples can be as high as 32. Relatively higher charge density is due to underestimation of the TSSA by nitrogen adsorption technique. The correlation between SSA/CEC and clay content/type are well studied in the literature. However the results of this study aid in understanding how mineralogy, geological factors, organic matter content and thermal maturity affect this correlation in mud rocks from various reservoirs.

Development of acute and chronic sediment bioassays with the harpacticoid copepod Quinquelaophonte sp

Reliable environmentally realistic bioassay methodologies are increasingly needed to assess the effects of environmental pollution. This study describes two estuarine sediment bioassays, one acute (96h) and one chronic (14d), with the New Zealand harpacticoid copepod Quinquelaophonte sp. utilising behavioural and reproductive endpoints. Spiked sediments were used to expose Quinquelaophonte sp. to three reference compounds representing important categories of estuarine chemical stressors: zinc (a metal), atrazine (a pesticide), and phenanthrene (a polycyclic aromatic hydrocarbon). Acute-to-chronic ratios (ACR) were used to further characterise species responses. Acute sediment (sandy and low total organic content) 96h EC50 values for the sublethal inhibition of mobility for zinc, atrazine and phenanthrene were 137, 5.4, and 2.6µg/g, respectively. The chronic EC50 values for inhibition of reproduction (total offspring) were 54.5, 0.0083, and 0.067µg/g for zinc, atrazine, and phenanthrene, respectively. For phenanthrene, a potentially novel mode of action was identified on reproduction. Quinquelaophonte sp. was found to be more sensitive than several other estuarine species indicating choice of test organism is important to characterising the effects of environmentally relevant levels of contamination. The bioassay sediment results demonstrate the sensitivity and suitability of Quinquelaophonte sp. as a tool for the assessment use of estuarine health.

Do benthic sediment characteristics explain the distribution of juveniles of the deposit-feeding sea cucumber Australostichopus mollis?

Despite the economic importance of many deposit-feeding sea cucumbers, the ecology of their juveniles is poorly understood and factors influencing juvenile habitat selection remain largely unexplained. We investigated the importance of the characteristics of the available sediment in determining the highly localised distribution of juveniles of the deposit-feeding Australasian sea cucumber Australostichopus mollis. Wild-caught juveniles were displaced to non-juvenile habitats with surface sediments characterised by lower total organic content (TOM) and nitrogen content, higher chlorophyll- a content and coarser grain size profiles compared to juvenile sites. The growth of displaced individual animals was monitored over 9 months and compared to control animals caged in the juvenile habitats. Displaced juvenile sea cucumbers had high survival rates that did not differ significantly from juvenile habitats. Displaced juveniles exhibited significantly higher specific growth rate (SGR) than those at juvenile sites ( p < 0.001), although the growth of individuals was highly variable within individual cages and among sites. The lower TOM and nitrogen content, and coarser grain size profiles at non-juvenile sites did not result in reductions in juvenile survival or growth. Higher microphytobenthic activity may have resulted in the higher growth rates observed at shallow non-juvenile sites. The SGR of juveniles over the first 6 months of the experiment ranged between 0.45% d − 1 and 0.74% d − 1 for all sites. This was followed by marked growth limitation between 6 and 9 months either as a result of increasing juvenile biomass in cages or seasonal growth limitation. A subsequent reduction in juvenile density resulted in markedly increased growth over the following 3 month period. Juvenile A. mollis show an ability to exploit a variety of benthic sediment food sources, indicating that their highly localised distribution is not due to differences in the food quality of sediments, but is more likely to be due to other localised effects, such as larval settlement or predation.

Meiofauna, trace metals, TOC, sedimentology, and oxygen availability in the Late Miocene sublittoral deposits of Lake Pannon

The Late Miocene fine-grained deposits have been investigated in the Vienna Basin to attest oxygen availability for infauna and epifauna in the sublittoral of the long-lived Lake Pannon. A clay and fine silt of the deeper lacustrine facies of a bay passed vertically into a silty clay, silt, and fine sand rhythmic deposition reflecting successive progradation of brackish prodelta to distal delta front colonized by a dense benthic population. A fully oxygenated environment is supposed in the Congeria subglobosa Beds and prodelta accentuated by ichnofauna, ostracods, and abundant in taxa and specimens, low total organic content, and trace elements concentration. A limited anoxic event caused by temporarily worsened circulation has been detected in non-calcareous greyish-blue homogenous clay with a noticeable high concentration of Ni, Co, and Pb coupled with absence of fossils, bioturbation, and low total organic carbon content.

Factors Affecting the Accumulation of Organic-Rich Deposits in a Modern Avulsive Floodplain: Examples from the Cumberland Marshes, Saskatchewan, Canada

Since the 1870s, the Saskatchewan River at the Cumberland Marshes (east-central Saskatchewan, Canada) has been undergoing progradational avulsion, resulting in development of a 500 km2 avulsion belt. The avulsion belt consists of an unstable network of active and abandoned channels, splays, and floodbasins, some containing small shallow lakes. Fine-grained deposits of varying total organic content (TOC) are currently accumulating within floodbasins inside, adjacent to, and outside the avulsion belt. The TOC of these deposits depends on factors that control the amount of siliciclastic sediment received by floodbasins. Five factors that affect TOC content are identified: distance from an active channel, position relative to the avulsion belt, presence of alluvial ridges, changes in local channel activity, and developmental stage of avulsion. A channel-to-basin trend of increasing TOC is present at many locations, reflecting greater suspended sediment loads received by near-channel areas, and locations within the avulsion belt generally accumulate sediment with lower TOC than those adjacent to or outside the belt. Alluvial ridges locally act as barriers to floodbasin deposition, and channel abandonment reduces suspended sediment to adjacent floodbasins, both of which increase TOC of sediment. Finally, as avulsion wanes, less siliciclastic sediment is distributed throughout the avulsion belt, resulting in increased TOC. In the geological record, such fine-grained avulsion deposits are likely to appear as intervals of mudrock between thin beds of coal or carbonaceous shale formed from organic-rich sediment deposited between avulsion events, a succession that is common in many ancient alluvial strata.

Preliminary 14C Dates on Bulk Soil Organic Matter from the Black Creek Megafauna Fossil Site, Rocky River, Kangaroo Island, South Australia

Radiocarbon age determinations and stratigraphy suggest that the deposits in Black Creek Swamp on Kangaroo Island record 3 phases of deposition and associated soil development which spanned at least the last 20,000 yr. Four new 14C age determinations on bulk soil organic matter and their stratigraphic context are presented in this paper. Three of these age determinations (FP6: 15,687 ± 110 BP [WK11487]; FP7: 16,326 ± 385 BP [WK11488]; and FP8: 17,618 ± 447 BP [WK11489]), are from the organic-rich fossil layer located 45–75 cm below the current floodplain surface. The fourth, a much younger date, FP5: 5589 ± 259 BP (WK11486), was obtained from the base of the overlying modern soil. The dates for the fossil layer increase systematically with depth and correlate well with 5 previous 14C dates (Hope et al., unpublished), ranging between 15,040 ± 120 BP and 19,000 ± 310 BP. This suggests that the data set represents a possible minimum age of the bulk organic matter, and considering the high organic matter contents of approximately 8%, has implications for the age of the megafauna buried in this layer. The overlying modern soil, with its much younger date, contains lower levels of organic matter (3–7%) and gastropods not seen in the fossil layer. This suggests a substantial change in environmental conditions probably due to an alteration in the floodplain drainage conditions. This chronological and sedimentalogical discontinuity indicates that 2 distinct depositional regimes existed and were separated by up to 10,000 14C yr. A calcareous, sandy silt deposit underlying the fossil layer is a calcarenite deposit with low total organic content and is considered the base of the section; it suggests a third separate depositional episode. As such, the Black Creek Swamp in the southwest corner of Kangaroo Island formed intermittently over at least the last 20,000 yr during 3 distinct depositional phases, one of which was the formation of the fossil-laden, organic-rich floodplain surface, which has a possible minimum age of approximately 15,000 to 19,000 BP.

LOW-DIVERSITY, LATE MAASTRICHTIAN AND EARLY DANIAN PLANKTIC FORAMINIFERAL ASSEMBLAGES OF THE EASTERN TETHYS

Research Article| January 01, 2004 LOW-DIVERSITY, LATE MAASTRICHTIAN AND EARLY DANIAN PLANKTIC FORAMINIFERAL ASSEMBLAGES OF THE EASTERN TETHYS GERTA KELLER GERTA KELLER Department of Geosciences, Princeton University, Princeton NJ 08544, USA Email: gkeller@princeton.edu Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (2004) 34 (1): 49–73. https://doi.org/10.2113/0340049 Article history received: 28 Oct 2002 accepted: 22 May 2003 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GERTA KELLER; LOW-DIVERSITY, LATE MAASTRICHTIAN AND EARLY DANIAN PLANKTIC FORAMINIFERAL ASSEMBLAGES OF THE EASTERN TETHYS. Journal of Foraminiferal Research 2004;; 34 (1): 49–73. doi: https://doi.org/10.2113/0340049 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract The eastern Tethys, from Israel to Egypt, experienced unusually adverse environmental conditions for planktic foraminifera during the last two million years of the Maastrichtian, as evident by very low species richness, blooms of opportunistic Guembelitria species in surface waters, dominance of low-oxygen-tolerant heterohelicids in subsurface waters, and near absence of deeper dwelling globotruncanids. Comparison of southern Israel (Mishor Rotem section) with central Egypt (Gebel Qreiya section) reveals that adverse conditions intensified towards the south with foraminiferal assemblages mimicking stress conditions of the early Danian, dominated (75–90%) by Guembelitria blooms. Faunal assemblages indicate an expanded oxygen minimum and dysoxic zone throughout the region, though at the greater depths represented by localities of southern Israel, bottom waters remained aerobic. Primary productivity was extremely low, as indicated by stable isotopes and low total organic content in sediments. These adverse environmental conditions are likely related to the regional paleobathymetry of the tectonically active Syrian Arc that spans Syria to Egypt. The paleorelief of intra-shelf and intra-slope basins of the Syrian Arc, with their differential rates of subsidence and sedimentation, active folding and faulting, likely controlled the intensity of circulation, upwelling, watermass stratification and the extent of the oxygen minimum zone. The late Maastrichtian rapid climate and sea level changes exacerbated these conditions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Cenomanian-Turonian Organic Facies in the Western Mediterranean and Along the Adjacent Atlantic Margin: ABSTRACT

Pre-Cenomanian sediments of the western Mediterranean and adjacent Atlantic margin are characterized by low total organic content (TOC) with an important terrestrial component. During the Cenomanian, TOC increased and the marine component became dominant, culminating around the Cenomanian-Turonian boundary with TOC up to 40%. After the Turonian, organic-rich sediments progressively disappeared and were replaced by more oxygenated sediments. Study methods include considering data from outcrops, DSDP/ODP sites, or petroleum wells. Detailed data from onshore locations allowed the development of high-resolution stratigraphy, analysis of depositional environment, and calculation of sedimentation rates. Analysis of these data indicates Cenoamnian-Turonian organic-rich sediments can be observed in a wide range of bathymetric settings. They are widespread in the western Mediterranean and Atlantic and have been especially studied in Italy (Apennines, southern Alps), Tunisia (Bahloul), Algeria, Morocco (Rif Mountains, Atlas Mountains, Tarfaya), Gibraltar arch, Spain (Betics, Bay of Biscay, Galicia margin), Senegal (Cape Verde basin, Casamance), and Nigeria (Benue, Calabar flank).