Gray Mudstone Research Articles

Permanganate diffusion and reaction in sedimentary rocks

In situ chemical oxidation using permanganate has frequently been used to treat chlorinated solvents in fractured bedrock aquifers. However, in systems where matrix back-diffusion is an important process, the ability of the oxidant to migrate and treat target contaminants within the rock matrix will likely determine the overall effectiveness of this remedial approach. In this study, a series of diffusion experiments were performed to measure the permanganate diffusion and reaction in four different types of sedimentary rocks (dark gray mudstone, light gray mudstone, red sandstone, and tan sandstone). Results showed that, within the experimental time frame (~2 months), oxidant migration into the rock was limited to distances less than 500 μm. The observed diffusivities for permanganate into the rock matrices ranged from 5.3 × 10(-13) to 1.3 × 10(-11) cm(2)/s. These values were reasonably predicted by accounting for both the rock oxidant demand and the effective diffusivity of the rock. Various Mn minerals formed as surface coatings from reduction of permanganate coupled with oxidation of total organic carbon (TOC), and the nature of the formed Mn minerals was dependent upon the rock type. Post-treatment tracer testing showed that these Mn mineral coatings had a negligible impact on diffusion through the rock. Overall, our results showed that the extent of permanganate diffusion and reaction depended on rock properties, including porosity, mineralogy, and organic carbon. These results have important implications for our understanding of long-term organic contaminant remediation in sedimentary rocks using permanganate.

Control of hydrocarbon accumulation by Lower Paleozoic cap rocks in the Tazhong Low Rise, Central Uplift, Tarim Basin, West China

Despite the absence of regional cap rocks in the Lower Paleozoic for the entire Tazhong Low Rise, several sets of effective local cap rocks are well preserved on the Northern Slope. Of these the best is the Ordovician mudstone of the Sangtamu Formation; the second is the Silurian Red Mudstone Member of the Tatairtag Formation and the marl of the Ordovician Lianglitag Formation; and the third is the gray mudstone of the Silurian Kepingtag Formation. The dense limestone of the Ordovician Yingshan Formation and the gypsum of the Middle Cambrian have shown initial sealing capacity. These effective cap rocks are closely related to the distribution of Lower Palaeozoic hydrocarbons in the Tazhong Low Rise. With well-preserved Sangtamu Formation mudstone and its location close to migration pathways, rich Lower Paleozoic hydrocarbon accumulation can be found on the Northern Slope. Vertically, most of the reserves are distributed below the Sangtamu Formation mudstone; areally, hydrocarbons are mainly found in the areas with well-developed Sangtamu Formation mudstone and Lianglitag Formation marl. Burial history and hydrocarbon charging history show that the evolution of Lower Palaeozoic cap rocks controlled the accumulation of hydrocarbon in the Tazhong Low Rise. Take the Red Mudstone Member of the Tatairtag Formation and Sangtamu Formation mudstone for examples: 1) In the hydrocarbon charging time of the Late Caledonian — Early Hercynian, with top surfaces at burial depths of over 1,100 m, the cap rocks were able to seal oil and gas; 2) During the intense uplifting of the Devonian, the cap rocks with top surfaces at burial depths of 200–800 m and 500–1,100 m respectively were denuded in local areas, thus hydrocarbons trapped in earlier time were degraded to widespread bitumen; 3) In the hydrocarbon charging time of the Late Hercynian and Himalayan, the top surfaces of the cap rocks were at burial depths of over 2,000 m without intense uplifting and denudation thereafter, so trapped hydrocarbons were preserved. Based on cap rocks, the Ordovician Penglaiba Formation and Lower Cambrian dolomite could be potential targets for exploration on the Tazhong Northern Slope, and combined with hydrocarbon migration, less risk would be involved.

Sedimentary Characteristics of Fuyu Oil Layer in the Southern Fuxin Uplift of Songliao Basin

Based on 22 well cores and logging data of nearly 800 well, sedimentary characteristics of Fuyu oil layer in the southern Fuxin uplift was analyzed. It is shown that types of sandstone in the Fuyu oil layer are main feldspathic litharenite, debris arkose and minor litharenite. Granularity probability curve is displayed as a typical of two-stage or three-stage. A large number of parallel bedding, one-way oblique bedding, small-scale cross bedding, the bottom scour structure and syngenetic deformation structure can be seen in the Fuyu oil layer. Mudstone color is main fuchsia, grey purple massive mudstone and gray-green, gray, dark gray massive mudstone. Combined with the analysis of the sedimentary facies sign, Fuyu oil layer in the southern Fuxin uplift is large fluvial-dominated shallow water delta deposition. The skeletal sand bodies in the delta system are distributary channelsand bodies that are large, dense, narrow strip, continuous distribution. The overall is south-southwest trending. Sand body is continuous and far underwater extension until it disappears into thin sandsheet. multi-branch fluvial-dominated ribbon-like bodies are formed.

The East Africa Oligocene intertrappean beds: Regional distribution, depositional environments and Afro/Arabian mammal dispersals

The East Africa Oligocene intertrappean beds: Regional distribution, depositional environments and Afro/Arabian mammal dispersals

Lower Triassic mixed carbonate and siliciclastic setting with Smithian–Spathian anoxic to dysoxic facies, An Chau basin, northeastern Vietnam

In the An Chau basin in northeastern Vietnam, the Olenekian (Lower Triassic) stage comprises mixed carbonate and siliciclastic shallow marine to marginal basin deposits that extend into the southern Nanpanjiang basin in South China. The upper Lang Son Formation, which is dominated by siliciclastic facies, is composed of storm- and wave-influenced shallow marine and slope deposits. The overlying and interfingering Bac Thuy Formation consists of tidal flat, wave-influenced carbonate platform, slope, and marginal basin plain deposits. The tidal flat deposits are composed mainly of lenticular, wavy-bedded, or thin flat-bedded carbonates containing desiccation cracks and ripples that are indicative of bidirectional paleocurrents. The platform carbonates are characterized by wave ripples, ooids, and abundant marine mollusks and microfossils; the molluscan fossil assemblage primarily contains Smithian ammonoids such as Owenites koeneni. The slope deposits are characterized by limestone breccia and slump beds. The marginal basin plain deposits consist of classical turbidite beds, minor limestone breccia, and hemipelagic mudstone and marl containing the Spathian ammonoids Tirolites and Columbites. The turbidite sets may represent frontal splay environments in the marginal basin plain. These Olenekian carbonate and siliciclastic facies are typical of a transgressive succession.The Smithian–Spathian boundary and the anoxic to dysoxic facies of the latest Smithian are characterized by organic-rich dark gray limestone and mudstone deposits intercalated in the succession of slope to marginal basin plain facies, which are composed mainly of gravity flow and hemipelagic deposits. The organic-rich deposits show no evidence of bioturbation and are characterized by low-diversity fauna. Clastics in the marginal basin plain deposits were apparently supplied from the west; hence, the paleocurrent direction of the siliciclastic gravity flows was approximately eastward.

Characteristics of the turbidite fan in the Wenchang Formation of the Enping Sag, Pearl River Mouth Basin, China and its hydrocarbon significance

A turbidite fan in the Eocene upper Wenchang Formation in the Enping Sag, Pearl River Mouth Basin (PRMB) has been studied using seismic, logging and borehole data. The fan is characterized by parallel progradation on the dip seismic profile and is mound-shaped or lenticular-shaped on the strike seismic profile. The study of the core and logging data from well EP17-3-1, which is located in the front side of the turbidite fan, shows that this fan is a set of normal grading sand beds, interbedded within thick dark grey mudstones of semi-deep to deep lake deposits in the Wenchang Formation. The fan is interpreted as a sand/mud-rich turbidite fan that has an area of over 140km2 and a maximum thickness of over 340 m. Combined with a study of the regional geological background and previous provenance analysis of the Eocene Wenchang Formation, the main potential provenances for the turbidite fan are considered to be the Panyu low-uplift and northern fault terrace zone. The Enping Sag is considered to be a half graben-like basin whose north side is faulted and whose south side is overlapped. Basement subsidence in the Eocene was mainly controlled by boundary faults which dip relatively steeply on the north side, causing the subsidence center of the Enping Sag in this stage to be close to the north boundary faults. Sustained faults developed in the Enping Sag during the Eocene caused an increase of the relative height difference between the north and the south uplift zone in the Enping Sag. Affected by the second episode of the Zhuqiong movement (39–36 Ma) in late Eocene, sediments which had accumulated on the Panyu low-uplift zone were triggered and moved toward the subsidence center of the Enping Sag and formed the turbidite fan. The second episode of the Zhuqiong movement is the most important triggering factor for the formation of the turbidite fan in the Wenchang Formation. Seismic attribute characterization shows that the low frequency energy is enhanced and high frequency energy is weakened when seismic waves propagate through the oil-bearing zone in this fan. Amplitude versus offset (AVO) anomalies are observed in the seismic data and abnormally high pressure is encountered. The turbidite fan in the Wenchang Formation has provided important information for sedimentary evolution in deep layers of the Enping Sag and pointed to a new direction for the hydrocarbon exploration in the study area.

Climatic and biotic changes around the Carboniferous/Permian boundary recorded in the continental basins of the Czech Republic

The paper provides an overview of a several decades-long study of transitional Carboniferous–Permian (Stephanian C–Autunian) sedimentary successions in continental basins of the Czech part of the Bohemian Massif. These predominantly monotonous fluvial red beds intercalate with laterally widespread grey to variegated sediments of dominantly lacustrine origin. Both, fossil and climatic records show that apart from a generally known long-term climatic shift to drier conditions in Early Permian, the climate oscillated on several time scales throughout the study interval. Climatic indicators in the red beds part of the succession include palaeosols ranging between red vertisols and vertic calcisols suggesting strongly seasonal dry sub-humid climate. This is in agreement with the rarity of plant remains, which were mostly completely oxidised and only rarely preserved as plant impression in red mudstones or as silicified mostly gymnosperm woods in sandy channel fills. Silicification instead of coalification was the dominant fossilisation process during red-beds deposition. Even drier, possibly semi-arid climate may be indicated by spatially and temporarily restricted bimodal sandstones, dominated by well-rounded quartz grains and interpreted as eolian in origin. Periods of moist sub-humid (or even humid) climate were accompanied by formation of perennial lakes containing grey laminated mudstones, dark grey bituminous mudstones or limestones, muddy limestones, chert layers or even spatially restricted coals, some of them, however, of economic importance. Shorter climatic oscillations operating on a scale of tens to possibly hundreds of thousands of years are represented by transgressive–regressive lacustrine cycles followed by significant changes in lake water salinity reflected by boron content.The fossil record indicates the presence of dryland and wetland biomes in basinal lowlands although their proportions varied significantly as the climate changed. During deposition of red beds, the alluvial plain was vegetated dominantly by dryland biome assemblages. The composition of these assemblages is indicated by fairly common silicified gymnosperm (cordaitalean and coniferous) woods in sandstone–conglomerate fluvial channel bedforms and by poorly preserved impressions of walchian conifer shoots and cordaitalean leaves in associated mudstone intercalations. This is in agreement with sub-vertical root rhizolites and haloes in calcic vertisols. Occurrence of “wet spots” colonised by wetland assemblages is indicated by rather exceptional findings of silicified calamite stems in fluvial red beds associated with gymnospermous woods.During the humid intervals parts of the basinal lowlands were occupied by lakes surrounded by broad belts of wetland biome floras. During the “Stephanian C” most of these floras were dominated by tree ferns, calamites and sub-dominant pteridosperms. Local peat swamps were colonised by lycopsids including Sigillaria brardii, Asolanus camptotaenia and even some lepidodendrid lycopsids. In contrast, the fossil record of “Stephanian C” dryland floras is rarely preserved in lacustrine sediments. The fossil record of “Autunian” lakes, however, suggests increasing proportions of dryland elements, including conifers and peltasperms.The response of lacustrine faunas to climatic oscillations around the Carboniferous–Permian transition is less prominent than that of plants. The origin of the transition between the local Elonichthys–Sphaerolepis and Acanthodes gracilis bio/ecozones around the Carboniferous/Permian boundary is impossible to deduce from the existing fossil record.

Neogene Eastern Amazon carbonate platform and the palaeoenvironmental interpretation

The Early Miocene Pirabas Formation represents extensive carbonate and siliciclastic belts deposited in marine coastal environments along the Eastern Amazon coast. This Formation was studied in its palynological, palaeocarcinological and sedimentary facies, in order to develop a model of its depositional processes, faunal and floral assemblages and the sedimentary environments, as observed in the B17 mine (Capanema, Pará). The sedimentary records consist mostly of light gray to greenish gray mudstones with tidal bedding, calciferous sandstones, stratified biocalcirudites and levels with conglomerates deposited in a carbonate/siliciclastic transitional system with lagoon, tidal flat, flood-tide delta and foreshore environments. Eighteen palynomorph species were identified in the tidal flat deposits including 1 alga, 3 fungi, 5 pteridophytes, and 9 angiosperms. Among the latter, mangrove pollen and spores of Zonocostites ramonae, Zonocostites minor, and Deltoidospora adriennis are reported. Nine species of crustacean decapods were recognized in the foreshore deposits, comprising 1 Callianassoidae, 2 Calappidae, and 6 Portunidae, represented by Euphylax, †Necronectes, Portunus, and Scylla, the ecology of which is associated with beaches of marginal lagoons. The main factor of the formation of these carbonate environments is assumed to have been related to the lack of a large-scale drainage system such as the Amazon River basin in the transition Oligocene–Miocene, which may also have influenced carbonate production and resulted in a strong decrease of palaeodischarges from incipient river systems along the Amazon coast.

Sequence stratigraphy and sedimentary facies in the lower member of the Permian Shanxi formation, northeastern Ordos Basin, China

The Lower Permian Shanxi (山西) Formation is one of the main gas-bearing stratigraphic units in northeastern Ordos (鄂尔多斯) Basin, China. Based on an integrated investigation of well logs, cores, and outcrop, we delineated the sedimentary facies of the lower member of the Shanxi Formation and divided the succession into three third-order sequences from base to top as SQ1, SQ2, and SQ3. The lower region of Shanxi Formation was deposited in the following sedimentary facies or subfacies: subaqueous braided channel, subaqueous interdistributary, mouth bar, swamp and shelf in the Daniudi (大牛地) Gas Field and braided channel, and shelf and lake at Heidaigou (黑岱沟) outcrop. Braided-river deposits form the lowstand systems tract (LST) in each sequence. Braided channels mark the sequence boundaries at Heidaigou outcrop. A shelf and lake depositional environment with dark gray mudstone forms the transgressive systems tract (TST). The location where dark gray mudstone first appears above the braided channel marks the first flooding surface (FFS), and the end of that marks the maximum flooding surface (MFS). The highstand systems tract (HST) deposits are fine-grained sediments with an aggradational parasequence at Heidaigou outcrop and swamp coalbed in the Daniudi Gas Field. Mouth-bar sand bodies in braided delta front, which form the LST in each sequence, form excellent reservoirs in the Daniudi Gas Field.

Geological and Geoengineering Properties of the 1997 Yangjia Shan Landslide, Enshi, China

Yangjia Shan instability has been evidenced by the occurrence of the July 16, 1997 landslide. The instability factor which leads to activating the landslide is the intense rainfall; lithology of Luoreiping Formation and the highly weathered slopes’ rocks have played a great role in starting and aggravation. Weathering at the landslide site consists largely of attack on the cement and removal of support of the sandy mudstone and sandstone and decompose of shale. The weathering degree of the rocks decreases vertically with increasing depth from high, medium to slightly weathered corresponding to grade IV, III and II, respectively. The slip surface consists of moderate to highly weathered intercalated layers of sandy mudstone (mudstone) and shale, while, the layer below the slip surface is characterized by dark gray, moderately weathered and thick layered mudstone. The moderate to highly weathered subsurface lithology is probably attributed to the accumulation of the infiltrated rainfall water through fractures and porosity, raising the ground water level and wetting of the sandy mudstone and shale rocks of Luoreping Formation. The wetting contributed more or less to the disintegration of the sandy mudstone and shale, lowered the shear strength and created cracks on the upper part of the slope leading thus to increase the landslide susceptibility. Therefore, the frequency and magnitude of landslide at the study area and its vicinity are expected to increase through the activation of old landslides and triggering of new ones under circumstances similar to those of the past.

Pliocene-Pleistocene Climate Change At the NE Tibetan Plateau Deduced From Lithofacies Variation In the Drill Core SG-1, Western Qaidam Basin, China

Abstract The Pliocene–Pleistocene sedimentologic evolution of the western Qaidam Basin at the NE Tibetan Plateau was studied on the nearly thousand-meter-deep drill core SG-1 (spanning ca. 2.8–0.1 Ma), recovered from the Chahansilatu sub-depression with an average recovery rate of 95%. Lithofacies variation records the regional climatic change in relation to Asian drying and Tibetan Plateau uplift. Sedimentary textures and structures demonstrate a continuous slight coarsening and an increase of evaporites upward. We recognized five lithofacies: (1) gray-black laminated mudstone, (2) gray massive mudstone and siltstone, (3) bedded halite, (4) loose muddy halite, and (5) brownish-yellowish saliferous siltstone and mudstone, representing (1) semi-deep fresh to semi-brackish lake, (2) shallow brackish lake, (3) perennial saline lake, (4) playa saline lake, and (5) saline mudflat conditions, respectively. Variation of the lithofacies through the core demonstrates a clear trend of lake shrinkage since the late Pliocene and the final termination of the Chahansilatu paleolake. Accelerations of lake shrinkages are observed at ca. 2.5 Ma, 2.2 Ma, 1.6 Ma, 1.2 Ma, 0.9 Ma, 0.6 Ma, and 0.1 Ma. Our results suggest that the long-term stepwise drying of the Asian inland may have been forced by the change of the global ice volume.

Seismic Prediction Method for Dark Mudstone Thickness of the Second Member of the Denglouku Formation in Northern Songliao Basin

The hydrocarbon source rocks in Denglouku formation of Northern Songliao Basin are mainly the grey mudstones in Deng 2 member. Combined with well and seismic information, this paper forecasts the mudstone thickness distribution of study area applying multiple seismic attribute quantitative prediction based on sedimentary characteristics. We also predict the plane distribution of dark mudstone-mudstone thickness ratio with stratigraphic sedimentary thickness information, horizontal result of seismic facies interpretation and dark mudstone-mudstone thickness ratio materials of well point. Eventually, we obtain the plane dark mudstone prediction result. Analysis indicates that the source rocks of Deng 2 member in Northern Songliao Basin mainly consist of three larger dark mudstone development areas and other sporadic small-scale development areas adjacent, which have the maximum dark mudstone thickness of about 357m located near Songji 6 well.

A new Oligo-Miocene Mammal-Bearing site from a sedimentary intercalation in the trap basalts of Central Eritrea

We report the findings of two proboscideans from a sedimentary intercalation within the Central Eritrea Tertiary Trap basalt succession. These intertrappean sediments can be traced continuously between Tera’emni and Adi Quala in the Mendefera region, and are interbedded between the underlying Asmara/Aiba-Alaji basalts and the overlying Adi Ugri basalt. This intercalation is up to 50 m thick and consists of a predominant intensely pedogenized red, green and gray mudstone and siltstone with subordinate channelized pebbly sandstone. The newly discovered mammal remains come from the coarse-grained deposits in the Mai Gobro section. Available radiometric datings of the host volcanic rocks constrain the age of the fossils between 24.6 and 22.1 Ma, i.e. at the transition between the Oligocene and the Miocene. The fossil vertebrate remains from Mai Gobro represent two proboscidean families, Deinotheriidae and Gomphotheriidae. The morphological grade of the two Mai Gobro proboscideans would suggest a more derived stage than that of representatives of the same families known from other Oligocene African sited (e.g. Chilga, Ethiopia), suggesting a possible Oligo-Miocene age.

The evolution of the Quaternary Eupcheon fault, SE Korea

The Dadaepo Basin is a small Late Cretaceous sedimentary basin in SE Korea, located on the eastern margin of Asia. The basin is an isolated extensional basin situated between the NNE-striking Yangsan and Dongnae faults. The basin-fill sediments, named the Dadaepo Formation, consist of channelized conglomerates and sandstones intercalated with dominantly purple mudstones in the lower part. The upper part is dominated by fine- to coarse-grained tuffaceous sandstones and olive to dark gray mudstones with abundant volcanic interbeds. The formation unconformably overlies dacitic rocks dated at ca. 94 Ma and is overlain by basaltic andesite dated at ca. 69 Ma (Ar–Ar ages). The overall configuration of the strata of the Dadaepo Formation indicates syndepositional tilting of the basin floor to the north-northeast. A number of outcrop-scale faults are observed in the basin-fill sediments, of which the majority are NW-striking normal faults, including syndepositional growth faults. The orientations of mafic (magmatic) and clastic dikes, interpreted as being approximately contemporaneous with the deposition of the Dadaepo Formation, are also nearly parallel to the strikes of outcrop-scale normal faults. All these extensional structures consistently indicate NE–SW extension of the basin and obliquely intersect the basin-bounding Yangsan and Dongnae faults at angles of 40°–60°. It is thus concluded that the Dadaepo Formation was deposited in a pull-apart basin that subsided as a result of NNE-striking sinistral strike–slip faulting in the southeastern part of the Korean Peninsula during the Campanian (Late Cretaceous). This strike–slip faulting was related to north-northwestward oblique subduction of the proto-Pacific (Izanagi/Kula) or Pacific plate under the eastern margin of the Eurasian plate.

Late Cretaceous stratigraphy, Songliao Basin, NE China: SK1 cores

The Songliao Basin is the largest Cretaceous oil and gas-producing lacustrine basin in China, with its greatest aerial extent in the middle Cretaceous. A coring program (SK1) has to date yielded 2485.89m of continuous core (96.46% recovery) and provides significant material for Cretaceous research. The sequence of the core consists mainly of lacustrine sandstone, dark grey mudstone, shale and oil-shale. The Upper Cretaceous stratigraphic section has been subdivided into the Quantou, Qingshankou, Yaojia, Nenjiang, Sifangtai and Mingshui formations in ascending order. Late Cretaceous microfossils are diverse and abundant. A detailed biostratigraphic study has subdivided the sequence into high precision biozones: 21 ostracode assemblages, 10 phytoplankton assemblages, 7 palynological zones and 4 charophyta assemblages, respectively. In addition, marine foraminifera were first discovered from the basin. Three 206Pb/238U ages and one 40Ar/39Ar age were analysed. Ten local magnetozones have been recognised in the SK1 (North), and two magnetozones have been indicated in the SK1 (South). Based on biostratigraphy, high-resolution magnetostratigraphy and SIMS U–Pb zircon analyses, the SK1 stratigraphy is correlated with Upper Cretaceous stages in the International Geologic Time Scale. The upper part of the Quantou Formation is the lower Turonian; the Qingshankou Formation is the upper Turonian–lower Coniacian; the Yaojia Formation is from the upper Coniacian to middle Santonian; the Nenjiang Formation is the upper Santonian to middle Campanian; the Sifangtai Formation is limited to the upper Campanian; and the Mingshui Formation is the uppermost Campanian to Maastrichtian. It is likely that the upper part of the Mingshui Formation belongs to the Paleocene, and the K/Pg boundary is within the Member 2 of the Mingshui Formation around the depth of 328m by new micropalaeontologic and magnetostratigraphic data.

Marcellus Shale Lithofacies Prediction by Multiclass Neural Network Classification in the Appalachian Basin

Marcellus Shale is a rapidly emerging shale-gas play in the Appalachian basin. An important component for successful shale-gas reservoir characterization is to determine lithofacies that are amenable to hydraulic fracture stimulation and contain significant organic-matter and gas concentration. Instead of using petrographic information and sedimentary structures, Marcellus Shale lithofacies are defined based on mineral composition and organic-matter richness using core and advanced pulsed neutron spectroscopy (PNS) logs, and developed artificial neural network (ANN) models to predict shale lithofacies with conventional logs across the Appalachian basin. As a multiclass classification problem, we employed decomposition technology of one-versus-the-rest in a single ANN and pairwise comparison method in a modular approach. The single ANN classifier is more suitable when the available sample number in the training dataset is small, while the modular ANN classifier performs better for larger datasets. The effectiveness of six widely used learning algorithms in training ANN (four gradient-based methods and two intelligent algorithms) is compared with results indicating that scaled conjugate gradient algorithms performs best for both single ANN and modular ANN classifiers. In place of using principal component analysis and stepwise discriminant analysis to determine inputs, eight variables based on typical approaches to petrophysical analysis of the conventional logs in unconventional reservoirs are derived. In order to reduce misclassification between widely different lithofacies (for example organic siliceous shale and gray mudstone), the error efficiency matrix (ERRE) is introduced to ANN during training and classification stage. The predicted shale lithofacies provides an opportunity to build a three-dimensional shale lithofacies model in sedimentary basins using an abundance of conventional wireline logs. Combined with reservoir pressure, maturity and natural fracture system, the three-dimensional shale lithofacies model is helpful for designing strategies for horizontal drilling and hydraulic fracture stimulation.

Clay mineralogy and calcareous nannofossils from Jagüel and Roca formations in the eastern sector of Pellegrini Lake, Neuquen Basin, República Argentina.

This study presents new mineralogical, sedimentological, and micropaleontological data from the Jagüel (Late Maastrichtian-Early Danian) and Roca (Danian) formations, located in the eastern sector of Pellegrini Lake, Río Negro province, República Argentina. According to the physical characteristics and the age of the sediments that conform these formations, two siliciclastic lithofacies and a carbonate one were recognized, they are named: Maastrichtian grayish yellow calcareous mudstones, Danian olive gray calcareous mudstones, and Danian carbonates. The rocks which constitutes siliciclastic lithofacies were classified as allochemical mudstones and the mineralogy is characterized by high proportions of clay minerals and, to a lesser extent, calcite. The clay mineral association is dominated by a random (R0) I/S mixed-layers (70-90% Sm) accompanied by lower proportions of illite and kaolinite. The mineralogy and the microfabric of the mudstones reflect that these sediments have not been affected significantly by diagenesis. Clay minerals would be of detrital origin and the predominance of the highly smectitic I/S along all sections would be associated with an active volcanism coming from the western magmatic arc, located in the Neuquén Basin during the Late Cretaceous and Paleocene. Micropalaeontological analyses confirmed the presence of Cretaceous-Paleogene transition in the Jagüel Formation beds. The calcareous nannofossils allowed to relate changes in the the mineralogical associations along the K/P transition. In this way, it was possible to detect an increase in kaolinite content close to the K/P boundary (>10%), that decreases towards higher positions of the Danian, which could indicate a warmer and wetter climate during this interval, that it would tend to be drier with seasonal conditions in the late Danian. The Maastrichtian calcareous nannofossil assemblages suggest oligotrophic environments and a well stratified photic zone, nevertheless, in some horizons, the nannoflora is abundant with lower richness which would indicate more restricted marine conditions.

Formation process of the trace fossil Phymatoderma granulata in the Lower Jurassic black shale (Posidonia Shale, southern Germany) and its paleoecological implications

The ichnogenus Phymatoderma is a subhorizontal branching burrow system consisting of radiating tunnels filled with fecal pellets. This ichnogenus has been interpreted as a product of a deposit-feeding animal, but the question of whether the Phymatoderma-producer was a subsurface deposit feeder or a surface deposit feeder is still a topic of controversy. Herein I present evidence, based on carbon–isotope analyses, for the formation of the trace fossil Phymatoderma granulata occurring in the lower Toarcian black shale in southern Germany. Carbon–isotope ratios of organic carbon (δ13Corg) in the pelletal infill of P. granulata, the surrounding black shale, and the overlying gray mudstone are −26.64±0.42 (2σ) ‰, –28.49±0.44 (2σ) ‰, and −26.27±0.13 (2σ) ‰, respectively. The difference between the pelletal infill and overlying mudstone in terms of δ13Corg is much smaller than that between the fillings and black shale; therefore, these data clearly indicate that the Phymatoderma-producer ingested the surface sediments and subsequently excreted fecal pellets into the subsurface sediments. Such a surface deposit-feeding style would be an especially effective means of absorbing nutrients, because surface sediments contain much fresh organic material, whereas organic matter in subsurface deposits consists mostly of refractory material that is poorly utilized by most marine benthos.

Cephalopod ancestry and ecology of the hyolith “Allatheca” degeeri s.l. in the Cambrian Evolutionary Radiation

Pyritized, elongate, conical conchs of “Allatheca” degeeri s.l. are common in dysoxic, dark gray mudstone intervals in the Early Cambrian (upper Terreneuvian–Series 2 boundary interval) Cuslett Formation at Keels, eastern Newfoundland. Wave-oriented, horizontal specimens are most abundant in this cool-water, high latitude, off-shore shelf facies of the Early Palaeozoic Avalon microcontinent. Based on conch morphology, shell microstructure, and the operculum, the species is an orthothecid hyolith. Comparison with the sizes of the early shells of planktic gastropods indicates a non-planktic life mode of “A.” degeeri s.l. hatchlings, although buoyancy calculations show that small juveniles with septate conchs to ca. 17mm long could have been nektic/planktic. If smaller “A.” degeeri s.l. individuals had a non-benthic mode of life, they and pseudoconodonts were the oldest skeletalized pelagic/nektic animals in the Cambrian Evolutionary Radiation. Most “A.” degeeri s.l. conchs at Keels are horizontally embedded and show a bimodal, wave-determined orientation, but about 10% of the large conchs are vertically embedded with their aperture down. As larger shells were not neutrally buoyant, the vertical orientations of about 10% of the conchs suggests an infaunal, likely detritivore, life mode suggestive of a scaphopod. Available morphologic and taphonomic evidence suggests that the vertically embedded conchs are in situ remains of dead benthic animals that colonized the bottom in better oxygenated intervals. Based on the current knowledge of Early Palaeozoic hyolith and cephalopod larval and adult morphologies, existing hypotheses of a planktic origin of cephalopods from hyolith ancestors are evaluated, and no evidence for such an evolutionary relationship is concluded to exist.

Exploration Tries To Answer Questions About the Lower Silurian Longmaxi Shale in China

This article, written by Editorial Manager Adam Wilson, contains highlights of paper IPTC 14487, ’Sichuan Basin Shale Gas, China: Exploring the Lower Silurian Longmaxi Shale,’ by Claudia Hackbarth, SPE, Danny Soo, and Navpreet Singh, SPE, Shell, prepared for the 2011 International Petroleum Technology Conference, Bangkok, Thailand, rescheduled to 7-9 February 2012. The paper has not been peer reviewed. Shale-gas exploration in China is already under way and rapidly increasing in activity level. The Sichuan basin, one of the most prolific petroleum basins in China, is at the forefront. However, exploration and assessment of an untested shale-gas play is typically lengthy and expensive. Compared with conventional oil and gas projects, shale-gas projects may require a number of early wells to prove the existence and distribution of the gas but then many more wells to test and optimize engineering techniques until a commercially viable combination is found. This process could be summarized into two overarching questions: “Is there a material amount of gas?” and, if yes, “Can it be produced economically?” Sichuan Basin Structure The topographic Sichuan basin today is a remnant of the originally much larger Upper Yangtze cratonic sedimentary basin (Fig. 1). In the southern Sichuan basin, structures are characterized by thin-skinned faulting and thrusting, often above an Upper Cambrian detachment surface, likely an evaporitic ductile layer that now cores the folds. The Sichuan-area stratigraphic column contains several potential source-rock intervals. Industry has so far focused attention on the Lower Cambrian Qiongzhusi and the Ordovician-Silurian boundary as potential shale-gas reservoirs. The Upper Ordovician Wufeng shale and Lower Silurian Longmaxi formation are generally regarded as belonging to the same black-shale succession, but an erosional surface and regional disconformity separate the two intervals. The Longmaxi formation is not as widespread as the Wufeng formation and is restricted to the Yangtze region. From the bottom up, the Ordovician/Silurian succession consists of A lower graptolite-bearing, black or dark-gray, carbonaceous/siliceous shale (Wufeng formation), generally several meters thick The Guoyinchao limestone or calcareous siltstone with abundant Hirnantian fauna and other shelly fossils, typically 0.5–3 m thick The Lower Longmaxi black, graptolite-bearing, carbonaceous/siliceous shale with cherty slate The Upper Longmaxi gray calcareous mudstones and siltstones, interbedded with an increasing number of thin limestone layers toward the top of the formation Regional studies indicate that Wufeng and Longmaxi shales were buried deeply enough over a large area of the Sichuan basin to have reached the gas-generation window.