最古老的脊椎动物:海口虫或原牙形类?

产自南非晚奥陶世索姆页岩中的牙形动物化石被认为是一类脊椎动物的摄食器官,而产自中国云南早寒武世早期的云南虫(Yunnanozoon)和海口虫(Haikouella)具有矿化的单锥形牙齿构造,被认为是保存了软部的脊椎动物的祖先.经比较研究后提出了产自比澄江动物群更低层位(梅树村阶)中的原牙形类Protohertzina和Protocanthocordylodus等应代表保存了硬部的最早的脊索动物,甚至是脊椎动物或它们的共同祖先.     

滇西澜沧江构造带南段沙乐花岗岩的锆石U-Pb年龄、地球化学特征及其地质意义

沙乐花岗岩位于滇西思茅地块南涧县南西沙乐乡一带,主要由黑云母二长花岗岩和花岗闪长岩组成,被少量正长斑岩侵入。LA-ICP-MS锆石U-Pb测年得出黑云母二长花岗岩的形成年龄为246.4±2.6Ma,花岗闪长岩的形成年龄为245.7±3.6Ma,表明该花岗岩体的形成时代属于早三叠世。岩石Si O2含量71.44%~76.39%,Al2O3含量12.72%~16.15%,K2O/Na2O=0.1~1.30,均属高钾钙碱性过铝-强过铝花岗岩。根据地球化学特征和微量元素构造判别图解,样品点主要落入"火山弧花岗岩"、"板内花岗岩"区域,少量落入"碰撞花岗岩"区域,表明其形成于俯冲-碰撞岩浆弧转换环境。在Sr-Yb花岗岩分类图解中,主要属常见的低Sr高Yb花岗岩,少数样品属低Sr低Yb花岗岩,其物质来源为含砂质的变质泥质岩。结合锆石定年结果及岩体产出的区域地质背景,认为沙乐花岗岩形成于缅泰马陆块与思茅地块大陆碰撞造山过程的初始阶段,同时表明昌宁-孟连洋碰撞最早时限为早三叠世。     

Chemical, Isotopic, and Fluid Inclusion Evidence for the Hydrothermal Alteration of the Footwall Rocks of the BIF-Hosted Iron Ore Deposits in the Hamersley District, Western Australia

Abstract. The petrography, chemical, fluid inclusion and isotope analyses (O, Rb-Sr) were conducted for the shale samples of the Mount McRae Shale collected from the Tom Price, Newman, and Paraburdoo mines in the Hamersley Basin, Western Australia. The Mount McRae Shale at these mines occurs as a footwall unit of the secondary, hematite-rich iron ores derived from the Brockman Iron Formation, one of the largest banded iron formations (BIFs) in the world. Unusually low contents of Na, Ca, and Sr in the shales suggest that these elements were leached away from the shale after deposition. The δ¹⁸O (SMOW) values fall in the range of + 15.0 to +17.9 per mil and show the positive correlation with calculated quartz/sericite ratios of the shale samples. This suggests that the oxygen isotopic compositions of shale samples were homogenized and equilibrated by postdepositional event. The pyrite nodules hosted by shales are often rimmed by thin layers of silica of varying crystallinity. Fluid inclusions in quartz crystals rimming a pyrite nodule show homogenization temperatures ranging from 100 to 240C for 47 inclusions and salinities ranging from 0.4 to 12.3 wt% NaCl equivalent for 18 inclusions. These fluid inclusion data give direct evidence for the hydrothermal activity and are comparable to those of the vein quartz collected from the BIF-derived secondary iron ores (Taylor et al, 2001). The Rb-Sr age for the Mount McRae Shale is 1,952 ± 289 Ma and at least 200 million years younger than the depositional age of the Brockman Iron Formation of ∼ 2.5 Ga in age. All the data obtained in this study are consistent with the suggestion that high temperature hydrothermal fluids were responsible for both the secondary iron ore formation and the alteration of the Mount McRae Shale.     

Syndepositional and diagenetic features in the pyrite ores of Amjhore,Bihar, India

The sedimentary pyrite deposit of Amjhore, Bihar associated with the Bijaigarh Shale of the Upper Vindhyan Group (Proterozoic age) exhibits characteristic syndepositional features suggestive of both calm and disturbed conditions of deposition. The pyrite ores also show typical diagenetic features.     

<Emphasis Type="Italic">Trachyhystrichosphaera</Emphasis>: An age-marker acanthomorph from the Bhander group,upper Vindhyan,Rajasthan

A highly diversified, advanced and exceptionally well preserved microfossil assemblage, dominated by a planktic community, has been recorded from petrographic thin sections of chert belonging to the Sirbu Shale Formation, Bhander group, upper Vindhyans, Rajasthan. Recently, it was noticed that the assemblage also contains well preserved, large-sized acanthomorphic acritarchs, Trachyhystrichosphaera considered to be an age-marker microfossil of the Cryogenian (850-630 Ma). It is reported for the first time from any Indian microfossil assemblage of Proterozoic succession. The other microfossils of the Sirbu Shale Formation are: well preserved simple, small and large-sized sphaeromorphs; complex acanthomorphs, cyanobacterial community; especially a very small-sized but exceptionally well preserved Obruchevella, a form resembling Volvox colonies; cf. vase-shaped microfossils and morphologies, possibly inclining towards fungal affinity, or lichenlike symbiotic associations of algae and fungi. Till date, Trachyhystrichosphaera has so far not been reported from successions older than the Tonian (1000850 Ma). It is believed that acanthomorphs attained maximum size in Ediacaran (630-542 Ma), and further decreased in size in the Cambrian. The global paleontological literature indicates that Trachyhystrichosphaera ranges in age from Tonian-Ediacaran (1000-542 Ma). The present record of Trachyhystrichosphaera as well as the earlier studies of micro and megascopic life of the Bhander Group in general and the Sirbu Shale in particular (aided by the absence of any Cambrian fossil record) indicate that in all possibilities, age of the Sirbu Shale should lie near Cryogenian (850-630 Ma) and the uppermost Bhander group, may incline towards the Ediacaran (630-542 Ma).     

Provenance and temporal constraints of the Early Cambrian Maotianshan Shale,Yunnan Province,China

The Cambrian Maotianshan Shale in Yunnan Province, China contains the well-preserved soft-body fossils of the Chengjiang Biota. The high quality preservation of the non-mineralizing biota (soft tissues and whole carcasses) shows regional and temporal differences, suggesting that paleogeography and local environmental conditions might have contributed to the taphonomy of these fossils. In this paper we present new results from petrographic, geochemical and detrital zircon analyses, and provide a new interpretation about the provenance of the Maotianshan Shale, as well as add to the understanding of the paleogeography of the South China Block during the Cambrian Stage 3. Results from petrographic analysis indicate that the provenance of the Maotianshan Shale is a recycled orogen overall, bordering the western and southwestern margin on the Yangtze Block. The most likely source of the terrigenous material is an exhumed area extending from the Kangdian paleoland to the southeast, paralleling the Song Ma fault zone. Minor regional differences in geochemical and petrographic proxies between the northwestern Jianshan/Ercai area and the southeastern Maotianshan/Xiaolantian area suggest influence of local sources. Sediments of the southeastern province are less mature and samples include minor elements commonly associated with mafic sources. Sediments from the northwestern province are more mature, largely lack mafic components and are enriched in Zr and Hf. The major population of the Maotianshan Shale detrital zircons group at ~ 800 Ma. This crystallization age matches well with the age of a widely spread felsic volcanic and intrusive event associated with the Neoproterozoic Kangdian rift, suggesting that these igneous rocks are most likely a major provenance for the Maotianshan sediments. The youngest zircon population yields consistent Concordia ages of ~ 520 Ma, representing a maximum age constraint on the timing of deposition of the Maotianshan Shale. The zircon crystals of the ~ 520 Ma populations are euhedral with magmatic zoning, indicative of short-distance transport. Volcanic activity along the Song Ma suture zone is a potential source for the ~ 520 Ma detrital zircon suite.     

Pleistocene recharge to midcontinent basins: effects on salinity structure and microbial gas generation

The hydrogeochemistry of saline-meteoric water interface zones in sedimentary basins is important in constraining the fluid migration history, chemical evolution of basinal brines, and physical stability of saline formation waters during episodes of freshwater recharge. This is especially germane for interior cratonic basins, such as the Michigan and Illinois basins. Although there are large differences in formation water salinity and hydrostratigraphy in these basins, both are relatively quiescent tectonically and have experienced repeated cycles of glaciation during the Pleistocene. Exploration for unconventional microbial gas deposits, which began in the upper Devonian-age Antrim Shale at the northern margin of the Michigan Basin, has recently extended into the age-equivalent New Albany Shale of the neighboring Illinois Basin, providing access to heretofore unavailable fluid samples. These reveal an extensive regional recharge system that has profoundly changed the salinity structure and induced significant biogeochemical modification of formation water elemental and isotope geochemistry.New-formation water and gas samples were obtained from Devonian-Mississippian strata in the Illinois Basin. These included exploration wells in the New Albany Shale, an organic-rich black shale of upper Devonian age, and formation waters from over- and underlying regional aquifer systems (Siluro-Devonian and Mississippian age). The hydrostratigraphic relations of major aquifers and aquitards along the eastern margin of the Illinois Basin critically influenced fluid migration into the New Albany Shale. The New Albany Shale formation water chemistry indicates significant invasion of meteoric water, with δD values as low as −46.05‰, into the shale. The carbon stable isotope system (δ¹³C values as high as 29.4‰), coupled with δ¹⁸O, δD, and alkalinity of formation waters (alkalinity ≤24.08 meq/kg), identifies the presence of microbial gas associated with meteoric recharge. Regional geochemical patterns identify the underlying Siluro-Devonian carbonate aquifer system as the major conduit for freshwater recharge into the fractured New Albany Shale reservoirs. Recharge from overlying Mississippian carbonates is only significant in the southernmost portion of the basin margin where carbonates directly overlie the New Albany Shale.Recharge of dilute waters (Cl⁻ <1000 mM) into the Siluro-Devonian section has suppressed formation water salinity to depths as great as 1 km across the entire eastern Illinois Basin margin. Taken together with salinity and stable isotope patterns in age-equivalent Michigan Basin formation waters, they suggest a regional impact of recharge of δ¹⁸O- and δD-depleted fluids related to Pleistocene glaciation. Devonian black shales at both basin margins have been affected by recharge and produced significant volumes of microbial methane. This recharge is also manifested in different salinity gradients in the two basins because of their large differences in original formation water salinity. Given the relatively quiet tectonic history and subdued current topography in the midcontinent region, it is likely that repeated cycles of glacial meltwater invasion across this region have induced a strong disequilibrium pattern in fluid salinity and produced a unique class of unconventional shale-hosted gas deposits.     

Preliminary paleomagnetic dating of the metalliferous (Zn–Pb rich), Stark black shale, Kansas City region, U.S.A.

The Stark metalliferous black shale is a member of the Dennis Formation, which is a cyclothemic limestone and shale unit in the Missourian (Upper Pennsylvanian) Kansas City Group. Paleomagnetic analysis of 96 specimens from 7 sites indicates that the characteristic remanent magnetization of the Stark Shale yields a Late Mississippian to Early Pennsylvanian age. This age is close to, but slightly older than, the Middle Pennsylvanian host rock age and implies that the metalliferous content of the shale is syngenetic in origin.     

Devonian fish remains,biostratigraphy and unconformities,Narromine 1:250 000 map sheet area,central New South Wales (Lachlan Fold Belt)

A fossil fish assemblage associated with marine invertebrates from the Coonardoo Sandstone (Wallingalair Group) at Boor Hill (eastern limb of Tullamore Syncline) contains phyllolepid and bothriolepid placoderms of probable Late Devonian age. An angular unconformity with the overlying Hervey Group indicates erosion and folding during the Middle – Late Devonian, and evidently younger than the main Tabberabberan orogenic event. Invertebrate remains demonstrate a Late Devonian marine interval, not previously recognised as far west as the Tullamore Syncline, and assumed to represent the global maximum sea-level in the late Frasnian immediately preceding the Frasnian – Famennian extinction event. A phyllolepid placoderm plate from a sedimentary interbed of the Dulladerry Volcanics in the Hervey Syncline compares with abundant phyllolepid material from the Merriganowry Shale Member of the Dulladerry Volcanics near Cowra, and similar occurrences in the Comerong Volcanics and Boyd Volcanic Complex in southeastern New South Wales. Biostratigraphic data suggest a late Middle Devonian (Givetian) age for the Merriganowry Shale Member of the Dulladerry Volcanics, which appears conformable beneath the Upper Devonian Hervey Group.     

Application of sequence stratigraphic concepts to the Upper Cretaceous Tununk Shale Member of the Mancos Shale Formation,south-central Utah: Parasequence styles in shelfal mudstone strata

Although sequence stratigraphic concepts have been applied extensively to coarse-grained siliciclastic deposits in nearshore environments, high-resolution sequence stratigraphic analysis has not been widely applied to mudstone-dominated sedimentary successions deposited in more distal hemipelagic to pelagic settings. To examine how sequence stratigraphic frameworks can be derived from the facies variability of mudstone-dominated successions, the Tununk Shale Member of the Mancos Shale Formation in south-central Utah (USA) was examined in detail through a combination of sedimentological, stratigraphic and petrographic methods. The Tununk Shale accumulated on a storm-dominated shelf during the second-order Greenhorn sea-level cycle. During this eustatic event, the depositional environment of the Tununk Shale shifted laterally from distal middle shelf to outer shelf, then from an outer shelf to an inner shelf environment. At least 49 parasequences can be identified within the Tununk Shale. Each parasequence shows a coarsening-upward trend via upward increases in silt and sand content, thickness and lateral continuity of laminae/beds, and abundance of storm-generated sedimentary structures. Variations in bioturbation styles within parasequences are complex, although abrupt changes in bioturbation intensity or diversity commonly occur across parasequence boundaries (i.e. flooding surfaces). Due to changes in depositional environments, dominant sediment supply and bioturbation characteristics, parasequence styles in the Tununk Shale show considerable variability. Based on parasequence stacking patterns, eleven system tracts, four depositional sequences and key sequence stratigraphic surfaces can be identified. The high-resolution sequence stratigraphic framework of the Tununk Shale reveals a hierarchy of stratal cyclicity. Application of sequence stratigraphic concepts to this thick mudstone-dominated succession provides important insights into the underlying causes of heterogeneity in these rocks over multiple thickness scales (millimetre-scale to metre-scale). The detailed sedimentological characterization of parasequences, system tracts and depositional sequences in the Tununk Shale provides conceptual approaches that can aid the development of high-resolution sequence stratigraphic frameworks in other ancient shelf mudstone successions.     

Radon hazards associated with outcrops of Ohio Shale in Ohio

The indoor (basement) radon concentrations and the uranium, organic carbon, and radon contents of samples from the underlying Ohio Shale (Upper Devonian) were investigated in six approximately 100 square kilometer areas of Ashtabula, Cuyahoga, Erie-Huron, Franklin, Pike, and Logan counties. The thickness and lithology of the sediment overburden above the Ohio Shale in these areas also was investigated.Results show that the amount of radon gas emanating from the Ohio Shale is a direct function of the uranium concentration in this geologic unit and that the uranium itself is ultimately controlled by the amount of organic matter. Uranium, organic matter (as measured by total organic carbon), and radon in the Ohio Shale outcrops all increase in a westward direction across Ohio. Similarly, the indoor radon concentration in houses increases from east to west across the state.Where the average thickness of the sediment overburden exceeds 27 m (Franklin and Logan counties), much of the radon in houses may be derived from Ohio Shale clasts in the glacial till. In other areas where the average overburden thickness is 6 m or less (Ashtabula, Cuyahoga, Erie-Huron, and Pike counties), the indoor radon levels appear to be directly controlled by emanations from the underlying Ohio Shale bedrock.     

Stratigraphical architecture at the muddy margin of the Cretaceous Western Interior Seaway, southern Utah

The Tropic Shale and correlative Tununk Shale Member of the Mancos Shale accumulated during Cenomanian-Turonian time, within prodeltaic environments near the western margin of the Western Interior Seaway of North America. Stratigraphical and sedimentological analysis has revealed a detailed history of relative sea level change in the thick, fine grained succession. The Tropic and Tununk shales were deposited during the Greenhorn second-order sea level cycle, over a time span of about 2–5 million years. In southern Utah, six depositional sequences are superposed upon the record of this long term sea level change. The sequences developed during third-order relative sea level cycles of hundreds of thousands of years duration and are composed of at least 37 parasequences, arranged in retrogradational, aggradational and progradational parasequence sets. The Tropic Shale and Tununk Shale Member accumulated just basinward of the axis of maximum subsidence of a foreland basin. Stratal geometries and facies distribution patterns in the succession indicate that in southern Utah the Greenhorn cycle was tectonically controlled. During the Greenhorn transgression and highstand, rapid rates of tectonic subsidence trapped terrigenous sediment to the west of the study area, in the more proximal foreland. At this time, hemipelagic facies accumulated at relatively slow rates in southern Utah and type 2 sequences developed during third-order sea level cycles. In contrast, during the Greenhorn regression rates of thrust-induced subsidence in the proximal foreland basin evidently slowed, and deltaic clinoforms prograded across the study area. At least one forced regression occurred in southern Utah at this time, and type 1 sequences developed. The formation of type 1 sequence boundaries in the upper part of the Tropic Shale and Tununk Shale Member points to episodes of base level fall and indicates that the six third-order sea level cycles recorded in the succession were not the result of changes in sediment supply alone. The third-order cycles may have been a consequence of episodic tectonism. The timing of these cycles, however, suggests that development of sequences and parasequences in the Tropic Shale and Tununk Shale Member may have been related to orbital forcing in the Milankovitch band. Glacioeustasy or climatically related fluctuations in the amount of groundwater stored on continents may explain these high frequency sea level changes.     

Reservoir Characteristics and Preservation Conditions of Longmaxi Shale in the Upper Yangtze Block, South China

The Upper Ordovician-Lower Silurian Longmaxi Shale in the Upper Yangtze block represents one of the most important shale gas plays in China. The shale composition, porosity, organic thermal maturity, and methane sorption were investigated at the Qilongcun section in the Dingshan area, southeastern Sichuan Basin. The results show that the Upper Ordovician-Lower Silurian Longmaxi Shale contains: (1) sapropelic I organic matter; (2) a 40-m thick bedded sequence where total organic carbon (TOC) content is > 2%; (3) a 30-m thick layer at the base of the Longmaxi Shale with a brittle mineral content higher than 50%; and (4) a mean methane adsorption capacity of 1.80 cm3/g (7 MPa pressure). A positive correlation between TOC and sorbed gas indicates that organic matter content exerts an important control on methane storage capacity. Based on the analysis of the shale reservoir characteristics, the lower member of the Longmaxi Shale can thus be considered a favorable stratum for shale gas exploration and exploitation. It has similar reservoir characteristics with the Longmaxi Shale in the Jiaoshiba area tested with a high-yield industrial gas flow. However, based on tectonic analysis, differences in the level of industrial gas flow between the low-yield study area and the high-yield Jiaoshiba area may result from different tectonic preservation conditions. Evidence from these studies indicates the shale gas potential of the Longmaxi Shale is constrained by the reservoir and preservation conditions.     

Fingerprinting Marcellus Shale waste products from Pb isotope and trace metal perspectives

Drill cuttings generated during unconventional natural gas extraction from the Marcellus Shale, Appalachian Basin, U.S.A., generally contain a very large component of organic-rich black shale because of extensive lateral drilling into this target unit. In this study, element concentrations and Pb isotope ratios obtained from leached drill cuttings spanning 600 m of stratigraphic section were used to assess the potential for short and long term environmental impacts from Marcellus Shale waste materials, in comparison with material from surrounding formations. Leachates of the units above, below and within the Marcellus Shale yielded Cl/Br ratios of 100–150, similar to produced water values. Leachates from oxidized and unoxidized drill cuttings from the Marcellus Shale contain distinct suites of elevated trace metal concentrations, including Cd, Cu, Mo, Ni, Sb, U, V and Zn. The most elevated Mo, Ni, Sb, U, and V concentrations are found in leachates from the lower portion of the Marcellus Shale, the section typically exploited for natural gas production. In addition, lower ²⁰⁷Pb/²⁰⁶Pb ratios within the lower Marcellus Shale (0.661–0.733) provide a distinctive fingerprint from formations above (0.822–0.846) and below (0.796–0.810), reflecting ²⁰⁶Pb produced as a result of in situ ²³⁸U decay within this organic rich black shale. Trace metal concentrations from the Marcellus Shale leachates are similar to total metal concentrations from other black shales. These metal concentrations can exceed screening levels recommended by the EPA, and thus have the potential to impact soil and water quality depending on cuttings disposal methods.     

Uranium mineralization in the Alum Shale Formation (Sweden): Evolution of a U-rich marine black shale from sedimentation to metamorphism

The Alum Shale Formation is a metal-rich black shale, deposited on the Baltoscandian platform between Middle Cambrian and Early Ordovician. These black shales may be of particular economic interest for their relatively high uranium content (100–300 ppm) and their wide distribution from Norway to Estonia. Scandinavian Alum Shale may thus constitute a great potential resource of uranium, as a low grade ore. The Alum Shale Formation is particularly interesting to study the mineralogical expression and content of uranium in series submitted to progressive burial and metamorphism. For this purpose, the behavior of U, P, Ti and organic matter was studied on a series of representative samples from most Alum Shale prospection zones. In southern Sweden, where Alum Shale underwent fairly shallow burial, uranium concentrations have no mineralogical expression except a rather high U content of biogenic phosphates. Calcite concretions (beefs) and fractures recorded the migration of hot overpressured hydrocarbons and brines from thermally mature areas to immature Alum Shale. However, thermal maturation and fluid migration did not allow remobilization of uranium and metals. At the opposite, in northern Sweden, where the series were folded, duplicated and submitted to low grade Greenschist metamorphism during Caledonian orogeny, phospho-silicates U-Si-Ca-P (±Ti ±Zr ±Y) and minor amounts of uraninite are identified and indicate that U, P, and Ti were mobile and precipitated as new phases. The effect of metamorphism is therefore important to consider as the leachability of U, especially during (bio)-hydrometallurgical processes, which will be by far different between the two considered areas.     

New U-Pb ages of zircons in the Owk Shale (Kurnool Group) with reflections on proterozoic porcellanites in India

Felsic tuff beds with some presumed sedimentary components were reported from the Owk Shale (Kurnool Group; bearing Neoproterozoic fossils) in the upper part of the sedimentary succession in the Cuddapah basin in India by Saha and Tripathy (2012a). Our optical and SEM petrographic study of three thin sections, however, indicates that the parent samples are sandy mudstones with variable amounts of a felsic volcaniclastic component. New highquality U-Pb (SHRIMP and LA-MC-ICPMS) ages of 133 detrital zircon grains from a sample show that one grain is ca. 1880 Ma, one grain is ca. 3300 Ma, and the ages of the remaining 131 grains fall between 2690 Ma and 2429 Ma, the population averaging 2522 ± 36 Ma. The data indicate that the zircons are detrital grains derived from the ca. 2.5 Ga granitic/gneissic/greenstone basement of the Dharwar cratons that also host minor older Archean enclaves. The single 1880 Ma grain could have come from a ca. 1.9 Ga LIP. In the absence of any younger magmatic zircon, the absolute age of the Owk Shale remains elusive.     

全球早、中寒武世藻类生物地理分区初探

澄江生物群、凯里生物群、加拿大布尔吉斯生物群和西伯利亚藻群中均有丰富的藻类化石。根据前寒武纪宏观藻类的分布以及凯里生物群和布尔吉斯页岩生物群中藻类和后生动物的相似性，讨论了前寒武纪至中寒武世期间生物地理分区的控制因素。对几个生物群中的藻类化石和后生动物化石的对比研究发现,在相近的纬度范围内, 动植物化石组合特征非常相似; 而纬度明显差异时, 藻类生物群及后生动物群也具有明显的差异。由于后生生物在前寒武纪至中寒武世期间具有低的演化程度和分异能力，因此生物地理分布的主要控制因素是古纬度。而Schopf (1976)的生物地理分区模式不适合这一时期的生物地理分区。结合前寒武纪至中寒武世后生生物化石的分布情况，建立了前寒武纪-中寒武世时期的生物地理分区模式。这个模式较好地解释了分布在北美大陆和华南大陆上的寒武纪生物群相似的原因。     

Correlation of Upper Cretaceous strata from Lima Peaks area to Madison Range, southwestern Montana and southeastern Idaho, USA

An⁴⁰Ar/³⁹Ar age of 85.81 Ma±0.22 my was obtained on sanidine from a volcanic procellanite bed near the top of the 2135+m-thick Upper Cretaceous Frontier Formation in the Lima Peaks area of southwestern Montana. This early Santonian age, combined with previously determined age data including a palynological age of Cenomanian for the lower Frontier at Lima Peaks, and a U-Pb isotopic date of about 95 Ma for the base of the Frontier Formation in the eastern Pioneer Mountains north of the Lima Peaks area, provides an age range for the nonmarine formation. In the Madison Range, farther east in southweastern Montana, this age range corresponds to marine strata of not only the Frontier Formation, but also the overlying Cody Shale and Telegraph Creek Formation, a sequence that totals less than 760 m thick.The Upper Cretaceous marine formations of the madison Range are closely zoned by molluscan faunas that are well constrained with radiometric dates. The⁴⁰Ar/³⁹Ar age of 85.81 Ma±0.22 my at Lima Peaks is bracketed by radiometric dates for theScaphites depressus—Protexanites bourgeoisianusbiozone and the overlyingClioscaphites saxitonianus—Inoceramus undulatopilcatusbiozone of the Western Interior. Fossils of both of these biozones are present in the Cody Shale and the Telegraph Creek Formation in the Madison Range. The Telegraph Creek contains two units of volcanic ash that are approximate time equivalents of the volcanic procellanite of the Lima Peaks area. Clasts in the conglomerate of the upper part of the Frontier in the Lima Peaks area were shed during the initial stages of uplift of the Blacktail-Snowcrest Highlands which rose to the north. The dated porcellanite lies above the conglomerates and indicates that the uplift was initiated by middle or late Coniacian, 87–88 Ma.     

Comparison of organic geochemistry and metal enrichment in two black shales: Cambrian Alum Shale of Sweden and Devonian Chattanooga Shale of United States

In most black shales, such as the Chattanooga Shale and related shales of the eastern interior United States, increased metal and metalloid contents are generally related to increased organic carbon content, decreased sedimentation rate, organic matter type, or position in the basin. In areas where the stratigraphic equivalents of the Chattanooga Shale are deeply buried and and the organic material is thermally mature, metal contents are essentially the same as in unheated areas and correlate with organic C or S contents. This paradigm does not hold for the Cambrian Alum Shale Formation of Sweden where increased metal content does not necessarily correlate with organic matter content nor is metal enrichment necessarily related to land derived humic material because this organic matter is all of marine source. In southcentral Sweden the elements U, Mo, V, Ni, Zn, Cd and Pb are all enriched relative to average black shales but only U and Mo correlate to organic matter content. Tectonically disturbed and metamorphosed allochthonous samples of Alum Shale on the Caledonian front in western Sweden have even higher amounts for some metals (V, Ni, Zn and Ba) relative to the autochthonous shales in this area and those in southern Sweden.     

An ancient submarine canyon in the Oligocene-Miocene of the western Niger Delta

ABSTRACT
An anomalous sequence of thick fossiliferous marine shale of late Oligocene-early Miocene age, here termed the Opuama Shale Member, occurs within the paralic Agbada Formation in the subsurface of the western Niger Delta. The Opuama Shale fills a deep palaeochannel which was cut into Eocene-early Oligocene paralic beds. Planktonic and benthic foraminifera suggest that deposition in the channel began in the late Oligocene-early Miocene at outer shelf-slope depths, and that by the late early Miocene the channel had filled to shallow neritic depths. The channel, which is believed to be of submarine origin, is termed the Opuama canyon. The Opuama canyon originated during the pronounced early-Middle Oligocene drop in sea-level, and was cut by turbidity currents. It was filled, during the major late Oligocene-early Miocene rise of sea-level.
The location of the Opuama canyon in the western re-entrant of the Niger Delta supports Burke's (1972) conclusion that the western and eastern (where ancient submarine canyon fills are known) re-entrants of the delta are potential sites for ancient submarine canyons. Burke based his conclusion on the observation that the eastern and western re-entrants of the modern delta are areas where opposing longshore drifts converge and generate turbidity currents which cut submarine canyons.