Shaly Facies Research Articles

Mineralogic Characterization and Petroleum Potential of Clays (Shales) of the N’Kappa Formation (Paléocene-Eocene) in the Douala Sedimentary Sub-basin (South-West Cameroon)

The aim of this research work was to report a facies analysis of the N’Kappa formation, identified the clay minerals present in those facies and evaluate their oil potential. For that to be done, Lithostratigraphic descriptions were performed on three natural outcrops chosen in three different localities of the northern border of Douala sedimentary basin. Ten shaly samples were then collected on those outcrops and submit to X ray diffraction and Rock-Eval pyrolysis. Lithologically, the N’Kappa formation is made up of dark to grey shales and fine to coarse sandtones. The mineralogic content of the shales is made up of Kaolinite, dickite, low quartz and vaterite. Those shaly facies present high amount of immature organic matter (average TOC content around 2%). The petroleum potential is fair to poor (average S2 for all the samples around 3.33 mg HC/g of rock) though some samples (M1 and M2) presenting a good petroleum potential up to 6.62 kg HC/t of rock and 6.44 kg HC/t of rock respectively. They have undergone a low degree of diagenesis (early to burying diagenesis). This is evidenced by the predominance of kaolinite and dickite, low quartz and vaterite which are minerals stable at low temperature.

Thermal maturity of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Range, Northern Iran) based on organic petrography, geochemistry and basin modelling: implications for source rock evaluation and petroleum exploration

AbstractOrganic petrography and geochemical analyses have been carried out on shales, carbonaceous shales and coals of the Shemshak Group (Upper Triassic–Middle Jurassic) from 15 localities along the Alborz Range of Northern Iran. Thermal maturity of organic matter (OM) has been investigated using vitrinite reflectance, Rock-Eval pyrolysis and elemental analysis of kerogen. Reflectance of autochthonous vitrinite varies from 0.6 to 2.2% indicating thermally early-mature to over-mature OM in the Shemshak Group, in agreement with other maturity parameters used. The shales of the Shemshak Group are characterized by poor to high residual organic carbon contents (0.13 to 5.84%) and the presence of hydrogen-depleted OM, predominantly as a consequence of oxidation of OM at the time of deposition and the hydrogen loss during petroleum generation. According to light-reflected microscopy results, vitrinite/vitrinite-like macerals are dominant in the kerogen concentrates from the shaly facies. The coals and carbonaceous shales of the Shemshak Group show a wide range in organic carbon concentration (3.5 to 88.6%) and composition (inertinite- and vitrinite-rich types), and thereby different petroleum potentials. Thermal modelling results suggest that low to moderate palaeo-heat flow, ranging from 47 to 79 mW m−2 (57 mW m−2 on average), affected the Central-Eastern Alborz basin during Tertiary time, the time of maximum burial of the Shemshak Group. The maximum temperature that induced OM maturation of the Shemshak Group seems to be related to its deep burial rather than to a very strong heat flow related to an uppermost Triassic–Liassic rifting. The interval of petroleum generation in the most deeply buried part of the Shemshak Group (i.e. Tazareh section) corresponds to Middle Jurassic–Early Cretaceous times. Exhumation of the Alborz Range during Late Neogene time, especially along the axis of the Central-Eastern Alborz, where maximum vitrinite reflectance values are recorded, probably destroyed possible petroleum accumulations. However, on the northern flank of the Central-Eastern Alborz, preservation of petroleum accumulations may be expected. The northern part of the basin therefore seems the best target for petroleum exploration.

Designation Of The Standard Stratotype And Age Of Nsukka Formation Of Anambra Basin, Southeastern Nigeria

The type locality of Nsukka Formation was designated north of Nsukka in an area along Nadu River, without any formal description of the type section. Field mapping of the type locality was undertaken with the intention to formally define the type section. The thickest and best exposed is a 40 meter thick, stream section at Ugwu Nkalagu-Obukpa, designated the unit stratotype, and complemented by the road section at Umulolo near Okigwe as the hypostratotype. The unit stratotype contains coal towards the base and falls within the lower shaly facies of the formation. The hypostratotype belongs to the top facies without coal, having at the base ca. 0.8 m thick coquina sandstone. The palynomorphs of the type section indicate paralic sedimentation while at the complementary section marine conditions prevailed and continued across the K/T boundary into the Paleocene. The formation dates Late Maastrichtian at the type section and Paleocene (Danian) at the hypostratotype where a sharp boundary with overlying Imo Formation. Journal of Mining and Geology Vol. 43 (2) 2007: pp. 147-166

Depositional environments and characterisation of the organic matter of the Lower Mundeck Formation (Barremian ?–Aptian) of the Kribi-Campo sub-basin (South Cameroon): Implications for petroleum exploration

Lacustrine and alluvial fan facies from the Lower Mundeck Formation (Barremian ?–Aptian) cropping out in the southern part of the Kribi-Campo sub-basin (Cameroon) have been characterised for their oil potential, using both Rock-Eval pyrolysis and palynofacies analyses. The shaly facies show good potential as oil-prone source rock, with TOC content around 4.4% and some intervals with an optimum potential to yield 45 kg hydrocarbons/t of rock. Along the studied outcrops, these organic-rich facies represent approximately a third of the total thickness. Although the studied samples come out from immature thin organic-rich beds within sand dominated beds, it is reasonable to think that these oil-prone facies increase in thickness and maturity in the offshore area, making this part of the southern margin of Cameroon of special interest for petroleum exploration.

<b>Comparison of authigenic minerals in sandstones and interbedded mudstones, siltstones and shales, East Berlin formation, Hartford Basin, USA</b>

The East Berlin formation consists mainly of alternating sequences of fluviatile, lacustrine and playa sediments. Diagenetic sequences reconstruction revealed the same range of authigenic minerals in the studied sandstones and the interbedded fine-grained sediments (mudstones and siltstones). This indicates that the diagenetic processes that took place in the sandy facies also took place in fine-grained sediments. Mechanically infiltrated clays, grain-coating clay/hematite, quartz and feldspar overgrowths, carbonate cements and pore-filling and pore-lining clay minerals that precipitated in the sandy facies also precipitated in the fine-grained sediments. The abundance of authigenic minerals in decreasing order include: sandstone > siltstone > mudstone > shale. Except minor amounts of authigenic illite-smectite and illite, the shaly facies dominated by detrital clay, carbonate, quartz and feldspars framework grains. Authigenic minerals such as quartz, albite and K-feldspar are absent in the shaly facies, possibly related to early destruction of porosity. The lacustrine sandstones, siltstones and mudstones followed marine diagenetic trend, whereas playa and fluviatile sandstones, siltstones and mudstones followed red bed diagenetic trend. Mechanically compacted mudstones, siltstones and shales expelled large volume of mineralized pore water, which might migrated into the sandstone-rich section. Part of the ions for the precipitation of quartz overgrowths and carbonate cements in the sandy facies possibly contributed from the interbedded siltstones, mudstones and shales facies. KEY WORDS: Authigenic minerals, Mudstone, Sandstone, Siltstone, East Berlin formation, Hartford Basin Bull. Chem. Soc. Ethiop. 2007, 21(1), 39-61.

Ventilation experiment in the Mont Terri underground laboratory

The required ventilation of the underground drifts during the construction and operational phases of a radioactive waste repository could give rise to a process of desaturation of the rock around the drifts, changing its hydraulic and thermal properties. This change of rock properties may have an impact on the design of the repositories (drift spacing and repository size), which depends on the thermal load that the clay barrier and the rock can accept. The ventilation experiment (VE) has been carried out at the Mont Terri underground laboratory (Switzerland). Its main objective was to evaluate ”in situ” and better understand the desaturation process of a consolidated clay formation, when subjected to a flow of dry air during several months. The experiment has been performed in a 10 m long section of a non-lined horizontal microtunnel (diameter = 1.3 m), excavated in 1999 in the shaly facies of the Opalinus clay. In the Summer of 2002 (3.4 years after the microtunnel excavation), the test section was sealed-off, and monitored with a total of 86 sensors (rock water potential, water content, temperature and displacement, and condition of the air in the test section). Specifically, in a rock thickness of approximately 2 m, 24 piezometers, 32 hygrometers, 8 extensometers and 5 electrode chains (geoelectrical survey) were installed. The ventilation equipment generates a flow of air ( Q in) with specified values of the relative humidity (RH in) and temperature ( T in), which is sent to one of the ends of the test section through an inflow pipe, and then evacuated with an outflow pipe in the other end. Values of Q out, RH out and T out are also measured in the outflow pipe. The desaturation period ( Q in = 30 m 3/h) began in July 2003, with a phase (≈2 months) where RH in was set equal to 30% and another one (≈5 months) with air inflow almost dry (RH in = 1–3%). After this desaturation period, the test was finished with a 3-months resaturation period (target Q in = 20 m 3/h and RH in ≈ 100%). The most important general conclusion obtained from this experiment, from the rock monitoring data and also from the modelling results, is the following: it can be reasonably predicted that, under real repository ventilation conditions (relative humidity of the air much higher than in the desaturation period of the VE test), the desaturation of clayey rocks of low hydraulic conductivity ( K < 10 −12 m/s) will not be a relevant issue. The thermal and hydraulic rock bulk characteristics will not be practically affected by the ventilation, except in a narrow ring around the wall of the galleries (thickness less than 30 cm), where the rock degree of saturation can be lower than 95%.

Gas Threshold Pressure Test Performed at the Mont Terri Rock Laboratory (Switzerland): Experimental Data and Data Analysis

Migration of gases in argillaceous formations increasingly attracts theattention of various geoscientific disciplines for purposes like CO2 sequestration, gas storage in geological formations and disposal of hazardous wastes. Quantitative assessment of gas transport in such ultra-low permeability formations requires information on gas transport properties of the argillaceous formation. A series of hydro- and gas tests in boreholes was performed at the Mont Terri Rock Laboratory in Switzerland to investigate gas transport in the Opalinus Clay, an indurated clay formation of Jurassic age. This paper presents the results of a comprehensive test campaign in the shaly facies of the Opalinus Clay, comprising a hydrotest with water injections followed by pressure recovery sequences and an extended gas threshold pressure test. A detailed interpretation of both the hydraulic and gas test sequences was conducted using numerical simulations for the data analysis (software TOUGH2/iTOUGH2). In contrast to former test analyses, the sequential interpretation of the hydro- and gas test sequences provided a consistent set of single-phase hydraulic parameters and two-phase flow parameters. The use of independent information from laboratory testing (porosity, capillary pressure curves) constrained distinctly the inverse problem of parameter fitting. Discrimination between different parametric models of the relative permeability was impaired by inherent limitations of the field data due to non-ideal test conditions. Nevertheless, a classical two-phase flow type capillary pressure - relative permeability relationship based on the Van Genuchten - Mualem approach was found to be valid. A supplementary design study was conducted to optimise the test procedures to better distinguish between relative permeability models. It is shown that long term (>1 year) injection tests are more adequate to constrain the models. This finding is important for the design of future gas threshold pressure tests in indurated clays.

Hydrothermal dolomitization in the Lower Silurian Sayabec Formation in northern Gaspé – Matapédia (Québec): constraint on timing of porosity and regional significance for hydrocarbon reservoirs

Abstract The study of dolostone of the Lower Silurian Sayabec Formation of the Lac Matapédia syncline, at the western end of the Gaspé Peninsula, sheds new light on porosity development and reservoir potential of the area. The dolomitized section is close to the Shickshock Sud Fault that cuts the southern limb of the syncline. The dolostone occurs either as a highly brecciated unit or as stratiform replacement of peritidal carbonates at the base of the formation. Residual bitumen is seen in the breccia as well as filling of small secondary vugs and fractures within the stratiform dolostone. The dolostone consists predominantly of replacive matrix dolomite; petrography and oxygen and carbon stable isotope ratios (δ18OVPDB = −6.3 to −7.8‰ and δ13CVPDB = 1.2 to 3.3‰) of the matrix dolomite indicate early burial formation with later recrystallization in the presence of high temperature fluids. Saddle dolomite is found as a pore-filling cement in secondary dissolution pores and fractures. Oxygen stable isotope ratios of the saddle dolomite cement (δ18OVPDB = −14.5 and −15.3‰) indicate precipitation at high temperature. Dull luminescent burial calcite cement follows saddle dolomite. Later dissolution is locally apparent in carbonates as scalloped surfaces covered by finely laminated, bright-very dull luminescent calcites. Petrography and stable isotope ratios of the calcite (δ18OVPDB = −10.1 and −11.2‰ and δ13CVPDB = −2.3 and −6.9‰) suggest precipitation from meteoric waters. Meteoric dissolution and luminescent-zoned calcite cements are related to a Pridolian sea level lowstand. This event provides a first age constraint on the timing of the hydrothermal dolomitization and hydrocarbon charge of the Sayabec Formation along the northern edge of the Gaspé Belt. The Shickshock Sud Fault channelled the hydrothermal fluids, which dolomitized the Sayabec Formation shortly after initial burial. A recent regional seismic program showed compressive structures (duplexes, backthrust, triangle zone) in the Sayabec Formation inferred to have occurred in latest Silurian–Early Devonian that generated structural traps superimposed on the stratigraphic (shaly facies) and diagenetic (tight non-dolomitized limestone) seals. Seismic anomalies (“flat spots”) in the Lower Silurian section in eastern Quebec suggest the presence of hydrocarbon-filled reservoirs.

Bakken and Other Devonian-Mississippian Petroleum Source Rocks, Northern Rocky Mountains-Williston Basin: Depositional and Burial History and Maturity Estimations: ABSTRACT

ABSTRACT The three member Devonian/Mississippian Bakken-Exshaw organic-rich shaly facies is widely distributed in the northern United States and southern Canadian Cordillera. Equivalent facies are also present as far south as Utah and Nevada. Paleogeographically, these rocks thin marked­ly or pinch out to the west approximately along the Devonian-Mississippian carbonate reef/mound belt of the Cordilleran shelf margin. Although these rocks reach maximum organ­ic richness approximately at the Devonian-Mississippian transition, similar but somewhat less organic-rich Bakken-like beds are also present in underlying Upper Devonian and overlying Lower Carboniferous carbonate depositional cycles. At least ten cycles are identified in the underlying Devonian carbonate units, characterized by basal organic-rich Bakken-like shale or shaly carbonate that grades upward into carbonate mound or reefal beds, overlain by evaporite or solution breccia. Cycles in the overlying Madison Group (Lodgepole/Mission Canyon for­mations), as many as 10 to 12 in number, are similar except that the carbonates are composed of algal-oolith, crinoid, or mixed skeletal beds. End-cycle evaporitic units are less prevalent in the lower cycles in the Williston Basin and are absent in north-central and western Montana. The organic-rich Devonian-Mississippian Bakken-Exshaw shales are the most important source of hydrocarbons in Montana and the Williston Basin.

Experiences With Waterflooding Lloydminster Heavy-Oil Reservoirs

Summary This paper compares observed and theoretical behavior of waterflood performance in heavy-oil reservoirs in the Lloydminster area of western Canada. Lack of reliable primary production history makes determination of primary recovery difficult and consequently makes additional oil recovery by waterflood difficult to quantify. Comparison of predicted and actual performance indicates that the floods ar-e behaving as well as, if not better than, expected. Extra oil recovery by waterflood is not expected to add to the primary recovery of 3 to 8% by more than 1 to 2% of original oil in place (OOIP). Introduction The heavy-oil sands of the Lloydminster area (Fig. 1) are the southern extension of the trend of Lower Cretaceous bitumen and heavy-oil deposits extending from Athabasca through Cold Lake to Lloydminster. Unlike the first two areas, many of the Lloydminster reservoirs produce under primary recovery mechanisms. Total oil-in-place (OIP) estimates vary from 8 × 109 to 11 × 10(9) m3 (50 to 70 billion bbl). Husky Oil Operations Ltd. leases cover nearly 8 × 109 M2 (2 million acres) in this area along the Alberta/Saskatchewan border, with current oil production of about 4000 m'/d (25,000 B/D) from some 2.000 wells. Total oil production from the area is about 9500 m3/d (60,000 B/D). The heavy oil is found in the Mannville Group (Fig. 2) of Lower Cretaceous age, and the reservoirs are typically very fine- to fine-grained, clean, highly porous, uncon- solidated quartz sand bodies that grade laterally into silty or shaly facies or are truncated abruptly by channeling. Some 80 % of the OIP is found in sands less than 5 m (16 ft) thick. High crude viscosity, low solution GOR, and low initial reservoir pressures result in primary recovery efficiencies from 3 to 8% of OOIP. Waterflooding has been carried out in most of the major reservoirs since the mid-1960's, with initial expectations of doubling primary recovery. This paper summarizes the performance of Husky's main reservoirs and compares actual with predicted waterflood performance. These predictions have been facilitated greatly by recent extensive core and log data obtained from drilling numerous wells on close spacing for tertiary pilot projects. Reservoir Characteristics Fig. 3 shows the major oil pools in the area. Two fields, Wildmere and Wainwright, that have slightly higher gravity and less viscous crude have not been included in this analysis. Reservoir characteristics of the remaining heavy-oil pools are summarized in Table 1. Reservoir dips are extremely low (less than 1/2 @), and many reservoirs are underlain by bottom water, with the oil/water contact varying considerably in the same reservoir because of varying sand quality and oil gravity. Disparities of 4 m (13 ft) are common, and differences of up to 10 m (32 ft) have been observed. Most reservoirs are thought to have been at the bubble point, and many initial gas caps were found. Individual well completion rates range up to 25 m 3/d (80 B/D) oil but average about 7 m3/d (23 B/D). Newly drilled wells typically have a sand cut of 15 %, which decreases over a 6-month period and then stabilizes at 0 to 1 % during the life of the well. The high viscosity, sand production, and low GOR result in numerous production problems. These have required development and application of specialized completion techniques to ensure efficient and profitable operation. During the first 6-month production period, a large volume of sand usually is produced. A peak productivity commonly is obtained that is an order of magnitude larger than would be predicted from the radial flow semisteady-state calculation. JPT P. 1643^

Clay Mineral Studies of the Lower Permian Havensville Shale in Kansas and Oklahoma

AbstractAnalyses of samples of the Havensville Shale, collected from six localities in Kansas and northern Oklahoma, showed that the distribution of clay minerals and chemical variations in the clay minerals were related to changes in the sedimentary facies. The major clay minerals assemblages were: (1) illite, mixed-layer illite—montmorillonite, and regularly interstratified chlorite-vermiculite in the shaly facies of northern and central Kansas, (2) montmorillonite, illite and mixed-layer illite-montmorillonite in the calcareous shale and algal limestone facies of southern Kansas, and (3) kaolinite, illite and mixed-layer illite—montmorillonite in the sandy facies of northern Oklahoma. Differential settling and transportation of clay detritus were the major factors in the pattern of distribution of the clay minerals. Regional differences were noted in the abundance of 2m illite polymorphs, the K/Rb ratio and the illite 001/002 intensity ratio. Some structural variations and chemical differences among the clay minerals were consequences of modifications during deposition in different environments and diagenesis.

Distribution and Extent of Beds in Flysch Deposits, Ouachita Mountains, Arkansas and Oklahoma

ABSTRACT The areal extent and distribution of individual beds in flysch are a matter of vigorous debate. The writers studied these problems by detailed investigation of lithologic variations in a stratigraphic interval between two tuffs in the lower Stanley Group of the Ouachita Mountains. A few key beds were recognized and compared in four stratigraphic sections; most individual layers are too discontinuous to be correlated over the area of approximately 20 by 40 km. The theoretical horizontal extent of sandstone and siltstone beds calculated from changes in their total and individual thickness between sections is limited to 20 to 60 km toward the north and east. A general northward decrease in the number and thickness of sandstone beds, in the sandstone to shale ratio, and in grain size in addition to the distribution of internal sedimentary structures and extent of tuff beds in the area studied indicate a southern, lateral source of sediment. The flysch beds probably were deposited in the form of a large fan. In addition to this regional pattern the vertical variation of proximal sandy facies and distal shaly facies was observed in each section. It is suggested that the sandy facies with granule conglomerate laminae, ripped-up pieces of shale, and plant debris was deposited in or near submarine channels, whereas the shaly facies with burrowed siltstone beds originated in a more quiet environment between channels. The migration of channels on a submarine fan may have been one factor influencing the distribution of these facies.

The Succession and Correlation of Ostracode Faunas in the Silurian of Gotland

Abstract Palaeocope ostracode faunas in the Siluro-Devonian sequence of Gotland and the submarine Hoburg Bank area enable detailed correlations with ostracode faunas in other areas around the Baltic to be made, and at several levels the faunas extend into areas where graptolite datings are possible. The late Leintwardinian–early Downtonian interval can be correlated with the British sequence, and the Whitcliffian–late pre-Gedinnian interval with sequences in Nova Scotia and Maine. The Silurian of Gotland starts with an almost entirely submarine Llandoverian sequence of unknown completeness, ranging from low Llandoverian Beds with Stricklandia lens into the zone of Oktavites spiralis, partly above sea-level. The supramarine sequence extends some distance into the Whiteliffian, and the younger submarine sequence in the Central Baltic comprises Whiteliffian and Downtonian rocks. The youngest fauna treated is found in the Beyrichienkalk, with equivalents in the Kaugatuma-Ohesaare Beds of Ösel, in cores from the South Baltic area, and in the upper part of the type section of the Stonehouse Formation of Nova Scotia, not ranging above the bouceki-transgrediens interval in the graptolitic sequence or the eosteinhornensis zonc in the conodont sequence. The Beyrichienkalk represents the youngest pre-Gedinnian ostracode fauna known. The Siluro-Devonian series boundaries in the Gotland area are drawn as follows: (1) Llandoverian-Wenlockian tentatively at or very slightly above the base of the Upper Visby Beds. (2) Wenlockian-Ludlovian (between the ludensis and nilssoni zones) in an almost inaccessible interval of the lower Hemse-Klinteberg Beds in the current stratigraphy. (3) Ludlovian-Downtonian at (or most inconsiderably below) the base of the sequence with Frostiella groenvalliana (F. lebiensis) and Londinia kiesowi (L. arisaigensis) on Ösel, in the Central Baltic, Pomerania, Scania, the Welsh Borderland, and Nova Scotia. The general facies trends in the supramarine Silurian of Gotland are along the SW-NE strike of the units as exposed in the present topography, with shaly facies dominating in the SW part of the island and at the sea-floor SW of the Karlsö Shelf and Hoburgen; subsurface tests are necessary to establish the relations between exposure trends and palaeogeographical trends. Surface evidence sufficiently disproves the existence of three major, successive barrier reefs along present strike, with SW-NE striking talus and lagoonal zones as suggested by Jux 1957. The reefs in his Folgen are of considerably different ages and do not display the size and longitudinal arrangement necessary for the barriers as constructed.

Quantitative paleoecologic analysis of ewekoro and oshosun formations of Western Nigeria

Abstract The problem of proving the genetic difference between the Ewekoro Formation in its shaly facies, and the Oshosun Formation, a shale, has been attacked by means of a multivariate statistical analysis of data on major chemical constituents of the rocks. It has been possible to demonstrate that the chemical constituents of the formations display a fundamentally different pattern of variation, particularly with respect to the elements P, Si, and Al. The data are analysed by the multivariate procedures of principal component analysis and factor analysis.

Organic Materials of Early Middle Devonian, Mt. Union Area, Pennsylvania

The name Newton Hamilton formation is here applied to the widespread shaly facies of the Onondaga group in central Pennsylvania. The formation is divisible into two members: the Hares Valley dark gray shale and limestone member, above, a new name; and the Beaverdam Run dark gray shale, below, a name modified from the usage of Willard. The bituminous materials of the Devonian shales in the Mt. Union area range from .002 to .24 per cent of the rock, with the Marcellus black shale containing the largest quantities. The bitumens, on separation by means of column chromatography, were found to contain fractions referable to saturated hydrocarbons, aromatic hydrocarbons, asphaltenes, and polar compounds. Experiments with gas chromatography of the bituminous materials suggest that most of the column chromatographic fractions consist of compounds having carbon numbers above 20. Upward from the Ridgeley sandstone to the Newton Hamilton, Marcellus, Mahantango, and Burket shales, the saturated hydrocarbons form an increasing percentage of the bitumens and of total hydrocarbons whereas the aromatic hydrocarbons decrease upward. This relation is believed to have a paleogeographic significance, resulting from the greater stagnation and poorer circulation of the Oriskany through Marcellus seas as compared with the Mahantango and Burket. A resume is given of some of the relations of the bitumens to the petrologic-environmental types (petrai); the nearshore petra and depressional sapropelic petra are relatively more favorable for hydrocarbon preservation than some of the other types. Free sulphur is found in many of the Newton Hamilton and Marcellus samples but is less common in the overlying Mahantango. The sulphur-bearing layers, also characterized by increased content of aromatic and tarry fractions, imply restricted poorly circulated seas under stillstand or regressive conditions during deposition of the Onondaga and Marcellus. Separation of a humic acid constituent having absorptive peaks at 264-272 mµ was made by sulphuric acid hydrolysis and paper chromatography. This material, believed to be a pyridine compound, ranges from .04 to 2 per cent of the Devonian rocks, with the greatest concentrations occurring in the Marcellus and Burket black shales.

STRATIGRAPHY AND STRUCTURE OF THE OAK HILL SUCCESSION IN VERMONT

North of the Winooski River, Vermont, the Oak Hill succession occupies the region between the eastern margin of the Champlain Lowland and the western foot of the Green Mountains. The lithologic units are traceable into southern Quebec, and some are traceable southward into west-central Vermont. Lower and middle Cambrian ages have been assigned to all units. The strata below the Gilman quartzite are tentatively correlated with the Mendon series in the Rutland-Brandon region. All units above the Gilman have stratigraphic equivalents in the adjoining Rosenberg succession. The earliest recorded differential downwarping of the local geosynclinal area immediately preceded the beginning of deposition of the Pinnacle sediments. The distribution of the shaly, sandy, and conglomeratic facies of the Pinnacle and West Sutton formations indicate a western source for the sediments and also that the sea was encroaching westward. The Gilman quartzite marks the first occurrence of reworked sands; reworked sediments formed practically all of the elastics sediments thereafter. A prominent anticlinorium occupies much of the southern part of the area. Northward it fades into a westward-dipping homocline. The western margin of the succession is formed in most places by a series of thrust faults, which may be continuous. The Oak Hill thrust, considered the western boundary of the succession in southern Quebec, has not been recognized in Vermont. The strata were strongly folded before thrusting; the thrusts are subsequent shear thrusts. Several klippen, related genetically to the thrusts, form prominent hills west of the western margin of the succession.

Stratigraphy of Lower Mississippian Rocks in Southwestern Missouri

Mississippian rocks in southwestern Missouri were studied in detail. Both lateral and vertical variations were studied and attempts were made to correlate with Mississippian rocks in northern Arkansas and northeastern Oklahoma. The basal Mississippian Sylamore sandstone is thin, locally developed and poorly exposed in southwestern Missouri. The Chattanooga shale occurs only in the extreme southern part of southwestern Missouri and there are no post-Chattanooga pre-Chouteau rocks. The Chouteau, Northview, and Sedalia formations are present in the northern part of the area studied but thin southward and are not present along the southern border of the state. It is recommended that the term Compton be dropped as a synonym of Chouteau. The Sedalia formation, as defined by Moore, is recognized as a valid formation, but it is Kinderhookian rather than Osagian in age. The lower two thirds of the Sedalia formation is a facies of the Northview formation. The upper non-cherty part of the Sedalia is much more extensive than the underlying part and overlaps the Northview formation over a wide area. The St. Joe and Reeds Spring limestones are present only in the southern part of southwestern Missouri and transgressively overlap northward. The St. Joe limestone is not typically developed in the Springfield area where it has been called the Pierson formation. The term Pierson should be dropped as a synonym of St. Joe. The Burlington limestone is divided into 6 faunal zones and they are correlated with equivalent zones in northeastern Missouri. The Burlington formation thins southwestward from Springfield and disappears from the section between Mt. Vernon, Lawrence County, and the Tri-State mining district. The Keokuk formation is present only in the western part of the area and is not present in the Springfield area. Keokuk limestone grades insensibly up into limestone of Warsaw age in the Tri-State mining district. None of the shaly facies that characterize the Warsaw in northeastern Missouri are developed in southwestern Missouri. Evidence is presented to prove that a part of the beds that have been referred to the St. Louis formation in western Dade County should be referred to the Keokuk.

VI - The British Silurian Rugose Corals with Acanthine Septa

This paper seeks to elucidate the phylogeny of those British Silurian Rugose Corals which have acanthine septa, i.e ., whose septa can be seen by the naked eye each to consist of a row of spines. Laboratory studies have been supported by field work, with the object of discovering the range of the species in time and space, and the conditions of life under which they lived ; and of determining whether the evolution of any character received impetus from a change in such conditions. It would appear that ancestors of that Rugose coral fauna which became dominant in the Wenlock, entered the British area in Llandovery times. The Streptelasmoid fauna characteristic of the Ordovician first shows intermixture with Wenlock forms at the top of the Lower Llandovery beds of Llandovery, where Calostylis occasionally occurs. In the Upper Llandovery the Calostylidae increase, and the Acanthocyclidae and primitive members of the Pycnactis-Phaulactis lineage appear. From Pycnaclis a large proportion of the Wenlock and Ludlow Rugose corals descended. Streptelasma seems to have died out at the top of the Wenlock. In the shaly facies of the British Wenlock-Ludlow, a characteristic fauna of Pycnactis mitrata, Syringaxon siluriensis, Acanthocyclus spp. and Spongophylloides spp. slowly evolved. When more calcareous conditions appeared, this was enriched by new forms. With the reef facies of the Wenlock limestone, a large number of new species appeared. The British area is a most interesting, though not the most useful, area for the study of the evolution of the Silurian Rugose corals, for here reef conditions were confined to the top of the Wenlock. It has to be decided which new forms evolved from species already present in the area, and which came in from other areas with the reef conditions. Such migrations can only be proved by reference to Scandinavia and N. America, where reef conditions occurred throughout the Silurian. In the present study such migrations cannot be taken into account, because field work has so far been confined to the British area.

Two Genera of Carboniferous Echinoidea ( Lepidocidaris and Hyattechinus ) new to Britain

Introduction The remains of echinoids occur at almost every horizon of crinoidal limestone in the Lower Carboniferous rocks of Britain; but they consist usually of isolated plates and radioles. Archæocidaris, Palœechinus, Perischodomus , and Lovenechinus must have thrived in our Carboniferous seas, and Melonechinus was by no means rare. But the conditions of deposition of the limestones, together with the collapsible nature of the tests, almost always resulted in disintegration and scattering of the remains. Only in the shaly facies of the Lower Carboniferous was the water sufficiently still, and sedimentation adequately rapid, to leave the component parts of echinoid tests in their natural association. Such conditions occurred in the Fifeshire area, where Mr. J. Wright has found fairly complete examples of the excessively fragile Lepidesthes together with great quantities of almost perfect crinoids. They also prevailed in the Bolland district of Lancashire, where Clitheroe has long been famed for its yield of crinoids, blastoids, and echinoids. A similar shaly development characterizes the “Lower Limestone Shales” and immediately succeeding strata at the base of the Carboniferous Limestone in South Wales. In this paper I am able to record an extraordinary find of echinoid tests at that horizon in Pembrokeshire. Perhaps the “Marbre noir de Dinant” may be cited as a neighbouring illustration of an argillaceous Carboniferous Limestone noteworthy for the wealth and preservation of its echinoid fauna. The abundance of echinoid fragments in the purer and more massive limestones shows that the sea-urchins lived quite as1 freely in the open water

XXXI.—The British and Belgian Carboniferous Bellerophontidæ

Bellerophontidæ occur in considerable numbers at certain horizons in the Scottish Carboniferous rocks. Many forms are represented, but few have been described or figured (see Historical Account, Section III). In undertaking the study of these fossils the writer's object was limited, primarily, to figuring and describing the Scottish forms and ascertaining their value as stratigraphical indices in the Scottish Carboniferous rocks. Many forms from the shaly facies have been recorded in Scottish stratigraphical literature under the names of English and Belgian species of limestone facies. Investigation proved that most of these records were invalid, the determinations being erroneous, and that revision of all the Anglo-Belgian Bellerophontidæ was necessary in order to define the Scottish forms. The present memoir embodies the results of the wider investigation.