Black Shale Formation Research Articles

Palaeontological and geochemical characteristics of Silurian black shale formations from the Central Brittany Domain of the Armorican Massif (northwest France)

Within the Armorican Massif, as well as throughout the major part of the Gondwanan northern margin, Llandovery to Ludlow deposits are mainly represented by black shales with subordinate sandy beds. In Brittany, these euxinic Silurian facies lie more or less conformably on Late Ordovician deposits. However, based on graptolite evidence, a stratigraphical break corresponding to part or whole of the Llandovery is noticed. The Silurian black shales of Brittany are devoid of benthic fauna, while pelagic or epipelagic elements are very common. These euxinic lithofacies are characterized by peculiar geochemical compositions which are discussed in terms of their stratigraphical and geographical distribution. Significant enrichment of Sr, Y, Rb, Cr and Ni, higher concentrations of V (up to 5600 ppm) and greater volatile contents are particularly apparent in contrast with other terrigenous deposits from Brittany. A model for the sedimentary environment of the Silurian black shales of the Armorican Massif is proposed: the transgression induces the individualisation of basins partially separated from the open ocean in which the water column is stratified; then the stratification disappears progressively during Ludlow times.

Zeitliche Klassifikation von Sedimentationsprozessen bei der Schwarzschiefer-Bildung

Zeitliche Klassifikation von Sedimentationsprozessen bei der Schwarzschiefer-Bildung

Violent volcanism, stagnant oceans and some inferences regarding petroleum, strata-bound ores and mass extinctions

Past changes from a well-mixed aerated ocean to a stratified stagnant ocean are indicated by decreasing δ 13C of limestone (opposite to prior conclusions) as well as by increasing δ 34S of marine sulfates. The proposed stagnant ocean model includes a warm CO 2-enriched atmosphere and a bathyal to abyssal marine system dominated by bacterial components in the food web and by consequent ‘light’ carbon in organic material and biogenic carbonates. Culminations of prolonged stagnant episodes correspond with marine faunal extinctions of Late Permian and Late Cretaceous time, and the protracted changes and correlations provide evidence against any hypothesis of mass extinction by sudden worldwide catastrophe, including the asteroid impact hypothesis. The Cretaceous stagnant ocean, taken as the prime example, is attributed to climatic warming triggered by volcanic CO 2 (greenhouse effect) and several feedbacks, including decreased Earth albedo and increased sinking of warm evaporite brines instead of aerated polar waters. Marine extinctions are attributed to upward expansion of the oxygen minimum zone and to catastrophic mixing of surface waters with poisonous sulfidic waters of the deeps. The stagnant ocean provided a counterbalance between deep reduction and shallow oxidation, conditions that favored maximal formation of black sulfidic shales, protopetroleum and sedimentary sulfide ores and shallow to mid-depth barite, phosphorite, iron ore, cherty iron formation, and sulfate-bearing red-beds. Trace elements concentrated in stagnant ocean sediments include chalcophile and Pt-group metals, negating claims that Ir provides a unique ‘fingerprint’ of meteorite impact and cosmic accretion.

DENISON TROUGH, QUEENSLAND – NEW SEISMIC INFORMATION AND ITS HYDROCARBON IMPLICATIONS

New data from a digital six-fold CDP seismic survey in the Permo-Triassic Denison Trough, Queensland by the Bureau of Mineral Resources in conjunction with the Geological Survey of Queensland are markedly better than the old. They improve the hydrocarbon prospects of the trough by showing (a) structures within the Reids Dome Beds which have clearly formed early in the history of the trough, including one with a probable flat spot, (b) pinchouts in the Reids Dome Beds and younger units, and (c) pronounced faulting which occurred at the commencement of Cattle Creek Formation deposition. Major thrusting is shown to have occurred on the Merivale Fault during Middle to Late Triassic, and a conjugate thrust fault is identified. Localised faulting of known gas fields is suspected. A reflection within the Black Alley Shale and lower Bandanna Formation interval showing angular discordance with the formation boundaries is thought to arise from a tuff band marking an isochronous surface; this establishes the direction of progradation of the upper Black Alley Shale and Bandanna Formation. The overall structure of the trough is considered to be less complex than previously thought. In the light of the much improved seismic data, a reassessment of hydrocarbon plays in the Denison Trough appears warranted.

A synthesis of organic petrographic and geochemical results from DSDP sites in the eastern central North Atlantic

A synthesis of organic analyses of deep sea drilling sites off Western Sahara, Morocco and Northern Iberia (Sites 397, 415/416 and 398) is attempted. Paleogeography and lithology are related to organic carbon contents, carbon normalized extract values, normal and branched/cyclic alkane distributions, odd/even carbon preference indices (CPI), pristane/phytane and sterane/triterpane relative abundances, hydrogen/carbon atomic ratios, stable carbon isotope compositions, and the kerogen type determined by microscopy. In the Tertiary at Site 397, allochthonous deposits orginally accumulated within a midwater oxygen minimum layer are contrasted with contiguous hemi-pelagic sediments. Higher and fluctuating organic carbon contents, bimodal n-alkane distributions, a dominance of steroidal hydrocarbons, and mixed terrestrial and aquatic liptinites in the former, and well rounded, fine vitrinite/inertinite-dominated kerogens in the latter characterize these 2 organofacies. Terrigenous organic matter dominates the Lower Cretaceous shales. The origin of these laminated (nonbioturbated) organic rich mudstones is ascribed to an oxygen deficit generated by the influx of major quantities of terrestrial plant debris from Wealden deltas and its subsequent (partial) oxidation. This oxygen deficit mechanism for black shale formations is identified by reinterpreting abnormally broad and multimodal vitrinite reflectance histograms as representing the remnants of oxidation. A ratio of altered to unaltered vitrinite particles at Site 398 is a measure of the degree of oxidation, and may be related to distance of transport or availability of oxygen during transport. Broad multimodal spreads in histograms of vitrinite reflectance values are the key character of this organofacies, though extract yields, H/C ratios and CPIs also seem to be influenced.

Novel Formation-Evaluation Concepts for Shale Reservoirs and Black Shale Formations: ABSTRACT

Highly radioactive, black and organic-rich shales are present in the United States, in several geologic provinces, and elsewhere. Such organic-rich shales are not only potential source rocks but commonly owe their localized but significant production potential to natural fracture systems in an otherwise impermeable rock. These natural fracture systems are concentrated in the interbedded brittle, calcareous, cherty or silty zones. Natural gamma-ray spectral information, such as that from the Spectralog, easily locates calcareous or silty zones, as both are characterized by low values of potassium and thorium, but excessively high values of uranium. These interpretive concepts have already assisted in many successful gas and oil well completion and recompletion attempts in the more permeable and/or fractured intervals of such shale formations. The Spectralog allows a continuous monitoring of the source rock potential (SRP) of shales in open and cased boreholes. Hence, SRP variations can be studied both versus depth and on a lateral basis using appropriate mapping techniques. Gamma-ray spectral data also assist in detailed stratigraphic correlations, for, in addition to total gamma-ray counts, the Spectralog measures the individual gamma rays emitted by potassium (K40), the uranium series nuclide bismuth (Bi214), and the thorium series nuclide thallium (T1208). Interpretive experiences with SRP, including SEM pore-system studies, in the Miocene Monterey Formation in California, the Cretaceous Niobrara and Pierre Shales of Colorado, the Lower Mississippian and Upper Devonian Woodford Shale of Oklahoma and West Texas, and the Eagle Ford Shale in the Cretaceous carbonate trend in south Texas indicate application potentials similar to those in the Devonian gas shales of the Appalachian basin. End_of_Article - Last_Page 1578------------

Use of scintillometer and gamma-ray logs for correlation and stratigraphy in homogeneous black shales: Summary

INTRODUCTION Widespread, thick, uniform black-shale units may defy all but the coarsest stratigraphic subdivision. The devonian and Mississippian black-shale formation such as the Ohio, New Albany, and Chattanooga Shales of the eastern and central United States are good examples. Exposures of these black organic-rich shale formations appear lithologically uniform except for a few interbeds of greenish-gray shale. These black shales make up as much as one-fourth of the Devonian sedimentary sequence in the Appalachian basin and are important sources of natural gas Avila, 1976). Yet, because most means of stratigraphic control are absent and paleontologic correlation is laboriously difficult in these shales, internal subdivision and correlation among Devonian-Mississippian black shales of some areas are wholly inadequate. In parts of Ohio, Indiana, and Tennessee, widespread bentonites or thick green-shale beds are present in the Devonian-Mississippian black-shale sequence, providing a basis for its subdivision (Campbell, 1946; Hass, 1956; Hoover, 1960; Conant and Swanson, 1961; Lineback, 1968, 1970). In eastern Kentucky (Fig. 1), however, similar marker beds are either very thin or absent. Thus, the Devonian-Mississippian black-shale sequence of eastern Kentucky has not been divided previously, because apparent homogenity impeded attempts to compare and correlate the sequence with subdivision in the better known black-shale sequences of adjacent states.

Progressive Low-Grade Metamorphism of a Black Shale Formation, Central Swiss Alps, with Special Reference to Pyrophyllite and Margarite Bearing Assemblages

The unmetamorphosed equivalents of the regionally metamorphosed clays and marls that make up the Alpine Liassic black shale formation consist of illite, irregular mixed-layer illite/montmorillonite, chlorite, kaolinite, quartz, calcite, and dolomite, with accessory feldspars and organic material. At higher grade, in the anchizonal slates, pyrophyllite is present and is thought to have formed at the expense of kaolinite; paragonite and a mixed-layer paragonite/muscovite presumably formed from the mixed-layer illite/montmorillonite. Anchimetamorphic illite is poorer in Fe and Mg than at the diagenetic stage, having lost these elements during the formation of chlorite. Detrital feldspar has disappeared. In epimetamorphic phyllites, chloritoid and margarite appear by the reactions pyrophyllite + chlorite = chloritoid + quartz + H2O and pyrophyllite + calcite ± paragonite = margarite + quartz + H2O + CO2, respectively. At the epi-mesozone transition, paragonite and chloritoid seem to become incompatible in the presence of carbonates and yield the following breakdown products: plagioclase, margarite, clinozoisite (and minor zoisite), and biotite. The maximum distribution of margarite is at the epizone-mesozone boundary; at higher metamorphic grade margarite is consumed by a continuous reaction producing plagioclase. Most of the observed assemblages in the anchi-and epizone can be treated in the two subsystems MgO (or FeO)-Na2O−CaO−Al2O3−(KAl3O5−SiO2−H2O−CO2). Chemographic analyses show that the variance of assemblages decreases with increasing metamorphic grade. Physical conditions are estimated from calibrated mineral reactions and other petrographic data. The composition of the fluid phase was low in XCO2 throughout the metamorphic profile, whereas XCH4 was very high, particularly in the anchizone where aH2O was probably as low as 0.2. P-T conditions along the metamorphic profile are 1–2 kb/200–300 °C in the anchizone (Glarus Alps), and 5 kb/500–550 °C at the epi-mesozone transition (Lukmanier area). Calculated geothermal gradients decrease from 50 °C/km in the anchimetamorphic Glarus Alps to 30 °C/km at the epi-mesozone transition of the Lukmanier area.

Cambrian–Silurian stratigraphy of Børglum Elv, Peary Land, eastern North Greenland

A sequence of Lower Palaeozoic carbonate and clastic rocks is described from Børglum Elv, Peary Land, eastem North Greenland, and briefly compared to Lower Palaeozoic sections elsewhere in Greenland and in Spitsbergen. Lower Cambrian clastic rocks of the Buen Formation are followed by dolomite of the Lower Cambrian Brønlund Fjord Formation (125 m). Succeeding dolomite and dolomitic limestone of the Wandel Valley Formation (320 m) of Early to Middle Ordovician age are overlain by limestone of the Børglum River Formation (430 m) of Middle to Late Ordovician age. Un-narned Early Silurian dolomite and limestone formations (150 m and 320 m respectively) are followed by an un.narned Middle Silurian black shale formation (c. 100 m) and at least 800 m of a late Middle Silurian and younger un-named flysch formation. Carbonate mounds, originating in the highest beds of the un-named Silurian limestone formation, occupy stratigraphic levels through the overlying black shale formation and into the flysch formation.

Preliminary studies on the recovery of oil from chattanooga shale

Three exploratory investigations have been performed to examine the recovery of oil from the Chattanooga black shale formation. Thermogravimetric data were analyzed to yield an average activation energy of 57.1 kcal mol −1 for the conversion process; positive deviations from a reaction order of 3.7 were observed suggesting the presence of autocatalytic effects at low conversion levels. Thermal chromatographic analysis indicated that the maximum organic product release occurred at approximately 435°C and resulted in an oil of relatively low distillation range. A packed bed of shale was retorted in the self-sustained combustion mode thus suggesting the feasibility of this mode for in situ oil recovery. Comparisons with oil shale from Colorado's Green River formation have been made throughout.

Geologic History of North-Central Siberia: ABSTRACT

The post-Archean history of north-central Siberia is essentially the reconstruction of the history of the North Asian craton in relation to the evolution of the surrounding mobile belts. The formation of the craton dates to the early Proterozoic (1,900 m.y. ago). It was bordered by the Olenek fold system on the east and in the west by geosynclinal belts, which completed their development through a succession of Baikalian, Caledonian, and Hercynian movements. The most ancient Archean rocks (charnokite) are exposed on the Anabar shield; the youngest rocks of the craton are represented by the Taimyr Kara gneisses. During the Proterozoic a sedimentary platform cover was deposited across the craton; this platform is broken into plates by troughs with eugeosynclinal formations (presumably-Grenville). The sedimentary cover rocks are unmetamorphosed-terrigenous and marine-carbonate deposits of Riphean age. Within the craton the Cambrian to Devonian is characterized by a platform regime. Troughs within the platform are filled with black shale and terrigenous-carbonate marine formations, including gypsiferous sequences. Mottled terrigenous and gypsiferous strata of a lagoonal facies and marine limestone and sandstone were deposited in the pericraton trough in Severnaya Zemlya. The Carboniferous to Triassic was marked by intensive movements of the Pacific orogenic cycle which also affected many areas outside of the geosynclinal belts. Pacific-cycle movements rejuvenated the craton structures and those of the Caledonian and Hercynian systems bordering it. The linear zones of arcogenesis and the associated parageosynclinal trough formed the Taimyr-Severnaya Zemlya fold system on the periphery of the craton. The Tunguska synclinorium and the Anabar anticlinorium formed in the center of the craton. In the eastern part of the region the area of activization joined the Verkhoyansk-Chukotsk geosyncline. The Tunguska synclinorium, the Taimyr trough, and the Verkhoyansk geosyncline formed a single system of troughs filled with continental coal-bearing, paralic coal-bearing, and marine terrigenous sediments, respectively. Plateau basalts also are present in the epicraton troughs; granitic magmatism is displayed in arcogenesis zones. The Jurassic to Paleogene was characterized by the return of a platform regime in former areas of activization. The basal layer of sedimentary cover becomes younger from west (Liassic) to east (Cenomanian) as the folding decreased. Terrigenous Mesozoic-Cenozoic marine and paralic formations filled isometric and linear troughs and swells. Two sedimentary basins representing the Kara and Laptev sea shelves formed on the platform basement during the Neogene-Quaternary stage. The structural framework of these basins differs; their formation is connected with the development of the Arctic Ocean basin. End_of_Article - Last_Page 2511------------

Turbidite cherts from northeast Devon

The succession above the Pilton Group (Famennian—Tournaisian) in northeast Devonshire consists of: (1) Basement Formation of cherty mudstones; (2) Chert Formation (Viséan), consisting of two facies, of which the northwestern consists almost entirely of radiolarian cherts, whilst the southeastern contains in addition some calcarenites; (3) Black Shale Formation (Namurian). The sedimentary structures in the Chert Formation are consistent with formation by turbidity currents flowing from east to west across a northwesterly inclined submarine slope, and gravity induced slumping and stratal flow down that slope.

Mineralogy, Geochemistry and Stratigraphy of the Besa River Shale, British Columbia

ABSTRACT The Besa River Formation is a black shale of Devono-Mississippian age which varies in thickness from less than 1,000 ft. to more than 7,000 ft. Results of X-ray diffraction and X-ray fluorescence studies are utilized to provide mineralogical and geochemical criteria for correlation within the formation and into equivalent shelf deposits to the east. The correlations presented indicate that the thin Besa River Shale sections of the Northern Rockies are fondothemic in character, and represent continuous deposition in deep water through a period extending from Givetian to Chesterian time. Thicker sections to the east and south represent the clinothem, and the undathem is represented by barrier reef complexes, blanket shelf carbonates and interbedded calcareous shales and limestones. Petrographic studies and relationship of mineral facies to basin topography suggest that the quartz fraction of the Besa River is largely of organic or chemical origin. The evidence suggests a southeasterly provenance for the clay minerals, and the difficulty in visualizing transport of these clays across the evaporite basins of southern Alberta and Saskatchewan leads to the suggestion that the clays were derived either from volcanic ash and moved to the shelf margins, or that they were generated within the basin from dilute solutions of their constituents. It is shown that depth of water is not a critical factor in the formation of the thin black radioactive shales of the Exshaw Formation and the Muskwa Member of the Horn River Formation. The position of these shales as the basal phase of a shale transgression across shelf carbonates is noted, and the hypothesis is advanced that resorption of shelf evaporites by the transgressing seas leads to density stratification which provides the physico-chemical environment required for the formation of this unique lithotype.

Kubiki Gas Field

In 1959, a new gas field was discoverd in the Kubiki district of south-western Niigata Prefecture. The Katamachi, Meiji, Kuroi and Asahi gas fields are included in this gas producing region. Ten exploration wells were drilled in this area between 1936 and 1941. Although all were abandaned because no oil was found, strong gas indications appeared in some of these wells. After gravity and seismic surveys, the first gas accumulation was found in the Meiji field in 1954 by the Teikoku Oil Company, and in 1959 extensive exploration activities were rewarded by discovery of the Katamachi and Kuroi gas fields.These gas fields are stracturally a domal anticline. The axis of the Katamachi and Kuroi structure lines off the coast, and extends along the coast line. The main gas reservoir is the sand lenses of the Teradomari black shale formation of the upper Miocene. The physical characteristics of these sands are variable, but a 100 millidarcy air permeability, a 30 percent porosity and a 40-65 percent interstitial water saturation can be regarded as average. The composition of the gas is 95 percent or more methane with very few heavy hydrocarbons. Recently, heavy oil was discovered within these gas reservoirs. The total gas reserve in the Kubiki region is estimated to be 4, 667 million cubic meters.

Yaizu Natural Gas Field

The Yaizu natural gas field, situated in the Pacific coast of central Japan, is small field with an area of less than 1km2.The total production of dry gas from 13 wells of 100-120 meters in depth, was 950, 000m3 in 1953.Gas reservoir, a gravel bed (G7) in the basal part of the youngest Quarternary deposits, covers a burried basaltic hill and has an elongated dome-shaped structure.Temperature gradient, chlorinity of water and gas-water ratio are high at the top of its structure. Moreover, strange to say, the annual production exceeds its estimated reserves. These phenomena are unusual in the Quarternary gas fields in this country. Therefore, the reservoir must be supplied incessantly with some amount of gas.The origin of supply is probably its underlying Miocene black shale formation which has an imbricated structure. But remarkable heat of the bottom has a different origin.

Characteristics of marine uranium-bearing sedimentary rocks

Many marine sedimentary black shale and phosphorite formations contain 0.01 to 0.02 percent uranium, and one, the alum shale of Sweden, contains as much as 0.5 percent. The published fact that uranium is already being recovered on a laboratory scale from Swedish deposits forcefully suggests that similar deposits in the United States and possibly many other countries may prove to be an important future source of uranium.The marine uranium-bearing black shales are rich in organic matter and sulfides and contain little or no carbonate. The best are found in relatively thin formations of pre-Mesozoic age. The nature of the uranium-bearing mineral or compound is not known. In contrast, nonmarine black shales, as a group, are not uraniferous.All marine phosphorites tested thus far are uraniferous and so too are the phosphatic nodules found in many marine black shales. With some exceptions, the uranium increases in a general way with increase in phosphate content and is believed to be in the phosphate mineral. Like the black shales, the phosphorite formations are characteristically thin; many are associated with unconformities or, in other words, periods during which little else in the way of sediment accumulated.Significant concentrations of uranium in marine sediments other than black shales and phosphorites are thus far known only in beach placer deposits and the gold-bearing conglomerates of the Witwatersrand district, South Africa.Uranium may be found in other types of marine sediments on further prospecting, but especially promising are the sediments rich in organic matter, phosphate, or both, found in relatively thin formations believed to be the entire depositional products of long periods of geologic time. Such formations are most characteristic of those areas where, at the time of deposition, the adjacent land masses were so stable and low that the influx of clastic materials was small; the basin of deposition was large or of such configuration that fine-grained sediments could accumulate; and chemical conditions in the seawater prevented deposition of large amounts of carbonate.

Geological Era of the So-called Black Shale Formation of Kubiki Oil Field

Geological Era of the So-called Black Shale Formation of Kubiki Oil Field

Sedimentation in Barred Basins, and Source Rocks of Oil

While the DOCTRINE OF UNIFORMITY must always form the basis of geological theory, it is necessary to admit that phenomena have occurred during geological time which have not been observed at all, or not in their entirety, during the very limited period of modern scientific investigation. Reasons are given for the belief that major coal measures, major primary salt deposits, major fresh-water series of sediments, and source rocks of oil deposits are not now being deposited anywhere on the earth. No continent-wide peneplanation of advanced maturity, comparable, for example, with the Middle Tertiary peneplanation of Australia, can be recognized at the present day. It is believed that the present is largely a period of orogeny rather than of peneplanation. It seems probable that periods of greatly enhanced humidity and of greatly enhanced aridity, and others of wide temperature fluctuations, have marked many eras in the geological past, and have left their impress on sediments formed during such eras. The present condition of the earth can not be assumed to be the only one in earth history. In cases where the characteristics of geological formations require explanations other than those afforded by the strict application of the Doctrine of Uniformity it is legitimate and necessary to invoke causes not now observed in operation, provided always that objective evidence, not conformable with conventional explanations, can be adduced. The close relationship between sediments and their has been emphasized by Twenhofel, and the fossil contents of such sediments generally but not always conform with this environment. The grade of this relationship under different circumstances is discussed in some detail. It is insisted that under normal conditions of deposition in any there should be preserved a BALANCED ASSEMBLAGE of fossil forms, including benthos, nekton, and plankton in suitable proportions. Any unbalance of assemblage indicates something abnormal in conditions of deposition, and demands explanation. The main thesis of this paper is an amplification of the Bar Theory of Ochsenius. It is suggested that, when all implications of this theory are considered, the possibility is indicated of existence in the geological past of of dimensions and characters entirely unrepresented at the present day. Reasons are given for associating barred basins chiefly with maturity of peneplanation. Climatic factors are considered and it is concluded that humidity favors development of lacustrine conditions, of coal, boghead, and oil shale; while aridity End_Page 1101------------------------------ controls formation of black shales, source rocks of oil, and ultimately salt deposit. Certain characteristics are common to all such deposits. The occurrence of unbalanced planktonic assemblages of fossils, generally erroneously interpreted as indicating pelagic conditions, is shown to be compatible with deposition in barred basins. Fineness of texture and lamination, blackness of shale deposits, high organic content, pyritization, and composition of oil-field waters are believed to be due to barred-basin and not to excessive depth of water. The suggestion is put forward, merely as a suggestion at this stage, that certain lithological characters and structural features may be genetically associated with such depositional environments. Amongst these may be mentioned concretionary structure cone-in-cone, barren argillaceous limestones, and organic siliceous cherts, particularly if dark in color. The relations of barred-basin deposits with the euxinic facies of van der Gracht, and the sargasso environment of Ruedemann are discussed. As possible examples of deposits of barred basins are cited the saline formations of New Mexico, Irwin River basin (Western Australia), shoestring sands of Kansas and Oklahoma, Cretaceous limestones of Venezuela, Yates pool (Texas), some of the formations of southern California, and black shale deposits of New York and elsewhere.

The Carbonaceous Shale or Richmond Formation of Jamaica.

The Carbonaceous or Black Shale or Richmond Formation of Jamaica is a deposit of considerable importance in connexion with the geological history of the Greater Antilles. R. T. Hill1 correlates provisionally the Richmond Formation, as he calls these beds, with the Scotland Series of Barbados, the oldest formation in that island, and also with certain of the Tertiary beds of Trinidad. In the present communication I shall endeavour to present some observations on the Carbonaceous Shale Series of Jamaica, together with a description of the fossils I collected in it. This series of deposits consists of a sequence of ferruginous sandstones both coarse and fine-grained, some of them very hard, others when weathered extremely friable; of impure carbonaceous limestones of a very unfossiliferous nature; of grey nodular friable shales often with carbonaceous plant-like remains in them, but scarcely any other fossils; and of coarse conglomerates which seem to occur chiefly in the lower part of the formation.