Level Of Organic Metamorphism Research Articles

Rock physics and basin modeling nexus for predicting pore pressure

Improving accuracy in pre-drill pore pressure predictions is a fundamental starting point for well design including setting boundaries for casing points and mud weights. Although rock physics modeling is used routinely in pore pressure estimates, existing rock physics modeling approaches have been largely empirical and face challenges to predict pore pressure accurately, especially for deeper drilling targets where rock matrix properties deviate from normal compaction trends, due to chemical alterations of the rocks. Moreover, existing rock physics models require petrophysical inversion for porosity and volume of shale. It is well-known that petrophysical inversion has non-uniqueness issues and creates additional uncertainty and inaccuracy in pore pressure prediction. Therefore, we developed an integrated modeling approach that involves rock physics modeling and physics-based basin modeling. Through fundamental rock physics modeling and in-depth understanding of the process of clay diagenesis, we recognize that the acoustic impedance from seismic inversions and level of organic metamorphism (LOM, as a proxy for thermal stress) estimated from basin modeling are critical for pore pressure prediction in mudrocks. Based on extensive post-drill data validation, we demonstrate that our modeling approach improves accuracy in pore pressure prediction for depth zones undergoing clay-diagenesis. In addition, we demonstrate that the integrated rock physics modeling greatly reduces the number of calibration parameters as needed in existing models. Blind tests of our method on well data in two different basins with drastically different burial history demonstrates the validity and generalizability of our approach.

Application of petrophysical methods to estimate total organic carbon in Lower Jurassic source rocks from the offshore Lusitanian Basin (Portugal)

Lower Jurassic outcrops in the westernmost part of the Lusitanian Basin (São Pedro de Moel area, Portugal) reveal three stratigraphic units with source rock potential: i) Unit F from the Coimbra Formation, ii) the Polvoeira Member of the Água de Madeiros Formation, and iii) the Marly Limestones with Organic-rich Facies Member of the Vale das Fontes Formation. Despite decades of research, these source rocks have not yet been characterised in the offshore areas of the Lusitanian Basin.As a consequence of the discrepancy between organic matter contents in correlative surface-subsurface intervals, this paper investigates the applicability of petrophysical methods to semi-quantitatively estimate total organic carbon (TOC) and delineate source rock intervals in Lower Jurassic (Sinemurian–Pliensbachian) units in the offshore Lusitanian Basin. This study is based on the i) high-resolution stratigraphic correlation between well 14A-1 and the São Pedro de Moel section and ii) calibration of the TOC curve calculated for well 14A-1 using the high-resolution TOC datasets from São Pedro de Moel.Sonic transit time vs resistivity cross-plot shows that several intervals of the aforementioned lithostratigraphic units deviate from the (organic) lean sediment baseline, interpreted to indicate the presence of hydrocarbons and low-density organic matter. Thermal maturity from cuttings samples were used to estimate vitrinite reflectance for each well point measurement. These values vary between 0.51 and 0.87, indicating that the studied interval has reached the oil generation window. The level of organic metamorphism is in accordance with the hydrocarbon generation window interval, varying between 9.49 and 9.76. Neutron/resistivity, density/resistivity, and sonic/resistivity cross-plots and the petrophysical-based method for TOC calculation outlined in Passey et al. (1990) demonstrate the close similarity between TOC curves calculated for well 14A-1 and TOC measurements from the São Pedro de Moel outcrops. This comparison highlights the organic-rich nature of Unit F, the Polvoeira Member and the Marly Limestones with Organic-rich Facies Member in the offshore areas of the Lusitanian Basin and their potential as hydrocarbons source intervals.This work demonstrates a feasible solution to semi-quantitatively estimate TOC in subsurface source rocks when there is large uncertainty regarding sample quality. Delineation of source rock intervals in the offshore wells of the Lusitanian Basin reduces uncertainty, minimises risk, and may aid in new exploration concepts for hydrocarbons offshore Portugal. On a broader scale, this work reinforces the importance of outcrop control to correlate and improve the current knowledge of Portugal's offshore areas.

Температурные условия преобразования и степень зрелости органического вещества и углеводородов в юго-восточной части Терско-Каспийского прогиба

Температурные условия преобразования и степень зрелости органического вещества и углеводородов в юго-восточной части Терско-Каспийского прогиба

Joint geophysical and geochemical evaluation of source rocks – A case study in Sayun-Masila basin, Yemen

Integration of geophysical and geochemical approaches is used for qualitative and quantitative evaluation of source rocks. The Upper Jurassic rocks in the Sayun-Masila basin are used as a case study due to its high hydrocarbon potentiality. Stratigraphically, these rocks could be differentiated from base to top into: Shuqra, Madbi and Nayfa formations. The total organic carbon (TOC) values were determined in the shale and/or carbonate intervals of these formations from four studied wells by the ΔlogR method using sonic, resistivity and gamma-ray log data. Then the discriminant analysis was applied in differentiating source from non-source rocks. Also, the effect of the burial and thermal histories on the organic material maturation and the oil and/or gas generation was studied through the application of two analytical methods, namely, the level of organic metamorphism (LOM) and the time-temperature index (TTI), depending on the corrected temperature logs integrated with the time and depth data. The reliability of the obtained results has been confirmed and combined with the results supplied from geochemical analyses. The Upper Jurassic sediments are found to be oil–prone source rock in a mature stage. The Madbi Formation is considered as the most effective source rock. The burial and thermal histories of the basin in four modeled wells showed that mature oil generation window and hydrocarbon expulsion would have been initiated in the depocenters from Upper Jurassic Madbi Formation source rock during Late Cretaceous to Middle Miocene time.

Petrophysical Quantification of Multiple Porosities in Shale-Petroleum Reservoirs With the Use of Modified Pickett Plots

Summary Previous petrographic work has shown that shale-petroleum reservoirs at discovery are characterized by a quad-porosity system. In this work, a petrophysical model is built that allows quantification of storage capabilities in shales through determination of adsorbed porosity (ϕads_c), organic porosity (ϕorg), inorganic porosity (ϕm), and fracture porosity (ϕ2). All these porosities are important because they provide reasonable input to physics-based numerical simulators for shale-petroleum reservoirs and thus more-realistic projections of reservoir performance and recoveries. Pattern recognition is used in a modified Pickett plot for distinguishing key shale components such as total organic carbon (TOC) and level of organic metamorphism (LOM) and to distinguish between viscous and diffusion-like flow. Results from the model compare well with laboratory data. The petrophysical model is easy to use, yet it is robust because it can handle at the same time the four porosities mentioned previously, but it can also handle simultaneously three, two, or only one of those porosities depending on the characteristics of the reservoir at a given depth. It is concluded that the petrophysical model presented in this paper constitutes a valuable tool for physics-based characterization of shale-petroleum reservoirs.

Revised models for determining TOC in shale play: Example from Devonian Duvernay Shale, Western Canada Sedimentary Basin

Determination of total organic carbon (TOC) is essential in unconventional shale resource play evaluation. Indirect method, such as petrophysical approach, can provide a fast, convenient and cost efffective means for TOC estimation from well logs. Among the publically available approaches, the ΔlogR method is a popular one in conventional source rock evaluation and has been applied to unconventional resource play evaluation by many practitioners. Careful examination of the method finds that improvements can be made for a better TOC estimation with relaxed limitations. This study proposes the following revisions on the original ΔlogR method: 1) allowing estimation of petrophysical parameters from the targeted source rock rather an assumed linear approximation, 2) using additional logs to improve TOC prediction, and 3) replacing LOM (level of organic metamorphism unit) with a more commonly used thermal indicator Tmax for convenience. Depending on data or preference, the choice of using different porosity logs (density versus sonic) and parameter estimation methods (cross-plot method versus data-driven approaches) makes the revised method flexible for application. We present the revisions along with application examples from the Devonian Duvernay Shale in the Western Canada Sedimentary Basin to demonstrate the application of the improved ΔlogR method in shale gas evaluation. Comparison of the results from the revised method and the original one reveals that the revised models provide better and unbiased estimates of TOC with a higher correlation coefficient and bell-shaped residues centered at zero.

The influence of heating rates on organic matter in laboratory and natural environments

Abstract This contribution to the Festschrift relates to one of Marie-Theresa Mackowsky's ‘industrial interests’, heating rate, but it is not solely focussed within the field of industrial coking. One intention is to stress the importance of heating rate in the natural environment to illustrate its broad pervasiveness. First discussed, however, are the effects of heating rate on the appearance, optical properties and molecular structures of organic matter in laboratory experiments, before considering instances of the influence of heating-rate variation on sedimentary organic matter within the natural environment. Notable illustrations within igneous provinces in the Midland Valley of Scotland and North-east England are described. Heating rate is obviously only one of a number of factors involved in the ultimate development of coal rank or level of organic metamorphism, but the instances cited here emphasize that heating rate is not only an important factor in industrial carbonisation but is also a widely effective contributor to the variable maturation of crustal organic matter.

Time-temperature and organic maturation relations at some wells at the northern Nile Delta, Egypt

Integrated time-temperature analysis of seven wells along an east-west profile in the northern Nile Delta is carried out. The level of organic metamorphism (LOM), total maturity level (ΣMAL) and total time-temperature index (ΣTTI) are calculated in order to identify the most appropriate analytical method of calculation of the maturation level inside each well at each sediment layer. Sediments in four of the seven wells (Sidi Salim, Abadiya, Abu Madi and El-Wastani) are found to have entered the oil window, as deduced from the three techniques. In Qawasim well, the LOM and ΣMAL show that this well enters the oil window at a specific depth. For the following wells, the mature depths are found to be 4031 m (Sidi Salim), 3777 m (Qawasim), 3717 m (Abadiya), 3603–4155 m (Abu Madi) and 3713 m (El-Wastani). The LOM method is found to quantitatively overestimate the level of organic metamorphism at shallow depths, and underestimate it at deeper levels relative to the other two maturity techniques. The ΣMAL and ΣTTI give results which compare more closely with previous published work than the LOM.

Discussion on vitrinite reflectivity and the structure and burial history of the Old Red Sandstone of the Midland Valley of Scotland

Gerald M. Friedman writes: the paper by Marshall et al. 1994 uses vitrinite reflectivities from Lower Old Red Sandstone (ORS) sediments of the Midland Valley of Scotland to interpret burial and uplift history. Vitrinite reflectivies give values of 1.3% for the Stonehaven Group (Kincardineshire) and 1.3% for the Strathmore Group (Perthshire). They conclude that 'the Stonehaven Group reflectivity values are considerably lower than expected under the 9 km of sediments aggregated for the Lower ORS of Kincardineshire and demonstrate a maximum burial of 3 to 5 km’. The ORS correlates with the Devonian red beds of the Appalachian Basin. Here carbonized plant debris in uppermost Middle Devonian strata within the eastern Catskill Mountains of New York have been converted to anthracite (Friedman & Sanders 1982). The anthracite has a vitrinite reflectance of 2.5%. This implies a level of organic metamorphism (LOM) of 16. A similar degree of thermal activity is implied by the black colour (Staplin kerogen alteration index of 4) of the associated (possibly recycled) carbonized kerogen; a conodont alteration index of 4; and authigenic chlorite and local sericite fillings of the interparticle pores of interbedded sandstones. The specimens are about 350 Ma old. If 200 Ma is taken as the duration of exposure to the maximum geothermal temperature, then the LOM of 16 and other thermal indicators imply a maximum temperature of 190 °C. Using a geothermal gradient of 26°C km −1 , a former depth of burial of 6.5 km is implied. Such a former depth is consistent with

Generation, migration and accumulation of oil of El-Ayun Field, Gulf of Suez, Egypt

This study is an attempt to solve the problem of oil generation, migration and accumulation of oil in El-Ayun Field, Gulf of Suez. The organic carbon, hydrogen and organic matter contents in addition to the composition of kerogen are determined. The degree of transformation of organic matter to hydrocarbon and the level of thermal maturity of these sediments to yield hydrocarbons are deduced. The geothermal gradient mnd level of organic metamorphism (LOM) are determined by using the bottom hole temperature. The vitrinite reflectance values are used in this respect. The determined trace element contents for both crude oils and sediments clarifies the process of oil migration from possible source rocks to oil reservoirs. Recommendations, concerning exploratory testing of favourable sites for oil accumulation, laterally and vertically, are postulated on the basis of the achieved results.

Vertical Movements of Crust, Uplift of Lithosphere, and Isostatic Unroofing: Case Histories from the Ozark Dome and Northern Appalachians: ABSTRACT

Evidence of former deep burial of Ordovician to Devonian strata of the Ozark dome and northern Appalachians has been obtained from petrographic and geochemical studies of carbonates and coal-bearing rocks. In diagenetic minerals of the carbonate rocks, fluid inclusion homogenization temperatures and delta/sup 18/O values indicate paleotemperatures of 100 to 200/sup 0/C. The geothermometers used also include vitrinite reflectance, level of organic metamorphism (LOM), Staplin kerogen alteration index, and conodont alteration index (CAI). Maximum depths of burial were calculated from the estimated paleotemperatures assuming a geothermal gradient of about 25/sup 0/C/km. Strata of the Silurian of the northern Appalachian basin and of the Ordovician of the Ozark dome are interpreted to have reached maximum burial depths of 5 and 4.3 km, respectively; Devonian strata in the Catskill Mountains of New York had former burial depths of about 6.5 km; Lower Ordovician carbonate sequences of the northern Appalachian basin were buried to more than 7 km; Middle Ordovician strata from the same basin had paleodepths of approximately 5 km, and Devonian strata, 4.5 to 5 km. If these strata were formerly buried much more deeply than previously thought, then unexpectedly large amounts of uplift and erosion, ranging from 4.3 to 7more » km, must also have occurred to bring these strata to the present land surface. The occurrence of such large-scale vertical movements of the crust and lithosphere needs to be recognized in paleogeographic reconstructions.« less

Visual Kerogen Assessment of Thermal History: ABSTRACT

The microscopic particulate organic matter occurring in sedimentary rocks is referred to as visual kerogen when examined by use of strew slides prepared from a kerogen concentrate. Examination under a high-powered microscope in transmitted light yields information on both the organic matter type present and the level of organic metamorphism (LOM). This presentation concentrates on the LOM aspects of visual kerogen and addresses it from a utilization point of view. The color of the kerogen, preferably plant cuticle fragments or pollen and spores, is used to determine the level of organic metamorphism. Various scales have been proposed to reflect this change in coloration. The TAI scale is most commonly used. Visual kerogen assessment is considerably less precise than vitrinite reflectance. It is a subjective call made by the analyst. Additionally, the equivalent reflectance range broadens as higher LOMs are attained. However, the ability to visually discern differences in the suite of organic material present can override its drawbacks in precision. Caved versus indigenous populations can be recognized, as can recycled versus primary vitrinite. Thermal history can also be established in sections that are barren of vitrinite. As is the case with early all organic geochemical techniques, reliable interpretations can be make if the limitations of the method are considered and the results are cross-correlated with other methods. End_of_Article - Last_Page 296------------

Global Source Rock Distribution in Time: ABSTRACT

Twenty-one layer maps are presented showing source rock distribution worldwide from the Precambrian to the Pleistocene. Data at hand are inadequate to display source rock distribution in meaningful quantitative terms (e.g., initial volume and type of organic matter for geological time intervals). The common procedure, therefore, is to relate source rock importance in time to measurable yardsticks such as ultimately recoverable hydrocarbon reserves alleged to have been generated from specific source rock intervals. Although source rock type, thickness, richness, and wide regional distribution are vital parameters to account for the hydrocarbon richness of a specific basin, other factors such as size of drainage area, level of organic metamorphism, migrational aspects, trap storage capacity, timing, and retention are of equal importance. Present concepts of source rock distribution and abundance in time are subject to revision when the sources of unconventional hydrocarbon resources such as heavy oil, asphalt, tar, and gas hydrates are considered. In addition, the source rock potential of undrilled areas and traps must also be incorporated in any worldwide material balance estimate. The hypothesis is advanced that the organic matter of Oligocene to Pleistocene sources has generated the largest portion of the world's hydrocarbon resources in terms of energy equivalents. The bulk of these resources is shallow bacterial gas trapped in the form of gas hydrates in permafrost areas and in shallow layers in the deeper parts of the oceans. End_of_Article - Last_Page 476------------

Time-temperature-burial significance of Devonian anthracite implies former great (∼6.5 km) depth of burial of Catskill Mountains, New York

Specimens of coalified plant debris in Tully-correlative strata of the Gilboa Formation (uppermost Middle Devonian) within the eastern Catskill Mountains of New York State have been converted to anthracite having a vitrinite reflectance of 2.5%. This implies a level of organic metamorphism (LOM) of 16. The specimens are about 350 m.y. old; if 200 m.y. is taken as the duration of the time of exposure to the maximum geothermal temperature, then the LOM of 16 and other thermal indicators imply a maximum temperature of 190/sup 0/C. Using a geothermal gradient of 26/sup 0/C.km/sup -1/ (17/sup 0/F.1,000 ft/sup -1/), a former depth of burial of 6.5 km is implied. Such former deep burial is not usually inferred for the Catskills, but it is consistent with the idea that the thick (about 6.4 km or 21,000 ft) Carboniferous strata of northeastern Pennsylvania formerly extended northeast far enough to bury the Catskills. The lack of metamorphism of the Paleozoic strata lying about 4.5 km beneath the Tully-correlative rocks and exposed in the adjacent Hudson Valley places low limits on the former geothermal gradient; this supports the concept of great depth of former burial of the Catskills. For example, 6.5 km of former burialmore » and a geothermal gradient of 26/sup 0/C.km/sup -1/ imply a temperature of 307/sup 0/C for the base of the Paleozoic. By contrast, only 1 km of former burial requires a geothermal gradient of 170/sup 0/C.km/sup -1/, which would have subjected the base of the Paleozoic to a temperature of 955/sup 0/GAMMA, which is far higher than the 600 to 650/sup 0/C recently inferred for the Acadian-age metamorphism of the Taconic allochthon in southwestern Massachusetts and adjoining areas.« less

Application of vitrinite reflectance anisotropy in the evaluation of coal metamorphism

Measurement of the maximum plus either the minimum or mean vitrinite reflectance provides a method for quantification of anisotropy of the reflectance. Previous research has suggested that anisotropy of vitrinite reflectance may be a direct indicator of static pressure (depth of burial) at which coal metamorphism occurred. The combination of thermal information (from vitrinite reflectance) and pressure information should, therefore, provide a means of evaluating the metamorphic history of a single coal seam or a series of coals in a sedimentary basin (given the independent placement of coal-rank parameters on a pressure-temperature grid). Occurrence of coals in strata with diagnostic metamorphic minerals is rare. Therefore, evaluation of coal metamorphic conditions can seldom proceed parallel to mineralogical evaluation of rock metamorphic conditions. Rather, the coal petrologist has generally relied upon time-temperature nomograms to estimate metamorphic temperature from coal rank. In this study, the level of organic metamorphism (LOM)-time-temperature scale of Hood and others (1975) was considered the most versatile nomogram for evaluation of metamorphic conditions. Coals from throughout the Appalachians were studied, but this study concentrates on coals from the Allegheny plateau in western Pennsylvania. Vitrinite maximum reflectance (in oil at 546 nm) and reflectance anisotropy ((R maximum − R mean )/R maximum = anisotropy) were measured on Pennsylvania coals. In order to estimate rank gradients and subsequently paleogeothermal gradients, however, it was necessary to rely upon previously published volatile matter data from the Lower Kittanning, Upper Freeport, and Pittsburgh seams. From equivalent metamorphic temperatures from the LOM-time-temperature scale and from vertical separation of the seams, paleogeothermal gradients were calculated for Somerset County, adjacent to the Allegheny front, (about 40°C/km) and for Westmoreland County to the west (about 33°C/km). Past depths of burial for both localities were calculated to have been 3.5 to 4 km for the Allegheny Group coals. Calculated gradients are each in areas on the plateau where vitrinite reflectance is nearly constant within each area. Two similar areas, for which geothermal gradient could not be calculated directly due to insufficient vertical exposure of coals, lie immediately to the north. The crustal blocks appear to be divided by the southwest-to-northeast Chestnut Ridge anticline, which marks a major tectonic division on the plateau, and by the southeast-to-northwest “Gwinn-type” lineament, which marks a northward reduction in amplitude of the plateau folds. Coal rank is 1.6% R (low volatile bituminous) in the Somerset County block (associated with the 40 °C/km gradient), 1.3% R (medium volatile) in the block northeast of the lineament (centered in Clearfield County), 0.9% R (high volatile A) in the Westmoreland County block (associated with the 33 °C/km gradient) west of Chestnut Ridge, and 0.8% R (high volatile A) in the block northeast of the lineament (Clarion County). The rank decrease west across Chestnut Ridge occurs in a zone about 50 km wide. Width of the zone of northeastward rank that decreases across the lineament is not as well defined but is probably of the same magnitude. As burial depths of the blocks appear to have been similar, the primary cause for rank variation was variation in geothermal gradients between blocks. Anisotropy did not change significantly across the region, suggesting that it can be correlated with past depth of burial.

福岡市周辺地域の第三紀層の沸石と石炭化度

Degree of diagenesis of the Tertiary sedimentary rocks distributed in the Fukuoka City area and its environs, Fukuoka Prefecture, was examined on the basis of the mineralogical and coal petrographical data. The Tertiary formations in the present areas contain authigenic minerals such as clinoptilolite and heulandite besides montmorillonite. The level of organic metamorphism (LOM) which obtained by coal ranks varies from about 5.5 at the upper horizon to 9.5 at the lowest one. These experimental results indicate that the degrees of diagenesis of the Tertiary formations in the areas studied are remarkably lower than those in other districts in Kyushu already reported (Miki, 1980, and others). The low grade diagenetic alteration of sediments and small decreasing rate of coal rank from the upper to the lower horizon support the field evidence that the development of sedimentary basin in the present area was small-scale and tectonically stable through the Tertiary age. Further continuous investigations of the equivalent formations in other adjacent districts are necessary to examine the detailed areal variation of the diagenetic conditions.

Subsidence and Thermal History of Southern Oklahoma Aulacogen: Implications for Petroleum Exploration

Reconstructed subsidence curves and the thermal history of the Southern Oklahoma aulacogen support the concept of thermally controlled isostatic subsidence for the formation of the basin and indicate the significance of this concept for petroleum exploration. Two mechanisms--initial elastic flexure, followed by detachment and differential subsidence of the aulacogen--are inferred from the subsidence curves. Two methods have been used for reconstruction of the thermal history. A tectonophysics model in combination with a history of basin evolution demonstrates that geothermal gradient and depth-of-burial were dynamic variables during the subsidence stage; maximum paleotemperatures were attained during Sylvan (Late Ordovician) time near the close of subsidence; and most of the Arbuckle Group had been subjected to the temperature conditions of oil formation (the oil liquid window) prior to the possible phase of fluid migration in Sylvan time. The second method, involving reconstruction of the geothermal history on the basis of geothermometry (palynomorph carbonization), suggests: (1) paleotemperatures exerted a significant effect on the level of organic metamorphism in the sedimentary rocks; (2) the geothermal gradient varied during the subsidence stage; (3) paleotemperatures were higher than those predicted by the theoretical model and support the hypothesis of formation of the basin by thermally controlled subsidence, and the application of this concept for petroleum exploration.

Organic Metamorphism and the Generation of Petroleum

A scale referred to as Level of Organic Metamorphism (LOM) describes how far the thermal metamorphism of sedimented organic matter has progressed during subsurface burial. It represents a single, continuous numerical scale which is applicable to the entire thermal range of interest in the generation and destruction of petroleum. It is based on coal rank and is convenient for interrelating other useful scales of organic metamorphism. A relation of temperature to time for petroleum generation is based on LOM values of sedimentary rocks in the 9- to 16-LOM range with reasonably dependable maximum temperatures and effective heating times. The relation is nearly equivalent to a doubling of the reaction rate for each additional 10°C, and the apparent activation energies increase from about 18 to 33 kcal/mole as LOM increases from 9 to 16. The principal metamorphic stages of petroleum generation and a zone of initial oil-source-rock maturity are superimposed on graphs of LOM versus depth for two wells to illustrate the prediction of specific depths where oil, gas condensate, and high-temperature methane would be generated in petroleum source rocks at any given location.

Microplankton zones of the Savik Formation (Jurassic) Axel Heiberg and Ellesmere Islands, District of Franklin

ABSTRACT Microplankton biostratigraphic zones are established in the thickest exposed section of the Savik Formation in the Sverdrup Basin. This section is located at Vantage Point, Axel Heiberg Island. The ranges of the following key taxa subdivide a sequence that ranges in age from Toarcian to Volgian: Gonyaulacysta jurassica (M. Call -- ?Top of Jur.); G. jurassica var. longicornis (Oxf.); Acanthaulax spp. (M. Call. -- L. Oxf.); Nannoceratopsis pellucida (M. Bath. -- M. Call.); Paragonyaulacysta calloviense n. gen., n. sp. (L. Call.); Pareodinia tripartitus var. obtusus n. sp., n. var. (M. Bath. -- U. Bath.); P. sp. 2 (U. Baj. -- M. Bath.); Nannoceratopsis gracilis (?Toar. -- U. Baj.). The lateral extent of these zones is demonstrated by correlations between the Vantage Point section and sections located on Bjarnasson Island and on Fosheim Peninsula of Ellesmere Island. Of the 34 microplankton species used in the zonation 8 are new. The following new taxa are named and described: Gonyaulacysta jurassica var. brevis n. var.; Paragonyaulacysta calloviense n. gen., n. sp.; Pareodinia tripartitus n. sp.; P. tripartitus var. obtusus n. sp., n. var.; P. tripartitus var. rotundus n. sp., n. var. The genus Pareodinia (Deflandre) is emended to include cysts with 3I archeopyles. Reworked microplankton indicate that the late Middle Jurassic sediments in the centre of the basin were in part derived from earlier Jurassic deposits along the margin. The level of organic metamorphism in samples from southern and western Axel Heiberg Island indicates that the prospects for liquid hydrocarbons in the pre-Cretaceous rocks of that area are minimal. Better prospects are indicated for rocks at least as old as early Jurassic on western Ellesmere Island.