Organic-rich Samples Research Articles

Lead isotope signatures of sedimentary rocks as a tool for tracing ore lead sources: a study of base-metal and barite occurrences in Jameson Land Basin, central East Greenland

Numerous sediment-hosted base-metal and barite occurrences are found within the post-Caledonian Jameson Land basin in East Greenland. A study was undertaken to evaluate the sources of lead in several base-metal occurrences by comparing the lead isotope signatures of sedimentary and intrusive rocks from the basin with ore lead signatures established in earlier studies. To differentiate mineral phases and simulate various degrees of natural hydrothermal processes the samples were leached sequentially with HCl, H2O2 (only in the case of organic-rich samples), HNO3 and HF + HNO3.The lead isotopic compositions of the sedimentary rocks were found to vary according to mineralogical paragenesis, and with origin and geographical position of the adjacent basement. All HF-soluble lead (after leaching with HCl and HNO3) in coarse-grained arkoses and conglomerates plotted on well-defined mixing lines in both uranogenic and thorogenic diagrams, whereas all other analyses were more radiogenic. Since feldspar is the dominant lead-carrying phase in the HF fraction of the coarse-grained clastic rocks, the mixing lines are referred to as the feldsparlead trends and are interpreted to reflect the presence of detrital feldspars from two well-defined basement sources. The radiogenic end of the feldspar-lead trend (high 207Pb/204Pb and 208Pb/204Pb ratios) is believed to represent feldspars derived by the breakdown of Caledonian granites on account of isotopic overlap with these. The lower end of the feldspar-lead trend more probably represents pre-Caledonian metasediments.Lead isotopes from the base-metal occurrences in the western part of the Jameson Land basin plot on the feldspar-lead trends, strongly suggesting that feldspars from the thick sequence of Devonian to Lower Permian continental clastic deposits are the source of ore lead. The position on the feldspar-lead trend of the individual west Jameson Land mineral occurrences varies according to the local geological environment. The Mesters Vig Pb-Zn veins plot nearest the low 207Pb/204Pb and 208Pb/204Pb end of the feldspar-lead trends in accordance with the scarcity of Caledonian granites in the nearby basement, whereas mineralization further to the south has more 'Caledonian granite-lead' incorporated.Mineral occurrences in east Jameson Land are slightly more radiogenic than those of west Jameson Land, showing a strong affinity towards the Caledonian lead component. The east Jameson Land ore lead defines a trend extending from the upper end of the feldspar-lead trends towards more radiogenic values. This trend away from the feldspar-lead fields probably reflects the fact that the Carboniferous-Permian sequence in the east is much thinner than in the west owing to the overall architecture of the basin. The east Jameson Land ore lead is interpreted as being derived from various local source rocks.

Sea-level and subsidence data from a Late Holocene back-barrier lagoon (Valle Standiana, Ravenna, Italy)

Late Holocene back-barrier sediments have been studied in a former lagoon reclaimed during the last century. Several shallow boreholes were cored, from which nine organic-rich samples were selected for radiocarbon dating, and others for palynological and palaeontological analysis. This enabled the reconstruction of the evolution of a back-barrier coastal basin during the late Holocene coastline progradation. Since late Roman times, the rate of relative sea-level rise (RSLR) has increased from 1.1 mm/yr to over 2 mm/yr, even after removal of the main human impacts during of the last century. This change is ascribed to sediment compaction related to changes in the hydrological regime, and possibly to an isostatic subsidence wave accompanying the northward shift of the Po Delta during the last 2000 years.

96/04641 Structural elucidation of Argonne premium coals: Molecular weights, heteroatom distribution and linkages between clusters

Organic-rich samples derived from a Middle Cambrian Formation in the Georgina Basin, and from the Middle Proterozoic of the McArthur Basin in northern and central Australia, yielded alginite ranging from immature oil shale material to overmature residue. A maturation scale has been developed based on the thermal evolution of alginite as determined from reflectance and fluorescence. The coalification path of alginite is marked by jumps in contrast to the linear path of wood-derived vitrinite. Six zones have been recognised, ranging from undermature (zone I), through the mature (zones II/III), followed by a stable stage of no change (zone IV) to the overmature (zones V and VI). The onset of oil generation in alginite as evident from the present study is at 0.3% Ro Alg. and is expressed in a change of fluorescence from yellow to brown, and a coalification jump from 0.3 to 0.6% Ro of Alg. In many boreholes zone III can be distinguished between 0.6 and 0.8% Ro of Alg. where subsequent oil generation occurs. Zones II and III represent the oil window.A zone of little or no change designated zone IV, at 0.91.0% Ro of alginite follows zones II/III. A marked coalification jump characterises zone V, where a pronounced change in reflectance occurs to >1.0% Ro Alg., signifying peak gas generation. The border of oil preservation lies at the transition of zone V and VI, at 1.6% Ro Alg. In zone VI gas generation only occurs.Comparison of reflectance results with experimental and geochemical pyrolysis data supports high activation energies for hydrocarbon generation from alginite, and therefore a later onset of oil generation than other liptinite macerals (i.e. cutinite, exinite, resinite) as well as a narrow oil window.Transmission electron microscopy (TEM) confirms that alginite does not go through a distinct intermediate stage but that the percentage of unreacted organic matter decreases as maturation proceeds. A clear distinction can be made in TEM between immature alginite, alginite after oil generation, and alginite residue following gas generation. Alginite beyond 1.6% Ro acquires very high densities and the appearance of inertinite in TEM.Bitumens/pyrobitumens make a pronounced contribution to the organic matter throughout the basins and have been shown to effect pyrolysis results by suppressing Tmax. The bitumens/pyrobitumens have been divided into four groups, based on their reflectance and morphology, which in turn appears to be an expression of their genetic history. Their significance is in aiding the understanding of the basins' thermal history, and the timing of oil and gas generation.

Geochemistry, Palynology, and Regional Geology of Worldclass Upper Devonian Source Rocks in the Madre de Dios Basin, Bolivia: ABSTRACT

Recent exploration drilling indicates the existence of world-class source rock in the Madre de Dios basin, Bolivia. In the Pando-1 X and -2X wells, over 200 m of poorly bioturbated, organic-rich (TOC = 3-16 wt.%) prodelta to shelf mudstones in the Frasnian-Famennian Tomachi Formation contain oil-prone organic matter (hydrogen index = 400-600 mg HC/g TOC). Our calculated source prolificity indices for this interval in these wells (SPI = 15-18 tons of hydrocarbons per square meter of source rock) exceed that for the Upper Jurassic in Central Saudi Arabia. The Tomachi interval is lithologically equivalent to the Colpacucho Formation in the northern Altiplano, the Iquiri Formation in the Cordillera Oriental, and is coeval with other excellent source rocks in North America, Africa, and Eurasia. All of these rocks were deposited under conditions favorable for accumulation of organic matter, including a global highstand and high productivity. However, the Madre de Dios basin was situated at high latitude during the Late Devonian and some of the deposits are interpreted to be of glacial origin, indicating conditions not generally associated with organic-rich deposition. A biomarker and palynological study of Upper Devonian rocks in the Pando-1X well suggests deposition under conditions similar to certain modernmore » fjords. High productivity resulted in preservation of abundant organic matter in the bottom sediments despite a cold, toxic water column. Low-sulfur crude oil produced from the Pando-1X well is geochemically similar to, but more mature than, extracts from associated organic-rich Tomachi samples, and was generated from deeper equivalents of these rocks.« less

A note of caution concerning the application of quantitative palynological data from oxidized preparations

Abstract. Kerogen extracted from rock samples for palynological studies frequently requires oxidative treatment in order to liberate palynomorphs from amorphous organic matter (AOM). Treatment with nitric acid (70% HNO3) is sometimes adequate though many Mesozoic organic-rich samples require more severe oxidation to break up clumped AOM. A widely used method involves the repeated oxidation of a preparation in Schulze’s solution (70% HNO3 supersaturated with KClO3), followed each time by rinsing with 2% potassium hydroxide solution (KOH) (Jones, 1994).The mid-Cretaceous Greenhorn Formation, exposed near Pueblo, Colorado, USA, is composed of interbedded bioturbated limestones and laminated calcareous shales (Cobban & Scott, 1972). In the middle part of the Bridge Creek Limestone Member, kerogen extracted from these two lithologies is markedly different. Diverse, predominantly gonyaulacineaen dinocyst assemblages are found in kerogen from the bioturbated limestone samples. These either require five minutes of nitric acid treatment or no oxidation at all. Most of the AOM is finely disseminated and passes through a standard 10 μm sieve mesh.Dinocysts in the >10μm kerogen fraction from the laminated calcareous shale samples are outnumbered by clumped AOM at a ratio of between 10 and 1000:1. Prior to oxidation, gonyaulacineaen and peridiniineaen dinocysts are seen to be present. However, if Schulze’s solution and KOH are applied until most of the clumped AOM has disintegrated (a process which takes from 1 to 48 hours), Gonyaulacineae are rare (<5%) in resulting dinocyst assemblages (which are dominated by well-preserved Peridiniineae). . . .

Comparison of the linear Van den Berg/Ružić transformation and a non-linear fit of the Langmuir isotherm applied to Cu speciation data in the estuarine environment

Abstract Copper complexation measurements in estuarine organic-rich samples with differential pulse anodic stripping voltammetry (DPASV) and differential pulse cathodic stripping voltammetry (DPCSV) show a relatively large scatter in the data, due to a high organic matter content. Two methods for the estimation of the complexation parameters according to the Langmuir isotherm are compared: the linear transformation of Van den Berg/Rǔzic and the non-linear method according to Wilkinson. For DPASV measurements in estuarine samples the values of the conditional stability constant (K′), estimated with the linearization method are systematically lower than those estimated with the Wilkinson method. The Van den Berg/Ružic linearization is more susceptible to outliers or data points that do not follow the model of the Langmuir isotherm. For DPCSV measurements, where the data followed the Langmuir isotherm more closely, this difference could not be demonstrated. The non-linear method is to be preferred because this method is more suited to the error structure of the data, which is of constant absolute magnitude. Moreover it offers the advantage that the standard error of the estimated parameters can be calculated consistently.

A Guide to the Extraction of Fossil Diatoms from Lithified or Partially Consolidated Sediments

Based on experience gained from processing samples from the Cenozoic basins of south-wesin bt Ecuador, a composite procedure for the processing of fossil diatoms from lithified or partially consolidated sediments is presented. The procedure is divided into four stages: (I) initial sample breakdown. (II) cemented rock breakdown and removal of carbonate component. (III) organic matter removal. (IV) clay removal. These are presented in the form of annotated tables linked by an accompanying flow chart. INTRODUCTION Marine Oligo-Miocene sediments from the Manabi and Progreso basins of south-west Ecuador were examined for diatoms. Lithologies encountered varied from partially consolidated clay-rich bentonites of the Portoviejo Formation, to lithified chocolate-brown shades and siltstones of the Tosagua Formation. These units contained a mixed marine fossil assemblage of foraminifera, (Whittaker 1988), radiolaria, diatoms and silicoflagellates. A biostratigraphy for the area has been erected using foraminifera (Whittaker 1988) and radiolaria (Robinson 1992); diatoms and silicoflagellates have also proved essential for palaeo-ecological interpretation and a refined biostratigraphy (Hinchey 1992). Diatomaceous sediments from Ecuador differ considerably in their lithology and therefore react differently to conventional diatom processing techniques (Lohmann 1972, Schrader 1973). Samples from the bentonitic Portoviejo Formation broke down fairly easily, but problems were encountered in the removal of clays from these sediments. Lithified samples from the clay-rich Tosagua Formation, however, proved very problematic; conventional processing techniques were ineffective in most stages of breakdown and the soaking of samples in petroleum spirit (Abelmann 1988, Boden 1991) also failed to disaggregate the samples satisfactorily. OBJ ECTIVES As standard diatom processing techniques failed to breakdown many of the samples collected from Ecuador, a different approach was clearly required. A literature review was conducted on previous techniques and experienced workers were asked for their comments (see acknowledgments). Techniques suggested were applied to material from Ecuador and the most effective methods noted. The result of this work has produced a composite processing procedure which can be generally applied to most types of diatomaceous sediments, including those which are lithified or partially consolidated. The procedure is presented in the form of a flow chart (text-fig. 1) and a series of annotated tables (1-4), each table representing a particular aspect of processing. The procedure is designed to be user friendly and emphasizes the use of wet mounts between certain stages (e.g. removal of clays and organic matter; text-fig. 1, Tables 3 and 4) to evaluate whether or not further processing is required. The tables are designed to work independently of each other and therefore should allow workers to initially assess the lithology of the sediments they are studying and to then determine which of the tables apply to that particular type of sediment. ADDITIONAL NOTES TO TABLES Table 1 Mechanical breakdown of the sediment should be done with as little damage to frustules as possible. Not all stages listed will be necessary. Physico-chemical breakdown (Table 2 (2a) and Table 3 (la-d)) can be used for more resistant samples. Table 2 Warming of sample + HCI (Ib) is not always necessary. Heat only if very little reaction occurs. Table 3 Addition of a few drops of methanol to a hydrogen peroxide solution (lb) prevents strong foaming in organic rich samples. Table 4 In some samples, all clay cannot be removed. As a consequence the worker must assess the residue (using wet mounts) to evaluate what is an acceptable amount of clay in their particular study. Note on the use of wet mounts. Tables 3 and 4 advocate the use of wet mounts at various stages of the cleaning procedure to check whether further processing is required. It must be noted that the removal of material for wet mount preparation will bias any quantitative examination (P. Boden, pers. comm.). Therefore, if high resolution quantitative studies are to be attempted it is suggested that either 1) wet mounts should not be used, or that 2) two splits of the same sample be processed. One split being used to assess whether further processing is necessary and the other used for quantitative work. The wet mount procedure forms an essential stage in the cleaning of diatomaceous lithified sediments from Ecuador. However, it has proved unnecessary for DSDP deep sea muds from the equatorial Pacific. Therefore the use of wet mounts is wholly dependant on the nature of sediment and the purpose of study. SLIDE PREPARATION The method of slide preparation utilized will depend on the type of study proposed. The pipetting method of Schrader and Gersonde (1978) proves suitable for biostratigraphic studies, while the ranmicropaleontology, vol. 40, no. 4, pp. 368-372, text-figure 1, tables 1-4, 1994 368 This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 06:45:44 UTC All use subject to http://about.jstor.org/terms Micropaleontology, vol. 40, no. 4, 1994 I.INITIAL SAMPLE BREAKDOWN

Speciation of manganese in Chesapeake Bay waters by voltammetric methods

The Mn(II) to Mn(O) reduction wave (peak) at a mercury electrode was investigated for its analytical usefulness in anoxic Chesapeake Bay waters which contain significant quantities of dissolved and particulate organic matter. The Mn(II) to Mn(O) reduction is characteristic for all Mn(II), MN(III) and MN(IV) complexes and thus represents total dissolved Mn. It does not provide information on only the Mn(II) oxidation state as suggested previously. Inorganic Mn(II) and organic Mn(III) complexes were studied by sampled d.c. polarography, differential pulse polarography, cyclic voltammetry and square wave voltammetry. All methods show that the Mn(II) to Mn(O) reduction is quasi-reversible in sea water. Square wave voltammetry was used for analytical work on field samples. Both Mn(II) and Mn(III) give similar current versus concentration slopes for the Mn(II) to Mn(O) peak when added to Chesapeake Bay samples. The minimum detection limit is near 200 to 300 nM. Comparison of organic free and organic rich laboratory and field samples shows that Ep shifts to more negative potentials for the organic rich samples. Thus, a major finding of this voltammetric study is that manganese can be complexed by organic ligands in marine systems with zones characterized by high organic matter decomposition and low O2 concentrations. Organic complexation of dissolved Mn may have important consequences for Mn chemistry in marine systems characterized by an oxic / anoxic interface.

Upper Cretaceous Organic-Rich Laminated Limestones of the Adriatic Carbonate Platform, Island of Hvar, Croatia

Several organic-rich samples taken from upper Santonian--late Campanian(?) laminated limestones of Hvar Island (Croatia) were investigated to characterize palynofacies, macerals, type of organic matter, and organic geochemistry. These characterizations, as well as the reconstruction of the depositional environment, are interpreted in terms of a source rock perspective. The results suggest that the laminated limestones were formed within shallow depressions of the carbonate platform in an anoxic, restricted-marine environment with increased salinity. The Hvar Island laminated limestones contain type II-S kerogen, and they are found to be marginally mature and oil prone.

Lower palaeozoic and precambrian petroleum source rocks and the coalification path of alginite

Organic-rich samples derived from a Middle Cambrian Formation in the Georgina Basin, and from the Middle Proterozoic of the McArthur Basin in northern and central Australia, yielded alginite ranging from immature oil shale material to overmature residue. A maturation scale has been developed based on the thermal evolution of alginite as determined from reflectance and fluorescence. The coalification path of alginite is marked by jumps in contrast to the linear path of wood-derived vitrinite. Six zones have been recognised, ranging from undermature (zone I), through the mature (zones II/III), followed by a stable stage of no change (zone IV) to the overmature (zones V and VI). The onset of oil generation in alginite as evident from the present study is at 0.3% R o Alg. and is expressed in a change of fluorescence from yellow to brown, and a coalification jump from 0.3 to 0.6% R o of Alg. In many boreholes zone III can be distinguished between 0.6 and 0.8% R o of Alg. where subsequent oil generation occurs. Zones II and III represent the oil window. A zone of little or no change designated zone IV, at 0.9 1.0% R o of alginite follows zones II/III. A marked coalification jump characterises zone V, where a pronounced change in reflectance occurs to >1.0% R o Alg. , signifying peak gas generation. The border of oil preservation lies at the transition of zone V and VI, at 1.6% R o Alg. In zone VI gas generation only occurs. Comparison of reflectance results with experimental and geochemical pyrolysis data supports high activation energies for hydrocarbon generation from alginite, and therefore a later onset of oil generation than other liptinite macerals (i.e. cutinite, exinite, resinite) as well as a narrow oil window. Transmission electron microscopy (TEM) confirms that alginite does not go through a distinct intermediate stage but that the percentage of unreacted organic matter decreases as maturation proceeds. A clear distinction can be made in TEM between immature alginite, alginite after oil generation, and alginite residue following gas generation. Alginite beyond 1.6% R o acquires very high densities and the appearance of inertinite in TEM. Bitumens/pyrobitumens make a pronounced contribution to the organic matter throughout the basins and have been shown to effect pyrolysis results by suppressing T max. The bitumens/pyrobitumens have been divided into four groups, based on their reflectance and morphology, which in turn appears to be an expression of their genetic history. Their significance is in aiding the understanding of the basins' thermal history, and the timing of oil and gas generation.

Relationships between depositional conditions and microtextures in the organic-rich Lower Oxford Clay sediments (U.K.)

Six representative samples of the Lower Oxford Clay (LOC) and the Middle Oxford Clay (MOC) sediments have been assessed for total organic carbon (TOC from 1.2 to 14.2%), hydrogen indices (HI from 813 to 130), and carbon isotopic values (δ13C from −23.1 to −27.7±) (Kenig et al., this symposium), and have been extensively studied using petrographic techniques. The use of the scanning electron microscope and particularly the backscattered electron mode was emphasized as it is the most suitable tool to study the relationships between organic matter and minerals at a micrometric scale.The bulk mineralogy appears similar in all samples studied. The argillaceous matrix is predominantly composed of illite and kaolinite with detrital mineral grains of quartz, feldspar, mica (biotite and muscovite) and calcitic bioclasts (e.g. coccoliths). Diagenetic features consist mainly of dissolution of quartz grains, rim epigenization of quartz grains to kaolinite, and the presence of pyrite. The concentration of pyrite increases with the concentration of organic matter. Both framboidal and euhedral forms of pyrite are present Euhedral pyrite crystals are more abundant in organic-rich samples, indicative of the more reducing conditions occurring in the organic-rich sediments. In organic-rich samples, coccoliths are concentrated in well preserved fecal pellets, suggesting a relatively high sedimentation rate. Preservation of coccospheres indicates a low energy environment of deposition and mild diagenesis. Unusually well-preserved biotite crystals may be indicative of the proximity of sediment sources and of the weakness of diagenetic processes.In organic-rich samples, organic matter is encountered as elongated “patches” 20 to 50 μm in length and composed of several particles of marine phytoplanktonic origin; and as thin isolated particles closely associated with clays. These thin particles are both of marine phytoplanktonic and of terrestrial origin (woody debris, vegetal tissues and rare palynomorphs). In organic-poor samples, the frequency and the size (5 to 20 μm) of the patchy composite particles of phytoplanktonic organic matter decrease. Palynological studies indicated that 80% to 95% of the organic matter is amorphous and probably of marine origin. However, the proportion of structured organic matter, woody debris and vegetal tissues, increases from 5% to 20% as the TOC decreases.None of the samples studied exhibited laminations at a sub-millimetric scale. However, the organic “patches” in the organic-rich samples lie parallel to the plane of stratification even if there is no obvious stratification of the mineral matrix. Clay minerals show a random and disorganized distribution that may be indicative of microbioturbation, even in the most organic-rich samples.Organic and mineral microtextures are controlled by the environment of deposition and the diagenetic history of the sediments and are related to geochemical parameters as HI, δ13C and TOC. Microbioturbation would indicate that the water column was never anoxic. In contrast, euhedral pyrites crystals suggest anoxia in the organic-rich sediments. The decrease in size of organic “patches” with decrease in TOC, as well as the variable distribution of coccoliths, may be indicative of changes in primary productivity and sedimentation rate.

Organic Geochemistry of Lower Tertiary Shales of Southern Louisiana: Regional Distribution of Source Potential: ABSTRACT

Outer continental shelf shales of the Paleogene/Eocene Wilcox Group and middle Eocene Sparta Formation are potential source rocks for hydrocarbons in southern Louisiana. Eight hundred and thirty-seven shale samples (Sparta 219) Wilcox, 618 from 24 wells across south Louisiana were analyzed using Rock-Eval pyrolysis; 24 organic-rich samples were analyzed using pyrolysis-gas chromatography and gas chromatography-mass spectrometry (GC-MS). Regional trends in organic geochemistry are related to two main factors: sedimentary facies transition from proximal deltaic to shelf/slope environments, and thermal maturity. According to geothermal gradient maps, thermal effects increase from east to west across southern Louisiana and from north to south as the lower Tertiary section is buried to greater than 30,000 ft. The Wilcox, and to a lesser extent the Sparta, are major regressive deltaic sequences whose primary deltaic depocenters are located in subsurface Texas. Volumetrically, smaller deltas prograded beyond the ancient Cretaceous shelf edge by as much as 50 mi across southern Louisiana. Source potential in both rock units becomes more oil prone from west to east across south Louisiana, with an apparent maximum in the shelf/slope flexure zone in south central Louisiana. In this area, Sparta Formation shales show good to excellent potential in shales overlain by shelf-edgemore » barrier sands. Wilcox source potential is fair to good in shales deposited in submarine fan environments. Source units are interpreted to be a product of transgressive episodes occurring within primarily regressive sequences. The close proximity of source units to the shelf-edge suggest that they may represent conditions deeper in the Eocene Gulf of Mexico basin.« less

The Henryville Bed of the New Albany shale—I. Preliminary characterization of the nickel and vanadyl porphyrins in the bitumen

The nickel, vanadium, Ni(II) porphyrin and VO(II) porphyrin concentrations in the bitumen of an organic rich sample of the Henryville Bed of the New Albany shale (Mississippian-Devonian; Indiana, U.S.A.) were determined. The bitumen contains 1776 μg nickel/g and 1550 μg vanadium/g bitumen. The porphyrin concentrations of 9900 μg/g and 9100 μg/g, respectively, are higher than those reported in most source rock bitumens or crude oils. The similar abundances of Ni(II) and VO(II) porphyrins indicates a depositional environment for this sample that is transitional between strongly anoxic (VO(II) porphyrins dominant) and less anoxic in which Ni(II) porphyrins dominate. The Ni(II) and VO(II) porphyrins in the bitumen occur as etioporphyrin (etio), deoxophylloerythroetioporphyrin (DPEP), and tetrahydrobenzo-DPEP (THBD) species in the order of abundance: etio>DPEP>THBD for Ni(II) and DPEP>etio>THBD for VO(II) porphyrins. The DPEP/etio ratios of 1.4 for the VO(II) series and 0.91 for the Ni(II) series and a Vitrinite reflectance of 0.5–0.6% are consistent with the organic matter in the New Albany shale being of intermediate maturity. The carbon-number distributions of the etio, DPEP, and THBD porphyrins of the two metals are very similar. This similarity and the fact that carbon numbers of both Ni(II) and VO(II) porphyrins extend at least to C 36 suggests that the Ni(II) and VO(II) porphyrins have originated via similar geochemical pathways in the New Albany shale. The major pathway appears to be release of the porphyrins during kerogen catagenesis.

Guidelines for Evaluating Petroleum Source Rock Using Programmed Pyrolysis

Rock-Eval pyrolysis is used to rapidly evaluate the petroleum-generative potential and thermal maturity of rocks. Accurate conclusions require programs every 30-60 ft (9-18 m), understanding of interpretive pitfalls, and supporting data, such as visual kerogen, vitrinite reflectance, and elemental analyses. The generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography. Most coals show high S2/S3 (>5) and low HI values (< 300 mg HC/g TOC). Migrated oil and mud additives, which alter Rock-Eval data, can sometimes be removed by special processing. For immature rocks, bimodal S2 peaks and PI values over 0.2 indicate contamination. Pyrolysis downgrades organic-poor, clay-rich rocks, which show lower HI and higher Tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays. Tmax values for small S2 peaks (< 0.2 mg HC/g TOC) are unreliable. Tmax is affected by maturation, organic matter type, contamination, and the mineral matrix. S3 is sensitive to inorganic and adsorbed carbon dioxide, and to instrumentation problems. Acidification of carbonate-rich samples and proper maintenance improves S3 measurement. Constant sample weights (100 mg) are recommended. Below a threshold weight, Tmax increases by up to 10°C, and other parameters decrease. Organic-rich samples, which overload the detector, can be diluted with carbonate. Detector linearity is determined by pyrolyzing various weights of an organic-rich rock.

Organic geochemical study of the Upper Kimmeridge Clay of the Dorset type area

Results are presented from an organic geochemical investigation of a suite of rock samples taken from the Upper Kimmeridge Clay near Kimmeridge, Dorset. All samples contain immature organic matter of marine origin, although one horizon, the Whitestone Band, contains an additional secondary input of partially biodegraded mature hydrocarbons, due to an oil seepage of unknown origin. With the exception of increased relative abundances of 4-methylsteroidal hydrocarbons in the more organic-rich samples, the immature molecular distributions are very similar, suggesting a consistent source of organic matter. The results are in agreement with the palaeoenvironmental model proposed by Tyson et al. (1979) for the deposition of the Kimmeridge Clay, where the different lithologies are controlled by a fluctuating oxic/anoxic boundary, with only the organic-poor mudstones being deposited in relatively oxygenated waters.

The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia

BOREAS Griffey, N. J. &amp; Worsley, P. 1978 03 01: The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia (Okstindan Research Project Report 26). Boreas, Vol. 7, pp. 1–17. Oslo. ISSN 0300–9483.Historical, lichenometrical and stratigraphical evidence is combined to establish a provisional history of Neoglacial glacier variation in a mountainous environment approx. 66oN. Attention is focussed on end moraine chronology. At five sites, derived organic materials have been located within end moraines and at two others in situ palaeosols occur buried beneath distal slopes. Organic rich samples from all the sites have been radiocarbon dated and the results permit the recognition of three major glacier expansion episodes, each of which contributes to the diachronous nature of the Okstindan outer Neoglacial limit. A widespread ‘Little Ice Age’ event with a maximum extent of probable eighteenth century age is confirmed. Limited areas of older moraine ridges peripheral to the ‘Little Ice Age’ maximal limit appear to date from about 3000‐2500 14C years B.P. and a younger period tentatively dated as about 1250‐1000 14C years B. P. which agrees with recent data from Engabreen in northwest Svartisen. No evidence for any extensive glacial activity after the inlandice wastage approx. 9000 14C years B. P. and prior to 3000 14C years B.P. was forthcoming.