Albany Group Research Articles

Letters

CMACE: assessing care at the Albany Group Practice.

Silicified Upper Ordovician trilobites from Pai‐Khoi, Arctic Russia

Abstract: A collection of silicified trilobites extracted from samples obtained by F. Nansen from the Upper Ordovician of Khabarovo, Pai Khoi, Russian Arctic is dominated by two new species of the proetide Lasarchopyge, a genus known hitherto only from the Argentine Precordillera. Comparison of Lasarchopyge with Scharyia reveals a range of common characters that support inclusion of both genera in the same family. The rest of the fauna comprises a metagnostid (Trinodus elspethi), an asaphid (Isotelus sp.), two remopleuridids (Remopleurides cf. caelatus and R. sp. nov. A), an aulacopleurid (Harpidella triloba), a lichid and an odontopleurid (Apianurus cf. barbatus), the last two being represented by very fragmentary material. T. elspethi, H. triloba, R. cf. caelatus and A. cf. barbatus are common to or closely resemble taxa from the Edinburg Formation, Virginia. Closely related taxa are present also in the Esbataottine Formation, NW Territories, Canada, and in the Albany Group, Girvan district, Scotland. All of these occurrences are of early Caradoc (Sandbian) age, and most lay at palaeolatitudes of 20°–30° south; all are interpreted as having been deposited on the outer shelf, which is consistent with their distribution.

Brachiopod biofacies in the Barr and Ardmillan groups, Girvan: Ordovician biodiversity trends on the edge of Laurentia

ABSTRACTLocally abundant and diverse brachiopod faunas, associated with unstable outer shelf and slope environments, occur throughout the Barr and Ardmillan groups (middle Llanvirn–upper Ashgill) in the Girvan district of SW Scotland. A dataset of 350 brachiopod species from 30 horizons through the Middle–Upper Ordovician succession forms the basis for a description of brachiopod diversity through the succession and comparison with global patterns and trends through this time interval. The Middle Ordovician Barr Group incorporates shallow water carbonate and clastic facies, characterised by Valcourea confinis, with deeper-water facies. The trilobite-dominated Albany Group preserves outer shelf biofacies. Deep-water facies occur in the Balclatchie Formation of the lower Ardmillan Group, including an early occurrence of a Foliomena-type species. High diversity brachiopod faunas occur in clastic facies, though many of the biofacies have a transported component to them. Representatives of the deep-water Foliomena fauna occur intermittently throughout the Upper Ardmillan Group, appearing in both the Whitehouse and Drummuck subgroups. This distinctive assemblage of small, thin-shelled brachiopods, including Dedzetina, Christiania, Cyclospira and Foliomena itself, is interbedded with a variety of other less cosmopolitan deep-water assemblages, including the Onniella–Skenidioides and Lingulella–Trimurellina associations. Shallower-water environments in the middle Ashgill Lower Drummuck Subgroup hosted the Fardenia–Eopholidostrophia association in sands, and the Christiania–Leptaena association in muds and silts. The remarkable Lady Burn Starfish Beds in the upper part of the group contain a variety of brachiopod-dominated assemblages, including the Eochonetes and Plaesiomys–Schizophorella associations, transported from various shelf locations, within a very diverse mid Ashgill biota. The upper Ashgill High Mains Formation contains abundant elements of the terminal Ordovician Hirnantia fauna, including Eostropheodonta, Hindella and Hirnantia itself, but also some taxa more typical of the Laurentian Edgewood Province. As a whole, the changing brachiopod biodiversity biofacies reflect environmental fluctuations, on this part of the Laurentian margin, driven by mainly eustatic and tectonic events against a background of global biotic radiation.

The faunas of the Albany Group in the Girvan area, and their palaeogeographical implications

Synopsis The Albany Group, off-shelf equivalent to the Barr Group of the Girvan cover-sequence, yields mid-Ordovician faunas from its constituent Doularg and Craigmalloch formations. The Doularg faunas have been largely described; they are shelly assemblages typical of the Laurentian margin and are correlated with the North American Whiterock Series. Some new trilobite discoveries are reported. The fauna of the Craigmalloch Formation is described here, and consists mainly of pandemic graptolites of the Nemagraptus gracilis Biozone, but includes two trilobites known principally from peri-Gondwanan sites; their occurrence on the Laurentian margin confirms that deep-water trilobites make poor indicators of faunal provinces.

Geochemical Character and Origin of Oils in Ordovician Reservoir Rock, Illinois and Indiana, USA

Twenty-three oils produced from reservoirs within the Ordovician Galena Group (Trenton equivalent) and one oil from the Mississippian Ste. Genevieve Limestone in the Illinois and Indiana portions of the Illinois basin are characterized. Two end-member oil groups (1 and 2) and one intermediate group (1A) are identified using conventional carbon isotopic analysis of whole and fractionated oils, gas chromatography (GC) of saturated hydrocarbon fractions, isotope-ratio-monitoring gas chromatography/mass spectrometry (irm-GC/MS) of n-alkanes ranging from C15 to C25, and gas chromatography/mass spectrometry (GC/MS) of the aromatic hydrocarbon fractions. Group 1 is characterized by high odd-carbon predominance in mid-chain n-alkanes (C15-C19), low abundance of C20+ n-alkanes, and an absence of pristane and phytane. Group 1A is characterized by slightly lower odd-carbon predominance of mid-chain n-alkanes, greater abundance of C20+ n-alkanes compared to group 1, and no pristane and phytane. The carbon isotopic composition of n-alkanes and the distribution of n-alkylarenes for groups 1 and 1A indicate that these oils were generated from strata containing abundant Gloeocapsomorpha prisca. In contrast, group 2 is characterized by low odd-carbon predominance in mid-chain n-alkanes, moderate abundance of C20+ n-alkanes, and the presence of pristane and phytane. The Mississippia -reservoired oil is characterized by low odd-carbon predominance in mid-chain n-alkanes and greater abundances of C20+ n-alkanes, pristane, and phytane compared to group 2. Distributions of isoprenoidal alkylarenes (aryl isoprenoids) for group 2 and the Mississippian-reservoired oil are similar, suggesting that aryl isoprenoids fail to provide a diagnostic characteristic that can be used to precisely correlate oils and source rocks. Conventional correlations of oil to source rock based on carbon isotopic-type curves and hopane (m/z 191) and sterane (m/z 217) distributions are of limited use in distinguishing Ordovician-reservoired oil groups and determining their origin. Oil to source rock correlations using the distribution and carbon isotopic composition of n-alkanes and the m/z 133 chromatograms of n-alkylarenes show that groups 1 and 1A originated from strata of the Upper Ordovician Galena Group. Group 2 either originated solely from the Upper Ordovician Maquoketa Group or from a mixture of oils generated from the Maquoketa Group and the Galena Group. The Mississippian-reservoired oil most likely originated from the Devonian New Albany Group. The use of GC, irm-GC/MS, and GC/MS illustrates the value of integr ted molecular and isotopic approaches for correlating oil groups with source rocks.

Long-Range Petroleum Migration in the Illinois Basin (1)

The distribution of oil fields in the Illinois basin overlaps but extends considerably northward from the area where the New Albany Group, the basin's most prolific source rock, has generated oil. Oils from reservoirs in Silurian strata from central and western Illinois can be correlated geochemically and isotopically to bitumen from the New Albany near the southern tip of Illinois. We believe that these oils migrated long distances, perhaps 100 km (62 mi) or more from the south or southeast. Migration probably occurred late in the basin's history, after basin sediments were fully compacted, in response to a regional northward flow system set up by tectonic uplift in the south. The hydrodynamic drive for migration during this period was comparable in magnitude to the comp nent of buoyant force acting along migration pathways; both hydrodynamic and buoyant forces contributed to migration. Migration efficiency and velocity are greatest when oil saturates a small part of the carrier bed's porosity. Capillary forces can aid migration by segregating oil into heterogeneities such as especially porous laminae, fractures, or karst channels in carrier beds. We suggest that the oil migrated through Devonian and Silurian carbonates along the weathered and karstified surface of a regional unconformity that formed during Kaskaskia deposition.

The trilobite fauna of the Middle Ordovician Doularg Formation of the Girvan district, Scotland, and its palaeoenvironmental significance

ABSTRACTThe Doularg Formation is defined within the Albany Group (Tappins Complex); the formation consists of the unfossiliferous Fence Member at the base, succeeded by the Gorse Member (formerly the “Albany mudstones with nodular limestones”), the Separation Sandstone and the Jubilation Member, a bedded, calcareous, silty mudstone. The last named has yielded the rich assemblage of trilobites described, representing thirty genera and including one new genus and seven new species—Bronteopsis matutina, Bumastoides? rivulus, Agerina laurentica, Tretaspis eximia, Ampyxina medici, Stiktocybele (gen. nov.) bathytera, Platycalymene metoeca: Nileus is the most common trilobite. The trilobite fauna indicates that the Doularg Formation should be correlated with some part of the Benan Conglomerate, the uppermost formation of the Barr Group to the north of the Stinchar Valley, and is probably of Llandeilo age. The trilobite association is most closely allied to that of the slightly older basal Superstes Mudstone, reflecting the strong ecological control affecting deeper water faunas. The affinity of the Jubilation Member trilobites with those of the middle Table Head Formation (Llanvirn) of western Newfoundland, is evidenced by the presence in both of Nileus, Cybelurus, Peraspis, and Bronteopsis. These are the four most common genera in the Jubilation Member, comprising over half the total trilobite specimens, and provide striking evidence of the longevity of deeper water genera.

Focusing Future Exploration in Mature Basin: Maturation and Migration Models Integrated with Timing of Major Structural Events in Illinois: ABSTRACT

Exploration risk can be decreased by highgrading areas where the timing of structural events and maturation of source rocks are nearly coincident. Knowledge of migration fairways further aids in focusing exploration. Four burial-history models have been constructed to accommodate (1) a rift-fill sequence in excess of 24,000 ft, (2) a hypothetical Fairfield basin model, (3) a model using a deep well, and (4) a model on the Sparta shelf. These complex models, which use several variables including compaction, thermal conductivity, kerogen kinetics, and multiple unconformities, indicate a possibility for multiple hydrocarbon-generative events and show that linear geothermal gradients are ineffective in explaining maturation in Illinois. Periods of oil generation determined from the models can be compared with known timing of structural events to predict trapping potential. Depths to the oil phase-out zone are also significant. Exploration risk can be reduced in Illinois by using a simple migration model that uses the basal Upper Devonian Sylamore Sandstone in central and western Illinois as a migration conduit and the New Albany Group as a source. Other migration conduits in the basin are discussed including faults associated with structures and fracture systems such as the Wabash Valley fault system.

Rock-Eval Data Relating to Oil-Source Potential of Shales of New Albany Group (Devonian-Mississippian) in Illinois Basin: ABSTRACT

Only limited data on petroleum source rock potential of New Albany Group (Devonian-Mississippian) shales have been reported, with the exception of vitrinite reflectance and some petrographic analyses. The New Albany Group contains the thickest and most widespread continuous black shale beds in the Illinois basin. The New Albany extends from northwestern Illinois to southwestern Indiana and western Kentucky and is thought to have played a major role in petroleum generation throughout the basin. In this study, Rock-Eval pyrolysis was used to measure the petroleum-generative potential and production index of the shale. Seven geochemical logs, based on 143 core samples from across the basin, and a production index map, based on a total of 252 samples (cuttings and cores) in Illinois, were generated. Systematic variations of petroleum-generative potential of the shale were observed. The variations are related to the differences in shale lithofacies, depth, and geographic location. The upper portion of the New Albany - the Hannibal and Saverton Shales - has the lowest oil-generative potential. The Grassy Creek, Sweetland Creek, and other stratigraphically lower shales of the New Albany Group generally have good oil-generative potential. However, samples from the Hicks dome area of extreme southern Illinois are overmature and havemore » no oil-generative potential. Source rocks that have both good oil-generative potential (> 6 kg hydrocarbons per ton of rock) and a higher production index (> 0.09) are generally located at depths of 2,500-5,300 ft.« less

C-S-Fe relationships and the isotopic composition of pyrite in the New Albany Shale of the Illinois Basin, U.S.A.

The relationship between pyritic sulfur content (S pyr) and organic carbon content (C org) of shales analyzed from the New Albany Group depends upon C org. For samples of <6 wt.% C org, S pyt, and C org are strongly correlated ( r = 0.85). For C org-“rich” shales (>6 wt.%), no S pty-C org, correlation is apparent. The degree of Fe pyritization (DOP) shows similar relationships to C org. These C-S-Fe relationships suggest that pyrite formation was limited by the availability of metabolizable organic carbon in samples where C org < 6 wt.% and by the availability of reactive Fe for samples where C org > 6 wt.%. Apparent sulfur isotope fractionations relative to contemporaneous seawater sulfate (Δ 34S) for pyrite formation average −40% for non-calcareous shales and −25%. for calcareous shales. Δ 34 S values become smaller with increasing C org, S pyt, and DOP for all C org-“poar” (<6 wt%) and some C org-“nch” (<6 wt.%) shales. These trends suggest that pyrite formation occurred in a closed system or that instantaneous bacterial fractionation for sulfate reduction decreased in magnitude with increasing organic carbon content. The isotopic trends observed in the New Albany Group are not necessarily representative of other shales having a comparable range of organic carbon content, e.g. Cretaceous shales and mudstones from the western interior of North America ( GAUTIER, 1986). Δ 34 S values in the remainder of the C org-rich New Albany Group shales are relatively large (−38 to −47%.) and independent of C org, S pyr, and DOP, which suggests that pyrite in these shales formed mostly at or above the sediment-water interface by precipitation from an isotopically uniform reservoir of dissolved H 2S.

Chemical characterization of gas- and oil-bearing shales by instrumental neutron activation analysis

The concentration of As, Ba, Ca, Co, Cr, Cs, Dy, Eu, Fe, Ga, Hf, K, La, Lu, Mn, Mo, Na, Ni, Rb, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, U, Yb, and Zn were determined by instrumental neutron activation analysis in block shale samples of the New Albany Group (Devonian-Mississippian) in the in the Illinois Basin. Uranium content of the samples was as high as 75 ppm and interfered in the determination of samarium, molybdenum, barium and cerium. In the determination of selenium a correction was made for interference from tantalum. U, As, Co, Mo, Ni and Sb as well as Cu, V and pyritic sulphur which were determined by other methods, were found to correlate positively with the organic carbon content of the samples.

Is Hodgkin's disease contagious?

In this issue of the Journal, Vianna and Polan present further evidence to support their view that Hodgkin's disease may be contagious. The hypothesis, as previously stated by the Albany group 1 , ...