Sven Egenhoff

GRAPTOLITES AS INDICATORS OF MAXIMUM FLOODING SURFACES IN MONOTONOUS DEEP-WATER SHELF SUCCESSIONS

Abstract The graptolitic Early Ordovician succession of the Mount Hunneberg locality, southern Sweden, shows the response of graptolite faunas to sea-level changes. The exposed interval consists of intercalated carbonates and shales at the base, grading into pure black shales in its central and upper part. This facies trend records a deepening of the depositional environment due to an overall sea-level rise. The Mount Hunneberg graptolite fauna is dominated by nearshore, shallow-marine forms found in most layers throughout the succession. Deeper-water pandemic species occur only rarely together with shallow-water graptolites but are dominant at four distinct traceable levels at Mount Hunneberg. This change in graptolite faunal composition is interpreted to indicate sea-level fluctuations. With rising sea level, shallow-water endemics and pandemics migrated landward, and deeper-water pandemic graptolites became increasingly frequent on the shelf. During the peak of the transgression, deep-water forms dominated. With falling sea level, shallow-water forms again appeared and replaced the deep-water graptolites. The four levels with deep-water graptolites at Mount Hunneberg are, therefore, interpreted to represent maximum flooding surfaces. This study demonstrates that changes in the faunal composition of such planktic organisms as graptolites provide a promising tool for recognizing maximum flooding surfaces. As these faunal turnovers are also detectable in monotonous parts of the Mount Hunneberg succession, this biofacies-based approach enables the recognition of maximum flooding surfaces even when no lithologic changes are present, enhancing the applicability of sequence stratigraphic interpretations to monotonous outer shelf strata.

New Ordovician-Silurian drill cores from the Siljan impact structure in central Sweden: an integral part of the Swedish Deep Drilling Program

New drill cores from the largest known impact structure in Europe, the relict of the Siljan meteorite crater, provide new possibilities to reconstruct Early Palaeozoic marine environments and ecosystems, and to document changes in sedimentary facies, sea level and palaeoclimate in Baltoscandia. The impact crater is an important target of the project “Concentric Impact Structures in the Palaeozoic” within the framework of the “Swedish Deep Drilling Program”. Two core sections, Mora 001 and Solberga 1, have been analysed. The sedimentary successions of these core sections include strata of late Tremadocian through late Wenlock ages. Our preliminary studies show not only that several of the classical Palaeozoic units of Sweden are represented in the area, but also that other significantly different facies are preserved in the Siljan district. An erosional unconformity representing a substantial hiatus occurs between Middle Ordovician limestone and a Llandovery-Wenlock (Silurian) shale succession in the western part of the Siljan structure and suggests an extended period of uplift and erosion. This may be related to forebulge migration due to flexural loading by the Caledonian thrust sheet to the west. Thus, this part of Sweden, previously regarded as a stable cratonic area, presumably was affected by the Caledonian collision between Baltica and Laurentia.

Biostratigraphic precision of the Cruziana rugosa group: a study from the Ordovician succession of southern and central Bolivia

Cruziana ichnospecies have been repeatedly reported to have biostratigraphic significance. This study presents a re-evaluation of the arthropod ichnotaxa of the Cruziana rugosa Group from bio- and/or lithostratigraphically well-defined Lower to Upper Ordovician siliciclastic sections of southern and central Bolivia. With the exception of Cruziana rouaulti , the ichnofaunas contain all the members of the Cruziana rugosa Group throughout the Ordovician (Arenig to Caradoc) successions in Bolivia. The Bolivian material therefore indicates that these arthropod ichnofossil assemblages are suitable for recognizing Ordovician strata in Bolivia. These findings cast doubt on their use as reliable indicators for a global intra-Ordovician (Arenig to Caradoc) biozonation of Peri-Gondwanan sedimentary successions.

Unconventional energy resources: 2015 review. Shale gas and liquids

This paper includes 10 summaries for energy resource commodities including coal and unconventional resources, and an analysis of energy economics and technology prepared by committees of the Energy Minerals Division of the American Association of Petroleum Geologists. Unconventional energy resources, as used in this report, are those energy resources that do not occur in discrete oil or gas reservoirs held in structural or stratigraphic traps in sedimentary basins. Such resources include coalbed methane, oil shale, U and Th deposits and associated rare earth elements of industrial interest, geothermal, gas shale and liquids, tight gas sands, gas hydrates, and bitumen and heavy oil. Current U.S. and global research and development activities are summarized for each unconventional energy resource commodity in the topical sections of this report, followed by analysis of unconventional energy economics and technology.This paper includes 10 summaries for energy resource commodities including coal and unconventional resources, and an analysis of energy economics and technology prepared by committees of the Energy Minerals Division of the American Association of Petroleum Geologists. Unconventional energy resources, as used in this report, are those energy resources that do not occur in discrete oil or gas reservoirs held in structural or stratigraphic traps in sedimentary basins. Such resources include coalbed methane, oil shale, U and Th deposits and associated rare earth elements of industrial interest, geothermal, gas shale and liquids, tight gas sands, gas hydrates, and bitumen and heavy oil. Current U.S. and global research and development activities are summarized for each unconventional energy resource commodity in the topical sections of this report, followed by analysis of unconventional energy economics and technology.

Sedimentology, facies architecture, and sequence stratigraphy of a Mississippian black mudstone succession—The upper member of the Bakken Formation, North Dakota, United States

The Lower Mississippian upper shale member of the Bakken Formation in the Williston Basin, North Dakota, consists of organic-rich, black siliciclastic mudstones deposited offshore on a low-gradient shelf. Twelve fine-grained facies are recognized and grouped into five facies associations. Very fine-grained, massive to faintly laminated mudstone (FA1) records deposition in the deepest, calmest parts of the basin, whereas well-laminated mudstones (FA2a), well-laminated clay-clast-bearing mudstones (FA2b), burrow-mottled mudstone with shells (FA3), and interlaminated siltstone and mudstone (FA4) suggest deposition in the shallower, less calm, and more proximal offshore environment. These proximal-offshore mudstones (FA2a, FA2b, FA3, and FA4) reflect (1) variation in bottom water oxygen levels, and (2) lateral changes in the input of silt and clay clasts. Ubiquitous Phycosiphon fecal strings, patches of shells, burrows, and rare agglutinated foraminifera indicate dysoxic to suboxic basinal deposition, and not a persistently anoxic environment. In all facies associations, storm event laminae are sparse to ubiquitous. Repeated stacking of facies associations defines up to ten coarsening-upward parasequences mostly 0.15-0.60 m (0.49-1.97 ft.) thick. Individual parasequences can be correlated for 300 km (180 mi) through the basin. The lower half of the succession (Interval 1) represents a transgressive systems tract and shows high radiolarian productivity with minor silt input. The upper half of the succession (Interval 2) represents the base of a highstand systems tract. In contrast to Interval 1, Interval 2 mudstones are characterized by high clay content, low radiolarian productivity, and intermittent colonization of the sea floor during higher order sea level lowstands.

The sediments of the Floian GSSP: depositional history of the Ordovician succession at Mount Hunneberg, Västergötland, Sweden

The succession at Mt. Hunneberg consists of intercalated siliciclastic mudstones and carbonates of Tremadocian to Floian age. Above an unconformity with underlying Furongian shales, siliciclastic mudstones with graptolites and overlying glauconite packstones of the upper Alum Shale Formation are exposed showing a sharp top contact to the carbonates of Bjørkåsholmen Formation. Above, the Tøyen Shale Formation consisting of siliciclastic mudstones and intercalated carbonate beds forms the stratigraphically youngest Ordovician unit at Mt. Hunneberg. The Tøyen Shale Formation is characterized by a lower marl- and carbonate-rich part, exclusively present in the southwest of Mt. Hunneberg, and an upper portion consisting of siliciclastic mudstones, extending from the Tetragraptus phyllograptoides graptolite Biozone on upwards. The siliciclastic mudstones of the Alum Shale Formation represent open shelf sediments reflecting sea-level highstands of two trans- and regressions. Overlying glauconite packstones indicate a transgression of Adelograptus zone age or younger. The Bjørkåsholmen Formation reflects a relative sea-level lowstand. The Tøyen Shale Formation records a deepening of the sedimentary environment during sea-level rise initially establishing offshore conditions, with the upper Tøyen Shale Formation siliciclastic mudstones indicating open shelf deposition. Abundant burrows throughout the succession reflect hospitable living conditions in the Mt. Hunneberg area, also during deposition of the Floian black shales. A pronounced decrease in thickness of the Hunneberg succession toward the northeast reflects erosion in the proximal compared to distal Hunneberg areas. The succession shows that alternating offshore to open shelf conditions is an ideal sedimentary environment to establish a Global Boundary Stratotype Section and Point with abundant and detailed biostratigraphic information.

Sedimentology of the Lower Ordovician (upper Tremadocian) Bjørkåsholmen Formation at Flagabro, southern Sweden

Abstract The Lower Ordovician Bjørkåsholmen Formation at Flagabro, Scania, southern Sweden, consists of a 0.8 m thick succession of carbonates with three siliciclastic mudstones, 5, 1 and 100 mm thick, intercalated in the central part of the unit. Carbonate and siliciclastic mudstone beds show both normal and inverse grading. The carbonates are mud-rich and subdivided into a mudstone, a wackestone and a packstone facies. Grain types in the carbonates are mostly shells and shell fragments of brachiopods and trilobites. The carbonate rocks are strongly bioturbated seen as in roundish burrows filled with mud and a clear cement; additionally, bioturbation is reflected in the random orientation of shells. The siliciclastic mudstones are subdivided into two facies; one contains large amounts of shells and is in part grain-supported, the other is matrix-dominated and laminated to massive. The succession reflects sedimentation on a low-inclined shelf equivalent to a mid-ramp to basinal setting. Most mud- and wackestones (facies 3 and 4) represent fair-weather sedimentation, and the intercalated wacke- and packstones (facies 4 and 5) represent concentration of shell debris during high-energy storm. The siliciclastic mudstones in the central part of the succession reflect deposition in a basinal setting. The entire Bjørkåsholmen Formation at Flagabro is equivalent to a lowstand of third (?) order without a well-developed internal cyclicity and is in that respect similar to the Bjørkåsholmen Formation of Öland, but different from the age-equivalent Norwegian sections.