Mudstone-dominated Succession Research Articles

Palynofacies as sea-level-sensitive proxy in Early Cretaceous marine mudstones – A critical evaluation

Stratigraphic distribution patterns of particulate organic matter (POM) have been widely used for facies recognition and paleoenvironmental interpretation as well as to decipher proximal to distal trends within fine-grained sediments. The Lower Cretaceous mudstone-dominated succession in the eastern Lower Saxony Basin (LSB) offers an excellent opportunity to critically evaluate such palynofacies parameters, commonly used to identify transgressive-regressive (T-R) cycles in marine sediments. For the seemingly monotonous succession, a robust sequence stratigraphic framework has been previously established by integrating high-resolution elemental intensity data from X-Ray Fluorescence (XRF) core scanning and biostratigraphy from four drill cores. In this study, the composition and distribution of the POM has been assessed by analysis of 220 strew mounts using transmitted-light microscopy. Overall, the POM composition indicates deposition in a mud-dominated proximal to distal shelf setting. The ratio of opaque versus translucent phytoclasts (OP/TR ratio) shows a distinct long-term increase from the Berriasian onwards with maximum values during the early Hauterivian, followed by a subsequent decrease in OP/TR ratio. This trend broadly reflects the overall T-R evolution of the succession interpreted from Si/Al changes. This also applies to the size and sorting of opaque phytoclasts, with the greatest amplitude changes in opaque particle size parameters being observed in the more proximal deposits of the studied succession. On the other hand, the ratio of terrestrial versus marine palynomorphs (T/M ratio), often applied as indicator of proximal to distal trends and distances from the coastline, shows no correlation with the T-R cycles. Systematic long- and short-term trends visible in T/M ratio correspond to variations in the XRF-derived Ca/Ti stratigraphic trend, which is interpreted to reflect variations in carbonate content. This may indicate that the T/M ratio in the LSB is largely controlled by variations in marine palynomorph flux, probably related to productivity changes of the organic-walled microplankton.

Longyearbyen CO2 lab project—from a vision of a CO2-neutral Svalbard to a geoscience data eldorado

The Longyearbyen CO2 lab project was initiated in 2006 by the University Centre in Svalbard (UNIS) to establish whether subsurface storage of locally produced CO2 is feasible. Over a decade of drilling operations and geoscientific research concluded that the subsurface was suitable for storing the CO2 generated from the local power plant. The geological ingredients for successful CO2 storage are in place, comprising a ca. 300 m thick, sandstone-dominated reservoir rock capped by an impermeable mudstone-dominated succession. No CO2 was ever injected for storage in Svalbard for economic and political reasons. However, the project generated a wealth of new data, some of which proved critical for studies related to CO2 storage elsewhere. The data were also key to the characterization of fluid flow and geothermal potential in Svalbard, deciphering past climatic changes, unravelling past tectonic events, some of relevance for understanding the plate tectonic evolution of the Arctic, as well as updating the global geological timescale. In this contribution, we briefly outline the history and main achievements of the Longyearbyen CO2 lab project, before describing, categorizing and openly sharing the publicly available data from the project, including peer-reviewed publications (123 so far) and theses (18 PhD and 34 MSc).

Upper Jurassic – Lower Cretaceous of eastern Wollaston Forland, North-East Greenland: a distal marine record of an evolving rift

Two drill cores covering the Upper Jurassic – Lower Cretaceous succession in Wollaston Forland, NE Greenland, offer an exceptional insight into mud-accumulation in an evolving distal fault block. Previous studies have revealed the presence of long-lasting black mudstone accumulation extending through the oxygen-restricted early rift and rift climax phases (Bernbjerg and Lindemans Bugt Formations). Here, we revisit the depositional evolution recorded in these cores to present a detailed description of the sedimentary succession extending into the late syn-rift settings (Palnatokes Bjerg and Stratumbjerg Formations). The results indicate that the Kimmeridgian – lower Volgian early rift-phase was characterized by suspension settling, laminae-scale event deposition in a tectonically-affected, prodeltaic offshore setting. The event-related depositional processes are expressed by starved wave-ripples, scour-and-fill structures, putative mud floccule ripples, and mud-dominated gravity-flow deposits. During the middle Volgian – Ryazanian rift climax phase, the depositional environment evolved into a narrow half-graben that was detached from the proximal depocentre flanking the coarse sediment fueled deltaic coastline. The correlative sedimentary facies in the detached half-graben are bioclastic and pyrite-rich black mudstones documenting suspension settling and gravity flow/mass wasting deposition in sub-storm wave-base slope and basin-floor environments. Black shale sedimentation ended abruptly in the late Ryazanian when the accumulation of condensed, bioturbated deep sea marls was initiated linked to broader oceanographic reorganization concomitant with waning rift activity in the west. Deposition of red bioclastic mudstones with a common gravity-flow component characterized the Hauterivian, potentially representing final draping of the submerged fault block crest. The top of the cored succession is demarcated by the appearance of dark grey bioturbated mudstones of Barremian age, reflecting the onset of regionally continuous deep-sea mud accumulation in thermally subsidizing basins. Although superficially monotonous, the mudstone-dominated succession reveals a highly dynamic depositional system that reflects shifting marine processes during almost a full rift cycle.

Untold muddy tales: Paleoenvironmental dynamics of a “barren” mudrock succession from a shallow Permian epeiric sea

During the late Paleozoic, the intracratonic Paraná Basin, Brazil, in central Gondwanaland, was covered by a huge (>1.600.000 km2), shallow and isolated epeiric sea. Within the Permian succession, oxygen-deficient facies are commonly recorded in the Mesosaurus-bearing Irati Formation (Cisuralian, Artinskian/Kungurian) and the overlaying Serra Alta Formation (Guadalupian, Wordian/Capitanian). Barren, dark-grey mudstones are the main facies preserved in this last unit, which has usually discouraged extensive and detailed stratigraphical and paleontological investigations. However, exhaustive sedimentological, taphonomic and paleontological surveys in those deposits reveal a dynamic and complex depositonal history. Based on sedimentary fabric, autochthonous to parautochthonous occurrences of shelly benthic invertebrates (bivalves) and the presence/absence of concretion-bearing and phosphate-rich layers, we report variations in the oxygen levels of bottom and pore waters, in bathymetry, sedimentation rates, and changes in benthic colonization. Our data indicate that the deposition of this “apparently barren” mudstone-dominated succession was driven by a complex interplay of variations in sedimentation rate and oxygen pulses tied to tectonic and climate changes. Three distinct populations or invertebrate paleocommunities were recorded, which were adapted to (a) normal background low-oxygen (dysoxic) conditions (i.e., minute infaunal suspension-feeding bivalves associated with the trace fossil Planolites), (b) chemically toxic (anoxic/extreme dysoxic) substrates, including gigantic burrowing bivalves (probable chemosymbiotic taxa), and (c) oxic/dysoxic substrates following short-term bottom disruptions.

Sedimentary Facies and Depositional Environment of the Middle Devonian Geneseo Formation of New York, U.S.A.

Abstract Detailed facies characterization of the Middle Devonian Geneseo Formation in the Northern Appalachian Basin (NAB) shows a rich assembly of sedimentary features and textures that suggest shelfal mud deposition in a storm-dominated, shallow epeiric sea. At the time of deposition, Acadian uplift supplied fine-grained detritus from the east and stimulated delta growth. As sediment was shed from the hinterland, distribution of mudstone facies was controlled by a combination of autogenic processes and a general rise in sea level. The vertical and lateral distribution of nine mudstone facies observed in this succession indicates an overall shallowing-upwards trend (westward progradation of Catskill delta) with multiple modes of sediment transport and deposition. The water column became more oxygenated upsection as indicated by an increase in benthic fauna diversity (e.g., Leiorhynchus and Orbiculoidea), increasing bioturbation diversity (e.g., Chondrites, Palaeophycus, Planolites, Teichichnus, Thalassinoides, and Zoophycos), and a decline of organic-carbon content (via oxidation and consumption). Physical and biological attributes of this mudstone-dominated succession are used to reconstruct sedimentary processes and depositional conditions. Although a stratified-basin model has previously been proposed for the Geneseo Formation, observations made in this study do not support that interpretation. Collectively, our observations indicate shelfal mud deposition above storm-wave base, in a relatively energetic environment with persistent lateral transport and advection by oscillatory flow, wave-induced currents, river-flood, and storm-wave generated offshore-directed underflows, as well as storm setup-relaxation flows.

A late eocene-early Oligocene transgressive event in the Golfo San Jorge basin: Palynological results and stratigraphic implications

A new Cenozoic dataset in the subsurface of the South Flank of the Golfo San Jorge Basin (Santa Cruz province) allowed to identify a non-previously recognized transgressive event of late Eocene to early Oligocene age. Below of a marine succession containing a dinoflagellate cyst assemblage that characterizes the C/G palynological zone of the Chenque Formation (early Miocene), a 80–110 m thick marine succession contains a palynological assemblage integrated by Gelatia inflata, Diphyes colligerum and Reticulatosphaera actinocoronata supporting the occurrence of a marine incursion in the basin during the Eocene–Oligocene transition (EOT). The new lithostratigraphic unit - here defined as El Huemul Formation – covers in sharp contact to the Sarmiento Formation, and become thinner from East to West; the unit has been identified in about 1800 well logs covering up to 3500 km2, and its subsurface distribution exceed the boundaries of the study area. The El Huemul Formation consists of a thin lag of glauconitic sandstones with fining-upward log motif, followed by a mudstone-dominated succession that coarsening-upward to sandstones, evidencing a full T-R cycle. Preservation of the El Huemul Formation in the subsurface of the South Flank has been favored by the reactivation of WNW-ESE late Cretaceous normal faults, and by the generation of N–S striking normal faults of Paleocene-Eocene age. Flexural loading associated to igneous intrusions of Paleocene?- middle Eocene age also promoted the increase of subsidence in the South Flank of the basin prior to the transgression.

Key aspects of the stratigraphy of the Upper Silesian middle Keuper, southern Poland

The stratigraphy of the Upper Silesian Keuper, a continental, mudstone-dominated succession is poorly known, although the already renowned, newly discovered vertebrate localities highlight the growing demand for a more precise intra-regional correlation and an appropriate stratigraphic reference framework. A major lithostrati- graphic unit, preliminarily proposed for the middle Keuper (i.e., above the Schilfsandstein; Stuttgart Formation in “Stratigraphische Tabelle von Deutschland”, 2002) by Szulc and Racki (2015; Przegląd Geologiczny , 63: 103– 113), is described in detail. The redefined Grabowa Variegated Mudstone-Carbonate Formation, the unit pre- viously based on inaccurately presented information, includes the Upper Gypsum Beds and the Steinmergel- keuper in the traditional scheme from Germany (= Weser and Arnstadt formations). Three members are formally defined: the Ozimek (Mudstone-Evaporite) Member, the Patoka (Marly Mudstone-Sandstone) Member and the Woźniki (Limestone) Member. Two significant bone-bearing horizons (Krasiejow and Lisowice) are placed within the Patoka Mbr. The formation thickness in a composite, regional reference section of the Upper Silesian Keuper, based on the new Woźniki K1 and Patoka 1 well profiles, is approximately 215 m thick. The Grabowa Fm generally correlates with the Norian stage, with the base located in the undefined upper Carnian, and is topped by a major, erosive disconformity and sedimentary sequence boundary, near the Norian-Rhaetian boundary. However, hiatuses in the Silesian middle Keuper succession are located and paired with a cannibalistic type of sand-mud flat deposition, largely controlled by Early Cimmerian movements of tectonic blocks associated with the Krakow– Lubliniec shear zone.

Basin-scale stratigraphic architecture and potential Paleocene distributive fluvial systems of the Cordilleran Foreland Basin, Alberta, Canada

The Paleocene Paskapoo Formation in western Canada is composed of several hundred meters of fluvial strata that were deposited in an actively subsiding retro-arc foreland basin adjacent to the southern Canadian Cordillera. Here, we utilize newly available subsurface data from down-hole gamma-ray well logs to reconstruct the large-scale fluvial stratigraphy and depositional history of the Paskapoo Formation in the central portion of the Cordilleran foreland basin in Alberta. Paleocene fluvial strata in this region contain several notable characteristics, including variable degrees of channel sandstone amalgamation, regionally-variable stratigraphic architecture, and a large fan-shaped sandstone unit that emanated from the adjacent fold-thrust belt. Fluvial channel sandstone bodies are abundant and amalgamated near the base of the formation in the southern portion of the basin, but become less apparent in the northernmost 100km of the basin. The middle interval of the Paskapoo Formation, characterized by abundant mudstone with isolated channel sandstone bodies, is prevalent across the entire study area. The upper portion of Paskapoo Formation is dominated by a large (5000km2), north-northwest trending, laterally continuous sandstone in the northern portion of the basin that abuts against the fold-thrust belt and fans outward into the basin. This feature is interpreted as either a distributive fluvial system or a fixed-outlet river system that experienced repeated avulsions. This area of the fold-thrust belt may be the site of a long-lived fluvial outlet. The variable degree of sandstone amalgamation in the Paskapoo Formation suggests two different modes in the relative ratio of accommodation to sediment supply. Periods of rapid subsidence, likely associated with thrust emplacement in the adjacent fold-thrust belt, resulted in mudstone-dominated successions with isolated sandstone bodies, whereas tectonically inactive periods, associated with less subsidence, resulted in amalgamated sandstone units. The principal stratigraphic features reconstructed from the data in this area can be used to better understand and predict fluvial stratigraphy within other foreland basins.

Sediment transport processes in an ancient mud-dominated succession: a comparison of processes operating in marine offshore settings and anoxic basinal environments

Abstract: Few studies describe and compare the transport mechanisms operating to disperse mud in different parts of basins. Instead, the physical processes operating to disperse mud in offshore environments, where storm and tidal processes are interpreted to dominate, are generally considered in isolation from those occurring in basinal settings where changes in bottom-water anoxia and suspension settling from buoyant plumes are mostly interpreted to dominate. Using microtextural, mineralogical and geochemical data derived from the analyses of 151 thin sections obtained from the Lower Jurassic mudstone-dominated succession exposed on the coast of NE England, we investigate how varying sediment dispersal mechanisms, bioturbation and early diagenesis operated to produce the lithofacies variability observed. In particular, we consider the processes of sediment delivery while bottom waters were interpreted to be euxinic. Analyses of these samples reveal that the succession is highly variable at millimetre to centimetre scales. Six main lithofacies were observed: (1) sand- and clay-bearing, silt-rich mudstones; (2) silt-bearing, clay-rich mudstones; (3) clay-rich mudstones; (4) clay-, calcareous nannoplankton-, and organic carbon-bearing mudstones; (5) fine-grained muddy sandstones; (6) cement-rich mudstones. These units are organized typically into stacked successions of sharp-based, normally graded, thin (<10 mm) beds. Single beds exhibit a variety of sedimentary structures. Specifically tempestites, wave-enhanced sediment gravity flows of fluid mud, ripples and gutter casts are common in the coarser-grained mudstone facies. In contrast, thin siltstone lags, compacted ripples and organo-mineralic aggregates are common in the finer grained mudstone facies and those with significant primary production-derived components. Bioturbation is common throughout. These data indicate that sediment was transported by density flows and traction currents operating at the sediment–water interface in all parts of the studied succession. Bioturbation has overprinted depositional fabrics in the majority of samples. The extent to which persistent bottom-water anoxia and low-energy suspension settling influenced lithofacies variability in the basinal parts of the succession has been overstated; these environments were more dynamic than most researchers have previously concluded.

Structures and hydrocarbon prospectivity in the northern Davis Strait area, offshore West Greenland

In the northern Davis Strait to southernmost Baffin Bay area, offshore West Greenland, deep basins with Mesozoic and Cenozoic sedimentary successions occur and a number of large structures and closures at likely reservoir levels have been found. Mid-Cretaceous, Upper Cretaceous and Paleocene sand-rich deposits are well known onshore east of the study area and in offshore wells, and equivalent deposits may also be present in the structures. Some of the potential structural leads have thick seals of late Cretaceous–Cenozoic deposits and short distances to deep possible kitchens with mid-Cretaceous and Paleocene source rocks, which mainly came into the oil window during the Neogene. Onshore oil seeps and gas shows, together with amplitude anomalies from seismic data, such as possible bright spots, support a live petroleum system in the region. During Early to mid-Cretaceous time a number of large structures and basins formed as a result of extensional faulting, including the Kangerluk Structure, the Aasiaat Structural Trend, structures in the Aasiaat and Sisimiut basins, and in the Nagssugtôq Sub-basin. A period with less tectonic activity followed in the Late Cretaceous, with deposition of thick, basinal mudstone-dominated successions. In the Late Cretaceous to Early Paleocene renewed tectonic activity caused uplift and faulting of large structures, such as the Davis Strait High and partly the Kangerluk Structure. Late Paleocene to Early Eocene strike-slip movements created thrust faults and compressional structures, mainly in the Ikermiut Fault Zone, associated with formation of the Ikermiut Basin. During the Paleocene and mainly the Early Eocene the >200 km long Ilulissat Graben developed. Paleocene and Eocene basalts occur west of Disko and Nuussuaq and narrow in distribution further south. The basalt cover offshore may be more limited than believed earlier. The area was offered for licensing in two periods from 2006 to early 2008.

Patterns of early post-depositional and burial cementation in distal shallow-marine sandstones: Upper Cretaceous Kenilworth Member, Book Cliffs, Utah, USA

There is a limited understanding of the spatial linkage between cementation processes in shoreface/coastal plain successions and those operating in distal offshore successions. To address this, an integrated sedimentological, sequence stratigraphic and diagenetic study was undertaken on a distal shallow-marine succession, the Upper Cretaceous Kenilworth Member Book, Cliffs, Utah, USA. Laterally extensive carbonate cement is the most volumetrically significant diagenetic feature. It constitutes up to 55 vol.% of the distal lower-shoreface sandstone and sandy siltstone units beneath major flooding surfaces. During rising relative sea-level major flooding events resulted in low sedimentation, which extended residence time of sediments in early diagenetic zones and promoted enhanced cementation beneath these boundaries. Carbonate for early calcite cements was probably derived from sulphate reduction, marine water and oxidation of organic matter. Stable-isotopic composition of later ankerite ( δ 18O ∼ − 11.9 to − 6.0‰ VDPB, δ 13C ∼ − 4.5 to − 0.3‰ VDPB) suggests precipitation during progressive burial ( c. 1.7 to 3.4 km, 72 to 122 °C) from evolved marine fluids. The carbonate and other mineralizing solutes were derived, increasingly with burial, from decarboxylation of organic matter and clay mineral transformations in adjacent siltstones and shales. These interbedded, overlying and underlying facies provided an important source of mineralizing solutes that influenced the extent of pervasive cementation during burial. The combination of stratigraphic and lithofacies control resulted in laterally extensive cements that differ to shoreface successions , although are similar in form to those described for many offshore mudstone-dominated successions. Limited early concretionary ferroan dolomite beneath the expression of the sequence boundary and some flooding surfaces, however, suggests cementation by meteoric fluids at times of relative sea-level lowstand. Similar processes have been demonstrated in more proximal successions in the Book Cliffs.

Mudstone Sedimentation at High Latitudes: Ice as a Transport Medium for Mud and Supplier of Nutrients

Abstract Controls on mudstone deposition at high latitudes are poorly known relative to low latitudes. In recent sediments deposited in these environments, ice significantly influences sediment transport and primary productivity. The products of ice transport are relatively well known in glacimarine settings, but are less well known from below melting sea ice. This latter setting is significant as today it is associated with high primary organic productivity. The aim of this study is to assess how sea ice might have controlled lithofacies variability and organic-matter distribution and preservation in an ancient marine, siliciclastic mudstone-dominated succession deposited at high latitudes. Combined sedimentary logging, optical and electron optical (backscattered electron imagery), geochemical, and isotopic methods were used to determine sample variability in forty-five samples collected from the Lower Cretaceous succession in the Mikkelsen Bay State #1 borehole (North Slope, Alaska). The succession overall fines upward and contains muddy sandstones and sand- and silt-bearing, clay-rich mudstones towards its base in contrast to clay-rich and clay-dominated mudstones towards its top. Some of the mudstone units exhibit thin (< 5 mm), relic-beds that fine upward weakly. In some units small (0.5 mm), bed-parallel silt-filled microburrows disrupt depositional laminae whereas in others pervasive burrowing completely obliterates original depositional textures. Many of the units are pelleted. These mudstones are unusual in that they contain minor but very striking outsize grains, composed of subrounded to rounded sand and granule-size material. In addition, they are good petroleum source rocks, with between 2.8 and 5.9 wt % total organic carbon, of predominantly Type II kerogen. The organic matter has an isotopic signature ranging from −25.4‰ δ13C to −28.1‰ δ13C. Thin tuffs (< 20 mm) and carbonate-cemented units are also present. Given the absence of significant polar ice in the Early Cretaceous the outsized grains are interpreted to have been deposited from a combination of melting, dirty anchor, and fast ice. The mud fraction, which forms the bulk of the sediment, is interpreted to have been deposited from melting, sediment-laden frazil ice, and fast ice. After deposition sediments were partially reworked by bottom currents generated by brine rejection during sea ice formation. Sympagic organisms, grazing on algae and bacteria both within and below the ice, pelleted the sediment. Bioturbation, which varies through the succession, indicates that sedimentation probably occurred beneath a predominantly oxic or dys-oxic water column. In this setting productivity was fueled by nutrients released from melting sea ice in the marginal ice zone. The good petroleum source potential of these mudstones is attributed to high organic productivity coupled to episodic and rapid sedimentation rather than existence of bottom-water anoxia linked to upwelling. Because sea-ice rafting was probably the dominant sediment transport mechanism it is not appropriate to use sequence stratigraphic methodology to predict lithofacies variability in this environment.

A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation

Research Article| March 01, 2004 A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation Ben Kneller; Ben Kneller 1School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Juan Pablo Milana; Juan Pablo Milana 2CONICET e Instituto de Geología, Universidad Nacional de San Juan, San Juan, Argentina Search for other works by this author on: GSW Google Scholar Clare Buckee; Clare Buckee 3School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Omar al Ja'aidi Omar al Ja'aidi 3School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar GSA Bulletin (2004) 116 (3-4): 348–367. https://doi.org/10.1130/B25242.1 Article history received: 15 Aug 2002 rev-recd: 18 Feb 2003 accepted: 14 Apr 2003 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ben Kneller, Juan Pablo Milana, Clare Buckee, Omar al Ja'aidi; A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation. GSA Bulletin 2004;; 116 (3-4): 348–367. doi: https://doi.org/10.1130/B25242.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The combination of high sediment supply rates and ample accommodation within fjords provides high-resolution records of deglaciation. Ancient fjord fills provide the potential for three-dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process. We describe the fill (Jejenes Formation) of a well-exposed Late Carboniferous (Pennsylvanian) glacial valley and its tributaries; these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments. The geometry of the valley and its tributaries is controlled by the underlying lower Paleozoic lithologies: a deep valley with steep sides exists where the bedrock is massive limestones, and a broader, shallower valley exists where the bedrock is generally a fine-grained olistostrome. The valleys are locally floored with diamictites, including both in situ tillites and remobilized diamictites. In the trunk valley these are locally overlain by a small, shallow-water delta. The major part of the valley fill consists of a ≤150-m-thick mudstone-dominated succession (probably generated by plumes of glacial outwash) containing numerous dropstones that decrease in abundance down the fjord. The mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys, each of which has a distinctive clast suite related to the local subcrop. The entire succession is overlain by >300 m of sandy turbidites, of which the upper part includes large mass-transport complexes.Intercalated within the succession in the trunk valley are structureless, graded, silty mudstones lacking dropstones but with abundant large wood fragments. Close to the steep western margin of the trunk valley, each of these massive mudstones is underlain by a slump or debris flow, locally containing meter-scale blocks of Ordovician limestone from the valley side. We interpret these as a consequence of rockfalls from the steeper valley sides, triggering debris flows on the subaqueous fjord slopes. We suggest that large solitary waves were generated as the rockfalls entered the water, traveling along the fjord and stripping vegetation from the shoreline. Large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds. These deposits, and other mass-flow deposits within the succession, emphasize the potential importance of catastrophic sedimentation within deglacial successions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

An offshore transgressive–regressive mudstone-dominated succession from the Sinemurian of Skåne, Sweden

A Sinemurian mudstone-dominated succession was exposed until recently in the Gantofta quarry in Skåne, southern Sweden. The deposits are placed in the Döshult and Pankarp Members of the Sinemurian–Aalenian Rya Formation. Similar facies of the same age are widespread in the Danish Basin where they constitute the F-Ib unit (F-I member) of the Fjerritslev Formation. The Gantofta succession thus represents the easternmost extension of the environment characteristic of the Fjerritslev Formation and is essentially the only locality where it has been possible to study the facies of this formation in outcrop. Sedimentation seems to have taken place under relatively quiet tectonic conditions except for the possible fault-control of the basin margin. The lower part of the Gantofta section is of Early and early Late Sinemurian age. It represents the upper part of the Döshult Member and consists of muddy, lower shoreface sandstones, abruptly overlain by dark, bioturbated, fossiliferous mudstones with thin storm siltstones and sandstones. They are overlain by the Upper Sinemurian Pankarp Member which comprises red-brown, restricted marine calcareous mudstones with an upwards increasing number of storm siltstones and sandstones reflecting general shallowing and shoreline progradation. The succession spans the greater part of two simple sequences with a distal sequence boundary located at the boundary between the Döshult Member and the Pankarp Member. The exposed part of the lower sequence includes a thick transgressive systems tract and a very thin highstand systems tract. The upper sequence is represented by an undifferentiated transgressive and highstand systems tract. An Early Sinemurian sea-level rise, a late Early Sinemurian highstand, an early Late Sinemurian fall and a Late Sinemurian minor rise and a major fall are recognised. Nearby boreholes show evidence for an end-Sinemurian – Early Pliensbachian major rise. This evolution corresponds well with trends recorded in the subsurface Fjerritslev Formation of the Danish Basin. Comparison with published European and British Jurassic sea-level curves show similar overall trends, but exhibit differences in the precise ages of sequence boundaries and maximum flooding surfaces. This may reflect poor biostratigraphical resolution of the Gantofta section, differences in sequence stratigraphic interpretation, real differences in the age of sequence stratigraphic key surfaces, or the basin marginal position of Gantofta in the Fennoscandian Border Zone.

Volgian–Ryazanian ‘hot shales’ of the Bo Member (Farsund Formation) in the Danish Central Graben, North Sea: stratigraphy, facies and geochemistry

Upper Jurassic – lowermost Cretaceous marine mudstones represent the most significant source of hydrocarbons in the Central and Northern North Sea. Of particular importance in the Danish sector of the Central Graben is a succession of radioactive ‘hot shales’ referred to the Bo Member, in the upper levels of the Farsund Formation (Kimmeridge Clay Formation equivalent). This mudstone-dominated succession is typically 15–30 m thick and has a total organic carbon (TOC) content of 3–8%, though locally exceeding 15%. Although truncated on some structural highs, the Bo Member is a persistent feature of the Danish Central Graben. Lateral variation in both thickness and organic richness is attributed to intrabasinal structural topography and to the location of sediment input centres. Detailed study of the dinoflagellate cyst biostratigraphy of 10 wells indicates that the onset of enhanced organic carbon burial began in the middle–late Middle Volgian in this portion of the Central Graben. The Bo Member, representing the peak of organic carbon enrichment, is largely of Early Ryazanian age. Core data (Jeppe-1, E-1 wells) indicate that the organic-rich shales of the Bo Member are not wholly of hemipelagic origin, as commonly assumed, but may locally be dominated by fine-grained turbidites. Absence of bioturbation, well-preserved lamination and high TOC values suggest that bottom waters were predominantly anoxic although the presence of in-situ benthic bivalves at discrete horizons in the E-1 well suggests that suboxic conditions prevailed on occasion. The Bo Member is a good to very good source rock, showing very high pyrolysis yields (10–100 kg HC/ton rock) and Hydrogen Index (HI) values in the range 200–600. In particular, the Bo Member is characterised by an abundance of 28,30 bisnorhopane (H28), a compound that is indicative of anoxic environments. These new data from the Danish sector of the Central Graben are compatible with the model of Tyson et al. (1979) in which the accumulation of organic-rich mudstones was controlled primarily by bottom-water anoxia beneath a stratified watermass. A number of factors probably contributed to the development of watermass stratification, both intrinsic such as the tectonic morphology of the graben system and extrinsic including climate and sea-level stand.

Palaeoenvironmental changes in the Pliocene Intra-Apenninic Basin, near Bologna (Northern Italy)

Combined palaeoecologic and sedimentologic studies reveal remarkable palaeoenvironmental changes in the Pliocene Intra-Apenninic Basin (PIB) of the Bologna Apennines (Northern Italy). At the northern margin of PIB, the stratigraphic succession is approximately 1000 m thick, and displays an overall coarsening-upward trend, including a lower mudstone-dominated succession (Argille Azzurre Formation) of Zanclean age, overlain by a sandstone-rich unit (M. Adone Formation), assigned to the Zanclean-Piacenzian. The vertical succession of biofacies within the Argille Azzurre Fm. indicates an obvious shallowing-upward tendency, from slope/outer-shelf (150–300 m water depths) to inner-shelf (30–50 m) environments. A vertical cyclic pattern of facies, with alternating sandy siltstones and sandstone bodies, characterizes M. Adone Formation. Each elementary cycle, about 30–50 m thick, includes a couple of siltstone-dominated inner-shelf and prodelta deposits, passing upwards into progradational delta front, tabular sand bodies. These high-rank cycles, spanning an interval of time in the order of magnitude of 40 ky, are separated by flooding surfaces, clearly recognizable on the basis of palaeoecologic analysis, and reflect an aggradational stacking pattern of parasequences superposed to the general shallowing-upward trend.

Depositional history of the fluvial Lower Carboniferous Sortebakker Formation, Wandel Sea Basin, eastern North Greenland

The Lower Carboniferous non-marine Sortebakker Formation is restricted to the south coast of Holm Land. It is estimated to exceed 1000 m in thickness and is subdivided by a low-angle disconformity into a lower mudstone-dominated unit (c. 335 m) and an upper sand-dominated unit (c. 665 m). The lower mudstone-dominated succession consists of stacked 0.5–6 m thick fining-upward cycles of fine- to medium-grained sandstone and mudstone. Cycles in the upper part of the formation are up to 20 m thick. They are dominated by thick tabular sandstones up to 13 m thick overlain by shaly units that resemble those in the lower mudstone dominated cycles. Six facies associations are identified and together describe a fluviatile–lacustrine depositional system. Five of the facies associations characterise different parts of a meandering riverdominated flood plain whereas the sixth facies association represents more permanent lakes.

Cyclicity of Triassic to Lower Jurassic continental red beds of the Argana Valley, Morocco: implications for palaeoclimate and basin evolution

Cyclical playa deposits form a prominent part of the continental clastic succession of the Argana Valley, Western High Atlas of Morocco. The red beds formed in Triassic to Lower Jurassic times during rifting of the North American and African plates. Detailed stratigraphic work revealed asymmetrical, metre-scale cycles in mudstone-dominated successions that constitute the intermediate and upper portion of the basin fill. Sedimentary cycles commonly comprise ephemeral lake shales at the base, playa mudflat mudstones in the intermediate part, and both fluvial and aeolian sandstones at the top. Cycles of the Aglegal Member (T4) are mainly characterized by analcime-rich playa mudflat deposits displaying features indicative of palaeo-Vertisols. Cycles of the Sidi Mansour (T7) and Hasseine (T8) Members are represented by ephemeral lake or dry playa mudflat deposits grading into saline mudflat mudstones that are overlain by sheet flow and minor aeolian sandstones. Sedimentary cycles of the Imerhrane Member (T9) comprise sheet delta sandstones at the base overlain by ephemeral lake and dry playa mudflat mudstones. Upper cycle portions consist of aeolian dune and sand sheet sandstones. Cyclicity is attributed to palaeoclimatic and associated palaeohydrological fluctuations, probably within the Milankovitch frequency band. Sedimentary facies of each cycle provide evidence for a gradual climatic drying with time. The asymmetrical drying-upward cycles possibly record the precession cycle, since they are modulated by symmetrical (i.e., oscillating drying/wetting) cycles of a lower frequency indicative of eccentricity. A long-term change in palaeoclimate ranging from semi-arid conditions with seasonal precipitation (T4) towards an arid, non-seasonal climate (T8) is preserved within the cyclical units spanning a time interval of several million years. Individual cycles can be traced laterally for tens of kilometres. Correlative sections are almost identical in thickness, suggesting a phase of tectonic quiescence during their deposition. Sediment accumulation was not restricted to small-scale grabens, but took place continuously throughout the exposed area of the Argana Valley, implying that accommodation space has not been controlled by syndepositional tectonism.

Early diagenetic pyrite morphology in a mudstone-dominated succession: the Lower Jurassic Cleveland Ironstone Formation, eastern England

Abstract Diagenetic pyrite in the mudstones and ironstones of the Lower Jurassic Cleveland Ironstone Formation of eastern England exhibits two distinct morphologies: framboidal pyrite, commonly associated with organic matter, and euhedral pyrite, associated with detrital clay pellets. These two morphologies are mutually exclusive in occurrence. Framboidal pyrite is present in clay-rich mudstones, ooidal ironstones, apatite-rich units and some silt-rich mudstones. Euhedral pyrite is present in silt-rich and sand-rich mudstones. δ34S isotopic analysis of six samples of pyrite suggests that both types of pyrite morphology precipitated during early diagenesis from porewaters with open access to overlying sea-water, although both probably acted as sites for continued pyrite precipitation during burial. It is proposed that framboidal pyrite precipitated from iron-dominated porewaters at sites of sulfide supply (i.e. in the region of organic matter as a result of bacterial sulfate reduction) where, locally, sulfide production rates were high enough for porewaters to reach supersaturation with respect to FeS. Euhedral pyrite also precipitated from iron-dominated porewaters, but sulfide production rates from organic matter was such that FeS saturation was not reached at the sites of sulfide production. Instead, euhedral pyrite was precipitated directly from porewater when FeS2 saturation was reached. The control over pyrite morphology was probably the amount and reactivity of the organic matter within the deposited sediments. The sand-rich mudstones contained less reactive organic matter due to clastic dilution and deposition in shallower environments with O2-rich bottom waters. The ironstones and apatite-rich units were deposited under very low sedimentation rates, and as a result organic matter contents were very low and iron reduction dominated early diagenesis, which inhibited sulfate-reduction. The presence of minor framboidal pyrite within these units, however, suggests that sulfide reduction took place in micro-environments during early diagenesis.

A sequence-stratigraphic interpretation of a mudstone-dominated succession: the Lower Jurassic Cleveland Ironstone Formation, UK

Microfacies analysis (using optical and backscattered electron imagery) has been undertaken on 37 samples from the Cleveland Ironstone Formation, Staithes, Yorkshire, UK. Four lithofacies were encountered: clay-rich mudstones, silt-rich mudstones, sand-rich mudstones and concretionary carbonates (two types: berthierine/siderite-rich ironstones and apatite-rich concretionary horizons). Successive units were found to stack systematically into upward-coarsening units on a small (0.1–1.0 m) scale. Upward-coarsening and upward fining packages were also found on a larger (1.0–3.0 m) scale. The small-scale upward-coarsening units are interpreted to be parasequences; while the large scale upward-fining and upward-coarsening packages are interpreted to be retrogradational and progradational parasequence sets respectively. The ironstones occur at the level where the stacking patterns change from being overall progradational to retrogradational, while the apatite-rich concretionary units occur at the level where the stacking patterns change from being retrogradational to progradational. The concretionary carbonates are interpreted to have formed close to/at major stratal surfaces. The ironstones are interpreted to be either the correlative equivalent of sequence boundaries or part/all, of the forced regressive system tract; while the apatite-rich units are interpreted to have precipitated close to/at maximum flooding surfaces (condensed sections) and/or major transgressive surfaces.