Bay Deposits Research Articles

Paleontology, Stratigraphy and Biogeography of the Late Precambrian and Phanerozoic Formations of Russia

Abstract —This special issue is dedicated to discussing the possibility of the stage division of the Vendian system, specifically, a composite section of the Siberian Platform is proposed as a stratigraphic standard. For the Ordovician system of the Siberian Platform and Northeastern Russia, certain changes in stratigraphic charts are proposed, nomenclative issues and different variants of correlations of regional horizons with the General Stratigraphic Scale (GSS) of Russia are considered. A geochemical analysis of Bajocian and Bathonian belemnite rostra of Arctic Siberia was carried out and for the first time a comprehensive C, O, and Sr isotope characterization of the sections was obtained, making it possible to propose a comparison of the studied sections with the European standard and to develop paleogeographic models. Comprehensive studies of the Upper Jurassic and Lower Cretaceous series of the Anabar Bay deposits (Laptev Sea) led to an improved biostratigraphic division for this reference section and to the identification of the levels for interregional and global correlation. The magnetostratigraphic division of the Jurassic–Cretaceous boundary interval and its comparison with the Tethyan regions are discussed. Taking into account biostratigraphic data, the δ13Corg variation curve can also serve as a correlation tool. The clinoform structure of Upper Jurassic strata was revealed in the northwest of the Anabar–Khatanga depression, based on the interpretation of seismic profiles calibrated against studied sections. The formation of this complex allows us to consider this stage as the initiation of the Verkhoyan orogeny in this folded area. Analysis of variations in the thickness of sediments allows us to deduce that intense tectonic-sedimentary processes took place during the Late Jurassic epoch, along with subsidence of the bed of the sedimentary basin. Analysis of a specific assemblage of lacustrine fossils from the reference section of the upper part of the Lower Cretaceous series of Transbaikalia and of published data showed that this fossil assemblage was widespread in East Asia. Biofacies analysis made it possible to reconstruct the paleoenvironments of this time.

Paleoproterozoic (Huronian) valley-controlled deglacial-fluvial sedimentation, northern Cobalt Basin, Ontario, Canada

Detailed sedimentological and stratigraphic analysis of pre-vegetation sedimentary systems that deposited across global-scale climate change episodes is key to fully understanding past feedback responses in Earth surface systems and the details of their paleoenvironments. The Cobalt Basin, recording the upper Huronian Supergroup, captures a transition from glacial (Gowganda Formation) to post-glacial (Lorrain Formation) deposystems in parallel with Earth's Great Oxidation Event and is ideal for sedimentological/stratigraphic analysis due to its limited post-depositional deformation. Stratigraphic measurements and correlations from the northern Cobalt Basin reveal that the Gowganda and Lorrain formations are preserved within a paleovalley, interpreted as a fjord. Sub-glacial deposits of the Coleman Member (lower Gowganda Formation) are preserved at the base of the paleovalley, unconformably above Archean volcanic and granitic rocks of the Abitibi subprovince. Subsequently, the fjord was filled by glaciomarine strata sourced from a grounded tidewater icesheet prior to climate warming. Above the glaciomarine deposits, deltaic deposits of the Firstbrook Member (upper Gowganda Formation) represent a transition to nonglaciogenic deposition under a warm and humid climate. The deltaic deposits comprise three facies associations: (1) delta front/slope strata dominated by horizontally stratified siltstone; (2) interdistributary bay deposits composed of symmetrically rippled and thinly laminated siltstone; (3) distributary mouth bar deposits dominated by very fine-grained arenite. Delta front/slope deposits occur directly above glaciomarine strata, while interdistributary bay and distributary mouth bar deposits occur above delta front/slope strata and are laterally discontinuous across the study area. Prodelta deposits are not preserved in the study area, although they are reported elsewhere in the basin. At the flanks of the paleovalley, alluvial fan deposits, confined by Archean rocks, interfinger with deltaic strata. Alluvial fan sedimentation, triggered by enhanced weathering in an unvegetated warm and humid setting, led to flashy sheetflood deposition due to significant topographic variations at the flanks of the valley setting. In some instances, sandstone beds of the overlying Lorrain Formation, comparable to distal to medial reaches of the modern South Saskatchewan River, cut down through delta strata. Up-section, the braidplain strata coarsen to gravel-rich facies representing Donjek River-type deposits. Overall, the stratigraphic succession in the northern Cobalt basin study area represents a single progradation from glaciomarine through deltaic deposition, into fluvial braidplain deposition. The succession is preserved at the cratonward limit of a passive margin, suggesting that progradation was likely influenced by relative sea-level fall linked to glacio-isostatic uplift, similar to fjord-filled sedimentary successions that have developed since the Last (Pleistocene) Glacial Period.

Reservoir quality evaluation and prediction in ultra-deep tight sandstones in the Kuqa depression, China

Core, thin sections, cathodoluminescence (CL), scanning electron microscopy (SEM), conventional well logs and image logs are used to unravel depositional microfacies, diagenetic facies and fractures in the deeply buried (6000–8100 m) Cretaceous Bashijiqike (K1bs) and Baxigai (K1bx) Formations in Kuqa depression of the Tarim Basin. Results show that depositional microfacies in core and well log data include distributary channel, river mouth bar and distributary bay deposits of fan-braided delta fronts as well as lacustrine deposits. We establish well log predictable models of depositional microfacies using conventional and image logs. The Cretaceous sandstones experienced low to medium mechanical compaction and low intensity dissolution. Dominant diagenetic minerals are carbonate cements, clay minerals and minor amounts of quartz cements. The pore spaces are primarily intergranular pores and rare dissolution pores. We identify three diagenetic facies according to compaction state and diagenetic minerals, including carbonate cemented facies, tightly compacted facies, and facies having limited compaction and lacking cement (slightly cemented and compacted facies). We use well log characteristics to interpret diagenetic facies in areas without core data. Fractures are also elements of reservoir quality, including vertical opening-mode fractures, high to medium dip angle fractures, low angle fractures that probably include small faults and horizontal fractures. Fractures include open, partially open, and closed (sealed) fractures. We used image logs to identify fracture attributes, and calculate fracture density, porosity, aperture, and length. Depositional microfacies and diagenetic facies determine the primary intergranular pores and diagenesis subsequently modified secondary pore spaces. Natural fractures acted as both reservoir porosity (probably less than 1%) and as hydrocarbon flow channels accounting for elevated permeability. We evaluate and predict reservoir quality by superposing depositional microfacies, diagenetic facies and fracture occurrence.

Late Quaternary sedimentary record of estuarine incised-valley filling and interfluve flooding: The Manfredonia paleovalley system (southern Italy)

Multiple paleovalley systems of late Quaternary age have been widely explored in previous research from the Gulf of Manfredonia on the basis of seismic data, but only limited information is available on their proximal (onshore) segments. Through an integration of sedimentary, paleoecological (mollusks, benthic foraminifers, ostracods), and geochemical analyses from three 30-50 m-long onshore cores and a sequence-stratigraphic framework chronologically constrained by 25 radiocarbon data, we document the stratigraphic architecture of three contiguous paleovalley systems (Candelaro, Cervaro and Carapelle rivers) and their sedimentary response to Late Pleistocene valley excavation, Holocene filling and basinwide interfluve flooding. Above a prominent sequence boundary formed during the Late Pleistocene relative sea-level fall, fluvial-channel gravels and sands (lowstand systems tract) are overlain by a deepening-upward, valley-fill succession of inner-estuarine (freshwater) to outer-estuarine (brackish) muds (lower transgressive systems tract – TST). The individual valley fills are overlain by laterally extensive bay deposits (upper TST) and by a progradational succession of prodelta/delta front and offshore/shoreface deposits that reflect normal regression under highstand conditions (HST). The transition from fluvial to inner-estuary (fluvial-dominated) and outer-estuary (wave-influenced) deposits records the progressive shift in sediment provenance from Southern Apennine source rocks to a mixed composition that reflects increasing alongshore sediment contribution from northern sources via the SE-directed Western Adriatic Current. The stratigraphic surface that demarcates the transition from estuarine to bay depositional systems (lower/upper TST boundary) represents the physical prolongation of interfluvial terrace surfaces, as valley margins were flooded during the Early Holocene transgression. This surface, typically recognizable on seismic profiles at the boundary between low-amplitude and overlying high-amplitude reflectors, has no obvious lithologic signature in core. However, it can be readily identified on the basis of paleoecologic features (sharp increase in species diversity and in the proportion of marine taxa) that reveal the abrupt transition from laterally confined to unconfined settings.

Facies characteristics and stratigraphy of an Upper Cretaceous mud‐dominated subaqueous delta: Medicine Hat Member (Niobrara Formation), Alberta, Canada

AbstractThe Medicine Hat Member in Alberta, Canada, is a muddy interval with thin sandstones. However, the sedimentology and stratigraphy are poorly understood – a reflection of the limited knowledge of mud‐dominated successions. Here facies analysis and stratigraphy from core and wireline logs were used to construct a depositional framework for the interval in a stratigraphical context. Sedimentological and ichnological results show that the Medicine Hat Member was deposited in shallow water within a mud‐dominated subaqueous delta system under the combined influence of river flow, waves, storms and longshore currents. Four facies are recognized, which are interpreted as distal delta front, proximal prodelta, distal prodelta and interdistributary bay deposits. The distal delta front is dominated by sandy storm deposits and thin storm‐flood hyperpycnites. The prodelta, on the other hand, is characterized by muddy storm deposits and wave‐enhanced sediment gravity flow deposits, with only subordinate hyperpycnites. Ichnological assemblages in both the delta front and prodelta are impoverished, indicating persistent physico‐chemical environmental stresses. Interdistributary bay deposits are uncommon and are differentiated based on more robust ichnological assemblages and higher bioturbation intensities. Subsurface correlations reveal shallowing‐upward parasequences that have aggradational and progradational stacking patterns and a very low depositional gradient (ca 0.03° to 0.1°). The stratigraphy reflects rapid progradation with fixed accommodation in a low‐gradient setting; coeval flexural subsidence in the foredeep was dampened by underlying basement structures. Furthermore, previous suggestions that the Bow Island Arch impacted sediment distributions are not substantiated by the low angle geometry of clinoforms. Data from this study supports the interpretation that Medicine Hat deltas were fed by rivers flowing north through Montana because parasequences are sandier towards the south. This study fills a crucial gap in the literature by providing a rock record example of a mud‐dominated subaqueous delta system and serves as a basis for comparison in core studies of similar units globally.

Mixed siliciclastic–carbonate sedimentation in an evolving epicontinental sea: Aptian record of marginal marine settings in the interior basins of north‐eastern Brazil

AbstractThe Aptian evaporitic transitional sequence (sag phase) of the Brazilian marginal basins records the first connection between the Central and South Atlantic oceans in the equatorial area. During this phase, lacustrine carbonate reservoirs and giant salt deposits developed in the southern basins of Santos and Campos, forming world‐class petroleum reservoirs. The sag succession is also well‐preserved in the interior rift basins of north‐eastern Brazil, where upper Aptian strata are represented by a continuous section. This contribution presents an interpretation of the evolution of a third‐order depositional sequence comprising lacustrine limestones, marine siliciclastic facies and evaporite deposits of the intracontinental Araripe Basin. The Lowstand Systems Tract is characterized by fluvial deposits filling accommodation generated during the syn‐rift phase. The overlying deposits comprise marine facies with preservation of dinoflagellates and marine ichnotaxa, evidencing marine deposition in bayhead delta settings. The transgressive surface is represented by limestones, including the Konservat–Lagerstätte laminites, onlapping the basement rocks. Above, tide‐dominated bay deposits with distinct subtidal, intertidal and supratidal portions are recorded. The Maximum Flooding Surface is a dark shale below foreshore to shoreface facies, marking the beginning of the Highstand Systems Tract, culminating with deposition of evaporites (gypsum and anhydrite). The stratigraphic architecture and palaeocurrents measured in different facies associations suggest that marine waters reached the basin from the south. The data unequivocally records late Aptian marine ingressions of an incipient South Atlantic Ocean over the interior basins of north‐eastern Brazil, while lacustrine conditions were still prevailing in the Pre‐Salt sag units of the Santos and Campos basins.

Multivariate taphonomic analysis of mollusk shell concentrations in Holocene deposits of southern Brazil: An integrated approach

Shell concentrations are one of the most distinctive features of the Holocene coastal stratigraphy in the southern portion of Santa Catarina State, southern Brazil. In this paper, we integrated stratigraphic, geochronological, geophysical, and taphonomic data to discuss the processes involved in the genesis of shell concentrations in a siliciclastic and subtropical setting, a useful analogy for ancient shell concentrations in semi-closed environments affected by storms. The data indicated the succession of three facies associations (FA): bay, lagoon, and back-barrier. This succession implies a grain size fining-upward trend that is representative of a gradual shallowing. Interpretation of GPR sections revealed that the passage from the bay to lagoonal deposits occurred by forming a laterally continuous, high-amplitude surface overlain by sigmoidal reflections, which characterized the progressive basinward backstepping of the lagoonal margin. Shell concentrations in bay deposits are an allochthonous product of storm flows in shallow waters. In contrast, accumulations of the bivalve Anomalocardia brasiliana had their valves reworked in the lagoonal margins and transported to the bottom, characterizing a parautochthonous accumulation. In this study, the correlation of taphonomy and grain size indicates that in bay FA, the loss of periostracum is correlated with increased gradients of fine sand, and part of the shell samples correlates to corrosion and abrasion in increased gradients of medium sand and decreased ones of fine sand. Additionally, in the lagoon FA, the loss of periostracum depends on the decrease in mud-enriched sediments and the increase in fine and medium sand, whereas brightness loss and color alteration are related to the increase in fine and medium sand, as well as margin modification. Corrosion was positively correlated to the mud-dominated fraction.

Multi-scale SR-μXRF Imaging and Characterization of Gold Mineralization at the Monument Bay Deposit, Stull Lake Greenstone Belt, Manitoba, Canada

Multi-scale SR-μXRF Imaging and Characterization of Gold Mineralization at the Monument Bay Deposit, Stull Lake Greenstone Belt, Manitoba, Canada

EPMA Characterization of Gold Associated with Different Sulfide Textures at the Monument Bay Deposit, Manitoba, Canada

Journal Article EPMA Characterization of Gold Associated with Different Sulfide Textures at the Monument Bay Deposit, Manitoba, Canada Get access Chunyi Hao, Chunyi Hao Western University, London, Ontario, Canada Search for other works by this author on: Oxford Academic Google Scholar Juliana Casali, Juliana Casali Western University, London, Ontario, Canada Search for other works by this author on: Oxford Academic Google Scholar Zohreh Ghorbani, Zohreh Ghorbani Western University, London, Ontario, Canada Search for other works by this author on: Oxford Academic Google Scholar Hannah Cavallin, Hannah Cavallin Western University, London, Ontario, Canada Search for other works by this author on: Oxford Academic Google Scholar Lisa Van Loon, Lisa Van Loon Western University, London, Ontario, Canada Search for other works by this author on: Oxford Academic Google Scholar Neil Banerjee Neil Banerjee Western University, London, Ontario, Canada Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 26, Issue S2, 1 August 2020, Pages 2182–2184, https://doi.org/10.1017/S1431927620020723 Published: 01 August 2020

The facies analysis of a fan delta by integrating multiple discipline data — A case study of the KL-A oilfield, Bohai Bay Basin, China

The third member of the Shahejie Formation (Es3) is the main hydrocarbon exploration target in the KL-A oilfield, Bohai Bay Basin, East China. The facies classification is an essential step in mapping the depositional system of Es3 within the Bohai Bay Basin. The facies model is important for identifying the “sweet” lithology within the reservoirs. We characterize the facies of Es3 by integrating cores, well logs, and seismic data. The analysis indicates that the Es3 consists of fan delta deposits. The analysis using well logs and cores indicates that there are five different lithofacies for the Es3 Formation: massive sandstone, horizontally bedded sandstone, trough cross-bedded sandstone, ripple cross-laminated sandstone, and massive mud. The microfacies of Es3 include distributary channel, distributary mouth bar, interdistributary bay, and lacustrine mudstone deposits. The sweet lithologies for hydrocarbon accumulation within the KL-A oilfield include the coarse- and fine-grained sand developed within the channels and distributary mouth bar. We use seismic rms amplitude strata slices to determine the horizontal distribution of facies of the fan delta. The correlation between rms amplitude and well logs indicates that relatively low rms amplitude anomalies on the strata slices can be used as an indicator for sandstone within the KL-A oilfield.

Ichnology and sedimentology of aeolian and shallow‐marine interactions in the Permian Unayzah Group of central Saudi Arabia: Towards a mechanism for infaunal colonization of coastal dune fields and erg margins

AbstractThis paper documents aeolian and shallow‐marine interactions and describes their ichnofossil suites from the early Permian Tinat Member of the Nuayyim Formation of subsurface Saudi Arabia, thereby confirming marine sedimentation in an interval historically interpreted as being dominated by continental settings wherein aeolian processes prevailed. This paper attempts to characterize in situ animal–sediment interactions in coastal dune fields and erg margins in arid to semiarid settings; where the description of organism–sediment relationships, until now, has been focused on the landward portion including freshwater suites. Sedimentological and ichnological assessments in the Tinat Member allowed the identification of aeolian and marginal‐marine, tidally influenced interactions in two facies associations that are conformably interbedded. Facies Association 1 includes sediment deposition in aeolian and continental, groundwater table‐related environments such as: aeolian dunes (facies 1); dry and damp aeolian interdunes (facies 2 and 3); ephemeral and perennial stream deposits (facies 4 and 5); and palaeosols (facies 6). Facies Association 2 reflects sedimentation in shallow‐marine, tidally influenced environments and includes punctuated occurrences of tidal flats and sheltered shallow bay deposits (facies 7 and 8) displaying a brackish‐water trace fossil assemblage. This suite exhibits a diminutive, highly stressed mixture with structures reflecting an impoverished Skolithos Ichnofacies and Cruziana Ichnofacies associated with tidal flat deposits displaying synaeresis cracks, lenticular bedding, low‐angle and wavy lamination, flaser bedding, reactivation surfaces, carbonaceous double mud drapes, current ripples and tubular tidalites. Aeolian sedimentation and trace fossil associations presented in this paper are significant because they provide evidence for shallow‐marine, tidally influenced and aeolian processes in the Unayzah Group during deposition of the Tinat Member of the Nuayyim Formation. More importantly, documenting marine and aeolian interactions and their resulting ichnofossil suite can be used: (i) to build integrated sedimentological and ichnological facies models; and (ii) to characterize the resulting trace fossil association in this particular interactive setting that can be used to identify similar successions elsewhere in the rock record.

Systems tracts and their bounding surfaces in the low- accommodation Upper Mannville group, Saskatchewan, Canada

Abstract Sequence stratigraphic interpretations of paralic successions can be challenging, because such settings are commonly controlled by a combination of allogenic controls and autogenic processes, leading to complex depositional architectures. In low-accommodation systems where parasequences are less than 15 m thick, the challenges in recognizing discrete stratigraphic surfaces are exacerbated by limited vertical separation between surfaces or their outright erosional amalgamation, requiring high-resolution facies analysis to resolve their geometries. Herein, we present criteria derived from core data and well logs to differentiate between allogenic and autogenic surfaces in a low-accommodation paralic setting, using the Lower Cretaceous Mannville Group of west-central Saskatchewan, Canada as a case study. The upper part of the Mannville Group (Sparky, Waseca and McLaren formations) displays complex stratigraphic relationships related to base-level changes. Marine flooding surfaces (MFS) and transgressive surfaces of erosion (TSE) of 3rd and 4th order record allogenic changes ( e.g., basin subsidence and/or eustatic changes in sea level), and are used to define parasequence boundaries of strandplain-shoreface successions. Deltaic deposits not only possess these allogenic transgressive surfaces, but autogenic 5th-order flooding surfaces, which are broadly similar in appearance, as well. These autogenic surfaces record responses to channel avulsion or lobe abandonment, separate discrete delta lobes, and display limited lateral extents. Shoreface-related flooding surfaces, by contrast, bound true allogenic parasequences and, therefore, have regional correlatability. The Waseca Formation also possesses surfaces related to base-level fall. To the north, a subtle regressive surface of marine erosion (RSME) marks the base of the falling stage systems tract. Elsewhere, a widespread subaerial unconformity (SU) separates the Waseca into lower and upper members. In most areas, the SU is amalgamated with surfaces generated by later base-level rise. Upper Mannville strata in the study area, therefore, can be separated into parts of two depositional sequences. The main deposits of the lower sequence comprise a highstand systems tracts (HST) in the Sparky Formation. The base of the Lower Waseca Member marks the onset of a transgressive systems tract (TST), associated with widespread shoreline retreat. A 3rd-order maximum flooding surface (MxFS) marks the end of transgression and resumption of normal progradational regression in a highstand systems tract associated with the Lower Waseca Member. Following highstand normal regression, a major base-level fall initiated a subaerial unconformity that marks the base of the upper sequence. Fluvial valley incision led to sediment bypass and deposition of forced regressive and lowstand shoreface and delta complexes of the falling stage systems tract (FSST) and lowstand systems tract (LST), respectively, in the northern part of the study area. Pedogenic modification of subaerially exposed sediment occurred in interfluve areas. Ensuing TST accumulation was initially confined to the tidal-fluvial estuarine infill of the incised valleys and transgressive bay deposits of the Upper Waseca Member. The Upper Waseca is capped by a 3rd-order maximum flooding surface (MxFS), which separates it from the overlying McLaren Formation. This marks the return to regional shoreline progradational regression and corresponds to the highstand systems tract (HST) of the upper sequence.

Facies and architecture of river-dominated to tide-influenced mouth bars in the lower Lajas Formation (Jurassic), Argentina

The Middle Jurassic Lajas Formation in the Neuquen Basin of Argentina has been considered an ideal analog for tide-dominated deposits because of the widespread presence of tidal sedimentary structures and its heterolithic nature. Outcrops of the Lajas in the Los Molles area provide excellent exposures allowing both sedimentary structures and large-scale architectural information to be documented in detail. The extensive event bed stratification that characterizes the delta front and interdistributary bay deposits is interpreted to be the result of river floods because of the sharp base, fining-upward grain size trend, and seaward-directed paleocurrent indicators within each bed. The absence of wave-generated structures precludes a storm wave origin for these beds. Interflood deposits have two forms. The first is fine-grained sandstone and siltstone that is highly bioturbated with no tidal structures and is indicative of an overall river-dominated system. The second is also finer grained than the river flood beds but shows distinctive tidal features, indicative of a tide-influenced system during times when river influence was least. Mouth bars can be classified as purely river-dominated or river-dominated with tidal influence, depending on the type of interflood beds present. Tide-influenced mouth bars tend to be muddier, with more internal flow baffles or barriers and a lower-angle dip than their river-dominated counterparts. This study suggests that heterolithic successions containing pervasive tidal structures need not be tide-dominated because not all tidal structures are of equal importance in environmental interpretations. Their location (in river flood layers versus interflood layers) can be used as a methodology for determining the dominant and subordinate processes responsible for shaping the delta.

Using Trampling Modification to Infer Occupational Intensity During the Still Bay at Blombos Cave, Southern Cape, South Africa

Demography probably had a significant influence on the transmission of cultural innovation during the late Pleistocene. In enclosed sites such as rockshelters, trampling marks are likely direct evidence for human occupations and can possibly be used to infer occupational patterns. In this study, we explore trampling modification as a proxy for occupational intensity. We examined trampling data at the Middle Stone Age site of Blombos Cave in South Africa to investigate whether these marks may inform on occupational intensity during the Still Bay period—a significant era for the development of behavioural modernity. Trampling is defined by pitting, scratches, abrasion and linear marks. These marks were then compared to other taphonomic proxies (e.g., faunal density per volume, transverse fractures, non-anthropogenic modification) to explore the relationships between these indicators. Our results indicate that trampling modifications can provide information on a site’s occupational history and that the data indicate that there are two phases within the Blombos sequence showing more intense/frequency occupations, corresponding to the early and middle Still Bay deposits.

Comparisons among the Oortsog, Dulaan, and Nomgon mafic-ultramafic intrusions in central Mongolia and Ni-Cu deposits in NW China: implications for economic Ni-Cu-PGE ore exploration in central Mongolia

Although there are many mafic-ultramafic intrusions in the western and central regions of Mongolia, Central Asian Orogenic Belt (CAOB), no economic-grade Ni-Cu deposits have yet been discovered. To understand the economic Ni-Cu deposit potential of the intrusions in central Mongolia, the parental magma affinity and sulfide saturation of the Oortsog, Dulaan, and Nomgon Ni-Cu mineralized mafic-ultramafic intrusions are studied. These three intrusions are predominantly gabbroic in composition, while the Oortsog and Dulaan intrusions also contain small proportions of peridotites. The parental magmas of the Oortsog and Dulaan intrusions are tholeiitic, as indicated by their Cr-spinel and clinopyroxene compositions, whereas the parental magma of the Nomgon intrusions is likely calc-alkaline. The compositions of Cr-spinel and clinopyroxene, combined with the presence of significant Nb-Ta depletions, indicate that these rocks were most likely derived from modified mantle sources. Both the Oortsog and Nomgon intrusions form two clusters in terms of their olivine composition, suggesting that multiple magma surges were involved during their emplacement. The relatively low Fo values and Ni contents in olivine from the three intrusions compared to those from Ni-Cu deposits in NW China, as well as those in the Voisey’s Bay deposit in Canada, indicate that the three intrusions were crystallized from relatively evolved magmas. The Cu/Zr ratios of rocks of the Oortsog, Dulaan, and Nomgon intrusions are higher than 1, suggesting that these rocks contain cumulus sulfide. This, coupled with the presence of rounded sulfide inclusions in olivine of the Oortsog and Dulaan intrusions, suggests that sulfide saturation occurred before or during olivine crystallization. The distribution patterns of platinum group elements (PGEs) of the Dulaan and Oortsog intrusions record slight Rh, Pt, and Pd (PPGE) enrichment relative to Os, Ir, and Rh (IPGE). Furthermore, the Ni/Cu ratios of sulfide-bearing rocks from the Oortsog intrusion vary from 1.8 to 3.8, which are consistent with those of the Ni-Cu sulfide deposits in NW China. In contrast, the Ni/Cu ratios of sulfide-bearing rocks from the Nomgon intrusion are extremely low (0.03 to 0.07). This, together with the significant enrichment in PPGE relative to IPGE, suggests that these sulfides of the Nomgon intrusion were segregated from a magma that was extremely enriched in Cu and PPGE but depleted in Ni and IPGE. The characteristics of the chalcophile elements in these intrusions are attributed to the fact that the derivation of the Nomgon magma was significantly different from that of the Dulaan and Oortsog parental magmas. Overall, although the parental magmas of the intrusions in central Mongolia are more evolved than those in NW China, they are comparable in terms of the sizes of their intrusions, constituent minerals, and mineral chemistry. These similarities suggest that the intrusions in central Mongolia have economic Ni-Cu sulfide potential. Furthermore, intrusions similar to the Nomgon intrusion may feature PGE mineralization potential.

テフラ編年と<sup>14</sup>C年代に基づく鹿児島湾奥，新島（燃島）の海成堆積物の編年とその意義

Shinjima (Moeshima) Island in Kagoshima Bay, southern Kyushu, Japan is noteworthy in volcanology, paleontology, and palaeo-environmental studies, because the island emerged from the bay bottom during volcanic activity at Sakurajima in 1780 AD. As a result, Holocene and late-Pleistocene deposits of the bay including muddy deposits, a thick pyroclastic flow deposit, and prominent molluscan shell beds occur on this island. Several tephras included in the bay deposits are critical for deriving their precise chronology. The chronology of those tephras was constructed on the basis of their identification using both refractive indices and major element compositions of constituent glass shards, as well as stratigraphic features in the field. Tephras identified in sediments from younger to older are Sakurajima-Taisho (Sz-Ts)-/P1, Sakurajima-Sueyoshi(Sz-Sy)-/P11, Yonemaru, Sakurajima-Uwaba(Sz-Ub)-/P12, Sakurajima-Takatoge3 (Sz-Tk3)-/P13, Sakurajima-Satsuma (Sz-S)-/P14, and Shinjima pyroclastic flow deposit. The Shinjima pyroclastic flow deposit, which differs stratigraphically between northern and southern areas of Shinjima Island, is the same tephra in the two areas, and is estimated to be c. 13,000 cal BP in age. The pumice clasts of Sz-Sy/P11 provided a suitable environment for the habitat of a prominent shell bed (Moeshima Shell Bed) composed mainly of Neopycnodonte musashiana. Sz-Ub/P12, Sz-Tk3/P13, and associate secondary deposits of Sz-S/P14 indicate that the deposit was formed in the last 13,000 cal BP. The chronology of the deposits of Shinjima Island is based on the findings of stratigraphic positions and ages of those tephras, and 14C ages obtained in this study, and will play an important role when examining the palaeo-environmental history of Kagoshima Bay since the last deglaciation.

Characterization, architecture and controls of Cold Lake marginal-marine oil sands: the Grand Rapids Formation (Upper Mannville) of east-central Alberta, Canada

Abstract Hydrocarbons have been produced from the Grand Rapids oil sands for decades; however, large volumes still remain in place, mostly due to the extreme complexity of the reservoirs. Detailed examination of wireline logs and cores from 1127 wells within the 400 km2 Manatokan Field (Twp 62–63; Rge 4–5 W4M) are used to characterize the deposits, define the stratigraphic framework, establish the depositional architecture, and infer the mechanisms and parameters controlling the deposition of the formation. Twenty-one facies are identified based on detailed core analysis (sedimentology, ichnology, geochemistry), and are organized into five recurring facies associations: 1) wave-dominated shoreface deposits; 2) delta-influenced shoreface deposits; 3) interdistributary bay deposits; 4) marine-influenced fluvial deposits; and 5) coastal plain deposits. Shoreface deposits, which form correlatable 3–30 m-thick coarsening-up cycles, are classified as wave-dominated fluvial-influenced to fluvial-dominated wave-influenced, potentially tide-affected (Wft to Fwt). Marine-influenced fluvial deposits are mostly emplaced as point bars within 100–2000 m wide and 3–30 m deep fluvial bodies distributed within the strata. The established stratigraphic framework subdivides the formation into 11 parasequences, 7 parasequence sets, 7 stratigraphic levels containing fluvial bodies and 2 depositional sequences capped by sequence boundaries. Those observations contrast with previous interpretations that recognized seven sequences boundaries capping each of the parasequence sets. However, stratigraphy of the Grand Rapids Formation is primarily controlled by eustacy: sequences and parasequence sets are primarily influenced by long-period moderate-amplitude (1.2–2.4 m.y.; 15–30 m) and short-period low-amplitude (0.4 m.y.; <10 m) glacio-eustatic sea-level cyclicity, respectively. Individual parasequences are likely controlled by short-period allocyclic (100 to 20 kyr climatic variations) and/or autocyclic parameters (delta lobe switching every 5 to 2 kyr) that affect regional and local sediment flux. These parameters and different timescales explain the peculiar distribution of reservoirs in the field with small and isolated geobodies.

Rhizocorallium in estuarine Ingersoll shale (Upper Cretaceous Eutaw Formation, Eastern Alabama coastal plain)

The ichnofossil Rhizocorallium—an oblique to horizontal U-shaped spreiten burrow—has been recognized in a broad range of Phanerozoic continental, marginal marine, and shallow to deep marine facies. Nonetheless, occurrences of this ichnotaxon in Cretaceous estuarine deposits are rarely described. Herein we document Rhizocorallium in the Ingersoll shale, a carbonaceous clay lens within an estuarine succession contained in the Upper Cretaceous (Santonian) Eutaw Formation exposed in the eastern U.S. Gulf coastal plain. The Ingersoll Rhizocorallium specimens, assigned to R. commune var. irregulare based on their basic morphology, horizontal disposition, dimensions, and actively filled spreiten, record a change in depositional conditions and substrate consistency linked to transgression. The Ingersoll shale accumulated rapidly in a restricted tidal channel in a bayhead delta setting and hosts an impoverished resident ichnofauna reflecting soupground conditions. In contrast, attributes of Rhizocorallium (e.g., burrow wall bioglyphs) and associated Thalassinoides in the upper part of the Ingersoll shale reflect firm substrates (i.e., Glossifungites ichnofacies). Firmground development and colonization reflect burial dewatering and subsequent exhumation by bay-shoreline ravinement of clays and the concomitant shift to estuarine central bay deposition. The biological affinity of the Rhizocorallium trace makers cannot be confidently established. However, based on relatively straight and seemingly current-aligned axes, passive burrow fills, lack of associated fecal pellets, and emplacement in firm clay, these structures were likely produced by suspension-feeding organisms—either crustaceans or worms—that took advantage of wave- or tide-induced currents in shallow areas near the estuary head.

Mid-Carboniferous diversification of continental ecosystems inferred from trace fossil suites in the Tynemouth Creek Formation of New Brunswick, Canada

We report Skolithos, Scoyenia and Mermia Ichnofacies from sub-humid tropical fluvial megafan deposits in the Lower Pennsylvanian Tynemouth Creek Formation of New Brunswick, Canada, and discuss their evolutionary and palaeoecological implications, especially regarding the colonization of continental freshwater/terrestrial environments. The Skolithos Ichnofacies comprises annelid/arthropod spreite in the upper storey of a fluvial channel. The Scoyenia Ichnofacies comprises tetrapod tracks, arthropleurid trackways, and shallow annelid/arthropod burrows in active/abandoned fluvial channels and rapidly aggrading levees/splays in proximal interfluve areas. The Mermia Ichnofacies comprises abundant xiphosuran trackways, along with diverse traces of other arthropods, annelids, mollusks, and fish, in shallow freshwater lakes, ponds, and coastal bays in slowly aggrading distal interfluve areas. Transitional Mermia/Scoyenia Ichnofacies comprise tetrapod, mollusk and annelid/arthropod traces in coastal bay deposits on the distal edge of the megafan. These trace fossil suites (1) provide the clearest documentation yet of the mid-Carboniferous diversification event, when tropical continental environments became more densely populated; (2) suggest that euryhaline visitors (xiphosurans, microconchids, and other taxa) from open marine settings played a key role in this episode of freshwater colonization; and (3) provide empirical support for the “Déjà vu Effect”, the evolutionary concept that new or empty ecospace, recurrent in spatially and temporally variable environments, is colonized by simple ichnocoenoses.

On the emplacement of the Voisey's Bay intrusion (Labrador, Canada)

The Mesoproterozoic Voisey’s Bay intrusion is a small (∼10 km3) mafic intrusive complex forming part of the 20,000 km2 Nain plutonic suite of Labrador (Canada) and hosting a world-class orthomagmatic Ni-Cu sulfide ore deposit. An extensive database of drill-core and down-hole televiewer data provides a wealth of subsurface three-dimensional information on the intrusion. The intrusion consists of the upper Eastern Deeps Chamber and lower Western Deeps Chamber, connected via a complex network of dikes. The Eastern Deeps Chamber can be divided into six units that are distinguished based on geometrical styles, dominant lithologies, and the occurrence of bodies of wall rock partly separating units. Unit I, occurring at the highest levels of the chamber, is tabular and consists dominantly of olivine gabbro with minor normal-textured (orthocumulate) troctolite. Units at midlevels of the Eastern Deeps Chamber (IIA, IIB, IIC) are sill-shaped bodies consisting of normal troctolite (i.e., orthocumulate, exhibiting tiling of plagioclase laths) with local variably textured troctolite (i.e., mesocumulate, locally pegmatitic, locally dynamically recrystallized). Units from the lowermost level (IIIA, IIIB) are irregularly shaped and consist of variable troctolite, breccias containing centimeter-sized xenoliths of host-rock paragneiss, and strongly sulfide-mineralized rocks. At least three different feeder dikes deliver magmas associated with unit IIIB. The overall dike system has an upward-curving geometry such that the dike dips shallow upward and as they approach the Eastern Deeps Chamber. This is analogous to fault geometries produced during caldera collapse or cauldron subsidence. Evolving emplacement styles reflect internal igneous processes and intermittent normal-sense activity along pre- to synemplacement brittle wall-rock structures. High-temperature normal-sense shear zones are prominent within the chamber within 100 m of its basal contact and are interpreted to have formed in response to late-stage normal faulting of the chamber floor. The geometry and internal structure of the Eastern Deeps Chamber are indicative of top-down incremental emplacement associated with floor subsidence. Our findings provide a kinematic and dynamic framework for petrogenetic models of Voisey’s Bay and other intrusion-hosted Ni-Cu sulfide deposits.