Sedimentology and Ichnology of Upper Montney Formation Tight Gas Reservoir, Northeastern British Columbia, Western Canada Sedimentary Basin

Several decades of conventional oil and gas production in Western Canada Sedimentary Basin (WCSB) have resulted in maturity of the basin, and attention is shifting to alternative hydrocarbon reservoir system, such as tight gas reservoir of the Montney Formation, which consists of siltstone with subordinate interlaminated very fine-grained sandstone. The Montney Formation resource play is one of Canada’s prime unconventional hydrocarbon reservoir, with reserve estimate in British Columbia (Natural Gas reserve = 271 TCF), Liquefied Natural Gas (LNG = 12,647 million barrels), and oil reserve (29 million barrels). Based on sedimentological and ichnological criteria, five lithofacies associations were identified in the study interval: Lithofacies F-1 (organic rich, wavy to parallel laminated, black colored siltstone);Lithofacies F-2 (very fine-grained sandstone interbedded with siltstone);Lithofacies F-3A (bioturbated silty-sandstone attributed to the Skolithos ichnofacies);Lithofacies F-3B (bioturbated siltstone attributed to Cruziana ichnofacies);Lithofacies F-4 (dolomitic, very fine-grained sandstone);and Lithofacies F-5 (massive siltstone). The depositional environments interpreted for the Montney Formation in the study area are lower shoreface through proximal offshore to distal offshore settings. Rock-Eval data (hydrogen Index and Oxygen Index) shows that Montney sediments contains mostly gas prone Type III/IV with subordinate Type II kerogen, TOC ranges from 0.39 - 3.54 wt% with a rare spike of 10.9 wt% TOC along the Montney/Doig boundary. Vitrinite reflectance data and Tmax show that thermal maturity of the Montney Formation is in the realm of “peak gas” generation window. Despite the economic significance of the Montney unconventional “resource-play”, however, the location and predictability of the best reservoir interval remain conjectural in part because the lithologic variability of the optimum reservoir lithologies has not been adequately characterized. This study presents lithofacies and ichnofacies analyses of the Montney Formation coupled with Rock-Eval geochemistry to interpret the sedimentology, ichnology, and reservoir potential of the Montney Formation tight gas reservoir in Fort St. John study area (T86N, R23W and T74N, R13W), northeastern British Columbia, western Canada.

Recent progress and focuses of ichnology:Outline of the 14^(th) International Ichnofabric Workshop

The 14^（th） International Ichnofabric Workshop was held successfully in Taipei, China from April 29 thto May 2^（nd）. From the oral presentations, posters, intra-and post-workshop field trips, and workshop discussions, a few promising aspects of ichnological study can be outlined：（1） Ichnotaxonomy is, and will be the major endeavour of ichnologists, supplying important behavioural information for palaeontological studies, and also providing reasonable, objective, and convenient taxonomical framework for further sedimentological and palaeoecological studies;（2） Ichnofabric analysis is widely applied to in-depth sedimentological, palaeoclimatical, and petroleum exploration studies, offering a wealth of biological information that cannot be properly obtained from traditional sedimentological and geochemical analyses;（3） Study of trace fossils in the context of evolutionary palaeoecology sheds light on some intriguing issues of the biological responses during certain critical periods in Earth＇s history;（4）Work on combining geomicrobiology and ichnology is under way;（5） Quantitative morphological characterization has become increasingly useful in grasping the finer ingredients of functional morphology.

Thalassinoides Ichnofabrics of Lower Cambrian Longwangmiao Formation(Stage 4,Toyonian)on the Yangtze Platform,South China:Improving Paleoenvironmental Interpretations

An analysis of Thalassinoides ichnofabrics in the Cambrian Stage 4 Longwangmiao Formation from six sections near Chonqing in the Middle and Upper Yangtze Block of South China was conducted to promote the understanding of the paleoenvironment of this period.Thalassinoides ichnofabrics are divided into three types according to their morphology,bioturbation index,abundance and related parameters:banded,mottled and grid.The completeness of the ichnofabrics gradually increases from banded to grid,the scale of the burrows expands,and the structure transitions from twodimensional to three-dimensional.Malacostracans,phyllocarids and enteropneusts are the most likely burrowers.The findings reveal that frequent changes in paleoenvironmental conditions are the dominant factors for generating the various Thalassinoides ichnofabrics.The changes in depositional rate,substrate properties and nutrient levels affect the behavior and building patterns of the burrowers,thus leading to the diversity of Thalassinoides ichnofabrics.In the lower Longwangmiao Formation beds,many incomplete Thalassinoides burrow systems were built in the substrates with terrigenous detrital minerals,revealing significant environmental pressure on the burrowers.Later,the Thalassinoides burrows went into complete three-dimensional boxworks.At the end of the stage,bioturbation almost disappeared,which indicates that burrowers were finding it difficult to survive in the harsh environment.

Using a modern analogue to interpret depositional position in ancient fluvial-tidal channels:Example from the McMurray Formation,Canada

The fluvial-tidal transition(FTT)is a complex depositional zone,where fluvial flow is modified by tides as rivers approach a receiving marine basin.Variations in the relative importance of tidal versus fluvial processes lead to a distinctive distribution of sediments that accumulate on channel bars.The FTT generally consists of three broad zones:(1)a freshwater-tidal zone;(2)a tidally influenced freshwater to brackish-water transition:and(3)a zone of relatively sustained brackish-water conditions with stronger tides.A very common type of deposit through the fluvial-tidal transition,especially on the margins of migrating channels,is inclined heterolithic stratification(IHS).At present,a detailed account of changes in the character of IHS across the FIT of a paleo-channel system has not been reported,although a number of modern examples have been documented.To fill this gap,we quantitatively assess the sedimentology and ichnology of IHS from seven cored intervals in three geographic areas situated within the youngest paleovalley("A"Valley)in the Lower Cretaceous McMurray Formation of Alberta.Canada.We compare the data to trends defined along the FTT in the present-day Fraser River in British Columbia.Canada to interpret paleo-depositional position in the ancient fluvial-tidal channels.Analysis determined that the mean mudstone thickness is 8.2 cm in the southern study area(SA).Mean thickness increases to 11 cm in the central study area(CA),and decreases again to 4.4 cm in the northern study area(NA).The proportion of mudstone is 31%in SA,44%in CA,and 27%in NA.Thicknessweighted mean bioturbation intensity in sands varied from 0.29 in SA and CA.to 0.28 in NA.On the other hand,thickness-weighted mean bioturbation intensity(Bl)in mudstone increases from 1.46 in SA.to 1.77 in CA.and is 1.94 in NA.The ichnological diversity also increased from south to north.Sedimentological results show sinilar trends to those of the Fraser River,enabling the identification of a freshwater to brackish-water transition zone with tidal influence.The interpreted position of the transition is underpinned by the bioturbation intensity and trace-fossil diversity trends,indicating periodic brackish-water conditions throughout SA in the McMurray Formation during low river flow conditions.Together,these data suggest that a broad FTT existed in the"A"Valley,with fluvial-dominated channels to the south that experienced seasonal brackish-water inundation during base flow,and channels experiencing increasing brackish-water influence lying further north towards a turbidity maximun zone.The FIT zone appears to have extended for several hundred kilometers fron south to north.Based on the sedimentological and ichnological data,as well as estimations of lateral accretion rates,we refute the colmonly applied Mississippi River depositional analogue for McMurray Formation channels.Rather,we show that while not a perfect fit,the tidally influenced Fraser River shows much greater agreement with the depositional character recorded in McMurray Formation IHS.Future work on the McMurray system should focus on characterizing tide-dominatecl deltaic and estuarine systems,such as the Ganges-Brahmaputra,and on forward-modeling the evolution of tide-dominated and tideinfluenced river systems.

Early Cambrian Ichnofossils from the Mussoorie Syncline and revision of Trace Fossil Biozonation of the Lesser Himalaya, India

A new locality bearing ichnofossils of the Cruziana Assemblage Zone-Ⅲ from the Mussoorie syncline,Lesser Himalaya,is located in rocks of Member-B of the Dhaulagiri Formation,Tal Group,exposed along the Maldewta-Chhimoli fresh road cut section.The site yielded ichnofossils Bergaueria perata,Cochlichnus anguineus,？Diplocraterion isp.,Dimorphichnus obliquus,diplichnitiform Cruziana bonariensis,Diplichnites gouldi,Glockeria isp.,Helminthopsis isp.,Monomorphichnus lineatus,Phycodes palmatum,Palaeophycus striatus,Planolites beverleyensis,Planolites montanus,Treptichnus cf.T.pedum,scratch marks and an undetermined worm impression.An Early Cambrian age （Cambrian Series 2） is assigned to the ichnofossil-bearing strata based on the stratigraphic position between the Drepanuroides and Palaeoolenus trilobite zones.A revised Cambrian ichnofossil zonation is presented for the Tal Group of the Mussoorie syncline.Together with their occurrence on rippled surfaces,and the lateral displacement of some trackways （due to current action）,a sub-aqueous shallow-marine depositional setting is proposed for the rocks of Member-B.

Delta asymmetry:Concepts,characteristics,and depositional models

Delta asymmetry forms in wave-influenced settings where there is strong net longshore drift. Asymmetric deltas typically have two sediment sources and are characterized by morphology and facies asymmetry between the downdrift and the updrift sides. The downdrift, sourced primarily by the feeding river, are commonly influenced by mixed river and wave processes. Deposits on this side are muddy and consist of barrier, bar, lagoon, bay-fill, and bayhead delta facies with variable bioturbation intensity. At or near the river mouth, heterolithic river-dominated successions are more typical. Deposits are overall unburrowed （BI 0-2）, but with high burrowing spikes. Ichnogenera are characterized by horizontal, morphologically simple, and facies-crossing structures. The updrift, in contrast, is sourced by a second sediment source and typically consists of laterally continuous sandy beach and shoreface facies. Bioturbation is overall high （BI 3-6） and ichnogenera are healthy and robust, attributable to the Cruziana and Skolithos lchnofacies. Depending on shoreline trajectory and depositional history, facies characteristics of asymmetric deltas preserved in the ancient record, however, can be different from those predicted by the models. Degree of asymmetry is indicated by the asymmetry index （A）, defined as the ratio between the rate of longshore transport at the river mouth and river water discharge. The indexes in symmetric waveinfluenced deltas is less than 200, whereas those in asymmetric and deflected deltas are larger than 200. Overall the larger the index, the higher the degree of asymmetry. Delta asymmetry concepts and models challenge the traditional definition of deltas and the delta classification scheme, in a hydrocarbon exploration perspective, asymmetric deltas bear very different types of sands and, thus, reservoirs between the updrift and the downdrift. The updrift consists of wellsorted, mature, and laterally continuous homogeneous beach-shoreface reservoirs. The downdrift, in contrast, is muddier and consists of less continuous, less mature, heterolithic reservoirs.

Bioerosion on Late Pleistocene Marine Mollusks:A Paleoclimatological and Paleoecological Comparison of MIS 7 and MIS 5e with Modern Beaches(Río Negro,Argentina)

The Late Pleistocene littoral ridges of southern South America,especially those of the north of Argentinean Patagonia,contain remains of mollusk shells with bioerosion traces.Eleven sites from marine isotope stages(2 from MIS 7,4 from MIS 5 e)and five sites from modern beaches from northern Río Negro Province,with 40 taxa(17 bivalves and 23 gastropods)were analyzed,in the area between west of Baliza San Matías and Las Grutas(41°S).Three ichnogenera were identified in deposits of MIS 7:Entobia,Gastrochaenolites(Domichnia)and Oichnus(Praedichnia)with one ichnospecies(G.torpedo).Six ichnogenera were identified in deposits of MIS 5 e:Entobia,Meandropolydora,Pinaceocladichnus,Iramena,Caulostrepsis and Oichnus with one ichnospecies(O.simplex).Seven ichnogenera were identified from modern beaches:Entobia,Meandropolydora,Iramena,Caulostrepsis,Pinaceocladichnus,Gastrochaenolites(Domichnia)and Oichnus(Praedicnia),with two ichnospecies(O.simplex and O.paraboloides).On this basis,it is inferred that Pleistocene benthic communities were constituted from cheilostome bryzoans and polychaete annelids,together with drilling bivalves,predatory gastropods and overall warm-water species of mollusks.Of these,Chama iudicai was found on Plicatula gibbosa from MIS 7 and MIS 5 e.The record of warm temperature species suggests a higher sea surface temperature(SST)than the present one and/or the influence of the warm southward Brazilian Current affecting the waters of Golfo San Matías.On the modern beaches surveyed,there is an increase in polychaete annelids,cheilostome bryzoans,temperate-cold species and drilling bivalves,as well as sandy substrate species,which together with an increase of Gastrochaenolites and Caulostrepsis,suggest a colder climate due to the greater influence of the Malvinas Current during the Holocene.

Ichnofossils from the Miocene Middle Bhuban Formation, Mizoram, Northeast India and their Paleoenvironmental Significance

An ichnofossil assemblage is preserved in sediments of the Middle Bhuban Formation, Surma Group, of Miocene age from the Durtlang and Chanmari sections, Aizawl district, Mizoram, northeastern India. The studied sections comprise a thick, bioturbated and thinly bedded sandstone-silty shale facies. The preserved ichnofossils show high density and low diversity with the assemblage represented by feeding and resting traces, i.e., Psilonichnus upsilon Frey et al., 1984, Ophiomorpha isp., Teichichnus spiralis Mikulas. 1990, Skolithos isp., Palaeophycus isp., and other horizontal burrows. Sedimentary structures associated with these traces are mainly cross bedding, flaser bedding and slump structures. Considering the distribution of the Psilonichnus ichnogenus across an integrated ichnological-sedimentological framework, the stratigraphic interval of the Middle Bhuban Formation, in which they occur, are interpreted to have been deposited under a shallow, marginal-marine channel complex dominated by tidal channels developed in quiet, brackish-water portions of a delta plain.

Continental Trace Fossils in the Semnan Area (Northern Iran)

Continental ichnology has been taking an ever increasing importance in stratigraphy. In this paper, Continental Trace Fossils in Semnan area have been studied. Semnan Province is one of the 31 provinces which is located in the north of Iran. In the East of Semnan City, Quaternary deposits occupy about 93% of the surface area, of which the Alluvial represents one of the most important geomorphological features in the area. Nevertheless, the outspread ichnological studies in Semnan City have received lesser attention in Continental Trace Fossils. Based on the systematic ichnology, 6 trace fossils are distinguished, namely Celliforma isp, Coprinisphaera isp, Palaeophycus tubularis, planolithes isp, Tombownichnus plenus, and Skolithos isp. The existence of Rhizoliths along with the tetrapod footprints and the survey of lithofacies all indicate that the trace fossils are related to Coprinisphaera ichnofacies. Based on ichnological and sedimentary facies analysis, the Continental Trace Fossils, in the study area, are located in the flood plain, point bar, and playa environment.

Trace fossil evidences of an Early Miocene paleoseismic event and depositional regime change from the Kutch(Kachchh) Basin

Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation(KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS,the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity,its ichnologic signature, and the depositional regime change refer to a higher-resolution(i.e., lower-order)sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.

Taenidium barretti ichnofabric and rainfall seasonality:Insights into dryland suites of Scoyenia ichnofacies

The present work analyzes the monotypic Taenidium barretti ichnofabric developed in abandoned channels and floodplains to understand its paleoecological significance in highly seasonal fluvial systems.The data come from the Cretaceous paleosols of the Marília Formation(Bauru Basin,SE Brazil),in which the T.barretti ichnofabric and rhizoliths represent the biotic record.Beetle larvae are considered to be the most likely T.barretti tracemakers in these paleosols.The intensity and recurrence of bioturbation suggest that the windows of opportunity for beetle population growth were very short and controlled by the progressive substrate desiccation after flood cessation.The characteristics of the trace fossil assemblage suggest soil colonization by r-strategic organisms triggered by flooding events that provided the resource inputs necessary for their living during rainy seasons.The results also show that in fluvial systems with high discharge variations,the boundaries between a“pre-desiccation suite”and a“desiccation suite”in the Scoyenia ichnofacies can be diffuse due to the short duration of colonization windows and progressive terrestrialization of floodplains and channels.Therefore,the frequency of flooding events,the lowered water table,and the rapidity of substrate desiccation constrained colonization by other burrowers and may be considered as firstorder factors controlling the generation of a monotypic T.barretti ichnofabric.Thus,the monotypic Taenidium ichnofabric in the Scoyenia ichnofacies context is an ichnomarker of brief windows for colonization in highly seasonal environments.