Sedimentary Facies Analysis Research Articles

Relative sea-level changes and sedimentary facies development of the lowermost Cretaceous (Berriasian–Valanginian) cycles in the north of Ar Riyad city, Saudi Arabia

A new high-resolution stratigraphic framework for the thick and well-exposed Lower Cretaceous rocks of Saudi Arabia has been provided. The studied successions consist mainly of carbonates with minor interbedded siliciclastics, forming the Silayy, Yamamah and Buwaib formations in the study area (north of Ar Riyad city). Based on the integrated sedimentary facies analysis, a relative sea-level curve for the Berriasian–Valanginian interval has been established, including stacking pattern of the different facies cycles. Two transgressive–regressive facies cycles have been identified and documented in the studied sections. The first cycle started during the middle Berriasian (∼143 Ma), comprising the Silayy and Yamamah formations. It terminated at the Yamamah–Buwaib formational contact during the early Valanginian (∼138 Ma), characterized by a friable brownish ferruginous sandstone bed at the base of the Buwaib Formation. The second transgressive–regressive cycle encompasses the entire lower Valanginian Buwaib Formation. A major unconformity surface formed during the early late Valanginian (∼136 Ma), marking the end of the second cycle and characterized by a distinctive hardground condensation. The correlation and dating of the recognized cycles, identified in central Saudi Arabia, shows a contemporaneity to equivalent surfaces globally and thus strongly supports an isochronous formation of Berriasian–Valanginian facies cycles by eustatic sea-level changes.

Geochronology and sedimentary environment at the Udu-dong archeological site, Chuncheon, South Korea

The Udu-dong archeological site in Chuncheon, South Korea, dates back to the Proto–Three Kingdoms Period (approximately 100 BC to AD 350). Many artifacts, including some earthenware, have been excavated in these ancient dwelling sites. We applied three geochronological dating methods (radiocarbon, optically stimulated luminescence (OSL), and archeomagnetic dating) to the archeological remains of this large-scale human settlement and reconstructed the history of depositional processes prior to human settlement. The timing of the ancient community’s settlement was investigated by radiocarbon dating of the charcoal fragments collected from old furnaces. Archeomagnetic dating allowed us to constrain the time period of the settlement’s abandonment by dating the last use of fire. The timing and development of fluvial deposits underlying the settlement site were reconstructed by OSL dating combined with sedimentary facies analysis. Our results show that, following the deposition of coarse sediments starting 10,000 years ago, the region formed a stable floodplain environment starting around 3000 years ago; people began to form clustered settlements approximately 50 years later. For the subsequent 150 years or so, the area was heavily used as a settlement site, with people evenly distributed across it, before eventual abandonment of the site around AD 200–250. Because the sedimentary deposits do not show any significant facies change during this period, we conclude that any catastrophic events were not the main reason for settlement abandonment. This study suggests that combining scientific and archeological analyses have significant benefits for studies of such archeological sites. Therefore, continuous collection of such data can provide important information for the excavation and protection of prehistoric or historic sites.

Sedimentary environment and depositional evolution of the Mesoproterozoic Bingmagou Formation on the southern margin of the North China Craton

The Precambrian sedimentary strata on the southern margin of the North China Craton are well developed and widely exposed, making the region ideal for the study of depositional processes. However, because of the length of the depositional history and the lack of biogenic criteria, interpretations of the sedimentary environments of the Precambrian strata are often based on the tectonic background, geographical environment, rock type and sedimentary structures, resulting in controversies in the literature. In this study of the Bingmagou Formation in the Ruyang Group on the southern margin of the North China Craton, analysis of petrologic features, palaeocurrents and sedimentary facies is combined with regional correlation of relevant strata and the reconstruction of ancient landforms to explain the depositional environments and environmental transitions. Dominated by marine deposits on the southern margin of the North China Craton, the sedimentary strata of the Ruyang Group unconformably overlie the Archean crystalline basement or Proterozoic Xionger Group. As the lowermost unit of the Ruyang Group, the Bingmagou Formation, which was depositionally controlled by topography and faults and received abundant detrital material, is a highly distinctive set of sedimentary strata and represents an environmental transition from alluvial fan to sandy coast.

Palaeoredox conditions and sequence stratigraphy of the Cretaceous storm-dominated, mixed siliciclastic-carbonate ramp in the Eastern Cordillera Basin (Colombia): Evidence from sedimentary geochemical proxies and facies analysis

The Cretaceous black shales of Colombia are among the most important successions in the north of South America and have attracted the attention of many geoscientists and exploration companies over the last few decades, because of their high hydrocarbon potential and the presence of emerald deposits. However, many uncertainties still remain with regard to their tectonic setting, sequence stratigraphy, depositional environments, palaeoxygenation conditions, and organic matter preservation. In order to develop a more integrated picture of these different processes and conditions, we conducted a detailed sedimentological, inorganic geochemical (U, V, Ni, Zn, Mn, Fe, Ti, Mo, Cu, Cr, Cd, Ba) and sequence stratigraphic analysis of the Cretaceous black shales in the Magdalena-Tablazo Sub-Basin (Eastern Cordillera Basin) of Colombia. Eleven lithofacies and five lithofacies associations of a storm-dominated, siliciclastic-carbonate ramp were identified, which range from basin to shallow inner ramp environments. These facies were grouped into six third-order stratigraphic sequences showing high-order cycles of marine transgression with constrained regressive pulses during the late Valanginian to early Coniacian. The black shales succession represents deposition under anoxic bottom water with some intervals representing dysoxic-suboxic conditions. The evolution of the sedimentary environments and their palaeoxygenation history reflect tectonic and eustatic sea-level controls that 1) produced a variable orientation and position of the coastline throughout the Cretaceous; 2) conditioned the low-gradient ramp geometry (<0.3°) and 3) modified the oxygenation conditions in the Magdalena-Tablazo Sub-Basin. An improved understanding of the sedimentary setting during deposition of the Cretaceous black shales in the Magdalena-Tablazo Sub-Basin assists in highlighting the interplay between the mechanism of sedimentation and continuum anoxic conditions prevailing in a basin, as well the important role of nutrient input from continental runoff as a trigger of high productivity and extended anoxia conditions.

Sedimentary facies analysis of the Mesozoic clastic rocks in Southern Peru (Tacna, 18°S): Towards a paleoenvironmental Redefinition and stratigraphic Reorganization

The Mesozoic rocks of southern Peru comprise a Middle Jurassic to Early Cretaceous sedimentary sequence deposited during a time interval of approximately 34 Myr. In Tacna, these rocks are detrital and constitute the Yura Group (Callovian to Tithonian) and the Hualhuani Formation (Berriasian). Basing on robust interpretation of facies and petrographic analysis, we reconstruct the depositional settings of such units and provide a refined stratigraphic framework. Accordingly, nine types of sedimentary facies and six architectural elements are defined. They preserve the record of a progradational fluvial system, in which two styless regulated the dispersion of sediments: (i) a high-to moderate-sinuosity meandering setting (Yura Group), and a later (ii) incipient braided setting (Hualhuani Formation).The Yura Group (Callovian-Tithonian) represents the onset of floodplain deposits and lateral accretion of point-bar deposits sited on a semi-flat topography. Nonetheless, the progradational sequence was affected by at least two rapid marine ingressions occurred during Middle Callovian and Tithonian times. Such marine ingressions reveal the proximity of a shallow marine setting and incipient carbonate deposition. In response to increase in topographic gradient, the Hualhuani Formation (Berriasian) deposited as extensive multistory sandy channels. The mineralogy of the Mesozoic sediments suggests sediment supplies and intense recycling from a craton interior (i.e. Amazon Craton and/or plutonic sources) located eastward of the study area.

Chemostratigraphy and sedimentary facies analysis of the Permian Lucaogou Formation in the Jimusaer Sag, Junggar Basin, NW China: Implications for tight oil exploration

The middle Permian Lucaogou Formation (P2l) in the Jimusaer Sag of the southeastern Junggar Basin, NW China hosts China’s first commercial tight (shale) oil production. Two tight-oil sweet spot intervals have been identified within the P2l formation. Coupled chemostratigraphic and sedimentary facies analysis reveals that the sweet spot intervals were deposited in deep–shallow saline lacustrine to nearshore environments under an overall dry climate setting. The sweet spot intervals in the P2l formation comprises several chemostratigraphically and lithologically distinct units deposited under the influence of subtle climatic and environmental changes that have previously not been recognized. A total of 11 depositional units have been identified within the two sweet spot intervals based on an Integrated Prediction Error Filter Analysis (INFEFA) of Gamma Ray logs and environmental parameters derived from chemostratigraphic data. The tight oil reservoir sweet spot intervals were found to be controlled by the spatial and temporal distribution of total organic carbon (TOC) and reservoir properties (e.g., porosity and permeability) and source-reservoir coupling. Two potential tight oil exploration plays are recognized, including those depositional units with porous reservoir beds interbedded with high-TOC source beds (a self-generation play), and those units with porous reservoir beds adjacent to high-TOC source beds (a near-source play).

Facies analysis, stratigraphy and marine vertebrate assemblage of the lower Miocene Chilcatay Formation at Ullujaya (Pisco basin, Peru)

ABSTRACTThis paper is the first integrated account of the sedimentology, stratigraphy, and vertebrate paleontology for the marine strata of the Chilcatay Formation exposed at Ullujaya, Pisco basin (southern Peru). An allostratigraphic framework for the investigated strata was established using geological mapping (1:4000 scale) and conventional sedimentary facies analysis and resulted in recognition of two unconformity-bounded allomembers (designated Ct1 and Ct2 in ascending order). The chronostratigraphic framework is well constrained by integration of micropaleontological data and isotope geochronology and indicates deposition during the early Miocene. The marine vertebrate fossil assemblage is largely dominated by cetaceans (odontocetes), whereas isolated teeth and spines indicate a well-diversified elasmobranch assemblage. Our field surveys, conducted to evaluate the paleontological sensitivity of the investigated strata, indicate that vertebrate remains only came from a rather restricted stratigraphic interval of the Ct1 allomember and reveal the high potential for these sediments to yield abundant and scientifically significant fossil assemblages.

Sedimentary facies analysis using sequence stratigraphy and seismic sedimentology in the Paleogene Pinghu Formation, Xihu Depression, East China Sea Shelf Basin

Abstract: Based on integrated investigation of seismic multi-attribute, well logs, cores and geological data, the sedimentary facies and lithofacies analysis are conducted in the Paleogene Pinghu Formation of the Xihu Depression, East China Sea. The Pinghu Formation is the main hydrocarbon-bearing strata and source rock interval in the Xihu Depression, and represents a second-order sequence. It can be subdivided into three third-order sequences, (from base to top: SQ1, SQ2, and SQ3), from SQ1 to SQ3 Sequences displayed almost similar depositional patterns, displaying different characteristics of lithology and facies distribution. The fan shaped and lobate proximal tidal-delta facies are deposited at the western edges with relatively strong hydrodynamics, while the lobate and belt shaped scattered tidal-flat facies are deposited at the center of the area with relatively weak hydrodynamics. From SQ1 to SQ3, the distribution of the sand-rich tidal-delta facies evolves from a large range to a small, then larger again, are predominantly influenced by the hydrodynamics, tectonic and topography. This study demonstrates facies analysis using sequence stratigraphy and seismic sedimentology provide useful insight to Paleogene oil and gas exploration in East China Sea Shelf Basin and other similar basins and can also be effectively used in areas which lack well or outcrop data.

Cyclic cold climate during the Nantuo Glaciation: Evidence from the Cryogenian Nantuo Formation in the Yangtze Block, South China

Geological and paleomagnetic data indicate that the ice sheets might have extended to low-latitude regions in the Cryogenian (720–635 Ma). The ‘snowball Earth’ hypothesis proposed that the Earth was completely ice-covered during global glaciation. However, the glacial sedimentary record seems to contradict with the snowball Earth hypothesis. Detailed sedimentological investigations of the glacial deposits would provide the first-order constraint on the nature of global glaciation. The Nantuo Formation (∼654–635 Ma) in the Yangtze Block of South China has been correlated with the Marinoan snowball Earth. In this study, we conducted systematic sedimentological analyses of six sections/cores of the Nantuo Formation. Three facies associations were recognized: the proximal glaciomarine, distal glaciomarine, and non-glacial marine facies associations. The vertical stacking pattern of facies associations can be correlated among the five slope and basin sections, while their correlation with the shelf section remains obscure. Our data indicate two episodes of glaciation that are separated by an interglacial interval during the Nantuo Glaciation. The first glacial episode is recorded by successions of coarse-grained facies (e.g., massive diamictite) in the lower part of the Nantuo Formation. The re-appearance of massive diamictite in the middle to upper part of the Nantuo Formation indicates onset of the second glacial episode. These two glacial episodes were separated by a siltstone/shale sequence of several 10 s m thick, suggesting an interglacial period with limited influence from glaciation. The top of Nantuo Formation consists of alternative distal-glaciomarine and non-glacial marine facies associations, representing the deglacial sequence of the Nantuo Glaciation. The sedimentary facies analysis indicates that the cold climate during the Nantuo Glaciation may be cyclic. Finally, our sedimentary analysis confirms a lag between the deglaciation and precipitation of cap carbonate.

Integrating subsurface stratigraphic records with satellite images to investigate channel change and bar evolution: a case study of the Padma River, Bangladesh

Landsat data and stratigraphic records were employed to determine channel changes and bar evolution of a selected reach of the Padma River in Bangladesh. Analysis of multi-temporal images showed that the selected reach of the Padma River has undergone significant morphological changes since 1973. The mean width of the river has almost doubled, having increased from 5458 m in 1973 to 10,638 m in 2014. Bank erosion, totalling 281 km2, was more than double the accretion (123 km2), and the left bank experienced higher levels of erosion than the right bank. Analysis of the stratigraphy of the bar head, middle and tail sections revealed that erosion occurred in the head section, but that the middle section seemed to be stable, whereas accretion was estimated to be high in the tail section of the bar. Sedimentary facies analysis indicated that bar evolution is largely influenced by the variation of both water and sediment flows, as bar areas tend to accrete substantially following large floods. However, the erosion–accretion process of both bars and river banks appeared to be stable during the periods when the river experiences no major flooding. The relationship between bank erosion and bar area expansion showed a moderately positive correlation (r2 = 0.64, p = 0.016), while a strong correlation was observed (r2 = 0.80; p = 0.008) between channel width and area of the bar, suggesting that river width is highly influenced by bank erosion. This implies that the growth of bars within the reach is largely determined by materials flowing from bank failure.

Northeast monsoon variations during the Holocene inferred from palaeochannels and active channels of the Palar River basin, Southern Peninsular India

The present-day Palar River and its palaeochannel located in the Southern Peninsular India were investigated with a multidisciplinary approach. The main aim of the study was to reconstruct the palaeoenvironment history of the Palar River basin and to delineate the role of Holocene fluctuations that played a major role in the geomorphological evolution of the region since the Holocene period. The results obtained based on sedimentary facies analysis supported by elemental concentrations and optically stimulated luminescence (OSL) dates reveal distinct seven climatic phases since the past ~10 ka. Phase 1 signifies a very high precipitation as attested by the low CWI with high Rb/Sr ratio. Subsequent to Phase 1, a decreasing trend in the northeast monsoon rainfall (NEMR) is observed (Phase 2). Phase 3 (~4.83–3.59 ka) reflects a decrease in NEMR further supported by low Mn/Al, Mg/Al and Chemical Index of Alteration (CIA) values. Phase 4 (~3.59 ka) is marked by high sand flux, higher K/Al, Ti/Al, Rb/Sr and Ba/Sr ratios coupled with lower values of CaO/MgO, Mn/Al and Fe/Al indicating wetter conditions in the catchment area resulting in the intense weathering of the bedrocks caused owing to the increase in NEMR precipitation. Phase 5 (3.26–2.42 ka) reveals a decline in NEMR precipitation coupled with rapid upstream avulsion because of neotectonic activity that occurred in an intense dry phase. Phase 6 (~1.88–1.44 ka) is marked by an augment NEMR causing higher K/Al, Mg/Al, Ti/Al ratios, CIA and CWI values. Finally, Phase 7 (~1.44 ka–present) is marked by lowered elemental solubility and mobility reflecting short periods of weaker or deteriorated NEMR. The documented record of the Palar River and palaeochannels suggests Holocene NEMR variability in the study region and is synchronous with the various proxy records of NEMR-dominated regions, however, revealing an inverse coupling with southwest monsoon rainfall (SWMR) during the Holocene period.

Depositional Environment of Siliciclastic Deposits on the Western Flank of the Anambra Basin, South West Nigeria: Insights from Sedimentary Facies Analysis

This paper presents one of the most detailed facies analysis of the siliciclastic rocks on the western flank of Anambra basin, Southwestern Nigeria. The study is based on four stratigraphic outcrop sections exposed as road cuts and cliff surface of river channel in Auchi and Fugar environs. The stratigraphic sections were studied in terms of lithology, textural characteristics, sedimentary structures, geobody geometry, paleocurrent signatures and bed forms, allowing the recognition and organization of facies into facies associations in order to interpret the depositional environments. Nine lithofacies were recognized namely, structured to massive conglomerate facies (Gmm), fine- to medium-grained, planar cross bedded, sandstone facies (Sx), thick-bedded, medium-grained, moderately-sorted, sandstone facies with rashes of sub vertical Ophiomorpha burrows (Sxb), medium-grained, moderately-sorted, planar cross laminated, quartzose sandstone facies (Sxl), coarse to medium-grained, massive, sandstone facies (Sm), fine- to coarse-grained, trough cross bedded, quartzose, sandstone facies (St), medium-grained, moderately sorted, herringbone cross stratified, reddish brown sandstone facies (Sxh), fine-grained, moderately sorted, fine-grained, white, hummocky cross stratified sandstone facies (Sh), and medium-grained, moderately sorted, rippled sandstone facies (Sr). The spaciotemporal examination of these facies allowed the identification of five facies associations (FAs). The facies associations are FA 1, FA 2, FA 3, FA 4 and FA 5. FA 1 consists of Gmm, St, Sm and Sx is interpreted as indicating deposition in braided fluvial channel. FA 2 is constituted by Sh, St and Sm and is interpreted as deposits of shoreface. Facies Sxh and Sm together with the occurrence of reactivation surfaces were identified in FA 3 and are interpreted as tidal channel deposition. FA 4 is interpreted as indicating deposition in delta front on account of fan- shaped paleocurrent signature and the presence of facies Sx, Sxl and Sxb. Lastly, FA 5 is comprised of Sx, Sm and Sr and strongly suggests deposition in distributary channel environment. Therefore, sediments in the four sedimentary outcrops in the study area were deposited in fluviodeltaic to shallow marine (shoreface) settings.

Late Quaternary environmental change in Oujiang delta along the northeastern Zhe-Min Uplift zone (Southeast China)

We present a history of late Quaternary coastal evolution based on the study of a 41.9-m-long sediment core from the Oujiang Delta. Multiple analytical methods are employed, including sedimentary facies analysis, radiocarbon dating, and the investigations of grain size, elemental, microfossil and pollen compositions. Two transgression-regression sequences, separated by a paleosol layer, are identified. Several lines of evidence indicate that the lower sequence was deposited during the mid-early MIS 3 stage, under a relatively warm and wet climate. An elevated MIS 3 highstand sea level (higher than −24m) is observed. The upper sequence was created after the paleosol was flooded during a marine transgression at ~9.5calkyr BP. Seven weak East Asian Summer Monsoon (EASM) events are identified with central years of ~8.4, 7.7, 6.3, 5.7, 4.7, 2.8 and 1.8calkyr BP. These coincide with those from the ECS sediment cores and the Dongge Cave δ18O record, indicating that EASM precipitation is a major controlling factor of sedimentation rates in the region. The Oujiang Delta is also subject to typhoon impacts and East Asian winter monsoon (EAWM)-induced coastal currents. Active typhoons and a relatively enhanced EAWM occurred during the weak EASM period between 4.9 and 6.4calkyr BP, producing high sedimentation rates in the middle Holocene. We emphasize the high sensitivity of small Asian river deltas as archives of the EASM, EAWM and typhoons. Such environments merit further as a means to understand past changes as well as future responses to projected climatic and sea-level change.

Paleoenvironments and relative sea-level changes caused by regional tectonics during the last 4500 years in Kumihama Bay, northern Kyoto Prefecture, central Japan

Ostracode assemblages were examined, and the grain size and chemistry of sediments were analyzed with the aim of clarifying paleoenvironmental and relative sea-level (RSL) changes relating to regional tectonics in Kumihama Bay, central Japan. Overall, 21 genera and 38 species of ostracode were identified from two cores taken in the northwestern and southeastern parts of the bay. The analysis of sedimentary facies, ostracode assemblages and geochemical records of sediments revealed the following environmental changes. A closed bay, with an area smaller than that of today, existed between 4500 and 4300 cal BP. A gradual increase in seawater influence in the bay was caused by an RSL rise between 4300 and 2000 cal BP with highest RSL occurring at 2000 cal BP. Between 4000 and 2500 cal BP, the RSL in Kumihama Bay has shifted from −3.8 m to −2.0 m at a rate of 1.2 mm/yr. This rate is inconsistent with the predicted RSL trend in surrounding regions, suggesting the occurrence of a subsidence in Kumihama Bay during the Late Holocene. The trend in tectonic movement and their rate are common in the San'in shear zone, implying that this subsidence might be related to the subducting of the Philippine Sea Plate.

Sedimentary facies analysis and seismic interpretation of deep-water reservoirs, “PAC” field, offshore depobelt, Niger Delta basin

A high-resolution study involving the integration of cores, wireline logs and reflection seismic dataset was used to unravel the facies assemblages, reservoir quality and hydrocarbon potential of E1 and H9 reservoirs in the “PAC” field, Offshore Niger Delta. Facies analysis of the cored PAC-14 well shows six lithofacies: massive mudstone, parallel-laminated mudstones with sideritic bands, fine-grained parallel-laminated sandstone, medium-grained parallel-laminated sandstone, fine-grained ripple laminated sandstone, and coarse massive sandstone. These lithofacies were grouped into five facies associations: channel story axis (CSA), channel story margin (CSM), inter-channel thin beds (ICTB), mud-rich thin beds (MRTB) and injectites (INJ). These facies associations are typical of a confined channel and basin floor fan deposit of a deep-water turbidite depositional environment. Reservoir unit E1 was dominated by the facies association CSA while the H9 reservoir consists mainly of the facies associations MRTB and INJ. The observed sand injectites are suggested to have formed due to overloading of compacted sands leading to upward remobilization of sand into the overlying shale. Seismic horizons and faults were mapped to understand the structures, trend and reflections within the study area. Results from petrophysical volumetrics estimated the net hydrocarbon pore volume for the E1 and H9 reservoirs as 456 MMBBL and 378 MMBBL, respectively. Exploration for deep-water reservoir mainly targets high amplitude and bright seismic reflectors and ignores the low amplitude reflectors (dim loops) which are typically interpreted as non-reservoir units. However, this study shows a low-amplitude reflector containing medium-grained sand injectite unit, which has high porosity (31.7%) and permeability (4472 mD) values, and contains recoverable hydrocarbon.

Sedimentary processes and depositional environments of the gas-bearing Horn River shale in British Columbia, Canada

The Horn River Basin in the northeastern British Columbia, Canada, is one of the largest unconventional gas-bearing basins in North America. The main reservoir of this gas accumulation is the Devonian Horn River Formation that is stratigraphically divided into three members, the Evie, Otterpark and Muskwa in ascending order. This study focuses on sedimentary processes and depositional environments of the Horn River Formation based on sedimentary facies analysis by the aid of well-log mineralogy (ECS) and total organic carbon (TOC) data from the Kiwigana well. The shales of the formation consist dominantly of silicate minerals (quartz, feldspar and mica) and subordinate clay mineral and carbonate materials, with TOC ranging from 0.3 to 7.6%. Three sedimentary facies were identified on the basis of centimeter-scale description of sedimentary structures and texture in borehole cores: homogeneous mudstone (HM), indistinctly laminated mudstone (ILM), and planar laminated mudstone (PLM). Integration of sedimentary facies, lithology and TOC suggests that the Horn River shale was primarily deposited in overall distal marine setting deeper than shelf or marginal slope, possibly base-of-slope to deeper basin plain off the carbonate reef (or shelf). Facies HM is siliceous and organic-rich, and dominant in the Evie and the overlying lowermost Otterpark members. It is interpreted as a pelagic to hemipelagic deposit formed mainly by suspension fall-out in an anoxic setting below maximum storm wave base. Likewise, facies ILM shows relatively high proportion of silicate minerals and TOC. This facies is identified frequently in the Muskwa and rarely in the Otterpark; it reflects a deposition from hemipelagic settling with an influence of persistent and weak bottom currents or nepheloid flows. Facies PLM, dominant in the large part of the Otterpark, is relatively depleted in silicate minerals and TOC. This facies indicates more frequent inflow of episodic turbidity currents punctuating the hemipelagic settling of the background sedimentation process. During the deposition of the Horn River Formation, the depositional site has experienced an earlier relative sea-level fall changing from a deep basin (Evie) to shallower marginal slope (middle Otterpark), and subsequent relative sea-level rise turning back to a deeper marine environment (Muskwa).

Paleomagnetism and rock magnetism from sediments along a continental shelf-to-slope transect in the NW Barents Sea: Implications for geomagnetic and depositional changes during the past 15 thousand years

Abstract Paleomagnetic and rock magnetic data were measured on glaciomarine silty-clay successions along an E-W sediment-core transect across the continental shelf and slope of the Kveithola paleo-ice stream system (south of Svalbard, north-western Barents Sea), representing a stratigraphic interval spanning the last deglaciation and the Holocene. The records indicate that magnetite is the main magnetic mineral and that magnetic minerals are distinctly less abundant on the shelf than at the continental slope. The paleomagnetic properties allow for the reconstruction of a well-defined characteristic remanent magnetization (ChRM) throughout the sedimentary successions. The stratigraphic trends of rock magnetic and paleomagnetic parameters are used for a shelf-slope core correlation and sediment facies analysis is applied for depositional processes reconstruction. The new paleomagnetic records compare to the PSV and RPI variation predicted for the core sites by a simulation using the global geomagnetic field variation models SHA.DIF.14k and CALS7K.2 and closest PSV and RPI regional stack curves. The elaborated dataset, corroborated by available 14C ages, provides a fundamental chronological framework to constrain the coupling of shelf-slope sedimentary processes and environmental changes in the NW Barents Sea region during and after deglaciation.

SEDIMENTARY FACIES ANALYSIS OF NAGRI FORMATION, KASHMIR BASIN, SUBHIMALAYAS, PAKISTAN

Nagri Formation, the subject of this study, lies in northeastern part of Kashmir basin, Pakistan along a belt of about 250-kilometer square. The Nagri Formation forms alternate beds of sandstone, claystone and/or mudstone. These are molasse deposits formed during the Himalayan orogeny and are early Pliocene in age. The Formation consists of six sedimentary facies: para-conglomerate (N1) comprised of massive conglomerates with the absence of grading and matrix supported fabric of clayey sand; ortho-conglomerate (N2) are normal graded conglomerates and are poorly sorted having clasts supported fine to very coarse grain matrix; massive sandstone (N3) is composed of medium to coarse sized grains, contains massive sandstone beds and is poorly sorted with scattered pebbles at some locations; cross bedded sandstone (N4) consist of to medium to coarse textured, cross bedded sandstone; parallel laminated sandstone (N5) comprising fine to coarse grained and poorly sorted sandstone beds with thin parallel laminations; and mudstone (N6) comprised of massive claystone’s, siltstones and mudstone that lack any noticeable sedimentary structure. The conglomerates, sandstone and mudstone/siltstone/claystone facies are stacked in ascending order and are deduced as a sequence of channel bar and floodplain or over bank deposits confined to a braided fluvial system.

Diverse Sedimentary Conditions During Deposition Of Coal And Oil Shale From The Meihe Basin (Eocene, Ne China)

The Meihe Basin in northeastern China is a normal-fault-controlled basin filled with Eocene nonmarine deposits, the sediments assigned to the Meihe Formation. Sediment grain-sizes, core study, well-log analysis and micropetrographic study combined with sedimentary facies analysis indicate that the main sedimentary facies of the Meihe Basin represent fan-delta, lake, and turbidite deposits. Thick coal seams that are mainly distributed in the eastern part of the studied area were deposited in the swamp facies of the Lower Coal-Bearing Member. Oil shale was mainly deposited in the deep lake represented by the Mudstone Member, and is mainly distributed in the southern part of the studied area. In the Lower Coal-Bearing Member, organic-rich sediments are characterized by TOC content between 0.6 wt.% and 43.1 wt.%and contain Type II and III kerogen. The thick coal seams are the result of high landplant productivity and good preservation conditions. Thin coal seams in the fan-delta plain resulted from the migration and erosion of the fan-delta channel. In the shallow lake and fan-delta front, limited productivity coupled with dilution by inorganic matter resulted in lower organic-matter content in theMudstoneMember. Oil shale and mudstone rich in organic matter were deposited in a deep lake with an average TOC content of 3.4 wt.%. The origin of the organic matter was mainly algae and aquatic plants mixed with land plants. The improved preservation conditions and high bioproductivity in this environment resulted in three oil-shale layers in the lower part of this sedimentary succession. Three coal-bearing and oil-shale-bearing fault basins lie adjacent to the Dunhua-Mishan Fault zone, among which the Fushun Basin is located in the southwest, the Meihe Basin is in themiddle, and theHuadian Basin is in the southeast. From the Fushun Basin to the Huadian Basin, the oil shale and coal seams have distinct sedimentation characters laterally. Vertically in each basin, the organic-matter sources all have the same variation trend from land plants to land plants mixed with algae to algae then to algae mixed with land plants, and the TOC content also shows a similar trend from high to medium-high then to low in each basin.

Stratigraphic distribution, taphonomy and paleoenvironments of Spinicaudata in the Triassic and Jurassic of the Paraná Basin

Due to the chitino-phosphatic nature of Spinicaudata conchostracan exoskeletons, their carapaces exhibit a low preservational potential compared to other bivalve groups. However, the recent studies point towards the increased tolerance of the carapace against the physical processes. Due to this peculiar characteristic, conchostracan carapace have been utilized as precise temporal markers in estimating stratigraphic and taphonomic parameters. The same characteristic also makes the spinicaudatans useful in evaluating the depositional processes and environments. The present work aims at providing a paleoenvironmental and stratigraphic analysis of conchostracans (Spinicaudata) from the Triassic-Jurassic of the Paraná Basin (Santa Maria and Caturrita formations) in terms of the sedimentary facies analysis, depositional system characterization, and analysis of the taphonomic signatures of the fossiliferous horizons within these formations. The results from the taphonomic study delineates the presence of 4 distinct fossil assemblages based on the causative mechanism and fundamental characteristics of the fossil concentrations: two taphonomic assemblages in the laminated mudstone beds deposited from the decanting fine-grained sediments in floodplains; the sandstone beds with plane parallel laminations and dune- and ripple-cross-stratifications deposited from the flooding-related overflow in the floodplains; and the association of laminated mudstone and massive sandstone beds deposited as the river mouth bars. The results show that the taphonomic signatures, e.g., closed valves, may indicate the various patterns of autochthony and allochthony. In the fine-grained floodplain assemblages, the high degree of preservation can be attributed to autochthony in the conchostracans, whereas the preservational condition of floodplain sandstone sheet and mouth bar assemblages point toward parautochthony and even allochthony. Therefore, the preservational quality of conchostracan exoskeletons is likely a function of parameters, e.g., the transport duration, the distance from life position, and the magnitude of events causing their final burial. Within the observed species, the recognition of Eustheria minuta in the stratigraphic level of the Passo das Tropas creek corroborates an age for these deposits between the late Middle Triassic and early Upper Triassic. The presence of a new form, likely related to the family Fushunograptidae in sediments from the Caturrita Formation, suggests a Jurassic age for these deposits.