Shallow-water Shelf Research Articles

Extension Structures in the Central Arctic Submarine Elevations Complex

Abstract—The available body of geological and geophysical data indicates that the morphologic structures of the Central Arctic submarine elevations complex (CAE) form a single complex block of continental crust that broke away from the Barents–Kara continental margin in the late Paleocene. Seismostratigraphic interpretation of the multichannel seismic reflection data acquired within the CAE, based on seismostratigraphic benchmarks confirmed by drilling and continuous tracing of pre-Cenozoic unconformities from the offshore North Chukchi Trough to its deep-water extension (Vilkitsky Trough), makes it possible to draw the following conclusions: The sedimentary-basin depocenters of the Vilkitsky Trough and Chukchi basin include pre-Upper Jurassic sediments in addition to Cretaceous complexes. However, the former are not common in the rest area of the CAE.Synrift extension of the continental crust is the key factor that affected the tectonic evolution of morphologic structures of the Central Arctic basin. Multichannel seismic reflection data show the clearest signs of the synrift extension in the Lomonosov Ridge, Mendeleev Rise, Chukchi plateau, and their flanks sloping to the sedimentary basins of the Vilkitsky Trough and Chukchi basin. At the same time, the depocenters of these sedimentary basins formed by pre-Upper Jurassic deposits are characterized by an almost undisturbed bedding of all sedimentary complexes.Pre-Upper Jurassic deposits might be interpreted as a relic of the Ellesmerian structural stage preserved in the deep-water extension of the North Chukchi Trough since the preoceanic evolution stage. Pre-Upper Jurassic complexes seem to be affected by deep rift activity only within the elevations of the Central Arctic area and near-flank zones of the depressions separating them. Pre-Upper Jurassic deposits in the sedimentary basin depocenters of the Vilkitsky Trough and Chukchi basin structurally linked to the shallow-water shelf were barely affected by the rifting processes. The tectonic evolution of the depocenters and their submergence relative to the flank zones might have been affected not only by crustal extension processes but also by compensation mechanisms.

Structure and depositional environment of the Valanginian-Hauterivian sections in the middle reaches of the Bodrak River (South-Western Crimea)

The materials, collected during the description of 17 outcrops of Karatlykh formation (Lower Valanginian) and Karaghach formation (Lower Hauterivian) in the Bodrak River middle course (South-Western Crimea), are analyzed. The results of microscopic descriptions of thin sections, computed micro-tomography of samples, carbonate content detection, and particle-size analysis of insoluble residue are presented, the remains of scleractinian corals and cartilaginous fish are studied. Descriptions and sedimentological interpretation of 8 lithological-genetic types of layers are also presented in this article. During Karatlykh time and regressive phases of Karaghach time, terrigenous sedimentation prevailed. From the coast to the center of the basin there were pebble-sandy beaches, sandy ripples, detrital ripples with sandy depressions, detrital ripples of the far part of the shallow-water shelf. During transgressive phases of the Karaghach time, there was a shortage of terrigenous sedimentary material and carbonate sedimentation dominated. The area with solitary corals was formed along the coast and separated from the sea by patch reefs zone, detritus and coral bioherms were located on the fore reef zone. Deeper there were detrital ripples with sandy depressions, detrital rippleswith single bioherms and detrital ripples with rare biostromes. According to bed’s vertical sequences, transgressive-regressive sedimentation cycles are established. It became the basis for a detailed correlation of sections. Paleogeographic schemes for the short range of geological time corresponding to transgressive and regressive maxima are compiled. It is shown that in the paleobasin there were two types of lateral sequences of accumulative landscapes. As a result, we demonstrate that in Lower Valanginian and Lower Hauterivian the studied territory represented a shallow offshore part of the sea, washed the land southeastward. This land represented the main terrigenous provenance for the basin.

Optimization of shale gas reservoir evaluation and assessment of shale gas resources in the Oriente Basin in Ecuador

The petroleum geological features of hydrocarbon source rocks in the Oriente Basin in Ecuador are studied in detail to determine the potential of shale gas resources in the basin. The favorable shale gas layer in the vertical direction is optimized by combining logging identification and comprehensive geological analysis. The thickness in this layer is obtained by logging interpretation in the basin. The favorable shale gas accumulation area is selected by referring to thickness and depth data. Furthermore, the shale gas resource amount of the layer in the favorable area is calculated using the analogy method. Results show that among the five potential hydrocarbon source rocks, the lower Napo Formation is the most likely shale gas layer. The west and northwest zones, which are in the deep-sea slope and shelf sedimentary environments, respectively, are the favorable areas for shale gas accumulation. The favorable sedimentary environment formed thick black shale that is rich in organic matter. The black shale generated hydrocarbon, which migrated laterally to the eastern shallow water shelf to form numerous oil fields. The result of the shale gas resource in the two favorable areas, as calculated by the analogy method, is 55,500 × 108 m3. This finding shows the high exploration and development potential of shale gas in the basin.

Seismic airgun sound propagation in Arctic Ocean waveguides

Underwater recordings of seismic airgun surveys in the deep-water Beaufort Sea and on the shallow-water Chukchi Sea shelf were made from sites on the continental slope and shelf break north-northwest of Point Barrow, Alaska. Airgun pulses from the deep-water survey were recorded more than 500 km away, and from the shallow-water survey up to ~100 km. In the deep-water, received sound pressure levels show spherical spreading propagation; whereas, sound exposure levels exhibit cylindrical spreading propagation. Over the shallow-water shelf, transmission losses were much greater than spherical spreading, due to energy loss in the seafloor. Understanding how sound propagates across large spatial scales in the Arctic Ocean is important for better management and mitigation of anthropogenic noise pollution in marine soundscapes, especially as diminished ice in the Arctic Ocean allows for longer range sound propagation.

Seasonality in the cross-shelf physical structure of a temperate shelf sea and the implications for nitrate supply

We address a long-standing problem of how nutrients are transported from the shelf edge and from rivers to support regular, seasonal primary production in the interior of a wide, temperate, shelf sea. Cross-shelf sections of hydrography and nutrients, from a series of cruises between March 2014 and August 2015, along with time series of river discharge and river nutrient load are used to assess the seasonality of cross-shelf transports. Riverine nitrogen inputs are estimated to account for 30% of the nitrate available for the spring bloom on the inner shelf, and 10% in the mid- to outer-shelf. In the bottom layer in summer, high salinity, nutrient-rich waters are transported on-shelf as a result of wind-driven Ekman transport, cross-shelf pressure gradients and/or internal tidal wave Stoke’s drift. In the centre of the shelf this advection is responsible for 25% of the increase in bottom water nitrate seen between April and November 2014. The remaining nitrate increase suggests that about 50–62% of the nitrogen fixed into organic material during spring, summer and autumn phytoplankton growth is recycled in the bottom water over the 12 months between March 2014 and March 2015. In winter, when the water column is vertically mixed, there is a weak net off-shelf transport of about 1 m2 s−1, possibly driven by a reversal of the horizontal density gradient caused by excess cooling of shallower shelf waters. Overall, shelf nitrate concentrations are maintained by a combination of riverine supply, recycling of organic material, and summer on-shelf transports. We suggest that the main driver of inter-annual variability in pre-spring nitrate concentrations is variability in the depth of the winter mixed layer over the shelf slope.

Upper Jurassic Rock Depositional Settings in the Baidar Valley and Evolution of the Crimean Carbonate Platform

The paper presents results of the lithological study of Upper Jurassic limestones, flyschoids and limestone breccias on the southern side of the Baidar Valley in the Crimean Mountains. Study of the microfacies revealed that the limestones are represented by deposits on lagoons, platform edge shoals, reefs, and forereef aprons on the carbonate platform slope. Flyschoids include deposits in the distributive turbidite channels and hemipelagic sediments in the deep-water part of the basin. Limestone breccias were formed by gravitation flows on the carbonate platform toe-of-slope and slope. The presence of gravitation deposits in the Upper Jurassic carbonate complexes of the Crimean Mountains can testify to the primary clinoform structure of this sedimentary sequence. Comparison of the obtained sedimentological data made it possible to reconstruct the facies model of the Crimean carbonate platform and main episodes of its formation. Development of the carbonate shelf was related to two transgressive-regressive cycles. A dome-shaped reef was formed away from the coast at the initial (Oxfordian) stage. The carbonate platform was formed at the early Kimmeridgian lowstand stage when sediments were deposited in the internal part of the platform adjacent to land. In the late Kimmeridgian and early Tithonian, configuration of the carbonate platform profile resembled a distally steepened ramp, and its active progradation and shelf expansion took place in the course of transgression. Regression in the late Tithonian–early Berriasian led to regressive transformation of the ramp into platform with a flattened shallow-water shelf. Tectonic deformations at the Jurassic/Cretaceous transition promoted the formation of megabreccias on the carbonate platform foreslope. The tectonically reworked rock sequence of the “extinct” carbonate platform was overlapped transgressively by the upper Berriasian or lower Valanginian, relatively deep-water deposits of the Cretaceous platform cover.

Long term movements and activity patterns of an Antarctic marine apex predator: The leopard seal.

Leopard seals are an important Antarctic apex predator that can affect marine ecosystems through local predation. Here we report on the successful use of micro geolocation logging sensor tags to track the movements, and activity, of four leopard seals for trips of between 142–446 days including one individual in two separate years. Whilst the sample size is small the results represent an advance in our limited knowledge of leopard seals. We show the longest periods of tracking of leopard seals’ migratory behaviour between the pack ice, close to the Antarctic continent, and the sub-Antarctic island of South Georgia. It appears that these tracked animals migrate in a directed manner towards Bird Island and, during their residency, use this as a central place for foraging trips as well as exploiting the local penguin and seal populations. Movements to the South Orkney Islands were also recorded, similar to those observed in other predators in the region including the krill fishery. Analysis of habitat associations, taking into account location errors, indicated the tracked seals had an affinity for shallow shelf water and regions of sea ice. Wet and dry sensors revealed that seals hauled out for between 22 and 31% of the time with maximum of 74 hours and a median of between 9 and 11 hours. The longest period a seal remained in the water was between 13 and 25 days. Fitting GAMMs showed that haul out rates changed throughout the year with the highest values occurring during the summer which has implications for visual surveys. Peak haul out occurred around midday for the months between October and April but was more evenly spread across the day between May and September. The seals’ movements between, and behaviour within, areas important to breeding populations of birds and other seals, coupled with the dynamics of the region’s fisheries, shows an understanding of leopard seal ecology is vital in the management of the Southern Ocean resources.

Early Oligocene calcareous nannofossils, planktonic and larger foraminifera from the United Arab Emirates, Oman Mountains

The Lower Oligocene Asmari Formation occupies the western and eastern flanks of the Jabal Hafit anticline and the western limb of the Jabal Malaqet-Mundassah anticline in the southeast of the United Arab Emirates near the Oman border. In this area the Asmari Formation unconformably overlies the Upper Eocene Dammam Formation. In this study an Early Oligocene characteristic assemblage of calcareous nannofossils, foraminifera, corals, calcareous algae, bryozoa, mollusks and echinoids is described from the carbonate rocks of the Asmari Formation. The Asmari stratigraphic succession is dated by analysis of the calcareous nannofossil assemblages and planktonic and larger foraminifera. The results of this study indicate that the succession falls within the Early Oligocene Zones NP24 and P20-P21. About seventeen nannofossil species are documented for the first time in this formation, along with three planktonic and larger foraminiferal species. The Oligocene rocks in the study area provide results consistent with a shallow-water inner shelf within the photic zone.

The marine soundscape off the Isle of Mull in Scotland's Inner Hebrides

The waters around the Isle of Mull, Scotland are home to minke whales, basking sharks, common and bottlenose dolphins, harbor porpoises, and many fish and marine invertebrates. This talk describes the soundscape of this region, measured as part of a study on minke whale (Balaenoptera acutorostrata) acoustic habitat use, conducted June–September 2016. The study area consists of shallow (<100 m depth) shelf waters between and around the Islands of Mull, Coll, and Muck. Measurements were made with a Soundtrap 300 from multiple points over the study area (~560 km2) at a sampling rate of 288k Hz. Recordings were taken at a depth of ~30 m from a whale watching vessel when it was stopped (usually observing marine wildlife). The study includes 131 recordings with durations of 5–40 min. Spectral density varies with location and time over the study. Temporal and regional variation and the identity of various sounds are analyzed. Most of the acoustic energy in the region is concentrated below 50 kHz. The soundscape is dominated by wave noise, snapping shrimp, and distant dredging. Local areas or times may be dominated by transient biological sounds, e.g., the calls of common dolphins. Regular but infrequent ferry passage temporarily alters the base soundscape.

“The Lost Princess (putri duyung)” of the Small Islands: Dugongs around Sulawesi in the Anthropocene

In the Spermonde as in the other main island groups around Sulawesi, seagrass and coral ecosystems are intimately linked ecologically and overlap extensively on the shallow water shelves surrounding most islands. One keystone species living in these shallow waters is the dugong (Dugong dugon). Officially fully protected under Indonesian Law (PP7/1999), published data on dugongs in the islands around Sulawesi are extremely limited. In this research, we collected, compiled and evaluated data and information (mostly unpublished) on the distribution, exploitation and community perceptions of dugongs around Sulawesi, including the Togean, Banggai, Spermonde, Taka Bone Rate/Selayar and Tanakeke Islands. Opportunities for dugong conservation, and potential benefits for coral reef ecosystems in a small island socio-ecological context, were considered. Once common within living memory, socio-economic data indicate that Sulawesi dugongs are now rare and under severe threat. Many fishing communities consider dugong meat superior to beef, and see it as a welcome change from fish, while certain body parts fetch a high price, as do dugong tears. In the Spermonde Islands, dugongs may already have been extirpated; the most recent reported sighting was in 1993 when the capture of an adult dugong by fishermen of Barranglompo Island resulted in an impromptu festival. All these Sulawesi small islands communities have dugong princess (putri duyung) legends with potential as an entry-point to hearts and minds. Preventing further extirpations and striving to bring back the “lost princess” could be an iconic component of moving towards sustainability in small-island socio-ecological systems.

The Corallian Group (Upper Jurassic) of Wiltshire, England. 3: Lyneham to Royal Wootton Bassett

New information from boreholes at Lyneham and the construction of a relief road south of Royal Wootton Bassett has been combined with field mapping to produce the first synthesis of the transition between the Upper Jurassic shelf sediments of the Wessex Basin and the laterally equivalent clay facies sediments overlying the East Midlands Microcraton. Periodic uplifts of the Wootton Bassett High at the northern margin of the Wessex Basin saw the repeated attempts to spread clay facies sedimentation southwards into central and southern Wiltshire frustrated by uplifts of the high. This resulted in periods of erosion followed by new episodes of shallow water shelf sedimentation succeeded by deeper water strata, these beds resting upon the eroded edges of the older sediments.

Integrated carbon, sulfur, and nitrogen isotope chemostratigraphy of the Ediacaran Lantian Formation in South China: Spatial gradient, ocean redox oscillation, and fossil distribution.

The Ediacaran Doushantuo Formation in South China is a prime target for geobiological investigation because it offers opportunities to integrate chemostratigraphic and paleobiological data. Previous studies were mostly focused on successions in shallow-water shelf facies, but data from deep-water successions are needed to fully understand basinal redox structures. Here, we report δ13 Ccarb , δ13 Corg , δ34 Spyr , δ34 SCAS , and δ15 Nsed data from a drill core of the fossiliferous Lantian Formation, which is a deep-water equivalent of the Doushantuo Formation. Our data confirm a large (>10‰) spatial gradient in δ13 Ccarb in the lower Doushantuo/Lantian formations, but this gradient is probably due to the greater sensitivity of carbonate-poor deep-water sediments to isotopic mixing with 13 C-depleted carbonate cements. A pronounced negative δ13 Ccarb excursion (EN3) in the upper Doushantuo/Lantian formations, however, is spatially consistent and may be an equivalent of the Shuram excursion. δ34 Spyr is more negative in deeper-water facies than in shallow-water facies, particularly in the lower Doushantuo/Lantian formations, and this spatial pattern is interpreted as evidence for ocean redox stratification: Pyrite precipitated in euxinic deep waters has lower δ34 Spyr than that formed within shallow-water sediments. The Lantian Formation was probably deposited in oscillating oxic and euxinic conditions. Euxinic black shales have higher TOC and TN contents, but lower δ34 Spyr and δ15 Nsed values. In euxinic environments, pyrite was predominantly formed in the water column and organic nitrogen was predominantly derived from nitrogen fixation or NH4+ assimilation because of quantitative denitrification, resulting in lower δ34 Spyr and δ15 Nsed values. Benthic macroalgae and putative animals occur exclusively in euxinic black shales. If preserved in situ, these organisms must have lived in brief oxic episodes punctuating largely euxinic intervals, only to be decimated and preserved when the local environment switched back to euxinia again. Thus, taphonomy and ecology were the primary factors controlling the stratigraphic distribution of macrofossils in the Lantian Formation.

The summer Bohai Sea hydrological environment analysis

The Bohai Sea is a nearly closed shallow sea which goes deep into china mainland, it has a supper shallow water shelf properties. The research about the Bohai Sea environment must consider the wind, tide, temperature and salinity. The fixed point observed temperature, salinity and current data were analysed. The results show that the Bohai Sea is regular half-day tidal current trend, and the tidal current trend is the substantially reciprocating flow properties. The reciprocating flow direction within the bay is trend towards the bay’s direction; the rest is trend towards the sea shore. During the observation, the current direction is stable and the current rate is small at all fixed points, with a good correlation with wind. Thereinto the Liaodong Bay has a clockwise circulation and the Laizhou Bay flows substantially clockwise either, which consistent with the historical trend observation. One fixed point in the Bohai Bay flows different trend compared with the historical observation. The Bohai Sea surface temperature is slightly lower than that in August of the calendar year; salinity has a decreased trend compared to historical statistics.

Cambrian–Ordovician conodonts from slump deposits of the Argentine Precordillera: new insights into its passive margin development

AbstractThe Los Sombreros Formation represents the western continental margin slope deposits of the Argentine Precordillera, a sub-terrane accreted to Gondwana as part of the Cuyania Terrane in early Palaeozoic times. The age of these gravity-driven deposits is controversial and, therefore, a precise biostratigraphic scheme is essential to reveal the evolution of the continental margin. New conodont samplings along with sedimentological and structural analysis carried out in the Los Sombreros Formation in the La Invernada Range provide clues to its depositional framework. The sedimentary succession is made up of dominantly calciturbidites, carbonate breccias and conglomerates, along with mudstones that represent the pelagic/hemipelagic background sedimentation. It displays hectometric to outcrop-scale slump folds with variable hinge-line orientations and pinch-and-swell structures, evidencing soft-sediment deformation, consistent with a slope to base-of-slope setting. Three limestone samples from this succession include conodonts referable to the pandemicHirsutodontus simplexSubzone of theCordylodus intermediusZone (upper Furongian, Cambrian) and from theMacerodus dianaeZone (upper Tremadocian, Ordovician), implying that a slope connected the shallow-water shelf with a deep-water (oceanic) basin at least since late Cambrian times. The conodont faunas show affinities to coeval assemblages from outer shelf and slope environments around Laurentia yet they are not conclusive to postulate a geographic origin for the Precordillera. The thermal alteration of the conodonts is consistent with sedimentary burial and nappe stacking in this sector of the Precordillera.

Upper Middle to lower Upper Ordovician chitinozoans and conodonts from the Bliudziai-150 core, southern Lithuania

Integration of chitinozoan and conodont biozones is based on detailed collections from the Bliudziai-150 well, southern Lithuania, that penetrated upper Darriwilian – lower Sandbian sedimentary carbonate rocks. The strata accumulated at the southeastern side of the Livonian Tongue and represent the transition from shallow shelf facies of the Lithuanian shallow-water shelf facies belt to the deeper-water shelf facies belt. Systematically collected and closely spaced samples of the carbonates from the Bliudziai-150 core yielded both chitinozoans and conodonts in abundance. The chitinozoans are assigned to the Laufeldochitina striata, Laufeldochitina stentor, Angochitina curvata – Armoricochitina granulifera, Lagenochitina dalbyensis, Belonechitina hirsuta, and Spinachitina cervicornis chitinozoan biozones, and the conodonts are assigned to the Pygodus serra Zone (with three subzones), Pygodus anserinus Zone (with two subzones), and the three subzones of the Amorphognathus tvaerensis Zone. The fossils are clearly of Baltoscandian affinity, and the integrated results support existing knowledge concerning the biostratigraphy of the two groups in Baltoscandia. Thus, the studied interval is confidently assigned to the Lasnamägi, Uhaku, Kukruse, and Haljala regional stages of the East Baltic regional chronostratigraphical scheme, corresponding to the global upper Darriwilian – lower Sandbian stages (Middle to Upper Ordovician). International correlation of the chitinozoan and conodont succession is presented, and the position of the base of the international Sandbian Stage is placed at 1380.00 m in the Bliudziai-150 core. A horizon marked by multiple discontinuity surfaces represents the base of Kegel depositional sequence and coincides with the appearance of Armoricochitina granulifera, Angochitina curvata, Lagenochitina dalbyensis, and Baltoniodus gerdae in the Bliudziai-150 core.

Modeling of ocean dynamics with large variations in sea level

The formulation and the algorithm of solving an ocean model for the prediction and assimilation of the observed data which makes it possible to reconstruct the circulation in the deep-water parts of the sea and at a shallow water shelf, as well as to describe the large time–space variability in the surface level, are considered. The model uses a vertical hybrid σ–z coordinate system: the several upper tens of meters of the ocean are described in the σ-coordinate system and the rest of the water column is described in the z coordinates. Such hybridization extends the possibilities of models for reconstructing thermo-hydrodynamic processes in different sea basins and the World Ocean. The differential formulation of the model in the σ–z coordinate system is presented; the simplified records of several operators that are allowable in the case of a small thickness of the ocean σ-layer are described. The construction of a computational grid, approximation of the bottom topography on it, and discretization of equations and boundary conditions of the models are considered; an approach to describing the bottom friction at shallow waters is offered. The results of the comparative experiments in the z and σ–z coordinate models are analyzed.

Mud volcanoes and ice-keel ploughmarks, Beaufort Sea shelf, Arctic Canada

The shallow shelf waters of the Beaufort Sea have experienced marine transgression during the Holocene (Hill et al. 1985; Taylor et al. 2013). This has led to a warming of what was terrestrial permafrost by water incursion, and to the dissociation of subsurface gas hydrates which now vent into marine waters. Accompanying this change is the development of conical submarine landforms produced through the extrusion of sediments, combined with the continuing reworking of the seafloor by the ploughing action of the keels of drifting ice (Fig. 1). Fig. 1. Multibeam swath bathymetry and bathymetric profiles of mud volcanoes and ice-keel ploughmarks on the Beaufort Sea shelf, Arctic Canada. ( a ) Sun-illuminated multibeam-bathymetric image showing mud volcanoes and ice-keel ploughmarks. Acquisition system Kongsberg EM302. Frequency 30 kHz. Grid-cell size 5 m. White arrows denote a curvilinear ploughmark cross-cutting its previous track. The image is a compilation of data from CCGS Amundsen -based surveys in 2009 and 2011. The NW–SE narrow, linear artefacts arise from instrumentation employed in the initial survey. Wide, curvilinear artefacts arise from different instrumentation employed in a subsequent survey. ( b ) Sun-illuminated multibeam-bathymetric image showing a swarm of mud volcanoes. Acquisition system Kongsberg EM3002. Frequency 300 kHz. …

Foraging behavior of a high-Arctic zooplanktivorous alcid, the little auk, at the southern edge of its breeding range

Zooplanktivorous seabirds as central-place foragers are constrained by the need to repeatedly return to the colony. Breeding within a cost-effective distance from food-abundant foraging grounds may be crucial for successful reproduction. In this study, foraging areas, ranges and habitats of high-Arctic little auks (Alle alle) breeding on Bjørnøya in the Barents Sea, at the southern edge of their breeding range, were investigated combining GPS-tracking and satellite remote sensing. Birds were expected to forage in areas with productive oceanographic features (cold shelf and frontal zone waters) close to their breeding colony. Contrary to expectation, they foraged in warm waters (sea surface temperature median 6.6°C), optimal for boreal zooplankton. Little auks preferred shallow shelf waters (mean depth 74m) characterized by higher chlorophyll a concentrations. Parent birds performed both short (ST) and long (LT) foraging trips, both of considerably longer duration compared to other colonies in more high-Arctic environment. During ST they probably spent more time searching for preferred Arctic prey (dominating in chick diet samples) among abundant Atlantic zooplankton. Long duration of LT resulted from exploring distant cold waters abundant in Arctic zooplankton community. This confirms that little auks are able to respond to various environmental conditions through the plasticity of their foraging behavior without negative consequences for chick survival. To date, observed changes in marine environment have not posed a threat to the ability of little auks on Bjørnøya to feed their chicks energy-rich zooplankton.

Lifestyle and Ice: The Relationship between Ecological Specialization and Response to Pleistocene Climate Change.

Major climatic changes in the Pleistocene had significant effects on marine organisms and the environments in which they lived. The presence of divergent patterns of demographic history even among phylogenetically closely-related species sharing climatic changes raises questions as to the respective influence of species-specific traits on population structure. In this work we tested whether the lifestyle of Antarctic notothenioid benthic and pelagic fish species from the Southern Ocean influenced the concerted population response to Pleistocene climatic fluctuations. This was done by a comparative analysis of sequence variation at the cyt b and S7 loci in nine newly sequenced and four re-analysed species. We found that all species underwent more or less intensive changes in population size but we also found consistent differences between demographic histories of pelagic and benthic species. Contemporary pelagic populations are significantly more genetically diverse and bear traces of older demographic expansions than less diverse benthic species that show evidence of more recent population expansions. Our findings suggest that the lifestyles of different species have strong influences on their responses to the same environmental events. Our data, in conjunction with previous studies showing a constant diversification tempo of these species during the Pleistocene, support the hypothesis that Pleistocene glaciations had a smaller effect on pelagic species than on benthic species whose survival may have relied upon ephemeral refugia in shallow shelf waters. These findings suggest that the interaction between lifestyle and environmental changes should be considered in genetic analyses.

Characteristics and origin of the heterogeneity of the Lower Silurian Longmaxi marine shale in southeastern Chongqing, SW China

The Lower Silurian Longmaxi marine shale from the productive shale gas block of southeastern Chongqing, Southern China, is one of the most important marine shale gas exploration formations in southern China; geologists have recently made significant shale gas discoveries there. However, the marine shale in southern China is noticeably heterogeneous, leading to difficulties in predicting potential productive zones in the shale formation. To better determine the “sweet spots” in the black shale formation, we carefully examined the heterogeneity of the Lower Silurian Longmaxi marine shale, which is controlled by sedimentary setting, and analyzed the macro- and micro-heterogeneity based on detailed core descriptions, optical microscopy, field emission scanning electron microscopy (FE-SEM), geostatistical analysis of well logging data, geochemical testing data and reservoir property testing data. According to our research, four sedimentary subfacies were recognized and have distinct heterogeneity features within and among them in terms of thickness, mineral composition, organic matter content, pore type and pore structure. The deep water shelf subfacies (DWS) of black carbonaceous and siliceous shale that was formed in anoxic, still water has a stable sedimentary thickness and mineral composition with an total organic carbon (TOC) content generally greater than 2 wt.%; furthermore, the DWS subfacies mainly has organic and intragranular pores, showing the least heterogeneity due to the highest pore throat homogeneity coefficient. The shallow water shelf subfacies (SWS) of gray-black siliceous and argillaceous shale was deposited in shallow water with relatively intense hydrodynamics and has a relatively stable sedimentary thickness and the lowest pore structure coefficient; however, it also comprises various shales and organic matter contents and mainly has intergranular pores showing a moderate heterogeneity that is relatively greater than the DWS subfacies heterogeneity. The tidal flat subfacies (TF) comprises gray calcareous shale with argillaceous siltstone that was greatly influenced by terrigenous sediment input. This facies mostly has a noticeably variable sedimentary thickness and mineral composition with a TOC that is generally less than 1 wt.% and well-developed microfractures, indicating high heterogeneity caused by a low homogeneity coefficient and a poor sorting coefficient of the pore throats. The lagoon subfacies (L) consists of black carbonaceous and siliceous shale formed in anoxic water between the sea and the land and has a relatively stable shale thickness and mineral composition but poor lateral and pore throat connectivity. This subfacies mainly has microfractures and intergranular pores, indicating extremely high heterogeneity. The paleotomography differences in the sedimentary environment determine the sedimentary thickness of the shale, the mineral composition, the organic matter content and other factors; these factors contribute to the macroscopic heterogeneity. Diagenesis controls the pore structure and pore type by compaction, cementation, and dissolution, combined with the generation of hydrocarbons and other phenomena. This process determines the microscopic heterogeneity.