Deep Shelf Environment Research Articles

Coupled δ56Fe and δ18O analysis of the Frere iron formation, Western Australia, and Paleoproterozoic ocean circulation

The Paleoproterozoic (ca.1.89 Ga) Frere Formation is a ca. 300-m-thick sedimentary succession of five stacked, Fe- and silicate-rich shallowing upwards cycles or parasequences that were deposited during marine transgression. Deposition in an oxygen-stratified water column is supported by the occurrence of magnetite-rich mudstones (anoxic and distal) beneath shallower, hematite- and chert-rich grainstones (suboxic and proximal). Minor (LREE/HREE)PAAS depletion and positive Ce anomalies in grainstones support this interpretation. Sequence stratigraphic relationships suggest that the Frere Formation accumulated on an unrimmed continental shelf associated with coastal upwelling of Fe.Large variations in oxygen isotope ratios (δ18O) of magnetite (–0.6 ‰ ≤ δ18O ≤ +2.8 ‰, n = 12) and quartz (+8.8 ‰ ≤ δ18O ≤ +20.1 ‰, n = 11) from lithofacies composing the Frere Formation indicate that pristine δ18O of minerals were overprinted by diagenesis. Highly variable δ18O values calculated at 200 °C in equilibrium with quartz (–3.0 to + 8.3 ‰) and magnetite (+8.0 to + 12.7 ‰) suggest that fluids with heterogeneous δ18O evolved through oxygen isotope exchange between minerals and porewater in accumulating sediment during diagenesis.The Fe isotope ratios (δ56Fe) of bulk rock (–0.50 ‰ ≤ δ56Fe ≤ +1.55 ‰, n = 20) and magnetite separates (–0.09 ‰ ≤ δ56Fe ≤ +2.06 ‰, n = 11) from deeper anoxic and shallow suboxic paleoenvironments define a decreasing trend through stratigraphically stacked parasequences. The high δ56Fe values of magnetite (+0.7 ‰ to + 2.06 ‰) characterizing the base of the Frere Formation is interpreted to reflect equilibrium isotopic fractionation between dissolved Fe2+aq and freshly precipitated Fe-(oxyhydr)oxide (Fe(OH)3) resulting from sluggish recharge of Fe2+aq from deeper shelf environments. These high δ56Fe values of magnetite from shallow paleoenvironments may also reflect microbial dissimilatory Fe reduction at the seafloor. As sea level rose, continued deepening and encroachment of a well-mixed water mass increased the oxidation of Fe2+aq, which ultimately increased the influence of kinetic isotopic fractionation between Fe2+aq and Fe(OH)3. Such a process produced δ56Fe compositions of magnetite that gradually decrease through the stratigraphic thickness of the Frere Formation (+2‰ to −0.1 ‰). Thus, Fe isotopic data framed in a sequence stratigraphic context provides greater insight into water column processes on Fe-rich, oxygen stratified Paleoproterozoic and Mesoproterozoic shelves, as well as geologically younger restricted basins with a redox gradient.

Microfacies analysis and Depositional Basin Model of the Upper Cretaceous, Kurdistan Region, Northern Iraq

This study focuses on the Upper Cretaceous system in the Zagros fold and thrust belt in the Kurdistan Region / Iraq. The impression of this study is created by the variety of formations, facies change, and age of the Cretaceous formations, as well as the different consequences of the contact situation between the formations, particularly the Qamchuqa-Bekhme and Kometan-Shiranish contacts formations. Through investigation, evaluation, and combination of results from Lithostratigraphy and Microfacies of seven sections in various locations of KRI/ Iraq, new paleogeography of the Late Cretaceous of Northern Iraq is constrained. The microfacies of entire Late Cretaceous formations in different sections outcome 16 sub-microfacies types demonstrating open marine deep shelf environment of Shiranish Formation, the entire reef (back-reef, fore-reef, reef body) environment of Bekhme Formation and pelagic open marine ramp depositional environment of Kometan Formation. The output results of stratigraphy and microfacies of Late Cretaceous depositional successions in the Kurdistan Region are paleogeography maps reconstruction. During the Turonian to Early Santonian periods, the Kurdistan Region and northern Iraq were pre-subduction basins due to the presence of open marine outer ramp carbonate of the Kometan Formation in the east (Sulaimaniyah province exceeding Hizop area) and inner shelf of Tanuma and Khasib formations in the center and west (Erbil province). Major regression and unconformities covered the West of the study region during the Middle-Late Santonian; the result of this regression degraded the entire inner shelf facies that deposited during Turonian-Early Santonian periods. During the Early-Middle Campanian, a foreland basin emerged in the extreme northeastern and the Kurdistan Region, which was covered by open marine of the Shiranish Formation and reef platform of the Bekhme Formation. The Kurdistan Region was an active foreland basin margin in the Upper Campanian-Maastrichtian, with a greatly expanded Tanjero Formation, an Aqra reef in the north, and an open marine Shiranish Formation in the center and west.

Characteristics and genesis of reef-bank complexes in deep shelf facies: A case study of the Middle-Late Jurassic in the northern Amu Darya Basin, Central Asia

A large-rimmed carbonate platform was developed in the Amu Darya Basin during the Middle-Late Jurassic Callovian-Oxfordian period. What distinguishes it from typical carbonate platforms is that a series of reef-bank complexes had extensively developed in the deep shelf depositional zone of the basin. However, only a few studies have reported on the classification, characteristics, and genesis of these reef-bank complexes in relatively deep water, greatly limiting the development of deep-water carbonate sedimentology. To address this issue, the types and the genesis of reef-bank complexes in the deep shelf environment have been clarified based on the systematic petrography, seismic sedimentology, and geomorphology study of the Callovian-Oxfordian carbonate rocks in the northern Amu Darya Basin during the Middle-Late Jurassic period. The results find that the reef-bank complexes are widely distributed in the deep shelf environment in the study area with laminar, reticulated, and zonal distributions. The reef-bank complexes include barrier-bonding reef-bank complexes, lime-mud mounds (LMMs), and granular shoals (GSs). The deep shelf environment can be further divided into an inner shelf, shelf margin, and shelf slope. The inner shelf and shelf margin have a relatively shallow water body and a strong sedimentary hydrodynamic force, mainly developing reticulated reef-bank complexes and laminar GSs, whereas the shelf slope mostly develops zonal LMM deposits in strips. The scale of the reef-bank complexes is mainly controlled by basement paleogeomorphology and water energy. Relatively high-energy reef-bank complex bodies are developed on the seaward side of the paleouplift limb with relatively turbulent hydrodynamic conditions, whereas low-energy LMMs are mostly developed on the high position of paleouplift and landward side. The obtained findings can deepen our understanding of relatively deep-water carbonate sedimentation and enrich the carbonate sedimentation theory.

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The Aaliji Formation in wells (BH.52, BH.90, BH.138, and BH.188) in Bai Hassan Oil Field in Low Folded Zone northern Iraq has been studied to recognize the palaeoenvironment and sequence stratigraphic development. The formation is bounded unconformably with the underlain Shiranish Formation and the overlain Jaddala Formation. The microfacies analysis and the nature of accumulation of both planktonic and benthonic foraminifera indicate the two microfacies associations; where the first one represents deep shelf environment, which is responsible for the deposition of the Planktonic Foraminiferal Lime Wackestone Microfacies and Planktonic Foraminiferal Lime Packstone Microfacies, while the second association represents the deep-sea environment that is responsible for deposition of Lime Mudstone Microfacies. The sequence boundaries were marked on SB1 surface on the bottom and the top of the succession while SB2 surface is placed at the top of the sequence (1) as shallowing-upward beneath deepening upward units. Sequence (1) placed on SB1 surface that separates the Cretaceous from the Palaeogene successions where it formed outer shelf to upper-middle bathyal, and comprised the Planktonic Foraminiferal Lime Wackestone Microfacies as a Transgression System Tract TST deepening-upward ended with Maximum Flooding Surface MFS represented by Mudstone microfacies in BH.188 Well. It is followed by the Planktonic Foraminiferal Lime Packstone Microfacies that represent the Highstand System Tract HST as a shallowing-upward ended by SB2. Sequence (2) begins with a new Transgression System Tract TST that formed the outer shelf and bounded with Maximum Flooding Surface MFS. The Highstand System Tract HST that shallowing-upward which ended by SB1 between the Aaliji and Jaddala Formations.

Occurrence and origin of glauconite in the Cambro-Ordovician Bliss Formation of southern New Mexico and West Texas (U.S.A.)

ABSTRACTIn southern New Mexico and West Texas, USA, the Late Cambrian–Early Ordovician Bliss Formation is a relatively thin and dominantly siliciclastic succession that was deposited on the Proterozoic basement during a major global transgression. The Bliss Formation can be divided into two members: 1) a lower, coarser-grained member composed mostly of sandstone (quartz arenite and subarkose) that lacks glauconite and calcite cement, and 2) an upper, finer-grained member that includes glauconitic sandstone, arkosic sandstone, and mixed siliciclastic–carbonate siltstone to fine-grained sandstone, intercalated with thin carbonate beds of grainstone, packstone, and rudstone. Iron oolite and oolitic sandstone are locally exposed at the base of the upper member. Sandstone of the lower member represents upper-shoreface to foreshore deposits, whereas sedimentary structures in the upper member indicate deposition in a middle- to lower-shoreface setting, and locally in a tidal-flat environment. Intercalated carbonate beds are storm layers (tempestites). Glauconite grains are abundant in the upper member as mostly rounded to well-rounded, spheroidal to ovoidal pellets. Two types of glauconite grains are present: homogeneous, dark green grains with high K2O contents (> 8 wt.%; stage 4) and mottled pellets composed of a mixture of glauconite and apatite. Glauconite of the Bliss Formation is not autochthonous as proposed by earlier workers, but of allochthonous (parautochthonous) origin. Thus, the glauconite grains were reworked from deeper shelf environments in northern Mexico to the south and were transported and deposited under regressive–transgressive conditions. Mottled glauconite grains formed by the reworking of phosphatized and glauconitized micritic sediments during regression and were transported and deposited by storm-induced currents, particularly in storm layers during transgressive events. Homogeneous, mature glauconite grains probably were derived from the reworking of glauconitized fecal pellets or completely glauconitized micritic sediments during regressive–transgressive cycles. The world-wide occurrence of glauconite in Cambrian–Early Ordovician sediments indicates that glauconite formation during that period can be considered as a “global event.”

The Permian–Triassic boundary section at Baghuk Mountain, Central Iran: carbonate microfacies and depositional environment

Sections at Baghuk Mountain, 45 km NNW of Abadeh (Central Iran), have excellent exposures of fossiliferous marine Late Permian to Early Triassic sedimentary successions. Detailed bed-by-bed sampling enables the analysis of microfacies changes of three successive rock units across the Permian–Triassic boundary. The Late Permian Hambast Formation is mainly the result of biogenic carbonate production. Its carbonate microfacies is dominated by biogen-rich and bioturbated nodular limestones, indicating a well-oxygenated aphotic to dysphotic environment. The biogen-dominated carbonate factory in the Permian ceased simultaneously with the main mass extinction pulse, which is marked by a sharp contact between the Hambast-Formation and the overlaying Baghuk Member (= ‘Boundary Clay’). The clay and silt deposits of the Baghuk Member with some carbonate beds show only a few signs of bioturbation or relics of benthic communities. The Early Triassic Claraia Beds are characterised by a partly microbially induced carbonate production, which is indicated by frequent microbialite structures. The depositional environment does not provide evidence of large amplitude changes of sea level or subaerial exposure during the Permian–Triassic boundary interval. The deposition of the Baghuk Mountain sediments took place in a deep shelf environment, most of the time below the storm wave base.

Lithostratigraphy and Sedimentological Characteristics of the Calciturbidites of the Babadağ Formation-Tavas Nappe (SW Turkey)

The Lycian Nappes contain slices of ophiolites and sedimentary rocks of various ages that crop out in SW Turkey. They evolved and were emplaced under the effect of the Late Cretaceous-Miocene compressional regime. The Tavas Nappe is part of the Lycian Nappes and contains Jurassic-Eocene sediments. The Babadağ Formation, forming the middle part of the Tavas Nappe, is composed of limestone at the base and various sized calciturbidites with chert intercalations in the upper part. The Standard Microfacies Classification (SMF of FLÜGEL, 2004) indicates that the entire unit was deposited mainly in a deep-shelf environment (Facies Zone – FZ-2), deep-sea (FZ-1), toe of slope (FZ-3) and on the continental slope (FZ-4). Calcite and quartz dominate the bulk mineralogy of the calciturbidites with higher SiO2 and CaO weight percentages than other major oxides. Additionally, the presence of Na2O, K2O, Al2O3, MgO, TiO2 and Fe2O3 is associated with the local sediment input. Tectonism and sea level fluctuations were the main triggering factors of the changes in the original depositional environment of the Babadağ Formation. Additionally, grain size and the amount of sediment input control the calciturbidite type and extension. Si enriched water circulation and Si and Ca substitution were responsible for the abundant chert formation during diagenesis of the units. Post depositional tectonic activities during transportation and emplacement of the nappes resulted in calcite filled cracks that cut both the calciturbidites and cherts. Study of the different nappe slices provides valuable information about syn- and post- depositional changes of the lithostratigraphic units.

The sedimentology and paleoclimatology of Early Triassic regional marine oxic event (Beduh Formation), Kurdistan region – Northern Iraq

Sedimentological study of Beduh Formation (Lower Triassic) is carried out through three outcrop sections at the Northern Thrust Zone – northern Iraq. Lithologically, the formation consists of alternation of dominantly purple and reddish brown shale with subordinate greenish grey shale and wisps of sandstone and/or siltstone.Beduh Formation comprises two lithofacies, dominantly shale lithofacies and wisps of sandstone lithofacies. These facies are divided into five subfacies on the basis of colour, composition, texture and sedimentary structures. Deposition took place in oxic offshore and deep shelf environment and lapping on the shoreface zone (shale-dominated ramp.X-ray diffractometry reveals that the shales are composed mainly of clay minerals such as illite, in a major proportion, kaolinite, chlorite and interstratified clays in minor proportions. In addition to clay minerals, the non-clay minerals are quartz and calcite with minor proportions of feldspar and hematite. Glass shards, foraminifera and conodonts are extracted by washing 26 samples. Petrographically the sandstone and siltstone beds are composed essentially of quartz with little proportions of rock fragments, feldspars and mica, in addition to some fossil remains (posidonia and microconchids).The clays originated from terrigenous influx from land and explosive volcanoes. The predominance of reddish colour and marine fossil content infer deposition in oxic condition during halmyrolysis with minor alternations with anoxic conditions.

Conodont biostratigraphy and astronomical tuning of the Lower–Middle Ordovician Liangjiashan (North China) and Huanghuachang (South China) marine sections

In this study, systematic conodont biostratigraphy and cyclostratigraphy are carried out on Ordovician sections from the North China and South China blocks. The Liangjiashan section, situated on the North China Block margin, accumulated shallow marine carbonate during the Early Ordovician. The Huanghuachang section (GSSP for the Dapingian Stage), situated on the South China Block margin, accumulated thinly bedded carbonates and minor clastics in a deep shelf environment. Conodont biostratigraphy and 405-kyr long-eccentricity cycles interpreted from the Liangjiashan and Huanghuachang sections are used to establish an Astronomical Time Scale (ATS) for the Early–Middle Ordovician period. The ATS indicates that the duration of the Floian Stage is 7.08 ± 0.405 Myr. The temporal ranges of Lower–Middle Ordovician conodont biozones are also estimated: the durations of the Serratognathus bilobatus, Serratognathus extensus, Oepikodus communis, Oepikodus evae, and Baltoniodus triangularis zones are 1.0 Myr, 5.1 Myr, 0.2 Myr, 0.8 Myr, and 0.2 Myr, respectively. The evolution of the ratio of obliquity to total power and short-eccentricity power to total power depicts periodicities of 1 Myr for the s4–s3 term, and 1.9 Myr shifting to 1 Myr for the g4–g3 term. The shift in the g4–g3 term may indicate a chaotic transition in the Mars and Earth orbital motions from a (s4–s3)–2(g4–g3) to (s4–s3)–(g4–g3) resonance state during the Early Ordovician.

Microfacies, foraminifers and carbon and oxygen isotopes in a basinal section of the Zechstein Limestone (Wuchiapingian): Bonikowo 2 borehole, western Poland

The Zechstein Limestone of the Bonikowo 2 borehole is composed of limestone with varied dolomite content and is slightly thicker (3.4 m) than other supposed condensed sections in SW Poland. The microfacies (mostly bioclastic wackestones-packstones) are characteristic of open marine limestone deposited in deep shelf environments. The common occurrence of echinoids in all parts of the section, except close to its top, indicates no essential change in sea water salinity. However, the palaeotemperature interpretation of the highest δ 18 O value of calcite recorded in the Bonikowo 2 borehole (+0.32‰) indicates a temperature of 22.9°C when a δ 18 O of water = 2‰ is assumed. The δ 13 C and δ 18 O curves for calcite and dolomite are similar in shape, and their mean values are similar: +1.8 ±1.5‰ for calcite, respectively, and +1.9 ±2.3‰ and –4.3 ±2.4‰, –3.8 ±4.3‰ for dolomite. There is a recrystallized interval in the lower part of the section with both δ 13 C and δ 18 O values reduced. This may be regarded as an aerobic equivalent of the Kupferschiefer. The diversity and abundance of foraminifers is significant throughout the section studied; lagenids prevail, and this is considered to be due to the dysaerobic conditions throughout the duration of deposition of the Zechstein Limestone

Features of the first great shale gas field in China

On the 28th of November 2012, high shale gas flow was confirmed to be 203 × 103 m3 in Longmaxi Formation; this led to the discovery of the Fuling Shale Gas Field. On the 10th of July in 2014, the verified geological reserves of the first shale gas field in China were submitted to the National Reserves Committee. Practices of exploration and development proved that the reservoirs in the Fuling Shale Gas Field had quality shales deposited in the deep-shelf; the deep-shelf had stable distribution, great thickness with no interlayers. The shale gas field was characterized by high well production, high-pressure reservoirs, good gas elements, and satisfactory effects on testing production; it's from the mid-deep depth of the quality natural gas reservoirs that bore high pressure. Comprehensive studies on the regional sedimentary background, lithology, micropore structures, geophysical properties, gas sources, features of gas reservoirs, logging responding features, and producing features of gas wells showed the following: (1) The Longmaxi Formation in the Fuling Shale Gas Field belongs to deep-shelf environment where wells developed due to organic-rich shales. (2) Thermal evolution of shales in Longmaxi Formation was moderate, nanometer-level pores developed as well. (3) The shale gas sources came from kerogens the Longmaxi Formation itself. (4) The shale gas reservoirs of the Fuling Longmaxi Formation were similar to the typical geological features and producing rules in North America. The findings proved that the shale gas produced in the Longmaxi Formation in Fuling was the conventional in-situ detained, self-generated, and self-stored shale gas.

Environmental measurements collected during TREX13 to support acoustic modeling

The major goal of TREX13 (Target and Reverberation EXperiment 2013) was to quantitatively investigate reverberation with sufficient environmental measurements to support full modeling of reverberation data. The collection of environmental data to support reverberation modeling is usually limited by the large ranges (10s of km) involved, the temporal and spatial variability of the environment and the time variation of towed source/receiver locations within this environment. In order to overcome these difficulties, TREX13 was carried out in a 20 m deep shelf environment using horizontal line arrays mounted on the seafloor. The water depth and well controlled array geometry allowed environmental characterization to be focused on the main beam of the array, i.e., along a track roughly 5 km long and 500 m wide. This talk presents an overview of the efforts made to characterize the sea surface, water column, seafloor, and subbottom along this track to support the modeling of acoustic data collected over the course of the experiment. [Work supported by ONR Ocean Acoustics.]

Aggregations and offshore movements as indicators of spawning activity of bonefish (Albula vulpes) in The Bahamas

To identify the timing and location of spawning activity for boneWsh (Albula spp.) in the Bahamian archi- pelago, we used an acoustic telemetry array spanning 44 km 2 of shallow tidal creeks, Xats, and adjacent deeper coastal waters near Cape Eleuthera. In two successive years, we surgically implanted transmitters in male and female boneWsh (n = 60) and examined their movement patterns within the array. Eight boneWsh surgically implanted with transmitters as part of an earlier study were also tracked. In 2009, the telemetry information was com- plemented with snorkeling observations, underwater video, and manual tracking of the same acoustically tagged Wsh, as well as Wsh (n = 3) gastrically implanted with continuous transmitters. During a period of 4-7 days spanning the full and new moons, primarily between October and May, boneWsh moved from their typical shallow Xats and aggre- gated at sites in close proximity to the deep water drop-oV of the Exuma Sound. Localized movements of the large schools of boneWsh (often >1,000 Wsh) at these presumptive pre-spawning aggregation sites included brief trips ( 1,000 m depth). Tagged boneWsh detected at these aggregation sites were subsequently detected back in the tidal creeks and coastal Xats shortly after new and full moons and remained at these more typical shallow sites (i.e., <2 m depth). Although we did not directly observe spawning events, we did observe ventral nudging and porpoising behaviors, which are poten- tially associated with courtship. Timing of the observed movements and possible courtship behaviors was coinci- dent with periods when gametes were well developed. Col- lectively, our study provides the Wrst objective evidence suggesting that the aggregation and seasonal migration of boneWsh to deep shelf environments during certain moon phases is for spawning.

Paraburdoo spherule layer (Hamersley Basin, Western Australia): Distal ejecta from a fourth large impact near the Archean-Proterozoic boundary

We report the discovery of the Paraburdoo spherule layer, which consists entirely of replaced impact-produced melt spherules. It is distal ejecta from a large impact close to the Archean-Proterozoic boundary in the Hamersley Basin of Western Australia. The spherule layer occurs in the Paraburdoo Member of the Wittenoom Formation and was deposited ca. 2.57 Ga (date via U-Pb age interpolation) in a deep shelf environment. The layer consists of microkrystites rich in plagioclase and ferromagnesian crystals, replaced by K-feldspar and a phlogopite-like sheet silicate, respectively. The skeletal textures indicate rapid cooling of a melt with mafic to ultramafic composition and suggest oceanic target rocks. The Paraburdoo spherule layer is 2 cm thick, normally graded, and was probably deposited by suspension settling, as there is no evidence of reworking; it is strikingly similar to the Reivilo spherule layer in the Griqualand West Basin (South Africa), appears to provide a third impact-related high-resolution stratigraphic correlation between these two basins, and points to a high frequency of large impacts around the Archean-Proterozoic boundary.

Franz Ritter von Hauer’s work and one of the first loess map of Central Europe

Franz Ritter von Hauer was the second Director of the Geological Survey in Vienna (1866–1885). The primary research of von Hauer was devoted chiefly to the evolutionary history of Cephalopods and geological mapping. Among several investigations of Cephalopods of the Triassic and Jurassic formations of the Alpine regions, he recognized and discovered 89 species and established the Middle and Late Triassic stratigraphical units of deep shelf environments: the Hallstadt facies. One of his main contributions to Quaternary science was the geology textbook of the former Austro-Hungarian Monarchy, which provided a resource to access recent developments in geology and notably loess research to many scientists. Besides the staff from the Geological Survey, von Hauer involved numerous local, well recognized experts and organized regional centres for geological investigations. This well managed and effective work resulted in a great number of publications, many of which were the reports published by the Geological Survey. The General Geological Map of the Austro-Hungarian Monarchy was one of the most comprehensive and complete geological map of Central Europe during that period of time. It was presented in Cologne (1865) and from 1867 until 1884 ran to four editions. The Quaternary formations were presented in two groups: Pleistocene and Holocene formations. The Pleistocene formations identified as “Dilluvial” formations and were represented predominantly as gravels and sand and also as loess. The Holocene formations were described as “Alluvial” formations. They were mapped as: peat, lime tuff, quicksand and other formations named only as “Alluvial formations”. Loess was mentioned exclusively as a Pleistocene (“Dilluvial”) formation. The distribution of loess was clearly outlined. Due to the development of the science at that time, the term loess was not clearly defined and as such at some places, loess-like sediments such as colluvial were also mapped as loess. Nevertheless it was one of the first maps which documented the extent of loess deposits and including the regions of Lower Austria with Vienna Basin, Bohemia and Moravia, the Carpathian Basin, parts of the Polish Lowland and Transylvania.

Oxygen and carbon isotope composition of Callovian–Lower Oxfordian (Middle–Upper Jurassic) belemnite rostra from central Poland: A record of a Late Callovian global sea-level rise?

Oxygen and carbon isotope data of well-preserved and stratigraphically well-dated belemnite rostra are presented from a Callovian–Lower Oxfordian succession of the Polish Jura Chain (south-central Poland) that was deposited in a deep shelf environment. Palaeotemperatures calculated from belemnite δ 18O values (9 to 14 °C) indicate relatively constant climatic conditions during studied Callovian and Early Oxfordian intervals. Belemnite δ 13C temporal trends, which are interpreted to record primary variation in the isotope composition of dissolved inorganic carbon reservoir, display a prominent positive carbon isotope shift (up to around 1.7‰ VPDB) in the Upper Callovian. This excursion is preceded and followed by a drop in average δ 13C values of belemnite rostra of around 1‰. The Late Callovian carbonate carbon isotope excursion is likely linked to the enhanced storage of organic carbon in shelf sediments during a global sea-level rise. The presented data are not compatible with the theory of prolonged global glaciation at the Middle–Late Jurassic transition.

Structural, Sedimentologic, and Sea-Level Controls on Sand Distribution in a Steep-Clinoform Asymmetric Wave-Influenced Delta: Miocene Billund Sand, Eastern Danish North Sea and Jylland

Abstract The lower Miocene Billund sand of Jylland, Denmark, provides an excellent opportunity to study the distribution of sands and the types of clinoform generated by a wave-dominated delta prograding into a deep shelf environment. In particular seismic sections, the sand-rich parts correlate with parallel clinoformal seismic facies, in which the clinoforms dip 7° to 10°. The stacking pattern of this seismic facies also indicates whether the progradation occurred during rising or falling sea level by displaying an ascending or descending shoreline trajectory, respectively. The Billund delta was deposited in the eastern North Sea Basin during the early Miocene and is on the available data recognized as a NW to SE trending feature. It forms a wave-dominated delta with thick sand bodies deposited in relatively deep waters (> 100 m) at the river mouth and in the up-drift area of newly formed delta lobes. Sands and muds associated with a spit complex or a lagoonal complex dominated the down-drift area. In the distal delta-front area, alternating sands and muds were laid down, the sands associated mainly with storm events. Progradation of the studied part of the delta occurred during high sea level and a subsequent fall in sea level that was caused by a eustatic fall during the mid Aquitanian (early Miocene). Although sand intervals 10 to 20 m thick are common throughout the delta complex, the thickest (up to 100 m) and cleanest sand is found in units deposited in narrow bands within structural lows and during periods of forced regression. The Billund delta may be an excellent analogue for hydrocarbon-bearing, wave-dominated deltas, and seems to exhibit similarities to Jurassic deposits in the North Sea area.

Assessing the biodiversity of Ordovician ostracods from the Argentine Precordillera

Ostracod faunas from the Lower to Middle Ordovician rocks of the Argentine Precordillera Basin (Gualcamayo and Las Aguaditas Formations) are studied. A new family, Garcianidae, is erected. One new genus,Jeanvannieria, and six species are recognized, two of which are new (Jachalipisthia bicornataandJeanvannieria bulbosa). The diversity and composition of the Precordilleran ostracods is evaluated on the basis of previous taxonomic analysis and the fauna studied here. The diversity is moderate, with a peak of 50 species during the early Caradoc. The composition of the fauna is characterized by the dominance of podocopes with a high percentage of binodicopes and a lack of palaeocopes, which is in agreement with a deep shelf environment. The carbonate slope setting of the Las Aguaditas Formation is the deepest environment yet found with Ordovician ostracods and records a relatively diverse fauna. The presence ofEctoprimitioidessuggests biogeographic affinities between the Precordillera and Laurentia. The rest of the fauna contains a high percentage of endemic genera and a mixture of genera with several affinities, Baltic, peri-Gondwanan, and Australian.

Altered volcanic ash as an indicator of marine environment, reflecting pH and sedimentation rate — Example from the Ordovician Kinnekulle bed of Baltoscandia

AbstractThe composition of altered volcanic ash of the Late Ordovician Kinnekulle bed was studied in geological sections of the Baltic Paleobasin. The composition of altered ash varies with paleosea depth from northern Estonia to Lithuania. The ash bed in shallow shelf limestones contains an association of illite-smectite (I-S) and K-feldspar, with the K2O content ranging from 7.5 to 15.3%. The limestone in the transition zone between shallow- and deep-shelf environments contains I-S-dominated ash with K2O content from 6.0 to 7.5%. In the deep-shelf marlstone and shale, the volcanic ash bed consists of I-S and kaolinite with a K2O content ranging from 4.1 to 6.0%. This shows that authigenic silicates from volcanic ash were formed during the early sedimentary-diagenetic processes. The composition of the altered volcanic ash can be used as a paleoenvironmental indicator showing the pH of the seawater or porewater in sediments as well as the sedimentation rate.

Use of high-frequency imaging sonar to observe fish behaviour near baited fishing gears

A high-frequency imaging acoustic camera was used to observe the behaviour of sablefish ( Anoplopoma fimbria) and Pacific halibut ( Hippoglossus stenolepis) around baited fish pots and baited hooks in the deep shelf environment (220–366 m depth) off Oregon. The acoustic camera, tested to a distance of 9.7 m (11.5–15.6 m 2 field of view), provided continuous high-resolution imagery of approaches of fish to the gear, entry into pot tunnels, bait attacks, and escapes in conditions of darkness and high turbidity. Fish inside and beyond the fish pot could also be observed. Fishes, including small individuals and “bait thieves” (>20 cm), could be measured and tracked in the digital images. Concurrent observations with a low-light video camera and infrared lighting yielded a field of view of approximately 1 m 2, limited to just one side of the fish pot. A large proportion of the video tape produced was unusable because of turbidity, and the patterns of fish movement around the pots and baited hooks were poorly characterized by the video camera. The large field of view provided by the acoustic camera showed that a very low percentage of sablefish and halibut approaching the gear were captured. Observations on different gear types, including fish pots with and without tunnel triggers, provide insights into how acoustic camera imagery can be used to improve our understanding of fish behaviour in the natural environment, to design increasingly selective and efficient fishing gear, and to improve bait-dependent stock assessments.