Facies Groups Research Articles

The role of the sedimentary regime in shaping the distribution of subtidal sandbank environments and the associated meiofaunal nematode communities: an example from the southern North Sea.

We combined sediment and faunal data to explore the role of the sedimentary regime in shaping the distribution of subtidal sandbank environments and the associated meiofaunal nematode communities at Broken Bank and Swarte Bank, in the southern North Sea. A variety of sediment transport processes occur in the area, differing in the frequency and magnitude of sediment mobility, and the continuum between erosion, translation and sediment accumulation. The seabed contained a variety of bedforms, including longitudinal furrows, and small to very large sandwaves. The bed sediments were dominated by fine and medium sands, with admixtures of silt and gravel. Based on sedimentary bedforms and grain size analysis, a total of 11 sedimentary facies were delineated, of which 8 were analysed in detail for their relationships with the meiofauna. The sedimentary facies fell clearly into groups of facies, respectively representing high, high-moderate and moderate, and episodic sediment mobility. For those sedimentary facies where daily movement of sediments and bedforms occurred (‘high’ sediment mobility), the resulting spatially homogeneous environments were dominated by an impoverished nematode community comprising small deposit feeders and large predators. Resistance to sediment movement and the ability to exploit alternative food sources were prominent functional features of the successful colonisers. Those facies characterised by relatively infrequent sediment mobility (‘episodic’ and ‘high-moderate and moderate’ sediment mobility) comprised a heterogeneous suite of benthic habitats, containing taxonomically and functionally diverse assemblages of nematodes of various sizes, feeding types and reproductive potential. Faunal distribution patterns here indicated trade-offs between the resistance to sediment movement, environmental tolerance and competitive abilities. Our focus on diverse assemblages of organisms with high turnover times, inhabiting highly dynamic sedimentary environments, has revealed new animal-sediment relationships of relevance to pure and applied science.

The Chenka sandstone Sequence (Lower Jurassic) of the Crimean Mountains: Stratigraphy and depositional environments

The position of the Chenka Sequence in the section, original data on its clay minerals, facies and structural parageneses with consideration of volcanic and climatic events, as well as the available published information provide grounds for accepting it as Pliensbachian-Toarcian in age. It is shown that the Chenka sandstones are a facies or group of facies deposited in deltaic-plain or delta-front environments and that it cannot be ranked as an autonomous formation or other stratigraphic unit.

Debris-Rich Basal Ice as a Microbial Habitat, Taylor Glacier, Antarctica

Two ∼4 m vertical sequences of basal ice were collected from tunnels dug into the northern lateral margin of Taylor Glacier, McMurdo Dry Valleys, Antarctica. In both cases the basal sequences exhibit two contrasting ice facies groups; clean (debris-free) and banded dispersed (debris-rich). Debris-rich ices exhibit elevated CO2 and depleted O2 concentrations compared to the clean facies. Bacterial cell numbers, respiration rates, and nutrient concentrations are highest in debris-rich layers. Together, our geochemical and biological data indicate that microbial heterotrophic respiration is likely occurring in situ within the basal ice matrix at ambient temperatures near −15°C. This implies that the basal ice zone of polar glaciers and larger ice sheets is a viable subglacial microbial habitat and active biome of significant volume that has not previously been considered.

Hydrochemical Study of Groundwater in Sidoarjo Mud Volcano Area, East Java Indonesia

Mudflow phenomena that was occured in the Porong, Sidoarjo since May 29, 2006 has resulted in environmenta l impacts. One of the impact is the decline in groundwater quality and the presence of gas bubbles in the wells of the population Hydrochemicha l analysis is used to evaluate the quality of groundwater, to know the genesis systems and groundwater aquifers. Hydrochemichalanalysis by Piper diagram show there are three groups of groundwater facies first is bicarbonate chloride facies, chloride bicarbonate facies and chloride facies. Analysis of isotope deuterium (δ2H) and oxygen-18 isotope (δ18O) showed that the water coming from the bubble is related to the hydrological cycle or meteoric water and groundwater around the center of the water spray is included in formation water. Multivariate analysis resulted in two groups: the groundwater in the area of wate r bursts originate from magmatic hydrothermal process while groundwater in wells comes from surface water. Compilation parameters total dissolved solids and dissolved ion of groundwater contamination is divided into three zones, namely a low polluted zone, middle polluted zone and high polluted zone with groundwater pollution spread pattern trending east/northeast in the direction of unconfined groundwater flow. The water that comes out with mud from the center bursts are thought to origina tefrom the volcanic sandstone confined aquifer lithology, the Upper Kalibengformation,Pliocene age.

Facies types of sedimentary iron ore deposits and their geochemical features: Communication 1. Facies groups of sedimentary ores, their lithology, and genesis

Economic significance of the sedimentary iron ore deposits is shown. The most important types of these deposits are characterized and their genesis is considered. Special attention is given to the formation of goethite-chlorite-siderite ooliths, which represent the main component of marine iron ore deposits. Geochemical and mineralogical features of different types of iron ores are examined.

New stratigraphic data from the Lower Penninic between the Adula nappe and the Gotthard massif and consequences for the tectonics and the paleogeography of the Central Alps

New stratigraphic data along a profile from the Helvetic Gotthard massif to the remnants of the North Penninic basin in eastern Ticino and Graubünden are presented. The stratigraphic record together with existing geochemical and structural data, motivate a new interpretation of the fossil European distal margin.We introduce a new group of Triassic facies, the North-Penninic-Triassic (NPT), which is characterised by the Ladinian “dolomie bicolori”. The NPT was located in-between the Briançonnais carbonate platform and the Helvetic lands. The observed horizontal transition, coupled with the stratigraphic superposition of a Helvetic Liassic on a Briaçonnais Triassic in the Luzzone-Terri nappe, links, prior to Jurassic rifting, the Briançonnais paleogeographic domain at the Helvetic margin, south of the Gotthard. Our observations suggest that the Jurassic rifting separated the Briançonnais domain from the Helvetic margin by complex and protracted extension.The syn-rift stratigraphic record in the Adula nappe and surroundings suggests the presence of a diffuse rising area with only moderately subsiding basins above a thinned continental and proto-oceanic crust. Strong subsidence occurred in a second phase following protracted extension and the resulting delamination of the rising area.The stratigraphic coherency in the Adula's Mesozoic questions the idea of a lithospheric mélange in the eclogitic Adula nappe, which is more likely to be a coherent alpine tectonic unit. The structural and stratigraphic observations in the Piz Terri–Lunschania zone suggest the activity of syn-rift detachments. During the alpine collision these faults are reactivated (and inverted) and played a major role in allowing the Adula subduction, the “Penninic Thrust” above it and in creating the structural complexity of the Central Alps.

Degassing in kimberlite: Oxygen isotope ratios in perovskites from explosive and hypabyssal kimberlites

Interest in the radiogenic and trace element characteristics of uncontaminated kimberlitic magma has been rekindled by recent isotope studies on groundmass perovskite, which is a major sink of most of the trace elements including rare earth elements (REE) in kimberlite magma. Perovskite is also quite resistant to sub-aerial weathering. In-situ trace element, oxygen isotope ratios and conventional TIMS Sr isotopic analyses of perovskites are presented for two kimberlites: one from Orapa, a crater facies group I kimberlite from Botswana, and the other from Wesselton, a hypabyssal facies group I kimberlite from South Africa. The perovskites from Orapa exhibit greater ranges in trace element abundances and 87Sr/ 86Sr ratios than those from Wesselton (La = ~ 7000–13,600 times primitive mantle and 87Sr/ 86Sr = 0.70310–0.70541 in Orapa perovskites, and La = ~ 4000–7000 times primitive mantle and 87Sr/ 86Sr = 0.70441–0.70558 in Wesselton). The δ 18O values from Orapa perovskites have two distinct peaks around + 3.6‰ and − 0.6‰, which are unlikely to reflect crustal assimilation processes. Wesselton perovskites in contrast are clustered around δ 18O values of + 4‰. Perovskite in equilibrium with the mantle has lower δ 18O than other common upper mantle minerals (olivine, orthopyroxene). The group of Orapa perovskites with δ 18O clustering around + 3.6‰, and the Wesselton perovskites are interpreted to have δ 18O values (~ 4.2‰) that reflect the δ 18O of uncontaminated kimberlite magma of an upper mantle origin (~ 5.2‰). The negative δ 18O values from the second group of Orapa perovskites are attributed to crystallisation of perovskite after magma degassing that depleted 18O in the residual magma. Abundance of magmatic carbonate in the Wesselton sill, together with the absence of any perovskite with very low δ 18O, indicates a lack of significant degassing for the Wesselton kimberlite.

Drowning discontinuities and stratigraphic correlation in platform carbonates. The late Barremian–early Aptian record of southeast France

In Provence and Languedoc, four drowning events were identified in platform carbonates of late Barremian–Bedoulian age. Their recognition is based on sedimentological and stratigraphical evidence, and their timing, referred to ammonite zones or subzones, is as follows: (1) Late Barremian, at the G. sartousiana– Imerites giraudi transition, or merely the lowermost part of the I. giraudi zone, (2) Middle Bedoulian, at the Deshayesitesweissi– Deshayesites deshayesi transition, (3) Mid late Bedoulian in correspondence with the “ Roloboceras hambrovi subzone”, (4) Late Bedoulian at the Deshayesites grandis– Deshayesites furcata transition. Corresponding events are also well expressed in basinal settings where they are marked by significant facies and faunal changes. These four successive drowning events distinguish four successive steps in platform development and demise. Step 1 was coeval with the onset of the Bedoulian palaeogeography and started after drowning event (1) with a drastic reduction of shallow platform settings with rudists, usually replaced by Palorbitolina facies. The ensuing recovery of rudist facies and, following drowning event (2), subsequent step 2 marked the developmental phase of the platform system, whereas steps 3 and 4, each prefaced by a drowning event, were associated with its demise. Step 1 represents the major spreading phase of the Urgonian type facies spectrum including bioclastics, coral and rudist facies groups. In Provence, step 1 was characterized by a bipolar (N-S) progradation, and aggradation was coeval with a maximum of subsidence. The termination of step 1 was marked by the emergence of the antecedent platform margin. Step 2, which followed the disappearance of rudist facies and the extreme spatial reduction of both coral and bioclastic facies, started with the flooding of the antecedent platform and the development of Palorbitolina and cherty limestones. Shallow water bioclastics and/or coral facies recovered rapidly on top of the pre-existing emerged areas and developed locally as bioclastic shoals. Step 2 documents a regional reorganisation of subsidence patterns. The infralittoral (high illuminated environments) “Urgonian facies” are therefore essentially present in the Lower Bedoulian, and circalittoral (relatively deep low illuminated environments) deposits dominate in the Upper Bedoulian. This pattern, typical for SE France and wide parts of the Helvetic shelf, departs from that of adjacent regions (e.g. SW France, Spain) where late Bedoulian platform carbonates have a significant record. The record thus shows that the demise of the Urgonian platform was a step-wise phenomenon which cannot be ascribed to a single event, i.e. the Goguel/Selli OAE1a main event.

Malacofauna of Holocene freshwater calcareous deposits of Lithuania

. Vilnius. 2010. Vol. 52. No. 1–4(69–72). P. 16–24. ISSN 1392-110XTh e malacofauna of freshwater calcareous deposits of Lithuania was studied. Sections of the Mūsos Tyrelis and Pabaliai peatbogs near the town of Siauliai, as well as Dubiciai section (three sites) in SE Lithuania and Dūkstos in Central Lithuania were investigated. Freshwater calcareous deposits are attributed to three groups of facies – lacustrine, valley-hollow-peatbog and terres-trial. Each group of facies consists of sub-facies (freshwater lime, “gazha” (limno-calcite), peat-tufa, calcareous tufa, “mada”) varying the formation conditions, composition and other charac-teristics. Th e mollusc fauna in the lacustrine facies group (Mūsos Tyrelis and Pabaliai sections) is represented by lacustrine species containing euryecological freshwater molluscs. Terrestrial and rheophilous species are rare or absent in the lacustrine group. Deposits of valley-hollow-peatbog facies contain shells of euryecological freshwater and lacustrine molluscs together with rheophyl shells, sometimes with abundant terrestrial shells, as was observed in the Dubiciai-4 section. A characteristic feature of the terrestrial facies group deposits is the occurrence of solely terrestrial mollusc shells (Dūkstos section).Key words: malacofauna, freshwater calcareous deposits, Holocene, LithuaniaReceived 23 October 2010, accepted 08 November 2010Aleksander Sanko. Belarusian State Pedagogical University, Sovetskaya St. 18, 220030 Minsk, Be-larus. E-mail: sankoaf@tut.by. Julius Vainorius . Nature Research Center Institute of Geology andGeography, T. Sevcenkos 13, LT-03223 Vilnius, Lithuania. E-mail: juliusvainorius@yahoo.com.Monika Melesytė. Department of Geology and Mineralogy, Vilnius University, M. K. Ciur-lionio 21/27, LT-03101 Vilnius, Lithuania. E-mail: monika.melesyte@gf.vu.lt

Late Quaternary (Weichselian) alluvial history and neotectonic control on fluvial landscape development in the southern Körös plain, Hungary

Four drill cores and a clay pit section have been examined in the southern part of the Körös plain to understand the history and controls on alluvial sedimentation for the last ~40ka. Four facies groups were identified, such as channel, channel margin, floodplain and floodbasin with seven distinctive facies. Magnetic susceptibility and mineralogy have further characterized the sedimentary facies indicating shifts in humidity conditions, variations in sediment flux and pedogenesis. Detailed pollen analysis of a 7.5m thick clayey succession indicated climatic variability within the MIS 3 period. The spatial distribution of the different facies allowed outlining alluvial architecture of the study area. Three depositional units composed of various facies were identified based on OSL and radiocarbon data. These packages correspond to three major phases of channel activity: (F-I) pre-LGM period (>30ka to 24ka), (F-II) post-LGM interstadial (18–16ka), and (F-III) Late Glacial <15ka to ~10ka). The pre-LGM and post-LGM “interstadial” phases are characterized by meandering river patterns, while the Late Glacial fluvial activity is characterized by a braided system in the area. Higher sediment supply feeding this braided river was probably caused by neotectonic uplift of the southern margin of the basin, documented by a significant stratigraphic gap between 25 and 14ka.

Wave-influenced deltaic sandstone bodies and offshore deposits in the Viking Formation, Hamilton Lake area, south-central Alberta, Canada

Abstract Subtle indications of deltaic influence can be overlooked in coarsening-upward units that resemble shoreface successions such as those found in the Cretaceous Viking Formation at Hamilton Lake (HL). Particular facies within HL strata contain physical and biogenic indicators of riverine discharge, and are interpreted as deltaic in origin. This study focuses on distinguishing between these deltaic deposits and strata reflecting normal-marine depositional conditions and relating facies within the stratigraphic framework. Based on detailed facies analysis, Viking deposits include: delta front, prodelta, upper offshore, lower offshore, shelf, slump and transgressive lag deposits. The principal group of facies, Facies Association 1 (FA1), is interpreted as deltaic in nature, which is indicated by evidence of: high sedimentation rates, salinity fluctuations, riverine discharge, hypopycnal and hyperpycnal flows, and moderately to subtly stressed ichnological suites. Trace fossil suites indicate suppression of suspension-feeding activities despite the presence of hummocky cross-stratified units that resemble shoreface deposition. Filter-feeding organisms are typically abundant in shoreface and wave-dominated deltaic successions. In the case of HL strata, hindrance of dwellings of inferred suspension-feeding animals in FA1 is attributed to increased water turbidity and suspended sediment associated with deltaic outflow. The presence of a restricted suite of structures of inferred suspension-feeders is uncharacteristic of river-dominated deltaic units, which are primarily reworked by deposit feeders. Accordingly, sedimentological evidence in combination with the proportion of dwellings of inferred suspension-feeders signifies moderate wave mitigation of environmental stresses induced by riverine discharge indicative of a wave-influenced deltaic system. In contrast to FA1, muddy sandstones to sandy mudstones of Facies Association 2 contain abundant and diverse suites of trace fossils interpreted to reflect deposition in the distal lower shoreface to upper offshore. Facies Association 3 is predominantly comprised of sandy mudstones with varying degrees of bioturbation indicative of lower offshore, shelfal, slump and transgressive lag deposits. The depositional history at HL includes periods of progradation alternating with transgressive flooding, subaerial exposure, stillstand progradation and wave ravinement. Four major bounding discontinuities and two major transgressive flooding surfaces separate units reflecting predominantly deltaic deposition, strictly offshore deposition, and mixed offshore and deltaic deposition. Variation in the deltaic and normal-marine signature of the deposits suggests changes in source area(s) over time, shifting shore-parallel deltaic influence, or fluctuations in riverine influx.

Fácies e associações de fácies de diamictitos do Subgrupo Itararé (Paleozóico superior) no norte de Santa Catarina e sul do Paraná, Bacia do Paraná, Brasil

Glacial diamictites provide information about glacial depositional environments. Similar characteristics found in other sediments, however, may lead to incorrect interpretation of diamictites since any sedimentary type can be deposited by glaciers. In addition diagenesis, compaction, water loss and weathering may obliterate diagnostic features. Most of the problems of interpretation of glacial sucessions must therefore be classified together with those related to the origin of the diamictites using the identification of sedimentary facies. These facies are compact massive diamictite; deformed diamictite; non compact massive diamictite; tabular diamictite; lenticular diamictite; laminated diamictite with massive diamictite lenses; clast rich massive diamictite; stratified diamictite with textural variation or intercalations of other rock types; diamictite with intercalations of various rock types containing icnofossils; and rhythmite of diamictite and shale. This approach was based in the interpretation of such facies in order to identify their paleoenvironmental setting. The diamictite facies were thus combined into facies associations or groups of facies genetically related, and with environmental significance. In regard to the fact that the interpretation of a sedimentary environment can rest on the association of universal facies with other diagnostic facies, their groups here recognized took into account those produced under specific depositional conditions related to the admitted glacial terrestrial and glacial-marine influences in the study area. So, terrestrial grounded glacier association, proximal platform grounded glacier association and distal platform association were defined.

Fácies e associações de fácies de diamictitos do Subgrupo Itararé (Paleozóico superior) no norte de Santa Catarina e sul do Paraná, Bacia do Paraná, Brasil

DIAMICTITE FACIES AND FACIES ASSOCIATIONS OF THE ITARARE SUBGROUP (UPPER PALEOZOIC) IN NORTHERN SANTA CATARINA AND SOUTHERN PARANA STATES, PARANA BASIN, BRAZIL. Glacial diamictites provide information about glacial depositional environments. Similar characteristics found in other sediments, however, may lead to incorrect interpretation of diamictites since any sedimentary type can be deposited by glaciers. In addition diagenesis, compaction, water loss and weathering may obliterate diagnostic features. Most of the problems of interpretation of glacial sucessions must therefore be classified together with those related to the origin of the diamictites using the identification of sedimentary facies. These facies are compact massive diamictite; deformed diamictite; non compact massive diamictite; tabular diamictite; lenticular diamictite; laminated diamictite with massive diamictite lenses; clast rich massive diamictite; stratified diamictite with textural variation or intercalations of other rock types; diamictite with intercalations of various rock types containing icnofossils; and rhythmite of diamictite and shale. This approach was based in the interpretation of such facies in order to identify their paleoenvironmental setting. The diamictite facies were thus combined into facies associations or groups of facies genetically related, and with environmental significance. In regard to the fact that the interpretation of a sedimentary environment can rest on the association of universal facies with other diagnostic facies, their groups here recognized took into account those produced under specific depositional conditions related to the admitted glacial terrestrial and glacial-marine influences in the study area. So, terrestrial grounded glacier association, proximal platform grounded glacier association and distal platform association were defined.

Stratigraphy, facies architecture, and palaeoenvironment of Neoproterozoic volcanics and volcaniclastic deposits in Fatira area, Central Eastern Desert, Egypt

Fatira area in the Central Eastern Desert, Egypt, is a composite terrane consisting of Neoproterozoic volcanics and sediments laid down in submarine to subaerial environment, intruded by voluminous old to young granitic rocks. The various lithofacies of the study area can be grouped in three distinct lithostratigraphic sequences, which are described here in stratigraphic order, from base to top as the Fatira El Beida, Fatira El Zarqa and Gabal Fatira sequences. Each depositional sequence, is intimately related to volcanic activity separated by time intervals of volcanic inactivity, such as marked hiatuses, reworked volcaniclasts, and or turbidite sedimentation. Four submarine facies groups have been recognized within the oldest, folded eruption sequence of Fatira El Beida. The southern part of the study area is occupied by sheet lava (SL), pillow lavas (PL), pillow breccias (PB), and overlying Bouma turbiditic volcaniclastites (VC). The four facies groups of Fatira El Beida sequence occur in a predictable upward-deepening succession, essentially from base to top, an SL–PL–PB–VC stacking pattern. The coeval tholeiitic mafic and felsic volcaniclastic rocks of this sequence indicate an extensional back-arc tectonic setting. The El Beida depositional sequence appears to fit a submarine-fan and slope-apron environment in an intra-arc site. The Fatira El Zarqa sequence involves a large volume of subaerial calc-alkaline intermediate to felsic volcanics and an unconformably overlying siliciclastic succession comprising clast-supported conglomerates (Gm), massive sandstone sheet floods (Sm) and mudstones (FI), together with a lateritic argillite paleosol (P) top formed in an alluvial-fan system. The youngest rock of Gabal Fatira sequence comprises anorogenic trachydacites and rhyolites with locally emergent domes associated with autobrecciation and sill-dyke rock swarms that could be interpreted as feeders and subvolcanic intrusions. Unconformity and lithofacies assemblages define seven events and three unconformity-bounded tectonic stages that record uplift-subsidence cycles in the study area. A proximal–distal relationship has been established within the depositional products, based on the relative dominance of erosional and depositional features.

The epicontinental subsiding margin of the Triassic in Northern Israel, North Arabian Plate

The Triassic sedimentary pattern of the north Arabian margin represents a transition from continental to deep-marine; we here present a transect part of this suite from southern to northern Israel. Cuttings from the Ramalla (S) and Devora (N) boreholes were studied by petrographic and cathodoluminescence microscopy. Biotic and sedimentological components were grouped into microfacies, upon which a carbonate-evaporitic depositional facies model was based. Mid-to-inner ramp conditions persisted along the transect, essentially following a S–N depositional strike, with outer-ramp to basinal facies to the west. Five low-order (LO) cycles were identified and integrated into a sequence-stratigraphic model with eustatic, tectonic, and differential subsidence components: LO cycle 1 is Late Anisian (Pelsonian), cycle 2 is Late Anisian to Longobardian, cycle 3 is Early Carnian, cycle 4 is Late Carnian, and cycle 5 is at the Carnian/Norian transition. Facies range from supratidal via lagoonal facies in late HST or LST, to calcarenitic shoals and short-term deepening to offshore at maximum flooding. Cycles 1 and 2 are non-evaporitic, with a clastic influx event in cycle 2. Cycles 3 and 4 contain sabkha or salina evaporites in the lagoonal facies that end in the lower part of cycle 5. These facies group into a higher-order cyclicity with discrete events that can be correlated between the boreholes. Depositional and burial history were correlated to Alpine and Arabian Plate stratigraphy over 20 Myr, from the Anisian (Pelsonian) to the Norian. Siliciclastic, carbonate and evaporite-dominated environments indicate climates ranging from relatively humid to extremely arid. Rapid subsidence in the Late Anisian is attributed to Neotethyan rifting of northeastern Gondwana. From latest Anisian to Early Carnian, reduced subsidence took place in the face of eustatic sea level rise. Renewed subsidence in the Carnian is attributed to further Neotethyan rifting. Subsidence terminated in the Norian with uplift to the north, attributed to pre-volcanic doming.

Calibration of facies proportions through a history-matching process

Abstract The facies-proportion calibration method is a new history-matching technique, which modifies facies proportions within a fine geological – geostatistical model until a good match of the field data is reached. The initial facies proportions in the model are usually locally constrained by well data, for example, but their spatial tendencies may be unreliable in some parts of the reservoir. The algorithm presented in this paper introduces average proportion ratios between facies groups in order to calculate new facies proportions while taking into account their initial values. It can be applied locally on specific regions or globally on the whole reservoir for stationary or non-stationary facies distributions. The proportion ratios can be manually adjusted or iteratively computed through an optimization process. The method has been successfully applied to a real field case.

High-frequency paleoclimate signals from Foulden Maar, Waipiata Volcanic Field, southern New Zealand: An Early Miocene varved lacustrine diatomite deposit

A freshwater diatomite deposit near Dunedin, South Island, New Zealand provides an exceptional archive of mid-latitude, seasonal climate variation during latest Oligocene-early Early Miocene time. The diatomite accumulated in a small ~ 1.5 km diameter maar-floored lake that formed during basaltic volcanism. Except for exposures of basanite dated at 23.2 Ma by 40Ar/ 39Ar, and remnants of a Paleogene sandstone and conglomerate cover, the diatomite body is surrounded by Otago Schist. Geophysical profiles indicate that the total diatomaceous sediment thickness may exceed 100 m. Two depositional facies are described from 15.5 m of weakly-consolidated fresh diatomite accessible in two pits. A thinly laminated facies, comprising 60% of the section, consists of dark brown and white couplets of average thickness 0.5 mm. Both brown and white laminae are composed essentially of frustules of a single pennate diatom, along with 1–2% of siliceous sponge spicules. Dark laminae also contain abundant 5–7.5 µm diameter siliceous chrysophycean stomatocysts and organic matter. Decalcified complete skeletons of Galaxias, a southern hemisphere group of freshwater or diadromous fish, are found throughout. Diverse well-preserved leaves, some with attached scale insects, are dominated by Lauraceae. Rare flowers are also present. Trace fossils preserved in the laminated comprise 1–1.5 mm wide pale diatomaceous strings of probable faecal origin, and isolated 20–40 mm diameter sand lenses interpreted as faecal remains of swimming waterfowl. The second diatomite facies group comprises dark brown speckled beds, interpreted as sediment gravity flows. Up to 14 cm thick and interspersed throughout the study section, they incorporate abundant laminated diatomite flecks and leaves, and minor woody plant matter and terrigenous silt. Almost all are capped by 1–8 mm of white diatomite that is interpreted as post-flow fall-out of resuspended diatom frustules. Associated breccia and swirly beds up to 8 cm thick are composed of variably contorted clasts of laminated diatomite in a speckled matrix. Nodules, spheroids, and films of authigenic framboidal pyrite are commonly associated with plant and fish remains. As in modern lakes, white laminae likely formed from diatom blooms when light flux, temperature, or nutrients were optimal during spring–early summer; dark laminae accumulating during autumn–winter months. Laterally continuous pinstripe lamination, absence of bioturbation, and excellent fish and plant preservation indicate that the profundal lake and floor were anoxic. Periodic variations in couplet thickness of ~ 3–10 years compare with Quaternary records of El Niño–Southern Oscillation variability and indicate that the early Early Miocene low altitude New Zealand climate was seasonal and strongly ocean-influenced, as it is today.

Integrated biostratigraphy and regional correlations of Upper Jurassic–lowermost Cretaceous series in northern Tunisia

Integrated biostratigraphy and palaeogeographical interpretations of Upper Jurassic–Lower Cretaceous (Callovian–Berriasian) successions are synthesised on the basis of published data and our recent investigations of key sections from the “Tunisian Dorasale” (TD) and “Tunisian Trough” (TT) domains of northern Tunisia. After a revised biostratigraphy had been proposed for the “rosso ammonitico” series, bed-by-bed sampling led to a radiolarian-based first direct dating of the partly coeval biosiliceous series in the TT. Upward within the Jurassic column, an integrated biostratigraphy (ammonites, calpionellids and associated biomicrofacies) allowed precise biozonation for the Kimmeridgian–middle Berriasian interval. The heterogeneity of the Late Jurassic facies in northern Tunisia is the result of two main geodynamical and palaeogeographical events. The first corresponds to the fragmentation of the initial Early Jurassic platform linked to Tethyan rifting. The second event, coeval to the radiolarian-bearing series of the TT, is expressed by a significant deepening in north-west Tunisian palaeoenvironments. During Kimmeridgian–Tithonian times, previous troughs evolved back into carbonate platforms. Within the Maghrebian Belt, Upper Jurassic–lowermost Cretaceous series comprising three major facies groups are easily correlated; minor differences in age are interpreted as due to local tectonic control. Regional correlations confirm, on the one hand, a common geological history for the external segments of the African margin and, on the other hand, a distinct palaeogeographical evolution of the inner domain including the “Dorsales calcaires” and ancient massifs, both being separated by intermediate flysch zone segments.

Relict conifers from the mid-Pleistocene of Rhodes, Greece

The mid-Pleistocene Kolymbia Flora of Rhodes, Greece occurs in the Lindos Bay Clay facies group of the Rhodes Formation and was deposited in a marine setting at about a depth of 200 m. Recorded in the flora are the youngest presence of Glyptostrobus in the eastern Mediterranean, an extinct species of Pinus very similar to the modern relict Pinus canariensis, and a new species of the disjunct Cedrus. These taxa indicate that some relict plant taxa existed on Rhodes later than previously recognised. The late presence of Taxodiaceae in the eastern Mediterranean may demerit its usefulness for determining the Pliocene–Pleistocene boundary. The finding of Liquidambar, Zelkova and Fagus in the flora supports the idea of Rhodes, and possibly the eastern Mediterranean, as a refugium during the mid-Pleistocene. Similar fossil assemblages should be found in adjacent Turkey because the Lindos Bay Clay records an extensive marine transgression probably resulting from graben tectonics that lead to the ultimate separation of Rhodes from mainland Turkey.

Hydraulic conductivity heterogeneity of a local deltaic aquifer system from the kriged 3D distribution of hydrofacies from borehole logs, Valcartier, Canada

Summary The deltaic aquifer system of the Valcartier sector in Quebec, Canada, is part of a quaternary valley fill contaminated by dissolved trichloroethene (TCE). The objective of our study is to define the aquifer system heterogeneity that should influence TCE transport. Heterogeneity is defined by the distribution of both hydrofacies and hydraulic conductivity ( K ). Hydrofacies are defined as lithologic facies with distinctive hydraulic conductivity ranges. Our approach was developed to take advantage of the abundant stratigraphic and lithologic data provided by borehole logs (7000 m logged from 430 locations). Four site-specific deltaic hydrofacies were defined on the basis of lithologic descriptions, supported by data from grain size analyses, slug tests and cone penetration tests. Each hydrofacies includes a group of geologic facies found in borehole log descriptors to which an initial mean horizontal conductivity K H is associated based on slug tests. Borehole logs were converted to hydrofacies proportions over 5-m intervals to provide 1350 data points. The spatial distribution of hydrofacies was interpolated by three successive interconnected 3D kriging steps using the new technique of “imbricated kriging”. Global dual kriging is directly carried out on the 3D grid of a numerical model. Finally, the proportions of hydrofacies were used to estimate horizontal ( K H ) and vertical ( K V ) hydraulic conductivity fields using generalized means for layered media. Final K H values assigned to the hydrofacies are calibrated by comparison with 2D trends in K H shown by slug tests. This approach also provides an estimated vertical K V field with a spatially varying proportion to K H , rather than a fixed anisotropy ratio. Imbricated kriging does not preserve the statistical variability of fine scale hydrofacies distribution representative of geological variability. However, the approach provides K H and K V estimates over a 3D numerical grid that are coherent with hydrofacies distribution, which in this case control K H and K V .