Marginal Facies Research Articles

The Rupel Clay Member in the Netherlands: towards a comprehensive understanding of its geometry and depositional environment

AbstractThis study presents the 3-D geometry of the Oligocene Rupel Clay Member and a review of its depositional environment based on new and published data. The Rupel Clay Member (RCM) is a clay layer in the Dutch subsurface which is informally known as the Boom Clay. New depth and thickness maps show that the member is present in nearly the whole subsurface of the onshore Netherlands to a depth of about 1500 m. The thickness of the member is variable but rarely exceeds 125 m. We identified three subunits: RCM-U, with a thickness of 15–40 m; RCM-M, with a thickness of 40–90 m; and RCM-L with a thickness of 25–50 m. The Rupel Clay Member is not a homogeneous clay; both vertical and lateral grain-size trends are present. These trends match with general palaeogeographic trends which foresee near-shore facies in the south and southeast of the onshore Netherlands and a more distal setting when moving northward. The three subunits are correlated with global climatic and regional tectonic events, which have mainly affected marginal facies. Faults are known to cut through the clay layer, but have not been mapped. A mismatch of lithostratigraphic nomenclature between the Netherlands and neighbouring countries is present. Part of the solution for this mismatch lies in the proper interpretation of well data in the Netherlands, both on- and offshore.

New insights into lithology and hydrogeology of the northern Newark Rift Basin

AbstractThe marginal facies of the Triassic rift basins in the eastern United States are poorly documented, particularly on the hinge or hanging wall margins. This study presents a lithological description and multiscale petrophysical analysis of basement rocks, overlying marginal facies of the early synrift strata, and the basal contact of the Palisade Sill that were drilled and cored in the northeastern part of the Newark Basin, near its terminus. The expression of the Stockton Formation differs from that in the central basin in having thinner layers, with uncertain temporal relationship to the type area. The bottom 50 m is lithologically distinct with brick‐red to dark‐purple mudstones and sandstones, abundant gypsum‐filled fractures, and a thin zone with anomalously high uranium concentration, not associated with organic‐rich mudstones as other occurrences in the basin. The crystalline basement is apparently Fordham gneiss, overlain by a thin sandstone layer and a dark‐purple hydrophilic mudstone. Despite the abundance of coarse‐grained strata and multiple sets of tectonic fractures, hydraulically transmissive zones are sparse, and do not uniquely correlate to fracture and/or matrix characteristics. Enhanced transmissivity may exist along intrusion boundaries due to enhanced thermal fracturing, but more hydraulic data are needed to verify it. Comparison of petrophysical data in two boreholes ∼210 m apart shows no direct correlation of individual lithological units and their hydraulic properties, although the overall formation characteristics are similar. The results highlight challenges for outcrop correlation at the marginal edges of the rift basins and estimating reservoir properties of these heterogeneous formations.

Late Oligocene macrofloras from fluviatile siliciclastic facies of the Köln Formation at the south-eastern border of the Lower Rhine Embayment (North Rhine-Westphalia, Germany)

Abstract The leaf remains described herein came from the oldest sites of the Cainozoic deposits in the Lower Rhine Embayment, located in the Siebengebirge Volcanic Field at the south-eastern border of this basin, in the area of Siebengebirge and vicinity. These revisited floras are bound to pre-volcanic siliciclastic facies of the Siebengebirge Mts., interpreted as marginal facies of the Köln Formation. Chronostratigraphically they are assigned to the late Oligocene (Chattian). The described leaf remains are partially compressions with preserved epidermal anatomy, and therefore highly useful for systematic determination of leaf impressions recovered from other localities of siliciclastic facies. On account of the epidermal characteristics of leaf compressions varying in gross morphology, the previously determined taxa Quercus goepperti, Laurus phoeboides, and Persea speciosa all fall into the abundantly represented Eotrigonobalanus furcinervis. The siliciclastic deposits originated in coastal and flood plain areas within fluviatile environments of variable deposition energy. Remains of Taxodium dubium, Eotrigonobalanus furcinervis, Populus germanica, and Daphnogene cinnamomifolia dominate among the recovered fossils. The general aspects of this plant assemblage correspond, together with their sedimentary settings, to riparian forest vegetation with mesophytic elements.

Depositional biofacies model for post-OAE1a Aptian carbonate platforms of the western Maestrat Basin (Iberian Chain, Spain)

Two well exposed platform successions of late Early Aptian age developed in the central part of the Galve sub-basin of the Maestrat Basin: the highstand ‘Camarillas–El Morrón’ platform, and the succeeding ‘Las Mingachas’ small lowstand platform, built out downslope in the former basin. Both platforms had a flat-topped non-rimmed depositional profile, showing similar platform-top to slope biofacies, which are described here in both qualitative and quantitative terms. The proximal platform top succession is characterized by a Toucasia-dominated rudist association. The margins of the two platforms consist of massive limestone characterized by a Polyconites-dominated association, in which clusters of Polyconites hadriani in life position are joined by both branching and domal corals, as well as the oyster-like Chondrodonta and nerineid gastropods. In Las Mingachas platform, where the massive rudist- and coral-rich platform limestones pass laterally into the slightly more marly and recessive clinoforms of the upper slope facies, Polyconites is especially abundant. Basinwards these slope deposits pass into basinal marls with orbitolinids and ammonoids. The distribution of the two distinct rudist associations recognized here is attributed to the different environmental tolerances of the rudists with respect to such factors as current regime and rate of sedimentation. The prevalence of polyconitids, in place of caprinids, in these late Early Aptian platform margin facies makes a striking contrast with older, earliest Aptian platforms.

Reorganisation of the Triassic stratigraphic nomenclature of northern Switzerland: overview and the new Dinkelberg, Kaiseraugst and Zeglingen formations

In the context of the harmonisation of the Swiss stratigraphic scheme (HARMOS project), the stratigraphic nomenclature of the Triassic sedimentary succession of northern Switzerland has been reorganised to six formations (from base to top): Dinkelberg, Kaiseraugst, Zeglingen, Schinznach, Bankerjoch, and Klettgau Formation. The first three are formally introduced in this paper. The Dinkelberg Formation (formerly «Buntsandstein») encompasses the siliciclastic, mainly fluvial to coastal marine sediments of Olenekian to early Anisian age. The formation is some 100 m thick in the Basel area and wedges out towards southeast. The Kaiseraugst Formation (formerly «Wellengebirge») comprises fossiliferous siliciclastic and carbonate sediments documenting a marine transgressive—regressive episode in early Anisian time. It starts with sandstone, dolomite, continues with subtidal limestone and marl and ends with bituminous shale and supratidal dolomite. Thickness decreases from approximately 50 m in the High Rhine area to 10 m in the south and east. In the Lake Constance area, a transition to the siliciclastic marginal facies of the Vindelician High (Eschenbach Formation in Germany) is documented by borehole evidence. The Zeglingen Formation (formerly «Anhydritgruppe») documents a regressive marine evaporitic megacycle during the Illyrian (late Anisian). At most places, except in far eastern Switzerland, it starts with massive halite deposits. It continues with sulfate and marl sequences and ends with littoral stromatolitic dolomite. In the WSW–ENE trending depot centre total formation thickness is 150 m and more, and thickness of salt layers reaches up to 100 m. In the High Rhine area, the thickness is reduced due to subrecent subrosion. At some places evidence points to syn- to early-post-diagenetic erosion. For practical reasons, the six formations are organised in three lithostratigraphic groups: Buntsandstein Group (with the Dinkelberg Formation), Muschelkalk Group (combining the Kaiseraugst, Zeglingen and Schinznach Formations) and Keuper Group (combining the Bankerjoch and Klettgau Formations).

Mode of occurrence and taphonomy of the heteromorph ammonite Pravitoceras sigmoidale Yabe from the Upper Cretaceous Izumi Group, Japan

The heteromorph ammonite Pravitoceras sigmoidale Yabe, of the family Nostoceratidae, is the zonal marker of the upper Campanian P. sigmoidale Zone in southwest Japan, and is the main component of ammonite assemblages in this zone. We explain the taphonomic processes underlying the occurrence of P. sigmoidale in the Izumi Group, specifically in the Minato (Awaji Island), Anaga (Awaji Island), Koike–Omoizaki (Shikoku), and Hidonodani sections (Shikoku). The first two sections consist mainly of the non-turbiditic Northern Marginal Facies (NMF), while the latter two sections comprise the Main Facies (MF), a turbiditic facies deposited in waters deeper than those of the NMF. We recognise three modes of occurrence of P. sigmoidale, as follows: (1) In nodules crowded with P. sigmoidale (NCP); this mode occurs only in the NMF, and includes juvenile and adult specimens, together with other ammonites such as Solenoceras (Oxybeloceras) aff. humei (Douvillé), (2) In mudstone with isolated P. sigmoidale (MIP), which is found in all of the sections studied, (3) In sandstone with isolated P. sigmoidale (SIP), which occurs only in the MF. Adult individuals of P. sigmoidale are dominant in most of the sections, while juveniles were observed only in the Minato section, which originally was closer to land areas. The number of specimens of P. sigmoidale and Solenoceras spp. tends to increase in sections representing depositional environments proximal to terrestrial areas. Ammonite assemblages could have been transported from shallow- to deep-water settings by turbidity currents. The sorting of components by transport processes likely contributed to the formation of these fossil assemblages in different areas. This is an important clue to understanding the habitat of heteromorph ammonite life assemblages consisting mainly of P. sigmoidale.

Espectrometria de raios gama e emissão de radônio em solos da região do Maciço Sienítico Piquiri (Cachoeira do Sul e Encruzilhada do Sul, RS)

Foram realizadas medidas de radiação gama e de concentração de radônio em solos da região do Maciço Sienítico Piquiri, região central do Estado do Rio Grande do Sul. Esta intrusão apresenta afinidade alcalina na qual a mineralogia acessória compreende presença relativamente abundante de titanita, apatita e zircão, entre outros minerais que podem conter elevadas concentrações de urânio. As medições de radiação gama foram feitas a partir de uma malha com quadrículas de 2 km de lado, utilizando o Espectrômetro de Radiação Gama RS-125, obtendo-se resultados em contagem por segundo (cps), taxa de dose (Dr) e concentrações de K, eU e eTh. As medidas de 220Rn e 222Rn no ar dos solos foram feitas com uso do equipamento AlphaGUARD. Os valores de cps obtidos neste estudo variam entre 130 e 1045, os de taxa de dose, entre 28,9 nSv/h e 424,6 nSv/h e as concentrações de K, entre 0,5 % e 8,3 %. As concentrações de eU se situam entre 0,8 ppm e 25,8 ppm, e as concentrações de eTh entre 3,0 ppm e 99,2 ppm. A distribuição de K permite definir com relativa precisão os contatos litológicos do Maciço sienítico Piquiri com as rochas adjacentes e entre as duas fácies (Fácies de Borda e Fácies Principal). As maiores concentrações de eTh estão na Fácies Principal do sienito, e as maiores concentrações de eU foram medidas na zona norte desta fácies. Os resultados de 220Rn e 222Rn para o ar contido no solo variam entre 10 kBq/m3 e 550 kBq/ m3 e entre 5 kBq/m3 e 400 kBq/m3 , respectivamente, para a Fácies Principal e de Borda. As elevadas concentrações de Rn na Fácies Principal podem indicar potencial risco à saúde dos habitantes da área.

新丰猴岩岩体LA-ICP-MS锆石U-Pb年龄及地质意义

猴岩岩体位于佛冈复式岩体北东缘，总体呈南北向展布，出露面积约30 km2，岩性多为中细粒黑云母二长花岗岩、花岗闪长岩。本文对猴岩岩体花岗闪长岩样品进行LA-ICP-MS锆石U-Pb测年，获得的同位素年龄为(155.5 ± 4.2) Ma (MSWD = 2.0)，表明猴岩岩体侵位时代为晚侏罗世中期，是燕山第三幕岩浆活动之产物。通过对比，猴岩岩体与佛冈主体花岗岩的侵位时代相一致, 表明二者形成于同期构造–岩浆活动，猴岩岩体是佛冈主体花岗岩分异结晶之产物。猴岩岩体的花岗闪长岩是岩浆分异结晶时捕掳地层残留体，导致岩石成分产生差异而形成，为岩体的边缘相。佛冈复式岩体形成于古太平洋板块向欧亚大陆板块俯冲的构造背景下，其主体花岗岩的地球化学特征表明其物质主要来源于地壳，属陆壳改造型(即S型)花岗岩。 Located at the northeast of Fogang composite pluton, Houyan pluton, which is mainly composed of intermediate-fine grained biotite monzogranites and granodiorites, generally presents a north- south directional distribution and covers an area of 30 km2. In this paper, the LA-ICP-MS zircon U-Pb age of granodiorites of the Houyan pluton is (155.5 ± 4.2) Ma (MSWD = 2.0). The result shows that the emplacement age of Houyan pluton belonged to the middle stage of Late Jurassic, and it was the product of the third magma activity of Yanshan. As its age is the same as the main granite of Fogang composite pluton, they were in the same period of tectono-magmatic activity, and Houyan pluton was crystallized from magmas of main granite of Fogang composite pluton. As the crystallization differentiation of magmas captured the remained stratums, it caused differences in rock composition, and formed the marginal facies which are composed of granodiorites. Fogang composite pluton was formed in the process of subduction of the Pacific plate under Eurasian plate. The geochemical characteristics of its main granite indicate that its source mainly derived from the crust, which belongs to crustal transformation type (S-type) granite.

The Application of Fuzzy Clustering Method in the Division of Reservoir Flow Unit

The reservoir of Beierxi-Puyizu in Sabei developed area comes into the special high water-cut stage. The distribution of residual oil at the later stage of polymer flooding is disperse quietly. The contradiction in layer or among layers is complex, the range of measure reduces gradually and routine measure takes effect poorly. According to the parameters such as permeability and formation capacity, the six sedimentary units of the block are divided into four flow units, the result will provides a more credible geological reference for the identification of single runway in complex channel sand and the adjustment of measures at the later stage of polymer flooding. The microfacies of the adjacent flow units are different, they are generally flow unit of margin facies belt. At the same time, the saturation of residual oil at the juncture of different microfacies belt is high. There is little residual oil exists in the channel sand flow unit of good type and more exists in very good type, it is the target of residual oil tapping at the middle and later stage of polymer flooding. The residual saturation of the flow unit in intermediate belt is high, but there are so many difficulties in tapping the residual oil.

Geological, geochemical, and geochronological characteristics of Caledonian W–Sn mineralization in the Baiganhu orefield, southeastern Xinjiang, China

The newly discovered large-scale Baiganhu W–Sn orefield, consisting of the Kekekaerde, Baiganhu, Bashierxi, and Awaer deposits, is located in Ruoqiang County, southeastern Xinjiang, China. These deposits comprise mainly three types of W–Sn mineralization: early-stage skarn-type, middle-stage greisen-type, and late-stage quartz-vein-type. In this study, we classified seven major vertical zones on the basis of petrographic characteristics, roughly from the bottom of the parental granitic intrusions upward, as (A) fresh syenogranite, (B) argillic alteration, (C) muscovite-dominated greisenization, (D) tourmaline-dominated greisenization, (E) marginal facies (including K-feldspar pegmatite and fine-grained granite), (F) aplitic apophysis, and (G1) skarn or (G2) infilled silification zones. According to the alteration–mineralization assemblages and cross-cutting relationships, five stages of mineralization are recognized in the orefield (I, skarn stage; II, greisen stage; III, quartz vein stage; IV, argillic alteration stage; and V, supergene stage), and reverse alteration zonation in the altered intrusion is also observed.The W–Sn deposits are spatially associated with syenogranite, which is part of the Caledonian Bashierxi magmatic series. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating of the syenogranite yields a weighted mean 206Pb/238U age of 413.6±2.4Ma (MSWD=0.36, n=30). Hydrothermal muscovite from three samples associated with W–Sn mineralization yields plateau 40Ar/39Ar ages of 411.7±2.6Ma (MSWD=0.21), 412.8±2.4Ma (MSWD=0.22), and 413.8±2.6Ma (MSWD=0.22), which is consistent with the zircon U–Pb age, thus indicating a temporal link between the emplacement of the syenogranite and the W–Sn mineralization. Our age data and previously published ages, along with geochemical data, for the granitoids in the Bashierxi magmatic series show a nearly contemporaneous evolution of A- and S-type granites, which were emplaced in a post-orogenic setting at ca. 432–413Ma. As compared with the A-type granites, the syenogranites with S-type affinities probably resulted from a lower degree of partial melting of metagreywackes, which was more likely to be enriched in the ore-forming elements W and Sn, as well as volatiles such as B and H2O. In addition, the syenogranites exhibit low oxidation states and underwent high degrees of factional crystallization, both of which favor post-magmatic W–Sn mineralization. We suggest that more attention should be given to buried syenogranites of S-type affinities during mineral exploration in this area, and that the proposed model of a vertical alteration zoning can act as a guide to the targeting of similar ore systems.

Wings, mushrooms, and Christmas trees: The carbonate seismic geomorphology of Central Luconia, Miocene–present, offshore Sarawak, northwest Borneo

Central Luconia is a geological province of the Sarawak Basin, offshore northwest Borneo, characterized by extensive development of Miocene to Holocene carbonate buildups. The buildups are up to 2-km (1-mi) thick and reveal complex seismic geomorphologies including out-building, in-building, carbonate-siliciclastic intercalations, and coalescence of neighboring carbonate bodies. Intermittent carbonate and siliciclastic deposition is interpreted to have been governed by frequently oscillating sea level and variable siliciclastic input. Location of the buildups with respect to deltaic facies and the seismic expressions of marginal carbonate strata, locally known as wings, are used here to classify carbonate seismic geomorphologies. Buildups encompassed by deltaic topsets are said to reside onshelf and are flanked by marginal carbonate deposits conformable with the onlapping siliciclastics and interpreted as thin carbonate platforms deposited in situ over prominent erosional unconformities and flooding surfaces. Such marginal facies are described on the basis of their appearance as open wings. In contrast, buildups downlapped by prodelta foresets or bottomsets, or those draped by pelagic sediments, are said to reside offshelf and are characterized by high relief, steeply dipping marginal carbonate strata discordant with respect to the relatively flat-lying platform carbonates as well as the onlapping siliciclastics. These marginal strata have an appearance of closed wings and are interpreted as slope aprons composed of carbonate material derived from the productive platform tops and deposited off-platform in deeper water. Carbonate geometries range from contracting-upward pinnacles to expanding-upward platforms in onshelf settings, whereas buildups located offshelf have mostly contracting-upward or aggrading morphologies. Buildups deposited onshelf have generally maintained a similar height of depositional slopes as they evolved, reflecting rates of background siliciclastic deposition approximating those of carbonate growth. In contrast, depositional slopes of offshelf buildups have become progressively higher, owing to limited siliciclastic input. Observations presented here on carbonate geomorphology and adjacent siliciclastic stratigraphy provide important clues for the understanding of the geology of the province. Because carbonates and siliciclastics intercalate frequently, siliciclastic biostratigraphy can be used to precisely date and correlate geographically remote carbonate-reservoir intervals and intrareservoir depositional and diagenetic events such as marine transgressive or exposure surfaces or karst networks. Conversely, basin paleobathymetry can be measured by the size of carbonate clinoforms and the thickness of buildups established over flooded siliciclastic surfaces. Deposition of low-relief carbonate platforms over siliciclastic substrates indicates shallow-marine conditions, as opposed to the prevalent notion of kilometer-scale paleobathymetry. These interpretations have important implications for understanding of the sedimentology and lithology of the ambient basinal siliciclastics, with fundamental applications to hydrocarbon exploration.

Drowning of the Triassic Yangtze Platform, South China, By Tectonic Subsidence Into Toxic Deep Waters of An Anoxic Basin

Abstract The Yangtze Platform drowned and was buried by pelagic facies and siliciclastic turbidites in western Guizhou Province during the Late Triassic, Carnian. The uppermost platform facies of the Ladinian Yangliujing Fm. consists of peritidal cyclic carbonate. Ladinian margin facies of the Longtou Fm. consist of grainstone and lenses of coral–Tubiphytes algal boundstone indicating high-energy shoals and patch reefs. The drowning horizon is laterally variable; it is either a sharp surface or a gradational shift to dark, nodular-bedded lime mudstone and wackestone of the Zhuganpo Fm. The contact lacks phosphatized or glauconitized hardgrounds that would indicate drowning by excess nutrient flux. Uppermost platform carbonates have a tropical photozoan biota and lack siliciclastic content indicating neither climate cooling nor siliciclastic flux played a role in drowning. The Zhuganpo Fm. contains a dominantly pelagic biota of ammonoids, planktonic bivalves, pseudoplanktonic crinoids, conodonts, and the marine reptile Keichousaurus. Rare bioturbation and benthic biota in the lower part indicate dysoxic conditions with an upward shift to anoxic conditions. The overlying Wayao Fm. is a pyritic, laminated, black argillaceous lime mudstone that grades to black shale with an exclusively pelagic fauna and marine reptile lagerstattes indicating anoxic deep-marine sedimentation. Syndepositional faults played a significant role in the evolution of the western sector of the Yangtze Platform and controlled three local, backstepped accommodation cycles in the Zhenfeng area. Faults that developed during the last accommodation cycle tip out at the drowning horizon and include a flower structure upon which a pinnacle reef developed while the rest of the platform drowned. Lateral variability in the drowning horizon and thickness of the post-drowning pelagic facies suggest that differential tectonic subsidence caused the platform to sink into deep water along faults. Magnetic susceptibility and paleomagnetic-reversal correlations demonstrate that the western sector of the platform drowned while shallow-marine, mixed carbonate siliciclastic sedimentation continued in the eastern sector which later terminated in shallow water by increasing siliciclastic flux. Starved black shale horizons in the basin indicate recurrent bottom-water anoxia. Elevated trace-metal concentrations in the pelagic facies of the Zhuganpo and Wayao formations indicate dysoxic to anoxic conditions and enhanced preservation of organic matter. Tectonic subsidence likely submerged the western sector into deep, toxic waters of the basin, killing benthic carbonate production. Previous studies have implicated the Carnian pluvial event as a cause of drowning of the Yangtze Platform and the shift to siliciclastic turbidites of the Laishike Fm., but the Yangtze Platform drowned earlier than western Tethys platforms and siliciclastics were already rapidly infilling the basin in the Anisian and Ladinian, indicating that the events are probably unrelated. Siliciclastics of the Laishike Fm. that overlapped and buried the platform only after the basin was filled are better interpreted as a response to tectonics than to a shift in climate.

The detrital zircon U–Pb–Hf fingerprint of the northern Arabian–Nubian Shield as reflected by a Late Ediacaran arkosic wedge (Zenifim Formation; subsurface Israel)

The Neoproterozoic Arabian–Nubian Shield (ANS), which comprises the northern sector of the East African Orogen (EAO), has been deeply denuded in Ediacaran times and its erosional products were deposited across NE Africa and Arabia; they are also found in a number of peri-Gondwana terranes. A vast Late Neoproterozoic clastic wedge, locally interbedded with volcanics, developed on the northern outskirts of the ANS and spread into areas currently at the foothills of the Taurus and Zagros belts to coalesce into a wide peri-Arabian-Mesopotamian basin. The southern limit of this basin is manifested in the subsurface of Israel and Jordan by a few km thick arkose sequence, the Zenifim Formation, which underlies the Cambro–Ordovician quartz-rich sandstones. The detritus stored in this formation was mostly eroded from the adjacent ANS at the cessation of Neoproterozoic orogeny.Along a ∼150km long transect in the subsurface of Israel, the arkosic facies of the Zenifim Formation changes from a proximal alluvial fan in the south, to a sea marginal facies in the north reflecting the transgression of the proto-Tethys onto the decaying Neoproterozoic orogen. We studied the detrital zircon U–Pb–Hf from core samples of arkose from different parts of the Zenifim Formation in order to constrain the composition of its provenance and to obtain the Late-Neoproterozoic detrital fingerprint of the ANS.The proximal alluvial fan and plain facies is dominated by a remarkable concentration of U–Pb detrital zircon ages between 0.6 and 0.7Ga with a peak around 0.63Ga, alongside a few older grains (0.8Ga and 0.9Ga). Pre-Neoproterozoic detrtital zircons are absent. The youngest detrital zircon population peaks at 0.60Ga. The entire inventory of detrital zircons yielded positive ɛHf values between +11 and +5, generally overlapping ɛHf values of Neoproterozoic rocks of the northern ANS. It is notable that little indication for the exposure of the Cryogenian rocks of the ANS is represented by the detrital zircon signal in the alluvial fan deposits, a feature indicating the prevalence of Ediacaran granitoids in the provenance. Towards the north, the youngest detrital zircons in the sea marginal facies concentrate at 0.58Ga implying this part of Zenifim Formation is among the youngest Late Neoproterozoic sedimentary units in the northern ANS. The detrital zircon signal exhibits a preponderance of Neoproterozoic-aged detrital zircons peaking at 0.6Ga and 0.75–0.8Ga, but Grenvillian-like age peaks at 0.92, 1.0 and 1.1Ga are also identified. Additionally, a small number of 1.8, 2.1 and 2.6Ga-aged zircons, and a few Late Neoproterozoic detrital zircons with negative ɛHf values also occur. Erosion of basement rocks in the northern ANS was generally capable of accounting for most of the detrital zircon spectra in the sea marginal facies, but we point out two other potential sources. Our preliminary investigations indicate that dike swarms that invaded the northern ANS in the mid Ediacaran carry abundant inherited pre-Neoproterozoic zircons and Neoproterozoic-aged zircons with negative ɛHf values. The presence of such zircons in post −0.58Ga sediments, subsequently to the major diking phases, can thus be accounted for, at least partly, by the erosion of dikes and associated volcanics. Likewise, a northern provenance that resided within the Cadomian realm or laterally along the Gondwana margin could also play a role in delivering zircons of this type to the sea marginal facies of Zenifim Formation.

Sequence stratigraphy and platform to basin margin facies transition of the Lower Cretaceous Dariyan Formation (northeastern Arabian Plate, Zagros fold-thrust belt, Iran)

Sequence stratigraphy and platform to basin margin facies transition of the Lower Cretaceous Dariyan Formation (northeastern Arabian Plate, Zagros fold-thrust belt, Iran)

Lithofacies, depositional environments and stratigraphic architecture of the Wajid Group outcrops in southern Saudi Arabia

ABSTRACT The Wajid Group is a Palaeozoic siliciclastic succession of southern Saudi Arabia. In the outcrop belt it is ca. 500 m thick, whereas in the subsurface, the thickness increases to more than 4,500 m. The siliciclastic sediments have great reservoir potential for hydrocarbons and for groundwater. Although they represent one of the most important aquifers of the Arabian Peninsula, neither their sedimentologic, lithostratigraphic, nor their reservoir characteristics are satisfactorily known. In this study, a detailed description of lithology and sedimentology is given and the Wajid Group sediments are interpreted in terms of depositional environment and facies architecture. Thirteen lithofacies (LF 1 to LF 13) have been recognised, most of them composed of different subfacies. These lithofacies are grouped into 9 lithofacies associations (LF-A1 through LF-A9). LF-A1 through LF-A3 and LF-A7 represent shallow-marine siliciclastic environments. The remaining lithofacies associations describe periglacial environments of the Hirnantian (Late Ordovician) and Permian Gondwana glaciations. Except for a few pro-glacial fluvial deposits, fluvial successions and aeolian sediments are absent in the outcrops of the Wajid Sandstone. Five formations are recognised in the Wajid Group: the Dibsiyah, Sanamah, Qalibah, Khusayyayn, and Juwayl formations. They are all separated by major unconformities. The Dibsiyah Formation represents a vast sand-sheet complex with core and margin facies formed under shallow-marine conditions. These marine conditions enabled an abundant fauna to proliferate and leave its traces in the form of Skolithos piperock and Cruziana sp. A late Cambrian to Early Ordovician age is inferred for these deposits from regional considerations. The Sanamah Formation records the Late Ordovician Hirnantian glaciation with coarse sandstones and conglomerates. A variety of glacier-induced sedimentary structures are present. The internal succession is composed of three major sediment packages reflecting three ice advance-retreat cycles. The latest of these cycles is overlain by a few metres of marginal-marine sediments of the Qalibah Formation. The Khusayyayn Formation was deposited probably during Early Devonian times. It also represents a sand-sheet environment characterised by the dominance of mega-scale and giant cross beds and bed sets. A marine depositional environment is assumed from scarce Skolithos sp., and because nearly all indicators of a braided river system are absent. The Juwayl Formation of Permian age was deposited at the interface of the Late Palaeozoic Gondwana ice shield with a large lake that may have covered most of southern Arabia and adjacent areas. Proglacial sandstones and conglomerates were deposited close to the glaciers, whereas fine-grained sediment with dropstones, boulder pavements and a wide spectrum of soft-sediment deformation are characteristic of the lake environment. While the two glacial successions and the Khusayyayn Formation can rather confidently be attributed to the geological time scale, either through seismic correlation or biostratigraphically, the Dibsiyah Formation has not yet been biostratigraphically well dated.

Middle Jurassic age of basalts and the post-obduction sedimentary sequence in the Guevgueli Ophiolite Complex (Republic of Macedonia)

The Guevgueli Ophiolite Complex near Demir Kapija (Eastern Vardar Ophiolitic Unit) was studied for the age and facies of the overlying sediments. Cherts in direct contact with basalts are dated to late Bathonian–early Callovian with radiolarians. The post-obduction sequence, here informally named the Demir Kapija group, is composed of polymictic conglomerate, probably Kimmeridgian in age, and a more than 350-m thick carbonate succession. The carbonate succession consists of hemipelagic, slope and platform margin facies and contains algae and benthic foraminifers indicative of the Tithonian age. These new data support the previously proposed palaeogeographical connection between the Guevgueli and South Apuseni ophiolite complexes.

Sedimentary fans: A new genetic model for sedimentary exhalative ore deposits

Sedimentary-exhalative (SEDEX) deposits are one of the most important types of metal ore deposits. The genesis of such economic deposits has been problematic; thus a holistic model is urgently needed to explain their formation. Based on field surveys and geochemical analyses of the Xitieshan Pb–Zn, the Zhaokalong Fe–Cu polymetallic, and several other typical sedimentary-exhalative deposits in China, this study proposes a “sedimentary fan model” to explain such deposits. The results of this research suggest that the ore forming fluid of sedimentary-exhalative deposits can be considered as a kind of turbidity current. These fluids originated from the exhalative process itself, passing through syngenetic faults, flowing into the marine basin, and forming fan-shaped sedimentary ore deposits. The ore bodies of sedimentary fans consist of three parts: pipe, central, and marginal facies. The fans typically show zonations of mineralization, trace elements, fluid inclusions, isotopes, redox environments, etc. Pipe facies is deeply sourced and proximal to synsedimentary faults, generally constituted by unstratified, altered stockworks, exhalite (e.g., siliceous rocks) and ore bodies, and characterized by high temperatures and salinities. Central and marginal facies mainly occur as stratiform ore bodies, exhibiting typical characteristics of sedimentary origin. From the central facies to the marginal facies, increasing seawater components enter into the ore-forming process, resulting in a gradual change of metallogenic environment. This sedimentary fan model is used with satisfactory results to predict metallogenesis in the Xitieshan, the Zhaokalong and other sedimentary-exhalative deposits in China.

The Cryogenian Balcanoona reef complexes of the Northern Flinders Ranges: Implications for Neoproterozoic ocean chemistry

The Cryogenian Balcanoona reef complexes of South Australia consist of several dolomite platforms with well-defined backreef, reef margin and slope/basinal facies. The mature platforms have prograded large distances into the basin (>15km) and have high relief margins (over 1km of relief at the platform margin). Backreef facies are dominantly ooidal–peloidal grainstones with abundant tepees and marine cemented sheet cavities. The reef margin facies consists of upper stromatolitic boundstones and, where present, deeper water non-stromatolitic chambered and clotted boundstones. The deepwater chambered and clotted boundstones grew on near vertical escarpments below 150m paleo-water depths and consist of a complex array of marine cemented cavernous and calcimicrobial material. The strongly prograding platforms range from accretionary low-angle stromatolitic boundstone margins, through to more mature escarpment margins. The mature escarpment margins (>200m high escarpment) are characterized by the development of both stromatolitic and non-stromatolitic boundstones. The slope/basin facies of the mature escarpment margins consists of coarse debris deposits (talus, debrites and allochthonous blocks) proximal to the platforms and calcareous/dolomitic mudrocks distal to the platforms. The development of an accretionary escarpment margin, together with the large proportion of deepwater boundstone suggests that these Cryogenian reefs were fundamentally different from Phanerozoic reefal systems. The enormous volume of deepwater boundstone in these reefs may be due to a severely anoxic water column that prevailed during this period of the Cryogenian. Anoxia led to greater degrees of carbonate saturation at depth that enabled the development of deepwater boundstones with escarpment margins. A community of anoxic-adapted non-photosynthetic organisms that were perhaps similar in their ecology to Phanerozoic coelobiontic reefal communities may have constructed the enigmatic deepwater boundstone.Just prior to the final termination of the reef, the system was subject to large-scale erosion and margin collapse, producing a major regional unconformity. Following this, the reefs briefly re-grew, before final and complete cessation of the reef complexes. The large-scale margin collapse event may have been triggered by sea level fluctuation, and/or changes in ocean chemistry associated with Late Cryogenian oxygenation.

Der Buntsandstein in der Kraichgau-Senke und der südwestdeutschen Randfazies (Baden-Württemberg)

Der Buntsandstein in der Kraichgau-Senke und der südwestdeutschen Randfazies (Baden-Württemberg)

Revision of Scheumann’s classification of melilitic lamprophyres and related melilitic rocks in light of new analytical data

Dykes of the Late Cretaceous to Early Tertiary (79.5 ± 3.5 to 60.7 ± 2.4 Ma) melilitic rock series of the Osecna Com- plex and the Devil’s Walls dyke swarm, including ultramafic lamprophyres – polzenites – of Scheumann (1913) occur dispersed in the entire Upper Ploucnice River basin in northern Bohemia. Polzenites and associated melilitic rocks are characterized by the mineral association of olivine + melilite ± nephe- line, hauyne, monticellite, phlogopite, calcite, perovskite, spinels and apatite. New data on their mineral and chemical compositions from original Scheumann’s localities (the Vesec, Modlibohov, Luhov types) argue against the abolition of the group of ultramafic lamprophyres and the terms ‘polzenite’ and ‘alnoite’ by the Le Maitre (2002) classification. Marginal facies and numerous flat apophyses of the lopolith-like body known as the Osecna Complex show an olivine micro-melilitolite composition (lamprophyric facies). The porphyritic texture, chemical composition and the presence of characteristic minerals such as monticellite and phlogopite point to their affinity with ultramafic lamprophyres – polze- nites of the Vesec type. Melilite-bearing olivine nephelinites to olivine melilitites (olivine + clinopyroxene + nepheline + melilite ± hauyne and spinels with apatite) form a swarm of subparallel dykes known as the Devil’s Walls. The Scheumann’s non-melilite dyke rock “wesselite”, spatially associated with polzenites and often erroneously attributed to the polzenite group, is an alkaline lamprophyre of monchiquite to camptonite composition (kaersutite + phlogopite + diopside + olivine phenocrysts in groundmass containing clinopyroxene, phlogopite, hauyne, analcime, titanian mag- netite, apatite ± glass/plagioclase). First K–Ar data show Oligocene ages (30.9 ± 1.2 to 27.8 ± 1.1 Ma) and an affinity to the common tephrite–basanite rock series.