Architecture and evolution of the Paine channel complex, Cerro Toro Formation (Upper Cretaceous), Silla Syncline, Magallanes Basin, Chile

The Upper Cretaceous Cerro Toro Formation in the Silla Syncline, Parque Nacional Torres del Paine, Magallanes Basin, Chile, includes over 1100 m of mainly thin‐bedded mud‐rich turbidites containing three thick divisions of coarse conglomerate and sandstone. Facies distributions, stacking patterns and lateral relationships indicate that the coarse‐grained sandstone and conglomerate units represent the fill of a series of large south to south‐east trending deep‐water channels or channel complexes. The middle coarse division, informally named the Paine member, represents the fill of at least three discrete channels or channel complexes, termed Paine A, B and C. The uppermost of these, Paine C, represents a channel belt about 3·5 km wide and its fill displays explicit details of channel geometry, channel margins, and the processes of channel development and evolution. Along its northern margin, Paine C consists of stacked, laterally offset channels, each eroded into fine‐grained mudstone and thin‐bedded sandy turbidites. Along its southern margin, the Paine C complex was bounded by a single, deeply incised but stepped erosional surface. The evolution of the Paine C channel occurred through multiple cycles of activity, each involving: (i) an initial period of channel erosion into underlying fine‐grained sediments; (ii) deposition of coarse‐grained pebble to cobble conglomerate and sandstone within the channel; and (iii) waning of coarse sediment deposition and accumulation of a widespread sheet of fine‐grained, thin‐bedded turbidites inside and outside the channel. The thin‐bedded turbidites deposited within, and adjacent to, the channel along the northern margin of the Paine C complex do not appear to represent levée deposits but, rather, a separate fine‐grained turbidite system that impinged on the Paine C channel from the north. The Cerro Toro channel complex in the Silla Syncline may mark either an early axial zone of the Magallanes Basin or a local slope mini‐basin developed behind a zone of slope faulting and folding now present immediately east of the syncline. If the latter, flows moving downslope toward the basin axis further east were diverted to the south by this developing structural high, deposited part of their coarse sediment loads, and exited the mini‐basin at a point located near the south‐eastern edge of the present Silla Syncline.     

Down‐slope facies variability within deep‐water channel systems: Insights from the Upper Cretaceous Cerro Toro Formation,southern Patagonia

In southern Patagonia, outcrops of the Upper Cretaceous Cerro Toro Formation preserve a >150 km long deep‐water axial channel belt in the Magallanes–Austral Basin, providing a unique opportunity to investigate longitudinal variations in the depositional characteristics of a deep‐water channel system. This study documents sedimentological, stratigraphical and geochronological data from the Cerro Toro Formation in the Argentine sector of the basin. New results are integrated with previous work from the Chilean basin sector to conduct a basin‐scale comparison of the timing of deposition, provenance and lithofacies proportions. The Cerro Toro channel belt includes a nearly 1000 m thick section characterized by high‐density turbidites and mass‐wasting deposits. Two ash beds from the base of the section yield U–Pb zircon ages of 90·4 ± 2 Ma and 88·0 ± 3 Ma, indicating similar initiation ages as documented in the Chilean sector. The U–Pb detrital zircon age spectra from samples in the study area reveal similar provenance trends to samples from the Chilean basin sector, with peak age populations at 310 to 260 Ma, 160 to 135 Ma and 110 to 82 Ma. The maximum depositional age of the channel belt in the Argentine sector is 87·8 ± 1·5 Ma and all new geochronology data corroborate an 86 to 80 Ma depositional age for the main Cerro Toro channel belt. Statistical analyses of 7370 beds from nearly 8000 m of new and previously published stratigraphic sections along the entire outcrop belt suggest progressive variations in the down‐system proportion of lithofacies. In the up‐slope region, lithofacies representing mass wasting processes (for example, debris‐flow and mass‐transport deposits) account for ca 29% of the stratigraphic thickness, as opposed to 5% in the down‐slope region of the channel belt, where turbidity current deposits are more prevalent. The proportion of beds >1 m thick also decreases systematically down slope, particularly for conglomeratic turbidite deposits. This work highlights that: (i) the proportion of thick beds and distribution of lithofacies are key down‐system changes in the stratigraphic fill of this deep‐water channel belt; (ii) detrital zircon trends suggest a relatively well‐mixed longitudinal depositional system; and (iii) geochronology of the main Cerro Toro outcrop belt supports but does not necessitate the model of a single, roughly age‐equivalent, channel system. This study has implications for understanding the downslope variability in depositional processes, stratigraphic architecture and reservoir quality of submarine channel systems.     

Deep‐water foreland basin deposits of the Cerro Toro Formation,Magallanes basin,Chile: architectural elements of a sinuous basin axial channel belt

Coarse‐grained deep‐water strata of the Cerro Toro Formation in the Cordillera Manuel Señoret, southern Chile, represent the deposits of a major channel belt (4 to 8 km wide by >100 km long) that occupied the foredeep of the Magallanes basin during the Late Cretaceous. Channel belt deposits comprise a ca 400 m thick conglomeratic interval (informally named the ‘Lago Sofia Member’) encased in bathyal fine‐grained units. Facies of the Lago Sofia Member include sandy matrix conglomerate (that show evidence of traction‐dominated deposition and sedimentation from turbulent gravity flows), muddy matrix conglomerate (graded units interpreted as coarse‐grained slurry‐flow deposits) and massive sandstone beds (high‐density turbidity current deposits). Interbedded sandstone and mudstone intervals are present locally, interpreted as inner levée deposits. The channel belt was characterized by a low sinuousity planform architecture, as inferred from outcrop mapping and extensive palaeocurrent measurements. Laterally adjacent to the Lago Sofia Member are interbedded mudstone and sandstone facies derived from gravity flows that spilled over the channel belt margin. A levée interpretation for these fine‐grained units is based on several observations, which include: (i) palaeocurrent measurements that indicate flows diverged (50° to 100°) once they spilled over the confining channel margin; (ii) sandstone beds progressively thin, away from the channel belt margin; (iii) evidence that the eroded channel base was not very well indurated, including a stepped margin and injection of coarse‐grained channel material into surrounding fine‐grained units; and (iv) the presence of sedimentary features common to levées, including slumped units inferring depositional slopes dipping away from the channel margin, lenticular sandstone beds thinning distally from the channel margin, soft sediment deformation and climbing ripples. The tectonic setting and foredeep architecture influenced deposition in the axial channel belt. A significant downstream constriction of the channel belt is reflected by a transition from more tabular units to an internal architecture dominated by lenticular beds associated with a substantially increased degree of scour. Differential propagation of the fold‐thrust belt from the west is speculated to have had a major control on basin, and subsequently channel, width. The confining influence of the basin slopes that paralleled the channel belt, as well as the likelihood that numerous conduits fed into the basin along the length of the active fold‐thrust belt to the west, suggest that proximal–distal relationships observed from large channels in passive margin settings are not necessarily applicable to axial channels in elongate basins.     

An ichthyosaur vertebra from the Cretaceous (Middle Cenomanian) Karai Formation,southern India

The note describes a well-preserved ichthyosaur vertebra from the upper Cretaceous Karai Formation (late Albian to late Cenomanian) of the Uttattur Group of rocks exposed near Ariyalur, Tamil Nadu, southern India.     

Foraminifera from the Vectis Formation (Wealden Group, Lower Cretaceous) of the Wessex Sub-basin, southern England: a preliminary account

Foraminifera are documented from the uppermost part of the essentially lagoonal Vectis Formation (Barremian to possibly early Aptian) of the Isle of Wight, southern England. Monospecific and low-diversity influxes of indigenous agglutinated taxa are identified from claystones of mudflat or subaqueous origin, and their palaeoecological significance is assessed. In contrast, reworked Upper Jurassic foraminifera are associated with coarser-grained bioclastic deposits and indicate the proximity of the Wessex Sub-basin margin, immediately to the north.     

Lower Cretaceous deposit reveals first evidence of a post-wildfire debris flow in the Kirkwood Formation,Algoa Basin,Eastern Cape,South Africa

The Algoa Basin is an onshore rift basin filled by an Upper Mesozoic non-marine and shallow marine sedimentary sequence. The middle unit of this clastic succession is assigned to the Lower Cretaceous Kirkwood Formation, known to host a wealth of plant and animal fossils together with poorly documented lignites, amber and charcoal clasts. This study is motivated by the growing interest in the impact of wildfires on the palaeoenvironment during the high-oxygen, Cretaceous world. It has been hypothesised that frequent and severe Cretaceous wildfires triggered large-scale non-marine denudation events, altering the sedimentation dynamics and influencing the evolution of ecosystems. In order to investigate this phenomenon, charcoal-bearing sedimentary rocks and plant fossil assemblages of the Kirkwood Formation have been studied at the Bezuidenhouts River locality, ∼50 km north of Port Elizabeth (Eastern Cape, South Africa).Detailed field observations of the sedimentary facies suggest that deposition occurred in a meandering fluvial environment with mature, vegetated floodplains. Depositional trends within a charcoal-rich bed (i.e., stratification, flattening and decrease in charcoal clast size down-current) indicate that a charcoal-rich debris flow, linked to a post-wildfire flood event, became diluted by fluvial flow. Palaeocurrent indicators (e.g., orientation of fossil logs) suggest unidirectional currents from SW to NE, which are somewhat inconsistent with the previously reported regional palaeocurrent directions in the Kirkwood Formation.To gain insights into the fire-influenced dynamics of the Early Cretaceous ecosystems, the macro-plant fossil assemblages of the Kirkwood Formation were considered, with reference to the responses of modern plant analogues to wildfire. Of the plant orders reported from macrofossils of the Kirkwood Formation, the Cycadales, Pinales and Filicales, are known to have produced large woody or fibrous trunks and stems, or in the case of the Bennettitales more densely branched, divaricate architectures, and are likely to have provided the bulk of fuel for wildfires, with fern elements dominating groundcover niches. The particular role of these plants in the Early Cretaceous wildfire palaeoecology of the Algoa Basin is a topic for an ongoing study, but the Bezuidenhouts River locality appears to record the aftermath of a severe crownfire that led to mass tree mortality.     

A possible azhdarchid pterosaur (Pterosauria,Azhdarchidae) in the Durlston Formation (Early Cretaceous,Berriasian) of southern England

A new specimen of pterosaurian metacarpal IV from the Early Cretaceous (Berriasian) Durlston Formation of Dorset, southern England, closely resembles those of the Chinese dsungaripterid Dsungaripterus weii Young, 1964 and the Central Asian azhdarchid Azhdarcho lancicollis Nessov, 1984. However, the new specimen lacks the thickened bony wall typical of Dsungaripteridae and is therefore regarded as azhdarchoid. An mcIV with a markedly offset distal condyle with well-developed diaphyseal constriction behind the distal condyle and asymmetrical condylar margins may be an autapomorphy of Dsungaripteridae + Azhdarchoidea, while the same condition with bone thickening may typify Dsungaripteridae. The new specimen also provides osteological evidence supporting claims for large wing-spanned pterosaurs in the Berriasian of southern England based previously only on ichnological finds. The new specimen suggests a wingspan of between 2.9 and 3.7 m and represents the largest pterosaur from the Berriasian.     

Slurry-flow deposits in the Britannia Formation (Lower Cretaceous), North Sea: a new perspective on the turbidity current and debris flow problem

The Lower Cretaceous Britannia Formation (North Sea) includes an assemblage of sandstone beds interpreted here to be the deposits of turbidity currents, debris flows and a spectrum of intermediate flow types termed slurry flows. The term ‘slurry flow’ is used here to refer to watery flows transitional between turbidity currents, in which particles are supported primarily by flow turbulence, and debris flows, in which particles are supported by flow strength. Thick, clean, dish‐structured sandstones and associated thin‐bedded sandstones showing Bouma T_b–e divisions were deposited by high‐ and low‐density turbidity currents respectively. Debris flow deposits are marked by deformed, intraformational mudstone and sandstone masses suspended within a sand‐rich mudstone matrix. Most Britannia slurry‐flow deposits contain 10–35% detrital mud matrix and are grain supported. Individual beds vary in thickness from a few centimetres to over 30 m. Seven sedimentary structure division types are recognized in slurry‐flow beds: (M₁) current structured and massive divisions; (M₂) banded units; (M₃) wispy laminated sandstone; (M₄) dish‐structured divisions; (M₅) fine‐grained, microbanded to flat‐laminated units; (M₆) foundered and mixed layers that were originally laminated to microbanded; and (M₇) vertically water‐escape structured divisions. Water‐escape structures are abundant in slurry‐flow deposits, including a variety of vertical to subvertical pipe‐ and sheet‐like fluid‐escape conduits, dish structures and load structures. Structuring of Britannia slurry‐flow beds suggests that most flows began deposition as turbidity currents: fully turbulent flows characterized by turbulent grain suspension and, commonly, bed‐load transport and deposition (M₁). Mud was apparently transported largely as hydrodynamically silt‐ to sand‐sized grains. As the flows waned, both mud and mineral grains settled, increasing near‐bed grain concentration and flow density. Low‐density mud grains settling into the denser near‐bed layers were trapped because of their reduced settling velocities, whereas denser quartz and feldspar continued settling to the bed. The result of this kinetic sieving was an increasing mud content and particle concentration in the near‐bed layers. Disaggregation of mud grains in the near‐bed zone as a result of intense shear and abrasion against rigid mineral grains caused a rapid increase in effective clay surface area and, hence, near‐bed cohesion, shear resistance and viscosity. Eventually, turbulence was suppressed in a layer immediately adjacent to the bed, which was transformed into a cohesion‐dominated viscous sublayer. The banding and lamination in M₂ are thought to reflect the formation, evolution and deposition of such cohesion‐dominated sublayers. More rapid fallout from suspension in less muddy flows resulted in the development of thin, short‐lived viscous sublayers to form wispy laminated divisions (M₃) and, in the least muddy flows with the highest suspended‐load fallout rates, direct suspension sedimentation formed dish‐structured M₄ divisions. Markov chain analysis indicates that these divisions are stacked to form a range of bed types: (I) dish‐structured beds; (II) dish‐structured and wispy laminated beds; (III) banded, wispy laminated and/or dish‐structured beds; (IV) predominantly banded beds; and (V) thickly banded and mixed slurried beds. These different bed types form mainly in response to the varying mud contents of the depositing flows and the influence of mud on suspended‐load fallout rates. The Britannia sandstones provide a remarkable and perhaps unique window on the mechanics of sediment‐gravity flows transitional between turbidity currents and debris flows and the textures and structuring of their deposits.     

A new hangingfly (Insecta,Mecoptera, Bittacidae) from the Purbeck Limestone Group (Lower Cretaceous) of southern England and a review of Cretaceous Bittacidae

Rapid radiation of the Bittacidae during the Jurassic resulted in high diversity within this family of Mecoptera. More than 40 species within 23 genera have been described from this period. However, around the end of the Jurassic the abundance and diversity of Bittacidae decreased and only seven species in five genera are known to date from the Cretaceous. A new specimen from the basal Cretaceous of England, Tytthobittacus jarzembowski sp. nov., described here, represents the eighth species and the second fossil representative of this family from the European Cretaceous. This hangingfly belongs to an extant and relictual genus previously known only from Australia. The paper also includes a review of all known Cretaceous bittacids and a re-examination of European species Antiquanabittacus nanus Petrulevičius and Jarzembowski, 2004.     

New symmetrodonts (Mammalia, Theria) from the Purbeck Limestone Group, Lower Cretaceous, southern England

Le genre Spalacotherium Owen fût initialement créé à partir de spécimens provenant du Groupe de Purbeck en 1854. Cet article décrit une nouvelle espèce, S. evansae, provenant d'un site purbeckien découvert en 1986; celle-ci est représentée non seulement par des molaires inférieures et supérieures mais peut-être aussi par des molaires de lait. Le genre Tinodon n'était, jusqu'à maintenant, connu que dans la Formation Morrison du Wyoming, USA, un peu plus ancienne que celle de Purbeck; quelques molaires inférieures et surtout une molaire supérieure du même gisement sont attribuées à une nouvelle espèce, T. micron, ce qui ajoute un genre à la liste des taxons communs aux deux formations. La molaire supérieure de T. micron est particulièrement intéressante en ce qu'elle fournit des indications sur un taxon occupant une position clé dans la phylogénie des symmétrodontes, tout en soulevant le problème d'homologie des tubercules.     

阿北凹陷下白垩统阿尔善组水下扇沉积特征

本文对二连盆地阿北凹陷主要产油层段阿尔善组水下扇体的沉积构造、粒度、重矿物以及电性等特征进行了详细的分析,并应用层序地层学方法将阿尔善组划分为2个三级层序,结合地震解释成果,首次以三级层序为单位勾绘了扇体平面形态展布图,确定了扇根、扇中和扇端3个亚相的沉积区域,建立了水下扇沉积相模式,并对其沉积演化做了简要的分析。     

西藏南部绒布地区晚白垩世宗卓组沉积相与沉积环境演化

宗卓组地层作为中生代海相沉积的重要组成部分,记载了西藏南部地区白垩纪古海洋、古气候等重要地质历史信息。通过对砂岩进行镜下观察、物源分析、粒度分析等方面的研究,本文对绒布地区宗卓组的沉积相类型和沉积环境演化有了新的认识。粒度分析指示沉积时期水体搬运动力较弱、存在浊流沉积;宗卓组内3种不同类型的砂岩镜下特征、地球化学特征和锆石U- Pb年龄,指示3类砂岩的物源不同。本文在宗卓组共识别出陆棚相、大陆斜坡相和深海盆地3类沉积相,并对其进行了更为详细的划分。晚白垩世新特提斯洋壳向北俯冲,俯冲结束后印度—亚洲大陆发生初始碰撞。结合研究区构造背景分析,本文推测这是导致研究区沉积环境由半深海环境变为深海环境的原因。对研究区宗卓组地层和砂岩来源进行分析后得出：在洋壳俯冲阶段,宗卓组为被动大陆边缘沉积;在之后印度—亚洲陆陆碰撞的初始碰撞阶段,特提斯喜马拉雅被动陆缘已不复存在,并完全过渡为前陆盆地。     

Leptolepid otoliths from the Hauterivian (Lower Cretaceous) Lower Weald Clay (southern England)

Teleostean saccular otoliths from the upper part of the late Hauterivian Lower Weald Clay Formation of the Wealden Supergroup exposed at Langhurstwood Quarry, West Sussex, UK, and Clockhouse Brickworks, Surrey, UK are described for the first time. Two new species of the genus Leptolepis, Leptolepis wealdensis and Leptolepis toyei are described. Many of the specimens are densely packed on individual bedding planes and they are interpreted as coprocoenotic accumulations. Additional mechanisms of deposition and concentration are discussed, in particular wave action. Ontogenetic series show isometric growth of the otoliths, and some specimens show growth rings on two orders of magnitude.     

A Pliocene mega-tsunami deposit and associated features in the Ranquil Formation,southern Chile

An exceptionally large tsunami affected the coastline of southern Chile during the Pliocene. Its backflow eroded coarse beach and coastal dune sediments and redistributed them over the continental shelf and slope. Sandstone dykes and sills injected from the base of the resulting hyperconcentrated flow into underlying cohesive muds, assisted in plucking up large blocks of the latter and incorporating them into the flow. Locally, the rip-up intraclasts were fragmented further by smaller-scale injections to form a distinct breccia of angular to rounded mudstone clasts within a medium to coarse sandstone matrix. Sandstone sills in places mimic normal sedimentary beds, complete with structures resembling inverse gradation, planar laminae, as well as ripple and trough cross-lamination. These were probably formed by internal sediment flow and shear stress as the semi-liquefied sand was forcefully injected into cracks. In borehole cores, such sills can easily be misinterpreted as normal sedimentary beds, which can have important implications for hydrocarbon exploration.     

New Aetheogrammatidae (Insecta: Neuroptera) from the Lower Cretaceous Yixian Formation,China

Two new genera and three new species of the Mesozoic family Aeotheogrammatidae are described from the Lower Cretaceous of Yixian Formation (Liaoning Province, China): Cyclicogramma rotundum gen. et sp. nov. and Aetheogramma bistriatum sp. nov. from Huangbanjigou, and Curtogramma ovatum gen. et sp. nov. from Dawangzhangzi. The hind wing of Cyclicogramma rotundum gen. et sp. nov. differs from that of other species by its smaller size, its overall shape, RP bearing only two oblique radial branches, and its configurations of CuP, AA1, and AA2. Aetheogramma bistriatum sp. nov. is closely related to A. speciosum Ren and Engel, 2008, but distinguished from the latter by its distinctive configuration of RP1, and the narrower and longer AA2 space in the hind wing. Curtogramma ovatum gen. et sp. nov. is distinguished from all other species of the family by the forewing with M forking very far from the wing base.     

Vertebrate remains from the Upper Cretaceous (Santonian) Ajka Coal Formation,western Hungary

Vertebrate remains from the Upper Cretaceous (Santonian) Ajka Coal Formation (Bakony Mountains, western Hungary) are described. Macro- and microfossils collected from two boreholes and from isolated chunks of sediment/matrix dumped on spoil heaps of the Jókai Mine represent pycnodontiform and lepisosteiform fishes, bothremydid turtles, the mosasauroid Pannoniasaurus inexpectatus, the crocodyliforms cf. Theriosuchus, Iharkutosuchus makadii and cf. Allodaposuchus, as well as ankylosaurian and theropod dinosaurs. This unit was deposited in a swampy lacustrine environment, in contrast with the neighbouring and contemporaneous floodplain deposit of the vertebrate-bearing Csehbánya Formation at Iharkút. Despite significant environmental differences, the faunal composition of the Ajka Coal Formation assemblage completely overlaps with that of the Csehbánya Formation, suggesting the occurrence of the same semi-aquatic and terrestrial species in both settings. The ankylosaurian remains further strengthen the previous view that ankylosaurus preferred wetland habitats such as fluvial systems and coastal regions.     

A new Osmylidae (Insecta,Neuroptera) from the Lower Cretaceous Crato Formation in Brazil

Cratosmylus magnificus gen. et sp. nov., type genus and species of the new osmylid subfamily Cratosmylinae, is described from the Lower Cretaceous of the Crato Formation, Brazil. The relationships of this taxon remain uncertain within the Osmylidae, mainly due to the lack of phylogeny of the whole family. Nevertheless, it shares with the Mesozoic subfamily Saucrosmylinae the Rs curved and bent anteriorly distally, even in a more pronounced state, i.e. Rs touching R1 in its distal part.     

Paleomagnetism of the Late Cretaceous intrusions from the Minusa trough (southern Siberia)

The paper summarizes paleomagnetic and rock-magnetic data on the Late Cretaceous diatremes and associated dikes from the Minusa trough located within the southwestern Siberian Platform. It is shown that the stable characteristic component of magnetization is superimposed magnetization (in physical sense). It is linked to Fe-rich titanomagnetite produced by the decay and oxidation of Ti-rich titanomagnetite derived from a primary magma. This process, however, coincides in time with the intrusion cooling, which is supported by paleomagnetic tests. Correlation of magnetic polarity with ³⁹Ar/⁴⁰Ar ages suggests that the acquired stable characteristic component of magnetization corresponds to magnetic Chrons C33-C32 and characterizes the Middle Campanian magnetic field (74–82 Ma). The mean paleomagnetic pole for this span is located at 82.8° N, 188.5° E, with α₉₅ = 6.1 and, within confidence intervals, coincides with the reference data from the European part of the Eurasian plate. The excellent agreement between virtual paleomagnetic poles testifies that the intraplate motions in the Mesozoic resulting in the crust deformation of Central Asia ceased in the late Cretaceous or were so small that elude detection by the paleomagnetic method.     

Possible retrogressive flow slide deposits from the Kongsfjord Formation: a Precambrian submarine fan, Finnmark, N. Norway

Three thinning and fining-upward turbidite sequences are described from the Precambrian Kongsfjord Formation, a 3.5 km thick flysch succession. Their thicknesses range between about 2 and 5 m. They show a progressive upward decrease in bed thickness, bulk mean grain size and the ratio of the higher to lower energy division of the Bouma sequence. In one case, however, there is an initial upward bed thickness and grain size increase, with an increase in the proportion of the higher energy division. The absence of structureless mud of the Bouma E division and the presence of wavy interfaces between beds, together with similar palaeo-currents within each sequence suggest that these sequences resulted from related depositional events. These sequences are interpreted as the deposits of retrogressive flow slides, as an alternative to the classic mechanism of channel fill after abandonment.