Magnetostratigraphy of the Miocene Las Arcas Formation,Santa María Valley,northwestern Argentina

The first magnetostratigraphic study of the Las Arcas Formation (Late Miocene) was carried out in Las Totoritas creek (26º12′S; 65º47′W, NW Argentina), a key place in between of two geological provinces: Northwestern Pampean Ranges and Eastern Cordillera, in northwestern Argentina. This was accompanied by isotopic dating (9.01 ± 0.12 Ma, ⁴⁰Ar–³⁹Ar in amphibole) of the unit, obtained from a 3.4 m thick tuff intercalated at ∼45 m above the base. The Las Arcas Formation is 810 m thick at the sampling locality and it is mainly composed of tabular reddish conglomerates, sandstones and siltstones in both coarsening- and thickening-upward arrangements. The exposed section was sampled at 48 sites, 26 of which are interpreted as carrying primary magnetization. The new magnetostratigraphic column was correlated with the Geomagnetic Polarity Time Scale (GPTS), and suggests that deposition of the Las Arcas Formation strata started at around 9.1 Ma and ended around 6.8 Ma. The paleomagnetic pole obtained for this unit (Dec = 8.7° Inc = −43.9° dp = 14.9 dm 9.3) indicates that this area underwent non-significant rotation (11.0° ± 13.6°) since the Late Miocene.     

Early Cretaceous Aleyrodidae (Hemiptera: Sternorrhyncha) from the Lebanese amber

Four new, monotypic genera of Aleyrodidae from the Lower Cretaceous Lebanese amber are described: Shapashe aithiopa gen. sp. nov.; Milqartis azari gen. sp. nov.; Aretsaya therina gen. sp. nov.; and Yamis libanotos gen. sp. nov. All new taxa represent subfamily Aleurodicinae. The key for identification of genera of Aleurodicinae from the Lebanese amber is provided. The morphological features of newly established taxa are discussed. The importance of the fossils for phylogenetic, evolutionary and ecological studies is presented.     

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 new genus and species of damsel-dragonfly (Odonata: Stenophlebiidae) from the Lower Cretaceous of Inner Mongolia,China

A taxon of the Stenophlebiidae, Yixianstenophlebia magnifica gen. et sp. nov., is described from the Lower Cretaceous Yixian Formation at Liutiaogou, Ningcheng County, Inner Mongolia of China. Its closest relative is the Late Jurassic European genus Stenophlebia. This new discovery is helpful to understand the Jehol Biota assemblage at Liutiaogou Locality. It also confirms that the Stenophlebiidae was a very diverse and widespread family during the Early Cretaceous. The causes of its extinction in the Late Cretaceous remain enigmatic.     

内蒙古银根-额济纳旗盆地白垩系中硅化木化石及其沉积环境

内蒙古银根额济纳旗盆地是我国北方重要的中一新生代陆内含油气盆地,主要出露白垩系冲洪积-河湖相碎屑岩及火山岩夹层.本文描述了在盆地东南部下白垩统巴音戈壁组下段(1号)和苏红图组二段底部(2号)发现的上、下两处原始埋藏的硅化木化石,并探讨了早白垩世时期盆地沉积时的气候环境.两处化石均保存完好,表面结构较为完整.巴音戈壁组上部和苏红图组下部泥岩段孢粉分析结果显示地层时代为早白垩世中晚期.同时,孢粉植物群揭示该时期银根-额济纳旗盆地气候环境温暖湿润,植被茂盛.根据化石保存特征和产出位置的地层岩性,初步推测1号硅化木化石点系冲洪积物快速堆积所致,2号硅化木化石点系火山喷发物瞬间埋藏所致,其埋藏时代大致为早白垩世晚期.     

郯庐断裂带莒县地区早白垩世中酸性火山岩成因及其地质意义

莒县早白垩世火山岩沿郯庐断裂带分布,由粗安岩、粗面岩和流纹岩组成,属高钾钙碱性-钾玄岩系列.岩石富集Rb、K、Ba等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、Ti等高场强元素和重稀土元素,Sr-Nd同位素组成((87Sr/86Sr)t=0.7082～0.7095,ENd(t)=-16.4～-19.8)与区内基性岩的相类似,而Pb同位素组成((206pb/204Pb)t=16.523～17.038,(207pb/204Pb)t=15.414～15.468,(208pb/204Pb)t=37.058～37.427)类似于EM1型富集地幔.(87Sr/86Sr)t和εNd(t)与SiO2没有明显的相关性,且较高的Th/U、Ce/Pb值和较低的Nb/La、Nb/U值均暗示岩浆在上升过程中未遭受明显的地壳混染.粗安岩具有高的Cr、Ni、MgO含量及Mg#值和古老Nd同位素模式年龄,暗示其起源于富集的岩石圈地幔.粗面岩与粗安岩的主要氧化物、微量元素与SiO2呈明显的相关性,这暗示可能为同源岩浆结晶分异而来.研究表明,莒县地区中酸性火山岩形成于岩石圈伸展减薄背景下,由曾遭受俯冲扬子陆壳熔体改造的华北岩石圈地幔部分熔融形成的岩浆分离结晶作用而成.郯庐断裂带的伸展活动控制着火山岩的分布,为岩浆的形成和运移提供了有利的场所,在华北克拉通破坏中可能起到了重要的作用.     

Field meeting report: the geology of some West London Churches, 22nd September 2012

This excursion report describes briefly the ecclesiastical geology of seven localities in West London. It reveals that building stones related to local geology were particularly important in the construction of early churches. For this reason wall building fabric analyses of churches are also able to indicate an enormous amount of local geological information. Where London Basin rocks were unsuitable for structural aspects of these churches it was sometimes necessary to use rock types from more distant sources.     

Microstratigraphy of a Miocene layered phosphatic pebble from the western margin of South Africa

Detailed microstratigraphy and geochemistry of a single‐layered phosphatic pebble from the Southern Rocky Plateau at the Head of the Cape Canyon on the western margin of South Africa are utilized to reveal a complex interplay between deposition, erosion and authigenesis in the Miocene. The phosphatic pebble has three micrite and carbonate fluorapatite cemented layers separated by Fe‐rich hardground surfaces. The layers contain a diverse grain assemblage of reworked glauconite, phosphorite, detrital quartz and biogenic carbonate. Overlapping Sr‐isotope derived ages of point‐drilled samples from the three layers range from 19·1 to 17·6 Ma, although a single point near the outer edge of the uppermost layer has a Sr age of 12·8 to 10·4 Ma, and a reworked bivalve shell fragment from the middle layer has a Sr age of 26·3 to 24·6 Ma. The microstratigraphy of the phosphatic pebble provides evidence of multiple Baturin cycles, where periods of deposition and carbonate fluorapatite authigenesis are followed by reworking, erosion and precipitation of iron oxide hardground surfaces. The condensed microstratigraphy of the pebble is consistent with the regional depositional history of the area and indicates significant fluctuations in the depositional environment related to changes in sea‐level, sediment supply and upwelling along the western margin of southern Africa during the early to middle Miocene.     

Osteology and ontogeny of Early Cretaceous Philydrosaurus (Diapsida: Choristodera) based on new specimens from Liaoning Province,China

Choristoderes are a group of extinct diapsid reptiles that once occupied the freshwater systems in the Northern Hemisphere from the Middle Jurassic through the Miocene. The Early Cretaceous monjurosuchid Philydrosaurus from western Liaoning, China, represents a transitional morphotype between a broad-snouted (crocodile-like) and a narrow-snouted (gavial-like) skull during the evolution of Choristodera. New specimens of the taxon from the Early Cretaceous Jiufotang Formation include an incomplete braincase and a nearly complete juvenile skeleton; the study of these specimens provides new information on the braincase and ontogenetic change of the skeleton of this transitional monjurosuchid. In the braincase floor, the foramen internus canalis caroticus externus opens in a groove lateral to the constricted lateral aspect of the parasphenoid, and ventral exposure of this foramen differs from Champsosaurus, in which parasphenoid/pterygoid fusion completely encloses the canal. On the occiput, the vagus nerve foramen penetrates the basioccipital, while the two foramina for the hypoglossal nerve open at the exoccipital/basioccipital suture. Comparative study of the new juvenile specimen with adult Philydrosaurus reveals previously unknown developmental changes of the cranial and postcranial skeleton of this monjurosuchid. Ontogenetically, Philydrosaurus underwent a dramatic change of skull proportions, including elongation of the antorbital and postorbital regions, and elongation of the jaws, with a great increase of the number of marginal teeth. The lower temporal fenestra is entirely closed in early ontogeny, as in large, fully-grown adults.     

Palynoassemblages associated with a theropod dinosaur from the Snow Hill Island Formation (lower Maastrichtian) at the Naze,James Ross Island,Antarctica

The Cape Lamb Member of the Snow Hill Island Formation at The Naze on the northern margin of James Ross Island, east of the Antarctic Peninsula, yielded a theropod dinosaur recovered near the middle of a 90 m thick section that begins at sea level, ends below a basalt sill, and is composed of interbedded green–gray massive and laminated fine-grained sandstones and mudstones. Sixteen palynoassemblages were recovered from this section, which yielded moderately diverse assemblages with a total of 100 relatively well-preserved species. The principal terrestrial groups (32%) are represented by lycophytes (8 species), pteridophytes (15 species), gymnosperms (13 species), angiosperms (21 species) and freshwater chlorococcaleans (3 species). Marine palynomorphs (68%) belong to dinoflagellates (61 species), chlorococcaleans (6 species), and one acritarch. The vertical distribution of selected species allows the distinction of two informal assemblages, the lower Odontochitina porifera assemblage from the base to its disappearance in the lower part of the section, and the remaining section characterized by the Batiacasphaera grandis assemblage. The global stratigraphic ranges of selected palynomorphs suggest an early Maastrichtian age for this section and the entombed dinosaur that is also supported by the presence of the ammonoid Kitchinites darwinii. These assemblages share many species with latest Campanian–early Maastrichtian palynofloras from Vega and Humps Islands, New Zealand, and elsewhere in the Southern Ocean, establishing a good correlation among them. The dominance or frequent presence of dinoflagellates throughout the section supports the general interpretation of a shelf marine depocenter. The consistent presence of terrestrial palynomorphs suggests contributions from littoral/inland environments.