Relationship between volcanism and marine sedimentation in northern Austral (Aisén) Basin, central Patagonia: Stratigraphic, U–Pb SHRIMP and paleontologic evidence

The northernmost part of the oil-producing Austral Basin, known as Aisén Basin or Río Mayo Embayment (in central Patagonian Cordillera; 43–46°S), is a special area within the basin where the interplay between volcanism and the initial stages of its development can be established. Stratigraphic, paleontologic and five new U–Pb SHRIMP age determinations presented here indicate that the Aisén Basin was synchronous with the later phases of volcanism of the Ibáñez Formation for at least 11 m.yr. during the Tithonian to early Hauterivian. In this basin marine sedimentary rocks of the basal units of the Coihaique Group accumulated overlying and interfingering with the Ibáñez Formation, which represents the youngest episode of volcanism of a mainly Jurassic acid large igneous province (Chon Aike Province). Five new U–Pb SHRIMP magmatic ages ranging between 140.3 ± 1.0 and 136.1 ± 1.6 Ma (early Valanginian to early Hauterivian) were obtained from the Ibáñez Formation whilst ammonites from the overlying and interfingering Toqui Formation, the basal unit of the Coihaique Group, indicate Tithonian, early Berriasian and late Berriasian ages. The latter was a synvolcanic shallow marine facies accumulated in an intra-arc setting, subsequently developed into a retro-arc basin.     

New abelisaurid remains from the Anacleto Formation (Upper Cretaceous), Patagonia,Argentina

New theropod remains with abelisaurid affinities from the Upper Cretaceous (Anacleto Formation, lower Campanian), NW Patagonia, Argentina, are here described. The specimen (MPCN-PV 69) consists of a partial premaxilla, fragmentary vertebrae, proximal portion of both humeri, distal portion of the pubis, and an incomplete pedal ungual. Characters linking with Abelisauridae are a premaxilla with a subquadrangular body, externally ornamented, and paradental plates with a striated surface; and humerus with bulbous proximal head, conical internal tuberosity, and reduced greater tubercle. The humerus is similar to those of Carnotaurus and Aucasaurus, due to the presence of a bulbous head and a discontinuity between the head and the internal tuberosity, but also differs from both taxa in the more distal location of the greater tubercle with respect to the internal tuberosity. Aucasaurus also comes from Anacleto Formation, but differences in the humeri suggest that MPCN-PV 69 is a different taxon. The phylogenetic analysis performed supports the affiliation to Abelisauridae, but fails to determinate a more precise relationship with others abelisaurids. However, a majority rule consensus of the analysis shows a position within Brachyrostra. Despite being fragmentary, MPCN-PV 69 probably represents a new abelisaurid from the Anacleto Formation, thus increasing the knowledge and diversity of Late Cretaceous South American abelisaurids.     

Small-sized abelisaurid (Theropoda: Ceratosauria) remains from the Upper Cretaceous of northwest Patagonia,Argentina

A new abelisaurid theropod from the Cenomanian of Candeleros Formation (Neuquén Province, NW Patagonia, Argentina) is described. It includes an isolated frontal, partial pelvis, two fused sacral centra, femoral shaft, rib fragments, partial metatarsal II and shaft of metatarsal III. A paleohistological analysis shows that MMCh-PV 69 was somatically mature at time of death. The prevalence of relatively ordered intrinsic fibers in the primary bone indicates a relatively lower growth rate of MMCh-PV 69 compared with other abelisauroids, such as Aucasaurus garridoi. Phylogenetic analysis found MMCh-PV 69 as a basal abelisaurid, sister group of the node formed by Majungasaurinae and Brachyrostra. We estimated the body mass of MMCh-PV 69 in 240 kg, which makes it one of the smallest abelisaurids recorded. This new form adds to the extensive theropod fauna of the Candeleros Formation, probably the most diverse association of meat-eating dinosaurs recorded in a Cretaceous Formation from South America.     

Notes on fossil remains from the Early Cretaceous Lohan Cura Formation, Neuquén Province, Argentina

In this contribution, we describe an association of fossil remains collected in the locality of Cerro de Los Leones, approximately 8 km southwest of the town of Picún Leufú, Neuquén Province, Argentina, from different levels of the Albian Cullín Grande Member, Lohan Cura Formation. The fossils include pelecypodan (Neocorbicula dinosauriorum, Neocorbicula pehuenchensis, and genus indet.) and gastropodan (Physa wichmanni) molluscs, a mesoeucrocodylian, possible pterosaurs, theropods, and sauropods. The sedimentary environment at Cerro de los Leones is characterized by fluvial deposits corresponding to a sandy meandering fluvial system. The most fossiliferous levels (located in the lower part of the exposed sequence) were developed in a distal flood plain and flood basin areas. Sedimentological and paleopedological features suggest semi-arid conditions during the deposition of the Cullín Grande Member. Despite the fragmentary nature of the specimens described here, the new information provided from the Albian assemblages of the Lohan Cura Formation at the Cerro de Los Leones locality provides a broader panorama of the composition of terrestrial faunas during the Early Cretaceous in Patagonia.     

Lower Cretaceous provenance in the northern Austral basin of Patagonia from sedimentary petrography

The northern Austral basin from Patagonia is characterized by an Early Cretaceous (Barremian–Albian) coarse-grained regressive sequence. These littoral to continental deposits conform a 150 km long basin cropping out along the Southern Patagonian Andes between 47 and 48°S. The basin fill consist of basal deltaic sandstones with interbedded shales and limestones from the Río Belgrano Formation, topped by up to 350 m of fluvial conglomerates and reworked tuffs of the Río Tarde and Kachaike formations. This continental depocenter represent a major geodynamic and paleoenviromental change from the underling marine Río Mayer Formation. In this study we analyze the tectonic setting and provenance during deposition of the coarse-grained sequence using sedimentary petrography of 37 thin sections in four stratigraphic profiles covering the northern basin. Our dataset indicates mainly a recycled orogenic sandstones provenance, in agreement with potential surrounding basement sources.     

湖南汝城盆地原定中侏罗世地层发现早白垩世孢粉组合

通过对湖南汝城盆地原定为中侏罗统的李家洞水库剖面28个孢粉样品的分析处理,发现24个样品有孢粉化石,化石呈现早白垩世孢粉化石组合特征。发现的早白垩世特征分子有高含量的无突肋纹孢Cicatricosisporites,徐氏孢Hsuisporites,刺毛孢Pilosisporites,膜环弱缝孢Aequitriradites,二连粉Erlianpollis,有突肋纹孢Appendicisporites,微囊粉Parvisaccites,以及少量被子植物花粉。依据孢粉化石组合特征,建议将本剖面时代重新厘定为早白垩世。     

Tectonic control of accommodation space and sediment supply within the Mata Amarilla Formation (lower Upper Cretaceous) Patagonia,Argentina

The Mata Amarilla Formation dates from the early Upper Cretaceous and was deposited during a transition in tectonic regime from the extensional Rocas Verdes Basin to the Austral Foreland Basin. Detailed sedimentological logs and architectural parameters were used to define 13 facies associations. The distribution of facies associations and associated variations in fluvial architecture have enabled large‐scale changes in accommodation space/sediment supply ratios (A/S ratio) to be defined for the three component sections of the Mata Amarilla Formation. The lower and upper sections are characterized by a high A/S ratio, whereas the middle section corresponds to a low A/S ratio. In the western part of the study area, small‐scale variations in the A/S ratio were recognized in the middle section. The strong west to east trend in evolution of the fluvial systems coincides with the direction of propagation of the Patagonian fold and thrust belt, which is located to the west of the study area. Intervals of high A/S ratio (i.e. lower and upper sections) are interpreted to have developed during periods of increased loading by the fold and thrust belt caused by tectonic uplift. In contrast, intervals of low A/S ratio (i.e. middle section) were developed during periods of tectonic quiescence. This article suggests that the large‐scale variations in A/S ratios are related to different rates of migration and growth of the Patagonian fold and thrust belt, whereas the small‐scale variation occurred in response to specific periods of thrusting and folding in the Patagonian fold and thrust belt (i.e. local loads). This field example of the effects of different scales of variation in A/S ratios across the Austral Foreland Basin could be used to recognize similar tectonically forced variations in stratigraphic architecture in other foreland basins throughout the world, as well as to understand the response of fluvial systems to such changes.     

First record of a clupeomorph fish in the Neuquén Group (Portezuelo Formation), Upper Cretaceous of Patagonia, Argentina

A new genus and species of clupeomorph fish, Leufuichthys minimus, is described from the fluvial deposits of the Portezuelo Formation, Upper Cretaceous (Turonian-Coniacian) of the Neuquén Group, Patagonia, Argentina. It is a small-sized fish with an estimated body length up to 46 mm. Among other characters, the new species shows the following: abdominal scutes; abdomen moderately convex; anal fin elongate-based; three uroneurals; two epurals; caudal fin bearing very elongate rays; and cycloid scales. Leufuichthys minimus gen. et sp. nov. shows a greater similarity with Kwangoclupea dartevellei, a clupeomorph described from a marine Cenomanian deposit of the Democratic Republic of Congo (Africa), mainly due to the presence of an elongate-based anal fin, bearing more than 20 fin-rays, differing from it by the presence of a not hypertrophied abdomen. As far as known, L. minimus gen. et sp. nov. is the first clupeomorph described in the Upper Cretaceous of Patagonia and represents one fortuitous preservation of an articulated fish in fluvial deposits.     

甘肃马鬃山地区早白垩世晚期恐龙化石

结合以往的研究对发现于甘肃马鬃山地区公婆泉盆地和俞井子盆地的恐龙化石进行了总结。基于恐龙化石的产出层位和组合成员的相似性,将两地的恐龙归入同一个恐龙化石组合——马鬃山恐龙化石组合,其时代为早白垩世阿普特中晚期—阿尔布早中期。另外,通过与辽西热河生物群早白垩世的恐龙化石进行对比,归纳出该组合的特点。马鬃山恐龙化石组合对深入研究中国北方早白垩世恐龙化石的演化过程具有重大意义。     

An anilioid snake from the Upper Cretaceous of northern Patagonia

We report the first record of anilioids from southern South America, a region where they do not live today. The fossils come from the Allen Formation (Late Campanian–Early Maastrichtian) at Bajo Trapalcó and Bajo de Santa Rosa localities, Río Negro province, Argentina. The remains consist of several vertebrae, most of which belong to the mid–posterior precloacal region of the column. Comparisons to other extant and extinct anilioid taxa indicate that these remains represent a new taxon, Australophis anilioides gen. et sp. nov. Australophis is morphologically closer to Palaeocene Hoffstetterella from Brazil and extant South American Anilius than to any other snake. These taxa might be closely related, in which case they would represent a lineage distinct from that including Cylindrophis and uropeltids. The two lineages must have diverged by the Late Cretaceous.     

Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia

Patagonia has yielded the most comprehensive fossil record of Cretaceous theropods from Gondwana, consisting of 31 nominal species belonging to singleton taxa and six families: Abelisauridae, Noasauridae, Carcharodontosauridae, Megaraptoridae nov. fam., Alvarezsauridae, and Unenlagiidae. They provide anatomical information that allows improved interpretation of theropods discovered in other regions of Gondwana. Abelisauroids are the best represented theropods in Patagonia. They underwent an evolutionary radiation documented from the Early Cretaceous through to the latest Cretaceous, and are represented by the clades Abelisauridae and Noasauridae. Patagonian carcharodontosaurids are known from three taxa (Tyrannotitan, Giganotosaurus and Mapusaurus), as well as from isolated teeth, collected from Aptian to Cenomanian beds. These allosauroids constituted the top predators during the mid-Cretaceous, during which gigantic titanosaur sauropods were the largest herbivores. Megaraptorans have become better documented in recent years with the discovery of more complete remains. Megaraptor, Aerosteon and Orkoraptor have been described from Cretaceous beds from Argentina, and these taxa exhibit close relationships with the Aptian genera Australovenator, from Australia, and Fukuiraptor, from Japan. The Gondwanan megaraptorans are gathered into the new family Megaraptoridae, and the Asiatic Fukuiraptor is recovered as the immediate sister taxon of this clade. Although megaraptorans have been recently interpreted as members of Allosauroidea, we present evidence that they are deeply nested within Coelurosauria. Moreover, anatomical information supports Megaraptora as more closely related to the Asiamerican Tyrannosauridae than thought. Megaraptorans improve our knowledge about the scarcely documented basal radiation of Gondwanan coelurosaurs and tyrannosauroids as a whole. Information at hand indicates that South America was a cradle for the evolutionary radiation for different coelurosaurian lineages, including some basal forms (e.g., Bicentenaria, Aniksosaurus), megaraptorans, alvarezsaurids less derived than those of Laurasia, and unenlagiids, revealing that Gondwanan coelurosaurs played sharply differing ecological roles, and that they were taxonomically as diverse as in the northern continents. The unenlagiids represent an endemic South American clade that has been recently found to be more closely related to birds than to dromaeosaurid theropods. Analysis of the theropod fossil record from Gondwana shows the highest peak of origination index occurred during the Aptian–Albian and a less intense one in the Campanian time spans. Additionally, peaks of extinction index are recognized for the Cenomanian and Turonian–Coniacian time spans. In comparison, the Laurasian pattern differs from that of Gondwana in the presence of an older extinction event during the Aptian–Albian time-span and a high origination rate during the Cenomanian time-bin. Both Laurasian and Gondwanan theropod records show a peak of origination rates during the Campanian.     

A Megatheropod Tooth from the Early Cretaceous of Fusui,Guangxi, Southern China

A nearly complete right maxillary or left dentary tooth（NHMG 10858） from the Lower Cretaceous Xinlong Formation of the Napai Basin, Fusui County, Guangxi, southern China, is described. The tooth is large in size, with a CBL of 37 mm. Given the geological age and its crown morphology, including the size, it is most likely that the tooth belongs to a carcharodontosaurid. The recovered specimen represents one of the largest theropod teeth hitherto reported from the Early Cretaceous of Asia.     

Early Cretaceous megaspore assemblages from southeastern Australia

Twenty-nine megaspore species including six new taxa (Bacutriletes otwayensis sp. nov.,Erlansonisporites cerebrus sp. nov., Erlansonisporites decisum sp. nov., Hughesisporites coronatus sp. nov., Hughesisporites dettmanniae sp. nov., and Verrutriletes depressus sp. nov.) are documented from Aptian and Albian strata of the Gippsland and Otway basins, southeastern Australia. Together with six taxa known only from underlying Neocomian strata, these megaspores are used to establish four provisional biozones for the Lower Cretaceous that complement existing biostratigraphic schemes based on miospores and plant macrofossils. Megaspores are best represented in silty floodbasin facies and it is likely that the parent plants predominantly occupied moist understorey to fully aquatic habitats on the floodplain. Megaspores are sparsely represented in most other fluvial facies chiefly due to reworking of floodbasin sediments into higher energy channel and crevasse deposits. The relatively high diversity of lycophyte and fern megaspores contrasts with the scarcity of these plant groups in macrofossil assemblages. The megaspore record suggests that heterosporous cryptogams may have been significantly more prominent in the vegetation of this region than previously suggested. Several megaspores from southeastern Australia are closely comparable to forms from India and Argentina indicating broad similarities between Early Cretaceous heterosporous fern and lycophyte communities across Gondwana. These similarities also suggest that megaspores may be useful for inter-continental biostratigraphic correlation.     

河南汝阳盆地早白垩世晚期禽龙类化石的发现 及其地层学意义

记述了产自河南汝阳盆地早白垩世晚期相互关联的禽龙类9个中前部尾椎椎体化石。由于化石只保存不完整的尾椎部分,其属种难以断定。但它的发现说明,汝阳巨型蜥脚类恐龙动物群中,除了植食性的大型蜥脚类恐龙外,也存在大型鸟脚类恐龙——禽龙类。保存的尾椎椎体系列与发现于比利时的早白垩世贝尼萨尔禽龙相比,不论是大小还是形态构造上均极为相似,从而判断这9个连续的尾椎体分别为第7到第15尾椎。进而推断,河南汝阳盆地产出巨型蜥脚类恐龙动物群化石的沉积地层形成于早白垩世晚期。     

内蒙银根-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－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。     

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.     

Zurupleuropholis gen. nov. (Teleostei,Albian, Argentina), first pleuropholids from the Cretaceous of South America

Although the Cretaceous is characterized by a rich fish diversity, Cretaceous continental fishes from Gondwana are poorly known and comparatively scarce. Among these fishes, the family Pleuropholidae is only known by a few species relatively poorly preserved, from the Middle Jurassic to Lower Cretaceous of Europe, Africa, North America, and South America. In this paper, two new species of the pleuropholid new genus Zurupleuropholis are described, Z. quijadensis gen. et sp. nov. and Z. decollavi gen. et sp. nov. The new fishes were recovered in the Lower Cretaceous lacustrine Lagarcito Formation of central-west Argentina. This taxon constitutes a relevant finding considering that the representation of the family Pleuropholidae is rare worldwide. Zurupleuropholis gen. nov. appears to be the youngest known member of Pleuropholidae, and it represents the second record of the family in South America and the first record in the Cretaceous of the continent.     

Orkoraptor burkei nov. gen. et sp., a large theropod from the Maastrichtian Pari Aike Formation, Southern Patagonia, Argentina

A new large theropod, Orkoraptor burkei nov. gen. et nov. sp., from the Upper Cretaceous (Maastrichtian) Pari Aike Formation of southern Patagonia is based on a postorbital, quadratojugal, coronoid?, several teeth, an atlantal intercentrum and neurapophysis, two caudal vertebrae, and the proximal half of tibia. This new theropod exhibits characteristics of maniraptorans (i.e., coelurosaurians more derived than tyrannosaurids) including an upturned rostral process of the postorbital, the caudoventral corner of which is widely concave. Furthermore, teeth without denticles and carina in the mesial margin resemble the condition of the maniraptoran clades Compsognathidae and Deinonychosauria. The new Patagonian theropod differs from other coelurosaurians (Ornithomimosauria, Compsognathidae, Alvarezsauridae, Dromaeosauridae, Aves) in having caudal vertebrae with a single pair of small pleurocoels on each side, and in having a median depression flanked by two longitudinal and narrow furrows on each tooth. Orkoraptor represents one of the southernmost carnivorous dinosaurs yet found in South America and adds valuable information about the diversification of tetanuran theropods in Gondwana.     

鸡西盆地早白垩世烃源岩可溶有机质地球化学特征

应用气相色谱、色谱-质谱等分析方法,对鸡西盆地早白垩世烃源岩生物标志化合物特征进行了讨论,揭示了生物标志化合物对该区有机质生物来源、成熟度及沉积环境的指示意义。有机质热演化已进入成熟阶段,且煤岩热演化程度略高于泥岩。泥岩有机质母质来源主要为水生生物,同时有高等生物的输入;煤岩以陆生高等植物输入为主,同时也有水生生物输入。煤岩沉积环境为弱氧化环境,经历过较强的降解作用过程;泥岩沉积环境为还原环境,沉积介质咸化程度较高,更有利于有机质的保存和转化。     

塔里木盆地早白垩世沉积相特征与古地理

根据大量的钻井和露头资料,对塔里木盆地早白垩世沉积相特征和古地理进行了研究。塔里木盆地下白垩统主要发育冲积扇-扇三角洲、辫状河三角洲、氧化宽浅湖泊等3种沉积体系,包括陆相冲（洪）积扇、扇三角洲、辫状河三角洲、滨浅湖等沉积相,分布于下白垩统不同层位。塔里木盆地早白垩世主要包括塔东北和塔西南两大沉积区,总体为干旱氧化的内陆拗陷分割盆地。在塔东北沉积大区,早白垩世早期卡普沙良群沉积物受周缘4大物源区控制,为多物源的氧化宽浅湖盆环境,古地势呈“南高北低、东高西低”,盆地边缘以冲（洪）积扇、扇三角洲、辫状河三角洲相为主,盆地内部为滨浅湖亚相。早白垩世晚期巴什基奇克组沉积时期,塔里木盆地周缘进入一个新的构造活动期,古气候更加炎热干旱,氧化宽浅湖盆消失。在塔东北沉积大区,盆地受周缘4个主要物源区影响,以广泛分布的冲积扇-辫状河三角洲沉积体系占主体,盆地内部普遍为辫状河三角洲前缘-滨浅湖亚相沉积。在塔西南沉积大区,早白垩世克孜勒苏群沉积时期古地势呈“东高西低”,受北部喀什北山前和西南部古昆仑山2个物源区的控制,沉积物沿古昆仑山前呈狭长的条带状分布,沉积厚度自西向东减薄,主要是一套冲积扇-扇三角洲相和滨浅湖亚相沉积。