Hekou Formation Research Articles

Hadrosauroid eggs and embryos from the Upper Cretaceous (Maastrichtian) of Jiangxi Province, China

BackgroundDinosaur eggs containing embryos are rare, limiting our understanding of dinosaur development. Recently, a clutch of subspherical dinosaur eggs was discovered while blasting for a construction project in the Upper Cretaceous red beds (Hekou Formation) of the Ganzhou Basin, Jiangxi Province, China. At least two of the eggs contain identifiable hadrosauroid embryos, described here for the first time.ResultsThe eggs, attributable to Spheroolithidae indet., are thin-walled and small (~ 660 mL) compared to those of Lambeosaurinae. The shape of the embryonic squamosal is reminiscent of that seen in the Late Cretaceous hadrosauroids Levnesovia transoxiana, Tanius sinensis, and Nanningosaurus dashiensis, suggestive of possible affinities.ConclusionThe small size of the eggs and embryos, similar to those of Hadrosaurinae, indicates that the larger eggs and hatchlings typical of Lambeosaurinae are evolutionarily derived.

Age and origin of tuffites from the Hekou Formation in the Napo basin, Southwest Guangxi and its tectonic implications

桂西南那坡盆地位于八布-Song Hien构造带，发育早-中三叠世岩浆岩和巨厚海相碎屑岩系，是研究华南地块南缘古特提斯造山过程的关键地区。本文对那坡盆地中三叠统河口组中-上部的两套沉凝灰岩开展了详细的岩石学、地球化学和锆石U-Pb-Hf同位素分析研究。两件沉凝灰岩样品LA-ICP-MS锆石U-Pb定年结果分别为240.6±1.0Ma和236.3±0.8Ma，指示河口组碎屑岩沉积时代为中三叠世拉丁期，部分为晚三叠世卡尼期早期。全岩地球化学结果显示，该沉凝灰岩属于亚碱性英安质，富集轻稀土（LREEs）和大离子亲石元素（LILEs）、Rb、Th和U，亏损高场强元素（HFSEs），具有显著的Nb、Ta和Ti负异常。沉凝灰岩锆石具有较低的ε_Hf（t）值（-18.6~-6.3）和较老的地壳模式年龄（t_DM^C=1664~2434Ma），结合锆石微量元素特征认为其形成于俯冲环境。整体上，那坡盆地河口组沉凝灰岩表现出俯冲作用形成的岛弧火山岩地球化学特征，推断其来源于桂西南凭祥地区的中-晚三叠世酸性火山岩。结合已有区域地质调查成果，认为华南地块南缘八布-Cao Bang古特提斯分支洋盆于晚二叠世至晚三叠世早期向北俯冲，随后自西向东呈剪刀式逐渐闭合。华南地块与北越地块完全碰撞拼合的时间发生在晚三叠世中晚期。;The Napo basin, Southwest Guangxi, locates in the Babu-Song Hien tectonic belt and shows widespread Early-Middle Triassic magmatic and massive marine clastic rocks, which plays a key role in studying the evolution of the Paleo-Tethys orogeny along the southern margin of South China block. In this paper, we have carefully analyzed the petrology, geochemistry and zircon U-Pb-Hf isotope for two sets of tuffites in the middle-upper part of the Middle Triassic Hekou Formation, Napo basin. LA-ICP-MS zircon U-Pb dating results of the two tuffite samples yield the ages at 240.6±1.0Ma and 236.3±0.8Ma, respectively, indicating that the clastic rocks of Hekou Formation should be deposited during the Middle Triassic Ladinian stage, some of which may extend to the early Carnian of Late Triassic. Whole-rock geochemical results indicate that the tuffites are subalkaline dacitic, enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs), Rb, Th and U, depleted in high field strength elements (HFSEs), and have significant negative anomalies of Nb, Ta and Ti. The tuffite zircons have lower ε_Hf(t) values (-18.6~-6.3) and older crustal model ages (t_DM^C=1664~2434Ma). Combined with trace elements, we suggest these zircons may have been formed in subduction-related setting. In summary, the tuffite samples from the Hekou Formation in Napo basin display the geochemical characteristics of island-arc volcanic rock, which are inferred to be derived from the Middle-Late Triassic acidic volcanic rocks in Pingxiang area, Southwest Guangxi. Given the existing geological survey results, it is concluded that the Babu-Cao Bang Paleo-Tethys branch ocean along the southern margin of the South China block should subduct northward during the Late Permian-early Late Triassic, and subsequently closed with scissor-style from west to east. The collision between the South China block and North Vietnam terrane should occur in the middle to late stage of Late Triassic.

An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on avian-like prehatching postures

SummaryDespite the discovery of many dinosaur eggs and nests over the past 100 years, articulated in-ovo embryos are remarkably rare. Here we report an exceptionally preserved, articulated oviraptorid embryo inside an elongatoolithid egg, from the Late Cretaceous Hekou Formation of southern China. The head lies ventral to the body, with the feet on either side, and the back curled along the blunt pole of the egg, in a posture previously unrecognized in a non-avian dinosaur, but reminiscent of a late-stage modern bird embryo. Comparison to other late-stage oviraptorid embryos suggests that prehatch oviraptorids developed avian-like postures late in incubation, which in modern birds are related to coordinated embryonic movements associated with tucking — a behavior controlled by the central nervous system, critical for hatching success. We propose that such pre-hatching behavior, previously considered unique to birds, may have originated among non-avian theropods, which can be further investigated with additional discoveries of embryo fossils.

A partial articulated hadrosaurid skeleton from the Maastrichtian (Upper Cretaceous) of the Ganzhou area, Jiangxi Province, China

ABSTRACT We describe the first partial articulated skeleton from the Ganzhou area, Jianxi Province, China. This basin has not been forthcoming in yielding hadrosaurid remains. The new specimen consists of an articulated rib cage belonging to a relatively large (no less than 9 m in length) hadrosaurid. It was collected from Maastrichtian strata of the Hekou Formation. This is the first partial skeleton of a large hadrosaurid dinosaur recovered from South southern China and confirms the presence of relatively large members of the clade previously suggested by ichnological evidence.

Dinosaur Eggs Associated with Crustacean Trace Fossils from the Upper Cretaceous of Jiangxi, China: Evidence for Foraging Behavior?

We report the discovery of concentrated invertebrate inchnofossils in close association with a dinosaur nest from the Hekou Formation in Jiangxi Province, China. The seven dinosaurian eggs reported clearly belong to the Elongatoolithidae and burrow traces were most likely made by small crustaceans. This association prompts the question as to whether invertebrate activity had relations with the buried eggs. This may be just an occasional case or the eggs may have organically increased the content of organic matter in soil which attracted the crustaceans.

Geochemical characteristics of newly discovered Elongatoolithidae eggs from the Upper Cretaceous of Jiangxi Province, southern China: Palaeoenvironmental and palaeoclimatic inferences

We analyzed identified oospecies and associated geochemical characteristics of newly discovered dinosaur eggs from the Cretaceous Hekou Formation in Yudu District, Jiangxi Province, China. Results reveal that the Yudu eggs can be identified as representatives of the known oospecies Macroolithus rugustus within Elongatoolithidae based on external shape, size, ornamentation, and internal microstructure between the columnar and cone layers. The major element found in Macroolithus rugustus shells is Ca, while trace elements mainly include Sr, Ba, As, Cr, Mn, Pb, Cd, La, and Ir, characterised by Ir and Sr abnormalities, as well as the toxic elements As and Pb. Enrichment of trace elements in shells might be due to the diet of dinosaurs and subsequent deposition in eggs, consistent with global Ir anomalies and the regional enrichment of trace elements. δ13C values for Macroolithus rugustus ranging between −8.81‰ and −7.65‰ are indicative of C3 plants with relatively high CO2 concentration and low mean annual precipitation (MAP), while δ18O values ranging between −8.51‰ and 3.14‰ indicate relatively low humidity and the alteration of water sources of female dinosaur. The Sr and Ca contents as well as δ18O values of eggshells could be associated with the drinking water and food materials together with dissolved bone apatite. In light of the red-brown colour of surrounding rocks, high Fe composition revealed by macroelement analysis, and the presence of a C3 vegetation with low MAP, the palaeoenvironment of Yudu dinosaur nesting area was most likely to be fluvial and the palaeoclimate was semi-arid to arid, which is conducive to the preservation of eggs.

Alluvial fan facies of the Yongchong Basin: Implications for tectonic and paleoclimatic changes during Late Cretaceous in SE China

Late Cretaceous continental redbeds, the Guifeng Group of the Yongchong Basin in SE China have been investigated to conduct detailed fan facies description and interpretation. Tectonic activities determined the alluvial fan development along the basin margin, but the alluvial facies was linked with paleoclimate changes. The Guifeng Group is divided into the Hekou, Tangbian and Lianhe formations in ascending order. The Hekou conglomerates are typically polymict, moderately sorted with erosional bases, cut-and-fill features, normal grading and sieve deposits, representing dominant stream-flows on alluvial fans during the initial opening stage of the basin infill. The Tangbian Formation, however, is characterized by structureless fine-grained sediments with dispersed coarse clasts, and couplets of conglomerate and sandstone or siltstone and mudstone, recording a change to a playa and ephemeral lake environments with occasional stream flooding, thus indicating a basin expanding stage. The hallmark of the Lianhe Formation is disorganized, poorly sorted conglomerates lack of erosional bases, and a wide particle-size range from clay to boulders together reflect mud-rich debris-flows accumulating on fans, likely related to reactivation of faulting along the northwestern mountain fronts during a post-rift stage. The depositional system changes from stream-flows up through playa with ephemeral streams to debris-flows during the accumulation of the three formations are thus attributed to different source rocks and climatic conditions. Therefore, the fluvial-dominated fans of the Hekou Formation recorded a subhumid paleoclimate (Coniacian-Santonian Age). The dominant semiarid climate during the Campanian Age produced abundant fine-grained sediments in the playa and ephemeral lake environments of the Tangbian Formation. A climatic change towards more humidity during the late stage of the Guifeng Group (Maastrichtian Age) probably yielded high deposition rate of coarse clasts in debris-flow dominated fans of the Lianhe Formation. Thus the Late Cretaceous climate changes are inferred to have influenced and preserved signals in the alluvial stratigraphy of the Yongchong Basin.

Evolution of the Late Cretaceous Yongfeng-Chongren Basin in Jiangxi Province, southeast China: insights from sedimentary facies analysis and pebble counting

The Gan-Hang Belt in Southeast China is characterized by several igneous and siliciclastic basins associated with crustal extension during Late Mesozoic. The sedimentary evolution of the red basins is still poorly understood. In this study, sedimentary facies analysis and pebble counting were performed on outcrop sections of the Late Cretaceous Guifeng Group inthe Yongfeng-Chongren Basin in central Jiangxi Province. Thirty-five conglomerate outcrops were chosen to measure pebble lithology, size, roundness, weathering degree and preferred orientation. Results show that gravels are mostly fine to coarse pebbles and comprise dominantly quartzites, metamorphic rocks, granitoids and sandstones. Rose diagrams based on imbricated pebbles indicate variable paleocurrent directions. Combining with typical sedimentary structures and vertical successions, we suggest that the Guifeng Group were deposited in alluvial fan, river and playa lake depositional systems. The proposed depositional model indicates that the Hekou Formation represents the start-up stage of the faulted basin, accompanied by sedimentation in alluvial fan and braided river environments. Then this basin turned into a stable expansion stage during the deposition of the Tangbian Formation. Except for minor coarse sediments at the basin margin, the other area is covered with fine-grained sediments of lake and river environments. The Lianhe Formation, however, is once again featured by conglomerates, suggesting a probable tectonic event. Therefore, the study region possibly suffered two tectonic events represented by the conglomerates of the Hekou and Lianhe formations in the context of the crustal extension in Southeast China.

Volatile and C-H-O isotopic compositions of giant Fe-Ti-V oxide deposits in the Panxi region and their implications for the sources of volatiles and the origin of Fe-Ti oxide ores

The Panzhihua, Hongge, and Baima Fe-Ti-V oxide deposits in the Panzhihua-Xichang (Panxi) region are hosted in large layered mafic-ultramafic intrusions. The layered intrusions intrude either the Neoproterozoic Dengying Formation, composed mainly of limestone, or the Paleoproterozoic Hekou Formation, composed of meta-sedimentary-volcanic rocks. It remains unclear if the wall rocks have been involved during the fractionation of magmas and have affected the sequence of crystallization of Fe-Ti oxide. Volatiles and their C-H-O isotopic compositions of magnetite, apatite, clinopyroxene, and plagioclase of different types of ores from the three intrusions are analyzed using a technique of stepwise heating mass spectrometer to evaluate the role of wall rocks in the formation of Fe-Ti oxide ores. Volatiles released from magnetite are composed mainly of H2O and CO2, whereas the other minerals are composed mainly of H2O, CO2 and H2. At 800–1200°C temperature interval, the average δ13C values of CO2 of all the minerals from the three intrusions range from −7.7‰ to −13.5‰ and the average \(\delta ^{18} O_{CO_2 } \) values from 19.1‰ to 19.5‰, which are scattered in a mixed field with basalt and the two types of wall rocks as end-members, indicating that CO2 from the wall rocks may have been involved in the magmas from which the three intrusions formed. At 400–800°C temperature interval, both δ13C values (−13.7‰ to −17.9‰ on the average) and δ18O values (16.2‰ to 19.2‰ on the average) of CO2 of all the minerals are lower than those for 800–1200°C temperature interval, and much closer to the values of the wall rocks. Abundant H2O released at the 400–800°C temperature interval has relatively low δD values ranging from −90‰ to −115‰, also indicating the involvement of fluids from the wall rocks. The average bulk contents of volatiles released from magnetite of the Hongge, Baima, and Panzhihua intrusions are 4891, 2996, and 1568 mm3 STP/g, respectively, much higher than those released from other minerals in total, which are 382, 600, and 379 mm3 STP/g, respectively, indicating that magnetite crystallized from magmas with much more volatiles than other minerals. This can be interpreted as that crystallization of clinopyroxene and plagioclase in the early fractionation of magmas resulted in volatiles such as H2O that were eventually enriched in the residual magmas and, at the same time, fluids from the wall rocks may have been involved in the magmas and were trapped in magnetite, which crystallized later than clinopyroxene and plagioclase.

Kumamotoa, an early Late Cretaceous non-marine bivalve, from Fujian, south China

The non-marine bivalve species Trigonioides ( Kumamotoa) quadratus Gu and Ma is described from the Fourth Member of the Hekou Formation in western Fujian, southeastern China. This species previously was regarded to belong to the subgenus Trigonioides (s.s.), which is restricted to the Early Cretaceous. Herein, it is included into the subgenus Kumamotoa. It is compared to Cenomanian (early Late Cretaceous) species from Japan and Korea such as Trigonioides ( Kumamotoa) mifunensis Tamura, Trigonioides ( Kumamotoa) matsumotoi Kobayashi and Suzuki and Trigonioides ( Kumamotoa) paucisulcatus Suzuki. The age of the Fourth Member of the Hekou Formation is discussed.

Diverse dinosaur-, pterosaur-, and bird-track assemblages from the Hakou Formation, Lower Cretaceous of Gansu Province, northwest China

Diverse and well-preserved assemblages of dinosaur (theropod, sauropod and ornithopod), pterosaur, and bird tracks from the Hekou Formation (Lower Cretaceous) in the Yellow River (Huang He) valley represent the first significant fossil footprint discoveries in Gansu Province, China. However, the sites are large, visually spectacular, and well-exposed thanks to labor-intensive hand excavation. The sites have the potential for development as educational and tourist destinations. These sites have become one of the National Geoparks in China. Dinosaur tracks include at least two theropod morphotypes that range in size from about 5 to >30 cm in length. Wide-gauge sauropod tracks ( Brontopodus) range in size from 25 to 90 cm (pes length) and are the best-preserved examples known from China, with clear claw impressions. One trackway suggests an accelerating/running individual. Parallel ornithopod trackways indicate gregarious behavior. An enigmatic trackway may be a manus-only ornithopod trackway. A pterosaur trackway (cf. Pteraichnus), the first reported from China, consists of 24 consecutive footprints, and is the longest, well-preserved trackway on record. Bird tracks (cf. Aquatilavipes) are also very well preserved. The tracks occur at multiple stratigraphic levels in fluvio-lacustrine sequences of paleosol mudstones and sandstones with mud cracks and wave ripple marks. A minimum ichnodiversity of eight, the highest reported from the Cretaceous of China, is estimated. The saurischian component (theropods and sauropods) compares well with Inner Mongolia ichnofaunas from the Jing Chuan Formation. However, the co-occurrence of ornithopod and sauropod tracks is rare in Asia and globally, and compares with assemblages from South Korea, a similar Cretaceous paleolatitude (ca. 30°).

A comparative study on the illite crystallinity and the clay mineral reflectance spectral index for subdividing the very low-grade metamorphic belt along the Lizhou-Hekou geological section in the Youjiang sedimentary basin, Guangxi, China

To examine the application potential of hyperspectral remote sensing techniques in classifying very low-grade metamorphic belts, the composition of clay minerals and the cyrstallinity of illite from mudstones were measured using XRD and VIS-SWIR (400—2500 nm) reflectance spectroscopy. Based on the illite cyrstallinity, Kubler Index (KI), the Early Triassic LuoLou Group and the Middle Triassic lower Baifeng Formation were classified as the lower Epizone with KIΔ2 θ ° ranging from 0.22 to 0.25, the upper Baifeng Formation as upper anchizone with KIΔ2 θ ° ranging from 0.26 to 0.33, and the Hekou Formation as lower anchizone with KIΔ2 θ ° ranging from 0.38 to 0.40. According to a KIΔ2 θ ° value of 0.43, it is possible that there may exist a local diagenetic zone in the upper strata. The illite cyrstallinity Kubler index and the metamorphic grade increase from the bottom to the top of the stratigraphic sequence. The metamorphic grade boundaries nearly match the stratigraphic boundaries, indicating a burial metamorphism nature for the stratigraphic sequence. From the bottom to the top of the sequence, the spectral absorption band center of clay minerals from fresh rocks is around 2200 nm. The absorption band centers change towards shorter wavelengths: the Luolou Group being at 2220 nm, the Baifeng Formation at 2217—2213 nm, the lower member of the Hekou Formation at 2214—2206 nm, and the upper member of the Hekou Formation at 2205—2197 nm. The spectral absorption band center of illite shows the same change pattern. These results indicate that very low-grade metamorphic belts can be subdivided using spectral indices of clay minerals, which are measured by using field portable spectroradiometers. However, it may not work well with satellite and airborne sensors.

New paleomagnetic data from the Huanan Block, China, and Cretaceous tectonics in Eastern China

A total of 72 grey-green fine-grained sandstone and siltstone core samples (from 10 sites) were collected from the Early Cretaceous Jieshan and Hekou Formations at Yongan, in the Huanan Block of southeastern China (Fujian Province). After removal of an erratic soft magnetic component in fields of 10–20 mT, stable magnetizations were retrieved from both rock units which are carried mainly by single-domain/pseudo-single-domain (SD/PSD) magnetite or titanomagnetite, as suggested by isothermal remanent magnetization, coercivity measurements and microscopic observations. The Hekou Formation yields a tilt-corrected pole at 66.9°N, 221.4°E ( n=5 sites, K=203.3, A 95=5.4°). A fold test on this result suggests that the magnetization was acquired before tilting which occurred shortly after deposition (between Early and Late Cretaceous). This magnetization is related to a primary sedimentary fabric, as indicated by the low-field anisotropy of magnetic susceptibility (AMS) measurements. The positive fold test and occurrence of a primary sedimentary fabric suggest a depositional origin for the stable magnetization. The Jieshan Formation gives a pole at 70.8°N, 228.7°E ( n=5 sites, K=47.7, A 95=11.2°) in geographic coordinates, which is statistically indistinguishable from the tilted pole for the Hekou Formation. The associated stable magnetization corresponds to a secondary fabric. These features indicate that the Jieshan Formation has been remagnetized during Cretaceous time. The predominance of SD/PSD magnetite or titanomagnetite and igneous activities in eastern Fujian during the Cretaceous suggest a viscous thermal remanent magnetization origin for the secondary magnetization. The Early Cretaceous pole from the Hekou Formation is similar to those for the Yangzi Block, suggesting that the Huanan Block has been accreted to the Yangzi Block at least since Early Cretaceous time. A high consistency of Cretaceous poles from the Sino-Korean, Yangzi and Huanan Blocks as well as Hainan Island indicates that eastern China has been a coherent tectonic unit since Cretaceous time, although there might have been a small amount of northward displacement of the sampling area with respect to the Yangzi Block during the Early-Late Cretaceous period as a result of the overthrust of the Huanan Block onto the Yangzi carbonate platform. Comparison of Cretaceous poles for eastern China with the Eurasian apparent polar wander path (APWP) suggests that no paleomagnetically detectable relative motion has taken place since the Cretaceous. The Cretaceous poles of eastern China, however, display a paleomagnetically significant westward motion (about 9° in angular distance), which is not observed in the Eurasian APWP. This difference may be indicative of a younger age corresponding to the Cretaceous-Tertiary boundary for all Late Cretaceous poles from eastern China, or more probably may imply a minor error in the definition of the Eurasian APWP.