Mesozoic

A new species of Heterochordeumatidae (Myriapoda: Diplopoda: chordeumatida) from mid-cretaceous Burmese amber

YI-TONG SU, CHEN-YANG CAI, DI-YING HUANG — Thu, 26 Sep 2024 00:00:00 +1200

A new species of millipede from the family Heterochordeumatidae, Heterochordeuma liae sp. nov., is described from mid-Cretaceous Burmese (Kachin) amber. The detailed morphological characteristics of this species are provided based on the examination of 14 specimens, primarily utilizing confocal laser scanning microscopy. This new species can be confidently assigned to the extant genus Heterochordeuma due to its extended and polydesmidan-like paranota, 32 body rings in male and distinctive curved anterior gonopods, modified coxites 9, and leg-pair 10. A comprehensive comparison with extant species is also presented.

**Investigation of Cretodorus (Hemiptera: Fulgoromorpha: Mimarachnidae) based on new adult and nymph fossils from mid-Cretaceous Myanmar amber**

Thu, 26 Sep 2024 00:00:00 +1200

Here we report a new species, Cretodorus lijuanae sp. nov., of extinct Mimarachnidae from mid-Cretaceous amber of northern Myanmar. C. lijuanae sp. nov. was described based on one adult and three nymphal fossils. The new adult specimen exhibits the diagnostic features of Cretodorus and possesses a unique number and arrangement of sensory pits in the pronotum: nine sensory pits on one side, with five sensory pits between median and pronotal carinae and four sensory pits between lateral carina and margin, which is consistent in the nymphs. We also conduct morphometric analyses of forewings of all known species of Cretodorus, demonstrating that morphometrics are effectively discriminative for identifying Cretodorus fossils featuring few longitudinal veins and minimal differences in venation. Additionally, we report the nymphal fossils of Mimarachnidae for the first time. Three nymphal fossils, preserved in the same piece of amber alongside the adult specimen, exhibit the same nodule pattern on the thoracic notum in dorsal view, suggesting a feature linking adult and nymph of Mimarachnidae. These new specimens show morphological characteristics of the different developmental stages of C. lijuanae sp. nov., increasing the diversity of the Mimarachnidae in mid-Cretaceous amber from Myanmar. The preservation of three nymphs of the same age with an adult in the same piece of amber likely indicates aggregation behaviour in Mimarachnidae.

New age constraints for the upper zongshan Formation: a morphometric study of the late cretaceous orbitoidal foraminifera in Gamba area of southern Xizang (Tibet)

PEI-YUE FANG, YUE SUN, HUI LUO, YOU-HUA ZHU — Thu, 26 Sep 2024 00:00:00 +1200

This study refines the biostratigraphic framework of the upper Zongshan Formation in southern Xizang (Tibet) by conducting a meticulous morphometric analysis of larger benthic foraminifera (LBF) from the Gamba area. Focusing on the genera Orbitoides and Omphalocyclus, we employed a comprehensive morphometric approach to delineate the stratigraphic transition within the formation. A total of 42 samples were collected across pivotal lithological intervals, leading to the identification of species groups that provide precise age constraints for the upper Zongshan Formation. Specifically, the O. tissoti–O. media group and Om. anatoliensis within Limestone II to Calcareous Marl II support a late Campanian age, while the presence of the O. megaloformis–O. gruenbachensis group and potential Om. cideensis in Limestone III suggest a younger age bracket extending into the early Maastrichtian. Our findings not only clarify the stratigraphic position of the upper Zongshan Formation but also contribute significantly to the ongoing investigations of final evolutionary stages of the eastern Neotethys.

New zircon U-Pb age of the top Duoni Formation, Basu County: constraits on the collision between Qiangtang and Lhasa blocks in Eastern Tibet

Thu, 26 Sep 2024 00:00:00 +1200

The Duoni Formation is widely distributed along the Bangong-Nujiang suture belt and surrounding blocks in Tibet, serving as a key sedimentary record of the collision between the Qiangtang and Lhasa blocks. The upper sections of the formation typically contain andesite, volcanic rocks and tuff offering potential for precise stratigraphic correlations across the suture belt. The Duoni Formation in the central and western belt has been well-constrained geochronologically through zircon U-Pb dating; however, the insufficient age constraints on Duoni Formation in eastern Tibet hinder effective stratigraphic correlation and limit the understanding of the timing of this collision. Building on prior stratigraphic and paleontological studies, we collected three tuff samples from the upper Duoni Formation at the Wada coal mine section in Basu County, eastern Tibet. Zircon U-Pb dating was used to determine the age of the Duoni Formation, yielding results of 112.8 ± 1.0 Ma for sample XZ01, 111.48 ± 0.37 Ma for sample XZ03, and 110.95 ± 0.41 Ma for sample XZ05. These absolute ages correspond with early Albian and are generally consistent with those absolute ages from the central and western suture belt. Our study therefore suggests the similar timing for the Qiangtang-Lhasa collision across the whole Bangong-Nujiang belt.

**A new species of Hadraulacus Li, Shih & Ren, 2023 (Hymenoptera: Praeaulacidae) from mid-cretaceous Kachin amber**

CORENTIN JOUAULT, DI-YING HUANG — Thu, 26 Sep 2024 00:00:00 +1200

A new praeaulacid species, Hadraulacus liae sp. nov., is described and illustrated based on a female specimen from mid-Cretaceous Kachin amber. This new species reinforces the validity of key diagnostic characters used to define the genus Hadraulacus Li, Shih & Ren, 2023, such as the absence of the 2rs-m crossvein in the forewing. However, it also demonstrates that some traits previously considered diagnostic for the genus, like the tibial spur formula (1-1-2), represent mere interspecific variation and have limited taxonomic value. While the discovery of this species adds to the known diversity of Praeaulacidae in the mid-Cretaceous Kachin amber, it also highlights that the diversity of the subfamily Praeaulacinae within this biota remains significantly underestimated.

The third mesomegaloprepid damselfly from the mid-Cretaceous Kachin amber (Odonata: Zygoptera)

ANDRÉ NEL, YE-HAO WANG, DI-YING HUANG — Thu, 26 Sep 2024 00:00:00 +1200

Mesomegaloprepus liea sp. nov., the third species of the family Mesomegaloprepidae, is described from mid-Cretaceous Kachin amber. To date, this family is only known from the Cretaceous Burma paleo-island (also referred to as the Burmese terrane), although it probably originated in the Gondwana continent during the early Cretaceous. It possibly knew a phenomenon of endemism diversification.

**First fruit record of Pterocarya (Juglandaceae) from the upper Eocene of the central Qinghai-Tibetan Plateau, China**

XIANG-BO SONG, ZI-XI WANG, TAO SU, CHONG DONG, DI-YING HUANG — Thu, 26 Sep 2024 00:00:00 +1200

The Juglandaceae family experienced significant diversification during the early Tertiary, as evidenced by fossil records showing a broad expansion of both extant and extinct taxa. The genus Pterocarya is characterized by its distinctive fruit with butterfly-shaped wings and a small nutlet. Macrofossil records suggest that this genus was distributed widely in the Northern Hemisphere. However, the fossil record of Pterocarya in China is limited. In this study, we describe a well-preserved Pterocarya fossil winged fruit from the middle-upper member of the Niubao Formation (the upper Eocene) of the central Qinghai-Tibetan Plateau, China. The winged fruit is identified as Pterocarya liae sp. nov. based on detailed morphological comparison, representing the earliest known record of Pterocarya winged fruit in Asia. The new finding extends the paleobiogeographic distribution of Pterocarya during the Eocene and provides new insights into the early stage of the diversification of this genus.

Cretabaltoraea volsella gen. et sp. nov. (Coleoptera: Nitidulidae) from Cretaceous Kachin amber and its relationship with Eocene Baltoraea (Coleoptera: Nitidulidae)

Thu, 26 Sep 2024 00:00:00 +1200

Here we describe Cretabaltoraea volsella Peris, Jelínek & Audisio gen. et sp. nov. of the family Nitidulidae (Coleoptera). As implied by its generic name, the new species is described after a fossil specimen preserved in the Upper Cretaceous Kachin amber from northern Myanmar. This new species is rather similar to the two fossil nitidulid species of Baltoraea Kurochkin & Kirejtshuk, 2010, previously described from the Eocene Baltic amber. The comparison between this group of fossils and the study of Baltoraea simillima Kurochkin & Kirejtshuk, 2010 using CT-scanning suggest that Cretabaltoraea volsella gen. et sp. nov. and the two Baltoraea species should be placed in the extinct Apophisandrinae, a basal subfamily of Nitidulidae which until now only includes a group of Cretaceous fossils from the Kachin amber, described as ancient pollinators of both gymnosperms and basal angiosperms.

Amberground serpulid polychaetes on mid-Cretaceous Burmese amber

YUAN-YUAN ZHANG, DI-YING HUANG — Thu, 26 Sep 2024 00:00:00 +1200

The mid-Cretaceous Burmese (Kachin) amber is renowned for its diverse inclusions and the insights they provide into ancient biodiversity. Several amberground marine animals have been hitherto reported. Here, we document a new amberground discovery: polychaete dwelling tubes, suggesting a coastal environment inhabited by multiple serpulid species. This finding provides further insights into the depositional palaeoenvironment and palaeoecology of the Burmese amber.

Late Cretaceous rapid exhumation of the Central Tibetan Plateau: Insights from low-temperature thermochronology

SI-QI LI, GAO-YUAN SUN, TIAN-NAN YOU, XIU-MIAN HU — Fri, 27 Sep 2024 00:00:00 +1200

The uplift history of the Tibetan Plateau is a hot topic for the geological study. The Lhasa terrane, situated on the southern edge of Eurasian plate, records the tectonic evolution of the Tibetan Plateau preceding the collision between the Indian and Eurasian continental plates. This paper employs low-temperature thermochronological methods, including zircon and apatite (U-Th)/He dating, as well as apatite fission track (AFT) analysis, to investigate the Bange pluton in the northern Lhasa terrane. The research results indicate that the zircon and apatite helium (ZHe and AHe) ages from the plutons range from 90 to 78 Ma and 83 to 63 Ma, respectively, while the AFT ages span from 65 to 46 Ma. Thermal history reveals that the Bange pluton experienced a rapid cooling phase during the Late Cretaceous (from ~94 to 70 Ma), with a cooling rate of ~4.2 °C/Ma, subsequently followed by a slow cooling rate with ~1.1 °C/Ma. These results suggest that the Bange pluton has underwent rapid uplift during the Late Cretaceous to Paleocene. This Late Cretaceous rapid cooling event is also observed in other regions of the Lhasa terrane, indicating a widespread period of rapid cooling and exhumation. Since the Cenozoic, the cooling rate of the Bange pluton has significantly decreased, which would suggest that the tectonic uplift of the central Tibetan Plateau may not be related to the India-Asia continental collision. Considering the regional tectonic context, the collision between the Lhasa terrane and the Qiangtang terrane during the Late Jurassic to Early Cretaceous may have initiated the exhumation of the Lhasa terrane in the Late Cretaceous.

An Early Cretaceous radiolarian assemblage from the strata south to the Zhongba microterrane in the Zhongba area, southern Tibet

ZHI-HAO HE, XIN LI, YA-LIN LI, JIAN-BO CHENG — Fri, 27 Sep 2024 00:00:00 +1200

The presence of the Zhongba microterrane causes the Yarlung–Tsangpo suture zone to be bifurcated into two parts in its western segment: the Northern Ophiolitic Belt and Southern Ophiolitic Belt. This indicates that the evolution of the Neo-Tethys Ocean in the western segment is more complex than previous interpretation. Between the Southern Ophiolitic Belt and the Zhongba microterrane, there exists a successive stratigraphic sequence. In this study, a total of 15 genera belonging to 20 species of radiolarians were identified from the siliceous strata of the Dangxin Formation within this sequence, constraining the age of the Dangxin Formation to the Barremian, Early Cretaceous. Additionally, a stratigraphic column was constructed based on the basic understanding of this stratigraphic sequence from regional geological surveys, and it was compared with deep-water sediments in the Tethyan Himalaya. The results show that this sequence can be correlated with the Rilang, Duobeng, Chuangde, and Zongzhuo formations, which were deposited on the passive margin of the Indian plate.

Discovery of ≥ 105 Ma continental redbeds in the Qiangtang Block: Implications for the early uplift of central Tibet

AN-LIN MA, XIU-MIAN HU, EDUARDO GARZANTI, WEI-WEI XUE — Fri, 27 Sep 2024 00:00:00 +1200

The Abushan Formation represents the oldest continental redbed deposit overlying Triassic-Jurassic marine strata in the Qiangtang Block. Knowledge of the exact depositional age of the Abushan Formation is important to reconstruct early history of surface uplift in central Tibet. Pollen and magneto-stratigraphy studies from central Qiangtang suggest that the Abushan Formation was deposited during the mid-Cretaceous; however, confirmation through isotopic geochronological data is still required. Here we describe the newly studied Madeng section exposing fluvial Abushan Formation redbeds at the base and felsic volcanic rocks at the top. SIMS U-Pb dating of zircons from one sample of these volcanic rocks yield a weighted mean ²⁰⁶Pb/²³⁸U age of 105.1 ± 0.9 Ma, indicating latest Early Cretaceous (late Albian) deposition of the Abushan Formation. Our data support the Abushan Formation redbeds were deposited in intermontane basins in an intra-plate tectonic setting following the collision, suturing, and amalgamation of the Qiangtang and Lhasa blocks.

The fate of the Xigaze forearc basin after Late Cretaceous filling (South Tibet)

Fri, 27 Sep 2024 00:00:00 +1200

The Xigaze forearc basin is a key region to understand the evolution of active continental margins related to Neo-Tethyan oceanic subduction. Most studies have focused on the sedimentary evolution during filling of the marine basin, but we here provide a detailed sedimentological and biostratigraphic analysis of the last, uppermost Cretaceous to Paleogene phases of forearc sedimentation documented by the shallow marine to deltaic to fluvial Qubeiya, Quxia, and Jialazi formations exposed in the Cuojiangding area. By comparing these sequences with regional tectonic and global climate events and sea-level curves, a reconstruction of the environmental evolution during this final filling stage is proposed, placing emphasis on the eustatic control of carbonate deposition in the Qubeiya and Jialazi formations. These transgressive intervals are separated by two regressive episodes unrelated to global sea-level trends that led to the demise of the carbonate platform. The first episode, documented by fan-delta deposits of the Quxia Formation, occurred at the time of initial India-Asia collision. The second episode, documented in the central part of the Jialazi Formation, occurred during the Paleocene-Eocene Thermal Maximum, likely driven by an intensified hydrological cycle. These results provide new insight into the palaeo-tectonic and palaeo-environmental evolution during the closure of the Neotethys seaway between India and Asia.

A review of the radiolarian faunas in the Bangong-Nujiang Suture Zone: Implications for the tectonic evolution of the Mesotethys Ocean

RUO-LAN LIAO, XIN LI, XIAO-HUI CUI, YI-CHUN ZHANG — Fri, 27 Sep 2024 00:00:00 +1200

The Bangong-Nujiang Suture Zone in the Qinghai-Tibet Plateau marks the evolution of the Mesotethys Ocean, which has been the subject of considerable debate regarding its opening time, evolutionary pattern, and closing process. This suture zone consists of three ophiolitic mélange zones, with their evolution and relationships far from being fully understood. As an important microfossil in deep-sea sedimentation, radiolarian plays an irreplaceable role in revealing the development timeline of oceanic basins and palaeogeographic reconstructions. This paper is designed to review the existing radiolarian records in the Bangong-Nujiang Suture Zone with the purpose of constraining the evolution of the Mesotethys Ocean. The radiolarian faunas in the Bangong-Nujiang Suture Zone suggest that the Mesotethys Ocean must have opened before the Middle Triassic according to the record of Anisian radiolarians. At the same time, the Beila-Nagqu Ocean, a branch of the Mesotethys Ocean, should have already opened. The presence of diverse Jurassic and Cretaceous radiolarians in the Shiquanhe-Namtso mélange zone confirms that the Mesotethys Ocean was still a broad oceanic basin during the Early Cretaceous. Many similar radiolarian assemblages were found in the western section of the Bangong-Nujiang Suture Zone and the Yarlung-Tsangpo Suture Zone, suggesting a connection between the Mesotethys and Neotethys oceans during that time.

Palaeoenvironmental analysis of the Langshan Formation in the Xiongba area

YI-WEI XU, WEN LAI, XIU-MIAN HU — Mon, 30 Sep 2024 00:00:00 +1300

The mid-Cretaceous Langshan Formation is a massive limestone unit, outcropping typically in the northern Lhasa block. A Xiongba section, measured near the type section of the Langshan Formation, is here described. The succession consists of orbitolinids limestone, where eight microfacies have been recognized. The lower part of the Langshan Formation consists of discoidal orbitolinids with other heterotrophic associations, including echinoderms, sponge spicules, and bivalves. In contrast, the upper part of the Langshan Formation features conical orbitolinids with an abundance of green algae and small benthic foraminifers. We interpret the morphological changes in orbitolinids as being influenced by bathymetry. Consequently, the microfacies variations in the Langshan Formation in the Xiongba section represent a shallowing upward sequence.

**New insights into Tibetodus gyrodoides Young & Liu, 1954 (Actinopterygii, Pycnodontiformes) from the Qinghai-Xizang Plateau based on micro-CT data**

GENG-YU FANG, FEI-XIANG WU — Mon, 30 Sep 2024 00:00:00 +1300

The Pycnodontiformes is a distinctive group of fossil actinopterygian (ray-finned) fishes from the Late Triassic to Palaeogene. Tibetodus gyrodoides, reported in 1954, represents the only known fossil record of this group in China, holding significant scientific and historical importance. In this study, non-destructive techniques such as scanning electron microscopy (SEM) and micro-computed tomography (micro-CT) were utilised to reexamine the specimen, providing new insights into both the surface morphology and internal structures of the vomer and its teeth and investigating the process of tooth wear. A tooth covered by matrix was also discovered. Furthermore, an Elliptical Fourier Analysis (EFA) was conducted to quantitatively analyse the morphology of the palatal teeth in this specimen, adding new data for future research on pycnodontiforms and their feeding behavior.

Temporal scaling of carbon emission accumulations and rates of the Meso-Cenozoic hyperthermal events: implication to the Anthropocene global warming

XIU-MIAN HU, JING-XIN JIANG, YUAN CAI, ZHONG HAN, YI-WEI XU — Mon, 30 Sep 2024 00:00:00 +1300

Anthropocene global warming is largely associated with fossil fuel carbon emissions. Temporal scaling provides a way to place current carbon emissions on a geological scale. The scaling of carbon emissions at the onset of hyperthermal events suggests that we might anticipate higher carbon emission rates over longer time scales than what we currently observe in the Anthropocene. However, this inference is uncertain due to limited data concerning the accumulations and time intervals of carbon emissions of Meso-Cenozoic hyperthermal events. While on the long-time hyperthermal-event scales of several to hundreds of kiloyears, modern carbon accumulations and emission rates are 9 times greater than those of the hyperthermal-event emissions. The present-day carbon release can be effectively compared to the onset of hyperthermal events through temporal scaling. If current carbon emission trends persist, we may reach the carbon emission thresholds for hyperthermal events in one to three hundred years, getting an intensified hydrological cycle, enhanced continental weathering and ocean acidification. And if the situation gets worse, we may reach the upper limit of the carbon emission threshold for hyperthermal events (e.g., Permian-Triassic Boundary event, PTB) with a biotic mass extinction over four to thirteen hundred years. This study offers new insights into current carbon emissions from a temporal scale perspective, enhancing our understanding of contemporary climate change.

The depositional differences of confined and unconfined turbidite sheet systems

QUN LIU, XIANG-YANG JI — Mon, 30 Sep 2024 00:00:00 +1300

The depositional architecture between unconfined and confined turbidite sheet systems are increasingly recognized, but the major differences are not summarized. This paper aims to summarize the major differences based on the well-studied published systems with known degree of confinement and depositional architectures. The unconfined and confined turbidite sheet systems differ greatly in four aspects: sedimentary facies, stacking patterns of individual beds, facies associations and onlap styles. The sedimentary facies in confined systems are mainly thick beds, occasionally with grain size breaks, overlain by thick mud caps; whereas beds in unconfined turbidite systems present less mud proportion. The stacking patterns in confined systems in mainly vertically stacked, whereas compensationally stacked in strike direction, and progradationally or retrogradationally stacked in dip direction. One facies association have only been identified in confined systems and four facies associations are found in unconfined systems. The vertical log of unconfined turbidite sheet systems presenting a transition of facies association, whereas no transitions in confined systems. The depositional architecture of turbidite sheet systems is controlled by both sediment supply and basin relief. The establishment between degree of confinement and various parameters in this study can be applied in the petroleum industry.

Influence of climate and marine transgression on Mesozoic–Cenozoic diagenesis of clastic rocks in the Tabei Uplift, Tarim Basin, China

Mon, 30 Sep 2024 00:00:00 +1300

The Mesozoic–Cenozoic clastic rocks in the Tabei Uplift form one of the most hydrocarbon-rich zones in the Tarim Basin of China. Understanding how diagenesis has affected the petrophysical properties of the sandstone is crucial for developing regional exploration strategies. Although most studies have investigated the physical conditions during sedimentation and chemical processes during diagenesis, the hydrochemical environment during sedimentation and subsequent diagenesis has received little attention. This study employed petrographic observations, paleo-geothermal reconstructions, and paleoenvironmental analysis to constrain the regional climatic conditions, hydrochemical environment of deposition, and diagenetic features of clastic rocks in the Tabei Uplift. The sandstone at depths of 3500–6000 m is located mainly in the A phase of the middle diagenetic stage, and exhibits three types of diagenesis. Triassic–Jurassic sandstones are dominated by silica, kaolinite, and chlorite cements, Cretaceous sandstones by mainly carbonate cements, and Paleogene sandstones by carbonate and evaporite cements. These diagenetic stages correspond to paleoclimatic changes during the earliest Late Jurassic and the maximum marine transgressions of the Proto-Tethys during the Paleogene, thereby highlighting the influence of climatic change and transgressions on the water conditions during deposition and the type of diagenesis.

In memory of Dr Juan Li, a young geologist (1987–2023) (Front matter)

XIN LI, AN-LIN MA — Thu, 26 Sep 2024 00:00:00 +1200

A special issue for Second Tibetan Plateau Scientific Expedition and Research project (grant no. 2019QZKK0706)

In memory of Dr Juan Li, a young geologist (1987–2023)

Thu, 26 Sep 2024 00:00:00 +1200

This special issue of Mesozoic is dedicated to the memory of a great specialist in carbonate sedimentology, Dr Juan Li, who passed away on July 19^th, 2023. Juan Li sadly left us while logging the Paleocene-Eocene thermal maximum (PETM) interval in the Tibetan Himalaya. This special issue has collected contributions to Mesozoic–Cenozoic geological studies from the Qinghai-Tibet Plateau from colleagues, friends, and fellow scientists to express our remembrance and regret.

**Updates to Burmapsyllidium setosum (Protopsyllidioidea: Paraprotopsyllidiidae)**

MARINA HAKIM — Thu, 26 Sep 2024 00:00:00 +1200

Burmapsyllidium Hakim, Azar & Huang, 2021 is an extinct hemipteran genus, known only from amber bioinclusions. To date, it encompasses the two species, Burmapsyllidium setosum Hakim, Azar & Huang, 2021 and Burmapsyllidium grimaldii Hakim, Azar & Huang, 2022, both discovered in mid-Cretaceous Burmese amber (Hakim et al., 2021, 2022). This genus is interesting amongst the Paraprotopsyllidiidae, as it is the only taxon displaying M two-branched in the forewings—like in other Protopsyllidioidea where M is two-, three- and rarely four-branched—while the rest of Paraprotopsyllidiidae have M simple. In this work, I revise the diagnosis of Burmapsyllidium setosum and provide a correction to the morphology of the tarsomeres (claws) observed in the type material.