11:00am - 11:15amID: 140
Topics: 1b - Non-marine Cretaceous stratigraphy and terrestrial ecosystem (Xi, Wang, Sames, Dermeval, Zhang)The diachronous development of the rift basins in the Early Cretaceous of northeastern China and its implications
Zhonghe Zhou
Institute of Vertebrate Paleontology and Paleoanthropology, China, People's Republic of China
The Early Cretaceous Jehol Biota that is best known for producing exceptionally complete fossils such as birds, dinosaurs, pterosaurs, mammals, insects, and flowering plants, is preserved in lacustrine deposits interbedded with volcanic ashes. The fossil-bearing beds are from bottom up referred to the Huajiying, Yixian and Jiufotang formations respectively, in rift basins in northern Hebei, western Liaoning provinces in northeastern China. Geochronologic studies have not only constrained the ages of the fossil-bearing beds but also revealed a diachronous distribution pattern of the rift basins, i.e., they progressively migrated eastward. The diachronous development of the rift basins led to the lateral variations of stratigraphic sequences and depositional environments, which in turn influenced the spatiotemporal evolution of the Jehol Biota, i.e., the first stage of the Jehol Biota is restricted to northern Hebei Province and represented by the appearance of basal member of numerous vertebrate lineages, and the second and third stages of the Jehol Biota began in western Liaoning Province and then expanded to a wider area and are represented by a greater vertebrate species diversity. The diachronous development of the rift basins in the Early Cretaceous of northeastern China is controlled by the eastward retreat of the subducting paleo-Pacific plate along the northern margin of the North China Craton and accompanied by other local tectonic and volcanic activities.
11:15am - 11:30amID: 172
Topics: 1b - Non-marine Cretaceous stratigraphy and terrestrial ecosystem (Xi, Wang, Sames, Dermeval, Zhang)Turtle remains from Koh Moul (Koh Kong Province, SW Cambodia) and their stratigraphical implications
Haiyan Tong1,2, Vanchan Lim3, Marc Philippe4, Nareerat Boonchai5, Mouyyi Heng3, Eric Buffetaut6
1Palaeontological Research and Education Centre, Mahasarakham University, Kantarawichai, Mahasarakham 44150, Thailand; 2Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China; 3Cultural Heritage Office, Department of Heritage Parks, Ministry of Environment, Phnom Penh 120101, Cambodia; 4Université Claude Bernard Lyon 1, LEHNA UMR 5023, CNRS, ENTPE, F-69622, Villeurbanne, France; 5Friends of Fossil Forests 705 SE 7th Ave, Gainesville, FL 32601, USA; 6Centre National de la Recherche Scientifique (UMR 8538), Laboratoire de Géologie, Ecole Normale Supérieure, PSL Research University, 24 Rue Lhomond, 75231 Paris CEDEX 05, France
The Mesozoic non-marine formations traditionally known as the so called ‘Grès Supérieurs’ cover vast areas in SW Cambodia. Although macroflora and palynomorphs were reported from the Kampot-Bokor area in the 1970s, other fossils are scanty. A fibula of a titanisauriform dinosaur, reminiscent of Euhelopodidae has recently been described from Koh Paur Island, Koh Kong Province, suggesting an Early Cretaceous age for the fossil-bearing deposits. Subsequent field surveys led to discovery of new fossil sites, with remains of plants, invertebrates and vertebrates.
Turtle shell fragments have been collected from Koh Moul Island in Koh Kong Province, along with abundant fossil wood. The outer surface of the shell is covered with ornamentation, consisting of vermiculated ridges and bulges. The carapace length is estimated at about 80 cm. The morphology of the wide diamond-shaped entoplastron is reminiscent of large basal trionychoid turtles known from the Khorat Goup in NE Thailand, such as Basilochelys macrobios from the Phu Kradung Formation.
Large basal trionychoid turtles are known from the top pf the Phu Kradung Formation and the Sao Khua Formation, as well as equivalent strata in eastern Thailand. They were also reported from Kut Island, Thailand, some 50 km NW of Koh Moul. The discovery of large basal trionychoids in SW Cambodia suggests that the fossil bearing deposits of Koh Moul are Early Cretaceous in age.
11:30am - 11:45amID: 306
Topics: 1b - Non-marine Cretaceous stratigraphy and terrestrial ecosystem (Xi, Wang, Sames, Dermeval, Zhang)Depositional systems, chronostratigraphy and environmental conditions of the rift phase in the central Gondwana context (Lower Cretaceous, Recôncavo Basin, Brazil)
André Pires Negrão1, Dermeval Aparecido Do Carmo2, Marcelo Araujo Carvalho3, Giovanni França Costa1, Rafaela Dantas1, Franklin Bispo4, Luigi Jovane4
1Universidade de São Paulo, Instituto de Geociências. São Paulo, Brazil.; 2Universidade de Brasília, Instituto de Geociências. Brasília, Brazil.; 3Universidade Federal do Rio de Janeiro, Museu Nacional, Departamento de Geologia e Paleontologia. Rio de Janeiro, Brazil.; 4Universidade de São Paulo, Instituto Oceanográfico. São Paulo, Brazil
The Recôncavo Basin, is an aulacogen linked to the opening of the South Atlantic. Currently, its physiography is part of a bay facing the Atlantic, and is located in the metropolitan region of Salvador, state of Bahia. The rift is filled by lacustrine sediments with fluvial systems and deltas on its flexural bounded, and fan deltas and alluvial fans on its active fault bounded. Turbidites and shales fill the central sectors of the lake. This study targets the turbidites of the Maracangalha Formation. Analysis of facies, depositional architecture, biostratigraphy and palynology contributed to the understanding of the paleoenvironmental, paleoclimatic and ages that mark the break-up of Gondwana. The studied outcrops represent part of the turbidite Bouma series, with sandstones beds being very recurrent, suggesting a high seasonal input and a probable link with deltas. Laterally distant outcrops present a scarcity of sandstone facies, suggesting a more distal position within the system or laterally distant from deltaic bodies. Biostratigraphic analyses identified five species of ostracods with chronobiostratigraphic value (Paracypridea brasiliensis, Cypridea ventronodata, Cypridea vulgaris, Theriosynoecum isoplektum and Clinocypris? weileri), correlatable to local biozones and which allowed the investigated deposits to be positioned in the Valanginian. Palynofacies data reveal two distinct depositional settings: one dominated by amorphous organic matter (AOM), consistent with a distal lacustrine environment; and another characterized by a predominance of phytoclasts, indicating a more proximal setting, including reworked Paleozoic material. Given these results, new contributions in terms of paleoenvironments and chronostratigraphic approach for the breakup stages of central Gondwana.
11:45am - 12:00pmID: 396
Topics: 1b - Non-marine Cretaceous stratigraphy and terrestrial ecosystem (Xi, Wang, Sames, Dermeval, Zhang)Evolution of pre-salt lake-systems during Barremian-Aptian: A multiproxy study of high-frequency paleoenvironmental variations
Ariany de Jesus Sousa, Rozileide de Oliveira Lima Costa, Cristiano Ng, Elisabete Pedrão Ferreira, Francisco Henrique de Oliveira Lima, Fábio de Araújo Carvalho, Carlos César Araújo, Carlos Manuel de Assis Silva, Caroline de Oliveira Nardi Leite, Milene Freitas Figueiredo, Isabela de Oliveira Carmo
Petrobras, Brazil
Characterizing paleoenvironments provides input for geological modeling of the Lower Cretaceous from the Santos Basin, thereby reducing the risks and uncertainties with exploration and production processes. Reconstructing and visualising the spatial distribution of paleoenvironments during the Buracica-Alagoas ages contributes to the understanding of the sedimentary and stratigraphic evolution of the basin. In this scenario, the ecological preferences of non-marine ostracods were used to reconstruct the Lower Cretaceous Pre-Salt paleoenvironments of the basin. This reconstruction was based on interpretations of ostracod abundance and diversity values. Three paleoenvironmental lacustrine conditions were recognized: (i) Deep Zone (anoxic conditions); (ii) Open Water Zone (Intermediate Lake); (iii) Littoral Zone (poor preservation in high energy areas). The ostracod rates made it possible to observe conditions in the Deep and Open Water Zones during the Buracica and early Jiquiá ages. In the upper portion of the Jiquiá, there was a high frequency of alternation between lake conditions. During the Alagoas age, the Littoral Zone predominated. In addition to the previous study, analysis of ratios, grades of minor elements and trace elements, as well as the calculation of rare earth element anomalies, was. The enrichment of certain minor elements and traces may reflect variations in the depositional environment's oxidation state and solubility. In the intermediate to upper Alagoas, thick intervals with positive Eu anomalies indicated the influence of mafic magmatism or reworking of mafic rocks to the basin.
12:00pm - 12:15pmID: 385
Topics: 1b - Non-marine Cretaceous stratigraphy and terrestrial ecosystem (Xi, Wang, Sames, Dermeval, Zhang)The Songhuajiang Biota, a window to understanding Late Cretaceous terrestrial ecosystem
Dangpeng Xi, Zihan Zhou, Zhongye Shi, Tianpeng Huang, Ziyuan Xiao, Xiaoqiao Wan
China University of Geosciences, Beijing, People's Republic of China
The Songliao Basin is one of the largest non-marine oil and gas bearing basins that developed during the Cretaceous period, recording an almost complete Cretaceous stratigraphy. Fossils are very abundant in the Songliao Basin, and three biotas, including the Jehol Biota sensu lato, the Songhuajiang Biota and the Mingshui Biota are recognized in the Songliao Basin. Of which the Songhuajiang Biota is the most typical and unique, serving as a window to understanding the Late Cretaceous terrestrial ecosystem. The Quantou to Nenjiang Formations yielded extremely abundant fossils,including: ostracoda, conchostraca, bivalvia, gastropoda, insecta, testudines, grocodylomorpha, dinosauria, palynofossils, dinoflagellates, charophyta, which are rich in quantity, diverse in types, and well-preserved in these strata, especially in the lower Qingshankou Formation and Nenjiang Formation. These fossil assemblages are named the Songhuajiang Biota. Here, we define and introduce the Songhuajiang Biota in terms of its definition, biological composition, and ecological significance. The Songhuajiang Biota, is defined by three typical elements: The ostracod Cypridea, the fish Sungarichthys, and the clam shrimp Eoestheria. The Songhuajiang Biota is the typical and unique terrestrial biota of the mid-late Cretaceous. As a typical and unique terrestrial biota of the mid-late Cretaceous, the Songhuajiang Biota is a key to decoding the Cretaceous terrestrial ecosystem.
12:15pm - 12:30pmID: 131
Topics: 1b - Non-marine Cretaceous stratigraphy and terrestrial ecosystem (Xi, Wang, Sames, Dermeval, Zhang)Upper Cretaceous (Maastrichtian) endemic ostracods, charophytes and dinosaurs from the Lameta Formation at Jabalpur, Madhya Pradesh, India: palaeoenvironment, palaeobiogeographic and biostratigraphical implications
Ashu Khosla
Geology department, Panjab University, Chandigarh, India
Ostracod assemblages comprising over 30 species and a charophyte gyrogonite assemblage—including Platychara cf. sahnii, Nemegtichara grambastii, and Microchara sp.—have been identified from the Lameta Formation at Bara Simla Hill and Chui Hill near Jabalpur. These fossil-rich beds, underlying the Deccan basalts, are interpreted as pedogenically modified alluvial plain deposits laid down in semi-arid conditions. They are notable for abundant dinosaur bones and nesting sites containing three eggshell oospecies (Megaloolithus cylindricus, M. jabalpurensis, and Fusioolithus baghensis), indicating a Late Cretaceous (Maastrichtian) age. The ostracods are mostly endemic, while Microchara and Nemegtichara are also restricted to the Indian subcontinent. Biogeographically, the assemblage aligns with other infratrappean and intertrappean deposits across India. The co-occurrence of dinosaur remains, ostracods, and charophytes suggests lacustrine to palustrine conditions, with alkaline, shallow freshwater environments. Charophytes confirm the non-marine nature of the sediments and support age estimates, with Platychara and Nemegtichara known from Upper Cretaceous to Lower Palaeocene strata elsewhere. A Maastrichtian age is further corroborated by the presence of freshwater fish (Rhombodus, Apateodus, Stephanodus), endemic ostracods (Candona, Cyclocypris, Cypridea (Pseudocypridina), Cypridopsis, Cyprois, Limnocythere, Mongolocypris, Paracandona, Paracypretta, Stenocypris, Zonocypris and Wolburgiopsis sp.), and Aquilapollenites in the pollen record. Stratigraphically, the Lameta beds at Chui Hill show reversed magnetic polarity (Chron C29R), overlain by normally magnetized basalts, then a thick reversed lava pile, matching the Cretaceous–Paleogene boundary sequence. The Lameta Formation’s faunal and floral evidence, along with geochronology and magnetostratigraphy of the Deccan basalts (65.6 ± 0.3 Ma), firmly places these deposits in the latest Maastrichtian.
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