Conference Agenda

The Late Jurassic to Early Cretaceous period is a crucial stage of dramatic climatic and environmental transition in the late Mesozoic. However, our understanding for the climate pattern and its dynamics are still unclear. This contribution presents a data set of magnetostratigraphy age of 151.3 Ma -129.96 Ma for the strata (1061 meters thick) on the Hongliugou Section in the northern Qaidam Basin (East Asia), and the high-resolution environmental magnetism (χ_lf, χ_ARM, χ_fd/HIRM, χ-T, Loop), chromaticity (L*, a*, Redness%, Hm/(Hm+Gt)) and TOC of the fluvial-lacustrine sediments along the Section. The depositional environments on the section from bottom to top are interpreted as shore-shallow lake facies, delta facies and meandering river facies, exhibiting an overall coarsening sequence upward. The variation of proxies depends on the lithology and environmental facies. This indicates their variation can be linked to the climate change. Hence the climate condition recorded by the proxies can be divided into four stages: warm and humid (151.3 Ma -147.5 Ma), hot and arid (147.5 Ma ~ 145 Ma), warm and arid (145 Ma ~ 136.4 Ma), and warm semi-arid (136.4 Ma ~ 129.96 Ma). The trends of the first to third stage are in accordance with variation of global temperature curves, and the transition from second to third stage may be linked to the Jurassic-Cretaceous boundary events. Those reveal that the climate changes in this region were influenced by global change. While the fourth phase, unlike the earlier stages, might have been affected by the paleogeomorphology in the interior Asia.

The carbonate reservoirs of the Brazilian Pre-salt are made up of lacustrine deposits formed in an evaporative and alkaline lake with high concentrations of silica and magnesium. The typical inland lake facies comprises spherulites, shrubs, and magnesian clays. At the marginal regions of the lake, reworked facies, such as grainstones and packstones, indicate an energetic and fluctuating coastline. Based on the analysis of drill cores and thin sections (Santos Basin), diagnostic features of paleosols were identified and described (horizons, structures, bioturbation, colours, dissolution, cementation, neoformation, and illuviation of clay minerals), allowing us to classify them as well-drained paleosols (WDP) and poorly drained (PDP). From an environmental perspective, well-drained paleosols (WDP) are rich in dolomite, overlying areas with karst porosity, indicating a drop in lake level and prolonged periods of subaerial exposure. In turn, poorly drained paleosols (PDP) are rich in organic matter, greenish-grey colours and minerals formed under reducing conditions. Such characteristics indicate palustrine regions (backshore) under the influence of saline waters rich in Mg, where the dolomitization of carbonates occurred due to high evaporation rates. A model of Aptian landscape evolution in the Santos Basin is proposed here, incorporating both tectonic and climatic aspects. The first and fourth authors thank the Brazilian National Council for Scientific and Technological Development (CNPq) for the productivity grants (process 310734/2020–7 and 311491/2019–7, respectively.

The Recôncavo Basin, dated to the Hauterivian–Barremian interval, represents a key yet understudied archive for understanding Early Cretaceous paleoclimatic conditions in Northeastern Brazil, then part of Western Gondwana. Located in the South Atlantic rift phase, this basin offers key insights into pre-Aptian climate dynamics. Palynological analyses from the Maracangalha Formation reveal a high floral diversity (H' = 3.1) and dominance of upland flora (44.7%). Xerophytes are present at relatively moderate levels (35.2%), while hygrophytes (15.2%), tropical lowland elements (4.3%), and hydrophytes (0.7%) are also represented. This composition indicates a humid setting, likely influenced by elevated terrain and a persistent humid belt, possibly associated with early Intertropical Convergence Zone. Globally, this interval coincides with a cooler climatic phase within the Early Cretaceous, characterized by moderate average temperatures that supported humid environments at low latitudes, particularly in regions affected by rifting. In contrast, upper Aptian climatic phases—based on composite records from other northeastern basins—exhibit pronounced environmental shifts. The evaporitic phase is marked by low diversity and strong dominance of xerophytes (up to 76.4%), indicating peak aridity. The post-evaporitic phase, however, shows a reduction in xerophytes (60.9%) and a relative increase in hygrophytes and upland flora, suggesting a return to more humid conditions. Remarkably, the Recôncavo record captures a humid and diverse landscape that is comparable to the pre- and post-evaporitic phases of the Aptian, both known for their more humid conditions. This highlights its importance as a unique paleoenvironmental archive for reconstructing Early Cretaceous climate evolution in South America.

The late Early Cretaceous (121.4 to 100.5 Ma) was characterized by a gradual warming trend superimposed on an already warm greenhouse climate. Whereas the evolution of ocean temperatures during this time interval is relatively well constrained, information on the climatic response of continental interiors is limited. Here we report new paleotemperature estimates based on brGDGT distributions, bacterial membrane lipids used as temperature proxy, from two different sites located within the Choir-Nyalga Basin of central Mongolia including the Shivee Ovoo (SVO) and Tevshiin Govi (TSG) opencast lignite mines. Both sites include lignite-rich continental successions assigned to the Khukhteeg Formation, well known for its exceptionally well-preserved fossil flora. The lignites from both sites exhibit low thermal maturity, as indicated by huminite reflectance, pointing to minimal post-depositional alteration. To reconstruct peat-forming conditions, we combined coal petrology and palynology, with geochemical analyses (TOC, TS, δ¹³C_org) and brGDGT-based paleothermometry. The brGDGT analysis yielded mean annual air temperatures estimates for both sites of approximately 12 ± 3°C at SVO and 10 ± 3°C at TSG. These results represent some of the oldest brGDGT-based paleotemperatures to date and support previous estimates for relatively cool paleotemperatures in Asia during the late Early Cretaceous. The data will be compared with climate model outputs to better constrain boundary conditions for intracontinental climates during greenhouse phases.

North America contains abundant Cretaceous continental strata that hosts potential archives of paleoclimate records. While detailed work has been done in Late Cretaceous strata which not only contains archives for stable isotope proxies, but also leaf physiognomic data, less study has occurred in the Early Cretaceous which lack angiosperm-dominated floras. Here we present new paleotemperature estimates from multiple stable isotope proxies including δ¹⁸O of pedogenic carbonates, clumped isotope paleothermometry, and paired stable isotopes of aquatic and semi-aquatic taxa. The southern-most data originate from the Hensel Formation of South Texas. Clumped isotope paleothermometry of pedogenic carbonates result in temperature estimates between 35°C and 42°C. Clumped isotope paleothermometry of lake and palustrine carbonates from the Cedar Mountain Formation range from 15°C and 31°C for lake carbonates and 20°C to 44°C for palustrine carbonates. Farther north in Wyoming, we utilize the oxygen isotope value of semi aquatic taxa such as crocodilians and turtles to provide a proxy for water and utilize the oxygen isotope value of fish scales and teeth to estimate temperature at 26°C though with significant error. Preliminary clumped isotope paleothermometry provides a temperature of 25°C. The farthest north locality, the Kootenai Formation contains lacustrine, palustrine, and pedogenic carbonates. Utilizing a previous empirically-derived latitudinal gradient of meteoric water, carbonate δ¹⁸O values were used to estimate a temperature range for the Kootenai Formation between 13°C and 28°C. These values provide a temperature gradient for the Aptian-Albian over the mid latitudes of North America of ~-1°C/degree of latitude.

The Early Cretaceous floras are well developed in the Tiefa and Fuxin Basins of western Liaoning and Shansong Floras in Jilin Province, northeastern China. Taxonomically, ferns and cycad are important plant groups in these floras. Among them, two fossil plant taxa are exceptionally significant for palaeogeographical implications, including Acanthopteris and Chilinia. Acanthopteris belongs to fern family Dicksoniaceae and 5 species have been described. Geographically, Acanthopteris shows limited distribution in North and NE China, Siberia and the Inner Zone of Japan, and is restricted to Aptian-Albian period, representing a climate index fossil for a warm and humid climate condition of tropical to subtropical zones during the Early Cretaceous. Chilinia is an extinct genus of cycads, established based on leaf fossils from the Early Cretaceous in Jilin Province, China. Fossil record shows that up to now, 9 species have been reported worldwide, representing an index fossil plant in the Jurassic to Early Cretaceous. Chilinia is mainly distributed from the Middle Jurassic to the late Early Cretaceous. It first appeared in mid-latitudes of both north hemisphere and south hemisphere of Pangea in the Middle Jurassic, and the flora was basically characterized by a humid subtropical climate. Subsequently, it migrated northward to the middle and high latitudes of Laurasia in the northern hemisphere, and seven species developed at the end of the Early Cretaceous. In late Early Cretaceous, the boundary of the flora moved northward, and the flora of Chilinia mainly lived under humid warm temperate climatic conditions with seasonal changes or short aridity.