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A continuous terrestrial succession was recovered from the Songke‐2 (SK‐2) borehole in the Songliao Basin, Northeastern China. This borehole provides a unique material for further research on the continental paleoclimate during Cretaceous greenhouse period, following a series of achievements of the Songke‐1 (SK‐1) core. In this study, thorium (Th) logging data were chosen as a paleoclimate proxy to conduct a detailed cyclostratigraphic analysis. The Th series varies quasi‐periodically; power spectra and evolutionary fast Fourier transformation (FFT) analysis reveal significant cycles in the Quantou (K2q), Qingshankou (K2qn), Yaojia (Ky and Nenjiang (K2n) formations. The ratio of cycle wavelengths in these stratigraphic units is approximately 20:5:2:1, corresponding to long orbital eccentricity (405 kyr), short orbital eccentricity (100 kyr), obliquity (37 kyr), and precession cycles (22.5 kyr and 18.4 kyr). The durations of the K2n, K2y, K2qn and K2q are estimated as 6.97, 1.83, 5.30 and 4.52 Myr, respectively, based on the constructed ∼18.62 Myr "floating" astronomical time scale (ATS). Comparison of the durations between the SK‐1 s and SK‐2 boreholes exhibits a slight difference of 0.06 Myr and 0.459 Myr for K2qn and K2y. Nevertheless, our ATS of K2n supports the chronostratigraphic frame constructed by the CA‐ID‐TIMS data of the SK‐1s borehole. This new "floating" ATS provides precise numerical ages for stratigraphic boundaries, biozones and geological events in the Songliao Basin, and can serve as a basis for correlation of strata and events between marine and terrestrial systems. [ABSTRACT FROM AUTHOR]

Abstract: The Early Cretaceous Jehol Biota in northeastern China provides an evolutionary window for ‘feathered’ dinosaurs, primitive birds, insects and early flowering plants. It also provides critical information for the biodiversity changes of the Early Cretaceous terrestrial ecosystem. Here we report a time series analysis for the 11.2-m-thick, fossil-bearing lacustrine deposits at the Sihetun section in western Liaoning, northeastern China on the basis of high-resolution magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) measurements. A hierarchy of sedimentary cycle bands of 120–260cm, 50–67cm and 18–42cm was recorded in the MS and ARM series. With available radioisotope age constraints from the same section, sedimentary cycles of 120–260cm, 50–67cm and 18–42cm were interpreted as Milankovitch cycles of short eccentricity (130 and 95kyr), obliquity (36.6 and 46kyr), and precession (22.1, 20.9 and 18kyr), respectively. The 100kyr-tuned ‘floating’ astronomical time scale indicates that the duration of the 11.2-m-thick section is ~0.67Myr and the average depositional rate is ~1.70cm/kyr. The duration of the 1.8-m-thick, main fossil-bearing interval that contains 8 beds of ‘feathered’ dinosaur/primitive bird fossils can be estimated as short as 150kyr. The results suggest that climate fluctuations manifested in paleobotanical, sedimentological and geochemical records of the Yixian Formation may have been controlled by orbital forcing during Early Cretaceous. [Copyright &y& Elsevier]

Abstract: The mechanism responsible for the regulation of long-term climate stability is still an enigma in principle. The geochemical CO2 cycle in the Earth''s surface system is thought to be a fundamental mechanism in the regulation of Earth''s climate. However, this idea has often been criticised for many reasons. Here, we conducted a spectrum analysis on the global marine phosphorus burial records of the Cretaceous ocean with the aim of determining the role of the phosphorus cycle in the regulation of the greenhouse climate. The results show that there are four periodicities of 38, 19, 5.5 and 12.1myr existing in the record, with the first three bands indicating the contribution of the semi-periodical burial of phosphorus in the ocean to the stabilisation of long-term Cretaceous greenhouse climate implemented by the coupling of carbon and phosphorus cycle. With stronger tectonic activity, more CO2 was emitted to the atmosphere, leading to a warmer climate. However, the chemical weathering was accelerated and at the same time, the input of phosphorus to the ocean increased the burial of organic carbon, resulting in a higher consumption of CO2. It is interesting to note that this is the first time that the palaeoclimatic significance of the 38myr band for the marine phosphorus burial record during the Cretaceous, and potentially for the greenhouse period of 34myr to the start of the Cretaceous, has been clearly identified. Further work is still needed to explore the significance of the band of 12.1myr. [Copyright &y& Elsevier]

Abstract: A paleomagnetic study has been carried out on the Early Cretaceous Zenong Group volcanic rocks (ca. 110–130Ma) near Cuoqin town in the central Lhasa terrane. Stepwise thermal demagnetization up to 680°C isolated a stable high-temperature component (HTC) including antipodal dual polarities. The HTC directions passed both a fold test at 99% confidence and a reversal test at 95% confidence, suggesting a primary origin. The tilt-corrected average direction for 18 sites is D=327.0°, I=35.7°, κ=59.3°, α95 =4.5°, which corresponds to a paleopole at 58.2° N, 341.9° E (A95 =4.6°), yielding a paleolatitude of 19.8°±4.6° N for the study area. Our results, combined with previous paleomagnetic data, suggest that southern Tibet was at a mean paleolatitude of 20° N during the Cretaceous and Paleogene. When compared with the apparent polar wander paths of Asia, the difference suggests that only ca. 870km north–south crustal shortening has accumulated between the Lhasa terrane and stable Asia since ca. 110Ma. When comparing the paleolatitudes of the Lhasa terrane and India, the results indicate that the width of the Neotethys was 6720±690km during the Early Cretaceous. [Copyright &y& Elsevier]

Abstract: The south borehole (SK-1s) of the China Cretaceous Continental Scientific Drilling project (Songke 1) penetrated the Late Cretaceous lacustrine sediments in the central depression of the Songliao Basin, Northeast China, in order to reveal the terrestrial records of the Cretaceous climate changes. High-resolution rock magnetic records were obtained on the Qingshankou Formation (K2qn) of SK-1s. The results indicate that detrital magnetite is the main remanence-carrier of the K2qn Formation; while both magnetite and paramagnetic minerals, including clay minerals and pyrite, dominantly contribute to magnetic susceptibility. Although reductive diagenesis may have more or less effect on the magnetic signals of the K2qn Formation, they recorded ancient lake-level changes well, resulting both from the tectonic development of the basin and from the Milankovitch astronomical paleoclimatic changes. The first-order vertical trends of the rock magnetic records were controlled by the shallowing-upwards of the lake-level, caused by the tectonic uplift of the basin. The short-term variations of the rock magnetic records were controlled by the lake-level periodical drift, caused by the fluctuations of the rainfall of the catchment area of the basin, which were controlled by astronomical orbital forcing. In addition, the magnetic records also distinguished two most anoxic periods during the lacustrine anoxic event 1 (LAE1): the sections of 1758–1761m and 1769–1771.5m, which may suggest the two most active periods of surface productivity of the lake. [Copyright &y& Elsevier]

The Cretaceous continental sedimentary records are essential to our understanding of how the terrestrial geologic and ecologic systems responded to past climate fluctuations under greenhouse conditions and our ability to forecast climate change in the future. The Songliao Basin of Northeast China preserves a near-complete, predominantly lacustrine, Cretaceous succession, with sedimentary cyclicity that has been tied to Milankocitch forcing of the climate. Over 900 meters of drill-core recovered from the Upper Cretaceous (Turonian to Campanian) of the Songliao Basin has provided a unique opportunity for detailed analyses of its depositional and paleoenvironmental records through integrated and high-resolution cyclostratigraphic, magnetostratigraphic and geochronologic investigations. Here we report high-precision U–Pb zircon dates (CA-ID-TIMS method) from four interbedded bentonites from the drill-core that offer substantial improvements in accuracy, and a ten-fold enhancement in precision, compared to the previous U–Pb SIMS geochronology, and allow a critical evaluation of the Songliao astrochronological time scale. The results indicate appreciable deviations of the astrochronologic model from the absolute radioisotope geochronology, which more likely reflect cyclostratigraphic tuning inaccuracies and omitted cycles due to depositional hiatuses, rather than suspected limitations of astronomical models applied to distant geologic time. Age interpolation based on our new high-resolution geochronologic framework and the calibrated cyclostratigraphy places the end of the Cretaceous Normal Superchon (C34n–C33r chron boundary) in the Songliao Basin at 83.07 ± 0.15 Ma . This date also serves as a new and improved estimate for the global Santonian–Campanian stage boundary. [ABSTRACT FROM AUTHOR]

To better constrain the Early Cretaceous paleogeographic position of the Tethyan Himalaya and the India–Asia collision process, a paleomagnetic study was performed on the Lakang Formation lava flows in the Cuona area in the southeastern Tethyan Himalaya. Stepwise thermal and alternating field demagnetizations successfully isolated reliable characteristic remanent magnetization (ChRM) directions that include antipodal dual polarities and pass positive fold tests at the 99% confidence level and reversal tests at 95% confidence level, indicating prefolding primary magnetizations. The distribution patterns of ChRM directions from the Lakang Formation lava flows are consistent with young lava flows at similar latitudes, suggesting that secular variation has likely been averaged out. The tilt-corrected site-mean direction for 31 sites is D = 261.6 ° , I = − 68.5 ° with α 95 = 3.6 ° , which provides a paleopole at 26.8°S, 315.2°E ( A 95 = 5.7 ° ), corresponding to a paleolatitude of 52.2 ° ± 5.7 ° S for the study area. Comparison of the paleolatitude observed from the Lakang Formation lava flows with that expected from the apparent polar wander paths of India at 130 Ma show a paleolatitude difference of ∼2.1° (∼230 km), indicating that neither a great north-south continental crustal shortening occurred between the Indian craton and the Tethyan Himalaya after 130 Ma, nor that a wide ocean separated them at that time. Comparison with reliable Cretaceous–Paleocene paleomagnetic results observed from the Tethyan Himalaya and the Lhasa terrane indicates that the latitudinal width of the Neo-Tethyan Ocean could have been up to ∼7000 km at 134–130 Ma and an extension should have existed between the Indian craton and the Tethyan Himalaya during the Late Cretaceous and Paleocene. Furthermore, reliable paleomagnetic results suggest that the India–Asia collision was a dual-collision process, consisting of a first collision of the Tethyan Himalaya with the Lhasa terrane (Asia) at 54.9 ± 2.3 Ma and a final continent–continent collision of the Indian craton with the Tethyan Himalaya at 40.0 ± 3.3 Ma . [ABSTRACT FROM AUTHOR]