Details of the three-dimensional morphology of the ichnofossil Phycosiphon incertum collected from deposits on submarine slopes are reconstructed by processing a series of images obtained from polished sections of the samples. Samples were collected from the mudstone around a slump scar in the Paleocene Shiomi Formation, northern Japan, which is characterized by the occurrence of slump scars. The reconstructed morphology of Phycosiphon incertum is a meandering tube with a flattened ellipse cross section. The tubes are flattened in a plane oblique to the bedding surfaces and aligned along the same direction at both the interior and exterior of the slump scar. Flattening of the tubes was likely caused by sediment compaction, and the tube flattens toward the horizontal plane that is oblique to the bedding plane because of the paleoslope inclination. The difference between the bedding and flattening planes of the tubes of Phycosiphon incertum may imply paleoslope inclination. When the inclination of the bedding plane of the Shiomi Formation is corrected using the flattened surfaces, the bedding plane dips by 9؇ toward the southeast, which conforms to the paleocurrent direction of the turbidites. The morphology of Phycosiphon incertum can, therefore, be used as a paleoslope indicator.

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This study investigates overpressure evolution and its relationship to the spatial and temporal changes in the sedimentation rate in the passive continental margin of offshore Suriname. We analysed well data to estimate pore pressure at the well locations and to interpret relevant overpressure-generating mechanisms. Three-dimensional basin modelling was performed to reconstruct overpressure evolution in the area. Highlights • Overpressure evolution and its relation to sedimentary history were examined in offshore Suriname. • Temporal changes in sedimentation resulted in cycles of overpressure generation and dissipation. • Spatial variation in sedimentation caused lateral changes in the amount of overpressure. • The sedimentation rate primarily controlled the overpressure evolution in the region. • The overpressure history in offshore Suriname is linked with the hinterland evolution. How to cite this article: Nifuku K, Kobayashi Y, Araki Y, Ashida T, Taniwaki T. Overpressure evolution controlled by spatial and temporal changes in the sedimentation rate: Insights from a basin modelling study in offshore Suriname.

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High-resolution stable carbon isotope stratigraphy of terrestrial organic matter was established for the upper Maastrichtian Senpohshi Formation of the Nemuro Group in eastern Hokkaido, northern Japan. The Senpohshi Formation, approximately 1,300 m thick, is dominated by hemipelagic mudstone deposited along an active margin in the North Pacific region. Microscopic observations of extracted kerogen samples from the formation revealed the presence of sedimentary organic matter (SOM), predominantly phytoclasts and a minor amount of non-fluorescent amorphous organic matter, indicating material of a terrestrial higher plant origin. The atomic hydrogen/carbon ratios of the kerogen samples indicated a coalification rank at the anthracite stage or below. Therefore, the stable carbon isotope values of the bulk SOM obtained for the Senpohshi Formation represent the unmodified, original values of terrestrial organic matter. The stable carbon isotope profile reconstructed for the Formation provides the first high-resolution terrestrial record of the Mid-Maastrichtian Event (MME), which is comparable to highresolution marine carbon isotope data from other sections. The carbon isotopic signatures defined by the marine records are recognized in the terrestrial data from the Formation, especially in middle to upper part of the event. However, the terrestrial record showed a discrepancy from the marine data in the lower part of the MME, suggesting local variation 3 of the hinterland environment in the North Pacific region. This study provides new insight into environmental changes during the late Maastrichtian by establishing a detailed carbon isotope record of terrestrial materials.