Abstract This study documents a variety of deposits created by submarine landslides within the Upper Cretaceous to lowermost Paleocene Chalk Group in the Danish Central Graben and investigates the impact of remobilization on porosity. Improved visualization of the landslides in 3D seismic data compared with previous studies was facilitated by better seismic data quality for the Chalk Group, the availability of a large stack of stratigraphy-consistent horizons and the use of spectral decomposition data. The illustrated examples are chosen to reflect the spectrum of deformation styles seen in the chalk and all have a well penetrating the affected succession. They include a large collapse (375 km 2 ) of an inversion ridge within the Kraka and Gorm formations, a field of large slide blocks (100–1000 m, 10–26 m) of likely lowermost Danian age embedded in the uppermost Ekofisk Formation, a debris flow system within the uppermost Tor Formation probably originating from the Ringkøbing–Fyn High and fine-grained bottom current sediment waves within the lowermost Danian Ekofisk Formation. In general, porosities are higher (10–25 porosity units) in the remobilized chalk compared with time-equivalent pelagic chalk in nearby reference wells. In earlier studies this has been linked to lack of bioturbation (resulting in limited grain repacking) in the remobilized chalks owing to high sedimentation rates, resulting in a relatively open fabric during initial burial. In contrast, surrounding and covering pelagic deposits could be much more effectively bioturbated, leading to tighter grain packing during burial. The insights of this study help in the seismic characterization of mud-grade carbonate oozes and have important applications in the reservoir modelling of mud-grade carbonate reservoirs (also in light of carbon capture and storage), and in palaeo-reconstructions of pelagic seafloors since submarine landslides provide kinematic indicators.

Abstract Mass transport deposits have long been known on the Exmouth Plateau, offshore NW Australia, identified in 2D and 3D industry seismic lines. The expedition SO257 in 2017 collected 30 high-resolution, shallow seismic lines along targeted transects on the northern Australian margin. Many of these imaged mass transport deposits, with the top 700–800 m of the section captured in detail not available with industry seismic data. We present nine new high-resolution seismic lines from three separate areas of the North West Shelf. Slides in the Roebuck Basin show complex anastomosing ductile extensional mechanisms, with multiple slip surfaces and no headscarps or adjacent faults. Slides on the Exmouth Plateau have fault control, with surface fault offsets of up to 300 m, indicating seismicity as a likely triggering mechanism. Slumps along the western margin of Western Australia are more limited in extent, associated with surface notches, with indications of previous activity at depth. All areas show a repeated history of mass transport deposits. The area of the active landslide province offshore of NW Australia is far larger than the individual slides recognized on the Exmouth Plateau.

Alluvial fans offer a means to unravel the intricacies of landscape, tectonic, and climatic dynamics. This book and accompanying geologic map highlight alluvial fans and their deposits exemplified by a suite of debris-flow alluvial fans emanating from the Holocene-active western range front of the Sangre de Cristo Mountains in south-central Colorado. The link between morphologies of fan surfaces and the sedimentary facies of their deposits permits a basis for evolutionary process interpretation of debris-flow alluvial fan geomorphology. A grasp of these processes will help earth scientists better discern complexities between buried paleo-surfaces (intraformational progressive unconformities), surficial deformation, and landform development as recorded in debris-flow fan deposits in the sedimentary record.