Biostratigraphic correlation,paleoenvironment stress,and subrosion pipe collapse: Dutch Rhaetian shales uncover their secrets

A subrosion pipe or sinkhole is a geologic phenomenon that occurs due to dissolution of strata in the subsurface causing the overlying sediments to collapse. The subrosion pipe in the Winterswijk quarry complex in the eastern Netherlands yielded rare, dark-colored shales. Bivalves and palynomorphs indicate that the shales were deposited during the Rhaetian (uppermost Triassic). In addition, detailed correlation with other NW European localities in Great Britain, Austria, and Germany further constrained the age of the shales to the middle of the Rhaetian. The shales were deposited in a near-coastal environment and contained a low diverse macroinvertebrate fauna with bivalves and some brittle stars that lived in a hostile environment, probably caused by low salinity and oxygen levels. These middle Rhaetian shales were mixed with dark-colored middle to late Hettangian sediments, both overlying Middle Triassic (Anisian) strata, which is present in the pipe as well. The presence of Rhaetian sediments in the subrosion pipe reopened the discussion on its age of formation. We suggest that a collapse in the Middle Eocene is most likely. This research expands the knowledge of the marine realms in the uppermost Triassic in Europe, just prior to the Permian–Triassic extinction event.