BIOSTRATIGRAPHIC CORRELATION, PALEOENVIRONMENT STRESS, AND SINKHOLE COLLAPSE: DUTCH RHAETIAN (UPPERMOST TRIASSIC) SHALES UNCOVER THEIR SECRETS

A sinkhole or subrosion pipe is a geologic phenomenon resulting from dissolution of strata in the subsurface causing the overlying sediments to collapse. The sinkhole 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 Rhaetian. The shales were deposited in a nearshore 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 are present in the pipe as well. The presence of Rhaetian sediments in the sinkhole reopened the discussion of 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.