Carbonate platforms as recorders of high‐amplitude eustatic sea‐level fluctuations: the late Albian appenninica‐event

摘要

AbstractThe mid‐Cretaceous was a time in which rapid vertical carbonate accumulation alternated with intervals of world‐wide crisis on carbonate platforms. Next to the well‐known mid‐Valanginian, mid‐Aptian and Cenomanian/Turonian event, the late AlbianRotalipora appennirjica‐7.oneis a period of severe platform crisis which is reflected differently on different platforms in the Tethys, the Pacific and the Atlantic Ocean. On the Dinaric Platform in western Slovenia (Tethys) karstification and subsequent temporary drowning of parts of the platform is recorded in sediment infillings of a cave system in a reef along the northern edge of the open ocean platform. Biostratigraphic analysis indicates that vertical aggradation, karstification, short‐term pelagic influx and subsequent shallow‐water carbonate production all took place in the late Albian. Simultaneous, but complete drowning can be observed in the north‐west Pacific which is an area where the demise of reefs is most obviously expressed by numerous sunken atolls. New sedimentological and palaeontological data, as well as seabeam and seismic data from several cruises, suggest a dramatic fall of sea level prior to a rise of even higher amplitude in theRotalipora appenninica‐zone.This sea‐level rise led to the deposition of a drowning succession and the formation of terminally drowned barrier reefs, rimming the top of many guyots. Karstification and drowning during the same biozone is also recorded on an isolated, shelf‐attached platform in the Basco‐Cantabrian Basin (North Atlantic) which shows similar cavity systems, infilling sediments and a thin drowning succession. Another example of late Albian platform drowning is the Maracaibo Platform in north‐west Venezuela. Thus, carbonate platforms can be used as recorders of high‐amplitude sea‐level changes, providing quantitative data on magnitude of fluctuations and their nature (relative vs. eustatic). In the case of theappenninica‐extnt, they also provide evidence that even during Cretaceous greenhouse climate period(s), dramatic disturbance of climatic equilibrium linked with short‐term high‐amplitude regressive‐transgressive cycle(s) occurred. The reason for this eustatic sea‐level fluctuation is yet unclear but could ultimately