ABSTRACT

World-wide changes in relative sea level, the sum of eustatic sea-level changes, sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time, producing characteristic responses in carbonate deposition. Relative rises in sea level, usually caused by cumulative effects of tectonic subsidence and eustatic rise, may result in the following three events. First, drowned carbonate reefs of platforms. Here carbonate growth potential is exceeded by relative sea-level rise, and is characterized by shallow-water sediments, overlain by hardgrounds and/or deep-water sediments, some of which may be condensed sequences. Second, platforms where only fast growing rim and patches of the interior are able to match sea-level rise while the remainder of the platform is drowned. Third, platforms which keep-up and maintenance at flat top at sea level and contain shallow water sediments whose thickness at least matches the height of sea-level rise. If terrigenous supply is limited, prograding sheets of shelf carbonates occur, with prograding shelf-margin carbonates clinoforms and turbidites. These are frequently capped by supratidal evaporites.

Relative drops in sea level cause karst and soil development over shelves and platforms. Simultaneously, deposition of "deep water" evaporites in adjacent semi-enclosed basins occurs and in open masive basins deltaic and aeolian clastics that bypassed the shelf margin are deposited. All of these are caused by crusteal uplift or by subsidence being outpaced by a eustatic drop in sea level.

Falls in sea level are accompanied by platform-wide fresh-water diagenesis. During relative sea-level rises marine diagenesis is common in subtidal portions of shoaling-upward carbonate sequences and fresh-water diagenesis, dolomitization and sulphate deposition are common to intertidal and supratidal portions.