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Abstract

Complete exposure of the Upper Miocene Reef Complex in the sea cliffs of the Island of Mallorca (Spain) allows for a high-resolution sequence-stratigraphic analysis. A 6-km-long cross section parallel to the direction of reef progradation displays four hierarchical orders of accretionary units. These accretionary units are composed of lagoonal horizontal beds, reefal facies with sigmoidal bedding, and gently dipping slope deposits. They are bounded at the top by erosion surfaces and basinward by correlative conformities. Thus, each of the four orders of accretionary units have many characteristics of depositional sequences. Due to the close relationship between coral reefs and the sea surface, vertical shifts of the reef accretionary units record four orders of sea-level fluctuations, longer and larger fluctuations being modulated by lesser ones of higher frequency. Additionally, the position of accretionary units in lower-order progradations allows the definition of: (1) progradational low-stillstand units; (2) aggradational units (sea-level rise); (3) progradational high-stillstand units; and (4) offlapping units (sea-level fall). Erosion truncates the previous progradational high-stillstand and offlapping units during low positions of sea level.

These architectural patterns are similar to progradational sequences seen on some seismic lines. The progradational pattern generally shows the following geometric details: (1) discontinuous climbing high-amplitude reflectors; (2) truncation of clinoforms by these high-amplitude reflectors; (3) discontinuous high-amplitude reflectors with basinward dips; and (4) transparent areas intercalated between clinoforms and horizontal low-amplitude reflectors. Based on facies architecture in the outcrops of Mallorca, the discontinuous climbing high-amplitude reflectors are interpreted as erosion surfaces truncating aggradational reef-core units (sequence boundaries), and are overlain (onlapped) by lagoonal sediments deposited during the next sea-level rise. The discontinuous high-energy reflectors with basinward dips are interpreted as downlap surfaces. The transparent zones correspond to aggradational reef-core facies.

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