Reef geometries, erosion surfaces and high‐frequency sea‐level changes, upper Miocene Reef Complex, Mallorca, Spain

Abstract

The upper Miocene Reef Complex of Mallorca is a 20‐km prograding unit which crops out in sea cliffs along the southern side of the island. These vertical and exceptionally clean outcrops permit: (i) identification of different facies (lagoon, reef front, reef slope and open platform) and their geometries and boundaries at different scales, ranging from metre to kilometre, and (ii) construction of a 6‐km‐long high‐resolution cross‐section in the direction of reef progradation. This cross‐section shows vertical shifts of the reefal facies and erosion surfaces linked to a general progradational pattern that defines the accretional units. Four hierarchical orders of magnitude (1‐M to 4‐M) of accretional units are identified by consideration of the vertical facies shifts and by which erosion surfaces are truncated by other erosion surfaces. All these orders show similar patterns: horizontal beds of lagoonal facies in the upper part (landward), reefal and slope facies with sigmoidal bedding in the central part, and open‐platform facies with subhorizontal bedding in the lower part (basinwards). The boundaries are erosion surfaces, horizontal over the lagoon facies, dipping basinwards over the reef‐front facies and connecting basinwards with their correlative conformities over the reef‐slope and open‐platform facies. The four orders of accretional units are interpreted in terms of four (1‐M to 4‐M) hierarchies of sea‐level cycles because (i) there is a close relation between the coral growth and the sea surface, (ii) there are vertical shifts in the reefal facies and their relation to the erosion surfaces, and (iii) there was very little tectonic subsidence in the study area during the late Miocene. Additionally, all these units can be described in terms of their position relative to the sea‐level cycle: (i) the reefs prograde on the open‐platform sediments during low stands of sea‐level; (ii) aggradation of the lagoon, reef and open‐platform facies dominates during sea‐level rises, and the lagoonal beds onlap landwards upon the previous erosion surface; (iii) reefal progradation occurs during high stands of sea‐level; and (iv) the 2‐M sea‐level fall produces an off‐lapping reef and there is progradation with downward shifts of the reefal facies and erosion landward on the emerged (older) reefal units (A‐erosion surfaces); the 3‐M and 4‐M sea‐level falls produce only erosion (B‐and C‐erosion surfaces). Although precise age data do not exist at present, some speculations upon the frequency of these Miocene relative sea‐level cycles can be made by comparisons with Pleistocene cyclicity. There is a good correlation between the Miocene 2‐M cycles and the 100‐ka Pleistocene cycles. Consequently, the 1‐M cycles can be assigned to a fourth order in relation to previously proposed global cycles and the 2‐M to fifth‐order cycles. All these accretional units could be defined as ‘sequences’, according to the definition as commonly used in sequence stratigraphy. However, they represent higher than third‐order sea‐level cycl...

Microbial communities in a coastal cave: Cova des Pas de Vallgornera (Mallorca, Western Mediterranean)

“…It corresponds to a littoral karstic region in a tabular platform built up by a Tortonian-Messinian reefal limestones sequence (Pomar, 1991) forming the best featured coastal karst area of the island, called Migjorn. The materials where the cave is developed show wide textural variability as a function of the reef architecture (Pomar et al, 1996;Fornós et al, 2002).…”

Geologic constraints and speleogenesis of Cova des Pas de Vallgornera, a complex coastal cave from Mallorca Island (Western Mediterranean)

“…Overlying the major Messinian erosion surface, a Pliocene regressive sequence fills the remaining reefrimmed basins above the Upper Miocene sequence (Pomar, 1991). Never more than 10 m thick in this area (Figs.…”

“…This unit consists in a series of progradational (towards the SW) reef-rimmed platforms that present different facies associations, characterized in this area by welldifferentiated reef front and back reef deposits. Their architecture shows complex accretional geometric relationships related to the high-frequency oscillations in relative sea level (Pomar, 1991). The lithofacies that compose this carbonate Reef Complex -defined mainly on the basis of lithology, texture and constituentsplays an important role in the development of the cave morphology (see below).…”

“…At the base of the studied sequences, the Upper Miocene limestones belonging to the Reef Complex (Pomar, 1991) crop out all along the littoral cliff (Fig. 5).…”

“…The islands were covered by an epicontinental sea that favored the development of a coral reef environment around the uplifted areas. Upper Miocene carbonate platforms grew in shallow submerged areas around all Balearic paleo-islands, but most extensively on their southern margins (Pomar, 1991). Specifically, in the southern margin of Mallorca (the Llucmajor Platform) a thick slab of carbonate deposits built up, creating a structural post-orogenic platform that stretches around the central and eastern folded ranges (Fig.…”