Sub‐wavebase cross‐bedded grainstones on a distally steepened carbonate ramp, Upper Miocene, Menorca, Spain

Abstract

Cross‐bedded grainstones on carbonate ramps and shelves are commonly related to the locus of major wave energy absorption such as shorelines, shoals or shelf breaks. In contrast, on the Early Tortonian carbonate platform of Menorca (Balearic Islands), coarse‐grained, cross‐bedded grainstones are found at a distance from the palaeoshoreline where they were deposited below the wavebase. Excellent exposures along continuous outcrops on the sea cliffs of Menorca reveal the depositional profile and three‐dimensional distribution of the different facies belts of the Tortonian ramp depositional system. Basinward from the palaeoshoreline, fan deltas and beach deposits pass into 5‐km‐wide gently dipping bioturbated dolopackstone (inner and middle ramp), then into 12–20°‐dipping dolograinstone/rudstone clinobeds (ramp slope) and, finally, into subhorizontal fine‐grained basinal dolowackestone to dolopackstone (outer ramp). In this Miocene example, coarse‐grained grainstones exist in five different settings other than beach deposits: (1) on the middle ramp, where cross‐bedded grainstones were deposited by currents roughly parallel to the shoreline at 40–70 m estimated water depth and are interbedded with gently dipping bioturbated dolomitized packstones; (2) on the upper slope, where clinobeds are composed mostly of in situ rhodoliths and red‐algae fragments; (3) on the lower slope, as small‐scale bedforms (small three‐dimensional subaqueous dunes) migrating parallel to the slope; (4) at the transition between the lower slope and the outer ramp, where mollusc‐rich and rhodolithic rudstones and grainstones, interbedded in dolomitized laminated wackestones containing abundant planktonic foraminifera, infill slide/slump scars as upslope‐backstepping bodies (backsets); (5) at the toe of the slope, where coarse skeletal grainstones indicate bedform migration parallel to the platform margin, induced by currents at more than 150 m estimated water depth. This Late Miocene example also illustrates how changes in intrabasinal environmental conditions (nutrients and/or temperature) may produce changes in stratal patterns and facies architecture if they affect the biological system. Two depositional sequences compose the Miocene platform on Menorca, where a reef‐rimmed platform prograded onto an earlier distally steepened ramp. The transition from the ramp to the reef‐rimmed platform was effected by an increase in accommodation space caused by ecological changes, promoting a shift from a grain‐ to a framework‐producing biota.

Clinoforms and clinoform systems: Review and dynamic classification scheme for shorelines, subaqueous deltas, shelf edges and continental margins

“…1988; Everts and Reijmer, 1995;Leeder, 1999;Bosence, 2002;Bosence andWilson, 2002a, 2002b;Pomar et al, 2002;Eberli et al, 2004;Maurer et al, 2010;Lanfranchi et al, 2011;Betzler et al, 2015) and siliciclastic systems (e.g., Schlee et al, 1979;Steckler et al, 1999;Adams and Schlager, 2000;Tesson et al, 2000;Howell and Flint, 2002a, 2002cCattaneo et al, 2003Cattaneo et al, , 2007Holgate et al, 2014Holgate et al, , 2015Pellegrini et al, 2018). Clinothems may be also formed by very shallow-water gypsum platform accretion (Tucker, 1991;Patruno et al, 2018, in press).…”

“…BE = Blake Escarpment; FHS = Florida-Hatteras Slope. (Klitgord and Schouten, 1986) 2001; Pomar et al, 2002;Quiquerez and Dromart, 2006;Maurer et al, 2010). Both clastic and carbonate delta-scale coarse-grained subaqueous topsets and foresets comprise high-energy facies with good reservoir quality (Maurer et al, 2010;Patruno et al, 2015b).…”

Heterozoan carbonates in subtropical to tropical settings in the present and past

“…An increasing number of ancient occurrences of heterozoan warm-water carbonates have been recognized lately; mostly from the Neogene of the Western Mediterranean (Brandano and Corda 2002;Pomar et al 2002Pomar et al , 2004; see also Halfar and Mutti 2005), but also from the Mesozoic (Hornung et al 2007). These occurrences are reminiscent of cool-water carbonates but have formed under warmwater conditions with increased trophic levels as evidenced by the predominance of nutrient-tolerant groups of calcareous organisms, supported in some cases by high amounts of suspension feeders and high rates of bioerosion.…”

The Triassic platform of the Gador-Turon unit (Alpujarride complex, Betic Cordillera, southeast Spain): climate versus tectonic factors controlling platform architecture

“…This is a common evolution for carbonate platforms, as emphasized by Wilson (1975) and by Read (1985), who illustrated the evolution of ramps into steeper-margined, rimmed shelves. Several well-exposed platforms showing this evolution exist in the Northern Calcareous Alps (Rüffer and Zamparelli 1997, and references therein), Mallorca (Pomar et al 2002), and the Nijar Basin of SE Spain (Dabrio et al 1981;Warrlich et al 2005). In the latter two, Upper Miocene homoclinal carbonate ramps change up-section into rimmed platforms.…”