Abstract
Carbonate platform sediments are often organized in successive series of coarsening-upward cycles. In one coarsening upward cycle the grain size is increasing upward implying that the hydraulic energy required to deposit coarser and heavier grains must be higher than the energy required for the fine grains deposition.Two types of coarsening-upward cycles are analyzed: (1) cycles with peloidal-bioclastic upper cycle members, and (2) cycles with oolitic upper cycle members. These coarsening-upward cycles are regarded here as a consequence of the sea-bottom oscillations below and above the fair-weather wavebase but only triggered by autocyclic processes, creating simple model for the coarsening-upward cycle origin.
Highlights
Samples and MethodsNumerous studies of the effects of high-frequency relative sea-level changes in carbonates show that cycles are excellent indicators of sea-level fluctuations because their formation is highly dependent on many various parameters [1,2,3,4,5,6,7]
Judging from this, one can presume that successive series of coarsening-upward cycles may be a record of changes in water depth through varying sediment accumulation, when sea-bottom seemingly oscillates around the fairweather wave-base
The examined coarsening-upward cycles were formed within the shallow-water realm of the carbonate platform area
Summary
Numerous studies of the effects of high-frequency relative sea-level changes in carbonates show that cycles are excellent indicators of sea-level fluctuations because their formation is highly dependent on many various parameters [1,2,3,4,5,6,7]. Coarse-grained particles are present within upper cycle members These wackestone/packstones to grainstones are abundant in peloids, coarser molluscan and sporadic echinoderm bioclasts (Figure 4 and Figure 5). Sporadic horizontal lamination observed within the packstone-grainstone intercalations and even wackestone/ packstone to grainstone beds was formed during periods of intensive unidirectional tidal and/or storm currents These currents eroded the subtidal bottom, winnowed the muddy-peloidal-bioclastic material, removed the carbonate mud, oriented elongated bioclasts parallel to bedding, and formed the horizontal, graded laminae. Elongated coarser-grained particles are mostly randomly oriented These cycles represent a sedimentary response to cyclic environmental changes from low-energy shallow subtidal to higher-energy subtidal above the fair-weather wave base. Rare findings of crystal silt in pore spaces of oolites indicate neighboring presence of the vadose zone from which. calcite crystals were washed and transported in suspension to the oolitic shoals
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