Unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates

Abstract

Carbonate sequence stratigraphy is founded on the principle that changes in relative sea-level are recorded in the rock record by the accumulation of sediment with relative water depth-dependent attributes. While at the scale of a shelf to basin transect, facies clearly arrange by water depth, the relation blurs for depths <40 m, the most vigorous zone of carbonate production. The reason for this change in behaviour is two-fold. Firstly, in shallow water, the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution. Secondly, facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers. Remote sensing imagery, field observations and hydrodynamic models for two reef-rimmed shore-attached carbonate platforms in the Red Sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation. Considered together, however, the predictive power of the two variables rises significantly. The results demonstrate it to be an oversimplification to assume a direct link between palaeo-water depth and depositional diversity of subtidal lithofacies, while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone. While the size distributions of facies extents in the two focus areas follow power laws, no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported. The work is relevant for the interpretation of metre-scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeowater depths from depositional facies.

Satellite‐ and field‐based facies mapping of isolated carbonate platforms from the Kepulauan Seribu Complex, Indonesia

“…Recent studies on carbonate sediment, especially in shallow water, have focused on whether facies distribution is related to bathymetry, questioning the long‐held concept in carbonate geology that changes in water depth can be recognized through analysis of the lithofacies (Bosence, ; Gischler et al., ; Purkis et al., ; Rankey, , ; Wilkinson, Diedrich, & Drummond, ). These authors briefly outline that the understanding of where and how carbonate sediments are produced and accumulated has evolved from the rather simple concept of direct productivity–depth relationships to the recognition that carbonate depositional environments are influenced to some degree by depth, and also by a complex suite of autogenic factors that lead to facies mosaics especially in shallow waters where sediments migrate and superimpose on each other over short distances as a result of subtle environmental changes.…”

“…() as: whereby n is the number of facies and p is the proportion of each facies within a depth interval. Evenness ( E ) can reach values from zero to one, with values near one indicating that only one facies is present, meaning that the facies present can be predicted with confidence for a given water depth (Purkis et al., ; Rankey, ). Because the sample distribution is skewed towards shallow water depth, the binning size of the depth intervals with water depth were increased following an exponential function (f(x) = 2 x ), resulting in depth bins from 0–1 m, 1–3 m, 3–7 m, 7–15 m, etc.…”

Morphometric patterns in Modern carbonate platforms can be applied to the ancient rock record: Similarities between Modern Alacranes Reef and Upper Palaeozoic platforms of the Barents Sea

“…m to be estimated, and so on. Such -scale invariance‖ is helpful for sedimentologists and stratigraphers working with ancient strata in outcrop, core, or even seismic as the occurrence of small facies bodies, which are typically challenging to detect, can be indirectly inferred from the frequency of large ones (Purkis et al, 2007(Purkis et al, , 2012a(Purkis et al, , 2014aHarris et al, 2011).…”

“…Following the protocol of Purkis et al (2014a) and Harris et al (2014), the slices were analysed using eCognition (v. 8.9, Trimble Inc.). By applying textural and edge-detection routines, refined by manual-editing, the polygonal buildup -ridges‖ and intra-buildup -ponds‖ were mapped and exported as GIS vector files for further analysis (Fig.…”

Sequence stratigraphic framework for mixed aeolian, peritidal and marine environments: Insights from the Pennsylvanian subtropical record of Western Pangaea

“…Similar mud‐dominated lithologies are generally deposited today in water depths exceeding 12 m (e.g. Wagner & Van der Togt, ; Purkis et al ., ). The Chaetetes colonies characterizing the framestone texture of Facies F3.2 are thought to have formed small patch reefs, developing in shallow marine waters (Connolly et al ., ).…”