Quaternary atoll development: New insights from the two‐dimensional stratigraphic forward modelling of Mururoa Island (Central Pacific Ocean)

Abstract

Knowledge about the Quaternary evolution of mid-ocean atolls comes mainly from drilling and field observations carried out on a number of Pacific carbonate islands. However, little is known about the early to mid Pleistocene atoll development history, especially at margin and foreslope settings. Using previous field and subsurface data from Mururoa Atoll and a processbased modelling software (DIONISOS), a two-dimensional forward stratigraphic model of atoll development is proposed for the past 1Á8 million years (Myr). Observational data from vertical to inclined coring, seismic and bathymetric surveys indicate that, from approximately 0Á45 to 0Á40 million years before present (Ma), carbonate deposition at Mururoa Atoll resulted in a series of mostly prograding reef units. The model is first constrained at the base by the shape and topography of the pre-Quaternary basement. A number of sensitivity tests were performed to define the respective influence of variant parameters. The best-fit development scenario that accounts for the overall geometry and stratigraphic architecture of the Quaternary sediment packages is obtained by using the sea-level curve by Miller et al. (2005), uniform subsidence rate of 105 m Myr À1 , and carbonate production rates gradually increasing from 0Á50 to 8 mm yr À1 between 1Á80 Ma and the present. Additional controlling parameters include subaerial erosion (at a constant rate of 0Á25 m/kyr), wave-energy and sediment-transport processes. The stratigraphic forward model predicts a succession of three distinct types of carbonate systems that have developed since the earliest Pleistocene: toe of slope systems from 1Á80 Ma to about 0Á80 Ma, open-platform systems from 0Á80 Ma to 0Á50 Ma, and framework-reef systems from about 0Á50 Ma to the present. The development of these different systems is most likely to be controlled by climate and changes in sea-level cycles. During the low-amplitude 41 kyr cycle periods of the earliest Pleistocene, ambient conditions were not conducive to framework-reef growth; shallow-water carbonate sedimentation was dominantly gravity-driven, operating along the platform foreslopes only. During the Mid-Pleistocene Climate Transition, narrow, open-platform units have developed at the upper parts of the pre-Quaternary basement flanks. With the onset of the high-amplitude 100 kyr sea-level modes and climate restoration, reef frameworks started to be generated. These models from Mururoa agree with a number of previous studies suggesting that most of the true framework reefs were not initiated prior to 0Á50 Ma. Mururoa Atoll is 466 demonstrated to be a robust analogue for providing more realistic interpretations of the development history of Pacific atolls. Further modelling with three-dimensional DIONISOS could generate better predictions by taking into account hydrodynamic and transport parameters more accurately.

Coral reef response to Quaternary sea‐level and environmental changes: State of the science

“…Montaggioni et al . () modelled the early to mid Pleistocene atoll development of Mururoa Atoll and confirmed the importance of the amplitude and frequency of sea‐level changes (i.e. 41 versus 100 kyr cycles) in controlling the gross morphology and architecture of these types of atolls.…”

Late Cenozoic sea level and the rise of modern rimmed atolls

“…This model is similar to, but simpler than, previous models used to study the evolution of island atoll systems (e.g., Montaggioni et al, 2015;Quinn, 1991a;Toomey et al, 2013;Warrlich et al, 2002). …”

Atolls of the World: Revisiting the Original Checklist

“…An example of hoa and ava entrances to the lagoon is shown in Figure 3b. Likewise, if the lagoon's fetch is large enough, and if the geometry of the bottom facilitates it, wind-driven waves inside the lagoon may be an additional and even a dominant circulatory force (e.g., Andréfouët et al, 2001;Montaggioni et al, 2015). There are even a few instances in which lagoons appear to be quite open but nonetheless develop a degree of hypersalinity, as on Glover's, Lighthouse and Turneffe reefs of Belize (Table B.1; Hauser et al, 2007).…”