Rapid Recycling of Organic‐Rich Carbonates during Transgression: A Complex Coastal System in Southwest Florida

Abstract

Coastal and shallow marine environments are actively responding to accelerated rise in sea-level, eroding in some areas and rapidly accreting in others. Cape Sable in southwest Florida, with several natural and anthropogenic triggering events in the past century, illustrates the nearly instantaneous response that can occur in a sediment-rich coastal system. This paper presents results of a field study that documents a shallowing-upwards sediment package as a response to a transgressive phase. Patterns and rate of sedimentation are reported, the different sediment sources identified and the governing processes which control sedimentation style determined. The study integrates sedimentological and geochemical data with hydrodynamic time series measurements of water level, currents, suspended sediment concentration and salinity. Results show a rapid, sequential infilling of the intertidal zone from the most seaward marine, to transitional marine-freshwater sub-environments, as accommodation space becomes available due to sea-level rise, increased flood tidal volume and collapse of interior freshwater marshes. Average in situ sedimentation rates of 6.2 cm/yr are reported on the intertidal mudflats and daily tides are the most important agent responsible for the erosion, transportation and deposition of the fine-grained sediment. A significant amount of sediment is sourced from one coastal compartment and transported to another within the intracoastal system. The shallowing-upwards sediment package contains organic-rich carbonates with 15-35% total organic matter. In contrast to common stratigraphic wisdom, the shallowing-upwards peritidal sediments as recorded in southwest Florida, are the depositional response to several small, rapid pulses of sea-level instead of being diagnostic single high-stand lithofacies such as commonly described in ancient epeiric sequences.

Geometric characteristics and evolution of a tidal channel network in experimental setting

“…Classically, studies of hydraulic geometry, network characteristics and morphometry of tidal channel systems use field observations (Van Straaten, 1949; Myrick and Leopold, 1963; Pestrong, 1965; Dury, 1971; Bayliss‐Smith et al ., 1979; Collins et al ., 1986; Leopold et al ., 1993; Eisma, 1998; Cleveringa and Oost, 1999; Zeff, 1999; Ginsberg and Perillo, 2004; Lawrence et al ., 2004; Vlaswinkel and Wanless, 2009), combined with aerial photographs or other remotely sensed data (Knighton et al ., 1992; Shi et al ., 1995; Fagherazzi et al ., 1999; Rankey, 2002; Mason et al ., 2006). More recent studies focus on developing mathematical and numerical models for these systems (Ichoku and Chorowicz, 1994; Rinaldo et al ., 1999; Fagherazzi and Furbish, 2001; Fagherazzi and Sun, 2004; Marani et al ., 2002; Marani et al ., 2004; D'Alpaos, et al ., 2005; D'Alpaos, et al ., 2006; Marciano et al ., 2005; Temmerman et al ., 2007).…”

The origins of shallow‐water carbonate lithofacies thickness distributions: one‐dimensional forward modelling of relative sea‐level and production rate control

“…This kind of complex response to simple external relative sea-level forcing is supported by evidence from modern carbonate systems (e.g. Vlaswinkel & Wanless, 2009) and is a form of autocyclicity, as each cycle is produced without any requirement for an oscillation in relative sea-level (Drummond & Wilkinson, 1993).…”

Florida Bay: Modern analogue for Lofer cyclothems?

“…Details of sedimentation within Florida Bay have been investigated by Ginsburg (1956, 1957), Enos & Perkins (1979), Bosence (1989a,b, 1995), Enos (1989), Wanless & Tagett (1989), Wanless et al . (1995), Swart & Kramer (1997), Prager & Halley (1999) and Vlaswinkel & Wanless (2009).…”