Carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp (Miocene, Great Bahama Bank)

Abstract

Depositional geometries as imaged in seismic lines, logging data, and quantitative petrographic data were used to analyse the slope and toe of slope deposits of the Miocene distally steepened carbonate ramp of Great Bahama Bank. The shedding pattern along the slope of this ramp is more complex than it is along the slope of the Pliocene±Pleistocene flattopped carbonate platform. Compositional changes and compositional trends of periplatform sediments correlate with the positions of geophysically-defined sequence boundaries. Two types of depositional sequences occur. The first sequence is characterised by laterally traceable sequence-internal reflections, whereas the second type contains major intrasequential incisions. Erosional incisions and sedimentary infills of these canyons by turbidites formed during sea-level lowstands, as is indicated by the composition of the turbidites having a mixture of shallow-water and pelagic particles. Highstand turbidites are characterised by more extensive, laterally traceable geometries and by the occurrence of abundant shallow-water particles. In contrast to highstand turbidites shed from the Pliocene±Pleistocene flat-topped platform, shallow-water components in highstand turbidites of the Miocene ramp are of skeletal origin. The stacking pattern of the periplatform deposits is controlled by sealevel fluctuations. Four orders of sea-level changes are distinguished. Third-order cycles are delimited by sequence boundaries, and fourth (100,000 a) order cycles govern the bundling of turbidites into packages. Fifth (40,000 a) and sixth (23,000 a) order cycles are recorded in the background sediments and resolvable with spectral analysis.

Compositional variations in calciturbidites and calcidebrites in response to sea-level fluctuations (Exuma Sound, Bahamas)

“…3), with echinoderms and green algae (Halimeda). This pattern was not only observed in Bahamian (Haak andSchlager 1989: Lantzsch et al 2007) and Caribbean (Pedro Bank;Andresen et al 2003) periplatform sediments but was also found in sediment export patterns of Triassic calciturbidites (Reijmer et al 1991Reijmer 1998), Cretaceous slope and slope apron deposits (Ferry and Monier 1987;Everts and Reijmer 1995;Everts et al 1999;Savary and Ferry 2004), Eocene periplatform sediments (Everts 1991), and Miocene slope deposits of the Bahamas (Betzler et al 2000).…”

Acoustic Properties of "Young" Carbonate Rocks, ODP Leg 166 and Boreholes Clino and Unda, Western Great Bahama Bank

“…Recently, new information on the sedimentation patterns and turbidite frequency along the Bahamas transect was published by Betzler et al (1999), Betzler et al (2000) and Bernet et al (2000). These authors document a depositional system that sheds calciturbidites during both highstands and lowstands of sea level and Globigerina ooze predominantly during lowstands of sea level.…”

Quantification of input and compositional variations of calciturbidites in a Middle Triassic basinal succession (Seceda, Dolomites, Southern Alps)

“…Sea-level-related changes in the composition of calciturbidites were also found in the distant past, for instance in the Tertiary of Australia (Betzler et al 1995) and in the Late Triassic (Reijmer et al 1991). In addition to sealevel variations, the morphology of the carbonate margin also determines the composition and stacking patterns of calciturbidites (Betzler et al 1999(Betzler et al , 2000Anselmetti et al 2000). Platforms with flat tops and steep slopes show clear variations in composition of calciturbidites, whereas on perfect ramps the facies zones are only migrating laterally without influencing the composition of the turbidites (Schlager et al 1994).…”