Carbonate Sedimentation Rates Today and in the Past: Holocene of Florida Bay, Bahamas, and Bermuda vs. Upper Jurassic and Lower Cretaceous of the Jura Mountains (Switzerland and France)

Abstract

Lagoonal to intertidal sediments from the Holocene in Florida Bay,on the Bahamas, and in Bermuda are compared to similar facies in theKimmeridgian and Berriasian of the Swiss and French Jura Mountains.Dating by 14C permits the estimation of sediment accumulationrates in the Holocene. In the ancient outcrops, the timing is givenby cyclostratigraphic analysis. Elementary depositional sequencesformed in tune with the 20-ka precession cycle, although much ofthis time may have been spent in non-deposition and/or erosion. Afterdecompaction of the ancient sequences, their accumulation rates canbe evaluated. It is suggested that the studied Holocene sedimentsaccumulated over the past 6000 years with rates of 0.3 to 3 mm/a,whereas the Kimmeridgian and Berriasian facies show somewhatlower rates of 0.07 to 0.6 mm/a. This difference may be due to methodological errors, but also to variable carbonate production. In shallow carbonate systems, much of the sediment produced may be redistributed over the platform or exported. Furthermore, basin morphology and currents can strongly influence facies and thickness of the accumulated sediment. Finally, the accumulated sediment may suffer further erosion before it is preserved in the sedimentary record. Consequently, when estimating sedimentation rates in ancient sequences, it is important to do this with the highest time resolution possible, and only after having decompacted the sediment and evaluated the time lost in hiatuses or condensed intervals.