ABSTRACT

A single supersequence can be defined within the late Oligocene mixed carbonate and siliciclastic sediments of southwest Florida. This supersequence was deposited beginning in Chron C8n.2n and ending in either Chron C7n or Chron C6Cr with an estimated age ranging between 26.5 and 24.2 Ma. The chronostratigraphy was established by using strontium isotope stratigraphy and magnetostratigraphy within three continuous cores through the sediments. The supersequence correlates to third order cycles 1.2 and 1.3 within supercycle TB1. The supersequence is bounded by regional unconformities with a hiatus of 2 million years at the base and 4 million years at the top.

Detailed descriptions of three continuous cores, including core and thin section microscopic examination and correlation with a continuous seismic reflection section, were used to define the sequence stratigraphy. From north to south in cores W-16242, W-16523, and W-17115, the number of stacked parasequences increases from 7 to 12. Parasequences range from 1.2 to 12.2 m in thickness. The depositional environments represented within all of the parasequences are all rather shallow water environments ranging from open shelf (less than 10 m of water depth) to peritidal. Most of the parasequences are capped with an exposure horizon or a laminated peritidal dolomite. There is a general increase of siliciclastic sediment within each parasequence from bottom to top.

The late Oligocene sediments of southwest Florida constitute a shallow-water ramp deposit. No sediments were deposited below the wave orbital base of 20 m. These late Oligocene sediments are located within the lower part of the Arcadia Formation (Hawthorn Group).