Quantifying carbonate sediment mixing across a formational boundary, an example from the Late Pleistocene Miami Limestone

Abstract

Holocene marine sediment from proto‐Florida Bay has been eroded, suspended, transported landward and has infiltrated downward (to 1 m depth) to fill secondary pores in subaerially exposed Late Pleistocene limestone. Sediment mineralogy (up to 95% aragonite), sediment texture (mostly needle‐like, <15 µm), and bulk sediment stable‐isotope values (upward trend in δ 18 O from −1 to −3‰ and δ 13 C from 3.5 to −2‰) of infill sediment is used to document inter‐stratal movement of sediment ahead of marine transgression. Nearby Florida Bay probably supplied needle‐like aragonite crystals by a storm surge mechanism that transported sediment landward and perhaps sorted the marine mud fraction. Currently, the core site is covered by freshwater microbial lime mud with a texture different than most infill sediment. That sediment crosses a formational and sequence boundary can have several implications: microfossil displacement; sedimentologic interpretation of mixed mud and sand‐size grains; porosity and permeability reduction; and associated diagenesis with perched ground water. If sediment infiltration is recognized in core and thin section, these mud‐filled pores can aid in recognition of subaerial exposure. Stratigraphically, the occurrence of marine sediments landward of the shoreline and below freshwater deposits may be interpreted as the result of a rapid rise and fall of sea level.