Anatomy of a Recent Biodetrital Mud‐Mound, Florida Bay, USA

Research output: Chapter in Book/Report/Conference proceedingChapter


Initial investigations of the Recent mud‐mounds of Florida Bay suggested that they are biogenic structures formed from the trapping and binding of locally produced (mainly algal) aragonitic mud. Later work showed that the mound sediments are composed of both calcite and aragonite derived from the breakdown of a range of shelly biotas within the bay. Sediment generated within the bay is transported, as both suspended‐ and bed‐load, largely by NE wind‐driven currents, towards the Gulf of Mexico to the SW. Recently the mounds in the centre of the bay have been shown to have low production rates, SW progradational geometries and physical rather than biogenic depositional structures. Large mounds at the mouth of the Bay have faster production rates, both progradational and aggradational sequences, and grow from amalgamation of former SW prograding mounds.

A detailed study of Upper Cross Bank, based on 67 cores, illustrates the sedimentary geometries, facies and evolution of central Florida Bay mounds. Measurements on staked margins to the mounds indicate decimetre‐scale erosion and deposition rates over a 5‐year period. Prograding and aggrading lenses of the following facies are found: basal (mollusc, intraclast) packstones; layered (mollusc, foraminifera) mudstone; skeletal (mollusc, foraminifera) packstone; winnowed, skeletal (foraminifera, mollusc) grainstone; and grass‐bed (peloid, mollusc, foraminifera) wackestone. Pelleted muds form 10% of windward and 40% of leeward surface facies. Muds are predominantly silt‐sized (4–8ϕ) grains composed of aragonite and high‐Mg calcite. SEM examination of muds of this modal size indicates skeletal fragments together with grains of plate, bun and prismatic shapes consistent with a mixed skeletal origin.

Strontium versus aragonite values indicate that the mud is of one population generated through local breakdown of low‐aragonite, low‐strontium foraminifera, Thalassia encrusters and lithoclasts, and high‐aragonite, high‐strontium green algae.

The stratigraphy of these mounds indicates that the earliest evidence of a mound comes from aggradational grass‐bed wackestones with tin wedges of layered mudstones. These are overlain with erosional contact by NE‐derived storm‐beds and then SE‐derived layered mudstones. Present‐day sedimentation is controlled by NE erosion with winnowed grainstones and mud‐pebble conglomerates and SW (leeward) deposition in grass‐beds and mud‐dunes. Thus the facies anatomy within the mound is a complex response of storm‐weather physical deposition and fairweather biogenic and physical deposition.

Biodetrital mounds differ from microbial mounds in their setting, sediment geometries, facies, structures, allochems, and mud size and composition.
Original languageEnglish
Title of host publicationCarbonate Mud‐Mounds
Subtitle of host publicationTheir Origin and Evolution
EditorsC L V Monty, D W J Bosence, P H Bridges, B R Pratt
Number of pages19
ISBN (Electronic)9781444304114
ISBN (Print)9780865429338
Publication statusPublished - 17 Jul 1995

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