Biogenic buildups and carbonate sedimentation, Dry Tortugas Reef Complex, Florida

<p>The Dry Tortugas, a horseshoe-shaped complex of carbonate banks and coral reefs, is located at the southern terminus of the Florida limestone shelf. The complex rises to the surface waters from a drowned Pleistocene surface that forms a circular platform having a general depth of 17-21 m.</p> <p>Three basic biogenic buildups (facies) comprise the reef complex: 1) detrital lagoonal bank, 2) Montastrea reef bank and 3) <i>Acropora palmata</i> reef. These facies lie adjacent to one another and are also present in vertical succession as individual growth stages of varying thickness and lateral extent. A zone of <i>Acropora gervicornis</i> is developed as a transition between the <i>Montastrea</i> and <i>A. palmata</i> growth stages.</p><p>The present organic assemblages and topography bear evidence of dominantly lateral progradation and cumulative storm effects that are linked to the slow eustatic sea-level rise for the past several millennia. Long-continued storm degradation is manifested by 1) continuous removal of <i>A. palmata</i> and its replacement by storm-resistant coralline algae and <i>Millepora</i> sp. to produce truncated rocky surfaces, 2) abundant reef rubble, 3) erosion of spur-grooves, and 4) development of intertidal rubbly reef flats.</p><p>Sediments ranging from cobble-sized rubble to medium silt are composed of <i>Halimeda</i>, coral and mollusc grains: coralline algae and foraminifers are present in minor amounts. Variations in texture and constituent particle composition are interpreted to be mainly a result of mode of sediment transport and effect of grain shape. Broadly-defined grain size populations produced by three modes of transport have characteristic assemblages of constituent particles. The populations include a gravel-sized surface creep population, sand-sized saltation population and very fine sand-to silt-sized suspension population. Strong mixing occurs between the gravel and sand population on the storm-degraded shoals, and between the sand and silt population on the lagoon bottom. Sands flanking the reefs and reef banks show minimum mixing hence good degree of sorting. Incongruous mixtures of the in-place fraction and varying proportions of the transported populations constitute detrital lagoonal banks as a substrate stabilized by seagrass and coral growth. The gravel-sand and sand-silt mixtures are related to deposition under highly variable energy conditions. Variability in energy conditions does not cause strong population intermixing on beaches. From the same reason, beach sediments show a high degree of sorting in all size grades from cobbles to fine sand.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geological Sciences

Year

1972

Author dc:creator

• Jindrich, Vladimir

Contributors dc:contributor

• James R. Beerbower
• James E. Sorauf
• Paul P. Enos

• Marine sediments
• Florida
• Sedimentation and deposition
• Reefs

Repository record dc:identifier

https://orb.binghamton.edu/dissertation_and_theses/177

OAI identifier oai:identifier

oai:orb.binghamton.edu:dissertation_and_theses-1183