Transcript Pleistocene Sediments of southern Florida Trevor Anson Pleistocene Aged Rock Units  Most of southern Florida is underlain by marine sedimentary sequences.  These sequences are punctuated by.

Pleistocene Sediments of
southern Florida
Trevor Anson
Pleistocene Aged Rock Units
 Most of southern
Florida is underlain by
marine sedimentary
sequences.
 These sequences are
punctuated by pockets
of freshwater
limestones, and
subaerial exposure
surfaces.
 This “wedge” of
Pleistocene aged
sediment is
approximately 200 ft
thick in the lower
Keys.
Key Largo Limestone (KLL)
 Longest period of deposition
of these three rock groups.
 Is mostly found as bedrock on
the main chain of the Florida
Keys.
 Consists of wave resistant
elements that were trapped in
coral reefs.
 Deposition occurred 120000,
130000 ybp
Fort Thompson Formation (FTF)
 Can be recognized as an equivalent to the lower facies
of the KLL.
 Has both marine and freshwater facies.
 Has a lower porosity than the KLL.
Miami Limestone (ML)
 Recognized as the
equivalent to the upper
facies of the KLL.
 Has two sub groups, a
bryozoan and a oolitic
facies.
 Has a lower porosity
than the KLL.
 Deposition of oolitic
facies occurred 120000130000 ybp.
The “Quaternary Units”
 R.D. Perkins was the
first person to
realize that the FTF,
and the ML could be
subdivided into 5
different units.
 Q1-Q5, Q1 is the
oldest unit.
Ages of Q Units
 Perkins did not actually give dates for each of the Q
Units, but based his assumptions off of data in a report
by Richard Mitterer. The five units recognized by
Mitterer (1975) are believed to correlate with the 5 Q
Units of this study.
 Mitterer recognized five distinct marine units in the
Pleistocene, the upper four of which he dated as:





Unit 5- 134,000
Unit 4-180,000
Unit 3-236,000
Unit 2-324,000
Unit 1- not dated.
Q1, Q2, and Q3 units
 Q1 is characterized by an abundance of quartz grains.
Mollusk fragments and benthic forams occur frequently.
The common lithology of this unit contains quartz
grainstones, mixed quartz/mollusk grainstones and
mixed quartz/mollusk wackestones.
 Q2 is characterized by grainstones and packstones
containing mollusks and forams, however, red corralline
algae is more common in Q2. This unit has a similar
lithology to Q1.
 Q3 is characterized by thick sequences of coral
boundstones. Also contains wackestones and packstones
with fragments of mollusks and forams. Multer et al.
only found quartz grains in one core sample.
Q4 and Q5 units
 Q4: Packstones and grainstones consisting of mollusk
and foram fragments. Less coral boundstone than in Q3.
 Q5: Corresponds to oxygen isotope stage 5. Coral and
coral boundstone occurs, red algae is abundant as well
as packstones and grainstones of mollusk and forams.
Unconformities between Q Units
 Perkins noted that these five sequences are “bounded
by discontinuity surfaces indentified by features
including (a) vadose sediment, (b) land-plant root
structures, (c) laminated crusts, (d) diagenetic
soilstones, (e) soils and soil breccias, (f) solution
surfaces, (g) bored surfaces, and (h) freshwater
limestones.
 These discontinuity surfaces were generally noted when
they occurred in combination with each other.
 Vadose Sediments: internal sediments that consist of
lime mud and detrital quartz. During the Pleistocene
was most likely introduced into cement-lined voids in
the bedrock during periods of subaerial exposure.
Pleistocene vadose sediment represents the last stage in
the filling of these voids.
 Land Plant Root Structures: The evidence of these
strucutures created by calcification of roots are
interpreted to have occurred during periods of subaerial
exposure.
 Laminated Crusts: Commonly found in Pleistocene
sequences of south Florida, similar to caliche crusts.
The laminated crusts found in southern Florida bear a
resemblance to “algally” laminated sediments, but it
has been shown they were created during periods of
subaerial exposure.
 Diagenetic Soilstone: Commonly occurs with root
calcification and laminated crusts. Caused by diagenetic
alteration of previously existing “textures” to a dense,
mottled mudstone.
 Soil Breccias: Commonly composed of poorly sorted,
subangular fragments of host rocks. Occur as pockets of
hardened soils or as paleosols.
 Solution Surfaces: In southern Florida, these
discontinuities are characterized by solution pipes.
Believed to be initiated by leaching of limestones by
plant activity.
 Freshwater Limestones: Pockets of freshwater caused by
low sea-level led to the formation of freshwater
limestones.
Topography
 The topography of southern Florida has had an
important impact on sedimentation patterns and biotic
distribution.
 Sinkholes are common features in the Florida Keys.
Sinkholes that developed in the KLL and the ML have
been dated at approximetely 110000 +/- 20000 ybp.
Conclusions
 Research of the Pleistocene aged rock groups of
southern Florida is important for several reasons:
 The changes in sea-level that have been observed are
significant because they show how the edges of continents
are impacted.
 Understanding the hydrogeology of southern Florida
bedrock allows for understanding of modern environmental
concerns.
Works Cited

Daley, G.M., 2002: Creating a Paleoecological Framework for Evolutionary and Paleoecological Studies: An Example from the Fort Thompson
Formation (Pleistocene) of Florida. Palaios, v. 17, p. 419-434.

Dodd, R.J., C.T. Siemers, 1971: Effect of Late Pleistocene Karst Topography on Holocene Sedimentation and Biota, Lower Florida Keys.
Geological Society of America Bulletin, v. 82, p. 211-217. Hickey, T.D., 2010: Pleistocene Carbonate Stratigraphy of South Florida: Evidence
for High-Frequency Sea-Level Cyclicity. Journal of Coastal Research, v. 26, p. 605-614.

Hickey, T.D., 2010: Pleistocene Carbonate Stratigraphy of South Florida: Evidence for High-Frequency Sea-Level Cyclicity. Journal of Coastal
Research, v. 26, p. 605-614.

Hoffmeister, J.E., H.G., Multer, 1968: Geology and Origion of the Florida Keys. Geological Society of America Bulletein, v. 79, p. 1487-1502.

Hoffmeister, J.E., K.W., Stockman, H.G., Multer, 1967: Miami Limestone of Florida and Its Recent Bahamian Counterpoint. Geological Society
of America Bulletein, v. 78, p. 175-190.

Mitterer, R.M., 1974: Pleistocene Stratigraphy in southern Florida Based on Amino Acid Diagenesis in Fossil Mercenaria. Geology, v. 2, p. 425428.

Multer, H.G., E. Gischler, J. Lundberg, K.R. Simmons, E.A. Shinn, 2002: Key Largo Limestone Revisited: Pleistocene Shelf-edge Facies, Florida
Keys, USA. Facies, v. 46, p. 229-272.

Neal, A., M., Grasmueck, D.F., McNeill, D.A. Viggiano, G.P., Eberli, 2008: Full-Resolution 3D Radar Stratigraphy of Complex Oolitic
Sedimentary Architecture: Miami Limestone, Florida, U.S.A. Journal of Sedimentary Research, v. 78, p. 638-653.

Perkins, R.D., 1977: Depositional Framework of Pleistocene Rocks in Southern Florida. Geological Society of America Bulletein, v. 147, p. 131198.

Schmoker, J.W., T.C. Hester, 1986: Porosity of the Miami Limestone (Late Pleistocene), Lower Florida Keys. Journal of Sedimentary Petrology,
v. 56, p. 629-634.

http://academic.emporia.edu/aberjame/ice/lec09/lec9.htm

http://www.uwosh.edu/faculty_staff/hiatt/Teaching/360_Florida/2012_Ancient.html