About This Item
Share This Item
Journal of Sedimentary Research, Section
A: Sedimentary Petrology and Processes
Vol. 67 (1997)No.
1. (January), Pages 36-46
210Pb Chronology Of Sequences Affected By Burrow Excavation
And Infilling: Examples From Shallow Marine Carbonate Sediment Sequences,
Holocene South Florida And Caicos Platform, British West Indies
Lenore P. Tedesco (1), Robert C. Aller (2)
A variety of sedimentological criteria and direct field observations indicate
that deposits of shallow carbonate platforms and mud banks are extensively
transformed during megafaunal bioturbation by deep-burrowing crustaceans.
210Pb dating of surficial sediment and burrow fills dissected
from the upper
1-3 m of sediments at four sites on the Caicos Platform and in South Florida
corroborates sedimentologic descriptions of rapid biogenic alteration of
entire facies. Deep burrow networks are either progressively filled when
vacated or catastrophically filled during storms. 210Pb distributions
from the study sites show that at least some infill is predominantly surficial
sediment (0-30 cm). Assuming that all identifi ble deep burrow fills containing
excess 210Pb derive from the uppermost 0-5 cm interval, an estimate
of facies replacement by "nonlocal" transport can be made based on measured
excess 210Pb values of fill and the corresponding total discernible
fill volume in cores. Although there is a large uncertainty in some cases,
calculations indicate that at the sites studied, burrow excavation and
infilling can completely transform the upper
1-2 m, and possibly 3.5 m, of deposits in
100-600 yr, depending on the exact sediment interval. More rapid transformation
of deposits is required if fill is derived from below
5 cm. Bioge ic transformation rates are sufficiently fast compared to net
sedimentation that burrow infills, not primary physical deposition, determine
the composition, porosity, fabric, and texture of the preserved facies.
The 210Pb profiles in the deepest regions of deposits in the
present cases are further complicated by basal enrichments of 226Ra,
which apparently diffuses upwards from Pleistocene calcrete surfaces into
overlying Holocene sediment. This diffusion requires careful documentation
of supported 210Pb near this contact, but also offers the potential
for an additional transport tracer internal to the deposits.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.