Ultra-High-Resolution Seismic Stratigraphy of Martha Brae Delta-Reef Complex, Falmouth, Jamaica
J. D. Pigott, J. D. Skinner, S. M. Roberts
Ultra-high-resolution seismic stratigraphy was conducted on a 10-km2
area of the Martha Brae delta-reef complex of Falmouth, Jamaica. The acquisition
involved a 120-MHz ground-penetrating radar, zero source-receiver offset, 0.2 m
SP interval, 15 km of total line, and 20 walk-away noise tests of grid
intersections. Post-acquisition processing
involved only stacking and analog
filtering. Subsurface penetration was in excess of 50 m, with minimum thin-bed
resolution of less than 1 m. Ground truth was provided by shallow (< 25 m)
boreholes with nine radiocarbon dates.
Application of conventional seismic stratigraphic techniques revealed four
sequences, differentiated by reflection configurations and interval velocities.
The oldest studied, S4, below 25 m is interpreted as a high-velocity subparallel
(dolomitic?) sequence, possibly the Hope Gate Formation. It is concordantly
overlain by a chaotically configured (frequent cave diffractions) carbonate
sequence, S3, which exhibits an uneven, karstic upper boundary at 13 m. Sequence
S3 is interpreted to be the Falmouth Formation, an upper Pleistocene coralgal
biolithite geologic sequence, which sequence S2 onlaps. The differing seismic
facies allows S2 to be divided into S2A, a mounded high-velocity coralgal
biolithite geologic sequence; S2B, a parallel transgressive delta sequence; or
S2C, a low-velocity mixed carbonate-clastic sequence. Sequence S2 tops from -1
to -5 m seaward in dip
section. Overlying sequence S2 is the mounded and
channeled S1 sequence, the modern Martha Brae delta-reef complex which seaward
passes into storm washover fans and paralics. Integrated geohistory analysis
reveals a relative fall in sea level following S3; a rise in relative sea level
accompanying S2 beginning more than 7,000 years ago; and a relative fall in sea
level for S1 commencing 3,000 years ago.
In summary, conventional sequence analysis using unconventional high-resolution methods affords better imaged geometric paradigms for contemporary seismic stratigraphic analysis.
AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.