Print this pageEffect of Rates of Relative Sea-Level Change and Setting on Carbonate Depositional Sequences
FRANSEEN, EVAN K., ROBERT H. GOLDSTEIN, and MARK R. FARR
Sequence stratigraphy, quantitative (pinning point) relative sea-level curves and magnetostratigraphy indicate how rates of sea-level change and setting controlled accumulation and geometries of Upper Miocene carbonates in SE Spain. Five 3rd- and 4th- order depositional sequences (DS1A, DS1B, DS2, DS3, TCC) formed with superimposed higher frequency events.
DS1A-DS1B, cooler water ramps, represent sediment bypass across steep paleoslopes to toes of slopes. Accumulation rates decreased from greater than 15.6 cm/ky to approx. 2 cm/ky and overall relative sea level rose at 17-21.4 cm/ky. Higher frequency sea-level rates were approx. 111 to greater than 260 cm/ky producing onlapping and draping, fining- (deepening-) upward cycles. Decreasing accumulation rates resulted from decreasing surface area for shallow-water production and drowning of shallow-water substrates. The bypass "ramp" processes precluded typical systems tract and parasequence development.
Basal and upper DS2 lowstand reef megabreccias reflect deposition during rapid falls, perhaps with short lowstand durations.
DS3 reefs (warmer conditions) formed where sea level coincided with gently sloping substrates. During the initial rise, rates were too rapid (>>19 cm/ky) to deposit a transgressive systems tract. Later reefs formed forced regressive systems tracts because rates of fall were less than or equal to 10 cm/ky. Slow progradation (0.39-1.45 km/Ma) resulted from the minor bank top, falling sea level, and land-derived excess nutrients and siliciclastics.
Topography-draping depositional sequences (TCC) formed where gentle topography and sea level coincided. The rapid sea-level changes (130-240 cm/ky) for TCC sequences prevented typical systems tract development.
These new results quantify settings and rates of sea-level change that prevent typical systems tracts and produce forced regressive systems tracts.