Mallarino, Gianni1, R.H. Goldstein2, Pietro Di Stefano3
(1) Rice University, Houston, TX
(2) University of Kansas, Lawrence, KS
(3) Universita` di Palermo, Palermo, Italy
ABSTRACT: Evaluating Uplift Rates, Subsidence Rates, and Origin of Drowning Unconformities Using Marine Cements
Fluid inclusions in marine cements can be used to determine the water depths in which drowning unconformites form. This paleobathymetric data can be used in modeling studies to determine uplift and subsidence rates.
The unconformity studied marks the termination of a Lower Jurassic carbonate platform cropping out at Monte Kumeta (Sicily). Crinoidal limestones, which formed during the transition to termination of the carbonate platform, are overlain by pelagic sediment (Rosso Ammonitico). Growth of syntaxial calcite cement is postdated by Rosso Ammonitico, indicating that the cement precipitated early, near the sea floor. CL shows three main growth zones. Analyses of 18O and 13C show a positive excursion from zone 1 to zone 3, suggesting cooling and methanogenesis during precipitation. Zone 1 contains all-liquid and two-phase inclusions trapped during growth and early recrystallization. Zones 2 and 3 contain all-liquid inclusions trapped during growth. All-liquid inclusions yield Tm ice of approximately -1.9°C, indicating seawater salinity. Crushing analyses of two-phase fluid inclusions yield paleo-water depths ranging from 23 to 112 m.
Paleo-water depths were combined with biostratigraphic data, chronostratigraphic data and eustatic curves to calculate subsidence rates. The best-fit model indicates an uplift rate of 2m/m.y. during the transition to platform termination, followed by a subsidence rate of 20 m/m.y. during platform termination. Termination of the carbonate platforms was submarine and slow rates of deepening are evidence that the platform's demise was caused by an environmental perturbation in shallow water, and not by rapid sea-level rise.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.