Jh. Shaw et al., EXTENSIONAL FAULT-BEND FOLDING AND SYNRIFT DEPOSITION - AN EXAMPLE FROM THE CENTRAL SUMATRA BASIN, INDONESIA, AAPG bulletin, 81(3), 1997, pp. 367
Citations number
19
Categorie Soggetti
Energy & Fuels","Geosciences, Interdisciplinary","Engineering, Petroleum
We describe an analytical method for interpreting the geometry and str
uctural history of asymmetric half grabens in rift basins with extensi
onal fault-bend fold theory. Using seismic reflection profiles from th
e Central Sumatra basin and balanced forward models, we show how local
variations in tectonic subsidence relative to deposition rates yield
distinctive patterns of folded synrift strata and unconformities that
record basin history. If the deposition rate exceeds the local subside
nce rate, folded growth strata form upwardly narrowing kink bands that
have been described previously as growth triangles, In contrast, if t
he deposition rate is less than or equals the local subsidence rate, g
rowth strata are folded and truncated at the surface on half-graben ma
rgins. Subsequent increases in deposition rate relative to subsidence
rate form angular unconformities near the half-graben margins. These u
nconformities develop without the necessity of erosion and are folded
by continuing fault slip. Strata above and below the unconformities ar
e concordant in the deeper parts of the half grabens. Thus, angular un
conformities on half-graben margins are helpful for defining sequence
boundaries that may reflect changes in deposition and tectonic subside
nce rates. In addition, fault-bend fold interpretations yield fault ge
ometry and measures of horizontal extension, both of which control thr
ee-dimensional half-graben geometry and accommodation space. We show h
ow along-strike variations in fault geometry produce intrabasinal stru
ctures that may form prospective fairways or local depocenters.