الفهرس | Only 14 pages are availabe for public view |
Abstract This study aims to tackle some unfathomed issues in syn-rift sequence stratigraphy and tectono-sedimentology. These are (i) figuring out how does the growth of rift-margin structures interact with sediment influx and eustatic sealevel changes to control the syn-rift sequence architecture, (ii) investigating the syn-rift sedimentary response to growth folding along a rift-margin transfer zone, and (iii) improving the understanding and prediction of early syn-rift deposition during early stages of structural deformation. To tackle these aims, a detailed field mapping of key stratal surfaces and structures, litho- and biofacies analyses were integrated with geochronologic data from biostratigraphy, strontium and oxygen isotopes. Eighteen key stratal surfaces of onlap, offlap and downlap were mapped within six 3rd order early Miocene syn-rift depositional sequences. The tectonosedimentary analysis revealed that vertical and lateral propagation of the basin bounding fault led to (i) development of a transfer zone at the fault tip which acted as the main sediment fairway for fan deltas entering the basin, and (ii) created a growth syncline in the hangingwall where coeval strata exhibit onlap and thinning landward and divergence basinward. Toward the fault center, subsidence was episodic and outpaced both eustatic falls and sediment influx leading to a predominance of retrogradational systems tracts (60-85 % of the sequences’ thickness). In contrast, at the transfer zone, sediment influx overwhelmed the developed accommodation, and resulted in prograditional to aggraditional systems tracts. Subtle eustatic sea-level change during the early Miocene was mostly masked by the tectonic subsidence and sediment influx. However, isotopic data reveals that eustatic falls contributed to the development of some sequence boundaries during tectonic quiescence stages and uplifting of an intrabasinal high. iii This study reveals also that rift-climax deposits associated with transfer zone growth monoclines are mainly sourced from a hinterland drainage catchment rather than local footwall scarps. The deposits form progressively tilted clastic wedges that onlap and pinch out up-dip toward the growth monocline. Such facies geometry is unlike those observed at faulted margins where the facies commonly thicken toward the fault. |