Geologic history of the eastern Argo Abyssal Plain based on ODP drilling and seismic data

A long regional single-fold seismic line (Line 1, Plate 1F) connecting DSDP Site 261 and ODP Site 765 was collected during ODP Leg 123 while transiting the eastern Argo Abyssal Plain (AAP) (Fig. 1). Based on various velocity data collected at Site 765, an excellent correlation was obtained between the seismic data and the drilling results, which allowed for a regional extrapolation of the drilling results and a preliminary interpretation of seismic Line 1. This interpretation provides several new observations about the geologic history of the eastern AAP: 1. A broad regional basement high progressively onlapped by sediments from the north and south has characteristics of an ocean spreading centre. This distribution , however, does not fit the interpreted magnetic anomalies, which show the crust getting progressively younger to the north. 2. Large faulted basement highs in oceanic crust are interpreted to be manifestations of a major group of northwest-trending oceanic fracture zones that are interpreted to offset magnetic anomalies in the eastern AAP. 3. Faults flanking these highs have been reactivated, indicating regional intraplate stresses have affected the oceanic areas at later times. 4. A broad uplifted area in the northeastern AAP provides the tilted surface onto which Cainozoic turbidites progressively thin and onlap. This uplift represents a regional tectonic event of early Tertiary or, possibly, Early Miocene age. This event may be related to subduction along the Sunda-Java trench to the north. 5. Early Cretaceous claystone deposition was generally quite uniform across the entire eastern AAP. 6. Deep-sea depositional moats (cut-and-fill structures) along the flanks of basement highs within the Early Cretaceous section indicate strong deep-sea current systems had become established in the deep AAP, possibly signaling regional changes in palaeoceanography. 7. Generally starved depositional conditions persisted across the eastern AAP for over 40 Ma from Late Cretaceous through Eocene. 8. Major carbonate turbidite deposition sourced from the adjacent plateaus began in Middle Miocene in the southeastern part of the basin, onlapping the uplifted northern part of the area at site261 , where turbidite sedimentation was generally absent. A major change in turbidite sedimentation and source area took place in Late Miocene.