Since Last Glacial Maximum (23–19 ka), Earth climate warming and deglaciation occurred in two major steps (Bølling‐Allerød and Preboreal), interrupted by a short cooling interval referred to as the ...Younger Dryas (12.5–11.5 ka B.P.). In this study, three cores (MV‐33, MV‐66, and MD‐40) collected in the central part of Pandora Trough (Gulf of Papua) have been analyzed, and they reveal a detailed sedimentary pattern at millennial timescale. Siliciclastic turbidites disappeared during the Bølling‐Allerød and Preboreal intervals to systematically reoccur during the Younger Dryas interval. Subsequent to the final disappearance of the siliciclastic turbidites a calciturbidite occurred during meltwater pulse 1B. The Holocene interval was characterized by a lack of siliciclastic turbidites, relatively high carbonate content, and fine bank‐derived aragonitic sediment. The observed millennial timescale sedimentary variability can be explained by sea level fluctuations. During the Last Glacial Maximum, siliciclastic turbidites were numerous when the lowstand coastal system was located along the modern shelf edge. Although they did not occur during the intervals of maximum flooding of the shelf (during meltwater pulses 1A and 1B), siliciclastic turbidites reappear briefly during the Younger Dryas, an interval when sea level rise slowed, stopped, or perhaps even fell. The timing of the calciturbidite coincides with the first reflooding of Eastern Fields Reef, an atoll that remained exposed for most of the glacial stages.
In tropical and sub‐tropical mixed siliciclastic–carbonate depositional systems, fluvial input and in situ neritic carbonate interact over space and time. Despite being the subject of many studies, ...controls on partitioning of mixed sediments remains controversial. Mixed sedimentary records, from Ashmore Trough shelf edge and slopes (southern Gulf of Papua), are coupled with global sea‐level curves and anchored to Marine Isotope Stage stratigraphy to constrain models of sediment accumulation at two different timescales for the past 130 kyr: (i) 100 kyr scale for last glacial cycle; and (ii) millennial scale for last deglaciation. During the last glacial cycle, carbonate production and accumulation were primarily controlled by sea‐level fluctuations. Export of neritic carbonate to the slopes was initiated during re‐flooding of previously exposed reefs and continued during Marine Isotope Stage 5e and 1 interglacial sea‐level highs. Siliciclastic fluxes to the slope were controlled by interplay of sea level, shelf physiography and oceanic currents. Heterogeneous accumulation of siliciclastic mud on the slope, took place during Marine Isotope Stage 5d to Marine Isotope Stage 3 sea‐level fall. Siliciclastics reached adjacent depocentres during Marine Isotope Stage 2. Coralgal reef and oolitic–skeletal sand resumed at the shelf edge during the subsequent stepwise sea‐level rise of the last deglaciation. Contemporaneous, abrupt siliciclastic input from increased precipitation and fluvial discharge illustrates that climate controlled deglacial sedimentation. Siliciclastic input persisted until ca 8.5 ka. Carbonate accumulation waned at the shelf edge after ca 14 ka, whereas it increased on the slopes since ca 11.5 ka, when previously exposed reef and bank tops were re‐flooded. When comparing the last sea‐level cycle sedimentation patterns of the southern Gulf of Papua with other coeval mixed systems, sea level and shelf physiography emerge as primary controls on deposition at the 100 kyr scale. At the millennial scale, siliciclastic input was also controlled by climate change during the unstable atmospheric and oceanic conditions of the last deglaciation.
The accurate reconstruction of the facies architecture in the Jurassic succession of Monte Kumeta, coupled with a detailed biostratigraphy, allow to define dynamics and genetic factors controlling ...the conversion of a Bahamian-type carbonate platform to a pelagic escarpment. A change from tidalites to oolites i.e. from the restricted, interior lagoon to a more open-marine sandy depositional environment, records the establishment of a basin south of the Monte Kumeta sector in late Hettangian-Sinemurian times. The oolitic limestones are overlain by earliest Carixian bioclastic grainstones and packstones with micritized grains and by wackestones with radiolarians and sponge spicules, organized in thin sand prisms. The decrease of carbonate productivity indicated by these sediments records the dissection of the platform and the subsequent isolation of a submarine topographic high in the Monte Kumeta sector. Though based only on indirect evidence, it is suggested that a tectonically controlled scarp must have existed between the Monte Kumeta "high" and the basin. Progressive northward retreat of this scarp resulted in the conversion of a shallow platform sector into a gradually steepening slope, along which the distribution of sediments was controlled by repeated tectonic and gravity-induced modifications of the topography of the substrate. Vertical and lateral changes and geometrical relationships of the recognized lithofacies suggest that they were deposited on a stepped surface brought about mainly by, repeatedly reactivated basin ward dipping normal faults. This scenario is clearly reflected by the relationship of platform strata and the overlying encrinites of Carixian/Domerian age. The encrinite bodies show again a prismatic geometry, becoming thicker towards the south and filling the first generation of neptunian dykes. The top of the encrinites is marked by a peculiar jagged dissolution surface with dm-scale pinnacles capped by a thick ferromanganese crust. The formation of this peculiar surface could have been controlled by complex changes in water chemistry probably related to the Early Toarcian anoxic event. The crust itself is dissected by faults of decimetres to metres of throw, sometimes organized into small-scale positive flower structures. In the hollows/depressions of this highly articulated substrate pelagic sediments of Bajocian to Oxfordian age were deposited. They display a clearly onlapping relationship to the encrinites and to the carbonate platform beds. Their thickness rarely exceeds 4 to 5 meters and they are present also as neptunian dykes filling a dense network of fissures. During Late Callovian and Oxfordian times synsedimentary tectonics has intensified resulting in an increase of the inclination of the slope. This led to more and more abundant, gravitationally controlled deformations (slumping and sliding) of semi-lithified and unlithified sediments along the Monte Kumeta escarpment.PUBLICATION ABSTRACT
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