Late Pliocene (2.9 Ma) Partial Recovery of Shallow Carbonate Banks on Queensland Plateau: Signal of Banktop Re-Entry into Photic Zone during Lowering in Sea Level

Abstract

Shedding of shallow carbonate material toward the deep slopes and basin floors is clearly tied to the position of the carbonate bank tops relative to the photic zone. The onset of bank shedding in periplatform sediments can record either the flooding of the bank tops within the photic zone during a rise in sea level following a period of exposure, referred to in the literature as the "highstand shedding" scenario, or the reentry of the bank tops into the photic zone during a lowering of sea level following a period of drowning, referred to as the "lowstand shedding" scenario. Results from Leg 133 post-cruise research on the Pliocene sequences, drilled in six sites within different slope settings of the Queensland Plateau, seem to point out that the latter "lowstand shedding" scenario can be applied to this particular carbonate system.At the Queensland Plateau sites, the early Pliocene (5.2-3.5 Ma) and the earliest part of the late Pliocene (3.5-2.9 Ma) age sequences were characterized, especially in the "deep" Sites 811 and 817, by pelagic sediments (foraminifers and coccoliths) and by typically pelagic sedimentation rates not exceeding 20 mm/k.y. The earliest part of the late Pliocene age section was characterized by well-developed hardgrounds in the "shallow" Sites 812 and 814 and by normal pelagic sediments mixed with reworked phosphatized planktonic foraminifers in Site 813. Finally, the early part of the late Pliocene (2.9-2.4 Ma) section was characterized by high sedimentation rates, related to the shedding and admixture into the pelagic sediments of bank-derived materials. These bank-derived materials consist of either diagenetically unaltered fine aragonite with traces of dolomite in Site 818 or micritic calcite resulting from seafloor and/or shallow burial alteration in the deepest Sites 817 and 811. The highest sedimentation rates (163 mm/k.y.) were recorded in Site 818, drilled nearest the modern carbonate bank of Tregrosse Reef. The sedimentation rates decrease with increasing distance from Tregrosse Reef-120 mm/k.y. in Site 817 and 47.5 mm/k.y. in Site 811. The initial appearance of fine aragonite in Site 818, corresponding to the transition from pelagic to periplatform sedimentation rates, has been dated at 2.9 Ma. This Pliocene sediment pattern on the Queensland Plateau is different from the pattern observed in sediments from two earlier ODP legs (i.e., Leg 101 in the Bahamas and in Leg 115 in the Maldives), where aragonite-rich sediments, characterized by high periplatform sedimentation rates, were observed in the lower Pliocene section (5.2-3.5 Ma), whereas the upper Pliocene (3.5-1.6 Ma) sediments are more pelagic in nature and are characterized by low sedimentation rates or major hiatuses. These Pliocene periplatform sequences in the Bahamas and in the Maldives and late Quaternary age periplatform sequences worldwide have pointed out that "highstand shedding" was the typical response of carbonate platforms to fluctuations in sea level, just opposite to a "lowstand shedding" response to...

Carbonate seismic stratigraphy of the Gulf of Papua mixed depositional system: Neogene stratigraphic signature and eustatic control

“…The transgression created accommodation space resulting in carbonate aggradation during the late Miocene and early Pliocene, though this was limited in some areas, in particular the southern part of Borabi Platform (Fig. 4b) where the carbonate system was able to keep up with the relative sea level rise after reentering the photic zone (Droxler et al, 1993). The neritic carbonate system in the southern part of the study area (in the vicinity of Anchor Cay well, Figs 4b and 5e), and on the isolated Ashmore-Boot-Portlock and EFR platforms (Figs 5e, 8b and d), was able to grow signi¢cantly during the late Miocene and Pliocene.…”

Neogene evolution of the mixed carbonate‐siliciclastic system in the Gulf of Papua, Papua New Guinea

“…[17] Our study reveals that the evolutionary history of the neritic carbonate system in the GoP was very similar to the evolution of the pure carbonate systems along the northeastern Australian margin and particularly on the Queensland and Marion plateaus [McKenzie et al, 1991;Droxler et al, 1993;Feary et al, 1993;Betzler et al, 1993Betzler et al, , 2000Brachert et al, 1993;Isern et al, 2002;John and Mutti, 2005]. We observe that during the overall late Oligocene and early Miocene sea level transgression, most of the platforms in the GoP experienced a general back stepping of environments, resulting in a systematic decrease of the surface area of neritic carbonate production.…”

Mixed Carbonate–Siliciclastic Sedimentation Along the Great Barrier Reef Upper Slope: A Challenge To the Reciprocal Sedimentation Model

“…Although the highstand shedding concept is consistent with Holocene sediment accumulation along the GBR margin, neritic carbonate accumulation and export appear to have been already initiated during the late transgression (Dunbar et al 2003b;Page et al 2005;Jorry et al 2010). Neritic carbonate production and export can also be triggered when sea level on a carbonate platform, drowned during a relative sea level highstand, starts to fall (Droxler et al 1993).…”

“…Mixed carbonate-siliciclastic systems have been common throughout the geologic past (Dorobek 2008); however, few outside of the GBR and Belize have been studied in the context of well-established sea level curves. In almost all cases, with the exception of the Late Pliocene Queensland Plateau (Droxler et al 1993), postulated for some Campanian-Maastrichtian deposits (Shanmugam and Moiola 1983), and Early Cretaceous platform in the French Alps (Jacquin et al 1990), the presence of carbonates is assumed to be the result of highstand shedding and a reflection of a period of elevated sea level (Schlager et al 1994). This is, however, a potentially false assumption as this study of the central GBR shows.…”