Pliocene-Pleistocene Aragonite Cyclic Variations in Holes 714A and 716B (the Maldives) Compared with Hole 633A (the Bahamas): Records of Climate-Induced CaCO3 Preservation at Intermediate Water Depths

Abstract

Ocean Drilling Program (ODP) Leg 115 post-cruise research was focused on two Maldives sites, more precisely on the top 108 m of Hole 716B (water depth, 540 m), equivalent to the past 3.5 m.y., and the top 19.5 m of Hole 714A (water depth, 2195 m), equivalent to the past 0.55 m.y. These sediments consist of mostly unaltered and undisturbed, turbidite-free, periplatform ooze. Results of our research are compared with existing data on Hole 633A (water depth, 1681 m), drilled in the Bahamas during ODP Leg 101, using age/depth models built on the basis of oxygen isotope, nannofossil, and magnetic stratigraphies. Climate-induced, long-term (roughly 0.5 m.y.) aragonite cycles, superposed on short-term (roughly 0.04 and 0.1 m.y.) aragonite cycles, have been established at least during the past 2.0 m.y., in the Maldives and the Bahamas. Our most interesting result is the clear correlation among the aragonite long-term cycles in the Maldives and the Bahamas and the carbonate-preservation, long-term cycles from the open Pacific, Indian, and North Atlantic oceans. The mid-Brunhes dissolution interval, corresponding to the youngest preservation minima of the carbonate-preservation, longterm cycles, is clearly defined by fine aragonite minimum values in the deep periplatform sites, and by maximum fragmentation of pteropod tests in the shallow sites. Aragonite and planktonic 5 18 O records, usually in phase during the late Pleistocene, display, further back in time, discreet intervals where the two records do not match with one another. Major mismatches between both records occur synchronously in the Maldives and Bahamas periplatform sites and seem to correspond to extreme events of either carbonate-preservation or dissolution in the deep pelagic carbonate sites of the equatorial Pacific Ocean. Based on our findings, short-and long-term aragonite cycles can no longer be explained only by variations of aragonite input from the nearby shallow carbonate banks, in response to their alternate flooding and exposure through cyclic sea-level fluctuations. The aragonite long-term cycles in the periplatform environments are interpreted as carbonatepreservation cycles at intermediate-water depths. Their occurrence shows, therefore, that the carbonate chemistry of the entire water column has been influenced by long-term (0.5 m.y.) cyclic variations during the past 2.0 m.y. These major changes of the water-column carbonate chemistry are linked to the climate-induced carbon cycling among the different atmospheric, oceanic, and sedimentary carbon reservoirs.

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

“…Calcareous nannofossil biostratigraphy and magnetostratigraphy agree particularly well in sediments from the past 2.9 Ma for the three shallow sites. The general trend of the Pliocene age/depth curves, already observed based on the shipboard data set and reinforced by results from our post-cruise research, was unexpected in the context of our previous results from studies of Pliocene periplatform sequences in the Bahamas and the Maldives (Droxler et al, 1988(Droxler et al, , 1990 (Fig. IB).…”

“…Though the link between aragonite content and stable isotopes is not always straightforward, heavy δ 18 θ and δ 13 C values tend to correspond to low aragonite values and vice versa. This trend is opposite to the light δ 18 θ values that usually correspond to high aragonite content values systematically observed in Quaternary periplatform sequences in the Bahamas and the Maldives (Boardman et al, 1986;Droxler et al, 1983Droxler et al, , 1988Droxler et al, and 1990, on the Nicaragua Rise (Glaser and Droxler, 1991), and on the Queensland Plateau (Haddad et al, this volume). Because 12 aragonite cycles can be identified in the interval between 2.9 and 2.4 Ma (500 k.y.…”

“…Furthermore, carbonate highstand shedding was also observed on a longer time scale in Pliocene-Pleistocene periplatform sequences drilled in the Bahamas and the Maldives during ODP Legs 101 and 115 (Austin, Schlager et al, 1988;Droxler et al, 1988 and.Early Pliocene, an interval of particularly high eustatic sea level (Haq et al, 1987;Raymoetal., 1986;Jansen et al, in press;Hodell and Venz, 1992;, that corresponded to a warmer climatic interval between 5.2 and 3.7 Ma than that during the late Pliocene and Quaternary, is characterized by higher sedimentation rates (Fig. IB) and aragonite-rich sediments in Site 633 (Exuma Sound, Bahamas, Droxler et al, 1988) and in Site 716 (Inner Sea, the Maldives, Droxler et al, 1990). In contrast, periplatform sediments deposited during the late Pliocene (3.5-1.6 Ma), an interval characterized by lower sea level and colder climate than during the early Pliocene (Haq et al, 1987;Raymo et al, 1986;Hodell and Venz, 1992;Jansen et al, in press), are characterized by a low content or absence of bank-derived aragonite and generally low sedimentation rates (Droxler et al, 1988(Droxler et al, , 1990.…”

“…IB) and aragonite-rich sediments in Site 633 (Exuma Sound, Bahamas, Droxler et al, 1988) and in Site 716 (Inner Sea, the Maldives, Droxler et al, 1990). In contrast, periplatform sediments deposited during the late Pliocene (3.5-1.6 Ma), an interval characterized by lower sea level and colder climate than during the early Pliocene (Haq et al, 1987;Raymo et al, 1986;Hodell and Venz, 1992;Jansen et al, in press), are characterized by a low content or absence of bank-derived aragonite and generally low sedimentation rates (Droxler et al, 1988(Droxler et al, , 1990. In summary, results from several late Quaternary and Pliocene-Pleistocene periplatform studies showed that sediments deposited in the vicinity of carbonate banks faithfully recorded fluctuations in sea level and demonstrated that "highstand shedding" is a common response of carbonate banks to fluctuations in sea level.…”

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“…On the Inner Sea side, terraced atoll slopes have the same dip angles but reach to water depths of only 150 m, where the gradient rapidly declines (Fürstenau et al, 2010). The Inner Sea is characterized by periplatform ooze deposition that locally accumulates into sediment drift bodies (Droxler et al, 1990;Malone et al, 1990;Betzler et al, 2009, Lüdmann et al, 2013.…”