Seagrass-related carbonate ramp development at the front of a fan delta (Burdigalian, New Caledonia): Insights into mixed carbonate-siliciclastic environments. (November 2020)

• Record Type: Journal Article
• Authors: Tournadour, E.; Fournier, F.; Etienne, S.; Collot, J.; Maurizot, P.; Patriat, M.; Sevin, B.; Morgans, H.E.G.; Martin-Garin, B.; Braga, J.C.
• Is Part Of: Marine and petroleum geology. Volume 121(2020)
• Publication Date: 2020-11
• Subjects: Miocene -- Seagrass -- Tropical carbonates -- Terrigenous inputs -- Alluvial fan -- Facies association -- New Caledonia; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2020.104581
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: Past shallow-water carbonate environments of the main island of New Caledonia (NC) have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate-siliciclastic systems under a tropical climate. More particularly, we focused on Burdigalian carbonate sedimentary records cropping out on the western coast of NC, in the Népoui area. Based on a comprehensive sedimentological study of cores and outcrops, we established a new depositional model of an alluvial fan to carbonate ramp transition. Shallow-water (euphotic) carbonate production was dominated by seagrass-related biota and corals derived from small-sized bioconstructions. Extensional tectonics and associated normal faulting, driven by post-obduction isostatic rebound, favored carbonate ramp aggradation and preservation. The carbonate ramp was incised by conglomerate-filled terminal distributary channels, which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories. Phytal substrates induced by seagrass and/or macro-algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal-coralline algal sediments. Seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter-feeding biota in such a high terrigenous influx setting. Highlights: Extensive development of seagrass carbonates occurs at the front of tropical fan delta. Seagrass meadows development favored carbonate production and preservation. The long-term preservation of the depositional system is due to the post-obduction subsidence regime.