#1ISTerre Institut des Sciences de la Terre Ccnes 14 DUNIVERSITÉ UNAEN DE ROUEN Imperial College UBO NORMANDIE London université de bretagne occidentale High-resolution topography of the uplifting Huon Peninsula (Papua New Guinea) reveals high interstadial sea-levels over the past ~400 ka Gino de Gelder¹, Laurent Husson1, Anne-Morwenn Pastier2, Denovan Chauveau³, David Fernández-Blanco4, Tamara Pico5, Christine Authemayou³, Kevin Pedoja, 1. ISTerre, Université Grenoble Alpes, France 2. Université de Rouen Normandie, France 3. Université de Bretagne Occidentale, France 4. CSIC, Barcelona, Spain 5. California Institute of Technology, US 6. Université de Caen Normandie, France#2Sea-Level Typically represented by curves that display changes throughout geological history Problem: Global Mean Sea-Level estimates from sea-level indicators and oxygen isotope curves mismatch for recent cold periods (MIS 3, 5a) Question: Is there a similar discrepancy for older cold periods (MIS 6, 9a, 11a)? Approach: We re-visit Huon coral reef terrace sequence with high-resolution topography and modelling Quantifying past sea-level is important... to support estimates of global ice-sheet volumes and its spatio-temporal response to climate change to deduce local tectonic uplift rates and estimate associated earthquake hazards to reconstruct paleogeography and test models of human migration And several other applications... sea level (m) 50 -50 -100 0 Global Mean Sea-Level estimates from sea-level indicators (Dutton et al., 2015; Pico et al., 2016; Creveling et al., 2017) 3 5e 5c 5a 6 9e 7a 7c 7e 9a 11a 11c Principal component analysis of 7 oxygen-isotope derived sea-level curves (Spratt & Lisiecki, 2016) -150 0 50 100 150 200 250 age (ka) 300 350 400 450#3Coral reef terraces Fossilised coral reefs, important relative sea-level indicators, only in (sub-)tropical climates. At tectonically uplifting/subsiding locations, they typically form 'staircases' with flat surfaces (terraces) bounded on either side by (paleo) sea-cliffs Complex interplay between reef growth, erosion and sedimentation, but to a first order, coral reef terraces mark relative sea-level highstands. SE-Cuba SE-Cuba Sulawesi, Indonesia#4-6.3 -6.2 -6.1 Huon Peninsula, Papua New Guinea 147.2 147.3 -5.9 0 5 10 15 20 Kilometers Pleiades DSM -6.0 147.4 0.5 - - One of the most important terrace sequences in the world High uplift rates have resulted in very complete SL record Over 120 dated corals Assumed NW-directed tilt But, few studies on large-scale terrace geometry since the 1970s We developed a 2m resolution Digital Surface Model (DSM) 147.2 147.3 CAA A A A 147.4 147.5 0.75 1.0 THE 147.5 147.6 147.7 147.8 1.25 1.5 1.75 2.0 2.25 2.5 2.75 0.5 Pleiades DSM (2m) 3.0 3.0 147.6 147.7 2.75 2.5 Legend Normal fault Dated sample (Compilation Hibbert et al., 2016) MIS 5e paleoshoreline (~128 ka) Uplift Rate (mm/yr) contour Chappell (1974) 147.8 4000 3000 Elevation (m) T 2000 1000 0 -6.3 -6.2 -6.1 -6.0 -5.9#5a Elevation (m) C Tilt direction Marine terrace (paleo-platform) Shoreline angle example 300F Shoreline angle 275 example 250 225 200 b Count 40 n = 171 20 147.5 147.6 147.7 147.8 Paleo-seacliff Shoreline Angle STD-4.94 m X²/X² = 0.90 crit95% min max 0 500 1000 -15 -10 Distance (m) -5 0 5 Residuals (m) 10 15 500- Shoreline angle surface fitting 400 Ο Ο 300 Elevation (m) 200 100 0- 30 25 20 15 10 Distance towards S (km) Fitted surface elevation (m) 50 100 150 200 250 300 350 400 450 5 25 10 15 20 Distance towards W (km) 0.75 1.25 1.5 75 Legend Normal fault Dated sample (Compilation Hibbert et al., 2016) MIS 5e paleoshoreline (~128 ka) 0.5 Uplift Rate (mm/yr) contour Chappell (1974) -5.9 -6.0 2.25 We systematically quantified ~300 shoreline angles for two terraces using the DSM For both, best-fitting planes indicate generally N-ward dipping terraces, unlike previous studies 4000 3.0 3.0 2.75 2.5 147.6 147.7 147.8 3000 2000 1000 0 T T Elevation (m) -6.2 -6.3#6Thanks GoogleEarth 146° 147° Large scale tectonics South Bismarck Plate Huon-Finisterre Ranges Ramu-Markham Fault 7° 6° New Guinea Highlands 148° Wonga Thrust Australian Plate Subduction Major active zone thrust fault 149° 100 km New Britain Faults modified from Holm and Richards (2013) Strike-slip fault Minor or inactive thrust fault N-wards tilt fits well within regional tectonic framework, with major N-dipping thrust faults S of Huon Peninsula#7Implications for RSL estimates: Sialum section example Previous uplift rate corrections to derive Huon RSL estimates inferred from MIS 5e paleoshorelines Correction based on coastline- perpendicular profiles (mostly NE- SW) 1 km Dated coral samples 85 ka 100 ka 105 ka 105 ka 122 ka MIS 5e (~129 kay 128 ка 29 ka 6 ka 52 ka 60 ka 90 ka 1.7 1.8 1.9 2.0 Uplift Rate (mm/yr) 2.1 Sialum section With a N-ward tilt, UR estimates at Sialum decrease by 0.05-0.13 mm/yr, and RSL estimates increase by 5-10 m#8MIS 5e 0 Relative Sea-Level (RSL) estimates beyond ~125 ka Distance (km) Stacked Swath Profile Topography looking W 1000 Elevation (m) 0 50 -100 Huon coral ages currently limited to past ~125 ka (MIS 5e - recent) High-resolution topography allows us to constrain the geometry of older terraces if the spatial uplift rate pattern has remained constant#9sea level (m) 50 Relative Sea-Level (RSL) estimates beyond ~125 ka -50 -100 -150 0 Spratt & Lisiecki, 2016 + RSL estimates Huon Deglaciation LGM Н 1 l Glaciation 100 200 300 400 age (ka) First order agreement between our estimates of Huon RSL and GMSL estimates from $180 curves Huon RSL highstand estimates during cold. periods systematically higher Why? Wrong calibration. with Last Glacial Maximum (LGM)? Differences glaciation/ deglaciation? GIA?#10sea level (m) -20 -40 -60 -80 -100 -120 20 20 22 Glacial Isostatic Adjustments (GIA) SL2016 GMSL curve SL2016 smoothed GMSL curve Huon RSL curve 71P-35 Huon RSL curve 48P-515 Huon RSL 0 50 100 150 200 250 300 350 age (ka) Fair comparison between Huon Relative Sea-Level (RSL) and Global Mean Sea-Level (GMSL) requires GIA correction We applied two different GIA models to the Spratt & Lisiecki 2016 GMSL- curve using ICE-5G 400 GIA-corrections can only account for a few meters of discrepancy between RSL and GMSL#11sea level (m) Reef modeling Verify if our Huon highstand adjustments also improve model fits Evaluate lowstand elevations and relative sea-level rise 50 -50 -100 0 Η Spratt & Lisiecki, 2016 Spratt & Lisiecki, 2016; highstands adjusted Spratt & Lisiecki, 2016; high- and lowstands adjusted + RSL estimates Huon AMY -150 0 50 50 100 150 200 250 age (ky) We initially test three different sea-level curves, For example video of reef model, see: on three different profiles across the terraces https://youtu.be/IFDAVSDEHYU#12Sialum Section -1.90 mm/yr Basal slope 7% Elevation (m) 400 300 200 100 0 Reef modeling 0.0 12.5 30.5 63.5 73.5 88.5 109.5 133.5 188.5 201.5 226.5 246.5 279.5 298.5 Age (ka) MIS 7e MIS 7c MIS 7a MIS 6 topography MIS 5e MIS 5c MIS 5a 0 2000 4000 Distance (m) 6000 MIS3 Spratt & Lisiecki 2016 curve Highstands adjusted High-lowstands adjusted - SL-curves with adjusted highstands fit better with observed morphology Differences between two adjusted curves very subtle Further analysis in progress: detailed assessment of rapid (<10 ky) oscillations and bayesian inversion of topography?#13Conclusions SL and Huon coral reef terraces At the well-studied Huon Peninsula, terraces appear to be tilted N-wards rather than NE-wards, in better agreement with the regional tectonic structures Terrace-geometry based Huon RSL highstand estimates during cold periods are systematically higher than ESL estimates from 8180 curves. 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