Age constraints on surface deformation recorded by fossil shorelines at Cape Range, Western Australia

Abstract

Laterally continuous terraces along the western flank of Cape Range, Western Australia, record both past sea-level highstands and postdepositional vertical displacement. Four distinct fossil coral reef terraces extend nearly the entire length of the slowly uplifting anticlinal structure (∼100 km), enabling documentation of the timing and degree of deformation-induced elevation contamination of past sea-level estimates from fossil shorelines. Here, we present detailed elevations of the four terraces using differential global positioning system (DGPS) and airborne light detection and ranging (LiDAR) data sets, along with new ages for the three upper terraces. Geochemical dating using strontium isotope stratigraphy techniques revealed, from highest to lowest elevation: a late Miocene reef terrace, a late Pliocene shoreline, and a prominent mid-Pleistocene reef terrace (probably associated with the marine oxygen isotope stage 33−31 interglacial), along with a broad last interglacial (Eemian) reef terrace and lagoon, which terminate at the modern shoreline. Laterally variable elevation data integrated with newly defined ages for the terraces demonstrate a gradual and continuous relative deformation in the region that spans at least the last 6.5 m.y. and constrains the emergence of the Cape Range to sometime prior to the late Miocene. This data set also shows that the most recent interglacial shoreline has undergone <1.3 m of vertical warping, suggesting minimal deformation since deposition. By tracing relative uplift rates over multiple terraces for ∼100 km of coastline, we placed constraints on maximum relative sea level (RSL) for the older terraces. Most notably, we were able to place strict maximum RSL elevations of <+34 m on the Pliocene terrace and <+16.5 m on the mid-Pleistocene terrace, with probable RSL being somewhat lower.

Higher than present global mean sea level recorded by an Early Pliocene intertidal unit in Patagonia (Argentina)

“…Three oyster shells from Roadcut and Caprock were analyzed by strontium isotope stratigraphy (SIS) relative dating techniques. Using sequential leaching to target the least altered inner carbonate of each shell, we obtained multiple SIS ages on three different shells (one from Caprock and two from Roadcut; see Sandstrom et al 11 for a detailed description of the adopted methodology). The shells yielded an age range of 4.69-5.23 Ma (n = 6, 2σ S EM ).…”

“…3-7, Supplementary Tables 3-4) with samples scoring above "2.0" excluded from results. The same screening criteria have recently been used by Hearty et al 10 and are discussed in Sandstrom et al 11 . The latter also gives an overview of the limits and implications of SIS analyses for Plio-Pleistocene marine samples.…”

“…Wellpreserved and dated RSL indicators are relatively rare for older time periods: another compilation of Pleistocene RSL indicators 7 reports more than 1000 Last Interglacial (MIS 5e, 125 ka) and only around 20 MIS 11 (400 ka) RSL indicators. Only a handful of sites exist that document sea level highstands beyond one million years ago 2,[8][9][10][11] . In general, robust RSL indicators predating 400 ka are rare to find because they are poorly preserved and are most often difficult to date with precision.…”

The effect of lateral variations in Earth structure on Last Interglacial sea level

“…Additional higher corals were interpreted to reflect a late rise in sea level. inferred a similar planated surface during the first half of the LIG and interpreted the higher corals to be tectonically deformed (see also Sandstrom et al, 2020). GIA and therefore inferred GMSL would be marginally impacted by 3D Earth structure at this location, which tends to increase inferred GMSL (by ∼ 0.5 m).…”

Pliocene‐Pleistocene Stratigraphy and Sea‐Level Estimates, Republic of South Africa With Implications for a 400 ppmv CO2 World

“…We used the "leach method" described by Bailey et al (2000), which measures four or five sequential leachates on a single sample and which assumes that the more loosely bound diagenetic 87 Sr/ 86 Sr reservoirs will tend to be partitioned into the first leaches (Bailey et al, 2000;Li et al, 2011;Sandstrom et al, 2014). This advanced leaching protocol has the additional benefit of providing minimum or maximum SIS ages on the samples, based on trends within each leach set.…”