Evaluation of morphometric proxies for uplift on sequences of coral reef terraces: A case study from Sumba Island (Indonesia)

Abstract

International audienceSequences of coral reef terraces characterized by staircase morphologies and a homogeneous lithology make them appropriate to isolate the influence of uplift on drainage morphology. Along the northern coast of Sumba Island, Indonesia, we investigated the correlations between landscape morphology and uplift rates, which range from 0.02 to 0.6 mm·yr− 1. We studied eight morphometric indices at two scales: whole island (~ 11,000 km2) and within sequences of reefal terraces (~ 3000 km2). At the latter scale, we extracted morphometric indices for 15 individual catchments draining mostly the reefal terraces and for 30 areas undergoing specific ranges of uplift rates draining only the reefal terraces. Indices extracted from digital elevation models include residual relief, incision, stream gradient indices (SL and ksn), the hypsometric integral, drainage area, mean relief, and the shape factor. We find that SL, the hypsometric integral, mean relief and the shape factor of catchments positively correlate with uplift rates, whereas incision, residual relief, and ksn do not. More precisely, we find that only the areas that are uplifting at a rate faster than 0.3 mm·yr− 1 can yield the extreme values for these indices, implying that these extreme values are indicative of fast uplifting areas. However, the relationship is not bivalent because any uplift rate can be associated with low values of the same indices. For all indices, the transient conditions of the drainage influence the correlation with Pleistocene mean uplift rates, illustrating the necessity to extract morphometric indices with an appropriate choice of catchment scale. This type of analysis helps to identify the morphometric indices that are most useful for tectonic analysis in areas of unknown uplift, allowing for easy identification of short spatial variations of uplift rate and detection of areas with relatively fast uplift rates in unstudied coastal zones

Unraveling the roles of asymmetric uplift, normal faulting and groundwater flow to drainage rearrangement in an emerging karstic landscape

“…We projected onto the same section the elevation of the MIS 11 coral reef terraces mapped by Nexer et al . (), in order to quantify Upper Pleistocene uplift pattern across West Sumba.…”

“…Mean, maximum and minimum elevations were projected onto a north-south (NS)-trending cross-section plane. We projected onto the same section the elevation of the MIS 11 coral reef terraces mapped by Nexer et al (2015), in order to quantify Upper Pleistocene uplift pattern across West Sumba.…”

“…Mean monthly precipitation averages from the spatial tropical rainfall measuring mission (TRMM), yearly averaged over the 1998-2009 period ( Figure 3A). Spatial variations in U were obtained from interpolation of uplift rates calculated from the elevation of the MIS 11 coral reef terrace (Nexer et al, 2015) ( Figure 3B). To the first order, the uplift pattern is asymmetric, increasing regularly southwards if one neglects small discrete downthrows produced by normal faulting.…”

“…The mean elevation of the swath profile exhibits a flat central part at an elevation of 400 m which corresponds to perched alluviated plains (see later). Numerous curved south-verging normal faults disrupt the Waikabubak plateau and the southern slope (Fleury et al, 2009, Nexer et al, 2015 ( Figure 1B). They offset the mean and maximum elevation profiles ( Figure 1C).…”

Geometrical trends within sequences of Pleistocene marine terraces: selected examples from California, Peru, Chile and New-Zealand

“…Coral reef terraces are widely distributed on earth and how they develop in function of sea level is well known (CHAPPELL 1974;MONTAGGIONI & BRAITHWAITE 2009;NEXER et al 2015;PIRAZZOLI et al 1991). Thus they deserve a comparison with the shore platform terraces on which our study focusses.…”