River response to an active fold-and-thrust belt in a convergent margin setting, North Island, New Zealand

Abstract

High-resolution digital elevation data (TOPSAR 10-m grid) are used to reconstruct Late Quaternary growth histories of subtle folding in the Wairarapa fold-and-thrust belt, North Island, New Zealand. Outcrop data of deformed latest Miocene and younger strata are combined with observations of warped and faulted late Quaternary terrace surfaces to unravel the geomorphic and structural history of the Huangarua River valley. Optically stimulated luminescence (OSL) dating of loess that accumulated on these strath terraces and paleosol stratigraphy allow temporal correlation among the terraces and with glacial climate cycles since the Last Interglaciation. These data indicate that five intervals of strath cutting occurred, at f 125, 60 -70, f 30, f 15, and < 10 ka. Strath beveling is largely independent of local folding or regional base-level change. We hypothesize that straths are cut when an increase in sediment supply, during cool climatic periods, brings river sediment load and river transport capacity into balance. In the Wairarapa, strath-cutting events appear to occur near the end of cool climatic cycles.This study shows that the identification of subtle departures from regional topographic trends becomes practical when a high-resolution DEM is available. After subtraction of an average valley gradient from the digital topography, the residual topography on the terrace treads reveals cross-valley and longitudinal tilting. Although rates of folding are slow and the magnitude of deformation is commonly limited to less than a few tens of meters, these topographic anomalies define fold axes that coincide with subsurface structures. When combined with time control, these anomalies serve to define the patterns and rates of fold growth over the past 125 kyears. D

Rates of river incision across the main tectonic units of the Pamir identified using optically stimulated luminescence dating of fluvial terraces

“…In erosional settings such as high mountains, fluvial terraces above a modern river record periods of fluvial stability that interrupt prevalent incision (e.g., Vandenberghe et al, 2011). The factors behind changes in the fluvial dynamic associated with sediment deposition, terrace abandonment and subsequent incision may be complex because of the interplay of tectonics and climate (e.g., Pazzaglia et al, 1998;Burbank and Anderson, 2001;Formento-Trigilio et al, 2002;Pan et al, 2009). Globally compiled fluvial records indicate that terrace formation is primarily a consequence of tectonic uplift combined with cyclic climate (e.g., Bridgland and Westaway, 2008;Westaway et al, 2009).…”

Reassessment of slip rate and implications for surface rupture hazard of the Martinborough Fault, South Wairarapa, New Zealand

“…Despite Fig. IB and C only showing one set of alluvial fans (Q4a), field investigations indicated that within some of the gullies incised into the fans, lower fan surfaces are preserved (see also Formento-Trigilio et al 2003). Approximately 100 m southeast of the foot of the fold-scarp, a stream flows southwest (Fig.…”

“…2. In profile E-E , the unevenness of topography on the footwall side makes interpretation difficult, but the maximum vertical separation is inferred to be c. 1.7 m. faN aND terrace ageS Age constraints for the deformed alluvial fans (Q4a) and little deformed fluvial terraces (Q2a) are provided by OSL ages reported by Formento-Trigilio et al (2003). The location of the two OSL sample sites closest to the Martinborough Fault are shown on Fig.…”

“…We present new mapping of the active fold trace using high resolution Light Detection and Ranging (LIDAR) data (1 m elevation contours and a 10 m cell Digital Elevation Model) and orthophotos (1 m pixels), and surveying of the scarp height using a Real Time Kinematic (RTK) Global Positioning System (GPS) (accurate to ±2 cm). By combining these data with published optically stimulated luminescence (OSL) ages of the alluvial fans and fluvial terraces (Formento-Trigilio et al 2003), we calculate a vertical slip rate which is a factor of 3-7 lower than the previous estimates of Nicol & Van Dissen (1997). Based on these results, we infer a longer recurrence interval than previously estimated, and thus a lower surface rupture hazard.…”

Conditional probability of rupture of the Wairarapa and Ōhariu faults, New Zealand

“…The Waiohine terrace is regarded as equivalent to the Ohakean terrace, both surface and fill, elsewhere in the North Island (Palmer 1984). The age of aggradation, cessation of aggradation and subsequent abandonment of the Ohakean (0Waiohine) terrace has been the subject of a good deal of recent investigation (Formento-Trigilio et al 2003;Litchfield & Berryman 2005;Wang & Grapes 2008;Carne et al 2011; see also references cited therein). Litchfield & Berryman (2005) interpret the timing of abandonment of the Ohakean terrace in the three largest catchments in southeastern North Island to be 15Á20 ka.…”