Abrasive notches along the Atlantic Patagonian coast and their potential use as sea level markers: the case of Puerto Deseado (Santa Cruz, Argentina)

Abstract

Patagonia Argentina is a key area for the study of sea level changes in the southern hemisphere, but the availability of reliable sea level markers in this area is still problematic. In fact the storm deposits (beach ridge) commonly used here to reconstruct past sea level oscillations introduce a wide error. Along the Puerto Deseado coast (Santa Cruz), morphometric analyses of 11 features were carried out using traditional measurement tools and a digital software‐based method (tested on one selected feature) with the aim to investigate the possibility of their use as sea level markers. By undertaking accurate topographic profiles we identified the relationship between notches and current sea level. In detail, we identified two clusters of notch retreat point elevations, with a very low internal variability. The lower was located a little below the mean high tide level (mHT) and the upper located at least 0.5 m above the maximum high tide level (MHT). Field observations of tidal levels and the position of notches suggest that the lower notches are active and the upper are inactive. This study on the abrasive notches attests their quality as sea level markers and opens up the use of fossil abrasive notches as palaeo sea level markers because the error linked to these features is substantially smaller than that introduced by beach ridges commonly used in the study area. Copyright © 2014 John Wiley & Sons, Ltd.

Coastal notches: Their morphology, formation, and function

“…Bini et al (2014) pointed out that the apex of abrasion notches in volcanic rocks in Patagonia (tidal range 4 to 5.5 m) is at the mean high tidal level, providing support for similar conclusions by Dickinson (2001) on Pacific islands, Irion et al (2012) in Brazil, and Trenhaile et al (1998) in the megatidal Bay of Fundy in eastern Canada (Fig. 2f).…”

“…Several workers have recorded notch profiles using laser distance metres to measure the height from the floor to the roof of the notch at prescribed intervals landwards along its floor (Kogure et al, 2006;Kázmér and Taboroši, 2012b;Trenhaile et al, 2013Trenhaile et al, , 2015Moses et al, 2015). Another promising technique was employed by Bini et al (2014), who used software-based technology to generate three-dimensional notch data from overlapping images taken with a digital camera.…”

“…Abrasion notches develop in the shallow subtidal zone if the wave-generated bottom currents are strong enough to agitate the abrasives, and they can also form above the high tidal level at the limit of storm wave swash, or where pebbles or other material is propelled landwards (Wziatek et al, 2011;Bini et al, 2014). Most abrasion notches are in the intertidal zone, in the surf and swash zones of broken waves, and particularly at the cliff foot where coarse, abrasive material tends to accumulate (Trenhaile, 2004b).…”

The temporal and spatial scales of rocky coast geomorphology: a commentary

“…For example Bini et al . () investigated a 100‐m stretch of the Argentinian coast to specifically quantify the relationship of erosive notches to sea level. Kennedy et al .…”

A fundamental equation for describing the rate of bedrock erosion by sediment‐laden fluid flows in fluvial, coastal, and aeolian environments

“…Abrasion occurring on bedrock coasts, usually called rocky or rock coasts, always exposed to oscillatory flow motion, may produce the basal erosion of sea cliffs (Trenhaile, 1987;Sunamura, 1992;Moses and Robinson, 2011), the formation of notches (Sunamura, 1976(Sunamura, , 1982aBini et al, 2014), the development of stacks (Trenhaile et al, 1998;Limber and Murray, 2015), the lowering of shore platforms (Hills, 1971(Hills, , 1972Sunamura, 1994;Foote et al, 2006;Blanco-Chao et al, 2007;Moses and Robinson, 2011), and the development of marine potholes (Abbott and Pottratz, 1969;Sunamura, 1992 and references therein). Clastic sediment in the rocky shore zone has two contradictory effects similar to the fluvial case: to accelerate erosion working as an abrasive (the positive effect) and to halt it as a protective layer (the negative effect) (Sunamura, 1976).…”