Coastal Boulder Deposits of the Neogene World: A Synopsis

Abstract

Modern geoscience research pays significant attention to Quaternary coastal boulder deposits, although the evidence from the earlier geologic periods can be of great importance. The undertaken compilation of the literature permits to indicate 21 articles devoted to such deposits of Neogene age. These are chiefly case studies. Such an insufficiency of investigations may be linked to poor preservation potential of coastal boulder deposits and methodological difficulties. Equal attention has been paid by geoscientists to Miocene and Pliocene deposits. Taking into account the much shorter duration of the Pliocene, an overemphasis of boulders of this age becomes evident. Hypothetically, this can be explained by more favorable conditions for boulder formation, including a larger number of hurricanes due to the Pliocene warming. Geographically, the studies of the Neogene coastal boulder deposits have been undertaken in different parts of the world, but generally in those locations where rocky shores occur nowadays. The relevance of these deposits to storms and tsunamis, rocky shores and deltas, gravity processes, and volcanism has been discussed; however, some other mechanisms of boulder production, transportation, and accumulation (e.g., linked to seismicity and weathering) have been missed.

Holocene Boulder Beach Eroded from Chromite and Dunite Sea Cliffs at Støypet on Leka Island (Northern Norway)

“…Differentiated from cobbles, the base definition for a boulder adapted in this exercise is that of Wentworth (1922) for an erosional clast equal or greater than 256 mm in diameter [13]. No upper limit for this category is defined in the geological literature [14]. Triangular plots were employed to show variations in clast shape, following the design of Sneed and Folk (1958) for river pebbles [15].…”

Finding Coastal Megaclast Deposits: A Virtual Perspective

“…Previous reviews of rocky shores [14] and megaclasts [3] confirm such research is promising. Undoubtedly, coastal megaclast deposits of Quaternary age are of special importance because the evidence of such deposits from the earlier geological periods remains scarce [3,15].…”

Evaluation of Boulder Deposits Linked to Late Neogene Hurricane Events

“…These Atlanticisland studies conform to the same procedures entailed in the analysis of boulder shapes as shown for the CBDs from Mexico's Gulf of California, and each pays attention to the key factor of rock density. Generally smaller in size, the cobbles and boulders at Støypet on Leka Island were eroded from low-grade chromite ore with a density of 3.32 g/cm 3 .This reflects the highest-density rock type yet studied for its hydrological properties in a coastal setting. The basalt from the Canary and Azores registers between 2.8 and 3.0 g/cm 3 .…”

“…Generally smaller in size, the cobbles and boulders at Støypet on Leka Island were eroded from low-grade chromite ore with a density of 3.32 g/cm 3 .This reflects the highest-density rock type yet studied for its hydrological properties in a coastal setting. The basalt from the Canary and Azores registers between 2.8 and 3.0 g/cm 3 . The density of granodiorite from Isla San Diego in the Gulf of California was found to be 2.5 g/cm 3 [6], whereas andesite samples from Puerto Escondido and Isla San Luis Gonzaga were found to register a density of 2.3 g/cm 3 or higher [4,5].…”

“…Major sea storms originating as subtropical depressions may have been more common on the high seas and more effective in making landfall over islands and continental shores. The survey conducted by Ruban (2019) [3] was the first contribution to this Special Issue. It reviews 21 studies almost evenly divided between the Miocene and Pliocene.…”