Rocky Shorelines - Trace Fossils as Indicators of Sedimentary Environments - page 426

Chapter 15
Rocky Shorelines
Jordi M. de Gibert, w Rosa Dom ` nech 1 and Jordi Martinell
Departament d'Estratigrafia, Paleontologia I Geocie`ncies Marines, Universitat de Barcelona,
Barcelona, Spain
1 Corresponding author: e-mail: [e-mail]
1. INTRODUCTION
Rocky coasts account for more than 33% of the world's coastline today
( Reading and Collinson, 1996 ). Their morphology is controlled by the interven-
tion of three major processes ( Anthony, 2008; Trenhaile, 1987 ): (1) mechanical
action, (2) weathering, and (3) biological erosion. Thus, benthic life plays a very
active role in shaping these environments through the action of bioeroders (e.g.,
Spencer and Viles, 2002 ). The identification of ancient rocky shores is important
as they serve as reliable markers of paleoshorelines. Bioerosion assemblages
play a key role for rocky-coast recognition (e.g., de Gibert et al., 1998 ) as bor-
ings are cavities in the rockground, which have a higher preservation potential
than any other component of the biota of these environments.
The geological significance of rocky-shore bioerosion was evinced as early as
in Charles Lyell's “Principles of Geology” ( Lyell, 1830 ), who started his seminal
masterpiece with a reproduction of the abundant bivalve borings found in the col-
umns of the temple of Serapis (Pozzuoli, Italy), and used them as a proof of relative
sea-level changes ( Fig. 1 ). Despite this pioneering contribution, fossil rocky shores
were considered uncommon (e.g., Boucot, 1981 ). Nevertheless, thanks to the stud-
ies carried out during the past two decades, in particular, those of Markes E. Johnson
and collaborators ( Johnson, 1988a,b, 1992, 2006; Johnson and Baarli, 1999 ), it is
clear today that rocky-shore surfaces and associated deposits can be found through-
out the geological column, commonly in relation to transgressive episodes.
2. MODERN ROCKY-SHORE HABITATS AND INHABITANTS
2.1 Rocky-Shore Habitats
As Johnson and Baarli (1999) highlighted, the land/sea interface is the most
definitive ecological limit of all existing on Earth. The transition between these
two contrasting settings is sharp and clearly juxtaposes different physical,
w Deceased.