Rapidly-cemented intertidal zone sediments often contain 'fossils" of human debris:-

http://csicop.org/si/2004-01/geologists-adventures.html

Beachrock is rock that forms near mid-tide level beneath the sand on tropical beaches. It is a very distinctive rock that forms rapidly. Tidal fluctuation constantly forces calcium carbonate-rich waters through the sands where evaporation and off-gassing of carbon dioxide probably help stimulate precipitation of calcium carbonate. Within a few years, crystals of aragonite, a common marine form of calcium carbonate, precipitate between the grains, welding them together to form a very hard limestone. There are beach rocks around some Pacific islands that contain human skeletons and shell casings from World War II. At Bimini and along other Bahamian islands, many swimming beaches are lined with beachrock that is forming today. They contain imbedded Coke and beer bottles.

http://en.wikipedia.org/wiki/Beachrock My University lecturer in carbonates, Terry Scoffin (referenced in the Wikipedia article) used to show a wonderful picture of a coke bottle encased in solid sandstone

Million Dollar Point, Vanuatu:-

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6X-3V60552-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=39aa749bdfd026c55761b0f8fe75a807

Rapidity of marine carbonate cementation — implications for carbonate diagenesis and sequence stratigraphy: perspective

Gerald M. Friedman*
Department of Geology, Brooklyn College and Graduate School of the City University of New York, Brooklyn, NY 11210, and Northeastern Science Foundation affiliated with Brooklyn College, Rensselaer Center of Applied Geology, 15 Third Street, P.O. Box 746, Troy, NY 12181-0746, USA
Received 20 February 1998; accepted 8 April 1998. Available online 25 November 1998.

Abstract

Lithification is a rapid process, but how rapid is rapid? A year after one of my visits to Joulter's Cay (Bahamas) I found a sardine can from my previous visit. The cementation of carbonate particles in and around the can was surprising. 382 g of ooids and skeletal material had filled the can and lithified therein, or had become cemented to the outside of the can. The rapidity of marine carbonate cementation implies that during highstand of sea level shallow-water platform carbonate sediments are subject to marine lithification which retards erosion. This conclusion is at variance with that of other workers who rely on freshwater cementation during lowstands to generate cement which retards reworking. Clearly the historical debate over highstand versus lowstand of shallow-water marine carbonates is not yet over.