Geology Reference
In-Depth Information
harbour using beachrock or a man-made material,
there should be abundant human artefacts at the
site. Scoffi n (1970) noted glass bottles being incor-
porated into contemporary beachrock at Bimini,
as did Shinn (1978). However, to date no obvious
human artefacts, such as tools, pottery, etc., have
been found incorporated within the Bimini Road
beachrock or otherwise conclusively linked with
formation of the stones.
The lack of certifi able artefacts presents a prob-
lem for those who believe the stones are anthro-
pogenic. The proponents generally describe the
fabled city/state of Atlantis, following descrip-
tions of Spence (1968), to be a highly technical
society. An advanced technical society, similar
to ours, should have produced many artefacts
much as those of other ancient cultures. Certifi able
artefacts that have been found in and near the
site post-date the stones by as much as 3 kyr and
consist mainly of shipwreck remnants such as
ballast stones, cement barrels or other material
discarded from ships. For example, Portland
Cement was originally transported aboard ships
in wooden barrels. When jettisoned overboard,
the wood decays, leaving cement cylinders
that can be confused with columns (Harrison,
1971). Finally, the alternative thinkers may be
infl uenced by myths of the so-called Bermuda
Triangle and the often repeated stories of bur-
ied pyramids and temples. The cement barrels
misidentifi ed as columns (Harrison, 1971)
probably initiated the stories of submerged tem-
ples. These legends abound and appear to be
proliferating with time.
same latitudes to which coral reefs are restricted,
the so-called Coral Seas.
Modern studies using petrography and car-
bonate chemistry began with Ginsburg (1953),
Stoddart & Cann (1965), Dunham (1970, 1971) and
Multer (1971). These workers, like those before,
recognized that beachrock formation is restricted
to the intertidal zone, but unlike previous
studies, they elucidated diagnostic attributes such
as the presence of internal laminations caused
by grain-size variations, seaward-dipping lay-
ers and bubble-shape voids, i.e. keystone vugs
(Dunham, 1970). Keystone vugs are features iden-
tical to those found in adjacent uncemented beach
sands. As rising tides and waves cover the part
of a sandy beach that dries during low tide, air
trapped within the sand is confi ned and coalesces
to form bubbles. Most such bubbles reach the
surface, producing the circular pits so common to
beachcombers. However, some air bubbles, how-
ever, remain over many tidal cycles. The bubbles
tend to push grains upward, forming an arch. These
arches function much like the keystone arches used
in stone buildings for millennia. Some of these
millimetre-size arches can remain locked in posi-
tion long enough to be 'frozen' in place by pre-
cipitation of calcium-carbonate cement between
the grains. This process results in the formation of
near-spherical to elongate voids within the form-
ing beachrock (Dunham, 1970).
Beachrock voids are similar to the more linear
fenestral birds-eye structures that are usually
restricted to fi ne-grained tidal-fl at accumulations
(Shinn, 1983). For a number of reasons, such
voids rarely form in beaches composed of quartz
sand. The lack of preserved voids in quartz-sand
beach accumulations is probably due to a com-
bination of mineralogy, shape of the grains, the
apparent inability of carbonate cement to initi-
ate precipitation on quartz grains and the colder
water temperature often associated with quartz
sand beaches. However, voids are very common
in carbonate-sand beaches, even those composed
of spherical ooid sands.
Many questions remain concerning beachrock
genesis including (1) cement mineralogy (not all
cements are aragonite; some are high-magnesium
calcite), (2) proper identifi cation of beachrock
(sediment cemented in a freshwater lens beneath
an island and later exposed in the intertidal
or subtidal zone by rising sea level and erosion
can be misidentifi ed as beachrock), (3) rate of
cementation, (4) infl uence of fresh water and
How underwater 'roads' are created
To evaluate the Bimini Road more accurately, it
is appropriate here to review the fundamentals
of beachrock formation and confi guration. For a
thorough review of beachrock origins and theo-
ries, see Gischler (2007). His scholarly review
includes observations by nineteenth-century
scientists Chamisso (1821), Lyell (1832), Darwin
(1842), Dana (1875) and Gardiner (1898). These
were the earliest scientists to recognize beach-
rock formation. Later in the twentieth century,
Vaughan (1914), Field (1919, 1920), Daly (1924)
and Keunen (1933) described or noted the pres-
ence, and rapidity, of beachrock formation in
various parts of the world. These twentieth-
century researchers noted that beachrock is
restricted to warm tropical seas, in essence the
