Geology Reference
In-Depth Information
Box 4.14.
Selected case studies of modern marine and non-marine ooids.
Note that Mediterranean references also
include studies of Early Holocene and reworked Pleistocene relict ooids.
Marine environments:
Bahamas
- Ball 1967; Bathurst
1967, 1968; Carney and Boardman 1993; Cros 1979; Fab-
ricius 1977; Gektidis 1997; Harris 1979, 1983; Illing 1954;
Loreau 1982; Newell et al. 1960; Purdy 1963; Reitner et
al. 1997; Strasser and Davaud 1986.
Caribbean
- Daetwyler and Kidwell 1959; Lloyd et al.
1987; Milliman 1969; Ward and Brady 1973; Zans 1958.
Persian Gulf
- Friedman 1995; Loreau 1982; Loreau and
Purser 1973; Nazhat 1998.
Gulf of Suez
- Anwar et al. 1981, 1984; Sass et al. 1972;
Sneh and Friedman 1984.
Mediterranean Sea
- Fabricius 1970; Richter 1976.
Great Barrier Reef
- Flood 1983; Marshall and Davies
1975.
Shark Bay, Australia
- Davies 1970.
Hypersaline and freshwater environments:
Saline lakes
- Great Salt Lake, Utah: Eardley 1938; Halley 1977; Kahle
1974; Sandberg 1975; Reitner et al. 1997.
Hypersaline lakes
- Baffin Bay, Texas (marine-hypersa-
line): Land 1970. Laguna Madre, Texas: Freeman 1962;
Rusnak 1960. Pyramid Lake, Nevada: Popp and Wilkinson
1983. Sea-marginal pools, Red Sea: Friedman 1978; Fried-
man et al. 1973; Friedman and Krumbein 1985. Dead Sea:
Garber and Friedman 1983; Garber et al. 1981.
Freshwater lakes
- Davaud and Girardclos 2001; Wilkinson
et al. 1980, 1984.
which tend to deviate from their spherical shapes and
are affected by biological degradation, cementation and
encrustation, form banks and widespread subtidal sheets
in areas of intermittent wind-wave-agitation across the
platform interior.
The ultrastructure of Bahamian ooids displays tan-
gentially arranged, subhedral needle-like crystals or
anhedral rod-like crystals. In contrast, ooids of the
Great
Salt Lake
are characterized by crystals whose long axes
are arranged perpendicularly to the ooid surface (Pl.
13/2). These radial-fibrous ultrastructures are common
in marine and hypersaline ooids. Ancient records of ra-
dial-fibrous structures were initially regarded as diage-
netic products of Bahamian-type aragonitic ooids (e.g.
Shearman et al. 1970), but are now recognized as pri-
mary features.
Modern depositional environments of marine ara-
gonite ooids like the Bahamian ooids are said to be
chemically not representative for ancient shallow-ma-
rine environments where calcite ooids have been formed
(Sandberg 1975).
Large and asymmetrical ooids, which are greatly dif-
ferent from Bahamian-type ooids, were described from
the Laguna Madre in Mexico (Rusnak 1960). Laminae
with radially and tangentially arranged crystals alter-
nate in these ooids. The formation of these
low-energy
or
quiet-water ooids
(Freeman 1962) appears to be re-
lated to the low water turbulence and to periodic varia-
tions in salinity. Low-energy ooids formed in lagoons,
coastal lakes and protected shallow environments with
different salinity are common in the geological record.
Low-energy and high-energy controls are not neces-
sarily separated at a clear-cut level, as demonstrated
by ooid sands occurring in lagoons along the Sinai
beaches of the Gulf of Suez. The ooids occur in car-
bonate mud; they represent wind-blown material and
ooids formed under low and high energy conditions,
differentiated by grain size and microfabric (Sass et al.
1972).
Deep-water ooids:
Modern and ancient ooids also
are found in deep-marine settings. The bulk of these
ooids represent allochthonous shallow-water material
transported into slope and basinal settings as debris
flows or turbidites. 'Pelagic ooids' (see Sect. 15.8) and
'seamount ooids' are found on the top of drowned plat-
forms and seamounts (e.g. Hesse 1973).
Controls on ooid formation
The exact nature of the formation of individual oo-
ids is still uncertain. It is generally accepted that most
ooid deposits form in shallow waters which are regu-
larly agitated over a long period of time by waves and/
or currents. Other environmental prerequisites include
minimal siliciclastic input and generally warm tempera-
tures, common in low-latitude settings.
Carbonate ooids form in settings where at least five
requirements must be met:
•
presence of nuclei,
•
bottom agitation to move grains,
•
a source of supersaturated water,
•
a process of water renewal, and
•
minimal amount of grain degradational processes.
Major controls on ultra- and microstructures of ooid
laminae are water chemistry, salinity and turbulence
(Lippmann 1973; Loreau 1973; Fabricius 1977). The
growth of radial-fibrous ooids in low-energy environ-
ments is apparently controlled by high or fluctuating
salinity. This assumption is supported by experiments
(Davies et al. 1978). A major and perhaps the essential
