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Abstract
Journal of Sedimentary Research, Section
B: Stratigraphy and Global Studies
Vol. 67 (1997)No.
2. (March), Pages 364-373
Temperate Carbonates on a Modern, Low-Energy, Isolated Ramp: The Balearic
Platform, Spain
J. J. Fornos (1), W. M. Ahr (2)
ABSTRACT
This paper presents a depositional model for a temperate, low-energy carbonate
ramp based on descriptive studies of five areas around the Balearic Islands
of Mallorca and Menorca. This low-energy ramp differs significantly from
other present-day temperate carbonate platforms that are primarily high-energy
open shelves. It is characterized by the following lithofacies (from shore
to basin): (1) lagoon, (2) barrier island, (3) shallow subtidal, (4) inner
ramp, (5) middle ramp, and (6) distal ramp. Subaqueous carbonate dunes
are present near slope breaks off Menorca and Cabrera, but they are not
representative of the entire ramp. Balearic ramp sediments differ in composition,
texture, biology, and degree of cementation from those on modern low-energy,
tropical ramps. Balearic ramp carbon tes lack ooids and peloids, hermatypic
coral buildups, and calcareous green algae (except in one restricted bay
where Halimeda is relatively common). Red algal sands and gravels
extend to depths of up to 90 m, and are coarser than their strandplain-equivalent
lime sands. Skeletal allochems consist of the bryomol-rhodalgal association,
marine cementation is rare, and the carbonate fraction of deep-water muds
is mainly Mg-calcitic and calcitic in composition. Aragonite is rare. Except
for the red alga Peyssonnelia, which is composed of aragonite, it
is neither a dominant skeletal constituent nor common as a cement.
The Mediterranean Sea off Mallorca and Menorca is a low-energy, temperate,
oligotrophic, clear-water environment. The depositional model for the region
is an isolated platform configured as a homoclinal ramp. Ancient counterparts
of the Balearic ramp are present in the Neogene of the Mediterranean Tethys
and the Paratethys, and though the constituents of fossil assemblages vary
with time, the biota of the Balearic ramp, such as bryozoans, red algae,
echinoderms, and mollusks, ranges from the Paleozoic Era to the present.
Echinodermal bryomols passing to basinal muds on carbonate ramps are particularly
characteristic of the Early Carboniferous in North America and Europe.
This suggests that the Balearic Islands temperate ramp may be more representative
of some ancient carbonate sequenc s than either temperate, high-energy,
open shelves or tropical ramps in the present oceans.
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