Geology Reference
In-Depth Information
14.1.7 Epeiric Platform Model
(1986) who proposed a 'tidal flat island model' assum-
ing the existence of small supratidal low-relief islands
and intertidal banks surrounded by open subtidal wa-
ters. This model overcomes many contradictions inher-
ent in fitting facies criteria to the epeiric platform model,
and adapts the tideless model to many Early Paleozoic
limestones and dolostones characterized by supra-, in-
ter- and subtidal cycles.
During the Phanerozoic epeiric seas covered extensive
areas of the cratons. These very shallow, low-energy
seas extended for hundreds to thousands of kilometers.
Epeiric seas first flooded the margins and later the inte-
rior of tectonically stable cratons. Modern epeiric seas
are rare. Examples of warm-water epeiric seas are the
Sunda Sea and Java Sea, cool-water examples are the
Baltic Sea, the North Sea, and the Hudson Bay (Edinger
et al. 2002).
Depositional patterns in epeiric seas are discussed
in the epeiric platform model and the epeiric ramp
model (Fig. 14.6).
14.1.8 Epeiric Ramp Model
The epeiric ramp model was proposed by Lukasik et
al. (2000) to describe temperate Tertiary carbonates
from the Murray Basin in Australia (Fig. 14.6B). Epeiric
ramps and normal carbonate ramps differ in
The epeiric platform model postulates clear-water
sedimentation extending over vast regions from hun-
dreds to thousands of kilometers wide, assuming that
tides were damped out by friction with the shallow sea
bottom and salinities increased seaward (Irwin 1965).
The depositional site should be characterized by a more
or less negligible, extremely low slope angle and re-
gionally extended low-energy conditions and distinct
salinity gradients. The inner platform is believed to have
been characterized by subtidal to intertidal mud flats
with widths of tens to hundreds of kilometers, and wa-
ter depths generally less than 10 m.
The model differentiates a low-energy, below wave
base zone X of the open sea, a relatively narrow zone
Y of higher energy where waves impinge on the sea
floor and strong tidal currents develop, and an extended
zone Z with restricted water circulation, minimal tidal
effects, only periodic storm effects, and hyper- and/or
hypo-salinity conditions. The tideless mode of the
model in zone Z was questioned by Pratt and James
the widths that may reach hundreds of kilometers
(normal ramp 1-100 km),
very low and negligible slope angles (ramp <1°),
water depths of only a few tens of meters, less than
20 m (ramp 10 to 100 m),
low water energy and subtidal to intertidal mud flats
in the inner part of epeiric ramps (ramps: high-en-
ergy shoreline with shoal/barrier-lagoon),
tidal flats extending hundreds of kilometers (ramps:
within kilometer scale),
dominant processes, such as storms and nearshore
tidal currents (on ramps: wind-induced waves and
storms).
Both the distal and the proximal parts of epeiric
ramps are characterized by burrowed silty, fine-grained
carbonate, forming mud flats near the coast and in dis-
tal sea-grass areas. Grainy sediments, produced by
storms, are commonly obliterated by bioturbation. The
Fig. 14.6. Epeiric platform and epeiric ramp models. The models refer to very shallow depositional settings that extend over
vast areas, comprising hundreds to thousands of kilometers for epeiric platforms, and hundreds of kilometers for epeiric
ramps. In contrast, carbonate ramps usually range between a few kilometers to 100 or 200 km. The inner platform of ramps
is characterized by high-energy facies, that of epeiric platforms and ramps by low-energy facies.
A: The epeiric platform model of epicontinental seas (Irwin 1965) differentiates three generalized zones, two of which lie in
low-energy environments (X and Z), and the third (Y) within higher energy areas.
B: The epeiric ramp model (Lukasik et al. 2000) differs from the epeiric platform model in the nature of the slope and the
extent of the basin.
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