ABSTRACT |
The Binangonan Formation consists of
carbonate deposits extending from Upper
Oligocene to Lower Miocene. ln the
Antipolo-Teresa area, shallow-water
turbidites (allodapic limestones)
comprising the Teresa Tuffaceous
Siltstone (lower member) gave way to
deposits of shallow-water reef complexes
comprising the limestone member (upper
member).
Sedimentological criteria indicate that
deposits of the Teresa Tuffaceous
Siltstone represent shallow water
proximal turbidites. Microfacies types
recognized in these turbidites include
lithoclastic-bioclastic packstones /
grainstones, hemipelagic wackestones/mudstones,
and minor rudstones.
The shallow water turbidites served as a
carbonate platform upon which reef
buildup and deposition of
reef-associated carbonate facies
commenced. Generally four facies can
be distinguished: (a) basin margin, (b)
foreslope, (c) main organic reefs, and
(e) open
marine lagoon.
The basin margin facies is composed
microbioclastic-calcisiltites,
bioclastic packstones, mudstones/marIs,
and minor hemipelagic wackstones. This
paleoenvironment was
characterized by limited light and
scarcity of grain-producing organisms
with predominance
of planktonic forms. lnitially, a high
rate of up-building of reefs in local
areas caused formation of restricted
basins and subsequent deposition of
reddish nodular limestones. The nodules
were derived by in situ brecciation
without reworking.
The foreslopes facies is characteized by
floatstones, bioclastic packstones,
minor microbioclastic calcisiltites and
boundstones. Association of limestone
types in this facies might suggest that
the foreslope had a generally gentle
inclination. Interbedded with these
deposits occur fining upwards cycles
composed of coral floatstones,
foraminiferal packstones/ wackestones,
and mudstones which are interpreted as
storm deposits (tempestites).
The main organic buildups are comprised
of boundstones, and minor bioclastic
packstones/ grainstones. The
distribution of the microfacies types in
the reef complex might indicate that
these reefs were discontinuous giving
way to extensive interreef areas.
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