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Rolando A. de Guzman
Exploration Manager, Western Minolco Corporation





The recognition of a Tertiary geosynclinal-type basin in Southern Mindoro resulted from a liberal interpretation of its lithologic and orogenetic features. The author proposes the term Southern Mindoro geosyncline to a sedimentary furrow which underwent four evolutionary stages, namely: 1) generative stage; 2) development stage; 3) orogenic or terminal stage;
and 4) post-geosynclinal period. Except for a Late Paleozoic orogeny, maturation of the geosyncline involved three orogenic periods, namely: 1) Late Mesozoic orogeny (Late Cretaceous) ; 2) Mid-Tertiary orogeny; and 3) Late Cenozoic orogeny (Late Pliocene-Pleistocene).

The geosyncline, fed from a tectonized provenance, is subdivided into the following two major zones.

A. Paleogene Eugeosynclinal Domain - consisting of two units, namely:

1) The main catastrophic group characterized by thrust-oriented deformative elements, gravity
welts, exotic or allochthonous blocks, heterogeneous breccia clastics and the presence of sedimentological features intimately associated with slumps and turbidity currents. Along the flanks of the basin, the infrajacent sedimentary beds were thwarted by ophiolitic magmatism, ultrabasic "cold" intrusion and keratophyric and andesitic volcanism.

2) The thick monotonous suite of paralic sediments composed mostly of black shales and mudstones within the axial zone of the eugeosyncline and, occasionally intruded by dikes and sills of dioritic and diabasic rocks. Elsewhere within the belt, alternation of contrasting thin beds of sandstone, shale, mudstone and dirty arenitic limestone truly represent a flysch-type association.

B. Neogene Miogeosynclinal Domain - consisting of three units, namely:

1) Paralic deposits, with coal measure, and sporadic occurrence of Late Neogene-Pleistocene lava flows of andesitic composition in the foredeep zone.

2) The non-turbulent carbonate platform association composed of reefal limestone build-ups, including calcarenites. The rocks are disposed along a belt occupied by an ill-defined miogeanticlinal ridge.

3) Clastic mixed shelf association, a combination of the carbonate rocks and the clastic shelf, which occupies the relatively shallow and stable portion of the miogeosyncline.

A marked dynamic polarity is demonstrated through the migration of flysch deposition, orogeny and molasse deposition from east to west across the Southern Mindoro geosyncline.




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