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Depositional Setting of the
Early Miocene Coal-Bearing Sequences,
Malangas District, Zamboanga Sibugay
Joseph M. Foronda, Grace Asio-Montes, John R. D. Biscaro, Ronald A. F. Boniquit
Philippine National Oil Co. Exploration Corp.
GeoCon 2011
8 December 2011
I. Geologic Setting
II. Sedimentology
III. Ash content
IV. Sulfur content
V. Isopach
VI. Conclusion
Outline
Determine environments of deposition of
the coal-bearing sequences
Objective
Pubellier et al. (2005)
Sibugay Peninsula
Rank:
subbituminous C
to high volatile B
bituminous coal
Local Stratigraphy
LA
LC/ B
Typ
ica
l G
ota
s
Correlation of Logs in Imelda & Malangas
Crevasse “subdeltas” in Mississippi delta. (Coleman & Gagliano, 1964)
Crevasse
channels
Distributary
channels
Levee
Crevasse splay Interdistributary bay
Underclays
Few underclays – with rootlet horizon
autochthonous (in situ) coal formation
rootlet
Most underclays – no soil or rootlet horizon
allochthonous (transported) coal formation
Slickensides
--- Coal Bed
Levee
Channel erosion and sediment deposition Levee
---Mudstone
Distributary
Channels
Levees
Composite Logs
Low
Med
High
Ash in LA Seam
LA Seam has medium to high ash
swamp was occasionally flooded.
Low (0-8%)
Medium (>8-15%)
High (>15%)
Low
Med
High
Ash in LC/B Seam
LC/B Seam has medium to high ash
swamp was occasionally flooded.
Low (0-1%) – freshwater influence
Medium (>1-3%) – brackish
High (>3%) – marine
Low
Med
Total Sulfur in LA Seam
LA Seam was influenced by fresh- to
brackish waters
Low
Med
Total Sulfur in LC/B Seam
LC/B Seam was influenced by fresh- (to
brackish) waters
1.0 m
1.5
2.0
2.5
3.0 m
n = 258
n = 76
LA Seam Isopach Map
LA Seam
• less extensive
• rarely exceeds 2.5 m thick
• may form isolated pods
LC/B Seam Isopach Map
n = 258
n = 76
LC/B Seam
• more extensive
• up to 3.5 m thick
• Trend of elongation: NE-SW
Conclusion • Economic coal (LA & LC) seams of the Lumbog Formation are
deposited on the delta plain of a fluvial-dominated delta
• Economic coals cap the two lowermost deltaic cycles; rider seams are common
• Lower Cycle is 35 to 50 m thick; Upper Cycle is 30-40 m thick
• Underclays indicate most coal seams are allochthonous; few underclays contain rootlets indicating autochthonous formation of some coals
• Both Seams: medium to high ash – swamp occasionally flooded
• Both Seams: low to medium sulfur – fresh- to brackish water influence on peat
• LA Seam less extensive, may form isolated pods, thinner (rarely exceeds 2.5 m thick)
• LC Seam more laterally extensive, thicker (up to 3.5 m thick); trend of elongation – NE-SW
Acknowledgements
• Aildrene Tan – cartography
• Former PNOC EC geologists Alvaine Ibarrola & Jessie James Lasconia – core logging
• Raymundo Savella – management support
