Microfossil Analysis - Applications for Determining
Geological Age and Reconstructing Paleoenvironments
S ummary

It is important to recognize the distribution of source and reservoir rocks and the migration pathways for hydrocarbon entrapment.
Microfossil analyses provide geological age, stratigraphic correlation and paleoenvironmental data. Multi-microfossil analysis provides moredetailed geological age data and high-resolution correlation of strata. Microfossil analysis contributes to accurate assessment of thesubsurface for oil and gas exploration. Because microfossil analysis can be performed quickly, it is suitable for wellsite operation.

Microfossils
ᴾᴾᵫᶇᶁᶐᶍᶄᶍᶑᶑᶇᶊᴾ

Foraminifera

Calcareous Nannofossils

Diatoms

0.01mmForaminifera

Pollen5-600
䡚5-6000species

Radiolaria

Nannofossils

Diatom

5-6000䡚
5-6㽢10species

0.05mm

0.05mmMicrofossils can be detected and identified under a microscope. Characteristics
that make microfossils useful are:
ӑ Their abundance in rockӑ The ease and speed with which they
can be analyzed
ӑ Their availability for wellsite
operation

Foraminifera have calcareous
tests with chambers andapertures of various shapes, andwere the first microfossils usedin the oil industry. Bothplanktonic and benthic
foraminifera exist.

Diatom Zone㻌 㻌 㻌 㻌 Range and Photo

Plio.

Diatoms are microfossils ofphytoplankton with siliceous valves,
and an important source material forhydrocarbons. These microfossils areeasily identified even fromfragments because of theirsymmetric morphological patterns.

-Stratigraphic horizon and correlation--Geological AgeAge.

Calcareous nannofossils areformed by phytoplankton as verysmall calcareous plates(coccoliths), and are particularly
useful index fossil because of
their worldwide distribution.

Bioevent
䕰K=Neodenticula kamtschatica (2.7)

K

Akita area

Niigata area

Grt. praeinflata

Late Miocene

Haizume F.
䕰D=Denticulopsis dimorpha (9.3)
䕦D=Denticulopsis dimorpha v. dimorpha (10.0)

PD
Middle Miocene

U. Tentokuji F.

䕰H=Denticulopsis katayamae (8.7)

D

Nishiyama F.

Grt. orientalis

䕦PD=Denticulopsis praedimorpha v. minor (12.7)

L
PLC䕰HY=Denticulopsis hyalina (13.1)

䕰PL=Denticulopsis praelauta (15.8)
䕦L=Denticulopsis lauta (15.9)

L. Tentokuji F.

Shiiya F.
Grt. ikebeiC䕰PD=Denticulopsis praedimorpha (11.4)

HYSasaoka F.

Funakawa F.

U. Teratomari F.
L.Teratomari F.

Spirosigmoilinella
compressa

Nanatani F.

Warm water species
abundant

Green Tf.

Onnagawa F.
Nishikurosawa F.
Green Tf.

䕦PL=Denticulopsis praelauta (16.6)
䕦=First occurrence䠈䕰=Last occurrence

The occurrence of the fossil Diatom Denticulopsis dimorpha in a rocksample indicates a Late Miocene geological age, from 10 million to 9.3
million years ago.

Key points-Sedimantary Sequence PaleodepthྂỈ῝ኚື Gamma Sedimentaryሁ✚䝅䞊 Cal.Nannofossils▼⅊㉁䝘䝜
(BenthicForam.) rayᗏ⏕᭷Ꮝ⹸໬▼sequenceabundance䜿䞁䝇໬▼⏘ฟ㔞㻌㻌
MFSDeep

䕦 (P)G.flexosa Ab(0.40)
Shallow

䕰(N)P.lacunosa(0.44)

1km

Sequence A

Bioevent⏕ᒙ‽

Seismic
profileᆅ㟈᥈ᰝ᩿㠃

Analyses of foraminifera, calcareous nannofossils and diatoms canbe performed.

MFS
SB

SB
SBMFS
㻌

㻌

Sequence B

HST(R/L)G.truncatulinoides(P)SB

Sequence C

㻌 MFS

TST
LST
SF

SB
SB

P. “anula”CS (N)
1st Trimosina A(B)

MFS

Sequence DSBSB

䕰(N)R.asanoi(0.91)

The occurrence of Grt. ikebei from the Niigata area well and its
stratigraphic horizons in the Shiiya Formation in the Niigata area andthe Funakawa Formation in the Akita area.

SB=sequence boudary
MFS=maximum flooding surface

This sedimentary sequence was interpreted with multi-fossil analysis,
logging data and a seismic profile. Microfossil analysis provides
geological horizon, fossil abundance, and paleodepth data. These results
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(1) From a small rock sample (5–6g to 100g), microfossil analysis
results can be obtained, often in a short period of time.
(2) Micropaleontology is a powerful tool for establishing achronostratigraphic framework and reconstructing thepaleoenvironment of a region. Multi-fossil analysis provides moredetailed geological age data and high-resolution correlation ofstrata.
(3) Microfossil analysis contributes to the interpretation ofsequence stratigraphy, high-resolution reservoir stratigraphy
and paleoenvironmental comparisons.
Microfossil analyses greatly contribute to the assessment of oil &gas distribution.

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