rise
!
fall
rise fall
!
rise
!
fall
(A)
1\ 1\ I\ 1\ I\ 1\ I\ I\ 1\ I\ 1\
~time~v~ ~~~v~ -.
, ... , ... , ... , ... , ...
I~.... , ...
·I~.... , ...
I~...
I~...
I~• I
-35-I (.0 :;]'\
I
rise
i
D falling phase of 4th-order cycle
D lowstand stable phase of 4th-order cycle
0
rising phase of - 4th-order cycle
D highstand stable phase of 4th-order cycle
th-order cycles
, . matrix trend
t
___ , (a portion of a
3rd-order cycle) fall
)- 4th-order cycle on
3rd-order rapid rising phase
~---...,__ _ _ _ _ rapid rising
~ matrix trend
_ <~ • (2)- 4th-order cycle on
3rd-order slow rising phase slow rising
r - - - -
matrix trend th-order cycle onrd .. order stillstand phase ' - - - -stillstand matrix trend
th-order cycle on
rd-order slow falling phase _____ slow falling
matrix trend 5)- 4th-order cycle on
3rd-order rapid falling phase
J---~----~r---rapid falling matrix trend
mflection point
Fig. 14. Phase variation diagram showing phase combination within 4th-order cycles superimposed by defferent
3rd-order phases. ( 1): The 4th-order cycle on 3rd-order rapid rising phase, (2): the 4th-order cycle on 3rd-order slow rising phase, (3): the 4th-order cycle on 3rd-order stillstand phase, ( 4): the 4th-order cycle on 3rd-order slow falling phase, and (5): the 4th-order cycle on 3rd-order rapid falling phase. The 4th-order cycle (1) consists mainly of rising and stillstand phases. In contrast to this, the 4th-order cycle (5) consists mainly of falling and stillstand phases. (from Arato and Hoyanagi, 1995).
(.;J 'J
Qi >
..! n,
Q) co
Q)
~ a;
~
rise
t
fall
D D D D
stable phase of 4th-order cycle
{highlt8ld) rising phase of 4th-order cycle stable phase of 4th-order cycle
(~
falling phase of 4th-order cycle
"0 CCJ
0') Cl:l :0
c: en~
=
m 3: o (I)-
-en c:
·;;;
·.:
~.!!
~~ c
.&::: Clflt
s =
-- cu
.&:
-~
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!.a
as=:- · -
.&:. ~cu
o cn .! .S!t 0 m- - ... .&:
-c: .... ~ Q')
VJm c
==-
c;; g•m 0(1) 1: C'G
- ... ·
-HAS
LPW
retrogradational and aggradational fourth-order depositional sequence
TAS HPW
progradational fourth-order depositional sequence
fan-detta fourth-order depositional sequence
SB: sequence boundary HAS: highstand stable aggradational sheet systems tract RPW: regressive progradational wedge systems tract ts: transgressive surface HPW: highstand stable progradational wedge systems tract TAB: transgressive aggradational bank systems tract mfs: maximum ftooding LPW: lowstand stable progradational wedge systems tract T AS: transgressrve aggradational sheet systems tract
surface RAM· regressive aggradational mound systems tract TAB: transgressive retrogradational bank systems tract
Fig. 15. Variations of 4th-order relative sea-level cycles and derived sequence models (from Arata and Hoyanagi, 1995).
J-6. Chronostratigraphic controls in the Kanbara area
The biostratigraphic analyses were carried out for the cuttings and sidewall core ample from the MITI "Niigata-heiya" well by Japan National Oil Corporation (1991 ), and the following biostratigraphic datums were identified.
(1) The planktic foraminifers Globorotalia inflata are abundantly recognized at 3,700- 3,820 meters, 2,540- 2,840 meters and 2,040- 2,200 meters in drilling depth. Each of these depth intervals is interpreted to correspond to the No.3, No.2 and No. 1 Globorotalia inflata Bed (Kudo, 1967) in ascending order.
(2) The calcareous nannofossil datun1s, discovered by Takayama and Sa to ( 1986), are recognized at the following depths: i) datums No. 11 (extinction of Gephyrocapsa caribbeanica) and No. 10 (extinction of Calcidiscus n1acintyrei and the first appearance of Gephyrocapsa oceanica) at 3,161 meters, ii) datum No. 9 (first appearance of Gephyrocapsa spp. (large form)) at 2,878 meters, iii) datum No. 8 (extinction of Hellicosphaera selli1) at 2,693 n1eters, iv) datum No.7 (extinction of Gephyrocapsa spp. (large forn1)) at 2,442 meters, v) datum No. 6 (first appearance of Gephyrocapsa parallela) at 2,326 meters, and vi) datum No. 5 (top acme zone of Reticulofenstra sp.) at 2,227 meters.
The above mentioned biostratigraphic datun1s (Japan National Oil Corporation, 1991) show the following relationship with the sequence stratigraphic framework (Arato et al., 1994b;
Fig. 16(D)).
(1) The No. 3 Globorotalia inflata Bed corresponds nearly to the bounding discontinuity between Sequences A and B.
(2) The No. 2 Globorotalia inflata Bed is correlated to Sequence C except for the uppermost and the lowermost parts.
(3) The No. 1 Globorotalia inflata Bed is recognized at the lowermost part of Sequence E l.
(4) The calcareous nannofossil datums No. 10 and 11 are included within the upper part of Sequence B.
(5) The calcareous nannofossil datum No. 9, which is included within the No. 2 Globorotalia inflata Bed, is recognized at the lower part of Sequence C.
- - 0 . 1 5 - - 0 . 2 4
- - 0 . 3 9 - - 0 . 4 8
6
- - 0 . 8 97
136
10~-1.57
11
- - 1 . 6 61 2 - - 1 . 9 1
13--2.37 14--2.4&
15--2.75
(Ma)
? SK020 1 G. lrrtlsta (no. 1)
7- SKOOO
I G
(no. 2).
/n-- SK100
?- SK 130
?
G. lntlata (no. 3}
140
UPPER UONUMA
LOWER UONUMA
SK 130
LOWER-MOST UONUMA
HACHIOJI
N
-J+K
?
-H
-F
... ? ...
G. inti E2
~-1) E1
~
- 6
D
·
7r
(no.w-
2)c
~10
~11
B
no.3GI
?
A
Fig. 16. Stratigraphic correlation chart showing A: calcareous nannofossil datum planes and their geological ages in the ODP Leg 94 reference section of the northeastern Atlantic (Takayama and Sate, 1986), B: stratigraphic column comprising selected calcareous nannofossil datum planes, planktic foraminiferal zones, and volocanic ash key layers (SKs) on the Aida route in the lzumozaki Town (Sato et al., 1987), C: stratigraphic subdivisions of the Uonuma Group and their relationship to main volcanic ash key layers (SKs) (Kazaoka, 1988; Kobayashi et al., 1988; Urabe et al., 1995; etc.), and D: sequence stratigraphic subdivisions and their relationship to selected
calcareous nannofossil datum planes and planktic foraminiferal zones (Japan National Oil Corporation, 1990; Arato et al., 1994a).
-
39-(6) The calcareous nannofossil datun1 No. 8, which is also included within the No. 2 Globorotalia inflata Bed, is recognized at the upper part of Sequence C.
(7) The calcareous nannofossil datum No.7 is contained within the lower part of Sequence D.
(8) The calcareous nannofossil datum No. 6 is recognized at the upper part of Sequence D.
(9) The calcareous nannofossil datum 5, which is recognized beneath the No. 1 Globorotalia inflata Bed, corresponds to the bounding discontinuity between sequences D and E I.
2. Morphological and distributional characteristics of systems tracts and depositional systems
2-1. Criteria for morphological features of depositional systetns
The depositional settings of each progradational fourth-order depositional sequence (Sequences J+K, L, M and N) are classified into higher flat planes, their margin , tilted plane , and lower flat planes, based on the geomorphological characteristics observed on the seismic profiles. For convenience, this study names tentatively those geomorphological unit as (1)
platform, (2) platform margin, (3) flank and (4) bottom, respectively (Fig. 17). The platfonn are relatively proximal higher flat planes occupying mainly the southern po11ion and ea tern and western marginal parts of the· "paleo-Niigata sea." In contrast to this, the bottoms are relatively distal lower flat planes occupying the northern central part of the "paleo-Niigata ea." The platform area and the bottom area are bounded by the area of flank between them. Moreover, the marginal area of the platform contiguous to the flank would be distinguished as a platform margin from the platform itself, because the sedimentary facies and their controlling processes in the platform margin are expected to be defferent from those in the platfonn.
Those geomorphological characteristics, even slightly valuable, can generally be applicable to the every systems tract building the progradational fourth-order depositional sequences. Such a geomorphological framework is widely identified on the seismic profiles in the study area, even it was slightly deformed by subsidence related to differential compaction of the underlying strata or local tectonic activities after the deposition of the subject strata.
The systems tracts of the progradational fourth-order depositional sequences are distributed and demonstrate individual morphological characters such as external forms, stratal termination patterns and stratal stacking patterns in response to the geomorphological features of their depositional locations. The external forms of the systems tracts are classified into I) sheet, II) wedge, III) bank, IV) sigmoid, V) mound, or VI) "channel" (Fig. 18-(1 )). The stratal termination pattems are classified into a) toplap, b) truncation, or c) apparent truncation at the upper bounding discontinuities, and into x) onlap or y) downlap at the lower bounding discontinuities of the systems tracts. Moreover, the upper and lower bounding discontinuities with rare stratal
-41
-I
~ N
I