seismic interpretation chapter 7 - university … 7 seismic interpretation ,~ the colour scheme used...

Chapter 7 Seismie Interpretation

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CHAPTER 7 SEISMIC INTERPRETATION�

A large volume of seismic data was collected during the course of this project. This was to

ensure that maximum benefit was gained from having the equipment and Mr. David

Mitchell in Tasmania. As a result, there is considerably more data than I hope to do justice

to and I am only presenting a fraction of it here as fully interpreted sections. I have chosen

eight complete cross-river profiles (lines 3, 5, 7, 16, 17, 21, 22 and 23) because they are

parallel, span a large portion of the study area, and the stratigraphy is largely unobscured

by acoustic turbidity. I have also interpreted a further 11 short profiles - these are all

affected by acoustic turbidity and are located off Taroona (lines 24 to 34). The short

profiles are less informative than the long profiles.

Along with the seismic interpretations, for the eight full length cross-river profiles I have

displayed a modelled profile ofTMI (except for line 7; there is no magnetic data for most

of this line). These magnetic profiles were extracted from the final gridded dataset using

the seismic trackpaths as a template, so they are truly coincident. In general terms, the

magnetic sources are buried more deeply than the seismic system is able to image, but I

hope that it is apparent (despite the necessary difference in display scales) that there are

features - particularly faults - that appear to be expressed on both the magnetic models

and seismic profiles.

For the shorter lines (numbers 24 to 34), I have displayed profiles of TMI without forward

models. Some ofthese have sections of 'no data' - this occurs where the seismic profile is

outside the magnetic grid.

Each profile is presented as a series of two sheets. The first has the uninterpreted, located

seismic profile and a profile of TMI. The second has the interpreted seismic profile and the

modelled magnetic profile for the long lines, and the interpreted and uninterpreted seismic

profiles for the short lines. The magnetic modeling has all been done using dolerite sources

only, with relatively low magnetic susceptibilities. Susceptibilities are shown on the

profiles. The observed magnetic response is shown in blue, and the calculated response in

red. The same points discussed in chapter 4 apply to these magnetic profiles.

A Geophysical Investigation of the Derwent Estuary 114

Chapter 7 Seismic Interpretation

Interpreted Seismic Lines Trackpaths Map 53500052~

r

5250000+

5245000 5245000+

5240000 5240000

5235000 5235000+ o

t5230000.. ! '>.a --:5'$)\.} t t 530000 535000 540000

c::J ~:JlCn... b+di(y 2500 o 2500 Meters Seine TuO:peIh. !!!!! -- Sti'!IllcTr.o<pelht N ""'pili«! Goologyo OJaI.rnay On-shore Geology Polygons o T.Il.-y from 1:250,000 Digital Coverage. D TII••1ll

Grid: Australian Map Grid, Zone 55CJ: f'lrml.n Datum: Australian Geodetic Datum, 1966 9lltOvsRo<:k$

c=J r''''.-yB.._ Ac=J JIor..IC;Do/toIU

Figure 7.1. Trackpaths map for 'long' seismic prOfiles chosenfor interpretation.



Interpreted Seismic Lines Trackpaths Map 2

+1-5252000

+1-5248000

+1-5246000

+1-5244000+

+1-5242000+

ooסס1-524+ 5240000

5238000-1 + S\ + I \ + + - =-"D +" +t5238ooo 526'000 528'000 530'000 532000 534000 530000

CJ ACOOJP.ocn...bIdIfy

2500 o 2500 Meters SoistOC Tra.ocpalls !"!! -- Stil'llicTI..::\(p.h::l N~fiodGoOOgy

CJ OJIll"~

On-5hore Geology Polygons Or......,from 1:250,000 Digital Coverage. CJ TIlASllic:

Grid: Australian Map Grid, Zone 55� Datum: Australian Geodetic Datum, 1966�

CJ P,mllan

~neou.Aodl;.

[==:J TCttIAl'f a.-. A[=:J .A.rllllilCOo'tnl.

Figure 7.2. Trackpmhs map for 'shon' seismic profiles chosen for interpretation.



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The colour scheme used for the seismic interpretation is as follows. The solid black lines

are traces of reflectors (or, rarely, diffraction patterns) from the section. These tend to be

discontinuous due to the nature of the data. The coloured blocks are interpretative - they r

typically extend past, join or cross several interpreted reflectors. An individual reflector

trace may represent an internal boundary within an overall depositional sequence, or may

represent a boundary between sequences. The colours are intended to show the different

r sequences. The colours for the long lines are:

Bright Yellow

r

Pale Yellow

re

Salmon Pink

Grey

n Deep Red

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Pale Orange

r:: Bright Red

Blue

Purple

Recent fluvial/estuarine sediments, including organic rich

sediments. Sometimes denoted as Cl (channel fill I). I have

indicated possible channel profiles for this sedimentary package in

the areas affected by acoustic turbidity - these are estimated.

Second-oldest channel fill sediments. Commonly overprinted by Cl.

Sometimes denoted as C2.

Third-oldest channel fill sediments. Generally not extensive.

Package of sediment that generally overlies acoustic basement or

(interpreted) older stratigraphy. Not always present.

Older, more consolidated (Tertiary?) sediment. Although it can be

extensive, it is often faulted and the surface is commonly heavily

dissected. It is almost certainly not exactly the same material on

every profile, but it has the same general reflection characteristics

and stratigraphic position.

Not common, may be very deep/old channel fill. Appears to

underlie relatively consolidated Tertiary(?) material in places.

Dolerite

Lower Parmeener Supergroup (ie. Permian) sedimentary rocks

Youngest sediment (marine sand?). Only present on line 7, ie. close

to Storm Bay

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The colour scheme is similar for the short profiles (24 to 34), with the addition of

Brown Possible landslip deposit, characterised by numerous diffractions.

Green Dipping strata of probable Oligocene age. Also exposed on shore at

Taroona.

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A Geophysical Investigation ofthe Derwent Estuary 117

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Also, although the age sequence of colours is the same (ie. bright yellow youngest and so

on) on all profiles, the absolute ages of the various packages of sediment may not be the

same on all profiles. This is one of the difficulties in interpreting the seismic data in the

absence of age control and with discontinuous reflections.

Apart from these points, I think the interpretations are largely self-explanatory. There is a

(short) discussion of some of the major features of each profile on the interpreted sections.

Some general conclusions are given in chapter 9.

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11 526969mE 5240253mN 11 527456mE 5240471mN I 1 528426mE 5240704mN I I 529331mE 5240893mN I I 530430mE 5241182mN I 1 531338mE 5241438mN I

.' l�'·1· .�

i ,j 1

i ,. * I East rl

1

. I

526000 528000 530000 534000 Profile of TMI (nT)

~~

5240000 + + +

L-~~

5240000 62650

62550

5238000 + / ~5

+ ~

./

+ 5238000

62450

5236000 + + 5236000 ~

:E I

62350

62250

~

5234000

5232000

+

+ +

5234000

5232000

62150

62050

Derwent Estuary Seismic Reflection Survey

526000 528000 530000 532000 534000

Arrows denote survey direction. Red dots mark position fixes on the seismic record.

61950 0 1000 30002000

Along profile distance (from 526917mE 5240234mN)

4000 5000 Line 3

Figure 7.3.1 119

526969mE 5240253mN� I 528426mE 5240704mN I I 529331mE 5240893mN I I 530430mE 5241182mN I I 531338mE 5241438mN I 'I� 'T'

Frequency I Adjustment

I�

~I

Acoustic�

Basement�

::~

,~ .~;; 12sms' ". I i

"

," .'. ~;

H, "'."

.''I';I West I�

;;; I East I

Line 3, This line in a good example of how the .=m~ occurrence of acoustic turbidity is associated with

Cl tie ,-obs«vation< ~ ,-_.do" lools :tie" 'l'I.- tjelp .=m~ sediment volume. Although the most recent sediments ~M!J~~ extend across the entire profile, the acoustic turbidity is

526000 528000 530000 532000 534000 I '[ only developed where the sediment has significant volume. There are several generations of channels and 200.0� .......~\ block faulted stratigraphy, particularly to the west. Interestingly, the interpreted fault positions are generally ~---- ~~ I� " in accordance with those modelled on the magnetic 5240oo0~ + I + +, ~ + /5240000 /" .I

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profile. This implies that some of the faults that extend 0.0� '\ nearly to the seatloor have depth extents of hundreds of\ metres, and we.re active during the break-up of the

, I dolerite (possibly in the early part of the Tertiary). This \ f could imply that these faults are long lived, or that early

52380001 + 1/y. _r, /~ \ +~ r5238000 TMI (nl) Tertiary stratigraphy is exposed close to the seatloor in parts of the Estuary. The major channel positions are co-200.0

incident with the major structures (indicated by the In absence of dolerite and offset of dolerite blocks). This 52360001 + '\ + 7 + ) + 'J.5236000�

~\

V J

implies that these structures have also been long lived, or

\1� -'---- the sediments associated with the faults are preferentially -r---

-� X 527200 528000 528800 529600 530400 531200 eroded during channel incision.

"y.........+

y~~.

5234000i + ~----e::::..-, +/ r5234000 -1~~e=0.,

,/"21 ./'--!... . - -. 9usc =,0.03000 Derwent Estuary _, Suse = 0.03000 ""'.. ·200 ., -� -- -+ ! .

l J, SU5C == 0.03000 i I t� Seismic Reflection Survey • Susc = 0.03000

5232000 i + V".-----. + /+ + r5232000 -400 I ) j Susc = 0.03000 \ ." ,- "t.;: ! I ,./ . -- ,~- - \ \ ,_1 susc = 0.03000

\ I-600 Line 3 I Az =76.0deg

526000 528000 530000 532000 534000 Z(m}

Arrows denote survey direction.� -600 ~~"'530489,6<'V.5NII99.' Figure 7.3.2 120Red dots mark position fixes on the seismic record. 'o<HeIp,p<=F1

I 527279mE 5238967mN I I 528102mE 5239072mN I I 529330mE 5239359mN I I 530480mE 5239625mN I I 531354mE 5239799mNJ I 532476mE 5239933mN I� ""'-'...-, 1,-,; ,~.... 't-' '" ryG-~t'---:,...~ .:..,., , .~:; _:.I;.;:,"'."!\:~;. L" I --,' ... ~,' -',''''--j -',J:' ',\', .£.;.....~f,,"'h - ...

-.+.. j,.~ ~ .... -.'\.j .. ~-~ -';;A;; '..,..;f~ ........ ''''~'''~'''''''' ... I;~:::::o;:.ijJ.... , , ...... _~L •• .~ ,:...;....u ,.j..;'-- T, ,',1-' .~

~ ...,t~

~~ I' :"'. t;.:,,~"t~ ;;.:

"I~1.,.

, ,., "I' :L.... ( t :~ I~

i~i� !

526000 528000 530000 534000�

Profile of TMI (nT)

.-::--~

5240000 5240000�+ 62650�

62550�

5238000-1 + 62450�

(i\.�

52360001 + '\ + +,;;..... + ~ 62350�

:E� I

.,........./ \1�

- r.-. 62250� ,/

52340001 + "'t ~ ~---k +/ ~5234000

__ ........'21-7'� 62150� Derwent Estuary

5=000. + +/~ + / + L32000 Seismic Reflection Survey 62050�

61950� 0 1000 2000 3000 4000 5000 6000� Line 23�

526000 528000 530000 532000 534000 Along profile distance (from 526959mE 5238895mN)� "I

Arrows denote survey direction. Figure 7 4.1 Red dots mark position fixes on the seismic record. •

121 J I

I 527279mE 5238967mN I I 528102mE 5239072mN I I 529330mE 5239359mN I I 530480mE 5239625mN I I 531354mE 5239799mN I� I 532476mE 5239933mN I ")' ~.; . . .

'.~ '. .L •

'1'

·1

West

~29

[J El< Qb«<""""'" !!:- .,.wo""" .I~. "'" ~" tl'" ~ Line 23. There is an extension of acoustic basement off °DI~II.i(BI'I!1 +i~q<iiG:'·H'\.[Q.I-- shore on this section - the lack of response in the

526000 528000 530000 532000 534000 magnetic data over this basement indicates that it is Parmeener Supergroup rather than dolerite. I have interpreted it as Permian. given that there is Permian

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nearby (onshore). There are fault blocks that appear to be rotated to the east of the main western fault (bounding 5240000 +� 5240000 the acoustic basement). There is also a large growth fault to the west, with at least 20m of displacement (using a conservative velocity estimate). The magnetic profile indicates a source below the channel containing the

5238000 +� 5238000 0.0 acoustic turbidity·· this appears to be out of place with \� ~ respect to the r~mainder of the dolerite and could in fact .,~...~

be basalt. /'V�TMI(nT)

5236000 +� + 5236000 -80.0

X 527200 528000 528800 529600 5:30400 5:31200 5:32000 -_ • .susc = 0 01500

5234000 +� 5234000

Susc = 0.02000� I -200 I + S~'G - 0.02000 • _ ~ _� Derwent Estuary

• J --., Susc = 0.02000

.� SU5C=O.01800 _/ I.

5232000 + + 5232000� -+ ~ ,isu5c=o02ooo---"""----..l~·-..-=--:---------1 Seismic Reflection Survey -400 I \ •.§.usc =0.02000 suSr;;ci:02000

.1

~ool \ Line 23 Zlmj� Az = 77.8deg526000 528000 530000 532000 534000 ~I I

Arrows denote survey direction.� - --_ •. - - - .~ ~_130.84 6!':S30673.3Ijv,5239632.JF<'x~,r.r~S'FI

Red dots mark position fixes on the seismic record.� Figure 7.4.2 122

I 527175mE 5237384mN I I 527836mE 5237799mN I I 528632mE 5238205mN I I 529540mE 5238456mN I I 530463mE 5238634mN I I 531323mE 5238767mN I I 532045mE 5238954mN I

~ "'s~ il' ......,}... l'"-:'<O~"- "J, . 't!..~

I\-.,,_r~:\,)- .,.h.j,......... '~, '-' ,-;;� , " ...~I~ ,"

~ : ~ -.".1~ '!! ;"

'I

....''''''~~;.

526,000 528pOO 530,000 .~/7 ~-

~ 534pOO Profile of TMI (nT)

5240000~

5238000~

+ I + + ~

~'

.--' ~

+ \ -!/ +

---"'---- .\

..-¥~

t

+\

l5240000

~5238000

62650

62550

62450

5236000 + 5236000 ~ 62350

~

~

62250 ('\

5232000

5234000 +

+ +

5234000

5232000

62150

62050


526000 528000 530000 532000 534000


61950 0 1000 2000 3000 4000

Along profile distance (from 527062mE 5237298mN)

5000 6000 Line 22

Figure 7.5.1 123

I 527175mE 5237384mN I I 527836mE 5237799mN I I 528632mE 5238205mN I I 529540mE 5238456mN I I 530463mE 5238634mN I I 531323mE 5238767mN I I 532045mE 5238954mN I

, I it :: I t

' ' ,~-

II

!25ms ,; ! , ; 1

l"

'1",

l~11.

I , t::;

r~estj[

,~-"l

I5l ElIo Ql>«<vation<_ !iodd ~"""""" loo!< _ _ ~ :i'I> -I~ Line 22. This profile is quite similar to the previous one

( 526000 528000 530000 532000 534000

DI~[1iI1 ~[~I+I~lo4~ ;\:-1'\.10..1 (# 23), showing the Parmeener Supergroup rocks extending off the eastern shore. In this case, they appear to be underlain by dolerite at a depth of between 300 and.

~ 400m. Again there are growth faults with significant

5240000 + ..,.-- +--,, 5240000 80.0

offset to the west. Note the absence of inferred magnetic sources beneath the channel containing the acoustic

~ ~ turbidity. The calculated magnetic profile does not fit the observed response well in this location and some of the

5238000 + ~--~

;-' + ~ 5238000 0.0

-----f

::::>

observed response is probably due to sources off section (i.e. the bodies on the previous profile terminating to the north of this profile). This could indicate a cross-river structure to the.north of this profile.

TMI (nT)

5236000 + 5236000

~o,o

5234000 + 5234000 x 527200 528000 528800 525600 530400 531200 5320C

5232000 + + 5232000

Susc =0,01800

-400 I

.200['1'

i 1 5 us c = 0 Q1BOQ. ,

Susc =0,01800 I


+ Susc =0,01800

~ool ' -------1 Line 22 526000 528000 530000 532000 534000 Z(m) Az = 73.2deg

Susc = 0,01800Arrows denote survey direction. -8001 ~ +

For~. press Ft P; "392,12 .. :r=: '129.05 -~: S3ii93.ti "(; S23e811.~r-Red dots mark position fixes on the seismic record. Figure 7.5.2 124

I 527466mE 5236189mN I I 528156mE 5236443mN I I 528883mE 5236816mN I I 529633mE 5237025mN I I 530046mE 5237209mN I I 531391mE 5237812mN I "CJ...-...l-_' .'-- _.!

j ;. ~ , ,..-s_. '=.

;-- :--;.'

<:

.'1A.~~,

526000 534000

Profile of TMI (nT) {\

5240000 + 5240000 62650

62550 {.

5238000 + + r 62450

5236000 + + ~ 62350

~ - -I

62250 5234000 + 5234000

5232000 + + 5232000 62050

62150 v Derwent Estuary Seismic Reflection Survey

Line 5 ~%ol I

526000 528000 530000 532000 534000 o 1000 2000 3000 4000 5000 Arrows denote survey direction. Along profile distance (from 527345mE 5236139mN)

Red dots mark position fixes on the seismic record. Figure 7.6.1 125

I 527466mE 5236189mN I I 528156mE 5236443mN I I 528883mE 5236816mN I I 529633mE 5237025mN I I 530046mE 5237209mN I I 531391mE 5237812mN I

El ~ Qbsm...... !1Odd ~~ IooIs ,..... ~ tie\> Oo-.~e

...,MJ-"l Line S. On this line the second-to-most-recent channel

DI~11iiiI1 el\'l +I-'\,IOJ;IG-+I"\.I~I (pale yellow) is very broad. It has increased in size down river to this point, and generally migrated further from

526000 528000 530000 534000 the eastern shore. This profile is interesting in that it

5240000 + +

.:::.-.3--'"--...-----+'23~---------- .

5240000

0.0

160.0

--

f\

---==~

--~

.L

clearly shows unconformable relationships between at least five generations of channels. There is no great extension of acoustic basement off the shore on this profile. Again, there appears to be growth faulting to the west. The magnetic anomalies here are low amplitude, indicating deep sources. This is borne out by the modeling. There is no deep 'recent' channel against the

5238000 + ~

y,....--' + .............-¥ 5238000 TMI (nT) western shore on this profile - compare this to the next profile..

.-r'

5236000 + ~-+

/ ~

7~+ ,'0./ +

./

j/))~ (

5236000

-160.0

521'1'200 528000 528600 529600 530400 531200 53200 -.-.. susc =0.03000

5234000 + t. ~._~;- ,/'

./

5234000

'200t~·------------------------------I Derwent Estuary

5232000 + + 5232000 -400 I .•. - . Susc = 0.01800 , I Seismic Reflection Survey

\. Susc = 0.01800 .... -po.. .. --.. _..

Susc = 0.01800-+1~

I L __ ,' , ------j

526000 528000 530000 532000 534000 Z(m)

~ool \

Az = 671ideg Line 5


~Ool

F«..,." """,Fl • - -: - . - -1

p: 4781.73 - 1': 245.18 .. ~: 53ln6.97f\', 5Zl793ur-

Figure 7.6.2 126


526000 528000 530,000 532000 5340007'r! Profile of TMI (nT) f\

~

--" 5240000~ + I + + ~

23 ;:;"-. ----",,---J ~ ~5240000 62650

.---------~ 62550

5238000j + /' + ~~ +\ ~5238000

62450

~

52360001 + + ~ J + 'lJ5236oo0 ~ 62350

~

5234000'1 + ,,+

,1 V ....· ./

./+ +_~ +/l5234000

I

62250

62150 Derwent Estuary

5232000 + + 5232000 62050 Seismic Reflection Survey

61950 Line 16 526000 528000 530000 532000 534000 0 1000 2000 3000 4000 5000 6000

Arrows denote survey direction. Along profile distance (from 527616mE 5234799mN)

Red dots mark position fixes on the seismic record, Figure 7.7.1 127

I

I 527587mE 5234805mN I I 528647mE 5235062mN I I 529656mE 5235543mN I I 530651 mE 5236015mN I I 531840mE 5236594mN 1� I 533260mE 5236994mN I I~.

I·~

·,i·

c

~ p

, ~

~

~'

( :

..

"

~29

E;J tie Qb....voOon< tlodel ~~ 1""" y_ l!!ndow ~ _Irao;;l Line 16. This line appears to show a very large extension DI~I"ISI"'1 +I~I~~+1'\.1«.1, of basement into the river - but due to the depth of the

526000 528000 530000 534000 reflectors it is difficult to be certain of this interpretation, Note the decrease in size of the 'recent' channel (containing the acoustic turbidity). The second youngest generation of channel fill is very extensive on this

80.0� profile, at both ends. The structural relationships on this 5240000~ +� 5240000 profile are not clear cut, particularly towards the west.

Interestingly, the upper surface of the acoustic turbidity is well beneath the seafloor on this profile - perhaps 5 to !Om below, This profile actually marks the furthest

5238000-1 + 5238000 0.0� southern extension of acoustic turbidity encountered in� the entire survey, and the deepest occurance with respect� to the riverbed,�

TMI(nn

5236000� 5236000+ -a0.0

x 528000 528800 529600 530400 531200 532000 532800

5234000 +� 5234000

Derwent Estuary

+� Susc =0-:-0i800 Seismic Reflection Survey 5232000 + 5232000� .. susc = 0.01800" --.)

-400 I� \ susc =0.01800 ~

-600 ~ · J~ .',.� \' I Line 16 _ •� -~ -' yI526000 528000 530000 532000 534000� Az =67.0deg

Z(m)Arrows denote survey direction.

-lIOO LI----::c=-::::-:c=----=-----=------=:-----__----=----=--=:-::=--,-------------------...JRed dots mark position fixes on the seismic record. FaH~,pressFI -----: - P:36S1.53 rF:111.61-'-~~'i.2.2/1V:52361-43.(~ Figure 7.7.2 128

I 528005mE 5233483mN I I 528826mE 5233659mN I I 529761mE 5234161mN I I 530960mE 5234762mN I I 531976mE 5235192m!"J I 532955mE 5235649mN I '~'.~' .. '-"''', ':J.!: ",.-",' .." ... .,:.

.. j ~ i 'I..'\.

----~ ~]".......... .,.; .. : ,,''1,. '(. I:~~ -o· I

~

526,000 528p00

/7 530,000 532000,

..-r 534000

Profile of TMI (nT)

~

52400001 + ) + + ~.\ 1 l5240000 62650

I I

-~ 62550

5238000~ + \ + ~..............-+"~ +\ ~5238000

62450

5236000 + 5236000 ~ 62350

~

I

62250

5234000 + 5234000

62150 Derwent Estuary

5232000 + + 5232000 62050 -J Seismic Reflection Survey

61950 Line 17 526000 528000 530000 532000 534000 0 1000 2000 3000 4000 5000 6000

Arrows denote survey direction. Along profile distance (from 528067mE 5233485mN)

Red dots mark position fixes on the seismic record. Figure 7.8.1 '129

I 528005mE 5233483mN I I 528826mE 5233659mN I I 529761mE 5234161mN I I 530960mE 5234762mN I I 531976mE 523519ZmNJ I 532955mE 5235649mN I

I 1: l

Seafloor

526000 528000 530000 534000

5238000

5240000

+

+

~

+ +

---~

~ / /,..-¥~'S.--r

5238000

5240000

5236000 + 5236000

5234000 + 5234000

5232000 + + 5232000

lJ

526000 528000 530000 532000 534000


.:.W29 I5l FAo Obs<ovations. t<odef QltwUcn Tool> View "Toclow ~ ~E

CJI~I"I ~I t I + 1.0,,1m:m; +1'\.1«.11

80.0

0.0

~

TMI(nT)

-80.0

!l28000 528800 529600 530400 531200 532000 532800 .018..0.' S

,2001-1--'-----------------------------------------1

-400 I :" taWS; * fJJJHI'lU� 'j ~-_ _ •. SUSC=0.01800�

Susc = 0.01800 ,"

!=;;II"'~=O.Q·

'. Il Az ",65.0~eg

Z(m) ..\

< ?' .025.36 ~'158.61 ~, 53[762.•~fi; snso.;.l ••r

Acoustic

Basement

fsms I East I

Line 17. On this line there again appears to be an extension of Permian rocks off the eastern shore. Note the complete absence of acoustic turbidity - the most recent channel sediments are still present, and the channel is in approximately the same position (i.e. the middle of the estuary), but there is no acoustic turbidity. At least three generations of channels are present, and the older generations are more extensive compared to further upriver. There are two prominent blocks separating the three main channels (west, central and east), and I interpret these as non-eroded cores of older Tertiary? sediments. The eastern block appears to be folded but this is probably a combination of erosion ad original repose angles (i.e. drape angles).


Line 17

Figure 7.8.2 130


526000 528pOO 530POO 532pOO =

- -

5 534,000 , • Profile of TMI (nT)

~

5240000-1 + J + +-" -----J ~~ * ~5240000 I 62650

5238000-1

5236000-1

5234000-1

5232000-1

~~--~ ~ l5238000+ \ +.....-+'"

7~

+ \~ + +Y . + S+J5236000 V).~/

,/

+ ".+ /'+ ~ . + 5234000 21 --7 , /' I

'\

+ V".--.. + !:4 + ~5232000

I 62550 [.. ','

62450

I~ 62350

:!i I

62250

I 62150

I 62050 ~ "J \j


526000 528000 530000 532000 534000 Arrows denote survey direction.

Red dots mark position fixes on the seismic record. I

61950

0 1000 2000 3000

Along profile distance (from 528350mE 5232081 mN)

4000 5000 Line 21

Figure 7.9.1 131

I I 528073mE 5231900mN I I 529147mE 5232586mN I I 530135mE 5233160mN I I 531053mE 5233617mN I I 532146mE 5233886mN I I 533106mE 5234124mN

I

Seatloor

I I. J:

rt ~ d"" I West I

~25.l

p1 E'" Q!>s«v~ _~ ~""'-"lloo loci< ."..., _ ~ -I~ Line 21. Unlike the previous line, this line only has two DI~II;II 81 ~ 1+14v1Or ~1+1:;'lo..I1 filled channels (not three). This suggests that one has

526000 528000 530000 534000 been diverted in another direction, or two have coalesced to form one (note that the channel to the west is very broad). The most recent cover of sediment on this profile

~ is thin, again suggestive of changes in channel 320.0

orientation (and hence sediment accumulation). 5240000-1 + 5240000

~.-::::::::=--'" ---\ --~

5238000 + 5238000 0.0 ~

./

!,

, ......--;;;? ~

TMI (nT)

5236000 5236000+ + ,;)20.0

52800. 528800 529600 530400 531200 532000 532801

5234000 5234000 O:,~ + ....... ~, + \ -

\ ._-t susc =0.01800,

\ --J Derwent Estuary -200 ----- ..- ...... .- Seismic Reflection Survey --' 5232000 + 5232000 ~,

~ ~

-600 Line 21A2 =66.8degZ(m)526000 528000 530000 532000 534000

Arrows denote survey direction. -800 f(lC'tietl, prC$sFl

Red dots mark position fixes on the seismic record. Figure 7.9.2 132

seismic interpretation chapter 7 - university … 7 seismic interpretation ,~ the colour scheme used...

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