Journal of Applied Geology, vol. 2(2), 2017, pp. 94–108 DOI: http://dx.doi.org/10.22146/jag.39988

Basin Evolution Palispatic Model of Bonaparte Basin, Northwest Shelf

Nomensen Ricardo,∗ Hendra Amijaya, and Salahuddin Husein

Department of Geological Engineering, Faculty of Engineering, Gadjah Mada University, Yogyakarta, Indonesia

ABSTRACT. This research area is located on the Australian NW Shelf close to the western edge of the Sahul Platform. This research is aimed to generate the palispatic basin model of Bonaparte Basin, Australian Northwest Shelf. It is to predict the impact of Neogene col- lision on the petroleum system distribution on Australian Northwest Shelf. The main data used in this research are seismic data using qualitative method analysis. The well data is used to well-seismic tied. After data acquisition, the seismic data are interpreted based on the horizon and structure interpretation. These interpretation are to reconstruct the basin evolution thorough geologic time. According to data analysis, the basin evolution pal- ispatic model are divided into Paleo-proterozoic, Paleozoic, Triassic, Early Jurassic, Mid- dle Jurassic, Late Jurassic, Early Cretaceous, Late Cretaceous, Early Eocene, Late Miocene and Recent condition. Regional tectonically there are at least three important events in NW Shelf: Middle Triassic-Jurassic NNE–SSW extension phase, Late Jurassic NE–SW ex- tension phase and the Neogen collision phase; the Neogen collision effects on Northwest Shelf Australia. These three events contributed in forming and disturbing the Paleozoic and Mesozoic petroleum system in Bonaparte basin especially. Keywords: Neogene collision · Basin evolution · Palispatic model · Petroleum system · Australian northwest self.

1I NTRODUCTION blocks and horst. This platform plunges to- Australian Northwest Shelf consist of 4 major wards the Southwest. The thin sediments of basins: the Northern Carnavon Basin, the Off- Perm, Triassic and Jurassic were deposited on shore Canning Basin, the Browse Basin and the Sahul Platform and progressed to the northeast. Bonaparte Basin or unitedly known as the Wes- It is estimated that this platform was formed tralian Superbasin / WASB (Yeates et al., 1987), due to Paleozoic openings that later rejuve- which is a field producer Large gas (reach- nated and lifted during the continental break- ing 84% of total Hydrocarbons) in addition to up event in Mesozoic and followed by a plate condesate and oilThere were 754 exploration collision of Australia with microplate Southeast drilling had bored at 233 Oil and Gas Fields in Asia at the end of Cenozoic. Two great Jurassic Australian North West Shelf basins.Australian Deposits to the Early Cretaceous identified in Northwest Shelf basin is estimated containing the Northern Bonaparte Basin, Malita Graben an oil reserve of 2.6 billion barrels, a condensate and Sahul Syncline. The collisions of the Aus- of 2.6 billion barrels and 152 tcf of gas. tralian and Eurasian Plates in the Miocene to The Sahul Platform, the northern part of Aus- the Pliocene resulted in a flexural down warp tralian basin, is defined as a large eastward on the Timor-Tanimbar Trench and resulted in trending basement that consists of tilted fault the reactivation of the Northwest Western Aus- tralian Margin. ∗ Corresponding author: N. RICARDO, Department The study area is located on the Australian of Geological Engineering, Gadjah Mada Univer- NW Shelf (Figure1) close to the western edge sity. Jl. Grafika 2 Yogyakarta, Indonesia. E-mail: of the Sahul Platform. To the north, the area is [email protected]

2502-2822/ c 2017 Journal of Applied Geology BASIN EVOLUTION PALISPATIC MODELOF BONAPARTE BASIN bounded by the Timor Trough with a NE–SW est rocks in Banda Forearc, extrapolation to trend. At thepresent day the Australian plate is the northwest of the Australian Margin Graben being subducted beneath the SE Asian margin system passes through West Timor and this and the northwestern part of Australia is cur- aulacogen clearly has a strong influence in the rently in collision with the Banda Arc in the area sequence of structural development at subse- around Timor Island (Hamilton, 1979). quent riftings. The second phase of rifting These studies have utilised predominantly spanned the Late Carboniferous-Early Permian 2D seismic data and have been concerned with continuing throughout the Permian, to the early petroleum exploration. The area discussed in mid Triassic. This rifting phase is associated this study is relatively understudied in compar- with the development of an intracontinental ison. The main focus here is the structural con- rift along the Southern Banda Band (Timor- figuration and an understanding of structural Tanimbar) line, with the North Banda Busur evolution of the northern Bonaparte Basin. (Buru-Seram) Island which is the northern rift margin. The third phase of openings occurs 2M ETHODOLOGY at the End of the Triassic. The major rifting The seismic lines of 11602 and 11609 are used phase is identified between the late Mid Juras- to generate the basin history/ evolution - sec- sic and Early Cretaceous. It had been well docu- tion through geologic time. Both of these lines mented by Pattillo and Nicholls (1990); Colwell intersect each other and have a reliable marker et al (1994). This rifting phase is associated with of Flamingo Well. All horizons we have are the opening of the ocean floor that occurs dur- elaborated using flattening features on Decision ing Oxfordian and Valanginian and continues Space Geoscience (DSG) Software. As the re- with the development of the Indian Ocean and sult, we have the model of the basin and its de- the passive continental margin of Western Aus- velopment from basement (Paleo-Proterozoic) tralia. to recent sequences. Seismic cross section used The intra-Valanginian regional unconformi- is 2D seismic which has medium to good qual- ties showed the absolute top of the pre-breakup ity. Mistie adjustment is also done before be- sequences around the Banda arcs, though post- ginning the interpretation of the seismic cross breakup succession is partially equivalent to section. Reliable section is used as a reference the Late Jurassic on the northern Banda Arc for mistie analysis. Based on the results of this (Audley-Charles et al., 1979; Kemp and Mogg, analysis, some vintage should be shifted and 1992). While pre-breakup succession is char- adjusted to the vintage reference. acterized by deposited in a All visible structures and horizons are inter- rifted continental margin environment, Banda preted based on seismic section through time Forearc post-breakup succession is character- geologic. Each horizon has a unique geologic ized by deep sea sediments that are deposited event. The product of these horizon and struc- on the outer shores of Australian continental. ture is a subsurface map. The Triassic time is The marine sediment (range in Cretaceous to the focused sequence in this research. The flat- Tertiary) has the potential to contain hydrocar- tening applied that are useful in basin evolution bons. The Perm rifting phase until the Early reconstruction. All horizons flatten at each time Triassic / Medium is the most significant de- to show the change of basin geometries. veloping structure, leading to the modifica- tion/evolution of the graben basin and inter- 3R EGIONAL GEOLOGY vening in the height of the horst block. As Metcalfe (2006) has explained in detail the evo- already mentioned, the northern and south- lution of the Australian Northwest Shelf basin. ern Banda Arcs developed as a complementary The initial phase of regional extensions are as- rifted margin during this period. sociated with the major aulacogenic rift, Bona- parte Graben (Petrel Sub-Basin), which devel- 4R ESULTS AND DISCUSSION oped during the Middle Paleozoic (Gunn, 1988; 4.1 Horizon interpretation O’Brien et al., 1993). Although the Bonaparte Horizon interpretation defines as identifying rifting phase is recognizably older than the old- the sequence/strata using geologic time datum.

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Figure 1: Basemap of research area: Australian Northwest Shelf.

The datum is distributed to other seismic sec- Middle Jurassic (Callovian) sequence. That is tion to estimate the development of strata later- consistent to well-seismic tied analysis which ally to the unknown/ unexplored area or some- shown Jurassic (middle) is the oldest sequence times call as stratigraphy seismic. Furthermore, penetrated by Flamingo Well in Sahul Syncline, the stratigraphy seismic is difficult to apply to NW Shelf Australia. Applying Flamingo well Northwest Shelf Australia – Timor and Tanim- marker, so the seismic section of 11602 and bar island geologic setting. The geology struc- 11609 are interpreted as shown on Figure2. tures developing in this research area are very The horizon picking was accomplished at some complex and complicated. Some horizons inter- geologic time from Proterozoic to recent con- preted are seismic section of 11602; 11603, 11608 dition. They are grouped into, Paleozoic se- and 11609. These section are representation of quence, Triassic, Early Jurassic, Middle Juras- all seismic that interpreted for subsurface map- sic, Late Jurassic, Early Cretaceous, Late Creta- ping. Totally, there are more than 30 line seis- ceous (Turonian), Early Eocene, Late Miocene, mic are interpreted. But some of them are not Recent. At Early Paleozoic, sediment filled the necessary. The limitation of well data and the rift basin and directly underlying Proterozoic distance of seismic line to Timor-Tanimbar area basement. The Triassic sequence overlying on are considered in determining/ selecting seis- Paleozoic sequence as a post-rift sediment in- mic line used in this research. In this term, a filling. Triassic sequence overlying on Paleozoic Flamingo well that located in Northwest Shelf sequence as a post-rift sediment infilling. At the Australia, is the only one trusted time geo- late Triassic as a Maximum flooding surface is logic marker used and applied to seismic sec- identified (Longley et al., 2002). This sequence tion. Seismic section NW–SE 11602 and NE–SW is dominated by fine clastic sediments. The new 11609 across the Flamingo well. These two seis- structure identified at SE side on seismic sec- mic section are much more analyzed than oth- tion. The early Jurassic sediment filled the rift ers. According to the published paper (e.g., basin as an early syn-rift sediment. The Late Longley et al., 2002), the lowest strata/ se- Jurassic sediment is the beginning of post-rift/ quence that is penetrated by Flamingo well is sagging phase. Early cretaceous sediment as a

96 Journal of Applied Geology BASIN EVOLUTION PALISPATIC MODELOF BONAPARTE BASIN part of postrift/ sag basin (or continuing of Late was filled by Late Jurassic syn-rift breakup sedi- Jurassic sediment) is overlied on Jurassic sedi- ments. Breakup was associated with the forma- ment. Turonian sequence infilling caused sub- tion of Jurassic oceanic crust. The Late Juras- sidence in southeast part of section. Pliocene sic normal faults predominantly trend E–W to to Miocene sequence developed as a sag of car- ENE–WSW with steep to moderate angles of bonate sequence. A thick carbonate formed on dip. The faults are believed to curve around to a Pliocene to Miocene interval. Carbonate Se- NE–SW direction. Tilted fault blocks developed quence dominated in Pliocene and still devel- in the northwest of the study area with faults oped in recent time. These all horizon seismic dominantly dipping to the NW suggest duc- geometry through geologic time are correlated tile deformation at the Triassic level during rift- to tectonic event in forming/ depositing sedi- ing. A low relief accommodation zone formed ments. in the eastern graben, striking NE–SW along an en echelon array of segmented rift faults. An- 4.2 Structure interpretation other rift segment also developed in the south- According to structure interpretation, three ma- west of the study area with no development of jor tectonic events with different fault trend di- an en echelon array or accommodation zone. rections have been identified in the research The Middle Triassic and Late Jurassic faults ap- area that associated with the Mid-Triassic ex- pears that older fabrics strongly influenced the tensional phase, Late Jurassic-Early Cretaceous development of this structure. The accommo- rifting and breakup event, and the Neogene col- dation zone in the eastern graben overlies the lision between Australia and the Banda Arc. depression that was created by the previous ex- The explanation of the structure configuration tensional phase. This accommodation zone was is described below according to the big event also oriented in a similar NE–SW trend, sug- through geologic time. gesting that movement occurred on the older faults. The interpreted extension direction is Middle Triassic extensional phase perpendicular to the strike of the faults. The ex- Based on observations from the seismic lines, tension direction is consistent with the orienta- this extensional phase produced normal faults tion of the fracture zones formed in the Juras- that cut the Early Triassic to Permian sequence sic oceanic crust. The interpretation also sup- with displacements of more than 200 ms. The ports different extension directions for the Early faults predominantly trend NNE-SSW. The tim- Mesozoic and Late Jurassic events ing of the fault movements is estimated to be younger than Early Triassic and older than Mid- Neogene collision dle Jurassic. Thick Triassic to Middle Juras- The Mesozoic faults was reactivated by the sic sediments are interpreted from the isochron Australia-Banda Arc collision in the Neogene. map of Permian to top Middle Jurassic hori- There is a complex vertical linkage of faults in zons, and suggests that this extensional phase the Cretaceous-Paleocene interval. In general, created a large depocentre in the northeast of the faults trend NE-SW and have a net normal the study area. In extended regions, basement displacement. The faults cut the Paleocene to fabrics commonly influence the development of approximately Upper Pliocene strata with sig- faults in the region, so it is possible that the nificant development of growth strata in the trend of the Middle Triassic faults reflects Paleo- Pliocene. This suggests that the faulting started zoic structural fabrics which controlled the fault during the Early Pliocene. In some places the geometry. Segmented faults with relay ramp faults die out in a significant distance below the transfer zones were developed at this time. sea floor, suggesting Late Pliocene cessation of fault activity. Selective reactivation of the faults Late Jurassic–Early Cretaceous rifting also occurred in this region. The dip direction The extensional phase in the Early Mesozoic ul- of the Mesozoic rift faults does not influence the timately initiated the breakup event in the Late younger structures. Jurassic. Displacement in the Jurassic was ap- The en echelon fault arrays located in the proximately half that of the earlier extensional southern part of the study area that dipping to phase. It created accommodation space that the southeast, linked to Mesozoic rift faults

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Figure 2: Seismic interpretation of seismic-lines 11602 and 11609. with similar dip direction, whereas in the (Audley-Charles, 2004; Hall, 2002) and ulti- northern part of the study area the opposite mately led to Timor over-thrusting the con- is the case. Conjugate fault structures are well tinental Australian plate, forming the Timor developed in the area where a narrow horst Trough fore-deep and later back-thrusting block was formed by the Late Jurassic rift- north of the Banda Volcanic Arc. This sug- ing. Right-stepping en echelon fault arrays gests that there are two possible mechanisms developed most likely in response to oblique that contributed to structural development in convergence between Australia and SE Asia. the early Pliocene, which are flexure induced The oblique motion also favoured the reacti- by the Timor thrusting and loading, and/or vation of the Early Mesozoic faults (Amir et oblique convergence along the margin. The al., 2010). The faults that cut the Permian and initial fault development in the study area Triassic sequence also cut the syn-rift and post- was induced by flexure after the Australian rift sequence, suggesting that the older fault continent reached the subduction system and plane was favoured for being re-used by the collided with the Banda Arc. The collision led latest applied stress direction in the Neogene. to the fore-deep Timor Trough development However, not all older faults were reactivated, with southward thrusting of the Australian which may be due to the thick overburden of margin. The Australian continental margin was the post-rift packages that prevented the fault evidently bent due to loading by thrusting on to propagate easily. No rifting occurred in the Timor. This probably induced uplift of part of Neogene and the development of the exten- the Australian margin and caused some erosion sional fault systems at this stage are not caused of the upper crust. This may have provided by stretching. sediment to the Pliocene growth sequence that In the Late Miocene the continental-oceanic filled the accommodation space during pro- transition reached the subduction system and gressive development of extensional faults re- collision of the Australia and Banda Arc be- lated to flexure. The uplift due to compression gan at approximately ~4 Ma in the Pliocene in the study area would be concentrated at a

98 Journal of Applied Geology BASIN EVOLUTION PALISPATIC MODELOF BONAPARTE BASIN lower interval such as the Mesozoic. Uplift was This rifting have a pronounced NW–SE struc- concentrated on several horst blocks within tural orientation (Barber, 2003). The seismic in- the area.The flexural mechanism alone is not terpretation shown the normal fault is domi- sufficient to explain the oblique displacement nantly as a product of rifting phase that inter- on right-stepping en echelon fault arrays, the preted to have a trend NE-SW orientation. This splay fault development, and the reactivation structure formed of Carboniferous-Permian as of NNE–SSW trending Early Mesozoic faults Barber (2003) mentioned. Five times of rift observed in the study area (Barber, 2003). The occurred during Late Carboniferous-Permian interpretations of the Late Miocene structural Extensional episode (Etheridge and O’Brien). configuration during collision, the relative plate Longley et al. (2002) identified there 3 cycles movements at ~5 Ma and present day suggest sag and syn-rift along early Paleozoic to Per- flexure and oblique convergence were both mian, shown on Figure4. The NW–SE orien- influences. Loading due to Timor thrusting tation rifting caused the forming of the great created near-surface extensional fault systems half-graben and some local sub-basin. The thick and uplift of Mesozoic horst blocks due to Paleozoic sediments filled the basin. By inten- compression in the middle-deeper part of the sively block faulted (normal fault) and gravity crust caused linkage to deeper faults. Oblique effect causing subsidence event at this time. It convergence created right-stepping en echelon caused basement uplift at the southern part of fault arrays trending NE–SW. this section. The up and down arrows show how the tectonic and gravity effect produce 4.3 Basin evolution the relatively movement of the basement (block The basin evolution of NW Shelf Australia faulted). Barber et al (2003) suggested that the through geologic time (Paleo-Proterozoic time Paleozoic event was the progenitor key rift- to recent condition) are summarized as below. ing episode that led to subsequent progressive Mesozoic continental breakup and related ther- Initial basement Paleo-Proterozoic (?) mal sag cycles. In addition, the Palaeozoic Building block formed during Proterozoic (Bar- basins could contain high quality and mature ber, 2003). This block become the first main oil-prone source rocks of Cambrian, Devonian basement of Northwest Shelf Basin (Western and Carboniferous age. Australia Superbasin/ WASB). According to geochronology data and provenance study, Triassic time it can estimated this basement rock mainly Triassic sequence overlying on Paleozoic se- formed of metamorphic rock (?), shown on quence as a post-rift sediment infilling. At the Figure3. It cannot identify the structure config- late Triassic as a Maximum flooding surface is uration. But In Timor, based on field study by identified (Longley et al., 2002). This sequence Sawyer et al., the basement rocks are uplifted is dominated by fine clastic sediments. The and outcropped to the surface area. The affin- new structure identified at SE side on seismic ity of basement rocks that outcrop on Timor section. Besides, also a fold geometry is iden- is not well understood. Schists, phyllites, am- tified that interpreted as reactivation fault of phibolites, and associated serpentinites of the older normal fault. Longley (2002) stated this Mutis/Lolotoi Complex (van West, 1941; Ro- structure as Fitzroy movement inversion oc- sidiet et al., 1981). The basement in Timor is curred at late Triassic, The Fitzroy Movement compositionally similar to the Mutis/Lolotoi, period of compression in the Middle–Late Tri- on the basis that Mutis/ Lolotoi lithologies assic resulted in reactivation and inversion of were associated in the field with Maubisse the previous Paleozoic fault systems (O’Brien Formation and Kekneno Sequence, and both et al., 1993; Colwell and Kennard, 1996) and contained accessory minerals similar to the caused widespread uplift and erosion on the Mutis/Lolotoi Complex. Ashmore Platform, Londonderry High and in the southern Petrel Sub-basin. Upper Trias- Paleozoic time sic–Lower Jurassic fluvial sedimentation de- At Early Paleozoic, sediment filled the rift basin posited the Malita Formation. This was fol- and directly underlying Proterozoic basement. lowed by the thick, widespread succession of

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Figure 3: Flattening of Paleo-Proterozoic basement top.

Figure 4: Flattening of Paleozoic top.

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Lower–Middle Jurassic fluvial and coastal plain sic (as explained above) to Middle Jurassic deposits of the Plover Formation across most of times, leading to deposition of the Malita and the Bonaparte BasinAs shown by Figure5, the overlying Plover Formation (fluvio-deltaic sed- Paleozoic sequence and also Triassic sequence iments). Plover Formation times were domi- that had been deposited are disturbed by Mid- nated by a series of widespread braided trunk dle to Late Triassic compression. The structures river systems feeding a relatively narrow wave- that developing at this time caused inversion dominated coastline and beyond, a wide ma- and uplifted event. The up-arrow shows the rine shelf (Barber, 2003).In response to south- uplift itself. These uplifted area is related to sur- west to northeast diachronous breakup Callo- face process (e.g. erosion, transport, and depo- vian to Oxfordian (Middle Jurassic), local de- sition). pocentres such as the Malita and Calder Graben developed, heralded by a marine transgres- Early Jurassic time sion (Laminaria/Elang Formation sands). The From Triassic section to Jurassic section, oc- shoreline was initially in the same position curred very deep subsidence that is identified as the preceding Plover succession but began as rifting phase after post-orogeny in late Tri- to move inboard as basinal deepening andr assic. This related to Lhasa and West Burma elated sediment starvation continued, the sands separation and rifting (Longley, 2002).The early being replaced by condensed shales (Frigate Jurassic sediment filled the rift basin as an Shale).The normal fault is clearer identified on early syn-rift sediment. Continental to shelfal this section. Then drag fold can be seen in given marine sedimentation continued throughout location. The basement on NW side little bit up- Early–Middle Jurassic times, leading to depo- lifted. It can be interpreted as a flexuring event, sition of the Malita Formation red beds and where the voluminous sediment supply filled overlying Plover Formation fluvio -deltaic sed- the basin depocenter, so it caused uplifting in iments up to 1500–2000 m thick The Plover for- basement high as shown on Figure7. mation sedimentation patterns during Plover Formation times were dominated by a series Late Jurassic time of widespread braided trunk river systems Further subsidence continued in these depocen- feeding a relatively narrow wave-dominated tres during latest Tithonian to early Cretaceous coastline and beyond, a wide marine shelf (Bar- times (Barremian), with deposition of over ber, 2003). Although the major structures are 500–1500m of marine shales and turbidite sands extension/ rifting, the reactivated structure is of the Upper Flamingo Group. By this time, the believed still occurring at this time. Seismic ev- palaeo-shoreline had receded some 120 km to- idence (Figure6) shows the inversion structure wards the craton, inducing starved argillaceous identification. The other new fault also found facies over much of the area, excepting for occa- on this section. The early Jurassic time produce sional turbidite sand. These sands were derived good reservoir (e.g. Plover Formation) that ex- from the continually flowing Goulburn Graben perienced complex and complicated structure. axial trunk river system, as observed by pro- It is indicated by the contradictive structure nounced incised channeling of late Tithonian found. At rifting phase, it still possibly found age which penetrated channel fill clays. The fi- the inversion structure (uplifted area) in lo- nal stage of starved sedimentation in the Upper cal area especially on the middle area of this Flamingo led to the preservation of enriched section. The left-right arrow shows the exten- marine organic shales in condensed sequences sion fault, while down-arrow shows the basin of the Echuca Shoals Formation.According to forming/ subsidence as shown on Figure6. Figure8, the Upper or Late Jurassic sediment is the beginning of post-rift/ sagging phase (par- Middle Jurassic time tially sag). Further subsidence continued in the This section shows the continuing deposition depocentres during Upper Jurassic. Longley of the syn-rift sediment, which the sediment et al. (2012) stated that the basin filled by ma- Mid-Jurassic was deposited over early Juras- rine shale and turbidite sands. On this section, sic sediment. The Continental to shelfal ma- the basement uplifted as thick sediment filled rine sedimentation continued from Early Juras- depocenters which causing flexuring on base-

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Figure 5: Flattening of Triassic top.

Figure 6: Flattening of Early Jurassic top.

Figure 7: Flattening of Middle Jurassic top.

102 Journal of Applied Geology BASIN EVOLUTION PALISPATIC MODELOF BONAPARTE BASIN ment highs. The main structures developing on related structures. Further the hinterland up- this time is normal fault that cut upper Jurassic lift resulted in a block rotation of the margin sequence. (where sediments inboard of the tilt line were eroded and redeposited into deeper water en- Early Cretaceous to Valanginian time vironments (Longley et al., 2002). Early cretaceous sediment as a part of postrift/ sag basin (or continuing of Late Jurassic sedi- Early Eocene time ment) is overlied on Jurassic sediment. Com- Early Eocene sequence overlie on Turonian se- pression tectonic identified on this section. It’s quence. Eocene sequence is believed as the late shown by anticline/fold geometry that was second phase of sagging event (after Turonian formed and some dragging folds found as sagging event) on open marine passive mar- caused by compression. In this section, the gin condition. In other words, this sequence is Jurassic Sequence uplifted and then a part of bounded by maximum flooding surface. The sequence was eroded by surface process. This subsidence occurred but not significant. Nor- erosion occurred in Valanginian, shown on mal fault developed and cut early Eocene se- Figure9. The succeeding intra-Valanginian quence, shown on Figure 11. Further sand in- unconformity marks the beginning of the fi- fluxes into the Caswell and southern Vulcan ar- nal post-breakup subsidence phase and com- eas occurred in the Maastrichtian, and follow- mencement of pronounced thermal sag and ing the base Tertiary onset of Coral Sea spread- passive margin cooling. The succession is char- ing, the North West Shelf had moved suffi- acterized by deposition of fine grained clastics ciently far north for carbonate factories to be es- of Mid to Late Cretaceous age, deposited in tablished in areas away from clastic input (Lon- an aggradational to progradational shelf slope gley et al., 2002). Following a major plate re- environment, interrupted by occasional low- organisation in the middle Eocene, Australia stand events especially in the Late Campanian, moved rapidly northwards, and carbonate de- sands being derived from the Goulburn Graben position became dominant (Baillie et al., 1994). proto-river trunk stream. Reworking of carbonates from the factory tops led to massive carbonate progradation, infilling Late Cretaceous time the underfilled accommodation space provided Continuing the sediment deposition of the by the underlying rift basins. Early Cretaceous, at Late Cretaceous age, also deposited in an aggradational to prograda- Late Miocene time tional shelf slope environment, interrupted After Eocene MFS, Pliocene to Miocene se- by occasional lowstand events especially in quence developed as a sag of carbonate se- the Late Campanian, sands being derived quence. A thick carbonate formed on Pliocene from the Goulburn Graben proto-river trunk to Miocene interval. Carbonate sequence devel- stream.Turonian sequence overlie on early oped on early Eocene sequence. Late Miocene Cretaceous and to Southwestward Turonian event is important, because it is identified as sequence overlie on Jurassic Sequence on this beginning of compressive orogeny that reacti- section. Turonian sequence infilling caused vated the older fault (inversion structure). This subsidence in southeast part of section. It also section shows significant uplifting, shown on caused flexuring. Normal fault structure de- Figure 12. The identified collision in the Neo- veloped intensively. Some research stated that gene reactivated older Mesozoic faults. The Turonian is a mark of maximum flooding event faults cut the Paleocene to approximately Up- in Cretaceous event that known as a thick seal per Pliocene strata with significant develop- and broadly distributed or called as regional ment of growth strata in the Pliocene. This sug- Seal, shown on Figure 10. During the Late Cre- gests that the faulting started during the Early taceous, uplift of the hinterland (in response Pliocene-Late Miocene. The Late Miocene hori- to rift events along the Australian southern zon can be considered as representative of the margin), resulted in a phase of inversion. This structural configuration in the Neogene (Figure tectonic event marked the onset of transpres- 12). In some places the faults die out in a sig- sional structural growth of pre-existing rift nificant distance below the sea floor, suggesting

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Figure 8: Flattening of Late Jurassic top.

Figure 9: Flattening of Early Cretaceous top.

Figure 10: Flattening of Late Cretaceous top.

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Figure 11: Flattening of Early Eocene top.

Late Pliocene cessation of fault activity. Selec- 5C ONCLUSION tive reactivation of the faults also occurred in The basin evolution palispatic model represents this region. The dip direction of the Mesozoic the structure contributions in petroleum system rift faults does not influence the younger struc- that formed in Sahul Platform, Bonaparte Basin, tures. This is clearly shown by the en echelon Australian Northwest Shelf. This model di- fault arrays located in the southern part of the vide the geologic events based on the geologic study area that dipping to the southeast, linked time such as Paleo-proterozoic, Paleozoic, Trias- to Mesozoic rift faults with similar dip direc- sic, Early Jurassic, Middle Jurassic, Late Juras- tion, whereas in the northern part of the study sic, Early Cretaceous, Late Cretaceous, Early area the opposite is the case. Eocene, Late Miocene and Recent condition. Recent condition Regional tectonically there are at least three im- portant events in NW Shelf: Middle Triassic- Pliocene age is the peak of compressive event Jurassic NNE–SSW extension phase, Late Juras- that triggered by oblique strike-slip fault. This sic NE–SW extension phase and the Neogen event related to curvilinear arc accretionary collision phase; the Neogen collision effects on prism and Timor-Tanimbar Trough as a con- Northwest Shelf Australia. These three events sequence of Neogene Australian continental contributed in forming and disturbing the Pale- plate collision with Indonesia arc system. The ozoic and Mesozoic petroleum system in Bona- structure associated with compression and parte basin especially. strike-slip developed especially in Miocene to Pliocene sequence. Carbonate Sequence domi- ACKNOWLEDGEMENTS nated in Pliocene and still developed in recent We thank STEPS-Halliburton Program for pro- time, shown on Figure 13. Amir et al. (2010) viding the dataset. Nomensen Ricardo’s Grad- suggested that the interpretations of the Late uate Programme at Universitas Gadjah Mada Miocene structural configuration during col- was made possible by this research programme lision, the relative plate movements at ~5 Ma who have supported the projects in Indonesia. and present day, and the stress map of the re- We thank Helen Smith, Jamie Higton and Co- gion suggest flexure and oblique convergence lette Lyle (from STEPS Halliburton) for super- were both influences. Loading due to Timor vision, discussion and help and the 2016’s Mag- thrusting created near-surface extensional fault ister programme of Geological Engineering De- systems and uplift of Mesozoic horst blocks partment students for support. due to compression in the middle-deeper part of the crust caused linkage to deeper faults. REFERENCES Oblique convergence created right-stepping en Amir, V., Hall, R., and Elders, C.F. (2010) Structural echelon fault arrays trending NE–SW. Evolution of Northern Bonaparte Basin, North-

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Figure 12: Flattening of Late Miocene top.

Figure 13: Flattening of recent condition.

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