energies

Review Geology and Petroleum Systems of the East China Sea Basin

Bing Wang 1, Harry Doust 2 and Jingyan Liu 1,*

1 School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China; [email protected] 2 Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam 1181 HV, The Netherlands; [email protected] * Correspondence: [email protected]



Received: 28 July 2019; Accepted: 23 October 2019; Published: 26 October 2019


Abstract: The back-arc East China Sea Basin lies on extended continental crust at the leading edge of the Eurasian plate. In this study, the basins are described and subdivided according to their tectono-stratigraphic evolution. In order to distinguish between different phases of deformation in basin development, standard basin evolution patterns related to geodynamic drivers are identified as a first step. On the basis of this, standard patterns are recognized in the sedimentary sequences that characterize the area and its tectonic evolution, and linking them to the petroleum systems present is attempted. This is achieved by characterizing and grouping them into basin cycle-related petroleum system types (PSTs). Finally, the development of plays is examined within the petroleum systems in the context of their tectono-stratigraphic evolution, and groups of sub-basins with similar geological history and, therefore, potentially similar petroleum prospectivity are identified. In the East China Sea Basin, four proven and potential PSTs were recognized: (1) Late Cretaceous to Paleocene oil/gas-prone early syn-rift lacustrine–deltaic PST; (2) Eocene gas/oil prone late syn-rift marine PST; (3) Oligocene to Middle Miocene gas/oil-prone early post-rift fluvial–deltaic PST; (4) gas-prone syn-rift turbiditic PST. The geology and petroleum systems of three major sub-basins of the East China Sea Basin, the Xihu Sub-basin, the Lishui Sub-basin, and Okinawa Trough, are discussed in detail, and their petroleum systems and play development are analyzed. Finally, the sub-basins are grouped into “basin families” distinguished by their tectono-stratigraphic development, namely, Northwest to Northeast Shelf Basin (NWSB–NESB), Southwest to Southeast Shelf Basin (SWSB–SESB), and Okinawa Trough basin families, respectively.

Keywords: petroleum systems; play; basin family; East China Sea Basin; Okinawa Trough

1. Introduction The East China Sea contains the largest Mesozoic–Cenozoic basin of the continental margin of China, covering an area of about 770,000 km2 [1] (Figure1). It includes the East China Sea Shelf Basin in the west and the Okinawa Trough in the east, separated from each other by the Diaoyudao paleo-uplift or Taiwan–Sinzi fold belt. The East China Sea Shelf Basin is divided into a series of sub-basins, separated by basement highs or paleo-uplifts, including the Hupijiao, Haijiao, Yushan, and Yandang paleo-uplifts. The sub-basins can be subdivided into a western group (West Shelf Basin), including the Lishui, Jiaojiang, Fuzhou, Minjiang, Qiantang, and Changjiang sub-basins, and an eastern group (East Shelf Basin), including the Diaobei, Xihu, and Fujiang sub-basins.

Energies 2019, 12, 4088; doi:10.3390/en12214088 www.mdpi.com/journal/energies Energies 2019, 12, 4088 2 of 28 Energies 2019, 12, x FOR PEER REVIEW 2 of 28

Figure 1. RegionalRegional location location and sub-units of the East East Chin Chinaa Sea Sea Basin. Basin. Pink Pink represents represents the the paleo-uplift, paleo-uplift, dark green indicates the sub-basin, yellow represents the local low-uplift, low-uplift, brown brown represents represents land area, area, and light blue represents sea.sea.

Several oil and gas fieldsfields and oil- and gas-bearinggas-bearing structures were discovered in the East China Sea Shelf Basin since thethe 1970s1970s [[2,3].2,3]. The known reservoirsreservoirs include fluvial,fluvial, lacustrine,lacustrine, deltaic, and shallow marinemarine sandstonessandstones ofof Paleocene–OligocenePaleocene–Oligocene ageage [4[4].]. Eocene–OligoceneEocene–Oligocene fluvial–lacustrinefluvial–lacustrine claystones and coals buried deeply in the sub-basi sub-basinsns are are believed believed to to be be the the main main source source rocks rocks [4]. [4]. Paleocene deltaic and shallow marine barrier sandstones form the main reservoirs of the West Shelf Basin [[5–7],5–7], whilewhile the the main main reservoirs reservoirs of theof Eastthe Ea Shelfst Shelf Basin Basin are Eocene, are Eocene, Oligocene, Oligocene, and Lower and Miocene Lower sandstones,Miocene sandstones, belonging belonging to marine to sedimentary marine sedimentary facies in facies the south in the [ 8south,9] and [8,9] fluvial–lacustrine–deltaic and fluvial–lacustrine– sedimentarydeltaic sedimentary facies infacies the northin the north [2,10– 12[2,10–12].]. Regional Regi sealsonal seals of the of Eastthe East Shelf Shelf Basin Basin are are believed believed to beto representedbe represented by Eocene–Mioceneby Eocene–Miocene fluvial–lacustrine fluvial–lacustrine claystones claystones [2], while,[2], while, within within the West the ShelfWest Basin,Shelf intra-formationalBasin, intra-formational claystones claystones serve asserve local as seals local [ 13seals]. Despite [13]. Despite extensive extensive petroleum petroleum exploration exploration in the area,in the the area, geological the geological evolution evolution and petroleum and petroleum geology geology of the of basins the basins remain remain poorly poorly documented. documented. The basinThe basin is also is aalso politically a politically sensitive sensitive region region because because China andChina Japan and are Japan in stalemate are in stalemate over a maritime over a boundarymaritime boundary dispute, a ffdispute,ecting potentialaffecting oilpotential and gas oil rights and gas in the rights area. in the area. Geology and petroleum systems over the East China Sea Shelf Basin were studied bits and pieces by various researchers over the past 20 yearsyears [[6,6,1010–15].–15]. However, there is no paper presenting an overview of the petroleum system over the entire basin, especially the OkinawaOkinawa Trough. This paper is intended to provide a full reviewreview ofof thethe petroleumpetroleum systemssystems developmentdevelopment over the East China Sea Basin utilizing a consistent methodology proposed by Doust [16], which is explained in detail in the next section.

2. Objectives and Methodology

Energies 2019, 12, 4088 3 of 28

Basin utilizing a consistent methodology proposed by Doust [16], which is explained in detail in the next section.

2. Objectives and Methodology In this study, the basins are described and subdivided according to their tectono-stratigraphic evolution. This is based on References [16–18]. The basins studied in the literature are Cretaceous to Tertiary in age and pass through a number of typical tectono-stratigraphic phases or basin cycles, which include extensional rifting, post-rift sag, and local inversion. In order to distinguish between different phases of deformation in basin development, standard basin evolution patterns related to geodynamic drivers are identified as a first step. The basic unit, the basin cycle, consists of the sediments deposited during one tectonic episode. Most rifted basins evolve through more than one cycle, and include episodes of extension, subsidence, and compression [19–21]. The depositional sequences belonging to the cycles by definition represent distinct phases of the basin history, and are often bounded by regional unconformities triggered by tectonic events [19–21]. Each sequence may contain one or more fully developed cycles of sedimentation, in which source rocks, reservoirs, and seals may be present. On the basis of this, standard patterns in the sedimentary sequences that characterize the area and its tectonic evolution are identified, and linking the petroleum systems present is attempted. This is achieved by characterizing them and grouping them into basin cycle-related petroleum system families or types (PSTs). Finally, the development of plays is examined within the petroleum systems in the context of the tectono-stratigraphic evolution, and groups of sub-basins with similar geological history and, therefore, potentially similar petroleum prospectivity are identified. It is believed that this process allows explorers to predict which petroleum systems and play types might be expected to occur in underexplored basins or parts of basins where subsurface data are limited. In particular, by comparing characteristic basin cycles and their characteristic PSTs (if present), comparisons can be made with similar basins elsewhere, potentially extending the analogues which can be brought to bear (i.e., Beglinger et al. [22]). Magoon et al. [23] defined petroleum systems as “encompassing a pod of active source rock and all of the genetically related oil and gas accumulations”. This implies an intimate link between the source of the petroleum and the latter’s ultimate destinations, the reservoir formations, or lithofacies. Since the link depends to a significant extent on the presence and efficiency of seals, the charge may reach several different reservoir formations, and these may lie either in the same or in different (usually younger) basin cycles. In all cases, therefore, following Magoon et al. [23], petroleum systems are grouped into types (PSTs) according to the source formation and cycle.

3. Geological and Tectonic Setting

3.1. Tectonic Evolution The East China Sea Basin comprises a complex of back-arc basins located on extended continental crust close to the leading edge of the Eurasian plate. It lies west of the Ryukyu Trench, where the oceanic crust of the Philippine Sea plate is subducted below the Eurasian plate (Figure2)[24]. The tectonic evolution of the East China Sea Basin is still not fully understood. Most of the detailed studies focused on the Okinawa Trough and the Ryukyu Arc [25–31]. Plate tectonic reconstruction of the Far East generally concentrates around southeast Asia and the southwest Pacific, with the East China Sea being a peripheral area [32,33]. It is generally accepted that the tectonic evolution of the East China Sea Basin is controlled by the interaction of the Eurasian, Pacific, and Philippine Sea plates; however, the details of the relationship between basin development and the interaction of these three plates remain elusive. Energies 2019, 12, 4088 4 of 28 Energies 2019, 12, x FOR PEER REVIEW 4 of 28

Figure 2. SchematicSchematic tectonic tectonic cross-section cross-section across across the Ea Eastst China Sea basins. The The East China Sea Shelf Basin and thethe westernwestern part part of of Okinawa Okinawa Trough Trough are are modified modified from from Reference Reference [1], while [1], while the eastern the eastern part of partthe Okinawa of the Okinawa Trough andTrough Ryukyu and Trench Ryukyu is aTrench schematic. is a Theschematic. thicknesses The indicatedthicknesses here indicated are approximate. here are approximate. Four main tectono-stratigraphic cycles are distinguished in the evolution of the basins [1,24,34–38]. It is importantFour main to tectono-stratigraphic note that these cycles cycles are not are time-equivalent distinguished in throughout the evolution the of area the (Figure basins3 [1,24,34–). 38]. ItA is riftimportant cycle (Lateto note Cretaceous that these cycles to Paleocene), are not time-equivalent during which throughout active back-arc the area extension (Figure 3). was • • Aaccompanied rift cycle (Late by active Cretaceous normal to faulting Paleocene), and theduring accumulation which active of mainlyback-arc deltaic extension to marine was accompaniedclastic sediments by active in rift normal grabens. faulting and the accumulation of mainly deltaic to marine clastic An early (or first) post-rift thermal sag cycle (Eocene to Oligocene), during which mainly deltaic • sediments in rift grabens. • Anand early marginal (or first) marine post-rift sediments thermal accumulated. sag cycle (Eocene There to was Oligocene), less faulting during during which this mainly cycle, anddeltaic the anddepositional marginal areas marine extended sediments over accumulated. large parts of There the rift was shoulders. less faulting during this cycle, and the depositionalAn inversion areas cycle extended (Oligocene over to la Miocene),rge parts of when the rift compression shoulders. affected the syn- and post-rift • • Ansequences, inversion forming cycle (Oligocene uplifted ridges to Miocene), in the basins.when compression Uplift was affected accompanied the syn- by and erosion post-rift and sequences,local deposition forming uplifted ridges in the basins. Uplift was accompanied by erosion and local depositionA late (or second) period of post-rift thermal sag cycle (Miocene to Quaternary), during which • • Aactive late extension(or second) and period faulting of post-rift shifted tothermal the Okinawa sag cycle Trough. (Miocene to Quaternary), during which active extension and faulting shifted to the Okinawa Trough. Many Late Mesozoic to Tertiary rift–post-rift basins in eastern China and southeast Asia follow a similarMany evolutionary Late Mesozoic history to ofTertiary cycle development. rift–post-rift basins Doust etin al.eastern [18], forChina instance, and southeast recognized Asia early follow and alate similar syn- andevolutionary post-rift cycles,history interrupted of cycle development. by local inversion Doust periods. et al. [18], In for the instance, next section, recognized the evolution early andof the late cycles syn- is and examined post-rift in morecycles, detail. interrupted by local inversion periods. In the next section, the evolutionThe tectonic of the cycles evolutionary is examined history in more of the detail. East China Sea Basin (Figure3) is described below. The tectonic rift cycle evolutionary: The East China history Sea of Basin the East was China formed Sea by Basin faulting (Figure during 3) is the described Late Cretaceous below. to Paleocene,The rift with cycle the: developmentThe East China of half-grabensSea Basin was under formed (trans)tensional by faulting during stresses. the The Late initial Cretaceous collision to of Paleocene,India with Eurasiawith the resulted development in the closure of half-grabens of the Tethys, under and (trans)tensional the southeastern stresses. Eurasia The continental initial collision margin ofwas India pushed with eastward Eurasia resulted along pre-existing in the closure major of the faults. Tethys, In the and east, the the southeastern Pacific plate Eurasia changed continental direction marginfrom north was to pushed northwest, eastward placing along the Eurasianpre-existing continental major faults. margin In underthe east, a transtensional the Pacific plate regime, changed and directionthe East China from Seanorth Basin to northwest, probably developed placing the as Eu a complexrasian continental area of pull-apart margin riftunder basins a transtensional [1,36]. In the regime,West Shelf and area, the East rifting China ceased Sea at Basin the end probably of the developed Paleocene, as but a itcomplex continued area in of the pull-apart East Shelf rift Basin basins to [1,36].encompass In the the West Eocene. Shelf area, rifting ceased at the end of the Paleocene, but it continued in the East ShelfThe Basin first to encompass post-rift thermal the Eocene. sag cycle : This corresponds to the Eocene in the West Shelf Basin and was broughtThe first to post-rift an end thermal by a short sag period cycle:of This uplift corresponds in the Oligocene. to the Eocene Post-rift in the conditions, West Shelf on Basin the other and washand, brought did not to reach an end the by East a short Shelf basinsperiod untilof uplift the Oligocene.in the Oligocene. The collision Post-rift between conditions, India on and the Eurasia other hand,continued did not during reach the the Late East Eocene–Oligocene; Shelf basins until however,the Oligocene. at the The end collision of Eocene, between the Pacific India plate and changedEurasia continuedits relative during direction the of Late movement Eocene–Oligocene; from north-northwest however, (NNW)at the toend northwest of Eocene, (NW) the [33Pacific] or NW plate to changedwest-northwest its relative (WNW) direction [1], becoming of movement more from perpendicular north-northwest to the Eurasian (NNW) continentalto northwest margin. (NW) [33] This or is NWmarked to inwest-northwest the East China (WNW) Sea Shelf [1], Basin becoming by the uplift more and perpendicular erosion of the to Diaoyudao the Eurasian Paleo-uplift, continental and margin.an eastward This shiftis marked of the in depo-centers the East China to the Sea Xihu Shelf and Basin Diaobei by the sub-basins. uplift and erosion of the Diaoyudao Paleo-uplift, and an eastward shift of the depo-centers to the Xihu and Diaobei sub-basins.

Energies 2019, 12, 4088 5 of 28 Energies 2019, 12, x FOR PEER REVIEW 5 of 28

FigureFigure 3. Tectono-stratigraphy3. Tectono-stratigraphy of theof the sub-basins sub-basins of theof Eastthe East China China Sea Basin,Sea Basin, showing showing regional regional tectonic eventstectonic and events (sub-)basin and (sub-)basin cycles. For cycles. each basin, For each the basi columnsn, the fromcolumns left tofrom right left show to right the show stress the regime stress and theregime cycle/ stageand the divisions. cycle/stage divisions.

TheThe inversion inversion cycle cycle:: By By thethe endend ofof thethe OligoceneOligocene/Early/Early Miocene Miocene period, period, the the northwestward northwestward subductionsubduction of of the the Philippine Philippine Sea Sea plate plate aaffectedffected the southern part part of of the the East East China China Sea Sea Basin, Basin, whereas whereas thethe northern northern East East China China Sea Sea Basin Basin waswas aaffectedffected byby thethe PacificPacific plate subduction. subduction. Related Related inversions inversions werewere accompanied accompanied by by a a hiatus hiatus in in thethe OligoceneOligocene in the West West Shelf Shelf Basin, Basin, but but only only affected affected the the Eastern Eastern ShelfShelf in in the the Late Late Miocene. Miocene. By By Middle Middle Miocene,Miocene, the Xihu Sub-basin Sub-basin depositional depositional trend trend shifted shifted from from southeast to northeast. The cause for this shift is not known; however, it is speculated that it is related southeast to northeast. The cause for this shift is not known; however, it is speculated that it is related to the northeastward migration of the Philippine Sea plate, early development in the North Okinawa to the northeastward migration of the Philippine Sea plate, early development in the North Okinawa Trough, and the opening of the Japan Sea to the north. At the end of the Middle Miocene to early Late Trough, and the opening of the Japan Sea to the north. At the end of the Middle Miocene to early Miocene, the northwestward subduction of the Philippine Sea plate increased, resulting in the Late Miocene, the northwestward subduction of the Philippine Sea plate increased, resulting in the development of the trench–arc–back-arc basin system (Ryukyu Trench–Ryukyu Arc–Okinawa developmentTrough) on of the the basement, trench–arc–back-arc east of the basin East system China (RyukyuSea Basin. Trench–Ryukyu The Xihu Sub-basin Arc–Okinawa underwent Trough) oncompression, the basement, and east high-relief of the East anticlines China Seawere Basin. developed The Xihumainly Sub-basin on the eastern underwent flank of compression, the sub-basin. and high-reliefThis Miocene anticlines compression were developed appears to be mainly confined on theto the eastern Xihu sub-basin. flank of the In the sub-basin. Diaobei Sub-basin This Miocene to compressionthe south, there appears are toonly be a confined few gentle to anticlin the Xihues sub-basin.with no associated In the Diaobei reverse Sub-basin faults [37]. to the south, there are onlyThe a few second gentle post-rift anticlines thermal with sag no associatedcycle: This cycle reverse commenced faults [37 ].in the Miocene in the west and in Thethe Pliocene second to post-rift the east. thermal Although sag the cycle Philippine: This cycle Sea plate commenced subduction in thebeneath Miocene the Eurasian in the west plate and incontinued, the Pliocene it appears to the east. to have Although mainly the affected Philippine the Okinawa Sea plate Trough subduction (which beneathprobably the commenced Eurasian plateits continued,syn-rift cycle it appears at this totime) have and mainly the Ryukyu affected Arc. the Most Okinawa of the Trough rest of (whichthe East probably China Sea commenced Shelf Basin its syn-riftunderwent cycle a at period this time) of regional and the sag. Ryukyu The rifting Arc. in the Most Okinawa of the restTrough of the took East place China in two Sea phases, Shelf and Basin underwentthe Pliocene a period brought of about regional a time sag. of The relative rifting calm in thein terms Okinawa of extensional Trough took tectonics place (Figure in two phases,3) [28]. and the PlioceneThe tectonic brought evolutionary about a time histor of relativey of the calm Okinawa in terms Trough of extensional according to tectonics References (Figure [24,34,35]3)[28]. is describedThe tectonic below evolutionary(Figure 3). history of the Okinawa Trough according to References [24,34,35] is describedThe below first syn-rift (Figure 3cycle). (Middle Miocene–Late Miocene): During this time, the first phase of riftingThe and first volcanism syn-rift cycle occurred. (Middle The Miocene–Latebasement began Miocene) to fragment: During with rapid this time,subsidence the first occurring phase of along major faults, which also defined the shape of the Okinawa Trough. rifting and volcanism occurred. The basement began to fragment with rapid subsidence occurring along major faults, which also defined the shape of the Okinawa Trough.

Energies 2019, 12, 4088 6 of 28

Energies 2019, 12, x FOR PEER REVIEW 6 of 28 The post-rift thermal sag cycle (Pliocene): The Pliocene brought about a time of relative calm in terms ofThe extensional post-rift thermal tectonics. sag Initial cycle thinning (Pliocene) of: theThe crust Pliocene in the brought back-arc about was a followed time of relative by a period calm of rapidin terms thermal of extensional subsidence tectonics. to equilibrate Initial isostaticthinning imbalance. of the crust Thein the overall back-arc effect was was followed the development by a period of largeof rapid volumes thermal of accommodation subsidence to equilibrate space. By isostati the latec Pliocene,imbalance. subduction The overall is effect thought was tothe have development slowed [35 ]. Volcanicof large activity volumes at of this accommodation time was probably space. reducedBy the late to Pliocene, a minimum. subduction is thought to have slowed [35].The Volcanic second activity syn-rift at cyclethis time (Quaternary) was probably: In reduced the Early to Pleistocene a minimum. came a second major phase of rifting andThe second volcanism, syn-rift which cycle is (Quaternary) still active today.: In the Fault Early scarps Pleistocene exposed came on a thesecond seabed major illustrate phase of the currentrifting activity. and volcanism, which is still active today. Fault scarps exposed on the seabed illustrate the currentFrom activity. the above, it is evident that the West and East Shelf basins passed through similar tectono-stratigraphicFrom the above, cycles, it is evident albeit atthat slightly the West diff anderent East times, Shelf possibly basins passed resulting through from similar extended tectono- periods ofstratigraphic active subsidence cycles, and albeit subduction at slightly roll-back different along times, the possibly Ryukyu resulting arc. In this from context, extended Uyeda periods et al. of [39 ] introducedactive subsidence two possible and subduction subduction roll-back models along depending the Ryukyu on the arc. type In ofthis stress context, field Uyeda under et which al. [39] the openingintroduced of the two back-arc possible (sub-)basins subduction took models place depending (Figure4). Compressionalon the type of stress stress field regimes under in thewhich back-arc the opening of the back-arc (sub-)basins took place (Figure 4). Compressional stress regimes in the back- region may occur if there is a relatively high-speed “shallow-slab” subduction (Figure4, top), whereas arc region may occur if there is a relatively high-speed “shallow-slab” subduction (Figure 4, top), tension stress regimes characterize the back-arc region when the subducting slab is relatively dense whereas tension stress regimes characterize the back-arc region when the subducting slab is relatively and steeply dipping (Figure4, bottom). During the Cenozoic tectonic evolution of the back-arc East dense and steeply dipping (Figure 4, bottom). During the Cenozoic tectonic evolution of the back-arc China Sea Basin, extension and compression events alternated with each other, and it is speculated East China Sea Basin, extension and compression events alternated with each other, and it is thatspeculated phases of that relative phases high-speed of relative high-speed subduction subduction of the Philippine of the Phi platelippine are plate associated are associated with inversion with processes,inversion while processes, phases while of relative phases lowof relative subduction low subduction rate characterize rate characterize the rifting the periods. rifting periods.

FigureFigure 4. 4.Two Two types types of of subduction subduction boundariesboundaries related to subduction steepness. steepness. Type Type 1 (“flat-slab 1 (“flat-slab subduction”)subduction”)= compression= compression/thrusting/thrusting in thein the back-arc back-arc region; region; type type 2 (“steep-slab 2 (“steep-slab subduction”) subduction”)= tension = intension the back-arc in the region back-arc (modified region (modified from Uyeda from et al.Uyeda [39]). et During al. [39]). type During 1, inversions type 1, inversions can be expected can be in theexpected back-arc in basin. the back-arc basin.

AA 2002 2002 study study by by van van Wijk Wijk [ 40[40]] providedprovided aa possiblepossible mechanism via via which which both both rift rift migration migration resultingresulting from from shifting shifting of of the the mainmain locuslocus ofof extensionextension and and local local uplift uplift could could result result from from variable variable stretchingstretching rates rates during during one one lithospheric lithospheric extensionextension episode.episode. In In the the East East China China Sea Sea Basin, Basin, rifting rifting started started in the West Shelf Basin and moved to the Okinawa Trough via the East Shelf Basin (Figure 3). These

Energies 2019, 12, 4088 7 of 28 in the West Shelf Basin and moved to the Okinawa Trough via the East Shelf Basin (Figure3). These rift zones formed respectively during the Cretaceous–Paleocene–Eocene episode (70–40 Ma), the Cretaceous–Miocene episode (70–5 Ma), and the Mid-Miocene–Quaternary episode (18–0 Ma), and extended in the northeast (NE)–southwest (SW) direction. The time gap between the successive rifting events was ~13–30 Ma. A striking feature of van Wijk’s model is the related uplift in the original basins and re-thickening of the pre-thinned crust. In the East China Sea Basin, the uplifted structures, Yandang Low-uplift, Yushan Paleo-uplift, and Diaoyudao Paleo-uplift, located between the sub-basins, are consistent with such modeling results.

3.2. Sedimentary Facies Development The basement of the East China Sea Shelf Basin consists of Proterozoic metamorphic rocks, believed to be part of the accreted complexes of eastern China, as well as Mesozoic volcanics and granite [1]. The Diaoyudao Paleo-uplift is a complex faulted and folded structure and consists of Paleogene–Lower Miocene sediments with welded tuffs and igneous intrusions of Miocene age and remnants of arc volcanism. The Diaoyudao Paleo-uplift is also called the Taiwan–Sinzi fold belt. During the opening of the Okinawa Trough, compression adjacent to the spreading center triggered uplift in this zone, probably at about mid-Miocene time. The Diaoyudao Paleo-uplift has a thin sediment cover lying on top of basement believed to comprise Late Paleozoic–Late Mesozoic granitoids or volcanic intrusions. The sediments of the Okinawa Trough become younger and thinner from north to south. In the north late Miocene to Quaternary, sediments have a thickness of up to 8 km, while, in the south, thickness is reduced to 3–4 km of Pliocene to Quaternary sediments. Lambiase et al. [41] studied the depositional models for syn- and post-rift stages of rift basins. The below discussion of the sedimentary history of the East China Sea Shelf Basin is based on [1,36,42]. The sedimentary sequences of the East China Sea Shelf Basin are ascribed to five stages in basin evolution (Figure5), as discussed below. Early syn-rift (Late Cretaceous to Paleocene): During the syn-rift phase, active faulting resulted in the formation of half-grabens developed both in the western shallow sub-basin area and in the eastern deep sub-basin area. These half-grabens were filled with lacustrine–deltaic clastic sediments, but were interrupted by periods of marine transgression starting in the Late Cretaceous. During the Paleocene, the East China Sea Shelf Basin became progressively more marine, with the sea invading from the southeast. The syn-rift sediments, the Shimentan, Yueguifeng, Lingfeng, and Mingyuefeng formations, were penetrated by wells in the western shallow depressions of the West Shelf Basin. The Paleocene Yueguifeng Formation, which forms a lacustrine sequence, is composed of two sedimentary cycles with a gross thickness of up to 470 m. The upper cycle contains more sands with coarser grain sizes than the lower. It is in unconformable contact with the Cretaceous Shimentan Formation. The Paleocene Lingfeng Formation, which comprises a littoral–neritic sequence, is composed of up to 700 m of primarily gray, dark-gray, and black claystones with interbedded thin-layered, light-gray calcareous siltstones, fine sandstones, and occasional thin-layered calcareous fine sandstones. The Paleocene Mingyuefeng Formation is composed of a regressive sequence, having a thickness of up to 1000 m, and contains coal beds that were deposited in a delta-plain environment. There is an angular unconformity at the top of the Mingyuefeng Formation [13]. Late syn-rift (Eocene): During the later syn-rift phase, deep depo-centers were formed in the eastern parts of the area. These depo-centers, Xihu and Diaobei, received more than 7 km of late syn-rift sediments (Oujiang, Wenzhou, and Pinghu formations) during the Eocene. In the western sub-basins, up to 2 km of late syn-rift sediments were deposited in some places. The Eocene Oujiang Formation is composed of a fluvial–littoral sequence, has a thickness of up to 1250 m, and contains light-gray and gray claystones in the upper part and primarily light-gray and gray fine–medium-grained sandstones in the lower part. It is in conformable contact with the Eocene Wenzhou Formation, which has a thickness of up to 661 m and is composed of coastal plain–littoral facies. It consists of a coarsening upward sequence with coal near the top [13]. The Eocene Pinghu Formation is predominantly claystone, Energies 2019, 12, 4088 8 of 28 intercalated siltstone, and coal with a thickness of up to 3000 m, deposited in estuarine and tidal flat environments. It unconformably overlies the Wenzhou Formation [2]. Energies 2019, 12, x FOR PEER REVIEW 8 of 28

FigureFigure 5. 5.Chrono-stratigraphy Chrono-stratigraphy of the West Shelf Basin Basin (i.e (i.e.,., Lishui Lishui Sub-basin), Sub-basin), East East Shelf Shelf Basin Basin (i.e., (i.e., Xihu Sub-basin), and the Okinawa Trough of the East China Sea Basin, showing lithofacies, (sub- Xihu Sub-basin), and the Okinawa Trough of the East China Sea Basin, showing lithofacies, (sub-)basin )basin cycles, and identified petroleum system types (PSTs) and their play levels. A = PST A; B = PST cycles, and identified petroleum system types (PSTs) and their play levels. A = PST A; B = PST B; C = PST C; D = PST D (black dashed lines show the extent of each PST). In the stratigraphic column, B; C = PST C; D = PST D (black dashed lines show the extent of each PST). In the stratigraphic green represents claystone, yellow indicates sandstone, blue stands for carbonate, black represents column, green represents claystone, yellow indicates sandstone, blue stands for carbonate, black coal, and red indicates volcanics. Time scale and lithology are based on data and analyses in represents coal, and red indicates volcanics. Time scale and lithology are based on data and analyses in References [1,24,27,34–36,42,43]. References [1,24,27,34–36,42,43]. Overall, the East China Sea Shelf Basin was tilted to the southeast and east-southeast, and many Overall, the East China Sea Shelf Basin was tilted to the southeast and east-southeast, and many authors [8,9] agreed that the southern portion was under shallow marine conditions during the authors [8,9] agreed that the southern portion was under shallow marine conditions during the Eocene Eocene when the northern portion was still under terrestrial–coastal plain–paralic conditions. when the northern portion was still under terrestrial–coastal plain–paralic conditions. Early post-rift (Oligocene–Middle Miocene): During the Oligocene, the West Shelf Basin was Early post-rift (Oligocene–Middle Miocene): During the Oligocene, the West Shelf Basin was uplifted, and sediments (Huagang Formation) were deposited mainly in the eastern part of the basin. uplifted,Terrestrial–deltaic–coastal and sediments (Huagang conditions Formation) prevailed were in the deposited north (Xihu) mainly and in theparalic eastern conditions part of thein the basin. Terrestrial–deltaic–coastalsouth (Diaobei). By the end conditions of Oligocene/Early prevailed Mi inocene the northtime, uplift (Xihu) of and the paralicDiaoyudao conditions Paleo-uplift in the commenced. It is marked by a strong unconformity and combined with a northeast tilt of the Xihu Depression. This created increased accommodation space in the northern half of the Xihu Sub-basin

Energies 2019, 12, 4088 9 of 28 south (Diaobei). By the end of Oligocene/Early Miocene time, uplift of the Diaoyudao Paleo-uplift commenced. It is marked by a strong unconformity and combined with a northeast tilt of the Xihu Depression. This created increased accommodation space in the northern half of the Xihu Sub-basin during the Early–Middle Miocene. The Miocene sediments (Longjing and Yuquan formations) consist of fluvial–alluvial and coastal plain deposits, with marine incursions to the northeast. The Diaobei Sub-basin continued to tilt toward the southeast, and the sediments were probably deposited in a transitional setting. The Oligocene Huagang Formation is composed of siltstone and claystone in the lower part and sandstone with interbedded claystone and coal seams in the upper part, and it has a thickness of up to 2000 m. Overlying the Huagang Formation is the Miocene Longjing Formation with a thickness of up to 1055 m. In the lower part, it consists of sandy conglomerate and/or conglomeratic sandstone intercalated with claystone, and, in the upper part, it consists of siltstone with interbedded claystone and coal [44]. The Miocene Yuquan Formation, lying conformably above the Longjing Formation, consists of sandy conglomerate and/or conglomeratic sandstone, siltstone, claystone, and coal with a total thickness of 200–1316 m. Inversion/compression (Late Miocene): During the Late Miocene, the westward subduction of the Philippine Sea Plate accelerated [45,46]. This is manifested in the Xihu Sub-basin by increased compression and uplift, starting from the end of Middle Miocene in the south and migrating and intensifying northeastward by the end of Late Miocene. This marks an erosional cycle, during which, however, local floodplain–marine coarse syn-inversion clastics belonging to the Liulang Formation accumulated on the flanks of the inversions in the East Shelf Basin. In the meantime, the fluvial and lacustrine Liulang Formation was deposited conformably above the Yuquan Formation in the West Shelf Basin. The Miocene Liulang Formation consists of 80–1600 m of siltstone and claystone [44]. Late post-rift/regional sag (Pliocene–Quaternary): The end of the compression phase (basin inversion phase) is marked by a top Miocene unconformity, and it was followed by a regional transgression during the Pliocene accompanied by renewed thermal subsidence without significant compression or extension, particularly in the Xihu Sub-basin. The Pliocene Santan Formation is composed of 200–750 m of marine claystone, silty claystone, argillaceous siltstone, and sandstone. It is in angular unconformable contact with the underlying Miocene Liulang Formation. The youngest sediments in the basin are those of the Pleistocene Donghai Group composed of 250–450 m of unconsolidated marine siliciclastic sediments [13,44]. The sedimentary fill of the Okinawa Trough is rather less well explored, mainly due to the fact that correlation and extrapolation are extremely difficult. Neogene outcrops are almost entirely absent on the Ryukyu Arc, and deep-water drilling is extremely sparse with only one deep exploration well, To-Ka-1, drilled in the Okinawa Trough by Shin Nishi Nihon Sekiyu Kaihatsu K.K. in 1978 [47]. The well penetrated the altered Cretaceous granodiorite basement overlain by Miocene to Quaternary sediments. Lithologies consist of thick, predominantly fine-grained turbiditic siliciclastics resting upon marine Middle Miocene volcanics. The siliciclastics are composed of deep marine silty claystones, which coarsen upward into shallow marine marls, clays, fine silts, and quartz-rich sandstone. The tectono-stratigraphic evolution of the basins is summarized at the end of this article.

4. Petroleum Systems and Play Developments Using the geological background described above as a base, the petroleum systems and plays in the East China Sea basins were investigated. Two major sub-basins, Xihu and Lishui, typically representing the East Shelf Basin and the West Shelf Basin, respectively, are discussed and studied below in detail.

4.1. Petroleum System Types (PSTs) Within the East China Sea Basin, it is proposed that four types of petroleum system, linked to stages in basin evolution (Figure5), may be represented. These are either proven (!) (i.e., they are represented by petroleum fields) or speculative (?) (i.e., it is believed they could be present based Energies 2019, 12, 4088 10 of 28 on the study). In the proven PSTs, it is noted that, in some (category i), both source rock and main reservoir lie within the same basin cycle (i.e., the petroleum system is integral to that cycle), while, in others, the reservoir may lie in another, usually younger, basin cycle than the source rock (category ii).

4.1.1. Early Syn-Rift Lacustrine–Deltaic PST (PST A) This PST is common in the West Shelf Basin and is relatively oil-prone due to widespread development of reportedly organic-rich type II source rocks of lacustrine–deltaic origin [5]. In the East China Sea basins, in general, the lacustrine facies appears to differ from that found in southeast (SE) Asian Tertiary basins, where more tropical conditions prevailed and where rich type I source rocks are common [18]. Within the upper part of the Paleocene sequence, relatively less developed gas-prone shallow marine type III source rocks can also be found. Reservoirs are shallow marine, lacustrine–deltaic sandstones with minor Precambrian fractured gneiss basement in the pre-rift fault blocks. Paleocene intra-formational claystones represent local seals in the West Shelf Basin. This PST was proven in the western sub-basins. The petroleum systems identified or proposed to be represented by this PST are the following: Yueguifeng–Lingfeng Petroleum System (!) (i.e., Lishui Sub-basin, other sub-basins of West Shelf Basin) Category (i); Cretaceous/Paleocene–Basement Petroleum System (?) (i.e., Xihu Sub-basin, other sub-basins of East Shelf Basin) Category (ii).

4.1.2. Late Syn-Rift Marine PST (PST B) Source rocks in this principally marine claystone sequence contain mainly gas-prone, type III kerogen with minor type II kerogen. The main reservoirs comprise shallow marine tidal channels, fluvial–deltaic distributary channels, and river-mouth-bar sandstones. In many sub-basins, this PST contains widespread regional seals in the form of thick Eocene–Miocene fluvial, lacustrine, and marine claystones. It was proven in the eastern sub-basins. The petroleum system represented by this PST is the following: Pinghu–Huagang Petroleum System (!) (i.e., Xihu Sub-basin, other sub-basins of East Shelf Basin) Category (ii).

4.1.3. Early Post-Rift Fluvial–Deltaic PST (PST C) The major source rocks for this proposed fluvial–deltaic PST comprise type III gas-prone shallow marine coal-bearing claystones, good-quality sandstone reservoirs deposited in braided river and deltaic environments, and thick Eocene–Miocene fluvial, lacustrine, and marine claystone seals. The anticipated petroleum systems that could be represented by this PST belong to category (i) and are the following: Huagang–Huagang Petroleum System (?) (i.e., Xihu Sub-basin, other sub-basins of East Shelf Basin); Miocene–Miocene Petroleum System (?) (i.e., Xihu Sub-basin, other sub-basins of East Shelf Basin).

4.1.4. Syn-Rift Marine Turbiditic PST (PST D) From observation of the tectono-stratigraphy, it is proposed that a speculative marine syn-rift turbiditic PST may be present in the Okinawa Trough. Even though a Pliocene post-rift thermal sag cycle was associated with the tectonic evolution of the Okinawa Trough, this relatively quiescent period took place against a background of continuing rifting. The potential source rocks for this turbiditic PST would probably comprise type III gas-prone re-worked coal-bearing claystones. Neogene–Quaternary turbidite sands are likely to have good reservoir quality, and seals could be distal turbidites, basin-floor muds, and pelagic sediments. The petroleum system that could be represented by this speculative PST belongs to category (i) and is the following: Energies 2019, 12, 4088 11 of 28

Energies 2019, 12, x FOR PEER REVIEW 11 of 28 Neogene/Quaternary–Neogene/Quaternary (?) (i.e., Okinawa Trough). The Xihu Sub-basin is one of the key sub-basins and also one of the prime targets for 4.2.hydrocarbon Xihu Sub-Basin exploration of the East Shelf Basin. It is a NE–SW trending sub-basin, about 400 km long and 130 km wide (Figure 6), and it can be divided into five sub-units. These are, from west to east, the BaoshuThe Xihu Slope Sub-basin Belt, isthe one Santan of the keyDepression, sub-basins the and Central also one Anticline of the prime Inversion targets forBelt, hydrocarbon the Baidi explorationDepression, ofand the the East Tianping Shelf Basin. Fault It Belt. is a NE–SW trending sub-basin, about 400 km long and 130 km wideMost (Figure of 6the), and oil and it can gas be discoveries divided into are five distribute sub-units.d along These the are, Central from Anticline west to east, Inversion the Baoshu Belt at Slopethe center Belt, theof the Santan sub-basin Depression, and along the Central the Baoshu Anticline Slope Inversion Belt in the Belt, western the Baidi part Depression, of the sub-basin. and the TianpingFigure 6 and Fault Table Belt. 1 illustrate the locations and key features of the hydrocarbon fields.

Figure 6.6. StructuralStructural units units of of the the Xihu Xihu Sub-basin Sub-basin (West (West Shelf Shelf Basin). Basin). Location Location of major of major hydrocarbon hydrocarbon fields andfields hydrocarbon-bearing and hydrocarbon-bearing structures structures and their and PSTs their are PS alsoTs are indicated also indicated in the map. in the Note map. that Note all belongthat all tobelong the late to syn-riftthe late marinesyn-rift PST. marine 1 = ChunxiaoPST. 1 = Chunxiao field; 2 = Tianwaitianfield; 2 = Tianwa field;itian 3 = Duanqiaofield; 3 = Duanqiao field; 4 = Canxue field; 4 field;= Canxue 5 = Pinghu field; 5 field; = Pinghu 6 = Baoyunting field; 6 = field;Baoyunting 7 = Wuyunting field; 7 = field; Wuyunt 8 = Wubeiing field; field; 8 9= =WubeiLaiheting field; field; 9 = 10Laiheting= Kongqueting field; 10 = field; Kongqueting 11 = Gushan field; 1 11 discovery; = Gushan 12 1 discovery;= Qiuyue 12 1 discovery; = Qiuyue 1 13 discovery;= Yuquan 13 discovery; = Yuquan 14discovery;= Huagang 14 = 1Huagang discovery; 1 discovery; 15 = Longjing 15 = 1Longjing discovery; 1 discovery; 16 = Longjing 16 = 2Longjing discovery; 2 discovery; 17 = Longjing 17 = 4Longjing discovery. 4 discovery.

Most of the oil and gas discoveries are distributed along the Central Anticline Inversion Belt at the center of the sub-basin and along the Baoshu Slope Belt in the western part of the sub-basin. Figure6 and Table1 illustrate the locations and key features of the hydrocarbon fields.

Energies 2019, 12, 4088 12 of 28

Table 1. Summary of hydrocarbon fields and discoveries of the Xihu Sub-basin.

Field/Discovery Reservoir Source Rock Name Unit Name Age Lithology Unit Name Age Lithology Huagang Pinghu Oligocene Sandstone Eocene Claystone Chunxiao field Formation Formation Pinghu Pinghu Eocene Sandstone Eocene Claystone Formation Formation Huagang Sandstone– Pinghu Tianwaitian field Oligocene Eocene Claystone Formation claystone Formation Huagang Sandstone– Pinghu Oligocene Eocene Claystone Duanqiao field Formation siltstone Formation Pinghu Sandstone– Pinghu Eocene Eocene Claystone Formation siltstone Formation Huagang Middle– Late Pinghu Canxue field Sandstone Eocene Claystone Formation Oligocene Formation Huagang Sandstone– Pinghu Oligocene Eocene Claystone Pinghu field Formation siltstone Formation Pinghu Sandstone– Pinghu Eocene Eocene Claystone Formation siltstone Formation Pinghu Pinghu Baoyunting field Eocene Sandstone Eocene Claystone Formation Formation Huagang Pinghu Wuyunting field Oligocene Sandstone Eocene Claystone Formation Formation Pinghu Pinghu Wubei field Eocene Sandstone Eocene Claystone Formation Formation Pinghu Pinghu Laiheting field Eocene Sandstone Eocene Claystone Formation Formation Kongqueting Pinghu Pinghu Eocene Sandstone Eocene Claystone field Formation Formation Gushan 1 Huagang Pinghu Oligocene Sandstone Eocene Claystone discovery Formation Formation Qiuyue 1 Huagang Pinghu Oligocene Sandstone Eocene Claystone discovery Formation Formation Yuquan Huagang Pinghu Oligocene Sandstone Eocene Claystone discovery Formation Formation Huagang 1 Huagang Pinghu Oligocene Sandstone Eocene Claystone discovery Formation Formation Longjing 1 Huagang Oligocene– Sandstone– Pinghu Eocene Claystone discovery Formation Miocene coal Formation Longjing 2 Huagang Pinghu Oligocene Sandstone Eocene Claystone discovery Formation Formation Longjing 4 Huagang Pinghu Oligocene Sandstone Eocene Claystone discovery Formation Formation Field/Discovery Seal Play Hydrocarbon Type Name Unit Name Age Lithology Play Name Trap Type Structural—inverted Gas, Huagang Huagang Oligocene Claystone anticline and reverse fault condensate, Chunxiao field Formation structural related footwall closures oil Pinghu Pinghu Structural—inverted Oil, gas, Eocene Claystone Formation structural anticline condensate Structural—inverted Huagang Huagang Gas, Tianwaitian field Oligocene Claystone anticline and reverse fault Formation structural condensate related footwall closures Structural—inverted Huagang Huagang Gas, Oligocene Claystone anticline and reverse fault Duanqiao field Formation structural condensate related footwall closures Pinghu Pinghu Structural—inverted Gas, Eocene Claystone Formation structural anticline condensate Energies 2019, 12, 4088 13 of 28

Table 1. Cont.

Field/Discovery Seal Play Hydrocarbon Type Name Unit Name Age Lithology Play Name Trap Type Huagang Huagang Structural—inverted Gas, Canxue field Oligocene Claystone Formation structural anticline and fault condensate Huagang Structural–stratigraphic Huagang Oligocene Claystone structural– —fault-bounded closures Oil, gas Pinghu field Formation stratigraphic with facies change Structural— fault Pinghu Pinghu Gas, Eocene Claystone bounded compressional Formation structural condensate hanging wall anticline Structural— fault Gas, Pinghu Pinghu Baoyunting field Eocene Claystone bounded compressional condensate, Formation structural hanging wall anticline oil Huagang Structural–stratigraphic Huagang Wuyunting field Oligocene Claystone structural– —fault-bounded closures Oil, gas Formation stratigraphic with facies change Structural—fault Pinghu Pinghu Gas, Wubei field Eocene Claystone bounded compressional Formation structural condensate hanging wall anticline Structural—fault Pinghu Pinghu Laiheting field Eocene Claystone bounded compressional Oil, gas Formation structural hanging wall anticline Structural—fault Kongqueting Pinghu Pinghu Eocene Claystone bounded compressional Oil, gas field Formation structural hanging wall anticline Gushan 1 Huagang Huagang Oligocene Claystone Structural—fault Oil, gas discovery Formation structural Qiuyue 1 Huagang Huagang Gas, Oligocene Claystone Structural—fault discovery Formation structural condensate Structural—inverted Yuquan Huagang Huagang Oligocene Claystone anticline and reverse fault Gas discovery Formation structural related footwall closures Structural—inverted Huagang 1 Huagang Huagang Oligocene Claystone anticline and reverse fault Gas discovery Formation structural related footwall closures Structural—inverted Longjing 1 Huagang Huagang Gas, Oligocene Claystone anticline and reverse fault discovery Formation structural condensate related footwall closures Structural—inverted Longjing 2 Huagang Huagang Oligocene Claystone anticline and reverse fault Gas discovery Formation structural related footwall closures Structural—inverted Longjing 4 Huagang Huagang Oligocene Claystone anticline and reverse fault Oil, gas discovery Formation structural related footwall closures

4.2.1. Tectono-Stratigraphy The Xihu Sub-basin evolved tectonically from a back-arc extensional rift basin to a passive margin post-rift (Figures3 and7) through early syn-rift (Late Cretaceous–Paleocene), late syn-rift (Eocene), early post-rift (Oligocene–Middle Miocene), inversion (Late Miocene), and late post-rift (Pliocene–Quaternary) cycles. The inversion cycle compressional events were associated with structural growth and unconformities (Figure5). The sedimentary formations and sediments deposited within each tectonic phase are shown in Figures3 and5. Energies 2019, 12, x FOR PEER REVIEW 14 of 28

Energiesstructural2019 , 12growth, 4088 and unconformities (Figure 5). The sedimentary formations and sediments14 of 28 deposited within each tectonic phase are shown in Figures 3 and 5.

FigureFigure 7.7. XihuXihu Sub-basinSub-basin tectonictectonic cross-sectioncross-section (seismic(seismic lineline locationlocation isis indicatedindicated inin FigureFigure6 ).6). The The seismicseismic horizonshorizons can can be referredbe referred to Figure to 3Figure. Question 3. marksQuestion indicate marks uncertainties indicate uncertainties in the interpretation. in the interpretation. 4.2.2. Petroleum System Development within Tectono-Stratigraphic Framework 4.2.2.In Petroleum the Xihu Sub-basin,System Development one proven within petroleum Tectono-Stratigraphic system, the Pinghu–Huagang Framework (!), is present, and threeIn speculative the Xihu petroleumSub-basin, systems,one prov theen petroleum Huagang–Huagang system, the (?), Pinghu–Huagang the Cretaceous/Paleocene–Basement (!), is present, and (?),three and speculative the Miocene–Miocene petroleum (?),systems, were proposed the Huag [2,10ang–Huagang,12]. (?), the Cretaceous/Paleocene– BasementPinghu (?),–Huagang and the Miocene–Miocen Petroleum Systeme (?),(!): were This proposed is the most [2,10,12]. important petroleum system of the XihuPinghu Sub-basin–Huagang (Figure8 )Petroleum and belongs System to the late(!): This syn-rift is the marine most PST important (PST B). petroleum All currently system discovered of the oilXihu and Sub-basin gas fields (Figure and non-commercial 8) and belongs to hydrocarbon the late syn-rift discoveries marine PST of the (PST Xihu B). Sub-basinAll currently belong discovered to this systemoil and (Tablegas fields1 and and Figure non-commercial6). hydrocarbon discoveries of the Xihu Sub-basin belong to this systemSource (Table Rocks 1 and and Figure Potential 6). Source Rocks • • BasedSource on Rocks the samplesand Potential from wells,Source Ye Rocks et al. [2] concluded that source rocks lie in dark claystone and coalBased of theon the Eocene samples Pinghu from Formation, wells, Ye et deposited al. [2] co inncluded estuarine that and source tidal-flat rocks environments.lie in dark claystone They typicallyand coal containof the Eocene type III Pinghu gas-prone Formation, kerogen; deposite however,d in becauseestuarine of and the tidal- greatflat thickness environments. (average They 628 m)typically of claystone, contain the type presence III gas-prone of up tokerogen; 28 m of however, coal, their because basin-wide of the distribution great thickness and (average relatively 628 high m) totalof claystone, organic carbonthe presence (TOC) of content up to 28 (average m of coal, 1.31 their wt.% basin-wide and maximum distribution 4.23 wt.% and for relatively the claystone high total and averageorganic 61.8carbon wt.% (TOC) for the content coal) (Table(average2), they1.31 arewt.% likely and tomaximum meet the standard4.23 wt.% as for a sourcethe claystone with good and petroleum-generativeaverage 61.8 wt.% for potentialthe coal) [(Table48]. Further 2), they geochemical are likely to data meet are the not standard available, as buta source the sequence with good is expectedpetroleum-generative to form the most potential significant [48]. Further source geochemical rock, having data reached are not a high available, level of but thermal the sequence maturity is (Roexpected= 1.30–2.20%) to form overthe most most significant of the area [source2]. Burial rock history, having modeling reached suggests a high thatlevel the of Pinghu thermal Formation maturity entered(Ro = 1.30–2.20%) the oil-window over during most theof the Early area Miocene [2]. Burial and ishistory presently modeling in the high-maturity suggests that stage. the Pinghu FormationReservoir entered Formations the oil-window during the Early Miocene and is presently in the high-maturity •stage. The reservoirs are predominantly fine-grained sandstones and siltstones of the Huagang and • Pinghu Reservoir formations, Formations deposited in fluvial–deltaic environments (Table1 and Figure5). The measured porosityThe values reservoirs range are from predominantly 10% to 35%, andfine-grained the measured sandstones permeability and siltstones ranges from of the 1 to Huagang 4000 mD and [2]. Pinghu formations, deposited in fluvial–deltaic environments (Table 1 and Figure 5). The measured porosity values range from 10% to 35%, and the measured permeability ranges from 1 to 4000 mD [2].

Energies 2019, 12, 4088 15 of 28

Seals • Fluvial–deltaic–littoral claystones of the upper Huagang Formation serve as a regional seal within the sub-basin, whereas local seals are present in the Longjing Formation. The overburden includes Oligocene to Quaternary marine sediments. Trap Formation • The principle traps are structural, including inverted anticline, fault, fault block, and reverse fault types, sometimes with a limited stratigraphic element, as, for example, where facies change is present (a detailed description of the trap types is given by Lee et al. [49]). The structural traps were formed between the Late Eocene and Miocene with the critical moment occurring around 7.0 Ma, close to the end of the Miocene. Huagang–Huagang Petroleum System (?) (Figure9) belongs to the early post-rift fluvial–deltaic PST. Source Rocks and Potential Source Rocks • These lie in fluvial–deltaic–littoral dark claystones and coals of the Huagang Formation. They contain typical gas-prone type III kerogen and have an average thickness of 358 m. The average and maximum TOC contents of the claystone are, respectively, 0.71 and 2.28 wt.% for the lower Huagang Formation, and 0.37 and 1.91 wt.% for the upper Huagang Formation (Table2)[ 2]. The best potential occurs in the central and southern part of the Santan Depression and in the Baidi Depression (Figure6), where generation, migration, and accumulation started in the Early Miocene and continues to the present day. In the northern part of the Santan Depression, the Huagang Formation reached a higher level of thermal maturity because of deeper burial. Reservoirs • The reservoir rocks are siltstones and sandstones of the Huagang and Longjing formations, deposited in fluvial–deltaic–littoral environments. Seals • The seals are fluvial–deltaic–littoral claystones of the upper Huagang and Longjing formations. The overburden rocks include Miocene to Quaternary strata. Trap formation • Trap types are similar to those of the Pinghu–Huagang Petroleum System (!). The trap development occurred from Oligocene to the end of Miocene and the critical moment was around 3 Ma. Other speculative petroleum systems (?): In the Xihu Sub-basin, the Cretaceous/Paleocene–Basement Petroleum System (?) (early syn-rift lacustrine–deltaic PST) and the Miocene–Miocene Petroleum System (early post-rift fluvial–deltaic PST) (?) are identified as the other two speculative, but possible petroleum systems. A single borehole studied by Xu et al. [50] shows that it penetrated into upper Paleocene rocks and contains abundant organic-rich dark claystone. These claystones are believed to be deposited in lacustrine–deltaic, littoral, and shallow marine environments. It is expected that the organic matter is highly mature (Ro = 1.30–2.20%) or overmature (Ro > 2.20%) for most of the sub-basin [50]. The Cretaceous/Paleocene–Basement Petroleum System (?) may occur locally along the Baoshu Slope Belt in the western part of the basin. Although most Miocene potential source rocks are still immature because of their shallow depth of burial, any source rocks within the Longjing Formation of the northern Santan Depression may have reached the oil-window because of their relative deep burial depth and the associated higher geothermal gradient. Some oil was possibly generated and migrated from the Longjing Formation. Thus, a Miocene–Miocene Petroleum System (?) may exist in the northern Santan Depression and adjacent areas. Energies 2019, 12, 4088 16 of 28 Energies 2019, 12, x FOR PEER REVIEW 16 of 28 Energies 2019, 12, x FOR PEER REVIEW 16 of 28

Figure 8. Event chart of the Pinghu–Huagang Petroleum System (!) in the Xihu Sub-basin. Figure 8. Event chart of the Pinghu–H Pinghu–Huaganguagang Petroleum System (!) in the Xihu Sub-basin.

Figure 9. Event chart of the Huagang–Huagang Petroleum System (?) in the Xihu Sub-basin. Figure 9. Event chart of the Huagang–Huagang Petroleum System (?) in the Xihu Sub-basin.

Energies 2019, 12, 4088 17 of 28

Table 2. Abundance of organic matter in the Xihu Sub-basin (from Ye et al. [2]).

TOC * EOM HC EnergiesStratigraphic 2019, 12, x FOR Unit PEER REVIEW Lithology † 17 of 28 ‡ Max. § Min. ¶ Avg. 1 n 2 ppm n 2 ppm n 2 Table 2. AbundanceMudstone of organic matter 0.97 in the Xi 0.14hu Sub-basin 0.37 (from 86 Ye et al. 139 [2]). 83 148 40 Liulang Formation Coal 68.00 28.54TOC * 48.27 2 EOM † HC ‡ Stratigraphic Unit Lithology MudstoneMax. 2.59 § Min. 0.15 ¶ Avg. 0.85 1 n 2 59ppm 330n 2 58ppm 173n 2 37 Miocene Yuquang Formation Mudstone 0.97 0.14 0.37 86 139 83 148 40 Liulang Formation Coal 67.00 19.00 47.24 6 19,281 6 4491 6 Coal 68.00 28.54 48.27 2 Mudstone 1.10 0.27 0.47 131 265 127 138 78 Longjing Formation Mudstone 2.59 0.15 0.85 59 330 58 173 37 Miocene Yuquang Formation CoalCoal 67.00 79.42 19.00 27.00 47.24 53.21 6 2 19281 6 4491 6 MudstoneMudstone 1.10 1.91 0.27 0.16 0.47 0.37 131 210 265 194 127 201138 106 78 115 UpperLongjing Huagang Formation CoalCoal 79.42 79.61 27.00 27.00 53.21 62.31 2 4 16,875 4 5472 4 Oligocene Formation Upper Huagang Mudstone 1.91 0.16 0.37 210 194 201 106 115 Mudstone 2.28 0.17 0.71 213 231 204 125 119 LowerFormation Huagang Coal 79.61 27.00 62.31 4 16875 4 5472 4 Oligocene Formation Coal 92.18 27.28 59.73 2 2013 4 7401 4 Lower Huagang Mudstone 2.28 0.17 0.71 213 231 204 125 119 Formation MudstoneCoal 92.18 4.23 27.28 0.31 59.73 1.31 2 1822013 5304 1767401 2544 134 Eocene Pinghu Formation MudstoneCoal 4.23 80.25 0.31 19.40 1.31 61.84 182 6 530 19,276 176 15254 8567134 12 Eocene Pinghu Formation Coal 80.25 19.40 61.84 6 19276 § 15 8567 12 * TOC = total organic carbon. † EOM = extractable organic matter. ‡ HC = hydrocarbons. Max. = maximum TOC values.* ¶TOCMin. == totalminimum organic TOC carbon. values. † EOM1 Avg. = extractable= average TOCorganic values. matter.2 n =‡ numberHC = hydrocarbons. of samples. § Max. = maximum TOC values. ¶ Min. = minimum TOC values. 1 Avg. = average TOC values. 2 n = number of 4.2.3. Playsamples. Development Currently,4.2.3. Play Development a universally agreed definition for “play” does not exist. Doust [16] proposed a hierarchicalCurrently, definition a universally of plays, agreed in which definition a distinction for “play” does is made not exist. between Doust the [16] petroleum proposed a charge characteristic,hierarchical which definition is typically of plays, definedin which by a thedistinction petroleum is made system, between the the play petroleum level, typicallycharge the formationcharacteristic, or lithostratigraphic which is typically unit of defined the main by reservoirthe petroleum horizons system, charged the play with level, hydrocarbons, typically the and the trap styleformation [21]. or lithostratigraphic unit of the main reservoir horizons charged with hydrocarbons, and the trap style [21]. Plays present in the Xihu Sub-basin can be tabulated based on the trap types and identified play Plays present in the Xihu Sub-basin can be tabulated based on the trap types and identified play levels (Figure 10). levels (Figure 10).

Figure 10. Proven and speculative plays of the Xihu Sub-basin shown on a composite cross-section Figure 10. Proven and speculative plays of the Xihu Sub-basin shown on a composite cross-section (refer (refer to Figure 6 for the section location). Note that all belong to the Pinghu–Huagang Petroleum to Figure6 for the section location). Note that all belong to the Pinghu–Huagang Petroleum System System (!). i-1 = Pinghu structural (proven); i-2 = Pinghu structural–stratigraphic (proven); i-3 = (!). i-1Huagang= Pinghu structural structural (proven); (proven); i-4 = i-2 Huagang= Pinghu stra structural–stratigraphictigraphic (proven); i-5 = Huagang (proven); structural– i-3 = Huagang structuralstratigraphic (proven); (proven); i-4 = ii-1Huagang = Basement stratigraphic structural–stratigraphic (proven); i-5(speculative);= Huagang ii-2 = structural–stratigraphic Miocene structural (proven);(speculative); ii-1 = Basement ii-3 = Miocene structural–stratigraphic stratigraphic (speculative). (speculative); Those indicate ii-2 =d Miocenein the graph structural for each play (speculative); are ii-3 = Mioceneonly examples. stratigraphic Please refer (speculative). to Table 1 for Those real indicatedexamples. S1 in the= early graph syn-rift; for each S2 = playlate syn-rift; are only IN examples. = Pleaseinversion; refer to Table P1 = early1 for post-rift; real examples. P2 = late S1 post-rift.= early syn-rift; S2 = late syn-rift; IN = inversion; P1 = early post-rift; P2 = late post-rift. Energies 2019, 12, 4088 18 of 28

In proven plays, the main trap types and related fields include the following:

(1) Pinghu structural (i-1), mainly inverted anticlines and fault bounded compressional hanging wall Energies 2019, 12, x FOR PEER REVIEW 18 of 28 anticlines, represented by the Chunxiao, Duanqiao, Pinghu, Baoyunting, Wubei, Laiheting, and KongquetingIn proven plays, fields. the This main play trap type types belongs and related to the fields Pinghu–Huagang include the following: Petroleum System (!). (2) (1)Huagang Pinghu structural structural (i-2),(i-1), mainlymainly inverted anticlines anticlines, and reverse-fault fault bounded related compressional footwall hanging closures and faults,wall represented anticlines, represented by the Chunxiao, by the Chunxiao, Tianwaitian, Duanqiao, Duanqiao, Pinghu, and Baoyunting, Canxue fields, Wubei, as Laiheting, well as by the Gushanand Kongqueting 1, Qiuyue 1, fields. Yuquan, This Huagang play type 1,belongs Longjing to the 1, Pinghu–Huagang Longjing 2, and LongjingPetroleum 4 System discoveries. (!). As (2)above, Huagang this play structural belongs (i-2), to mainly the Pinghu–Huagang inverted anticlines, Petroleum reverse-fault System related (!). footwall closures and (3) Huagangfaults, represented structural–stratigraphic by the Chunxiao, (i-3), Tianwaitian, mainly fault-boundedDuanqiao, and Canxue closures fields, with as well facies as change,by representedthe Gushan by 1, the Qiuyue Pinghu 1, Yuquan, and Wuyunting Huagang fields.1, Longjing This 1, play Longjing also belongs2, and Longjing to the Pinghu–Huagang4 discoveries. As above, this play belongs to the Pinghu–Huagang Petroleum System (!). Petroleum System (!). (3) Huagang structural–stratigraphic (i-3), mainly fault-bounded closures with facies change, For speculativerepresented by plays, the Pinghu the main and typesWuyunting are likely fields. to This include play also the belongs following: to the Pinghu–Huagang Petroleum System (!). (1) Miocene structural (ii-1) pop-up faulted anticlines, and stratigraphic (ii-2) sub-unconformity For speculative plays, the main types are likely to include the following: traps. Such plays could belong to the Miocene–Miocene Petroleum System (?).

(2) (1)HuagangMiocene stratigraphic structural (ii-1) (ii-3), pop-up sand faulted pinch-outs anticl onines, basin and flank.stratigraphic Such a(ii-2) play sub-unconformity might belong to the traps. Such plays could belong to the Miocene–Miocene Petroleum System (?). Huagang–Huagang Petroleum System (?). (2) Huagang stratigraphic (ii-3), sand pinch-outs on basin flank. Such a play might belong to the (3) PinghuHuagang–Huagang structural–stratigraphic Petroleum System (ii-4), mainly (?). occurring in inverted anticlines. This play could (3)belong Pinghu to the structural–stratigraphic Pinghu–Huagang Petroleum (ii-4), mainly System occurring (!). in inverted anticlines. This play could (4) Basementbelong structural–stratigraphicto the Pinghu–Huagang Petroleum (ii-5), porous System basement (!). in topographic relief. This play could (4)be relatedBasement to thestructural–stratigraphic Cretaceous/Paleocene–Basement (ii-5), porous basement Petroleum in topographic System (?). relief. This play could be related to the Cretaceous/Paleocene–Basement Petroleum System (?). 4.3. Lishui Sub-Basin 4.3. Lishui Sub-Basin The Lishui Sub-basin, situated in the southwestern East China Sea is a faulted half-graben lying The Lishui Sub-basin, situated in the southwestern East China Sea is a faulted half-graben lying on Mesozoic basement with its main boundary fault on the eastern side. The sub-basin extends in a on Mesozoic basement with its main boundary fault on the eastern side. The sub-basin extends in a NE–SW direction and is divided into two depressions (Figures 11 and 12). The East Depression has an NE–SW direction and is divided into two depressions (Figures 11 and 12). The East Depression has 2 area ofan aboutarea of 4800about km 4800and km2a and maximum a maximum thickness thickness over over 7.5 7.5 km, km while, while thethe West Depression Depression covers covers an 2 area ofan aboutarea of 9800about km 9800and km2a and maximum a maximum thickness thickness of of 12 12 km. km.

FigureFigure 11. 11.Location Location map map of of major major hydrocarbon fields, fields, non-commercial non-commercial discoveries, discoveries, and sub-units and sub-units of of thethe Lishui Lishui Sub-basin. Sub-basin. Blue Blue areas areas indicate indicate the region the regionss of the ofmature the mature source rocks source (modified rocks (modified from Chen from et al. [3]). Chen et al. [3]).

Energies 2019, 12, 4088 19 of 28

Energies 2019, 12, x FOR PEER REVIEW 19 of 28

Figure 12. Schematic geological cross-section of the Lish Lishuiui Sub-basin, and its proven and speculative plays. Note Note that that all all belong to the Yueguifeng–LingfengYueguifeng–Lingfeng PetroleumPetroleum SystemSystem (!).(!). Line location is indicated in FigureFigure 1111.. All the redred lineslines areare normalnormal faults;faults; SS == syn-rift;syn-rift; P1P1 == early post-rift;post-rift; P2P2 == late post-rift; i-1 == Lingfeng structural (proven); i-2 == Mingyuefeng structural (proven); i-3i-3 == Basement structural–stratigraphic (proven); ii-1ii-1 == Oujiang structural (speculative).

Hydrocarbons werewere locatedlocated in in wells wells LF-1, LF-1, LS LS 36-1-1, 36-1-1, SMT-1, SMT-1, and and WZ WZ 13-1-1, 13-1-1, but but only only the the LS LS 36-1-1 36- gas1-1 gas field field is of is commercialof commercial value. value. Figure Figure 11 11 illustrates illustrates the the locations locations of of thethe hydrocarbonhydrocarbon fieldsfields and non-commercial hydrocarbon discover discoveriesies within the Lishui Sub-basin. Table Table 33 isis aa summarysummary ofof keykey features of these fieldsfields andand discoveries.discoveries.

Table 3. Summary of hydrocarbon fields and discoveries of the Lishui Sub-basin. Table 3. Summary of hydrocarbon fields and discoveries of the Lishui Sub-basin. Field/Discovery Reservoir Source Rock Field/Discovery Reservoir Source Rock Name Name UnitUnit Name Name Age Lithology Lithology Unit Unit Name Name Age Age Lithology Lithology MingyufengMingyufeng Late SandstoneSandstone LS 36-1-1 field FormationFormation Paleocene LS 36-1-1 field LingfengLingfeng Late LingfengLingfeng SandstoneSandstone Late PaleocenePaleocene Claystone Claystone FormationFormation Paleocene FormationFormation YueguifengYueguifeng LF-1LF-1 discovery discovery Basement Basement Precambrian Gneiss Gneiss Early PaleocenePaleocene Claystone Claystone FormationFormation WZ 13-1-1 Lingfeng Late Lingfeng WZ 13-1-1 Lingfeng Late Sandstone Lingfeng Late Paleocene Claystone discovery Formation Paleocene Sandstone Formation Late Paleocene Claystone discovery Formation Paleocene Formation Lingfeng Late Yueguifeng Lingfeng Late Sandstone Yueguifeng Early Paleocene Claystone Formation Paleocene Sandstone Formation Early Paleocene Claystone SMT-1SMT-1 discovery discovery Formation Paleocene Formation Lingfeng Early Yueguifeng Lingfeng Early Sandstone Yueguifeng Early Paleocene Claystone Formation Paleocene Sandstone Formation Early Paleocene Claystone Formation Paleocene Formation Field/Discovery Seal Play Hydrocarbon FieldName/Discovery Unit Name Seal Age Lithology Play Name Play Trap HydrocarbonType Type Name Unit Name Age LithologyMingyuefeng Play Name Structural—inverted Trap Gas structural anticlines LS 36-1-1 field Mingyuefeng Structural—inverted Lingfeng Late Lingfeng Structural—inverted GasGas, LS 36-1-1 field Claystone structural anticlines Formation Paleocene structural anticlines condensate Lingfeng Late Lingfeng Structural—inverted Gas, Claystone Structural– Formation Paleocene Basementstructural anticlines condensate Lingfeng Late stratigraphic—porous LF-1 discovery Claystone structural– Structural– Oil, gas Formation Paleocene Basement basement in Lingfeng Late stratigraphic stratigraphic— LF-1 discovery Claystone structural– topographic relief Oil, gas Formation Paleocene porous basement in WZ 13-1-1 Lingfeng Late stratigraphicLingfeng Structural—footwall Claystone topographic relief Gas discovery Formation Paleocene structural closures WZ 13-1-1 Lingfeng Late Lingfeng Structural—footwall Lingfeng Late Claystone Lingfeng Structural—footwall Gas discovery Formation Paleocene Claystone structural closures Gas Formation Paleocene structural closures SMT-1 discovery Lingfeng Late Lingfeng Structural—footwall Lingfeng Late Claystone Lingfeng Structural—footwall Gas SMT-1 discovery Formation Paleocene Claystone structural closures Gas Formation Paleocene structural closures Lingfeng Late Lingfeng Structural—footwall Claystone Gas Formation Paleocene structural closures 4.3.1. Tectono-Stratigraphy The evolution can be summarized as follows based on the studies in References [6,13,51–53] (Figures 3, 5, and 12):

Energies 2019, 12, 4088 20 of 28

4.3.1. Tectono-Stratigraphy The evolution can be summarized as follows based on the studies in References [6,13,51–53] (Figure3, Figure5, and Figure 12): Early syn-rift (Late Cretaceous–Paleocene): The area was under tensional stress and active faulting controlled the deposition, which shows typical characteristics of fast subsidence with a maximum rate of 700 m/Ma. The sequence includes the Shimentan, Yueguifeng, Lingfeng, and Mingyuefeng formations. Late syn-rift (Early–Middle Eocene): Fault activity waned in this stage and did not influence the sedimentation, which is characterized by a low subsidence rate. The Oujiang and Wenzhou formations were deposited at this stage. Inversion (Late Eocene–Oligocene): During this period, most of the region was uplifted and eroded. Post-rift (Miocene–Quaternary): Regional subsidence took place with a number of small faults being active. Deposits include the Longjing, Yuquan, Liulang, and Santan formations and Donghai Group.

4.3.2. Petroleum System Development within the Tectono-Stratigraphic Framework Only one proven petroleum system, the Yueguifeng–Lingfeng (!) system, belonging to the early syn-rift lacustrine–deltaic PST, was identified. Yueguifeng–Lingfeng Petroleum System (!): This is the most important petroleum system of the Lishui Sub-basin (Figure 13). All of the currently discovered oil and gas fields and non-commercial hydrocarbon discoveries in the Lishui Sub-basin belong to this system (Table3 and Figure 11). Source rocks and potential source rocks • The source rocks lie in lacustrine claystones and coals of the Lower Paleocene Yueguifeng Formation with TOC contents of 1.16–4.08 wt.%, together with shallow marine claystones of the Upper Paleocene Lingfeng Formation with an average TOC content of 1.52 wt.%. Claystones and coals of the Upper Paleocene Mingyuefeng Formation may also form minor source rocks (average TOC content of 2.3 wt.% and a thickness of 120–200 m). The organic material is dominated by type II kerogen with minor type III and I kerogen. The locations of mature source rocks can be seen in Figure 11. Hydrocarbon generation, migration, and accumulation started during the Early Miocene and continues to the present day. Reservoirs and potential reservoirs • The reservoirs are dominated by fine-grained shallow marine sandstones of the Paleocene Lingfeng Formation with minor Precambrian fractured gneiss basement and shallow marine sandstones of the Mingyuefeng Formation and, potentially, the Eocene Oujiang Formation. Seals • The Paleocene intra-formational claystones of the Lingfeng and Mingyuefeng formations are effective cap rocks. Overburden rocks include Eocene, Miocene, Pliocene, and Quaternary sediments. Trap formation • In the Lishui Sub-basin, the major trap types are structural, including inverted anticlines, with a few combined structural–stratigraphic trap styles. The structural traps were formed during the Eocene and Oligocene inversion cycle. Thus, the critical moment of this system occurred at 8.0 Ma, close to the end of the Miocene. Energies 2019, 12, 4088 21 of 28

4.3.3. Play Development Three play or reservoir levels were identified in the Lishui Sub-basin. These are pre-rift basement, early syn-rift Paleocene Yueguifeng Formation, and (potentially) the late syn-rift Eocene Oujiang Formation. The proven and speculative play types (Figure 12), all belonging to the Yueguifeng–Lingfeng Energies 2019, 12, x FOR PEER REVIEW 21 of 28 Petroleum System (!), are summarized in below. In proven play types, the main trap types include the following: In proven play types, the main trap types include the following: (1) Lingfeng structural (i-1), mainly inverted anticlines and footwall closures, represented by the LS (1) Lingfeng structural (i-1), mainly inverted anticlines and footwall closures, represented by the LS 36-1-1 field, and the WZ 13-1-1 and SMT-1 discoveries. 36-1-1 field, and the WZ 13-1-1 and SMT-1 discoveries. (2) Mingyuefeng structural (i-2), mainly inverted anticlines, represented by the LS 36-1-1 field. (2) Mingyuefeng structural (i-2), mainly inverted anticlines, represented by the LS 36-1-1 field. (3) BasementBasement structural–stratigraphic structural–stratigraphic (i-3), (i-3), porous porous basement basement in in topographic relief, represented by thethe LF-1 LF-1 discovery. discovery. For speculative plays, the main trap types are likely to include the following: For speculative plays, the main trap types are likely to include the following: (1) Oujiang structural (ii-1), hanging wall fault blocks. (1) Oujiang structural (ii-1), hanging wall fault blocks.

Figure 13. Event chart of the Yueguifeng–Lingfeng Petroleum System (!) in the Lishui Sub-basin. Figure 13. Event chart of the Yueguifeng–Lingfeng Petroleum System (!) in the Lishui Sub-basin.

4.4. Okinawa Trough The Okinawa Trough (Figures(Figures1 1 and and2 )2) started started to to form form in in the the Middle Middle Miocene Miocene as as a a result result of of rifting rifting between the Diaoyudao Paleo-uplift Paleo-uplift and and the the Ryukyu Ryukyu Arc Arc [24,34]. [24,34]. By By the the end end of of the the Late Late Miocene, Miocene, a asedimentary sedimentary basin basin was was already already developed developed [24,34]. [24,34]. With With the the opening opening of of the the Okinawa Okinawa Trough, Trough, all extensional stresses being generated by subduction in the Ryukyu Trench became concentrated, and the active extension of the Xihu Sub-basin ceased at this time. At At present, present, the the Okinawa Okinawa Trough Trough is over 2 km deep and is generally considered toto bebe aa currentlycurrently openingopening back-arcback-arc basin.basin. The sediments within the Okinawa Trough mainlymainly consist of neriticneritic andand deep-waterdeep-water turbiditic volcaniclastics [24,27,34,35] [24,27,34,35] (Figure 55).). Typically,Typically, thesethese rocksrocks areare regardedregarded asas havinghaving poorpoor reservoirreservoir potential. Moreover, as a result of the recent opening of the Okinawa Trough as a back-arc basin, any potential source rocks are likely to be immature. In addition, a water depth of over 2 km is a major reason why petroleum explorationexploration isis yetyet toto commencecommence inin thisthis area.area. In thisthis section, section, the the possibility possibility that that a petroleum a petroleum system system may be may developed be developed in this basin in isthis speculated; basin is furthermore,speculated; furthermore, which source, which reservoir source,/seal, reservoir/se and trap elementsal, and trap it could elements contain it and,could if contain present, and, which if typespresent, of playwhich could types occur of play are could also suggested. occur are Suchalso suggested. speculations Such rely speculations on comparison rely withon comparison analogous basinswith analogous in similar basins geologic in similar situations geologic (i.e., Takano situations [54]). (i.e., Takano [54]).

4.4.1. Tectono-Stratigraphy Based on the studies in References [26,27,29,35,47,55], the evolution can be summarized as follows (Figures 3, 5, and 14): Early syn-rift (Middle Miocene–Late Miocene): The first phase of rifting created the shape of the Okinawa Trough and strong volcanism resulted in a stratigraphy dominated by Middle Miocene volcanics and tuffaceous conglomerates followed by Late Miocene turbiditic siliciclastics.

Energies 2019, 12, 4088 22 of 28

4.4.1. Tectono-Stratigraphy Based on the studies in References [26,27,29,35,47,55], the evolution can be summarized as follows (Figure3, Figure5, and Figure 14): Early syn-rift (Middle Miocene–Late Miocene): The first phase of rifting created the shape of the Okinawa Trough and strong volcanism resulted in a stratigraphy dominated by Middle Miocene Energies 2019, 12, x FOR PEER REVIEW 22 of 28 volcanics and tuffaceous conglomerates followed by Late Miocene turbiditic siliciclastics. Post-riftPost-rift (Pliocene)(Pliocene):: AfterAfter thethe initialinitial stagestage ofof rifting,rifting, therethere waswas aa periodperiod ofof quiescencequiescence wherewhere thethe basinbasin subsidedsubsided rapidlyrapidly andand uniformly.uniformly. ThisThis subsidencesubsidence plungedplunged thethe troughtrough intointo deeperdeeper andand deeperdeeper waterwater resultingresulting inin aa rapidrapid changechange fromfrom non-depositionnon-deposition toto aa deep-waterdeep-water depositionaldepositional environment.environment. ByBy thisthis time,time, sedimentssediments fromfrom thethe YangtzeYangtze RiverRiver filledfilled thethe EastEast ChinaChina SeaSea ShelfShelf BasinBasin andand enteredentered intointo OkinawaOkinawa Trough,Trough, which which was was filled filled rapidly rapidly by by deep-water deep-water turbidites. turbidites. LateLate syn-riftsyn-rift (Quaternary)(Quaternary):: TheThe secondsecond majormajor phasephase ofof riftingrifting and volcanism is still active today. OverallOverall continuedcontinued subsidencesubsidence andand relentlessrelentless input input of of sediment sediment resulted resulted in in a a rapidly rapidly filling filling basin. basin.

FigureFigure 14.14. Schematic tectonic cross-section of the northernnorthern part of thethe OkinawaOkinawa TroughTrough andand itsits speculativespeculative plays,plays, allall ofof whichwhich relaterelate toto aa speculativespeculative NeogeneNeogene/Quaternary–Neogene/Quaternary/Quaternary–Neogene/Quaternary PetroleumPetroleum SystemSystem (?).(?). TheThe seismicseismic lineline andand thethe To-Ka-1To-Ka-1 wellwell locationlocation areare indicated indicated in in Figure Figure1 .1. All All the the redred lineslines areare normal normal faults; faults; i-1 i-1= =Neogene Neogenestructural; structural; i-2i-2= =Neogene Neogene stratigraphic;stratigraphic; i-3i-3= = QuaternaryQuaternary structural;structural; i-4 i-4= =Quaternary Quaternary stratigraphic. stratigraphic. The The location location of of well well To-Ka-1 To-Ka-1 in thein the Okinawa Okinawa Trough Trough and and the seismicthe seismic profile profile across across the well the well are shown are shown in Figure in Figure1. 1.

4.4.2. Petroleum System Development within Tectono-Stratigraphic Framework 4.4.2. Petroleum System Development within Tectono-Stratigraphic Framework No petroleum system is proven to exist in the Okinawa Trough. The only petroleum system No petroleum system is proven to exist in the Okinawa Trough. The only petroleum system proposed here, the Neogene/Quaternary–Neogene/Quaternary (?) (Figure 15), is highly speculative proposed here, the Neogene/Quaternary–Neogene/Quaternary (?) (Figure 15), is highly speculative and belongs to syn-rift turbiditic PST. and belongs to syn-rift turbiditic PST. Potential source rocks •• Potential source rocks Gas exploration in the Okinawa Trough concentrated on the identification of gas hydrate potential, Gas exploration in the Okinawa Trough concentrated on the identification of gas hydrate and investigations by Japan Agency for Marine-Earth Science and Technology revealed methane potential, and investigations by Japan Agency for Marine-Earth Science and Technology revealed seepage, as well as hydrothermal CO2 fields (http://www.jamstec.go.jp/chikyu/e/expedition/). Outcrops methane seepage, as well as hydrothermal CO2 fields of the Oligo-Miocene on the Ryukyu islands contain coals, however, and it is possible that marginal (http://www.jamstec.go.jp/chikyu/e/expedition/). Outcrops of the Oligo-Miocene on the Ryukyu quantities of gas-prone source rock may be present along the trend. The most likely occurrence would islands contain coals, however, and it is possible that marginal quantities of gas-prone source rock be in the form of re-worked coal-bearing clastics brought in by turbidites, similar to some of the source may be present along the trend. The most likely occurrence would be in the form of re-worked coal- rocks in the shelf sub-basins. There were reports that C –C gas was recovered from the To-Ka-1 bearing clastics brought in by turbidites, similar to some 1of the5 source rocks in the shelf sub-basins. well in the northern part of the basin; however, these cannot be confirmed by the authors. From There were reports that C1–C5 gas was recovered from the To-Ka-1 well in the northern part of the the profile (Figure 14), this well appears to have been drilled on a very young structure, outside the basin; however, these cannot be confirmed by the authors. From the profile (Figure 14), this well main basin-deep. appears to have been drilled on a very young structure, outside the main basin-deep. • Potential reservoirs Reservoir potential may exist in regressive delta-front and trough-fill turbidite sandstones in the shallower part of the sequence. The cyclicity of fluctuating Neogene sea levels [56] might provide an excellent natural mechanism for the development of reservoir-seal couplets in these sediments, particularly after the initial rifting event when there was a period of quiescence. Potential reservoirs could also include turbidite fans deposited at earlier stages during phases of rapid subsidence. • Potential seals

Energies 2019, 12, 4088 23 of 28

Potential reservoirs • Reservoir potential may exist in regressive delta-front and trough-fill turbidite sandstones in the shallower part of the sequence. The cyclicity of fluctuating Neogene sea levels [56] might provide an excellent natural mechanism for the development of reservoir-seal couplets in these sediments, particularly after the initial rifting event when there was a period of quiescence. Potential reservoirs could also include turbidite fans deposited at earlier stages during phases of rapid subsidence. EnergiesPotential 2019, 12 seals, x FOR PEER REVIEW 23 of 28 • Potential sealsseals areare probablyprobably widespread widespread in in thick thic basin-floork basin-floor marlstone marlstone or claystoneor claystone overlying overlying the theMiocene Miocene volcanics volcanics and and in Pliocene in Pliocene transgressive transgressive intervals. intervals. • Potential trap formation • Potential trap formation Numerous trappingtrapping configurations,configurations, mainly mainly structural, structural, but but possibly possibly also also stratigraphic, stratigraphic, could could have haveformed formed in this in area this of area back of arc back extension. arc extension. These couldThese includecould include localized localized inversion inversion features features related relatedto the transtensional to the transtensional/transpressional/transpressional tectonic tectonic environment environment created created by the by oblique the oblique subduction subduction of the ofPhilippine the Philippine Sea plate Sea beneathplate beneath the Eurasian the Eurasian plate [ 46plate]. [46].

Figure 15. Event chart of the speculative Neogene/Quaternary–Neogene/Quaternary Petroleum Figure 15. Event chart of the speculative Neogene/Quaternary–Neogene/Quaternary Petroleum System System (?). Question marks indicate uncertainties. The sea level curve is from Haq et al. [56]. (?). Question marks indicate uncertainties. The sea level curve is from Haq et al. [56].

4.4.3. Play Play Development Development It is envisaged that the following play types may be developeddeveloped (Figure(Figure 1414):):

(1) Neogene–QuaternaryNeogene–Quaternary structural structural (i-1), (i-1), such such as as footwall footwall or or hanging wall closures and inversion anticlinesanticlines in in normally normally faulted faulted half half grabens. grabens.

(2) Neogene–QuaternaryNeogene–Quaternary stratigraphic stratigraphic (i-2), (i-2), resultin resultingg from from facies facies changes changes along along depositional depositional dip, dip, onlaponlap onto onto structures, structures, or or drape drape over over the the existing existing structures. structures.

4.5. Trends Trends in Basin Evolution and Their Prospectivity The distribution distribution of of the the petroleum petroleum systems systems is isdepe dependentndent on onthe the sedimentary sedimentary basin basin history. history. It was It wasdemonstrated demonstrated that thatknowledge knowledge of the of syn- the syn-and andpost-rift post-rift basin basin evolution evolution and and the thesuccession succession of depositionalof depositional environments environments makes makes it itpossible possible to to identify identify potential potential petroleum petroleum systems systems and and their constituent plays (see also Doust et al. [[18]).18]). To To support this approach, a number of characteristic trends in the East China Sea Basin were distinguished,distinguished, which have distinct “trajectories” through a matrix of changing depositional environments and basin development phases (Figure 16). This is the first time that this approach was applied in the East China Sea Basin. • Northwest Shelf Basin group (NWSB) These basins are located at the northern part of the West Shelf Basin and include the Changjiang and Qiantang sub-basins. These sub-basins are the most proximal in this part of the East China Sea and lie between basement high zones or paleo-highs. As a result, they were the most protected from marine influence during both syn-rift and early post-rift cycles. Accordingly, the dominant petroleum system type is PST A, early syn-rift lacustrine–deltaic. • Southwest Shelf Basin group (SWSB)

Energies 2019, 12, x FOR PEER REVIEW 24 of 28

These basins are located at the southern part of the West Shelf Basin, and comprise the Lishui, Jiaojiang, Fuzhou, and Minjiang sub-basins. They are also proximal and are relatively protected from open marine environments by a NE–SW trending paleo-high. Their basin history is similar to that of the Northwest group, with the exception that a southeastward tilt in the late syn-rift resulted in marine incursions from the end of the early syn-rift into the late syn-rift stages. Type III shallow marine claystone source rocks accumulated in the late syn-rift, but the dominant petroleum system type is PST A, early syn-rift lacustrine–deltaic, with reservoirs located in the early post-rift. • Northeast and Southeast Shelf Basin groups (NESB, SESB) These basins include the Xihu and Fujiang sub-basins, the northern part of the East Shelf Basin, and the Diaobei sub-basin to the south. All three petroleum system types, i.e., PST A, PST B, and PST C, may be developed in this group. Among them, the most dominant one is PST B, late syn-rift marine. As with the western group of basins, the early syn-rift and late syn-rift basin evolution phases in the southern group were subject to marine incursions, but these did not reach the northern area. This is reflected by the source material for PST B. Although fluvial–deltaic lithofacies are present throughout, claystones with type II organic material are better developed in the Diaobei Sub-basin [1,57]. Energies 2019, 12, 4088 24 of 28 • Okinawa Trough The Okinawa Trough Basin is distinct from the other basins, showing the typical characteristics matrix of changing depositional environments and basin development phases (Figure 16). This is the of young rifting processes within deeper marine depositional environments. The presence of a syn- first timerift turbiditic that this petroleum approach system was applied type (PST in D) the is East highly China speculative. Sea Basin.

FigureFigure 16. Petroleum 16. Petroleum system system types types in in the the EastEast China Se Seaa Basin Basin showing showing the the depositional depositional environment environment evolutionevolution in relation in relation to tectonicto tectonic basin basin stages. stages. TheThe tectono-stratigraphic situation situation of PSTs of PSTs is indicated is indicated by colored ovals: A (yellow) = PST A; B (green) = PST B; C (mauve) = PST C and D; (pink) = PST D. by colored ovals: A (yellow) = PST A; B (green) = PST B; C (mauve) = PST C and D; (pink) = PST NWSB = Northwest Shelf Basin; NESB = Northeast Shelf Basin; SWSB = Southwest Shelf Basin; SESB D. NWSB = Northwest Shelf Basin; NESB = Northeast Shelf Basin; SWSB = Southwest Shelf Basin; = Southeast Shelf Basin. The red dashed area shows the inversion cycle, which is largely an SESBunconformity= Southeast and Shelf a depositional Basin. The hiatus. red dashed area shows the inversion cycle, which is largely an unconformity and a depositional hiatus. 5. Summary and Conclusions Northwest Shelf Basin group (NWSB) • The sub-basins of the East China Sea Basin share a common tectonic evolution, from Paleogene Thesesyn-rift basins to Neogene are located post-rift. at They the northern are filled partwith ofsediments the West deposited Shelf Basin in en andvironments include that the evolved Changjiang and Qiantang sub-basins. These sub-basins are the most proximal in this part of the East China Sea and lie between basement high zones or paleo-highs. As a result, they were the most protected from marine influence during both syn-rift and early post-rift cycles. Accordingly, the dominant petroleum system type is PST A, early syn-rift lacustrine–deltaic. Southwest Shelf Basin group (SWSB) • These basins are located at the southern part of the West Shelf Basin, and comprise the Lishui, Jiaojiang, Fuzhou, and Minjiang sub-basins. They are also proximal and are relatively protected from open marine environments by a NE–SW trending paleo-high. Their basin history is similar to that of the Northwest group, with the exception that a southeastward tilt in the late syn-rift resulted in marine incursions from the end of the early syn-rift into the late syn-rift stages. Type III shallow marine claystone source rocks accumulated in the late syn-rift, but the dominant petroleum system type is PST A, early syn-rift lacustrine–deltaic, with reservoirs located in the early post-rift. Northeast and Southeast Shelf Basin groups (NESB, SESB) • These basins include the Xihu and Fujiang sub-basins, the northern part of the East Shelf Basin, and the Diaobei sub-basin to the south. All three petroleum system types, i.e., PST A, PST B, and PST C, may be developed in this group. Among them, the most dominant one is PST B, late syn-rift marine. As with the western group of basins, the early syn-rift and late syn-rift basin evolution phases in the southern group were subject to marine incursions, but these did not reach the northern area. This is reflected by the source material for PST B. Although fluvial–deltaic lithofacies are present throughout, claystones with type II organic material are better developed in the Diaobei Sub-basin [1,57]. Energies 2019, 12, 4088 25 of 28

Okinawa Trough • The Okinawa Trough Basin is distinct from the other basins, showing the typical characteristics of young rifting processes within deeper marine depositional environments. The presence of a syn-rift turbiditic petroleum system type (PST D) is highly speculative.

5. Summary and Conclusions The sub-basins of the East China Sea Basin share a common tectonic evolution, from Paleogene syn-rift to Neogene post-rift. They are filled with sediments deposited in environments that evolved from terrestrial lacustrine to transitional into more marine, and they were subject to a series of compressional/inversion events. The only exception is the Okinawa Trough, which is a very young, back-arc sub-basin in which rifting started during the Middle Miocene. Petroleum systems identified and potentially present in the various sub-basins of the East China Sea Basin can be grouped into four types (PSTs), which can be directly related to the main stages of basin development. These PSTs are the following:

Early syn-rift lacustrine–deltaic PST: Oil/gas-prone, with charge from type II source rocks • complemented with limited charge from type III shallow marine source rocks and type I lacustrine source rocks. Late syn-rift marine PST: Gas/oil-prone, derived from type III shallow marine source rocks. • Early post-rift fluvial–deltaic PST: Gas/oil-prone, with the main source rock in marginal deltaic to • shallow marine sediments. The charge and the reservoir are commonly not in the same basin evolution stage. Syn-rift turbiditic PST: Gas-prone, with the re-worked type III coal-bearing claystones brought in • by turbidites as the potential source rocks.

Differences in paleogeographic position influence the distribution and development of the petroleum systems in the sub-basins. In particular, the balance between non-marine, more proximal environments and the presence of marine incusions in both syn- and post-rift in the southern area impacts the source facies.

In the northwest (Changjiang and Qiantang sub-basins), only the early syn-rift lacustrine–deltaic • PST is found. Basins in the southwest (Lishui, Jiaojiang, Fuzhou, and Minjiang sub-basins) also contain the early • syn-rift lacustrine–deltaic PST only, but the depositional environments include marine intervals. The position of the basins in the northeast (Xihu and Fujiang sub-basins), with an evolution from • non-marine to marine conditions, allows all three PSTs to be developed. The most dominant petroleum system type, however, is the late syn-rift marine PST. Further to the south (Diaobei Sub-basin), the late syn-rift marine PST is dominant, but the potential for the early syn-rift lacustrine–deltaic and early post-rift fluvial-deltaic PSTs to be developed exists. In the Okinawa Trough, no proven petroleum systems or reservoir formations are yet identified, • and the proposed syn-rift turbiditic PST is highly speculative.

Author Contributions: B.W. performed the research and drafted the article; H.D. supervised the research and reviewed it critically; J.L. completed the review and English check. Funding: The publication of the paper was funded by the Key National Natural Science Foundation of China (Grant No.91328201), the National Natural Science Foundation of China (Grant No. 40972081), and the Fundamental Research Funds for the Central Universities (Grant No. 2-9-2013-095). Acknowledgments: The authors thank Suzanne Beglinger for original data preparation and acknowledge informal discussions with former Shell colleagues. The authors also thank the great contribution and valuable time of anonymous reviewers. Conflicts of Interest: There are no known conflicts of interest. Energies 2019, 12, 4088 26 of 28

References

1. Zhou, Z.; Zhao, J.; Yin, P. Characteristics and tectonic evolution of the East China Sea. In Chinese Sedimentary Basins; Zhu, X., Ed.; Sedimentary Basins of the World; Elsevier Science: Amsterdam, The Netherlands, 1989; Volume 1, pp. 165–179. 2. Ye, J.; Qing, H.; Bend, S.L.; Gu, H. Petroleum systems in the offshore Xihu Basin on the continental shelf of the East China Sea. AAPG Bull. 2007, 91, 1167–1188. [CrossRef] 3. Chen, J.; Ge, H.; Chen, X.; Deng, C.; Liang, D. Classification and origin of natural gases from Lishui Sag, the East China Sea Basin. Sci. China Ser. D Earth Sci. 2008, 51, 122–130. [CrossRef] 4. Silverman, M.R.; Wang, Q.; Byrd, B.L.; Zhao, J.K.; Zhang, H.Y.; Chen, M.; Weimer, P. 3-D evaluation of the Ping Hu field, East China Sea. In Applications of 3-D Seismic Data to Exploration and Production; Weimer, P., Davis, T.L., Eds.; AAPG Studies in Geology; American Association of Petroleum Geologists: Tulsa, OK, USA, 1996; Volume 42, pp. 91–101. 5. Chen, Z. Analysis of hydrocarbon potential and selection of exploration prospect of Lishui and Jiaojiang sags. China Offshore Oil Gas (Geol.) 1997, 11, 451–458. 6. Chen, Z.; Wu, P.; Wu, Z. Petroleum geology and exploration potential of Lishui Sag. China Offshore Oil Gas (Geol.) 2000, 14, 384–391. 7. Chen, J.; Li, G.; Chen, G. Petroleum prospects of Mesozoic and Paleocene in the Western Depression of the East China Sea Shelf Basin. Mar. Geol. Lett. 2003, 19, 17–19. 8. Yu, H.; Ji, W. Geology of the Taiwan Basin. Pet. Geol. Taiwan 1992, 27, 73–88. 9. Liu, J.; Wu, J.; Fang, Y.; Wang, S. Pre-Cenozoic groups in the shelf basins of the East China Sea. Acta Oceanol. Sin. 2007, 29, 66–75. 10. Tian, H. Research on the oil-bearing series of Xihu Depression. J. China Univ. Pet. 2000, 24, 38–43. 11. Wang, L.; Wang, L. Petroleum geology in Sudi Structural Belt, Xihu Trough. China Offshore Oil Gas (Geol.) 2000, 14, 392–397. 12. Ye, J.; Gu, H. Characteristics and exploration evaluation of the petroleum systems in Xihu Depression of East China Sea. Nat. Gas Ind. 2004, 24, 8–11. 13. Jiang, Z.; Li, Y.; Du, H.; Zhang, Y. The Cenozoic structural evolution and its influences on gas accumulation in the Lishui Sag, East China Sea Shelf Basin. J. Nat. Gas Sci. Eng. 2015, 22, 107–118. [CrossRef] 14. He, D.; Mao, X.; Yang, J.; Wu, J.; Pan, M. Development of petroleum pool-forming dynamics simulation and evaluation system. Pet. Geol. Exp. 2007, 29, 527–530. 15. Huang, Z.; Hao, S.; Jiang, L. Assemblages and patterns of forming oil and gas reservoirs in Lishui Seg of East China Sea Basin. Nat. Gas Ind. 2001, 21, 17–21. 16. Doust, H. Placing petroleum systems and plays in their basin history context: A means to assist in the identification of new opportunities. First Break 2003, 21, 73–83. 17. Kingston, D.R.; Dishroon, C.P.; Williams, P.A. Global basin classification system. AAPG Bull. 1983, 67, 2175–2193. [CrossRef] 18. Doust, H.; Sumner, H.S. Petroleum systems in rift basins—A collective approach in Southeast Asian basins. Pet. Geosci. 2007, 13, 127–144. [CrossRef] 19. Ziegler, P.A.; Cloetingh, S. Dynamic processes controlling evolution of rifted basins. Earth Sci. Rev. 2004, 64, 1–50. [CrossRef] 20. Cloetingh, S.; Ziegler, P.A. Tectonic models for the evolution of sedimentary basins. In Treaties on Geophysics; Watts, A.B., Schubert, G., Eds.; Crustal and Lithosphere Dynamics; Elsevier, B.V.: Amsterdam, The Netherlands, 2007; Volume 6, pp. 485–611. [CrossRef] 21. Corver, M.P.; Doust, H.; Van Wees, J.D.; Bada, G.; Cloetingh, S. Classification of rifted sedimentary basins of the Pannonian Basin System according to the structural genesis, evolutionary history and hydrocarbon maturation zones. Mar. Pet. Geol. 2009, 26, 1452–1464. [CrossRef] 22. Beglinger, S.E.; Corver, M.P.; Doust, H.; Cloetingh, S.; Thurmond, A.K. A new approach of relating petroleum system and play development to basin evolution: An application to the conjugate margin Gabon coastal and Almada-Camamu basins. AAPG Bull. 2012, 96, 953–982. [CrossRef] 23. Magoon, L.B.; Dow, W.G. The petroleum system. In The Petroleum System—From Source to Trap; Magoon, L.B., Dow, W.G., Eds.; Memoirs 60; American Association of Petroleum Geologists: Tulsa, OK, USA, 1994; pp. 3–24. Energies 2019, 12, 4088 27 of 28

24. Letouzey, J.; Kimura, M. Okinawa Trough genesis: Structure and evolution of a backarc basin developed in a continent. Mar. Pet. Geol. 1985, 2, 111–130. [CrossRef] 25. Lee, C.; Shor, G.G., Jr.; Bibee, L.D.; Lu, R.S.; Hilde, T. Okinawa Trough: Origin of a back-arc basin. Mar. Geol. 1980, 35, 219–241. [CrossRef] 26. Kimura, M. Back-arc rifting in the Okinawa Trough. Mar. Pet. Geol. 1985, 2, 222–240. [CrossRef] 27. Sibuet, J.C.; Hsu, S.K.; Shyu, C.T.; Liu, C.S. Structural and kinematic evolutions of the Okinawa Trough back-arc basin. In Backarc Basins: Tectonics and Magmatism; Taylor, B., Ed.; Plenum Press: New York, NY, USA, 1995; pp. 343–379. [CrossRef] 28. Sibuet, J.C.; Hsu, S.K. Geodynamics of Taiwan arc–arc collision. Tectonophysics 1997, 274, 221–251. [CrossRef] 29. Park, J.-O.; Tokuyama, H.; Shinohara, M.; Suyehiro, K.; Taira, A. Seismic record of tectonic evolution and backarc rifting in the southern Ryukyu island arc system. Tectonophysics 1998, 294, 21–42. [CrossRef] 30. Sibuet, J.C.; Deffontaines, B.; Hsu, S.K.; Thareau, N.; Formal, J.P.L.; Liu, C. Okinawa trough backarc basin: Early tectonic and magmatic evolution. J. Geophys. Resour. 1998, 103, 30245–30267. [CrossRef] 31. Kong, F.; Lawver, L.A.; Lee, T.-Y. Evolution of the southern Taiwan–Sinzi Folded Zone and opening of the southern Okinawa trough. J. Asian Earth Sci. 2000, 18, 325–341. [CrossRef] 32. Hall, R. Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: Computer-based reconstructions, model and animations. J. Asian Earth Sci. 2002, 20, 353–431. [CrossRef] 33. Jolivet, L.; Huchon, P.; Rangin, C. Tectonic setting of Western Pacific marginal basins. Tectonophysics 1989, 160, 23–47. [CrossRef] 34. Letouzey, J.; Kimura, M. The Okinawa Trough: Genesis of a back-arc basin developing along a continental margin. Tectonophysics 1986, 125, 209–230. [CrossRef] 35. Sibuet, J.-C.; Letouzey, J.; Barbier, F.; Charvet, J.; Foucher, J.-P.; Hilde, T.W.C.; Kimura, M.; Chiao, L.-Y.; Marsset, B.; Muller, C.; et al. Back Arc Extension in the Okinawa Trough. J. Geophys. Res. 1987, 92, 14041–14063. [CrossRef] 36. Yang, Z. The type and basining period of Cenozoic sedimentary basin in East China Sea. Mar. Geol. Quat. Geol. 1992, 2, 3–13. 37. Wang, G.M.; Coward, M.P.; Yuan, W.; Liu, S.; Wang, W. Fold growth during basin inversion-Example from the East China Sea basin. In Basin Inversion; Buchanan, J.G., Buchanan, P.G., Eds.; Special Publication 88; The Geological Society: London, UK, 1995; pp. 493–522. [CrossRef] 38. Li, C.; Zhou, Z.; Ge, H.; Mao, Y. Rifting process of the Xihu Depression, East China Sea Basin. Tectoniphysics 2008, 472, 135–147. [CrossRef] 39. Uyeda, S.; Kanamori, H. Back-arc opening and the mode of subduction. J. Geophys. Res. 1979, 84, 1049–1061. [CrossRef] 40. Van Wijk, J.W. Passive Margin Formation: Tectonic Modeling of Pre- and Syn-Rift Lithospheric Controls. Ph.D. Thesis, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands, 2002. 41. Lambiase, J.J.; Morley, C.K. Hydrocarbons in rift basins: The role of stratigraphy. Philos. Trans. R. Soc. Lond. Ser. A Math. Phys. Eng. Sci. 1999, 357, 877–900. [CrossRef] 42. Lin, Z.; Zhou, P. Evolution of Cenozoic sedimentary facies of Xihu Depression of the shelf basin of the East China Sea. Mar. Geol. Quat. Geol. 1994, 2, 63–70. (In Chinese) 43. Harland, W.B.; Armstrong, R.L.; Cox, A.V.; Craig, L.E.; Smith, A.G.; Smith, D.G. A Geological Time Scale 1989; Cambridge University Press: Cambridge, UK, 1990. [CrossRef] 44. Zhao, Y. Pool-forming geology of Xihu depression in the East China Sea. Mar. Geol. Lett. 2003, 19, 20–24. 45. Miller, M.S.; Kennett, B.L.N.; Toy, V.G. Spatial and temporal evolution of the subducting Pacific Plate structure along the western Pacific margin. J. Geophys. Res. 2006, 111, B02401. [CrossRef] 46. Lallemand, S.; Theunissen, T.; Schnürle, P.; Lee, C.-S.; Liu, C.-S.; Font, Y. Indentation of the Philippine Sea plate by the Eurasia plate in Taiwan: Details from recent marine seismological experiments. Tectonophysics 2013, 594, 60–79. [CrossRef] 47. Nash, D.F. The geological development of the north Okinawa Trough area from Neogene times to Recent. J. Jpn. Assoc. Pet. Technol. 1979, 44, 109–119. [CrossRef] 48. Peters, K.E.; Cassa, M.R. Applied source rock geochemistry. In the Petroleum System—From Source to Trap; Magoon, L.B., Dow, W.G., Eds.; Memoir 60; American Association of Petroleum Geologists: Tulsa, OK, USA, 1994; pp. 93–120. Energies 2019, 12, 4088 28 of 28

49. Lee, G.H.; Kim, B.; Shin, K.S.; Sunwoo, D. Geologic evolution and aspects of the petroleum geology of the northern East China Sea shelf basin. AAPG Bull. 2006, 90, 237–260. [CrossRef] 50. Xu, X.H.; Chen, B.; Wei, H.K. Analysis of oil and gas accumulating condition in the north area of Xihu Basin. Offshore Oil 1998, 3, 40–43. 51. Wang, Y. Relation between extensional movement and formation of oil-gas pools in Lishui-JiaoJiang Sag. Oil Gas Geol. 1999, 20, 316–320. 52. Wang, Y.; Jiang, L.; Yang, W. Kinematical analysis on faults in the Lishui-Jiaojiang Sag. Sci. Geol. Sin. 2000, 35, 441–448. 53. Jia, C.; Xia, B.; Wang, H.; Zhang, S. Characteristic of teoconic evolution and petroleum geology in Lishui Sag, East China Sea Basin. Nat. Gas Geosci. 2006, 17, 397–401. 54. Takano, O. Changes in depositional systems and sequences in response to basin evolution in a rifted and inverted basin: An example from the Neogene Niigata-Shin’etsu basin, northern Fossa Magna, central Japan. Sediment. Geol. 2002, 152, 79–97. [CrossRef] 55. Hsu, S.-K.; Sibuet, J.-C.; Shyu, C.-T. Magnetic inversion in the East China Sea and Okinawa Trough: Tectonic implications. Tectonophysics 2001, 333, 111–122. [CrossRef] 56. Haq, B.U.; Hardenbol, J.; Vail, P.R. Chronology of Fluctuating Sea Levels since the Triassic. Science 1987, 235, 1156–1167. [CrossRef] 57. Bai, Y. Evolution Features and Tectonic Migration Trends of the Mesozoic and Cenozoic Basins in Eastern China. Master’s Thesis, China University of Geosciences, Beijing, China, 2014.

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).