Alluvial architecture of reworked pyroclastic deposits in peri-volcanic basins: Castillo Fm (Albian) of the Golfo San Jorge basin, Argentina

ALLUVIAL ARCHITECTURE OF REWORKED PYROCLASTIC

DEPOSITS IN PERI-VOLCANIC BASINS: CASTILLO

FORMATION (ALBIAN) OF THE GOLFO SAN JORGE BASIN,

ARGENTINA

José M. PAREDES1_{, Nicolás FOIX}1,2_{, José O. ALLARD}1_{, Ferrán COLOMBO}3 _{and Maisa A. TUNIK}2,4

1 _{Dpto. de Geología, Universidad Nacional de la Patagonia “San Juan Bosco”, (9005) Comodoro Rivadavia, Chubut, Argentina.} E-mail: paredesj@unpata.edu.ar

2&21,&(7&RQVHMR1DFLRQDOGH,QYHVWLJDFLRQHV&LHQWtÀFDV\7pFQLFDV

3'SWRGH(VWUDWLJUDItD3DOHRQWRORJtD\*HRFLHQFLDV0DULQDV)DFGH*HRORJtD8QLYHUVLGDGGH%DUFHORQD%DUFHORQD6SDLQ 4 _{Universidad Nacional de Río Negro, Cipolleti, Río Negro. Argentina.}

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Keywords: &XHQFDVSHULYROFiQLFDVDUTXLWHFWXUDÁXYLDOFXHQFDGHO*ROIR6DQ-RUJH&UHWiFLFR3DWDJRQLD

INTRODUCTION

)URPWKHHDUO\VXSWRGDWHVHYHUDO studies have addressed volcaniclastic re-sedimentation processes and deposits in

DUHDVORFDWHGGLVWDOO\WRYROFDQLFVRXUFHV 0RRUH  6KDQH  6PLWK  7XUEHYLOOH  1DND\DPD DQG <RV-KLNDZD.DWDRNDDQG1DNDMR Segschneider HWDO.DWDRND 8PD]DQRHW DO D 8PD]DQR HW DO E.DWDRNDHWDO8PD]DQRHWDO 6XFKVWXGLHVKDYHVKRZQYDULDEOH

VHGLPHQWDU\UHVSRQVHWRYROFDQLFHYHQWV DV D FRQVHTXHQFH RI GLIIHUHQW WHFWRQLF settings, changes in basin conditions (e.g. K\GURORJ\VXEVLGHQFHKLVWRU\EDVLQFOL-mate), variable distance to the volcanic source, basin location in relation to acti-ve volcanoes, and nature of the eruptions .DWDRNDHWDO 2009). The occurrence of

HFRQRPLF DFFXPXODWLRQV RI K\GURFDU-bons in non-marine, volcaniclastic suc-cessions preserved in peri-volcanic ba-VLQVPDNHVQHFHVVDU\WKHXQGHUVWDQGLQJ of the main forcing-factors in order to explain the spatial and temporal variabi-OLW\LQLQWHUQDOFKDUDFWHULVWLFVVKDSHDQG GLVWULEXWLRQ RI SRWHQWLDO K\GURFDUERQ UHVHUYRLUV 0DWKLVHQ DQG 0F3KHUVRQ )RUWKHVHUHDVRQVGHWDLOHGREVHU-vation of lithofacies and lithofacies asso-ciations from outcrops, spatial variation LQÁXYLDOVW\OHVDQGDOOXYLDODUFKLWHFWXUH data constitute strong tools for the deve-lopment of accurate volcaniclastic facies PRGHOVLQSHULYROFDQLFEDVLQV6WUDQJHO\ the number of published case studies GHDOLQJZLWKWKHVHLVVXHVLVOLPLWHG.D-WDRNDDQG1DNDMR.DWDRND 8PD]DQRHWDO 2012), in particular from

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The Cretaceous sedimentation of the *ROIR6DQ-RUJH%DVLQZDVLQÁXHQFHGE\ WKHLQFRUSRUDWLRQRI ODUJHTXDQWLWLHVRI  SULPDU\DQGUHZRUNHGS\URFODVWLFVSURYL-GHGE\DVXEGXFWLRQUHODWHGPDJPDWLFDUF $QGHDQ0DJPDWLF$UFGHYHORSHGLQWKH ZHVWHUQPDUJLQRI 6RXWK$PHULFDZKR-VH DFWLYLW\ VWDUWHG GXULQJ WKH %DUUHPLDQ (Ramos HWDO$FDPWKLFN succession of non-marine, volcaniclas-WLFGHSRVLWVRI &UHWDFHRXVDJHNQRZQDV Chubut Group (Barremian-Campanian?) ZDV GHSRVLWHG LQ WKH *ROIR 6DQ -RUJH EDVLQFRYHULQJDUHDVXSWRNP )LW]JHUDOGHWDO)LJDULHWDO 1999). 7KH$OELDQ&DVWLOOR)RUPDWLRQ/HVWDDQG )HUHOORLVDYROFDQLFODVWLFXQLWWKDW UHSUHVHQWVWKHUHZRUNLQJRI ÀQHJUDLQHG DVKLQÁXYLDOSOD\DODNHDQGUDUHO\ODFXV- WULQHHQYLURQPHQWV7KHXQLWLVZLGHO\H[-posed in the N-S trending San Bernardo )ROG%HOW)LJDJURXSRI UDQJHVOR-FDWHGaNPHDVWZDUGRI WKH$QGHDQ 0DJPDWLF $UF 7KH &DVWLOOR )RUPDWLRQ DQG FRUUHODWDEOH XQLWV DUH K\GURFDUERQ SURGXFHUV LQ PRVW RI  WKH ÀHOGV LQ WKH VXEVXUIDFHRI WKHEDVLQZKHUHWKLQDQG GLVFRQWLQXRXVÁXYLDOVDQGERGLHVDQGGLD-JHQHWLFDOO\DOWHUHGWXIIDFHRXVEHGVDUHWKH main reservoirs (Acuña HWDO 2011), pro-GXFLQJ DERXW  RI  WKH K\GURFDU-ERQVRI WKHEDVLQ$VWKHWKLFNQHVVHVRI  UHVHUYRLUVDUHFRPPRQO\PLQRUWKDQWKH

UHVROXWLRQ RI  DYDLODEOH VHLVPLF VXUYH\V outcrop-based studies constitute a good approach to predict the pattern of change LQÁXYLDOVW\OHVVKDSHDQGFKDUDFWHULVWLFV of the unit in surrounding areas. In spi-te of their importance as oil reservoir and ODUJHDUHDOGLVWULEXWLRQWKHODFNRI HYLGHQW lithological changes among exposures and the development of sedimentologi-cal studies covering small areas of the fold EHOWGLGQRWDOORZGRFXPHQWDWLRQRI WKH basin-scale alluvial architecture up to date. 7KHDLPRIWKLVVWXG\ZDVWRGRFXPHQW WKHVSDWLDOYDULDWLRQLQWKHVHGLPHQWRORJ\ ÁXYLDODUFKLWHFWXUHDQGVWUDWLJUDSKLFHYR-OXWLRQ RI WKH &DVWLOOR )RUPDWLRQ EDVHG RQWKHDQDO\VLVRIVHYHUDOVWUDWLJUDSKLFDO VHFWLRQVDQGDUFKLWHFWXUDOGDWDRIÁXYLDO channels obtained from a basin-boun- GDU\DUHDWRWKHWKLFNHVWH[SRVHGGHSRFHQ-tre. Having this goal in mind, the authors aim to improve understanding of the main forcing-factors controlling the sedimen-WDU\ HYROXWLRQ RI YROFDQLFODVWLF VXFFHV-sions preserved in peri-volcanic basins.

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The Golfo San Jorge basin is a domi- QDQWO\H[WHQVLRQDOEDVLQIRUPHGDVDUHV-SRQVHWRWKHEUHDNXSRIWKH*RQGZDQD

Figure 1: a) Location map and VWUDWLJUDSK\ RI WKH *ROIR 6DQ Jorge basin (ages after Bridge et al. 2000). The dotted line PDUNVWKH&UHWDFHRXVERXQGDU\ of the Golfo San Jorge basin. The boxed area indicates the location of the San Bernardo )ROG %HOW E 6LPSOLÀHG JHROR-gical map of the San Bernardo )ROG%HOWVKRZLQJWKHORFDWLRQ of measured outcrop sections (encircled numbers) and other outcrop sections referred to in the text, main localities and ac-cess roads.

supercontinent during the Jurassic and (DUO\&UHWDFHRXVDQGVXSHULPSRVHGRQ WKH3DOHR]RLFFRQWLQHQWDOFUXVW%DUFDWHW DO7KHLQÀOORIWKHEDVLQVWDUWHG GXULQJWKH0LGGOHWR8SSHU-XUDVVLF)LJ ZLWKGHSRVLWLRQRIDWKLFNVXFFHVVLRQ GRPLQDWHGE\EDVDOWVULROLWHVDQGLJQLP-EULWHVNQRZQDV/RQFR7UDSLDORU%DKtD /DXUD*URXSV/HVWDDQG)HUHOOR representing the climax of the rift event WKDWOHGWRWKHIUDJPHQWDWLRQRI*RQGZD-na in southern South America. A second H[WHQVLRQDOHYHQWWRRNSODFHLQWKHXSSHU-PRVW-XUDVVLFDQG(DUO\&UHWDFHRXVZLWK the conformation of E-W, NNW-SSE or 1(6: VWULNLQJ KDOIJUDEHQV ÀOOHG E\ EODFN VKDOHV DQG FRDVWDO ZHGJHVKDSHG VDQGVWRQHERGLHVRIODFXVWULQHRULJLQ)L-gari HWDOWKHVWUDWDFRPSRVHGWKH /DV+HUDV*URXSRQO\SUHVHUYHGLQWKH subsurface of the basin.

The initial Patagonidic tectonic pha-se (compressional) in the Andean Ran-JHV SURGXFHG WKH HDVWZDUG VKLIWLQJ RI the main depocentres of the basin over DUHJLRQDOXQFRQIRUPLW\DQGWKHLQFRU-SRUDWLRQRIODUJHYROXPHVRIS\URFODVWLF detritus. At the same time, the genera-WLRQRIQHZ:1:(6(WR(:VWULNLQJ normal faults (Uliana HWDO&KHORWWL 3DUHGHVHWDO 2013) resulted in the

creation of accommodation space for the deposition of the Chubut Group (Barre- PLDQWR&DPSDQLDQ"LQÁXYLDODQGODFXV-trine environments (Hechem HWDO 1990, +HFKHPDQG6WUHONRY7KH&KXEXW *URXSLVFRQIRUPHGE\ÀYHFRQWLQHQWDO IRUPDWLRQV3R]R'0DWDVLHWH&DV-tillo, Bajo Barreal and Laguna Palacios )RUPDWLRQV ,QLWLDO VHGLPHQWDWLRQ RFX-UUHGLQDZLGHO\GLVWULEXWHGODFXVWULQHXQLW 3R]R')RUPDWLRQ%DUUHPLDQWR $SWLDQZKLFKZDVVRXUFHGIURPWKHQRU- WKE\ÁXYLDOV\VWHPVNQRZQDV0DWDVLH-WH)RUPDWLRQ6FLXWWR3DUHGHVHWDO

2003 and Paredes HWDO%RWKXQLWV DUH FRYHUHG E\ WKH &DVWLOOR )RUPDWLRQ $OELDQZKLFKVKRZVDODUJHSURSRUWLRQ RI UHZRUNHG S\URFODVWLF URFNV PDLQO\ SUHVHUYHGLQÁXYLDOHQYLURQPHQWV/HVWD /HVWDDQG)HUHOOR3DUHGHVHW DO7KH&DVWLOOR)RUPDWLRQLVFRYH-UHGE\WKHÁXYLDO%DMR%DUUHDO)RUPDWLRQ 6HQRPDQLDQWR&DPSDQLDQ"ZKLFKKDV WZRPHPEHUVWKH/RZHU0HPEHUZKR-VHRXWFURSVDUHFRPPRQO\FRPSRVHGRI FKDQQHOHG VDQGVWRQHV LQWHUEHGGHG ZLWK WKLFNHUDQGÀQHUJUDLQHGYHU\ÀQHVDQG VL]HWXIIDFHRXVVWUDWDWKH8SSHU0HP-EHULVFRPSRVHGE\JUH\PXGVWRQHVZLWK isolated channel sandbodies (Sciutto )LJDULHWDO5RGULJXH] 8PD]DQRHWDOD7RZDUGWKHEDVLQ PDUJLQWKH8SSHU0HPEHURIWKH%DMR %DUUHDO)RUPDWLRQLVODWHUDOO\UHSODFHGE\ WKH/DJXQD3DODFLRV)RUPDWLRQ6FLXWWR  *HQLVHHW DO  *HQLVH HW DO ZKLFKLVFKDUDFWHUL]HGE\WKHVWDF-NLQJRIS\URFODVWLFSDOHRVRLOVDQGPLQRU channels. The Chubut Group contains WKHPDLQVRXUFHURFN3R]R')RU-mation) and oil reservoirs of the basin &DVWLOOR DQG %DMR %DUUHDO )RUPDWLRQV DQGLWPDLQO\FURSVRXWLQWKH6DQ%HU-QDUGR)ROG%HOWZKLFKZDVIRUPHGDVD result of the tectonic inversion of exten-VLRQDO GHSRFHQWUHV GXULQJ WKH 7HUWLDU\ (Peroni HWDO 1995, Homovc HWDO 1995). 7KH 3DOHRFHQH VHGLPHQWDWLRQ )LJ  LV IRUPHG E\ WKH PDULQH 6DODPDQFD )RU-mation and the continental Rio Chico *URXS7KHUHPDLQLQJRI WKH&HQR]RLF VXFFHVVLRQ LV FRPSOHWHG ZLWK WKH 6DU- PLHQWR*URXS&KHQTXH)RUPDWLRQ6DQ- WD&UX])RUPDWLRQDQGJODFLRÁXYLDOJUD-YHOVWUDWDRI 3OLR3OHLVWRFHQHDJHNQRZQ as “Rodados Tehuelches".

Castillo Formation: previous studies 'HSRVLWVRIWKH&DVWLOOR)RUPDWLRQ/HV- WDDQG)HUHOORUHFHLYHGWKHHDUO\GH-QRPLQDWLRQRI´*UHHQ7XIIVµ)HUXJOLR DQGWKH\DUHHTXLYDOHQWWRWKH´0L- QDGHO&DUPHQµ)RUPDWLRQLQWKHVXEVXU-IDFHRIWKHEDVLQ/HVWD$YDLODEOH radiometric ages suggest that the Castillo )RUPDWLRQUDQJHVIURPWR0D VSDQQLQJ DERXW  0\U %ULGJHHW DO

7KH&DVWLOOR)RUPDWLRQDVDZKR- OHLVXSWRPWKLFNLQWKHVXEVXU-IDFHRIWKHEDVLQ)LW]JHUDOGHWDO DQG LW WKLQV QRUWKZDUGV IURP P WR aPRYHUFDNPLQWKHRXWFURSVRI WKH6DQ%HUQDUGR)ROG%HOW)LJ7KH XQLWVKRZVJUDGXDOWKLFNQHVVYDULDWLRQV and a centripetal distribution at

regional-VFDOH)LW]JHUDOGHWDO 1990) suggesting a

thermal (post-rifting) mechanism of sub-VLGHQFHDOWKRXJK)LJDULHWDO (1999)

ha-YHUHFRJQL]HGDQHSLVRGHRIH[WHQVLRQDO reactivation during the initial stages of GHSRVLWLRQRIWKH&DVWLOOR)RUPDWLRQ 3LRQHHURXWFURSEDVHGVWXGLHVZHUHGH-YHORSHG E\ RLO JHRORJLVWV :LQGKDXVHQ )HUXJOLRLQWKH6DQ%HUQDUGR )ROG%HOWZKHUHWKH&DVWLOOR)RUPDWLRQ LVWKHPRVWZLGHO\H[SRVHGXQLW6FLXWWR ZDVDEOHWRUHFRJQL]HDORZHU´VHF-WLRQµFRPSRVHGE\WXIIEHGVZLWKPLQRU proportion of epiclastic material and an upper “section” consisting of tuff beds and sandstone bodies. Hechem HW DO  LQWHUSUHWHG WKH ORZHU ´VHFWLRQµ as lacustrine and the upper “section” as GHSRVLWHGE\PHDQGHULQJÁXYLDOV\VWHPV 7KHWKLFNHVWH[SRVXUHRIWKHXQLWP outcrops in the Codo del Senguerr anti-FOLQHDQG0HFRQLLQWHUSUHWHGLWV GHSRVLWVDVUHODWHGWRDEUDLGHGÁXYLDOV\V-WHPZLWKVKHHWDQGULEERQJHRPHWULHV$ UHYLHZRIWKHXSSHUSDUWRIWKDWVHFWLRQ aPZDVFDUULHGRXWE\%ULGJHHWDO

 ZKR LGHQWLÀHG PDLQO\ VLQJOH RU PXOWLVWRUH\ ORZVLQXRVLW\ VDQGERGLHV GUDLQLQJ WR WKH 6( ž ZLWK D PHDQ WKLFNQHVVRIPDODWHUDOH[WHQVLRQRI PDQGD:LGWK7KLFNQHVVUDWLRRI Q $UHJLRQDOUHYLHZRIWKH&DVWLOOR )RUPDWLRQZDVFDUULHGRXWE\8OLDQDDQG /HJDUUHWDLGHQWLI\LQJWKUHHPDLQ groups of environments in the basin: the RXWFURSVRIWKH6DQ%HUQDUGR)ROG%HOW ZHUHDVVLJQHGWRPXOWLVWRUH\RUHSKHPH-UDOÁXYLDOV\VWHPVLQVWHDGWKRVHRIWKH VXEVXUIDFHRIWKHEDVLQZHUHLQWHUSUHWHG DVKLJKVLQXRVLW\ÁXYLDOV\VWHPVDQGOD- FXVWULQHHQYLURQPHQWV)LJ7KHH[- SRVXUHVRIWKH&DVWLOOR)RUPDWLRQDW&H-UUR&RORUDGRGH*DOYHQL]PWKLFN DQG 3XHUWD GHO 'LDEOR P DOORZHG 8PD]DQRHWDOEDQG8PD]DQRHW DOWRFDUU\RXWDVHPLTXDQWLWDWLYH

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stage during the deposition of the Casti-OOR)RUPDWLRQ,QWKH&HUUR&RORUDGRGH *DOYHQL]ORFDWLRQLQ)LJWKHVWDFNLQJ SDWWHUQVDQGWKHDOOXYLDORUJDQL]DWLRQZH-UHOLQNHGSUREDEO\WRWHFWRQLFDFWLYLW\DQG QRFKDQJHVZHUHUHFRJQLVHGLQWKHFOLPDWH RI WKHVWXG\DUHD8PD]DQRHWDO 2012).

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Figure 2:,VRSDFKPDSRIWKH&DVWLOOR)RUPDWLRQLQWKH6DQ%HUQDUGR)ROG%HOWDQGVXUURXQGLQJDUHDV DQGRIWKHDJHHTXLYDOHQW0LQDGHO&DUPHQ)RUPDWLRQLQWKHVXEVXUIDFH)LW]JHUDOGHWDO0DLQ GHSRFHQWHUVDUHORFDWHGLQWKHHDVWHUQSDUWRIWKHEDVLQZKHUHPDMRUWKLFNQHVVFKDQJHVDUHUHODWHGWRIDXOW UHDFWLYDWLRQ*HQHUDOGLVWULEXWLRQRIHQYLURQPHQWVEDVHGRQ8OLDQDDQG/HJDUUHWD7KHS\URFODVWLF PDWHULDOZDVSURYLGHGIURPWKH$QGHDQ5DQJHVORFDWHGaNPZHVWZDUGRIWKH6DQ%HUQDUGR)ROG %HOW7KHHQFLUFOHGQXPEHUVPDWFKWKRVHLQ)LJ 5DPVD\XVLQJDGHFOLQDWLRQRIž( 7ZRGLPHQVLRQDOSDQHOVRIPXOWLVWRUH\ ÁXYLDOFKDQQHOVRUVKHHWÁRRGFRPSOH[HV include information of bounding surfa-FHV FURVVVHFWLRQDO JHRPHWU\ LQWHUQDO lithofacies and bedding architecture to depict lateral and vertical lithofacies re-ODWLRQVKLSV7KHUHDOGLPHQVLRQVZLGWK WKLFNQHVVDQGZLGWKWKLFNQHVVUDWLRRI LQGLYLGXDORUPXOWLVWRUH\FKDQQHOVZHUH measured using GPS point data in their margins, and correcting their apparent ZLGWKXVLQJWKHPHDQRIWKHSDOHRFXUUHQW GDWDIRUHDFKFKDQQHO7KHUHDOZLGWK WKLFNQHVV UDWLR RI ÁXYLDO FKDQQHOV KH-UHDIWHU DEEUHYLDWHG DV :7K ZDV RE-tained and plotted in log-log diagrams. 7KLFNQHVVGDWDRILQGLYLGXDOÁXYLDOFKDQ- QHOVIURPHDFKVWXG\ORFDWLRQDUHSUHVHQ- WHGDQGVWDWLVWLFDODQDO\VHVRIWKHPHD-VXUHPHQWV DUH SURYLGHG *HRPHWU\ RI ÁXYLDO FKDQQHOV ZHUH EURDGO\ FODVVLÀHG DV ULEERQV :7K QDUURZ VKHHWV !:7K DQG EURDG VKHHWV : 7K! IROORZLQJ )ULHQGHW DO 

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7KH&DVWLOOR)RUPDWLRQLVDÁXYLDOVXFces- VLRQPDLQO\FRPSRVHGRIUHZRUNHGS\UR-clastic sediments, and it consists of tuffa-ceous gravels, tuffatuffa-ceous sandstones and WXIIDFHRXVPXGVWRQHVLQWHUFDODWHGZLWK DVKIDOO WXIIV %DVHG RQ WKHLU OLWKRORJ\ JUDLQVL]H VHGLPHQWDU\ VWUXFWXUHV JHR- PHWULHVDQGERXQGDULHVZHKDYHLGHQWL-ÀHGÀIWHHQOLWKRIDFLHV$EULHIVXPPDU\ RIWKHLUPDLQDWWULEXWHVÁRZSURSHUWLHV and interpretation is presented in Table DQGW\SLFDOIHDWXUHVDUHVKRZQLQ)LJ  0HWHUVFDOH DUFKLWHFWXUDO HOHPHQWV HTXLYDOHQW WR OLWKRIDFLHV DVVRFLDWLRQV %ULGJH D UHFRUG VKRUWWHUP SK\-VLFDOSURFHVVHV0LDOOSURYLGLQJD basis for understanding the nature of the GHSRVLWLRQDOV\VWHP6L[PDLQOLWKRIDFLHV DVVRFLDWLRQVRFFXULQWKHÁXYLDOVXFFHV-sion, their descriptive aspects and inter-SUHWDWLRQV DUH JLYHQ EHORZ 7KH PDLQ lithofacies associations are interpreted DVLVXEDHULDOÁRRGSODLQVDQGHSKHPH-UDOSRQGVLLSUR[LPDOÁRRGSODLQVZLWK WKUHH VXEW\SHV FUHYDVVHVSOD\ RYHU-EDQN ÀQHV DQG FUHYDVVH FKDQQHOV LLL ORZVLQXRVLW\RUEUDLGHGÁXYLDOFKDQQHOV LYVKHHWÁRRGGHSRVLWVYVXEDHULDOGH-EULVÁRZGHSRVLWVDQGYLUHZRUNHGDVK fall beds. The names of the lithofacies associations and individual lithofacies, DOWKRXJKSDUWO\LQWHUSUHWDWLYHZHUHFKR-VHQGHOLEHUDWHO\LQRUGHUWRVLPSOLI\WKH

IROORZLQJGLVFXVVLRQ,QWHUPVRIIDFLHV DQGGHSRVLWLRQDOSURFHVVHVRXUÀQGLQJV expand the results of Paredes HWDO (2009) DQG8PD]DQRHWDO (2012) in relation to

ODUJHSDUWRIWKH6DQ%HUQDUGR)ROG%HOW ,QWKLVFRQWH[WVLJQLÀFDWLYHFKDQJHVLQ the proportion of the different facies as- VRFLDWLRQVZHUHREVHUYHGDORQJWKHH[SR-VXUHVLPSO\LQJLQWUDEDVLQYDULDELOLW\LQ ÁXYLDOG\QDPLFV'HWDLOHGVHGLPHQWROR- JLFDOVHFWLRQVZLWKLQGLFDWLRQRIIDFLHVDV-VRFLDWLRQVDUHVKRZQLQ)LJ

LA1. Tabular tuffs and reworked tuffs: VXEDHULDO ÁRRGSODLQV DQG HSKHPHUDO ponds

'HVFULSWLRQ This lithofacies association

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Figure 3: Regional strati-graphic cross-section of the &DVWLOOR )RUPDWLRQ LQ WKH 6DQ%HUQDUGR)ROG%HOW'D-tum is the top of the Castillo )RUPDWLRQ 'UDLQDJH ZDV PRVWO\ WR WKH HDVWVRXWKHDVW in the southern regions, and to the south-southeast in the northern areas. The north is DWWKHWRSRI WKHSDJH)RXU main Regions (e.g. Region 1 WRFDQEHGHÀQHGRZLQJWR WKH SUHVHUYHG WKLFNQHVV DQG characteristics of the unit. 7KH ODFN RI  GHWDLO LQ ÀQH grained lithologies of the Pa-pelía anticline section is due WREDGTXDOLW\RI H[SRVXUHV 6HHÀJXUHVDQGIRUORFD-tion of the sec6HHÀJXUHVDQGIRUORFD-tions.

TABLE 1:/LWKRIDFLHVLGHQWLÀHGLQWKH&DVWLOOR)RUPDWLRQ

LF1: Massive, matrix supported conglomeratates and tuffaceous sandstones: Individual beds are up to 1 m thick and have planar or slightly erosive base, sheet-like or ribbon geometry and bimodal grainsize. Coarse to medium-grained tuffaceous sandstones contain outsized clasts up to 20 cm in size. Elongate clasts could be vertically-oriented. Ungraded throughout the bed or coarse-tail normally graded at lowermost part and ungra-ded at upper part.

LF2: Fine conglomerates and tuffaceous sandstones, inversely graded: Individual beds are several cm thick and show planar or gradational base. They show matrix or clast-supported framework and lack of sedimentary structures. Upward increase in the content of tuffaceous and/or pumice clasts. Broken or low-rounded clasts are common.

LF3: Medium- to fine-grained tuffaceous sandstones with antidune bedding: Planar or gradational base, fre-quently interbedded with plane-laminated, fine tuffaceous sandstones. Dome-shaped stratification with stee-per dipping stoss-than-lee side (12º and 8º). Amplitudes of 0.2-0.4 m and wave lengths of 1-3 m.

LF4: Parallel-laminated tuffaceous conglomerates and sandstones: Planar base, laminae are few mm to 1 cm in thick, with gradational contacts between laminae and occasional outsized clasts. Horizontal lamination or crude, horizontal bedding, defined by changes in the grain size. Frequently interbedded with low-angle cross bedding and massive sandstones.

LF5: Low angle cross-bedded tuffaceous gravels and sandstones: Erosive or planar base. Moderate grain size selection, occasionally with fining upward trend from coarse to fine sandstones. Sets are < 0.5 m thick and 1-4 m of lateral extent. Foresets dip less than 10º. Individual laminae show plane-parallel lamination. Could contain a tuffaceous gravel lag in the base of the set. Interbedded with massive, plane-laminated and trough cross-bedded strata. Trunk remains.

LF6: Trough cross-bedded tuffaceous gravels and sandstones: Planar to slightly curved and erosive base, tuffa-ceous clasts are poorly-to-well rounded. Clast-supported framework. Cross-bedding range from 0.2 to 1 m in thickness, sets dip from 15º to 25º, they are fining upward, but many sets are poorly organized.

LF7: Planar cross-bedded tuffaceous gravels and sandstones: Planar or erosive base, with clast supported framework. Moderate to well rounded clasts. Individual sets are 0.2 to 0.8 m thick, internally ungraded or that fine upward. The dip of foresets is between 16º-23º. Could contain trunk remains.

LF8: Medium-to-fine tuffaceous sandstones with asymmetrical ripples: Planar or gradational base, asymmetri-cal ripples present straight crest lines and are 2-5 cm in amplitude and 5-15 cm in wavelength. Ripples could preserve the lee and stoss side. Rare plant remains and Planolites traces on bedding surfaces.

LF9: Gravels and tuffaceous sandstones with convex-up top: Planar lower and upper contact with finer litho-facies, tabular or double-wedge shape. Individual bodies are 0.2-0.7 m and 15-40 m in length. Strata can be massive, or they could contain parallel lamination and low angle cross bedding. Planolites and Skolithos fossil traces on bedding surfaces, and grey mottling.

LF10: Massive, medium-to-fine tuffaceous sandstones. Gradational to sharp base from other sandstone-domi-nated lithofacies (e.g. LF8, LF6, LF5 is common). Preserved in upper reaches of set of strata with fining-upward trend or on top of multistory sandbodies. Massive appearance is due to the presence of near-vertical to hori-zontal burrows and trails of Planolites, Palaeophycus and Skolithos.

LF11: Tabular, massive or laminated tuffs: Planar base, extension of thousand of meters with gradual variations in thickness. Strata are massive, but could contain parallel lamination, pumice clasts or tuffaceous fragments. Could show small trunks, plant remains, roots and desiccation cracks on bedding surfaces. Common Planolites, Skolithos, Palaeophycus fossil traces. Scattered to densely-packed, core-type accretionary lapilli beds, aggre-gated are 3-7 mm in diameter or have oval shape.

LF12: Tabular, laminated tuffs with asymmetrical ripples: Planar base and tabular geometry, strata are finely laminated and contain straight-crest ripples of 0.5-1 cm in amplitude and 3-7 cm in wavelength. Organic debris and mudcracks can be found. Common Planolites, Skolithos, Palaeophycus and Taenidium fossil traces.

LF13: Fine, massive tuffs with lenticular geometry: Planar base on tabular tuff beds. Strata are < 0.5 m thick and several meters width, composed by clay-sized particles and internally ungraded. Frequently interbedded with plane-laminated and low angle cross-bedded tuffs. Could contain pumice clasts and tuffaceous, outsized clasts.

LF14: Plane-laminated, fine tuffs with lenticular geometry: Planar base. Strata range from few cm to several tens of cm. Laminae is < 5 mm thick, but changes in the thickness laminae into the same strata are common, as well as inverse grading. Could contain pumice outsized clasts interbedded parallel to the planar lamination. Frequent low-angle truncations of laterally extensive laminae.

LF15: Low angle cross-bedded tuffs with lenticular geometry: Erosive or planar base. Sets are < 0.3 m thick and 1-3 m of lateral extent and present asymptotic base. Individual laminae are unstructured and ungraded, with gradational contacts between coarse and fine strata. Foresets dip less than 10º. Frequently Interbedded with massive or plane-laminated beds.

Volcaniclastic, cohesive debris flow: lahar. (Coussot and Meunier 1996, Dasgupta 2003). Bulking from initial tur-bulent flow and rapid deposition from suspension (Smith and Lowe 1991).

Inverse grading is due to kinematical sieving (Segschnei-der et al. 2002) in a high-particle concentration flood-flow.

Migration of antidunes under upper-flow regime condi-tions. (Alexander and Fielding 1997).

Hyperconcentrated flood flow, aggradation in upper-flow regime conditions developed in very shallow water depth (Tunbridge 1981, Tooth 1999).

Migration of low-relief bedlforms with high wavelength/ amplitude ratio. Upper flow regime (flash flood) or lower flow regime (downstream accretion of bedforms, Miall 1996). Hyperconcentrated flood flow (Smith 1987a).

Migration of sinuous-crested dunes in mobile channels or infilling of scours (Bridge 1993a, Miall 1996, Todd 1996).

Migration of straight-crested dunes in mobile channels (Miall 1985) or avalanching processes in lateral, transver-se or medial bars (Todd 1996).

Migration of small bedforms by dilute flows in lower flow regime with turbulent behavior.

Transportation in dune to upper plane bed flow condition. Rapid deposition by deceleration of turbulent flows as a crevasse splay (Smith et al. 1989, Farrell 2001). Incipient paleosol development.

Disruption of the sediment by burrowing organisms due to exposition of braid-lateral-longitudinal bars during low-stages flood flows or abandonment of channels.

Ash-fall deposits on extensive lowland areas (Cas and Wright 1987). Subaerial, inmature paleosol.

Reworking of ash-beds in ephemeral ponds. Subaqueous paleosol.

Reworking of pyroclastic material in fluvial channels. La-minar flood-flow conditions (Dasgupta 2003).

Upper-flow regime conditions and high-bedload concen-trations in fluvial channels (Tunbridge 1989, Bridge and Best 1997). Some beds represent very shallow (< 2 cm) water depth.

Hyperconcentrated flood flow (Smith 1987a). Migration of low-amplitude, long-wavelength dunes in ash-reworked fluvial channels (Zanchetta et al. 2004). Upper and lower flow regime conditions.

Taenidium and insect pupation cham-EHUV ZHUH LGHQWLÀHG 3DWFKHV RI SODQH ODPLQDWHG WXIIV OLWKRIDFLHV /) ZHUH found. Strata could also contain vertica-OO\RULHQWHGUKL]ROLWKVXSWRPGHHS SDOHJUH\PRWWOLQJRUGHVLFFDWLRQFUDFNV RQEHGGLQJVXUIDFHV5KL]ROLWKV.ODSSD DUHIUHTXHQWO\UHSODFHGE\LURQR[L-GHVZLWK\HOORZEURZQFRORXUWKH\VKRZ JUH\DQGUHGULPVZLWKFLUFXODUFURVVVHF- WLRQV)LJN3DOHRVRLOVVKRZQRGHYH- ORSPHQWRIDQ\W\SLFDORUGLDJQRVWLFKR-UL]RQEXWLQWKH6LHUUDGHO&DVWLOORDQG QRUWKZDUGH[SRVXUHVWKHSUHVHQFHRIFDU-ERQDWHFRQFUHWLRQVLVUHODWLYHO\FRPPRQ (Bellosi HWDO 2002). Interbedded sandsto-nes and tuffs preserved in the Sierra del Castillo contain internal moulds of mo-OXVNVRIWKH&XUELFXORLGHD6XSHUIDPLO\ and gastropods that belong to Vivipa-ULGDH )DPLO\ &DHQRJDVWURSRGD DQG WR 3K\VLGDH3XOPRQDWD/D]RHWDO 2011).

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ocurrence of Taenidium isp. is attributed WR WKH GLVSODFHPHQW RI ZRUPV LQ GULHG VXEVWUDWHV %URPOH\  0LQWHUHW DO

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could contain parallel-lamination (lithofa- FLHV/)7KHFRDUVHUJUDLQHGFRPSR-QHQWUDQJHVIURPFPXSWRFPWKLFN PRVWO\ IRUPLQJ ÀQLQJXSZDUG VHTXHQ-ces of parallel-laminated or cross-bedded VWUDWDOLWKRIDFLHV/)/)/)/)7D- EOH,ZLWKRFFDVLRQDOSUHVHUYDWLRQRIDV-\PPHWULFDOULSSOHVDWWKHLUWRSVOLWKRIDFLHV /) DQG EXUURZLQJ OLWKRIDFLHV /) The sandstone and tuff alternations occur in three distinctive arrangements: (a) tuffa-ceous sediments and sandstone bodies can GLVSOD\DVKHHWOLNHJHRPHWU\ZLWKPHGLXP WR ÀQHJUDLQHG VDQGERGLHV RI SODQH ED- VHDQGFRQYH[XSZDUGWRS)LJJLQWH-JUDWHGE\OLWKRIDFLHV/)/)/)DQG

UDUHO\E\OLWKRIDFLHV/)EWKLQO\ODPL-nated (1 cm to 10 cm) alternations of non-HURVLYH VKHHWOLNH VDQGVWRQH OLWKRIDFLHV /)/)DQGWXIIDOWHUQDWLRQVWKDWWKLF- NHQXSZDUGLQYHUWLFDOVHFWLRQVDQGFWD-EXODUWXIIEHGVOLWKRIDFLHV/)ORFDOO\ GLVVHFWHGE\FRDUVHWRÀQHJUDLQHGVDQGV-WRQHVZLWKHURVLYHFRQFDYHXSZDUGEDVDO ERXQGDU\DQGULEERQJHRPHWU\LQWHJUDWHG E\OLWKRIDFLHV/)/)DQGUDUHO\E\OLWKR-IDFLHV/)

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VHGLPHQWVXSSO\WRWKHÁRRGSODLQOLNHO\ DVVRFLDWHGWRÁRRGV/REDWHERGLHVZHUH GHSRVLWHGIURPXQFRQÀQHGÁRZVGXULQJ high-discharge events (Smith HWDO DVFUHYDVVHVSOD\V0DVVLYHVDQGVWRQHDO- VRHYLGHQFHVUDSLGGHSRVLWLRQ7KLQO\OD-minated sandstone and tuff beds repre-VHQW RYHUEDQN VHGLPHQWDWLRQ LQ ZKLFK FRDUVHQLQJXSZDUG VXFFHVVLRQV UHÁHFW WKH LQFUHDVH LQ WKH LQYROYHG ÁRZV DUUL-YLQJDWDORZHQHUJ\HQYLURQPHQW6PLWK

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related to the increase in the distance to DPDLQÁXYLDOFKDQQHORUWKHJUDGXDOGH-FUHDVHLQWKHÁRZFRQGLWLRQV-RQHVDQG +DMHN6FRXUHGEDVHGVDQGERGLHV are interpreted as crevasse channels, for-med as a result of the crevassing of a ma-MRUULYHUFKDQQHO&ROHPDQ0MRVHW DO)DUUHOO

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in-FOXGHV SRRUO\VRUWHG FRQJORPHUDWHV DQG YHU\ FRDUVH WR ÀQHJUDLQHG VDQGVWRQH EHGV WKDW FRQIRUP XQJUDGHG RU ÀQLQJ XSZDUG VXFFHVVLRQV XS WR  P WKLFN The base of this lithofacies association is a FKDQQHOVKDSHGVFRXUVXUIDFHXSRQZKLFK SHEEOHWRFREEOHVL]HGFODVWVXSWRFP DUHFRQFHQWUDWHG7KHLQÀOORIWKLVOLWKRID-FLHVDVVRFLDWLRQHLWKHUFRQVLVWRIDXQLTXH FKDQQHO ÀOO VXFFHVVLRQ ZLWK  P WKLFN DQGPZLGHRUDQXPEHURIQHV-WHGFKDQQHOÀOOVWKDWDUHXSWRPWKLFN DQGaPZLGHVHSDUDWHGHDFKRWKHUE\ VFRXUVXUIDFHV)LJF6WUDWDDUHSRRUO\ VRUWHGDQGFRQWDLQPDLQO\ORZDQJOHDQG WURXJKFURVVEHGGLQJV)LJG/)DQG /)UHVSHFWLYHO\SDUDOOHOODPLQDWLRQOL WKRIDFLHV /) DQG PLQRU SODQDU FURVV EHGGLQJ OLWKRIDFLHV /) $W WKH EDVH OLWKRIDFLHV/)FDQEHIRXQG8SSHUUHD-ches of the sandbodies can contain trails, URRWWUDFHVPRWWOLQJDQGEXUURZVOLWKR- IDFLHV/)%XUURZVDUHVLPSOHDQGXQ-EUDQFKHG 7KH\ KDYH XQOLQHG ZDOOV DQG VKRZPDVVLYHRUPHQLVFDWHÀOOV3DOHRFX-UUHQWPHDVXUHPHQWVLQVLQJOHFKDQQHOÀOOV DUHXQLPRGDODQGJHQHUDOO\VKRZORZGLV-SHUVLRQDURXQGWKHPDLQYHFWRU $OWKRXJKPDQ\VDQGERGLHVODFNRIFOHDU macroscale inclined strata set (VHQVX Brid-JHEWZRPDLQW\SHVRIODUJHVFDOH ORZDQJOHLQFOLQHGERXQGLQJVXUIDFHVZH-UH LGHQWLÀHG LQ QRUPDO YLHZV WR WKH SD-OHRFXUUHQW GLUHFWLRQV RI FKDQQHOÀOOV L 7KH PRVW FRPPRQ W\SH FRQVLVWV RI VH-YHUDOLQFOLQHGVXUIDFHVƒXSWRP WKLFNDQGPZLGHGHÀQLQJVDQGVWRQH ERGLHVRIOREDWHJHRPHWU\SUHVHUYHGRQD VLQJOHPDUJLQRIWKHFKDQQHOÀOOV)LJ ZLWKORZDQJOHGLSVƒWRDVVRFLDWHG FURVVEHGGHGVWUXFWXUHVDQGLLFRQYH[ XSZDUG ERXQGLQJ VXUIDFHV XS WR  P WKLFNDQGPZLGHWKDWGLSLQRSSRVLWH

GLUHFWLRQWRZDUGDGMDFHQWFKDQQHOÀOOVRQ ERWKVLGHVODUJHVFDOHERXQGLQJVXUIDFHV have high-angle dips (>65) to the paleocu-UUHQWVREWDLQHGIURPWKHFKDQQHOÀOOV

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7KH LQÀOOLQJ VW\OHV RI  WKH ÁXYLDO FKDQ-QHOVDOORZXVWRUHFRJQL]HLVLQJOHWKUHDG FKDQQHOÀOOVLQWHUSUHWHGGXHWRWKHODFN of internal erosion surfaces and the uni-IRUPLW\RI FURVVVHWVRI WKHFKDQQHOÀOOV Figure 6: )HDWXUHVRIWKHSUR[LPDOÁRRGSODLQDQGÁXYLDOFKDQQHOOLWKRIDFLHVDVVRFLDWLRQV7KLFNHQLQJXSZDUGDOWHUQDWLRQRIWXIIDFHRXVVWUDWDDQGÀQHJUDLQHG

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WKDQWKHUHVXOWLQJFKDQQHOVDQGERG\ 7KH ÁXYLDO FKDQQHO OLWKRIDFLHV DVVRFLD- WLRQFDQDOVREHFKDUDFWHUL]HGE\LWVLQ-WHUQDO DUFKLWHFWXUH LQ L ORZVLQXRVLW\ ÁXYLDO FKDQQHOV LQWHUSUHWHG GXH WR WKH SUHVHUYDWLRQ RI GRZQVWUHDP PLJUDWLQJ macroforms located in the margin of the

DFWLYHFKDQQHOÀOOVDQGORZSDOHRFXUUHQWV spread in individual channels, that su- JJHVWUHODWLYHO\VWUDLJKWÁRZSDWKVSURYL-GLQJHYLGHQFHIRUWKHORZVLQXRVLW\RIWKH channels (Bridge HWDO 2000). The absence of lateral accretion surfaces also implies WKDW WKH FKDQQHOV ZHUH ODWHUDOO\ VWDEOH Figure 7: Schematic representation of a PXOWLVWRUH\ ORZVLQXRVLW\ ÁXYLDO FKDQ-nel (Codo del Senguerr anticline sec-WLRQ 7KH ORZHU SDFNDJHV VKRZ VHYHUDO large-scale inclined surfaces at bases of FRDUVHJUDLQHG VWRULHV WKDW ÀQH XSZDUG 7KHXSSHUSDUWRIWKHFKDQQHOÀOOVKRZV DVOLJKWO\DJJUDGLQJVLQJOHFKDQQHOVWDJH ZLWK ZHOO GHYHORSHG DOWHUQDWH EDUV $% DQGÀQHUJUDLQVL]H3DOHRÁRZUHDGLQJLV UHSUHVHQWHGE\HQFLUFOHGDUURZV7KHQRU-WKLVDWWKHWRSRIWKHÀJXUH7KHGHWDLOHG YHUWLFDO VHFWLRQ LQVHW VKRZV D W\SLFDO OLWKRIDFLHVVXFFHVVLRQRIWKHÁXYLDOFKDQ-nel lithofacies association.

)LJXUH  /LQH GUDZLQJ RI  D VKHHWÁRRG FRPSOH[ &R-do del Senguerr anticline section). Individual laminae FDQ EH WUDFHG ODWHUDOO\ IRU PHWHUVDQGWKH\FDQEHDVVR-FLDWHG ZLWK ORZ DQJOH FURVV EHGGLQJ /RZ UHOLHI VFRXU VXUIDFHV VHSDUDWH SDFNDJHV ZLWK GLIIHUHQFHV LQ JUDLQVL]H and internal arrangement of VHGLPHQWDU\VWUXFWXUHV1RWH WKHORZGLVSHUVLRQLQWKHSD-leocurrent. The detailed ver-WLFDO VHFWLRQ LQVHW VKRZV D W\SLFDOOLWKRIDFLHVVXFFHVVLRQ RI WKHVKHHWÁRRGGHSRVLWV

(Bridge 2003), or that the regional depo- VLWLRQDOGLSZDVUHODWLYHO\LPSRUWDQW6H-FRQGO\LLEUDLGHGFKDQQHOVLQWHUSUHWHG E\WKHLGHQWLÀFDWLRQRIODWHUDOO\DGMDFHQW FKDQQHOÀOOVZLWKFRQYH[XSZDUGODUJH scale inclined strata, interpreted as braid bars (Bridge 2003). Braided sandbodies UHSUHVHQWDPLQRUSURSRUWLRQRIWKHÁX-vial channel lithofacies association. LA4. Parallel-laminated conglomera-WHVDQGVDQGVWRQHVVKHHWÁRRGV

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LV FRPSRVHG RI FRDUVH WR ÀQHJUDLQHG VDQGVWRQHEHGVWKDWDUHXSWRPWKLFN DQGPZLGH7KHEDVDOVXUIDFHFDQEH HLWKHUDVFRXUVXUIDFHFRYHUHGE\SHEEOH VL]HGFODVWVRUDQHDUO\ÁDWVXUIDFHWKDW ODFNVRIDEDVDOODJ)LJHDQG)LJK &RPPRQO\ DVVRFLDWHG OLWKRIDFLHV LQFOX-de coarse- to medium-grained sandstone EHGV ZLWK KRUL]RQWDO ODPLQDWLRQ OLWKR-IDFLHV/)DQGORZDQJOHFURVVEHGGLQJ OLWKRIDFLHV/)RQVFRXUVXUIDFHV)LJ 0DVVLYHFRDUVHJUDLQHGOHQVHVFRQV-WLWXWHG E\ ÀQH JUDYHO FODVWV OLWKRIDFLHV /) RU LVRODWHG RXWVL]HG SHEEOH FODVWV FDQEHIRXQG0RVWRIWKHVDQGVWRQHVWUD-WDDUHÀQHO\ODPLQDWHGZLWKGLIIHUHQFHV LQ JUDLQVL]H EHWZHHQ ODPLQDH DQG WKH\ FRXOGFRQWDLQYHU\ORZDQJOHVFRXUVXU- IDFHVWKDWVHSDUDWHSDFNDJHVZKHUHLQGL-YLGXDOODPLQDHFDQEHWUDFHGODWHUDOO\E\ VHYHUDOPHWHUV)LJI3DOHRÁRZGLUHF- WLRQVKRZVYHU\ORZGLVSHUVLRQRIPHD- VXUHPHQWV6W'ƒ/RFDOO\FRQYROX-te lamination and carbonaVXUHPHQWV6W'ƒ/RFDOO\FRQYROX-te concretions ZHUH REVHUYHG 0RVW RI WKH VKHHWOLNH sandbodies ( VHQVX)ULHQGHWDOGH-velop scouring at the bases and margins, DQG KDYH D ZLGWKWKLFNQHVV UDWLR EHW-ZHHQDQGEXWWKLQQHUVDQGERGLHV can be broad sheets (Gibling 2006) of SODQHEDVHZLWKDZLGWKWKLFNQHVVUDWLR RIXSWR&RPPRQO\WKHUHDUHEX-UURZVLQWKHXSSHUSDUWRIWKHVDQGERGLHV OLWKRIDFLHV/) ,QWHUSUHWDWLRQ6KHHWÁRRGGHSRVLWVUHFRUG WKHÁDVK\QDWXUHRIWKHGLVFKDUJHRIWKH ÁXYLDO V\VWHP WKURXJK GHSRVLWLRQ RI XQFKDQQHOL]HG ÁRRG ZDWHUV DFURVV WKH DOOXYLDOSODLQ)ULHQG*UDI 7KH GRPLQDQFH RI KRUL]RQWDO

ODPLQD-WLRQLQWKHLQÀOOUHÁHFWVGRPLQDQWEHG load transport (Hampton and Horton WKHRFFXUUHQFHRIVKDOORZKLJK HQHUJ\ÁRZFRQGLWLRQVDQGYHUWLFDODJ-JUDGDWLRQRIWKHVXEVWUDWH0F.HHHWDO  7XQEULGJH  7KH WUDQVSRUWD-WLRQRISDUWLFOHVWRRNSODFHLQDQXSSHU WRWUDQVLWLRQDOÁRZUHJLPHGXULQJKLJK GLVFKDUJH HYHQWV )LHOGLQJ  ZLWK PLQRUUHZRUNLQJDQGJHQHUDWLRQRIORZHU ÁRZUHJLPHVWUXFWXUHVOLWKRIDFLHV/) GXULQJZDQLQJÁRZV7KHODFNRIRWKHU W\SLFDO VHGLPHQWDU\ VWUXFWXUHV RI ORZHU ÁRZUHJLPHHJDV\PPHWULFDOULSSOHVLV GXHWRWKHJHQHUDOFRDUVHJUDLQVL]HRIWKH GHSRVLWV!PPEXWLWFRXOGDOVREH due to high concentration of coarse ash fragments carried in suspension into the ÁRZZKLFKFRXOGVXSSUHVVWKHÁRZVHSD-ration and reduce the turbulence (Allen DQG/HHGHU%ULGJHDQG%HVW Soft-sediment deformations indicate ra-SLG GHZDWHULQJ SUREDEO\ GXH WR TXLFN DFFXPXODWLRQ RI WKH VDQG $OOHQ  0RVW RI WKHLU IHDWXUHV DUH SUHVHUYHG LQ DFWXDOHSKHPHUDOÁXYLDOV\VWHPVLQDULG %URPOH\7RRWKRUVHPLDULG (Turbeville 1991) regions.

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FRPSRVHGE\FREEOHWRSHEEOHVL]HGWXIID-ceous conglomerates and sandstone beds XSWRPWKLFNDQGPHWHUVZLGHEXW PRVWRIWKHPDUHOHVVWKDQPWKLFNDQGD IHZWHQVRIPHWHUVZLGH7KH\IUHTXHQWO\ KDYHDVOLJKWO\LUUHJXODUWRSODQDUEDVH)LJ E7KHLQÀOORIWKHVHVDQGERGLHVLVPD-trix supported, it has a bimodal grainsi-]H GLVWULEXWLRQ DQG FRXOG VKRZ VOLJKWO\ ÀQLQJXSZDUGWUHQGV7KHPDWUL[LVFRP-SRVHG RI ÀQH WR PHGLXPJUDLQHG WXIID-FHRXVVDQGVWRQHVODUJHUFODVWVFRQVLVWLQJ RIYDULDEO\URXQGHGJUDYHOFODVWVUDQJLQJ LQVL]HIURPWRFP7KH\ODFNDQ\ SUHIHUUHGRULHQWDWLRQ)LJDRUWKH\FDQ EHVOLJKWO\LPEULFDWHGVRPHWLPHVIRXQGLQ XSSHUUHDFKHVRIWKHVDQGERGLHV0RVWRI  WKHVWUDWDDUHFRQVWLWXWHGE\PDVVLYHFRQ-JORPHUDWHV OLWKRIDFLHV /) RU LQYHUVHO\ JUDGHG OLWKRIDFLHV /) FRQJORPHUDWHV

DQGVDQGVWRQHVIHZVDQGERGLHVSUHVHUYH parallel-laminated sandstones (lithofacies /)DQGORZDQJOHFURVVEHGGLQJOLWKR-IDFLHV/)RQWRS7UDLOVYHUWLFDOEXUURZV DQGPXGFUDFNVDUHDOVRFRPPRQRQXS-SHUUHDFKHVOLWKRIDFLHV/)

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grain-VL]HPDVVLYHDSSHDUDQFHDQGJHQHUDOODFN of current structures evidence transpor-WDWLRQDQGUDSLGGHSRVLWLRQ6PLWKD Smith 1991) from a cohesionless, subae-ULDOGHEULVÁRZ1HPHFDQG6WHHO The small scale of the involved sandbo-GLHVFRDUVHJUDLQVL]HDQGLQWHUQDOIHDWXUHV DUHFRQVLVWHQWZLWKWKHWUDQVSRUWDWLRQLQD JUDYLW\GULYHQFDWFKPHQWVXJJHVWLQJDOR-FDOVRXUFHRIGHWULWXVDQGWKHUHZRUNLQJ RIS\URFODVWLFPDWHULDODVDUHVXOWRIKHD-YLO\ VHGLPHQWODGHQ VWUHDP ÁRRGV +LJK FRQFHQWUDWLRQ RI SDUWLFOHV LQ WKH ÁRZ DYRLGVWKHGHYHORSPHQWRIVWUXFWXUHVW\-SLFDORIGLOXWHÁRZVHJULSSOHVDQGFURVV bedding) due to suppressed turbulence in WKHÁRZ)LVKHU0DUWLQDQG7XUQHU 'LOXWLRQE\VWUHDPZDWHULVLQWHU- SUHWHGE\WKHRFFXUUHQFHRIFXUUHQWVWUXF-WXUHV$OH[DQGHUDQG)LHOGLQJDQG ÀQHU OLWKRORJLHV XSZDUG )LJ G 0XG FUDFNVUHFRUGGHVLFFDWLRQRIWKHEHGVXUID-FHDIWHUÁRRGHYHQWV&ROOLQVRQ /$/HQWLFXODUWXIIVUHZRUNHGDVK fall beds

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propor-WLRQDPRQJWKHP)LJE([FHSWIRUWKH VKHHWÁRRGFRPSOH[HVWKHVDQGERGLHVLQ-FUHDVHWKHLUWKLFNQHVVVRXWKZDUGV)LJ 2QWKHRWKHUKDQGORJORJSORWVRI:7K data of coarse-grained sandbodies from WKUHHVHOHFWHGVWXG\ORFDWLRQVVKRZQRVLJ-QLÀFDQWFKDQJHVLQWKHDYHUDJHGH[WHUQDO VKDSHDQGIXUWKHUDQDO\VLVRIWKHVHYDOXHV ZLOOEHJLYHQEHORZ

The interpretation of the spatial organi-]DWLRQRIOLWKRIDFLHVDVVRFLDWLRQVDQGWKH WKLFNQHVVRIÁXYLDOVDQGERGLHVKDYHEHHQ integrated into an overall depositional mo-GHO7KHUHZRUNLQJRIS\URFODVWLFSDUWLFOHV WRRNSODFHPDLQO\LQDORZJUDGLHQWÁXYLDO EDVLQZLWKVHYHUDOYDULHWLHVRIÁXYLDOVDQ-GERGLHVFRHYDOODFXVWULQHIDFLHVVKRXOGEH PDLQO\SUHVHUYHGLQWKHVXEVXUIDFHRIWKH basin (e.g. Uliana and Legarreta 1999, He-FKHPDQG6WUHONRY

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The occurrence of small-scale sandbodies PDLQO\ DVVRFLDWHG WR GHEULVÁRZV /$ RU VKHHWÁRRG SURFHVVHV /$ DV WKR-VHPDLQO\SUHVHUYHGLQWKHQRUWKHUQSDUW RIWKHVWXG\DUHD5HJLRQ6LHUUD1HYD-GDDQG6LHUUDGHO&DVWLOORDQWLFOLQHV)LJ 9b) is indicative of variable and episodic GHOLYHU\RIZDWHUDQGYROFDQLFODVWLFSDUWL- FOHVLQDSRRUO\LQWHJUDWHGQHWZRUNRIÁX- YLDOFKDQQHOV6XFKSURFHVVHVRIÁXYLDOUH-VHGLPHQWDWLRQ RFFXUUHG SUREDEO\ GXULQJ short-lived periods of seasonal, high-dis-FKDUJHHYHQWV7KXVWKHKLJKO\FKDQJLQJ EHKDYLRXURIWKHÁXYLDOV\VWHPLQWKHVH VWXG\ORFDWLRQVLVOLNHO\DUHVSRQVHWRWHP- SRUDOYDULDELOLW\LQSUHFLSLWDWLRQVZKLFKID-vours the development of a channel net-ZRUNWKDWLVQRWLQHTXLOLEULXPZLWKWKHLU VORSHVRUGLVFKDUJHFRQGLWLRQV)XOO\ODFXV- WULQHFRQGLWLRQVZHUHLQIUHTXHQWEXWRFDV-VLRQDOO\RFFXUU $TXLWHVLPLODUVLWXDWLRQFDQEHLQWHUSUHWHG )LJXUHD6SDWLDOYDULDWLRQLQSURSRUWLRQ to the lithofacies associations of the Castillo )RUPDWLRQ7KHSURSRUWLRQRI FRDUVHJUDL-ned sandbodies (LA3+LA4+LA5+LA6) DQGSUR[LPDOÁRRGSODLQGHSRVLWV/$LV TXLWHVLPLODUDORQJGLIIHUHQWDUHDVZLWKWKH exception of the northern basin-margin ORFDWLRQ 5HJLRQ  ZKHUH RQO\ GHSRVL-tion of ash-fall strata (LA1) is preserved. b) Spatial changes in the proportion of coarse-grained sandbdodies of the Casti-OOR )RUPDWLRQ IURP H[SRVXUHV DW WKH ED-sin margin (Region 1) to the southern San %HUQDUGR)ROG%HOW5HJLRQ'DWDVKRZ GRPLQDQFHRI VXEDHULDOPXGÁRZGHSRVLWV /$ DQG VKHHWÁRRG GHSRVLWV /$ LQ ORZVXEVLGHQFH DUHDV HJ 5HJLRQ  DQG GRPLQDQFH RI  ORZVLQXRVLW\ ÁXYLDO VDQG-ERGLHV /$ LQ VRXWKHUQ VWXG\ ORFDWLRQV HJ 5HJLRQ  ZKHUH KLJKHU VXEVLGHQFH UDWHYDOXHVRFFXUUHG,QLQWHUPHGLDWHVWXG\ locations (e.g. Region 3) there is a tripartite VXEGLYLVLRQRI ÁXYLDOVW\OHV

IRUWKHÁXYLDOV\VWHPSUHVHUYHGLQDUHDV of increasing subsidence (Region 3: Sie-rra Silva and Las Pulgas anticlines) due to the common occurrence of subaerial de-EULVÁRZV /$ DQG VKHHWÁRRGV /$ +RZHYHUWKHLQFUHDVHLQWKHSURSRUWLRQ RI ORZVLQXRVLW\ ÁXYLDO FKDQQHOV /$ and the larger scale of the coarse-grained sandbodies suggest a more integrated dra-LQDJHQHWZRUN

7KH ÁXYLDO VXFFHVVLRQ SUHVHUYHG DW WKH southernmost part of the San Bernardo )ROG%HOW5HJLRQ3DSHOtDDQG&RGRGHO 6HQJXHUUDQWLFOLQHVZDVSUHVHUYHGLQDQ area of higher relative subsidence.

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Changes in the characteristics of the Cas-WLOOR)RUPDWLRQDUHUHODWHGWRWKHYDULDEOH importance among four main controls:

tectonics, base level changes, climate and S\URFODVWLFVXSSO\

7HFWRQLFV The deposition of the Castillo

)RUPDWLRQKDVEHHQSURGXFHGGXULQJD SHULRGRIUHGXFHGWHFWRQLFDFWLYLW\ZKLFK LVHYLGHQFHGE\WKHGRPLQDQFHRIFDNH OD\HU VXFFHVVLRQV DQG JUDGXDO WKLFNQHVV YDULDWLRQVDWUHJLRQDOVFDOH)LW]JHUDOGHW DO  )LJ  +RZHYHU WKH WHFWRQLF FRQWURORFFXUHGGXHWRWKHLGHQWLÀFDWLRQ RI KLJKDQJOH V\QVHGLPHQWDU\ QRUPDO IDXOWVLQWKHVXEVXUIDFH)LJDULHWDO 1999,

&D\RHWDO 2011, Paredes HWDO 2013) and at

RXWFURSV7KHV\QVHGLPHQWDU\IDXOWVRE-served in the Codo del Senguerr anticli-Figure 10:&RPSDUDWLYHSORWVIRUGLIIHUHQWW\SHVRI FRDUVHJUDLQHGVDQGERGLHV/$/$/$DQG/$RI WKH&DVWLOOR)RUPDWLRQDPRQJVWXGLHGORFDWLRQV6WDWLVWLFDO

YDULDWLRQVDUHSUHVHQWHGDVER[GLDJUDPV)ROORZLQJFRQYHQWLRQWKHER[GHÀQHVWKHDUHDEHWZHHQWKHWKDQGWKSHUFHQWLOHVDQGWKHFHQWUHOLQHUHSUHVHQWVWKHPHGLDQ )RUDSRSXODWLRQZLWKOHVVWKDQSRLQWVWKHER[LVRPLWWHGDQGWKHFHQWUHOLQHUHSUHVHQWVWKHPHGLDQQ RUPD[LPXPWKLFNQHVVQ ([FHSWIRUWKHVKHHWÁRRG FRPSOH[HVWKHVDQGERGLHVVKRZDQLQFUHDVHLQWKHLUWKLFNQHVVLQWKHVRXWKHUQH[SRVXUHV%UDLGHGÁXYLDOFKDQQHOVDUHH[WUHPHO\UDUHLQWKHXQLW

QHDUHKLJKDQJOH!ƒQRUPDOIDXOWV ZLWK$]RIƒDQGDGLSVOLSGLV-SODFHPHQWRIWHQVRIFHQWLPHWUHVWRDIHZ PHWHUV)LJ7KHQRUPDOIDXOWVVKRZ WKLFNQHVVYDULDWLRQVDFURVVIDXOWSODQHV XSZDUGUHGXFWLRQLQWKHGLSVOLSGLVSOD-cement, and the presence of small-scale GRPLQRIDXOWVZLWKGLVSODFHPHQWRIDIHZ centimetres. Paleocurrent measurements LQWKH&RGRGHO6HQJXHUUDQWLFOLQHVKRZD FRQVLVWHQWSDOHRÁRZGLUHFWLRQWRZDUGWKH VRXWKHDVWPHDQƒQ 6W' ƒ SDUDOOHO WR WKH RULHQWDWLRQ RI WKH (DUO\ Cretaceous normal faults mapped in the subsurface of surrounding areas (Homo-vc HWDO 1995), suggesting the occurrence RI WHFWRQLFDOO\ FRQWUROOHG ORQJLWXGLQDO YDOOH\V7KHVWURQJSRVLWLYHLQYHUVLRQRI WKH6DQ%HUQDUGR)ROG%HOWDQGH[WHQVLYH ÁRRGEDVDOWVRI1HRJHQHDJHDYRLGIXU-WKHUDQDO\VLVRIWHFWRQLFFRQWUROVRQWKH sedimentation at outcrops. %DVHOHYHOFKDQJHV0DMRUUHOLHIDWWKHEDVH RIPXOWLVWRUH\V\VWHPVDQGWKHSUHVHQFH RIPDWXUHLQWHUÁXYHSDOHRVRLOVDUHFRP-PRQO\FRQVLGHUHGWREHVWURQJHYLGHQFH IRU VLJQLÀFDQW EDVHOHYHO IDOOV DQG WKH SUHVHQFHRIVHTXHQFHERXQGDULHV9DQ Wagoner HWDO 1990). Neither feature has EHHQLGHQWLÀHGLQWKHDQDO\]HGRXWFURSV WKHODFNRIVLJQLÀFDQWFRHYDOODFXVWULQH VXFFHVVLRQV DOVR SUHYHQWV WKH DQDO\VLV RIEDVLQZDUGIDFLHVVKLIW%DVHGRQWKH VHFWLRQRI&HUUR&RORUDGRGH*DOYHQL] 8PD]DQR

HWDOLGHQWLÀHGWKUHHGH-SRVLWLRQDO V\VWHP WUDFWV LQ WKH &DVWLOOR )RUPDWLRQIROORZLQJWKHFULWHULDSURSR-VHGE\/HJDUUHWDHWDO (1993) to relate

ba-se-level shifts using the vertical variation in the proportion of channel belts and ÁRRGSODLQÀQHVDQGGHÀQLQJ´IRUHVWHH-SLQJµ EDFNVWHHSLQJµ DQG ´DJJUDGDWLR-QDOµV\VWHPWUDFWVVHQVX Legarreta HWDO

1993). Although this approach is valid for IXOO\FRQWLQHQWDOVXFFHVLRQVLWVDSSOLFD-ELOLW\XVLQJDVLQJOHVHFWLRQLVVSHFXODWLYH and the results can be of local character, ZLWKQRUHODWLRQWRFRQWHPSRUDU\EDVH level shifts.

0LG&UHWDFHRXVFOLPDWH7KHLQÁXHQFHRIWKH

climate has been commented above in the development of the depositional mo- GHORIWKH&DVWLOOR)RUPDWLRQ$GGLWLRQD-OO\GDWDIURPWKLVVWXG\FDQEHLQWHJUDWHG WRWKHVSDUVHGDWDRIWKH0LG&UHWDFHRXV climate of the Golfo San Jorge basin in &HQWUDO 3DWDJRQLD 7KH /RZHU &UHWD-FHRXV 0DWDVLHWH3R]R ' GHSRVLWLR-QDO V\VWHP VKRZV VRPH HYLGHQFHV WKDW point to a semiarid environment, such as the presence of &ODVVRSROLVpollen, the common occurrence of oolitic grainsto-nes and %RWU\RFRFFXVOLNHDOJDOIRUPVLQWKH lacustrine facies (Hechem HWDO9DQ 1LHXZHQKXLVHDQG2UPLVWRQ7KH presence of vertisoils and the abundan-FHRIFDUERQDWHFRQFUHWLRQVLQÁRRGSODLQ IDFLHVRIWKH0DWDVLHWH)RUPDWLRQ3DUH-des HWDODOVRSRLQWWRDVHPLDULG environment. In contrast, studies in the

RYHUO\LQJ/RZHU%DMR%DUUHDO)RUPDWLRQ $UFKDQJHOVN\HW DO 1994) evidence

hu-PLG FRQWLQHQWDO PLOG WR ZDUP FOLPDWH during Late Albian-Cenomanian. Simi-lar conditions have been also reported from the southernmost areas of Patago- QLDLQWKH/DWH$OELDQ&HQRPDQLDQ.D- FKDLNH)RUPDWLRQ%DUUHGDDQG$UFKDQ-JHOVN\7KRVHVWXGLHVHYLGHQFHWKDW during the mid-Cretaceous a climatic shift from semi-arid environments to more humid conditions occurred in the Golfo San Jorge basin and surrounding areas of Southern Patagonia. A compa-UDWLYHDQDO\VLVRIWKHÁXYLDODUFKLWHFWXUH RIWKH0DWDVLHWHDQG&DVWLOOR)RUPDWLRQV VKRZVDQRWLFHDEOHUHGXFWLRQLQWKHWKLF- NQHVVDQGODWHUDOH[WHQWRIÁXYLDOVDQGER-GLHVRIWKH&DVWLOOR)RUPDWLRQ3DUHGHV HWDOWKHLUÀJDQGWKHHQGLQJRI

regional lacustrine deposition. Reduction LQWKHVHGLPHQWVXSSO\DQGGLVFKDUJHRI WKHÁXYLDOV\VWHPVFRXOGEHLQWHUSUHWHGDV DUHVSRQVHWRWKH0LG&UHWDFHRXVFOLPD-tic variation from semi-arid to more hu-PLGFRQGLWLRQV6FKXPP6FKXPP SUREDEO\UHODWHGWRFKDQJHVLQWKH W\SHRIYHJHWDWLRQZLWKLQFUHDVLQJSUHFL-SLWDWLRQ/DQJEHLQDQG6FKXPP 3\URFODVWLFVXSSO\'HOLYHU\RIDODUJHYROX- PHRIS\URFODVWLFSDUWLFOHVGXULQJHUXS-tions and resedimentation processes of such particles are major control on the characteristics of volcaniclastic succes-sions preserved close to volcanoes (e.g. Figure 11:6\QVHGLPHQWDU\IDXOWLQJGXULQJWKHGHSRVLWLRQRI WKH&DVWLOOR)RUPDWLRQD+LJKDQJOHV\QVHGLPHQWDU\QRUPDOIDXOW7KHJHRORJLVWLVPWDOO1RWHWKH

YHUWLFDOUHGXFWLRQLQIDXOWGLVSODFHPHQWDQGWKHFKDQJHVLQWKLFNQHVVDFURVVWKHIDXOWSODQHE6PDOOVFDOHGRPLQRIDXOWV\VWHPSUHVHUYHGLQWKHIDXOW]RQHRI DPDMRU extensional fault. The pen is 0.14m long.

YROFDQLFODVWLFDSURQV,WLVJHQHUDOO\DV-VXPHGWKDWUDWHVRIS\URFODVWLFVXSSO\DUH high enough to impose major changes in WKHQDWXUHRIWKHÁXYLDOV\VWHPDVFDQEH the occurrence of braided channels du-ULQJV\QHUXSWLYHRUHDUO\LQWHUHUXSWLYH VWDJHV 9HVVHOO DQG 'DYLHV  6PLWK D 6PLWK E 6PLWK  %HVW  1DND\DPD DQG <RVKLNDZD  .DWDRNDDQG1DNDMR,QWKH*RO-IR6DQ-RUJHEDVLQWKHWZRVWDJHPRGHO ÀUVWSURSRVHGE\6PLWKKDVEHHQ WHVWHG E\ 8PD]DQRHW DO D DQG 8PD]DQRHW DO  LQ WKHLU VWXGLHV WKH\KDYHIRXQGQRV\VWHPDWLFDOUHODWLRQV EHWZHHQFKDQQHOSDWWHUQVRUÁXYLDOVW\OHV and the occurrence of inter-eruptive and V\QHUXSWLYH VWDJHV HYLGHQFLQJ D QRQ SUHGLFWDEOHEHKDYLRXURIWKHÁXYLDOV\V-WHPZLWKYROFDQLFDFWLYLW\$GLVWLQFWLYH IHDWXUHRIWKH&DVWLOOR)RUPDWLRQLVWKH unusual occurrence of braided channels, EHLQJRQO\UHFRJQL]HGLQWKHVRXWKHUQ-PRVWSDUWRIWKHVWXG\DUHDHJ5HJLRQ DVDVXERUGLQDWHVW\OH6FDUFLW\RIEUDL-ded channels implies that the deposition RIS\URFODVWLFSDUWLFOHVDVDVKIDOOPDWH-ULDO GHOLYHUHG WR ÁXYLDO FKDQQHOV QHYHU exceeded the in-channel threshold for DJJUDGDWLRQ VXJJHVWLQJ DQ HTXLOLEULXP EHWZHHQWKHUDWHRIS\URFODVWLFVXSSOLHV and the rate of aggradation during erup-WLRQV )XUWKHUPRUH YROFDQLFODVWLF XQLWV in distal environments that contain brai-ded channels could not have a direct rela-WLRQZLWKWKHDFWLYLW\RIYROFDQLFFHQWUHV EHFDXVH WKH DJJUDGDWLRQ DQG VXSSO\ RI ash to the receiving basin could have oc-curred long time after the ending of the HUXSWLYHHYHQWVRWKHEUDLGHGVW\OHFRXOG KDYHQRWHPSRUDOUHODWLRQVKLSZLWKHUXS- WLRQV)DFLHVVWXGLHVLQWKH&DVWLOOR)RU-PDWLRQ8PD]DQRHWDO 2012) advocated

WKHRFFXUUHQFHRIGHEULVÁRZSURFHVVHV WR WKH FROODSVH RI YROFDQLF HGLÀFHV UH- PRYLOL]DWLRQRISULPDU\S\URFODVWLFGH-SRVLWVE\LQWHQVHUDLQVRUVQRZPHOWLQJ 2XUGDWDLQGLFDWHWKDWGHEULVÁRZGHSR-sits of the Castillo formation are domi-QDQWLQWKHXQLWWRZDUGWKHQRUWKRIWKH VWXG\DUHD)LJEZKHUHWKH\PDLQO\ RFFXU LQ VPDOOVFDOH FKDQQHOV )LJ 

ZLWKQRHYLGHQFHRIDODUJHVFDOHGUDLQD-JHQHWZRUNWKDWFRXOGWUDQVSRUWGHWULWXV IURP WKH $QGHV ORFDWHG XS WR  NP ZHVWZDUG )URP WKLV ZH FRQVLGHU WKDW PRVWRIWKHGHEULVÁRZGHSRVLWVDUHDVVR-FLDWHGZLWKORFDOVRXUFHVLQIHUHQFHWKDWLV FRQVLVWHQWZLWKWKHODFNRIZHOGHGLJQLP- EULWHVRUDQ\RWKHUHYLGHQFHRIWUDQVSRU-WDWLRQUHPRYLOL]DWLRQRISDUWLFOHVE\KRW S\URFODVWLF ÁRZV $OWKRXJK WKHUH DUH VHYHUDOSDSHUV0RWKHV

HWDO0DQ-ville HWDO 2009) that have demonstrated the transportation of volcaniclastic par-WLFOHVE\DPL[WXUHRIGXVW\JDVDQGKRW ZDWHUIRUGLVWDQFHVXSWRNLORPHWHUV from the source, the transpotation of particles in hot conditions has not been proven, and the inferred relief of the vol-FDQLFDUFFRHYDOZLWKGHSRVLWLRQRIWKH &DVWLOOR )RUPDWLRQ VKRXOG EH VLJQLÀFD-WLYHO\ORZHUWRWKRVHDQDOL]HGE\0RWKHV

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about 3,000 m above sea level. Thus, in spite of the importance of the volcani-clastic participation in the composition RIWKHÁRRGSODLQDQGFKDQQHOLQÀOODGL- UHFWOLQNEHWZHHQWKHDFWLYLW\RIWKHYRO-FDQRHVLQWKH$QGHVDQGWKHG\QDPLFVRI WKHÁXYLDOV\VWHPLVVWLOOXQSURYHG:H advocate the idea that the occurrence of H[WHQVLRQDOWHFWRQLFVFRHYDOZLWKGHSRVL- WLRQRIWKH&DVWLOOR)RUPDWLRQKDVIDYRX-red the creation of intrabasin highs that SURPRWHSURFHVVHVRIUHPRYLOL]DWLRQRI YROFDQLFSDUWLFOHVLQVPDOOVFDOHSDUWLDOO\ LVRODWHG EDVLQV ERXQGHG E\ ORFDO WKUHV-KROGDVKDVEHHQGHPRQVWUDWHGE\&D\R

HWDO (2011) and Paredes HWDO (2013) in the

subsurface of the basin. In this scenario, LQWHQVHUDLQVIDYRXUHGUHZRUNLQJRIFRDU-se grained particles in small-scale chan-QHOEHOWV)LJ7KHÀHOGLQIRUPDWLRQ collected during this research does not VXSSRUW UHJLRQDO GUDLQDJH V\VWHPV WKDW GLUHFWO\WUDQVSRUWYROFDQLFODVWLFSDUWLFOHV from proximal volcaniclastic sources. $SSOLFDWLRQ WR K\GURFDUERQ H[SORUD-tion

,QWHJUDWLRQRI'VHLVPLFVXUYH\VZHOO ORJVDQGFRUHVDOORZVXVWRFRYHUGLIIH-rent scales of observation of geological features during exploration and the de-

YHORSPHQWRIRLOÀHOGV'VHLVPLFGD-ta can provide deYHORSPHQWRIRLOÀHOGV'VHLVPLFGD-tailed images of the SODQIRUP JHRPHWU\ RI ÁXYLDO FKDQQHOV (e.g. Posamentier HW DO  (WKULGJH DQG6FKXPP(OHFWULFZHOOORJV DQGFRUHVDOORZDUHOLDEOHUHFRJQLWLRQRI drilled sandstone bodies, their internal heterogeneities, vertical arrangement of lithofacies and lithofacies associations, DQGSHWURSK\VLFDOGDWD+RZHYHUWRGH-ÀQHWKHYROXPHRIK\GURFDUERQVWKDWFDQ EHUHFRYHUHGIURPDVLQJOHUHVHUYRLUWKH real lateral extent of the potential reser-voir must be obtained from seismic data RUIURPWKHDQDO\VLVRIFRUUHODWDEOHRXW-crop sections.

7KH&DVWLOOR)RUPDWLRQLVFXUUHQWO\DULV-N\K\GURFDUERQUHVHUYRLULQWKH*ROIR6DQ -RUJHEDVLQ8QFHUWDLQW\LVGXHWRWKHSUH-sence of oil-bearing reservoirs that are DERXWPWKLFNEHORZWKHDYDLODEOHYHU-WLFDOUHVROXWLRQRIVHLVPLFVXUYH\Va PDQGE\WKHDEXQGDQFHRIYROFDQLFODVWLF SDUWLFOHVLQFKDQQHOVDQGERGLHVDQGÁRR-GSODLQDUHDVPDNLQJLWGLIÀFXOWIRUXVWR LGHQWLI\WKHUHVHUYRLUVXVLQJHOHFWULFZHOO logs. Another intrinsic source of uncer- WDLQW\LVGXHWRWKHODWHUDOH[WHQWRIWKHSR-WHQWLDO RLOEHDULQJ UHVHUYRLUV ZKLFK DUH PDLQO\VPDOOHUWKDQPHWUHV)LJ )LJ6XFKDOLPLWHGODWHUDOH[WHQWDYRL-ds a reliable correlation of potential re-VHUYRLUVEHWZHHQZHOOORJVRISURGXFWLYH ZHOOVZKLFKDUHIUHTXHQWO\VHSDUDWHG PIURPHDFKRWKHUEXWRQWKHRWKHU hand this implies that a large number of coarse-grained volcaniclastic sandstones KDVQRWEHHQGULOOHG\HWXVLQJWKHFXUUHQW ZHOOWRZHOOVHSDUDWLRQ

Published data on the dimensions of the VDQGVWRQHERGLHVRIWKH&DVWLOOR)RUPD-tion correspond to Bridge HW DO (2000) DQG 8PD]DQRHW DO (2012). The former

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