Tectonic and structural controls on Neogene fluid release in the Patagonian Continental Margin

ISOLA, J.I.; ORMAZABAL, J.P.; FLORES, G.; ARISMENDI, S.; DRUET, M.; MUÑOZ, A.; RÍO, J.L. DEL; ETIENOT, S.D.A.; GOMEZ BALLESTEROS, M.P.; PRINCIPI, S.; BOLATTI, N.D.; TASSONE, A.A.

MARINE AND PETROLEUM GEOLOGY

ELSEVIER SCI LTD

Año: 2020 vol. 115

0264-8172

Analysisofhigh-resolutionmulti-beambathymetry,2Dmulti-channelseismic,andhigh-resolutionseismicsubbottomprofilesrevealedthepresenceofwidespreadfluidescapefeaturesinthemiddleslopeofthePatagonian ContinentalMargin.Onthesea-bottom,thesefeaturescorrespondtopockmarksandmudvolcanoes,whereasin the sub-surface they are represented in the seismic records by several acoustic anomalies such as chimneys, acoustic blanking, enhanced reflectors, and reverse-phase enhanced reflectors among others. Some of these acousticsignaturescanbetracedtosyn-riftdepositsthatfilladeepre-activatedandinvertedgraben.Analysisof pockmarks elongation and pockmarks alignments show a good correlation with inverted normal faults, suggesting that faults and fractures have influenced the pockmark´s shape and might have acted as pathways for upwardfluidmigration.Someoftheacousticanomaliesassociatedwithpockmarksareinterpretedasevidence ofgas.Thegasobservedintheseismicdataseemstobethermogenic,andtheseismicdatasuggestsadeeporigin associated with over-pressured syn-rift deposits. Two morphometrically different sets of pockmarks were identified:anoldersethostedbyMioceneagedrocks,andayoungersethostedbyQuaternarydeposits.Different potentialtriggersarediscussedforthegenesisoftheMiocenepockmarksinrelationtotheseismostratigraphy, structural geology and regional tectonics. It is concluded that, tectonic activity associated with the Neogene inversion of the graben faults, due to Andean compression, is the most likely cause for the formation these pockmarks. The presence of gas charged sediment and young pockmarks also suggest that after the Middle Miocenetectonicclimax,amorerecentpulseofreleaseoffluidsoccurred.