Baumgartner, Peter O.

Baumgartner-Mora, Claudia

Buchs, David M.

Ferràndez-Cañadell, Carles

English

Serveur académique lausannois

FORAMS 2023, June 26th–30th, 2023, Perugia, Italy – Abstract BookLarger benthic foraminifera from the Azuero Peninsula (SW-Panama) define Eocene accretionary events and an arc gap along the trailing edge of the Caribbean PlateBAUMGARTNER-MORA Claudia1*, BAUMGARTNER Peter O.1, FERRÀNDEZ-CAÑADELL Carles2 and BUCHS David M.31Institut des sciences de la Terre, Université de Lausanne, Mouline 11-Géopolis, CH-1015 Lausanne, Suisse; claudia.baumgartner@unil.ch; peter.baumgartner@unil.ch2Departament Dinàmica de la Terra i de l'Oceà, Facultat de Ciències de la Terra, Universitat de Barcelona,  Marti i Franqu`es s/n, Barcelona, 08028, Spain; carlesferrandez@ub.edu3School of Earth and Ocean Sciences, Cardiff University, Main Building, Cardiff, CF10 3AT, United Kingdom; BuchsD@cardiff.ac.uk*Corresponding authorThe Azuero Plateau, the trailing edge of The Caribbean Large Igneous Province (CLIP), is overlain by ribbon-cherts dated by radiolarians  as  Coniacian-Santonian.  Proto-arc  dikes  crosscut  the  Azuero Plateau and the  unconformably overlying Upper Cretaceous sediments. The latter consist of hemipelagic carbonates, the Ocú Formation (Fm.), and of volcaniclastics, the Quebrada Quema Fm., both dated by globotruncanids as Late Campanian to Maastrichtian. Upper Cretaceous larger benthic foraminifera (LBF) and rudist fragments were reported by early workers in the Ocú area, suggesting  the  presence  of  carbonate  shoals  on  early  arc  volcanic  edifices.  A recently  published  crystallization 238U/206Pb-age  of  zircons  dates  the  oldest  (Cerro  Montuoso)  batholith  of  W-central  Azuero as  66.4±0.3  Ma (latest Maastrichtian). The Azuero Plateau is bounded towards the SW by the Azuero-Soná Fault Zone and the adjacent Azuero Subduction Mélange that contains fragments of oceanic seamounts dated by globotruncanids as early Maastrichtian. The Azuero Accretionary Complex occupies the SW-corner of the Azuero Peninsula. It is principally composed of two well-preserved oceanic seamounts. The Hoya seamount to the W is made of intrusives, subaerial and submarine lava flows with interbedded carbonates. Pelagic carbonates yielded  Morozovella sp. indicate a late Paleocene – early Eocene age. Shallow water carbonates yielded the association of Neodiscocyclina barkeri, Eoconuloides sp. cf. E. wellsi and Amphistegina undecima, indicating an early Eocene age.The Punta Blanca Seamount to the E is characterized by a several km thick sequence of submarine/subaerial basaltic lava flows regularly interbedded with carbonates.  Most shallow water facies only contain rhodophytes and bivalve bioclasts. Only one calcarenite yielded Pseudophragmina anconensis and orthophragminids suggesting an early-middle Eocene age.The Covachón Fm. is the first overlap sequence in which chaotic deposits with up to 50 m sized blocks document the accretion of the seamounts. LBF collected from several localities indicate a middle Eocene age of the accretionary events. These resulted in a shutdown of the arc between 49 and 36 Ma (late Ypresian – earliest Priabonian), reflected by a lack of 238U/206Pb zircon ages from intrusives. Covachón facies range from distal volcaniclastic turbidites to chaotic megabreccias and up to nearshore conglomerates, documenting fast tectonic uplift.At Puerto Escondido,  a stratigraphic base of the Covachón Fm.,  is  formed by cross-bedded detrital  limestones unconformably on seamount basalts. They contain winnowed small LBF: Eoconuloides sp., Amphistegina grimsdalei, A. praegrimsdalei and Pseudophragmina sp. suggesting a Middle Eocene age. In the chaotic facies at Covachón Beach the  matrix  of  the  debris  flows  yielded  Asterocyclina ssp.,  Neodiscocyclina  marginata,  Lepidocyclina spp.  and Polylepidina sp. suggesting a middle Eocene maximum age. Detrital zircons form the turbiditic facies yielded a 42 Ma minimum age (late Lutetian).The Tonosí  Fm.  represents a several 100 m thick deepening upwards forearc series that ranges from paralic to turbiditic facies of late Eocene to Oligocene age. Its base onlaps time-transgressive on older formations and basements documenting progressive drowning of the Azuero Arc Complex. The youngest zircons of the upper Tonosí yielded 238U/206Pb  ages  around  36  Ma  (Priabonian).  The  Río  Pedregal  paralic  facies  include  polymict  conglomerates  and encroach unconformably on accreted seamount rocks and deformed packages of Covachón  Fm. The conglomerates contain  pavements  of  oysters  (Pycnodonte sp.)  and  a  detrital  matrix  with  abundant  large  Lepidocyclina ssp., pseudophragminids and Asterocyclina spp. indicating a late Eocene age.The Guerita River exposes herringbone cross-bedded bioclastic limestones,  unconformably overlying the Upper Cretaceous Rio Quema Fm. They are made of abundant  Operculinoides spp., suggesting an Oligocene age. Another inland outcrop is rich in large Lepidocyclina spp., among them L. tournoueri and L. undosa with an Oligocene age.1

Larger benthic foraminifera from the Azuero Peninsula (SW-Panama) define Eocene accretionary events and an arc gap along the trailing edge of the Caribbean Plate

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Larger benthic foraminifera from the Azuero Peninsula (SW-Panama) define Eocene accretionary events and an arc gap along the trailing edge of the Caribbean Plate

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