The Cabo Domingo Group, Tierra del Fuego: Biostratigraphy, paleoenvironments, and events of the marine Eocene-Miocene

Abstract

The Cabo Domingo Group, upper Eocene to middle Miocene, includes a gently deformed marine episodic sequence, mainly exposed to the north of the Punta Gruesa fault in Tierra del Fuego. Deposition of the Group started in the late Eocene with the basin deepening, resulting from global high sea level, the effects of which were amplified by regional tectonism (Incaica Phase). The Group is represented in the basin depocenter by the upper member of the Cerro Colorado Formation (140 m, mudstones and sandstones, 36-34 Ma), which records the LAD of Globigerinatheka index (34.3 Ma) and the FAD of Praetenuitella insolita and Isthmolithus recurvus (36.6 Ma). Outside the depocenter this time interval is reflected by the Tchat-Chii Conglomerate (70 m, latest Eocene-earliest Oligocene), and by the Glauconítico A in the subsurface of the northern part of the island. The low smectite content and the abundance of Chiloguembelina ototara indicate active tectonism and falling temperatures during the deposition of the upper member and the Glauconítico A . Deposition of the Cabo Domingo Group was followed by that of the Estancia María Cristina beds (>75 m, claystones and sandstones, earliest Oligocene, 34-30 Ma) and the Puesto Herminita beds (200 m, claystones, Oligocene, 30-26.5 Ma), which mainly contain residual agglutinated foraminifera deposited below the calcite compensation depth. These beds were deposited during the maximum deepening of the basin that allowed for the entrance of corrosive, Antarctic waters. The following Desdémona Formation (250 m, tuffaceous, bioturbated mudstones deposited at or near the lisocline), consisting of the Cabo Ladrillero beds (80 m, basal glauconite sandstones and mudstones with outer neritic foraminiferal assemblages, and 75 m of carbonaceous mudstones, fine-grained sandstones and claystones with residual assemblages of the benthic foraminifera Spirosigmoilinella-Martinottiella), and the Cabo San Pablo beds (30-40 m of sandstones and claystones) represents the latest Oligocene-early Miocene high sea-level conditions. An extended unconformity and generalized regression is documented at c. 21 Ma (Early Miocene) . Finally, the Carmen Silva (>50 m, deltaic mudstones and conglomerates) and Castillo (50 m, conglomerates) Formations, and the Cabo Viamonte beds (>40 m, coarse breccias, conglomerates, sandstones and mudstones), all with basalt clasts, represent the Neogene high sea-level and climatic optimum, the latter reflected by the middle Miocene smectite-rich clay composition.