Shell beds from the Low Head Member (Polonez Cove Formation, early Oligocene) at King George Island, west Antarctica: new insights on facies analysis, taphonomy and environmental significance

Autor(es)

Quaglio, Fernanda ^[1] ; Warren, Lucas Verissimo ^[2] ; Anelli, Luiz Eduardo ^[1] ; Dos Santos, Paulo Roberto ^[1] ; Rocha-Campos, Antonio Carlos ^[1] ; Gazdzicki, Andrzej ^[3] ; Strikis, Pedro Carlos ^[1] ; Ghilardi, Renato Pirani ^[4] ; Tiossi, Andressa Barraviera ^[4] ; Simoes, Marcello Guimaraes ^[5]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo - Brazil

^[2] Univ Estadual Paulista, Inst Geociencias & Ciencias Exatas, BR-13506900 Rio Claro, SP - Brazil

^[3] Inst Paleobiol PAN, PL-00818 Warsaw - Poland

^[4] Univ Estadual Paulista, Fac Ciencias Bauru, Dept Ciencias Biol, BR-17033360 Sao Paulo - Brazil

^[5] Univ Estadual Paulista, Inst Biociencias, Dept Zool, BR-18618000 Sao Paulo - Brazil

• Tipo de documento: Artigo Científico
• Fonte: ANTARCTIC SCIENCE; v. 26, n. 4, p. 400-412, AUG 2014.
• Citações Web of Science: 4

Resumo

Shell bed levels in the Low Head Member of the early Oligocene Polonez Cove Formation at King George Island, West Antarctica, are re-interpreted based on sedimentological and taphonomic data. The highly fossiliferous Polonez Cove Formation is characterized by basal coastal marine sandstones, overlain by conglomerates and breccias deposited in fan-delta systems. The shell beds are mainly composed of pectinid bivalve shells of Leoclunipecten gazdzickii and occur in the basal portion of the Low Head Member. Three main episodes of bioclastic deposition are recorded. Although these shell beds were previously interpreted as shelly tempestites, we present an alternative explanation: the low fragmentation rates and low size sorting of the bioclasts resulted from winnowing due to tidal currents (background or diurnal condition) in the original bivalve habitat. The final deposition (episodic condition) was associated with subaqueous gravity driven flows. This new interpretation fits with the scenario of a prograding fan-delta front, which transported shell accumulations for short distances near the depositional site, possibly between fair-weather and storm wave bases. This work raises the notion that not every shell bed with similar sedimentological and taphonomic features (such as geometry, basal contact, degree of packing and shell orientation in the matrix) is made in the same way. (AU)

• Processo FAPESP: 10/19584-4 - Tectônica e sedimentação do grupo Itapucumi no contexto das plataformas carbonáticas ediacaranas: abordagem geoquímica, geocronológica, paleomagnética e bioestratigráfica
• Beneficiário: Lucas Verissimo Warren
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado