Facies and depositional architecture according to a jet efflux model of a late Paleozoic tidewater grounding-line system from the Itararé Group (Paraná Basin), southern Brazil

• Published in: Journal of South American Earth Sciences
• Main Authors: Aquino, Carolina Danielski, Buso, Victoria Valdez, Faccini, Ubiratan Ferrucio, Milana, Juan Pablo, Paim, Paulo Sergio Gomes
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon-Elsevier Science Ltd
• Subjects: GROUNDING-LINE SYSTEMS; HYDRAULIC JUMP; HYPERCONCENTRATED FLOWS; PLANE-WALL JET; TIDEWATER GLACIER; https://purl.org/becyt/ford/1.5; https://purl.org/becyt/ford/1; Tidewater
• Online Access: http://hdl.handle.net/11336/61137

During the Late Paleozoic, the Gondwana supercontinent was affected by multiple glacial and deglacial episodes known as "The Late Paleozoic Ice Age" (LPIA). In Brazil, the evidence of this episode is recorded mainly by widespread glacial deposits preserved in the Paraná Basin that contain the most extensive record of glaciation (Itararé Group) in Gondwana. The Pennsylvanian to early Permian glaciogenic deposits of the Itararé Group (Paraná Basin) are widely known and cover an extensive area in southern Brazil. In the Doutor Pedrinho area (Santa Catarina state, southern Brazil), three glacial cycles of glacier advance and retreat were described. The focus of this article is to detail the base of the second glacial episodes or Sequence II. The entire sequence records a deglacial system tract that is represented by a proximal glacial grounding-line system covered by marine mudstones and shales associated with a rapid flooding of the proglacial area. This study deals with the ice proximal grounding-line systems herein interpreted according to lab model named plane-wall jet with jump. Detailed facies analysis allowed the identification of several facies ranging from boulder-rich conglomerates to fine-grained sandstones. No fine-grained deposits such as siltstone or shale were recorded. According to this model, the deposits are a product of a supercritical plane-wall outflow jet that changes to a subcritical jet downflow from a hydraulic jump. The hydraulic jump forms an important energy boundary that is indicated by an abrupt change in grain size and cut-and-fill structures that occur at the middle-fan. The sedimentary facies and facies associations show a downflow trend that can be subdivided into three distinct stages of flow development: (1) a zone of flow establishment (ZFE), (2) a zone of transition (ZFT), and (3) an established zone (ZEF). The proximal discharge is characterized by hyperconcentrated-to-concentrated flow due to the high energy and sediment-laden nature of the flows. At the transitional zone, a ...