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River-dominated deltas; upscaling autogenic and allogenic processes observed in laboratory experiments to field examples of small deltas in southern Brazil

Maria Luiza Correa da Camara Rosa, David Hoyal, Eduardo G. Barboza, Juan J. Fedele and Vitor Abreu
River-dominated deltas; upscaling autogenic and allogenic processes observed in laboratory experiments to field examples of small deltas in southern Brazil (in Autogenic dynamics of and self-organization in sedimentary systems, David A. Budd (editor), Elizabeth A. Hajek (editor) and Sam J. Purkis (editor))
Special Publication - Society for Sedimentary Geology (2016) 106: 176-197

Abstract

Determining how autogenic and allogenic processes and responses in deltas scale up from meter-scale laboratory experiments to actual field examples remains a challenge. This study was devised to bridge that scale gap using field data from small, hundreds of meter-scale natural deltas. Ground-penetrating radar and core data were collected from four different river-dominated delta morphotypes developing at the margins of freshwater coastal lagoons in southern Brazil. Since the sediment supplying these deltas is sourced from a nearby dune field and is similar between the deltas, it is hypothesized that major morphological differences in the four deltas are primarily the result of differences in sediment discharge rates (sediment-water ratio). As observed in published tank experiments, channel cross-section and distributary channel patterns in the deltas vary as a function of sediment discharge, from shallow sheet-like flow at high discharge to well-established, stable distributary channels (i.e., birdsfoot pattern). A contributing factor may be the development of vegetation on the slower growing deltas influencing sediment cohesion, a key control in laboratory-scale deltas. As in many tank experiments, these lagoon deltas are steep and sandy, with the Froude number modulated to just below Froude critical flow (i.e., they are Froude-scaled). Ground-penetrating radar sections were processed, interpreted, and integrated with cores, allowing the definition of radar units. Analysis of the radar units demonstrates the presence of both allogenic and autogenic signals. Allogenic control is identified in the stacking of clinoforms and is perceptible in both sides of a single delta (delta 4), as well as in two other deltas (deltas 1 and 2). An autogenic signal varies according to delta planform shape and was identified by the stacking of lobe elements, both in dip and strike. Base-level change (lake level) and autogenic avulsion cycles occur on similar timescales, and therefore it is a significant challenge to separate these different processes in the stratigraphy. The potential uses of these types of data include understanding the link between delta dynamics, channel patterns, and stratigraphy to develop improved genetic models of steep sandy deltas common in the stratigraphic record.


ISSN: 1060-071X
EISSN: 2159-5755
Serial Title: Special Publication - Society for Sedimentary Geology
Serial Volume: 106
Title: River-dominated deltas; upscaling autogenic and allogenic processes observed in laboratory experiments to field examples of small deltas in southern Brazil
Title: Autogenic dynamics of and self-organization in sedimentary systems
Author(s): da Camara Rosa, Maria Luiza CorreaHoyal, DavidBarboza, Eduardo G.Fedele, Juan J.Abreu, Vitor
Author(s): Budd, David A.editor
Author(s): Hajek, Elizabeth A.editor
Author(s): Purkis, Sam J.editor
Affiliation: Universidade Federal do Rio Grande do Sul, Centro de Estudos de Geologia Costeira e Oceanica, Porto Alegre, Brazil
Affiliation: University of Colorado, Department of Geological Sciences, Boulder, CO, United States
Pages: 176-197
Published: 2016
Text Language: English
Publisher: Society for Sedimentary Geology (SEPM), Tulsa, OK, United States
Meeting name: SEPM research conference; Autogenic dynamics of sedimentary systems
Meeting location: Grand Junction, CO, USA, United States
Meeting date: 20140803Aug. 3-6, 2014
References: 83
Accession Number: 2017-082536
Categories: Sedimentary petrology
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 2 tables, geol. sketch maps
S29°58'00" - S29°58'00", W50°07'60" - W50°07'60"
Secondary Affiliation: ExxonMobil Upstream Research Company, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 201743
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