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Paleoenvironmental significance of microbial mat-related structures and ichnofaunas in an Ordovician mixed-energy estuary, Aspero Formation of Santa Victoria Group, northwestern Argentina

Maria Duperron and Roberto Adrian Scasso
Paleoenvironmental significance of microbial mat-related structures and ichnofaunas in an Ordovician mixed-energy estuary, Aspero Formation of Santa Victoria Group, northwestern Argentina
Journal of Sedimentary Research (April 2020) 90 (4): 364-388

Abstract

The study on a unique set of outstandingly preserved sedimentary surface textures (SSTs) found in the late Tremadocian Aspero Formation of northwestern Argentina, coupled with the sedimentological and ichnological analysis, indicate that they were formed in the intertidal to supratidal setting of a mixed-energy estuary recording storm and tide sedimentation. We recognize seven types of SSTs: probably biotic microbial mat-related SSTs (Kinneyia, elephant skin, exfoliating sandy laminae), abiotic SSTs (elliptical scours and convex parallel ridges type I "wrinkle marks" sensu Allen 1985), and problematic (convex parallel ridges type II and dot matrix texture). Elliptical scours and convex parallel ridges type I show features which indicate reworking of a cohesive sandy substrate in an intertidal or supratidal setting. Abundance of biotic SSTs with specific associated trace fossils reflect matground development and mat-grazing ichnofaunas, indicating the suppression of intense, penetrative bioturbation due to intense physicochemical stress. The "dot matrix" texture, described here for the first time, consists of a regular horizontal network of millimeter-scale pits; it appears associated with exfoliating sandy laminae, probably reflecting a mat-related origin. Three facies associations are defined through paleoenvironmental analysis. Facies association 1 is dominated by high-energy sandy and bioclastic storm deposits with tidal flat facies, and corresponds to the outer bay of a mixed-energy estuary; highly impoverished Cruziana assemblages and distal expressions of the Skolithos Ichnofacies reflect high energy and sedimentation rate. Facies association 2 shows tidal-channel and tidal-flat facies with subordinated storm deposits, representing the middle bay; impoverished Cruziana assemblages dominated by simple facies-crossing structures, with high-density monogeneric opportunistic suites, evidence physicochemical stress associated with subaerial exposure, frequent episodic deposition, high water turbidity, and/or brackish water conditions in these relatively sheltered tidal flats. Facies association 3 is formed by interdistributary-bay deposits with intercalation of channel-fill deposits in the upper part, and represents the river-dominated bay-head delta; low degrees of bioturbation in fine-grained facies indicate brackish- to fresh-water conditions. SSTs are found in tidal flat facies of facies association 2; they indicate an intertidal to supratidal environment subject to localized conditions of intense physicochemical stress. The paleoenvironmental interpretation of SSTs converges with the one performed through sedimentological and ichnological analysis, producing a robust and more detailed paleoenvironmental model for the Aspero Formation. Our study highlights the use of SSTs as a tool for supporting and refining paleoenvironmental analysis.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 90
Serial Issue: 4
Title: Paleoenvironmental significance of microbial mat-related structures and ichnofaunas in an Ordovician mixed-energy estuary, Aspero Formation of Santa Victoria Group, northwestern Argentina
Affiliation: Universidad de Buenos Aires, Instituto de Geociencias Basicas, Aplicadas y Ambientales, Buenos Aires, Argentina
Pages: 364-388
Published: 202004
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 70
Accession Number: 2020-047181
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 2 tables, geol. sketch map
S24°10'60" - S24°10'60", W65°17'60" - W65°17'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 202013
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