Taphonomy and palaeoecology of benthic macroinvertebrates from the Agua de la Mula Member of the Agrio Formation, Neuquén Basin (Neuquén province, Argentina) [Elektronische Ressource] : sequence stratigraphic significance / vorgelegt von Fernando Archuby

Fernando Ortiz

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• Publié par: julius-maximilians-universitat_wurzburg
• Publié le: 01 janvier 2009
• Nombre de lectures: 28
• Poids de l'ouvrage: 129 Mo

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Archuby, F: Taphonomy, palaeoecology and sequence stratigraphy.











To my parents, César and Liliana.


Pág. 2 Archuby, F: Taphonomy, palaeoecology and sequence stratigraphy.

Index
Abstract......................................................................................................6
1. Introduction............................................................................................9
2. Geological setting ................................................................................11
Lithostratigraphy: the Agrio Formation.................................................13
Biostratigraphy .....................................................................................14
Sequence stratigraphy.........................................................................15
3. Materials and methods ........................................................................18
Field work.............................................................................................18
Faunal content .....................................................................................19
Trace fossils.........................................................................................20
Data analysis........................................................................................21
Abbreviations used in the text..............................................................21
4. The sections ........................................................................................22
Bajada del Agrio...................................................................................25
Agua de la Mula ...................................................................................26
Results.....................................................................................................27
5. Facies analysis ................................................................................27
Methods............................................................................................30
Facies and facies associations ........................................................36
Facies successions ..........................................................................84
Discussion ........................................................................................86
6. Stratigraphy..................................................................................92
6.1. Lithostratigraphy....................................................................92
6.2. Biostratigraphy......................................................................93
6.3. Anoxic events........................................................................99
6.4. Sequence stratigraphy........................................................101
7. Trace fossils................................................................................141
8. The benthic macrofauna ................................................................149
Autoecological remarks..................................................................155
Synecology.....................................................................................157
Discussion ......................................................................................202
9 Taphonomy .....................................................................................215

Pág. 3 Archuby, F: Taphonomy, palaeoecology and sequence stratigraphy.

Types of skeletal concentrations....................................................218
Taphonomic patterns and trends along starvation/dilution sequences
..................................................................................................................231
Taphonomic trends in higher hierarchy sequences .......................234
The taphonomic “windows” ............................................................237
10. General remarks and conclusions...................................................241
Plates.....................................................................................................253
Acknowledgements ...............................................................................274
Reference List........................................................................................275
Appendix A. Taxonomic list ...................................................................292
Kingdom Protista ...............................................................................292
Kingdom Animalia ..............................................................................293
Phylum Cnidaria.................................................................................293
Class Anthozoa ..............................................................................293
Phylum Echinodermata......................................................................294
Class Echinoidea............................................................................294
Class Crinoidea ..............................................................................294
Phylum Annelida ................................................................................295
Phylum Mollusca................................................................................296
Class Scaphopoda .........................................................................296
Class Gastropoda...........................................................................296
Class Pelecypoda...........................................................................300
Phylum Bryozoa.................................................................................312
Appendix B: Taxonomic counts section BAL ........................................313
Appendix C: Taxonomic counts section AML........................................318
Appendix D: samples per cluster, section BAL .....................................320
Appendix E: samples per cluster, section AML.....................................322
Appendix-figures 1-3 .............................................................................324
Erklärung ...............................................................................................350


Pág. 4 Archuby, F: Taphonomy, palaeoecology and sequence stratigraphy.


Taphonomy and palaeoecology of benthic macroinvertebrates from
the Agua de la Mula Member of the Agrio Formation, Neuquén
Basin (Neuquén province, Argentina): sequence stratigraphic
significance

1 Fernando Archuby

1Institut für Paläontologie der Universität Würzburg


Pág. 5 Archuby, F: Taphonomy, palaeoecology and sequence stratigraphy.

Abstract.
The taphonomic and paleoecologic aspects of the Upper Hauterivian to
Lower Barremian Agua de la Mula Member of the Agrio Formation (Neuquén
Basin, Argentina) were studied in the frame of the sequence stratigraphic
paradigm. The Agua de la Mula Member, a ca. 600 m thick succession of highly
cyclic marine sediments was surveyed at two localities. Detailed bed-by-bed
sedimentologic, stratigraphic, ichnologic, taphonomic and paleoecologic data
collection allowed a precise paleoenvironmental, stratigraphic, taphonomic and
synecologic interpretation, in a controlled sequence stratigraphic framework.

The main architectural stratigraphic component is the Starvation-Dilution
Sequence, interpreted as a the effect of a sixth-order, Milankovitch precession-
driven cycle. Dilution hemisequences are siliciclastic-dominated and show
evidence of depth changes. Starvation hemisequences show a diverse variation
of mixed carbonate-siliciclastic facies that is linked to sequence stratigraphy.

Ammonite-based biostratigraphy was revised and new knowledge
proposed. The stratigraphic framework was improved by combining
biostratigraphy, sequence stratigraphy and event stratigraphy. Nine main
sequences were described, linked to other stratigraphic markers and correlated
with other sequence stratigraphic charts.

Several orders of cyclicity were inferred. Third- and fourth-order
sequences are the major sequences, not subordinated to higher hierarchies
(lower order). Precession, obliquity, and short and long eccentricity cycles of the
Milankovitch band are proposed. Among the different sequence stratigraphic
models the transgression-regression model fits the majority of the sequences
described in this work. The depositional-sequence model could be applied only
to the first third-order sequence, in which the true sequence boundary is
identifiable. Starvation-dilution sequences, however, are composed by to
components that are not completely explained by those models. Starvation
hemisequences developed in intermediate to deep settings record the

Pág. 6 Archuby, F: Taphonomy, palaeoecology and sequence stratigraphy.

transgressive phase as well as the earLy regressive one without visible
stratigraphic boundaries.

112 samples with 22,572 individuals were grouped into fifteen fossil
associations and one assemblage that reflect the interaction of different factors:
age, position in major, medium and starvation dilution sequences and,