Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton

ABSTRACT The upper Neogene Pisco Formation of Peru is known worldwide as one of the most significant Cenozoic marine vertebrate Konservatt-Lagerstatten, even featuring cetacean specimens that retain remains of soft tissues or stomach contents. Previous works showed that biomediated precipitation of...

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Autores principales:	Gioncada,Anna, Gariboldi,Karen, Collareta,Alberto, Celma,Claudio Di, Bosio,Giulia, Malinverno,Elisa, Lambert,Olivier, Pike,Jennifer, Urbina,Mario, Bianucci,Giovanni
Lenguaje:	English
Publicado:	Servicio Nacional de Geología y Minería (SERNAGEOMIN) 2018
Materias:	Marine vertebrates Taphonomy Pisco Formation Fossilization Phosphatization Early diagenesis
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062018000300379
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spelling	oai:scielo:S0718-710620180003003792018-11-05Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeletonGioncada,AnnaGariboldi,KarenCollareta,AlbertoCelma,Claudio DiBosio,GiuliaMalinverno,ElisaLambert,OlivierPike,JenniferUrbina,MarioBianucci,Giovanni Marine vertebrates Taphonomy Pisco Formation Fossilization Phosphatization Early diagenesis ABSTRACT The upper Neogene Pisco Formation of Peru is known worldwide as one of the most significant Cenozoic marine vertebrate Konservatt-Lagerstatten, even featuring cetacean specimens that retain remains of soft tissues or stomach contents. Previous works showed that biomediated precipitation of dolomite concretions around large-sized decaying carcasses was one of the most relevant processes responsible for exceptional fossil preservation. In turn, little is known about the modes of fossilization of well-preserved small-sized vertebrates, which are rather common in the Pisco Formation, but mostly do not exhibit dolomite concretions. We report on a cetacean specimen, identified as belonging to the extinct short-snouted, small dolphin species Brachydelphis mazeasi (Pontoporiidae), preserved within a late Miocene sandy deposit at the site of Pampa Corre Viento. This specimen consists of a moderately disarticulated partial skeleton exhibiting well-mineralized bones; it is not enclosed within a dolomite concretion, being however delimited by an evident dark boundary in the host sediment. Scanning electron microscopy and microanalytical investigations identify Mn-oxides and apatite as early diagenetic minerals around the skeleton. We argue that a rapid burial of the specimen was pivotal for the preservation of the bones, and allowed the early establishment of anoxic processes for degradation of organic matter. Coupled with availability of P in porewater, the reducing conditions and the lowered pH allowed precipitation of Ca-phosphate while increasing Mn solubility close to the pontoporiid carcass. Mn-oxides precipitated at the redox boundary, the latter defining the outer edge of the volume of sediment affected by altered chemical conditions due to the decaying processes. The permeability of the sediment and the small size of the carcass were possible factors unfavorable to extensive sulfate reduction, thus preventing the formation of a dolomite concretion and allowing bone phosphatization. This record emphasizes the role of conditions favorable to bone mineralization in absence of an isolating carbonate concretion, in cases of high quality preservation of small-sized vertebrates observed in the Pisco Formation. The observation of patterns in the distribution of diagenetic minerals in the sediment enclosing vertebrate remains without, or with limited carbonate concretions provides insights into early taphonomic processes.info:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Andean geology v.45 n.3 20182018-01-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062018000300379en10.5027/andgeov45n3-3122
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	Marine vertebrates Taphonomy Pisco Formation Fossilization Phosphatization Early diagenesis
spellingShingle	Marine vertebrates Taphonomy Pisco Formation Fossilization Phosphatization Early diagenesis Gioncada,Anna Gariboldi,Karen Collareta,Alberto Celma,Claudio Di Bosio,Giulia Malinverno,Elisa Lambert,Olivier Pike,Jennifer Urbina,Mario Bianucci,Giovanni Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
description	ABSTRACT The upper Neogene Pisco Formation of Peru is known worldwide as one of the most significant Cenozoic marine vertebrate Konservatt-Lagerstatten, even featuring cetacean specimens that retain remains of soft tissues or stomach contents. Previous works showed that biomediated precipitation of dolomite concretions around large-sized decaying carcasses was one of the most relevant processes responsible for exceptional fossil preservation. In turn, little is known about the modes of fossilization of well-preserved small-sized vertebrates, which are rather common in the Pisco Formation, but mostly do not exhibit dolomite concretions. We report on a cetacean specimen, identified as belonging to the extinct short-snouted, small dolphin species Brachydelphis mazeasi (Pontoporiidae), preserved within a late Miocene sandy deposit at the site of Pampa Corre Viento. This specimen consists of a moderately disarticulated partial skeleton exhibiting well-mineralized bones; it is not enclosed within a dolomite concretion, being however delimited by an evident dark boundary in the host sediment. Scanning electron microscopy and microanalytical investigations identify Mn-oxides and apatite as early diagenetic minerals around the skeleton. We argue that a rapid burial of the specimen was pivotal for the preservation of the bones, and allowed the early establishment of anoxic processes for degradation of organic matter. Coupled with availability of P in porewater, the reducing conditions and the lowered pH allowed precipitation of Ca-phosphate while increasing Mn solubility close to the pontoporiid carcass. Mn-oxides precipitated at the redox boundary, the latter defining the outer edge of the volume of sediment affected by altered chemical conditions due to the decaying processes. The permeability of the sediment and the small size of the carcass were possible factors unfavorable to extensive sulfate reduction, thus preventing the formation of a dolomite concretion and allowing bone phosphatization. This record emphasizes the role of conditions favorable to bone mineralization in absence of an isolating carbonate concretion, in cases of high quality preservation of small-sized vertebrates observed in the Pisco Formation. The observation of patterns in the distribution of diagenetic minerals in the sediment enclosing vertebrate remains without, or with limited carbonate concretions provides insights into early taphonomic processes.
author	Gioncada,Anna Gariboldi,Karen Collareta,Alberto Celma,Claudio Di Bosio,Giulia Malinverno,Elisa Lambert,Olivier Pike,Jennifer Urbina,Mario Bianucci,Giovanni
author_facet	Gioncada,Anna Gariboldi,Karen Collareta,Alberto Celma,Claudio Di Bosio,Giulia Malinverno,Elisa Lambert,Olivier Pike,Jennifer Urbina,Mario Bianucci,Giovanni
author_sort	Gioncada,Anna
title	Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
title_short	Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
title_full	Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
title_fullStr	Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
title_full_unstemmed	Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
title_sort	looking for the key to preservation of fossil marine vertebrates in the pisco formation of peru: new insights from a small dolphin skeleton
publisher	Servicio Nacional de Geología y Minería (SERNAGEOMIN)
publishDate	2018
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062018000300379
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Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton

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