Hematite and calcite coatings on fossil vertebrates

Bao, Huiming; Koch, Paul L.; Hepple, Robert P.

doi:10.2110/jsr.68.727

Cited by 47 publications

(35 citation statements)

References 86 publications

(45 reference statements)

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“…As the specimen was screen washed from a load of five tonnes of excavated material, more precise depositional relationships are unknown. It shares with all of the fossil bones from this deposit a thin coating of haematite and calcite cementation, consistent with the specimen being interred in these sediments for some time, rather than a modern specimen or a reworked fossil [23]. However, a Triassic age for Tikiguania does not necessarily follow.…”

Section: Discussionsupporting

confidence: 61%

Tikiguania and the antiquity of squamate reptiles (lizards and snakes)

2012

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Tikiguania estesi is widely accepted to be the earliest member of Squamata, the reptile group that includes lizards and snakes. It is based on a lower jaw from the Late Triassic of India, described as a primitive lizard related to agamids and chamaeleons. However, Tikiguania is almost indistinguishable from living agamids; a combined phylogenetic analysis of morphological and molecular data places it with draconines, a prominent component of the modern Asian herpetofauna. It is unlikely that living agamids have retained the Tikiguania morphotype unchanged for over 216 Myr; it is much more conceivable that Tikiguania is a Quaternary or Late Tertiary agamid that was preserved in sediments derived from the Triassic beds that have a broad superficial exposure. This removes the only fossil evidence for lizards in the Triassic. Studies that have employed Tikiguana for evolutionary, biogeographical and molecular dating inferences need to be reassessed.

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Section: Discussionsupporting

confidence: 61%

Tikiguania and the antiquity of squamate reptiles (lizards and snakes)

2012

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“…Periods of low net deposition would have also favored the accumulation of time-averaged assemblages in this particularly fossiliferous part of the formation, mixing fossils with different stages of alteration and potentially different overall taphonomic histories. Finally, the seasonal dry weather during deposition of the Cancha de Bochas Member provided one last necessary condition to preserve an abundance of fossils, namely an alkaline geochemical environmental that promoted the widespread calcite mineralization of bone characteristic of this portion of the formation (Bao et al, 1998). This mineralization was presumably contemporaneous with pedogenesis, which is suggested by the close relation between the calcic mineralization of bones and mineralized features in associated calcic paleosols (Fig.…”

Section: Discussionmentioning

confidence: 96%

“…There is no indication that the vertebrate carcasses were transported by currents on these hydromorphic floodplains. Decay of the carcasses both pre-and post-burial under anoxic poorly drained conditions led to the precipitation of iron minerals, most notably hematite, in the La Peña Member (Bao et al, 1998;Downing and Park, 1998).…”

Section: Discussionmentioning

confidence: 99%

“…The fossils preserved in the proximal facies exhibit variable weathering stages and varying states of disarticulation and association. The hydromorphic and potentially somewhat acidic conditions associated with prolonged wet seasons apparently led to the partial dissolution of some bones (Behrensmeyer, 1975) and prompted permineralization with iron complexes (Bao et al, 1998;Downing and Park, 1998).…”

Section: Discussionmentioning

confidence: 99%

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Vertebrate taphonomy of the Ischigualasto Formation

Colombi

Rogers

Alcober

2012

Journal of Vertebrate Paleontology

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ABSTRACT-Trends of preservation are established on the basis of 385 fossil occurrences in the Ischigualasto Formation. The distribution and preservational quality of vertebrate fossils are related to sedimentary facies and stratigraphic position and follow trends in basin evolution and paleoclimate. Fossils in the Ischigualasto Formation are mainly concentrated along the margins of the basin. Floodplain deposits preserve ca. 88% of fossils, which range from unidentifiable fragments to articulated skeletons. The remaining fossil occurrences (ca. 12%) come from coarser-grained fluvial channel deposits and exhibit variable preservational quality, including some well-preserved cynodont skulls. Fossils in the basal La Peña Member (ca. 4% of occurrences) are generally highly weathered and disarticulated with hematitic permineralization. The majority of collected specimens (ca. 65% of occurrences) come from the overlying Cancha de Bochas Member and range from isolated bones to articulated skeletons. Calcite, rather than hematite, is the predominant agent of permineralization. The succeeding Valle de la Luna Member (ca. 30% of occurrences) preserves an association between vertebrate fossils and plant remains. Fossil preservation suggests prolonged exposure prior to burial under wetter conditions with superficial and penetrating precipitation of hematite. The uppermost Quebrada de la Sal Member of the Ischigualasto Formation is nearly barren of fossil remains.RESUMEN-Se establecieron las tendencias en la preservación de restos de paleovertebrados a lo largo de la Formación Ischigualasto en base a 385 fósiles. La distribución y la calidad de preservación de los fósiles de vertebrados en esta unidad está relacionada con las facies sedimentarias y la posición estratigráfica de los mismos, variando según la evolución de la cuenca y del paleoclima. Los fósiles en la Formación Ischigualasto están principalmente concentrados en los márgenes de la cuenca. Paleoambientalmente, los depósitos de llanura de inundación preservan alrededor del 88% de los fósiles de la unidad, los cuales van desde fragmentos inidentificables hasta esqueletos articulados. Las restantes ocurrencias de fósiles (alrededor del 12%) provienen de depósitos de canal de grano grueso y también exhiben variables calidades de preservación, incluyendo algunos pequeños cráneos de cinodontes en excelente estado de preservación. Estratigráficamente, los fósiles en el miembro basal La Peña (alrededor del 4% de los hallazgos) están generalmente muy meteorizados, desarticulados y permineralizados con hematita. La mayoría de los especímenes colectados (alrededor del 65% de los hallazgos) provienen del suprayacente Miembro Cancha de Bochas, los cuales van desde huesos aislados hasta esqueletos articulados completos. Estos restos están permineralizados principalmente con calcita en lugar de hematita. En el siguiente, Miembro Valle de la Luna (alrededor del 30% de los hallazgos), se preserva una peculiar asociación de restos fósiles de vertebrados y plantas. La preservación ...

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“…carbonate cement in such concretions is not always clear, potentially coming from organic-matter degradation including biogenic carbonate Hendry et al 1996;Boggs 2009), deeply buried marine rocks (Enos and Kyle 2002), proximal limestone deposits (McBride 1987;Boggs 2009), or pedogenesis (Kraus 1987;Bao et al 1998;Beckner and Mozley 1998). Some authors suggest that concretions commonly form during early burial at or just below the sediment-water interface, sometimes during single precipitation episodes (Hudson 1978;Carpenter et al 1988;Mozley and Burns 1993;Duck 1995;Middleton and Nelson 1996;Raiswell and Fisher 2000;Woo and Khim 2006).…”

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confidence: 99%

Depositional Environment of the Lower Cretaceous (Upper Albian) Winton Formation At Isisford, Central-West Queensland, Australia, Inferred From Sandstone Concretions

Syme¹,

Welsh²,

Roberts³

et al. 2016

Journal of Sedimentary Research

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Numerous vertebrate and plant fossils have been found in ex-situ sandstone concretions near Isisford in central-west Queensland since the mid-1990s. These concretions are found in the Lower Cretaceous portion (upper Albian, 100.5-102.2 Ma) of the Winton Formation. The lower most Winton Formation is thought to have formed in a fluvial channel or flood-basin setting proximal to the Eromanga Sea, but due to the scarcity of good exposures, the local depositional environment at Isisford has not been ascertained. Minimal compression of vertebrate and plant fossils, a lack of grain suturing, predominantly cement-supported fabric, and fractures running through calcite cement, as well as fossil bone and framework grains, indicates that concretions formed during early diagenesis (pre-compactional or syndepositional). Calcite stable-isotope δ 18 O VPDB values range from -12.25 to -4‰, indicating mixed marine and meteoric pore waters, and δ 13 C VPDB values range from -5.3 to 4.1‰, indicative of both sulfate reduction and methanogenesis of organic material (including decaying vertebrate soft tissues) in the burial environment. The mixed marine and freshwater signature suggests a marginal marine setting, possibly deltaic or estuarine, connected to the regressive epicontinental Eromanga Seaway at around 102-100 Ma. This is not inconsistent with the lithology from nearby cores, coupled with Isisford fossil-vertebrate ecology (personal observation). Our research demonstrates the utility of investigating ex-situ concretions to refine paleoenvironments at localities where little or no outcrop is available and traditional facies analysis is impractical. INTRODUCTIONSandstone concretions cemented with calcium carbonate have been reported worldwide, ranging from the centimeter scale (Dix and Mullins 1987;Allison and Pye 1994;Mozley and Davis 2005; Tabor et al. 2007), the decimeter to meter scale (Dix and

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Hematite and calcite coatings on fossil vertebrates

Cited by 47 publications

References 86 publications

Tikiguania and the antiquity of squamate reptiles (lizards and snakes)

Tikiguania and the antiquity of squamate reptiles (lizards and snakes)

Vertebrate taphonomy of the Ischigualasto Formation

Depositional Environment of the Lower Cretaceous (Upper Albian) Winton Formation At Isisford, Central-West Queensland, Australia, Inferred From Sandstone Concretions

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