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Published By Society For Sedimentary Geology

0883-1351

Palaios ◽  
2021 ◽  
Vol 36 (12) ◽  
pp. 377-392
Author(s):  
SEBASTIAN VOIGT ◽  
KARL OLIVER ◽  
BRYAN J. SMALL

ABSTRACT The Pennsylvanian–Permian Maroon Formation of northwest Colorado is an up to 4,600 m thick succession of mainly siliciclastic continental red-beds deposited in equatorial intermontane basins of the Ancestral Rocky Mountains. Sedimentary surfaces of fluvio-lacustrine to eolian siltstones and fine-grained sandstones from various stratigraphic levels within the Maroon Formation preserve cm-sized straight to gently curved sediment-filled acicular structures referred to five morphological groups: single, branched, stellate, rosette, and bunched. Depositional environment, shape, and size of the structures are most similar to ice crystal marks that result from freezing of water-saturated fine-grained substrate at the sediment-air interface. They differ from other syngenetically produced crystals and crystal pseudomorphs in sedimentary rocks mainly by crystal shape and environmental conditions. The potential ice crystal marks of the Maroon Formation are notable for the fidelity and morphological diversity of the crystal casts and could be a key for the understanding of similar but hitherto often only called enigmatic structures of the sedimentary rock record. The ice crystal mark occurrences in the Maroon Formation suggest that night frost affected lower elevation equatorial areas during the climax of the Late Paleozoic Ice Age and may stimulate research on evolutionary adaptations of early terrestrial biota to overcome significant air temperature fluctuations.


Palaios ◽  
2021 ◽  
Vol 36 (12) ◽  
pp. 353-355
Author(s):  
M. GABRIELA MÁNGANO

Palaios ◽  
2021 ◽  
Vol 36 (12) ◽  
pp. 356-376
Author(s):  
MARCOS ANTONIO BATISTA DOS SANTOS FILHO ◽  
GERSON FAUTH ◽  
BENJAMIN SAMES ◽  
ERIK WOLFGRING ◽  
JORGE VILLEGAS-MARTÍN

ABSTRACT This paper presents the results of a paleoenvironmental study of two Hauterivian–Aptian adjacent sections (Transnordestina A/B) of the Iguatu Basin using ostracods and aided by X-ray fluorescence (XRF), total organic carbon (TOC), total sulfur (S), and spectral analyses. Cluster analysis divided the 10 genera found into two main groups: one composed of Alicenula-Pattersoncypris?-Brasacypris-Hastacypris-Ilyocypris?, and the second composed of Cypridea-Looneyellopsis-Rhinocypris?. The first group is interpreted as representing paleoenvironments with permanent waterbodies, such as lakes, and the second as being indicative of ephemeral settings, such as temporary pools in an inundation plain. XRF analysis using the positive peaks of Ca/Ti and Ca/ΣTi, Fe, Al ratios show a few dry periods, particularly in the lower and middle part of Transnordestina A, between 0 to 175 m and 385 to 475 m, which also display a small number of ostracods. Total S shows several high peaks which might be indicative of gypsum deposition during droughts. Spectral analysis of molar Ti/Al ratio shows two intervals with different sedimentation rates, between 0 and 233 m, and 233 to 836 m. For the first interval, six 100 ka eccentricity cycles were identified; the low number of ostracods for the interval and highly variable Ca/Ti and Ca/ΣTi, Fe, Al values indicate a different sedimentation rate in a drier environment. For the second interval, ten 405 ka cycles were identified; its higher ostracod count and more stable Ca/Ti and Ca/ΣTi, Fe, Al values could be indicative of increasing humidity.


Palaios ◽  
2021 ◽  
Vol 36 (11) ◽  
pp. 331-338
Author(s):  
BRENT H. BREITHAUPT ◽  
MARJORIE A. CHAN ◽  
WINSTON M. SEILER ◽  
NEFFRA A. MATTHEWS

ABSTRACT Within the eolian Lower Jurassic Navajo Sandstone, exposed in the Coyote Buttes area of Vermilion Cliffs National Monument in Arizona, a site (informally known as the “Dinosaur Dance Floor”) is reinterpreted as an enigmatic, modified (possibly pedogenic) eolian surface that was exposed and further modified and accentuated by modern weathering and erosion. The resultant surface is covered with small, shallow potholes or weathering pits, with no direct evidence of dinosaur activity.


Palaios ◽  
2021 ◽  
Vol 36 (11) ◽  
pp. 339-351
Author(s):  
SARADEE SENGUPTA ◽  
DHURJATI P. SENGUPTA

ABSTRACT A bonebed of multiple skeletons of the Triassic horned reptile Shringasaurus indicus was discovered in the upper Denwa Formation, Satpura Gondwana Basin, India. The monotaxic bonebed contains multiple individuals of different ontogenic stages indicating herding behavior by Shringasaurus indicus. The herd was a mixed-sex herd. The adult and sub-adult bones in the bonebed exceed the number of juvenile bones. The distribution of the bones was slightly patchy, bones of different individuals were admixed, and several bones were piled up implying mass mortality. The bonebed occurs in a fine-grained mudrock that is hydraulically incompatible with long-distance transport and concentration by currents. Sedimentary facies analysis indicates that the bonebed accumulated and was buried in a crevasse splay deposit between two ENE-WSW trending channel-fill complexes. The northern channel-fill complex was formed by unidirectional flow with lateral channel migration towards the south and with minor contemporaneous tectonic subsidence. Repeated breaching of the levee by this channel flow led to the incremental development of the crevasse splay deposit. The herd of Shringasaurus indicus, which lived near to the perennial channel, was drowned en masse and the carcasses were trapped within the muddy sediments of the crevasse splay deposit. Apart from a partially articulated skeleton, the rest of the bones were disarticulated but remained associated. The bones show little evidence of post-mortem modifications. With a continuous supply of the sediments through the spillover channels, the bones were buried before complete disarticulation and dispersal had taken place.


Palaios ◽  
2021 ◽  
Vol 36 (10) ◽  
pp. 326-329
Author(s):  
MARK A. WILSON ◽  
ANNA M. COOKE ◽  
SHELLEY A. JUDGE ◽  
TIMOTHY J. PALMER

ABSTRACT Ooimmuration is here defined as a taphonomic process by which fossils are preserved within ooids. It is a form of lithoimmuration, although depending on the role of microbes in the formation of the ooid cortex, ooimmuration can also be considered a type of bioimmuration. Fossils enclosed within ooids are protected from bioerosion as well as the abrasion common in energetic depositional environments such as ooid shoals. Many taxa in some fossil assemblages may be known only because they were ooimmured. We describe as examples of ooimmuration fossils preserved in an oolite from the Middle Jurassic (Bajocian) Carmel Formation in southwestern Utah.


Palaios ◽  
2021 ◽  
Vol 36 (10) ◽  
pp. 313-325
Author(s):  
BRIAN R. PRATT

ABSTRACT A category of wrinkle structures, often termed Kinneyia structure or Runzel marks, comprises bedding plane features consisting typically of anastomosing, low-relief, flat-topped ridges with intervening depressions. Topographic relief is usually less than a millimeter. They are locally common on the upper surfaces of fine- to medium-grained sandstone beds interbedded with mudstone deposited in offshore settings, especially in Precambrian and lower Paleozoic strata but as young as Cretaceous. For more than the last two decades these wrinkle structures have been widely regarded as due to microbial mats, and have been taken as evidence for dominance in the Proterozoic of microbially stabilized sediment and, in the Phanerozoic, a matground marine benthic ecology which gradually gave way to a mixground ecology. The detailed morphology and cross-cutting relationships demonstrated by a range of specimens of Proterozoic, Cambrian, and Silurian age, however, cast this interpretation into doubt. The relationship between the wrinkled surface and bioclasts such as shells and both prior- and later-formed scour surfaces, and horizontal and vertical burrows show that these wrinkles did not develop due to the surface topography of microbial mats or compaction of microbial mats during burial, but instead formed at the top of a sand bed at the interface with an overlying layer of mud. Deformation is ascribed to vibration from low-magnitude earthquakes. The presence in some units of small-scale sedimentary dikelets and crack arrays that formed later after some stiffening, along with locally associated seismites and other evidence for nearby faulting, show that syndepositional tectonic activity was not unexpected and support the interpretation that this category of wrinkle structures is a type of seismite.


Palaios ◽  
2021 ◽  
Vol 36 (9) ◽  
pp. 301-312
Author(s):  
RANITA SAHA ◽  
SHUBHABRATA PAUL ◽  
SUBHRONIL MONDAL ◽  
SUBHENDU BARDHAN ◽  
SHILADRI. S DAS ◽  
...  

ABSTRACT Gastropod drillholes on prey shells provide an opportunity to test the importance of predation in an evolutionary context. Although records of drilling predation are widespread across the Phanerozoic, the temporal distribution and relative importance of this mode of predation is still controversial. Further, some studies indicate a decline of drilling predation in the Mesozoic but other studies do not. In this study, we present a new dataset of gastropod drilling predation on Kimmeridgian and Tithonian bivalves of Kutch, India. Our study suggests that drilling was one of the prevailing modes of predation in the Upper Jurassic of Kutch with strongly variable intensities, ranging from 2% in the Kimmeridgian Seebachia to 26% in the Tithonian Pinna. A significant, albeit small, increase in drilling intensity from the Kimmeridgian to the Tithonian assemblages is associated with a change in relative sea-level and depositional environment. The morphology of drillholes and recent discovery of body fossils from the same stratigraphic units suggest naticid gastropods as the most likely drillers. A literature survey, along with previously collected specimen from the Jurassic of Kutch, reveals a more complex history of drilling predation than previously assumed.


Palaios ◽  
2021 ◽  
Vol 36 (9) ◽  
pp. 283-300
Author(s):  
WILLIAM J. FREIMUTH ◽  
DAVID J. VARRICCHIO ◽  
KAREN CHIN

ABSTRACT The terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the Pleistocene and is characterized by tubular burrows with ellipsoidal fecal pellets, indicating substrate feeding by earthworms or other invertebrates. We describe 11 specimens attributable to Edaphichnium isp. from Egg Mountain, a terrestrial locality with a diverse fossil assemblage from the Upper Cretaceous Two Medicine Formation in Montana, USA, and assess their paleoenvironmental and paleoecological implications. These ichnofossils were recovered from a 1.5 meter stratigraphic succession comprised of calcareous siltstones and limestones with abundant fossil insect pupal cases, representing well-drained paleosols. Although burrows are not always present, three recurring arrangements of Edaphichnium isp. fecal pellets are identified: linearly arranged pellets, horizon-confined pellets, and pellets in clusters dispersed vertically and horizontally throughout the matrix. Two color patterns (light and dark pellets) are also distinguished. Pellets are fine-grained and have a consistently ellipsoidal shape (length:diameter of 1.57), with maximum lengths ranging from 1.9–6.7 mm (mean 4.1 mm) and maximum diameters ranging from 1.0–4.1 mm (mean 2.6 mm). Geochemical analyses indicate pellets are comprised of varying proportions of calcite, plagioclase, and quartz, and are enriched in phosphorus relative to the sedimentary host matrix. Possible trace makers include chafer or other coleopteran larvae, millipedes, and earthworms, suggesting a range of capable trace makers of Edaphichnium-like fecal pellets. Edaphichnium isp. at specific stratigraphic horizons suggests increased organic content in the subsurface, potentially connected to depositional hiatuses. Edaphichnium isp. adds a secondary component to the Celliforma ichnofacies known from Egg Mountain and surrounding strata, and to the array of nesting, feeding, and dwelling traces of wasps, beetles, other invertebrates, mammals, and dinosaurs from the locality.


Palaios ◽  
2021 ◽  
Vol 36 (8) ◽  
pp. 269-282
Author(s):  
FELLIPE P. MUNIZ ◽  
MARCOS CÉSAR BISSARO-JÚNIOR ◽  
EDSON GUILHERME ◽  
JONAS PEREIRA DE SOUZA FILHO ◽  
FRANCISCO RICARDO NEGRI ◽  
...  

ABSTRACT The Niterói and Talismã sites comprise two of the most important fossiliferous deposits of the Neogene in Brazil. After 30 years of research, these sites have revealed rich assemblages of vertebrates and provided a glimpse of the Amazonian fauna and environment during the Miocene. Despite this, detailed studies that attempt to explain the genesis of these bonebeds are still scarce and hamper more robust paleoenvironmental and paleoecological reconstructions. Here we provide the first in-depth taphonomic analysis for both locations. Sedimentological and taphonomic evidence suggest that the depositional environments of Niterói and Talismã were similarly represented by shallow and calm waters in lacustrine/swampy contexts. We propose that the accumulation of bones and teeth is the result of attritional (day-to-day) mortality of organisms of the local community in a low sedimentation environment. The thanatocoenosis was exposed to biostratinomic processes for longer periods of time, which explains the high disarticulation, disassociation, fragmentation and loss of skeletal elements. The almost absence of weathering indicates that the aquatic environment slowed down the organic degradation of bioclasts, while the rarity of abrasion shows a limited influence of hydraulic flows in transporting and remobilizing bioclasts. Thus, both sites preserve mostly autochthonous to parautochthonous bioclasts, with a moderate level of time-averaging. Our results corroborate the hypothesis that lentic environments can present remarkable preservational conditions for the formation of attritional accumulations of vertebrate remains. Moreover, we show how the different collecting methods affect the description of preservational features and taphonomic interpretations of both fossil assemblages.


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