Saradee Sengupta , Dhurjati Prasad Sengupta & Saswati
Stratigraphy of the upper Gondwana formations around Sohagpur, western
part of the Satpura Gondwana Basin, Central India.
Journal of the Geological Society of India 87(5): 503-519
The present work provides a detailed lithological map of the western
part of the Satpura basin around Sohagpur and reports the presence of new
archosauromorph fossil bones from that region. The study area is dominated by
the Bagra Formation along with a narrow patch of the underlying upper part of
the Denwa Formation. The lower Denwa and the underlying Pachmarhi formations
are absent here. The presence of the Pachmarhi Formation, as a tongue shaped
area, as mapped by Crookshank (1936) is discarded in this study on the basis of
lithology and petrographic analyses, instead the presence of the Bagra
Formation is suggested in this area. A comparison of the lithologies and the
vertebrate faunas of the upper Gondwana formations between eastern and western
part of the basin has been carried out for the first time. The comparison
indicates that the Denwa Formation present in the western sector represents
only the topmost part of the formation while the complete succession of Denwa
is preserved in the eastern sector. The Bagra Formation in the western sector
documents the presence of sheet-like sandstone bodies unlike the eastern part.
The vertebrate fauna of the eastern part is dominated by temnospondyl
amphibians while that of the western part is dominated by archosauromorph. The
vertebrate fossils of upper part of Denwa Formation, found from similar
lithologies in west and east though, have differences in the amount of
transportation before their burial.
Patrick J. Orr, Laetitia B. Adler, Susan R. Beardmore, Heinz Furrer,
Maria E. McNamara, Enrique Peñalver-Mollá & Ragna Redelstorff (2016)
"Stick 'n' peel": Explaining unusual patterns of
disarticulation and loss of completeness in fossil vertebrates.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online
Most fossil vertebrate skeletons are incomplete and/or disarticulated;
this is often the result of disturbance by water currents.
Existing taphonomic models emphasise the size, shape and density of
bones when determining whether or not they will be transported in currents.
Decay fluids leaking from a carcass stick it to the substrate; bones
on the downward-facing side are preferentially affected.
If subjected to a current, these bones are less likely to be removed
than others; this anomaly, 'stick 'n peel', can impact significantly on the
skeletal taphonomy of a carcass.
The phenomenon is common in the fossil record and can be identified
retrospectively by a characteristic set of unusual taphonomic features.
Few fossil vertebrate skeletons are complete and fully articulated.
Various taphonomic processes reduce the skeletal fidelity of decaying
carcasses, the effects of most of which are reasonably well understood. Some
fossil vertebrates, however, exhibit patterns of disarticulation and loss of
completeness that are difficult to explain. Such skeletons are one of two
variants. They are incomplete, often markedly so, but the preserved parts are
highly articulated. Alternatively, they are complete, or nearly so, but articulation
varies markedly between parts of the body. A characteristic feature is the
absence of skeletal elements that, on the basis of their larger size and/or
greater density, would be predicted to be present. Here we erect a model,
termed "stick 'n' peel", that explains how these distinctive patterns
originate. The model emphasizes the role of decay products, especially fluids
released from the carcass while resting on the sediment surface. These fluids
permeate the sediment below and around the carcass. As a result, skeletal
elements on the downward facing side of the carcass become adhered to the
sediment surface, and are less likely to be remobilized as a result of current
activity than others. The pattern of articulation and, especially, completeness
is thus not what would be predicted on the basis of the size, shape and density
of the skeletal elements. The effects of stick ‘n’ peel are difficult to
predict a priori. Stick ‘n’ peel has been identified in vertebrate fossils in
lacustrine and marine settings and is likely to be a common feature of the
taphonomic history of many vertebrate assemblages. Specimens becoming adhered
to the substrate may also explain the preservation in situ of the multi-element
skeletons of invertebrates such as echinoderms, and integumentary structures
such as hair and feathers in exceptionally preserved fossils.