Enigmatic Ediacaran megascopic bedding plane structures on the Sonia Sandstone, Jodhpur Group, Marwar Supergroup, India: seaweed or problematica?

The present study discusses the origin and affinity of enigmatic Ediacaran bedding plane structures reported earlier from the Sonia Sandstone of the Marwar Supergroup (Ediacaran to Lower Cambrian). These forms are conspicuously large, non‐carbonaceous and three‐dimensionally preserved. Morphologically, these structures are not comparable with any known plant/animal fossil, trace fossil, microbially induced sedimentary structures (MISS) found in the Ediacaran assemblages or any other extant forms and are invariably associated with MISS. Past researches on these fossils did not resolve their affinity, form and function. The present forms have certain features akin to seaweed organization such as thallus, loop pattern within the thallus, variously positioned nodes/swellings, tapering at the end of thallus, branching pattern and rarely occurring holdfast‐like features. Systematic description, incorporating detailed morphological features, population size, their relationship with associated sediments and stratigraphic distribution, is based on the study of 54 specimens. Subtidal to intertidal models of depositional sedimentary environment, palaeoecology, biogenicity, affinity, taphonomic changes, association of these forms with MISS and other parameters are also discussed. A succession of plausible interpretations is offered; seaweed is the most likely interpretation. The Marwar Supergroup, thus, unravels some of the hitherto enigmatic forms of the Ediacaran Period (635–541 Ma). Copyright © 2016 John Wiley & Sons, Ltd.

South Pole: Nature and Culture by Elizabeth Leane. Reaktion Books, London, 2016. No. of pages: 232. Price: UK£14‐95. ISBN 978‐1‐78023‐596‐7 (paperback).

Book Review Authors Stephen K. Donovan Naturalis Biodiversity Center, Leiden, the Netherlands Search for more papers by this author No abstract is available for this article. Ancillary Article Information DOI 10.1002/gj.2851 View/save citation Format Available Full text: HTML | PDF Copyright © 2016 John Wiley & Sons, Ltd. Request Permissions …

The invalidity of the trace fossil Tremichnus Brett

The ichnogenus Tremichnus Brett was established for small round pits in echinoderm endoskeletons, principally crinoids. It is morphologically identical to Oichnus Bromley. It is significant that infestation of the echinoderm test is an integral part of any diagnosis of Tremichnus. This is an unacceptable ichnotaxobase; the diagnosis should only define morphology and, with reservation, substrate, such as unlithified (= soft), lithic or wood. From a recent revival of Tremichnus, Tremichnus paraboloides Brett is a junior homonym of Oichnus paraboloides Bromley; both share a similar morphology. Tremichnus puteolus Brett is more correctly referred to Lacrimichnus Santos et al. Tremichnus excavatus (Donovan and Jagt) could only be force‐fitted into Tremichnus following a drastic revision of the original diagnosis and is here reassigned to Oichnus, as originally described. Copyright © 2016 John Wiley & Sons, Ltd.

Significance of seismites in the Late Cretaceous transgressive Nimar Sandstone succession, Son‐Narmada rift valley, Central India

Detailed facies architecture study of the Late Cretaceous (Cenomanian) Nimar Sandstone (Bagh Group), from Son‐Narmada rift valley, Central India, reveals deposition in a fluvial–marine environment. The lower part of the Nimar Sandstone succession depicts deposition in predominantly fluvial setting, whereas the middle–upper part of the succession manifests sedimentation under a tide‐dominated estuarine to a tide–wave influenced shoreface environment. Retrogradational nature of the successions in the upper part and lateral facies change from west to east signifies an eastwardly decreasing marine influence. This attests to a sustained event of marine transgression from the west affecting the Son‐Narmada rift valley during the Late Cretaceous time. Beds with various soft‐sediment deformation structures (SSDS), viz., convolute laminae, load and flame structures, pseudonodules, contorted beddings, syn‐sedimentary faults, and sand/silt dykes, occur in distinct stratigraphic levels within the middle part of the succession. These beds are separated by thick successions of undeformed beds. This paper reports these beds as seismites for the first time from the Son‐Narmada rift valley. The seismites signify instantaneous liquefaction and fluidization of unconsolidated sediments triggered by passage of repetitive earthquake shock waves during sedimentation in fault‐bound rift basin. These seismites are important as they mark a new phase of reactivation of the Son‐Narmada South Fault within the Son‐Narmada rift valley during the Cenomanian time. This reactivation of the Son‐Narmada South Fault led to basinal subsidence under prevalent extensional tectonism, which controlled the sedimentation during the Late Cretaceous time. Copyright © 2016 John Wiley & Sons, Ltd.

Clinopyroxenites (diopsidites) and metabasites from the East Sarmatian Orogen, East European Craton

The East Sarmatian Orogen was built through successive subduction and collision processes at the junction of the Sarmatia and Volga‐Uralia segments of the East European Craton. In this paper we present petrological and geochemical characteristics of diopsidites and host amphibolites from the central part of this orogen. We report a new occurrence of metabasites (meta‐gabbros and amphibolites) and anorthite–bytownite‐bearing diopsidites from the Palaeoproterozoic Vorontsovka terrane of the East Sarmatian Orogen. The diopsidites occur as networks of veinlets and dykes within the metabasite layers (thickness up to 100 m) and are composed predominantly of high‐Mg diopside (Mg# up to 0.87) and calcic plagioclase (An99–73) with traces of K‐feldspar, titanite, calcite, quartz with retrograde chlorite and epidote. The diopsidites are low in Ti and K and high in Mg (Mg# greater than 0.82) rocks. They have low REE; positive Ce, U and Sr anomalies; and negative Th, Nb and Ti anomalies. The meta‐gabbros and amphibolites are composed of calcic amphibole, albite, quartz, biotite, zoisite, prehnite and ore minerals (sulphides + ilmenite). The amphibolites are low Al, low K, magnesian–ferroan (Mg# = 0.46–0.75) and medium Ti (TiO2 0.75–1.37 wt.%) (SiO2 40.1–47.3 wt.%). The meta‐gabbros exhibit slight LREE and LILE enrichment, particularly in Rb, Ba and Sr. The amphibolites are tholeiitic in composition and have N‐MORB‐like REE and HFSE features, with high 143Nd/144Nd (0.512736) and positive εNd(T) (6.0).
The diopsidites reported in our study compare with convergent‐margin rocks formed via metasomatic processes associated with slab subduction. The metabasite protoliths represent oceanic crust with N‐MORB‐type features with the LILE enrichment accompanying the subduction zone process. Copyright © 2016 John Wiley & Sons, Ltd.

Strata and Time: Probing the Gaps in our Understanding, edited by D.G. Smith, R.J. Bailey, P.M. Burgess and A.J. Fraser. Geological Society, London, Special Publication, 404, 2015. No. of pages: vii+325. Price: UK £120.00. ISBN 978-1-86239-655-5 (hardback).

Book Review Authors Nigel Ainsworth PalaeoDate Ltd., 39 De Tany Court, St. Albans, AL1 1TU, UK Search for more papers by this author No abstract is available for this article. Ancillary Article Information DOI 10.1002/gj.2846 View/save citation Format Available Full text: HTML | PDF Copyright © 2016 John Wiley & …

Depositional processes in the distal part of a large alluvial fan’s feeder channel in Himalayan foothills, India

This paper presents results of detailed facies and architectural element analyses of the sedimentary fill of the Ranibag valley in the Himalayan foothills of north‐western India. Forming a buffer zone between the source and sink of the Ganga foreland basin’s Gola alluvial fan, the Ranibag valley is filled with coarse gravels comprising five distinct facies. These are clast‐supported massive gravel, horizontal‐bedded gravel, crudely bedded gravel, sandy gravel and matrix‐supported disorganized gravel facies. The specific assemblages and sequences of these facies, defined by fifth‐ and fourth‐order bounding surfaces, belong to mutually associated channel (CH) and gravel bar and bedform (GB) architectural elements. Both the elements have accreted only during floods by combined fluvial and debris‐flow processes, but dominantly by the fluvial processes under conditions of high water‐to‐sediment ratio. Depositional processes in the valley are akin to those of the proximal alluvial fans of the Ganga Basin. Nonetheless, voluminous alluviation of coarser gravels in this extreme distal feeder channel valley has affected the fan processes downstream. It reduced the sediment budget and thus increased water‐to‐sediment ratio downstream to favour fluvial processes on the Gola fan. Copyright © 2016 John Wiley & Sons, Ltd.

Geomorphic fluvial markers reveal transient landscape evolution in tectonically quiescent southern Peninsular India

The morphology of 19 adjacent westward‐flowing and four eastward‐flowing major catchments draining across the Western Ghat escarpment in southern Peninsular India was studied to examine how the channel patterns and their longitudinal profiles reflect the landscape evolution. Field surveys were complemented with the quantitative morphometric analysis of fluvial channel profiles using digital topographic data. Results show distinctive differences between eastward‐ and westward‐flowing drainage systems. The channel profiles of eight westward‐flowing drainage basins show an apparent morphological equilibrium characterized by concave upward shape, whereas most channels from the other westward‐flowing basins display knickpoint(s). All studied eastward‐flowing drainage basins display the morphological signature of disequilibrium in the form of knickpoints. The eastern and western margins of southern Peninsular India have experienced major tectonic events ~120 and ~65 Ma ago, respectively, and are since then tectonically quiescent. All studied westward‐flowing basins share the same Arabian Sea base level, flow over comparable lithologies and developed under similar climatic conditions. The studied eastward‐flowing basins have the Bay of Bengal as base level and similar climatic conditions. Therefore, the spatial variations in catchment morphometry is interpreted as a dynamic response to complex interactions and feedbacks between (i) pre‐existing topography along and across the escarpment margins, and (ii) vigorous drainage piracy in more recent times. We hypothesize that the studied drainage basins have experienced different forcing magnitudes that can be quantified to a first order using the present day topography. Copyright © 2016 John Wiley & Sons, Ltd.

Estimated predation rate of the stalked bourgueticrinid (Crinoidea) Democrinus from Roatán, Honduras

Crinoids have the ability to regenerate their crowns when arms are autotomized or bitten off by predators. The evidence of predation is visible in many populations of crinoids, including the deep water stalked crinoid Democrinus off the coast of Roatán, Honduras. Throughout the videos taken in a submersible, many individuals displayed arms that are significantly shorter relative to their stalk lengths than the full‐grown adults in the area, indicating arm regeneration. Some individuals were missing crowns completely, strongly suggesting predation by fishes. Our calculated predation rate of 17.25% including individuals missing a crown or regenerating their arms in situ is significantly greater than that rates determined in previous studies of predation on Democrinus. Copyright © 2016 John Wiley & Sons, Ltd.

Arthur Smith Woodward: His Life and Influence on Modern Vertebrate Palaeontology, Edited by Z. Johanson, P.M. Barrett, M. Richter and M. Smith. Geological Society, London, Special Publication 430, 2016. No. of pages: 362. Price: UK£110‐00. ISBN 978‐1‐86239‐741‐5 (hardback).

Book Review Authors Stephen K. Donovan Naturalis Biodiversity Center, Leiden, The Netherlands Search for more papers by this author No abstract is available for this article. Ancillary Article Information DOI 10.1002/gj.2841 View/save citation Format Available Full text: HTML | PDF Copyright © 2016 John Wiley & Sons, Ltd. Request Permissions …