Ernst Julius Öpik's (1916) note on the theory of explosion cratering on the Moon's surface—The complex case of a long‐overlooked benchmark paper

High‐velocity impact as a common phenomenon in planetary evolution was ignored until well into the twentieth century, mostly because of inadequate understanding of cratering processes. An eight‐page note, published in Russian by the young Ernst Julius Öpik, a great Estonian astronomer, was among the key selenological papers, but due to the language barrier, it was barely known and mostly incorrectly cited. This particular paper is here intended to serve as an explanatory supplement to an English translation of Öpik's article, but also to document an early stage in our understanding of cratering. First, we outline the historical–biographical background of this benchmark paper, and second, a comprehensive discussion of its merits is presented, from past and present perspectives alike. In his theoretical research, Öpik analyzed the explosive formation of craters numerically, albeit in a very simple way. For the first time, he approximated relationships among minimal meteorite size, impact energy, and crater diameter; this scaling focused solely on the gravitational energy of excavating the crater (a “useful” working approach). This initial physical model, with a rational mechanical basis, was developed in a series of papers up to 1961. Öpik should certainly be viewed as the founder of the numerical simulation approach in planetary sciences. In addition, the present note also briefly describes Nikolai A. Morozov as a remarkable man, a forgotten Russian scientist and, surprisingly, the true initiator of Öpik's explosive impact theory. In fact, already between 1909 and 1911, Morozov probably was the first to consider conclusively that explosion craters would be circular, bowl‐shaped depressions even when formed under different impact angles.     

Preservation of a heavily bored belemnite rostrum from the upper Maastrichtian of north-east Belgium

The robust calcite rostra (or guards) of belemnites were attractive substrates for some boring organisms in the Mesozoic. The rostra of belemnitellid coleoids are common at certain levels within the Gulpen and Maastricht formations of the extended type area of the Maastrichtian Stage (Upper Cretaceous) in the south-east Netherlands and north-east Belgium. A range of episkeletozoans have been reported from these substrates hitherto. A new specimen preserved as a natural mould in flint from the province of Liège, north-east Belgium, is distinctive, preserving a dense three-dimensional infestation of long, slender, unbranched and unsculptured borings of constant diameter, Trypanites? isp. These may be the spoor of polychaetes. Variations in diameter between borings suggests that the traces in this specimen may represent four separate infestations.     

Proceedings of the Third European Workshop on Vertebrate Palaeontology (Maastricht,May 6-9, 1998): Preface

Geologie en Mijnbouw -     

Adaptive morphologies and guild structure in a high-diversity bivalve fauna from an early Campanian rocky shore, Ivö Klack (Sweden)

The bivalve fauna from a late early Campanian rocky shore at Ivö Klack (southern Sweden), comprises just over sixty species, a very high diversity in comparison to other Late Cretaceous and modern rocky shore bivalve assemblages. This high diversity is here considered to represent a reliable census of the fauna; only in part can it be explained by the cumulative effect of generations of bivalves inhabiting this coastal environment. The high density and diversity and the wide range of shell morphologies allow interpretation of different modes of life in this variable environment with many contrasting habitats. Study of the functional morphology of bivalve shells and comparison with extant relatives has resulted in a subdivision of the fauna into seven guilds and five habitats. The bivalve fauna represents a within-habitat, time-averaged assemblage to which none of the species was introduced from adjacent environments. It includes some of the most northerly known, very small rudistid bivalves, in addition to the oldest known occurrences of Mytilus and Barbatia in association with rocky shores. Bivalves constituted the most important invertebrate group inhabiting the late early Campanian rocky shore at Ivö Klack, in terms of diversity, density and biomass.     

Site selectivity of the boring Rogerella isp. infesting Cardiaster granulosus (Goldfuss) (Echinoidea) in the type Maastrichtian (Upper Cretaceous,Belgium)

A burrowing spatangoid echinoid (heart urchin), Cardiaster granulosus (Goldfuss), from the type area of the Maastrichtian Stage (Upper Cretaceous) in Belgium, was infested only in the plates of the ambulacral petals by acrothoracian barnacle borings, Rogerella isp. This infestation was after the death and exhumation of the echinoid. The distribution of Rogerella may indicate the azimuth of current flow at the time of exhumation prior to final burial. Copyright © 2015 John Wiley & Sons, Ltd.     

Preservation of borings: contrasting examples from the type Maastrichtian (Upper Cretaceous), southern Limburg,the Netherlands

The taphonomy of trace fossils and their substrates remains an understudied facet of sedimentary geology. Contrary to common prejudice, trace fossils are not invariably preserved in situ, but may be exhumed and reworked following lithification. The trace fossils most commonly found ex situ are borings in mobile shelly substrates. Two notable, but contrasting, examples of post-mortem transport of borings are described from the Maastrichtian (Upper Cretaceous) of southern Limburg, the Netherlands. A long, unusually straight and complete calcareous tube assigned to Teredolites longissimus Kelly and Bromley is an organically secreted internal mould, produced by a teredinid or pholadid bivalve boring in wood and lining their tube. Strictly, this is part of the body fossil of the producing bivalve, but it is also an organically generated internal mould of the boring. A flint steinkern of a right valve of Crassatella bosquetiana d’Orbigny preserves a suite of silicified borings. Caulostrepsis taeniola Clarke is a U-shaped boring with a vane connecting the parallel limbs. Talpina isp. is a slender, simple, branched tunnel. Most unexpected, Spirichnus spiralis Fürsich et al. is a spiral ‘worm’ boring hitherto only known from the Upper Jurassic. This stratigraphic gap is likely an artefact; only mouldic preservation of the bored substrate would expose the distinctive Spirichnus boring. These ichnofossils are united in their occurrence in unusual preservational systems.     

Dinosaur remains from the type Maastrichtian: an update

Isolated cranial and post-cranial remains of hadrosaurid dinosaurs have been collected from various outcrops in the type area of the Maastrichtian stage during the last few years. In the present contribution, dentary and maxillary teeth are recorded from the area for the first time. Post-cranial elements comprise a newly collected, fragmentary, large right metatarsal III and a broken ?right humerus, recently recognised in the collections of Teylers Museum (Haarlem). Unfortunately, none of these remains can be identified to species level. The available material suggests, however, that more than one taxon of non-lambeosaurine hadrosaurid and a possible euhadrosaurian are represented. Most of the new finds are stratigraphically well documented, which means that they may be linked to the recently published sequence-stratigraphic interpretation of the type Maastrichtian. Dinosaur remains recorded previously from the Maastrichtian type area are tabulated.