Micraster Cor-anguinum Research Articles

The stratigraphy of the Chalk Group (Upper Cretaceous) of the Gipping Valley, near Ipswich, Suffolk, UK

The Chalk outcrops in the Gipping Valley, northwest of Ipswich are of great significance in providing a rare glimpse of the often Drift-covered inland East Anglian Chalk succession. The exposures show an unusually thick development of virtually flintless and virtually marl-free chalk, unlike any chalk seen elsewhere in the UK. Macrofossil and microfossil data show that this chalk belongs to the Marsupites testudinarius and O ffaster pilula macrofossil zones, and is coeval with the Newhaven Chalk Formation of southern England. The Uintacrinus anglicus Zone appears to be absent. This chalk is herein named the Blakenham Chalk, provisionally regarded as a Member of the Newhaven Chalk Formation. Similar, virtually flintless chalk, up to 63.5 m thick, occurs in boreholes in Ipswich, beneath a variable cover of Cenozoic and Quaternary strata. This chalk belongs to the basal Gonioteuthis quadrata Zone, and extends down through the O. pilula, M. testudinarius, Uintacrinus socialis and topmost Micraster coranguinum zones, equivalent to the Newhaven Chalk and topmost Seaford Chalk formations of southern England. At outcrop and in boreholes, the virtually flintless chalk is overlain by regularly flinty chalk, up to 8.5 m thick. Macrofossil data show that this chalk belongs to the lower part of the G. quadrata Zone, and that records of Belemnitella from this interval probably correlate with an acme of this belemnite in the lower G. quadrata Zone of southern England. Microfossil data are more equivocal, but this may reflect unusual environmental conditions. Lithostratigraphically, the flinty chalk succession is correlated with the lower part of the Culver Chalk Formation of southern England. The unusual lithology of the Blakenham Chalk Member may reflect the influence of local structural highs rejuvenated by Late Santonian-Early Campanian (Wernigerode Phase) tectonism.

Anomalous Turonian-Campanian Chalk deposition in south Dorset; the influence of inherited pre-Albian structures

The Turonian-Campanian Upper Chalk in the area between Dorchester and Weymouth in Dorset shows an abnormal development of hard chalk beds in the late Coniacian-Santonian Micraster coranguinum to the early Campanian Gonioteuthis quadrata zones. The chalk is also strongly affected by faults representing the surface expression of reactivated underlying pre-Albian structures. This suggests a link between tectonism and Turonian-Campanian chalk deposition, which may be related to the proximity of the south Dorset disturbance.

Thermal diffusivity of upper chalk from Hampshire, England

The thermal diffusivity of Upper Chalk from the Micraster coranguinum zone had been calculated from 8 year temperature data obtained from depths between 30 cm and 21.34 m at Harestock, near Winchester, Hampshire. Amplitudes and phase lags were calculated from these data using Fourier analysis. Values of thermal diffusivity were calculated from the variation of amplitude with depth and phase lag with depth for the first harmonic using the Fourier heat flow equation. Agreement between the two methods was very good between 30 cm and 914 cm depth. An overall mean value is 0.004489 ± 0.00052cm −2s −1. Using appropriate values of porosity (47%) and density the mean thermal conductivity is 1.519W m −1°C −1± 0.326, for the water saturated state.

Coastal Platforms of the Isle of Thanet, Kent

The Isle of Thanet consists of a shallow monocline of Upper Chalk, whose gentle limb dips northward (Fig. I). Minor upfolds appear in the east. The rolling land surface rises to I80 feet just north of the east-west fold axis. In the north and the east, roundbacked ridges are separated by coombes. Over half of the coast runs east-west facing the North Sea while the remainder forms part of the entrance to the Straits of Dover. The coast is highly indented; projecting headlands result in a variety of local exposure to wave action. Except where the coast has been protected, subvertical cliffs dominate. Flanking these seaward, and exposed at low water, there are wide platforms except where beaches occur. The north coast runs with the strike of the soft, marly Marsupites Testudinarius chalk. Firmer lenticles of the lower Uintacrinus Band have given rise to ramp-like cliff bases, ledges rising above platforms, and thresholds attached to stacks. On cliff faces at Minnis Bay and Birchington3, rectangular caves form doorways (Fig. 4) along prominent joint and shear zones, together with numerous geo-like inlets and chimneys. Between Foreness and Whiteness, fresh talus heaps rest against the cliff foot, indicating recent cliff falls. On the north coast platforms are 200-300 yards wide at ordinary low water. Their width increases to one-third of a mile at Foreness. Along joint zones platforms tend to be dissected, and this becomes modified at Botany Bay where curvitabular jointing approximates to bedding planes in the Uintacrinus Band. At their seaward margins platforms may show distinct breaks of slope or low-tide cliffs. Since there are few flints in the chalk, little shingle remains on the platforms, but infilling of their surface hollows by sand can be considerable. The seaweed cover is extensive except for a narrow zone against the cliff foot. The coast between Whiteness and Pegwell lies in the Micraster Coranguinum Zone, in part overlain by the Uintacrinus Band. The chalk is more compact and markedly jointed; shallow anticlines and synclines traverse the coast. Sub-vertical cliffs rising to 6o-Ioo feet are studded with caves in Kingsgate Bay. Farther south and around Joss Bay they become degraded, partly laden with frost soil, and hidden by falling debris, but the interbedded loam and chalky wash at Stone Gap are less influential. Numerous faults, mostly striking between north and west, accompany some caves. Dumpton Gap, occupying a chalk coombe, follows a fault with downthrow on the south while a walled cave at Pegwell is bounded by a pair of faults. At Ramsgate the coast begins to swing westward and has been partly walled and groyned. Attempts to

On New Ammonites from the English Chalk

Ammonites are comparatively common in the Cenomanian or Lower Chalk, become rarer in the Turonian or Middle Chalk, and are very scarce in the Upper Chalk. On a former occasion, when pointing out that while ammonites were unknown from the Micraster cor-testudinarium Chalk of England, they occurred in the same Chalk in the north of France, the writer was inclined to attribute this absence or scarcity to limited horizontal distribution of the ammonites. The possibility, however, of there being gaps in the Chalk succession, for example at the horizon of Actinocamax plena, at the Chalk-Rock, in and above the cor-anguinum zone, etc., cannot be denied. The zone of Micraster cor-anguinum is not quite so barren as the zone below, but the only ammonites hitherto known from it are doubtful examples, probably referable to Parapuzosia. One impression, on an oyster, of part of the ventral area of a large specimen, possibly of P. corbarica Grossouvre sp., was collected by Mr. Dibley in the London-Portland Pit at Northfleet, Kent, and Dr. Rowe recorded probably comparable Parapuzosia (“ammonites of the leptophyllus group”) from Dorset and Yorkshire.

On the Geological Importance of the Primitive Reptilian Fauna in the Uppermost Cretaceous of Hungary; with a Description of a New Tortoise ( Kallokibotion )

In Eastern Hungary the Upper Cretaceous can be divided into two horizons with an unconformity between them (53, 66). The lowest deposits in some places, as near Szászcsor (53), are red conglomerates; in other places (as, for example, Ohaba Ponor) they are red laterites filling fissures in the Tithonian limestone (28). Then follow, extending farther than the red deposits, grey marls and sandstones containing at their base seams of coal (28), and somewhat higher up several ammonites, such as: Acanthoceras newboldi Kossmat. A. cenomanense Pictet. A. harpax Stoliczka. A. rhotomagense (Defrance). Acanthoceras mantelli (Sowerby). A. morpheus Stoliczka. Puzosia planulata (Sowerby). Crioceras sp. (53). These help to fix the age of the marls as Cenomanian. Overlying the ammonitiferous strata are coarser sandstones, crammed with enormous numbers of Actæonella sp. (28, 53); then come marls and sandstones containing some rare examples of Actaeonella gigantea (53), attaining a diameter of 6 inches and more; and lastly, a great complex of rough blue and white sandstones is met with (7), corresponding to the Emscher Sandstone of German geologists or to the zone of Micraster cor-anguinum in England. These strata are characterized throughout Transylvania by remarkably large Inocerami (53, 65). In Inoceramus giganteus Pálfy, for example, each valve attained a length of nearly 2 feet (65). Unconformably upon these beds rest younger marine layers containing Pachydiscus neubergicus Hauer, P. colligatus Binck, Scaphites constrictus Sowerby (53), and numerous bivalves and gasteropods (51, 64), among which it is sufficient to mention Melanopsis galloprovincialis Matheron and Pyrgulifera pichleri

II.—Notes on New or Imperfectly Known Chalk Polyzoa

The group of Membraniporæ, with a small median barred avicularium placed immediately above the oæcium, of which M. Griffithi, Bryd., is a leading instance, contains several Senonian members in addition to the Trimingham forms (M. Triminghamensis, M. anterides, M. humiliata) which I have already described in this Magazine. They seem to arise first in the zone of Micraster cor-anguinum.Membranipora Simulacrum, sp. nov. (Pl. XXVI, Figs. 1, 2.)Zoarium unilaminate, always adherent.Zoæcia large, very slightly subpyriform, areas oval, with average length .5 to .55 mm. and breadth .3 mm.; side walls bent slightly inwards, and so low and slender that at a hasty inspection they might be taken to be mere ghosts of some species with a low arched front wall.

On the Teeth of Ptychodus and their Distribution in the English Chalk

Introductory Remarks. A mong the remains of fishes found in the Chalk, the teeth of Ptychodus are so conspicuous and so easily recognized by the quarrymen that they have long been collected in large numbers and distributed to various museums. Most of these fossils, however, bear no record of the exact locality or zone from which they were obtained, while groups of associated teeth have often been scattered without any note of the circumstances of their discovery. I have, therefore, devoted much attention during the past twenty years to the careful collecting of teeth of Ptychodus from the chalk-pits of the South-East of England, and I now propose to discuss their classification and the zonal range of the various species. I have collected especially in the Gravesend, Rochester, and Medway-Valley area, where there are great excavations in a continuous series of Chalk-deposits, from the base of the zone of Ammonites rhotomagensis to the top of that of Micraster coranguinum . I have also obtained specimens from the Caterham Valley, Oxted, Merstham, and Betchworth; from Berkshire, Hampshire, Bedfordshire, and Cambridgeshire; and I have studied all the material in the British Museum, the Museum of Practical Geology (Jermyn Street), and the museums of Salisbury, Brighton, and Rochester. I have been particularly fortunate in discovering fifty sets of associated teeth, and have examined many more in the museums just enumerated. The arrangement of the teeth of Ptychodus in the mouth is already known from specimens of Pt. decurrens found in the The arrangement of the

V.—Actinocamax verus in the Upper Part of the Micraster cor-anguinum Zone at Walmer and St. Margaret at Cliffe

The known occurrences of Actinocamax verus in this zone are comparatively few. Northfleet in Kent, Micheldever in Hampshire, and Great Fimber in Yorkshire are our only records.

The Phosphatic Chalks of Winterbourne and Boxford (Berkshire)

I. Introduction. In the latter part of July 1905 we remarked, among the fossils exhibited in the recently-founded Museum at the Cloth Hall, Newbury, a group of guards of the belemnoid Actinocamax granulatus (Blainville), labelled ‘Winterbourne’—the name of a village 3 1/2 miles to the north-west of the above-named town. To us, these specimens were objects of more than usual interest, inasmuch as our examination of the Upper Chalk in the western part of the London Tertiary Basin, so far as it then extended, had shown us (1) that Actinocamax granulatus was a rare fossil in that area; (2) that it was there confined to beds of the Marsupites -Band and of later age; and (3) that such beds, although well-developed to the south of the Kennet, were cut out, by the Eocene overstep, to the north of that river, along a line passing 2 or 3 miles south of the parish of Winterbourne. Assuming the guards to be correctly labelled, they seemed to indicate the existence of an outlying mass of Marsupites -, or newer, Chalk rather rich in belemnoids, within a tract of country where the Eocene deposits were known to be generally in contact with some part of the older, Micraster cor-anguinum - Chalk; and as we had but recently given some attention to just such a mass in the shape of the Phosphatic Chalk of Taplow, the possibility of the recurrence of phosphatic conditions near Newbury at once presented itself to our minds. On our making

An Analysis of the Genus Micraster, as determined by rigid zonal collecting from the Zone of Rhynchonella Cuvieri to that of Micraster cor-anguinum

I. G eneral C onsiderations . T he Micrasters dealt with in this paper were collected from the sections exposed at Gravesend, the Thanet Coast, Dover, Beachy Head, the Dorset Coast, and Beer Head, in the zones indicated above. Two thousand examples have been measured and analysed, and no specimen has been included in the summary unless its zonal origin is accurately determined. Six hundred photomicrographio negatives of the special features of the test have been made, in order that mere conjecture may play no part in the enquiry, and that these important aids to specific and zonal determination may be placed on a permanent and scientific footing. The field-work has been extended over as wide an area as possible, so that conclusions should not be vitiated by being drawn from any one isolated district. In this paper, the term ‘low-zonal’ will apply to the zones of Rhynchonella Cuvieri, Terebratulina gracilis, Holaster planus, Micraster cor-testudinarium , and the lower third of the zone of M. cor-anguinum (80 feet); and the term ‘high-zonal’ will refer to the remainder of the zone of M. cor-anguinum , and to the zones above it Though all the accessible literature on the subject has been studied, the conclusions here set forth have not been influenced by previous publications, for rigid zonal collecting has been the paramount object, and the facts brought out by analysis have been allowed to speak for themselves. The scope of the present paper will not admit of the discussion of questions of nomenclature, which must be left

IV.—Micrasters in the English Chalk—Two or more Species?

To the student of Cretaceous palæontology there could be suggested, probably, no more puzzling question than that of the determination of the species of the genus Micraster. It seems not unlikely that Professor Forbes was of this opinion when, in 1850, he reduced to varieties of a single species—that of Micraster cor-anguinum—no fewer than seventeen previously supposed species, or subspecies, of the genus. It is true that, out of compunction, perhaps, for such wholesale slaughter, he forthwith established one new species, the Mieraster cor-bovis, and pointed out the probable existence of another —“a small Micraster with a very elevated extremity from the Chalk of Lyme.” This, however, seems scarcely to make up for the absorption or obliteration of all but one of the previously described species. And, seeing that several of these so-called varieties of Micraster cor-anguinum are recognized as species by many continental palæontologists, it becomes an interesting subject for inquiry whether our English Chalk does not contain more than one species in addition to the recognized Micraster cor-anguinum, and cor-bovis?

IV. Note on Plicatula sigillina, an undescribed Fossil of the Upper Chalk and Cambridge Phosphate-bed

Everyone who has collected the fossils of the Upper Chalk will have noticed how the Echinoderms and Belemnites are overgrown by small oyster-like shells with a striated disk, commonly passed by as the fry of Ostrea vesiculosa. There is a beautiful example of Micraster cor-anguinum in the Museum of the Geological Society (given by Mr. Bayfield, of Norwich, to the late Daniel Sharpe), on which a dozen of these little shells, each about half an inch across, have left their lower valves; and above twenty are congregated on a fragment of Ananchytes (occupying a space of about three square inches) in the British Museum.