Jake M. Hancock

Sea-level changes in the British region during the Late Cretaceous

The numerous oscillations in the high sea-levels during the Late Cretaceous have been plotted from the distribution of nodular chalks and hardgrounds in the British Chalk. The five widespread strong transgressive peaks recognised by Hancock & Kauffman in 1979 can now be dated: the early Late Albian peak was in the early part of the Subzone of Callihoplites auritus ; the Early Turonian peak was later than previously realised and lies early in the Zone of Collignoniceras woollgari ; the Coniacian peak was late in the age, about a third of the way up in the Zone of Inoceramus involutus , but is relatively weak; the Middle Santonian peak lies in the middle of the Zone of Uintacrinus socialis ; the Late Campanian peak lies early in the Zone of Belemnitella langei . For the highest part of the Cretaceous it is necessary to consider evidence from the continent. It is difficult to estimate how long sea-level-highs lasted, but several of the sea-level-lows were prolonged, with extensive erosion in regions marginal to the sea. There were two very marked regressive troughs: early late Turonian, ranging from the end part of the Zone of Collignoniceras woollgari to somewhere about the middle of the Zone of Subprionocyclus neptuni ; and the Late Maastrichtian fall which is difficult to quantify. Where there have been improvements in the accuracy and resolution of long distance correlations, the theory of eustasy has been further strengthened; but there are substantial disagreements with the much quoted EXXON curve after the Santonian.

Ammonite scales for the Cretaceous System

Abstract Geological charts for various purposes, e.g. that by Haq, Hardenbol & Vail (1987) on Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change, quote zonal schemes for the Cretaceous system which give a false impression of accuracy; and that they can be applied all over the world, or at least throughout either the boreal realm or the tethyan realm. In this paper an attempt is made to give ammonite-zonations for each stage of the Cretaceous system, and also to state the geographical limitations of each zonal scheme. Particular attention is give tto the definition of the base of each stage. Some 26 to 41 zones are suggested for the Lower Cretaceous and some 22 to 55 zones for the Upper Cretaceous.

Ammonites and inoceramid bivalves from close to the middle-upper Albian boundary around Fort Worth, Texas

The Goodland/Comanche Peak Limestone, Kiamichi Formation and basal Duck Creek Limestones around Fort Worth Texas yield a limited number of cosmopolitan ammonite and inoceramid bivalve taxa that allow precise correlation with the sequence that has been used as a standard in northwest Europe. The upper part of the Goodland/Comanche Peak Limestones yields species of Dipoloceras that show the base of the Upper Albian substage, provisionally defined as the first appearance of D. cristatum (Brongniart, 1822), to lie within this unit. Brancoceras aff. cricki Spath, 1934, Mortoniceras (Deiradoceras) beloventer new species, and Actinoceramus cf. concentricus (Parkinson, 1819) parabolicus Crampton, 1996a, co-occurs with D. cristatum in the Comanche Peak Limestone. The Kiamichi Formation yields rare Mortoniceras (Mortoniceras) pricei (Spath, 1922), M. (Deiradoceras) prerostratum Spath, 1921, M. (D.) bipunctatum Spath, 1933, and Actinoceramus sulcatus (Parkinson, 1819) morphotypes that allow correlation with the European Hysteroceras orbignyi and Hysteroceras varicosum subzones of the Mortoniceras inflatum zone. The basal Duck Creek Limestone yields Mortoniceras (Deiradoceras) sp. and Hysteroceras cf. varicosum (J. de C. Sowerby, 1824), and can also be correlated with the varicosum subzone.

Lower sea levels in the Middle Cenomanian

It has been known since the 1970s that the relatively high sea levels during the Cenomanian in southern England and northern France were interrupted by a strong fall in sea level early in the Middle Cenomanian. This was a eustatic trough whose effects can be found not only in north-west Europe, but also from western Kazakhstan in central Asia to Texas, Colorado and South Dakota in the U.S.A.

The Gribun Formation: clues to the latest Cretaceous history of western Scotland

Synopsis In the Inner Hebrides the Gribun Conglomerate Formation (possibly Maastrichtian in age) lies above the Cretaceous Chalk and below the Palaeocene basalts. It is best developed on the Island of Mull, but is also found further north in Skye. The Gribun Formation and the Chalk record several episodes of widespread silicification during the Late Cretaceous and possibly again very early in the Palaeocene. This silicification is evidence of arid or semi-arid terrestrial conditions. The possible absence of Campanian sediment may have been caused by magmatic underplating.

Upper Maastrichtian Ammonitesfrom the marnes de Nay between Gan and Rébénacq (Pyrénées-Atlantiques), France

The Marnes de Nay are the highest unit in the Maastrichtian succession in the Pyrenees-Atlantiques to the south-east and south-west of Pau. An Upper Maastrichtian ammonite fauna from quarries north of Rebenacq is referred to a Menuites fresvillensis Zone, equivalent to a part of the Abathomphalus mayaroensis planktonic foraminiferan Zone, with Pseudophyllites indra (Forbes, 1846), Desmophyllites larteti (Seunes, 1892), Brahmaites (Anabrahmaites) vishnu (Forbes, 1846), Pachydiscus (Pachydiscus) armenicus Atabekian & Akopian, 1969, P. (P.) jacquoti jacquoti Seunes, 1890a, Menuites fresvillensis (Seunes, 1890a), Glyptoxoceras indicum (Forbes, 1846), and G. rugatum (Forbes, 1846).

Real chalk balances the water supply

Abstract Chalk is a limestone but should not be confused with normal limestones whose porosities and permeabilities are distinct from those in chalks. Typical chalk has a high porosity of around 30–45%, a low matrix permeability (2–3 mD) and a very high mass permeability (30–3000 mD). These properties mean that chalk provides an ideal drainage for vines, both holding water for the roots during drought and draining easily during heavy rain.

The geological controls in Coonawarra

The special feature of the Coonawarra district for the production of quality wines is not the famous Terra Rossa but the underlying limestone. This is an unusual solution-breccia with ideal drainage for holding and providing moisture to the vines.

Names are better than numbers: Nomenclature for sequences

The large body of data on the Mesozoic and Cenozoic sequence stratigraphy of European basins can be used as solid evidence to test the EXXON curve. The use of numbers to distinguish sequences leads to ambiguities, anomalies, and confusion. Different authors tend to use different numbers for the same sequences, often because there is disagreement on how many sequences there are. If a mistake occurs, all the other numbers for succeeding sequences have to be changed. There are also the problems of the insertion of extra sequences if they are discovered, and how to discard sequences that are no longer recognized.