Abstract Phylum Echinodermata Subphylum Echinozoa Class Echinoidea — Late Ordovician-Recent Echinoids (sea urchins) live in normal marine environments because they with a very limited range of salinity tolerance (generally only a few ppm). They occur mainly as grazers or burrowers in sandy shelf areas or as grazers and bioeroders along rocky shorelines. They occur in deeper waters as well, extending to abyssal depths. Fossil forms are most common in normal marine, open shelf or platform deposits. Echinoids are common in both warm- and cold-water settings, although they rarely are major rock-forming organisms (i.e., they rarely exceed 10-15% of the total sediment). Modern and ancient echinoids are/were composed of moderate- to high-Mg calcite. Modern forms contain between 2 and 17 mole% Mg; the Mg content varies with generic group and increases with increasing water temperature (see Milliman, 1974 , p. 130-134, for details and citations). Echinoids, like all echinoderms at some stage in their life cycle, show pentameral (five-fold) symmetry. They have heavily calcified, globular to discoidal, hollow, endoskeletal tests (coronas) that are composed of individual sutured, interlocking or imbricated calcite plates. The calcitic coronal plates are porous and sponge-like; echinoids with rapid growth rates have spongier plates (with more holes and less calcification) than slowgrowing counterparts. Thus, slow growing, cold-water forms can be more heavily calcified than those from warmer waters ( Raup. 1958 ) In life, echinoid tests are covered with elongate, moveable spines (in some species extremely short, but in others longer than 8 cm). The spines normally detach after death and can themselves be significant sediment contributors. Generally, each plate of an echinoid behaves optically as a single, extensively perforated, calcite crystal (see comments below). Echinoid teeth, however, are polycrystalline.

Abstract: Late Cretaceous-Danian cool-water carbonate deposition in northwest Europe lasted for more than 35 my and covered an area of about 5,250,000 km 2 with east-west and north-south extents of at least 3,500 km and about 1,500 km, respectively. Maximum thicknesses of the succession amount to more than 2 km. The region was situated between paleolatitudes 35° 50° N, and the study area, comprising the Danish Basin and its margins, was situated at about 45° N. The relatively deep-water basinal sediments are mainly coccolithic chalks with a sparse benthic fauna. The shallow-marine faunas are of high diversity, belong to the Boreal Realm and are dominated by bryozoans, echinoids, bivalves, brachiopods, ser- pulids, and in the Danian also azooxanthellate scleractinian corals and octocorals. Marginal Tethyan influence is only seen in the Early Campanian and Late Maastrichtian. The succession represents one of the largest and longest-lived accumulations of cool-water carbonates on earth. A transect from the paleo-coastline to the basin shows a succession of broad facies belts deposited on a gentle, distally steepened, carbonate ramp. Three carbonate factories are recognized. High-diversity oyster bank communities flourished along the rocky shorelines and represent the first factory which produced skeletal gravels and coarse-grained sands. These sediments pass offshore into cross-bedded, well-sorted skeletal sands deposited in sub- aqeous dune fields which migrated parallel to the shore. Further offshore, the clastic carbonate belt gives way to the second carbonate factory represented by a broad belt of bryozoan wackestones and packstones deposited in impressive mound complexes in relatively deep water below the photic zone. The proportion of coccolithic chalk ooze increases in a seaward direction, the mounds become smaller and more mud-rich, and the slope and basin are dominated by pure coccolithic chalk with few benthic fossils. The pelagic chalk represents the third carbonate factory. Large, asymmetric bryozoan wackestone and packstone mounds of Early Danian age are beautifully exposed in the cliff, Stevns Klint, where they overlie smaller, matrix-rich wackestone mounds of latest Maastrichtian age. The bryozoan mounds migrated towards the southeast, parallel to the coastline and towards the nutrient-carrying currents by combined progradation and aggradation. The mounds overlap and interfinger and form complexes separated by erosion surfaces and hardgrounds developed during falls in relative sea level. A sequence stratigraphic model is proposed for cool-water carbonate ramps in an arid climate. It is characterized by the symmetrical packaging of facies dominated by simple landward-seaward shifts of facies belts, lack of facies differentiation between lowstand and transgressive systems tracts, and absence of karst features at the sequence boundaries due to the arid climate and calcite-dominated mineralogy.