The faunas discussed in the preceding pages are typical of the Boreal Realm and can be traced as far as Transcaspia and northern Iran, facies of different ages tending to yield broadly similar faunas throughout the region (Fig. o, p. 281).
As they did in the Jurassic, these Boreal faunas merge into Tethyan (or Mesogean) associations as they progress southward. These Tethyan faunas are as diverse and variable as those of the Jurassic of the same areas, and carbonate sequences are prominent. Particularly distinctive are the spectacular occurrences of the aberrant heterodont bivalves known as the rudists, which were abundant and varied in the late Cretaceous in the tropical shallow water areas of southern Europe. Taking the place, in many respects, of hermatypic corals, they form thickets and framework structures. Other shallow water Tethyan facies are dominated by algae, or by giant Foraminiferida. Deeper water facies include pelagic marls and clays with ammonite-belemnite faunas; these are closely similar to the Jurassic clays of northern Europe. The more calcareous facies resemble the clay-rich parts of the northern chalks. Deep water deposits are also found, similar to those of the Jurassic and including radiolarian sediments; in Cyprus and some other areas where Cretaceous ocean floor sediments are exposed, deep sea chalks occur. In other areas of central and southern Europe there are widespread turbidite successions.
Rudist-algal-foraminiferidal shallow water facies occur in the Caribbean Sea, Mexico and parts of Texas. During the late Cretaceous (chiefly the Coniacian to Campanian) chalks were deposited in many areas of North America from Texas in the south to the Western Interior towards the north. However, they yield very different faunas from those of the European chalks, lacking brachio-pods, bryozoa and various others, and were perhaps deposited in an epeiric, landlocked sea like that of Jurassic Europe, with reduced or perhaps fluctuating salinity. In many other respects besides this the Cretaceous successions of the North American Western Interior more closely resemble those of the terrigenous clastic facies of the European Jurassic.
In contrast, the sequences of the Atlantic seaboard, the Gulf Coast and the Mississippi embayment, which include greensands, calcarenites and chalks, are reminiscent of many of the more marginal facies of the European Cretaceous.
Was this article helpful?