Fossils of the Carpathian Region

1. The Paleozoic

3 The Precambrian, which makes up about 85 percent of the history of the solid Earth, is represented by very sporadic fossil assemblages in the Carpathian region. A few poorly preserved organic-walled microfossils extracted from “crystalline” metamorphic rocks in a few areas including the Apuseni Mountains of Romania are thought to come from the latest Precambrian. However, due to the scarcity of fossil assemblages of this age, a detailed treatment of the two eons of the Precambrian, the Archaic and Proterozoic, is unjustified given the general scope of this book. Our present knowledge indicates that the living world of the Precambrian was immensely poorer than that of the Paleozoic; there were no organisms possessing hard skeletons at this time, for example, and the most widespread traces of life in the Precambrian are biosedimentary structures called stromatolites. These are mounds of mud and blue-green algae, or cyanobacteria, that have been found on almost all continents, and are particularly characteristic of the Ediacaran (i.e., the period immediately preceding the Phanerozoic). As noted above, fossils from the Paleozoic are rare in the Carpathian Region. There are, however, a few localities that have yielded attractive fossil assemblages. Paleozoic sedimentary rocks are much more widespread in the Carpathian region than are those from the Precambrian and, indeed, some of them contain fossil assemblages of scientific value. These fossil floras and faunas, however, are rather isolated in space and time and hardly any can be said to be spectacular or notable. Although many of the known Paleozoic successions were deposited in freshwater environments, sediments yielding exceptionally preserved fossils, such as those from the celebrated Carboniferous Mason Creek biota of North America, are lacking. These fossil assemblages are much less diverse than are those of coeval marine deposits, and many Paleozoic successions in the Carpathian area in general have been metamorphosed by the heat and/or pressure of orogenic processes resulting in the partial or total destruction of fossils. With this in mind, Carpathian Paleozoic assemblages are treated in a single chapter, rather than discussed period by period. MEMORIALS OF LOST PEOPLES AND FARAWAY COUNTRIES: PALEOZOIC PERIODS The Paleozoic, also called the “Primary” in older literature , was at least 290 million years long and, as such, was longer than both the Mesozoic and Cenozoic put together. It is subdivided into six periods that can be distinguished in sections all around the world. The earliest of these periods , the Cambrian, was named after the Roman name for North Wales (Cambria). Indeed, the next youngest, the Ordovician and Silurian Periods, are named for tribes that once lived in the area of present-day Wales; the Devonian was named for the county of Devonshire. The name Carboniferous refers to the Latin name for coal (carbo) and, as such is, a rare example among geochronological names; finally, the youngest period of the Paleozoic, the Permian, was named after the Perm Province of Russia. EARTH HISTORY IN A NUTSHELL Over the course of the almost 300 million years of the Paleozoic , the face of the Earth changed fundamentally. At the beginning of the Cambrian most of the ancient shields forming the so-called core of the present-day continents were concentrated between the 60th latitudes, principally in the Southern Hemisphere. Their arrangement differed markedly from that of today. Some continents (Africa, India, South America, Australia, New Guinea, and Antarctica ) formed a huge supercontinent (Gondwanaland) in the Cambrian—the latter three being its northernmost “tongue,” lying on the northern hemisphere. North America (Laurentia) and the landmass that would eventually constitute Europe (Baltica) were separated from one another by the Iapetus Ocean. The microcontinents Kazakhstania and Siberia, separated from all other landmasses , were situated near the equator. 1 The Paleozoic 4 t h e pa l e o z o i c The climate of the Cambrian is thought to have been warmer and more balanced than that of the present day and, in contrast to the Precambrian and Ordovician, no traces of glacial sediments have been found. At the very beginning of the Cambrian the biggest event in the history of life is thought to have taken place, the sudden and almost simultaneous appearance of both fossils with hard skeletons and several animal phyla, an event usually described as “the Cambrian explosion.” This remains one of the most puzzling enigmas in evolution. In the Cambrian (actually until the end of the Silurian) life was mostly restricted to oceans. During the Ordovician, the Northern Hemisphere was almost entirely covered with oceans...