Existence of different palaeoenvironments can be traced in rocks, and their changes can be easily followed in open geological profiles. On the basis of biotic and abiotic factors such changes can be recognized and classified (duration: abrupt or gradual; intensity: slight, up to catastrophic; geographic range: local, regional or global; causes: different terrestrial or extra-terrestrial). Abiotic evidences can be seen in rock features (mineral composition, textures, elemental and isotopic composition, etc.), while biotic factors can be recognized from quantitative and qualitative composition of fossil communities, as well as by modern biogeochemical methods.
At the territory of Croatia, rocks from different palaeoenvironments and geological ages can be found. At the area of Karst Dinarides, outcrops of carbonate rocks deposited within the platform environments prevail, ranging in age from the Late Palaeozoic up to the beginning of the Cenozoic. In this area gradual changes within the geological stages can be traced, but there is also evidence of the two global catastrophes, at the boundaries of the Palaeozoic and Mesozoic era (ca. 251 Ma ago) and the Mesozoic and Cenozoic era (ca. 65 Ma ago). Cretaceous/Palaeogene boundary is rather well known and documented, and the events at the Permian/Triassic boundary are recently subject of the intense research. This event is marked by the most dramatic mass extinction in the Phanerozoic fossil record, and was followed by drastic shifts in isotope composition of carbon, sulphur and strontium isotopes. Scientists are still curious about the cause of this event. In the Velebit Mt. outcrops with rocks of this age can be found, and there is a great possibility to discover the exact time, and, perhaps, the cause of this event. In Northern Croatia most of the older Variscan and Pre-Variscan structures are covered with younger, Cenozoic, dominantly clastic deposits. Environmental changes in these rocks are not so abrupt and dramatic, as at the boundaries of eras, but are well documented, and can be investigated at larger number of localities. The dominant causes of changes in the Cenozoic of this area were the intense tectonic activity and eustatic changes of the sea-level. These events enabled the formation of the Paratethys, which had occasional communication with wider ocean basins. Due to that, multiple changes in geographic distribution and palaeoecological characteristics of this area can be followed at open sections. More or less gradual changes from the marine, through brackish, up to the fresh-water and continental palaeoenvironments can be traced. Croatian part of the Paratethys was situated at the southwestern margin of the Central Paratethys realm, near the shore. Therefore, a high diversity of environments, from the land through fresh-water biotopes (lake, marsh, rivers and streams), up to the different parts of the shelf, and, possibly, even deeper basins can be found. Shallow water environments are the most sensitive to all kinds of changes. Formation of basins, and isolation of brackish, and later fresh-water lakes, caused the development of endemic faunas, which are sometimes not easy to correlate with other areas. Global climate changes, with gradual cooling, have also left evidences within these rocks. Valuable data on these events can be obtained from palaeopalinological analyses.