Exceptionally preserved fossils

Remarkable fossil deposits are known as fossil lagerstätten. Lagerstätten is a German word that is applied to deposits of economic importance. The term fossil lagerstätten is used to describe fossiliferous formations particularly rich in paleonto-logical information. There are two types of fossil lagerstätten: Konzentrat-Lagerstätten and Konservat-Lagerstätten (Figs 1.6 and 1.7). Occurrences where the number of fossils preserved is extraordinarily high are termed Konzentrat-Lagerstätten or concentration deposits. In Konservat-Lagerstätten the quality of preservation is exceptional, soft tissues are fossilized, and the skeletons are articulated. Konservat-Lagerstätten are a rich source of paleontological information. Preservation of the soft tissues helps explain the paleobiology of extinct organisms and the preservation of an entire community provides an insight into the structure of ancient ecosystems. Konservat-Lagerstätten can be considered as "preservation windows" that provide an exceptional view of past life.

Konservat-Lagerstätten generally form in environments that are hostile to life or in environments with very high sedimentation rates. Carcasses may be transported into hypersaline or anoxic lakes that are devoid of scavengers. Such occurrences produce stagnation deposits. Rapid burial also minimizes the effect of scavengers. This can occur in deep marine environments where turbidity currents may suddenly deposit large quantities of sediment or in a delta where large volumes of

Fig. 1.6 Classification of fossil lagerstätten.

material are being discharged into the sea. These deposits are called obrution deposits. Konservat-Lagerstatten are also associated with conditions that cause instant preservation. These situations are known as conservation traps and include insects preserved in amber (fossilized tree resin) and animals trapped in peat bogs.

Conservation traps

Resin oozing from trees entraps small organisms, particularly insects. As the resin hardens it forms a tight seal around the organism. Some specimens are preserved as carbonized films but some specimens retain their original biochemistry. The resin may accumulate in the soil around the trees or be transported and deposited in fluvial or marine environments as placer deposits

Fissure fillings, cave deposits, or river bone beds. Biological material is concentrated in "traps" such as caves or fissures, or is concentrated by sedimentary processes

Stratified lakes or marine basins. Carcasses or organisms transported into these environments are preserved in the anoxic or hypersaline basin waters

Fissure fillings, cave deposits, or river bone beds. Biological material is concentrated in "traps" such as caves or fissures, or is concentrated by sedimentary processes

Stratified lakes or marine basins. Carcasses or organisms transported into these environments are preserved in the anoxic or hypersaline basin waters

Deep marine basins. Mud slides rapidly bury organisms

Fig. 1.7 Types of fossil lagerstätten.

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