Stratigraphic record interpretation

It was stated earlier that the primitive crust of the Earth was most likely of basic composition. Massive meteorite bombardments and associated crustal resorption prior to 3.9 billion years ago musthave erased the former records. In further crustal evolution at least three cycles can be distinguished. They were laid down between 4.0 and 2.5 billion years ago. The oldest terrestrial rocks from 3.8 billion years ago, gneisses of west Greenland, contain metabasaltic and metasedimentary enclaves having the age of about 4.0 billion years. They can be interpreted as relics of the early crust. So, the first 500 to 700 million years of Earth s geological history have apparently left no stratigraphic records. 

Stratigraphic contacts interpreted from lithology in borir and geologic structure imaged in geophysical records... 

For geologic entities (e.g., crustal segments, mineral deposits, tectonic domains, and fossils), the age distribution patterns can be extracted from their stratigraphic and geochronologic assignments. At present, only major features of the record can be quantitatively interpreted, because the database is usually not of the desired reliability. 

The various effects of deep water, illustrated in Figure 8, mean that a trace element concentration peak in the sediment of a deep lake need not imply a supply event. While the model makes this clear, as discussed above, unique deconvolution of the smoothed and distorted sediment record is not possible. However, the model does allow constraints to be placed on possible interpretations of the record. For example, m Lake Baikal the model served to demonstrate that the sediment Pb record is compatible with the expected Pb supply history (Boyle et al., 1998). It also showed that observed stratigraphic changes in the sediment trace element concentration were too sharp to be explained by supply effects, and that changes m needed to be considered. 

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