The Materials of Stratigraphy
Historical geology involves concepts of time, life and environments that are unfamiliar to us in terms of personal experience, but it is founded upon the study of materials and of structures that accumulated unevenly across the earth and at greatly varying rates in time. The stratigraphie column provides these basic materials, not only as sedimentary rocks and fossils but also as igneous and metamorphosed rocks of many kinds. Studies of clastic, carbonate, volcanic and metamorphic rocks have become so specialised that the significance of events that led to the accumulation of a varied pile of rock units may be missed by a specialist who is working in isolation. Help from the structural geologist, the palaeontologist or the geochemist may be needed to explain the evolution of a succession of rocks. Nevertheless, the unravelling of the record begins with the study of its sedimentary or volcanic deposits. Investigation starts with litho-logical and stratigraphical (or structural) features, proceeds to sedimentology and palaeontology, perhaps to experimental and comparative studies, and hopefully reaches a point where hypotheses can be put up like ‘Aunt Sallys’.
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