| Only very fine-grained facies referred to as porcellaneous have provided biostratigraphically indicative fauna, i.e. calpionellids. |
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| Because of their non-marine depositional setting, the Wealden sediments are not biostratigraphically constrained with a high degree of certainty. |
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| These taxa are biostratigraphically and biogeographically significant and are discussed more fully below. |
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| They have been widely used biostratigraphically in Jurassic to Pleistocene rock sequences. |
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| So far, only few biostratigraphically well-constrained isotopic ages constitute the geochronological framework of the Devonian period. |
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| In all cases, biostratigraphically well-dated reference sections, against which the relevant geochemical data have been calibrated, are required in the first instance. |
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