LINKING REPETITIVE PSEUDO-CYCLICAL VARIATIONS IN INORGANIC WHOLE ROCK GEOCHEMICAL DATA TO SEA LEVEL FLUCTUATIONS; EXAMPLES FROM DEVONIAN REEF COMPLEXES, PALAEOCENE / EOCENE INTERTIDAL DOLOMITES (1st EOCENE RESERVOIR) AND UPPER JURASSIC BLACK SHALES (HAYNESVILLE FORMATION)

Whole rock inorganic geochemical data are commonly used to define stratigraphic correlation schemes. Typically, such chemostratigraphic zonations and correlations use changes in the whole rock chemistry through time to define a series of iso-chemical rock units that are referred to as chemostratigraphic packages and geochemical units. The changes in whole rock geochemical data are then linked to changes in mineralogy and ultimately to changes in geological parameters such as palaeoclimate, provenance, basin redox conditions or sedimentary facies. As a result, the chemostratigraphic correlation produced is essentially a high resolution lithostratigraphic scheme. In this paper, geochemical data that have previously been used to define chemostratigraphic package and geochemical unit correlations are revisited and pseudo-cyclical repetitive fluctuations in geochemical parameters are linked to sea level changes. Three examples from markedly different successions will be used to demonstrate this approach.

The first example is a well exposed Devonian reef complex from the Canning Basin of Australia, where a robust integrated stratigraphic framework has been established between two field sections. Repetitive fluctuations in Zr/Al₂O₃ values are linked to a sequence stratigraphic scheme which has been independently defined using facies stacking patterns and suggest that this elemental ratio is reflecting subtle changes in grain-size of terrestrial debris. The second example is from the 1^st Eocene reservoir of the Partition Zone, a heavily dolomitized Paleocene / Eocene age shallow to intertidal marine hydrocarbon reservoir. In this example, variations in the amount of terrigenous material, modeled from geochemical data, incorporated into the sediments define long term allocyclic fluctuations and parasequence-scale autocyclic variations, which are linked to changes in sea level. The final example is from the Haynesville Shale in Louisiana and Texas, where variations in Rb/K₂O, V/Al₂O₃ and Zr/Nb are used to define a series maximum regressive and maximum flooding surfaces and associated systems tracts.