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Analysis of the ~2.57 Ga Hamersley Basin Using Statistical and Petrographic Techniques

Abstract

The ~2.57 Ga Paraburdoo Spherule Layer (PSL) serves as a distinctive marker layer

within a series of alternating beds of crystalline dolomite grains and dolomitic mud. These beds

alternate on the scale of ~0.5-10 cm and extend vertically for hundreds of meters. Deposition of

this strata within the Wittenoom Formation of the Hamersley Basin occurred below storm wave

base (several hundred meters deep) in a marine basin that deepened to the southwest, possibly to

an open ocean. Sediments were likely deposited in a deepwater slope, shelf, or submerged

platform paleoenvironment via either turbidity currents or pelagic sedimentation. Bed

thicknesses were recorded at the cm-scale of three correlating sections surrounding the PSL.

These locations lie in an approximately southwest-northeast line across the basin. Statistical tests

were performed on the measured bed thickness data in order to determine existing patterns not

readily apparent by field and laboratory techniques. Periodograms showing spectral analyses

were calculated in order to delineate existing periodicities in the cyclic stratigraphy. Cumulative

distributions and fractal dimensions of this same stratigraphy were also calculated to assess

differences between stratigraphic sections and aid in paleoenvironmental evaluation. These

statistical analyses reveal a southwest-northeast trending pattern consistent with general basinal

trends presented in the published literature. Each of the three sections demonstrates a distinct

signature viewable by statistics that are also consistent with both field observations and

petrographic analyses. Examinations at the field and hand sample scale as well as stratigraphic

correlation support a larger volume of sediment input to the northeast as well as a possibly

shallower sedimentary environment. Petrographic observations demonstrate a higher mud

content, less distinctive bed boundaries, and finer carbonate grain size to the northeast. Overall

stratigraphy appears to thin to the southwest, consistent with published literature. These analyses

suggest a type of non-turbidity current cyclic sedimentation, which has implications for

paleoenvironmental reconfiguration. Results from the aforementioned statistical tests in

conjunction with field, hand sample, and petrographic techniques demonstrate a tool applicable

to basinal stratigraphy displaying a repetitive signature, and will aid a thorough basin analysis by

helping to identify periodicities in bed thickness data.