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.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019