From Quantitative 3-D Seismic Stratigraphy to 3-D Sequence Stratigraphy: Insights Into the Vertical and Lateral Variability of Basin-Margin Depositional Systems at Different Stratigraphic Orders

Abstract

A major challenge of sequence stratigraphy is to recognize objectively different orders of stratigraphic surfaces and sequences. Their identification is commonly dependent of the resolution of the data used, its dimension (2D vs. 3D) or the criteria chosen to select sequence boundaries. In this study, we propose an innovative data-driven approach to develop sequence stratigraphic frameworks across different stratigraphic orders.

High-quality 3D seismic data are used to interpret an Early Cretaceous shelf margin, the Lower Barrow Group (LBG; North West Shelf, Australia). The method is based on full-volume seismic interpretation techniques that integrate the 3D variability of the data when identifying seismic unconformities. A 5^th order, high-resolution seismic stratigraphic framework was constructed (73 interpreted clinothems with a duration of ~63,000 yrs each).

The computation of high-frequency shelf-edge trajectory angle (T_se) curves on selected seismic cross-sections was used to objectively pick sequence stratigraphic surfaces. The definition of stratigraphic sequences (4^th order) and composite stratigraphic sequences (3^rd order) via this workflow is then used to (1) quantify the vertical and lateral variability in stratal stacking patterns; and (2) discriminate the allogenic and autogenic controls responsible for this 4D variability at multiple timescales.

The results show that the 4^th to 5^th order stratigraphic architecture of the LBG results from the interplay between short-term glacio-eustasy (Milankovitch cycles of ~100,000 yrs) and sediment supply (location of fluvial feeder systems along the margin). At the 3^rd order, tectonic subsidence overprinted the eustatic signal in the main regional depocenter and accelerated the rates of accommodation creation. However, identification of long-term glacio-eustatic Milankovitch cycles (~400,000 yrs) in coeval sequences outside this depocenter, where the rates of accommodation creation due to rift-related subsidence are more limited, also suggests a low-frequency eustatic control.

Quantitative 3D seismic stratigraphy provides an observation-based and model-independent tool allowing the definition of stratigraphic sequences with results reproducible by different stratigraphers. It represents a first step towards the creation of 3D sequence stratigraphic workflows that could improve the prediction of stratigraphic patterns and facies relationships (source, reservoir, seal distribution) across continental margins.

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