Seismic Fault Mechanical Stratigraphy of a Complex Impact Structure, Chukchi Sea, Offshore Alaska

Abstract

Complex impact structures are often misinterpreted in seismic sections as tectonic structures (e.g.: wrench faults, reactive diapirs, volcanism, etc.). Using Seismic Fault Mechanical Stratigraphy (SFMS), we propose a methodology for the differentiation of complex impact structures from tectonic structures. The case study is conducted on 2D seismic lines in the Chukchi Sea, offshore Alaska.

SFMS is a method used to analyze the geological ages of the faults in seismic sections. The rationale behind this method consists of two premises: Steno’s law of superposition and cross-cutting relationships and the deterministic and empirical description of the bulk modulus as affected by increasing sediment depth and age. From these principles, it can be said that most deep-seated faults propagate from the bottom to the top and thus the youngest strata that a fault cuts indicates the most recent age at which a fault has been active. Additionally, the proper delineation of fault timing is critical to the assessment of petroleum system migration dynamics. For this feature, the fault mechanical stratigraphy identifies four fault generations and clearly shows that the faults related to the structure can be isolated to the Middle Eocene.

Within seismic resolution two structural features of complex impact structures are identified: a central uplift in the crater floor produced by rebound, and gravity-collapsed terraced faults rimming the crater. These structural features are generated within minutes, a time range drastically shorter than that required for tectonic structures (i.e. ka to ma). The tightly constrained timing and short duration of these associated concentric faults defined by SFMS strongly suggest this Chukchi Sea structure to be a complex impact structure.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018