Impact of igneous intrusion and associated ground deformation on the stratigraphic record

Abstract

The geomorphology and sediment systems of volcanic areas can be influenced by uplift (forced folding) related to subsurface migration and accumulation of magma. Seismic geomorphological analysis presents a unique tool to study how surface morphology and subsurface magma dynamics relate, given seismic reflection data can image buried landscapes and underlying intrusions in 3D at resolutions of only a few metres-to-decametres. However, differential compaction of the sedimentary sequence above incompressible igneous intrusions during burial modifies palaeosurface morphology. Here we use 3D seismic reflection data from offshore NW Australia to explore how the stratigraphic record of igneous intrusion and associated ground deformation can be unravelled. We focus on a forced fold that formed in the Early Cretaceous to accommodate intrusion of magma, but which was later amplified by burial-related differential compaction of the host sedimentary sequence. We show how: (1) marine channels and clinoforms may be deflected by syn-depositional intrusion-induced forced folds; and (2) differential compaction can locally change clinoform depth post-deposition, potentially leading to erroneous interpretation of shoreline trajectories. Our results demonstrate seismic geomorphological analysis can help us better understand how magma emplacement translates into ground deformation, and how this shapes the landform of volcanic regions.

Fractures and faults across intrusion-induced forced folds: a georesource perspective

“…In contrast, uplift driven by forced folding creates a non-developable surface with non-zero Gaussian curvature (modified from Lisle 1999). (c) Seismic reflection image from the Glencoe 3D survey offshore NW Australia depicting a forced fold above a thick sill (same sill as studied by Dobb et al 2022). Field photograph showing forced folding above the dioritic Trachyte Mesa intrusion in the Henry Mountains, Utah.…”

“…However, there are some uncertainties in the measurement of forced fold length and amplitude: (1) we can rarely establish the original surface topography prior to emplacement and folding, so often cannot accurately constrain true amplitudes; (2) syn-or post-emplacement deposition of sediments or resurfacing by lavas may alter apparent forced fold heights or regional base levels (e.g. Dobb et al 2022;Warsitzka et al 2022) ; (3) fold crests may have been eroded (e.g. Hansen and Cartwright 2006); and/or (4) measurements from 2D seismic reflection data, which are rarely depth-converted and decompacted (Magee et al 2019), or physical model crosssections may not intersect forced fold maximum amplitude or length (e.g.…”