Facies analysis provides new insights into event bed deposition in a hadal trench environment
Journal
Sedimentology
Journal Volume
73
Journal Issue
2
Start Page
441
End Page
477
ISSN
0037-0746
1365-3091
Date Issued
2025-12-22
Author(s)
Muthre, Mishelle
Proust, Jean‐Noël
Pizer, Charlotte
Ikehara, Ken
Naruse, Hajime
Strasser, Michael
Abstract
Hadal trenches preserve exceptional sedimentary archives of past geological events, yet their depositional processes remain poorly constrained. The Japan Trench captures complex earthquake-triggered event beds that record repeated sediment-gravity flows that deliver terrigenous and biogenic material into the trench, informing palaeoseismic reconstructions. Classical event stratigraphy treats such event beds as products of brief, isochronous processes. This study aims to build on that concept to document hydrodynamic conditions and the relative depositional timing and duration within single event beds. Using four well-documented historical earthquake-triggered beds recovered during IODP Expedition 386, high-resolution analyses of sedimentary structures were conducted—integrating physical, chemical and biogenic characteristics—to develop a systematic, facies-based framework for identifying event-internal characteristics. Six event-internal facies (F1–F6), bounded by hemipelagic facies (F0), form a fining-upward sequence that records the shift from high-energy, non-cohesive, bedload-dominated flows to low-energy, cohesive, suspension-dominated deposition. A 32-μm grain-size threshold separates coarse-grained (F1–F3; >32 μm) from fine-grained (F4–F6; <32 μm) facies. Event-internal facies organise into pulses and pulse groups that stack hierarchically into three patterns: single-pulsed, multi-pulsed and amalgamated. Amalgamated patterns comprise two or more single- or multi-pulsed successions separated by breaks in the fining-upward trend. Breaks marked by opportunistic trace fossils or by F6 indicate pauses during deposition (quasi-synchronous flows), whereas their absence suggests synchronous flows. Most event beds are amalgamated and comprise flows emplaced at different times and sourced from different directions, as reflected by variable composition, facies and palaeo-flow indicators. Basin physiography strongly influences facies development and thickness: basin highs record erosion–deposition stages, whereas depocentres pond turbid water masses in prolonged suspension, producing thick fine-grained tops. Transitional facies (F4) forms where new flows interact with a still-settling suspension cloud, providing a basis to interpret complex mainshock–aftershock sequences. By providing new insights into hydrodynamic conditions and relative depositional timing and duration, this facies-based framework advances event stratigraphy and improves global understanding of deep-marine sedimentary dynamics.
Subjects
Earthquake-triggered event bed
Event stratigraphy
Hydrodynamic flow conditions
Japan Trench
Relative depositional timing
Turbidite stacking pattern
Publisher
Wiley
Type
journal article