Koh Ker Urban Trajectories

Sediments, chronology, and new directions after the 2026 field season

W. Christopher Carleton | 2026-09-24

Introduction

Update for NAPV and ICC on sediment-based reconstruction at Koh Ker, Cambodia.

Open with Koh Ker as the object of the talk: the historical and archaeological landscape whose urban trajectory we want to reconstruct.

Overview

• The Koh Ker reconstruction challenge
• 2024 results published in Carleton et al. (2026)
• New lab results
• March 2026 fieldwork and future directions

THE KOH KER CHALLENGE

A Capital With an Uneven Archive

Use a Koh Ker landscape or lidar map. Frame the problem around Koh Ker’s political prominence, extensive urban fabric, and uneven archaeological visibility.

The Reconstruction Problem

Landscape evidence

• Extensive urban features.
• Strong spatial patterning.
• Limited direct timing.

Subsurface evidence

• Stratified deposits.
• Datable materials.
• Narrow windows into a large city.

How did activity at Koh Ker vary across space and through time?

Why Sediments Matter Here

• Koh Ker’s urban history is recorded in shallow, spatially variable deposits.
• Anthropogenic sediments can preserve activity where architecture is absent or ambiguous.
• Rapid, low-impact sampling can expand beyond the small number of excavated contexts.

Keep this Koh Ker-specific. The key point is not method in the abstract, but why sedimentary proxies can help recover the city’s changing occupation and use.

Working Aim

Build a dated, spatially distributed reconstruction of human activity at Koh Ker.

Use this to transition from the Koh Ker problem to the published pilot study.

THE 2024 PILOT STUDY

Published Framework

• Carleton et al. (2026) modelled sedimentary traces of human activity at Koh Ker.
• The study used eight test trenches from the 2024 fieldwork.
• The goal was to estimate a latent human influence field from multiple proxies.

Pilot Sampling

• Eight test trenches at Koh Ker, Cambodia.
• Paired magnetic susceptibility and ceramic abundance.
• Depth-wise observations from shallow urban sediments.

Two Observation Channels

Magnetic susceptibility

Ceramic abundance

Show paired observations from one trench. Emphasise what each proxy contributes to the Koh Ker reconstruction.

Latent Human Influence Field

• Latent: human influence is inferred from its traces.
• Field: influence can vary across the sediment archive.
• Both proxies are noisy observations of a shared LHIF.

The model estimates the activity signal we care about, rather than treating any single proxy as the answer.

Model and Result

• Bayesian hierarchical latent-variable model.
• Proxy channels linked within a causal framework.
• Depth-wise reconstructions for the pilot trenches.

Use the model diagram or a simplified result schematic. This is the condensed version of the other talk, so do not dwell on mathematical details unless asked.

Published Takeaways

• Magnetic susceptibility broadly tracks ceramic-rich anthropogenic horizons.
• Joint modelling clarifies where proxy records agree and where uncertainty remains.
• The pilot justifies moving from trenches toward denser, less invasive sampling.

This is the hinge: the publication established that sediment proxies can recover activity structure at Koh Ker, but it also showed that chronology and additional proxies are needed.

NEW LAB RESULTS

FTIR

• FTIR adds mineralogical and combustion-sensitive information to the sediment record.
• It helps separate anthropogenic alteration from natural sediment variation.
• These measurements extend the pilot beyond magnetic susceptibility and ceramics.

Insert the actual FTIR plot when ready. Keep the interpretation tied to Koh Ker deposits and what the method adds to the published proxy set.

pXRF

• pXRF provides elemental profiles through the sampled deposits.
• Elemental patterning can identify activity-related enrichment, sediment sources, and post-depositional change.
• Together with FTIR, pXRF begins to define a richer geochemical signature for Koh Ker activity.

Use the clearest initial pXRF result, preferably one that aligns with a visible stratigraphic or magnetic susceptibility change.

Initial Chronological Results

• First new chronological results are beginning to anchor the sediment profiles in time.
• The immediate goal is to connect depth-wise proxy changes to phases of activity at Koh Ker.
• Better temporal control is what turns proxy profiles into urban trajectories.

Add the dates once they are ready to show. Avoid overclaiming: describe them as initial chronological anchors unless the model is already stable.

2026 FIELDWORK AND NEXT STEPS

March 2026 Field Season

• We returned to Koh Ker to collect terrestrial sediment cores as planned.
• The coring strategy was designed to expand spatial coverage while limiting disturbance.
• The new cores target deposits that can connect landscape features, geochemistry, and chronology.

Insert fieldwork photographs and/or a coring location map. Emphasise that this is the planned next step emerging from the pilot.

Cores Now in the Lab

• The terrestrial sediment cores are now at our institute.
• Processing and subsampling will begin soon.
• The first priorities are logging, magnetic susceptibility, FTIR, pXRF, and chronological sample selection.

The next phase moves from proof of concept to a spatially broader Koh Ker reconstruction.

A Larger Tropical Urban Archaeology Programme

• MPG has recently established a new international tropical research centre in São Paulo with the university there.
• Part of this centre includes funding for a Cambodian PhD student supervised at our institute in coordination with São Paulo.
• This sits within a major new initiative in tropical urban archaeology, with Koh Ker planned as one of the main study locations.

Koh Ker is becoming a core site for a broader, collaborative programme on tropical urbanism.

Confirm the official centre name and partner-unit wording before final delivery. Use São Paulo, not Sao Palo, on the slide.

Take-Home Points

• Koh Ker’s urban trajectory needs integrated spatial, sedimentary, and chronological evidence.
• The 2024 publication established the modelling framework and proxy logic.
• FTIR, pXRF, new dates, and the 2026 cores are expanding the reconstruction.
• The new São Paulo-centred programme creates a path for long-term Cambodian-led research.

Reference

Carleton, W. Christopher, Thon Tho, David Brotherson, Samnang Phin, Huw Groucutt, Jürgen Renn, and Patrick Roberts. 2026. “Bayesian modelling of the latent human influence field in archaeological urban sediments at Koh Ker, Cambodia.” Journal of Archaeological Science 193: 106663. https://doi.org/10.1016/j.jas.2026.106663

Discussion

What would a genuinely spatial and chronological reconstruction of Koh Ker change?