Plant Fossil Preservation and Coal

Plants fossilize through distinctive modes such as compression, petrifaction, and charcoalification, and their mass burial forms coal, a key record and resource.

Definition

Plant fossil preservation is the set of processes by which plant tissues become fossils, ranging from flattened compressions to three-dimensional petrifactions; coal is the rock formed from accumulated, buried plant matter.

Scope

This topic covers the modes of plant preservation including compressions and impressions, permineralization and petrifaction, coal balls, and fossil charcoal, together with the formation of peat and coal and the use of these materials in reconstructing ancient vegetation and fire.

Core questions

• What are the main ways plant tissues become fossilized?
• How do coal balls preserve plant anatomy in three dimensions?
• How does peat transform into the ranks of coal?
• What does fossil charcoal reveal about ancient wildfires?

Key concepts

• Compression and impression fossils
• Permineralization and coal balls
• Peat formation and coal rank
• Fossil charcoal and paleofire

Key theories

Modes of plant preservation

Plant fossils form by compression, impression, permineralization, molding, and charcoalification, each preserving different information about anatomy and morphology.

Coalification and coal rank

Burial and heating convert peat through lignite and bituminous coal to anthracite, with rank reflecting the degree of thermal alteration.

Clinical relevance

Coal is a globally important fossil fuel and an archive of ancient wetland ecosystems, while exceptional preservation such as coal balls and fossil charcoal provides detailed anatomical and paleoenvironmental information, including evidence of past wildfire regimes.

History

Study of coal-ball anatomy in the nineteenth and twentieth centuries revealed the structure of coal-forming plants in remarkable detail. Recognition of fossil charcoal as inertinite later opened a record of deep-time wildfire and atmospheric oxygen.

Debates

Controls on exceptional plant preservation

Why certain sites preserve delicate plant anatomy while most yield only compressions is an active area of taphonomic research.

Key figures

• Andrew C. Scott
• Gar W. Rothwell
• Thomas N. Taylor

Seminal works

• taylor2009
• stewart1993

Frequently asked questions

What is a coal ball?

A coal ball is a lump within coal seams where plant tissues were mineralized before compaction, preserving the plants' three-dimensional cellular anatomy.

How does coal form?

Coal forms when plant matter accumulates as peat in wetlands and is then buried and compressed and heated over time, increasing in rank from lignite to anthracite.