Sedimentary Structures and Trace Fossils: Environments and Indicators

Current ripples

Features observed in sandstone formed by flowing water.

Soft sediment deformation

Structures created by loading, pore water escape, slumping.

Hummocky Cross-Stratification (HCS)

A sedimentary structure characterized by undulating layers.

Laminae

Thin layers of sedimentary rock, less than 1 cm thick.

Beds

Thicker layers of sedimentary rock, greater than 1 cm thick.

Heterolithic Bedding

Interbedded sand and mud, typically in tidal-dominated environments.

Flaser bedding

Cross-laminated sand with thin mud layers.

Wavy bedding

Ripple cross-laminated sands alternating with mud.

Graded Bedding

Vertical gradation in texture or grain size indicating transport energy change.

Normal grading

Fining upwards in sedimentary layers.

Reverse grading

Coarsening upwards in sedimentary layers.

Massing Bedding

Structureless, uniform beds with no internal laminae.

Cross-bedding

Layers formed by the migration of ripples or dunes.

Herringbone Cross-bedding

Bi-directional cross-bedding produced by tidal currents.

Bedding Plane Marking

Marks in sediment surface from various processes.

Sole marks

Marks like flutes, scours, grooves on the sediment surface.

Tool marks

Grooves or pits produced by impact on sediment bed.

Mud cracks

Cracks formed by drying and desiccation of mud surfaces.

Syneresis Cracks

Sub-aqueous cracks formed in mud due to clay contraction.

Load Casts/Flame Structures

Structures formed by loading of denser sandstones into less dense mud.

Folds

Soft sediment deformation due to slumping and passive folding.

Ball and Pillow Structures

Loading of sand into mud layers, can occur spontaneously.

Trace fossils

Records of biological activity of organisms, excluding body fossils.

Ichnofauna

Collective term for trace fossils.

Ichnology

The study of trace fossils.

Repichnia

Crawling tracks or trails in sediment.

Cubichnia

Resting traces in sediment.

Domichnia

Dwelling traces or burrows in sediment.

Fodinichnia

Feeding traces in sediment.

Agrichnia

Burrow networks designed to capture fauna or culture bacteria.

Fugichnia

Escape burrows in sediment.

Ichnofossils

Grouped into taxa based on morphological characteristics.

Ichnofacies

Indicators of past marine paleoenvironments.

Skolithos Assemblage

Characteristic of sandy high-energy shorelines with tubular burrows.

Cruziana Assemblage

Variety of traces produced by organisms in sub-littoral zones.

Zoophycos Assemblage

Produced by deposit-feeding polychaete worms in deep marine environments.

Nereites Assemblage

Horizontal traces in abyssal zones, possibly by deposit feeders.

Way-up Indicators

Sedimentary structures that indicate the orientation of sedimentary rocks.