Stromatolitic sediments and structures in Hamelin pool, Western Australia, are formed by interactions between blue-green algae (which trap and bind sediment particles) and a variety of mechanical and diagenetic processes. The algae form a cohesive mat that tends to cover intertidal, supratidal, and some shallow subtidal surfaces. The mat is differentiated into 7 intergradational types as an expression of variations in algal species present, ratio of filamentous to unicellular forms, quantity of mucilaginous matrix, life habits, and quantity and nature of the host sediment. The distribution of mat types is controlled by environmental factors such as elevation of substrate, drainage, depth and nature of interstitial groundwater, and sediment influx. In tidal flats with gent e gradients there is a broad zonation of mat types, whereas on headlands and locations with irregular topography the mat is highly differentiated with a condensed, patchy development of types.

The sediments trapped and/or bound by the algal-mat communities commonly are imprinted with distinctive fabrics. These fabrics, which can be related to specific mat types, reflect a complex interaction between the algae, and processes of sedimentation and diagenesis. Important factors in the development of fabric are surface texture and internal structure of the mat, rate and frequency of sediment influx, and processes such as oxidation, cementation, and lithification. Changes in mat type with changes in environmental conditions (e.g., shoaling and sediment influx) lead to the development of successions of fabrics in the sediment pile.

The mat-sediment complex is shaped by physical factors into a variety of structures ranging from extensive flat-lying sheets through linked ellipsoids and columns to discrete ellipsoids and columns. The size range of structures is variable from a few centimeters to several meters; confluent and branched structures are also common. The gross morphology of the structures is largely independent of the mat type (or types) involved in the primary trapping and/or binding processes. Major environmental factors involved in shaping of structures are waves, currents, substrate gradient, and long-term sea-level change; minor factors include burial, exhumation, growth of epiphytes, activity of browsing organisms, gas evolution, corrosion, precipitation, desiccation, and variation in sediment type These factors also influence the external surface texture of structures.

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