Abstract

Archetypal cements from their deposition to the time they are sampled preserve a record of subsurface fluid evolution that can cover many millions of years. Their morphological development after nucleating on fissure walls is simulated by graphical models showing maturation from isolated to competitive to parallel growth. Graphical models are not available for the cementation of pores that are more complex and diverse. The reconstruction of cement growth in pores is accomplished here using multiple cathodoluminescent (CL) growth zones.

Sediment pores are filled in two stages separated by a cementation threshold associated with a rapid drop in permeability. Pre-threshold cement is centripetal ordered, regularly distributed, and nurtured by a megapore network. Post-threshold cement is disordered, sporadically distributed, and nurtured by labile micropore connections.

The crystallographic form of euhedral crystals at cement's growing front has environmental significance while the anhedral shape of aggregate crystals it leaves behind is controlled by geometrical selection.

Growth of seeded cement is divided into epitaxial and mantle stages; syntaxial when these two are not identified. The epitaxial stage begins with a seed at multiple points then coalesces, simplifies, and morphs towards the Wulff or equilibrium surface. The extent of epitaxial growth is correlated with the size of crystals forming pore walls. Increments of mantle growth can be initiated over the whole surface of a pre-existing crystal, or can be restricted to its edges and/or corners. Restricted seeding is often linked with changes of crystal habit resulting in the reorientation of the crystal's fastest growth direction and the direction of maturation.

Some impingement intercrystalline boundaries have offset growth zones explained by dissolution; such a self-cannibalization process is new. The existing explanation that some enfacial junctions are due to pauses in growth is confirmed by the arrangement of growth zones around triple points, but a new type is recorded formed from continuously growing crystals whose intercrystalline boundaries become modified.

The presence of the cement's internal growth surfaces allow its development to be reconstructed, providing the foundation for further cement studies; however, one example is presented where the disproportionate filling of pores in adjacent millimeter-thick layers is obscure because its crystals lack internal growth surfaces.