Hydrocarbon reservoirs are present in algal-laminated carbonate rocks, especially in those that have become dolomitized. Analogous modern algal-mat environments are rare; an example is a hypersaline pool along the shores of the Gulf of Aqaba. This pool should provide a better understanding of the environments in which algal-laminated limestones and dolostones formed in the geologic past. The study of this pool is concerned with the formation of various kinds of particles as well as with the formation of laminites which ultimately would give rise to algal-laminated limestones and dolostones and interlaminated calcite and dolomite.

The hypersaline pool is isolated from the Gulf waters by a gravel bar. Finely laminated algal mats carpet the shallow "shelf" of the pool and gypsum floors the slope and bottom. Algae precipitate pellets, ooids, oncolites, grapestones, flakes, and carbonate laminites. The ooids have a radial texture; hence, contrary to statements in the literature, ooids with a radial texture are formed in the depositional environment. Some laminites consist of fibrous aragonite, others are cryptocrystalline high-magnesian calcite; the latter enclose abundant dispersed organic matter. Cryptocrystalline laminites mimic the micrite of the rock record including its pelletlike fabric; even after the organic matter has disappeared these laminites can preserve the morphology of the mats. Scanning electron m crographs show that cryptocrystalline laminites consist of a mosaic of micron-size rhombohedrons which during diagenesis would stabilize to low-magnesian calcite. Hence, the origin of some ancient stromatolitic limestones (pelmicrites) may be explained in terms of precipitation of cryptocrystalline high-magnesian calcite laminites.

These laminites are lithified within the algal mats and do not require postdepositional cementation. These laminites prove that algal precipitation can be a potent force in lithification. This conclusion may supersede the concept that all micrites result from neomorphic replacement of aragonite.

The algae create a microenvironment in which magnesium becomes enriched in organic matter and in which high-magnesian calcite with up to 40 percent molecular MgCO₃ is precipitated. The total molecular percent MgCO₃ between the magnesium organic complex and high-magnesian calcite may reach 60. This preferential concentration of magnesium may explain the high level of dolomitization of stromatolitic rocks in the geologic record. Alternation of aragonite and high-magnesian calcite laminites would yield interlaminated calcite and dolomite in the rock record. As part of the biologic system amino acids devoid of sulfur, especially aspartic acid, may exert considerable influence on the precipitation of the carbonate laminites and particles.