Recrystallized massive stromatopores, halysitis, solenoporids and Renalcis.

Barrier reef with Epiphyton, other calimicrobes, and aphrosalpingid sponges (sphinctozoans).

Abstract ref. 1650:
Lower to Upper Silurian (upper Llandovery-Ludlow) limestones belonging to the Heceta Formation record several episodes of reef growth in the Alexander terrane of southeastern Alaska. As the oldest carbonates of widespread distribution in the region, the Heceta limestones represent the earliest development of a shallow-marine platform within the Alexander arc and the oldest foundation for reef evolution. The excellent preservation of biostromes, fringing and barrier reefs, and a mud mound in shelf, shelf margin, and slope deposits, respectively, contrasts with the restricted occurrence of many marine sediments that originated within other island arcs. Hence, these deposits provide important insights into the dynamic processes, styles, and bathymetry associated with reef growth in tectonically active oceanic islands. Massive stromatoporoids, corals, and red algae are preserved in fragmental rudstones and represent a fringing reef that formed at the seaward edge of the incipient marine shelf. Accessory constitutents in this  reef include crinoids and the cyanobacterium Girvanella. Small biostromes were contructed by ramose corals and stromatoporoids on oncolitic substrates in backreef or lagoonal environments. These buildups were associated with low-diversity assemblages of brachiopods and with gastropods, amphiporids, calcareous algae and cyanobacteria. Microbial boundstones reflect the widespread encrustation of cyanobacteria and calcified microproblematica on shelly debris as stromatolitic mats that resulted in the development of a stromatactoid-bearing mud mound and a barrier reef complex. Epiphytaceans, other microbes, and aphrosalpingid sponges were the primary framebuilders of the barrier reefs. These buildups attained significant relief at the shelf margin and shed detritus as slumped blocks and debris flows into deep-water sites along the slope. The similarity of these stromatolitic-aphrosalpingid reefs to those from Siluro-Devonian strata of autochthonous southwestern Alaska suggests paleobiogeographic ties of the Alexander terrane to cratonal North America during the Silurian. 