Sedimentologic role ofin situ Beresellid algal colonies, Holder Formation (Upper Pennsylvanian), New Mexico, U.S.A.

In situ Beresellid algal colonies up to 0.1 m in thickness were found in landward intermound deposits between contemporaneous phylloid algal buildups in the Holder Formation (Upper Pennsylvanian), USA. The Beresellid algae in these algal colonies are interpreted to bein situ because: 1) pore spaces are filled with internal sediment and calcite cement surrounded by Beresellid algae, 2) cup-shaped, uncalcified phylloid algae are preserved in upright positions surrounded by masses of Beresellid algae, and 3) Beresellid algae appear to encrust uncalcified stems of phylloid algae together with encrusting foraminifera. These observations suggest early lithification and preservation of Beresellid algal growth fabric within the Beresellid boundstone. The morphology, size, and preserved growth pattern of Beresellid algae suggest that instead of being a sediment “baffler”, it might be possible that Beresellid algae tend to bind larger organisms and formin situ masses of algal thalli without creating significant constructional pore spaces.