Lime Peak is an Upper Triassic carbonate complex approximately 40 km northeast of Whitehorse. It is one of many carbonate buildups in the Whitehorse Trough which occur as isolated lenses surrounded by Triassic greywacke and volcanic-clast conglomerates derived from an arc to the southwest. The carbonates at Lime Peak are particularly well-exposed and have been shown to be a series of organic reefs which shed debris into surrounding inter-reef areas. Fieldwork at Lime Peak in 1980 established the existence of massive reefal limestones occurring in 3 distinct forms. The variability of both the geometry and the lithology of the massive limestones was observed in 1980 but was not studied in detail. Considerable effort was spent in 1981 mapping lithology in order to establish the nature and extent of organic framework in the reefal bodies and to develop an explanation for the three distinct growth forms.

In the southern Great Barrier Reef a relativel y thin (< 20 m) Holocene reef has developed on a foundation comprising a succession of older reefs. This reef foundation extends to a depth of up to 420 m in the subsurface and ranges from late Pleistocene to middle Miocene in age. The boundary between the Holocene and late Pleistocene reef is marked by a prominent solution unconformity that shows development of soils, calcrete, and extensive leaching in the underlying limestone. This has resulted from relative lowering of sea level during the period from the last interglacial to the post-glacial transgression. Late Pleistocene reef lithologies within individual drill holes are similar to their overlying Holocene counterparts, and there seems to have been a duplication of environments during both growth periods. However, Halimeda limestones, which are a prominent framework infill in the Pleistocene reef are not as abundant in the Holocene reef. Petrographic analysis of the late Pleistocene reef limestones shows that they have been subjected to near-surface subaerial diagenesis in both the vadose and phreatic freshwater zones. The effects of subaerial diagenesis increase progressively with depth below the solution unconformity, initially within the vadose zone and, ultimately, into the underlying phreatic zone. In the vadose zone, aragonite skeletons (e.g. corals. Halimeda) show two distinct processes of transformation to calcite: (1) total leaching and subsequent infill by sparry calcite cement: and (2) neomorphic replacement of aragonite by calcite, by a process of thin-film transformation. Variations in vadose and phreatic environments suggest that a more permanent freshwater lens was established around reef perimeters than beneath lagoons during the period of subaerial exposure.

In the southern Great Barrier Reef a relativel y thin (< 20 m) Holocene reef has developed on a foundation comprising a succession of older reefs. This reef foundation extends to a depth of up to 420 m in the subsurface and ranges from late Pleistocene to middle Miocene in age. The boundary between the Holocene and late Pleistocene reef is marked by a prominent solution unconformity that shows development of soils, calcrete, and extensive leaching in the underlying limestone. This has resulted from relative lowering of sea level during the period from the last interglacial to the post-glacial transgression. Late Pleistocene reef lithologies within individual drill holes are similar to their overlying Holocene counterparts, and there seems to have been a duplication of environments during both growth periods. However, Halimeda limestones, which are a prominent framework infill in the Pleistocene reef are not as abundant in the Holocene reef. Petrographic analysis of the late Pleistocene reef limestones shows that they have been subjected to near-surface subaerial diagenesis in both the vadose and phreatic freshwater zones. The effects of subaerial diagenesis increase progressively with depth below the solution unconformity, initially within the vadose zone and, ultimately, into the underlying phreatic zone. In the vadose zone, aragonite skeletons (e.g. corals. Halimeda) show two distinct processes of transformation to calcite: (1) total leaching and subsequent infill by sparry calcite cement: and (2) neomorphic replacement of aragonite by calcite, by a process of thin-film transformation. Variations in vadose and phreatic environments suggest that a more permanent freshwater lens was established around reef perimeters than beneath lagoons during the period of subaerial exposure.

In the southern Great Barrier Reef a relativel y thin (< 20 m) Holocene reef has developed on a foundation comprising a succession of older reefs. This reef foundation extends to a depth of up to 420 m in the subsurface and ranges from late Pleistocene to middle Miocene in age. The boundary between the Holocene and late Pleistocene reef is marked by a prominent solution unconformity that shows development of soils, calcrete, and extensive leaching in the underlying limestone. This has resulted from relative lowering of sea level during the period from the last interglacial to the post-glacial transgression. Late Pleistocene reef lithologies within individual drill holes are similar to their overlying Holocene counterparts, and there seems to have been a duplication of environments during both growth periods. However, Halimeda limestones, which are a prominent framework infill in the Pleistocene reef are not as abundant in the Holocene reef. Petrographic analysis of the late Pleistocene reef limestones shows that they have been subjected to near-surface subaerial diagenesis in both the vadose and phreatic freshwater zones. The effects of subaerial diagenesis increase progressively with depth below the solution unconformity, initially within the vadose zone and, ultimately, into the underlying phreatic zone. In the vadose zone, aragonite skeletons (e.g. corals. Halimeda) show two distinct processes of transformation to calcite: (1) total leaching and subsequent infill by sparry calcite cement: and (2) neomorphic replacement of aragonite by calcite, by a process of thin-film transformation. Variations in vadose and phreatic environments suggest that a more permanent freshwater lens was established around reef perimeters than beneath lagoons during the period of subaerial exposure.

In the southern Great Barrier Reef a relativel y thin (< 20 m) Holocene reef has developed on a foundation comprising a succession of older reefs. This reef foundation extends to a depth of up to 420 m in the subsurface and ranges from late Pleistocene to middle Miocene in age. The boundary between the Holocene and late Pleistocene reef is marked by a prominent solution unconformity that shows development of soils, calcrete, and extensive leaching in the underlying limestone. This has resulted from relative lowering of sea level during the period from the last interglacial to the post-glacial transgression. Late Pleistocene reef lithologies within individual drill holes are similar to their overlying Holocene counterparts, and there seems to have been a duplication of environments during both growth periods. However, Halimeda limestones, which are a prominent framework infill in the Pleistocene reef are not as abundant in the Holocene reef. Petrographic analysis of the late Pleistocene reef limestones shows that they have been subjected to near-surface subaerial diagenesis in both the vadose and phreatic freshwater zones. The effects of subaerial diagenesis increase progressively with depth below the solution unconformity, initially within the vadose zone and, ultimately, into the underlying phreatic zone. In the vadose zone, aragonite skeletons (e.g. corals. Halimeda) show two distinct processes of transformation to calcite: (1) total leaching and subsequent infill by sparry calcite cement: and (2) neomorphic replacement of aragonite by calcite, by a process of thin-film transformation. Variations in vadose and phreatic environments suggest that a more permanent freshwater lens was established around reef perimeters than beneath lagoons during the period of subaerial exposure.

Upper Triassic corals and spongiomorphs dredged during BMR Cruise 95 from the Rowley Terrace, offshore Canning Basin of northwestern Australia, indicate possible new occurrences of reef facies. These are comparable to counterparts known from the Northern Limestone Alps of central Europe. A branching spongiomorph, represented by the genus Spongiomorpha sp. and two coral taxa, Pamiroseris rectilamellosa (Winkler) and Retiophyllia tellae (Stoppani), are reported herein. Collectively, these fossils indicate a Late Triassic (Norian- Rhaetian) age. Although different in taxonomic composition, the fauna compares with one previously reported from a Late Triassic ODP reef site (sitc 764) on the Wombat Plateau, some 350 km to the west. The Rowley Terrace occurrences may represent an eastward extension of the Wombat reefs, developed along the rifted margin of Gondwana.

Upper Triassic corals and spongiomorphs dredged during BMR Cruise 95 from the Rowley Terrace, offshore Canning Basin of northwestern Australia, indicate possible new occurrences of reef facies. These are comparable to counterparts known from the Northern Limestone Alps of central Europe. A branching spongiomorph, represented by the genus Spongiomorpha sp. and two coral taxa, Pamiroseris rectilamellosa (Winkler) and Retiophyllia tellae (Stoppani), are reported herein. Collectively, these fossils indicate a Late Triassic (Norian- Rhaetian) age. Although different in taxonomic composition, the fauna compares with one previously reported from a Late Triassic ODP reef site (sitc 764) on the Wombat Plateau, some 350 km to the west. The Rowley Terrace occurrences may represent an eastward extension of the Wombat reefs, developed along the rifted margin of Gondwana.

Upper Triassic corals and spongiomorphs dredged during BMR Cruise 95 from the Rowley Terrace, offshore Canning Basin of northwestern Australia, indicate possible new occurrences of reef facies. These are comparable to counterparts known from the Northern Limestone Alps of central Europe. A branching spongiomorph, represented by the genus Spongiomorpha sp. and two coral taxa, Pamiroseris rectilamellosa (Winkler) and Retiophyllia tellae (Stoppani), are reported herein. Collectively, these fossils indicate a Late Triassic (Norian- Rhaetian) age. Although different in taxonomic composition, the fauna compares with one previously reported from a Late Triassic ODP reef site (sitc 764) on the Wombat Plateau, some 350 km to the west. The Rowley Terrace occurrences may represent an eastward extension of the Wombat reefs, developed along the rifted margin of Gondwana.

Upper Triassic corals and spongiomorphs dredged during BMR Cruise 95 from the Rowley Terrace, offshore Canning Basin of northwestern Australia, indicate possible new occurrences of reef facies. These are comparable to counterparts known from the Northern Limestone Alps of central Europe. A branching spongiomorph, represented by the genus Spongiomorpha sp. and two coral taxa, Pamiroseris rectilamellosa (Winkler) and Retiophyllia tellae (Stoppani), are reported herein. Collectively, these fossils indicate a Late Triassic (Norian- Rhaetian) age. Although different in taxonomic composition, the fauna compares with one previously reported from a Late Triassic ODP reef site (sitc 764) on the Wombat Plateau, some 350 km to the west. The Rowley Terrace occurrences may represent an eastward extension of the Wombat reefs, developed along the rifted margin of Gondwana.

Upper Triassic carbonate, volcanic and clastic rocks deposited in the Whitehorse Trough, a Mesozoic forearc basin, are well-exposed at Hill 4308. The deposition of these rocks occurred in three distinct stages: 1) sedimentation of lime sands and clastics on the flank of a volcanic high, 2) development of reefal carbonates and associated limestones, and 3) renewal of clastic deposition with both erosion and continued growth of patch reefs. The reefal carbonates are similar in structure and composition to reefal carbonates at Lime Peak about 6 km to the south, but the stratigraphic section at Lime Peak differs from that at Hill 4308, the former representing more continuous deposition of carbonate on an underlying clastic foundation. Differences between Hilll 4308 and Lime Peak may reflect local variation in relative sea level and in the distribution and intensity of clastic sedimentation experienced by nearby localities in tectonically active areas.