Upper Triassic paleogeographic map showing the global distribution of Upper Triassic reefs (after Flügel, 2002). Although many of these are scleractinian reefs others are dominated by coralline sponges, ‘ Tubiphytes ’ , serpulids or algae (after Flügel, 2002). Note that the paleogeographic placement of allochthonous terranes remains highly contentious however a growing body of evidence supports the hypothesis that several of these terranes occurred as shown, in close proximity to the North America autochthon during the early Mesozoic (i.e. Unterschutz et al., 2002; Peterson et al., 2004). With the exception of the Pardonet Hill patch reefs, Upper Triassic reefs in the eastern Panthalassa are limited to these allochthonous terranes. 1 = Pardonet Hill; 2 = Quesnel terrane reefs; 3 = Stikine Terrane reefs; and 4 = Wrangellia Terrane reefs. 

Contexts in source publication

Context 1

... and occa- sionally entire patch reefs in siliciclastic sand, resulting in recolonization by infaunal organisms. Taxa, such as Retiophyllia and Isocrinus , that were tolerant of multiple substrate types (i.e. Rasmussen, 1977; Stanley, 1989; Baumiller and Hagdorn, 1994) thrived in this dynamic sedimentary setting. Re-exhumation by storm-generated currents resulted in recolonization by epifaunal organisms. Quartz-dominated sandstone intervals between the patch reefs as well as laterally restricted sandstone lenses within individual reefs reflects continuous turnover of infaunal and epifaunal communities on the edges of the Baldonnel patch reefs. A number of factors have been shown to affect compositional variation in bioclastic accumulations, including temperature, nutrient availability, salinity, turbidity/clastic influx and/or substrate availability (Stanley, 2001). Of these, temperature is often cited as playing a dominant role in their presence and taxonomic composition (Lees, 1975; Brookfield, 1988; Beauchamp and Desrochers, 1997). Thus, the composition of benthic faunal associations is often used to infer paleolatitude or paleoclimatic setting. Coral/spongiomorph complexes on allochthonous terranes west of the study area are interpreted to have Tethyan affinities and thus are interpreted as warm water, tropical to subtropical assemblages (Eliuk, 1989). Although some researchers have suggested that the absence of “ warm water faunas ” such as corals, sponges and megalodontid bivalves in the Triassic strata of western Canada implies deposition in frigid seas (Tozer, 1981; Gibson and Barclay, 1989), other researchers have suggested that the relationship is more ambiguous (i.e Zonneveld, 2001). The distribution of Triassic sponges and megalodontids is too poorly known to place undue significance on their presence or absence. Similarly, the environmental tolerances of early scleractinian corals remains unknown. Although they originated in the equatorial Tethys region in the Middle Triassic, evidence that early scleractinians were limited to warm tropical or subtropical settings is lacking. It has recently been suggested that scleractinian corals may have had wider or different environmental and latitudinal tolerances than their modern counterparts (Stanley, 1981; Flügel, 1994; Kiessling, 2001; Stanley, 2001, 2003). The water temperature, light requirements and turbidity tolerance of Triassic reef organisms likely differed significantly from that of Holocene equivalents (Flügel, 1994). Stanley (1988a) indicated that most Triassic corals appeared to have preferred low energy environments such as lagoons, protected shoals, and deeper shelf slope. Modern hermatypic corals (reef- building corals possessing zooxanthellae) habitually occur in warm, shallow tropical seas. Scleractinian corals may have evolved from a soft-bodied anemone- like metazoan that eventually developed the ability to produce a hard skeleton (Stanley, 1988b, 2001; Stanley and Fautin, 2001). It remains unknown when the symbiotic relationship between these calcifying metazoans and one-celled zooxanthellae developed (Stanley, 2001, 2003). Thus, it remains unknown when corals differentiated into ‘ hermatypic ’ and ‘ ahermatypic ’ forms. Stanley (1979, 1981) postulated that Triassic corals were largely ahermatypic since such corals have wide distributions in cool water. The presence or absence of reefs or corals should thus not be used as evidence for specific temperature regimes. The general paucity/absence of reefs and scleractinian corals on the western margin of Triassic Pangaea is most likely attributable to other factors, possibly related to regional oceanic circulation patterns and/or availability of suitable substrates. The Triassic was a seminal interval in the history of reefs. The terminal Permian biotic crisis heralded the final disappearance of archaic Paleozoic reef communities resulting in a lengthy interval ( ∼ 12 – 14 million years) during which metazoan reefs were globally absent (Stanley, 2001, 2003). Metazoan reefs, represented by diminutive mounds with variably abundant scleractinian corals, reappeared first in the peri-Tethys and Tethys region in the Anisian (early Middle Triassic; i.e. Kolosvary, 1958; Scholz, 1972; Fan, 1980; Gaetani et al., 1981; Flügel, 1982, 2002). During the Ladinian (late Middle Triassic) metazoan reefs became wide spread in the Tethys region and made their first appearance outside the Tethys, in the eastern Panthalassa (Flügel, 1982, 2002). These latter reefs occur in the northwestern Sonora and the western Great Basin of Nevada, on a terrane regarded as parauthocthonous to the North American Craton (Stanley, 1988a). Large, extensive metazoan reefs became common in the Upper Triassic, primarily in the Tethys and western Panthalassa ocean (Flügel, 1981, 1982; Stanley, 1988a, b; Flügel, 2002; Fig. 15). At this time small to moderate sized metazoan reefs also occur throughout the Panthalassa Ocean (Fig. 15). In the eastern Panthalassa most of these Upper Triassic reefs developed in shallow marine carbonate platforms that developed on volcanic islands which now make up displaced, allochthonous terranes fringing the Pacific ocean (Tozer, 1981; Stanley, 1988a; Flügel, 2002; Fig. 15). Stanley (1988a) suggested that terrane-hosted reefs may have had a profound effect on the evolution of reefs and reef organisms by serving as refugia as well as dispersal agents for Triassic reefal communities connecting the Tethys with North America by a series of islands or ‘ stepping stones ’ . All previously reported Triassic reef accumulations in western North America occur on these terranes (i.e. Bosellini and Rossi, 1974; Jones et al., 1977; Irving, 1977; Stanley, 1979; Coney et al., 1980; Stanley, 1982; Pincha-Wegener, 1982; Reid and Ginsburg, 1986; Reid and Tempelman-Kluit, 1987; Stanley, 1989; Eliuk, 1989; Reid, 1989). The exception, presently located in Nevada, occurs on a parautochthonous terrane which may have accreted to the North American plate prior to, or shortly after, reef initiation and development. The allochthonous terranes now comprise part of the North American Cordillera extending from Alaska to California however their position (latitude and proximity/ distance to North America) during the Triassic remains controversial (i.e. Irving, 1977; Jones et al., 1977; Coney et al., 1980; Umhoefer, 1987; Gabrielse et al., 1991; Carter et al., 1991; Flügel, 2002; Katvala and Henderson, 2002). The Pardonet Hill buildups are the only known examples of North American scleractinian corals/coral reefs that do not occur on allochthonous terranes. These reefs document certain occurrence of Triassic corals on the North American craton margin at ∼ 30° N paleolatitude (Fig. 15). The Pardonet Hill patch reefs have a morphology, architecture and taxonomic composition comparable to carbonate buildups at Cowichan Lake, southern Vancouver Island (Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999). The geograph- ically closest known coral reefs during the Triassic occur on the Quesnel (Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999), Stikine (Reid and Ginsburg, 1986; Reid and Tempelman-Kluit, 1987; Reid, 1989) and Wrangellia terranes (Clapp and Shimer, 1911; Stanley, 1979; Stanley, 1989). These terranes are all interpreted (based in part on paleontologic and paleo- magnetic data) to have originated well to the south of their present locations and moved northward both before and after collision with each other and with the North American plate (Irving and Yole, 1972; Coney et al., 1980; Gabrielse et al., 1991; Carter et al., 1991). If the interpreted southern origin of Quesnel, Stikine and Wrangellia is true, than it is unlikely that these terranes were the source of craton-bound corals reported on in the present study. As well, most of the terrane coral occurrences (including Cowichan Lake) are considerably younger than the Pardonet Hill locality (i.e. lower to upper Norian) suggesting either that the terranes were not necessary ‘ stepping stones ’ for faunal migration from the Tethys region to the study area or that a number of older (Ladinian or Carnian) Triassic reefs once populated the terranes. The presence of reef-associated faunal communities on the craton margin similar to those characteristic of reefs on accreted terranes emphasizes that faunal evidence for terrane placement must be used judiciously and furthermore provides support for the hypothesis that several of the terranes occurred in close proximity to the autochthon during the early Mesozoic (Unterschutz et al., 2002; Peterson et al., 2004). Despite extensive regional exposure of the Baldonnel Formation in the Rocky Mountain Foothills and Front Ranges of northeastern British Columbia, Triassic reefs have only been observed in the lower Baldonnel Formation at Pardonet Hill. With the exception of anthozoans overall identical faunal assemblages characterize the Baldonnel Formation throughout its stratigraphic and geographic range (i.e. Zonneveld et al., 2004), thus, reasons for such sparse reef distribution remain uncertain. The lower Baldonnel Formation occurs only in westernmost Triassic outcrop exposures and is well- exposed at only a few localities partially explaining the severely limited occurrence of Triassic coral reefs. We believe that coral reefs are limited to the lower Baldonnel Formation due to regional sea level flux. The lower Baldonnel Formation was deposited during an interval of prolonged ( ∼ 5 – 10 my) regional sea-level lowstand (Zonneveld and Orchard, 2002). Coeval strata at localities to the east are represented by marginal marine and continental strata of the Charlie Lake Formation (Zonneveld and Orchard, 2002). During this interval (lowermost Upper Carnian; lower nodosus zone; Fig. 2), the regional shoreline migrated to its westernmost Triassic position, apparently adjacent to a steep ramp margin (Zonneveld ...

Context 2

... in this dynamic sedimentary setting. Re-exhumation by storm-generated currents resulted in recolonization by epifaunal organisms. Quartz-dominated sandstone intervals between the patch reefs as well as laterally restricted sandstone lenses within individual reefs reflects continuous turnover of infaunal and epifaunal communities on the edges of the Baldonnel patch reefs. A number of factors have been shown to affect compositional variation in bioclastic accumulations, including temperature, nutrient availability, salinity, turbidity/clastic influx and/or substrate availability (Stanley, 2001). Of these, temperature is often cited as playing a dominant role in their presence and taxonomic composition (Lees, 1975; Brookfield, 1988; Beauchamp and Desrochers, 1997). Thus, the composition of benthic faunal associations is often used to infer paleolatitude or paleoclimatic setting. Coral/spongiomorph complexes on allochthonous terranes west of the study area are interpreted to have Tethyan affinities and thus are interpreted as warm water, tropical to subtropical assemblages (Eliuk, 1989). Although some researchers have suggested that the absence of “ warm water faunas ” such as corals, sponges and megalodontid bivalves in the Triassic strata of western Canada implies deposition in frigid seas (Tozer, 1981; Gibson and Barclay, 1989), other researchers have suggested that the relationship is more ambiguous (i.e Zonneveld, 2001). The distribution of Triassic sponges and megalodontids is too poorly known to place undue significance on their presence or absence. Similarly, the environmental tolerances of early scleractinian corals remains unknown. Although they originated in the equatorial Tethys region in the Middle Triassic, evidence that early scleractinians were limited to warm tropical or subtropical settings is lacking. It has recently been suggested that scleractinian corals may have had wider or different environmental and latitudinal tolerances than their modern counterparts (Stanley, 1981; Flügel, 1994; Kiessling, 2001; Stanley, 2001, 2003). The water temperature, light requirements and turbidity tolerance of Triassic reef organisms likely differed significantly from that of Holocene equivalents (Flügel, 1994). Stanley (1988a) indicated that most Triassic corals appeared to have preferred low energy environments such as lagoons, protected shoals, and deeper shelf slope. Modern hermatypic corals (reef- building corals possessing zooxanthellae) habitually occur in warm, shallow tropical seas. Scleractinian corals may have evolved from a soft-bodied anemone- like metazoan that eventually developed the ability to produce a hard skeleton (Stanley, 1988b, 2001; Stanley and Fautin, 2001). It remains unknown when the symbiotic relationship between these calcifying metazoans and one-celled zooxanthellae developed (Stanley, 2001, 2003). Thus, it remains unknown when corals differentiated into ‘ hermatypic ’ and ‘ ahermatypic ’ forms. Stanley (1979, 1981) postulated that Triassic corals were largely ahermatypic since such corals have wide distributions in cool water. The presence or absence of reefs or corals should thus not be used as evidence for specific temperature regimes. The general paucity/absence of reefs and scleractinian corals on the western margin of Triassic Pangaea is most likely attributable to other factors, possibly related to regional oceanic circulation patterns and/or availability of suitable substrates. The Triassic was a seminal interval in the history of reefs. The terminal Permian biotic crisis heralded the final disappearance of archaic Paleozoic reef communities resulting in a lengthy interval ( ∼ 12 – 14 million years) during which metazoan reefs were globally absent (Stanley, 2001, 2003). Metazoan reefs, represented by diminutive mounds with variably abundant scleractinian corals, reappeared first in the peri-Tethys and Tethys region in the Anisian (early Middle Triassic; i.e. Kolosvary, 1958; Scholz, 1972; Fan, 1980; Gaetani et al., 1981; Flügel, 1982, 2002). During the Ladinian (late Middle Triassic) metazoan reefs became wide spread in the Tethys region and made their first appearance outside the Tethys, in the eastern Panthalassa (Flügel, 1982, 2002). These latter reefs occur in the northwestern Sonora and the western Great Basin of Nevada, on a terrane regarded as parauthocthonous to the North American Craton (Stanley, 1988a). Large, extensive metazoan reefs became common in the Upper Triassic, primarily in the Tethys and western Panthalassa ocean (Flügel, 1981, 1982; Stanley, 1988a, b; Flügel, 2002; Fig. 15). At this time small to moderate sized metazoan reefs also occur throughout the Panthalassa Ocean (Fig. 15). In the eastern Panthalassa most of these Upper Triassic reefs developed in shallow marine carbonate platforms that developed on volcanic islands which now make up displaced, allochthonous terranes fringing the Pacific ocean (Tozer, 1981; Stanley, 1988a; Flügel, 2002; Fig. 15). Stanley (1988a) suggested that terrane-hosted reefs may have had a profound effect on the evolution of reefs and reef organisms by serving as refugia as well as dispersal agents for Triassic reefal communities connecting the Tethys with North America by a series of islands or ‘ stepping stones ’ . All previously reported Triassic reef accumulations in western North America occur on these terranes (i.e. Bosellini and Rossi, 1974; Jones et al., 1977; Irving, 1977; Stanley, 1979; Coney et al., 1980; Stanley, 1982; Pincha-Wegener, 1982; Reid and Ginsburg, 1986; Reid and Tempelman-Kluit, 1987; Stanley, 1989; Eliuk, 1989; Reid, 1989). The exception, presently located in Nevada, occurs on a parautochthonous terrane which may have accreted to the North American plate prior to, or shortly after, reef initiation and development. The allochthonous terranes now comprise part of the North American Cordillera extending from Alaska to California however their position (latitude and proximity/ distance to North America) during the Triassic remains controversial (i.e. Irving, 1977; Jones et al., 1977; Coney et al., 1980; Umhoefer, 1987; Gabrielse et al., 1991; Carter et al., 1991; Flügel, 2002; Katvala and Henderson, 2002). The Pardonet Hill buildups are the only known examples of North American scleractinian corals/coral reefs that do not occur on allochthonous terranes. These reefs document certain occurrence of Triassic corals on the North American craton margin at ∼ 30° N paleolatitude (Fig. 15). The Pardonet Hill patch reefs have a morphology, architecture and taxonomic composition comparable to carbonate buildups at Cowichan Lake, southern Vancouver Island (Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999). The geograph- ically closest known coral reefs during the Triassic occur on the Quesnel (Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999), Stikine (Reid and Ginsburg, 1986; Reid and Tempelman-Kluit, 1987; Reid, 1989) and Wrangellia terranes (Clapp and Shimer, 1911; Stanley, 1979; Stanley, 1989). These terranes are all interpreted (based in part on paleontologic and paleo- magnetic data) to have originated well to the south of their present locations and moved northward both before and after collision with each other and with the North American plate (Irving and Yole, 1972; Coney et al., 1980; Gabrielse et al., 1991; Carter et al., 1991). If the interpreted southern origin of Quesnel, Stikine and Wrangellia is true, than it is unlikely that these terranes were the source of craton-bound corals reported on in the present study. As well, most of the terrane coral occurrences (including Cowichan Lake) are considerably younger than the Pardonet Hill locality (i.e. lower to upper Norian) suggesting either that the terranes were not necessary ‘ stepping stones ’ for faunal migration from the Tethys region to the study area or that a number of older (Ladinian or Carnian) Triassic reefs once populated the terranes. The presence of reef-associated faunal communities on the craton margin similar to those characteristic of reefs on accreted terranes emphasizes that faunal evidence for terrane placement must be used judiciously and furthermore provides support for the hypothesis that several of the terranes occurred in close proximity to the autochthon during the early Mesozoic (Unterschutz et al., 2002; Peterson et al., 2004). Despite extensive regional exposure of the Baldonnel Formation in the Rocky Mountain Foothills and Front Ranges of northeastern British Columbia, Triassic reefs have only been observed in the lower Baldonnel Formation at Pardonet Hill. With the exception of anthozoans overall identical faunal assemblages characterize the Baldonnel Formation throughout its stratigraphic and geographic range (i.e. Zonneveld et al., 2004), thus, reasons for such sparse reef distribution remain uncertain. The lower Baldonnel Formation occurs only in westernmost Triassic outcrop exposures and is well- exposed at only a few localities partially explaining the severely limited occurrence of Triassic coral reefs. We believe that coral reefs are limited to the lower Baldonnel Formation due to regional sea level flux. The lower Baldonnel Formation was deposited during an interval of prolonged ( ∼ 5 – 10 my) regional sea-level lowstand (Zonneveld and Orchard, 2002). Coeval strata at localities to the east are represented by marginal marine and continental strata of the Charlie Lake Formation (Zonneveld and Orchard, 2002). During this interval (lowermost Upper Carnian; lower nodosus zone; Fig. 2), the regional shoreline migrated to its westernmost Triassic position, apparently adjacent to a steep ramp margin (Zonneveld and Orchard, 2002). The presence of several angular unconformities in the Charlie Lake Formation to the east and preservation of an inordinately thick package of marginal marine and continental strata in western Canada provide evidence that this regional lowstand may have been ...

Context 3

... too poorly known to place undue significance on their presence or absence. Similarly, the environmental tolerances of early scleractinian corals remains unknown. Although they originated in the equatorial Tethys region in the Middle Triassic, evidence that early scleractinians were limited to warm tropical or subtropical settings is lacking. It has recently been suggested that scleractinian corals may have had wider or different environmental and latitudinal tolerances than their modern counterparts (Stanley, 1981; Flügel, 1994; Kiessling, 2001; Stanley, 2001, 2003). The water temperature, light requirements and turbidity tolerance of Triassic reef organisms likely differed significantly from that of Holocene equivalents (Flügel, 1994). Stanley (1988a) indicated that most Triassic corals appeared to have preferred low energy environments such as lagoons, protected shoals, and deeper shelf slope. Modern hermatypic corals (reef- building corals possessing zooxanthellae) habitually occur in warm, shallow tropical seas. Scleractinian corals may have evolved from a soft-bodied anemone- like metazoan that eventually developed the ability to produce a hard skeleton (Stanley, 1988b, 2001; Stanley and Fautin, 2001). It remains unknown when the symbiotic relationship between these calcifying metazoans and one-celled zooxanthellae developed (Stanley, 2001, 2003). Thus, it remains unknown when corals differentiated into ‘ hermatypic ’ and ‘ ahermatypic ’ forms. Stanley (1979, 1981) postulated that Triassic corals were largely ahermatypic since such corals have wide distributions in cool water. The presence or absence of reefs or corals should thus not be used as evidence for specific temperature regimes. The general paucity/absence of reefs and scleractinian corals on the western margin of Triassic Pangaea is most likely attributable to other factors, possibly related to regional oceanic circulation patterns and/or availability of suitable substrates. The Triassic was a seminal interval in the history of reefs. The terminal Permian biotic crisis heralded the final disappearance of archaic Paleozoic reef communities resulting in a lengthy interval ( ∼ 12 – 14 million years) during which metazoan reefs were globally absent (Stanley, 2001, 2003). Metazoan reefs, represented by diminutive mounds with variably abundant scleractinian corals, reappeared first in the peri-Tethys and Tethys region in the Anisian (early Middle Triassic; i.e. Kolosvary, 1958; Scholz, 1972; Fan, 1980; Gaetani et al., 1981; Flügel, 1982, 2002). During the Ladinian (late Middle Triassic) metazoan reefs became wide spread in the Tethys region and made their first appearance outside the Tethys, in the eastern Panthalassa (Flügel, 1982, 2002). These latter reefs occur in the northwestern Sonora and the western Great Basin of Nevada, on a terrane regarded as parauthocthonous to the North American Craton (Stanley, 1988a). Large, extensive metazoan reefs became common in the Upper Triassic, primarily in the Tethys and western Panthalassa ocean (Flügel, 1981, 1982; Stanley, 1988a, b; Flügel, 2002; Fig. 15). At this time small to moderate sized metazoan reefs also occur throughout the Panthalassa Ocean (Fig. 15). In the eastern Panthalassa most of these Upper Triassic reefs developed in shallow marine carbonate platforms that developed on volcanic islands which now make up displaced, allochthonous terranes fringing the Pacific ocean (Tozer, 1981; Stanley, 1988a; Flügel, 2002; Fig. 15). Stanley (1988a) suggested that terrane-hosted reefs may have had a profound effect on the evolution of reefs and reef organisms by serving as refugia as well as dispersal agents for Triassic reefal communities connecting the Tethys with North America by a series of islands or ‘ stepping stones ’ . All previously reported Triassic reef accumulations in western North America occur on these terranes (i.e. Bosellini and Rossi, 1974; Jones et al., 1977; Irving, 1977; Stanley, 1979; Coney et al., 1980; Stanley, 1982; Pincha-Wegener, 1982; Reid and Ginsburg, 1986; Reid and Tempelman-Kluit, 1987; Stanley, 1989; Eliuk, 1989; Reid, 1989). The exception, presently located in Nevada, occurs on a parautochthonous terrane which may have accreted to the North American plate prior to, or shortly after, reef initiation and development. The allochthonous terranes now comprise part of the North American Cordillera extending from Alaska to California however their position (latitude and proximity/ distance to North America) during the Triassic remains controversial (i.e. Irving, 1977; Jones et al., 1977; Coney et al., 1980; Umhoefer, 1987; Gabrielse et al., 1991; Carter et al., 1991; Flügel, 2002; Katvala and Henderson, 2002). The Pardonet Hill buildups are the only known examples of North American scleractinian corals/coral reefs that do not occur on allochthonous terranes. These reefs document certain occurrence of Triassic corals on the North American craton margin at ∼ 30° N paleolatitude (Fig. 15). The Pardonet Hill patch reefs have a morphology, architecture and taxonomic composition comparable to carbonate buildups at Cowichan Lake, southern Vancouver Island (Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999). The geograph- ically closest known coral reefs during the Triassic occur on the Quesnel (Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999), Stikine (Reid and Ginsburg, 1986; Reid and Tempelman-Kluit, 1987; Reid, 1989) and Wrangellia terranes (Clapp and Shimer, 1911; Stanley, 1979; Stanley, 1989). These terranes are all interpreted (based in part on paleontologic and paleo- magnetic data) to have originated well to the south of their present locations and moved northward both before and after collision with each other and with the North American plate (Irving and Yole, 1972; Coney et al., 1980; Gabrielse et al., 1991; Carter et al., 1991). If the interpreted southern origin of Quesnel, Stikine and Wrangellia is true, than it is unlikely that these terranes were the source of craton-bound corals reported on in the present study. As well, most of the terrane coral occurrences (including Cowichan Lake) are considerably younger than the Pardonet Hill locality (i.e. lower to upper Norian) suggesting either that the terranes were not necessary ‘ stepping stones ’ for faunal migration from the Tethys region to the study area or that a number of older (Ladinian or Carnian) Triassic reefs once populated the terranes. The presence of reef-associated faunal communities on the craton margin similar to those characteristic of reefs on accreted terranes emphasizes that faunal evidence for terrane placement must be used judiciously and furthermore provides support for the hypothesis that several of the terranes occurred in close proximity to the autochthon during the early Mesozoic (Unterschutz et al., 2002; Peterson et al., 2004). Despite extensive regional exposure of the Baldonnel Formation in the Rocky Mountain Foothills and Front Ranges of northeastern British Columbia, Triassic reefs have only been observed in the lower Baldonnel Formation at Pardonet Hill. With the exception of anthozoans overall identical faunal assemblages characterize the Baldonnel Formation throughout its stratigraphic and geographic range (i.e. Zonneveld et al., 2004), thus, reasons for such sparse reef distribution remain uncertain. The lower Baldonnel Formation occurs only in westernmost Triassic outcrop exposures and is well- exposed at only a few localities partially explaining the severely limited occurrence of Triassic coral reefs. We believe that coral reefs are limited to the lower Baldonnel Formation due to regional sea level flux. The lower Baldonnel Formation was deposited during an interval of prolonged ( ∼ 5 – 10 my) regional sea-level lowstand (Zonneveld and Orchard, 2002). Coeval strata at localities to the east are represented by marginal marine and continental strata of the Charlie Lake Formation (Zonneveld and Orchard, 2002). During this interval (lowermost Upper Carnian; lower nodosus zone; Fig. 2), the regional shoreline migrated to its westernmost Triassic position, apparently adjacent to a steep ramp margin (Zonneveld and Orchard, 2002). The presence of several angular unconformities in the Charlie Lake Formation to the east and preservation of an inordinately thick package of marginal marine and continental strata in western Canada provide evidence that this regional lowstand may have been tectonically mediated. Significantly lower sea-level, combined with increasingly close proximity of Panthalassan island arcs, may have resulted in significant deflection of regional oceanic circulation patterns temporarily allowing viable anthozoan larvae to colonize local patches of stable substrate. An abrupt, regionally correlatable transgressive surface of erosion occurs at the top of the Lower Baldonnel Formation (Zonneveld and Orchard, 2002), just above the patch reef interval ( ∼ 156 m; Fig. 3). This transgressive surface resulted in rapid migration of the shoreline several 10's of kilometres to the east and signifies the end of scleractinian colonization in the study area. It is postulated that regional oceanic circulation patterns returned to ‘ normal ’ and anthozoan larvae either were not transported to the northwestern Pangaea coast or were transported but had travelled too great a distance, possibly through frigid arctic or sub- arctic regions and were not viable upon arrival. The Pardonet Hill patch reefs developed in a dynamic sedimentary setting characterized by strong currents and sporadic influx of large volumes of clastic sediment. A number of lines of evidence indicate that the lower Baldonnel Formation was deposited in a storm-dominated setting characterized by episodes of sudden deposition and intervals of erosional exhumation. These include: abundant carbonate breccia within reefal limestones; hummocky cross-stratified to current ripple bedded sandstone interbeds; ...

Context 4

... debris. Storm currents, as well as normal shoreface currents, likely frequently buried patch reef fringes, and occa- sionally entire patch reefs in siliciclastic sand, resulting in recolonization by infaunal organisms. Taxa, such as Retiophyllia and Isocrinus , that were tolerant of multiple substrate types (i.e. Rasmussen, 1977; Stanley, 1989; Baumiller and Hagdorn, 1994) thrived in this dynamic sedimentary setting. Re-exhumation by storm-generated currents resulted in recolonization by epifaunal organisms. Quartz-dominated sandstone intervals between the patch reefs as well as laterally restricted sandstone lenses within individual reefs reflects continuous turnover of infaunal and epifaunal communities on the edges of the Baldonnel patch reefs. A number of factors have been shown to affect compositional variation in bioclastic accumulations, including temperature, nutrient availability, salinity, turbidity/clastic influx and/or substrate availability (Stanley, 2001). Of these, temperature is often cited as playing a dominant role in their presence and taxonomic composition (Lees, 1975; Brookfield, 1988; Beauchamp and Desrochers, 1997). Thus, the composition of benthic faunal associations is often used to infer paleolatitude or paleoclimatic setting. Coral/spongiomorph complexes on allochthonous terranes west of the study area are interpreted to have Tethyan affinities and thus are interpreted as warm water, tropical to subtropical assemblages (Eliuk, 1989). Although some researchers have suggested that the absence of “ warm water faunas ” such as corals, sponges and megalodontid bivalves in the Triassic strata of western Canada implies deposition in frigid seas (Tozer, 1981; Gibson and Barclay, 1989), other researchers have suggested that the relationship is more ambiguous (i.e Zonneveld, 2001). The distribution of Triassic sponges and megalodontids is too poorly known to place undue significance on their presence or absence. Similarly, the environmental tolerances of early scleractinian corals remains unknown. Although they originated in the equatorial Tethys region in the Middle Triassic, evidence that early scleractinians were limited to warm tropical or subtropical settings is lacking. It has recently been suggested that scleractinian corals may have had wider or different environmental and latitudinal tolerances than their modern counterparts (Stanley, 1981; Flügel, 1994; Kiessling, 2001; Stanley, 2001, 2003). The water temperature, light requirements and turbidity tolerance of Triassic reef organisms likely differed significantly from that of Holocene equivalents (Flügel, 1994). Stanley (1988a) indicated that most Triassic corals appeared to have preferred low energy environments such as lagoons, protected shoals, and deeper shelf slope. Modern hermatypic corals (reef- building corals possessing zooxanthellae) habitually occur in warm, shallow tropical seas. Scleractinian corals may have evolved from a soft-bodied anemone- like metazoan that eventually developed the ability to produce a hard skeleton (Stanley, 1988b, 2001; Stanley and Fautin, 2001). It remains unknown when the symbiotic relationship between these calcifying metazoans and one-celled zooxanthellae developed (Stanley, 2001, 2003). Thus, it remains unknown when corals differentiated into ‘ hermatypic ’ and ‘ ahermatypic ’ forms. Stanley (1979, 1981) postulated that Triassic corals were largely ahermatypic since such corals have wide distributions in cool water. The presence or absence of reefs or corals should thus not be used as evidence for specific temperature regimes. The general paucity/absence of reefs and scleractinian corals on the western margin of Triassic Pangaea is most likely attributable to other factors, possibly related to regional oceanic circulation patterns and/or availability of suitable substrates. The Triassic was a seminal interval in the history of reefs. The terminal Permian biotic crisis heralded the final disappearance of archaic Paleozoic reef communities resulting in a lengthy interval ( ∼ 12 – 14 million years) during which metazoan reefs were globally absent (Stanley, 2001, 2003). Metazoan reefs, represented by diminutive mounds with variably abundant scleractinian corals, reappeared first in the peri-Tethys and Tethys region in the Anisian (early Middle Triassic; i.e. Kolosvary, 1958; Scholz, 1972; Fan, 1980; Gaetani et al., 1981; Flügel, 1982, 2002). During the Ladinian (late Middle Triassic) metazoan reefs became wide spread in the Tethys region and made their first appearance outside the Tethys, in the eastern Panthalassa (Flügel, 1982, 2002). These latter reefs occur in the northwestern Sonora and the western Great Basin of Nevada, on a terrane regarded as parauthocthonous to the North American Craton (Stanley, 1988a). Large, extensive metazoan reefs became common in the Upper Triassic, primarily in the Tethys and western Panthalassa ocean (Flügel, 1981, 1982; Stanley, 1988a, b; Flügel, 2002; Fig. 15). At this time small to moderate sized metazoan reefs also occur throughout the Panthalassa Ocean (Fig. 15). In the eastern Panthalassa most of these Upper Triassic reefs developed in shallow marine carbonate platforms that developed on volcanic islands which now make up displaced, allochthonous terranes fringing the Pacific ocean (Tozer, 1981; Stanley, 1988a; Flügel, 2002; Fig. 15). Stanley (1988a) suggested that terrane-hosted reefs may have had a profound effect on the evolution of reefs and reef organisms by serving as refugia as well as dispersal agents for Triassic reefal communities connecting the Tethys with North America by a series of islands or ‘ stepping stones ’ . All previously reported Triassic reef accumulations in western North America occur on these terranes (i.e. Bosellini and Rossi, 1974; Jones et al., 1977; Irving, 1977; Stanley, 1979; Coney et al., 1980; Stanley, 1982; Pincha-Wegener, 1982; Reid and Ginsburg, 1986; Reid and Tempelman-Kluit, 1987; Stanley, 1989; Eliuk, 1989; Reid, 1989). The exception, presently located in Nevada, occurs on a parautochthonous terrane which may have accreted to the North American plate prior to, or shortly after, reef initiation and development. The allochthonous terranes now comprise part of the North American Cordillera extending from Alaska to California however their position (latitude and proximity/ distance to North America) during the Triassic remains controversial (i.e. Irving, 1977; Jones et al., 1977; Coney et al., 1980; Umhoefer, 1987; Gabrielse et al., 1991; Carter et al., 1991; Flügel, 2002; Katvala and Henderson, 2002). The Pardonet Hill buildups are the only known examples of North American scleractinian corals/coral reefs that do not occur on allochthonous terranes. These reefs document certain occurrence of Triassic corals on the North American craton margin at ∼ 30° N paleolatitude (Fig. 15). The Pardonet Hill patch reefs have a morphology, architecture and taxonomic composition comparable to carbonate buildups at Cowichan Lake, southern Vancouver Island (Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999). The geograph- ically closest known coral reefs during the Triassic occur on the Quesnel (Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999), Stikine (Reid and Ginsburg, 1986; Reid and Tempelman-Kluit, 1987; Reid, 1989) and Wrangellia terranes (Clapp and Shimer, 1911; Stanley, 1979; Stanley, 1989). These terranes are all interpreted (based in part on paleontologic and paleo- magnetic data) to have originated well to the south of their present locations and moved northward both before and after collision with each other and with the North American plate (Irving and Yole, 1972; Coney et al., 1980; Gabrielse et al., 1991; Carter et al., 1991). If the interpreted southern origin of Quesnel, Stikine and Wrangellia is true, than it is unlikely that these terranes were the source of craton-bound corals reported on in the present study. As well, most of the terrane coral occurrences (including Cowichan Lake) are considerably younger than the Pardonet Hill locality (i.e. lower to upper Norian) suggesting either that the terranes were not necessary ‘ stepping stones ’ for faunal migration from the Tethys region to the study area or that a number of older (Ladinian or Carnian) Triassic reefs once populated the terranes. The presence of reef-associated faunal communities on the craton margin similar to those characteristic of reefs on accreted terranes emphasizes that faunal evidence for terrane placement must be used judiciously and furthermore provides support for the hypothesis that several of the terranes occurred in close proximity to the autochthon during the early Mesozoic (Unterschutz et al., 2002; Peterson et al., 2004). Despite extensive regional exposure of the Baldonnel Formation in the Rocky Mountain Foothills and Front Ranges of northeastern British Columbia, Triassic reefs have only been observed in the lower Baldonnel Formation at Pardonet Hill. With the exception of anthozoans overall identical faunal assemblages characterize the Baldonnel Formation throughout its stratigraphic and geographic range (i.e. Zonneveld et al., 2004), thus, reasons for such sparse reef distribution remain uncertain. The lower Baldonnel Formation occurs only in westernmost Triassic outcrop exposures and is well- exposed at only a few localities partially explaining the severely limited occurrence of Triassic coral reefs. We believe that coral reefs are limited to the lower Baldonnel Formation due to regional sea level flux. The lower Baldonnel Formation was deposited during an interval of prolonged ( ∼ 5 – 10 my) regional sea-level lowstand (Zonneveld and Orchard, 2002). Coeval strata at localities to the east are represented by marginal marine and continental strata of the Charlie Lake Formation (Zonneveld and Orchard, 2002). During this interval (lowermost Upper Carnian; lower nodosus zone; Fig. 2), the regional ...