In particular, these beds showed a high diversity of brachiopods (27 species), including atrypids, Striispirifer, rhynchonellids, and Leptaena and abundant, tiny bilobed shells of Dicoelosia and pyramidal Skenidioides. Echinoderms of 18 species, included Caryocrinites, and abundant Stephanocrinus angulatus. Crinoids included Macrostylocrinus, calceocrinids and rare Icthyocrinus and Lecanocrinus. Trilobites were under-represented in washings because they tend to breakdown to unrecognizable fragments but inspection of bedding planes showed that the most common forms were Bumastus, Calymene, and Dalmanites.
Unfortunately, the level of the Lewiston B-C transition is poorly exposed at Middleport, but it is well represented near Lockport where these beds, referred to as the "Homocrinus beds" (Figures 4 and 6; Taylor and Brett, 1996, 1999) yielded a very distinctive fauna of moderate diversity (about 40 species), including a great abundance of the spiriferid brachiopod Striispirifer niagarensis. Distinctive echinoderm elements include the delicate disparid crinoid Homocrinus parvus, the small flexible crinoid Asaphocrinus ornatus, the ophiuroid Protaster and the edrioasteroid Hemicystites parasiticus, typically cemented to Striispirifer valves, as well as more widespread elements: Caryocrinites, Crinobrachiatus, Macrostylocrinus, and Icthyocrinus laevis. Conversely, Stephanocrinus, calceocrinids, and many less common crinoids, were completely absent. This distinctive fauna must have occupied a relatively narrow belt of transitional conditions between the highly diverse, bryozoan-rich thickets in shallower water to the north and the nearly barren Lewiston C facies to the south. This also appears to be the optimal facies for the large lichid trilobite, Arctinurus.
Moving to slightly deeper, muddier facies the fauna drops off rapidly, with scattered patches of Striispirifer giving way to small flat brachiopods, such as Amphistrophia, Coolinia and Leptaena. Upward, the mudstones of the upper B submember of Lewiston showed an abruptly decreased diversity and the addition of new elements, in particular large dendroid graptolites, Conularia, the trilobite Arctinurus and the crinoids Dendrocrinus and Dimerocrinites were present with fewer bryozoans or Caryocrinites.
The only trilobites that typify these deeper facies were Dalmanites and small Trimerus. These same genera characterize most all of the upper Rochester Burleigh Hill Member and represent the most tolerant of forms. Most all echinoderms fade out into deeper facies with the exception of widely scattered, long-stemmed Dendrocrinus and Dimerocrinites.
Silty beds tend to show a diversity of well-preserved trace fossils, but body fossils are generally absent. The middle part of the Lewiston C submember is nearly barren of fossils and with very low species richness; the total diversity over about 4 meters of section is only about 10 species. The near barren nature of Lewiston C in most locations probably reflects strongly stressed conditions of soft substrate, high turbidity, low light and perhaps low oxygen and/or elevated salinity conditions.
Interestingly, the faunal transition seen in the Lewiston B-C boundary deepening is closely mirrored in the C to D submember shallowing transition. Particularly notable is the return of elements of the Homocrinus fauna, including Homocrinus parvus, Macrostylocrinus and Icthyocrinus, the ophiuroid Protaster and the rare edrioasteroid Hemicystites. Oddly, however, the flexible, Asaphocrinus, a relatively common form in the Homocrinus beds, is rare or absent in the upper transition but its ecological role may have been filled by Lecanocrinus, which is very rare in the lower Lewiston. The trilobite Arctinurus reappears, but is associated with more abundant Calymene. Clumps of well-preserved Caryocrinites reappear in the C-D, as in the B-C transition.
The upper portion of unit D and Lewiston E bryozoan beds display a distinctive abrupt increase in faunal diversity with more than 90 species recorded in the 1.5 meters thickness of this unit. The fauna is very similar but not identical to that of Lewiston B carrying most of the same bryozoans and brachiopods, although with somewhat higher diversity. Notably absent or very rare in D-E submembers are the tiny brachiopods Dicoelosia and Skenidioides.
Unfortunately, the level of the Lewiston B-C transition is poorly exposed at Middleport, but it is well represented near Lockport where these beds, referred to as the "Homocrinus beds" (Figures 4 and 6; Taylor and Brett, 1996, 1999) yielded a very distinctive fauna of moderate diversity (about 40 species), including a great abundance of the spiriferid brachiopod Striispirifer niagarensis. Distinctive echinoderm elements include the delicate disparid crinoid Homocrinus parvus, the small flexible crinoid Asaphocrinus ornatus, the ophiuroid Protaster and the edrioasteroid Hemicystites parasiticus, typically cemented to Striispirifer valves, as well as more widespread elements: Caryocrinites, Crinobrachiatus, Macrostylocrinus, and Icthyocrinus laevis. Conversely, Stephanocrinus, calceocrinids, and many less common crinoids, were completely absent. This distinctive fauna must have occupied a relatively narrow belt of transitional conditions between the highly diverse, bryozoan-rich thickets in shallower water to the north and the nearly barren Lewiston C facies to the south. This also appears to be the optimal facies for the large lichid trilobite, Arctinurus.
Moving to slightly deeper, muddier facies the fauna drops off rapidly, with scattered patches of Striispirifer giving way to small flat brachiopods, such as Amphistrophia, Coolinia and Leptaena. Upward, the mudstones of the upper B submember of Lewiston showed an abruptly decreased diversity and the addition of new elements, in particular large dendroid graptolites, Conularia, the trilobite Arctinurus and the crinoids Dendrocrinus and Dimerocrinites were present with fewer bryozoans or Caryocrinites.
The only trilobites that typify these deeper facies were Dalmanites and small Trimerus. These same genera characterize most all of the upper Rochester Burleigh Hill Member and represent the most tolerant of forms. Most all echinoderms fade out into deeper facies with the exception of widely scattered, long-stemmed Dendrocrinus and Dimerocrinites.
Silty beds tend to show a diversity of well-preserved trace fossils, but body fossils are generally absent. The middle part of the Lewiston C submember is nearly barren of fossils and with very low species richness; the total diversity over about 4 meters of section is only about 10 species. The near barren nature of Lewiston C in most locations probably reflects strongly stressed conditions of soft substrate, high turbidity, low light and perhaps low oxygen and/or elevated salinity conditions.
Interestingly, the faunal transition seen in the Lewiston B-C boundary deepening is closely mirrored in the C to D submember shallowing transition. Particularly notable is the return of elements of the Homocrinus fauna, including Homocrinus parvus, Macrostylocrinus and Icthyocrinus, the ophiuroid Protaster and the rare edrioasteroid Hemicystites. Oddly, however, the flexible, Asaphocrinus, a relatively common form in the Homocrinus beds, is rare or absent in the upper transition but its ecological role may have been filled by Lecanocrinus, which is very rare in the lower Lewiston. The trilobite Arctinurus reappears, but is associated with more abundant Calymene. Clumps of well-preserved Caryocrinites reappear in the C-D, as in the B-C transition.
The upper portion of unit D and Lewiston E bryozoan beds display a distinctive abrupt increase in faunal diversity with more than 90 species recorded in the 1.5 meters thickness of this unit. The fauna is very similar but not identical to that of Lewiston B carrying most of the same bryozoans and brachiopods, although with somewhat higher diversity. Notably absent or very rare in D-E submembers are the tiny brachiopods Dicoelosia and Skenidioides.
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