Salinity: Salinity in the Rochester depositional basin was mostly normal marine (about 35 parts per thousand salinity) as evidenced by the numerous organism groups that are known to be quite intolerant to conditions other than normal salinity, such as echinoderms and cephalopod mollusks. However, the barren character of certain portions of the Rochester despite evidence, in the form of burrows, for benthic oxygenation suggests that somewhat stressed conditions existed at least locally near the basin center.
Substrates and Sedimentation: The substrates were mainly soft muds but with local accumulation of skeletal hard parts. It is clear that the distribution of certain organisms was more specifically controlled by substrate. Direct colonization of the muddy sea bed was difficult for many organisms, but some mobile forms such as the trilobite Dalmanites, were able to survive here, and other sedentary forms have morphologies that aided in support on soft, muddy substrate. The thin, flattened forms of many of the most widespread brachiopods probably allowed them to rest freely on the mud. Likewise, the broad flattened shape of some bryozoan colonies, such as Lichenalia may have been adaptive for spreading out on muddy sea floors. Dendrocrinus possessed flexible rootlets (Figure 272) that may have permitted adjustment of attachment sites and facilitated colonization of the soft seafloor directly.
Other brachiopods (attached by pedicle stalks), bryozoans, corals and a majority of echinoderms and worm tubes required hard substrates for settlement. In some areas stable hard substrate was provided by skeletal debris, particularly brachiopod shells. The cystoid Caryocrinites appears to have preferentially settled on branching bryozoans and the occurrence of these cystoids therefore mirrors the occurrence of small patches of Chilotrypa and Hallopora bryozoans (Figures 7 - 13a). Other echinoderms utilized small fragments of skeletal material as an initial substrate. Both Caryocrinites and certain crinoids like Eucalyptocrinites possessed strongly branched radicles or rootlets that penetrated into soft substrate (Brett, 1978c). In turn, these organisms provided substrates for other organisms such as the small coral Favosites parasiticus (Figures 55 and 56), which encircled the columns, and even other echinoderms, which were attached by distal coils or cemented holdfasts to their hosts.
The process of "taphonomic feedback" (Kidwell and Jablonski, 1983) played a critical role in the build-up of local patches of more diverse organisms. This means that the accumulation of dead shells, initially of "pioneering" mud dwelling brachiopods, trilobite molts, etc, provided substrates for more diverse communities, including twig bryozoans and echinoderms, which, in turn, may have been favored by intervals of drier climate and/or minor to more major sea level rise. The rise of base level affects offshore sedimentation by creating bays and estuaries that may serve as coastal "traps" for sediment delivered by rivers from Taconic highlands. Thus, many of the thicker shell beds in the Rochester Shale probably accumulated during times of offshore sediment starvation, preferentially associated with intervals of sea level rise following shallowing episodes. The amalgamation of shelly debris was further aided by occasional storms or hurricanes, during which large waves touched down on a normally quiet water area and fragmented, winnowed and concentrated accumulating skeletal debris. Thus, some shell beds have sharp, scoured bases and rippled tops. These features were the mark of the final process that disrupted and concentrated shelly debris and sometimes whole, live organisms that had accumulated during previous periods of up to centuries duration.
Environmental Energy: Most Rochester seafloor settings were predominantly low energy (current velocities generally not exceeding 20 cm/sec). Low current energy means that organisms could be relatively weakly attached to the seafloor and still maintain their position. Some crinoids such as Dimerocrinites (Figures 294 - 306) simply laid a section of the column or a distally coiled area on the seafloor for adequate support in low energy environments. Other organisms were free lying or weakly tethered by small holdfasts, cemented pads or pedicle stalks (brachiopods). Evidently, this was adequate anchorage for stability during the majority of the time. However, during the rare storm events such weak tethering became a major weakness as storm waves and currents disrupted the normally quiet seafloor, dislodging millions of individuals of bryozoans, echinoderms, and brachiopods, and other organisms and in some instances rapidly burying them in layers of muddy sediment resuspended by waves from shallower areas.
Substrates and Sedimentation: The substrates were mainly soft muds but with local accumulation of skeletal hard parts. It is clear that the distribution of certain organisms was more specifically controlled by substrate. Direct colonization of the muddy sea bed was difficult for many organisms, but some mobile forms such as the trilobite Dalmanites, were able to survive here, and other sedentary forms have morphologies that aided in support on soft, muddy substrate. The thin, flattened forms of many of the most widespread brachiopods probably allowed them to rest freely on the mud. Likewise, the broad flattened shape of some bryozoan colonies, such as Lichenalia may have been adaptive for spreading out on muddy sea floors. Dendrocrinus possessed flexible rootlets (Figure 272) that may have permitted adjustment of attachment sites and facilitated colonization of the soft seafloor directly.
Other brachiopods (attached by pedicle stalks), bryozoans, corals and a majority of echinoderms and worm tubes required hard substrates for settlement. In some areas stable hard substrate was provided by skeletal debris, particularly brachiopod shells. The cystoid Caryocrinites appears to have preferentially settled on branching bryozoans and the occurrence of these cystoids therefore mirrors the occurrence of small patches of Chilotrypa and Hallopora bryozoans (Figures 7 - 13a). Other echinoderms utilized small fragments of skeletal material as an initial substrate. Both Caryocrinites and certain crinoids like Eucalyptocrinites possessed strongly branched radicles or rootlets that penetrated into soft substrate (Brett, 1978c). In turn, these organisms provided substrates for other organisms such as the small coral Favosites parasiticus (Figures 55 and 56), which encircled the columns, and even other echinoderms, which were attached by distal coils or cemented holdfasts to their hosts.
The process of "taphonomic feedback" (Kidwell and Jablonski, 1983) played a critical role in the build-up of local patches of more diverse organisms. This means that the accumulation of dead shells, initially of "pioneering" mud dwelling brachiopods, trilobite molts, etc, provided substrates for more diverse communities, including twig bryozoans and echinoderms, which, in turn, may have been favored by intervals of drier climate and/or minor to more major sea level rise. The rise of base level affects offshore sedimentation by creating bays and estuaries that may serve as coastal "traps" for sediment delivered by rivers from Taconic highlands. Thus, many of the thicker shell beds in the Rochester Shale probably accumulated during times of offshore sediment starvation, preferentially associated with intervals of sea level rise following shallowing episodes. The amalgamation of shelly debris was further aided by occasional storms or hurricanes, during which large waves touched down on a normally quiet water area and fragmented, winnowed and concentrated accumulating skeletal debris. Thus, some shell beds have sharp, scoured bases and rippled tops. These features were the mark of the final process that disrupted and concentrated shelly debris and sometimes whole, live organisms that had accumulated during previous periods of up to centuries duration.
Environmental Energy: Most Rochester seafloor settings were predominantly low energy (current velocities generally not exceeding 20 cm/sec). Low current energy means that organisms could be relatively weakly attached to the seafloor and still maintain their position. Some crinoids such as Dimerocrinites (Figures 294 - 306) simply laid a section of the column or a distally coiled area on the seafloor for adequate support in low energy environments. Other organisms were free lying or weakly tethered by small holdfasts, cemented pads or pedicle stalks (brachiopods). Evidently, this was adequate anchorage for stability during the majority of the time. However, during the rare storm events such weak tethering became a major weakness as storm waves and currents disrupted the normally quiet seafloor, dislodging millions of individuals of bryozoans, echinoderms, and brachiopods, and other organisms and in some instances rapidly burying them in layers of muddy sediment resuspended by waves from shallower areas.
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