. Bulletin of the British Museum (Natural History), Geology. ENVIRONMENTAL CHANGES 381 Glacial sequences 1 Central Sahara North Africa P acuminatus G persculptus. Central Portugal 3 Celtiberia Fluvio-glacial sand varved and slumped clay Fluvio-glacial sand Varved clay Terrestrial tillite Pro-glacial and sub-glacial melt-out sands RAWTHEYAN Deep shelf Fault Sub-glacial manne-tilloid Shallow massive sands Regressive shelt sequence Calcareous tuff Sub-glacial marine tilloid Bedded sandstones 9 karstified surface Mid-deep shelf Carbonate shelves 4 Manitoulin Ontario, Canada 5 Anticosti E
. Bulletin of the British Museum (Natural History), Geology. ENVIRONMENTAL CHANGES 381 Glacial sequences 1 Central Sahara North Africa P acuminatus G persculptus. Central Portugal 3 Celtiberia Fluvio-glacial sand varved and slumped clay Fluvio-glacial sand Varved clay Terrestrial tillite Pro-glacial and sub-glacial melt-out sands RAWTHEYAN Deep shelf Fault Sub-glacial manne-tilloid Shallow massive sands Regressive shelt sequence Calcareous tuff Sub-glacial marine tilloid Bedded sandstones 9 karstified surface Mid-deep shelf Carbonate shelves 4 Manitoulin Ontario, Canada 5 Anticosti P acuminatus G persculptus HIRNANTIAN 3 RAWTHEYAN Shallow high energy shelf Karst Shallow shelf (wave baffle to intertidal) Patch reefs - Oncolites Above wave base Shallow shelf Above wave base Carbonate mud mounds 6 Kalholn Central Sweden P acuminatus t -25m HIRNANTIAN RAWTHEYAN 7 Keisley Deep shelf Karst Coqumoid limestone/above storm wave base ZQ Carbonate mud mound/below wave base Deep shelf * *l Syn - sedimentary breccia Shallow carbonate sands with Girvanella Carbonate mud mound below wave base Fig. 2 Generalized sections to show the sequence of environmental changes near the Ordovician- Silurian boundary. Data for the interpretations are to be found in the following references. Section 1: 'Unit IV; Beuf et al. 1971. 2: (a) Porto de Santa Anna Formation, (b) Ribeira do Bracal Formation, (c) Ribeira Cimeria Formation; Young 1985. 3: (a) Cystoid Limestone, (b) Orea Shale; Carls 1975. 4: Georgian Bay Formation, (b) Manitoulin Formation; Copper 1978; Kobluk 1984. 5: (a) Ellis Bay Formation (up to Oncolites), (b) Becscie Formation; Petryk 1981a, 19816. 6: Boda Limestone; Jaanusson 1979; Brenchley & Newall 1980. 7: Keisley Limestone; Wright Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemb
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