South-west England Chalk Group Lithostratigraphy: Jarvis & Woodroof (1984) & Jarvis & Tocher (1987) - Pinnacles Glauconitic Limestone: Difference between revisions
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The Pinnacles Glauconitic Limestone is named after The Pinnacles [SY 219 879 to SY 222 879] landslip below Hooken Cliffs, Devon. In expanded sections, such as at the Beer Stone Adit [SY 219 879], the member comprises a c. 2.3 m succession of sandy, glauconitic, nodular limestones, with hardgrounds in the middle part (the informally named limonitic nodule hardground) and at the top (Haven Cliff Neocardioceras Hardground) (Jarvis & Woodroof, 1984). The limonitic nodule hardground comprises orangey-yellow, limonite-stained, indurated and phosphatised sandy, nodular limestone, underlain and overlain by friable, sandy, glauconitic limestone (Jarvis & Woodroof, 1984). The Haven Cliff Neocardioceras Hardground, marking the top of the member, is an indurated, glauconitised and limonitised hardground characterised by the ammonites ''Sciponoceras gracile'' and ''Neocardioceras juddii'', and having common cidarid echinoid spines cemented to its upper surface (Jarvis & Woodroof, 1984). The base of the member is immediately above the upper surface of the Humble Point Hardground, at the top of the underlying Little Beach Bioclastic Limestone. The brachiopod ''Orbirhynchia wiesti'' is particularly characteristic of the member, and the belemnite ''Praeactinocamax plenus'' also locally occurs (Jarvis & Woodroof, 1984). At many localities the member is strongly attenuated, and sometimes absent, the Haven Cliff Neocardioceras Hardground being the most laterally persistent feature, which is also sometimes associated with a pebble bed (Neocardioceras Pebble Bed of Rawson ''et al''., 1978). | The Pinnacles Glauconitic Limestone is named after The Pinnacles [SY 219 879 to SY 222 879] landslip below Hooken Cliffs, Devon. In expanded sections, such as at the Beer Stone Adit [SY 219 879], the member comprises a c. 2.3 m succession of sandy, glauconitic, nodular limestones, with hardgrounds in the middle part (the informally named limonitic nodule hardground) and at the top (Haven Cliff Neocardioceras Hardground) (Jarvis & Woodroof, 1984). The limonitic nodule hardground comprises orangey-yellow, limonite-stained, indurated and phosphatised sandy, nodular limestone, underlain and overlain by friable, sandy, glauconitic limestone (Jarvis & Woodroof, 1984). The Haven Cliff Neocardioceras Hardground, marking the top of the member, is an indurated, glauconitised and limonitised hardground characterised by the ammonites ''Sciponoceras gracile'' and ''Neocardioceras juddii'', and having common cidarid echinoid spines cemented to its upper surface (Jarvis & Woodroof, 1984). The base of the member is immediately above the upper surface of the Humble Point Hardground, at the top of the underlying Little Beach Bioclastic Limestone. The brachiopod ''Orbirhynchia wiesti'' is particularly characteristic of the member, and the belemnite ''Praeactinocamax plenus'' also locally occurs (Jarvis & Woodroof, 1984). At many localities the member is strongly attenuated, and sometimes absent, the Haven Cliff Neocardioceras Hardground being the most laterally persistent feature, which is also sometimes associated with a pebble bed (Neocardioceras Pebble Bed of Rawson ''et al''., 1978). | ||
Latest revision as of 15:10, 7 October 2013
The Pinnacles Glauconitic Limestone is named after The Pinnacles [SY 219 879 to SY 222 879] landslip below Hooken Cliffs, Devon. In expanded sections, such as at the Beer Stone Adit [SY 219 879], the member comprises a c. 2.3 m succession of sandy, glauconitic, nodular limestones, with hardgrounds in the middle part (the informally named limonitic nodule hardground) and at the top (Haven Cliff Neocardioceras Hardground) (Jarvis & Woodroof, 1984). The limonitic nodule hardground comprises orangey-yellow, limonite-stained, indurated and phosphatised sandy, nodular limestone, underlain and overlain by friable, sandy, glauconitic limestone (Jarvis & Woodroof, 1984). The Haven Cliff Neocardioceras Hardground, marking the top of the member, is an indurated, glauconitised and limonitised hardground characterised by the ammonites Sciponoceras gracile and Neocardioceras juddii, and having common cidarid echinoid spines cemented to its upper surface (Jarvis & Woodroof, 1984). The base of the member is immediately above the upper surface of the Humble Point Hardground, at the top of the underlying Little Beach Bioclastic Limestone. The brachiopod Orbirhynchia wiesti is particularly characteristic of the member, and the belemnite Praeactinocamax plenus also locally occurs (Jarvis & Woodroof, 1984). At many localities the member is strongly attenuated, and sometimes absent, the Haven Cliff Neocardioceras Hardground being the most laterally persistent feature, which is also sometimes associated with a pebble bed (Neocardioceras Pebble Bed of Rawson et al., 1978).
Macrofossil Biozonation: (see under Cenomanian Limestone Bed C of Jukes-Browne & Hill (1903))
Correlation: see Correlation with other lithostratigraphical schemes for south-west England
see Correlation with other UK regions
References
JARVIS, I & WOODROOF, P B. 1984. Stratigraphy of the Cenomanian and basal Turonian (Upper Cretaceous) between Branscombe and Seaton, S E Devon, England. Proceedings of the Geologists' Association, Vol. 95 (3), 193-215.
JUKES-BROWNE, A J & HILL, W.1903. The Cretaceous rocks of Britain. Vol. 2 - The Lower and Middle Chalk of England. Memoir of the Geological Survey of the United Kingdom.
See: Cenomanian Limestone Bed C, hardground