Acanthoceras rhotomagense Zone - Revision history

Dbk at 11:45, 26 September 2013

2013-09-26T11:45:53Z

← Older revision		Revision as of 12:45, 26 September 2013
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	'''Bio-markers''': At the base of the zone, ''Inoceramus tenuis'' is abundant in a hard limestone band (= top of couplet B43 of Gale, 1995; also known as the Tenuis Limestone), although this bed has been removed by erosion in basin-margin settings (see: standard macrofossil zonation and correlation of the UK Chalk Group). Immediately above this, there is an abundance of small brachiopods (''Capillithyris squamosa'', ''Grasirhynchia martini'', ''Kingena concinna'', ''Modestella geinitzi'') and ''Entolium orbiculare'' in a bed of silty chalk. In expanded successions, this horizon was identified as the lower part of couplet C1 in Gale's (1995) cyclostratigraphical scheme for the Cenomanian, but it has traditionally been referred to as the Cast Bed. In basin-margin settings, the fauna of the Cast Bed and some adjacent horizons is caught up in an erosive sandy deposit, named the Totternhoe Stone. Towards the middle of the zone there is an acme of the brachiopod ''Orbirhynchia mantelliana'', representing the highest of three widely developed acmes of this brachiopod in the Cenomanian. The ammonite ''Sciponoceras baculoides'' is common in the lower part of the zone and has an acme in a limestone bed coincident with the top of the acme of ''O.'' ''mantelliana''. ''Concinnithyris subundata'' is locally common in the higher part of the zone, where ''Inoceramus atlanticus'' is also characteristically common.		'''Bio-markers''': At the base of the zone, ''Inoceramus tenuis'' is abundant in a hard limestone band (= top of couplet B43 of Gale, 1995; also known as the Tenuis Limestone), although this bed has been removed by erosion in basin-margin settings (see: standard macrofossil zonation and correlation of the UK Chalk Group). Immediately above this, there is an abundance of small brachiopods (''Capillithyris squamosa'', ''Grasirhynchia martini'', ''Kingena concinna'', ''Modestella geinitzi'') and ''Entolium orbiculare'' in a bed of silty chalk. In expanded successions, this horizon was identified as the lower part of couplet C1 in Gale's (1995) cyclostratigraphical scheme for the Cenomanian, but it has traditionally been referred to as the Cast Bed. In basin-margin settings, the fauna of the Cast Bed and some adjacent horizons is caught up in an erosive sandy deposit, named the Totternhoe Stone. Towards the middle of the zone there is an acme of the brachiopod ''Orbirhynchia mantelliana'', representing the highest of three widely developed acmes of this brachiopod in the Cenomanian. The ammonite ''Sciponoceras baculoides'' is common in the lower part of the zone and has an acme in a limestone bed coincident with the top of the acme of ''O.'' ''mantelliana''. ''Concinnithyris subundata'' is locally common in the higher part of the zone, where ''Inoceramus atlanticus'' is also characteristically common.
			{\| class="Wikitable"
	'''Subzones''': ''Turrilites acutus''		\|'''Subzones''': \|\| ''Turrilites acutus''
			\|-
	'' Turrilites costatus''		\| \|\|'' Turrilites costatus''
			\|}
	'''Age''': Mid Cenomanian		'''Age''': Mid Cenomanian

	[[category:Standard zonation \| 007]]		[[category:Standard zonation \| 007]]

Dbk at 11:45, 26 September 2013

2013-09-26T11:45:03Z

← Older revision		Revision as of 12:45, 26 September 2013
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	{\| class="Wikitable"		{\| class="Wikitable"
	\| Brachiopoda: ''Capillithyris squamosa''		\| Brachiopoda: \|\| ''Capillithyris squamosa''
	\|-		\|-
	\| \|\| ''Concinnithyris subundata''		\| \|\| ''Concinnithyris subundata''

Dbk: Created page with "'''Base''': The base of the zone is immediately below the first appearance of the index species, which in expanded successions is within couplet B43 of Gale's (1995) cyclostra..."

2013-09-26T11:44:54Z

Created page with "'''Base''': The base of the zone is immediately below the first appearance of the index species, which in expanded successions is within couplet B43 of Gale's (1995) cyclostra..."

New page

'''Base''': The base of the zone is immediately below the first appearance of the index species, which in expanded successions is within couplet B43 of Gale's (1995) cyclostratigraphical scheme for the Cenomanian.

'''Top''': The top of the zone is immediately below the first appearance of the ammonite ''Acanthoceras jukesbrownei'' (Gale, 1995).

'''Range of index species''': The index species ranges through the lower and middle part of the nominate zone (Robaszynski ''et al''., 1998).

'''Key fauna''':

{| class="Wikitable"
| Brachiopoda: ''Capillithyris squamosa''
|-
| || ''Concinnithyris subundata''
|-
| || ''Grasirhynchia martini''
|-
| || ''Kingena concinna''
|-
| || ''Modestella geinitzi''
|-
| ||'' Orbirhynchia mantelliana''
|-
| Bivalvia: || ''Entolium orbiculare'' (locally abundant)
|-
| ||''Inoceramus atlanticus''
|-
| ||''I. tenuis''
|-
| ||''Oxytoma seminudum''
|-
| Ammonoidea:|| ''Acanthoceras rhotomagense''
|-
| ||''Sciponoceras baculoides'' (locally abundant)
|-
| ||''Turrilites acutus''
|-
| ||''T. costatus''
|}

'''Faunal abundance & preservation''': Some of fauna found at the base of the zone may be reworked and phosphatised from the underlying ''C. inerme'' Zone. Some components of the fauna are extremely abundant and vertically restricted in their occurrence (see Bio-markers).

'''Bio-markers''': At the base of the zone, ''Inoceramus tenuis'' is abundant in a hard limestone band (= top of couplet B43 of Gale, 1995; also known as the Tenuis Limestone), although this bed has been removed by erosion in basin-margin settings (see: standard macrofossil zonation and correlation of the UK Chalk Group). Immediately above this, there is an abundance of small brachiopods (''Capillithyris squamosa'', ''Grasirhynchia martini'', ''Kingena concinna'', ''Modestella geinitzi'') and ''Entolium orbiculare'' in a bed of silty chalk. In expanded successions, this horizon was identified as the lower part of couplet C1 in Gale's (1995) cyclostratigraphical scheme for the Cenomanian, but it has traditionally been referred to as the Cast Bed. In basin-margin settings, the fauna of the Cast Bed and some adjacent horizons is caught up in an erosive sandy deposit, named the Totternhoe Stone. Towards the middle of the zone there is an acme of the brachiopod ''Orbirhynchia mantelliana'', representing the highest of three widely developed acmes of this brachiopod in the Cenomanian. The ammonite ''Sciponoceras baculoides'' is common in the lower part of the zone and has an acme in a limestone bed coincident with the top of the acme of ''O.'' ''mantelliana''. ''Concinnithyris subundata'' is locally common in the higher part of the zone, where ''Inoceramus atlanticus'' is also characteristically common.

'''Subzones''': ''Turrilites acutus''

'' Turrilites costatus''

'''Age''': Mid Cenomanian

[[category:Standard zonation | 007]]