The Upper Ordovician Succession at N Orderhov and on Frognøya in Ringerike, Norway
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The upper Ordovician succession at N orderhov and on FrognØya in Ringerike, Norway ALAN W. OWEN Owen, W. : The upper Ordovician succession at Norderhov and on Frognøya in Ringerike, Norway. A. Norsk Geologisk Tidsskrift, Vol. 58, pp. 245-258. Oslo 1978. ISSN 0029-196X. Lithostratigraphical units in the Ordovician succession in Ringerike are named formally for the first time. The distribution of species of Tretaspis indicates that the highest beds of the oldest unit studied, the Solvang Formation, are younger on Frognøy a (lowest PusgiUian) than at Norderhov (highest Onnian). The overlying shale unit, the Frognøy a Shale, contains weU preserved graptolites of the Pleurograptus linearis Zone (mid-Onnian to ?mid-Pusgillian) . The succeeding units described are dominantly calcareous and are named the Sørbakken Limestone (late Pusgillian to ?low Rawtheyan) and the Bønsnes Formation (probably whoUy Rawtheyan) . Owen, Department ofGeo/ogy, The University, Dundee, DD14HN, Scotland. A. W. Historically, the description of Cambro-Silurian succession referred to herein are interpreted successions within the Oslo Region has been purely lithostratigraphically. undertaken largely with direct reference to the named units of the Oslo-Asker sequence (e. g. Strand 1933, Størmer 1953, Strand Hennings & Setting moen 1960). This has led to imprecision and misconceptions in correlation, examples of The Ringerike district is situated to the north which are detailed below for the Ringerike dis west of Oslo (StØrmer 1953, fig. 1). The local trict. The primary aim of this paper is to Lower Palaeozoic succession has a general establish a named lithostratigraphical framework north-east to south-west strike and youngs for the upper Ordovician succession in Ringerike south-eastwards. The succession rests on Pre prior to the description of the trilobite faunas. cambrian gneiss and is overlain in the east by It must be stressed from the outset that the Permian lavas. In the north-east, Ordovician writer advocates the discontinuation of the etas rocks of Ringerike abut Silurian sediments of the je nomenclature originally applied to the Oslo Hadeland district against the Randsfjorden fault Asker succession but subsequently imposed on (Holtedahl 1960, pl. 13). A brief general account other sequences in the Region. This terminology of the geology of the district and an extensive list was devised by Kjerulf (1857) and subsequently of papers published since 1950 are given by developed by, amongst others, BrØgger (1882, Whitaker (1977). 1887), Kiær (1897, 1902, 1908), StØrmer (1953), The sections described here are the most and Henningsmoen (1957). Originally no more complete upper Ordovician exposures in the than a shorthand method of expressing litho- and district and are at Norderhov, 3 km south of biostratigraphical units, this nomenclature de Hønefoss and, 11 km along the regional strike, veloped a chronostratigraphical connotation and on the island of Frognøya (Fig. 1). At Norderhov Henningsmoen (1955) outlined a scheme for its 70 m of strata crop out by the roadside, dipping use purely in chronostratigraphy. While this may gently southwards, but only the lowest 15 m is be feasible for the Cambrian Alum Shale and readily accessable as much of the exposure is Ceratopyge beds (Henningsmoen 1957:34-61), high and overhanging. The succession on evidence is accumulating to show that the Frognøya (Fig. 2) is well exposed on the north Silurian etasjer may lack even local and west coasts of the istand and there is in chronostratigraphical significance (W orsley termittent outcrop on the east coast: exposure 1971, Bassett Rickards 1971) and work on inland is very limited. & upper Ordovician successions in Ringerike and Few accounts of the Ordovician rocks of Hadeland shows that many of the se units have a Ringerike have appeared in the literature very limited application. Units of the Oslo-Asker although Kiær carried out extensive fieldwork. 16 - GeologiskTidsskr. 4/78 246 A. W. Owen NORSK GEOLOGISK TIDSSKRiFf 4 (1978) "+ + + + + + + + + + "· + + + + + + + J Jevnaker. rvvvl Permian + + + + + + + + � + + + + + + + + 1111 .l VY + + + + + + vvvvvv + + + + + + + + '1111Jf Ringerike Group + + + + + +.�1 vvvvvvvv + /. 1 vvvvvvvvvv + + + + + 1 vvvvvvvvvvv Marine Silurian + + + + + + + + + + +.� vvvvvvvvvvvv + 1 vvvvvvvvvvvvv Ordovician + + + + .111 1 vvvvvvvvvvvvv + 1 ,'L vvvvvvvvvvvvvv + + +,ni\IY /VVVVVVVVVVVVVV Cambrian +: +: : :_ /,�1 � vvvvvvvvvvvvvvv vvvvvvvvvvvvvvv + + +,ni iJU' �vvvvvvvvvvvvvvv Hønefoss V V V V V V V V V V V V V V V Precambrian r-'---r-..__,--'---r-"'-r-'-r"--Atvvvvvvvvvvvvvvvv + vvvvvvvvvvvvvvvv l7 �� vvvvvvvvvvvvvvvv 5km vvvvvvvvvvvvvvvv :Mil V V V V V V V V V V V V V V V _.·:·:·.'o/ + + N + + + + + + + + + + + + + + + + + + + + + + + + + + + \ + + + ++ + + + + + + l + + + + ++ + + NORWAY ) + + +.+ ( + + Ringerike + + + 'j ++ + ++ + + + + o o�1o + + + \) + + ++ + + + + + ++ ++ + + + + + + ++ Fig. Simplified geological map of the Ringerike district (based on Holtedahl 1%0, pl. I. 3). His collections and fieldnote hooks pertaining to Nerby Member) and as interbedded limestones the Ordovician succession are housed in Pale and shales (the Lieker Member) in the south-east ontologisk museum, Oslo. More recently, David . of the district. The concept of the Solvang For L. Bruton of Paleontologisk museum, Oslo has mation is here broadened to include a coeval examined the Frognøya succession and has limestone unit in Ringerike, and the outcrop at kindly given the writer free access to his col Norderhov (NM71256585) is designated an lections. A summary of the lithostratigraphical hypostratotype. Although the base of the forma units defined and newly named herein and their tion is not seen at Norderhov, the upper 12 m interpretation by previous workers is given in (Fig. 4) is exposed and small outcrops to the east Fig. 3. suggest that this is close to the total thickness of the unit here. 80 m to the north of the Norderhov section, shales containing Broeggerolithus dis cors (Angelin, 1854) and Lonchodomas The Solvang Formation at aff. Norderhov rostratus (Sars, 1835) crop out by the roadside ( = Upper Chasmops Shale of Størmer 1953:86) Owen (1978:8-10) defined the Solvang Forma and are interpreted as belonging to the unit tion in Hadeland where it is developed as a below the Solvang Formation. nodular limestone over much of the area (the The Solvang Formation at Norderhov is com- NORSK GEOLOGISK TIDSSKRIFT 4 (1978) Upper Ordovician succession in Ringerike 247 N o 200m Limeston e 32/Dip in degrees -+- Vertical strata --"' Fault � / _....,..,../4' / 100m / s Fig. Geological map (omitting Permian dykes) of Frognøya and section along the west coast. Horizontal line on section 2. representsfjord leve!- approximately 60 m a.s.l. Inset map shows the position of the major dislocations on Frognøy a and the mainland and is taken from an unpublished study of aerial photographsby F. Bockelie ( 1970). J. 248 A. W. Owen NORSK GEOLOGISK TIDSSKRIFT 4 (1978) Størmer Strand Kiær This paper 1953 1933 1921 ����!,'-,>:�·\:���.�;;1··�)���}��� '.· .\1. \ •.• & \ . �e,",.��r.�o1Æ��',1;{�\�1� GASTROPOD M BØNSNES FORMATION >.� 'T LIMES TONE ��i{' K\' ·' ·:(li.\"''�\J�}p'}�� %: ��1· ... f,, . r\ ...�)���-· 4 • ���\:�@·h�i·.. ; ..�§�1·... ��it��; ISOTELUS LIMESTONE 4d r-disconformity- SØR BA KKEN LIMESTONE TRINUCLEUS l l l l TRINUCLEUS LIMESTONE 4cØ LIMESTONE · .·········...........................······················. ....···....... ······································· ·································••••••••••••••••••• •••••••••••• ••••••••···· ·· ·o · ·····••••••••····••••••••••·········· ••••••••••••······· ·······••••••••······ o ........... ........ LOWER ··················· ....·········. .....······ · ····-·····-···..····...·····.... TRINUCLEUS TRINUCLEUS ········· ········· · ····.........······ ········· · ···...·······...... TRETA SPIS · ········· FROGN . · ····· · · · ØYA ·········· SHALE ··········....... ··· ······ · . ·········· ·········· ·········· SHALE · ········ ·········· ·········.· ········· · 4ca SHA LE ········ SHALE ········· · · ········· · ········ · · ········ · ········· 4ccr ··· ······· · · ······ ·· ········· · ········· · ····· ···· · ···· ···· · .·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·:.·.·.·.·.·.·.·.·.·:.·.·.·.·. · · · · · · · · · · · · · · ··· ······ · · ··· · · · · · · · · · · · : LOWER :::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::� 4c . TRINUCLEUS : -:·: -:·: -: -: -: -: -:·:-: -:-:·: -:·:-: -: -: -:-::: " . 4b02 .·::.·::.·:.·.·.·::.·.�gberg Mbr LIMESTONE · · ···· · · · · · ··· · . ····· ······· ·· UPP ER UP PER ·········· · - - - -- -- :-:·: -::::_.:..:.r ·- - - - - - - - - - - - - - - - - - CHASMOPS UPPER � - -1-1-1 - l. �.J - - - - - - - CHASMOPS - - - -- � SOLVANG - - -- LIMESTONE CHASMOPS � - - - - - 4b61 - - FORMATJO - - � - - N - -- LI MESTONE - - - - 4bo LIMESTONE � - - -- - - - - - - - - -- -- - - -- - - - - - - - - - - - - - -- - - - - Fig. The historical development of terms applied to the upper Ordovician successions at Norderhov and on Frognøy a (not to 3. scale). The Solvang Formation was originaUy recognised in Hadeland (Owen 1978), all other terms are new. The Høgberg Member of the Sol vang Formation on Frognøy a is the lateral equivalent of the lowest part of the Frognøya Shale at Norderho" NORSK GEOLOGISK TIDSSKRIFT 4 (1978) Upper Ordovician succession in Ringerike 249 ally impersistent and nodular horizons predomi nate in the lowest 2 m of the section. Between 2.07 and 2.27