Definition of the Frasnian/Famennian Stage Boundary
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4 了了 勿 G M apper, R Feist, R T Becker and M R H ouse 'vW'%efinition of the Frasnian/Fam ennian Stage b oun d ary 盆 The boundaryfor the F rasnianlF am ennian Stage G lobal low er thanform erly used boundary levelsfor the base of Stratotype Section and P oint (G SSP) has been ratif ed 勿 the F a m en n ian . IC S and IU G S and is draw n in a section exp osed near the Upp er C oum iac Q uarry in the southeastern M on- tagne N oire, F rance. The p osition of the boundary w as In tro d u ctio n selected 勿 the Subcom m ission on D evonian Stratigra- phy in 1991 to coincide w ith the low er boundary of the H istorically, several different levels have been used to define the Low er Palm atolepis triangularis Zone in the conodont base of the Fam ennian. In the type area for the nam ing of the stages biostratigraphy. The revised defi nition of the low er in southern B elgium , precise docum entation in recent years has been boundary of the zone, p rop osed herein, excludes the given to a new reference section replacing the now -infilled classic section in the Senzeilles railw ay cutting (B ultynck and others, 1988). extrem ely rare occurrences of Palm atolepis triangularis L argely resulting from w ork in the first quarter of this century in G er- a few centim etres low er, w ithin the upperm ost conodont m any, another boundary w as used that w as based on the entry of the zone. The G SSP also coincides w ith the boundary goniatite C heiloceras in the pelagic realm . In the latter half of this betw een the C rickites holzapfeli Zone and the Phoenix- century the considerable grow th of conodont studies has led to m uch refinem ent of the biostratigraphy. H ow ever, the level taken as the ites frechi Z one in the goniatite scale. The p osition of t he b ase o f th e F am en nian h as varied b etw een a le vel at the b ase o f the G SSP is im m ediately above a m ajor horizon of extinction crep ida Zone dow n to the base of the L ow er triangularis Z one. The w ithin the D evonian and is stratigraphically som ew hat need for an international definition has becom e urgent. The Subcom - 0 1 0 K M ，B e d a r ie u x A -?00/ 因 ．．二，二， ，气 Les D E V O N ！A N ／了 阅 花 二 ／ 夕与'0OUUAI RIRI:Ym ．沙uranqe5 区鼓习 尹 洲 }"Q飞，’ 一／’“’7 妙 牙'to cessenon 。Q户 w l}- 二又弓一扮代v O C o u m ia c 0 10 0 m L一一 」 N a za ir e d e La d a re z P R O V ／刀 C E 六 B e d a rieu x A u rig n a c 子 +叼o n tp e llie r To u lo u s e N ，亡a u sse s e t 。。瞿 Vey ra n M ag a la s L卜14 阿 E D I T E R R A N E A N A 卜 、＿， ．、 0 一 10 0 K M ＋C e s s e n o n s 尸 A I N ． 一」 － Figure] M aps showing theposition oft he M ontague Noire in southeastern Francea nd oft he Upper户umiac ＿ Quar7y near Cessenon, the site oft he GlobalS tratotype Section and Point (GSSP)fort he definition oft he base oft he F am ennian Stage (insetm ap A ). M odifi edfrom B eckera nd oth ers (1989). E pisodes, Vol. 16, no. 4 4 3 4 m ission on D evonian Stratigraphy (SD S) has given careful consider- adjacent to the southeastern border oft he disused upper m arble quarry ation to w hich level is m ost appropriate for international correlation (U Q ) of Courniac, 175 in W SW of the Les G ranges farm house, about and it decided, at a m eeting in W ashington in 1989, that a GSSP 1.5 km N IE of C essenon village and 2 100 m SW of C ausses et V eyran. should be sought in relation to the base of the L ow er triangularis It can be reached easily by a path up the hill from near the track to L es conodont Zone. Final ballots and ratification by ICS and IU GS (in G ranges farm house from the road D 136 betw een C essenon and St January 1993) led to a level in a section at C ourniac, southern France N azaire-de-L adarez. T he ground is ow ned by the com m une of being designated as the G lobal Stratotype Section and Point (G SSP). Cessenon and is already protected as part of a w ater supply area. C on- A briefr eview of the docum entation leading to this decision is given servation and protection oft he section has been assured by com m unal here. The conodont and goniatite biostratigraphic divisions are and departm ent ofi cials. Free access for scientists is confirm ed. show n in figures 5 and 6. The sequence is one of pelagic calcilutites, m ostly red t in t e d It has been recognise d b y the Subcom m ission that, in general, and w ell bedded, w ith bedding probably controlled by M ilan- D evonian sections in pelagic realm facies are m ore likely to be com - kovitch-B and clim atic oscillations during sedim entation. T he plete than those in the neritic fa,cies. T he pelagic facies form s a better sequence has been described in published accounts (H ouse and oth- basis for the biostratigraphical precision needed for international cor- ers, 1985; M apper, 1989; B ecker and others, 1989 ; Schindler 1990; relation. In particular the conodont and goniatite records are better in B ecker 1993a) and is depicted in figure 2. T he boundary is draw n those facies. That is not to im ply that there are not facies rich in other betw een B eds 31g and 32a as show n in figures 2 and 3. D istinctive is groups, for exam ple spores and brachiopods, w hich are very im por- B ed 3 1 g w hich is correlated w ith the U pper K ellw asser L im estone ot tant for correlation, but it is norm ally easier to correlate into such sec- G erm any and w hich is a hypoxic dark grey calcilutite to calcarenite tions secondarily from prim ary sections in the pelagic facies. In the above w hich is the m ost m arked faunal boundary. B oth B eds 31g last resort the Subcom m ission concentrated on tw o such sections, one and 32a are characterized by pelagic faunas. at Steinbruch Schm idt in the R henish Slate M ountains, G erm any 0 ？ a l︵ e The sequence chosen show s a com plete s u c cession through the (Sandberg and others, 1990 ; Schindler, I 了 ‘ o th e r a t 价 early Frasnian to late Fam ennian. It is unfaulted and has no tectonic 以 e － a V C ourniac in the M ontague N oire (Feist, 1990 汀The latter w。 as finally 仁 a C t 理 problem s. T he beds are approxim ately vertical. Equivalent sections se le c te d b e c a u se o f th e b e tte r d o c u m e n ta tio n s sil g rou ps. can be found elsew here in the area. T he rocks are of low -grade m eta- m orphism and therm al m aturity (C A I 2-3) and com prise an hom oge- neous pelagic calcilutite sequence w ithout m arly or shaly interbeds. R ecom m ended stratotype T here is a com plete zonal succession w ith a rich fossil content, espe- cially of the biostratigraphically significant groups of conodonts, T he recommended boundary GSSP between the Frasnian and am m onoids, trilobites, tentaculites and ostracods. D etailed docu- Fam ennian Stages (D evonian) is above the U pper C ourniac Q uarry, m entation has been provided of this (Feist, 1990). G eochem ical near Cessenon, M ontague N oire, France (figure 1). T he section is sit- w ork across the boundary at C ourniac has also been published uated in the southeastern M ontagne N oire, D 6partm ent 1-16rault, D is- (G oodfellow and others, 1989; G randjean and others, 1989; G rand- trict of Cessenon (topographic sheet 1:25 000, N o. 2544 E , M urviel- jean-L6cuyer and others, 1993; Joachim ski and B uggisch, 1993; 1} s -13 6 zier s；L am bert's coordinates: x ＝130 375, y ＝658 55). It is G irard and others, 1993) and currently other investigations are being N D eta iled Z V F igure 2 V m ap of t he 之加per － N一 N Q uarry at C ourniac, S N near C essenon, 喊 山 showing th e bed 比 乏 匡 哎 num bering and the 比 I I I4-r position of t he G SSP ！1 -1 }邢1 40 defi ning the base of th e F a m en nia n 1341二 口 州 日 ！ b etw een B eds 3 1 313 ． 3.6 , J7 ： and 32.