- Email: [email protected]
Flysch-type agglutinated foraminifera and the Maestrichtian to Paleogene history of the Labrador and North Seas — Comments
Marine Micropaleontology, 7 (1982) 359--361
359
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Discussion FLYSCH-TYPE AGGLUTINATED FORAMINIFERA AND THE MAESTRICHTIAN TO PALEOGENE HISTORY OF THE LABRADOR AND NORTH SEAS -- COMMENTS
w. WINKLER and J. VAN STUIJVENBERG Institut de G~ologie, P~rolles, CH-1700 Fribourg (Switzerland) Geologisches Biiro Dr. H. Wanner AG, Friedhofstrasse 9, CH-9014 St. Gallen (Switzerland)
(Accepted for publication March 3, 1982)
Gradstein and Berggren (1981) stress the fact that paleobathymetrical interpretations of agglutinated foraminifera associations are very divergent. They compare their own investigations made in neritic and bathyal deposits of the Labrador and North Seas (but whose sedimentology is not well known: turbidites?) with flysch data, and conclude that the socalled R h a b d a m m i n a - f a u n a s of agglutinated foraminifera lack paleobathymetrical significance. The present authors have studied aspects of this subject within the Gurnigel/ Schlieren Flysch (Switzerland). These deposits have been associated with this topic since Brouwer (1965). We maintain that much of the conflicting evidence arises not so much from poor knowledge of the physico-chemical life conditions of the R h a b d a m r n i n a - f a u n a (e.g., Moorkens, 1975) but more from the neglect of sedimentological information and the incorporation of inappropriate data from the literature. From the sedimentological point of view one must consider that an idealized turbiditic deposit, as described by Bouma (1962), consists of a graded sequence of sandy to pelitic material arranged with characteristic sedimentary structures (see also Stanley and Maldonado, 1981). At the top of the pelitic interval (Te), a layer of marl or clay representing the normal (= autochthonous = hemipelagic or p e l a g i c = T f ) sediment can be found; it is present if the time between turbiditic events was long enough to allow pelagic matter to settle and if the layer was 0377-8398/82/0000--0000/$02.75
not eroded by the next turbidity current. This logical model is well known from flysch or flysch-like turbiditic deposits (Hubert, 1967; Scholle, 1971; Rupke, 1975; Hesse, 1975; Hesse and Butt, 1976; Butt, 1981, a.o.). Such investigations have also shown that the bulk of pelitic material in turbidite deposits is resedimented, whereas the autochthonous sediment is generally of subordinate importance. It is therefore not correct to simply equate pelitic intervals in turbiditic series with autochthonous sediments (Gradstein and Berggren, 1981, p. 213). This correlation was frequently made before requisite sedimentological data became available. Consequently, data from the literature cannot be used without reservation if there is no indication that faunas were isolated from autochthonous deposits: little or no precision concerning the autochthonous or resedimented nature of shales was found when reviewing Gradstein and Berggren's (1981) flysch references for that. From the lithological description alone, one is often in doubt as to the autochthonous nature of the pelites under discussion. Brouwer's (1965) own investigations as far as concerns the Gurnigel/Schlieren Flysch, represent an exception as he tried to treat samples from the uppermost part of the pelitic intervals (Te,f) to get a maximum of autochthonous foraminifera. However, in using data from the literature he was less critical, and unfortunately these doubtful data were used fully by Gradstein and Berggren (1981).
© 1982 Elsevier Scientific Publishing Company
360
As data from the Upper Maastrichtian to Eocene Gurnigel/Schlieren Flysch are frequently used in the literature we would like to shortly resume our results (Van Stuijvenberg, 1979; Winkler, 1981). In our case, the autochthonous shales (Tf) generally consist of lime-free green clays and silts bearing arenaceous agglutinated foraminifera exclusively; the fauna is more "primitive" than found by Brouwer (1965) but there is a high species diversity. Following the range of organization from very primitive tests to more evolved ones, the most evolved genus observed is Spiroplectammina. These hemipelagic layers are rarely thicker than 5 cm, contain some quartz in the medium and fine fractions and have glauconite in the fine fraction. In the underlying dark grey turbiditic shales (Te) we observed calcareous planktonic and benthonic foraminifera (Gaudryina,
Nodosaria, Fissurina, Boliuina, Cibicides, Verneuilina, etc.) and calcareous nannofossils together with arenaceous agglutinated foraminifera of low species diversity and partly more evolved organization (e.g., Textularia). These turbiditic shales contain some 20% of carbonate (foraminifera, pelagic bivalve debris, etc.) as well as glauconite and quartz in all fractions. They are in general much thicker than the autochthonous shales, and may reach considerable thicknesses (up to 200 cm and more). The turbiditic shales grade up from the sandy Bouma-intervals (Ta,b,c,d) which contain a rich fauna of calcareous foraminifera (Nummulites, Globigerinas, etc.) and debris of algae, bryozoans, bivalves, echinoderms, etc. The turbiditic deposits (sandstones and shales) of the Gurnigel/ Schlieren Flysch therefore contain heterogeneous faunas derived from littoral, neritic and bathyal environments. We interpret the Gurnigel/Schlieren Flysch as having been deposited in a deep-water basin, in lower bathyal, abyssal to hadal environment, below the CCD, with life conditions only suitable for primitive agglutinated foraminifera. Our interpretation of the paleobathymetry as abyssal finds further support in the presence of red shales, brown manganiferous clays and
volcanic ash-layers which are associated with the green hemipelagic clays. Our model fits very well with the global distribution pattern for Mid-Cretaceous foraminiferids described by Haig (1979). We find his Recurvoides and lowest Marssonella association in the hemipelagic clays, and the Ammobaculites and upper Marssonella association in the turbidites. The fauna of the hemipelagic layers corresponds to those described by Krasheninnikov (1974) and Krasheninnikov and Pflaumann (1977) in Upper Cretaceous/ Paleogene non-turbiditic deep-sea clays. We suggest that discussions of paleobathymetry of flysch deposits based on the so-called Rhabdammina-fauna, or any other paleobathymetric consideration in turbidite deposits, should be based on both micropaleontological and sedimentological arguments in order to avoid misleading conclusions. This is necessary since Rhabdamrnina-faunas are not restricted to deep-water, abyssal environments, and may very well develop in neritic and bathyal environments if physico-chemical conditions are appropriate (Moorkens, 1975). References Bouma, A.H., 1962. Sedimentology of Some Flysch Deposits. Elsevier, Amsterdam/New York. Brouwer, J., 1965. Agglutinated foraminiferal faunas from some turbiditic sequences, I, II. Proc. K. Ned. Akad. Wet., (B), 68(5): 309--334. Butt, A., 1981. Depositional environments of the Upper Cretaceous rocks in the northern part of the Eastern Alps. Cushman Found. Foram. Res., Spec. Publ., 20. Gradstein, F.M. and Berggren, W.A., 1981. Flyschtype agglutinated foraminifera and the Maestrichtian to Paleogene history of the Labrador and North Seas. Mar. Micropaleontol., 6: 211--268. Haig, D.W., 1979. Global distribution pattern for Mid-Cretaceous foraminiferids. J. Foram. Res., 9(1): 29--40. Hesse, R., 1975. Turbiditic and nomturbiditic mudstone of Cretaceous flysch sections of the East Alps and other basins. Sedimentology, 22: 3 8 7 416. Hesse, R. and Butt, A., 1976. Paleobathymetry of Cretaceous turbidite basins of the East Alps relative to the calcite compensation level. J. Geol., 84(5): 505--533.
361
Hubert, J.F., 1967. Sedimentology of Prealpine Flysch Sequences, Switzerland. J. Sediment. Petrol., 37:885 907. Krasheninnikov, V.A., 1974. Upper Cretaceous benthonic agglutinated foraminifera, Leg 27 of the DSDP. Init. Rep. Deep-Sea Drill. Project, 27: 631--661. Krasheninnikov, V.A. and Pflaumann, U., 1977. Cretaceous agglutinated foraminifera of the Atlantic Ocean off West Africa (Leg 41, Deep Sea Drilling Project). Init. Rep. Deep-Sea Drill. Project, 41:565 -580. Moorkens, T.L., 1975. PalSkologische Bedeutung einiger Verg'esellschaftungen von sandschaligen Foraminiferen aus dem NW europ~/ischen Altterti//r und ihre Beziehung zu Muttergesteinen. Comp. Z. ErdSl und Kohle, Erdgas-Petrochemie, p p 77- 95.
Rupke, N.A., 1975. Deposition of fine-grained sediments in the abyssal environment of the Algero-Balearic Basin, Western Mediterranean Sea. Sedimentology, 22: 95--109. Scholle, P.A., 1971. Sedimentology of fine-grained deep-water carbonate turbidites, Monte Antola Flysch {Upper Cretaceous), Northern Apennines, Italy. Bull. Geol. Soc. Am., 82: 629--658. Stanley, D.J. and Maldonado, A., 1981. Depositional models for fine-grained sediment in the western Hellenic Trench, Eastern Mediterranean. Sedimentology, 28: 273--290. Stuijvenberg, J. van, 1979. Geology of the Gurnigel area (Prealps, Switzerland). Beitr. Geol. Karte Schweiz, N.F., 151. Winkler, W., 1981. Stratigraphie, Sedimentologie und Sedimentpetrographie des Schlierenflysches (Zentralschweiz). Diss. Univ. Fribourg.
FLYSCH-TYPE AGGLUTINATED FORAMINIFERA AND THE MAESTRICTIAN TO P A L E O G E N E H I S T O R Y O F T H E L A B R A D O R A N D N O R T H SEAS -- R E P L Y
F.M. GRADSTEIN and W.A. BERGGREN Geological Survey of Canada, Dartmouth, N.S. (Canada) Department of Geology and Geophysics, Woods Hole Oceanographic Institute, Woods Hole, Mass. 02543 (U.S.A.)
T h e a u t h o r s Winkler and van S t u i j v e n b e r g t o u c h u p o n an i m p o r t a n t issue, i.e., t h e relat i o n , geologically speaking, of t h e so-called R h a b d a m m i n a or " f l y s c h - t y p e " a g g l u t i n a t e d f o r a m i n i f e r a l f a u n a w i t h t u r b i d i t e sequences. L i t e r a t u r e on this s u b j e c t is scarce a n d o f a qualitative nature. Since t h e basins w h e r e t h e a g g l u t i n a t e d f o r a m i n i f e r a thrive are o f t e n p r o n e to t u r b i d i t y c u r r e n t activity, s e d i m e n t / f a u n a relationships p r o v i d e valuable insight in ( p a l e o ) e c o l o g y a n d basin analysis. F o r this reason we f o c u s e d a l r e a d y at a n early stage o f t h e s t u d y o f t h e L a b r a d o r and N o r t h Sea on t h e f a u n a / s e d i m e n t relationship. Results have b e e n limited so far, h i n d e r e d n o t t h e least b y
t h e d i f f i c u l t y in recognizing t u r b i d i t i c seq u e n c e s in e x p l o r a t o r y wells. The use o f t h e term "flysch-type" agglutinated f o r a m i n i f e r a is explicitly a faunistic one, as we have d o c u m e n t e d . T h e t e r m d r a w s a t t e n t i o n t o a qualitative similarity o f basinal a g g l u t i n a t e d assemblages w i t h t h o s e first d e s c r i b e d f r o m the C a r p a t h i a n flysch deposits. O u r c o n c l u s i o n , using m u l t i p l e geological a n d g e o p h y s i c a l criteria, t h a t R h a b d a r n m i n a or " f l y s c h - t y p e " a g g l u t i n a t e d f o r a m i n i f e r a assemblages are n o t strictly d e p t h - d e p e n d e n t is a p p a r e n t l y shared b y Winkler and van Stuijvenberg. O p i n i o n s have converged.
359
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Discussion FLYSCH-TYPE AGGLUTINATED FORAMINIFERA AND THE MAESTRICHTIAN TO PALEOGENE HISTORY OF THE LABRADOR AND NORTH SEAS -- COMMENTS
w. WINKLER and J. VAN STUIJVENBERG Institut de G~ologie, P~rolles, CH-1700 Fribourg (Switzerland) Geologisches Biiro Dr. H. Wanner AG, Friedhofstrasse 9, CH-9014 St. Gallen (Switzerland)
(Accepted for publication March 3, 1982)
Gradstein and Berggren (1981) stress the fact that paleobathymetrical interpretations of agglutinated foraminifera associations are very divergent. They compare their own investigations made in neritic and bathyal deposits of the Labrador and North Seas (but whose sedimentology is not well known: turbidites?) with flysch data, and conclude that the socalled R h a b d a m m i n a - f a u n a s of agglutinated foraminifera lack paleobathymetrical significance. The present authors have studied aspects of this subject within the Gurnigel/ Schlieren Flysch (Switzerland). These deposits have been associated with this topic since Brouwer (1965). We maintain that much of the conflicting evidence arises not so much from poor knowledge of the physico-chemical life conditions of the R h a b d a m r n i n a - f a u n a (e.g., Moorkens, 1975) but more from the neglect of sedimentological information and the incorporation of inappropriate data from the literature. From the sedimentological point of view one must consider that an idealized turbiditic deposit, as described by Bouma (1962), consists of a graded sequence of sandy to pelitic material arranged with characteristic sedimentary structures (see also Stanley and Maldonado, 1981). At the top of the pelitic interval (Te), a layer of marl or clay representing the normal (= autochthonous = hemipelagic or p e l a g i c = T f ) sediment can be found; it is present if the time between turbiditic events was long enough to allow pelagic matter to settle and if the layer was 0377-8398/82/0000--0000/$02.75
not eroded by the next turbidity current. This logical model is well known from flysch or flysch-like turbiditic deposits (Hubert, 1967; Scholle, 1971; Rupke, 1975; Hesse, 1975; Hesse and Butt, 1976; Butt, 1981, a.o.). Such investigations have also shown that the bulk of pelitic material in turbidite deposits is resedimented, whereas the autochthonous sediment is generally of subordinate importance. It is therefore not correct to simply equate pelitic intervals in turbiditic series with autochthonous sediments (Gradstein and Berggren, 1981, p. 213). This correlation was frequently made before requisite sedimentological data became available. Consequently, data from the literature cannot be used without reservation if there is no indication that faunas were isolated from autochthonous deposits: little or no precision concerning the autochthonous or resedimented nature of shales was found when reviewing Gradstein and Berggren's (1981) flysch references for that. From the lithological description alone, one is often in doubt as to the autochthonous nature of the pelites under discussion. Brouwer's (1965) own investigations as far as concerns the Gurnigel/Schlieren Flysch, represent an exception as he tried to treat samples from the uppermost part of the pelitic intervals (Te,f) to get a maximum of autochthonous foraminifera. However, in using data from the literature he was less critical, and unfortunately these doubtful data were used fully by Gradstein and Berggren (1981).
© 1982 Elsevier Scientific Publishing Company
360
As data from the Upper Maastrichtian to Eocene Gurnigel/Schlieren Flysch are frequently used in the literature we would like to shortly resume our results (Van Stuijvenberg, 1979; Winkler, 1981). In our case, the autochthonous shales (Tf) generally consist of lime-free green clays and silts bearing arenaceous agglutinated foraminifera exclusively; the fauna is more "primitive" than found by Brouwer (1965) but there is a high species diversity. Following the range of organization from very primitive tests to more evolved ones, the most evolved genus observed is Spiroplectammina. These hemipelagic layers are rarely thicker than 5 cm, contain some quartz in the medium and fine fractions and have glauconite in the fine fraction. In the underlying dark grey turbiditic shales (Te) we observed calcareous planktonic and benthonic foraminifera (Gaudryina,
Nodosaria, Fissurina, Boliuina, Cibicides, Verneuilina, etc.) and calcareous nannofossils together with arenaceous agglutinated foraminifera of low species diversity and partly more evolved organization (e.g., Textularia). These turbiditic shales contain some 20% of carbonate (foraminifera, pelagic bivalve debris, etc.) as well as glauconite and quartz in all fractions. They are in general much thicker than the autochthonous shales, and may reach considerable thicknesses (up to 200 cm and more). The turbiditic shales grade up from the sandy Bouma-intervals (Ta,b,c,d) which contain a rich fauna of calcareous foraminifera (Nummulites, Globigerinas, etc.) and debris of algae, bryozoans, bivalves, echinoderms, etc. The turbiditic deposits (sandstones and shales) of the Gurnigel/ Schlieren Flysch therefore contain heterogeneous faunas derived from littoral, neritic and bathyal environments. We interpret the Gurnigel/Schlieren Flysch as having been deposited in a deep-water basin, in lower bathyal, abyssal to hadal environment, below the CCD, with life conditions only suitable for primitive agglutinated foraminifera. Our interpretation of the paleobathymetry as abyssal finds further support in the presence of red shales, brown manganiferous clays and
volcanic ash-layers which are associated with the green hemipelagic clays. Our model fits very well with the global distribution pattern for Mid-Cretaceous foraminiferids described by Haig (1979). We find his Recurvoides and lowest Marssonella association in the hemipelagic clays, and the Ammobaculites and upper Marssonella association in the turbidites. The fauna of the hemipelagic layers corresponds to those described by Krasheninnikov (1974) and Krasheninnikov and Pflaumann (1977) in Upper Cretaceous/ Paleogene non-turbiditic deep-sea clays. We suggest that discussions of paleobathymetry of flysch deposits based on the so-called Rhabdammina-fauna, or any other paleobathymetric consideration in turbidite deposits, should be based on both micropaleontological and sedimentological arguments in order to avoid misleading conclusions. This is necessary since Rhabdamrnina-faunas are not restricted to deep-water, abyssal environments, and may very well develop in neritic and bathyal environments if physico-chemical conditions are appropriate (Moorkens, 1975). References Bouma, A.H., 1962. Sedimentology of Some Flysch Deposits. Elsevier, Amsterdam/New York. Brouwer, J., 1965. Agglutinated foraminiferal faunas from some turbiditic sequences, I, II. Proc. K. Ned. Akad. Wet., (B), 68(5): 309--334. Butt, A., 1981. Depositional environments of the Upper Cretaceous rocks in the northern part of the Eastern Alps. Cushman Found. Foram. Res., Spec. Publ., 20. Gradstein, F.M. and Berggren, W.A., 1981. Flyschtype agglutinated foraminifera and the Maestrichtian to Paleogene history of the Labrador and North Seas. Mar. Micropaleontol., 6: 211--268. Haig, D.W., 1979. Global distribution pattern for Mid-Cretaceous foraminiferids. J. Foram. Res., 9(1): 29--40. Hesse, R., 1975. Turbiditic and nomturbiditic mudstone of Cretaceous flysch sections of the East Alps and other basins. Sedimentology, 22: 3 8 7 416. Hesse, R. and Butt, A., 1976. Paleobathymetry of Cretaceous turbidite basins of the East Alps relative to the calcite compensation level. J. Geol., 84(5): 505--533.
361
Hubert, J.F., 1967. Sedimentology of Prealpine Flysch Sequences, Switzerland. J. Sediment. Petrol., 37:885 907. Krasheninnikov, V.A., 1974. Upper Cretaceous benthonic agglutinated foraminifera, Leg 27 of the DSDP. Init. Rep. Deep-Sea Drill. Project, 27: 631--661. Krasheninnikov, V.A. and Pflaumann, U., 1977. Cretaceous agglutinated foraminifera of the Atlantic Ocean off West Africa (Leg 41, Deep Sea Drilling Project). Init. Rep. Deep-Sea Drill. Project, 41:565 -580. Moorkens, T.L., 1975. PalSkologische Bedeutung einiger Verg'esellschaftungen von sandschaligen Foraminiferen aus dem NW europ~/ischen Altterti//r und ihre Beziehung zu Muttergesteinen. Comp. Z. ErdSl und Kohle, Erdgas-Petrochemie, p p 77- 95.
Rupke, N.A., 1975. Deposition of fine-grained sediments in the abyssal environment of the Algero-Balearic Basin, Western Mediterranean Sea. Sedimentology, 22: 95--109. Scholle, P.A., 1971. Sedimentology of fine-grained deep-water carbonate turbidites, Monte Antola Flysch {Upper Cretaceous), Northern Apennines, Italy. Bull. Geol. Soc. Am., 82: 629--658. Stanley, D.J. and Maldonado, A., 1981. Depositional models for fine-grained sediment in the western Hellenic Trench, Eastern Mediterranean. Sedimentology, 28: 273--290. Stuijvenberg, J. van, 1979. Geology of the Gurnigel area (Prealps, Switzerland). Beitr. Geol. Karte Schweiz, N.F., 151. Winkler, W., 1981. Stratigraphie, Sedimentologie und Sedimentpetrographie des Schlierenflysches (Zentralschweiz). Diss. Univ. Fribourg.
FLYSCH-TYPE AGGLUTINATED FORAMINIFERA AND THE MAESTRICTIAN TO P A L E O G E N E H I S T O R Y O F T H E L A B R A D O R A N D N O R T H SEAS -- R E P L Y
F.M. GRADSTEIN and W.A. BERGGREN Geological Survey of Canada, Dartmouth, N.S. (Canada) Department of Geology and Geophysics, Woods Hole Oceanographic Institute, Woods Hole, Mass. 02543 (U.S.A.)
T h e a u t h o r s Winkler and van S t u i j v e n b e r g t o u c h u p o n an i m p o r t a n t issue, i.e., t h e relat i o n , geologically speaking, of t h e so-called R h a b d a m m i n a or " f l y s c h - t y p e " a g g l u t i n a t e d f o r a m i n i f e r a l f a u n a w i t h t u r b i d i t e sequences. L i t e r a t u r e on this s u b j e c t is scarce a n d o f a qualitative nature. Since t h e basins w h e r e t h e a g g l u t i n a t e d f o r a m i n i f e r a thrive are o f t e n p r o n e to t u r b i d i t y c u r r e n t activity, s e d i m e n t / f a u n a relationships p r o v i d e valuable insight in ( p a l e o ) e c o l o g y a n d basin analysis. F o r this reason we f o c u s e d a l r e a d y at a n early stage o f t h e s t u d y o f t h e L a b r a d o r and N o r t h Sea on t h e f a u n a / s e d i m e n t relationship. Results have b e e n limited so far, h i n d e r e d n o t t h e least b y
t h e d i f f i c u l t y in recognizing t u r b i d i t i c seq u e n c e s in e x p l o r a t o r y wells. The use o f t h e term "flysch-type" agglutinated f o r a m i n i f e r a is explicitly a faunistic one, as we have d o c u m e n t e d . T h e t e r m d r a w s a t t e n t i o n t o a qualitative similarity o f basinal a g g l u t i n a t e d assemblages w i t h t h o s e first d e s c r i b e d f r o m the C a r p a t h i a n flysch deposits. O u r c o n c l u s i o n , using m u l t i p l e geological a n d g e o p h y s i c a l criteria, t h a t R h a b d a r n m i n a or " f l y s c h - t y p e " a g g l u t i n a t e d f o r a m i n i f e r a assemblages are n o t strictly d e p t h - d e p e n d e n t is a p p a r e n t l y shared b y Winkler and van Stuijvenberg. O p i n i o n s have converged.