The Turonian/Coniacian (T/C) boundary in the Upper Cretaceous of the Elbe Valley/Saxony (Germany)

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Acta Geologica Polonica, Vol. 48 (1998), No.4, pp. 387-394

The Turonian/Coniacian (T/C) boundary in the Upper Cretaceous of the Elbe Valley/Saxony

(Germany)

KARL-ARMIN TROGER1 & MARIO WEJDA2

1 University of Mining and Technology, Bergakademie Freiberg, Geological Institute, Bernhard-von-Cotta-StrafJe 2, Freiberg/Saxony, D-09596 Germany

2 HGN Hydrogeology Ltd., Bertolt-Brecht-Allee 9, Dresden/Saxony, D-01309 Germany

ABSTRACT:

TRaGER, K.-A. & WEJDA, M. 1998. The TuronianlConiacian (TIC) boundary in the Upper Cretaceous of the Elbe ValleylSaxony (Germany). Acta Geologica Polonica, 48 (4),387-394. Warszawa.

Three lithofacies characterize the TuronianlConiacian sequences in the Upper Cretaceous of the Elbe Valley. The marly lithofacies, between Weinbohla - Dresden - Heidenau, consists of marls and calcareous clays (Strehlen Formation). A transitional lithofacies , with alternations of marls, clays and blocky sandstones, follows to the southeast (area between Rosenthal - Pima - Lohmen). A sandy lithofacies, with blocky sandstones, is developed even farther to the southeast (Elbsandsteingebirge).

The TIC boundary is situated in the lower part of the Strehlen Formation in the marly lithofacies, known from several boreholes. Coniacian index ammonites are absent across the TIC boundary in the three investigated boreholes apart from a deformed and incomplete specimen of Placenticeras cf.

orbignyanum (GEINITZ). Therefore, bivalves must be used to place the TIC boundary. The Didymotis event II (Dresden- Marienhof Borehole), with Cremnoceramus waltersdorfensis (ANDERT), lies at the top of the Upper Turonian M. scupini Zone. The rarity or absence of the bivalve Didymotis in the Dresden-Blasewitz and Graupa boreholes is caused by facies changes. The FAD of Cremnoceramus rotundatus (TRaGER non FIEGE) , especially the C. rotundatus Event (Graupa Borehole, Hinterjessen Marl), can be used to place the TIC boundary. A small interval below the FAD of C. rotundatus and above the Didymotis II event, which may belong to the basal Coniacian, yields Cremnoceramus wal- tersdorfensis (ANDERT), Cremnoceramus waltersdorfensis hannovrensis (HEINZ), Mytiloides car- pathicus (SIMIONESCU) and Placenticeras cf. orbignyanum (GEINITZ). In the sandy lithofacies fossils

are rare. It is not possible to place the boundary in either the Herrenleite Sandstone or in sandstone d. In the marly lithofacies of the Upper Cretaceous of Saxony bracketing of the TIC boundary is possible by means of planktonic foraminifera. It is possible to identify the evolution of planoconvex double-keeled globotruncanids of the Dicarinella hagni - Dicarinella primitiva -Dicarinella concava- ta group from the Upper Turonian. In the Dresden-Blasewitz and Dresden-Marienhof boreholes this group is represented in the TIC boundary interval by Marginotruncana paraconcavata PORTHAULT and Dicarinella cf. concavata (BROTZEN). They are of rare occurrence because they are facies con- trolled. It is not possible to recognize the boundary between the schneegansi and concavata zones because of the restricted occurrence and rarity of the index forms in the investigated sections. In the Dresden-Blasewitz and Dresden-Marienhof boreholes the benthonic species Stensioeina granulata (OLBERTZ) was identified.

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388 KARL-ARMIN TROGER & MARIO WEIDA

INTRODUCTION

The TuronianlConiacian (TIC) was fixed dur- ing the Cretaceous Stage Boundaries Meeting in Brussels (1995) in the following manner after having discussed different criteria for the defini- tion using ammonites, bivalves (especially inoceramids), echinoids, planktonic and benthonic foraminifera and nannoplankton:

"Thus, the boundary will lie between the LAD (last appearance datum) of Prionocyclus germari and the FAD (first appearance datum) of Forresteria (Harleites) petrocoriensis, and at the FAD of Cremnoceramus rotundatus (sensu TROGER non FIEGE) (KAUFFMAN & al. 1996)".

At the chosen basal boundary stratotype section, the Salzgitter-Salder Quarry in Lower Saxony (Germany), the FAD of C. rotundatus is coincident with the C. rotundatus Event, which lies immediately above the second Didymotis bioevent and an acme of C. waltersdorfensis (ANDERT) (WOOD & al. 1984, KAUFFMAN & al.

1996). Scaphitids and baculitids are common at several levels below and above the TIC bound- ary. The vertical range of Scaphites kies- lingswaldensis doylei WRIGHT extends above the

\ ,

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TIC boundary. The FAD of Scaphites kies- lingswaldensis kieslingswaldensis LANGENHAN

& GRUNDEY and of Scalarites turoniensis (SCHLUTER) is situated significantly above the TIC boundary (crassus = schloenbachi Zone).

It is possible to recognize three facies developments in the Upper Turonian and Coniacian of the Upper Cretaceous of the Elbe valley, including the TIC boundary. A marly lithofacies (Strehlen Formation) is restricted to the NW part of the Upper Cretaceous of the Elbe Valley between Weinbohla - Dresden - Heidenau. The southernmost part of this marly lithofacies consists of the Graupa Marls (Upper Turonian and Lower Coniacian near Pima, including the Bonnewitz Marls (Lower and Middle Coniacian). The adjacent transitional lithofacies between Pima - Graupa - Konigstein consists of an alternations of marls (Hinterjessen Marl - Lower Coniacian; Zatzschke Marl - Lower Coniacian; Brausnitzbach Marl Lower Coniacian), clays (Zeichen-Burglehn Clay) and blocky sandstones (Herrenleite Sandstone - uppermost Turonian and Lower Coniacian;

Liebethal sandstone-Upper Turonian and Lower Coniacian (7); Lohmen Sandstone - Lower

Boreholes with the Turonian/Coniacian boundary DM = Dresden-Marienhof

DB = Dresden-Blasewitz G = Grupa

Transitionallithofacies:sandstones in part ca/careons (Pimaer Oberquader: t2-t3; Herrenleite Sandstone - t3-cn; Liebethal Sandstone: t3-cno; Lohrnen Sandstone: en) with intercalated clal's and lI1ar/s(BUl~glehn-Zeichen Clay: 13; i

Graupa. Marl: t3-en

1' Hilflerjessen Marf: en; Zatsehke Marl: en)

Brausllltzbaeh Mar: en) I

- Sandy lithofacies

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. Turonian/Coniacian boundary Lithofacies boundary

LF = Lusatian Overthmst KF ⁼KarsdorfFault NF = Niedelwartha Fault

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Fig. 1. Facies developments of the Upper Turonian and Coniacian in the Cretaceous of the Elbe Valley

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TURONIAN/CONIACIAN BOUNDARY IN SAXONY, GERMANY 391

investigation of this boundary. However, exten- sive exposures of the Strehlen Formation are absent, except for the backfilled quarries in the vicinity of the Christus-church in Dresden- Strehlen and in Weinbohla. Upper and topmost Upper Turonian limestones were exploited in both cases. The entire Strehlen Formation was penetrated in the Dresden-Marienhof Borehole (Text-fig. 2), Dresden-Blasewitz Borehole (Text- fig. 3) and Graupa Borehole (Text-fig. 4).

The ranges of planktonic foraminifera in the TIC boundary interval, and their application to the delimitation of the boundary, have been the subject of discussion for a long time (see ROBASZYNSKI &

al. 1979, WEIDICH 1984, ROBASZYNSKI & CARON 1995). According to the zonation presented by ROBASZYNSKI & al. (1979) the TIC boundary is situated at the top of the Marginotruncana schnee- gansi Zone, and the succeeding Dicarinella con- cavata Zone should be assigned to the lowermost Lower Coniacian. WEIDICH (1984) distinguished a Dicarinella primitiva Zone at the TIC boundary and equated this zone with the base of the Coniacian. However, ROBASZYNSKI & CARON (1995) demonstrated that D. concavata (BROTZEN) and D. primitiva both appear already in the Upper Turonian, together with the ammonite Subprionocyclus neptuni (GEINITZ); and that con- sequently the previously used D. primitiva Zone becomes redundant. They noted that the TIC boundary cannot readily be drawn by means of planktonic foraminifera. In spite of this, the entry of the planoconvex double-keeled globotruncanids seems to be a useful datum in Upper Cretaceous planktonic foraminiferal biostratigraphy.

The recorded ranges and first occurrences of many of the benthonic foraminifera in the TIC boundary interval differ greatly from author to author, depending on the facies and localities in question. TRUMPER (1968) pointed to the large intraspecific variability of the genus Stensioeina BROTZEN and the consequent limited use of this genus in microfossil biostratigraphy. Following KOCH (1977), many authors took the base of the Coniacian at the FAD of Stensioeina granulata (OLBERTZ). However, KOCH used SEITZ'S concept (based on inoceramids) for determining the TIC boundary. The base of the Coniacian as under- stood today is actually situated below SEITZ'S inoceramid datum.

In the following sections, the faunal changes in bivalves, ammonites and foraminifera in the TIC boundary interval will be discussed.

OCCURRENCE OF BIOSTRA TIGRA- PHICALLY IMPORTANT BIVALVES IN THE UPPER TURONIAN AND LOWER CONIACIAN SUCCESSION

Upper Turonian

The Mytiloides scupini Zone in the three boreholes is characterized by the occurrence of Mytiloides scupini (HEINz), Inoceramus striato- concentricus striatoconcentricus GUMBEL, and Inoceramus dresdensis TROGER. The Didymotis I and II events were observed in the higher parts of the M. scupini Zone of the Dresden-Marienhof Borehole. Didymotis costatus (FRIc) is common.

The following inoceramid species occur in the interval between the Didymotis I and II events, confirming its Late Turonian age:

Mytiloides scupini (HEINZ) Inoceramus dresdensis TROGER Mytiloides carpathicus (SIMIONESCU) Inoceramus lusatiae ANDERT and ancestors

Cremnoceramus ex gr. waltersdorfensis (ANDERT)

There is a difference between the Dresden- Marienhof, Dresden-Blasewitz and Graupa boreholes concerning the occurrence of the Didymotis events I and II. Didymotis is very rare in the Upper Turonian of the Dresden - Blasewitz Borehole and is missing in the Graupa Borehole. It is possible that this is caused by the facies change to the SE in the direction of the sandy lithofacies; in which Didymotis is absent or rare. It is noteworthy that CECH (1987) has also observed the Didymotis events in the marly lithofacies in the northern Czech successions and has not recorded Didymotis from the sandy lithofacies.

Lower Coniacian

The Lower Coniacian starts with an acme of Cremnoceramus rotundatus (TROGER non FIEGE) in Lower Saxony. The FAD of Cremnoceramus crassus (PETRASCHECK) is situated above this level. This is also the case in the Graupa Borehole, in which there is a well developed rotundatus event. However, the FADs of Cremnoceramus rotundatus (TROGER non FIEGE) and Cremnoceramus crassus (PETRAS CHECK)

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392 KARL-ARMIN TRaGER & MARIO WEJDA (= Inoceramus schloenbachi BaHM) are in the

same bed in the Dresden-Marienhof and Dresden- Blasewitz boreholes. Between the Didymotis II event (Dresden-Marienhof) and the LAD of Mytiloides scupini (HEINZ) (Dresden-Blasewitz) an interval (TIC) of 5-7 metres is to be found which yields the following inoceramids:

Cremnoceramus waltersdorfensis (ANDERT) Cremnoceramus waltersdorfensis hannovrensis

(HEINZ)

Inoceramus dresdensis TRaGER Mytiloides carpathicus (SIMIONESCU)

Inoceramus lusatiae ANDERT

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It is possible that the absence of the C. rotun- datus event in these latter boreholes was caused by a gap, and that the TIC interval described rep- resents a reduced C. rotundatus Zone.

OCCURRENCE OF AMMONITES IN THE TURONIAN - CONIACIAN SUCCESSION

The index ammonite for the topmost Upper Turonian - Prionocyclus germari - and that for the basal Lower Coniacian - Forresteria (Harleites) petrocoriensis - were not found in the three boreholes. However, scaphitids and baculitids are common in the Upper Turonian/Lo-

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TURONIAN/CONIACIAN BOUNDARY IN SAXONY, GERMANY 393

wer Coniacian succession at several horizons. All of the ammonites are highly deformed by com- paction, in the same way as the bivalves, and in most cases they are incompletely preserved. The hooks and shafts of the scaphitids are not preserved. For this reason they could be determined only as Scaphite's sp. aff. geinitzii or Scaphites sp. In the Upper Turonian M. scupini Zone, Scaphites geinitzii (D'ORBIGNY) occurs together with Hyphantoceras flexuosum (SCHUlTER) and Hyphantoceras cf. reussianum (D'ORBIGNY).

The Lower Coniacian Scaphites kies- lingswaldensis kieslingswaldensis LANGENHAN

& GRUNDEY first occurs above the C. rotundatus Event (Graupa Borehole). An incomplete and deformed specimen of Placenticeras cf.

orbignyanum (GEINITZ), determined by H.

SUMMESBERGER (Vienna), was found in associa- tion with Mytiloides cf. scupini (HEINZ) in the Dresden-Blasewitz Borehole near the TIC boundary. The FAD of Scala rites in the three boreholes is situated in the C. crassus Zone in each case. In conclusion it must be said that the TuronianlConiacian boundary cannot be fixed using ammonites alone.

OCCURRENCE OF PLANKTONIC FORAMINIFERA IN THE TURONIAN - CONIACIAN SEQUENCE

In the Dresden-Blasewitz Borehole the planktonic foraminifera fauna is composed of globotruncanids. In the TIC boundary interval the absence andlor rarity of the index forms renders it impossible to recognize the boundary between the schneegansi Zone and the succeeding conca- vata Zone. There is a significant development in the hagni - primitiva - concavata group involv- ing the development of planoconvex tests through the migration of the keels onto the spiral side of the tests. Marginotruncana schneegansi occurs together with M. coronata BOLLI, Dicarinella hagni (SCHEIBNEROVA) and D.

imbricata (MORNOD) in the 160 - 115 m interval, and does not range above this level. The FAD of D. concavata, represented by atypical, transi- tional forms referred to D. cf. concavata, is at 60 m depth, coincident with the FAD of Stenioeina granulata.

The composition of the foraminiferal fauna in the Dresden-Marienhof Borehole is remarkably homogeneous, especially in the TIC boundary

interval. The proportion of planktonic species ranges between 70 and 90 %. Marginotruncana paraconcavata PORTHAULT (which replaces the species Dicarinella concavata in the Boreal Realm) was identified at a depth of 70 m.

Stensioeina granulata (OLBERTZ) appears in the highest part of the section at a depth of 60 m. No representatives of the schneegansi - renzi - sigali group were identified, which means that the schneegansi Zone cannot be recognized in this borehole.

Acknowledgements

The research was supported by the Deutsche Forschungsgemeinschaft in the years 1992-1995. We are obliged to the Sachsische Landesamt fUr Umwelt und Geologie (section Boden and Geologie) for per- mission to use the three described boreholes for our investigations. We are indebted to Dr. H.

SUMMESBERGER (Vienna) for the determination of the Placenticeras species.

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The Turonian/Coniacian (T/C) boundary in the Upper Cretaceous of the Elbe Valley/Saxony (Germany)