Acta Geologica Polonica, Vol. 54 (2004), No. 4, pp. 639-656

20 years of event stratigraphy in NW Germany; advances and open questions

FRANK WIESE1, CHRISTOPHER J. WOOD2 & ULRICH KAPLAN3

1Fachrichtung Paläontologie, Institut für Geologische Wissenschaften der FU Berlin, Malteserstr. 74-100, D-12249 Berlin, Germany. Email: [email protected] 2Scops Geological Services Ltd., 31 Periton Lane, Minehead Somerset, TA24 8AQ, UK. Email: [email protected] 1Eichenalle 141, D-33332 Gütersloh, Germany. Email: [email protected]

“The being determines consciousness” (Karl Marx) For Gundolf

ABSTRACT:

WIESE, F., WOOD, C.J. & KAPLAN, U. 2004. 20 years of event stratigraphy in NW Germany; advances and open ques- tions. Acta Geologica Polonica, 54 (4), 639-656. Warszawa.

The application of event stratigraphy in the Cenomanian to Lower Coniacian (Upper Cretaceous) Plänerkalk Gruppe of northwestern Germany has advanced stratigraphic resolution considerably. For a short interval in the Upper Turonian, various genetically variable events (bioevents, tephroevents, stable isotope marker, eustatoevents) are reviewed and new data are partly added. In addition, the lateral litho and biofacies changes within individual events are discussed and provide a basis for a tentative high-resolution correlation between distal and proximal settings. The dense sequence of events permits a stratigraphic resolution of 50 – 100ky for some intervals. Beyond stratigraphic purposes, the alternation of fossil barren intervals with thin fossil beds still demands explanations. As taphonomic processes are considered to be play only a minor role, other explanations are required. It appears that trophic aspects and a calibra- tion of planktic and benthic faunal assemblages may result in a better understanding of this biosedimentary system and its faunal characteristics.

Key words: Events, Event stratigraphy, Upper Cretaceous, Upper Turonian, Germany, Correlation.

INTRODUCTION Basin (LSB) into the Subhercynian Cretaceous Basin (SCB) and the Münsterland Cretaceous Basin (MCB), the In 2003, the classic work of Gundolf ERNST and his co- Anglo-Paris Basin (APB) of England/France, to northern authors on the event stratigraphy of the Cenomanian and Spain and to Poland have successfully been attempted. Turonian in the Lower Saxony Basin of NW Germany The event stratigraphic concept has been a large advance (“Event-Stratigraphie im Cenoman und Turon von NW- in subdividing the apparently monotonous grey to white Deutschland”) had its 20th anniversary. Since then, this limestone of the “Plänerkalk Gruppe” (Pläner Limestone stratigraphic framework has been continually added to Group). In the 1990s, event stratigraphy was progressively and refined. In the course of these later studies additional combined with sequence stratigraphy, leading to a more correlations of individual events outside the Lower Saxony dynamic understanding of sedimentation processes in the 640 FRANK WIESE, CHRISTOPHER J. WOOD & ULRICH KAPLAN

Pläner Limestones and a better understanding of lateral ties from the Münsterland Cretaceous Basin. It must be facies changes, including biofacies changes within event emphasised that the sequence stratigraphic framework beds (ERNST & al. 1996). The same authors presented a and genetic event interpretations presented in this paper is catalogue of criteria for sequence and event stratigraphy in not to be taken as a definitive statement. We explicitly Boreal pelagic systems, giving an overview of work in want to make clear that this is to be regarded rather as a progress. More recently – as the stratigraphic framework topic for discussion by the Cretaceous community in the had already been established – event stratigraphic investi- spirit of Gundolf ERNST’S own work. gations began to concentrate on the refinement of sequence stratigraphic subdivisions in the Plänerkalk Group and the reasons for the occurrence of distinct fossil GEOLOGICAL FRAMEWORK AND HISTORICAL beds. In this contribution, we want to review the current ACCOUNT event stratigraphic subdivision within a sequence strati- graphic context, exemplified by a case study (lower Upper The so-called Pläner (Unterer Pläner, Obere Pläner; Turonian). As working progress is best in Lower Saxony VON STROMBECK 1857) of northern Germany (Lower and Saxony-Anhalt, we specifically refer to these areas Cenomanian to Lower Coniacian) forms a well mappable (Text-fig. 1). Where possible, we also consider locali- lithounit in Westphalia, Lower Saxony and Saxony-Anhalt,

Fig. 1. Working area of the former Ernst Working Group. Area 1: Lower Saxony Cretaceous Basin (LSB) and Subhercynian Cretaceous Basin (SCB), Area 2: Münsterland Cretaceous Basin (MCB) EVENT STRATIGRAPHY 641 with an extent of several 100 km2. In the text, we will refer lithounits. There is clearly an urgent need for the litho- to it informally as “Pläner Gruppe” (Pläner Group). It stratigraphic nomenclature of the Plänerkalk Group to be ranges in thickness from tens metres to a maximum thick- rationalised in the sense of the International Stratigraphic ness of at least 500 m (Lengerich area, Westphalia). Guide (SALVADOR 1994) (a definition and formalization Lithologically, the succession of marl/limestone alterna- process is currently undertaken by the German tions and white and red bedded to nodular limestones rep- Subcommission on Cretaceous Stratigraphy). The first resents Boreal pelagic limestones [mainly composed of coc- purely biostratigraphic zonal schemes, based on inoce- colithophorids (matrix); calcareous dinoflagellate cysts ramid bivalves and ammonites, were developed in the sec- (here referred to as calcispheres), planktonic foraminifera ond part of the last century (e.g. BRÄUTIGAM 1962, TRÖGER and bioclasts (mainly inoceramid bivalves, echinoderms)]. 1967, KELLER 1982, KAPLAN & al. 1985, KAPLAN 1986). The The base of the Pläner Gruppe is taken at a facies change first event stratigraphic approaches were presented by in the context of the global Cenomanian transgression, ERNST & al. (1979) and the key paper was done by ERNST accompanied by a change from (glauconitic) siliciclastic- & al. (1983) followed by a large number of studies progres- dominated sedimentation to progressively distal, pelagic sively elaborating and updating the event framework in marl/limestone alternations, monotonous, massively bed- north Germany (WOOD & al. 1984, ERNST & WOOD 1995, ded, white and red limestone bodies and red marls. The ERNST & WOOD 1997, WRAY & al. 1995, WRAY 1999) uniform Cenomanian sedimentation occurred on a tecto- nically poorly structured shelf (WILMSEN 2003). From the terminal Cenomanian to the earliest Turonian on, local A CASE STUDY: THE LOWER UPPER TURONIAN movements of salt pillows occurred in Lower Saxony and Saxony-Anhalt. This resulted in a narrowly differentiated In the lower Upper Turonian of north Germany, shelf into more subsiding areas (here referred to as “basi- numerous events of different origins provide a compara- nal”) and off-shore, pelagic swells with water depth perio- tively high frequency of stratigraphic markers (see also dically above storm wave base (tempestites with hummocky Text-fig. 2a). A possible relation between events and cross stratification). The top of the Pläner Group is marked sequences has already been proposed (ERNST & al. 1996, by a fundamental turnover from pelagic limestones towards WILMSEN 2003). Within the biostratigraphic and litho- dark marls (Emscherian Marls), the base of which can be stratigraphic framework (Text-figs 2-3), we present first a characterized by sand layers, glauconite and phosphatic sequential subdivision, in part with new data. Events will nodules. A particularly characteristic feature of the be described and discussed with reference to depositional Turonian part of the Pläner Group is the occurrence of sequences. (typically relatively thin) fossiliferous strata separated by thick intervals with very scarce fossil records. The fine- Biostratigraphic framework grained white splintery limestones mostly provide no macroscopic information regarding grain-size and sedi- Biostratigraphic subdivision of the north German mentary structure/texture and are, therefore, difficult to Turonian is based on ammonite and inoceramid bivalve interpret by means of conventional sequence stratigraphic (assemblage/concurrent range) zones. The various zonal analysis. Formerly, only lateral faunal changes were consid- schemes and their progressive elaboration are discussed ered to distinguish between near-swell and more basinal in the literature at length (e.g. KELLER 1982, WOOD & al. settings. Therefore, early stratigraphic subdivision of the 1984, ERNST & WOOD 1995, KAPLAN & KENNEDY 1996, Plänerkalk Group was based mainly on fossil contents WALASZCZYK & WOOD 1999, WIESE & al. 2000). The (where present) and then on lithological characteristics reader is referred to Text-fig. 2a, which provides an (where visible) (ROEMER 1850; STROMBECK 1857, 1859). overview of the currently accepted zonal framework for This resulted in an incoherent mixture of lithostratigraphic the interval considered. and biostratigraphic terminology, and fossil names have been used (incorrectly) to designate mapped lithostrati- Sequential framework: Eustatoevents sensu ERNST & al. graphic units. However, many of these units have never 1983 been properly defined (notably the Lamarcki-Schichten, Scaphiten-Schichten, Schloenbachi-Schichten), and their ERNST & al. (1983) applied the term eustatoevent to supposed limits do not in any meaningful way correspond define a relative sea level fall and the succeeding trans- to the ranges of the eponymous taxa. This framework has gression. As they pointed out, a clear distinction between repeatedly been emended (e.g. STILLE 1904, SCHULTE 1937, rocks representing regression and rocks representing SEIBERTZ 1979, CLAUSEN 1984, SKUPIN 1985, FRIEG & al. transgression was not always possible due to the often 1989). In addition, there has been a continual mixing of dif- monotonous lithology of the Pläner Limestones. In addi- ferent lithostratigraphic terms established for the same tion to some lithological features (erosional surfaces, 642 FRANK WIESE, CHRISTOPHER J. WOOD & ULRICH KAPLAN

Fig. 2. A. Integrated stratigraphic framework for the Middle Turonian to Lower Coniacian of northwest Germany. Biostratigraphy compiled from the litera- ture (see text). Stable carbon isotopes after VOIGT & HILBRECHT (1997) and WIESE & KAPLAN (2001). Sequence stratigraphy: own field data. B. Interbasinal δ13C correlation of the potential Middle/Upper Turonian boundary interval between the Salder (LSB, data after VOIGT & HILBRECHT 1997), Lengerich (MCB, data after WIESE & KAPLAN 2001) and Dover (Anglo-Paris Basin, data after GALE 1996). Bentonites and the costellatus/plana Event/Caburn Sponge Bed aid interbasinal calibration of the boundary interval hardgrounds and hiatuses, glauconite occurrences, nodu- stratigraphie” – gap stratigraphy of ERNST & al. 1996). lar limestone, abrupt facies changes and fossil accumula- While the lateral relations of litho- and biofacies in the tions), fossils/fossil assemblages of mainly of oysters and Turonian of Lower Saxony have been elaborated in detail echinoids were used to indicate a regressive-transgressive in the past (ERNST & WOOD 1995, see also NIEBUHR & al. event. They also made the important observation that fos- 2001), it has always been problematic to evaluate the exact sil accumulations associated with sea level events have timing and duration of hiatuses and thus the stratigraphic potentially a diachronous character (see below). completeness in on-swell settings. The classic bioevents of Owing to its often monotonous lithology, shallow- the basinal areas (where ERNST & al. 1983 recognized ing/sequence boundaries in the Pläner limestones must most of their bioevents) change both lithologically and also be inferred from faunal development (e.g. Conulus faunistically (disappearance of biostratigraphically signifi- Facies: LÖSCHER 1912, ERNST & al. 1979, WIESE & cant taxa, occurrence of biostratigraphically insignificant KRÖGER 1998) and stratigraphic gaps (“Lücken- shallow water assemblages) towards swells (Text-fig. 3). EVENT STRATIGRAPHY 643

Fig. 3. Revised Middle to Upper Turonian facies framework in a swell-basin transect with event stratigraphic marker. Compiled after ERNST & WOOD

(1995) and NIEBUHR & al. (2000)

Fig. 4. Putative lithostratigraphic/sequence stratigraphic correlation from a basinal (Salzgitter-Salder) onto a pelagic swell (Hoppenstedt). Shaded correlation intervals: potentially not preserved; white correlation intervals: Potentially preserved. R: Rotpläner (Red coloured limestones). Black triangles: deepening and shallowing, respectively 644 FRANK WIESE, CHRISTOPHER J. WOOD & ULRICH KAPLAN

The resulting lack of stratigraphic control prevented, on brate faunas – during shallowing phases or in near-swell the one hand, a precise correlation with basinal sections settings (NEUWEILER & BOLLMANN 1991; ERNST & al. and an understanding of the sedimentary dynamics and, 1998, NEUMANN 1999). In the depositional system con- on the other hand, a prediction as to which parts of the sea sidered here, we observe a decrease in planktonic calcare- level cycle were potentially preserved on swells. ous bioproductivity (calcispheres) during transgression in The occurrence of bentonites within the Pläner context with marl-dominated intervals intercalated with Limestones succession enable the establishment of foraminiferal wackestone/mudstones. Relative sea level isochronous time lines, thereby permitting the under- trends can, consequently, be recognized (similar to the standing of lateral lithofacies relationships within small- case of siliciclastic systems) by coarsening-up and – if suf- scale lithofacies units. This then aids a tentative calibra- ficient accommodation space is available – thickening-up tion of the stacking patterns in basinal and swell areas, developments. Such depositional features are found dur- resulting in a conceptually dynamic interpretation of ing regression. In contrast, thinning-up sequences can potentially preserved – not preserved/not deposited parts occur both during transgression or, if accommodation of sedimentary sequences (Text-fig. 4) see also WIESE & space progressively decreases, during regression. The lat- al., this volume). A tentative correlation diagram between ter trend however, is always associated with the deve- the Upper Turonian of the Hoppenstedt section (HORNA lopment of griotte-like sediments (flasery undulating 1996) and Salzgitter-Salder (HORNA & WIESE 1997) limestones, marls with abundant lithoclasts) and is easily shows how individual sequences can either pinch out com- distinguishable from the first. pletely or be reduced to only tens of centimetres. The lateral facies relations and the facies successions Assuming the sequential interpretations presented here within the lithologic column and relations of litho- and to be correct, the lateral litho/biofacies diagram of ERNST biofacies were summarized and figured by ERNST & & WOOD (1995) needs some minor revision, since red and WOOD (1995, p. 47, text-fig. 1.4), revised by NIEBUHR & al. pink coloured limestones (Rotpläner) range stratigraphi- (2000, p. 104, text-fig. 36; here in part reproduced and cally well above the so-called Basal Upper Turonian emended in Text-fig. 3). In addition, biostratigraphic gaps Facies Turnover (see Text-figs3, 4), a sudden development were used to detect and correlate intervals of non-deposi- of a unit of white massive limestones, which has an excel- tion/erosion. However, sequence boundaries in the Pläner lent lithostratigraphic correlation potential within Lower Limestones are often impossible to detect as a definite Saxony and Saxony-Anhalt. surface. On the other hand, the maximum flooding inter- Owing – to some extent – the monotony of the litho- vals are not only well developed and readily identifiable, logy, the precise stratigraphic/lithostratigraphic position- but they can be used for can be used for intrabasinal cor- ing of sequence boundaries is sometimes difficult to reco- relation within north Germany and for the recognition of gnize, and our tentative interpretations given in Text-figs sequence numbers (genetic sequence model: GALLOWAY 3-4 are therefore open to discussion. Easier to recognize 1989; see also ERNST & al. 1996, WILMSEN 2003). than the sequence boundaries, and less open to question, In this paper, a transgression is expressed by the clas- are the maximum flooding intervals, which are mostly well sic Transgressive Systems Tract (TST); for maximum flood- developed and aid interbasinal correlation within north ing, the term “maximum flooding zone” (mfz) is used; and Germany (for more details see ERNST & al. 1996, progradational/shallowing sediments are termed regres- WILMSEN 2003). sive systems tracts (RST). Following the recommendation The lateral position of the Pläner Limestones within a by HANCOCK (2000), we favor the designation of sequences proximal/distal transect is located between the siliciclastic by names rather than by numbers. In total, four Upper and/or glauconitic near-shore successions in the vicinity of Turonian sedimentary sequences can be recogni- ancient massifs (Sudetic Islands, Bohemian Massif, zed, in ascending order Inoceramus perplexus Sequence I, Rhenish Massif; see ZIEGLER 1988) and the coccolithic Inoceramus perplexus Sequence II, un-named small bra- white chalk sediments (Schreibkreide) of the fully pelagic chiopod Sequence; Hyphantoceras Sequence. These settings (TRÖGER 2000). The Pläner limestones form a sequences reflect fluctuating but comparatively constant highly productive carbonate belt, where calcispheres in water depths, with the lowest sea level (estima- particular can occur in abundance (NEUWEILER & ted ca. 50 m to slightly above storm wave base) at the base BOLLMANN 1991, NEUMANN 1999, WILMSEN 2003). In the of the Hyphantoceras Sequence (see explanations below, context of relative sea level changes two main features can Text-figs 2a, 3). The succeeding Didymotis Sequence (not be observed: slight lateral facies migration and an abrupt considered here; Text-figs 2a, 3) marks the turnover breakdown in calcareous bioproductivity in association towards a major late Late Turonian transgressive pulse. with transgressions. Thus, the carbonate belt is most Judging from absolute time plotted against biostratigra- strongly developed (thickly bedded limestones, no marl phy, the investigated interval represents an approximate seams) – in association with peak occurrences of inverte- time of ca. 800 ky to 1 my (VOIGT 2000), resulting in EVENT STRATIGRAPHY 645 sequences between of a duration of ca. 250 ky. In this con- uppermost part of the event reflects renewed deepening text, the sequences observed here reflect high-frequency (Text-fig. 5). In the LSB (e.g. Salzgitter-Salder, sequences, which will, in the following parts, be briefly Flöteberg, Söhlde), the event is less distinctively devel- described. oped as a thin fossil bed and is difficult to discern with- in a thick limestone package. As a consequence, the Inoceramus perplexus Sequence I. This sequence, inflection point towards a renewed transgression (per- named after the inoceramid bivalve Inoceramus per- plexus II Sequence) falls into the c/p Event. In Lower plexus WHITFIELD, can best be demonstrated in the basi- Saxony, a clearly-defined sequence boundary (erosional nal setting of the Lengerich area of Westphalia (Hohne unconformity) cannot be recognized. The cryptic working quarry of Dyckerhoff cement work, see Text- sequence boundary is tentatively taken with the thin c/p fig. 5). Its mfz is characterized here by thinly laminated Event. Rare occurrences of tempestites at Lengerich and black marls, whereas in the LSB a marl/limestone and Hilter-Hankenberge (Westphalia) below the event sequence occurs in basinal sections (Salzgitter-Salder, (costellatus/plana calcarenite; NEUWEILER 1989, WIESE Flöteberg). The RST is associated with the main part of & KAPLAN 2001) suggest water depths at least tem- the costellatus/plana Event, an abundance peak of a rich porarily above storm wave base. invertebrate assemblage in an otherwise poorly fossilife- rous interval (see below). In Westphalia, it is developed Inoceramus perplexus Sequence II. In Westphalia, as the top of a well developed progradationally stacked excellent exposures in this sequence exist at Lengerich. In marl/limestone alternation, representing the RST. The Lower Saxony, the perplexus Sequence II is ideally exposed

Fig. 5. Detailed litho-log of the lower Upper Turonian of the Lengerich area (MCB), combined section abandoned Wicking II and Hohne working quarries. The costellatus/plana Event is well developed and shows clear lithologic and faunal changes during the regressive-transgressive inflection point (IP). RST: Regressive Systems Tract, HST: Highstand Systems Tract, mfz: maximum flooding zone, PSB: Parasequence Boundary. Black triangles indicate shallowing and deepening, respectively 646 FRANK WIESE, CHRISTOPHER J. WOOD & ULRICH KAPLAN in the Salgitter-Salder, Flöteberg and Söhlde sections; for is indicated by a Conulus Facies with Micraster ex gr. leskei localities see Text-fig. 1). As at Lengerich, the c/p Event DESMOULINS, large brachiopods [Cretirhynchia cuneiformis incorporates an inflection point towards progressive deep- (PETTITT)] and a low diverse hexactinellid sponge assem- ening, indicated by retrogradational stacking patterns. The blage, including Cystispongia bursa (QUENSTEDT) indica- mfz is represented by a well developed marl/limestone tive of comparatively shallow settings (WIESE & WOOD alternation which includes the costellatus/plana Marls and 2001). At Hoppenstedt, the terminating sequence bound- marl/limestone alternations some tens of cm above (ERNST ary is expressed by an erosion surface, overlain with major & WOOD 1995; Text-fig. 2a). Within the mfz, the bentonite hiatus by the mfz of the succeeding Hyphantoceras

TD (Text-fig. 3) is located. After some meters of aggrada- Sequence (Micraster Marls; see Text-fig. 3). This is likewise tionally stacked marl/limestone alternations, the RST the case at Söhlde (WOOD & ERNST 1997), where shallow- (massively bedded limestone) shows a progressive but ing in the calcisphere chalk facies is indica- weak increase in macrofauna (brachiopods, sponges) in ted by the progressive establishment of a weakly developed basinal settings, while shallower water and thus thinner, sponge/brachiopod fauna. Stable isotope curves show that more condensed sections are characterized by the so- this cryptic sequence boundary is associated with a massive called Conulus Facies (see discussion in ERNST & WOOD hiatus, comprising an interval from well below the 1995, p. 47, Text-fig. 1.4; WIESE & WOOD 2001). A clear Hyphantoceras Event to correlatives of the Micraster Marls, sequence boundary in the form of an erosional surface is i.e. the mfz of the succeeding Hyphantoceras Sequence not visible, and a possible boundary interval can only be (VOIGT & HILBRECHT 1997) As in the LSB, shallowing is estimated from faunal criteria (increase of macrofauna) indicated by an increase in faunal abundance and diversi- ca. 10 m below TE, where a fossil bed (Allocrio- ty, an increase in the development of limestones and by ceras/Orbirhynchia Event) occurs both in Westphalia and renewed occurrences of tempestites in the MCB. Lower Saxony. Time-equivalent sections in condensed swell settings are characterized by very nodular limestones Hyphantoceras Sequence. Originally introduced as the with abundant lithoclasts and partly red coloration. In rela- Hyphantoceras flexuosum Sequence by WIESE & KRÖGER tion to the basin position, the interval from the c/p Event (1998), we now refer to this sequence as the Hyphantoceras to the inferred level of the succeeding sequence boundary Sequence, as it comprises the main occurrence of the nos- is highly variable. In basinal areas, it reaches ca. 18 m toceratid ammonite genus Hyphantoceras in NW Germany. (Halle, Westphalia) to 20 m (Salzgitter-Salder, Lower In basinal areas, the Hyphantoceras Event, a peak occur- Saxony) and only a maximum of 0.5 on swells (Hoppen- rence of a diverse invertebrate fauna, shows a transgressive stedt) (compare Text-fig. 4). character, lithologically indicated by an overall fining-up trend. Progressive deepening is also shown by the succes- unnamed brachiopod Sequence. The sequence starts sion of ammonite morphotypes (KAPLAN 1991). In more some distance below TE presumably around the level of positive areas of the LSB and the SCB, the Hyphantoceras the Allocrioceras/Orbirhynchia Event (see above). The mfz Event is not developed (e. g. Söhlde, Hoppenstedt), and incorporates marl ME and MEchen and is specifically cha- the mfz (Micraster Marls) onlaps regional erosional uncon- racterized by an abundance peak of two irregular echi- formities, sealing an existing relief (see above). In proximal noids, Infulaster excentricus (WOODWARD) and Plesiocorys settings of the southwestern MCB, the upper sequence [formerly Sternotaxis] plana (MANTELL). Small rhyn- boundary of the Hyphantoceras Sequence is associated with chonellid and terebratulid brachiopods of uncertain sys- a large hiatus, overlain with a sharp boundary by a green- tematic status are very common particularly above ME in sand tongue (lowstand/regressive sediments of the suc- all localities exposing this interval irrespective of their posi- ceeding Didymotis Sequence) prograding from near-shore tion within the basin (e.g. Salzgitter-Salder, Flöteberg: settings close the Rhenish Massif into the MCB ("Untere basinal settings; Beuchte, Hoppenstedt: swell settings) and Werksteinbänke" of the Soest Greensand; see sections in have been used to name this sequence. The RST is indi- WRAY & al. 1995). In the Teutoburger Wald, in the north- cated by a progressive increase in macrofauna, especially eastern margin of the MCB, the Rothenfelde Greensand sponges and brachiopods. The terminating sequence (debris flows, turbidites) was shed contemporaneously boundary cannot be recognized in subsiding areas such as from the NE into the basin (ELBERT 1901, KAPLAN & BEST Salzgitter-Salder, although VOIGT & HILBRECHT (1997) 1984, KAPLAN 1994) representing distal tongues, analogous have suggested a sequence boundary based on microfacies to a Lowstand Fan in sequence stratigraphic terminology, changes. In accordance with the latter authors it is sug- but here shed from a swell (nordwestfälische -Lippische gested that the sequence boundary is located well below Schwelle; HAACK 1925) into an intra-shelf depression. the succeeding Hyphantoceras Event (see discussion In Lower Saxony, the terminating boundary is character- below). In more condensed/incomplete sections ized either by reworking, hardground development (e. g. (Hoppenstedt section; HORNA & WIESE 1997), shallowing Flöthe; WIESE & KRÖGER 1998) or by slumping possibly EVENT STRATIGRAPHY 647 associated with minor hiatuses (e.g. Salzgitter-Salder; ation is less clear. The c/p Event is only developed as a few WIESE 1999). cm thin abundance peak of the index taxa, and stacking patterns are not recognizable. However, with/above the Events (excluding tephro events) event, retrogradation starts, indicated by the progressive intercalation of marl seams terminating in the costella- In the original concept of ERNST & al. (1983), the eco- tus/plana Marls (mfz). events were characterized by a sudden and stratigraphical- Although the fauna of the event is well-known, little, ly short-termed abundance peak of fossils and/or the estab- however, is known of its possible lateral and vertical fau- lishment of a distinctive faunal assemblage. Some of these nal changes as a response to sea level changes or shifting events have received much attention in the past due to the environmental conditions. In Westphalia (Lengerich faunal abundance; moreover, their faunal developments area), the c/p event exhibits a clear faunal succession with- are well known and documented in the extensive lite- in a 280 cm interval (Text-fig. 5). After an abrupt increase rature (e.g. WOOD et al. 1984, DAHMER & ERNST 1986, in inoceramid abundance but with a low diversity, scaphi- KAPLAN 1992, METZDORF 1992, ERNST & WOOD 1995, tid and baculitid ammonites become frequent one metre WOOD & ERNST 1997, ERNST & al. 1998, WIESE & KAPLAN higher in the lower part of the main event. Only a short 2001, WILMSEN 2003). Ecoevents as understood here are distance above, allocrioceratid and collignoniceratid often not well-defined beds but reflect acme occurrences ammonites enter. Higher up-section, inoceramids are still of a distinct faunal assemblage. In most cases, these events very frequent; however, ammonites, become significantly begin rapidly (however without a sharply defined base) rarer. According to the model of TANABE (1979), the and end gradually. The concept of ecoevents applied by ammonite morphotype succession observed in the event ERNST & al. (1983) equates roughly with the proliferation shows shifting from a more distal to a more proximal epibole concept of BRETT & BAIRD (1997a) and the eco- fauna, indicative of a regressive development (see also logical diversification bioevent as introduced by SAGEMAN KAPLAN 1991, WIESE & KRÖGER 1998). No such succes- et al. (1997) for the Cenomanian/Turonian of the Western sions have been reported so far from the LSB, but this Interior of the USA. Beside ecoevents, ERNST & al. (1983) may be due either to sampling failure or to a weaker also distinguished lithoevents, of which only one with development of the event in the area. regional correlation potential will be considered (c/p Lateral facies variations within the c/p Event are diffi- Marls, see below). cult to evaluate. In condensed sections (e.g. Hoppenstedt), the tentatively identified stratigraphic costellatus/plana Event (c/p Event). The c/p Event equivalents of the c/p Event are located well above ben- marks an acme occurrence of Inoceramus perplexus and tonite TC2, here developed as griotte in Redpläner Facies. Plesiocorys plana together with a diverse ammonite assem- However, in this shallow water setting stratigraphic con- blage; it also marks the approximate FO of the Upper trol is poor, and correlation with other sections can only Turonian index ammonite Subprionocyclus neptuni be based on event bed correlation and assumptions (GEINITZ) (faunal details are given by KAPLAN 1992, derived from sedimentary geometry (see tentative corre- WOOD & ERNST 1998, KAPLAN & KENNEDY 1996, WIESE & lation between Salzgitter-Salder and Hoppenstedt in Text- KAPLAN 2001). As discussed elsewhere (WIESE & KAPLAN fig. 4). If this tentative lateral correlation should prove to 2001), a re-naming of the event in the light of inoceramid be correct, the Redpläner Facies extends – contrary to taxonomic advances (the eponymous Inoceramus costella- previous interpretations – as high as the lowermost Upper tus is a synonym of I. perplexus; see discussion in Tu ronian in Saxony-Anhalt. WALASZCZYK & WOOD 1999) as the perplexus/plana Event (e.g. NIEBUHR & al. 2000) appears – for the sake of cohe- costellatus/plana Marls. The c/p Marls are a lithomarker, rent stratigraphic nomenclature – unwise. distinctively developed only in Lower Saxony and the Little attention has been paid so far to the lithologi- eastern MCB, where limestone deposition clearly domi- cal/palaeontological development of the costellatus/plana nates over marl deposition. Two distinct marly beds in Event. In the MCB, the c/p Event – ca. 280 cm in thickness Lower Saxony and their correlatives in the MCB that can – is characterized by marl/limestone alternations exhibit- be correlated with confidence into any section with "nor- ing thickening-up development in the lower part but a mal accumulation rates" (e.g. Söhlde, Salzgitter-Salder, thinning-up trend in its upper parts. The inflection point Flöteberg, Kahnstein, Sack Syncline in Lower Saxony, is located in the main event body. Thus, the lower part of Halle and Oerlinghausen in Westphalia). Only few centi- the event appears to fall into the upper part of the RST of metres above, the bentonite TD is located, thus forming a the perplexus Sequence I, while the upper part may well good recognizable triple marl sequence. Lithologically, already be the transgressive part of the succeeding per- the c/p Marls develop rapidly but progressively from the plexus II Sequence (Text-fig. 5). In Lower Saxony the situ- top of the c/p Event by an increase of marls and a 648 FRANK WIESE, CHRISTOPHER J. WOOD & ULRICH KAPLAN decrease of bed thickness of the limestones, thus suggest- concerns mainly burial strategies and feeding efficiency ing retrogradation. The c/p Marls are interpreted to (GALE & SMITH 1982), which may suggests a better explo- reflect the lower part of the mfz of the perplexus II ration potential for food in basinal settings. Within this Sequence (see above). Consequently, only in very con- context it may be argued that it is not only the dominance densed sections are the marls missing (Hoppenstedt, of Infulaster itself, but also the almost exclusive absence of Woltwiesche). In contrast to other maximum flooding any other irregular echinoids which may provide a base zones (see discussion below), no distinctive fauna has for future discussion. been collected, although this may be due to collection failure, rather than an absence of fauna. In basinal parts Hyphantoceras Event. The Hyphantoceras Event is an of Westphalia, the c/p Marls are not developed because abundance peak of a diverse and abundant invertebrate the distal setting is in any case dominated by marl/lime- fauna. It can be correlated between N Germany and stone alternations England with some confidence, and comparable faunal assemblages are also known from Saxony (limestones of Orbirhynchia/Allocrioceras Event. A minor fossil event Weinböhla and Strehlen), Bohemia, Czech Republic occurs between the c/p marls and the Marl ME/Infulaster (WIESE & al. 2004) and Poland (TARKOWSKI 1991). Where acme, ca. 10 m below ME both in the MCB (Halle quarry; data exist, it is isotope stratigraphically positioned in the KAPLAN 1991) and Salzgitter-Salder (WOOD & al. 1984; uppermost part of a distinct positive δ13C peak (GALE Te xt-fig. 2). It is represented by a short interval only few 1996, VOIGT & HILBRECHT 1997; Peak +1 of WIESE 1999; cm in thickness with an increase of fauna, specifically Te xt-fig. 2b). Its faunal characters have been adequately inoceramids, Allocrioceras and Orbirhynchia. This event described in the literature, key references being DAHMER has not yet been investigated in detail. Sequence strati- & ERNST (1986), METZDORF (1992) and WOOD & ERNST graphically, it may be associated with the sequence (1997). In a sequence stratigraphic context, it is interpret- boundary between the perplexus II and the unnamed bra- ed to reflect a transgressive trend, indicated by the chiopod Sequence ammonite assemblage (see discussion in KAPLAN 1991). The event itself shows lateral differentiation of biofacies:

Marl ME/Infulaster acme. ME is considered to reflect with progressively shallower settings, ammonites become the mfz of the unnamed brachiopod Sequence. It has an rarer and brachiopods begin to dominate. This is also the overlapping character and can, in accordance with this case towards distal settings, where ammonite get less interpretation, be correlated in virtually all sections expos- abundant and diverse. In consequence, the main ing this interval in NW Germany, irrespective of the posi- Hyphantoceras Event represents a kind of biofacies belt tion within the swell/basin transect. Even at Hoppenstedt, changing in its faunal composition within a swell-basin the shallowest section exhibiting this interval, a thin marl transect considerably. It must be emphasized that, due to can tentatively be identified as ME based on the charac- the strong succeeding sea level fall and associated erosion, teristic small brachiopod assemblage that occurs in abun- the event is not preserved everywhere. For example, in dance in the immediately overlying limestones. In the swell settings localities like Söhlde (VOIGT & HILBRECHT MCB, the level represents the highest marl contents. 1997) and Hoppenstedt (HORNA 1996) the event falls

Previously, ME has only been regarded as a lithomarker. within a hiatus. However, in the marls and limestones immediately above and below, an abundance peak of the irregular echinoid Micraster Event (= Micraster Marls). The Micraster Infulaster excentricus together with Plesiocorys plana Event was first recognized by FÖRSTER (1876), mentioned occurs in the LSB (e. g. Salzgitter-Salder, Flöteberg) and by BESCHOREN (1927) and later used as a marker by parts of the MCB (Halle-Westfalen, Bielefeld-Senne). We BRÄUTIGAM (1962: Micraster-Schicht) or Micraster-Lage interpret the unique abundance peak of Infulaster as an (ERNST & al. 1979, KELLER 1982). From 1983 (ERNST & ecological response to changing environmental conditions al. 1983, Micraster Marl, MG) to 1984, in the spirit of the due to maximum flooding conditions. In the strongly sub- event stratigraphic concept, the Micraster Bed finally sident Lengerich area of the MCB, which represents the mutated to Micraster Ecoevent in the literature (WOOD & deepest part of the basin for the interval in question al. 1984). There is a repeated mixing of the terms (WIESE & KAPLAN 2001), Infulaster shows, accordingly, no Micraster Event and Micraster Marls. In sections like short-term, event-like occurrence but is fairly common Salzgitter-Salder, Flöteberg or Nettlingen, Micraster throughout the entire interval from the perplexus I occurs in fact in a distinct marl. In sections of the north- Sequence to the Hyphantoceras Sequence. The reason for eastern MCB, the event is characterized by a succession of the abundance of Infulaster remains open to discussion. It marl seams and thin limestone beds (comp. Text-fig. 6), lived presumably infaunal with the apex below/just above and Micraster occurs scattered throughout this entire the sediment surface and its morphological specialisation interval. Thus, the term Micraster Marls is favoured here. EVENT STRATIGRAPHY 649 1996). Shaded box: RÖGER 1996, K ÜLLER -M ÖRDENS 1996, J ÖTTCHER Marls Micraster Sequence between the MCB and LSB. Quantitative microfaunal data (in %: orking Group (B . M.: W M foraminifera and non-keeled/keeled ratio show minor fluctuations, specifically clacisphere Didymotis RNST Sequence); Hyphantoceras Sequence and the TST of succeeding Hyphantoceras approximate extension of the mfz ( Marls), the RST of Micraster Calcispheres, bulk foraminifera, non-keeled/keeld ratio, plankton) are plotted against the lithological column. While E abundance shows a strong relation to relative sea level fluctuation; data compiled from diploma thesises of the former Fig. 6. Correlation of the mfz ( 650 FRANK WIESE, CHRISTOPHER J. WOOD & ULRICH KAPLAN

The Micraster Marls represent a mfz with – as in the case tonites can be correlated between north Germany and of ME – a clear overlapping character. As can be seen England with great confidence (WRAY 1999; see also dis- from Text-fig. 6, the relative increase in the marl content cussion in this volume) and correlation with French vol- may be in part the response of the biosedimentary system canogenic marl seams is possible (DECONINCK & al. 1991; to a transgressive pulse, expressed by a significant decrease VANDERAVEROET & al. 2000). As bentonites are strictly in calcispheres and thus calcareous bioproductivity. isochronous markers, their value for calibrating the bio- Palaeontologically, the Micraster Marls mark a first events and evaluating possible diachronous developments abundance peak of the M. ex gr. precursor/normanniae lin- in the sequence stratigraphic development is of outstand- eage together with large Plesiocorys ex gr. plana/placenta. ing relevance (see below). Preservation of bentonites in It represents a new branch of Micraster – in the literature particular is controlled by subsidence versus relative sea often referred to as "modern" or "advanced" forms – that level: they are best and most thickly developed in subsid- succeeds the "primitive" group of M. leskei/borchardi. Seen ing, basinal areas and tend to be eroded after deposition in an interbasinal context (Germany, England/France, in shallower settings. High sea level and sufficient accom- Spain), the turnover towards the new Micraster occurs – modation space also favour the preservation of ben- where well dated – isochronously in both Boreal chalk and tonites. In this context is becomes clear that the best Pläner limestones as well as in temperate ramp settings preservation potential of bentonites occurs during late (WIESE 1999). In Lower Saxony and Saxony-Anhalt, it is transgression (TST) or maximum flooding (mfz). As a associated with the mfz of the Hyphantoceras Sequence in result, all of the (Middle and Upper) Turonian bentonites more basinal settings. In sections representing presum- identified so far fall into such a setting. However, in view ably deepest settings (Lengerich area of Westphalia), M. of the fact that evidence for volcanic activity without any ex gr. precursor/normanniae is absent. It is noteworthy that well defined bentonites may be derived from magnetic

– as in the case of ME/Infulaster Acme – again a mfz is minerals, as shown by HAMBACH (1987) for the Lower characterized by a specific irregular echinoid assemblage. Turonian, it may also be worth considering whether or not the bentonites identified in the European Turonian really Heteromorph Beds. The Heteromorph Beds (HORNA represent the total number of ash falls. & WIESE 1997) form a second, albeit brief and poorly dif- ferentiated peak occurrence of heteromorph ammonites of the genus Hyphantoceras (H. ernsti WIESE) together DIACHRONEITY VERSUS ISOCHRONEITY with scaphitids, baculitids and Subprionocyclus cf. bran- neri (ANDERSON). This event is much more weakly devel- As shown above, ecoevents and several lithomarkers oped than the Hyphantoceras Event both with respect to (the mfz) show a clear relation to sea level. Considering the faunal abundance and diversity. It is situated well above theoretical background of the sequence stratigraphic the Micraster Marls and represents the RST of the model, at least some of the markers may potentially be Hyphantoceras Sequence. There is only limited know- diachronous. The bentonites, in combination with the ledge regarding its potential for regional correlation, but peaks of the carbon isotope curves, provide unequivocal it is known from several localities in the SCB isochronous time-lines that permit an estimation of a possi- (Hoppenstedt), the LSB (Größ-Flöthe: well developed, ble diachroneity. Taking the lower Upper Turonian as an Nettlingen, Dorstadt; WIESE & KRÖGER 1998) and the example, it can be shown by the relationship between the

MCB (Halle). Although WIESE (1999) suggested a hiatus bentonite TD and isotope peak Peak-1 that the c/p Event is in this interval based on an interbasinal δ13C correlation virtually isochronous in a geological sense. The Caburn at Salzgitter-Salder, an ammonite-rich layer with scaphi- Sponge Bed of southern England (APB) can also be tids, baculitids and H. ernsti was found in the correct unequivocally correlated with the c/p Event using this stratigraphic position (Bed MK 15, comp WOOD & method (WIESE & KAPLAN 2001). A comparable good ERNST 1997, p. 96, text-fig. 55), expanding the range of interbasinal calibration of ecoevents such as the the event also into distal settings. Hyphantoceras Event also appears to be possible (VOIGT & HILBRECHT 1997). Of particular interest is the position of the maximum flooding zones, as they show also compara- Tephroevents tively constant stratigraphic positions within the integrated stratigraphic column. The entire integrated event frame- Bentonites are well known from northern Germany work is thus demonstrably broadly isochronous in a geo- since DORN & BRÄUTIGAM (1959) and treated partly in logical sense and any possible diachroneity, which may the- great detail (BRÄUTIGAM 1962, ERNST & al. 1979, ERNST oretically be inferred from sedimentological assumptions, is & al. 1983, WRAY & al. 1995, WRAY & WOOD 2002; see below the level of stratigraphic resolution (see summary in also this volume). At the moment, five Turonian ben- ERNST & al. 1996). Stable isotope correlation, furthermore, EVENT STRATIGRAPHY 651 suggest that the mfz of the Micraster Marls is located in for any further palaeontological (e. g. palaeoecological/ comparable stratigraphic positions in both northern Spain palaeobiogeographic) investigation also in an interbasinal and Bohemia (WIESE 1999, WIESE & al. 2004), suggesting a context (ERNST & al. 1996, KÜCHLER 1998). true eustatic nature for the observed sea level change. But what are the reasons for the alternations of frus- trating thick fossil-barren intervals and short-term fossil abundance peaks? ERNST & al. (1996) and WILMSEN DISCUSSION (2003; with detailed discussion) demonstrated a relation- ship between ecoevents and relative sea level cycles for Going back to MARX's approach "the being determines the Cenomanian of the LSB and the SCB. They observed consciousness", it may well be argued that the specific litho- clustering of events at the base of a sequence in a trans- logical/palaeontological characteristics of the Pläner gressive setting (onlapping bioevent), at the mfz (maxi- Limestones resulted inevitably in a particular view of the mum flooding bioevent of WILMSEN 2003) and at the top successions: the occurrence of (highly) fossiliferous beds of the RST (Late Highstand Bioevent of WILMSEN 2003). or thin intervals intercalating with fossil-depleted rocks in In the case of the Upper Turonian, the Hyphantoceras an otherwise monotonous sedimentary setting almost Event and possibly parts of the Heteromorph Beds may without macroscopic features of necessity shifted attention reflect onlapping events in a transgressive setting; the to the fossiliferous strata. For stratigraphers to realize that complex Marl ME/Infulaster acme and the Micraster these fossil beds can be recognized in neighbouring sec- Marls can be shown to represent maximum flooding bio- tions must have resulted in the insight that these beds events; and the c/p Event occurs in the upper part of the might be of value for regional correlation in an otherwise RST (or late Highstand Systems Tract in traditional ter- poorly differentiated succession. It can be argued that the minology). Judging from the literature, the formation of geological setting created a specific consciousness that shell-beds or shell accumulations are conventionally inevitably resulted in event stratigraphic thinking. interpreted to be triggered by physical parameters: water Although event stratigraphy is well-established and turbulence results in a variety of taphonomic processes applied virtually in all settings and all systems (e.g. in the (e. g. corrosion, erosion, winnowing, relative enrichment, Devonian; WALLISER 1996; see also BRETT & BAIRED current-induced accumulations, time-averaging, imbrica- 1997b for further data) the high resolution subdivision of a tion, amalgamation), and fossil beds are explained main- Mesozoic lithogroup by genetically different short-termed ly to be result of these processes (e.g. BANERJEE & events of quasi-isochronous character within an integrated KIDWELL 1991, FÜRSICH & OSCHMANN 1993, DI CELMA stratigraphic framework is specifically advanced in north- & al. 2002). However, none of the Turonian ecoevents ern Germany, and – to some extent – also in the discussed above shows any significant sedimentological Cenomanian/Turonian of the Western Interior Seaway of characteristics indicative of short-term shedding and win- the USA (KAUFFMAN & HART 1996, SAGEMAN & al. 1997). nowing-derived accumulations (see discussion in BRETT This event stratigraphic concept and its application to the & BAIRD 1997a). Although slight winnowing and some Cretaceous in north Germany, has advanced regional current induced enrichment of shell debris cannot be stratigraphic resolution considerably. Using stratigraphic excluded, the faunal development and the entry of entire- markers of different disciplines (lithostratigraphy, ly new faunal assemblages point at other factors than sim- sequence stratigraphy, stable isotope stratigraphy, event ple enrichment due to physical parameters. Microfacies stratigraphy including tephro events and bioevents), a analyses of the Pläner Limestones show that the macro- closely-spaced succession of isochronous or near-isochro- fossil debris is mainly floating within the matrix (calci- nous markers has been established. From the base of the sphere/foraminiferal wackestones, bioclastics wacke- Upper Turonian to the base of the so-called Grey and stones), and faunal abundance never reaches that of clas- White Alternation (basal part of the upper Upper sic coquinas or Fossillagerstätten. In addition, the base Turonian), 12 markers (four bentonite layers, three detri- and top of the beds show always gradational contacts, and tal marls and five bioevents) plus five δ13C time-lines with the development of the events reflects a progressive varying relevance for interregional but invariably good increase in fauna, as ideally developed in the case of the potential for regional correlation are recognized (Text-fig. costellatus/plana Event at Lengerich (MCB; Text-fig. 5). 2). Given a very rough estimate of ca. 750 – 800 ky for the In addition, the development of the events is not only lower part of the Upper Turonian (based on an approxi- accompanied by a faunal increase in terms of abundance mate duration of 1.5 my for the late Turonian; GRADSTEIN but also by a diversity increase or significant faunal & al. 1995, VOIGT 2000), a relative resolution between 50 change compared to the underlying strata. This trend is and 100 ky appears to be possible in some intervals. This associated with a shallowing pulse, while the contrary situ- resolution is not attainable by means of conventional ation (faunal and abundance decrease) occurs during stratigraphic methods alone, and it provides a good basis transgression. Thus, the development of bioevents and 652 FRANK WIESE, CHRISTOPHER J. WOOD & ULRICH KAPLAN the establishment of distinct faunas show a relationship were generated by in situ planktonic bioproductivity. to sea level. Strong lateral differentiation of biofacies is Consequently, the explanation of ecoevents in the well known from the Turonian, suggesting, at first sight, a Pläner Limestones may be found by more detailed highly sensitive relationship between bathymetry and palaeoecologic understanding of the depositional sys- faunal characteristics. However, the relationship to tem and the complex interaction of planktonic versus bathymetry can at best be a passive one, as already dis- benthic biotic developments. cussed for trace fossil assemblages (FREY & al. 1990). In extant shelf seas with normal aerobic conditions, faunal abundance and faunal compositions are controlled pri- CONCLUSION AND PERSPECTIVES marily by food availability (ROSENBERG 1995), which – from an actualistic point of view – is also a reasonable In 20 years of event stratigraphy in N Germany, a assumption for the Pläner Limestone seas. Thus, the stratigraphic framework has been established that pro- alternation of ecoevents with macrofossil-barren inter- vides an excellent framework of isochronous events, vals may – excluding taphonomic implications – be reaching in parts a time resolution around 100 ky. Most of explained by food web responses to trophic changes these events show a clear relation to sea level fluctuations, (WILMSEN 2003, WIESE & al. 2004). either by faunal responses to deepening or shallowing As bioproductivity of the main planktic carbonate and related environmental changes or, as in the case of constituents in Boreal pelagic systems (e.g. coccoli- bentonites, by variations in their preservation potential. thophorids, calcispheres) is controlled mainly by nutri- As the stratigraphic framework is now well established ent supply, relative water depth and temperature and works extremely well even in an interbasinal context, (BRAND 1994, ZÜGEL 1994, ROTH 1994, ZONNEVELD & investigation of the biosedimentary system of the Pläner al. 1999, GALE & al. 2000, PRAUSS 2000, VINK & al. Limestone touches increasingly on palaeoecological ques- 2002, WENDLER & al. 2002), quantitative compositional tions in an attempt to decipher at least parts of the feed- changes may indicate shifting environmental conditions. back systems between fauna and environmental changes. Recently, WENDLER & al. (2002) suggested trophic Still inexplicable are the dramatic changes from highly changes – from oligotrophic to eutrophic – as a possible fossiliferous beds to (typically) thick barren intervals with triggering mechanism for the alternation of calcisphere- apparently identical litho- and taphofacies. As diversity rich calcareous beds and calcisphere-poor marls in and composition of recent faunas are controlled mainly by Cenomanian marl/limestone cycles of NW Germany food availability, more work needs to be done to resolve and France. This has also been also confirmed by the trophic conditions and their changes within the Pläner WILMSEN (2003) for the Cenomanian of NW Germany. Limestone Facies. It is important to accept that the plank- However, in other areas (e.g. Bohemia; WIESE & al. tonic calcareous bioproductivity is difficult to interpret by 2004), calcisphere packstones and, thus, abundance means of trophic conditions if there is no control on pos- peaks of calcispheres, are associated with faunas of low sible benthic feedback as observed in modern day seas. If diversity and abundance, which are suggested to reflect we interpret calcisphere abundance to reflect eutrophic or rather oligotrophic instead of mesotrophic or even mesotrophic conditions, why is benthos abundance and eutrophic conditions. As shown by quantitative analyses diversity so low during Turonian times? Clearly, in order of calcisphere and foraminiferal content (counting in to understand the biodynamics better, we need to consid- thin-sections; planktonic vs. benthic, keeled-non-keeled er data from both surface primary producers and from ratio) in several diploma theses of the former working those organisms dependent on them. Consequently, a syn- group of Gundolf Ernst (BÖTTCHER 1996, JÖRDENS- thesis of environmental changes, planktonic calcareous MÜLLER 1996, KRÖGER 1996), foraminifera and espe- productivity and benthic microfaunal and macrofaunal cially calcispheres appear to show a sensitive response responses in context with a reconstruction of the Corg flux to relative sea level fluctuation (Text-fig. 6), even needs to be established for a better understanding of bio- though the available data set is still comparatively events in the Pläner Limestones. crude. In particular, the interbasinal observable and repeated breakdown in calcisphere bioproductivity in the context of maximum flooding events and a recovery Acknowledgments during shallowing (Text-fig. 6), strongly suggests a rela- tionship of some kind between nutrient fluxes in surface We kindly thank the cement works Dyckerhoff (Lengerich, waters and sea level fluctuations. This also suggests that Westphalia), Loges and Dammann (both Söhlde, Lower Saxony) lithological and specifically macrofaunal characteristics for working permission in their quarries. We further thank M. must be seen in the entire context of the biosedimenta- WILMSEN (Würzburg) and K.-A. TRÖGER (Freiberg), the journal ry system, the main carbonate constituents of which referees, for their keen reviews of the manuscript. EVENT STRATIGRAPHY 653

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Manuscript submitted: 10th December 2003 Revised version accepted: 20th August 2004