Orbital forcing in a ‘Boreal’ Cretaceous epeiric sea: high-resolution analysis of core and logging data (Upper Albian of the Kirchrode I drill core — Lower Saxony basin, NW Germany)

Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

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Orbital forcing in a `Boreal' Cretaceous epeiric sea: high-resolution analysis of core and logging data (Upper Albian of the Kirchrode I drill core Ð Lower Saxony basin, NW Germany) Andreas Prokoph a,*, JuÈrgen Thurow b,1 b

a Department of Geology, University of Ottawa, PO Box 450, Station A, Ottawa, ON, Canada K1N 6N5 Department of Geological Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom

Received 10 September 1996; Revised 14 August 1997; Accepted for publication 17 September 2000

Abstract A 245 m (0±245 m subsurface) core of Upper Albian marine sediments from North Germany (research well Kirchrode I) was studied to identify sequences and cycles of sedimentation and related forcing mechanisms on sedimentation in an epeiric sea of the (sub)-`Boreal' realm. The core consists of monotonous gray marls with an exceptionally high sedimentation rate of 8± 12 cm ka 21. In total, it represents a period of approximately 2.5±4 Ma. A silty glauconite-rich condensed layer marks a change in the succession at 132 m and is paralleled by the ®rst occurrence of E. turriseiffelii and G. bentonensis. The lower part of the core shows lenticular bedding, siderite nodules, average CaCO3 content of ca. 40% and an abundance of inoceramids (Inoceramus anglicus, Birostrina lissa, Actinoceramus sulcatus). The upper part is characterised by plane bedding, common siderite layers, an average CaCO3 content of ca. 35% and an abundance of aucellinas (Aucellina gryphaeoides). According to lithology and ichnofacies, the succession represents a transgressive±regressive cycle with distinct bimodality of lithology, fossil, and trace fossil content together with reworking and redeposition at the base and top. We studied well-log-data, sediment composition, sediment color, and carbonate content and applied various mathematical analysis techniques to these data (principal component analysis, spectral analysis (Fourier-transform), autocorrelation). Spectral analysis revealed well-pronounced periodic cyclicity in the upper part of the Upper Albian (12, 8, 4.5, 3.4, 1.7 m). The 12 m-eccentricity cycles are the most intense cycles re¯ecting periodic changes in the terrigenous clastic supply. Chaotic transitional intervals occur around the Middle±Upper Albian, Upper Albian and topmost Albian parts of the core. They are characterised by non-cyclic changes in litho- and biofacies. Mathematically, these changes correspond to singularity points. They are preceded by non-orbital high-frequency variations in carbonate content and in g -ray. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Cretaceous; Cycles; Time-series analysis; Sedimentology; Quantitative stratigraphy; Lower Saxony basin

1. Introduction * Corresponding author. Tel.: 11-613-562-5800 (ext 6799); fax: 11-613-562-5192. E-mail addresses: [email protected] (A. Prokoph), [email protected] (J. Thurow). 1 Fax: 144-207-388-7614.

The Late Albian is characterised by a global high sea level stand, comprising several second and third order cycles (Haq et al., 1988). During the Cretaceous the sea level rose up to 300 m above the present sea level, resulting in large-scale ¯ooding of shelves and

0031-0182/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0031-018 2(01)00287-5

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A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

Fig. 1. Late Albian palaeogeography around the Lower Saxony basin. The location of the Kirchrode I drill hole is marked by an arrow and the letter `K' (modi®ed after Ziegler, 1982).

intracratonic areas. The mid-Cretaceous Lower Saxony basin was then part of a large epicontinental basin (Fig. 1) extending from England far into Russia (Diener, 1966; Naidin, 1981; Ziegler, 1982; Betz et al., 1986). As a consequence of maximum ¯ooding and the formation of vast epeiric seas special lithologies (e.g. the chalk of Northern Europe) which are virtually unknown in modern environments were formed. Comparable geological conditions have never been realised in geological history since, thus actualistic models for depositional processes in such environments are not valid. It has been known for about a hundred years that mid-Cretaceous sequences show well-pronounced cyclic deposition (Gilbert, 1895), probably related to orbital forcing within the Milankovitch frequency band (Schwarzacher and Fischer, 1982; Research of Cretaceous cycles (ROCC-) group, 1986; Park and Oglesby, 1991; Erba and Premoli-Silva, 1994). Milankovitch cycles of Cretaceous orbital eccentricity (400, 115 and 92 ka), obliquity (approximately 43 ka) and precession (23 and 18.5 ka) (Berger and Loutre, 1989) were recognised as important controlling parameters of pelagic sedimentation, particularly in the Tethyan realm (Herbert and Fischer, 1986; Fischer et al., 1991). In particular the cyclicity of the Upper Albian sediments in the Piobicco-core (Marche, Italy) shows well-preserved bundling of layers within the Milankovitch band (Premoli-Silva et al., 1989). Previous investigations in the `Boreal' realm pioneered by Schneider (1964) have demonstrated

rhythmic bedding in early Lower Cretaceous sediments, but without statistical evidence of climatic control. Based on the distribution and faunal assemblages of foraminifera and ostracods in the midCretaceous of northern Germany, Kemper (1987) provided some evidence for climatic changes. Detailed research on chalk sedimentation patterns in England proved that sedimentation in epicontinental seas was in particular sensitive to orbital/climatic forcing down to millennia scale (Gale, 1989). The latter author counted and correlated bedding couplets to introduce a Milankovitch Time Scale for the Cenomanian chalk in the Anglo±Paris basin. This paper contributes to studies of the interdisciplinary `Boreal' Cretaceous Cycles Group (B.C.C.P.) on the signi®cance and effect of sea level change on depositional patterns and sediment and faunal composition in the Lower Saxony basin. For several reasons, the Lower Cretaceous in general and the Albian of northern Germany in particular are highly supportive towards global correlation attempts of marine strata: (a) sediments have not been strongly in¯uenced by tectonic processes, (b) sedimentation rates during the Lower Cretaceous were high, (c) sediments show no evidence for major erosional events during the Late Albian, and (d) strata can easily be cored by shallow drilling due to the tectonic inversion of the Lower Saxony basin during the Late Cretaceous. Therefore a research core was drilled in the outskirts of Hannover (Kirchrode I, Fig. 2). The drill-site was chosen in a `hemipelagic' setting where high sedimentation rates and a record as continuous as possible could be expected (subsiding basin west of the Lehrte± Sehnde diapir; Fenner, 2001a). A detailed high resolution core and sediment description was published by Prokoph (1994). Well and core were analysed with sedimentological, geophysical, geochemical, and palaeontological methods by members of the B.C.C.P-Group (B.C.C.P.-Group, 1994). This paper summarises the results of sedimentological studies (semi-quantitative core description, thin sections, trace fossils), well-log and sediment color interpretation, and statistical evaluation of the multiple sediment parameters. 2. Methods and data Sedimentological studies are based on a continuous,

A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

69

Fig. 2. Lithology and biostratigraphy of the Kirchrode I core (biostratigraphy after Cepek, 2001; Wiedmann and Owen, 2001).

semi-quantitative lithological description of the split core, namely rock-color (MUNSELL-Rock Color Chart), trace fossils, and lithological features (Fig. 3). In addition 24 thin sections were studied and point-counted for their composition and structures. The entire dataset is published elsewhere (Prokoph, 1994). In addition geophysical logs from 13 tools, grayscale camera scanning, and 488 spatially equidistant (50 cm) CaCO3 analysis (Jendrzejewski, 1996; Jendrzejewski et al., 2001) form the database for further interpretations.

2.1. Core description Lithological changes were subsequently quanti®ed with separately classi®ed lithological parameters following a method which was used by GroÈtsch (1994) to characterise reef-guilds. The data consist of 14 lithological parameters (Table 1) compiled in 10 cm spacing which have been continuously recorded down-core. The Rock Color Chart (The Geological Society of America, 1991) with genuine Munsell color chips has been used for rock color

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A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

Fig. 3. Results of semi-quantitative analysis of 14 lithological features. Stippled lines mark synchronous strong variations in several parameters.

1 Grain size (visual estimate)

3 Grayscale

4 Color (MUNSELL-CHART)

5 Color enhancement (MUNSELL-CHART)

6 Bivalves (visual estimate)

2 Carbonate content (10% HClreaction) 1 Ð No carbonate 2 Ð Marly clay 3 Ð Clayey marl 4 Ð Marl 7 Plant debris (visual estimate)

8 Glauconite (visual estimate)

9 Pyrite (visual estimate)

1 Ð Barren 2 Ð Rare 3 Ð Common

1 Ð Barren 2 Ð Fare 3 Ð Common

1 Ð Barren 2 Ð Few 3 Ð Abundant

1 Ð Barren 2 Ð Rare 3 Ð Common

4 Ð Abundant 5 Ð Lag

4 Ð Abundant

11 Cementation (estimated)

12 Siderite layers (layers/d 10 cm)

10 Bioturbation intensity (visual estimate) 0 Ð No bioturbation 1 Ð Sinusites only 2 Ð Sinusites and Chondrites only 3 Ð Distinct/low intensity 4 Ð Distinct/high intensity 5 Ð Mottled

1 2 3 4 5

0±20

1 Ð Clay 2 Ð Silt 3 Ð Sand

Ð Ð Ð Ð Ð

Low Low-medium Medium Medium/lithi®ed Lithi®ed

4 Ð Abundant 13 Concretions (estimated number/10 cm) 0±10

14 Strati®cation 1 2 3 4

Ð Ð Ð Ð

Planar Undulated Lenticular Homogenuous

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Table 1 Digitised and classi®ed descriptive lithological parameter

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classi®cation. This chart is referred as MUNSELLchart in the following text. 2.2. Logging The borehole was logged by British Plasterboard applying 13 geophysical tools, including three different g -ray tools and spectral tools (Fig. 4). The resolution for the logs was set at 1 data point/10 cm. The logged section covers the depth from 8.3 to 235 m continuously. Some of the logs, e.g. both resistivitylogs, g -ray-logs, and the acoustic-log produced reliable data only below 12 m. Data are enclosed in Tables 8 and 9 (in the background dataset, see http://www.elsevier.com/locate/palaeo). 2.3. Camera-scanning In addition to color determination (MUNSELLRock Color Chart), we digitised the core with a camera scanning system. This method (Schaaf and Thurow, 1994) allows the discrimination of 256 grayscales. Of the continuous scans we used 1 measurement every 10 cm resulting in a time-series with a resolution comparable to the logging data. Artefacts and diagenetic features in the sedimentary sequence, i.e. concretions, cracks, voids, have been eliminated from the time-series. Intervals with no core recovery (,1% of the entire core) have been linearly interpolated. 2.4. Data processing The study of temporal variations of geochemical, geophysical and lithological parameters involved statistical methods. The type of methods applied were modi®ed depending on sample-spacing, accuracy of measurements, correlation between sets of parameters, and the geological signi®cance of the studied parameter/set of parameters. Most calculations have been performed with the software package SPSS for PC. The datasets obtained from the lithological parameters have been transformed to an equidistant sampling space (10 cm) by linear interpolation to meet the requirements for SPSS. Linear interpolation is reliable, as the variance of sedimentary changes have only been reduced in 10 cm intervals

at strata-boundaries. These interpolated intervals contain less than 5% of the total data set. The sampling space corresponds to the observed maximum depth of bioturbation and exceeds the average core displacement (core catcher, core loss) of 8 cm m 21. The data have been combined with independent factor sets using Principal Components Analysis (PCA, Davis, 1986). Their interpretation allows the combined study and interpretation of groups of lithological parameters. The resulting components are linearly independent, i.e. they do not show any correlation. We used this method because the ¯uctuations of each single parameter were too low for separate interpretation, otherwise errors in single parameters may sometimes have a signi®cant in¯uence. The time series of the components are calculated by adding the weighted raw data. The factor loading represents the relative in¯uence of each parameter in each component. Therefore, high negative loadings (, 2 0.5) indicate negative correlation with the component, high positive loadings (.0.5) and moderate loadings (20.5 to 0.5) characterise no correlation (in¯uence) for the component. With the PCA-method relations between parameters are recognised and can be used for the description of the depositional system. The order of the processing function used for multiple datasets of core descriptions and logging was modi®ed after methods described by Davis (1986) and applied by Tornaghi et al. (1989). 1. Optional: calculation of the correlation of the variables to reduce self-correlating variables (trivial relations, circular reasoning) in the PCA. 2. Optional: by applying PCA the data matrix of the original sedimentary parameters is transformed by rotation into components re¯ecting linear variability. All original parameters in the matrix are therefore given the same weight by standardisation to a mean of 0 and to a standard deviation of 1. Thus, the original spread of quanti®ed parameters is not important. 3. Smoothing of the data with moving average window-®lters (Davis, 1986), reducing the white noise (window covers 5 £ the sampling interval). 4. Reducing superimposed trends by estimating the gradients between the sampling intervals

A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

Fig. 4. Geophysical borehole measurements of the Kirchrode I borehole.

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(as a low-bandpass ®lter), which enhances stationarities and high frequencies (Davis, 1986). 5. Subdivision (zonation) of the ®ltered data at locations where discontinuities divide two units with different trends above and below. 6. Identi®cation of systems with no abrupt changes in sedimentation pattern and periodic-cyclic ¯uctuations (stable system), unstable (chaotic) systems with nonperiodic-cyclic changes, and chaotic transitions (short intervals between systems, characterised by highly intensive abrupt changes). De®nitions of chaotic and stable systems are taken from the `thermodynamics of open systems' (Nicolis and Prigogine, 1977). 7. Fourier-transform (after Davis, 1986) of the individual intervals (see 5) by computing the periodogram of the power spectrum. The power spectra are displayed as perioddependent (period ˆ wavelength) because one can directly approach the length/thickness of the individual cycles in such displays. We repeated the procedure for different systems and subdivided them until a minimum of 80 data points was reached. However, only stable systems with more than 400 data points ( ˆ 40 m) were reliable for signi®cant analysis. This improves the con®dence level of `chaos' or `stability' and the identi®cation of singularities and boundaries between systems but reduces the time interval for each individual system. The data can be found in Tables 8 and 9 in the background dataset. 2 3. Lithology, trace fossils, and principal component analysis 3.1. Core description and lithological subdivision The 245 m core comprises clayey marls and marls with a dip of 7±108. They are unconformably capped by 1.5 m of Pleistocene boulder clays and Holocene soils. The sequence shows disturbance at about 32, 65, 106 and 137 m, and below 242 m, characterised by high angle dipping faults lined with pyrite or gypsum. The sediments are dominated by dark gray marls. According to thin section analysis, the clay±carbonate 2

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matrix (the latter coccolithophorids) shows varying contents of quartz silt (1±8%), bioclasts (1±10%), microfauna (1±10%), and rare glauconite, pyrite and mica (Table 2). Below 132 m the marls are gray± green colored with well-pronounced ichnofabric dominated by Teichichnus, Chondrites and Thalassinoides (Plate 1.3). Many P±Fe±Mn-carbonate nodules and layers of redeposited inoceramid prisms (Fig. 2) are present. Above 132 m the sediment is gray to dark gray clayey marl with condensed horizons of aucellinas, low intensity bioturbation and bundled layers of yellowish P±Fe±Mn-carbonate (`siderite') concretions (Plate 1.4). Distinct lithologies include redeposited sediments below 205 m and above 28 m. Among them are layers with evidence for bottom currents and transport (imbrication of inoceramid prisms, grading), concentration of redeposited bivalve shells below 205 m (Plate 1.7), a horizon strongly enriched in algal fragments at 27.55 m (Plate 1.2), and green marls with transported and condensed phosphorites and microfossils at 12.3 and 7.25 m (Plate 1.1). Throughout the sequence there are intervals rich in macrofossils (bivalve-maxima) with aucellinas (A. gryphaeoides), inoceramids (I. anglicus, B. lissa, A. sulcatus) and belemnites (Neohibolites minimus). Various sideritereplaced molluscs (ammonites, belemnites), ®sh remains and glauconite are concentrated in a paleyellowish±grayish horizon (silty marls) at 132 m (Fig. 5, Plate 1.5). The sequence can be subdivided into 9 lithologic units. The subdivision is based on (Table 3): carbonate content, minor variations in grain size and color; condensed horizons with enrichments of macrofossils; intervals with redeposited sediments; relative abundance of siderite concretions; and changes in intensity of bioturbation. Unit 1 (245±233.5 m) is characterised by alternations of intensively bioturbated silty marl and dark, clayey marls. Colors vary between dark gray (5Y3/1) and olive gray (5GY4/1). Condensations of bivalve fragments, especially A. sulcatus (B. sulcata), and concretions of siderite and pyrite are rare to abundant. Intervals with redeposited sediments increase towards the top of the unit. The characteristics of these horizons are redeposited inoceramids and belemnites, gradual changes in the grain size Ð from silty marls to dark gray clayey marls (slightly bioturbated)

Depth (m)

Sample No.

Calcisphaeres (%)

Forams benthic (%)

Forams planktonic (%)

Calcite Prisms Inoceramus (%)

Bioclasts (%)

Glauconite (%)

Quartz (%)

Matrix (%)

Opaques (%)

Fe-Staining (%)

Concretions (%)

12.34 40.50 69.50 83.05 83.15 83.60 89.92 132.00 136.40 146.05 146.20 146.35 149.15 169.55 170.90 187.24 188.35 204.65 205.60 211.45 211.95 222.75 228.25 233.70

P21 P28 P108 P39 P38 P40b P1 P92 P47 P49 P48a P50 P51b P56 P57 P61 P63 P72 P73 P79 P78 P 75 P90 P100

4 1 1 0.3 1 0.6 1.3 0.6 0.3 0 0.6 2.3 0 0.3 0 0.3 0.3 2.6 1.3 0.6 0 0.6 1 1.3

1.3 0.3 0 1 0.3 0.3 0 0.6 0.3 1.3 0.6 1.6 0.3 2 1.3 1.3 2 2.3 2 1 1.6 0.6 1.6 1

1 0 0.3 0.6 0 0 0 1 0.3 1.6 0 1.3 0 0.3 0.3 1.3 0.6 1.6 1 0.3 0.3 1.6 0.3 0.3

1 0 0 0 0 0 0 0 0 0.6 0 5.3 0 0 0.3 0.3 0 2 8 0 0 0.3 0.3 6.6

10.6 5.6 3 6 4.6 3 4 2 5.3 4.3 2.3 6.3 1.6 1.6 3 3 3.3 4 4 2 0.6 2 3.3 3

1 0 0 0 0.3 0.3 0 0 0 0 0 0.3 0 0 0 0 0 0.3 0.3 0 0 0 0 0

8.6 4.3 3.3 4.6 3.3 0.6 4.6 3.6 7.6 2.6 2.6 9.6 1.6 2 1 3.6 2 9 3 3 2.6 3.3 0.3 3.3

72 83.6 87.3 84.3 79.3 82 84.3 89.6 83 84 89 70.6 93 91 92.6 79.7 88.6 75.6 78 91.6 93.6 88.6 89 52.6

0.3 4.9 5 1.6 1.3 12 4.3 1.6 3 5 4 2 3.3 2.3 1.3 8 3 2.3 2.3 1.3 1 2.6 3.6 3.6

0 0 0 0 0 0.6 0.3 0.6 0 0.3 0.3 0 0 0.3 0 2.3 0 0 0 0 0 0 0.3 0

0 0 0 1.3 9.6 0.3 1 0 0 0 0.3 0.3 0 0 0 0 0 0 0 0 0 0 0 28

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Table 2 Sediment composition based on pointcounting of thin sections

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A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

Fig. 5. Lithological features of interval 131.8±132 m (core Kirchrode I).

with increasing content of plant remains in the latter, intensely bioturbated olive gray marls at the top. A redeposited layer marking the boundary to Unit 2 is the best-preserved example of a transition from silty olive gray marls, with well-de®ned trace fossil burrows and redeposited inoceramid shells (Plate 2.7), to dark gray clayey marls, slightly bioturbated and with abundant pyrite and plant debris (Fig. 6). Unit 2 (233.5±205 m) consists of alternations of dark gray clayey (5Y3/2) marls and olive-gray (5GY4/1) marls. Plant remains (replaced by pyrite) are abundant and macrofossils (inoceramid fragments, belemnites, ammonites) are common. Weakly bio-

77

turbated dark layers contain well-preserved inoceramids (B. lissa, I. anglicusÐ Plate 1.9). Belemnites (N. minimus) are condensed with accumulations of 1± 4 individuals/200 cc in seven distinctive horizons (Belemnite Horizons B1±B7) below 207 m (Fig. 7). The topmost horizon with the up-core transition from silty marls with redeposited inoceramids (Plate 2.5, 2.8) to dark-brownish±grayish (5Y3/1) clayey marls contains abundant pyrite and some ammonites. Unit 3 (205±163.5 m) is dominated by olive-gray marls with well-de®ned trace fossils. This unit shows ten 0.5 cm thick pale-green glauconite-rich layers in a ®ne-grained matrix (Plate 2.6). Pyrite, siderite concretions are mostly rare and plant remains are common. Lenticular strati®cation with minor planar intervals and undulated strati®cation is dominant. A few weakly bioturbated, planar strati®ed horizons are bundled between 180 and 188 m (Plates 1.6 and 2.4). Macrofossils are rare. Inoceramid prisms, however, are concentrated at about 177±179 m (bivalvemaximum G). At the boundary to Unit 4, a slightly bioturbated, dark grayish horizon with abundant yellowish sideritic concretions is intercalated. Unit 4 (163.5±132 m) consists of uniformly olivegray marls (5GY4/1±5GY5/1) with lenticular strati®cation and well-de®ned bioturbation (Plate 2.3). The basal part of the unit is characterised by highfrequency alternations of dark and pale gray layers with varying amounts of scattered pyrite concretions and siderite concretions up to a size of 10 cm. At 157 m inoceramid prisms are concentrated in a thin layer (Bivalve Maximum F). Plant remains are common. Unit 5 (132±118 m) is characterised by non-cyclic transitions of dark gray clayey marls (5GY3/2) and

PLATE I. Core surfaces 1. 2. 3. 4. 5. 6.

7.25 m, Ð greenish-gray clayey marl layer containing black phosphorite nodules (condensation horizon). 27.6 m, Ð lag of redeposited white calcareous algae. 42.9 m, Ðolive-gray marl with ichnofossils (Teichichnus, Planolites, Chondrites). 69.5 m, Ð dark gray, weakly bioturbated marly clay with P±Fe±Mn-Carbonate-concretionary layers (`siderite layers'). 132±132.2 m, Ð siderite- and macrofossil-rich condensed horizon and marly clays with dipping P±Fe±Mn-carbonate layers. 187.15±187.40 m, Ð alternation of olive-gray marls with concretions and ichnofossils (Chondrites, Teichichnus Ð penetration depth up to 1 cm) and dark gray marly clays with ¯attened Chondrites and thin ®ligree green layers. 7. 232.75±233 m, Ð transition from pelagic, intensively bioturbated marls (mudturbidite with inoceramid-debris) to weakly bioturbated marly clays with autochthonous A. sulcatus. 8. 52.5 m, Ð olive-gray weakly bioturbated marly clay with sinusoidal grazing trace (Sinusites) and abundant plant debris. 9. 236.5 m, Ð planar bedded, dark gray marly clays with the bivalve A. sulcatus.

Medium High Medium Low low Medium High Medium Medium Silt Clay Clay Clay Clay Clay Clay Clay Silt Common Common Common Common Rare Abundant Common Common Abundant Common Common Abundant Common Rare Rare Rare Abundant Common Common Abundant Abundant Common Abundant Common Common Abundant Abundant Common Rare None None None None None Common Common High High Medium Low Medium High High High High silty 1 glauconite-rich layers transported sediment abundance of Aucellina sideritic layers random color changes large concretions distinct greenish lamina clayey 1 redeposited layers silty 1 redeposited layers 1.5±12.4 12.4±40 40±62.5 62.5±118 118±132 132±163.5 163.5±205 205±233.5 233.5±245 9 8 7 6 5 4 3 2 1

5GY5/1±5GY6/1 5GY4/1±5G5/1 5GY4/1±N4 5GY3/1±5GY4/1 5GY3/2±5BG5/1 5GY4/1±5GY5/1 5GY4/1 5Y3/2±5GY4/1 5Y3/1±5GY4/1

Grainsize Carbonate content Macrofauna Pyrite Plant debris Transported sediment Bioturbation intensity Color (MUNSELL) Characteristics Unit Depth (m)

Table 3 Main characteristics of lithological subunits

Rare Common Abundant Abundant Common Common Rare Rare Rare

A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96 Sideritic concretions

78

Fig. 6. Transition from redeposited sediments to dark gray clayey marls at about 233.5±233.63 m.

green±gray marls (5BG5/1±5GY4/1). The latter are intensively bioturbated with well-de®ned trace fossils in contrast to the slight and indifferent bioturbation of the darker layers. Bivalves are rare (A. gryphaeoides), but ammonites are more common. Pyrite concretions and plant remains are concentrated at 123±126 m. Siderite concretions (nodules and thin layers) are common throughout the whole unit. There are drilling disturbances in some parts. Unit 6 (118±62.5 m) consists of dark gray soft clayey marls and less dominant olive gray marls with gradual lithological transitions. The former show rare, low penetration trace fossils (Sinusites, Chondrites), abundant plant debris and planar strati®cation (Plate 2.2). The latter are characterised by intense bioturbation with well-de®ned deeply penetrating trace fossils. Pyrite and some bivalves are common. In particular aucellinas are concentrated in two horizons (Maxima D and E). Ammonites and belemnites are rare. Thin layers of yellowish siderite concretions are abundant (5±60 layers m 21). Unit 7 (62.5±40 m) is composed of monotonous gray and olive gray clayey marls (5GY4/1±N4) with gradual variations. Layers of siderite concretions are abundant up-core to 47 m. Well-preserved aucellinas are concentrated at 38±42 m (Maximum C). Pyrite and plant remains are common and further enriched in bioturbated intervals at approximately 50±52 m (Plate 1.8). Unit 8 (40±12.4 m) comprises pale-olive gray, burrow mottled marls (5GY4/1±5G5/1). Siderite concretions, plant remains and pyrite commonly occur. Aucellinas and a few belemnites are concentrated in two horizons at 27±29 and 24 m (Maxima

A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

79

Fig. 7. Location of belemnite maxima (N. minimus, 207.6±232 m), and occurrences of bivalves and glauconite.

B 1 A). Ammonites and other macrofossils are very rare. At 27.55 m a redeposited horizon of calcareous algae is intercalated. Individual algae are 1±3 cm long. Unit 9 (12.4±1.5 m) consists of burrow mottled micaceous silty marls with grayish colors. Layers of ¯attened siderite concretions are rare. Two glauconiterich horizons at 12.32 and 7.2 m contain black phosphorite nodules and redeposited material (bioclasts,

quartz grains, Plate 2.1). Aucellinas are common, but not concentrated in distinctive horizons. 3.2. Ichnofacies patterns Variations in the ichnofacies patterns are characteristic and distinct in all lithological units. Their identi®cation is based on Chamberlain (1978). The trace fossil

80

A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

assemblage of the core investigated includes Sinusites, Chondrites, Thalassinoides, Teichichnus and Planolites. Following a model of Savrda and Bottjer (1986) the bioturbation was studied (a) by identi®ca-

tion of the trace fossils assemblage, (b) by semiquantitative description of the intensity of bioturbation (barren, surface sediment feeders only, burrows (slight bioturbation), burrows (strong bioturbation),

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burrow mottled), and (c) by estimation of the penetration depth (Table 4). Between 90 and 116 m the data are poor because of the frequent drilling disturbances and the dark color of the sediment which prevents a detailed analysis of bioturbation patterns. Six different ichnofacies with different assemblages, varying burrowing depths, and intensity of bioturbation were subdivided (Fig. 8): Facies 1 and 2 consist of slightly bioturbated clayey marls with shallow penetration depth. Facies 1 is characterised by Sinusites only, in facies 2 small Chondrites occur in addition. Such low diversity trace fossil assemblages are known from organic rich sediments and are interpreted as well-adapted to oxygen depleted bottom water and pore water conditions (Bromley and Ekdale, 1986). Facies 3 and 4 are characterised by slightly bioturbated marls with wellde®ned trace fossils (including Teichichnus and Chondrites). The penetration depth in Facies 3, especially that of Teichichnus, is up to 10 cm. In Facies 4, the penetration depth is less than 5 cm but the intensity of bioturbation is stronger. In Facies 5 and 6, Thalassinoides, Planolites and Teichichnus dominate, Chondrites is rare with a distinct outline of trace fossils with burrowing depths up to 10 cm in Facies 5, and mottled burrowing in Facies 6. Variations in the ichnofacies are the most persistent sedimentological features in the core. Except for Sinusites, all trace fossils observed are not controlled by

81

bathymetry. Their occurrence include environments ranging from the wave base to the abyssal realm (Cruziana-, Zoophycus- and Nereites-facies of Seilacher, 1967). Bottjer et al. (1986) and Savrda et al. (1991) argued that the intensity of bioturbation, trace fossil assemblage, and penetration depth have been strongly in¯uenced by bottom water oxygenation. Related to dysaerobic bottom water conditions, Teichichnus is considered less tolerant than Chondrites and both Thalassinoides and Planolites are less tolerant than Teichichnus. Sinusites belongs to the Nereites-facies, which is typical for abyssal ¯ysch deposits (Seilacher, 1967). Yet, preservation and density of trace fossil assemblages is also controlled by changes in the sedimentation rate/nutrient supply. The distribution of the different ichnofacies in the sedimentary sequence shows a superimposed cycle with strong intensity of bioturbation at the base followed by weak intensity of bioturbation (Ichnofacies 1) at about 116±30 m and then a return to highly burrow mottled sediments at the top of the Upper Albian interval (Fig. 9). Well-de®ned burrows of Thalassinoides, Planolites, Teichichnus and Chondrites (Ichnofacies 5) dominate from the base at 245 m up-core to 207 m (Units 1 and 2), and show a good correlation with the distribution of olive gray marls. Horizons with Chondrites and Sinusites are less common and related to dark gray clayey marls and mudturbidite horizons.

PLATE II. Thin sections 1. Sample P21 (12.34 m): Micritic clayey marls with calcisphaeres, planktonic foraminfera and silt-sized quartz; strongly altered. Scale: Width of photograph ˆ 2.2 mm, II Pol. 2. Sample P38 (88.15 m): Concretions with siderite, fractures due to compaction, and fragments of bivalves in ®ne grained matrix. Scale: Width of photograph ˆ 2.8 mm, II Pol. 3. Sample P49 (146.05 m): Fine-grained clayey-calcareous matrix with calcisphaeres, benthic foraminifera, glauconite, biotite and silt-sized quartz, strongly bioturbated. Scale: Width of photograph ˆ 0.7 mm, II Pol. 4. Sample P40b (183.6 m): Fine-grained clayey-calcareous matrix, weakly bioturbated. Scale: Width of photograph ˆ 1.1 mm, II Pol. 5. Sample P73 (205.6 m): Fine-grained clayey-calcareous matrix rich in silt-sized quartz. Scale: Width of photograph ˆ 1.1 mm, X Pol. 6. Sample P72 (204.65 m). Glauconite-bearing layer with common silt-sized quartz and foraminifera. Scale: Width of photograph ˆ 1.1 mm, II Pol. 7. Sample P100 (233.7 m). Transported silt-sized quartz and inoceramid prisms. Scale: Width of photograph ˆ 2.2 mm, II Pol. 8. Sample P73 (205.6 m). Fragment of inoceramid in matrix rich in foraminifera and calcisphaeres. Scale: Width of photograph ˆ 2.2 mm, II Pol.

Low , 1 cm Intensity of bioturbation Depth of penetration

Low Grazing

Moderate , 10 cm

Moderate , 5 cm

Thalassinoides sp. Planolites sp. Teichichnus sp. Moderate , 10 cm Teichichnus sp. Sinusites sp. Chondrites sp. Trace fossil

Sinusites sp.

Teichichnus sp. Chondrites sp.

5 2 Ichnofacies No.

1

3

4

6

Mottled

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Table 4 Trace fossil distribution within distinctive ichnofacies

82

Fig. 8. Trace fossil assemblages.

Between 207 and 116 m (Units 3±5 of Chapter 3) Ichnofacies 3, dominated by Chondrites and Teichichnus, indicates a decrease in oxygenation of bottom water or a decrease in fertility. Slight bioturbation with Sinusites and Chondrites appears in ®ve horizons, related to dark clayey mud with common plant remains. Between 116 and 90 m (Unit 6pars), penetration depths and intensity of bioturbation decrease, Sinusites is now common, especially in dark semidurated clayey marls. From 90 m up to the top of the core (Units 6pars±9), intensity of bioturbation increases and the ichnofauna is increasingly diverse (Chondrites, Teichichnus, Planolites). This is paralleled by strongly increased penetration depths, especially in pale gray horizons with condensations of aucellinas. Above 30 m, strongly burrowed pale marls with Thalassinoides, Planolites, Teichichnus dominate, indicating an increase in fertility and/or an increase in oxygenation of the bottom water. At about 7.2 m a phosphorite-bearing layer of clayey marl is intercalated. It shows green-colored Planolites burrows and is only slightly bioturbated. 3.3. Principal component analysis (PCA) of lithological variations Following the terminology used in thermodynamics of open systems by Nicolis and Prigogine (1977) we discriminated in all datasets chaotic, unstable intervals without prevailing periodic cyclicity, and stable systems with periodic cyclicity. Abrupt changes

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83

Fig. 9. Ichnofacies distribution and bioturbation intensity (based on visual description).

resulting in subsequent changes in the general trend are described as chaotic transitions. PCA of 14 independently described and ranked lithological parameters produced ®ve, linearly independent sets of components with eigenvalues .1. Each of these sets combines the variability of several lithological features with weightings between 11 and 21 (Table 5). A low number of components show eigenvalues .1 (5), a result of the occurrence of

single load components from the parameters glauconite and pyrite. These weightings (factor loadings) describe the correlation between an independent parameter and the new component set. Communality expresses the match of the descriptions of all lithological parameters by the ®ve components. All parameters, with the exception of glauconite (0.12), are well described by the communality. Altogether the ®ve new component sets describe only 55.6% of the

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Table 5 Results of PCA of lithological parameters Factor loadings Parameter

Communality

Component 1

Grain size Carbonate content (estm.) Concretion density Siderite layers Grayvalue Color Color enhancement Bivalves Plant debris Pyrite Bioturbation intensity Cementation Glauconite Strati®cation

0.72 0.55 0.61 0.62 0.63 0.59 0.60 0.60 0.51 0.56 0.57 0.49 0.12 0.63

0.46 0.58 0.64 0.08 20.12 20.18 20.52 20.07 0.54 0.12 0.49 20.56 20.39 0.66 20.01 20.07 20.14 20.07 0.34 20.35 0.48 0.22 0.34 20.30 0.26 20.07 0.58 0.36 Eigenvalue % of variance

Component 1 Component 2 Component 3 Component 4 Component 5

2.47 1.55 1.40 1.28 1.11

variability of all parameters studied. The occurrence of glauconite would appear to be independent from the ¯uctuations of the entire lithology. Component 1 (17.6% of total variance) combines the ranked ¯uctuations of carbonate content (estimated from core description Ð HCl-test), grayvalue, strati®cation, and inversely the enrichment of sideritic layers. Color (0.49) and bioturbation intensity (0.48) probably also in¯uence this component. Therefore, the ¯uctuations of the Component 1 time series may result in high values for marly, light, well bioturbated and oxygenated sediments and low values for clayey, well strati®ed, dysoxygenated sediments enriched in sideritic layers. These features can re¯ect changes in bottom water strati®cation, carbonate productivity and/or terrigenous, clayey input. Component 2 (11% of total variance) combines ¯uctuations in grain size, color enhancement and sediment color. Its time series ¯uctuations can be interpreted as changes in the composition of the non-calcareous ¯ux. Component 3 (10% of total variance) combines

Component 2

Component 3

Component 4

Component 5

0.37 0.25 0.18 0.52 0.56 0.08 20.10 0.21 20.37 20.26 20.50 0.03 0.00 20.27

0.18 0.18 20.18 0.16 20.05 20.12 0.02 0.73 0.56 0.47 20.16 20.15 20.11 0.06

0.08 20.17 0.71 0.23 0.09 0.13 20.04 20.16 0.17 0.20 0.11 20.51 0.19 0.30

17.60 11.00 10.00 9.10 7.90 sum 55.6

¯uctuations in the grayvalue record, intensity of bioturbation, and abundance of sideritic layers. Variations, however, do not parallel ¯uctuations in the carbonate content. Component 4 (9.1% of total variance) combines variations in the abundance of bivalves and plant remains. Variations in the time series can be interpreted as changes in the preservation of organic matter. Component 5 (7.9% of total variance) combines variations of the abundance of sideritic concretions (nodules) and inversely cementation of the sediment. These variations are best explained by a ¯uctuating degree of diagenesis. The time series of Component 1 can be subdivided in four distinctive units (Fig. 10). The mean value was set as zero and the standard deviation 1/21. An unstable system from the base of the section (245 m) up to 132 m re¯ects irregular high-frequency ¯uctuations in ranges between values of 0 and 3, interrupted by single-event like peaks with irregular values of about 23. With respect to earlier interpretations in this paper values of 0±3 can be interpreted as

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85

Fig. 10. Temporal variability of Component 1 (Lithology) and CaCO3-content. Subdivision into unstable and stable depositional systems by dashed lines.

characteristic for a carbonate-rich, well-oxygenated environment with strong benthic activity (bioturbation). Between 132 and 116 m, Component 1 shows strong chaotic ¯uctuations and a superimposed strong descendent trend. This unit can be interpreted as chaotic transition between carbonate-rich, welloxygenated and clay-rich, less well-oxygenated environments.

A stable system was established between 116 and 40 m characterised by long-term ¯uctuations between 22 and 1 with an slight ascendant trend. Four superimposed periodic cycles of about 21±23 m with positive peaks at about 108, 87, 64 and 43 m are well pronounced (Fig. 10). This stable system is interpreted as characteristic for clay-rich, slightly bioturbated sediments.

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From 40 m up to the top of the section, Component 1 is characterised by moderately expressed high frequent ¯uctuations with a superimposed strong ascendant trend. Hence this trend is interpreted as re¯ecting a strong increase in both carbonate content and bottom water oxygenation. Compared to the chemically analysed carbonate content (Jendrzejewski et al., 2001), Component 1 (based on semiquantitative data including a CaCO3 (est.)) corresponds well to the trend in carbonate ¯uctuations between 245 and 40 m, as expected. In particular, there is a good correlation between the negative peaks of Component 1 and the carbonate content at about 240, 237, 207, 182 and 132 m as well as the positive peaks at about 238, 232, 187, 137 and 64 m. However, between 40 and 1.5 m there is less correspondence between the trends of Component 1 set and carbonate content in particular. A possible explanation might be the fact that light biogenic and terrigenous silica which is affecting Component 1 but not the CaCO3 content became increasingly important in this interval.

4. Logging 4.1. Log interpretation vs. observed lithology The interpretation of logging data is based on Serra (1984), individual logs are shown in Fig. 4. Overall radioactivity increases down-core (,65 API). Highest values .261 (.87 API) occur from 220 to 217 m and from 189 to 182 m. Values of 150±300 ( ˆ 50±100 API) are typical for clayey marls and marls rich in illite (Serra, 1984). The lack of signi®cant peaks in the data suggests relatively stable depositional conditions with none or minor redeposition. Below 164 m, high g -ray-values are paralleled by mm-thick green layers. Low values (,230) above 40 m correspond to high CaCO3 contents (.40%). Low values at 226, 180, 163, and 64 m parallel condensation. Low values at 113 m re¯ect lower illite/smectite-ratios. Strong variations from 235 to 210 m correlate to rapid lithological changes, especially expressed in plant remains, CaCO3 content and macrofossil-condensation. High caliper values and low density values characterise unstable borehole conditions and low permeability as typical in clay-rich sequences. Clay-

rich intervals occur in particular from 225 to 206 m, at 165 m, from 135 to 106 m, at 85, and at 61 m. Sandstone neutron porosity describes the porosity of the sequence; it is especially high from 220±206 m, at 162 m, from 130±105 m, and above 12 m. Acoustic-log and resistivity-log re¯ect acoustic properties and electric conductivity of the sedimentary sequence. Measurements above 40 m depth are not reliable as values tend to be too high because of weathering. Relatively soft, conductive layers occur from 216 m to 204 m, at 164 m, from 130 to 105 m, and from 55 to 50 m. Increased resistivity values corresponding to the latter interval have been observed by Frieg and Kemper (1989) in various boreholes from the North German basin (Fig. 4). 4.2. PCA and Fourier-transform of logging data By applying PCA to 11 different well logs Ð we eliminated resistivity 1 and acoustic log transition time 60 from the PCA due to excellent correlation (linear dependence) of .0.9 correlation coef®cient Ð we were able to discriminate three sets of components which are linearly independent (non-correlative) (Table 6). They are characterised in Component 1 by g -ray 1±3, K-g , Fe-resistivity 2, acoustic-log transition time 20. Component 2 is characterised by linear density, caliper and sandstone±neutron-porosity. Component 3 is characterised by uranium-g , thorium-g . Both Component 1 and 2 can be subdivided in 3 stable/unstable intervals (A1, B1, C1) and 3 chaotic transitional intervals. The onset of each stable/ unstable interval is marked by a major singularity on top of each underlying transitional zone (Fig. 11). Detailed spectral analyses of the individual stable systems revealed for the late Upper Albian (interval C1) well-developed cyclicity with periods of 24, 12 and 8 m, and subordinate periods of 5, and 4.3 m. In interval B1 (corresponding to the lower auritussubzone) periods of 16 and 2.4 m dominate (Fig. 12). However, we cannot totally exclude the possibility of linear harmonics. g -Ray: The time-series from the additive g -ray log (g -ray 1 1 2 1 3) are subdivided at singularity points (major changes in sedimentation patterns) into seven units. Spectral analysis of individual lithological units was applied to check for periodic cyclicity. The seven units show various periodicities (Fig. 13).

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Table 6 Results of PCA of logging data Factor loadings

1 2 3 4 5 6 7 8 9 10 11 12 13

Parameter

Communality

Component 1

g -Ray 1 Linear Density Caliper g -Ray 2 Sandstone neutron porosity Acoustic., transit. time 20 Acoustic., transit. time 60 Fe-resistivity 1 Fe-resistivity 2 g -Ray 3 Potassium-g Uranium-g Thorium-g

0.42 0.80 0.74 0.59 0.66 0.68

0.57 0.28 0.45 20.77 20.45 0.72 0.70 0.26 20.46 0.66 20.70 20.20 self-correlated self-correlated 20.75 20.20 0.76 0.13 0.60 0.23 0.13 20.16 0.35 0.18 Eigenvalue % variance

0.69 0.60 0.52 0.86 0.70 Component 1 Component 2 Component 3

Units 1±4 (below 164 m) and Unit 7 (above 40.5 m): Large variations in sedimentary cycles' thickness combined with many minor changes of the sedimentary patterns characterise the latter interval as an unstable system. 2.1 m cyclicity around 214± 180 m and the 5 m cyclicity from 224 to 214.1 m coincide with the repeated occurrence of mm-thick greenish layers. However, the small number of data points (100) which are available in this interval preclude signi®cant de®nition as a stable system. Below 224 m the spectra show only noise. Unit 5 (163±114 m): There is a distinct cyclicity of 12 m which is repeated four times. Unit 6 (114±40.5 m): Constant periods of 12 and 24 m are dominant. Of subordinate importance are 8, 4.2, 3.4, 2.4 and 1.7 m cycles. 4.3. Camera scanning and sediment color A continuous time-series from sediment color variations could be divided into seven intervals based on singularities (jumps, changes in the general trend of the time-series). Spectral analyses revealed different frequencies of periodicity (Fig. 14). Signi®cant periodicities with respect to the color of

3.70 1.90 1.60

Component 2

Component 3 20.07 0.07 20.14 20.15 20.07 0.16 0.13 20.04 0.33 20.90 0.74

33.80 17.50 14.60 sum 65.9

the sedimentary record are observed in the interval 40.95±114.95 m (Units 6 and 7) with periods of 22, 11, 5.3 and 4.4 m and those in the interval 116.05± 162.95 m (Units 4 and 5) with periods of 22 and 6.8 m. The 22 m periodicity in Units 6 and 7 could easily be a linear harmonic of the 11 and 4.4 m cyclicity but is probably insigni®cant. Other peaks in the power spectra are less signi®cant due to lack of precision and number of data points. 5. Cyclostratigraphy Cyclostratigraphic data analysis (methods 1, 2, 5, 6, 7) has been performed for all time-series. The most convincing results were achieved from the analyses of a combined g -ray log (sum of three individual g -ray-logs), carbonate content, and a line scan of sediment color. Cyclostratigraphy allows calculation of sedimentation rates (sr) if relative or absolute time information is available, e.g. relations between different orbital parameters (Fischer and Schwarzacher, 1982). The criteria used to separate different systems are sudden `jumps' in the time-series. For different

88

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Fig. 12. Cyclicity in Logging-Component 1 from Kirchrode I.

Fig. 11. Component 1 and 2-logging with subdivision in stable/ unstable systems and chaotic transitional intervals.

parameters these `jumps' occur in different depths. Most parameters (e.g. carbonate content, Component 1 and 2-logging, g -ray-log) show sudden intense changes in the interval 132±115 m. Thus this interval is described as a chaotic transition. A stable system, pronounced in all parameters, characterises the interval between 115±40 m. It is characterised by weak low-frequency changes in all parameters studied. Just the opposite accounts for the interval from 132 m down-core, which is characterised by an unstable system with four short subordinate stable intervals at different datasets. Chaotic transitional

intervals are con®ned to distinct unequivocal changes from condensation to clastic dilution. Interval 232±207 m (Unit 2); unstable system: periodic cyclicity, with variable periods, of several parameters is well pronounced in this interval. However, these periodicities are not consistent or correlated. 1.5 m-cycles are obvious from PCA-logging data (Fig. 12). 5 m-cycles occur in g -ray logs and in the grayscale from camera scanning (Figs. 13 and 14). They are, however, not of stratigraphic signi®cance. In contrast to the cyclicity in the intervals up-core these cycles are unlikely to represent true depositional periods because of the discontinuous occurrence of mudturbidites. Such a quasi-periodicity of turbidite deposits, induced by autocyclic instabilities of sediments deposited in more proximal areas, is described as turbidite-cyclicity (Einsele, 1982). Weltje and De

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89

Fig. 13. Cyclicity of g -ray logs (mean of three added g -ray logs, Well Kirchrode I) subdivided in stable and unstable intervals.

Boer (1993) interpreted turbidite deposition as the result of paleoclimatic oscillation. However, we were unable to ®nd any evidence for such an interpretation. Interval 204±167 m (Unit 3); unstable system: cyclostratigraphic subdivision and dating is hardly possible in this interval, for no signi®cant ratios of cycles could be detected. Periodic cycles of several parameters occur at ca. 3.4, 2.1 and 1.2 m. If the 3.4 m-cycle corresponds to the dominant cycle of the obliquity 1 (ca. 38 ka), the 2.1 m-cycle would correspond to the precession (ca. 23 ka). Consequently, assuming a sedimentation rate of ca. 8.7 cm ka 21 (corresponding to 410 ka-cycles) supports the existence

of periods of these orbital parameters during Cretaceous time. Lithologic variations are predominantly triggered by variations in the redox potential and in the volume of terrigenous ¯ux (re¯ected in the cyclicity (Prokoph, 1994)). Interval 161±132 m (Unit 4); unstable system: there are no cycles which could be detected constantly. Signi®cant cycles of different parameters have periods of 22, 16, 12, 6.8, and about 3.1 m. The periodic cyclicity can not be converted directly into stratigraphic data. But the dominant 3.1 m cycle may correspond to the 3.4 m obliquity-cycle of the stable system (obliquity 1 ˆ 38.1 ka). According to

90

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Fig. 14. Time-series from sediment color (grayscales 0±255). Note seven intervals with periodic cyclicity.

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these astronomical ¯uctuation, the average sedimentation rate can be calculated as 3:1 m=3:4 m p 8:7 cm=1 ka ˆ 7:9 cm=1 ka The sedimentation rate for this interval varies from 7.9 cm ka 21, which corresponds to about 370 ka period for the deposition of the sediment. Interval 116±42 m (Units 6 and 7); stable system: cyclostratigraphy and the calculation of sr in this stable system is the base for further cyclostratigraphic subdivision of the Upper Albian in northern Germany. This interval, which ranges from the ®rst appearance of E. turriseiffelii to the base of the perin¯atumSubzone, shows the most remarkable continuous hemipelagic sedimentation throughout the basin. Periodic changes in sedimentation can be assigned to two bundles of cycles cycle (a) 11±12 m : 4:4±4:8 m : 2:2±2:4 m ˆ 5 : 2 : 1 length (b) 8 m : 3:4 m : 1:7 m ˆ 5 : 2 : 1

Such a pattern correlates well with the midCretaceous long and short Milankovitch cycles (Berger and Loutre, 1989).

orbital (a) cycles (b)

eccentricity: obliquity: precession 111:5 ka : 51 ka : 22:5 ka ˆ 5 : 2 : 1 92 ka : 38:1 ka : 18:5 ka ˆ 5 : 2 : 1

Correlation between observed cyclicity, the datasets, and Milankovitch-cyclicity are more or less evident in the following parameters: Logging (sum of all logs), grayscale, g -ray (separate), CaCO3 (Fig. 15). Interestingly, if 12 m-cycles (111.5 ka Ð eccentricity-cycle) dominate, the corresponding 4.8 and 2.4 m-cycles (obliquity- and precession-cycles) are suppressed, while far weaker 8 m-cycles (short eccentricity-cycle) are paralleled by well-pronounced obliquity- and precession-cycles (Fig. 15). The 11± 12 m-cycle is the most constant and best detectable cycle in the stable system. By using eccentricity cycles for a calculation of the sr (thickness of cycle (m)/orbital cyclicity (a)), the latter vary in the interval 115±41 m from 8.7 to 11 cm ka 21 (mean 10 cm ka 21). Therefore, sediments

91

of the stable system represent a record of 670±850 ka, with a mean of 740 ka. Other cycles with periods of 5, 6.5, 15, 18 and 24 m are limited to some parameters. A relatively high carbonate content (42%) in the stable system at 62 m parallels a condensation horizon with enrichments of bivalves and corresponds to strong and deeply penetrating bioturbation. Additionally the occurrence of the species Mortoniceras rostratum (characterising the rostratum-Subzone) at 64 m (Wiedmann and Owen, 2001) indicates shallowing in this area. These ®ndings correspond to the onset of mathematically expressed unstable conditions in the depositional environment. The sudden change in carbonate content, however, still matches the 12 mcyclicity, since increased carbonate values occur also at 52 m (37%) and 75 m (35%). Interval 39±1.5 m; unstable system: no further subdivision, although there are repeatedly periodic cycles of about 5.6 and 2 m. They do not, however, coincide with Milankovitch-cyclicity. Chaotic Transitional Intervals occur at 232±207 m (limited database), 207±204, 167±161 m (boundary upper±lower auritus-subzone), 42±39 m. Their expression is weak at 64±60 m (boundary dispar/ in¯atum-subzones) but especially pronounced at 132±116 m (boundary columnata/turriseiffelii-zone, Unit 5). The sedimentation patterns of these intervals are similar and their bases are always characterised by high-frequency alternations of clayey marls and marls (Fig. 16). The intervals correspond with changes in environment and in marker fossils. A precise dating of the stratigraphic range of the Upper Albian is not possible because the transitions to both Cenomanian and Middle Albian are not covered by the borehole. Furthermore there is an ongoing debate about the precise dating of the Albian± Cenomanian-boundary, e.g. 96 Ma Ð Haq et al. (1987), 98.9 Ma Ð Gradstein et al. (1994). Applying cyclostratigraphy to the stable depositional environment in the late Upper Albian (0.7 Ma) results in a mean sedimentation rate of ca. 10 cm ka 21 (8.7±11 cm ka 21) in this interval. This ®gure can be used to calculate the sedimentation rate (srn) for intervals without apparent Milankovitchperiodicity, srn ˆ Cstable =Cunstable £ srstable ;

92

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Fig. 15. Periodic cyclicity in the stable system between 40±115 m with corresponding cycles of orbital eccentricity (E), 8±13 m; obliquity (O), 4.5±3.4 m; precession (P), 2.4±1.6 m. Note the good match between the power spectra of CaCO3 and grayscale, and Component 1-logging and g ray. Note also the apparent mismatch between the power spectra of CaCO3 and g ray, Component 1-logging and grayscale, CaCO3 and Component 1-logging, and g ray and grayscale.

Where Cstable is the dominant cycle of the stable system, Cunstable the dominant cycle of unstable system, and srstable the sedimentation rate of stable system. The dominance of a cycle is determined by applying a Fourier-transform to a time series. By de®nition, dominant cycles in an unstable system are less prominent than in the stable systems and cover a broad range of frequencies. Therefore, our estimation for the durations of unstable systems is also less signi®cant in relation to stable systems. Based on the calibration of the sr with the periodic cyclicity in the stable interval of Kirchrode I it is possible to date certain individual depositional intervals. These intervals are separated by either strongly enhanced clastic supply or by condensation (Fig. 17). 1(a) base of late Upper Albian (®rst appearance of

E. turriseiffelii) Ðmiddle part of bivalve maximum -EDuration: ca. 500 ka (470±600 ka) 1(b) middle part of bivalve maximum -E- to middle part of bivalve maximum -DDuration: ca. 200 ka (180±230hsp sp ˆ 0.25 . ka) 1(c) middle part of bivalve maximum -D- to middle part of bivalve maximum -C1 Duration: ca. 200 ka (180±230 ka) 1(d) middle part of bivalve maximum -C- to middle part of bivalve maximum -ADuration: ca. 200 ka (180±230 ka) Interval 1c is the best dated interval with respect to cyclostratigraphy. Using the information obtained from interval 1c it is evident that even in more proximal sections pelagic sedimentation is prevailing

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Fig. 16. Chaotic-transitional interval from 160 to 166.3 m. Note extremes in g -ray and carbonate content and oscillation of parameters before and after the `clastic-dilution'-event at 163.5±165 m.

(Prokoph, 1994). This interval also contains the most pronounced Milankovitch like ratios between dominant periodicities. A cyclostratigraphic interpretation of the lower part of the Upper Albian is more dif®cult because (a) cyclicity is less stable and shows only short-term periodicity, (b) redeposited layers and hiatuses occur even in the basinal sections (top of varicosum-subzone), and (c) bivalve maxima are less pronounced. 2 early Upper Albian (top of belemnite maximum) to ®rst appearance of E. turriseiffelii Duration: ca. 800 ka This interval can be subdivided by the occurrence of sudden clastic input in the basinal sections and redeposited layers on swells. 2(a) top of belemnite maximum to the clastic horizon between bivalve maxima -G- and -FDuration: ca. 490 ka 2(b) clastic horizon between bivalve maxima -Gand -F- to ®rst appearance of E. turriseiffelii Duration: ca. 310 ka

6. Discussion of the depositional environment and sequence stratigraphic interpretation According to faunal content, carbonate content,

93

Fig. 17. Cyclostratigraphic dating of bio- and lithological marker horizons (Core Kirchrode I).

sediment composition and grain sizes, the Upper Albian section investigated was deposited under fully marine conditions showing no prominent facies changes. In the interval from 245 to 204 m the sedimentation pattern is characterised by non cyclic alternations of redeposited silty-marly layers and marly background sedimentation. These alternations are similar to mudturbidites as described by Einsele and Seilacher (1991), which result from non-regular occurrences of strong bottom water currents below the storm-wave base in epicontinental seas. Ichnofacies 5 and 6, dominated by Thalassinoides and Planolites, indicate well-oxygenated bottom water conditions with high fertility at the base and the top of the Upper Albian section, while redeposited sediments and silt indicate a lower relative sea level and/or bottom currents compared to the interval from 205 to 40 m. Furthermore, the decreasing content of silt in the mudturbidite interval can indicate increased water depth up-section. Alternatively, redeposited material, relatively small volumes of sediment in the cristatumand orbignyi-Subzones, and condensed horizons with macrofossils (inoceramids, ammonites, belemnites) may point to so far undetected stratigraphic hiatuses in this interval. Stratigraphically, the interval is equivalent to red-colored, redeposited horizons on the submarine Pompeckj swell in the East German basin (Frieg and Kemper, 1989; Diener, 1966; Prokoph, 1994).

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Table 7 Cycles/depth vs. mean CaCO3 and TOC Depth (m)

Cycles (m)

CaCO3 (%) (mean)

TOC (%) (mean)

040.5±048.5 048.5±059.5 059.5±070.0 070.0±082.5 082.5±095.0 095.0±106.5 106.5±118.5

8 11 10.5 12.5 12.5 11.5 11.5

35.2 32.4 34.9 32.5 32.5 32.7 30.1

0.35 0.40 0.38 0.42 0.41 0.41 0.43

Between 204 and 132 m (lower auritus-Subzone) there is no prominent variation in the sedimentation. Ichnofacies, absence of redeposited material, and pelagic fossil assemblages (Wiedmann and Owen, 2001; Keupp, 2001; Weiss, in Fenner et al., 1996) indicate stable depositional conditions, relatively deep waters, and a well-oxygenated sea ¯oor. At 132 m occurs an important break in the deposition marked by decreasing carbonate content, minor bioturbation, and changes in the fossil assemblages. E. turriseiffelii and the planktonic foraminifer Globigerinelloides bentonensis have their ®rst appearances and B. lissa disappears in the North German basin at this level, forming a major event marker in the epeiric `Boreal' realm (Prokoph, 1994). The prevailing sedimentation in the basin remains pelagic during this time interval (upper auritus-Subzone). There is no sedimentological evidence for tectonic or halokinetic movements. The concentration of fossils and the high content of glauconite at 132 m indicates a condensed horizon (maximum ¯ooding surface in shallower areas), correlative with a `downlap surface' (e.g. Loutit et al., 1988). This horizon, which is prominent throughout the basin, marks the transition from retrograding to ®rst aggrading (132±39 m) and later prograding (39±1.5 m) depositional patterns. Furthermore, this indicates that there is no diapirism at this time. From 132 to 39 m (upper auritus- and rostratumSubzone) the slight bioturbation, the dominance of the ichnofossil Sinusites sp., and the relatively low carbonate content suggest a relatively poor oxygenation of the benthic boundary layer and an increase in sr, controlled by an increasing ¯ux of terrigenous clayey material. This interval is well represented in the entire

Fig. 18. Power spectrum of the intensity of bioturbation based on a Fourier-transformation (core interval 90±40 m).

basin, characterised by continuous deposition of marls and pelagic fossils (Diener, 1966; Prokoph, 1994), suggesting a long distance to the coastline (source rock area) and relative deep water. Such a scenario strongly supports changes towards a more humid climate, with increased river runoff. Increased availability of nutrients results in surface water strati®cation and reduced bottom water circulation (De Boer, 1991; Bottjer et al., 1986). Mathematically expressed, the interval represents a stable system dominated by a cyclic dilutive terrigenous input with the thickest cycles (12 m) having the relatively highest proportion of terrigenous, non-carbonate particles. The particles are, for example coal (presumably reworked Carboniferous coal, Jendrzejewski et al., 2001) (Tables 7, 8 and 9). In contrast the shortest cycles (e.g. 8 m) show the highest mean carbonate content. In depth from 90 up to 40 m, an even shorter stable periodic cyclicity of bioturbation intensity (3.2 m, Fig. 18) is evident. We thus assume that changes in surface water strati®cation are eventually periodic and are in phase with the orbital forcing mechanisms. From 39 up to 1.5 m (rostratum- and perin¯atumSubzones) a strong increase in bioturbation intensity (Ichnofacies 4 and 6), increasing carbonate content, redeposition, condensed horizons, and a high content of radiolarians (Fenner, 2001b) underline both decreasing ®ne-grained terrigenous supply and increasing surface productivity. Thus, it seems, both the water depth decreases rapidly and water circulation become intensi®ed, resulting in regressive facies

A. Prokoph, J. Thurow / Palaeogeography, Palaeoclimatology, Palaeoecology 174 (2001) 67±96

and increasing ¯ux of terrigenous nutrients. This scenario may represent an superposition of a relative sea level fall and decreasing chemical weathering due to change to dryer climate, also described and interpreted from the mid-Cretaceous of the Western Interior Seaway North Americas (Glancy et al., 1993; Pratt et al., 1993). In general, the sediment distribution is controlled by a transgressive-regressive cycle with similarities to depositional sequences in the sense of van Wagoner et al. (1988), although the upper and lower sequence boundaries may not have been drilled. Similarities are: maximum ¯ooding surface with condensation, aggradational stacking pattern with periodic-cyclic deposition in the early highstand, and progradational stacking patterns in the late highstand. In a wider sense it is rather dif®cult, however, to apply the concept of sequence stratigraphy to the sedimentation in epeiric basins, in particular because of the lack of coarser clastic material deposited as typical lowstand facies. Furthermore, it is more dif®cult to recognise sequence boundaries in such monotonous sedimentary sequences compared to the four Late Albian sequences, as described by Hesselbo et al. (1990) from the Wessex basin. Acknowledgements We thank all members of the B.C.C.P.-Group for exhausting discussions and for providing data. The German National Science Foundation (DFG) supported the project (grant Wi 112/32). We thank Juliane Fenner, Andrew Gale, and Olaf Podlaha for helpful comments and advise in their reviews. Michael Schaaf considerably improved earlier drafts of this paper. This is a contribution to the DFG special topic `Global and Regional Controls on Biogenic Sedimentation'. References B.C.C.P.-Group, 1994. The Upper Albian of northern Germany: results from the Kirchrode 1/91 borehole, `Boreal' Cretaceous Cycles Project (B.C.C.P.). Zbl. Geol. Palaeont. pt. I 1993 (7/8), 809±822. Berger, A., Loutre, M.F., 1989. Pre-quaternary Milankovitch frequencies. Nature 342, 133. Betz, D., FuÈhrer, F., Greiner, G., Plein, E., 1986. Compressional

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