Newsletters on Stratigraphy, Vol. 44/2, 123–135 Article published online April 2011 Ammonite biostratigraphy and correlation of Middle/Late Albian drilling cores in the Hannover area (northern Germany) Jens Lehmann1 With 3 figures, 1 plate, and 1 table Abstract. The ammonite biostratigraphy of the Middle/Late Albian boundary interval in northern Germa- ny has been significantly improved in the past few years by the Hannover-Lahe and Hannover-Kirchrode borehole sections. Both sections show are monotonous claystone successions deposited in a deep sub-basin of the Lower Saxony Basin. Here ammonite data of the Hannover-Lahe core are revised and re-evaluated, placing the section into the latest Middle/early Late Albian and allowing a correlation with the neighbouring Hannover-Kirchrode succession as well as the standard section for ammonite biostratigraphy on the Europe- an shelf – the Folkestone section in the UK. It demonstrates that sedimentation rates in this sub-basin of the Lower Saxony Basin were extremely high during the earliest Late Albian Dipoloceras cristatum Zone and the Hysteroceras orbignyi Subzone of the Hysteroceras varicosum Zone compared to all other well-dated sections available. The succession in the H. binum/choffati Subzones, indicates a short period of distinctly reduced sediment accumulation, before the greatly increased sedimentation rate during the Callihoplites auritus Subzone of the Mortoniceras inflatum Zone. Key words. Ammonites, Albian, Cores, Hannover area, northern Germany, Correlation 1. Introduction to the area focused on here. Hitherto, in the Lower Saxony Basin, earlier contributions were limited in Middle and Late Albian ammonite faunas of the their results by the lack of continuous outcrop succes- Boreal Sea are characterized by fast evolutionary sions containing a reasonable number of ammonites rates, particularly the endemic hoplitid ammonites and (e. g. Ernst 1921, 1927; Althoff and Seitz 1934; Stol- provide a high-resolution stratigraphic tool in this ley 1937; Owen 1979). Outcrops are widely missing in realm. Well-preserved ammonite successions in the the basinal claystone facies of the Lower Saxony Anglo-Paris Basin are the base for a well-elaborated Basin, but three borings were drilled in the 1990’s and detailed zonal and subzonal scheme (e. g. Owen, provide a good data base: Hannover KirchrodeI and II 1984, 1999; Fig. 1 and 2) and range charts (Amédro and Hannover Lahe. Macrofossils in these borings and Destombes 1978, Amédro 1992). In many other conform with a main pre-condition, they contained European basins, the ammonite biostratigraphy of the sufficiently well-enough preserved and fairly nume- Middle/Late Albian is poorly known in sharp contrast rous ammonite specimens. These ammonite faunas Authorʼs address: 1 Faculty of Geosciences, University of Bremen, Klagenfurter Strasse, 28357 Bremen, Germany. E-Mail: jens.lehmann@ uni-bremen.de © 2011 Gebrüder Borntraeger, Stuttgart, Germany www.borntraeger-cramer.de DOI: 10.1127/0078-0421/2011/0008 0078-0421/2011/0008 $ 3.25 124 Jens Lehmann Fig. 1. Palaeogeography of the early Late Albian in northern Europe with localities and areas mentioned in the text. Localities: Fs= Folkestone, Kent; HL, HK = Drilling core Lahe and Kirchrode I and II at the city limits of Hannover, Lower Saxony. KO = Schacht Konrad 1 section. APB = Anglo-Paris Basin, LSB = Lower Saxony Basin. Map modified after Ziegler (1990). have been described in greater detail (Wiedmann and Albian in the Lower Saxony Basin underlines that the Owen 2001; Owen 2007; Lehmann et al. 2007). The more advanced analysis and revision of the taxonomy taxonomy is based mainly on the monograph by Spath of the Hannover-Lahe fauna given in the present paper (1923–1943) on the British Albian fauna. Although is relevant and a correlation of the biostratigraphical still the most comprehensive systematic paper on this data is needed. subject, it contains much inadequacies that make identifications difficult without a study of a larger quantity of three-dimensional well preserved speci- 2. Geological setting mens. For this reason the present author decided to revise the taxonomy of the Hannover-Lahe core (Leh- All core sections referred to here have been obtained mann et al. 2007) by examining a large number of the around the city of Hannover in northern Germany. relevant types and further reference material in the During the Early Cretaceous this area has been the Natural History Museum in London. Determination of deepest part of the Lower Saxony Basin (Kemper distorted and predominantly fragmentary ammonites 1979), called ‘Harz foredeep’ by Owen (1979). Halo- is nevertheless challenging. The overall scarce know - kinesis influenced large parts of northern Germany ledge on the ammonite fauna of the Middle/Late during the Mesozoic and Cenozoic (e.g. Jaritz 1973), Ammonite biostratigraphy and correlation of Middle/Late Albian drilling cores in the Hannover area 125 and Cretaceous sediments in the eastern city limits of and lithological succession are given in Lehmann et al. Hannover were deposited in a subbasinal deep be - (2007). The ammonite biostratigraphy of Lahe revised tween the saltdomes of Benthe and Lehrte (e. g. Fen- in the present paper is based on 55 specimens that are ner et al. 1996; Fenner 2001b). Nevertheless, these sufficiently well preserved among a total number of sub-basins were in open connection to the Boreal Sea 72 specimens obtained from the core. in the north and to the adjacent areas of the foredeep Hannover-Kirchrode is located at the southeastern bordered on the south and west by the Harz and city limit of Hannover, only about 5 km S of the Lahe Brabant-Rhenish Massifs (e.g. Fenner 2001b, Fig. 1). drilling site. Two cores were drilled in 1991 and 1994 A more comprehensive introduction with respect to the (Kirchrode I and Kirchrode II respectively), less than Hannover-Lahe boring focussed herein was given by 2 km apart; details can be obtained e. g. from Fenner et Lehmann et al. (2007). al. (1996) and Fenner (2001). The Hannover-Kirchro- de sites are referred to as Kirchrode I and II in the following for simplicity. The ammonite data used 3. Locality and core section here is based on the work of Wiedmann & Owen (2001) details, conventions and Owen (2007). The latter paper furthermore figures a profile of the Schacht Konrad 1 section, referred to The Hannover-Lahe core (referred to as Lahe below) in chapter 5 below with respect to the lithostrati - was drilled in 1996 in the northeastern city limits of graphic subdivision. Basic information on the dating Hannover. There are no ammonites recorded for the of Schacht Konrad 1 sediments are given by Owen initial 15–30 m depth and other details about the exact (1979). ‘BGR’ is the acronym of the Bundesanstalt für location, core handling, sampling history, repository Geowissenschaften und Rohstoffe (Federal Institute Fig. 2. Significant ammonite occurrences in and biozonation of the Lahe core, Hannover, northern Germany. MA = Middle Albian. 126 Jens Lehmann for Geosciences and Natural Resources), Hannover, Ger- 96.50 m Euhoplites trapezoidalis; BGR 13941 many. All numbers following the BGR abbreviation are in- (Lehmann et al. 2007: Fig.9b). The expanded, smooth ventory numbers of the BGR collection. FO means ‘first lower flank was the argument for the former determi- occurrence’– the lowest stratigraphic occurrence of a ta- nation as Euhoplites nitidus. However, one of the xon – and LO means ‘last occurrence’. ventrolateral tubercles is preserved and this is a clavus as in E. trapezoidalis rather than a tubercle as in E. nitidus. 4. Revision of ammonite ranges 95.34 m Euhoplites sp.; BGR 13936. This specimen for the Lahe boring is a flattened ventral aspect fragment considered here to be indeterminable at species level; thus, the 4.1 General introduction former identification as Euhoplites cf. lautus is changed. The revised ranges of ammonite taxa from Lahe are presented in Fig. 2. The zonal scheme used in Figs. 2 93.66 m Euhoplites cf. sublautus; BGR 13931. The and 3 is founded on early work in the Anglo-Paris flexuous and generally fairly smooth ribbing requires Basin (e.g. Spath 1923–1943). Owen (1979, 1984) the former identification as Euhoplites nitidus to be adapted it to northern Germany and Lehmann et al. revised. (2007) gave a full account on definitions and limits 93.31 m Euhoplites cf. trapezoidalis; BGR 13930. The with respect to the Lower Saxony Basin. The chart same arguments as given for BGR 13916 (86.12 m) is (Table 1) here is different from that used by Lehmann relevant to the change of the former identification of (2007), following recent modifications by Owen Euhoplites cf. nitidus. (2007) and Owen in Lopez-Horgue et al. (2009). 93.09 m Euhoplites sp.; BGR 13927 (Lehmann et al. 4.2 Ammonite occurrences and 2007: Fig. 9e). A re-evaluation of the features shown taxonomic notes by this specimen indicate that these are insufficient for a determination at species level, thus the former iden- In the following list of ammonite occurrences, revised tification as Euhoplites nitidus is revised herein. identifications are given where applicable, the phrase ‘former identification’ each refers to Lehmann et al. 91.74 m Euhoplites armatus; BGR 13925 (Lehmann et (2007). Furthermore, critical features and important al. 2007: Fig. 9c). species discriminations are presented, particularly 87.40 m Euhoplites armatus; BGR 13918 (Lehmann et where details are difficult so see on the photos on al. 2007: Fig. 9h). Plate1 or in Lehmann et al. (2007). Determinations are given as core depth, in ascending order from the 86.57 m Euhoplites sublautus, BGR 13917. The for- base of the Lahe core to its top. mer identification as Euhoplites sp. was careful, but Ammonite identifications and revisions for those this fairly well-preserved specimen shows a good given in Lehmann et al. (2007) are as follows, given in resemblance with the type of E.