Journal of Mil_ropalaroniolog, 15: 37-54. 0262-821 X/96 $07.00 0 1996 British Micropalaeontological Society.
Foraminifera1 assemblages from the late Lower and Middle Cenomanian of Speeton (North k'orkshire, UK): relationships with sea-level fluctuations and watermass distribution
S. F. MITCHELL Department of Earth Sciences, The Jane Herdman Laboratories, Liverpool University, Brownlow Street. PO Box 147. Liverpool L60 3BX, UK
ABSTRACT - Twenty-seven marl samples from the late Lower and Middle Cenomanian of Speeton (North Yorkshire, UK) have been studied and six benthic foraminiferal assemblages (A to F) have been recognized by cluster analysis. These assemblages can be classified according to their constituent agglutinated foraminifera. Assemblages characterinxi by high abundances of non-calcareous agglutin- ates (A and E) have low numbers of planktics and ar .ociated with cold-water pulse faunas of mid Russian affinity (bclemnites, brachiopods and bivalvcs). These arc interpreted as representing a cold North Sca watermass. Assemblages characterized by high abundances of planktics (B and C) are associated with pulse faunas that lack cold-water elements and are interpretcd as representing a warm waterinass. lhe foraminiferal assemblages are also related to sea-level lluctuations and individual asscmblages weire probably depth controlled. The assemblages can. therefore. be used to construct a sea-level curve and this agrees with the placement of critical sequence atratigraphic surfaces (e.g. sequence boundaries and flooding surfaces). Journd of Mic.ropcr/aeonfo/oev.15: 37-54,
INTRODUCTION Lithostratigraphy The early Middle Cenomanian event like the Cenomanian- The section consists of alternations of thin flaser-mark and Turonian boundary event (CTBE) represented a time of micritic to calcarenitic, well-cemented limestones. The mark major environmental change (e.g. Paul et al., 1994: Mitchell are thin, usually about 1 cm in thickness, but occasionally up el a/., in press). Both events were associated with thc influx to l0cm in thickness. They have been piped down by of certain fauna I elements (e.g. the belemnite Actinocatnax burrows in places indicating that they are primary and the bivalves Oxytomu seminiiditm (Dames) and sedimentary phenomena and are not purely due to pressure Lyropecien (Aivqiiipectrr.1) urlesiensis (Woods)), a stable solution. The limestones are generally coccolith-rich micrites carbon isotope excursion and changes in sea-level (Paul rf with sparse shell fragments (predominantly inoceramid al.. 1994: Ih4itchell et al.. 1996; Robaszynski et al., in press). prisms and foraminifera) although two units of gritty Previous studies on foraminiferal changes have largely (calcarenitic) chalk are present (the Totternhoe and concentrated on the Cenomaniari-Turonian boundary event Nettleton stones). Stained acetate peels indicate that the (e.g. Jefferies, 1962; Jarvis et ol., 1988). This event was limestones have a ferroan calcite cement. characterized by extinctions of both benthic and planktic A lithostratigraphic numbering scheme for the chalk at foraminifera. The mechanism usually used to explain these Speeton (prefixed by SLC - Speeton Lower Chalk, above extinction. is the expansion of ithe oxygen minimum zone the Red Chalk - see Mitchell 1995) is shown in Fig. 2 (a key (Schlanger er al., 1987: Jarvis et ul., 1988). Previous studies to the symbols on the graphic log is shown in Fig. 3). The on the late Lower and early Middle Cenomanian have succession contains a number of distinctive lithological units, included those of Burnaby (19bl) and Paul ei a/. (1994, these are as follows: which included a summary of the results presented here). SLC6: six massive weathering chalk beds SLCA to F In this paper the foraminiferal succession from the late (Jeans' (1980) 6-chalk unit). Lower to late Middle Cenomanian of Speeton is presented. SLCX: a conspicuous massive weathering chalk bed. The data obtained are analysed using various statistical SLCIOA: a thin massive weathering chalk bed. techniques and the results compared with the palaeoccanog- SLCll: the Totternhoe Stone (or Grey Bed of Hill. 1888). raphic changes that occurred during this interval. with a prominent. thick marl (SLCIIA) at the base and another (SLCI 1C) near the top. The section at Speeton SLC13: prominent marl. During the: late Lower and Middle Cenomanian, Spceton SLClS: prominent marl. was situated in tlhe Cleveland Basin on the southern margin SLC17: the Nettleton Stone (SLC17B, a grcy weathering of the Southern North Sea Basin (Fig. I). To the south lay calcarenitic chalk) overlying a prominent marl (SLC17A, the East Midlands Shelf and beyond this the Anglo-Paris the Nettleton P2ycnodorzte Bed of Gaunt el ul.. 1992). Basin. The section studied here is situated below Buckton Cliffs [grid ref. TA 183 7471 and is part of the Ferriby Chalk MarlLchalk rhythms (couplets) in the Cenomanian of the Formation (Wood & Smith, 1978). Section details have Anglo-Paris Basin are currently interpreted as productivity previously been given by Hill (1888), Wright (1968). Jeans cycles under Milankovitch climatic control (Hart, 1987: (IYSO), Paul eta/. (1994) and Gale (1995). Ditchfield & Marshall, 1989: Leary & Ditchfield. 1989: Gale,
37 S. F. Mitchell
Speeton but based on couplet correlation with southern England (Mitchell, unpublished data; Paul et a/., 1994) the base of this zone (and thus the base of the Middle Cenomanian) is provisionally placed in couplet B38. Diagnostic Middle Cenomanian ammonites have not been found above SLCl 1C and neither the Tiirrilites uclrtus Subzone or the Acanthoceras jukeshrownei Zone can be recognized at present. Inoceramids. Inoceramid bivalves have bccn widely used in correlating the Cenomanian of NW Europe and this group of bivalves is common at Speeton. Zonal schemes have been developed by Keller (1982), TrBger (1989) and Wiedmann et a/. (1989), while Gale (1990, 1995) has related the inoceramid succession to his couplet-based Cenomanian timescale. The distribution of inoceramids is shown in Fig. 2. Inocerumiis virgatiis Schliiter occurs abundantly from SLC6A to SLC6F. This bioevent was recognized by Ernst et a/. (1983) in NW Germany and represents Gale’s (1995) B-division in the M. dixoni Zone (couplets B13-B 18). lnocerarnus schoendorfi Heinz occurs in beds SLCllA and SLCIIC, the presence of this species Fig. 1. Map showing locations of sections mentioned in the text. in the former bed agrees with its placement in the C. inerme Ammonite Zone. Fragments of inoceramids tentatively identified as Inoceranzirs utlanticits (Heinz) 1995). Individual, or distinctive groups of. couplets have occur in the upper part of bed SLC16 while occasional been correlated both within the Anglo-Paris Basin (Gale, well-preserved specimens occur in the Nettleton 1990) and between different basins in NW Europe (Mitchell, Pycnodonte Bed (bed SLC17A). Identifiable inoceramids unpublished data: Gale, 1995) using a variety of distinctive have not bcen found in the Nettleton Stone at Speeton, faunal, geochemical and lithological markers. Gale (1995) but the earliest examples of Inocerumics pictus Sowerby demonstrated, by comparing numbers of rhythms verses appear in the chalk bed immediately above the Nettleton radiometric dates, that these rhythms were likely to Stone (Fig. 2). represent the Milankovitch (21 ka) precession cycle. He Foraminifera. Planktic foraminifera, particularly the genus introduced a numbering system for these rhythms and the Rotaliporu, have been used to correlate Tethyan Cenoma- applicable portion of this scheme as applied to Speeton is nian succcssions (Kobaszynski & Caron, 1979). Unfortun- shown in Fig. 2. ately, in NW Europe many of the important planktic species are rare or absent, although a few species that Biostratigraphy occur at Speeton have proved to be useful (Paul et a/.. Biozonal schemes based on ammonites, inoceramid bivalves 1994). Rorulipora ex gr. reichrli Mornod has a limited and planktic foraminifera have been applied to the distribution in Tethyan regions (Robaszynski & Caron, Cenomanian of NW Europe, while several other groups 1979). At Speeton R. ex gr. reicheli occurs in small (belemnites, brachiopods and oysters) have been used as numbers in the marl at the base of SLCIOC and relatively biostratigraphic markers. These schemes, with regard to commonly in the prominent marl in mid bed SLC14 (Fig. Speeton, are discussed below. 2). The former occurrence finds a parallel in southern Ammonites. Unfortunately ammonites are rare and often England where R. ex gr. reicheli occurs in the mark of poorly preserved at Speeton but, where present, are couplets B40 and B41 (Mitchell & Carr, in prep.), and not invaluable. A poorly preserved example of Mantellieeras with the acme occurrence in couplets B34-B36 (as implied dixoni Spath was collected from bed SLC6F (Fig. 2) and by Paul et a/., 1994, p. 726). The concentration of R. ex this indicates the M. dixoni Zone of the Lower gr. reicheli in bed SLC14 is particularly significant since Cenomanian. Occasional, well-preserved ammonites are similar concentrations have been recognized at this level found in bed SLCl 1C; these include Acanthocerus at South Ferriby (Mitchell, unpublished data) and possibly rhotomagense (Brongniart), Turrilites costatus Lamarck also from Bornholm, Denmark (Hart, 1979). This pulse of and Sciponoceras haculoides (Mantell). This assemblage is R. ex gr. reicheli in the early T. acutus Subzone may characteristic of the T. acittiis Subzone of the A. prove to be a valuable faunal marker in the Middle rhotornagense Zone. In southern England, ammonites of Cenomanian. The absence of Rotaliporu below SLClOB this subzone appear in couplet B43 (Paul et a/., 1994) and means that the base of the R. rriclwli Zone is undefined the base of SLCllC (couplet C1) at Speeton can be at present. Rotaliporu cirshmani (Morrow) appears in bed provisionally taken as the base of the A. rhotomagense SLC13 at Speeton and marks the base of the R. cushmani Zone. There is no ammonite evidence for the early Zone (Fig. 2). Middle Cenomanian Cunningtoniceras inerme Zone at Carter and Hart (1977) recognized a significant increase in
38 Foraminifera from the Cenomanian of Yorkshire, UK
Proportion of ZONES ..- Carbon isotopes planktic su and foraminifera in Sequence stratigraphy 250 - 500 pm fraction (P 70)
FI3C (%P PDB) 2.0 3 .0 111
I 2s so 7s I(
L
4 SLC16 \ c 46 4
SLC14 7d -PB Break
A 841 I C 6 30
B I3 19 A Fs 7X b 17 F 16 35 a E E 14 b 33 E 12 SLC9 3I
B 30 8 2') B 28 B 27 B Zh I? 25 SLCS I324
1 KEY ,
i Identification cf I Present 1 Common 1 Abundant FS - initial flooding surfac ,B -sequence houndary iS - Ncltlelon Stone '3 - Nettlcton Pvcnodonl< BCd
'S ~ Tottcrnhoe Stone ' - 1. prcrus
Fig. 2. Lirhostratigraphy, rnacrofossil hiostratigraphy, planktic foraminifera] hiostratigraphy, sequence stratigraphy. stable isotope stratigraphy and inferred ammonite zonation of the late Lower and Middle Cenomanian at Speeton.i See Fig. 3 for key to symbols on graphic log.
39 S. F. Mitchell
by Robaszynski et al. (in press). They recognized six A Massive chalk horizons (onlap surfaces) which onlap the basin margins, _- Marl band locally onto Palaeozoic basement. Sequence boundaries preceding these onlap surfaces were placed at levels where 1Calcarenitic chalk there was a significant increase in the proportion of clay (increased acid insoluble residues). Jeans (1980) recognized a series of fining-upwards cycles in the Cenomanian of northeast England. Each cycle commenced with a thin winnowed calcarenitic chalk, often containing glauconitized reworked pebbles, and was followed by a thicker succession of coccolith-rich chalk. It is the bases of these fining-upwards cycles that correspond T\ Burrows with the onlap surfaces recognized by Robaszynski et al. (in press). Portions of three of these cycles are in the section Fig. 3. Kcy to symbols uscd in (he graphic logs. considered in this paper, with the Totternhoe Stone and Nettleton Stone representing the lower portions of two of thc proportion of planktic foraminifera in the mid- these cycles. On the East Midlands Shelf (e.g. South Cenomanian. They suggested that this represented a Ferriby, Hunstanton, etc.) the Totternhoe Stone rests on an significant break in the succession and called it the erosion surface cut into the Lower Cenomanian and ‘mid-Cenomanian non-sequence.’ This has proved to be a contains examples of A. primus (indicating lower couplet useful marker horizon (Carter & Hart, 1977: Paul et al., C1) and reworked chalk pebbles at its base (Jeans, 1980: 1994) at the base of couplet C11 (Fig. 2) for which the Gaunt et al., 1992; Mitchell, unpublished data; Paul et ul., non-interpretative term PB break has been applied as there 1994). At Speeton, however, A. primus occurs in the upper is no apparent break at this level (see Paul et al., 1994). part of the Totternhoe Stone (i.e. bed SLCllC), the lower Other faunal groups. Some other fossil groups are part showing a passage downwards into coccolith-rich chalks important stratigraphically, these include belemnites, (transition in SLCIOC). The base of SLCllC is interpreted brachiopods and oysters. The belemnite Actinocamax as the onlap surface while the calcarenitic chalks below primiis Arkhangelsky is restricted to bed SLCl 1C (i.e. represent part of the lowstand deposits. In the absence of lower couplct CI) at Speeton (Fig. 2). This species occurs clastic (clay) input into the Cleveland Basin, sequence in lower couplet C1 throughout NW Europe (Paul et a/., boundaries are difficult to recognize at Speeton and 1994: Gale. 1995). At Speeton this belemnitc is accom- correlative horizons are suggested in Fig. 2 from the work of panied by common examples of the small bclemnite Robaszynski et al. (in press) in the Anglo-Paris Basin. Helrnznocaniux howrri Crick which ranges from bed SLCllC to bed SLC12A (couplets CILC2). This species Stable isotope geochemistry occurs at the same level throughout NE England and in Stable isotopes of carbon (6I7C) have been used as a northern Germany (Christensen et a/., 1992). powerful stratigraphic tool (Scholle & Arthur, 1980: Gale et The rhynchonellid brachiopod Orhirhynchiu niuntelliuna a/.. 1993; Jenkyns et a/., 1994; Paul et al., 1994; Mitchell et (J. de C. Sowerby) occurs at three levels at Speeton (Fig. 2). ul.. 1996). Within the interval considered in this paper, two The three concentrations of this species are well recorded short-term carbon stable isotope (6°C) excursions are elsewhere in NW Europe (e.g. Jeans, 1980: Gale, 1990, 1995; present, superimposed on a long-term general increase in Paul et ul., 1994) but show minor diachroneity. For instance, background 6°C (Fig. 2). The long-term 6°C curve the lowest concentration (see Gale. 1995 for details) occurs correlates with progressive sea-level rise during the in couplets B22-23 at Speeton. B21 at Southerham (Sussex) Cenomanian (Hancock, 1989; Gale, 1995) and can be and B19-22 at Raddeckenstedt (Lower Saxony, Germany). explained through increased storage of organic carbon in These concentrations of Orhirhynchia at Speeton are also deep water masses or burial of organic carbon (Mitchell et characterized by the appearance of other brachiopods that al., 1996). The short-term excursions are associated with are otherwise absent: 7’erehratLdinn protosfriatitla Owen in sequences boundaries and/or onlap surfaces (Mitchell & the lowest pulse and T. protostriatiilu and Grusirhynchia Paul, 1994: Mitchell et al., 1996). The lower excursion (MCE grusiuna (d’orbigny) in the middle pulse (Fig. 2). I) is represented by two positive peaks (MCE Ia and Ib) Concentrations of oysters have also been used as which occur in the same couplets (peaks in B41 and CI) biostratigraphic markers. Small Pycnodonir sp. occur at two throughout all sections studied to date (Paul et a/., 1994, levels within the succession studied: beds SLC13 and Gale, 1995, Mitchell et al., 1996). The lower excursion SLC17A. The latter horizon (the Nettleton Pycnodorite Bed occurs in the lowstand deposits while the upper peak occurs of Gaunt ct ul., 1992) can be traced into Germany (the in the early transgressive deposits just above the onlap Pycnodonte evcnt of Ernst et a/.. 1983) and southern surface. Thc upper excursion (MCE 11) is represented by a England (base of ‘Jukes Browne’s bcd VII,’ Jukes-Browne small negative excursion associated with lowstand deposits & Hill. 1903: Gale. 1995). at Speeton. Short-term carbon excursions in the Cenoma- Sequence stratigraphy nian have been explained through changes in carbon cycling The sequence stratigraphy of the Cenomanian of the relatcd to variations in nutrient fluxes controlled by Anglo-Paris Basin has recently been documented in detail sea-level fluctuations (Mitchell et a/., 1996).
40 roraminitera ifrom the Cenomanian of Yorkshire. UK
TECHNIQUES AND METHODS Diversity. The characterization of diversity is difficult because the number of taxa in a sample is dependent on the number of specimens picked. Furthermore, simply express- Sampling and processing ing the number of species present gives no information on Trial attempts demonstrated that the chalks at Speeton are the population structure (i.e. relative abundance of different too strongly cemented to process for their foraminifera. In species). In this paper three methods are used to investigate contrast. the mark are easily processed. About 200 g of each diversity. Graphical methods are frequently advocated since marl (27 samples in total) was carefully collected in the field these provide all the information contained in the to avoid contamination. The samples were then placed in population (see Magurran. 1988 for details). In particular, suitable containers and processed by freeze-thawing with rank/abundance (cumulative percentage using a com- water until disaggregated (usually two to three freeze-thaw plimentary logarithmic scale vs. species rank) plots can be cycles). The residues were then sieved through standard used to differentiate communities. meshes. In each case at least 300 specimens were picked The logarithmic series model was introduced by Fisher et from the 250-500pm size fraction. In all cases the number al. (1943). This model has been widely applied to of specimens recovered from the 500-1000 pm size fraction foraminiferal assemblages (see Murray, 1973, I99 1) and the was significantly smaller (by two orders of magnitude) than a-diversity index is applicable as a measure of species those present in the 250-500 um size fraction. Because of richness where the model holds. Values can be read from the problem of combining size fractions that arc not plots on previously prepared graphs (see Murray, 1991 for completely picked, all statistical studies were carried out on details). Values typically range from 5 to 20 on recent the 250-500 pni size fraction. Furthermore all species in the normal marine shelves and 5 to 25 in slope or bathyal 500-1000 um fraction were also present in the 250-500 pm environments (Murray, 1991, p. 291). size fraction. All benthic foraminifera1 data are expressed as The Shannon index (H'). based on information theory, is percentages of the total benthic fauna in the 250-500 pm also relatively popular (Peet, 1974; Magurran, 1988). This is size fraction. sensitive to both species richness and the underlying species Forami niferall taxonomy follows Loeblich & Tappan abundance distribution. Values typically fall within the (1987) with additional data from Carter & Hart (1977), range 1-35 (May. 1975) with higher values representing Barnard Kc Banner (1980), Hart rt (1989) and Meyn & al. both greater species richness and greater evenness in the Vespermann ( 1994), amongst others. Representative taxa species abundance distribution. For modern assemblages, H' are illustrated on Plate 1 and Fig. 5. ranges from 0.6 to 2.75 on modern shelves and, 0.75 to 4.1 on slopes (Murray, 1991, p. 289). Triangle diagrams. Triangle diagrams represent a method Statistical techniques and indices of plotting three variables on the same graph (strictly the While living foraminiferal assemblages provide information relative variation) and have been widely used in on biomass (it species living together), fossil assemblages foraminiferal studies. Three triangles arc used here: the provide information only on species that are preserved suborder (test structure: agglutinated vs. , calcareous together and are therefore dependent on changes in hyaline vs. calcareous porcellaneous) diagram (see Murray, production rate, transport and non-preservation/dissolution. 1973, I99 1. for details): the feeding strategy (herbivores A number of statistical techniques and indices have been vs. detritivores vs. suspension feeders) diagram (see Jones used in this studly; these are outlined below. & Charnock, 1985); and a diagram showing the variation P (planktonic)%,and NCA (Non-Calcareous Agglutinate)%. in agglutinates (introduced here). The latter diagram uses P Yo is often incorrectly called the PB ratio but is actually the NCA, the Murssnnel/u1 Trituxia lP.seiid~~t~.~[iilari~ll~iand expressed as a percentage. In modern oceans P Y is the t'lrctina/ArenohLilinlinu on the vertices (see below). generally very low on shelves arid high in basins, the main Cluster analysis. Cluster analysis is a collective term for a rise occuring either in the outer shelf or at the shelf variety of agglomerative hierarchical methods that operate margin (Stehli XC Creath, 1964; Kafescioglu, I971 ; Gibson. on a matrix of similarities among a set of samples (Digby 1989 and Murray, 199 1). llsing this as a basis, P % has & Kempton. 1987). Different clustering criteria give rise been used to infer palaeobathymetry in the Cenomanian to different cluster diagrams. Complete linkage (or (Hart & Carter, 1975; Carter & Hart. 1977 and Hart, furthest member) cluster analysis tends to produce a large 1980). In this paper P YO is used for the proportion of number of very compact spherical clusters, and this planktic foraminifera in the 250-500 pm size fraction method of clustering has been used here. The dataset used expressed as a percentage of the total foraminifera. here is particularly suitable for cluster analysis as all but The use of the proportion of NCA foraminifera as an one of the species range throughout the stratigraphical index was introduced by King ef a/. (1989) and King (1989). interval investigated. Cluster analysis, by itself, does not NCA-dominated assemblages occur in deep water and Flysh justify the clusters produced, but the technique can be type assemblage:; with low nutrient supplies (Moullade st al., easily integrated with other techniques such as principal 1988, Kuhnt & hloullade, I9Y1 and Kuhnt et a/., 1989, 1992). component analysis (PCP). NCA Oh, as used in this paper, is the proportion of Principal component analysis. Principal component analy- non-calcareous agglutinated foraminifera in the 250-500 pm sis (PCP) is an indirect ordination method that creates a size fraction expressed as a percentage of the total benthic new set of orthogonal axes with axes ranked to contain foraminifera. the maximum amount of variance possible in the sample
41 S. F. Mitchell
(Krzanowski, 1988). For instance, in a data set of n RESULTS AND STATISTICAL ANALYSES samples containing say N species (i.e. N dimensions The distribution of the benthic foraminifera recovered in expressed as orthogonal axes, where N sn), a PCP this study is shown in Fig. 4, a list of all the benthic taxa analysis creates a new set of orthogonal axes (the recorded is given in Table 1 and representative taxa are eigenvectors) such that eigenvector 1 contains the greatest shown in Plate 1 and Fig. 5. A spindle diagram showing the variance possible within the sample by one variable. variation in the relative abundance of the most important eigenvector 2 the next greatest amount of variance, etc. In taxa is shown in Fig. 6. Up section. there is a gradual this manner the variation in the sample can be reduction in the proportion of NCA taxa (particularly approximated by a smaller number of dimensions. Ammodiscus cretaceous and Hyperumminu guultinu (samples
m E D 5 SPEETON c -0e, D
m
D8 to D1
;Lc1 t
C 46 to 11 SLClS c
jLC14
FLC13. __ c 10 1: 1: 3; I. . -c I- C6 :c s1 C3 IC 2: CI = .. B 43 . B 42 B 41 . .. B 40 B 39 I1 .. sz I B 34
B 33 a SLC9 B 31 B.10
B 28 . m B 26 B 25 ___ ~ SLC8 B 24 . ZLC7 B 23 Fig. 4. Distribution of benthic foraminifera from the late Lower and Middle Ccnornanian at Speeton. Successive occurrences joined. See Fig. 3 for key to symbols on graphic log.
42 TEXTULARIINA ROTALIIXA a- Non-calcareous agglutinated (NCA) taxa Chilostomellacea 3 Hyperumminu guultinu Ten Dam. Bartenstein & Bolli 1986, pl. 1, figs 14-17. Guvelinellu berthelini (Keller). Jarvis et uI. 1988, figs Ilk, I. Ammodiscus cretuceus (Reuss). King 1989, pl. 9.1, fig. 3. Guvelinellu reussi Khan. Khan 1950, pl. 2, figs 17-18. Ammodiscus sp. 386 of Kuhnt & Moullade, 1991, pl. 4, fig. C. Guvelinellu cenomunicu (Brotzen). Hart et ul. 1989, pl. 7.10, figs 9-11. Glomospirellu guultinu (Berthelin). Loeblich & Tappan 1987. pl. 38, figs. 3-4. Guvelinellu intermedia (Berthelin). Hart et ul. 1989, pl. 7.1 I, figs 7-9. Huplophrugmoides nonioninoides (Reuss). Meyn & Vespermann 1994, pl. 1, figs. 1-8 Linguloguvelinellu tormarpensis Brotzen. Carter & Hart 1977, pl. 1, figs 31-32. Pelosinu sp. Linguloguvelinelluglobosu (Brotzen). Carter & Hart 1977, pl. 1, figs. 12-14. Ammovertellina sp. Linguloguvelinellujurzevue (Vasilenko). Carter & Hart 1977, pl. 1, figs. 29-30. Turritellellu sp. Gyroidinoidespurvu Khan. Khan 1950, pl. 2, figs 12-14, 19. 3, Verneuilinacea Nodosariacea Plectinu cenomunu Carter & Hart. Hart et u1. 1989, pl. 7.2, fig. 10. Lenticulinu muensteri (Roemer). Meyn & Vesperman 1994, pl. 24, figs. 1-17. Plectinu maria (Franke). Carter & Hart 1977, pl. 2, fig. 81. Surucenuriu,frunkeiTen Dam. Bartenstein & Kovatcheva 1982, pl. 3, fig. 19. Guudryinu uustiniunu Cushman. Carter & Hart 1977, pl. 2, fig. 10. Astucolus schloenbuchi (Reuss). Meyn & Vesperman 1994, pl. 42, figs. 1-6. Spiroplectinutu plunu (Gorbenko). Loeblich & Tappan 1987, pl. 143, figs. 6-8. Astucolus humilis (Reuss) Meyn & Vesperman 1994, pl. 39, figs. 6-17. Eggerellinu brevis Marie. Jarvis et ul. 1988, fig. lO(0 Astucolus sp. nov. A. C Eggerellinu murue Ten Dam. Hart etul. 1989, pl. 7.2, figs 1-2. Frondiculuriu gaultinu Reuss. Chapman 1894a. pl. 111, fig. 7. 7: Tritcuriu pyrumiduru Reuss. Hart et al. 1989, pl. 7.3, figs 2-3. Frondiculuriu perovutu Chapman. Chapman 1894a. pl.IV, fig. 5. Psilocithurellu recta (Reuss). Bartenstein & Bolli 1986, pl. 6, figs 7-8. Ataxophragmiidae Psikucithurellu striolutu (Reuss). Bartenstein & Bolli 1986, pl. 6, fig. 10. Arenobuliminu advenu Cushman. Hart eral. 1989, pl. 7.1, fig. 5. Plunuluriu strombecki(Reuss).Bartenstein, Bettenstaedt & Bolli 1966, pl. 2, figs 11 1-1 14. Arenobuliminu elongatu Bamard & Banner (1980). pl. VI, figs. 2-4 Plunuluriu biochei Berthelin. Chapman 1894b, pl. VIII, fig. 14. Arenobuliminupseudulbiunu Bamard & Banner (1980), pl. VII, figs. 15-16. hevidentulinu grucilis d'orbigny. Bartenstein & Bolli 1986, pl. 3, figs 4-6. Hugenowello elevatu (d'orbigny). Bamard & Banner 1953, pl. 8, figs. 11A-D. Luevidentulinu subguttiferu Bartenstein. Bartenstein & Bolli 1986, pl. 3, fig. 13. Ataxophrugmiumdepressurn (Perner). Jarvis et ul. 1988, fig. 10(0). hevidentulinu cylindroides Reuss. Bartenstein & Bolli 1986, pl. 2, figs 38-39. Pseudotextuluriellu cretosu (Cushman). Hart et ul. 1989, pl. 7.2, figs 11-12. hevidentulinu cf. nunu (Reuss). Meyn & Vespermann 1994, pl. 7, figs. 8-16. Pyrumidulinu puuperculu (Reuss). Bartenstein & Bolli 1986, pl. 5, figs. 30-31. Textulariacea Pseudonodosuriu humilis (Roemer). Bartenstein & Bolli 1977. pl. 6, figs 9-12. Murssonellu rrochus (dorbigny). Bamard 1962, text-fig. 3. Nodosuriu nudu (Reuss). Meyn & Vespermann 1994, pl. 6, figs. 4-9. Murssonellu sp. nov. A. Dentulinu sp. Dorothia gruduta Berthelin. Bartenstein & Bolli 1986, pl. 1, figs 38-39 Guttulinu sororiu (Reuss). Barnard 1962, Text-figs. 6a-b. Dorothiu,filtformis (Berthelin). Hart et ul. 1989, pl. 7.1, figs 11-12. Globulins priscu (Reuss). Bartenstein, Bettenstaedt & Bolli 1966; PI. 3, figs 24-25. Dorothiu sp. nov. A. Oolinu globosu (Monyagu). Chapman 1893, pl. VIII, figs. la-b. Textuluriu chapmuni Lalicker. Hart er al. 1989, pl. 7.3, fig. 1. Bulluporu luevis (Sollas). Bartenstein & Bolli 1986, pl. %fig. 16. Textuluria sp. nov. A. Rumulinu uculeutu Wright fusiform variety. Bartenstein, Bettenstaedt & Bolli 1966, pl. 4, figs 316-329 Textuluriu sp. nov. B. Rumulinu uculeutu Wright. Bartenstein & Bolli 1986, pl. 3, figs 29-32. Rumulinu grundis (Fuchs). Bartenstein & Bolli 1986, pl. 3, figs 39-40.
MILIOLINA Spiroloculinu papyrucem (Burrows, Sherborn &Bailey). Carter & Hart 1977, pl. I, fig. 6.
Table 1. List of all benthic foraminifera1 taxa recorded from the late Lower and Middle Cenonianian at Speeton.
wP S. F. Mitchell
Plate 1 44 Foraminifera from the Cenomanian of Yorkshire, UK
I-Y), althouglh A. cretaceous ireappears in samples 12-18). (ii) calcareous taxa occur throughout; Plectiriu and Arenobriliminu become the most important (iii) Acid resistant taxa (Arenabiilinzinu and NCAs) show taxa between these two pulses of NCA taxa (i.e. in samples quite different abundance patterns suggesting primary 9-1 1). Above sample IS certain calcareous agglutinated control on the assemblages; (7rilaxiiz pyramiduta) and calcareous hyaline (Gavelinc~lla (iv) samples with high proportions of NCA taxa contain very reiissi, Gyroidinoides parua and Leniiculinu mueristeri) taxa well preserved planktic foraminifera (e.g. sample 8). increase in nuinbers (Fig. 6). Dissolution can be rejected as the major control on the foraminiFera1 assemblages for the following reasons: Triangular diagrams (test structure and feeding strategy) All the samples plot within the normal marine field on the (i) all the rnarls sampled throughout the section are test structure diagram (Fig. 7A). On the feeding strategy visu;illy very similar;
Fig. 5. RepresentaLtive calcareous hyaline foraminifera from Speeton. 1-2, Gauelinella ceriomanica (Rrotzen). (X83): 3-4. Gavelinella reussi Khan (X78); 5-6. Gavelinella herrhelini (Keller) (X89): 7-8. Gvroidinoirles parva Khan (7. X102: 8. X120). All from sample 23.
Explanation of Plate 1. Represenlative agglutinated foraminifera from Speeton. Figs 1-2. fkctitm ccwommu Carter bi Hart, sample 1 1 (XSX): Fig. 3. Plecrina muriue (Franke), sample 11 (~58).Fig. 4. Spiroplecrinarn plnnu (Gorhenko), samplc 23 (~54).Fig. 5. Tritaxiu pyranzidatu Reuss, sample 23 (X69). Fig. 6. Arenobulrmina pseudulbiczna Barnard bi Banner, sample 11 (XXX). Figs 7-8. Arenobrtlin?ina udvena Cushman. sample 11 (XYS). Figs 9-10. Pseiidotexrltrhrlella crelosu (Cushman), sample I1 (XSO). Fig. 1 I. Aruxophrugrnium depressurn (Perner), sample 22 (X6X). Fig. 12. Hyperumniiria gaulrina Ten Dam, sample 2 (X47). Fig. 13. Anzmodiscus crttawus (Keuss). Tamplc 2 (X58). Fig. 14. Dorofhiu gradurn Berthelin. sample 23 (X54). Fig. 15. Marssonella rrochrrs (d’orhigny), sample 23 (X83). Fig. 16. Eggerellinu hrruis Marie. sample 23 (X 104)
45 S. F. Mitchell
SPEETON cretosa nominoides .-c globosa -1 udvena
OgU parva gaultina cretaceous trochus reussi cenomanica intermedia muensteri gradata cenomanica mariae pyramidata Pseudotextulariella Lenticulinu Plectina Lingulogavelinella Gyroidinoides Plectina Gavelinella Gavelinella Haplophragmoides Gavelinella Marssonella Dorothia Ammodiscus Arenobulimina Hyperamminu Tritaxia I1
/SLC1 6 ~
I sLc9 k
ii m mQ m m U m 0 C .e M P -.e '6 0% 1 sE - Proportion of benthics Ys - 0 ? a 8 in250-500pmsize 4 9 fraction .- z" 72 e 8
Fig. 6. Spindle diagram showing the percentage abundance of the morc important benthic foraminifera from the late Lower and Middle Cenomanian at Speeton. See Fig. 3 for key to symbols on graphic log. diagram samples 1-7 plot in the upper bathyal field and are shown in Fig. 9. All curves approximate to the log series samples 8-27 plot in the shelf field (Fig. 7B). model and this justifies the use of Fisher's a-diversity index. The graph illustrating Fisher's a-diversity index shows two Diversity peaks (Fig. 9): a minor one in samples 7-10 and a more Figure 8 shows a rank/abundance plot for all the samples significant one in samples 21-25 The Shannon index (H') and shows that there are significant variations in population graph shows a similar pattern (Fig. 9). Additionally sample structure. Five groups can be recognized (1 to 5) and these 12 shows high values of both a and H' (Fig. 9).
46 Foraminifera from the Cenomanian of Yorkshire. UK
Herbivores B Suspension Calcareous A Agglutinated feeders hyaline
Fig. 7. Triangle diagrams. (A) tat structure diagram. (B) feeding strategy diagram.
Cluster analysis significantly higher percentages of Lenticulina muensteri, A complete linkage cluster analysis for all samples of Gyroidinoides parua, Gauelinella reussi, Lingiilogauelinellu benthic foraminifera is shown in Fig. 10. The samples cluster glohosa and L. tormarpensis than the other assemblages, into six assemblages labelled A to F and the stratigraphic assemblage B always having more than assemblage C. This distributjlon of these is shown in Fig. Y. The relative equates directly with P YO and suggests coeval changes in abundance of lthe important benthic species (together with P both planktic and benthic foraminiferal communities. Yo which was not used in the clustering) is shown in Fig. 11. Assemblages may most easily be classified by the dominant Principal Component Analysis (PCP) agglutinated foraminiferal species found in each assemblage. The results of a PCP on the benthic foraminifera from Speeton is shown in Table 2. The PCP shows that 75 YOof A. Ammodiscus-Hyperammina assemblage. the variance is represented by the first three eigenvectors. B. Tritaxiu assemblage. The first eigenvector accounts for 44.7 YO of the variance C. Tritaxia -Marssonella assemblage. and shows a strong positive correlation with Hyperammina D. Ti.itaxirc-Marssonella-Dorothiu assemblage. gadtinu and Ammodiscus cretaceous and moderate negative E. hqarssonella-Pseudotextulariella-Ammodiscits assem- correlations with blage. Triraxia pyramidata, Lenticulina muensteri and many of the Gavelinella species. The second eigenvector F. A renobiilimina - Plectinu assemblage. accounts for 19.1 YO of the variance and shows strong It is also significant that assemblages B and C have negative correlations with Arenobuliniina aduena and
0
99.9 0 10 2 0 30 40 SPECIES RANK Fig. 8. Rank/ahundance plot for the samples from Speeton. Note five groupings.
47 S. F. Mitchell
3 SPEETON - D8 to D1 __ - 27 W-
C 46 to c 11
- c 10 c 9- C 81 c 7- C6 c 5 c4I C3 :c 2 : CI B 41 3 42 m 3 40
3 39 318
3 34 __ 3 33
3 31 330 329 3 28 rnmi 3 25 - 3 24 - 3 23 e, 121 0 20 40 60 8 1 2s so 75 1 0 - F 0 2.5 7.5 I I12 - S B 22 5 Fisher’s Shannon index P% - $5 a-diversity H’
Fig. 9. Comparison bctwcen various benthic diversity indices (a, H‘ and five groupings from Fig. 8) compared with NCA %, P ‘/o and cluster analysis assemblages (A-F).
Plectinu cenomaria and moderate positive correlations with Psei*dotexticlariella-Marssonella groups and the third, the Tritaxia pyramidata, Pseiidotextiilariella cretosa, Marssonella ratio between the Tritaxia and the Pseudotextuluriella- trochus and Gavelinella herthelini. The third eigenvector Marssonella groups. accounts for 11.4 % of the total variance and shows a Figure 12 shows the six assemblages recognized in the positive correlation with Tritaxia pyramidata, Gavelindla cluster analysis plotted on a rotated three-dimensional plot reussi and Imzficiilina muensteri, strong negative correla- using the first three eigenvectors as axes. This clearly tions with Pseiidote.vtuluriellu cretosa and Marssonella separates assemblages A, E and F. Figure 13 shows the trochus and moderate negative correlations with Plectina variation represented by the first two eigenvectors as a and Arenobulimina udvena. In terms of the agglutinates, the triangular diagram (vertices: NCA, Arenobulirnina + first eigenvector may he interpreted as representing the Plectina, Marssonella + Trituxia + Pseudotextulariella) and proportion of NCAs in the assemblage, the second, the ratio separates assemblages A and F from all the other between the Arenohiilimina-Plectina and the Tritaxia- assemblages. Figure 14 shows the variation represented by
48 roramlnvtera from the Cenomanian of Yorkshire. UK
2 E
A
1ID F 11 '9
20 D 1') 1%
C
E
B Fig. 10. Complete linkage cluster analysis of the samples of benthic foraminifer,~from Speeton.
Fig. 11. Average abundancc of the more important taxa in the six assemblages recognized in the cluster analysis. the third eigenvector (proportion of Trituxia amongst Variance Speeton T'ritaxia, Marsisonella and P.Feunotexrulariella) plotted Value Proportion against hCA % and this plot separates the remaining el 302.553 44.7 assemblages. 129.164 19.1 77.020 11.4 Principal Component Analysis 61.759 9.1 32.772 4.8 INTERPRETATION Based on Covariance 21.071 3.1 The distribution of modern planktic foraminifera is 15.536 2.3 controlled by both watcr deptlh and the distribution of 10.953 I .6 7.333 1.1 different watermasses (c.g. temperature, salinity, nutrients. 1;el0 5.871 0.9 Murray, 1995). Previous work on the distribution of planktic EigenVectors foraminifera in I.he Cenomanian (Carter & Hart, 1977) has VI v2 v3 v4 v5 Hyperammina gaulrina 0.297 -0.114 0. I38 -0.1 10 0.257 largely concentrated on water dcpth. The PB break clearly Ammodiscus ereraceus 0.853 0.006 0.091 -0. I46 -0 172 represents a dramatic change in the mid-Cenomanian. Haploph. nonioninoides 0.053 -0.050 0.022 -0.004 0.043 Plecrina cenomana -0.067 -0.275 -0.279 0.081 0.015 Long-term oxygen isotope curves through the Cenomanian Plecrina marire -0.049 -0.083 -0. I84 0.059 -0012 (Jenkyns tit al.. 1994) suggest a progressive warming of Arenobul. advena -0.101 -0.674 -0.338 -0.029 -0.179 Arenobul. elongala -0.009 -0.01 I -0.045 0.014 -0.022 surface water with a reversal in this trend at the Arenobul. pseudalbiana -0.004 -0.001 0.003 0.016 0.020 <:enomani;in-Tul-onian boundary event. It is therefore Hagenowella ellevara 0.009 -0.022 -0.010 0.007 0.024 Araxophragmium depressum 0.017 -0.032 0.003 -0.013 0.024 possible that the appearance of abundant large planktic Eggerelii~brevis -0.026 0.064 -0.089 -0.000 0.031 Eggerellina mnrilr -0.CQ3 -0.016 -0.014 0.020 -0.001 foraminifera at the PB break might be related to surface Tritaxia pyramidara -0.132 0.190 0.299 0.213 -0.755 warming or thc progressive northerly movement of a warm Spiroplecfi~plana -0.019 0.005 0.058 0.049 0.008 Pseudorexrulariella crerosa -0.013 0.219 -0.297 0.062 -0.001 watermass. Marssonella rrochus 0.030 0.501 -0.555 0.061 -0.102 Both long-term changes in the foraminifera1 abundances Dorothia gradata -0.003 0.057 -0.013 -0.104 0.215 Texrularia chnpmani -0.01 1 0.009 0.018 -0.003 0.017 and the foraminiferal assemblages (A-F) can be related to Gavelinella berrhelina -0.101 0.261 -0.027 0.108 0.344 changes in sea-level. During the Cenomanian there was a Gavelinella reussi -0.141 0 100 0.309 -0 002 0.244 Gavelinella cenomanica -0 295 0 083 0. I06 -0.859 -0. I 08 progressive rise in sea level which saw the spread of chalk Gavelinella intermedia -0.099 -0.083 0.138 0 032 -0 131 deposition across the whole of England (Hancock, 1989, Gavelinella rormarpensis -0.007 0.005 0.016 -0.003 -0.008 Gyrordinordes parva -0.050 -0.002 0.1 13 0.124 -0.014 Robaszynski et ul. in press). This is reflected in the Lenticulino muensreri -0.116 -0.108 0.307 0.337 0.179 progressivt incr'ease in 6°C (Mitchell et ul., 1Y96). At Other Nodosartaceans -0.035 -0.007 0.110 0.092 0.025 Speeton the foraminifera1 assemblages show a change from Table 2. Summary of Principal Component Analysis (PCP) of NCA-dominated assemblages in the late Lower Cenomanian bcnthic foraminifera from the 250-500 lm size fraction from to planktic-dominated assemblages in the late Middle Specton.
49 S. F. Mitchell
1 4
u2
U 9
27 19 2 0 22
u2 a C
Fig. 12. Plot of six assemblagcs recognized in the cluster analysis on the rotated fii'st three eigenvectors.
Cenomanian. This change in the foraminiferal assemblages smaller-scale variations with the appearance of different can be related to more open oceanic circulation with benthic foraminiferal assemblages. The late Lower to early increases in eustatic sea-level (King et al., 1989). Although Middle Cenomanian sequence (Sequence 3 of Robaszynski the high NCA samples (1 to 7) plot in the upper bathyal et nl. in press) is characterized by three foraminiferal field in the feeding strategy triangular plot (Fig. 7B), the low assemblages (Fig. IS). The highstand deposits arc a-diversity (a = 2.5-5.0) of these samples does not suggest characterized by assemblage A (NCA dominated) which an upper bathyal environment (compare Murray, 1991, p. passes to assemblages D and F in the lowstand deposits. The 291). These assemblages were probably controlled by lowstand is also associated with an increase in diversity from nutrient supply rather than water depth (see discussion in a = 2.5-5.0 in the high stand deposits to a = 5-7 in the low Jones &L Charnock, 1985, p. 312-313). stand deposits. At Speeton, the correlatives of the sequences recognized The Middle Cenomanian sequence (Sequence 4 of by Robaszynski et al. (in press) do not show alternations of Robaszynski et al. in press) is characterized by a succession NCA - and planktic-dominated assemblages that charac- of foraminiferal assemblages (Fig. 15). The transgressive terize long-term sea-level change. Instead, these show deposits are characterized by assemblages E and D, the highstand deposits by assemblages C and B and the lowstand deposits by a return to assemblage C. Diversity is
NCA \ 'B Anglo Pan\ Bwn 80 )'. . Eddy Middle Cenommim !\ / A\\emblage A c' A A\\ernblage B 60 A\\embldge C \ / A\\embldge I> \ A\\emhlage E 40 As\ernbldge F
20
0 .. -.. I00 80 60 40 20 0 Arenohuiiminu Mur~~otiellu+ Trituxia NCA (9%) + Plectinu + Pseudotextuluriellu Fig. 14. Scatterplot showing T % {Trifuxiu/(Trirmiu + Fig. 13. Trianglc diagram (based on PCP analysis). Note distinction Murssonelltr + fseudotexri~~ariell~)}against NCA %. showing of assemblages A and F from the cluster analysis. distinction of cluster assemblages.
5 0 Foramintt'era from the Cenomanian of Yorkshire, UK
ASSEMBLAGE A 3 SPEETON - FEDCB ;;I; D8 ,,#',,#I ,>IN to ;;,II, TD DI ,,## - ...... ,...... /;,s,i
,,'I ,,#I
,,IS~ , ~ SMV I,;;
2 46 to 211
- :: 10 c 9- c 81 c 7- C6 c 5: TD c4 C3 c2. c1 I41 ...... I42
I 40 - SMW i 39 - -____ -38 37 36 35 ...... 34 - 33 - 32 31 - -30 29 HS -28 27 x25 - 24 __ - RISE 1 0 2.5 5 7.5 I' 1 20 40 60 E 0 Fisher's NCA (%) a-diversity
Fig. 15. Us(: of foraminiferal assemblages to produce sea-level curve. Note close agreement between sea-level curve and sequence stratigraphic surfaces (except lower sequence boundary which could be placed in couplet B39). and relationships with diversity and NCA %. low in the transgressive deposits (a = 2.5-5.0) reaches a model agrees with the independently derived sequence peak in the highstand deposits (a = 7-8) and falls again in stratigraphic surfaces (sequence boundaries and flooding the lowstaind deposits (a = 3). surfaces), although the sequence boundary in sequence 3 (of Burnaby (I9Ol) discussed the depth of the benthic Robaszynski et ul. in press) would be better placed a little foraminifera from the Chalk Marl of Cambridgeshire. By higher in couplet B39. It is perhaps significant that the comparison with living species he suggested a depth range highest diversities are found in the lowstand deposits in for four tam from the Chalk Marl. Arenobulitnina spp. were sequence 3 and the highstand deposits in sequence 4 and not interpreted as living in very shallow water, Textidaria in in the transgressive deposits. intermediate water depths and Gyroidinoides and 7ritaxiu in deep water. These results are consistent with the sequence DISCUSSION stratigraphy and foraminiferal assemblages from Speeton. In Jefferies (1962) studied the faunas of the plenus marls in Fig. 15 a sea-level curve is constructed assuming that the detail and recognizcd the appearance of species with central foraminiferal assemblages (A-F) were depth related. This Russian affinity (Actinocumux, Aequipecten (Lyropecten)
51 S. F. Mitchell
planktic foraminifera is associated with an increase in arlesien.sis, Oxytoma seminudum). He considered these to represent a cold-water migration event. In the early Middle diversity of benthic foraminifera in the Cleveland Basin. All Cenomanian a succession of similar, or the same, taxa this together suggests the rapid movement of a southerly appear in mark (the lower parts of couplets B41 and C1) watermass northwards displacing colder water faunas. In the characterized by a cold surface water oxygen isotope signal Cleveland Basin planktic foraminifera increase in numbers (see Paul et a/., 1994, fig. 5). The influx of the brachiopod up to assemblage B and thenceforth decrease in numbers Orhirhynchia (together with other hrachiopods of Anglo- towards the next sea-level fall in the late Middle Paris Basin affinity in the Cleveland Basin) is also associated Cenomanian. This sea-level fall is not associated with the with these belemnite/bivalve incursions. entry of pulse faunas of cold water type but only with oyster With progressive temperature rise during the Cenomanian events since both the Anglo-Paris and the Cleveland basins (Jenkyns c>t a/., 1994) major changes can be recognized in were under the influence of the warm water mass. certain faunal groups. Cold water faunal incursions (belemnites, bivalves and brachiopods) are restricted to the ACKNOWLEDGEMENTS interval below thc PB break. where foraminiferal as- 1 would like lo thank the following people for help at some semblages are characterized by high proportions of NCAs. stage with this project:.Iain Carr, Dan Ellis, Ed Jones, Paul Above the PB break these cold-water faunal elements are Leary, Dave Owen and Chris Paul. I am grateful to lain absent and incursions are characterized only by oysters, Carr, Marc Evans, Debbie Langner, Hazel McGoff, Chris while foraminiferal assemblages are characterized by high Paul and Richard Watkins for making valuable comments proportions of planktics. The PB break is interpreted as a on the manuscript. The isotope data used here were run at significant level where a northern watermass with high the Liverpool University Stable Isotope Laboratory funded proportions of NCAs was replaced by a southern watermass by grants to Jim Marshall from NERC and the University. with high proportions of planktic foraminifera. A model of Thanks to Mr. K. J. Veltkamp for the SEM photomicrog- this general form was used by Reid (1976) to explain gross raphs in Plate 1. An NERC studentship at Liverpool faunal changes in the whole of the Upper Cretaceous of the University is gratefully acknowledged. United Kingdom.
Manuscript received August 1992 Manuscript accepted 1995 CONCLUSIONS During the late Lower Cenomanian, the Cleveland and the Anglo-Paris basins had different foraminiferal assemblages REFERENCES and both basins lacked significant planktic taxa. The Barnard, 1'. 1962. Polymorphinidae from the Upper Cretaceous of Anglo-Paris Basin was characterized by a diverse calcareous England. Palaeontology, 5: 712-726. benthic assemblage including abundant Tritaxia and Barnard, T. & Banner, F. T. 1953. Arenacaceous foraminifera from Gauelinrlla, while the Cleveland Basin contained a the Upper Cretaceous of England. Quarterly Journal of the Geological Society London, 109 173-216. restricted fauna dominated by NCA foraminifera. Barnard, '1'. & Banner, F. T. 1980. The Ataxophragmiidae of The sea-level fall in the early Middlc Cenomanian England: Part I, Alhian-Cenomanian Arenobulirnina and produced a major change in the benthic fauna of the Crenaverneuilinu. Rcvistu Espukiola de Micropaleontologiu, 12: Cleveland Basin showing a transition through assemblage D 383-430. to the shallow water Bartenstein. H.. Bettenstaedt, F. & Bolli, H. M. 1966. Die (Trituxia-MarssoneIla-Uorot/lia) Foraminifercn der Unterkreide von Trinidad, W.I. Zweiter Teil: assemblage F (Arenohiilinzinri-Plectinu) and an increase in Maridale-Formation (Typlokalit5t). Eclogae Geologirar benthic foraminiferal diversity. Associated with these Heluetiae, 59: 129-177. foraminiferal assemblages is the appearance of a series of Bartenstein, H. & Bolli. H. M. 1986. The foraminifera in the Lower pulse faunas of central Russian affinity. These occur both in Cretaceous of Trinidad. W.I. Part 5: Maridale Formation, upper part: Praeglohotruncana rohri Zone. Eclogae Geologicae the Anglo-Paris Basin and in the Cleveland Basin but, in the Helvetiue, 78: 945-999. latter, include pulse faunas of Anglo-Paris Basin affinity. It Bartenstein, H. & Kovatcheva, T. 1982. A comparison of Aptian seems apparent that such incursions were times of faunal foraminifera in Bulgaria and NW Germany. Eclogue Geologicue migrations due to the relatively low sea-level and the Helvetiue, 75: 621 -667. relatively southerly extension of a cool North Sea Burnaby, T. P. 1961. The palaeoecology of the foraminifera of the Chalk Marl. Palaeontology, 4: 599-608. watcrmass. Carter. D. J. & Hart. M. B. 1977. Aspects of mid-Cretaceous As sea-level rose again, foraminiferal faunas underwent stratigraphical micropalaeontology. Bulletin of the British progressive changes in the Cleveland Basin through Museum of Natural History (Geology),29 1-135. assemblages E to B. Assemblage E is related to the North Chapman, F. 1893. The foraminifera of the Gault of Folkestone. Joirrnal of the Royal Microscopical Society: Part IV, volume for Sea watermass and contains relatively high proportions of 1893,579-595. NCAs. Assemblage C marks the sudden appearance of vast Chapman. F. 1894a. The foraminifera of the Gault of Folkestone. numbers of planktic taxa characteristic of a warm water Joirrnal of the Royal Microscopical Society. Part VI (volume for mass. The sudden influx of planktic foraminifera is 1894): 42 1-427. synchronous across England (Paul 1994) and displaces Chapman, F. 1894b. The foraminifera of the Gault of Folkestone. et al., Joirrnul of the Royal Microscopical Society, Part VII (volume for the pulse faunas of mid Russian affinity. This migration of 1894): 645-654.
52 Foraminifera from the Cenomanian of Yorkshire. UK
Christensen. W. K., Diedrich, C. & Kaplan. U. I<)O~. ~~~~~~~~i~~~ Jukes-Brownc, A. I. & Hill, W. 1903. The C‘rrruc.eorr.s rocks of helcnin i tes from t he Te utohurge r Wald. N W Germany. Britain. Volume 2, The Lower and Middle Chalk. Memoir of the Plrlflorfl(Jlog;.S~’h(~~eitsc/rrlfl. 66: 265-275, Geological Survey of the United Kingdom. Digby. P. G. N. & Kempton, R. ,4.1987. Micltiuuriott, tI}7~/y,yi,(,j Kafcscioglu, A. 1971. Specific diversity of planktonic foraminifera ccologic~rrl cot?~rnnniric~~.Population and community biology on the continental shelf as a paleobathymetric tool. series. Chapman & Hall. London. Mic~ro~puleonrologv.17: 455-470. Ditchfield, P. & Marshall, J. D. 1989. Isotopic vktriation in Kcller. S. 1982. Die Oberkreide der Sack-Mulde bei Alfeld rhythmically bedded chalks: paleotemperaturc variation in the (Cenoman-~Jntcrconiac): Lithologie, Biostratigraphie und Inoce- Upper (3etaceous. Grology 17: 842-845. ramen. Geologisches Jurbuch (A), 64 3-171. Ernst. G.. Schmid. F. & Seibertz. E. 1983. Event-Stratigraphic in1 Khan, M. H. 1950. Note on the depth and temperature of the Gault Cenoman und Turon von NW-Deutschland. Zittclirincr. 10 sea as indicated by foraminifera. Geological Magazine, 87: 53 1 -554. 175- 180. Fisher, K. A.. Corbet. A. S. & Williams, C. R. 1943. .I’he relation King, C. 1989. Cenozoic of thc North Sea. In Jenkins, D. G. & between the number of species and the number of individuals in ;I Murray, J. W. (Eds) Srrutigraphical Atlas of Fossil Foruniiniferu random sample of an animal population. .lorirnu/ of’ Animal (second edition). British Micropalaeontological Society Series, 41 8-489. ilankovitch scale for Cenomanian time. 7iJrrtr King, C.. Bailey, H. W., Burton, C. & King, A. D. 1989. Cretaceous of the North Sea. In Jenkins. D. G. & Murray. J. W. (Eds) Gale. A. S. 1’995. Cyclostratigraphy and correlation of the Strutigraphicul Atlas of Foril Foruniiniferu (second edition). Cenomanian Stage in Western Europe. Itr House, M. 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