Taphonomic experiments on marginal marine foraminiferal assemblages: how much ecological information is preserved?

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1 ELSEVIER Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Taphonomic experiments on marginal marine foraminiferal assemblages: how much ecological information is preserved? John W. Murray a,ł, Elisabeth Alve b a School of Ocean and Earth Science, Southampton Oceanography Centre, European Way, Southampton SO14 3ZH, UK b Department of Geology, University of Oslo, PO Box 1047 Blindern, N-0316 Oslo, Norway Received 10 December 1996; revised version received 3 July 1997; accepted 8 June 1998 Abstract The most important taphonomic processes affecting the composition of benthic foraminiferal assemblages are transport and destruction of tests. The latter includes dissolution of calcareous tests. We have previously simulated nature experimentally by dissolving mainly shelf to deep sea samples in weak acid to give acid-treated assemblages (ATA). In this study we sampled the marginal marine environments of the Skagerrak=Kattegat and found that the main taphonomic process there is dissolution of calcareous tests. Consequently, the taphonomic processes occurring in this area represents a perfect natural analogue of what we suspect to be the main mechanism for the formation of some fossil agglutinated assemblages. The evidence for this is that some living assemblages dominated by calcareous forms become original dead assemblages (ODA) often consisting entirely of agglutinated species and equivalent to ATAs. The principal ATA is dominated by Miliammina fusca and this ATA can be derived from 10 different types of ODA including those that are strongly dominated by various calcareous taxa. This residual M. fusca assemblage represents a broad range of intertidal to shallow subtidal environments. On the other hand, marsh living assemblages are completely agglutinated and obviously give rise to agglutinated ODA=ATAs but not necessarily dominated by the same taxa. All the ATAs faithfully record the low species diversity characteristic of marginal marine environments. The principal conclusion is that in spite of the severe taphonomic loss, the preserved assemblages record much ecological detail. This is in accordance with similar investigations of deeper water assemblages and has important consequences for palaeoecology. This study demonstrates unequivocally that it is always essential to compare data on living and dead assemblages in order to determine the pathways to fossilisation. The use of total (living plus dead) assemblages in this area would give unrepresentative and misleading results Elsevier Science B.V. All rights reserved. Keywords: taphonomy; agglutinated foraminifera; ecology; marginal-marine; dissolution 1. Introduction Palaeoecological studies are normally carried out by comparing fossil assemblages with their modern Ł Corresponding author. Fax: C ; jwm1@mail.soc.soton.ac.uk analogues. Although fossil assemblages consisting exclusively of non-calcareous, organo- and ferroagglutinated foraminifera are known from Mesozoic and Cenozoic rocks (for example, Charnock and Jones, 1990), the only modern analogues appear to be either intertidal marshes or seas deeper than the calcium carbonate compensation depth (Alve and /99/$ see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S (98)

2 184 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Murray, 1995). It seems unlikely that all fossil examples fit into one or other of these two extreme environments so that has limited their interpretation. A reasonable assumption is that some of the fossil agglutinated assemblages are the residuum of diagenetic dissolution of the calcareous component. Therefore, in the past few years we have carried out experimental studies to help to determine the origin of agglutinated fossil assemblages (Alve and Murray, 1994, 1995; Murray and Alve, 1994, in press). We simulated natural dissolution of the original dead assemblage (ODA) by treating the samples with dilute acid and called the resultant residue the acid-treated assemblage (ATA). The initial studies considered environments ranging from deep sea, through slope and shelf, to intertidal but with only 8 samples from shallow marginal marine settings. The coastal zone of the Skagerrak=Kattegat is an ideal area in which to investigate shallow marginal marine subenvironments in more detail. These range from small areas of marsh with various combinations of Phragmites, Carex and Salicornia developed in the sheltered parts of bays, through intertidal flats to subtidal areas, with or without seagrass. The area is microtidal with an astronomical tidal range of cm along the Skagerrak and about 40 cm along the Kattegat coast. However, meteorological effects (surge, caused by wind and barometric pressure) generally have a stronger impact on the prevailing sea level in this area than the astronomical tide implying that ranges of about 1 m occur several times a year (R. Braaten, pers. commun., 1997). However, the general range of variation is probably less than 0.5 m with the marshes being developed at the upper limit. These shallow waters generally lack currents and develop stratification (at least during the summer). At most stations, there is low input of freshwater from the surrounding land. The annual temperature range is from at least 0 to 28ºC and salinities ranged from 10 to 30 at the time of sampling. From previous studies by Alexandersson (1979) it is known that carbonate dissolution is active in this area. In order to evaluate the ATA results, it was essential to investigate the ecology and distribution of the living assemblages (Alve and Murray, 1999) and the taphonomy of the ODAs (Murray and Alve, 1999). The most important taphonomic processes affecting the composition of benthic foraminiferal assemblages are transport and destruction of tests, the latter including dissolution of calcareous tests. Longdistance transport is not significant here; all the dead taxa are represented by living individuals and there is no introduction of exotic species. This is consistent with the small microtidal regime. There is some local transport due to waves. However, natural dissolution of calcareous tests is shown to be of major importance in this area. This makes it a very worthwhile natural laboratory in which to study taphonomy and the origin of agglutinated assemblages. 2. Material and methods From 1994 to 1996, 171 samples were collected from 27 localities along the Skagerrak=Kattegat coast from the intertidal zone (including marsh) to a water depth of 6 m (Fig. 1) but two (162, 163) were not used in this study. Because of the irregular tidal pattern, it was impossible to know the position of average sea level in the investigated areas. When sampling, it was sometimes clear that the water level was low because there was an exposed tidal flat. However, for a number of stations from water depths of less than around 0.5 m at the time of sampling, it has not been possible to be certain whether they are normally subtidal or intertidal. The depths recorded are those at the time of sampling. In areas exposed at the time of collection, samples were scraped from the sediment surface (to a depth of 1 2 cm). The subtidal samples were collected with a small grab. Most samples were about 100 cm 3. The grab was carefully operated so that negligible loss of surface sediment took place. On removal from the water, it was gently opened in a bowl. The surface oxidised sediment layer was scooped off and placed in a container. The samples were preserved in 70% ethanol. At Tjøme (in the area of samples 86 and 87), a 9 cm core (sta. 172, diameter 6.8 cm, taken in 0.8 m of water in September 1996) was sectioned into 1 cm slices in the field and all slices were preserved in 70% ethanol. In the laboratory, the foraminiferal samples were processed by washing on a 63 µm sieve, stained in rose Bengal for 1 hour, washed again on a 63 µm sieve to remove excess stain, and dried at 50ºC. The

3 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Fig. 1. Map showing the 27 sampling areas. foraminifera in those samples not rich in organic detritus were concentrated using tetrachloroethylene. Living and dead assemblages (each of around 250 individuals) were picked from a representative >63 µm portion of each sample. Another >63 µm portion of those samples with a dominance of calcareous tests was digested in acetic acid ph 2.5 for at least 2 hours (to remove the calcareous material), washed on a 63 µm sieve (to remove the acid) and dried. The purpose of acid treatment was to concentrate the agglutinated tests in samples predominated by calcareous forms. Whenever possible, 250 individuals were picked from each acid-treated sample to give the ATA. For the 98 ODA samples with a high proportion of agglutinated tests (>50%), it was unnecessary to treat them with acid; additional agglutinated specimens were simply picked from the ODA to increase the agglutinated count to 250 individuals. The term ATA refers to all residual agglutinated assemblages re-

4 186 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999)

5 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) sulting from dissolution, regardless of whether the process was natural or carried out by us. In some instances (notably marshes), both the living and dead assemblages were entirely agglutinated. Most Reophax moniliformis tests were fragmented so it was impossible to decide exactly how many individuals were present. In order to reduce over-representation, we decided to count only those specimens with 3 or more chambers. Another problem is that individuals of Goesella waddensis lacking their initial chambers are impossible to distinguish from R. moniliformis. Consequently, we have included all G. waddensis in R. moniliformis and the few instances where we are confident that it is present are given in Murray and Alve (1999). Ammotium cassis and Ammobaculites balkwilli were also commonly fragmented. We therefore counted only those fragments including the initial part. Thirty-six samples yielded fewer than 50 individuals (Appendix A) and therefore have been omitted from the statistical discussion. Species diversity was calculated using the Fisher alpha index (Fisher et al., 1943) and the information function (see Murray, 1991) but only on those samples with at least 100 individuals. The similarity values given in Table 2 were calculated using the Sanders method (see Mur- Fig. 2. SEM photographs of agglutinated taxa. The scale bar is 100 µm for all except Ammotium cassis (V) where it is 1 mm. # refers to sample no.; the localities are given in Appendix A. A C. Balticammina pseudomacrescens Brönnimann, Lutze and Whittaker, #159. A. Showing typical collapsed chamber walls on the spiral side. C. Showing the deep umbilicus with primary apertural rim and secondary pore apertures. D, E. Haplophragmoides wilberti Andersen, #126. F H. Jadammina macrescens (Brady), #153. I. Ammobaculites balkwilli Haynes, #98. J. Ammotium salsum (Cushman and Brönnimann), #168. K. Eggerelloides scaber (Williamson), #18. L. Miliammina fusca (Brady), #122. M. Ammoscalaria runiana (Heron-Allen and Earland), #100. N P. Tiphotrocha comprimata (Cushman and Brönnimann), #166. Q S. Trochammina inflata (Montagu), #126. T. Goesella waddensis Van Voorthuysen, #122. U. Reophax moniliformis Siddall, #122, note the similarity to the uniserial portion of T. V. Ammotium cassis (Parker), #100. ray, 1991, p. 322). Most of the agglutinated taxa are illustrated in Fig. 2. Paratrochammina (Lepidoparatrochammina) haynesi is illustrated in Brönnimann and Whittaker (1986). 3. Results Appendix A lists all ATA data from the 27 areas (Fig. 1). Rare occurrences are listed at the bottom of the table as other agglutinated. Table 1 gives a list of species arranged according to water depth distribution. The only species totally restricted to intertidal areas is Balticammina pseudomacrescens. Other species which are dominant from intertidal to 0.5 m include Trochammina inflata and Haplophragmoides wilberti, whereas Jadammina macrescens can dominate down to1m.miliammina fusca and R. moniliformis dominate over the greatest depth range, from intertidal to 6 m. All other species, except Ammotium cassis (upper depth limit 2 m), have a total range extending from the intertidal zone to subtidal areas and commonly to 6 m. In intertidal subtidal areas, 73 ATAs (½50 individuals) are dominated by M. fusca and, of these, 50, ranging in depth from the shoreline to 6 m, have ½60% of this form (see Appendix A). The species diversity values are very low: Fisher alpha and H.S/ for all environments (Appendix A). The diversity data presented in this paper have been plotted together with previously published data giving a total of 191 samples (Figs. 3 and 4). The results from the Tjøme core are given in Table 2. The surface (0 1 cm) living assemblage has 57% calcareous forms (Ammonia beccarii, Elphidium oceanensis, Elphidium williamsoni) whereas the ODA has just 5% (A. beccarii). No living forms were encountered below the 0 2 cm layer (examination of the 1 2 cm interval revealed 1 live per 250 dead). Dead calcareous forms are further reduced down to 4 5 cm and they are absent below this. Therefore, the ODA is a natural ATA from 5 cm downwards. 4. Discussion The dead assemblages represent the time-averaged contributions of empty tests from the produc-

6 188 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Table 1 Water depth ranges of ATA species Species Overall range Makes up ½5% of Makes up ½10% of As dominant species (m) assemblage assemblage B. pseudomacrescens IT IT IT IT T. comprimata IT 2 IT 0.1 IT 0.1 not dom. H. wilberti IT 6 IT 4.5 IT 4.5 IT <0.5 A. salsum IT 5.5 < <0.5 not dom. J. macrescens IT 6 IT 2 IT 1 IT 1 T. inflata IT 5.5 IT 4.5 IT 4.5 IT <0.5 M. fusca IT 6 IT 6 IT 6 IT 6 R. moniliformis IT 6 IT 6 IT 6 IT 6 A. runiana IT 6 IT 6 IT A. balkwilli IT 6 IT 6 IT E. scaber IT 6 IT 6 IT P. (L.) haynesi IT 6 IT 5 2 not dom. A. cassis IT D intertidal. tion of successive living assemblages and subsequent modification due to postmortem processes. In general, the most significant postmortem processes are transport (which can lead to loss or gain of tests) and destruction (especially dissolution of the calcareous tests but also disintegration of fragile agglutinated taxa). In the Skagerrak=Kattegat area, there is some local transport due to wind and wave activity and this extends the depth ranges of typical marsh species into shallow subtidal waters (see Table 1 and Murray and Alve, 1999). There may be some loss of agglutinated tests (M. fusca is sometimes rather fragile). Dissolution is widespread (Alexandersson, 1979) and a significant modifying process (Murray and Alve, 1999). Those living assemblages which are dominantly calcareous in many cases give rise to ODAs rich in agglutinated tests as a result of dissolution under natural conditions. This is a major difference from other areas that we have studied (Alve and Murray, 1994, 1995; Murray and Alve, 1994) and makes the Skagerrak=Kattegat highly distinctive. Fig. 3. Fisher alpha values for ODA and ATA data from this study and published data (Alve and Murray, 1995). The shaded marginal marine area includes the new data together with those published on the Hamble estuary. Fig. 4. Information function values [H.S/] for ODA and ATA data from this study and published data (Alve and Murray, 1995). Shaded area as in Fig. 3.

7 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Table 2 Data on core 172 Stained Dead Total Dead Dead Dead Dead Core depth (cm): %values Ammobaculites balkwilli Ammoscalaria runiana Eggerelloides scaber Jadammina macrescens Miliammina fusca Reophax moniliformis Ammonia beccarii Ephidium oceanensis Ephidium williamsoni Number counted No. spp % agglutinated % calcareous % similarity with dead % similarity with total The origin of the ATAs In our previous studies on the development of wholly agglutinated assemblages, we have simulated natural dissolution on predominantly calcareous assemblages through laboratory experiments. However, an important aspect of this study is that samples from the Skagerrak=Kattegat already show significant natural dissolution; many living calcareous assemblages become agglutinated ODAs which are natural ATAs. The results from core 172 demonstrate very clearly that natural dissolution is proceeding beneath the sediment surface so that at a depth of 1 cm a predominantly calcareous surface living assem- Table 3 Different pathways from live through ODA to ATA assemblages for samples where the living assemblages are dominated by agglutinated taxa (½50 individuals) Sample No. No. of samples Live ODA ATA 37, 42, 80, 84, 17 M. fusca M. fusca M. fusca 86, 98, 134, 135, M. fusca M. fusca M. fusca 143, 144, 146, M. fusca M. fusca M. fusca 148, 158, 160, M. fusca M. fusca M. fusca 161, 165, 168 M. fusca M. fusca M. fusca M. fusca T. inflata T. inflata 124, 127, M. fusca J. macrescens J. macrescens 61, 57 2 A. runiana M. fusca M. fusca 31 1 R. moniliformis R. moniliformis R. moniliformis R. moniliformis A. runiana A. runiana 152, 153, 154, 6 J. macrescens J. macrescens J. macrescens 156, 166, 171 J. macrescens J. macrescens J. macrescens J. macrescens H. wilberti H. wilberti J. macrescens M. fusca M. fusca A. balkwilli M. fusca M. fusca H. wilberti H. wilberti H. wilberti B. pseudomacr. B. pseudomacr. B. pseudomacr.

8 190 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Table 4 Different pathways from live through ODA to ATA assemblages for samples where the living assemblages are dominated by calcareous taxa (½50 individuals) Sample No. No. of samples Live ODA ATA 16 1 A. beccarii A. beccarii A.balk.=A. run A. beccarii E. williamsoni M. fusca 64 1 A. beccarii R. moniliformis R. moniliformis 32, 65, 68, 70, 11 A. beccarii M. fusca M. fusca 71, 74, 81, 82, A. beccarii M. fusca M. fusca 88, 89, 87 A. beccarii M. fusca M. fusca 15, 99, 100, A. beccarii A. runiana A. runiana 1 1 A. beccarii A. beccarii R. moniliformis 17, 28 2 A. beccarii E. scaber E. scaber A. beccarii E. williamsoni A. runiana A. beccarii A. beccarii A. runiana 2, 67 2 E. excavatum A. beccarii M. fusca 3, 26, 43, E. excavatum M. fusca M. fusca 48 1 E. excavatum A. beccarii A. runiana 130, E. excavatum A. runiana A. runiana 140, 119, E. excavatum E. excavatum M. fusca 47, 49 2 E. excavatum A. cassis A. cassis 66 1 E. excavatum H. germanica M. fusca E. excavatum E. excavatum A. runiana 1C, 20, 23, 46, 18 E. williamsoni M. fusca M. fusca 55, 58, 59, 60, E. williamsoni M. fusca M. fusca 72, 75, 77, 79, E. williamsoni M. fusca M. fusca 85, 91, 141, E. williamsoni M. fusca M. fusca 142, 164, 167 E. williamsoni M. fusca M. fusca 44 1 E. williamsoni J. macrescens J. macrescens 51 1 E. williamsoni E. williamsoni R. moniliformis 52, 54, E. williamsoni E. williamsoni M. fusca 73, 76, 90 3 E. williamsoni E. williamsoni M. fusca 92 1 E. williamsoni A. beccarii M. fusca 121, E. oceanensis M. fusca M. fusca 45 1 H. germanica J. macrescens J. macrescens 63 1 H. germanica M. fusca M. fusca 11 1 C. lobatulus C. lobatulus M. fusca 13 1 N. depressulus C. lobatulus M. fusca blage has become an almost completely agglutinated assemblage. Dissolution of calcareous tests has previously been recorded from shallow subtidal sediments in Oslo Fjord where sites with >20% calcareous tests during the spring had <3% during the other seasons and organic linings were frequent (Alve and Nagy, 1986). Severe dissolution was also reported in subtidal sediments in Long Island Sound, USA (Green et al., 1993). Here, the calcareous foraminifera disappeared during the course of a year due to frequent occurrence of irrigated burrows and tubes of macrofauna which prevent the buildup of carbonate alkalinity (see also Aller, 1982). Dissolution has also been reported from intertidal sediments in the northern Gulf of California, Mexico (Martin et al., 1995) and marsh sediments are well known for having poor preservation of calcareous tests due to postmortem dissolution (see, for example, Parker and Athearn, 1959; Murray, 1971; Scott and Medioli, 1980a,b; Williams, 1989; Jonasson and Patterson, 1992). In the present investigation, the simplest relationship between live assemblages, ODAs and ATAs is found in areas where the living assemblages are composed mainly of agglutinated forms and they in turn give rise to agglutinated ODAs. The dominant

9 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Table 5 Different pathways from ODA to ATA for those samples with living assemblages of <50 individuals Sample No. No. of ODA ATA samples 5 1 E. williamsoni M. fusca 78 1 R. moniliformis R. moniliformis 4, 7, 8, 14, 15 M. fusca M. fusca 21, 22, 27, M. fusca M. fusca 35, 36, 56, M. fusca M. fusca 83, 141, 145, M. fusca M. fusca 147, 157 M. fusca M. fusca 19, 24, 25, 5 E. scaber E. scaber 29, 30 E. scaber E. scaber 6 1 E. excavatum M. fusca 18 1 A. beccarii E. scabrus taxon may be the same in both the living assemblage and ODA but in some instances the dominant taxa are different (Table 3). For example, a living R. moniliformis assemblage may go to an A. runiana ODA, or a living J. macrescens assemblage to a H. wilberti ODA. Also, some living agglutinated assemblages (A. runiana, J. macrescens, A. balkwilli) go to M. fusca ODAs. This is most probably due to the presence of a bloom in the dominant living species at the time of sampling. Although no dissolution may be apparent, the reality is that these Scandinavian intertidal environments are not favourable for the existence of calcareous foraminifera. The calcareous living assemblages may follow two alternative routes. In one pathway, both the living assemblage and the ODA are dominated by a calcareous species (either the same or a different one) and the ATA by an agglutinated form (Table 4). For example, an A. beccarii living assemblage may give rise to an A. beccarii or an E. williamsoni ODA. These then give rise to different ATAs (see Tables 4 and 5). In the other case, the living calcareous assemblage goes directly to an agglutinated ODA and this is a naturally formed ATA. The commonest examples are those of living A. beccarii or E. williamsoni giving rise to an M. fusca ODA=ATA. It is significant that the most abundant ATA (M. fusca) can be derived from numerous different parent living assemblages and ODAs. Indeed, ten assemblages, 7 of them calcareous, follow this pathway (A. balkwilli, A. runiana, M. fusca, A. beccarii, Cibicides lobatulus, Elphidium excavatum, E. oceanensis, E. williamsoni, Haynesina germanica, Nonion depressulus). This leaves M. fusca as the most ubiquitous agglutinated shallow water species Preserved ecological information Because the marshes are developed on such a small scale and the area is microtidal, the intertidal subenvironments are severely compressed and there is no obvious differentiation into low and high marsh as seen in more tidally influenced areas. The marsh ODAs are composed entirely of agglutinated taxa so they are naturally occurring ATAs. J. macrescens dominates the marsh assemblages at Bunnefjorden, Hålkedalskilen and Kalundborg. It commonly occurs together with M. fusca, T. inflata and sometimes with B. pseudomacrescens (Hunnebotn), H. wilberti (Kalundborg), or Tiphotrocha comprimata (Bunnefjord, Hunnebotn, Horten). Of these, T. comprimata and B. pseudomacrescens have the most restricted depth range (Table 1). As discussed above, by far the most abundant ATA is that of M. fusca which can be derived from numerous different living assemblages. This implies that a fossil M. fusca assemblage could represent a wide range of marginal marine subenvironments, from marsh edge to 6 m water depth, salinity (at the time of sampling but undoubtedly lower during other seasons), on sediments varying from carbonate shell sand to clastic sands and organic-rich muds, with low to high TOC ( %), in a temperate area (seasonal range from 0 to 28ºC). In the shallow depth range studied, there are few obvious depth boundaries in either the ODAs or the ATAs. Ammotium cassis (shallowest depth limit 2 3 m) is the only agglutinated species encountered which does not extend into the intertidal zone. Whereas typical live marsh assemblages (J. macrescens, T. inflata, T. comprimata, H. wilberti, B. pseudomacrescens) can be readily distinguished from the assemblages living on bare intertidal flats, and from those ODAs not too seriously affected by dissolution, it is not possible to distinguish between marsh and shallow subtidal environments using ATAs. This is because J. macrescens, T. inflata and H. wilberti extend down to m water depth. However, they still indicate close proximity to a marsh.

10 192 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Comparison with previously analysed ATAs In the first experiments on dissolution, Alve and Murray (1994) used 8 shallow subtidal and intertidal samples from the Hamble estuary in southern England. This estuary has a tidal range of m (neaps to springs) and the salinity in the area studied ranged from 30 to 33. Seven ODAs were dominated by calcareous taxa. Four A. beccarii ODAs gave rise to A. balkwilli ATAs; two H. germanica ODAs gave rise to E. scabrus ATAs while another gave rise to a Textularia tenuissima=paratrochammina (Lepidoparatrochammina) haynesi ATA. A single marsh sample had an ODA in which J. macrescens was the dominant species although the assemblage also comprised more than 50% calcareous forms; the ATA was likewise dominated by J. macrescens. The results from the Hamble estuary are comparable with those from this study except that here A. beccarii ODAs gave rise to A. runiana, R. moniliformis and M. fusca as well as A. balkwilli ATAs. This may be partly a reflection of the larger number of samples studied. However, the H. germanica ODAs of this study gave rise to M. fusca ATAs probably because of the more brackish waters (Alve, 1995; table 1). In terms of species diversity, using either the Fisher alpha index or the information function, both studies show that the low diversity ODAs give rise to low diversity ATAs. This linkage of diversity patterns between ODAs and ATAs has also been established in the other experimental studies involving the deep sea (Murray and Alve, 1994) and shelf seas (Alve and Murray, 1995). From marginal marine to deep sea environments there is a progression from low to high diversity [for Fisher alpha and H.S/] both for the ODAs and ATAs (Figs. 3 and 4). This means that even though some ODAs have been seriously altered by severe dissolution, the residual ATA still retains the ecological information necessary to recognise the environment of deposition. Overall, it appears that in all the environments studied, from deep sea to intertidal, the ATAs preserve a remarkable amount of ecological information. Therefore, by comparison with our accumulated database on modern forms it should now be possible to make palaeoecological interpretations of fossil agglutinated assemblages with more confidence Comment on the use of living, dead and total assemblages Some authors add together the living and dead assemblages to give so-called total assemblages in the belief that these are more representative of what becomes preserved in the fossil record (see discussion in Murray, 1982). This study shows unequivocally that the concept of the total assemblage as a better analogue of a fossil assemblage than the time-averaged dead assemblage (which has experienced postmortem modification) is incorrect. Only by investigating the consequences of the taphonomic processes that affect all tests after death is it possible to properly determine the pathways to fossilisation. As we have shown here, in the Skagerrak=Kattegat area, many calcareous living assemblages give rise to exclusively agglutinated ODAs that become part of the fossil record (e.g., below 5 cm in core 172). This would not have been shown by using total assemblages because they would have been a mixture of calcareous and agglutinated forms (compare stained, dead and total data for 0 1 cm; Table 2). Furthermore, the magnitude of the loss of tests through dissolution would have been seriously underestimated. 5. Summary and conclusions The shallow water environments of the Skagerrak= Kattegat are unusual in that they are characterised by naturally occurring carbonate dissolution on a large scale. This leads to major taphonomic change in the transition from live to dead assemblage. In many cases calcareous dominated living assemblages become preserved as agglutinated original dead assemblages (ODAs). In those instances where natural dissolution has not taken place, we have treated the samples with acid to simulate the natural process and this gives rise to acid treated assemblages (ATAs) of agglutinated foraminifera. The term ATA refers to any residual agglutinated assemblage resulting from dissolution, whether natural or carried out by us. The pathways from living assemblage to ODA to ATA are varied and complex. In the simplest case, the living assemblages are agglutinated and they give rise to similar ODAs and ATAs. This is

11 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) the case for most marshes where the environment is commonly hostile to the existence of calcareous taxa. In other types of intertidal and subtidal areas, calcareous-dominated living assemblages may give rise to calcareous or agglutinated ODAs the latter being natural ATAs. The marsh ATAs are found to a water depth of m (due to local transport into subtidal waters) but are still fairly reliable indicators of sea level. The most widespread ATA is dominated by Miliammina fusca but this can be derived from 10 different living assemblages (including 7 calcareous ones). It therefore represents a broad range of environments, from intertidal to 6 m, salinity at least 15 30, temperature 0 28ºC, TOC ( %) and sediments ranging from carbonate sands, through clastic sands to organic-rich muds. The living foraminiferal assemblages have low species diversity and this is faithfully preserved in both the ODAs and ATAs. Although there is severe information loss through taphonomic change (notably dissolution of calcareous tests), the ODAs and ATAs still give a fairly reliable record of the ecology of the environments. This has very important implications for the palaeoecological interpretation of fossil agglutinated assemblages. This study demonstrates unequivocally that it is always essential to compare data on living and dead assemblages in order to determine the pathways to fossilisation. The use of total (living plus dead) assemblages in this area would give unrepresentative and misleading results. Acknowledgements We are grateful to the Natural Environment Research Council for grant GR9=1591 A and the Industrial Liaison fund (Oslo University) for financial support. The following people helped in various ways in the field: Pål Glad for help with sampling in Norway; Eva Larsen, Siggurd Gausdal, Arne M. Svendsen, Bent Åsnes, Trond Smith, John Ingebrigtsen, and Tjärnö marinbiologiska laboratorium for provision of boats. Karen Luise Knudsen and Marit- Solveig Seidenkrantz are thanked for taxonomic discussions. Barbara Cressey and Barry Marsh assisted with the preparation of material for SEM and for photography. We thank Jean-Pierre Guilbault and an anonymous referee for helpful comments on the manuscript.

12 194 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Appendix A Relative abundance data for the acid treated assemblages (ATAs) Area (area no.): Isefjærfjord (1) Kvastadkilen (2) Lyngør, Dype Holla (3) Lyngør, Tøkersfjord (4) Hasdalen (5) Environment: I I S S S S I S S S S S I S S S S I S S S S S S S S I S S S Sample no.: a 10 a a C Water depth (m): %values(ata) Ammobaculites balkwilli Ammoscalaria runiana Ammotium cassis Ammotium salsum Balticammina pseudomacr Eggerelloides scaber Haplophragmoides wilberti Jadammina macrescens Miliammina fusca Paratroch. (L.) haynesi Reophax moniliformis Tiphotrocha comprimata Trochammina inflata Other agglutinated Total counted No.spp Alpha-index ATA H.S/ ATA Area (area no.): Kilsfjorden (6) Tjøme, NE Gåsholmen (7) Borre (8) Horten (9), mainland side Horten (9), island side Environment: I S S S S S S I S S S S S M I I I I M M M I S S S I S S S Sample no.: a Water depth (m): %value(ata) Ammobaculites balkwilli Ammoscalaria runiana Ammotium cassis Ammotium salsum Balticammina pseudomacr Eggerelloides scaber Haplophragmoides wilberti Jadammina macrescens Miliammina fusca Paratroch. (L.) haynesi Reophax moniliformis Tiphotrocha comprimata Trochammina inflata Other agglutinated Total counted No.spp Alpha-index ATA H.S/ ATA

13 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Appendix A (continued) Area (area no.): Sandebukta (10) Bunnefjord (11) Hunnebotn (12) Hålkedals. (13) Tjärnö (14) Environment: I I S S S S S S M M M M=I S M M M I I S M I I S S S S S S S S Sample no.: a 38 a 34 a 40 a 41 a Water depth (m): %value(ata) Ammobaculites balkwilli Ammoscalaria runiana Ammotium cassis Ammotium salsum Balticammina pseudomacr Eggerelloides scaber Haplophragmoides wilberti Jadammina macrescens Miliammina fusca Paratroch. (L.) haynesi Reophax moniliformis Tiphotrocha comprimata Trochammina inflata Other agglutinated Total counted No.spp Alpha-index ATA H.S/ ATA Area (area no.): Gullm.fj., Finnsbobukten (15) Gullmarsfjord, Gullmarsvik (16) Hafstensfjord (17) Kungsbackafjord (18) jetties (18) Jonstorp (19) Environment: I I I I S S I I I S S S S S I I S S I I I S S S S S S S S S S Sample no.: a a a a 137 a Water depth (m): %value(ata) Ammobaculites balkwilli Ammoscalaria runiana Ammotium cassis Ammotium salsum Balticammina pseudomacr Eggerelloides scaber Haplophragmoides wilberti Jadammina macrescens Miliammina fusca Paratroch. (L.) haynesi Reophax moniliformis Tiphotrocha comprimata Trochammina inflata Other agglutinated Total counted No.spp Alpha-index ATA H.S/ ATA

14 196 J.W. Murray, E. Alve / Palaeogeography, Palaeoclimatology, Palaeoecology 149 (1999) Appendix A (continued) Area (area no.): Kildehuse (20) Kalundborg (21) Brejning, Vejle Fjord (22) Kalø Vig, Havhuse (23) Environment: S S S S S S S M M M I S S S S S S S S S S S S I S S S S S Sample no.: a 132 a 131 a a 117 a 116 a a 112 a 107 a Water depth (m): %value(ata) Ammobaculites balkwilli Ammoscalaria runiana Ammotium cassis Ammotium salsum Balticammina pseudomacr Eggerelloides scaber Haplophragmoides wilberti Jadammina macrescens Miliammina fusca Paratroch. (L.) haynesi Reophax moniliformis Tiphotrocha comprimata Trochammina inflata Other agglutinated Total counted No.spp Alpha-index ATA H.S/ ATA Area (area no.): Kalø Vig, Vosnæs pynt (24) Løgstør (25) Valsted (26) Fredr. havn (27) Environment: I I I S S S S S S S S S S S S S S S S S Sample no.: 104 a 105 a 106 a a 103 a a 96 a 95 a 94 a 93 a a 150 a 149 a Water depth (m): %value(ata) Ammobaculites balkwilli Ammoscalaria runiana Ammotium cassis Ammotium salsum Balticammina pseudomacr Eggerelloides scaber Haplophragmoides wilberti Jadammina macrescens Miliammina fusca Paratroch. (L.) haynesi Reophax moniliformis Tiphotrocha comprimata Trochammina inflata Other agglutinated Total counted No.spp Alpha-index ATA H.S/ ATA The data are presented by geographic area (see Fig. 1 for locations numbered 1 27). M D marsh; I D intertidal; S D subtidal. a Samples which yielded fewer than 50 specimens.

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