Quantitative taphonomic analysis and taphofacies in lower

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Palaeogeography, Palaeoclimatology, Palaeoecology 207 (2004) 83–103

Quantitative taphonomic analysis and taphofacies in lower Pliocene

temperate carbonate–siliciclastic mixed platform deposits

(Almerıa-Nıjar basin, SE Spain)

Jesus Yesares-Garcıa, Julio Aguirre*

Dpto. de Estratigrafıa y Paleontologıa, Facultad de Ciencias, Universidad de Granada, Campus de Fuentenueva s/n, 18071 Granada, Spain

Received 31 July 2003; received in revised form 21 January 2004; accepted 6 February 2004

Abstract

Actualistic assessments emphasize the power of carrying out quantitative analysis of the taphonomic traits, as well as the use

of multivariate statistical tests for the definition of taphofacies models. Nonetheless, in the palaeontological literature,

taphonomic analyses are often based on qualitative observations or on semi-quantitative studies involving only a few

taphonomic attributes. In this paper, a quantitative study for analyzing taphonomic signatures and proposing taphofacies in the

fossil record is presented. This methodology is applied in lower Pliocene carbonate–siliciclastic mixed deposits of the Almerıa-

Nıjar basin (SE Spain). Selected taphonomic attributes that are quantitatively analyzed are: (1) abundance, (2) packing

(percentage of fossils per rock volume), (3) fragmentation, (4) articulation, (5) left/right valve proportion, (6) biofabric (original

growth position, the lowest angle of the shells to the stratification surface and the concavity orientation), (7) preservation of the

original mineralogy, (8) edge rounding and (9) biological interactions (encrustation and boring). All of these taphonomic

signatures are tabulated as percentages. These values are then analyzed with a Q-mode cluster analysis for the definition of the

taphofacies. Three taphofacies models are proposed: (1) outer-platform taphofacies, (2) biotic accumulations taphofacies and (3)

inner-platform taphofacies. This study shows that, when more taphonomic attributes are used in the cluster analysis, the results

are better and more robust.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Taphonomy; Taphofacies; Siliciclastic–carbonate sediments; Pliocene; Almerıa-Nıjar basin

1. Introduction

Taphofacies models have proved to be an impor-

tant and useful tool for both palaeoenvironmental

reconstructions and palaeoecological interpretations

(Speyer and Brett, 1986, 1988, 1991). Several actual-

0031-0182/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.palaeo.2004.02.002

* Corresponding author. Tel.: +34-958-248332; fax: +34-958-

248528.

E-mail address: [email protected] (J. Aguirre).

istic analyses have validated its usefulness by study-

ing the preservation states of organisms in different

present-day shallow settings, such as salt marshes,

tidal flats, coastal and shallow subtidal settings (Fur-

sich and Flessa, 1987; Powell et al., 1989; Davies et

al., 1989; Staff and Powell, 1990a,b; Meldahl and

Flessa, 1990; Feige and Fursich, 1991; Flessa et al.,

1993), carbonate and mixed siliciclastic–carbonate

tropical platforms (Nebelsick, 1999; Best and Kid-

well, 2000a,b; Kidwell et al., 2001), deep hydrocar-

J. Yesares-Garcıa, J. Aguirre / Palaeogeography, Palaeoclimatology, Palaeoecology 207 (2004) 83–10384

bon seeps (Callender and Powell, 1992; Callender et

al., 1990, 1992), as well as platform margin and slope

of carbonate platforms (Llewellyn and Messing, 1993;

Powell et al., 2002; Callender et al., 2002; Staff et al.,

2002).

Powell et al. (1989) proposed a numerical meth-

odology for defining taphofacies in Recent and sub-

Recent settings, pointing out its potential use in the

fossil record. These authors emphasized quantification

of a number of taphonomic signatures potentially

preserved in the fossil record. They also proposed to

analyze the data using multivariate statistical techni-

ques (see also Meldahl and Flessa, 1990). Neverthe-

less, it is still relatively common to carry out

taphonomic interpretations based only on qualitative

observations, or on the quantification of a few taph-

onomic attributes, mostly degree of breakage, articu-

lation and/or abrasion (Fursich and Oschmann, 1993;

Fursich and Pandey, 1999; Li and Droser, 1997;

Fernadez-Lopez, 1997; Monaco, 1999; Dominici,

2001; Mandic and Piller, 2001; Parras and Casadıo,

2002; Nielsen and Funder, 2003).

As far as we know, taphofacies have been defined

by quantifying multiple taphonomic traits only in a

few examples (i.e. Jimenez and Braga, 1993; Aguirre,

1996; Aguirre and Jimenez, 1998; Oloriz et al.,

2002a,b). Additionally, only Jimenez and Braga

(1993) treated the data applying multivariate statistical

methods (ANOVA and cluster analysis) to propose

taphofacies models in tropical carbonate deposits.

Temperate siliciclastic–carbonate mixed deposits

have not been yet studied.

In this paper, a quantitative taphonomic approach

has been carried out. This methodology was applied to

the lower Pliocene temperate siliciclastic–carbonate

mixed platform deposits of the Almerıa-Nıjar basin

(SE Spain). The aim is to propose taphofacies models

in these settings following a quantitative procedure. In

the study area, lower Pliocene deposits can be traced

continuously along a proximal–distal transect, and

both the palaeoenvironmental conditions and the

palaeogeographic framework, as well as the tectonic

evolution, are known (Aguirre, 1998; Aguirre and

Yesares-Garcıa, 2003; Braga et al., 2003; Martın et

al., 2003). Therefore, this is a unique scenario to test

the validity of the taphofacies models in temperate

carbonates, as well as the analytical procedure used.

We have employed a methodology inspired in the

previous actualistic works by Powell et al. (1989),

Davies et al. (1990) and Meldahl and Flessa (1990),

and then used in the fossil record by Jimenez and

Braga (1993). The necessity of applying a quantitative

approach to avoid any subjective interpretation de-

rived from qualitative observations is emphasized.

Further, it is shown that interpretations based on as

many taphonomic signatures as possible will provide

much more reliable interpretations than using only a

few ones (Yesares-Garcıa and Aguirre, 2002).

2. Methodology

Firstly, a description of the fossil accumulations

was performed based on the taxonomic composition,

biofabric, geometry and inner structure according to

the terminology proposed by Kidwell et al. (1986).

Secondly, the bioclast packing and the percentage of

bioclasts per rock volume following the tables used by

Kidwell and Holland (1991) was estimated. Thirdly,

several selected taphonomic attributes were quanti-

fied. Powell et al. (1989) provided an extended list of

taphonomic signatures that are potentially measurable.

Nonetheless, since these authors studied Recent and

sub-Recent deposits, some of these potential features,

such as presence–absence of periostracum, color or

ligament, are in fact rarely preserved in the fossil

material and are therefore omitted in this study.

Selected taphonomic attributes are size sorting, artic-

ulation, fragmentation, left/right valve proportion,

orientation (angle with respect to stratification, life

orientation and concavity orientation), skeletal pres-

ervation, edge rounding and biotic interactions (bor-

ings and encrustations). Number of taxa (as an

indication both of the abundance and diversity) and

shell sizes have been also quantified. Measurement of

shell size provides information concerning the size

sorting, which can be related, in turn, to environmen-

tal conditions. All these values are tabulated as

percentages. In addition to the numerical data, histo-

grams of size sorting and shell inclination (biofabric)

are considered.

Measuring the inclination of bioclasts with any tool

is a difficult task due to multiple factors, such as the

irregularities of the surface of the outcrop or the small

size of the fossil remains (0.5 cm, see below). Thus,

this attribute was estimated visually with the help of a

J. Yesares-Garcıa, J. Aguirre / Palaeogeography, Palaeoclimatology, Palaeoecology 207 (2004) 83–103 85

template in which four angles (0j, 30j, 60j and 90j)were marked for reference (Yesares-Garcıa and

Aguirre, 2002; Aguirre and Yesares-Garcıa, 2003).

These angles separate the biofabric categories already

established by Kidwell et al. (1986): concordant,

oblique and perpendicular.

Actualistic works relied on dredged samples of a

certain volume (e.g. Fursich and Flessa, 1987; Staff

and Powell, 1990a,b; Davies et al., 1990; Meldahl and

Flessa, 1990). In the case of the fossil record, how-

ever, sampling based on sediment volume is not

practicable. Moreover, taphonomic attributes such as

biofabric (life position, concavity orientation or incli-

nation of bioclasts) are lost with this technique.

Additionally, transportation of the fossils from the

outcrops to the laboratory might produce a significant

bias in fragmentation (Flessa et al., 1992). Finally,

degree of cementation of the rocks prevents any

accurate sampling of loose sediment. To prevent these

biases, all measurements of the taphonomic attributes

were made directly in the outcrops.

Sampling sites for the quantification of taphonom-

ic attributes were selected according to the facies and

lithologies, thus allowing taphofacies models to be

established considering all the different materials

recorded in the study area, and all the types of fossil

concentrations. In each sampling site, measurements

were made in 10 quadrats of 20 cm in length-side

perpendicular to the stratification. Quadrats were

randomly distributed both in fossil concentrations

and in interbedded sediments. Special fossil concen-

trations (such as channel lag deposits, fossil clumps,

pods, etc.) were considered as different sampling

sites from the surrounding sediments. Occasionally,

these fossil concentrations are small and do not

allow 10 quadrats to be distributed in a single

accumulation of fossils. In these cases, taphonomic

attributes of all the organisms within individual pods

were computed as independent sampling sites for

statistical treatments.

Fossil remains larger than 0.5 cm were counted

within each quadrat. This size limit, although arbi-

trary, is established as the minimum size to directly

identify in the field most of the fossil remains and

assign them to a higher taxonomic group (genus,

family, order). Taphonomic signatures were quantified

in the totality of fossil remains, thus avoiding the

effect of target taxa that can bias the results (Best and

Kidwell, 2000b). The only fossil remains excluded

from the analyses were coralline red algae (both

fragments and rhodoliths). Nonetheless, their abun-

dance was computed by estimating the percentage of

rhodoliths and coralline fragments using the tables for

visual appraisal of the proportion of bioclasts per rock

volume (Kidwell and Holland, 1991).

The resulting data have been analyzed applying a

Q-mode cluster analysis. This statistical procedure

allows to establishing groups of samples (in this case

corresponding to the different sampling sites) based

on the taphonomic traits of the fossil assemblages that

the samples contain. Similar to Meldahl and Flessa

(1990), we have used the unweighted pair-group

average cluster method with Euclidean distances.

3. Geographic area and geological setting

The study area, the Los Ranchos site, is located in

the northeastern corner of the Almerıa-Nıjar basin (SE

Spain), close to El Argamason hamlet (Fig. 1). The

Almerıa-Nıjar basin is a post-orogenic basin bounded

by the Betic basement of Sierra Alhamilla and Sierra

Cabrera to the N and Sierra de Gador to the W. The

volcanic complex of Sierra de Gata limits the basin to

the E. These elevated terranes constituted the palae-

omargins of the basin during the Pliocene (Fig. 2).

The sedimentary record of the Almerıa-Nıjar basin

comprises several unconformity bounded units rang-

ing from the Miocene to the Pleistocene. A detailed

account of these deposits can be found in several

review papers (Goy and Zazo, 1982, 1986; Dabrio et

al., 1981; Montenat et al., 1990; Serrano, 1990; Van

de Poel, 1994; Aguirre, 1998). The Pliocene deposits

can be divided into two unconformable units, Units I

and II (Aguirre, 1998; Aguirre and Jimenez, 1997,

1998). The lower unit ranges from the early Pliocene

at the base to the lowermost late Pliocene at the top,

and the upper one is late Pliocene in age (Aguirre,

1998; Aguirre and Jimenez, 1998; Aguirre and San-

chez-Almazo, 1998). In the area surrounding the El

Argamason, only the lower unit is present, uncon-

formably overlying uppermost Messinian marls and

Miocene volcanic rocks.

In this area, the Pliocene sediments were deposited

on a very irregular palaeotopographic surface, leading

to important variations in thickness and to abrupt

Fig. 1. Geological map of the study area indicating the location of the two sampled sections.

Fig. 2. Palaeogeographic map of the Almerıa-Nıjar basin during the early Pliocene (after Braga et al., 2003).



lateral facies changes (Aguirre, 1998; Aguirre and

Yesares-Garcıa, 2003). This is an excellent setting

allowing taphonomical assessments to be undertaken

in a relatively small area where rapid sedimentological

and facies changes are easily observable and fossil

assemblages also show controllable variations.

3.1. Stratigraphy of the studied deposits

Los Ranchos is a hill oriented N–S coinciding with

a palaeogeographic proximal–distal trend. Two strati-

graphic sections have been studied, one in the distal-

most southern end of the site (Los Ranchos I section)

and the other in the northern part (Los Ranchos II

section) (Fig. 1). The Pliocene sequence can be

continuously followed along the outcrop, and it can

be laterally traced without interruption further to the

south for nearly 1.5 km.

Below, we outline a general description of the

studied sections and provide the palaeoenvironmental

interpretation based on extensive studies already made

in the area (Aguirre, 1998; Aguirre and Yesares-

Garcıa, 2003; Aguirre et al., 2002; Yesares-Garcıa

and Aguirre, 2002). Then, we concentrate on the

quantitative taphonomical assessment and the propo-

sition of taphofacies models.

3.1.1. Los Ranchos I section

At the Los Ranchos I section, which is 76 m thick,

the Pliocene sequence starts with bioturbated silts and

fine-grained sands (Fig. 3). The most abundant fossils,

although very dispersed in the sediment, are the

bivalves Korobkovia oblonga and Chlamys spp., and

the gastropod species Scalaria tenuicostata and S.

frondiculoides. Higher up in the sequence, the sedi-

ment gradually changes to medium-grained sands

with occasional trough cross-lamination. The fossil

content progressively increases toward the top, with

more diverse fossil assemblages, characterized by

pectinids (Chlamys, Pecten, Flexopecten and Flabel-

lipecten), Neopycnodonte cochlear, bryozoans (most-

ly fragile and robust erect colonies) and echinoids

(mainly cidarids and Clypeaster). The bryozoans are

especially abundant in the medium-grained sand close

to the top of the sequence. This part of the sequence is

45 m thick.

A striking feature of the sands is the presence of

concentrations of fossils in small pods (Fig. 3), mostly

dominated by Neopycnodonte and fragments of

branching bryozoans. These accumulations of fossils

are slightly irregular and, occasionally, cylindrical in

longitudinal section and circular in cross-section.

They are a few centimetres in diameter (less than 10

cm) and some tens of centimetres in length (up to 25

cm). Fossils are parallel to the limits of the concen-

tration, producing an almost concentric arrangement.

The gross morphology of these fossil concentrations,

together with the disposition of the shells, allows them

to be interpreted as burrows filled with bioclasts

(Yesares-Garcıa and Aguirre, 2002; Aguirre and Yes-

ares-Garcıa, 2003; Aguirre et al., 2002).

Three characteristic beds between 3 and 6 m in

thickness of highly cemented calcarenites–calciru-

dites are intercalated in the sand in the upper half

(Fig. 3). The lower contact of the lower two calcar-

eous beds shows a gradual transition from the sands to

the cemented calcarenites. This transition is due to a

progressive cementation of the sediment. In contrast,

the lower limit of the uppermost calcareous bed is

represented by an erosive surface characterized by

channeled, normal-grading lag concentrations of fos-

sils (Fig. 3). This bed is characterized by large-scale

cross-stratification indicating a northward-moving

palaeocurrent.

All three beds are quite fossiliferous and show

similar sedimentological features. Nonetheless, there

are some differences among them. First, the fossil

content and the size of the bioclasts increase from the

lower calcarenitic-calciruditc bed to the upper one.

Second, trough cross-lamination and lag accumula-

tions of fossils are present in the three beds, although

they are smaller in scale in the lower bed than in the

uppermost one. In addition, the lag concentrations

present in the uppermost bed are often amalgamated.

Finally, coralline red algae (occurring as rhodoliths or

branch fragments) are present in all three beds, but

there is an appreciable change in the other compo-

nents of the fossil assemblages. Thus, the lower bed is

dominated by the pectinids Pecten, Chlamys and

Flabellipecten, bryozoans, echinoids and serpulid-

worm tubes, while the uppermost bed is clearly

dominated by the oyster Ostrea lamellosa and the

pectinid Flabellipecten bosniasckii, with minor

amount of other components (such as Chlamys, Pec-

ten, bryozoans, echinoids and balanids). The genus

Isognomon is characteristically quite abundant in the

Fig. 3. Stratigraphic columns of the Los Ranchos I and Los Ranchos II sections.


middle bed and can form locally dense lag concen-

trations of valves.

Taphonomic analysis was carried out in 10 sam-

pling sites distributed along the Los Ranchos I section

(Fig. 3). The distribution of these sampling sites takes

into consideration the different modes of fossil con-

centrations and lithologies. One sampling site (LRI-

3b-p) includes a single pod concentration of fossils in

a filled burrow and the remaining sampling sites are

distributed in the sands and calcareous beds. The

results of the taphonomic measurements are summa-

rized in Table 1.

3.1.2. Los Ranchos II section

The Pliocene sequence at the Los Ranchos II

section, in the northernmost part of the outcrop, is

similar to the one described above, reaching about 90

m thick (Fig. 3). Nevertheless, there are some differ-

ences that should be mentioned. The base of the unit

consists of bioturbated silts and fine-grained sands

with a higher fossil content than in the base of the Los

Ranchos I section. Fossil assemblages are dominated

by the bivalves Korobkovia oblonga, Chlamys spp.,

Amusium cristatum, Neopycnodonte cochlear and N.

navicularis, the gastropod Scalaria spp. and scarce

solitary corals such as Flabellum.

These sediments progressively change to medium-

grained sands to the middle part of the unit and the

fossil content progressively increases in the same

direction. The total thickness of this part of the

sequence is 56 m. Concentrations of the serpulid

worm Ditrupa can often be found here, and numer-

ous pod concentrations of shells (filled-burrows)

occur in the sands. Bryozoans are also very abun-

dant; they occur as robust and delicate erect, foliate

erect, nodular and free-living lunulitiform colonies. It

Table 1

Average values of taphonomic attributes measured in the Los Ranchos I section

Site N Vol. Fragm. Shell size Articula. Angle Orientation Shell preser. Edges Interactions

(%)Ave. S.D. Max Ave. S.D. Up D. Vertic. Platy Orig. Mold. Re. S. R. Boring Encos.

1 0.004 < 5 87.5 1.5 1.4 5.0 0.0 28.3 30.4 43.8 31.3 12.5 12.5 100.0 0.0 0.0 100. 0.0 0.0 0.0

2 0.053 5–10 98.1 0.8 0.3 1.8 0.0 45.8 34.1 21.1 18.9 21.1 38.9 100.0 0.0 0.0 25.7 74.3 0.0 0.0

3 0.134 30–60 98.6 1.1 0.6 5.7 0.0 21.7 24.8 30.9 19.1 2.6 47.4 100.0 0.0 0.0 24.8 75.2 0.0 0.9

3a 0.029 < 5 99.1 0.8 0.5 4.0 0.0 44.7 33.3 27.5 26.6 15.6 30.3 100.0 0.0 0.0 52.6 47.4 2.6 0.0

3b 0.076 5–15 94.7 1.1 0.7 5.5 0.0 46.1 30.6 26.6 21.1 12.8 39.4 100.0 0.0 0.0 44.9 55.1 2.6 1.7

3b-p 0.200 40 94.0 1.1 0.6 3.0 0.0 51.4 30.3 35.1 21.6 17.5 25.8 100.0 0.0 0.0 76.0 24.0 9.0 0.0

4 0.149 50–55 96.5 1.2 1.0 14.0 0.0 32.1 27.5 26.3 25.4 6.8 41.5 86.4 13.4 0.2 19.1 80.9 0.4 0.0

5 0.152 40–55 97.9 1.0 0.6 4.7 0.0 31.4 28.5 18.4 12.5 7.5 61.6 100.0 0.0 0.0 21.5 78.5 0.3 0.8

6 0.165 40–60 95.5 2.6 1.9 15.0 0.5 34.0 27.3 32.2 24.5 6.3 37.0 100.0 0.0 0.0 15.2 84.8 10.8 2.4

7 0.082 20–40 95.7 2.1 1.6 11.2 0.0 33.9 25.5 31.4 22.2 2.6 43.8 100.0 0.0 0.0 22.0 78.0 5.1 3.3

Values are expressed as the average percentages obtained from the 10 quadrats distributed in each sampling site. N is calculated as the number of

bioclast per sampling area (10 quadrats of 20 cm per side, that is 4000 cm2). Vol. = volume, Fragm. = fragmentation, Ave. = average,

S.D. = standard deviation, Max = largest shell size, Articula. = articulation, D. = down, Vertic. = vertical, Shell preser. = skeletal preservation,

Orig. = original, Mold. =moulds, Re. = recrystallized, S. = sharp, R. = rounded, Encos. = encrusting.


is worth mentioning that many of the erect colonies

are preserved complete and in their original, vertical

life position. Furthermore, a bed a few centimetres

thick dominated by Neopycnodonte cochlear is in-

tercalated in the sands (Fig. 3). Other organisms

accompanying this bivalve are Chlamys, Flabelli-

pecten, Spondylus, Ditrupa, echinoids, bryozoans

and brachiopods. The base of this bed is locally

modified by bioturbation, forming pod-like accumu-

lations of fossils in burrow fills (Fig. 3).

In the upper half of the unit, which is 34 m thick,

calcarenitic–calciruditic beds are intercalated in bio-

turbated bioclastic sands (Fig. 3). The fossils in the

sands outline the margins of the burrows; they are

oriented parallel to the walls and are concentrically

arranged in the inner part of the dens, producing

funnel-like structures. Individual filled burrows are

up to 1 m long and up to 20 cm across. Although

individual trace fossils are visible, the bioclastic sands

are intensely bioturbated and, consequently, the filled-

burrow concentrations of fossils cross-cut each other.

The most abundant fossils are the mytilid Modiolus,

followed by Anomia, Amusium, Chlamys, Neopycno-

donte, bryozoans, echinoids and barnacles.

At the Los Ranchos II section, the middle and the

upper calcarenite–calcirudite beds are amalgamated,

forming a single 9-m-thick bed due to the wedging-

out of the interbedded sands (Fig. 3). The calcaren-

ites–calcirudites are characterized by large-scale

trough cross-laminations, indicating a north-directed

palaeocurrent. Frequent clasts of quartzites, schists,

limestones and dolostones are found in these beds.

Lag concentrations of fossils occur in the troughs of

the cross-lamination and in the bases of channels.

Fossil assemblages are dominated by bivalves

(Ostrea, Chlamys, Pecten, Macrochlamys, Isogno-

mon, Spondylus, Neopycnodonte and Flabellipecten),

gastropods (moulds of Turritella and other unidenti-

fiable moulds), bryozoans (fragments of erect colonies

are very abundant), balanids, serpulids (mostly

Ditrupa), echinoids and coralline red algae. Isogno-

mon and pectinids characteristically form amalgamat-

ed lag concentrations in the bases of channels.

Fourteen sampling sites were distributed through-

out the Los Ranchos II section for the taphonomic

analysis (Fig. 3). They were located along the section

including the different lithologies and kinds of shell

concentrations. Quantitative data on the taphonomic

attributes are shown in Table 2.

3.2. Palaeoenvironmental interpretation

The upward increase in grain size and the presence

of cross-lamination in the upper half of the unit

suggest that the studied Pliocene unit represents a

shallowing-upward sequence. The silts and fine-

grained sands of the base of the studied sections are

interpreted as outer platform deposits, formed below

the storm wave base, while the calcarenites–calciru-

dites are attributed to inner shelf deposits affected by

Table 2

Average values of the taphonomic attributes measured in the Los Ranchos II section

Site N Vol. Fragm. Shell size Articula. Angle Orientation Shell preser. Edges Interactions

(%)Ave. S.D. Max Ave. S.D. Up D. Vertic. Platy Orig. Mold. Re. S. R. Boring Encos.

1 0.023 5 95.7 0.8 0.6 5.5 0.0 42.0 32.5 19.3 17.0 14.8 48.9 100 0.0 0.0 47.3 52.7 0.0 0.0

2 0.028 < 5 91.2 0.8 0.4 3.0 0.0 43.5 33.6 22.9 21.1 15.6 40.4 100 0.0 0.0 24.8 75.2 0.0 0.9

2-p1 0.183 55 90.9 1.4 1.1 6.9 0.0 39.9 32.8 39.6 15.1 13.2 32.1 100 0.0 0.0 30.9 69.1 1.8 1.8

2-p2 0.157 55 83.0 1.2 0.6 2.9 0.0 40.9 30.3 44.7 19.1 10.6 25.5 100 0.0 0.0 31.9 68.1 2.1 4.3

3 0.136 27 96.6 1.4 0.7 5.0 0.6 44.3 30.7 51.6 20.6 11.0 16.8 100 0.0 0.0 56.2 43.8 6.6 3.1

4 0.028 < 5 86.4 0.9 0.6 5.5 4.7 48.3 32.5 25.7 15.8 16.8 41.6 100 0.0 0.0 21.8 78.2 1.8 0.9

4-p1 0.219 55 68.0 1.4 0.6 3.3 0.0 51.6 28.4 44.0 28.0 12.0 16.0 100 0.0 0.0 48.0 52.0 4.0 10.0

4-p2 0.118 55 66.7 1.7 0.7 3.4 11.5 40.6 30.9 54.2 33.3 8.3 4.2 100 0.0 0.0 48.1 51.9 11.1 11.1

4-p3 0.123 55 64.3 1.6 0.7 3.5 0.0 50.4 32.2 37.0 37.0 22.2 3.7 100 0.0 0.0 25.0 75.0 25.0 14.3

5 0.118 55 95.1 1.0 0.5 4.7 0.0 22.0 22.1 39.7 22.2 2.9 35.2 75.5 24.5 0.0 13.2 86.8 0.3 0.3

6 0.123 50 96.1 1.1 0.7 10.0 2.2 25.3 25.6 31.1 26.8 3.6 38.4 80.0 20.0 0.0 1.0 99.0 0.0 1.0

7 0.205 35 94.3 0.8 0.4 5.8 0.1 49.9 29.0 35.2 24.0 13.4 27.5 100 0.0 0.0 94.4 5.6 0.6 0.4

8 0.167 60 94.7 1.3 1.3 13.0 1.4 29.2 27.9 34.8 23.9 7.3 34.0 92.2 7.8 0.0 11.9 88.1 2.5 0.9

9 0.130 50 93.4 2.1 1.7 8.5 0.0 29.1 23.7 32.7 22.0 0.8 44.5 87.6 12.4 0.0 7.6 92.4 3.9 1.5

Values and abbreviations as in Table 1.


the storm waves (Aguirre, 1998; Aguirre and Yesares-

Garcıa, 2003; Aguirre et al., 2002). This interpretation

coincides with the sequence stratigraphic model pro-

posed for the lower Pliocene sedimentary evolution of

the Almerıa-Nıjar basin (Montenat et al., 1990;

Boorsma, 1992; Aguirre, 1998; Aguirre and Yes-

ares-Garcıa, 2003; Aguirre et al., 2002; Braga et al.,

2002) and other basins distributed along the S and E

Spain (Montenat, 1977; Martinell, 1988; Sierro et al.,

1990; Civis et al., 1994; Aguirre, 1995, 2000). Thus,

the inner-platform calcarenites–calcirudites of the

upper part of the unit prograded on the silts and

massive sands formed in deep outer-shelf settings

(Yesares-Garcıa and Aguirre, 2002; Aguirre and Yes-

ares-Garcıa, 2003; Aguirre et al., 2002).

This interpretation is supported by the changes in

the fossil assemblages and taphonomic signatures

(Yesares-Garcıa and Aguirre, 2002; Aguirre and

Yesares-Garcıa, 2003). Thus, fossil assemblages

dominating the silts and fine-grained sands at the

base of the unit consist of Korobkovia, Amusium and

Neopycnodonte, organisms adapted to low-energy

deep environments (Gould, 1971; Carter, 1972; Stan-

ley, 1972, 1988; Peres, 1989; Poppe and Goto, 1993;

Aguirre et al., 1996).

Upward in the unit, the fossil content increases, and

the fossil assemblages diversify and are composed of

organisms typical of shallower settings. Among the

pectinids, the number of strongly ribbed species and

high shell-inflation indices (such as Chlamys sienen-

sis) increase indicating shallower conditions (Aguirre

et al., 1996). Moreover, there is a diversification in the

growth morphology of bryozoan colonies, which is

consistent with the shallowing trend (Harmelin, 1988;

McKinney and Jackson, 1989; Moissette, 2000).

Finally, the calcareous beds with cross-lamination

and cross-stratification represent the shallower inner-

platform facies. In agreement with this interpretation,

these deposits are dominated by Ostrea lamellosa, an

organism that characteristically inhabits intertidal or

shallow subtidal settings (e.g. Stenzel, 1971). Anoth-

er representative organism in these sediments, espe-

cially in the uppermost calcarenitic–calciruditic bed,

is Flabellipecten bosniasckii, a pectinid species quite

abundant in inner-shelf, medium-grained sands and

conglomerates of the Almerıa-Nıjar and the Campo

de Dalıas basins (both in SE Spain) (Aguirre et al.,

1996).

Fossils occur dispersed in the matrix and concen-

trated in lags both at the base of the channels and at

the troughs of the shoals. The normal-graded channel

lag accumulations of fossils are interpreted as storm

deposits. The amalgamation of channels observed in

the uppermost calcarenitic–calciruditic bed and in the

calcareous beds of the Los Ranchos II section is

interpreted as a sedimentary feature indicating depo-

sition in proximal settings (Seilacher and Aigner,

1991). Similar storm lag deposits are found through-

Fig. 4. Q-mode cluster analysis, using the unweighted pair-group average method and Euclidean distances.


out the Almerıa-Nıjar basin (Aguirre, 1996, 1998;

Aguirre et al., 1996, 2002).

4. Taphonomic results

A Q-mode cluster analysis of all the sampling sites

in both sections allows four groups of samples to be

distinguished (Fig. 4). Cluster A can be divided into

three distinctive subgroups. Subgroup A1 includes

only one sampling site, LRI-1, located at the base

of the Los Ranchos I section (Fig. 3). This sample

stands out from the others due to its lower fossil

abundance (0.004 bioclasts/cm2), the highest percent-

age of complete organisms, and because all the shell

fragments show sharp edges indicating an absence of

Fig. 5. Histograms of the size sorting, biofabric and taphonomic attribute

Artic. = articulation, E.R. = edge rounding, j = platy fragments, P= perpend

abrasion (Table 1). In addition, this cluster is charac-

terized by a great dispersion in the size of the

bioclasts (Fig. 5).

Subgroup A2 incorporates the remaining sampling

sites distributed in the massive sands in both sections

(LRI-2, LRI-3a, LRI-3b, LRII-1, LRII-2 and LRII-4)

(Figs. 3 and 4). According to the taphonomic data, all

these samples have in common almost barren or

dispersed packing (0.023–0.028 bioclasts/cm2) and

a low percentage of bioclasts per rock volume (5%)

(Tables 1 and 2). These samples include the lowest

values of the average shell size. As a consequence,

this results in a high degree of sorting characterized by

a markedly unimodal frequency distribution with a

maximum of the smallest class size (Fig. 6). The small

size of the shell fragments, in turn, accounts for the

s characterizing cluster A1. Vol. = volume, Fragm. = fragmentation,

icularly oriented shells, Encrust. = encrusting organisms.

Fig. 6. Histograms of the size sorting, biofabric and taphonomic attributes characterizing cluster A2. Abbreviations as in Fig. 5.


dominance of platy fragments since it is not possible

to distinguish the curvature in small remains. How-

ever, considering those fragments with a distinctive

curvature, there is no preferred orientation in relation

to concavity. In addition, fossils of these sampling

sites show a moderate to low degree of abrasion.

Finally, with respect to the biofabric, this subgroup

is characterized by a bimodal distribution with shells

mostly concordantly and perpendicularly oriented

(Fig. 6).


Subgroup A3 comprises some of the sampling sites

located in the pod accumulations of fossils filling

burrows (LRI-3b-p, LRII-2-p1 and LRII-2-p2), as well

as the sampling site corresponding to the intensively

bioturbated sand with individualized filled burrows

(LRII-7) (Figs. 3 and 4). It also includes sampling site

LRII-3, located in the Neopycnodonte cochlear pave-

ment, with the base modified by bioturbation at the

Los Ranchos II section (Fig. 3). This subgroup shows

the highest values of fossil abundance (dense packing:

0.136–0.219 bioclasts/cm2) and, consequently, a high

Fig. 7. Histograms of the size sorting, biofabric and taphonomic at

to very high content of bioclasts per rock volume (30–

40%) (Tables 1 and 2). Except for sampling sites LRII-

2-p1 and LRII-2-p2, one of the most striking tapho-

nomic signatures that characterizes this subgroup is

the relatively high proportion of shell fragments with

sharp edges (Fig. 7). Additional distinctive taphonom-

ic attributes are: (a) domination of concave-up orient-

ed fossils, (b) low degree of size sorting, (c) dispersed

to bimodal (concordant and perpendicular preferred

biofabrics) frequency distribution of angles and (d)

frequent biotic interactions (Fig. 7).

tributes characterizing cluster A3. Abbreviations as in Fig. 5.

Fig. 8. Histograms of the size sorting, biofabric and taphonomic attributes characterizing clusters B1 and B2. Abbreviations as in Fig. 5.



Cluster B lumps together all the sampling sites

situated in the calcarenites–calcirudites (LRI-3, LRI-

4, LRI-6, LRI-7, LRII-5, LRII-6, LRII-8 and LRII-9)

and sample LRI-5, which corresponds to the highly

fossiliferous sands with cross-stratification and lami-

nation immediately above the first calcareous bed in

the Los Ranchos I section (Figs. 3 and 4). These

sampling sites are characterized by a high percentage

of bioclasts per rock volume (f 30%) (Tables 1 and

2). Furthermore, they are the only sites with moulds

(Fig. 8). The highest proportion of fragments showing

rounded edges, which indicates a high degree of

abrasion–corrasion, is also typical of this cluster.

The sampling sites gathered in this cluster show a

dispersed or slightly bimodal size sorting, with the

two lowest class sizes dominating. In relation with the

preferred orientation of fossils, concordantly arranged

shells dominate this cluster. Therefore, it shows the

lowest values of average bioclast inclination (Tables 1

and 2). Platy fragments are quite abundant, followed

by concave-up oriented fossils. Finally, this cluster

displays the lowest percentage of organic interactions

(borings and encrustations) (Fig. 8).

Cluster B can be divided into two subgroups (Fig.

4). Subgroup B1 includes the sampling sites situated

Fig. 9. Histograms of the size sorting, biofabric and taphonomic attrib

in the calcareous matrix (LRI-3, LRI-5, LRI-4, LRII-

8, LRII-5 and LRII-6), while subgroup B2 comprises

lag concentrations of fossils in channels and at the

base of trough cross-lamination (LRI-6, LRI-7 and

LRII-9) (Fig. 3). Both subgroups show similar taph-

onomic attributes. Nonetheless, subgroup B2 is dis-

tinguished from subgroup B1 by: (a) denser packing,

(b) a higher dispersion of the size of the bioclasts,

with a larger proportion of bioclasts belonging to the

largest class sizes, and (c) the lower values of biotic

interactions (Fig. 8).

Clusters C (LRII-4-p1 and LRII-4-p3) and D

(LRII-4-p2) also correspond to shell-filled burrow

accumulations (Fig. 3). However, they are separated

from each other and from subgroup A3 (Fig. 4). The

split of clusters C and D is related with the markedly

bimodal biofabric arrangement observed in sampling

site LRII-4-p2 (Fig. 9), as well as with the presence of

some articulated fossils (Table 2). In addition, the

difference of these two clusters with subgroup A3 is

the lower proportion of fragmentation and the espe-

cially high percentage of interactions (both borings

and encrustations) (Figs. 7 and 9). Otherwise, the rest

of the taphonomic attributes are similar to those

measured in the sampling sites of subgroup A3 (Tables

utes characterizing clusters C and D. Abbreviations as in Fig. 5.


1 and 2). Fragmentation and biotic interactions are

two taphonomic attributes not directly related with the

processes taking place within the burrows. Rather,

they depend on the taphonomic processes that the

organisms underwent before they became trapped in

burrows. Galleries merely offer protection to fossils

against biostratinomic destructive processes. There-

fore, the cluster analysis gives special weight to these

signatures for dividing all these sampling sites into

different clusters.

5. Taphofacies models

Using Q-mode cluster analysis as an analytical

procedure to define taphofacies allows the sampling

sites to be grouped according to the taphonomic

attributes of the fossils they contain. Therefore, the

resulting clusters would represent, by definition,

taphofacies (as originally defined by Speyer and Brett,

1986). This statistical technique was satisfactorily

applied for defining taphofacies by Meldahl and

Flessa (1990) in present-day intertidal setting and

shallow-shelf, and by Jimenez and Braga (1993) in

upper Miocene coral reefs.

The different groups resulting from the Q-mode

cluster analysis can be assigned to three taphofacies

models, each of them characterized by different taph-

onomic traits (Table 3). These taphonomic attributes

are related, in turn, to the palaeoenvironmental set-

tings in which the fossil assemblages were accumu-

Table 3

Summary table indicating the taphonomic attributes that characterize the

Outer platform Biotic acc

Sedimentation rate Moderate–high Absent– lo

Hydraulic energy Absent– low Low

Accumulations Simple Simple, co

Bioclastic fabric Barren– loosely Dense

Abundance Very low– low High–ver

Percentage per volume Very low– low Moderate–

Life position Rarely Absent

Fragmentation High–very high Moderate–

Disarticulation Very high– total Very high

Abrasion Absent–high Variable

Sorting High Disperse

Orientation Concordant, perpendicular Concordan

Concavity orientation Variable Concave-u

Biotic interactions Absent– low Common

lating (i.e. Speyer and Brett, 1986; Brett and Baird,

1986), thus giving a valuable information on the

original conditions.

5.1. Outer-shelf taphofacies model

This taphofacies comprises subgroups A1 and A2

of cluster A. The low abundance of bioclasts per rock

volume and the almost barren packing suggest that

relatively high sedimentation rates prevailed during

the deposition of these sediments, producing a dilu-

tion of the shell remains (Brett and Baird, 1986;

Speyer and Brett, 1986, 1988; Kidwell and Bosence,

1991). The low to moderate percentage of edge

rounding, as well as the near absence of interactions,

confirms that the fossils remained on the water–

sediment interface only briefly, probably due to rapid

burial. The dominance of sharp-edged fragments is

consistent, in turn, with a low hydraulic setting (Table

3). In such environmental conditions, a high percent-

age of fragmentation and disarticulation of fossils is

most likely related with the activity of other organ-

isms (Powell et al., 1989; Callender et al., 1990;

Parsons and Brett, 1991; Kidwell and Bosence,

1991; Cadee, 1992, 1994; Best and Kidwell,

2000a,b). This biological activity in the sea bottom

is shown by intense bioturbation of the sediment (ii3–

ii4, ichnofabric index sensu Droser and Bottjer, 1993).

The lack of clear preferred concavity arrangement

could be also correlated with the burrowing activity

that produced a random orientation of organisms

taphofacies proposed herein

umulations Inner platform

w Low

High-variable

mpound Compound

Loosely–dense

y high Low–high

very high Moderate–very high

Absent

very high Very high

– total Very high– total

High–very high

Moderate

t, perpendicular Concordant

p (scarce platy fragments) Predominantly platy (concave-up)

Low–Common


within the matrix (Clifton, 1971; Salazar-Jimenez et

al., 1982).

In short, this taphofacies represents the silts and the

fine-to medium-grained massive sands deposited in

deep, low hydraulic energy conditions (Aguirre and

Yesares-Garcıa, 2003). Subgroups A1 and A2 of the

cluster analysis are assigned to this taphofacies,

named outer-shelf taphofacies model, because they

show similar taphonomic signatures. In addition,

according to the palaeoenvironmental interpretation,

the sediments represented by these subgroups were

formed in similar conditions. The only substantial

taphonomic difference between the two subgroups is

that subgroup A1 is characterized by 100% of frag-

ments with sharp edges. This taphonomic signature is

overweighted in the statistical procedure, thus isolat-

ing fossils with sharp edges into a single group.

The preservational states of the fossils of this

taphofacies, as well as the inferred palaeoenvironmen-

tal settings in which they formed, allow this cluster to

be correlated with the ‘‘outer-platform taphofacies’’

described by Aguirre (1996) in the centre and western

parts of the Almerıa-Nıjar basin. This taphofacies also

partially coincides with the ‘‘Model V’’ of Speyer and

Brett (1991) described from the Middle Devonian of

New York State.

5.2. Biotic accumulation taphofacies model

This taphofacies lumps together the pod concen-

trations of fossils inside burrows produced by the

direct or indirect activity of burrowing organisms as

well as the bioclastic sands intensively modified by

bioturbation (subgroup A3 and clusters C and D). The

close connection of this taphofacies with the previous

one (they are both grouped in the cluster analysis and

included in massive fine- to medium-grained sands)

suggests that they formed under similar environmental

conditions (Table 3). Shells are expected to be con-

cave-down since this is the most stable position.

However, burrowing activity may alter this preferred

orientation, as observed by the predominance of con-

cave-up shells in this taphofacies. Burrows acted as

traps for sediment and skeletal remains, accounting for

the dense packing and the high percentage of bioclasts

per rock volume. This trap effect is also responsible for

the low size sorting (Martinell and Domenech, 1990),

as well as for the wide range of the preferred orienta-

tion of fossils. In this taphofacies, fragmentation and

abrasion/corrasion are low, while the proportion of

articulated organisms can be moderate to high (Table

3). These taphonomic attributes are also connected

with the protection offered by the burrows. Neverthe-

less, these attributes, together with biotic interactions,

are quite variable since they depend upon the biostra-

tinomic processes affecting shells before they accu-

mulated in the burrows. This also explains the

separation of groups C and D in the cluster analysis.

Similar bioclastic concentrations in pockets were

described as tubular tempestites by Wanless et al.

(1988) in Recent and Pleistocene deposits of the

Bahama platform. These authors proposed that the

skeletal remains were swept within the burrows made

by the crustacean Callianassa during storm events.

Each storm event produced the flattening of the

surface and the consequent infilling of the burrows.

After a period of repeated storms and hurricanes, it

resulted in the superposition of several tubular tem-

pestites forming almost continuous shell beds. The

biotic accumulation taphofacies, as described in this

paper, can be equivalent to these tubular tempestites.

5.3. Inner-shelf taphofacies model

This taphofacies is represented by the sampling

sites grouped in cluster B of the cluster analysis. All

these sampling sites are characteristically in calcaren-

ites–calcirudites deposited in high-energy, low sedi-

mentation-rate inner-platform settings above the storm

wave base (Table 3). The taphonomic signatures that

characterize this taphofacies are related to the combi-

nation of long exposure on the taphonomic active

zone with high hydraulic energy in fair-weather con-

ditions: high fragmentation, high abrasion/corrasion,

high disarticulation, predominantly concordant ar-

rangement, concave-down preferred orientation, low

percentage of interactions and absence of life position

(Table 3). Moreover, the high proportion of fragmen-

tation produces low size sorting.

As commented above, cluster B can be divided into

two subgroups. Subgroup B1 lumps the sampling sites

of the background calcarenites–calcirudites, while

subgroup B2 includes those sampling sites in chan-

neled storm-lag deposits and in the troughs of the

shoals. This differentiation enables event fossil con-

centrations formed in higher hydraulic energy con-


ditions (subgroup B2) to be separated from those

deposits representing the background, normal deposi-

tion (subgroup B1).

According to the taphonomic attributes, subgroup

B1 can be correlated with the ‘‘distal inner platform

taphofacies’’ described by Aguirre (1996) or with the

‘‘Model III’’ from Speyer and Brett (1991). One of the

sedimentary features of the distal inner-platform

taphofacies proposed by Aguirre (1996) is the fre-

quent presence of distal storm shell concentrations

(see also Aguirre et al., 1996). However, in the Los

Ranchos outcrop there are no recognizable distal

tempestites (Yesares-Garcıa and Aguirre, 2002;

Aguirre and Yesares-Garcıa, 2003). This sedimento-

logical difference between the central part and the NE

corner of the Almerıa-Nıjar basin can be related to the

inferred palaeogeography of the basin (Fig. 2). In this

palaeogeographic scenario, the NE edge of the basin

was protected by the volcanic highlands of the Sierra

de Gata, while the centre of the basin remained open

to the Mediterranean and, therefore, exposed to storm

events (Fig. 2). In short, the palaeogeographic con-

figuration of a basin controls the sedimentary signa-

ture of the deposition.

Regarding the style of preservation of fossils

different palaeoenvironmental conditions can produce

similar taphonomic signatures, a principle of the

comparative taphonomy as stated by Brett and Baird

(1986). Thus, sediment starvation with long exposure

of the remains within the taphonomic active zone

seems to be the determinant factor characterizing this

taphofacies in the Los Ranchos area. However, cata-

strophic sedimentation due to high energy storm

events appears to be the key factor in the preservation

of fossils in the centre of the basin. This demonstrates

the validity of the taphonomic approach to the inter-

pretation of palaeoenvironmental settings regardless

of the facies and sediments. Obviously, a combination

of approaches (facies and taphonomic studies) can

help to reconstruct a more precise and realistic sce-

nario of the depositional conditions.

On the other hand, subgroup B2, characterizing

particular storm events of fossil accumulations, shows

similar taphonomic signatures to the ‘‘proximal inner

platform taphofacies’’ of Aguirre (1996), which char-

acterizes those sediments deposited above the fair-

weather wave-base, and ‘‘Model I’’ of Speyer and

Brett (1991).

6. Alternative taphofacies models: a discussion

As commented above in the Introduction, tapho-

nomic analysis is often based on just two or three

taphonomic attributes. An unweighted pair-group av-

erage cluster with Euclidean distances considering

only three taphonomic signatures, i.e. fragmentation,

articulation and edge rounding, was produced (Fig.

10). The resulting cluster can be divided into five

groups, one of them subdivided in turn into four

subgroups (Fig. 10). The first group, cluster A,

includes the lowest sampling site of the Los Ranchos

I section (LRI-1), the intensely bioturbated sands of

the Los Ranchos II section (LRII-7) and one of the

filled-burrows of the Los Ranchos I section (LRI-3b-

p). The virtual absence of abrasion (e.g. 100% of

sharp edges in LRI-1, Table 1) is the distinctive

taphonomic signature that defines this group.

The second group, cluster B, is the most diversified

one, comprising nearly all the sampling sites located

both in the massive sands and in the cross-laminated

calcarenitic–calciruditic beds of the two sections, as

well as one of the filled burrows at the Los Ranchos II

section (LRII-2b-p). All these sampling sites have in

common a high proportion of fragmentation and abra-

sion. Cluster B can be divided into four subgroups.

This distinction is based on subtle differences in values

of these two taphonomic attributes. Each subgroup

includes sampling sites located in the massive sands, in

the calcarenites–calcirudites and in the filled burrows

thus, they do not correspond with any distinctive facies

or with any kind of fossil concentration.

Cluster C groups together a filled burrow (LRII-2-

p2) and a sampling site of the massive sands (LRII-4),

both at the Los Ranchos II section. These sampling

sites share taphonomic attributes with those included

in the cluster B; however, the sites belonging to

cluster C are characterized by a lower degree of

abrasion.

Cluster D is composed of two filled burrows at the

Los Ranchos II section (LRII-4-p1 and LRII-4-p3).

These two sampling sites are included together based

on the lower percentages of fragmentation and abra-

sion than those sites included in clusters B and C. In

fact, they show intermediate levels of fragmentation

(ca. 65%) and abrasion (52%–75%) (Table 2).

Finally, cluster E comprises only one sampling site

of a filled burrow from the Los Ranchos II section

Fig. 10. Unweighted pair-group average Q-mode cluster with Euclidean distances considering only three taphonomic signatures: fragmentation,

articulation and edge rounding. The resulting dendrogram shows unrelated and incoherent groups of samples. Therefore, this cluster requires a

more artificial and complex interpretation.


(LRII-4-p2). The discriminating taphonomic trait that

separates this cluster from the others is the highest

values of articulation (11.5%, Table 2). Moreover, this

sampling site is also characterized by an even lower

abrasion value than those belonging to cluster D.

Fig. 10 shows that the resulting Q-mode cluster

analysis involving just three taphonomic attributes

produces groups linking sampling sites located in

different lithologies with disparate sedimentary traits,

which furthermore represent different environmental

conditions. That is, this procedure unites unrelated

and incoherent groups of sampling sites. The use of

just a few taphonomic traits accounts for this result.

Therefore, this cluster requires more artificial and

complex explanations for justifying the resulting

groups and subgroups, as well as for establishing

taphofacies models.

In short, this demonstrates that the more different

taphonomic attributes used in the Q-mode cluster

analysis, the better and the more robust the results

are. Otherwise, the possible taphofacies models based

on cluster analysis including only a few taphonomic

signatures may produce unrelated and incoherent

groups of samples that require a more artificial and

complicated palaeoenvironmental explanations. How-

ever, it should be stressed once again, that the prop-

osition of taphofacies models should rely not only on

the cluster analysis, but also on other pieces of

evidence (i.e. sedimentology, facies, trace fossils,

ichnofabric, fossil assemblages and type of fossil

concentrations).

7. Conclusions

Quantifying taphonomic attributes is tedious work

that consumes considerable time in the field to obtain

data. Nonetheless, numbers provide objective results

that elude interpretations based on subjective evalua-

tions such as ‘‘very much’’, ‘‘a few’’ or ‘‘a great

amount of’’. All these terms will unavoidably depend

upon the interest, skills or even emotions of the

investigator. Therefore, quantifying taphonomic prop-

erties is needed for a more rigorous, understandable

and universal way of expressing results instead of

qualitative estimates.

The methodology proposed herein is applicable to

sediments dominated by molluscs, echinoids, bryozo-

ans and barnacles, particularly in Neogene deposits.

Based on this fossil content, potentially observable

taphonomic signatures, such as size sorting, packing,

articulation, fragmentation, left/right valve proportion,


orientation (the lowest angle of the bioclasts with

respect to the bedding, concavity orientation, original

life position), skeletal preservation, edge rounding and

biotic interactions (borings and encrusting organisms)

have been measured. All these taphonomic attributes

have been tabulated as percentages and analyzed with

an unweighted Q-mode cluster analysis for taphofa-

cies definition. This multivariate statistical procedure

assembles samples based on the taphonomic attributes

of the fossils. Furthermore, the more taphonomic traits

included in the cluster analysis, the more reliable and

more accurate are the palaeoenvironmental interpre-

tations. Otherwise, resulting clusters considering just a

few taphonomic signatures (e.g. fragmentation, artic-

ulation and/or edge rounding) may produce unrelated

and incoherent groups of samples that require a more

artificial and complicated explanation.

The methodology has been applied to mollusc-

dominated deposits. However, it attempts to be inde-

pendent of other factors, such as age, palaeoenviron-

mental conditions, geographic area or tectonic setting.

It is necessary to choose the taphonomic attributes

potentially measurable in other groups of organisms.

In this respect, there are many actualistic assessments

dealing with the taphonomy of different kinds of

organisms (see a review in Behrensmeyer et al.,

2000), as well as other studies based on fossil groups

(e.g. Monaco, 1999; Oloriz et al., 2002a,b).

The quantitative methodology proposed herein has

been then applied to lower Pliocene mixed carbon-

ate–siliciclastic deposits of the Almerıa-Nıjar basin

(SE Spain). Two sections located along a proximal–

distal transect were sampled. The Q-mode cluster

analysis produced three taphofacies models based on

the taphonomic attributes, which are intimately related

to the palaeoenvironmental settings where the fossil

assemblages were accumulating. (1) The outer-plat-

form taphofacies characterized by a low abundance of

non-abraded fossils. Sediments of this taphofacies

model were deposited in deep, low energy waters

and under moderate to high sedimentation rates. The

high to very high fragmentation is probably due to

biological activity. (2) The biotic accumulation

taphofacies differentiated by a very high abundance

of bioclasts forming densely to very densely packed

fossil concentrations. This taphofacies refers to accu-

mulations of fossils within burrow traps. The tapho-

nomic attributes of the shells depend on the

taphonomic processes that affected them before they

were included in the burrow-fills. Therefore, some of

the measured taphonomic traits have enough weight in

the cluster analysis to separate some of the filled

burrows despite their sharing the rest of their tapho-

nomic properties. (3) The inner-platform taphofacies

distinguished by loose to dense packing and moderate

fossil abundance. Sediments included in this taphof-

acies were formed in low sedimentation rate, high

energy settings, which account for the high degree of

taphonomic destruction (high abrasion, fragmentation,

disarticulation, etc.) of fossils.

Acknowledgements

We sincerely appreciate the collaboration of Dr.

Isabel Ma Sanchez-Almazo for her suggestions and

comments during the field work. We are also indebted

with Dr. Franz T. Fursich and Dr. Carlton E. Brett for

their revisions and constructive comments, which

have improved substantially the quality of the paper.

This research has been supported by the projects

BTE2001/3023, funded by the Ministerio de Ciencia

y Tecnologıa of Spain, and RNM 0190, funded by the

Junta de Andalucıa. Special thanks go to Christine

Laurin for correcting the English text.

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Quantitative taphonomic analysis and taphofacies in lower