Palaeogeographical significance of clay mineral assemblages in the Permian and Triassic sediments of the SE Iberian Ranges,

eastern Spain Jacinto Alonso-Azcarate a, Alfredo Arche C, Jose F. Barrenechea b, Jose L6pez-G6mez C,

F. Javier Luque b, Magdalena Rodas b,*

a Departarnento de Geologia, Facultad de Ciencias Experirnentales, Universidad de Huelva, E-21819 La Rilbida, Huelva,

Spain b Departarnento de Cristalograjla y Mineralogia, Facultad de Geologia, Universidad Cornplutense, E-28040 Madrid, Spain

c Instituto de Geologia Econ6rnica, Departarnento Estratigrafia, C. S. I. C- U. C. M., Facultad de Geologia,

Universidad Cornplutense, E-28040 Madrid, Spain

Abstract

The evolution of the palaeogeography of the SE Iberian Basin during the Permian and Triassic represents a general

evolution from continental to marine environments. It has been recently studied from the sedimentological,

strati graphical, tectonic and palaeontological points of view. In spite of these results, many aspects of this

palaeogeography are still a matter of discussion. In this study, clay mineralogy analysis complements previous studies representing a new aspect for understanding the evolution of the sedimentary environment and the palaeogeography of the Iberian Basin during the periods in question and thus of the palaeogeography and the location of the major

high areas in the westernmost border of the Tethys sea. In spite of late diagenetic transformations the original clay mineral associations of the Permian-Triassic sediments

of the SE Iberian Ranges can be reconstructed. Seventy-seven samples of siliciclastic and carbonate sediments of these

ages have been studied (SEM and XRD), revealing six new aspects that help to precise the palaeogeographical

interpretation of the area: (1) Two major mineral assemblages have been found: illite + kaolinite + pyrophyllite in the continental facies and

illite + chlorite + vermiculite + mixed-layer clays in the marine facies.

(2) The Mg-rich clay minerals are here considered to be of marine origin. (3) Active phases of basin boundary faults are marked in the sediments by the presence of pyrophyllite, derived

directly from the Palaeozoic metamorphic basement. (4) Unconformities separating major depositional sequences also separate formations with different clay mineralogy.

(5) Different groups of clay minerals can be separated clearly coinciding with the different palaeogeographical stages also distinguished in the westernmost border of the Tethys sea.

(6) The clay mineral associations back up the data of a previous hypothesis of a humid climate for the end of the Permian in the study area just prior to the first incursion of the Tethys sea. © 1997 E1sevier Science B.V.

Keywords: Iberian Ranges; Permian; Triassic; clay mineralogy; palaeoclimatology

l. Introduction

The I be rian Ran ge s form a linea r a lpine st ruc­t ure t ren din g NW-SE in t he cen t ra l an d ea ste rn I be rian Pen in sula ( Fig. I). This int ra plate st ruc­t ure sta rte d it s de ve lopment durin g t he ea rly Pe rmian a lon g a He rcyn ian or olde r sut ure bet ween t he I be rian Ma ssif t o t he SW an d t he

an ce st ra l Ebro Block t o t he NE. The ma in com­pre ssive pe riods, wit h in ve rsion te ct on ics, t ook pla ce in t he Late lura ssic-Ea rly Creta ce ous an d t he Late Oligocene -Ea rly Miocene, wit h e xten sion pe riods durin g t he Ea rly Pe rmian t o Late lura ssic. Creta ce ous, Eocene -Oligocene an d Late Miocene �

P liocene. The re wa s n o metamorphism an d vol­can ic rock s we re int rude d in t he Ea rly Pe rmian . Late Tria ssic an d Middle lura ssic.

This pa pe r dea ls wit h t he Ea rly Pe rmian t o Late

Tria ssic rock s of t he sout hea ste rn I be rian Ran ge s ( Fig. I ) . The y pre sent t he cla ssic Ge rman ic fa cie s t rilogy of Buntsan dste in . Musche lka lk an d Ke upe r, a lt hough t he re a re substant ia l fa cie s an d t hickne ss chan ge s ( Ca st illo. 1 974; L6pe z-G6me z an d Arche, 1 993a) ( Fig. 2 ) . Some re cent st udie s ha ve e sta blishe d a deta ile d st rat igra phy of t he se se diment s wit h up t o 1 2 50 m of t ota l t hickne ss, de fin in g format ion s. dat in g most of t he m wit h rea sona ble pre cision ( D oubin ge r et a l. , 1 990; Ma rque z et a I. , 1 994) , fin din g re giona l un confor­mit ie s an d un ra ve llin g t he comple x re lat ion ship bet ween te ct on ics an d se dimentat ion ( L 6pe z­G6me z an d Arche, 1 992, 1 993a, b. 1 994 ; Arche an d L6pe z-G6me z. 1 996) ( Fig. 3) .

The obje ct ive of t his work is t o cont ribute t o t he kn owle dge of t he gene ra l e volut ion of t he SE I be rian Ba sin durin g t he Pe rmian t o Tria ssic pe riod wit h t he st udy of t he, up t o n ow poorly kn own, cla y mine ra logy. In a broa de r sen se . t he obje ct ive is a lso t o re fine t he pa lae oge ogra phy of t he we st ­e rn most borde r of t he Tet hys ba sin durin g t he tran siti on from t he cont inenta l cla st ics t o t he first ma rine in cursion in t he st udy a rea. This st udy con cent rate s on t he cla y mine ra logy of t he fine fra ct ion, it s genet ic re lat ion ship wit h t he se di­menta ry en viron ment of ea ch format ion an d it s det rita l or dia genet ic origin in se diment s re pre ­sente d by Bunt san dste in an d Musche lka lk fa cie s. P re vious gene ra l studie s on t he mine ra l a ssocia -

t ion s of Span ish Pe rmian an d Tria ssic se diment s can be foun d in Ca ba lle ro an d Ma rt in -Viva ldi ( 1 972 ) , Ruiz Cruz an d Ca balle ro ( l976a , b,c, d), Arriba s ( 1 984 ), Mora d et a l. ( 1989, 1 990), lean s et a l. ( 1 994) , Ma rtil et a l. ( 1 996) , an d R uiz Cruz ( 1 996) .

2. Stratigraphy and sedimentology

This st udy in ve st igate s sa mple s from e ight out crops in t he SE I be rian Ran ge s, in cludin g cont i­nenta l re d be ds an d sha llow-ma rine ca rbonate s of Ea rly Pe rmian t o Middle Tria ssic a ge ( Fig. 3). The se diment s a re subdivide d int o four De posit iona l Sequen ce s boun de d by un conformit ie s or hiat use s ( L6pe z-G6me z an d Arche . 1 992, 1 993a; D oubin ge r et a I. , 1 990). Ea ch sequen ce con sist s of t wo format ion s. The Ta ba rre fia Bre ccia s Format ion is n ot in clude d in t he sche me of de posi­t iona l sequen ce s.

The main se diment ologica l an d lit ho logica l cha r­a cte rist ics of t he n ine format ion s a re summa rize d in Ta ble I, an d t he ir deta ile d de script ion , datat ion an d inte rpretat ion can be foun d in L6pe z-G6me z an d Arche ( 1 985, 1 992, 1 993a ,b, 1 994 ), Sope iia et a l. ( 1 988), L6pe z-G6me z an d Mamet ( 1 990) , L6pe z-G6me z e t a l. ( 1 993) , Arche an d L6pe z­G6me z ( 1 996).

The Pe rmian an d Tria ssic se diment s of t he I be rian Ba sin we re de posite d un de r an e xten siona l re gime, in a rift ba sin t ren din g NW-SE. Pe riods

of subsiden ce an d se diment a ccumulat ion a lte rnate wit h pe riods of t ilt in g, pa rt ia l e rosion an d weat he r­in g when t he un conformit ie s an d hiat use s boun d­in g t he De posit iona l Sequen ce s we re forme d ( Sope fia e t ai ., 1 988; Arche an d L6pe z-G6me z,

1 996). The se surfa ce s a re of re giona l importan ce an d can be t ra ce d a ll a lon g t he I be rian Ran ge s.

3. Analytical methodology

The cla y mine ra logy of t he Pe rmian an d Tria ssic se diment s of t he Ibe rian Ran ge s is ve ry poorly kn own . Howe ve r, in t he st udy a rea , ea ch format ion is mea sure d, date d an d corre late d wit h nea rby a rea s. U sin g t his fra me work, se vent y-se ven

1- PYR E NEES

2- IBERIAN MASSIF

3- DUERO BASIN 4- IBE RIAN RANGES

5- EBRO BASIN

6- TAJO BASIN

7 - CATALONIAN RANGES 8 - BEll CS

9- GUADALQUIV IR BASIN

o

S TUDY AREA

\f---- TETHYS -----1 REALM -----1

o 1000 Km. H-B R

&..' _ ............ '

I B M: IBERIAN MASSIF

C-V-PB: {CATALAN - VALENCIA­

PREBE TIC BASIN C-S-BB: {CO RSICAN - SARDINIAN­

BALEARIC BLOCK H-BR: HESSE- BURGUNDY RIFT

h : CONTINENTAL BASINS {o - SHALLOW MARINE (CARBONATES) : b - EVAPORITES, CLASTICS, CARBONATES

C - SHALLOW MARINE (CARBONATES AND CLASTICS )

FAULTS, WRENCH, NORMAL

• !�;{��I

STUDY AREA

PERMIAN AND T RIASSIC ROCKS

MESOZOIC ROCKS

• LOWER PALEOZOIC ROCKS

D INAC TIVE FOLD BELTS. ANOROGENIC CRATONIC

(IN FIGURE 1 B I

Fig. I. A. Present sedimentary basins in the Iberian Peninsula, main outcrops of the Permian-Triassic sediments in the SE Iberian Ranges and location of the study area (modified from Arche and L6pez-G6mez, 1996).

B. Tentative palaeogeographical reconstruction of the western Tethys realm during the Late Permian (modified from Ziegler, 1988 ) .

samples were selected from fine-grained intervals (siltstones and mads) from both siliciclastic and carbonate units (Fig. 3). In addition, several

samples of shales from the Lower Palaeozoic meta­morphic basement outcropping in the margins of the basin were investigated, as they might represent

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RE PRESENTED

FORMATIONS: 1 - TABARRENA, 2- BON/CHES, 3-ALCOTAS, 4- CANIZAR

5-ESLID A, 6-MARINES, 7-LANDETE, 8-MAS, 9-CANETE * * - KEUPER FACIES, * - COAL AND SANDSTONES

LOCATIONS: A - VALD EM ECA, B -BONICHES, C-HENAR EJOS, D-TALAYUELAS, E-CHELVA, F-EL M OLlNAR

Fig. 2. Age, stratigraphical and geographical distribution of the Permian-Triassic sediments (formations) of the SE Iberian Range,.

Units 2·-3. 4-5. 6-7 and 8-9 are Depositional Sequences bounded by unconformities.

NW

A B C

1:--' BRECCIAS CON G LOMERATES

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r:::l � SANDSTONES

F G H

r=:=l �

.. Tepees ..,.. Muckrock � Current ripple � Wave ripple o Algal Mound

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t Bloturbation

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SE

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An. et r -- oc I Scy. r-

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'/ Th"

'I u.

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53 DOLOMITES

Fig. 3. Studied sections of the Permian-Triassic sediments and location of the samples (black dots). The localities are: A=Cueva de Hierro; B = Masegosa; C = Valdemeca; D = Caiiete; E = Boniches; F = Henarejos; G = Landete; H = Talayuelas; 1= Chelva; J = Segorbe; K = Eslida. See also Fig. I for their location. The formations are: Tb = Tabarreiia; BC = Boniches; AMS = Alcotas; CS = Caiiizar; EMS-Eslida; MCMM=Marines; LD=Landete; MAMG=Mas; CDL=Caiiete.

pro bable pro venance areas fo r so me o f the Permi an-Tri assi c materi als.

Samples were analyzed by X-ray di ffractio n (XRD) and scanni ng electro n mi cro sco py (SEM) metho ds. The bulk mi neralo gi cal study was carri ed o ut usi ng the crystalli ne po wder di ffractio n metho d. Fo r the study o f the clay mi nerals, three o ri ented aggregates (OA) o f bo th, the 2-20- and < 2-!lm fractio ns, were o btai ned by sedi mentatio n fro m an aqueo us suspensio n. The first OA o f each fractio n was ai r dri ed, the seco nd o ne was heated

at 550°C fo r 2 h and the last o ne was so lvated wi th ethylene glyco l (EG) at 65°C fo r 48 h.

Samples were run o n a Phi li ps PW 1730/90 X-ray di ffracto meter, usi ng Cu-Ko; radi atio n, graphi te mo no chro mato r, sli ts 1 0 � 0. 2 mm � 1 0,

ratemeter 1 x 103 to 1 X 104 c. p. s. at ti me co nstant

1, 40 kV, 30 mA, scan rate 2°,128/mi n. A scan rate o f 1°/mi n and a ti me co nstant o f 2 have been emplo yed i n the po wder di ffracto grams o f the fine fractio ns 2-20 and < 2 !lm i n the range o f 59° to 64°(28) i n o rder to measure the (060) reflectio n,

Table I Synthesis of the stratigraphy and some of the main sedimentary characteristics of the different formations for the PermianTriassic sediments of the SE Iberian Ranges

Facies "Saxonian" Buntsandstcin Muschelkalk

Oep. sequence OS-I OS-2 OS-3 OS-4

Formation Tabarreiia Boniches Alcotas Caiiizar Eslida Marines Landete Mas Caiiete

Lithology quartzite subangular mud stones pink arkosic red mudstones. grey mudstones. grey and slate quartzite alternating with sandstones mudstones marls and dolostones marls and dolostoncs pebble pebbles and sandstones alternating intercalated alternating breccias scarce sandy with sandstones sandstones

matrix sandstones and gypsum

Maximum 33 210 175 210 650 135 <)5 150 9.\ thickness (m)

Age Autunian TUringian Tliringian TUringiall Anisian Anisian Anisian Anisian-LadiniJrudinian ('!) Anisian

Some of the Fe-·Mn- 3 4-m-thick lenticular thinning- multistorey gradual gradually very poorly severe main oxide tabular intercalculations upwards lenticular lateral pinch out exposed in dolomitizatioll characteristics varnishes bodies of the sandstone sequences up tll sandstone thickness towards the outcrops processes

bodies :Um thick bodies change W

Main none or mainly p.C.s. p.c.s .. I.l'.s. and p.l'.S .. h.s .. I.e.s .. p.e.s .. c./".. W.!" .• Ill.L and p.c.s .. w.r. w.r.. c.r.. w./". r.c.s .. m.c. sedimentary some p.c.s. but also h.s. cr. C.r. and r.s. I.c.s. and r.s. f.&l.b. m.c. structures at the top

Palaeocurrent base: N N 137 N 160 NI70 NW-SE (average) 80 ;top: N bimodal

130

Sedimentological slope scree alluvial fans braided fluvial sandy braided braided distal fluvial Shallow Intertidal shallow interpretation deposits and braided systems with river deposits fluvial to estua rine carbonate flats and carbonate

fluvial system extensive flood- systems with deposits ramp coastal ramps deposits deposits plain deposits extensive deposits sabkha

flood-plain deposits deposits

Reference(s) [1] [2], [3] [3). [4] [3], [5] [3]. [6] [7] [8] [3). [9) [8]. [10]

See also Fig. 2 for the stratigraphic locations of the formations. Sedimentary structures: W.r . = wave ripples: c. r. = current ripples; p.C.s. = planar cross-stratification: t.C.s. =trough cross-stratification: h.5. = horizontal stratification; m.c. =Illud-cracks; t. = "tepees"; f.&l.b. =flaser and linsen bedding. ReFerences: [I] = L6pez-G6mez and Arche (1994): [2]=L6pez-G6mez and Arche (1985): [3J=L6pez-G6mez and Arche (1<)93a); [4]=L6pez-G6mez and Arche (l993b); [5)=Arche and L6pez-G6mez (1996); [6] = Lopez-Gomez and Arche (1992); [7] = L6pez-Gomez et al. (1993): [8] = Sopefia et al. (1988): [9] = L6pez-G6mez and Mamet ( 1990): [10] = Ooubinger et al. (1990).

using the (211) reflection of quartz as an internal standard. I llite-chlorite mixtures were treated with HCl, to eliminate the chlorite and differentiate the reflections in this zone (Hillier, 1993).

I n order to determine the degree of the postsedi­mentary processes that have affected these samples, the half-height width of the (illite) lO-A reflection

(the so-called illite "crystallinity", IC), was mea­sured on the < 2-llm fraction diffractograms. This fraction was chosen for the IC measurements because presumably it has very small amounts of detrital material and most of the illites are authi­genic (Robinson et aI., 1990). However, SEM

imaging is also used here for distinguishing between both detrital and authigenic phases and corroborate the results.

Using rock chip standards a calibration was performed for standardizing the IC values against the CIS data of W arr and Rice (1994 ). The regres­sion line obtained is: IC (Madrid) =

0.86945*CIS - 0. 00224 and the anchizone bound­aries proposed by Kiibler (1967) of 0.420 and 0. 25° 1'l2e have been used in this paper. Samples were prepared following the recommendations of the "I GCP W orking Group on I llite Crystallinity" (Kisch, 1991).

The polytypes of the illite in the < 2-llm fraction have been determined following the method of Caillere et al. (1982). Chlorite polytypes have proven impossible to determine because of the high percentage of illite in all the samples, overlap­ping the chlorite reflections in the critical interval of 2. 2-2. 6 A (Hayes, 1970). I n samples with high amounts of "k aolin group clay", polymorphs have been determined using the diagnostic reflections given by Ehrenberg et al. (1993).

4. Analytical results

The Lower Palaeozoic shales outcropping in the southwestern and northeastern margins of the basin are formed by quartz, phyllosilicates and feldspar. The clay mineral association consists of pyrophyllite, illite and chlorite (Fig. 4 ).

The analytical results of the clay fraction of the Permian and Triassic sediments of the SE I berian Ranges, summarized in Fig. 5 and Table 2, indicate

that these materials can be subdivided into four

groups with close relationships with the four depo­sitional sequences described previously. Three of the groups are continental facies and the upper­most one has a shallow-marine origin.

4.1. First group

The first group includes the Tabarrefta Formation and the Boniches Formation. The bulk mineralogy (Fig. 6) consists of phyllosilicates, quartz and hematite. Minor amounts of feldspar have been found at the top of the middle and

upper units within the Boniches Formation. The mineralogy of the <2- and 2-20-1lffi fractions consists of illite, k aolinite and pyrophyllite (Figs. 5 and 6), but the percentage of the latter decreases gradually towards the top of the Boniches Formation and this mineral disappears completely at the base of the upper unit. Kaolinite is the only "k aolin group clay" polymorph identified in the samples by XRD methods.

4.2. Second group

The second group consists of the Alcotas Formation and the Caftizar Formation. The bulk mineralogy of the Alcotas Formation includes phyllosilicates, quartz, and varying proportions of feldspar, hematite and dolomite. The clay mineral­ogy of the < 2- and 2-20-llm fractions consists exclusively of illite (Figs. 5 and 6) and it is possible to find both authigenic and detrital particles (Fig. 7).

4.3. Third group

The bulk mineralogy of the Eslida Formation consists of phyllosilicates, quartz and hematite. The mineralogy of the fine fraction is formed by illite and variable percentages of pyrophyllite, that disappears towards the middle part of the forma­tion (Figs. 5 and 8).

4.4. Fourth group

The fourth group consists of the Marines, Landete, Mas and Caftete Formations. The bulk

Prl

Prl Dl

III Prl ChI ChI Dl

A

B

24 14 4

Fig. 4. X-ray diffraction traces of the air-dried oriented aggregates for the 22fH.lm fraction from: (A ) sample BAS-I (lower Palaeozoic metamorphic slate); and (B) sample EMS-24 (Eslida Fonnation). III = illite; Chi =chlorite; Prl =pyrophyllite.

mine ra logy of t he Ma rine s Format ion is composed of phyllosilicate s, qua rt z and min or a mount s of fe ld spa r and he mat ite . D olomite is pre sent in high proport ion s (up t o 55%) at t he t op of t he forma ­t ion . The 2-2 0-l.lm fra ct ion shows a clea r ve rt ica l e volut ion from illite wit h t ra ce s of chlorite, ve rmic­ulite and mixed -la ye r illite /chlorite and chlorite / ve rmiculite in t he lowe r ha lf of t he format ion t o illite and t riocta hed ra l chlorite s t o t he t op. The < 2-l.lm fra ct ion ha s a simila r composit ion , but chlorite is re pla ced by ve rmiculite (Figs. 5 and 9) .

In t he Landete, Ma s and Caiiete Format ion s t he bulk mine ra logy con sist s of d olomite, phyllosili-

cate s and va ryin g proport ion s of ca lcite and qua rt z. The cla y mine ra logy of t he se format ion s chan ge s ve rt ica lly from illite ± sme ct ite t o illite + mixed -la ye r chlorite /sme ct ite ( Fig. 1 0) and fina lly t o illite + t riocta hed ra l Mg-chlorite s (lood fOOl va lue s in t he X-ra y d iffra ct ion patte rn s ran ge from 1 .23 t o 1 .42; Fig. 10) ± sme ct ite (Fig. 5) . A re ma rka ble feat ure wit hin t he se mate ri­a ls is t he mutua lly e xclusive re lat ion ship obse rved bet ween chlorite and d olomite (Fig. 9).

For fut ure compa rison some sample s of t he Keupe r fa cie s (Fig. 2 ) ha ve been ana lysed . Bulk mine ra logy con sist s of phyllosilicate s ( 55-90%) ,

CLAY Mlnerols

-- - E ;: c -= ... H U > a.. �

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0-" ENVIRONMENTS

IJ) FORMATIONS

ci " 0

KEUPER I ��fstar evaporltrc

--. CANETE Shallow carbonate

Fm. ramp V

MAS Fm. Coastal evaporltic flat

Shallow

LANDETE carbonate

Fm. ramp [V

MARINES Fm . Estuary

�

MeanderlnQ

rivers and ESLlDA floodplalns

Fm.

III

CANIZAR Sandy bralded

rivers Fm.

Ephemeral

ALCOTAS rivers and

sIIaIow lake. Fm. 11

BONICHES Alluvial fans

Fm .

TABARRENA Fm Slope brecctas I

Fig. 5. Synthetic section in stages of the Pennian-Triassic sediments of the SE Iberian Ranges and the distribution of clay mineral assemblages for each formation. For legend. see also Fig. 3.

Table 1 Crystallochemical parameters of illites from the ditli?rent formations

Formation

Tabarrena Breccias Boniches Conglomerates Aicotas M udstones and Sandstones

Canizar Sandstones Eslida M udstones and Sandstones Marine Clays and Marls Landcte Dolostones

Mas Marls and Gypsum Canete Dolostones and Limestones

101 III er ID

o z o U 101 III

t Q.. ;;) o a:: C!)

AUTUNIAN. SAXONIAN /IH) LOWER EU/TSANlSTEIN FACIES

d"lt>", (A)

1.502 ±O OOI

1.499 ± 0.002

1.502±O.OOO

1.500±0.OOI

1.503 ±0 005

1.501 ±0.001

1500±0.OO2

1503 ± O(J02

1.502±O.001

TOTAL �RALOGY

m PHYLLOfIIlICATES 0 QUARTZ

� D<>-Of«<l£ Bm F£L.DIIP .....

Crystallinity index r(20))

mean value range

0.707 0.692 0.711

0.514 0.433-0.606

0.584 0.4620.807

0.659 0.433 0.779

0.383 0.261 0.520

0.394 0.290 0.462

0.599 0.491-0.635

0.868 0.520 - 1.158

O.nR 0.721 0.865

CLAY tMERALOGY

20 Micron. 2 Microns

Fig. 6. Bulk mineralogy and evolution of the day mineral lIssemblage in the Tabarrena, Boniches ( First Group) and A1colas (base of Second Group) Formations. See also Table:2 for a more detailed sedimentological description of the section.

Fig. 7. Scanning electron microscopy image of authigenic illite particles together with a detrital muscovite plate.

quartz (5%), do lo mite (0-15%) and hematite (5%).

The co mpo sitio n o f the fine fractio n (Fig. 5) changes fro m illite + mixed-layer chlo rite/smectite to illite + trio ctahedral Mg-rich chlo rite (up to 30%), which beco mes mo re Fe-rich to wards the to p (l00dfo02 ratio decreases) .

The general analytical results are summarized in Table 2. The mo st abundant clay mineral thro ugho ut the pro files is illite (60-100%). I t is a dio ctahedral illite with a mean spacing d(33 1,060) = 1.501 +0.001 A. These illites are mix­tures o f 2Ml and IM po lytypes in varying amo unts, with a higher co ntent o f the 1 M po lytype in the marine sediments.

The illite "crystallinity" index (IC) (Kiibler, 1967 ) has been determined in the < 2-l1m fractio n o f every sample. Mo st samples o nly reached diage­netic co nditio ns, o r are in the limit between the

fields o f diagenesis and anchizo ne (Table 2) . I n the co ntinental sediments, the IC is so mewhat lo wer than in the marine fo rmatio ns. There are so me samples fro m the Teruel area (Eslida and Marines Fo rmatio ns) well into the anchizo ne and epizo ne fields. These apparently ano malo us data will be discussed belo w.

5. Interpretation and discussion

Our initial hypo thesis was that clay mineralo gy o f the Permian and Triassic fo rmatio ns sho uld reflect the changes in so urce area, sedimentary enviro nments and palaeo current patterns revealed independently by sedimento lo gical and palaeo geo ­graphical metho ds. Their extrabasinal vs. intra­basinal o rigin co uld pro vide a means o f no n-

UPPER BUNTSANOSTEIN FACES

TOTAL hlNERALOGY

o 50 100% 0 I

mm PHYLLOSILICATES 0 QUARTZ e:::I DOLOMITE mJ FELDSPARS

CLA Y MINERALOGY 20 Microns

50 100% 0

o HEMATITE

_ILUTE.

m CHl.ORITE t::ZJ PYRoPHYLUTE

2 Microns 50

e KAOLNTE

100%

Fig. 8. Bulk mineralogy and evolution of the clay mineral assemblage of the !::slida I-'onnation. Sec also Table 2 ror a more detailed

sedimentological description of the section.

biost rat igra phic correlat ion an d discriminat ion a mon g red bed sequen ce s wh ich a re common ly very simila r in a spe ct . If t he origina l clay mine ral­ogy chan ge s vert ica lly an d can be relat ed t o forma ­t ion s an d en vironm ent s. then it ha s pot ent ia l \0 provide a m ean s of corre lat ion an d discriminat ion a mon g the se re d bed sequen ces.

Sign ificant differen ces in th e clay mine ra l a ssoci­at ion s ha ve been observe d bet ween the cont in enta l an d sha llow-ma rin e format ion s. Our int erpretat ion from the ma in ana lyt ica l result s a re a s follows:

5.1. Firsl group

The most out stan din g cha ra ct erist ic of th e Ta ba rreiia Format ion is th e presen ce of py rophy l-

lite . Th is min era l is genera lly con side red a s in dica ­tive or an chizonal con dit ion s. but in t his ca se it seem s t o come direct ly from t he Ordovicia n-­Silurian meta morphic ba sement . It s high percen­ta ge ( Fig. 6) re vea ls a very short t ran sport from s ource a rea t o sediment . in good a gree ment with the scree-ty pe deposit inferred from t he fa cies ana ly sis. Py rophy llite in t hese rocks is int erpret ed a s an in herit ed mine ra l, sin ce t he breccia s, a ccord­in g t o th e le data for th e <2 -l.lm fra ct ion . rea ched on ly th e dia gen et ic sta ge an d t he py rophy llit e ha s been ident ified in t he ba sement slat es ( Fig. 4 ) .

Th e Bon ich es Forma tion shows a more complex ve rt ica l evolut ion . Py rophy llit e is present . but in sma ller percenta ges than in t he previous format ion an d decrea ses st ea dily t owa rds th e t op. disa ppea r-

UPPERMOST BUNTSANDSTEIN FACIES

TOTAL MlERALOGY

o 50

IIIDD PHYLLOSLJCATES 0 QUARTZ m DOLOMTE Il:El FELDSPARS

CLAY MINERALOGY < 20 Microns < 2 Microns

50

I2J HEMAnTE ELUTE

Cl CH..OAITE E3 VERMICULlTE m PYIIOPHYLLITE

Fig. 9. Bulk mineralogy and evolution of the clay mineral assemblage of the Marines Formation. See also Table 2 for a more detailed sedimentological description of the section.

ing near the to p o f the upper co nglo merates unit (Fig. 6) . This trend can be explained by the sedi­men to lo gical evo lutio n pro po sed by L6pez-G6mez and Arche (1993a): retro grading alluvial fans co n­tro lled by back faulting and increasing transpo rt distance with time. The pyro phyllite disappears co mpletely during sediment transpo rt in the upper, mo re distal unit when it evo lves to fluvial.

Kao linite is typical o f lo w-temperature co ndi­

tio ns, as indicated by its o ccurrence as a residual weathering pro duct and in lo w-grade diagenetic settings (Ehrenberg et aI. , 1993). In the studied materials, the presence o f k ao linite in substantial percentages is related to the develo pment o f k ao lin­itic sapro lites in the Palaeo zo ic basement o f the

so urce area; the climate was humid, at least seaso n­ally, with heavy rains, and mo derate to high tem­perature, and never o f desert type. This palaeo enviro nmental interpretatio n is suppo rted by sedimento lo gical data such as the massive o r cro ss-bedded nature o f the co nglo merates, the scarcity o f the matrix and the pebble-suppo rted fabric, indicating depo sitio n fro m running-water in braided rivers under wet, po ssibly seaso nal climate; the absence o f debris and mud-flo ws is against a sedimentary pro cess develo ped in an arid climate. Palaeo nto lo gical data, such as the pres­ence o f plant remains and po llen assemblages, also indicate a humid enviro nment at least in the fan areas. Co mminuted vascular plant remains are

A

B

24 14

ChlISm ill

12.0

15.2

4

very co mmo n in the sandsto ne wedges interpreted as waving-stage channel depo sits. Under these co nditio ns, advanced chemical weathering wo uld favo ur the leaching o f mo st o f the catio ns and k ao linite wo uld be a residual mineral. Our data and interpretatio ns are similar to tho se o f Fisher and Jeans (1982) fo r the Permian Red Beds o ff­sho re Devo n, U. K.

5.2. Second group

The clay mineralo gy o f the Alco tas and Caftizar Fo rmatio ns co nsists exclusively o f illite, in spite o f

the unco nfo rmity that separates bo th units (the o nly case in the Permian and Triassic sediments o f the area). The lo w IC values measured in these samples, to gether with the predo minant presence o f the 2Ml po lytype, indicate that illites in these samples are mainly detrital, altho ugh a small pro ­po rtio n o f authigenic illites (with a higher pro po r­tio n o f the 1 M po lytype) have been reco gnized in the < 2-J..lm fractio n.

The palaeo geo graphic reco nstructio ns sho w a pro gressive widening o f the sedimentary basin and mo re remo te so urce areas, pro bably in the meta­mo rphic co re o f the I berian Massif (Fig. 11, I ), to the west o f the I berian Basin. The drainage was lo ngitudinal, with transverse supply reduced to a minimum, and the basin o pened to the Tethys sea during the sedimentatio n o f the Caftizar Fo rmatio n (L6pez-G6mez and Arche, 1993b).

The illitic nature o f the clay fractio n indicates that illite was very abundant in the so urce area during a lo ng perio d o f time during active ero sio n. We interpret the presence o f illite as the so le

co mpo nent o f the clay fractio n o f the Alco tas and Caftizar Fo rmatio ns as the co nsequence o f lo ng weathering pro cesses in the high metamo rphic­granitic so urce area to the NW (the IBM in Fig. IB) under semi-arid, seaso nal co nditio ns (Fig. 11, I). The lo ng fluvial transpo rt allo ws fo r repeated ero sio n-sedimentatio n cycles and the to tal destructio n o f clays o ther than illite in an

aqueo us enviro nment. Recently, Jeans et al. (1994)

have pro po sed the po ssibility o f an aeo lian dust input co ming fro m the Ger man-Po lish Zechstein basin as an alternative so urce fo r illite. This sugges­tio n is difficult to pro ve, but it is a clear po ssibility as the clo ck wise anticyclo nic wind pattern wo uld pro vide a feasible transpo rt mechanism.

5.3. Third group

The Eslida For matio n represents a majo r read­justment in the geo metry o f the basin and its drainage pattern. The areal extent was reduced, a depo center was created in the N E margin and palaeo currents fro m the N were do minant (L6pez­G6mez and Arche, 1994; Arche and L6pez-G6mez, 1996) (Fig. 11, 11). The presence o f pyro phyllite (Fig. 8 ) in this fo rmatio n acco mpanying the do mi­nant illite in the clay fractio n can be readily explained as the main so urce area was the uplifted Palaeo zo ic metamo rphic basement alo ng the Ateca-Mo ntalba n-Maestrazgo high (Fig. l A), and transpo rt was very sho rt by so uthward-flo wing rivers (Fig. 11, II ). The presence o f pyro phyllite in the Ateca- Mo ntalba n-Maestrazgo Palaeo zo ic slates has been pro ven (Fig. 4) and is the o bvio us so urce o f this mineral.

The change in so urce area fro m the SW and NW to the N E basin margin is a respo nse to repeated basin extensio n (Fig. 11) and the migra­tio n o f the depo centers away fro m the o riginal basin bo undary fault (Arche and L6pez-G6mez, 1996), as predicted in the mo dels o f Gibbs (1984). The sho rt transpo rt and rapid burial, especially in the lo wer part o f the fo rmatio n made preservatio n o f pyro phyllite po ssible. As in the case o f the Bo niches Fo rmatio n, pyro phyllite disappears in the mo re distal facies o f the upper part o f the Eslida Fo rmatio n. The activity o f this new pro ve­nance area was sho rt, co inciding with a pro ­gressively develo pment o f the Hesse-Burgundy rift during the Anisian (Fig. 1B) (Arche and L6pez­G6mez, 1996). It was also a very sho rt activity

Fig. 10. X-ray diffraction traces of the oriented aggregates for the <2-v.m fraction from: (A) sample LD-3 ( Landete Formation); and (B) sample MAMG-4 ( Mas Formation). III = illite; Chi =chlorite; ChI/Srn = mixed-layer chlorite/smectite. O.A. air-dried = air­dried sample; O.A. + E.G. = after ethylene glycol solvation; O.A. + 550°C = after heat treatment. Spacing values expressed in A.

II

III

(CANIZAR Fm.)

(ESLlDA Fm)

(MARINES Fm.)

x ---

MAESTRAZGO HIGH

\

x

\

x '---­x

... PALEOCURRENT T REND

MAESTRAZGO HIGH

)( )( BASEMENT

\ ------­

MAESTRAZGO

� x

H IGH

i *

, ,

- - ;)

---

________ __ ____ _ -_I t _________ __ _

IBERIAN BASIN EBRO BASIN

because the very fast subsidence of the area in which the Eslida Formation was deposited allowed the incursion of the Tethys sea represented by the Marines Fm.

As the Eslida Formation is litho logically very similar to the Alcotas Formation and this has led to some confusion in the mapping of some areas of the Mediterranean coast, the clay mineralogy

can provide a reliable correlation/discrimination criterion in the absence of pollen and spores, the only available biostratigraphic significant fossils (Boulouard and Viallard, 1982; L6pez-G6mez and Arche, 1992).

5.4. Fourth group

This group consists of the Marines, Landete, Mas and Cafiete Formations. They represent a

drastic change in the mineralogy, the result of an evolution from continental to marine environments (Fig. 11, Ill), as shown independently by sedimen­tological data (see discussion in L6pez-G6mez and Arche, 1993a). The detrital clay association of illite, kaolinite and pyrophyllite is succeeded by a clay mineral assemblage of illite, chlorite, vermicu­lite and regular and irregular mixed-layer chlorite/ smectite, chlorite/vermiculite and illite/chlorite. The presence of some of these mixed-layer clays (chlorite/smectite and chlorite/vermiculite) was originally described in the Rot Formation of the classic Buntsandstein facies near Gottingen, Germany (Lippmann, 1956), of similar age and

environment to the Marines Formation studied in this paper.

The continental-marine transition takes place in the Marines Formation, which is still almost entirely siliciclastic. The lower part contains illite with traces of mixed-layer illite/chlorite and chlorite/vermiculite, but in the upper half chlorite is present in the 2-20-J..Lm fraction and vermiculite in the < 2-J..Lm fraction (Fig. 9) ; the latter can be interpreted as an oxidation product of the former,

by a vermiculitization process in oxidizing estua­rine and very shallow-marine environments. The experimental transformation of chlorite into ver­miculite by reaction in saturated bromine water has been documented by Ross (1975).

Thus, there is a vertical evolution in the clay mineral assemblages of this formation from illites and mixed-layer clays into Mg-chlorites. The detri­

tal illites coming from the continental source areas were deposited in a shallow-marine hypersaline environment and experienced an early environ­ment-related diagenesis. The most degraded illites fixed Mg and formed mixed-layer clays that evolved vertically to chlorites when passing to more marine environments, in a similar way to that described by Lucas (1962) and Lucas and Ataman (1968) for the Triassic sediments of the French Jura. Thus, the presence of chlorite and mixed-layer clays in these samples can be consid­ered as the first indication of a marine-related environment. However, when dolomite is present it fixes the Mg, inhibiting the formation of chlorite. This negative correlation between chlorite and dolomite is a primary or very early diagenetic feature as a detailed petrologic study confirms. The calcite present in the formation is a dedolomi­tization product (L6pez-G6mez et aI., 1993). An alternative explanation for the origin of these chlorites is that they were formed during burial diagenesis by reaction among dioctahedral clay minerals, quartz and dolomite, as it was described by Hillier (1993) for the lacustrine mudrocks in the Orcadian basin. Such a reaction was postulated by Hutcheon et al. (1980) as follows:

5 dolomite + 2 illite + 3 quartz + 11 HzO -->

3 chlorite+ 15 calcite+2 K + +2 OH- + 15 CO2

Accordingly, the mutually exclusive relationship found in the rocks studied in our work between chlorite and dolomite is in good agreement with

F ig. 11. Tentative reconstruction in stages I-Ill of the palaeogeographical evolution of the Alcotas, Caftizar, Eslida and Marines Formations for the easternmost border of the study area. See Fig. I for the present and palaeogeographical locations and Fig. 2 for the stratigraphical arrangement of the units. Observe how the palaeocurrent trend changes correspond with the main changes in the clay mineralogy showed in Figs. 5, 6, 8 and 9. Stage I I I shows an exchange between continental and marine waters and sediments.

t his or igin . N evert hel ess, t he a bo ve r ea ct ion would in vol ve an important in cr eas e in t he per centa ge of cal cit e and pr esu ma bl y of K-felds par in t hos e

sa mpl es conta in in g chlor it e, and t her e is no evi­d en ce for su ch chan ge in t he min eral asso ciat ions of t he Mar in es Format ion ( Fig. 9) . Althou gh wit h t he data a va ila bl e t her e is not a con clud in g cr it e­r ion to d is cr iminat e bet ween t he s yn gen et ic (or

earl y d ia gen et ic) and t he bur ial d ia gen et ic hypot h­es es, we pro pos e t he for mer mod el as t he most l ik el y ex planat ion of t he o bs er ved cla y min eral asso ciat ion for t his format ion, becaus e of t he a bs en ce of K -felds par and cal cit e in t he per cent­

a ges r equ ir ed by t he d eep bur ial d ia gen es is mod el . Ho wever, t he cla y min eral ass emblage can be us ed

in bot h cas es as an ind icator of a mar in e s ed i­mentary en viron ment, s in ce t he in it ial pr es en ce of dolo mit e would be n ecessar y for t he Mg-rich cla ys to for m in t he bur ial d ia gen et ic mod el.

T he Land et e, Mas and Caii et e For mat ions pr e­s ent a co mpara bl e vert ical evolution of t he cla y min erals, wit h ill it e and mix ed -la yer cla ys evol vin g into Mg-chlorit es . T he pr es en ce of Mg-r ich cla ys is not an un equ ivo cal proof of a mar in e or igin. T hey ar e pr es ent in contin ental d epos its su ch as t he Mer cia Mudston e Grou p ( U pper Tr iass ic) of En gland ( Lesli e et aI . , 1993 ; Wright and Sandl er, 1 994; Tal bot et aI . , 1994) , t he East Berl in For mat ion (Earl y Jurass ic U . S. A . ) ( Gierlo wsk i­Kad es h and Rust, 1 994) , and r ecent lacustrin e d epos its of C entral Austral ia and Sudan ( Morgan, 1993 ; Jaco bson et aI . , 1 994; Salama, 1994) , but t he pr es en ce of marin e foss ils in t he Land et e, Mas and Caii et e For mat ions rul es out t his int er pretat ion .

T he anal yt ical r esults, su mmar ized in Fig. 5 . s ho w cl earl y t hat ea ch d epos it ional s equ en ce, with t he ex cept ion of DS- 2, has a chara ct er ist ic d istr ibu­t ion of cla y min erals ( Fig. 1 2) , so t hat t he s equ en ce bound in g un conformit ies mark s harp chan ges in th e cla y min eral ass embla ges . T hus, t he or iginal cla y min eralo gy of ea ch for mation can be inferr ed in s pit e of important lat e d ia gen et ic chan ges . The ma in controls on t he cla y min eralo gy wer e extra­bas in ai, nota bl y weat her in g pro cess es and t he pet­rolo gic natur e of t he source ar ea and intra bas inal, su ch as t he s ed imentary en viron ments and t ypes and durat ion of t he trans port pro cess es.

A ccord in g to t he IC data, most of t he sa mpl es fall wit hin t he dia gen et ic r eal m ( lC > 0.4201120) . Ho wever, t he sl ightl y lo wer " cr ystall in it y" values measur ed in t he cont in ental s ed iments pro ba bl y refl ect t he pr es en ce of s mall a mounts of d etrital ill it es in t he < 2-ll m fra ct ion . Furt her mor e, t he pr es en ce of car bonat es in t he mar in e s ed iments would ha ve d ela yed t he ill it izat ion pro cess, r esult­

in g in higher IC val u es t han in t he non -cal car eous sa mpl es (Alonso -A zcarat e et aI . , 1 995) . T he in cr eas e in t he " cr ystall init y" o bs er ved in so me sa mpl es fro m t he Esl ida and Mar in es For mat ions is r elat ed to an important Al pin e hor izontal d eta chment alon g t he Middl e Triass ic, bet ween t he Lo wer Pala eo zo ic to Lo wer Triass ic mat er ials and t he Lat e Tr iass ic-Jurassic co ver . T he " cr ystall­in it y" of t he ill it e was pro ba bl y mod ifi ed du e to t he pr essur e and t emperatur e in cr eas e dur in g t his a ct ive period, as d emonstrat ed by R o berts et al . ( 1991) and Fermind ez-Cal ian i and Galan ( 1 992) for t he Corris Slat e Belt and t he I berian P yr it e Belt, res pect ivel y.

6. Conclusions

( I ) The cont in ental P er mian--Lo wer Triass ic s ed i­ments of t he SE I ber ian Ran ges conta in an asso ciat ion of ill it e ± kaol in it e ± pyro phyll it e, and t he s hallo w-marin e Middl e-Lat e Triass ic s ed iments of ill it e ± chlorit e ± ver micul it e ± mix ed -la yer cla ys .

( 2 ) T he cla y min eral asso ciat ions of ea ch for ma­t ion r efl ect t he or iginal cla y ass embla ges, in s pit e of lat e d ia gen et ic chan ges .

( 3 ) T he Ta barr eiia, t he Bon iches and t he Esl ida For mat ions conta in su bstant ial a mounts of pyro phyll it e, an an chizon e min eral r ework ed fro m t he Pala eo zo ic meta mor phic bas ement

out cro ppin g in t he SW and NE mar gins of t he basin into t he allu vial fan and flu viat il e s ed iments .

( 4 ) I l\ it e in t he Al cotas and Caii izar For mations co mes fro m a high-meta mor phic, gran it ic sour ce ar ea in t he NW . T he in put of d es ert dust co min g fro m t he Bor eal bas in is poss ibl e, but not pro ven .

( 5 ) Mg-ri ch cla y min erals in t he Mar in es, Caii et e,

III

STAGE A :

Age: Thuringian (upper Permian)

Fm.: Boniches Conglomerates.

Prl - PyrophyLlite

KLn - KaoLinite

ilL - !LLite

STAGE B :

Age: Thuringian (Upper Permian)

Fm.: ALcotas MUdstones and Sandstone s .

STAGE C :

Age: Anisian (MiddLe Triassid

Fm.: Marines CLays, Mudstones and MarL s .

ChL - ChLorite

Vrm - VermicuLite

ML - Mixed - Layer clays

STAGE D :

Age: Anisian - Ladinian (Middle Triassid

Fms.: Landete DoLomites. Mas Mudstones, Marls and Gypsum . Canete Dolomites and Limestones.

Fig. 12. Tentative palaeogeographical reconstruction and locations of the clay mineral assemblage for each differentiated stage. See also Fig. 2 for a more detailed stratigraphical information.

Lan dete and Mas Formations are re lated to sha llo w-marine env ironments, with sea water causing a very early diagenesis of the detrital c lays carried by the r ivers into the bas in . A continenta l orig in is exc lu ded by the presence of marine fossi ls an d se dimento logica l data.

( 6) In the a bsence of fossi l ev idence, c lay m ineral­

ogy is an usefu l metho d of corre lation/

discrim inat ion among continenta l and sha l­lo w-marine Permian and Triass ic formations of the SE I ber ian Ranges, in goo d agreement with other pa laeoenvironmenta l interpretat ion methods.

( 7) C lay mineralogy analysis can clearly improve the kno wle dge a bout pa laeogeograph ica l evo ­lut ion, that wou ld inc lu de source areas and coast line changes, of the westernmost border of the Tethys bas in during the first incurs ion of the Tethys sea.

( 8 ) There is a c lear re lationsh ip bet ween the c lay minera l assem blages an d the ma in pa laeogeo ­graph ica l stages of evo lution of the bas in in the stu died area and in the westernmost coast­line of the Tethys basin dur ing the Permian Triassic transition.

( 9) The c lay m inera log ica l stu dy backs up the data of c limate evo lution in an interva l ( Permian-Tr iassic ) of marke d change in the western Tethys area, especia lly in se diments wh ich lac k fossi ls.

Acknowledgements

We thank Car los Sanchez for dra wing the figures. Th is I S a contr ibut ion to Projects PB92 -004 1 an d PB95 -0084 finance d by the D GICYT, M inistry of Educat ion Research, Spain. The manuscript was improve d by the comments of S. Hill ier, an anonymous r eferee and F. Surlyk as e ditor.

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