Clim. Pas , 20, 1659–1686, 2024
h ps://doi.o g/10.5194/cp-20-1659-2024
© Au ho (s) 2024. This wo k is dis ibu ed unde
he C ea i e Commons A ibu ion 4.0 License.
O bi ally o ced en i onmen al changes du ing he accumula ion
o a Pliensbachian (Lowe Ju assic) black shale
in no he n Ibe ia
Na oa Ma inez-B ace as1,2, Ai o Pay os1, Jaume Dina ès-Tu ell3, Idoia Rosales4, Ja ie A os egi1, and
Roi Sil a-Casal5
1Depa men o Geology, Facul y o Science and Technology, Uni e si y o he Basque Coun y (UPV/EHU),
P.O. Box 644, 48080 Bilbao, Spain
2Labo a o io de E olución Humana, Depa amen o de His o ia, Geog a ía y Comunicación, Uni e sidad de Bu gos,
Edi icio I+D+I, Plaza de Misael Bañuelos s/n, 09001 Bu gos, Spain
3Is i u o Nazionale di Geo isica e Vulcanologia, Via di Vigna Mu a a 605, 00142 Rome, I aly
4Cen o Nacional Ins i u o Geológico y Mine o de España (IGME, CSIC), La Cale a 1, T es Can os, 28760 Mad id, Spain
5Dp o. Dinàmica de la Te a i de l’Oceà, Facul a de Ciències de la Te a, Uni e si a de Ba celona, 08028 Ba celona, Spain
Co espondence: Na oa Ma inez-B ace as ([email p o ec ed])
Recei ed: 27 Feb ua y 2024 – Discussion s a ed: 11 Ma ch 2024
Re ised: 22 May 2024 – Accep ed: 24 May 2024 – Published: 29 July 2024
Abs ac . Lowe Pliensbachian hemipelagic successions
om he no he n Ibe ian palaeoma gin a e cha ac e ized
by he occu ence o o ganic- ich calca eous hy hmi es o
decime e- hick limes one and ma l beds as well as hicke
black shale in e als. Unde s anding he gene ic mechanisms
o he cyclic li hologies and p ocesses in ol ed along wi h
he na u e o he ca bon cycle is o p ima y in e es . This cy-
clos a ig aphic s udy, ca ied ou in one o he black shale in-
e als exposed in San iu de de Reinosa (Basque–Can ab ian
Basin), e eals ha he calca eous hy hmi es esponded o
pe iodic en i onmen al a ia ions in he Milanko i ch-cycle
band and we e likely d i en by eccen ici y-modula ed p e-
cession.
The main en i onmen al p ocesses ha de e mined he o -
ma ion o he hy hmi e we e deduced on he basis o he
in eg a ed sedimen ological, mine alogical, and geochemical
s udy o an eccen ici y bundle. The o ma ion o p ecession
couple s was con olled by a ia ions in ca bona e p oduc-
ion and dilu ion by e igenous supplies, along wi h pe iodic
changes in bo om-wa e oxygena ion. P ecessional con ig-
u a ions wi h ma ked annual seasonali y inc eased e ige-
nous inpu (by i e s o wind) o ma ine a eas and boos ed
o ganic p oduc i i y in su ace wa e . The g ea accumula-
ion o o ganic ma e on he seabed e en ually dec eased
bo om-wa e oxygena ion, which migh also be in luenced
by educed ocean en ila ion. Thus, deposi ion o o ganic-
ich ma ls and shales occu ed when annual seasonali y was
maximal. On he con a y, a educ ion in e es ial inpu s
a p ecessional con igu a ions wi h minimal seasonali y di-
minished shallow o ganic p oduc i i y, which, added o an
in ensi ica ion o e ical mixing, con ibu ed o inc eas-
ing he oxida ion o o ganic ma e . These condi ions also
a ou ed g ea e p oduc ion and basinwa d expo o ca bon-
a e mud in shallow ma ine a eas, causing he o ma ion o
limy hemipelagic beds. Sho eccen ici y cycles modula ed
he ampli ude o p ecession-d i en a ia ions in e igenous
inpu and oxygena ion o bo om seawa e . Thus, he ampli-
ude o he con as be ween successi e p ecessional beds in-
c eased when he Ea h’s o bi was ellip ical and diminished
when i was ci cula . The da a also sugges ha sho eccen-
ici y cycles a ec ed sho - e m sea le el changes, p obably
h ough o bi ally modula ed aqui e eus asy.
1 In oduc ion
As a consequence o he g a i a ional in e ac ion be ween as-
onomical bodies, he Ea h’s axial o ien a ion and o bi a y
cyclically a imescales ha ange om ens o housands o
Published by Cope nicus Publica ions on behal o he Eu opean Geosciences Union.
1660 N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale
a ew million yea s (Be ge and Lou e, 1994). These a ia-
ions in o bi al con igu a ion egula e he la i udinal and em-
po al dis ibu ion o sola adia ion (insola ion), which de e -
mines he con as be ween seasons. These pe iodic changes
in he clima ic sys em can a ec he e olu ion o a wide
ange o sedimen a y en i onmen s, om e es ial o deep
ma ine (Einsele and Ricken, 1991). As he open ocean is
ha dly a ec ed by p ocesses ha may e ode he seabed o
in e up he con inuous se ling o ine-g ained pa icles,
deep-ma ine pelagic and hemipelagic sedimen s accumula e
a a gene ally cons an , bu slow, a e (a ew cen ime es pe
housand yea s). Thus, pelagic and hemipelagic successions
om bo h oceanic sedimen co es and ou c ops con ain ac-
cu a e eco ds o o bi ally modula ed, quasi-pe iodic clima e
change episodes (Hinno , 2013). These pe iodic changes in
he clima ic sys em a e gene ally eco ded as cyclic s a i-
g aphic successions, he so-called hy hmi es, in bo h pelagic
and hemipelagic successions (Einsele and Ricken, 1991).
Signi ican p og ess in Ea ly Ju assic cyclos a ig aphy
has been made in he las ew decades hanks o he s udy
o excep ional o bi ally modula ed sedimen a y eco ds ob-
ained om deep-ma ine en i onmen s o he pe i-Te hyan
ealm (e.g. Ca digan and Cle eland basins by Hüsing e al.,
2014; Ruhl e al., 2016; S o m e al., 2020; Pie´
nkowski e
al., 2021; Pa is Basin by Cha bonnie e al., 2023). Al hough
hese s udies p o ided ele an as och onological in o ma-
ion, hey did no ocus on he clima ic and en i onmen al
impac o he o bi al cycles. O he s udies deduced a con ol
o long- e m o bi al cycles on he Ju assic ca bon cycle (Ma -
inez and De a, 2015; Ikeda e al., 2016; Holla e al., 2021;
Zhang e al., 2023), bu he clima ic and en i onmen al in lu-
ence o sho - e m cycles has been less s udied (Hinno and
Pa k, 1999; Ikeda e al., 2016; Holla e al., 2023).
The aim o his s udy is o analyse he clima ic and en-
i onmen al impac o sho - e m o bi al cycles on Lowe
Ju assic deep-ma ine deposi s. To his end, a hemipelagic
al e na ion o limy and ma l–shale beds was analysed in
he San iu de de Reinosa sec ion (he ea e e e ed o as
he San iu de sec ion), Basque–Can ab ian Basin (BCB),
Can ab ia p o ince, Spain. In o de o de e mine i sedimen-
a ion was o bi ally o ced, a cyclos a ig aphic analysis o
he hemipelagic hy hmi es was unde aken. Subsequen ly,
an in eg a ed mul ip oxy s udy was pe o med in a selec ed
in e al o he sec ion in o de o disen angle wha en i on-
men al ac o s in luenced he o ma ion o he hemipelagic
hy hmi es.
2 Geological se ing
In Ea ly Ju assic imes he BCB was loca ed o he sou h o
he A mo ican massi and o he no h o he Ibe ian massi ,
wi hin he Lau asian epicon inen al seaway ha connec ed
he Bo eal Sea wi h he no hwes e n Te hyan Ocean (Fig. 1a;
Au ell e al., 2002; Rosales e al., 2004). P e ious palaeo-
geog aphic econs uc ions loca ed he no he n Ibe ian ma -
gin a app oxima ely 30° N palaeo-la i ude (Quesada e al.,
2005; Ose e e al., 2011). Hence, he eme ged Ibe ian sou ce
a ea was loca ed in he semia id bel bu close o he bound-
a y wi h he humid clima ic zone ( empe a e clima e cha ac-
e ized by mega-monsoons; De a e al., 2009; Deconinck e
al., 2020), which made i especially sensi i e o as onom-
ically d i en clima e change. Such pe iodic clima e change
episodes al e na ely inc eased and dec eased he in luence o
one o he o he clima ic bel s (Ma inez and De a, 2015).
He angian and lowe Sinemu ian deposi s accumula ed in
e apo i ic idal la s and shallow ca bona e amps, whe eas
he o e lying Sinemu ian–Callo ian succession accumula ed
in an open-ma ine, ou e - amp en i onmen , which was gen-
e ally in deep and quie condi ions below s o m wa e base
(Au ell e al., 2002; Quesada e al., 2005). Hemipelagic sed-
imen a ion (sensu Hen ich and Hüneke, 2011) p e ailed in
he ou e amp, as au och honous pelagic p oduc ion was
mixed wi h pe ipla o m ca bona e ad ec ion and siliciclas-
ic inpu om he sou he n con inen al ma gin. Di e en ial
subsidence du ing he Ju assic ela ed o ea ly mobiliza ion
o unde lying T iassic sal esul ed in he c ea ion o se e al
oughs in he BCB (Fig. 1b, Quesada e al., 2005).
Pliensbachian hemipelagic successions o he BCB
(Camino Fo ma ion; Quesada e al., 2005) a e cha ac e -
ized by he occu ence o h ee black shale in e als (BSIs),
each se e al ens o me es hick (B aga e al., 1988; Que-
sada e al., 1997, 2005; Quesada and Robles, 2012; Ros-
ales e al., 2001, 2004, 2006). These h ee BSIs a e com-
posed o al e na ing black shale laye s and limes one–ma ly
limes one beds and a e sepa a ed om each o he by deca-
me ic in e als de oid o black shale laye s, in which only
hemipelagic ma ls, ma ly limes ones, and limes ones occu .
The h ee BSIs can be co ela ed wi h simila coe al de-
posi s in neighbou ing basins in As u ias (Bo ego e al.,
1996; A mendá iz e al., 2012; Bádenas e al., 2012, 2013;
Gómez e al., 2016). Coe al o ganic- ich ma ine acies ha e
also been obse ed in o he Te hyan Lowe Ju assic succes-
sions om Po ugal (Sil a e al., 2011), he Uni ed King-
dom (Hüsing e al., 2014), F ance (Bougeaul e al., 2017),
and Ge many (Pie´
nkowski e al., 2008). The BCB Pliens-
bachian BSIs p esen ela i ely high o ganic ca bon con-
en (2 w %–6 w %), high py i e concen a ions, and sca ce
ben hic aunas. The mal ma u i y analysis showed ha he
BSIs ound a he depocen es a e o e ma u e oday, bu hey
sou ced he only oil ese oi disco e ed in inland Ibe ia
(Quesada e al., 1997, 2005; Quesada and Robles, 2012; Pe -
manye e al., 2013). Py olysis o he mally imma u e sam-
ples om ma ginal a eas showed o al o ganic ca bon al-
ues o up o 20 w % and hyd ogen index alues up o 600–
750 mg HC g−1o TOC 1987; Quesada e al., 1997). Anal-
yses o o ganic ma e (OM) showed ha he assemblage
is mainly composed o ma ine ype-II ke ogens, in which
amo phous and algal ma e ial p e ails (Quesada e al., 1997,
2005; Pe manye e al., 2013). Mo e speci ically, he anal-
Clim. Pas , 20, 1659–1686, 2024 h ps://doi.o g/10.5194/cp-20-1659-2024
N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale 1661
Figu e 1. (a) Palaeogeog aphy and clima ic zona ion (modi ied om Quesada e al., 2005; De a e al., 2009; Ose e e al., 2011) o wes e n
Eu ope in Ea ly Ju assic imes. IB: Ibe ian massi , AR: A mo ican massi , AB: As u ian Basin, BCB: Basque–Can ab ian Basin, CEB:
Cen al Eu opean Basin, NWEB: NW Eu opean Basin, SBB: sou he n bo eal basin. (b) Simpli ied geog aphic and geological map o Lowe
and Middle Ju assic ou c ops in he BCB a ea, wi h he loca ion o he s udied San iu de sec ion ( ed s a ). The supe imposed isopach map
shows he hickness o he Lowe Ju assic ocks and he basin con igu a ion in sedimen a y oughs and swells (modi ied om Quesada e
al., 2005).
ysis e ealed a low con en o gammace anes, which sug-
ges s no mal salini y condi ions, and a g ea abundance o i-
clinic i e panes, which can be associa ed wi h Tasmani es-
ype unicellula g een algae wi h o ganic heca. In addi ion,
he high con en o iso enie a ene byp oduc s, such as a yl-
isop enoids, indica es he occu ence o pho osyn he ic and
sul u ous g een algae communi ies (Chlo obiaceae) de el-
oped in oxygen-deple ed condi ions.
The San iu de sec ion s udied he ein is exposed a exi
144 o mo o way A67 (UTM X411431.091 Y4769002.593;
Fig. 1b), app oxima ely 50 km sou hwes o San ande and
1 km no hwes o a coe al sec ion s udied by o he s a he
ain s a ion in he same locali y (e.g. Rosales e al., 2001,
2004, 2006; Quesada e al., 2005; Fig. S1 in he Supple-
men ). The s udied succession begins wi h 2.5 m o al e -
na ing g ey limes ones and hin ma ls ones (Pue o Poza-
zal Fo ma ion), ollowed by 20 m o he lowe pa o he
Pliensbachian Camino Fo ma ion, which a e mainly made up
o al e na ions o hemipelagic ma ls, limes ones, and o e -
ma u e black shales (Rosales e al., 2004; Quesada e al.,
2005). Thus, he s udied sec ion includes he oldes BSI o
he Camino Fo ma ion (BSI-1 in Fig. 2a), which acco ding
o egional bios a ig aphy co esponds o he olde pa o
he ea ly Pliensbachian Up onia jamesoni ammoni e zone
(B aga e al., 1988) and o he la e pa o calca eous nan-
no ossil zone NJ3 (F aguas e al., 2015).
h ps://doi.o g/10.5194/cp-20-1659-2024 Clim. Pas , 20, 1659–1686, 2024
1662 N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale
Figu e 2. (a) Syn he ic li hological log o he San iu de sec ion, including ch onos a ig aphy om Quesada e al. (2005) and Rosales e
al. (2006). Columns B and C o he le o he li hological log co espond o bedding bundles and couple s, espec i ely, which we e de ined
isually in he ou c op. (b) Calca eous couple s (yellow numbe s) o bundles 8 o 10 (whi e numbe s) in he San iu de ou c op. The yellow
cu e shows he elie o successi e beds in he ou c op (le , ecessi e; igh , esis an ), which is mainly de e mined by hei ca bona e
con en . The whi e cu e shows bedding bundles. (c) Close-up o a ma ly limes one wi h a pa ly py i ized belemni e. (d) Close-up o a
lamina ed black shale. Scale ba in millime es.
3 Ma e ials and me hods
3.1 Cyclos a ig aphic analysis o he San iu de sec ion
A de ailed cen ime e-scale s a ig aphic log was measu ed
in a 22.5 m hick succession ha exposes he ansi ion om
he Pue o Pozazal Fo ma ion o he Pliensbachian Camino
Fo ma ion. A b oad ange o sedimen ological ea u es, such
as bed shape, hickness, composi ion, and palaeon ological
con en and s uc u es, we e anno a ed. A o al o 373 hand
samples we e collec ed, wi h a esolu ion o a leas 3 sam-
ples pe bed, a oiding isible skele al componen s, bu ows,
and eins. The mass-no malized low- ield magne ic suscep-
ibili y (MS) o he samples was measu ed using a Kap-
pab idge KLY-3 ins umen (Geophysika B no) housed a he
Geology depa men o he Uni e si y o he Basque Coun-
y, Bilbao, Spain. Subsequen ly, ock-powde samples we e
ob ained and s o ed in anspa en an igla e p isma ic ials,
which we e scanned in a da k oom using a desk op o ice
scanne . The a e age colou (RGB alue) o he scanned im-
ages o ock-powde samples was de e mined using he Im-
ageJ so wa e and ollowing he p o ocol in Dina ès-Tu ell e
al. (2018) and Ma inez-B ace as e al. (2023).
Clim. Pas , 20, 1659–1686, 2024 h ps://doi.o g/10.5194/cp-20-1659-2024
N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale 1663
In o de o ca y ou a cyclos a ig aphic analysis, he Acy-
cle so wa e (Li e al., 2019) and he As och on package o
R (Meye s e al., 2014) we e used. The MS and colou da a
se ies we e linea ly in e pola ed and de ended i s . Subse-
quen ly, powe spec a we e ob ained using he 2πmul i a-
pe me hod (MTM) wi h h ee ape s, and con idence le els
(CLs) we e calcula ed ollowing obus ed-noise modelling
(Mann and Lees, 1996). In addi ion, e olu i e ha monic anal-
ysis (EHA; Meye s e al., 2001) and wa ele analyses (To -
ence and Compo, 1998) we e also ca ied ou in o de o ex-
amine he a iabili y o he main equency bands h oughou
he succession. Finally, he mos signi ican equency bands
iden i ied in he da a se ies we e isola ed by Gaussian band-
pass il e ing.
3.2 Mul ip oxy analysis o bundle 9
An in eg a ed analysis o se e al en i onmen ally sensi i e
p oxies was unde aken in he 19 beds ound be ween 12.4
and 15.95 m o he s a ig aphic succession. This in e al in-
cludes a comple e eccen ici y bundle (B9, see esul s be-
low), as well as he uppe mos and lowe mos couple s o
he unde lying and o e lying bundles, espec i ely. A o al
o 57 samples, wi h a esolu ion o 3 samples pe bed (21
shales, 9 ma ls, 12 ma ly limes ones, and 15 limes ones),
we e collec ed in o de o pe o m a calcime ic analysis
by measu ing he ca bona e pe cen age in 1g o powde o
each sample using a FOGL digi al calcime e (BD In en-
ions; accu acy o 0.5%) housed a he Uni e si y o he
Basque Coun y. These samples we e also analysed o in-
o ganic δ13Cca b and δ18Oca b con en a he Leibniz Labo-
a o y o Radiome ic Da ing and S able Iso ope Resea ch
(Kiel Uni e si y, Ge many) using a Kiel IV ca bona e p epa-
a ion de ice connec ed o a The mo Fishe Scien i ic MAT
253 mass spec ome e . P ecision o all in e nal and ex e nal
s anda ds (NBS19 and IAEA-603) was be e han ±0.05 ‰
o δ13Cca b and ±0.09 ‰ o δ18Oca b. All alues a e e-
po ed in he VPDB no a ion ela i e o NBS19.
In addi ion, one sample om he cen al pa o each
bed (19 samples) was s udied o pe og aphic and scanning
elec on mic oscope (SEM) analysis, mine alogical con en ,
elemen al composi ion, and o ganic geochemis y. Fo he
mine alogical and geochemical analyses, he samples we e
g ound in he labo a o y. Whole- ock mine alogy was ob-
ained by analysing andomly o ien ed ock powde by X-
ay di ac ion (XRD) using a Philips PW1710 di ac ome e
(Mal e n Panaly ical, Mal e n, UK) a he Uni e si y o he
Basque Coun y. The s ep size was 0.02° 2θwi h a coun ing
ime o 0.5 s pe s ep. Majo and ace elemen concen a ions
we e de e mined a he Uni e si y o he Basque Coun y
using a Pe kinElme Op ima 8300 spec ome e (ICP-OES;
Pe kinElme ) and a The mo XSe ies 2 quad upole induc-
i ely coupled plasma mass spec ome e (ICP-MS; The mo
Fishe Scien i ic) equipped wi h a collision cell, an in e -
phase speci ic o ele a ed o al dissol ed solids (X cones),
a shielded o ch, and a gas dilu ion sys em. Analysis o
he JG-2 g ani e s anda d and e o es ima es o each ele-
men showed ha he unce ain y o he esul s co esponds
o he 95 % con idence le el. Finally, o ganic ca bon (Co g)
and o ganic ni ogen (No g) con en s, as well as hei iso-
opic δ13Co g and δ15No g alues, we e ob ained by combus-
ion o powde ed and deca bona ed samples in an elemen-
al analyse Flash EA 1112 (The mo Finnigan) connec ed
o a Del aV Ad an age mass spec ome e (The mo Fishe
Scien i ic) a he Uni e si y o A Co uña, Spain. Calib a ion
o 13Co g and 15No g was done agains ce i ica ed s anda ds
USGS 40, USGS41a, NBS 22, and USGS24. Resul s a e ex-
p essed in he VPDB no a ion, wi h accu acy (s anda d de i-
a ion) being ±0.15 ‰.
In o de o explo e composi ional ela ionships and ends
using comp ehensi e mul i-elemen al da ase s, Pea son co -
ela ion coe icien s ( ) and hei signi icance (p alues) we e
es ima ed o pai s o a iables using he SPSS 28 s a is i-
cal package (IBM Co po a ion, SPSS s a is ics o Windows,
e sion 28.0.1.1, 2022, A monk, NY, USA). In addi ion, a
mul i a ia e ac o analysis was unde aken wi h he aim o
iden i ying he numbe o i ual a iables ( ac o s) ha ex-
plains he highes pe cen age o he a iabili y in he analysed
da ase .
4 Resul s
4.1 Gene al San iu de sec ion
4.1.1 Sedimen ology and pe og aphy
The ou c op displays a succession o decime e-scale plane-
pa allel beds, in which ligh -colou ed, bio u ba ed lime-
s ones o ma ly limes one beds esis an o wea he ing al e -
na e wi h ecessi e, da k-colou ed, lamina ed ma ls o shales
(Fig. 2). In he ou c op, limes ones and ma ly limes ones
we e dis inguished based on hei ha dness and colou , as
p ominen limes one beds a e s i and ligh g ey, whe eas
ma ly limes ones a e less p ominen , a e so e , and show
da ke g ey shades. The ossil eco d o bo h limes ones
and ma ly limes ones is domina ed by isola ed ammoni es,
belemni es, and b achiopods (Fig. 2c), and bu ows a -
ibu able o Chond i es and Planoli es ha e been obse ed.
Thin sec ions show muds ones and wackes ones wi h dis-
pe sed ben hic o amini e a, agmen ed echinode ms, b a-
chiopods, and py i ized bi al e shells (mainly pec inids) in
a mic ospa ma ix (Fig. 3a and c). Well-p ese ed placoli hs
o coccoli hopho ids and calcisphe es we e also iden i ied by
SEM (Fig. 3c and g). Some signs o diagene ic o e p in ing
we e iden i ied, such as he occu ence o seconda y cemen s,
calci e o e g ow hs, ea ly amboidal py i e, and he g ow h
o py i e c ys als in es s.
Bo h ma ls and shales cons i u e iable beds mo e suscep-
ible o wea he ing. Shales gene ally show da ke colou and
mo e p ominen lamina ion (Fig. 2d), also obse ed in hin
h ps://doi.o g/10.5194/cp-20-1659-2024 Clim. Pas , 20, 1659–1686, 2024
1664 N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale
Figu e 3. Pe og aphic iews o limes one C41 (a) and shale
C36 (b). The whi e ba s ep esen 1 mm. (c) Gene al ex u e o a
limes one bed (couple 37), showing pa ly dissol ed and b oken
coccoli hs and calcisphe es. (d) Gene al ex u e o a ma ly bed (cou-
ple 37) wi h e idence o bio u ba ion. Panels (e) and ( ) show p ob-
able bio ilms. ( ) Well-p ese ed coccoli h. (g) Py i e amboid.
sec ions (Fig. 3b). The ma ls con ain nek o-plank onic ossils
(ammoni es, belemni e, and calca eous unicellula algae) and
e idence o ben honic communi ies (py i ized shells o bi-
al es and hynchonellid b achiopods; ace ossils, such as
Chond i es and Planoli es), whe eas he la e a e absen in
shales. This is con i med by SEM analysis, as ma ls con ain
isola ed, b oken, and andomly o ien ed clay mine als ha
w ap well-p ese ed coccoli hs and calcisphe es wi h signs
o bio u ba ion (Fig. 3c, d, and g). Nek onic o ganisms and
plank onic unicellula algae also occu in shales, bu ben-
honic auna and bio u ba ion a e i ually absen . SEM ob-
se a ions also showed ha he lamina ion in shales is caused
by he al e na ion o de i al componen s (mainly clays bu
also qua z) and o ganic componen s (such as bi umen, poly-
me ic ex acellula subs ances linked o bio ilms, ilamen ous
bac e ial ma s, o ungal hyphae; Fig. 3e and ). Py i e am-
boids a e mo e common in shales han in limy beds (Fig. 3h).
The abo emen ioned li hologies we e used o de ine cha -
ac e is ic in e als in he succession (Fig. 2a). Based on he
occu ence o black shale laye s, he BSI-1 spans om 2.55
o 16.5 m (13.95 m hick). Black shale laye s, wi h indi id-
ual hicknesses o up o 79 cm, p edomina e in he lowe -
mos pa o he BSI, bu in e cala ions o limes ones, ma ly
limes ones, and ma ls become p og essi ely mo e abundan
upsec ion.
4.1.2 Bed a angemen
Cyclic bedding a angemen s o di e en scales can be ob-
se ed in he s udied li hological al e na ion. The e m cou-
ple e e s o he li hological pai o a wea he ed ma l o shale
bed and he o e lying esis an limes one o ma ly limes one
bed. A o al o 62 calca eous bedding couple s (C1 o C62)
we e iden i ied in he s udied succession, wi h hei indi id-
ual hicknesses a ying om 8 o 97 cm and a e aging 36 cm
(Figs. 2a and 4). These couple s ex end beyond he s udied
sec ion, as shown by a bed-by-bed co ela ion wi h he co-
e al ailway sec ion 1 km o he sou heas (Fig. S1).
The li hological con as be ween he ma l–shale and he
(ma ly) limes one o he couple s is no cons an h oughou
he succession, as some couple s a e composed o shale and
limes one beds bu o he s a e cons i u ed o ma l and ma ly
limes one beds. These a ia ions in he li hological con as
o couple s do no occu a andom bu allow he a angemen
o he succession in o bundles o i e ( ou o six) couple s.
Bundles, as de ined he ein, ypically con ain h ee p ominen
cen al couple s wi h g ea li hological con as be ween suc-
cessi e limes one and ma l–shale beds (e.g. couple s 34, 35,
38, 39, 40, and 43 in Fig. 2b), which a e unde lain and o e -
lain by less ob ious couple s wi h lowe li hological con as
be ween successi e ma l and ma ly limes one beds (e.g. C36,
C37, C41, C42 in Fig. 2b). In San iu de, 12 comple e bundles
and ano he 2 incomple e bundles a he base and op o he
sec ion we e de ined, which ange in hickness om 126 o
208 cm (a e age: 167.3cm).
Two successi e bundles can be eadily obse ed in some
in e als o he s udied succession (e.g. B9 and B10 in
Fig. 2b). Howe e , he delimi a ion o bundles is no s aigh -
o wa d in o he equally hick in e als (Fig. S1). These in-
e als wi h well-de ined and less ob ious bundles al e na e
egula ly h oughou he San iu de sec ion, which sugges s
he occu ence o a la ge -scale (6.6m hick) cyclic a ange-
men in he li hological succession.
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N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale 1665
Figu e 4. S a ig aphic log and ch onos a ig aphy (Quesada e al., 2005 and Rosales e al., 2006) o he s udied sec ion, showing he
de ended colou cu e. Bundles (B) and couple s (C) iden i ied in he sedimen a y al e na ion a e numbe ed in ascending s a ig aphic o de .
The g ey backg ound shows he ex en o he Up onia jamesoni BSI-1, and he pink in e al in i s uppe pa shows he in e al s udied he ein
in de ail. The 2πMTM, EHA, and wa ele spec a o he colou da a se ies show he occu ence o ou main pe iod bands: 30–42 cm cycles
(in blue in he 2πMTM spec um), in e p e ed as p ecession (P) couple s; 1 m cycles (g ey), possibly ela ed o obliqui y (O?) cycles; 1.67 m
cycles (g een), ep esen ing sho eccen ici y (e) bundles; and 5–10 m cycles (peak a 6.6 m; o ange), which co espond o long eccen ici y
(E) bundles.
4.1.3 Colou and magne ic suscep ibili y
Colou alues (mean RGB) ange om 69.87 o 158.99, a e -
aging 102.73 (Fig. S1; Table S2). The colou cu e oscilla es
in line wi h he li hological al e na ion, wi h colou alues
gene ally being highe in limes ones and ma ly limes ones
(a e age o 115.14) han in in e ening ma ls o shales (a -
e age o 90.71). The a ia ions in colou alues a e g ea e
in he cen al couple s o bundles han a bundle bounda ies.
This sugges s ha , as shown in p e ious s udies (Dina ès-
Tu ell e al., 2018; Ma ínez-B ace as e al., 2023), colou
alues a e ep esen a i e o he ca bona e con en o he sam-
ples. This is con i med by he ca bona e con en analysis ca -
ied ou be ween couple s 35 o 44 (see below), as bo h colou
and ca bona e con en show he same a angemen in cou-
ple s and bundles ( : 0.89, p<0.001; S2).
Mass-no malized magne ic suscep ibili y alues ange
om 5.08 ×10−6 o 1.67 ×10−5m3kg−1, a e aging 9.9×
10−6m3kg−1(Fig. S2, Table S1). In mos cases, lime-
s ones and ma ly limes ones ha e highe suscep ibili y (a -
h ps://doi.o g/10.5194/cp-20-1659-2024 Clim. Pas , 20, 1659–1686, 2024
1666 N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale
e age: 1.08 ×10−5m3kg−1) han shales and ma ls (a e -
age: 8.99×10−6m3kg−1). The MS o hemipelagic deposi s
is commonly de e mined by hei pa amagne ic componen s
(mos ly de i al clays; Kodama and Hinno , 2015). Howe e ,
in San iu de his pa ame e does no show a g ea co ela-
ion wi h colou ( : 0.48, p<0.001, whole sec ion; Fig. S2)
o calcium ca bona e ( : 0.36, p<0.001, be ween C35 and
C44; Fig. S2). The e o e, he San iu de ela ionship sugges s
ha he MS signal is mo e likely con olled by e omagne ic
mine als, such as magne i e (Fig. S3).
4.1.4 Time se ies analysis
P io o spec al analysis, he colou da a se ies was eg-
ula ly in e pola ed (spacing o 0.06 m) and he hi d-o de
polynomial end was sub ac ed. The 2πMTM powe spec-
um o he colou da a se ies shows peaks a ou pe iod
bands: 30–42 cm (peaking a 37 cm), 1 m, 1.67 m, and 5–
10 m (Fig. 4). The sho pe iod band shows signi ican peaks
abo e 99 % CL. In he in e media e pe iod band, he 1 m peak
exceeds 95%CL and he 1.67m peak eaches 90%CL. The
long pe iod band, wi h a main pe iodici y o 6.6 m, is abo e
99 % CL. The sho pe iod band ma ches he a e age hick-
ness o couple s and he longes in e media e band he a e -
age hickness o bundles. The EHA and wa ele spec a also
highligh he ou main pe iod bands, al hough he 1m pe-
iodici y is ela i ely less ele an . The pe iod bands a e no
con inuous and he e a e se e al in e als whe e he signal
loses powe , such as he 11–16 and 24–36 m in e als o he
sho pe iod band. Spec al analysis ca ied ou on MS da a
co obo a es he p e alence o he abo emen ioned ou pe-
iod bands, al hough he in e media e bands do no each high
con idence le els (Fig. S4).
The 30–42 cm and 1.6 m pe iod componen s we e sepa-
a ely ex ac ed om he colou da a se ies h ough Gaus-
sian bandpass il e ing (Fig. 5) using he a e age alues o
he pe iod bands iden i ied by spec al analysis ( equencies
o 2.85 ±0.65 and 0.6±0.15 cycles m−1, espec i ely). The
numbe o oscilla ions in he sho es pe iod il e ma ches
he numbe o couple s de ined in he ou c op and in he
colou cu e. Simila ly, he oscilla ions in he in e media e
pe iod il e ma ch he numbe and hickness o bundles.
4.2 De ailed analysis o bundle 9 (C35–C44 in e al)
4.2.1 L /M a io and calcium ca bona e con en
The limes one o ma ls one (L /M) hickness a io o cou-
ple s a ies be ween 0.33 (C42) and 1.36 (C39), wi h an a -
e age alue o 0.90 (Fig. 6a, Table S2). The highes L /M
alues a e ound in he couple s a he cen al pa o bundle
9, while he lowes alues co espond o couple s 41 and 42
a he bounda y be ween bundles 9 and 10.
The CaCO3con en anges om 24.63 % o 88.97 %, a -
e aging 49.78 % (Fig. 6b; Table S3). In gene al, %CaCO3
luc ua es in line wi h he isually de ined li hology, wi h
limes one and ma ly limes one beds being iche in %CaCO3
(a e age: 66.36%) han ma ls and shales (a e age: 34.86%).
Ma ls and shales di e by 10 %–15 % in hei CaCO3con-
en , whe eas limes one beds a he cen al pa o bundle 9
show 20 %–40 % mo e CaCO3 han ma ly limes ones a bun-
dle bounda ies.
4.2.2 Ca bon and oxygen iso opes
δ13Cca b alues ange om −1.5 ‰ (C35L) o 0.70 ‰
(C35M) and a e age −0.25‰ (Fig. 6c). The δ13Cca b cu e
shows lowe alues in limy beds and highe alues in shales
and ma ls. The ampli ude o he luc ua ions is signi ican ly
g ea e in he cen al couple s o bundle 9. δ18O alues ange
om −5.84 ‰ (C43L) o −5.25 ‰ (C36L) and a e age
−5.52 ‰, wi h he δ18O cu e being a he spiky. δ13Cca b
and δ18Oca b da a show in e media e posi i e co ela ion ( :
0.53; p<0.005; Fig. S5a; Table S3).
4.2.3 Gene al mine alogy
XRD esul s (Fig. 6d; Table S2) show ha calci e is he mos
abundan mine al in limy beds and in some o he ma l and
shales (28 % o 84 %, a e age: 54%). Clay mine als cons i-
u e he second mos abundan phase (9 % o 50 %, a e age:
32 %), ollowed by qua z (3 % o 13 %, a e age: 9 %) and
o he mino componen s (py i e, gypsum, and dolomi e).
The mine alogical con en luc ua es in line wi h li hology,
as i shows maximum alues o clays and qua z, and minima
o calci e, in ma ls and shales. Mo eo e , he ampli ude o he
de i al–ca bona e mine alogical oscilla ions inc eases in he
cen al couple s o bundle 9. Py i e, despi e being a mino
componen (0.5 % o 9 %, a e age: 4%), also oscilla es wi h
li hology, p esen ing maximum alues in ma ls and shales,
bu does no ma ch he ampli ude a ia ion associa ed wi h
he bundle a angemen .
4.2.4 O ganic ma e geochemis y
The con en in o ganic ca bon a ies be ween 0.26 % (C39L)
and 4.03 % (C41M) (a e age o 1.91%), wi h maximum
alues being ound a black shales. O ganic ni ogen also
co a ies wi h li hology, wi h alues anging om 0.02%
(C39L) o 0.09 % (C36M) (a e age o 0.06%). Bo h ele-
men s show high-ampli ude oscilla ions a he cen al pa
o bundle 9 and subdued oscilla ions a bundle bounda ies.
The ela ionship be ween he wo o ganic componen s was
calcula ed by he C /N a io (Fig. 7; Table S2)
δ13Co g alues a y be ween −29.6 ‰ (C40M) and
−27.2 ‰ (C40L) and a e age −28.6 ‰. δ15No g anges om
1.1 ‰ (C38L) o 3.2 ‰ (C40M), wi h an a e age alue o
2.5 ‰ (Fig. 7). Bo h da a se ies al e na e in line wi h li hol-
ogy, bu wi h opposi e ends. The δ13Co g luc ua ions a he
cen al couple s o bundle 9 show he g ea es ampli ude.
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N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale 1667
Figu e 5. Colou il e ou pu s o sho (in blue) and in e media e (g een) pe iod bands, which a e ela ed o p ecession couple s and sho
eccen ici y bundles, espec i ely.
Figu e 6. Li hological log o he San iu de in e al s udied in de ail (da k g ey: shale; in e media e g ey: ma l; ligh g ey: ma ly limes one;
whi e: limes one), showing (a) he limes one–ma l (L /M) hickness a io o couple s, (b) %CaCO3con en , (c) δ13Cca b and δ18Oca b
cu es, and (d) whole- ock mine alogy. Numbe ed couple s and bundles a e labelled C and B, espec i ely.
4.2.5 Elemen al geochemis y
The a e age abundance o majo and ace elemen s is shown
in Fig. 8 (Table S4). SiO2, Al2O3, and CaO cons i u e 48 %
o limes ones and 63 % o ma ls and shales. A e age alues
o mos majo and ace elemen s a e highe in ma ls and
shales han in limy beds, he excep ions being CaO, MnO,
Ba, and S . The co ela ion ma ix shows ha he abundance
o MnO does no co ela e wi h any majo and ace elemen s,
bu all he o he majo elemen s p esen s ong nega i e co -
ela ion (>−0.88) wi h CaO (Table 1) and high posi i e co -
ela ion wi h mos edox-sensi i e ace elemen s (Co, Cu,
Ni, V, and Zn); he only excep ion is Zn, which shows in e -
media e posi i e co ela ions. S and Ba display in e media e
posi i e co ela ion wi h each o he .
In o de o compa e he abundance o some el-
emen s wi h he e e ence a e age shale composi ion
(Li and Schoonmake , 2003), en ichmen ac o s (XEF;
T ibo illa d e al., 2006) we e calcula ed as ollows:
XEF =(X / Al)sample /(X /Al)a e ageshale. Al and K a e com-
monly hough o be ela ed o he clay ac ion, whe eas
Si and Ti a e o en associa ed wi h he coa se ac ion o
qua z and hea y mine als (Cal e and Pede sen, 2007). En-
ichmen in Ti has also been ela ed o s onge aeolian in-
pu (Rachold and B umsack, 2001). In San iu de KEF, TiEF,
and SiEF co a y wi h li hology, showing maximum alues in
ma ls and shales and inc easing ampli ude o a iabili y in
he middle pa o bundle 9 (Fig. 9).
Ma ine palaeop oduc i i y is commonly associa ed wi h
algal g ow h, which a ies wi h he a ailabili y o mac o-
nu ien s, such as P and N (Cal e and Pede sen, 2007). PEF
alues om San iu de show ha hese deposi s a e deple ed
in P (Li and Schoonmake , 2003). Howe e , PEF shows
highe alues in ma ls and shales han in limy beds in almos
all couple s (excep in C35L and C43L; Fig. 9). Au higenic
Ba in ma ine sedimen s is commonly associa ed wi h ba i e
and i s abundance is gene ally de e mined by o ganic C ex-
po om su ace wa e in o deep-ma ine en i onmen s (T i-
bo illa d e al., 2006). In o de o minimize he in luence o
de i al ba ium in palaeoen i onmen al analyses, BaEF and
h ps://doi.o g/10.5194/cp-20-1659-2024 Clim. Pas , 20, 1659–1686, 2024
1674 N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale
Figu e 12. C oss-plo o Co g agains (a) phyllosilica e and (b)
calci e con en . Po en ial dilu ion lines o Co g a e ma ked in bo h
g aphs. (c) Ca–Al–Co g e na y plo wi h San iu de samples, which
ollow a cons an Co g /Al2O3.
he Co g /Al2O3 a io is ela i ely cons an , whe eas highe
a iabili y is obse ed in he CaO/Al2O3and Co g /CaO a-
ios. The e o e, Co g luc ua ions could ha e esul ed om
cyclic a ia ions in he dilu ion a e by calci e inpu . In ac ,
he c oss-plo be ween calci e and Co g shows a s ong neg-
a i e co ela ion (Fig. 12b; :−0.83; p<0.005), which is
ypical o dilu ion-d i en OM luc ua ions (A hu and Dean,
1991; Beckmann e al., 2005). In o de o disen angle he o i-
gin o he cyclic sedimen a ion, bed hickness and du a ion
mus be aken in o conside a ion (Einsele and Ricken, 1991).
I a ia ions in he a e o ca bona e sedimen a ion had been
he only p ocess con olling o ganic ma e dilu ion, while
OM and clay mine al inpu s s ayed cons an , limes one beds
would ha e been signi ican ly hicke han ma ls and shales,
which is no he case in San iu de (Fig. 6a). This sugges s
ha a g ea e inpu o clay mine als mus ha e also occu ed
du ing he deposi ion o ma ls and shales. Mo eo e , ma ls
and shales display g ea e dispe sion in he Co g s. calci e
c oss-plo (Fig. 12b), which sugges s ha he e migh ha e
been o he ac o s con olling OM con en , such as changes
in OM p oduc ion o p ese a ion (Bohacs e al., 2005).
Acco dingly, he sedimen ological and geochemical e i-
dence s ongly sugges s ha he luc ua ions in OM con-
en we e closely ela ed o a ia ions in he a e o o ganic
ma e emine aliza ion (p ese a ion) as a consequence o
secula a ia ions in seawa e oxygen concen a ions. The
well-p ese ed lamina ion, he absence o bu ows, and he
sca ci y o ben hic auna (Figs. 2 and 3) o shales s ongly
sugges ha he sea loo was deple ed in oxygen. Con-
e sely, bio u ba ion s uc u es and ben hic auna a e mo e
di e se and abundan in limes ones, sugges ing be e oxy-
gena ion o he seabed (Figs. 2 and 3). Changing edox con-
di ions can also be deduced om δ13Co g eco ds (Algeo and
Liu, 2020). Mic obial chemoau o ophy, which is ypical o
oxygen-deple ed en i onmen s, ixes ca bon en iched in 12C,
p oducing lowe δ13Co g alues han OM p oduced by pho o-
syn he ic euka yo ic algae (Nijenhuis and Lange, 2000; Luo
e al., 2014). Acco dingly, minima in δ13Co g om OM- ich
ma ls and shales om San iu de a e e y likely ela ed o e-
ducing deep-wa e condi ions, simila o hose deduced o
some Pliocene sap opels (Nijenhuis and Lange, 2000). The
s ong nega i e co ela ion be ween Co g con en and δ13Co g
( :−0.945, p<0.0001) suppo s he close ela ionship be-
ween seabed oxygena ion condi ions and OM p ese a ion.
This in e p e a ion is in line wi h ha de i ed om he abo e-
men ioned C /N a io (Appendix A), which also sugges s
ha deni i ica ion in ensi ied du ing deposi ion o ma ls and
shales due o mo e educing sea-bo om condi ions.
The in e p e a ions abo e a e also suppo ed by No g and
δ15No g da a. Deni i ica ion can esul in δ15No g iso ope
ac iona ion in poo ly oxygena ed condi ions, as deni i-
ica ion and anae obic ammonium oxida ion eac ions in-
c ease 15No g in OM (Robinson e al., 2012). In San iu de
δ15No g iso opes luc ua e in line wi h he li hological hy h-
mi es (Fig. 7), showing maxima a ma ls and shales and
hence a signi ican nega i e co ela ion wi h δ13Co g ( :
−0.70p<0.005) and posi i e co ela ions wi h Co g ( : 0.66,
p<0.005) and No g ( : 0.73, p<0.005) con en . I can he e-
o e be concluded ha δ15No g alues inc eased du ing he
accumula ion o ma ls and shales, when bo om-wa e oxy-
gena ion dec eased and deni i ica ion in ensi ied.
Py i e and Co g con en s also show an in e media e posi-
i e co ela ion in San iu de ( : 0.6, p<0.01). Py i e migh
be o med du ing e y ea ly diagenesis due o eac ions be-
ween Fe and H2S. H2S is gene ally eleased in o po ewa e
when sul a e- educing bac e ia use sedimen a y o ganic ma -
e as a educing agen and ene gy sou ce (Be ne , 2013).
Mo e oxygena ed condi ions du ing he deposi ion o lime-
s ones could ha e inhibi ed he o ma ion o py i e. Con-
e sely, limes ones p esen highe MS alues han ma ls and
shales, possibly associa ed wi h a g ea e concen a ion o
magne i e (Fig. S3). Magne i e could be ei he de i al in o i-
gin o ela ed o pos -deposi ional changes in edox s a e,
as mo e oxygena ed condi ions a ou he pa ial eplace-
men o py i e wi h i on oxides, such as magne i e (Lin e
al., 2021).
Finally, he co ela ion ma ix (Table 1) and he ac o
analysis (Fig. 11) also show a close ela ionship be ween
some edox-sensi i e elemen s (Fig. 10; V, Zn, Co, Cu, Ni),
py i e, and Co g con en (Cal e and Pede sen, 2007; Al-
geo and Liu, 2020). En ichmen ac o s and a ios highligh
a ela i e en ichmen in edox-sensi i e elemen s h ough-
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N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale 1675
ou he succession, which suppo s he gene al deposi ional
model o a sea loo deple ed in oxygen (Quesada e al.,
2005; Rosales e al., 2006). T ace-me al en ichmen ac o s
and bi-elemen al a ios associa ed wi h bo h sul ides and o -
ganic ma e a y in line wi h he li hological hy hmi es and
suppo he in e p e a ion o al e na ing en i onmen al edox
condi ions.
To sum up, he mul ip oxy analysis (δ15No g,δ13Co g, ace
elemen s, mine alogy, and sedimen ology) shows ha he
highe Co g con en in ma ls and shales was ela ed o less
oxygena ed sea loo condi ions, which enhanced he p ese -
a ion po en ial o o ganic ma e . The PEF eco d sugges s
ha he p oduc ion o o ganic ma e may ha e also inc eased
du ing he o ma ion o ma ls and shales, bu his signal is no
cohe en h oughou he s udied in e al. Gi en he close e-
la ionship be ween hese p ocesses and he li hological hy h-
mi es, i can be concluded ha he e mus ha e been an o -
bi ally d i en en i onmen al ac o ha igge ed luc ua ions
in bo om-wa e oxygena ion and, possibly, palaeop oduc i -
i y.
5.3 O bi ally modula ed en i onmen al changes
P e ious s udies o no he n Ibe ian Pliensbachian eco ds
ha e demons a ed ha his a ea was subjec o semia id cli-
ma ic condi ions, wi h physical e osion being p e alen in he
con inen and seawa e being empe a e (Rosales e al., 2004;
A mendá iz e al., 2012; Gómez e al., 2016; Deconinck e
al., 2020). The BCB, being loca ed close o he bounda y
be ween he a id and humid clima ic bel s a app oxima ely
30° N palaeo-la i ude, was especially sensi i e o o bi ally
d i en clima e change episodes, which we e eco ded by he
ou e - amp hemipelagic hy hmi es om San iu de. These
hy hmi es a e bes cha ac e ized in he s a ig aphic succes-
sion by decime e-scale calca eous couple s, which ep esen
p ecession cycles, and me e-scale bundles linked o sho ec-
cen ici y cycles. The imp in o long eccen ici y cycles can
also be iden i ied in he ield and deduced by spec al analy-
sis (Fig. 4). Based on he numbe o o bi al cycles ound in
San iu de (62 p ecession couple s and 13.4 sho eccen ici y
bundles) and he a e age du a ion o 20 ky o p ecession
cycles and 100ky o sho eccen ic cycles, he s udied suc-
cession has an es ima ed du a ion o 1.29±0.05 My and he
BSI-1 in e al o 750 ±30 My (36 p ecession couple s and
7.8 sho eccen ici y bundles).
5.3.1 Fo ma ion o p ecession-d i en calca eous
couple s
The sedimen a y p ocesses behind he o ma ion o p eces-
sion couple s can be analysed on he basis o hickness e-
la ionships be ween he cons i uen li hologies (Einsele and
Ricken, 1991). When limy beds a e hicke han ma ly beds,
he o ma ion o calca eous couple s is commonly a ibu ed
o luc ua ions in ei he ca bona e dissolu ion o ca bona e
p oduc ion. Con a ily, ma ls and shales a e usually hicke
han limes ones when pe iodic changes in he a e o dilu ion
by e igenous componen s o igina e he couple s. Pe iodic
ca bona e dissolu ion can be uled ou in San iu de, as he e
is nei he mac oscopic no mic oscopic e idence o pe asi e
ca bona e dissolu ion and he ou e -ca bona e- amp seabed
was pe manen ly abo e he ca bona e compensa ion dep h
(Bje um e al., 2001). The L /M a io is close o 1 in mos
o he couple s (Fig. 6a). Consequen ly, he o ma ion o he
San iu de p ecession-d i en couple s mos likely esponded
o pe iodic changes in bo h ca bona e p oduc ion and ca -
bona e dilu ion by e igenous ma e ial, inc easing accumu-
la ion and p ese a ion o Co g when ma ls and shales we e
deposi ed. In ac , ac o analysis poin s ou ha p ecession-
d i en li hological al e na ion (Fig. 11) is s ongly associa ed
wi h edox-sensi i e a iables and e igenous p oxies.
Gi en he gene ally semia id Pliensbachian condi ions de-
duced o he BCB (De a e al., 2009; Deconinck e al, 2020),
a clima e cha ac e ized by a p olonged d y season and a sho
we season can be en isaged. D y sub-humid clima es, wi h
3 o 5 we mon hs pe yea and a maximum deg ee o season-
ali y, p oduce maximum alues o lu ial sedimen discha ge
in o he sea (Cecil and Dulong, 2003). Such high seasonal-
i y condi ions a e gene ally p oduced when he p ecessional
con igu a ion esul s in summe s occu ing a pe ihelion and
win e s a aphelion (Fig. 13). In San iu de bo h he L/M a-
io and he e igenous con en o couple s sugges ha shales
and ma ls we e o med in such an as onomical con igu a-
ion. In ensi ied monsoons du ing he we season could ha e
inc eased he lu ial discha ges ha eached pe ipla o m a -
eas, p oducing maxima o geochemical p oxies associa ed
wi h coa se de i al g ain size, such as SiE o TiEF (Fig. 9;
Cal e and Pede sen, 2007). Howe e , ino ganic and o ganic
s able iso ope eco ds do no suppo an inc eased inpu o
esh wa e o e es ial OM when ma ls and shales we e
deposi ed. Al e na i ely, i is also possible ha he e ige-
nous ma e ial was anspo ed by wind. Indeed, o he s ud-
ies ha e also ela ed an en ichmen in Si and Ti con en in
pelagic sedimen s o s onge aeolian inpu (Rachold and
B umsack, 2001) and inc eased dus p oduc ion and ans-
po a ion du ing high seasonali y condi ions (Wooda d e al.,
2011). Thus, i can be assumed ha dus gene a ion inc eased
in he con inen s nea San iu de du ing ex emely d y sea-
sons a p ecessional con igu a ions leading o maximum sea-
sonali y. Ex eme seasonali y condi ions may ha e also in-
c eased dus s o ms and dus inpu in o he adjacen ocean
(McGee e al., 2010). Ei he aeolian o lu ial, inc eased e -
igenous inpu du ing maximum seasonali y condi ions may
ha e also supplied nu ien s o he ocean (PEF), igge ing
o ganic phy oplank on blooms and o ganic ma e p oduc-
ion. This si ua ion p omo ed g ea e OM accumula ion and
oxygen deple ion in deep-sea sedimen s (e.g. Nijenhuis and
Lange, 2000; Wang, 2009; Ch ous o a e al., 2021). Gi en
ha he e idence o changing palaeop oduc i i y is sca ce, i
is also possible ha o bi ally o ced mechanisms also modu-
h ps://doi.o g/10.5194/cp-20-1659-2024 Clim. Pas , 20, 1659–1686, 2024
1676 N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale
la ed he amoun o dissol ed oxygen in seawa e . As he e is
no e idence o a g ea in luence o con inen al wa e masses
ha could ha e p omp ed densi y s a i ica ion o he wa-
e column (e.g. A hu and Dean, 1991; Ch ous o a e al.,
2021), i is mo e likely ha he mechanism was ma ine in o i-
gin. In e es ingly, nume ical simula ions sugges ed ha du -
ing he La e C e aceous ho house bo h p ecession and eccen-
ici y cycles modula ed seawa e en ila ion and oxygena-
ion, d i en by changes in deep-ocean ci cula ion (Sa e al.,
2022). Acco ding o his model, basins ha we e deple ed in
oxygen we e especially sensi i e o o bi ally o ced en ila-
ion a ia ions. Mo e speci ically, he p ecessional con igu a-
ion wi h he highe seasonali y eco ded he g ea es oxygen
deple ion a in e media e and deep-wa e dep hs, p oducing
a s ong e ical oxygen g adien and seawa e s a i ica ion.
In San iu de, simila ly educed e ical mixing may ha e oc-
cu ed du ing he accumula ion o ma ls and shales, which
would ha e enhanced deep-wa e anoxia. Indeed, in Ea ly
Ju assic imes, lowe - equency o bi al cycles also igge ed
pe iodic changes in he en ila ion and oxygena ion o bo -
om sedimen s, con olling ca bona e and OM accumula ion
(Pie´
nkowski e al. 2021). Thus, he sou hwa d low o A c ic
wa e om he Bo eal Sea in o he Lau asian epicon inen al
seaway a ou ed he mohaline ci cula ion and he en ila ion
o deep wa e . Howe e , in pe iods o high a mosphe ic CO2,
mo e sluggish cu en s o s agnan condi ions p e ailed due
o he in lux o wa m and saline wa e om he Te hyan a ea.
I is possible ha he ea ly Pliensbachian BCB hy hmi es
eco ded simila , bu p obably weake , palaeoceanog aphic
changes a p ecession imescales. Anoxic bo om-wa e con-
di ions allowed OM o be p ese ed, a ou ed he p ecipi-
a ion o au higenic sul ides and he dissolu ion o Fe and
Mn oxo-hyd oxides (Cape e al., 2013), and al e ed he o -
ganic iso opic signal (en ichmen in 13Co g and deple ion in
15No g). Inc eased OM bu ial also esul ed in a dec ease in
he 12C con en o ino ganic ca bon dissol ed in seawa e
(Mackensen and Schmiedl, 2019). Al hough he 13Cca b sig-
nal ound in San iu de eco ds his C s o age ac iona ion, i
is no possible o quan i y he diagene ic imp in .
In con as , OM-poo limy beds accumula ed du ing low
seasonali y p ecessional s ages. Such low seasonali y condi-
ions (mild summe s and win e s) esul ed when summe s
occu ed a aphelion and win e s a pe ihelion (Fig. 13).
Mild we and d y seasons caused a dec ease in de i al in-
pu (by wind and i e s), as well as in nu ien supply. Con-
sequen ly, o ganic ma e p oduc ion and bo om-wa e oxy-
gen consump ion declined (e.g. Nijenhuis and Lange, 2000;
Wang, 2009; Ch ous o a e al., 2021). Mo eo e , acco ding
o he o bi ally modula ed ocean ci cula ion model (Sa e
al., 2022), low-seasonali y p ecessional s ages would ha e
also a ou ed e ical mixing o he wa e column, b ing-
ing oxygen o bo om wa e , which allowed he oxida ion
o o ganic ma e (Cape e al., 2013). Rega ding ca bon-
a e componen s, p e ious s udies ha e shown ha Ju assic
shel al ca bona e ac o ies we e mo e e icien han pelagic
ooze in mic i e p oduc ion (Hinno and Pa k, 1999; Bádenas
e al., 2012). I can he e o e be concluded ha dec eased e -
igenous inpu s in o shallow ma ine a eas u he inc eased
shel al ca bona e mud p oduc ion, wi h su pluses being ex-
po ed in o deepe a eas (Tucke e al., 2009; Bádenas e al.,
2012). Assuming he gene al δ13Cca b end o be p ima y,
he en ichmen in 12C o limes ones could co espond o
he OM balance in he ma ine en i onmen (Mackensen and
Schmiedl, 2019). Thus, well-oxygena ed bo om wa e al-
lowed mos o he 12C- ich OM o be oxidized be o e bu ial,
dec easing he δ13C o ino ganic ca bon dissol ed in seawa-
e .
The palaeoen i onmen al model de i ed om he San-
iu de p ecession couple s di e s signi ican ly om hose
p esen ed by o he s o lowe Pliensbachian successions
om NW and cen al Eu ope (Fig. 1; Ma inez and De a,
2015; Holla e al., 2023). Howe e , i should be aken in o
accoun ha hese models we e de eloped o successions
accumula ed in he humid clima ic bel , whe e we condi-
ions p e ailed h oughou he yea and seasonali y was gen-
e ally weak. In such se ings, e igenous and nu ien inpu s
inc eased a p ecessional con igu a ions wi h highe season-
ali y, causing g ea e p oduc i i y du ing he we es season
and s onge e ical wa e mixing du ing he d ie season.
Consequen ly, he mo e calca eous OM-poo beds accumu-
la ed a high-seasonali y p ecessional s ages.
5.3.2 Fo ma ion o eccen ici y-d i en bundles
Du ing an eccen ici y cycle, he ampli ude o p ecession-
d i en seasonali y cycles is modula ed by a ia ions in he
shape o he o bi o he Ea h a ound he Sun (Be ge and
Lou e, 1994). A maximum eccen ici y he o bi o he
Ea h is ellip ical, and, consequen ly, insola ion changes as
much as 24 % in 1 single yea , causing signi ican ly con as -
ing seasonali y condi ions (Fig. 13). On he con a y, a min-
imum eccen ici y he o bi o he Ea h is almos ci cula ,
which esul s in ela i ely small a ia ions in insola ion be-
ween aphelion and pe ihelion, ega dless o he p ecession-
d i en o ien a ion o he axis o he Ea h. In sho , wo ex-
eme clima ic si ua ions (maximum and minimum season-
ali y) al e na e h oughou 20 ky p ecession cycles a maxi-
mum eccen ici y, whe eas clima ic condi ions emain s able
o longe pe iods a eccen ici y minima.
In San iu de he a angemen o couple s in bundles is
he li hological exp ession o he modula ion o he ampli-
ude o p ecession-d i en seasonali y by eccen ici y cycles
(Fig. 2b). In he in e al s udied in de ail, couple s 36–37
and 41–42, loca ed a he bounda ies be ween bundles 8–9
and 9–10, show ela i ely li le li hological con as (ma ls
al e na ing wi h ma ly limes ones), which sugges s o ma-
ion a eccen ici y minima. The es o he couple s a e si u-
a ed in he cen al pa s o bundles and show a ma ked li ho-
logical con as (shales al e na ing wi h limes ones), which
sugges s o ma ion in he wo ex eme si ua ions ha occu
Clim. Pas , 20, 1659–1686, 2024 h ps://doi.o g/10.5194/cp-20-1659-2024
N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale 1677
Figu e 13. O bi ally uned deposi ional model o he o ma ion o he calca eous couple s and bundles om San iu de. Schemes on he le
ep esen en i onmen al condi ions du ing p ecessional s ages wi h low annual seasonali y (bo eal summe ime a aphelion). Schemes on he
igh ep esen en i onmen al condi ions du ing p ecessional s ages wi h high annual seasonali y s ages (bo eal summe ime a pe ihelion).
The in luence o maximum eccen ici y is shown a he op and ha o minimum eccen ici y a he bo om. DIC: dissol ed ino ganic ca bon.
ODZ: oxygen-deple ed zone.
du ing p ecession cycles a maximum eccen ici y. This am-
pli ude modula ion is also eco ded by se e al geochemical
and mine alogical p oxies, co obo a ing he impac o ec-
cen ici y cycles on he o ma ion o he hy hmi e.
The luc ua ions in some edox-sensi i e (Co g, No g, ace
elemen s, δ13Co g, MnEF) and p oduc i i y ( ep esen ed by
PEF) p oxies, some o hem associa ed wi h ac o 1 in he
ac o ial analysis (Fig. 11), display g ea e ampli ude du -
ing eccen ici y maxima. This sugges s ha in ensi ied p e-
cessional seasonali y a maximum eccen ici y caused an in-
c ease in e es ial sedimen and nu ien inpu o he sea,
which ul ima ely esul ed in he in ensi ica ion o OM p o-
duc ion and oxygen consump ion (e.g. Nijenhuis and Lange,
2000; Wang, 2009; Ch ous o a e al., 2021). P ecession-
d i en a ia ions in oceanic cu en s, which con olled e -
ical oxygen g adien and seawa e s a i ica ion, also con-
ibu ed o p omo ing bo om-wa e anoxia in his o bi al
con igu a ion (Sa e al., 2022).
Eccen ici y cycles also modula ed he low-seasonali y
p ecessional s ages, in which ca bona e accumula ion was
a ou ed (Hinno and Pa k, 1999; Bádenas e al., 2012). A
ex emely low seasonali y condi ions a eccen ici y max-
h ps://doi.o g/10.5194/cp-20-1659-2024 Clim. Pas , 20, 1659–1686, 2024
1678 N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale
ima, con inen al inpu s we e minimal and, consequen ly, so
was ma ine OM p oduc ion. A he same ime, oceanic cu -
en s in ensi ied e ical mixing o wa e , a ou ing a well-
oxygena ed wa e column and ca bona e p oduc ion (Sa e
al., 2022). Mo eo e , ac o 2, which comp ises p oxies asso-
cia ed wi h dilu ion o ca bona e by e igenous inpu , shows
an in e es ing end in line wi h eccen ici y bundles. Sco es
o ac o 2, in addi ion o luc ua ing wi h he li hological al-
e na ion o calca eous couple s, also display a la ge -scale
end wi h minimum alues a eccen ici y maxima and max-
imum alues a eccen ici y minima. This end is mainly
p oduced by Na2O and 13Cca b (Table S5). Indeed, NaEF also
shows a simila end, wi h gene ally lowe alues a eccen-
ici y maxima (Fig. 9). This may eco d inc eased chemical
wea he ing in he con inen and he elease o Na2O (Ma -
shall, 1992). This goes agains he o bi ally modula ed cli-
ma ic model o Ma inez and De a (2015), who concluded
ha chemical wea he ing inc eases du ing low seasonali y
and annually we clima es de eloped a eccen ici y minima.
Da a om San iu de, howe e , sugges ha he clima e was
d ie a eccen ici y minima.
5.3.3 O bi ally paced sea le el changes?
I is well known ha , du ing icehouse pe iods, clima e
change d i en by high- equency o bi al cycles a ec s sea
le el due o luc ua ions in he s o age o wa e in con inen al
ice, causing so-called glacio-eus a ic sea le el changes (S e -
en e al., 2010). High- equency sea le el changes ha e also
been deduced om many shallow ma ine pla o ms de el-
oped in ice- ee g eenhouse pe iods (Haq, 2014). In he ab-
sence o ex ensi e ice caps, sea le el changes mus ha e been
caused by o cing mechanisms o he han glacio-eus asy,
which a e s ill deba ed. The he mal expansion and con ac-
ion o wa e masses cause sea le el changes bu do no p o-
duce high-ampli ude a ia ions (Con ad, 2013). Fluc ua ions
in wa e s o age in con inen al a eas (p incipally in aqui e s)
seem o be a plausible o cing mechanism o decame ic sea
le el changes du ing g eenhouse condi ions (Wendle and
Wendle , 2016). Acco ding o he aqui e –eus a ic model,
low sea le els occu when la ge olumes o wa e a e s o ed
in he con inen s du ing humid s ages, whe eas sea le el ises
du ing d y epochs due o inc eased aqui e discha ge (Sames
e al., 2020). Consequen ly, in a g eenhouse con ex , o bi ally
d i en al e na ions o a id and humid pe iods can p oduce
hi d- and ou h-o de sea le el luc ua ions (Wendle and
Wendle , 2016; Sames e al., 2020). G ea e accumula ion o
δ18O- and δ13C-deple ed esh wa e in he con inen esul s
in hea ie δ18O and δ13C o ino ganic ca bon dissol ed in
seawa e , and ice e sa.
Second-o de sea le el changes occu ed in Ea ly Ju as-
sic imes in he BCB, which we e eco ded by δ13C in well-
p ese ed belemni es (Rosales e al., 2006). Highs and de-
posi s show maximum alues in OM con en and δ13C al-
ues in belemni es, while lows and in e als a e cha ac e ized
by ca bona e- ich sedimen a ion and lowe δ13C alues in
belemni es. These ca bon iso ope eco ds e lec luc ua ions
in he δ13C composi ion o he ino ganic ca bon dissol ed
in seawa e , which we e con olled by pe iodic a ia ions in
OM bu ial and s o age o 12C in he seabed (Quesada e al.,
2005; Rosales e al., 2006). This sugges s ha wa e s a i-
ica ion inc eased and en ila ion o he seabed dec eased in
highs ands. Ma inez and De a (2015) showed ha δ13C al-
ues om Ju assic and Lowe C e aceous Pe i he yan succes-
sions also eco ded second- and hi d-o de sea le el changes
modula ed by o bi al cycles. Acco ding o his s udy, lood-
ing o con inen al a eas a highs ands igge ed ma ine p o-
duc i i y, and, consequen ly, seawa e δ13C alues inc eased
in ne i ic domains.
In San iu de, se e al lines o e idence sugges ha sho
eccen ici y cycles could ha e modula ed sea le el. Fac o 2
sco es (Table S5) change in line wi h eccen ici y bundles,
displaying highe alues a eccen ici y minima and lowe
alues a eccen ici y maxima (Fig. 14). A e age δ13Cca b,
%CaCO3, and TiEF alues pe couple show high alues a
eccen ici y minima. A e age Co g and No g alues pe cou-
ple also luc ua e in line wi h eccen ici y bundles, showing
maximum (o minimum) alues in he in e als ha co e-
spond o low-eccen ici y (o high-eccen ici y) con igu a-
ions. This may indica e ha he a e age OM con en pe
p ecessional s age was highe a eccen ici y minima, al-
hough shales a eccen ici y maxima eco ded maximum
OM alues. Using he aqui e –eus a ic model, i can be pos-
ula ed ha low sea le els may ha e occu ed du ing ec-
cen ici y maxima. Lows and deposi s eco ded he highes
and p obably coa ses e igenous inpu s (TiEF; Olde e al.,
2015) bu also he mos calca eous sedimen a ion due o
pla o m p og ada ion. A lowe sea le el would ha e acil-
i a ed seawa e en ila ion and OM deg ada ion a eccen ic-
i y scale. Howe e , en ila ion a maximum eccen ici y de-
c eased when p ecession-d i en seasonali y inc eased, which
empo a ily enhanced OM p oduc ion and p ese a ion, and
caused he accumula ion o shales on he seabed. Simila ly, a
highe sea le el a eccen ici y minima could ha e dec eased
bo om-wa e en ila ion, con ibu ing o OM p ese a ion.
These condi ions p omo ed OM accumula ion e en i e ige-
nous and nu ien inpu s we e no high when shales we e de-
posi ed.
Minima o NaEF a high-eccen ici y lows ands (Fig. 8)
sugges ha he clima e may ha e been mo e humid han
du ing low-eccen ici y highs ands. The Ln(Al2O3/Na2O)
index is a palaeo-wea he ing index based on a s a is ical
model o linea composi ional and wea he ing ends (Von
Eyna en e al., 2003). This index is especially ecommended
o ocks wi h a high pe cen age o biogenic ca bona e
Clim. Pas , 20, 1659–1686, 2024 h ps://doi.o g/10.5194/cp-20-1659-2024
N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale 1679
Figu e 14. Li hological log o he San iu de in e al s udied in de ail, showing he a e age alue pe couple o δ13Cca b, %CaCO3, TiEF,
Co g and No g. The palaeo-wea he ing index Ln(Al2O3/Na2O) o all beds, he sho eccen ici y colou il e ou pu (Fig. 5), and a en a i e
sea le el cu e a e also shown.
(Mon e o-Se ano e al., 2015), such as hose om San iu de.
Ln(Al2O3/Na2O) alues in San iu de show a g adual end
in line wi h eccen ici y bundles (Fig. 14). Maximum al-
ues, which indica e g ea e chemical wea he ing in he con i-
nen , a e eco ded a eccen ici y maxima. This con igu a ion
ag ees wi h he aqui e –eus a ic sea le el model, in which
humid clima es esul in inc eased eshwa e s o age in he
con inen and lowe sea le els, whe eas aqui e s a e emp ied
in d ie pe iods and sea le el ises (Wendle and Wendle ,
2016). Ju assic sea le el changes deduced om shallowe a -
eas om he Ibe ian basin we e also associa ed wi h o bi ally
paced aqui e eus asy (Seque o e al., 2017; Val e al., 2017).
5.3.4 Compa ison wi h o bi al o cing du ing Mesozoic
OAEs
Fou Lowe Ju assic BSIs occu in he BCB and he As-
u ian basin (Bo ego e al., 1996; Rosales e al., 2006). The
lowe Toa cian BSI co ela es wi h he globally eco ded
ea ly Toa cian Oceanic Anoxic E en (T-OAE; Jenkyns and
Clay on, 1986; Hesselbo e al., 2000; Rosales e al., 2006),
which was ela ed o a pe u ba ion in he Ea h’s clima e
o igina ed by an ab up addi ion o 12C in o he ca bon cy-
cle. Many s udies ha e p e iously demons a ed he in luence
o o bi al o cing on he T-OAE in wes e n, sou he n, and
no he n Te hys a eas (Huang and Hesselbo, 2014; Boulila
and Hinno , 2017; Boulila e al., 2019). These s udies e-
ealed he gene al p e alence o 405 ky eccen ici y cycles
in Lowe Ju assic eco ds, along wi h a s ong exp ession
o bo h p ecession and obliqui y cycles, al hough he in lu-
ence o he la e only inc eased du ing he anoxic e en . The
palaeoen i onmen al changes d i en by obliqui y cycles p o-
duced a ia ions in p oduc i i y, seabed oxygena ion, and/o
OM o igin du ing he T-OAE (Suan e al., 2015). The shi in
as onomical o cing du ing he T-OAE has also been linked
o he leng hening o he e es ial p oduc i i y season due o
inc eases in global empe a u es and humidi y (Boulila and
Hinno , 2017; Boulila e al., 2019).
In San iu de, he in luence o eccen ici y and p eces-
sion cycles p e ailed du ing he o ma ion o he Pliens-
bachian BSI-1, wi h li le o no e idence o obliqui y o c-
ing. In e es ingly, howe e , p ecession cycles also modu-
la ed he palaeoen i onmen al changes (con inen al wea h-
e ing, oceanic p oduc i i y and edox condi ions) ha oc-
cu ed du ing o he Mesozoic OAEs associa ed wi h he e-
lease o g eenhouse gases, such as he C e aceous OAE 1a
and 1b e en s (Giogio ni e al., 2015; Benama a e al., 2020).
I can he e o e be concluded ha he Pliensbachian BSI-1
o he BCB shows g ea e simila i ies o C e aceous OAEs
han wi h he Toa cian OAE. Howe e , i should be no ed
ha mos o he as och onological s udies o he Ea ly Ju as-
sic, including hose ocused on o bi al o cing on he T-OAE,
we e p e iously ocused on successions loca ed a la i udes
highe han San iu de (Suan e al., 2015; Ma inez and De a,
2015; Boulila and Hinno , 2017; S o m e al., 2020). I is pos-
sible ha , simila o he eccen ici y-modula ed p ecessional
deposi ional model, clima ic bel s de e mined he esponse
o he sedimen a y en i onmen o simila clima ic o cings.
h ps://doi.o g/10.5194/cp-20-1659-2024 Clim. Pas , 20, 1659–1686, 2024
1680 N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale
6 Conclusions
Lowe Pliensbachian o ganic- ich calca eous hy hmi es
om he BCB a e he exp ession o pe iodic en i onmen al
a ia ions ha occu ed in he Milanko i ch-cycle band. The
cyclos a ig aphic analysis o ock colou and magne ic sus-
cep ibili y da a se ies showed ha calca eous couple s ep e-
sen p ecession cycles, whe eas hicke bundles eco d sho
eccen ici y cycles; he e ec o long eccen ici y cycles was
also iden i ied.
The in eg a ed sedimen ological, mine alogical, and geo-
chemical analysis o a sho eccen ici y bundle allowed he
iden i ica ion o he en i onmen al ac o s ha go e ned he
o ma ion o he hy hmi e, as well as he assessmen o di-
agene ic o e p in ing. Mos o he composi ional pa ame e s
eco d p ima y cha ac e is ics ela ed o he o ma ion o he
calca eous hy hmi es, bu ino ganic s able iso ope eco ds
and he dis ibu ion o se e al ace elemen s may ha e been
somewha a ec ed by diagenesis du ing bu ial. Howe e , he
esul s allowed he de ini ion o an o iginal o bi ally mod-
ula ed deposi ional model which p o ides new insigh in o
he o ma ion o lowe Pliensbachian o ganic- ich calca eous
hy hmi es.
The o ma ion o p ecessional calca eous couple s was
egula ed by a ia ions in ca bona e p oduc i i y and in di-
lu ion by e igenous supply. Thus, o ganic- ich ma ls and
shales we e deposi ed du ing p ecessional con igu a ions,
which led o ma ked annual seasonali y (bo eal summe a
pe ihelion and win e a aphelion). Inc eased seasonal ain-
all on land and e igenous inpu (by i e s o wind) o ma-
ine a eas boos ed o ganic p oduc i i y in su ace wa e . In-
c eased accumula ion o o ganic ma e on he seabed e en-
ually caused poo ly oxygena ed bo om wa e . Deep-sea de-
oxygena ion and seawa e s a i ica ion we e enhanced due
o changes in ocean ci cula ion. Con e sely, limy beds we e
o med when seasonali y was minimal (bo eal win e a pe -
ihelion and summe a aphelion). The consequen dec ease
in e igenous inpu s a ou ed a g ea e p oduc ion and bas-
inwa d expo a ion o ca bona e sedimen in shallow ma ine
a eas. A lowe p oduc ion o OM and inc eased e ical sea-
wa e mixing due o changes in oceanic cu en s esul ed in
he oxida ion o o ganic ma e in he deepes en i onmen s.
In addi ion, se e al p oxies suppo he idea ha he
p ecessional con as be ween he in ensi y o seasonally
con olled en i onmen al ac o s, such as e igenous in-
pu and oxygena ion o bo om wa e , diminished when he
Ea h’s o bi was ci cula (minimum eccen ici y) and in-
c eased when i was mo e ellip ical (maximum eccen ic-
i y). The a ailable da a u he sugges ha sho - e m sea
le el changes may ha e occu ed in line wi h sho eccen ic-
i y cycles (highe sea le el a eccen ici y minima), p obably
h ough o bi ally modula ed aqui e eus asy.
The compa ison wi h Lowe Ju assic successions om
o he a eas sugges s ha palaeo-la i udinal clima ic bel s
played a signi ican ole in he esponse o he en i onmen
o as onomically o ced clima e change episodes.
Appendix A
P e ious s udies demons a ed ha he g ea es pa o he o -
ganic ma e ound in he BCB Pliensbachian black shales
had a ma ine o igin, being domina ed by amo phous and
s uc u ed lip ini ic o ganic ma e (Suá ez-Ruiz and P ado,
1987; Quesada e al., 1997, 2005; Pe manye e al., 2013).
The s udy o sa u a ed bioma ke s co obo a ed a dominan
pa e n o ma u e ex ac s de i ed om ma ine algal compo-
nen s. Addi ionally, SEM analysis ca ied ou in he p esen
s udy p o ided e idence o he occu ence o bio ilms wi h
spo adic occu ences o i ini e (Fig. 3e and ).
The a e age o ganic C /N a io o 30.45 ob ained in San-
iu de (Fig. 7) is signi ican ly highe han ha o mode n ma-
ine o ganic ma e , which usually displays alues be ween
5 and 18 (Meye s, 2006). Howe e , C/N a ios obse ed in
cu en ese oi s canno be di ec ly ex apola ed o ancien
ocks, especially o hose deposi ed unde high-p oduc i i y
condi ions (Nijenhuis and Lange, 2000; Meye s e al., 2006;
Schneide -Mo e al., 2012). Meye s e al. (2006) obse ed
ha o ganic componen s om Albian o San onian black
shales om Deme a a Rise we e mainly ma ine in o igin,
bu hei C /N a io a ied be ween 20 and 45, which is com-
monly assigned o e es ial plan s. Those high C /N alues
we e ela ed o a mo e apid ecycling o N han C du ing
OM decomposi ion. Mode n ma ine o ganic ma e is com-
monly deg aded ia deni i ica ion, p incipally decomposing
ni ogen- ich amino acids and educing he o al o ganic N
o sedimen s (Al abe e al., 1995; Van Mooy e al., 2002).
Thus, high C /N alues o some Medi e anean sap opels
and C e aceous black shales ha e been ela ed o he d aw-
down o dissol ed oxygen in he wa e column unde condi-
ions o high expo p oduc i i y (Nijenhuis and Lange, 2000;
Schneide -Mo e al., 2012). Simila p ocesses migh ha e
p oduced he abo emen ioned high C /N a io in San iu de.
In his ega d, conside ing ha he C/N a io o ypical ma-
ine OM is close o ∼6, a leas ∼23 % o he o iginal N
mus ha e been emo ed om he San iu de deposi s due o
deni i ica ion. This pe cen age is highe han ha calcula ed
by expe imen a ion (∼9%) in ecen sedimen s (Van Mooy
e al., 2002) bu signi ican ly lowe han he 70 % deduced
om C e aceous indu a ed successions (Schneide -Mo e
al., 2012). This sugges s ha o he p ocesses ela ed o OM
deg ada ion de e mine he loss o N due o di e en ial deg a-
da ion.
The δ13Co g signal om San iu de is also ela i ely de-
ple ed i compa ed o mode n ma ine OM, being close
o alues o e es ial plan s (Schneide -Mo e al., 2012).
Howe e , simila ly deple ed δ13Co g alues o ma ine OM
ha e also been ound in o he indu a ed successions (Nijen-
huis and Lange, 2000; Schneide -Mo e al., 2012). This gen-
Clim. Pas , 20, 1659–1686, 2024 h ps://doi.o g/10.5194/cp-20-1659-2024
N. Ma inez-B ace as e al.: O bi ally o ced en i onmen al changes du ing accumula ion o black shale 1681
e al deple ion o δ13Co g compa ed o a e age algal issue
is associa ed wi h selec i e decomposi ion o ca bohyd a es
and p o eins en iched in 13Co g, which a e mo e easily de-
composed, and he o i ica ion o he lipid ac ion en iched
in 12Co g (Jenkyns and Clay on, 1986). A simila ac iona-
ion p ocess was in oked in o he sec ions, such as he C e a-
ceous oil shales om Is ael (Schneide -Mo e al., 2012) and
he Medi e anean Pliocene sap opels (Nijenhuis and Lange,
2000).
In conclusion, poo ly oxygena ed backg ound condi ions
o bo om wa e igge ed deni i ica ion o ma ine OM in
San iu de, p omo ing a selec i e decomposi ion o ni ogen-
ich amino acids and he ac ion en iched in 13Co g. This
p ocess may ha e been s onge du ing he deposi ion o
OM- ich shales.
Da a a ailabili y. All da ase s a e a ailable open-
access in PANGAEA. These include magne ic sus-
cep ibili y (h ps://doi.o g/10.1594/PANGAEA.967720,
Ma ínez-B ace as e al., 2024a) and colou alues
(h ps://doi.o g/10.1594/PANGAEA.967723, Ma ínez-B ace as
e al., 2024b) o he en i e succession s udied in he San-
iu de sec ion (0–22.5 m), as well as he calcium ca bon-
a e con en (h ps://doi.o g/10.1594/PANGAEA.967730,
Ma ínez-B ace as e al., 2024c), elemen al geo-
chemis y (h ps://doi.o g/10.1594/PANGAEA.968044,
Ma ínez-B ace as e al., 2024d), o ganic geochemis y
(h ps://doi.o g/10.1594/PANGAEA.967947, Ma ínez-
B ace as e al., 2024e), whole- ock mine alogy
(h ps://doi.o g/10.1594/PANGAEA.967852, Ma ínez-
B ace as e al., 2024 ), and ino ganic C and O iso opes
(h ps://doi.o g/10.1594/PANGAEA.967761, Ma ínez-B ace as e
al., 2024g) o he in e al s udied in de ail (12.4–15.95 m).
Supplemen . The supplemen ela ed o his a icle is a ailable
online a : h ps://doi.o g/10.5194/cp-20-1659-2024-supplemen .
Au ho con ibu ions. NMB: concep ualiza ion, o mal analysis,
in es iga ion, me hodology, and w i ing (o iginal d a p epa a ion).
AP: concep ualiza ion, unding acquisi ion, o mal analysis, in es-
iga ion, me hodology, and w i ing ( e iew and edi ing). JDT: o -
mal analysis, in es iga ion, me hodology, and w i ing ( e iew and
edi ing). IR: o mal analysis, in es iga ion, and w i ing ( e iew and
edi ing). JA: o mal analysis, in es iga ion, and me hodology. RSC:
o mal analysis and in es iga ion.
Compe ing in e es s. The con ac au ho has decla ed ha none
o he au ho s has any compe ing in e es s.
Disclaime . Publishe ’s no e: Cope nicus Publica ions emains
neu al wi h ega d o ju isdic ional claims made in he ex , pub-
lished maps, ins i u ional a ilia ions, o any o he geog aphical ep-
esen a ion in his pape . While Cope nicus Publica ions makes e -
e y e o o include app op ia e place names, he inal esponsibili y
lies wi h he au ho s.
Acknowledgemen s. This esea ch was unded by p ojec
PID2019-105670GB-I00/AEI/10.13039/501100011033 o he
Spanish Go e nmen (MCIN/AEI) and by he Consolida ed
Resea ch G oup IT602-22 o he Basque Go e nmen . Na oa
Ma ínez-B ace as is g a e ul o pos -doc o al specializa ion
g an s DOCREC19/35 and ESPDOC21/49 om he Uni e si y
o he Basque Coun y (UPV/EHU) and a Ma ga i a Salas con-
ac (MARSA22/05) om he Spanish Go e nmen wi h Nex
Gene a ion unds om he Eu opean Union. Thanks a e due o
Ca l Shea e o his language co ec ions on an ea lie e sion
o he pape . This a icle bene i ed om insigh ul commen s on
a p e ious e sion o he manusc ip by edi o Ge ilyn (Lynn)
So eghan and e iewe s Bea iz Bádenas and Sie ske Ba enbu g.
Financial suppo . This esea ch was unded by p ojec
PID2019-105670GB-I00/AEI/10.13039/501100011033 o he
Spanish Go e nmen (MCIN/AEI) and by he Consolida ed
Resea ch G oup IT602-22 o he Basque Go e nmen . Na oa
Ma ínez-B ace as ecei ed pos -doc o al specializa ion g an s
DOCREC19/35 and ESPDOC21/49 om he Uni e si y o
he Basque Coun y (UPV/EHU) and a Ma ga i a Salas con-
ac (MARSA22/05) om he Spanish Go e nmen wi h Nex
Gene a ion unds om he Eu opean Union.
Re iew s a emen . This pape was edi ed by Ge ilyn (Lynn)
So eghan and e iewed by Bea íz Bádenas and Sie ske Ba enbu g.
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