DINOFLAGELLATE CYSTS, PALYNOFACIES AND OR GANIC
GEO CHEM IS TRY OF THE CRE TA CEOUS-PALAEOGENE (K–Pg)
BOUND ARY TRAN SI TION AT THE ELLêS SEC TION,
NORTH EAST ERN TUNISIA
Amel M’HAMDI1, Hamid SLIMANI2, Kmar BEN ISMAIL-LATTRACHE1& Walid BEN ALI1 1
Uni ver sity Tunis El Manar, Fac ulty of Sci ences of Tu nis, De part ment of Ge ol ogy, UR 11 ES 15 Cam pus Universitaire, 2092, El Manar II, Tu ni sia; e-mail: mhamdiamel25@ya hoo.fr
2
De part ment of Earth Sci ences, Lab o ra tory of Ge ol ogy and Re mote Sens ing, URAC 46, Sci en tific In sti tute, Uni ver sity Mo ham med V-Agdal, av e nue Ibn-Batouta, P.B. 703, 10106 Ra bat-Agdal, Mo rocco M’Hamdi, A., Slimani, H., Ben Ismail-Lattrache, K. & Ben Ali, W. 2014. Dinoflagellate cysts, palynofacies and or ganic geo chem is try of the Cre ta ceous-Palaeogene (K–Pg) bound ary tran si tion at the EllÀs sec tion, north east ern Tu ni sia. Annales Societatis Geologorum Poloniae, 84: 235–247.
Ab stract: A palynofacies study car ried out across the Cre ta ceous–Palaeogene (K–Pg) bound ary in the El Haria For ma tion at EllÀs, north east ern Tu ni sia, re vealed the pres ence of or ganic mat ter dom i nated by ma rine palyno-morphs, mainly dinoflagellate cyst as sem blages. Con ti nen tal palynomorphs (sporomorphs) and amor phous or ga-nic mat ter (AOM) are also pres ent in all sam ples. The to tal or gaga-nic car bon (TOC) con tent is gen er ally less than 0.7 wt.%. The Rock-Eval S1 pa ram e ters vary from 0.01 to 0.3 mgHC/g rock. The Rock-Eval S2 pa ram e ters vary from 0.15 to 0.57 mgHC/g rock. The hy dro gen in dex (HI) and ox y gen in dex (OI) val ues range from 61 to 214 mgHC/g TOC and 149 to 638 mgHC/g TOC, re spec tively. The Tmax val ues range from 420 to 440°C. The TOC, Rock-Eval py rol y sis and palynofacies anal y ses in di cate that the El Haria For ma tion is char ac ter ized by im ma ture or ganic mat ter type II and III and a low ther mal al ter ation in dex (TAI). Also, the au thors pres ent in this pa per the biostratigraphic, palaeoenvironmentl and palaeobiogeographic frame work for the dinoflagellate cyst as sem blages be low and above the Cre ta ceous–Palaeogene bound ary in the EllÀs sec tion.
Key words: Cre ta ceous–Palaeogene (K–Pg) bound ary, dinoflagellate cysts; palynofacies, or ganic mat ter, EllÀs sec tion; Tu ni sia.
Manu script re ceived 16 April 2014, accepted 1 September 2014
IN TRO DUC TION
The EllÀs sec tion al ready has been the sub ject of sev eral stud ies, based on min er al ogy, geo chem is try (Adatte et al., 2002; Stüben et al., 2002), biostratigraphy of plank tonic and ben thic foraminifera (Said-Benzarti, 1978; Yaa-koub, 1999; Zaaghbib-Turki et al., 2000, 2001; KarouiYaakoub et al., 2002; Coccioni and Marsili, 2007) and cal -car e ous nannofossils (Gardin, 2002). This sec tion has been pro posed as a parastratotype and even as a new stratotype of the K–Pg bound ary (Zaaghbib-Turki et al., 2000, 2001; Ka- roui-Yaakoub et al., 2002), since it con tains, ac cord ing to the lat ter au thors, one of the most com plete Cre ta ceous– Palaeogene (K–Pg) bound ary tran si tion and is better expo-sed than the El Kef stratotype sec tion. Re cent palynological stud ies, based on dinoflagellate cyst (dinocyst) as sem blages from this sec tion, in di cated con tin u ous sed i men ta tion in the K–Pg tran si tion (M’Hamdi et al., 2013a) and per mit ted palaeoenvironmental and palaeobiogeographical in ter pre ta -tions (M’Hamdi et al., 2013b, in press; M’Hamdi, 2014).
The aim of this pa per is to pres ent an anal y sis of the pa-lynofacies and geo chem is try, which com bines Rock-Eval py rol y sis and TOC mea sure ments at the K–Pg bound ary tran si tion in the EllÀs sec tion.
GEO LOG I CAL BACK GROUND
The EllÀs sec tion is lo cated near the small set tle ment of EllÀs, be tween the cit ies of Siliana and Maktar, about 137 km from Tu nis, 43 km from El Kef and 65 km from Kalaat Senan (Fig. 1). This sec tion is well ex posed in the EllÀs Syncline (PervinquiÀre, 1903), with a com plete Cre ta ceous–Palaeogene tran -si tion. The sec tion sam pled is ori ented NW–SE, be tween Argoubet el AÎeicha and Jebel Madkour. It is sim i lar to the sec tion, stud ied by ZaaghbibTurki et al. (2000, 2001). Its Lam -bert co or di nates on the Maktar map (scale 1/50000) are: 426/ 295.7; 426.5/294.1. Spe cif i cally, it has the geo graphic co or -di nates: N35°56'40.4", E009°04'49.9" (Carthage) and N3 977974, E507310 (UTM co or di nates) at an al ti tude of 725 m.
The EllÀs sec tion is sit u ated in the Karma Val ley, Tu ni -sian Cen tral At las. Its palaeogeographic set ting is sim i lar to that of the El Kef sec tion. Both lo cal i ties were sit u ated on the south ern mar gin of the Tethys Ocean, on the Af ri can continental shelf. The sed i ments in this sec tion were de pos -ited at wa ter depths, cor re spond ing to the mid dle to outer shelf, rel a tively close to the emerged zone of Kasserine Is -land (Burollet, 1956; Adatte et al., 2002; Galeotti and Co-ccioni, 2002; Gardin, 2002; Karoui-Yaakoub et al., 2002; Keller et al., 2002; Coccioni and Marsili, 2007). This sec -tion is lo cated in a slightly more prox i mal po si -tion than the El Kef sec tion, with a gen er ally higher terrigenous con tent and hence a sed i men ta tion rate ex ceed ing that of the El Kef sec tion (Adatte et al., 2002; Stüben et al., 2002). The EllÀs sec tion con tains one of the most com plete K–Pg bound ary tran si tions in Tu ni sia.
MA TE RIAL AND METH ODS
Sam ple prov e nanceThis study fo cuses on only 2 m of marly and clay de -pos its around the Cre ta ceous–Palaeogene bound ary, expo-sed at the EllÀs sec tion. This in ter val ex tends from 92 cm be low to 108 cm above the K–Pg bound ary and in cludes the Maastrichtian–Danian tran si tion. Among the twenty-five samples col lected, eleven are from the up per most Maastri-chtian marls and four teen from the Danian clays and marls, with tighter sam pling near the K–Pg bound ary (Fig. 2).
Palynological prep a ra tion
In to tal, 25 sam ples from the EllÀs sec tion were processed, fol low ing stan dard palynological pro cess ing tech -niques. Pro cess ing in volved an ini tial treat ment of 50 g of
Fig. 1. Lo ca tion of study area. A, B. Geo graph ical lo ca tion of the EllÀs sec tion in north east ern Tu ni sia. C. Geo log i cal set ting of the sec -tion stud ied. D. De tail lo ca -tion of the EllÀs area. Adapted from the geo log i cal map of Tu ni sia, 1:500,000 (Ben Haj Ali et al., 1985).
sed i ment per sam ple with cold HCl (20%), fol lowed by di -ges tion in HF (40% at 70°C), to dis solve the car bon ates and sil i cates, re spec tively. The sam ples were rinsed with dis til-led wa ter un til neu tral be tween the acid treat ments. Silico-flu o rides were re moved in warm HCl (20%). The res i dues were sieved on a ny lon screen with a mesh of 15 µm and mounted in glyc er ine jelly on mi cro scope slides. Pho to mi cro graphs of palynomorphs were taken with a dig i tal Olym -pus C-400 Zoom cam era, mounted on an Olym -pus BX53 mi cro scope. The tax on omy of the dinoflagellate cyst spe -cies is based on Dinoflaj 2 (Fensome et al., 2008) and Slimani et al. (2008, 2010, 2012). All sam ples were pre -pared at the De part ment of Ge ol ogy, Fac ulty of Sci ences, at the Uni ver sity of Tu nis (Tu ni sia), with ad di tional prep a ra tion (di ges tion of silicofluori des, siev ing, slide prep a ra -tion) at the Lab o ra tory of Ge ol ogy and Re mote Sens ing, Sci en tific In sti tute of Ra bat (Mo rocco).
For the quan ti ta tive anal y sis, two ra tios that are of ten used as palaeoenvironmental prox ies were cal cu lated (Fig. 3). The
ra tio be tween num bers of autotrophic and heterotrophic dino-cycts or peridinioid/gonyaulacoid (P/G) dinocyst ra tio (P/G = nP/(nP+nG) sensu Versteegh (1994) pro vided in for ma tion about the sea-sur face pro duc tiv ity. The sporomorph/dinocyst (S/D) ra tio (S/D = nS/(nD+nS) sensu Versteegh (1994), with S = num ber of spores and pol len and D = dinocysts and acri- tarchs, was used to es ti mate the con ti nen tal in flu ence.
The quan ti fi ca tion of the kerogen con tent and com po si -tion was car ried out in or der to ana lyse the palynofacies. At least 300 par ti cles were counted in each sam ple, fol low ing Tyson (1995), to dif fer en ti ate three groups: amor phous or -ganic mat ter (AOM), phytoclasts (black and trans lu cent mat ter) and palynomorphs (dinocysts, acritarchs, or ganic li- nings of foraminiferal tests and spores and pol len grains).
Geo chem i cal pro ce dures
The to tal or ganic car bon (TOC) con tent and Rock-Eval pa ram e ters were de ter mined at the Lab o ra tory of Or ganic
Fig. 2. Lith o logic de scrip tion, cal cium car bon ate con tent (CaCO3) and to tal or ganic car bon (TOC) of the Cre ta ceous–Palaeogene
Geo chem is try of the Tu ni sian Oil Com pany. The Rock-Eval anal y ses were per formed us ing the in stru ment Rock-Eval II, fol low ing the pro ce dures pro posed by Espitalie et al. (1977).
STRATI GRAPHIC FRAME WORK
The sub di vi sion, used here for the EllÀs sec tion, fol lows Zaaghbib-Turki et al. (2000, 2001) and Karoui-Yaakoub et
al. (2002) on lithostratigraphy and plank tonic foraminifera,
Gardin (2002) and Coccioni and Marsili (2007) on cal car e -ous nannofossils and M’Hamdi et al. (2013a) and M’Hamdi (2014) on dinoflagellate cysts.
Lithostratigraphy
The Cre ta ceous–Palaeogene bound ary sec tion of EllÀs be gins, in the up per most me ters of the Maastrichtian de pos -its of the El Haria For ma tion (Burollet, 1956), with gray marls (CaCO3 con tent 30–60%) con tain ing gyp sum and
Fe-ox ides. These marls end up wards with an irid ium-rich layer, mark ing the fall out from the Chicxulub im pact event and the K–Pg bound ary. This irid ium-rich layer con sists of a rusty red layer, 2–3 mm thick and rich in Fe-ox ides (Adatte et al., 2002). Cos mic mark ers, such as an anom a
-lous con cen tra tion in Ir, Ni-rich spi nels and al tered mi cro-tek tites, are also pres ent in this thin layer (Gardin, 2002). Just above the layer, the Palaeo cene suc ces sion be gins with a bound ary clay layer, dark and 50 cm thick (CaCO3 con tent
10%). In its basal part it is rich in jarosite nod ules, Feox ides and gyp sum, but en riched to ward the top in beige nod u -lar car bon ate in ter ca la tions. This unit is over lain by 5.8 m of gray marls, rich in jarosite con cre tions. This study fo cuses on 2 m of de pos its around the K–Pg bound ary of the EllÀs sec tion (Fig. 2).
Biostratigraphy
Most microfossil stud ies re al ized in the EllÀs sec tion con cern foraminifera, nannofossils and dinoflagellate cysts. In the top metres of the up per most Maastrichtian marls, planktonic and ben thic foraminifera are abun dant, var ied and char ac ter ise the plank tonic foraminiferal
Abathomphalus mayaroensis (CF1) Zone. The foraminiferal group un
der goes pro gres sive dis ap pear ances, al ready from 4 m be low the K–Pg bound ary and up wards, and then a mass ex tinc tion at the K–Pg bound ary. About twothirds of the spe -cies dis ap peared and a third sur vived above the bound ary. A gradual re newal led to the es tab lish ment of the typ i cal as -so ci a tions of the Palaeo cene. The basal Palaeo cene clays
Fig. 3. Rel a tive abun dances of se lected spe cies and groups of mor pho log i cally re lated spe cies, biozones, bioevents, di ver sity pat terns and palaeoenvironmental changes of dinoflagellate cysts across the Cre ta ceous–Palaeogene bound ary at the EllÀs sec tion, north east ern Tu ni sia. P/G – peridinioid/gonyaulacoid dinocyst ra tio sensu Versteegh (1994) (P/G = nP/(nP+nG), S/D – sporomorph/dinocyst ra tio sensu Versteegh (1994) (S/D = nS/(nD+nS), with S – num ber of spores and pol len and D – dinocysts and acritarchs.
contain a fauna, char ac ter is tic of the plank tonic foramini-feral Globoconusa conusa (P0) Zone. The
Parvularugoglo-bigerina eugubina (P1a) Zone be gins at the end of the
Pala-eocene marls, at about 67 cm above the irid ium-rich layer (Zaaghbib-Turki et al., 2000, 2001; Karoui-Yaakoub et al., 2002).
The K–Pg in ter val stud ied cor re sponds to the Up per Maastrichtian cal car e ous nannofossil Nephrolithus
fre-quens Zone (Miculaprinsii Subzone [CC26b]) and the
Lo-wer Danian NP1 Zone (Gardin, 2002).
The dinoflagellate cyst as sem blages in di cate con tin u -ous sed i men ta tion in the in ter val of the sec tion stud ied. They per mit the K–Pg bound ary to be placed just above the up per most Maastrichtian global marker acme of
Manumie-lla seelandica and the high est oc cur rence of a few
Cretace-ous taxa, such as Dinogymnium spp., Alisogymnium
eucla-ense and Pterodinium cretaceum, and di rectly be low the
low est oc cur rence of the basal Danian mark ers
Damassadinium californicum, Membranilarnacia? te-nella, Senoniasphaera inornata and Carpatella cornuta.
The quan ti ta tive anal y sis of the dinoflagellate cyst as so ci a -tions does not re flect a dis tinct ex tinc tion at the K–Pg boundary, but shows sig nif i cant changes in the rel a tive abun dance of spe cies or groups of spe cies that are mor pho log i -cally re lated.
The lithostratigraphy and plank tonic foraminiferal (Zaaghbib-Turki et al., 2000, 2001; Karoui-Yaakoub et al.,
2002), cal car e ous nannofossil (Gardin, 2002) and dinofla-gellate cyst (M’Hamdi et al., 2013a, b, in press; M’Hamdi, 2014) biostratigraphy to gether con firm a com plete re cord of the K–Pg bound ary tran si tion at EllÀs.
PALAEOENVIRONMENTAL AND
PALAEOBIOGEOGRAPHIC FRAME
-WORK OF DINOFLAGELLATE CYSTS
The Maastrichtian–Danian tran si tion in the EllÀs sec tion shows im por tant changes in the rel a tive abun dances of mor -pho log i cally re lated dinoflagellate cysts, prob a bly reflec-ting changes in palaeoenvironmental con di tions (M’Hamdi et
al., 2013b, in press; M’Hamdi, 2014). The Up per Maa-strichtian marls con tain dinoflagellate cyst as sem blages, cha-racterized by a great abun dance of the Cordosphaeridium and Glaphyrocysta groups (Brinkhuis and Zachariasse, 1988; Eshet et al., 1992; Slimani et al., 2010). Both groups thrived in a shal low ma rine en vi ron ment. The great est abun dance (50–65%) of Manumiella seelandica in the up per most part of the Up per Maatrichtian (Fig. 3) in di cates a deep ma rine en vi ron ment un der a re gres sive re gime dur ing cool cli ma tic con -di tions Habib and Saee-di (2007), caused by the as tro nom i cal event, re corded at the K–Pg bound ary event. A sim i lar acme of Manumiella seelandica was ob served by Strong et al. (1977), Wil son (1978), Firth (1987), Habib and Saeedi (2007), Slimani et al. (2010), Slimani and Toufiq (2013) and Mohamed et al. (2013).
In the lower Danian sed i ments, the de crease in abun -dance of Manumiella seelandica and the Glaphyrocysta and
Cordosphaeridium groups and the abrupt rel a tive in crease
in Areoligera spp., es pe cially in the basal Danian, a great
rel a tive abun dance of Senegalinium spp. (Fig. 3) and
Spini-ferites group sensu Slimani et al. (2010), and the great
abundance of dinoflagellate cyst spe cies in di cate more open ma rine con di tions un der a transgressive re gime (Brinkhuis and Zachariasse, 1988; Slimani et al., 2010).
The P/G ra tio (peridinoid/gonyaulcoid ra tio of dinofla-gellate cysts sensu Versteegh, 1994) var ies be tween 0.3 and 0.55 in the Up per Maastrichtian, de creases sharply at the K–Pg bound ary and sub se quently in creases in the Danian to achieve val ues sim i lar to those of the Cre ta ceous (Fig. 3). The in crease of the P/G ra tio within the Danian in di cates an in crease in food and palaeoproductivity (Brinkhuis et al., 1998). The peridinoid group con sists of heterotrophic dino-flag el lates, such as Senegalinium spp., Palaeocystodinium spp. and Andalusiella spp.
The dinoflagellate cyst as sem blages of the Maastrich-tian–Danian tran si tion in the EllÀs sec tion re flect pro nounced pro vin cial ism. The dom i nance of dinoflagellate cyst taxa of the Malloy suite (Lentin and Wil liams, 1980), such as spe cies of Lejeunecysta, Cerodinium, Andalusiella and Senegalinium (Figs 7, 8) in di cate de po si tion in a sub trop i cal to warm tem -per ate prov ince (M’Hamdi et al., 2013b, in press; M’Hamdi, 2014). Sim i lar as sem blages have been ob served in other Tethyan ar eas by Brinkhuis and Zachariasse (1988), De Coninck and Smit (1982), Rauscher and Doubinger (1982), Soncini and Rauscher (1988), Soncini (1990), Slimani et al. (2010) and Slimani and Toufiq (2013).
RE SULTS
Palynofacies anal y sisThe dis tri bu tion of palynofacies in the EllÀs sec tion was eval u ated on the ba sis of qual i ta tive and quan ti ta tive anal y -ses of dis persed or ganic con stit u ents. In the ma jor ity of the sam ples, palynomorphs (con ti nen tal and ma rine), amor phous or ganic mat ter (AOM) and phytoclasts (P) are pres -ent. Dinoflagellate cysts dom i nate the to tal palynofacies. The chorate and prox i mate dinoflagellate groups are pres ent through out the en tire sec tion. The abun dances of both groups are rel a tively con stant through out the Maastrichtian and Danian stages.
Acritarchs are pres ent, but rarer than dinoflagellate cysts. The foraminiferal test lin ings group is pres ent through out much of the sec tion. Pol len and spores are rare in this sec tion. AOM was re corded con stantly through out the sec tion.
Ma rine palynomorphs ac count for more than 80% of the to tal or ganic mat ter. These palynomorphs are good in di -ca tors of ma rine con di tions (Tyson, 1995). The pres ence of the foraminiferal test lin ings and acritarchs con firm the ex -is tence of ma rine con di tions dur ing sed i men ta tion.
All of the or ganic com po nents counted were plot ted in the AOM-Phytoclast-Palynomorph ter nary di a gram of Tyson (1993) in Fig ure 4A. Dif fer ent pro por tions of the com -po nents of this or ganic mat ter in di cate that the palynofacies is dom i nated by palynomorphs (65%).
The or ganic mat ter ob served is very abun dant and well pre served. Pro jec tion of dif fer ent pro por tions of the or ganic mat ter com po nents in the palynofacies di a gram of Ronca-glia and Kuijpers (2006) shows that ma rine-de rived or ganic
mat ter is dom i nant (Fig. 4B). This is sup ported by the litho-log i cal char ac ter is tics and in ferred sed i men ta tion, namely for the most part marls and clay, rich in plank tonic foramini- fera, re flect ing a deep ma rine en vi ron ment (Gallala, 2010).
The ma rine or ganic mat ter rep re sents 50% to 80% of the to tal or ganic mat ter in the palynofacies, and microplan-kton rep re sents 70% to 95% of the to tal palynomorphs. The fre quency of spores and pol len grains does not ex ceed 12%.
The S/D ra tio, at the EllÀs sec tion is gen er ally low, not ex ceed ing 12%. It reaches its max i mum at the K–Pg bound ary, show ing a con ti nen tal in flu ence. The max i mum en rich -ment of ter res trial palynomorphs is re corded in sam ple Es11, just be low the K–Pg bound ary (Fig. 3). Ac cord ing to Brinkhuis and Zachariasse (1988), this in crease in abun -dance and at tain ment of peak pro por tions within the land-de rived or ganic mat ter is in ter preted as a re sult of a rap idly re treat ing sea. This re gres sion, oc cur ring at the end of Late Maastrichtian, is also in di cated by the acme of Manumiella
seelandica just be low the K–Pg bound ary (Es 9–Es10) (M’Hamdi et al., 2013b, in press; M’Hamdi, 2014). The acme of Manumiella seelandica re corded be low the K–Pg bound ary is re lated to a global cool ing (Habib and Saeedi, 2007). In the lower Danian, there is a de crease in the abun -dance of ter res trial palynomorphs, whereas AOM is still pres ent and the palynofacies is dom i nated by ma rine in di ces. An abun dance of dinocysts and foraminiferal test lin -ings points to a rise in sea-level in the Danian. The palyno-morphs are dom i nated by peridinoid dinocyts, such as Sene-
galinium spp., Lejeunecysta spp., Andalusiella spp., and Cerodinium spp. The gonyaulacoid dinocysts are rep re -sented by Areoligera spp., Cordosphaeridium in spp. and
Spiniferites spp. The pre dom i nance of peridinoid dinocysts
cited above re flects a pe riod of trans gres sion (Dam et al., 1998) and there fore an in crease in sea-sur face tem per a ture. This agrees with the re turn to rel a tively warm con di tions,
pre vi ously known to have oc curred dur ing the Danian (Brinkhuis et al., 1998; Slimani and Toufiq, 2013). The small grain size of the Lower Danian clays re in forces the ar gu ment for an in crease in sea level and de po si tion in an en -vi ron ment far ther off shore (Keller and Lindinger, 1989).
To tal or ganic car bon (TOC) and Rock-Eval py rol y sis
The geo chem i cal study in volved 12 sam ples from the K–Pg bound ary tran si tion in the EllÀs sec tion. The re sults of the TOC and Rock-Eval py rol y sis are given in Fig ure 5 and Ta ble 1. The TOC con tent is gen er ally low and var ied be -tween 0.07 to 0.53 wt.%, in di cat ing a low or ganic car bon con tent (Pe ters and Cassa, 1994).
The Rock-Eval S1 and S2 pa ram e ters var ied from 0.02 to 0.31 mgHC/g rock and 0.14 to 0.57 mgHC/g rock, re -spec tively (Fig. 5, Ta ble 1). The Tmax val ues ranged from 420 to 440°C.The hy dro gen in dex (HI) and ox y gen in dex (OI) val ues ranged from 61 to 214 mgHC/g TOC and 149 to 638 mgHC/g TOC, re spec tively. They in di cate a ma rine plank tonic or ganic mat ter (Type II) al tered and/or mixed with a con ti nen tal or ganic mat ter (type III). Ac cord ing to Tissot et al. (1977), the low hy dro gen in dex val ues are pro-bably due to the con tri bu tion of or ganic mat ter type III and/or the poor pres er va tion of or ganic mat ter. The low Tmax val ues (420–440°C) in di cate an immature state of the organic matter.
The pe tro leum po ten tial (PP) is also low, rang ing from 0.14 to 0.57 kg HC/t rock with an av er age of 0.27 kg HC/t rock. The PP/TOC di a gram shows that the El Haria For ma tion gen er ally has a low over all pe tro leum po ten tial (Ta ble 1).
The HI/Tmax and PI (pro duc tion in dex)/Tmax di a grams in di cate that the or ganic mat ter is im ma ture. The PP/Tmax dia- gram shows that the sam ples are im ma ture in terms of ther mal evo lu tion, which does not ex ceed the Tmax of 440° C (Ta ble 1).
Fig. 4. Palynofacies pro por tions in sam ples from the EllÀs sec tion as ex pressed by ter nary kerogen and palynomorph plots. A. AOM-Phytoclast-Palynomorph plot (Tyson, 1993), field I – kerogen type III, field II – kerogen type III, field III – kerogen type III or IV, field IV – kerogen type III or II, field V – kerogen type III IV, field VI – kerogen type II, field VII- kerogen type II, field VIII – kerogen type II I, field IX - kerogen type II I. B. AOM–PS–FDAO (Roncaglia and Kuijpers, 2006). AOM – amor phous or ganic mat ter, PS – phytoclasts + sporomorphs, FDAO – foraminifera lin ings + dinoflagellate cysts + acritarchs + other ma rine al gae.
Op ti cal meth ods: spore col or ation and ther mal al ter ation in dex (TAI)
Mi cro scopic stud ies of or ganic mat ter are now widely used for palaeoenvironmental re con struc tion, as well as for the eval u a tion of source rocks and kerogen types (Staplin, 1969; Fisher et al., 1980; Jones and Demaison, 1982; Bat
-ten, 1982, 1983; Van Bergen and Kerp, 1990; Bertrand et
al., 1994; Tyson, 1995; Pavlus and Skupien, 2014). The re
-sults of the study of or ganic mat ter ma tu rity and po ten tial hy dro car bons in the EllÀs sec tion are re ported in Ta ble 2.
The ob served sam ples show well-pre served or ganic matter. It is gen er ally com posed of amor phous mat ter, palynomorphs in clud ing dinocysts, sea weed and al gae frag
-Ta ble 1
Rock-Eval anal y sis from sam ples at the EllÀs sec tion, north east ern Tu ni sia
Samples S1 (meg) S2 (meg) S3 (meg) PI Tmax (°C) IH IO TOC (%) PP
Es 19 0.03 0.22 0.96 0.11 432 61 267 0.36 0.22 Es 16 0.09 0.28 1.11 0.25 445 74 292 0.38 0.28 Es 15 0.02 0.25 0.52 0.09 431 71 149 0.35 0.27 Es 13 0.02 0.24 0.55 0.09 427 65 149 0.37 0.26 Es 12 0.06 0.39 0.95 0.13 436 74 179 0.53 0.39 Es 11 0.07 0.32 2.26 0.18 432 73 514 0.44 0.32 Es 9 0.05 0.21 0.67 0.18 435 131 419 0.16 0.21 Es 8 0.31 0.57 0.61 0.35 423 141 156 0.39 0.57 Es 7 0.1 0.23 0.68 0.3 439 70 206 0.33 0.23 Es 6 0.11 0.25 0.56 0.3 431 83 187 0.3 0.25
S1 – free oil, S2 – free oil by crack ing, S3 – CO2 pro duced dur ing crack ing, PI – pro duc tion in dex, Tmax – tem per a ture max i mum, IH – hydrogen in dex,
IO – oxygen in dex, TOC – to tal or ganic car bon, PP – pe tro leum po ten tial.
Fig. 5. Quan ti ta tive and qual i ta tive char ac ter is tics of or ganic mat ter from the El Haria For ma tion at the EllÀs sec tion, north east ern Tu -ni sia. TOC – to tal or ga-nic car bon, Tmax – Py rol y sis max i mum tem per a ture, PP – pe tro leum po ten tial, HI – hy dro gen in dex.
ments, some spores and pol len and woody de bris with an gu -lar contours.
The rel a tive per cent age of or ganic frac tions is of ten vari able and some are rel a tively rich in woody de bris, re -flect ing a con ti nen tal in flu ence. The ma tu rity was as sessed on the ba sis of ob ser va tion in trans mit ted light. The spore col or ation in dex (SCI) is in the or der of 1, the or ganic ma te -rial is con sid ered im ma ture and the spores have a yel low
color. The ap pear ance of palynomorphs is fresh and clear and the SCI is low vary ing be tween –1 and +1, and the ther -mal al ter ation in dex (TAI) is also low (Bat ten, 1996). The or ganic mat ter (kerogen) is of type II and III. It is im ma ture and can gen er ate only gas. With re gard to the re sults of the sam ples stud ied from the EllÀs sec tion, the or ganic mat ter as so ci ated with sed i ments of the El Haria For ma tion is well pre served, but im ma ture.
Ta ble 2
Kerogen (trans mit ted light) in sam ples from the EllÀs sec tion, north east ern Tu ni sia
ELLêS SECTION Substage Lthology Formation Samples Kerogen type Spore colour
index S.C.I. Thermal alteration index (TAI) Preservation Maturity Lower Danian Marly limestones El Haria Es 25 II-III yellow 1 1 good Immature Es 22 1+ Clays Es 20 1/1+ ES 18 1 ES 15 1– Es 12 1– Upper Maastrichtian Marly limestones ES 6 1 Es 3 1 Es 1 1/1+
SCI – spore col or ation in dex.
Fig. 7. Pho to mi cro graphs of dinoflagellate cysts from the Cre ta ceous–Palaeogene bound ary sec tion at EllÀs, north east ern Tu ni sia. Scale bar rep re sents 40 µm for all spec i mens. A. Riculacysta amplexa Kirsch, 1991, sam ple Es 1, slide 1, EF D44/1. B. Pterodinium cretaceum Slimani et al., 2008, sam ple Es 7, slide 3, EF N65/4. C. Andalusiella mauthei subsp. punctata (Jain and Millepied, 1973) Masure et al., 1996, sam ple Es 7, slide 3, EF G49/3. D. Cribroperidinium septatum Hultberg, 1985, - sam ple Es 7, slide 3, EF R34/3. E. Trithyrodinium evittii Drugg, 1967, sam ple Es14, slide 2, EF Q29. F. Manumiella seelandica (Lange, 1969) Bujak and Davies, 1983, sam -ple Es 10, slide 2, EF W36. G. Cordosphaeridium fibrospinosum (Hultberg, 1985) Fensome et al., 1993, sam -ple Es 1, slide 6, EF C36/4. H. Phelodinium pentagonale Corradini, 1973, sam ple Es12, slide 3, EF U31/3. I. Damassadinium californicum (Drugg, 1967) Fensome et
al., 1993, sam ple Es 7, slide 3, EF U31/2. J. Deflandrea obliquipes (Deflandre and Cookson, 1955), sam ple Es 1, slide 1, EF C36/4 X40.
Fig. 8. Pho to mi cro graphs of dinoflagellate cysts and palynofacies from the Cre ta ceous–Palaeogene bound ary sec tion at EllÀs, north -east ern Tu ni sia. Scale bar in (A) rep re sents 40 µm for spec i mens (A–C, E), scale bar in (F) rep re sents 200 µm for D, F, G. A. Palaeocystodinium golzowense Al ber ti, 1961 – sam ple Es 7, slide 2, EF H41/2. B. Cerodinium pannaceum (Stan ley, 1965) Lentin and Wil liams, 1987. sam ple Es 7, slide 3, EF X34/4. C. Andalusiella mauthei Riegel, 1974 subsp. punctata Jain and Millepied, 1973, sam ple E1, slide 6, EF Y39. D. Palynofacies as sem blages, abun dance of peridinoid cyst, sam ple Es 15. E. Cerodinium mediterraneum Slimani et al., 2008 – sam ple Es 7, slide 3 EF V46/2. F. Palynofacies as sem blages, sam ple Es 20.G. Abun dance of peridinoid cysts, sam ple Es 14.
CON CLU SIONS
The palynofacies study of the Cre ta ceous–Palaeogene tran si tion de pos its of the El Haria For ma tion at EllÀs, north ern Tu ni sia, re vealed the pres ence of or ganic mat ter, dom i -nated by ma rine palynomorphs, con ti nen tal palynomorphs (sporomorphs) and amor phous or ganic mat ter. The palynomorphs are dom i nated by dinoflagellate cysts, which are di -ver si fied and well pre served. The dinoflagellate cysts allo-wed biostratigraphic, palaeoenvironmental and palaeobio-geo graphic in ter pre ta tions of the K–Pg tran si tion at EllÀs (M’Hamdi et al., 2013a, b, in press; M’Hamdi, 2014).
The dis tri bu tion of the palynofacies is eval u ated on the ba sis of qual i ta tive and quan ti ta tive anal y ses of the dis persed or ganic con stit u ents in the EllÀs sec tion. The palynomorphs are dominanted by dinoflagellate cysts; how ever, sporomorphs are rare. In the AOM Phytoclast Palynomorph ter -nary di a grams of Tyson (1993), the dif fer ent pro por tions of com po nents of this or ganic mat ter in di cate that the palyno-fa cies is dom i nated by palynomorphs with higher pro por tions of 65%. Pro jec tions on the palynofacies di a gram of Ronca-glia and Kuijpers (2006) show that dif fer ent pro por tions of the com po nents of the or ganic mat ter are dom i nated by ma -rine-de rived or ganic mat ter, such as dinoflagellate cysts, acri- tarchs and foraminiferal test lin ings. In terms of palynofacies, this as so ci a tion is char ac ter ised by the dom i nance of ma rine or ganic mat ter, the pro por tion of which var ies be tween 50 and 80%, and palynomorphs are dom i nated by microplank-ton. The palynofacies anal y sis sug gests a re gres sion at the end of the Late Maastrichtian, just be low the K–Pg bound ary, re lated to a global cool ing, and a trans gres sion, re lated to a re turn to rel a tively warm con di tions in the Danian.
The geo chem i cal data from the EllÀs sec tion per mit the char ac teri sa tion of the or ganic mat ter. The kerogen has low TOC con tents (<7 wt.%) and is pre dom i nantly char ac ter ised by ma rine or ganic mat ter and ma rine palynomorphs, preser- ved in a ma rine en vi ron ment. The re sults (low val ues of TOC, S2 and HI) show that the El Haria For ma tion at the EllÀs sec tion con tains kerogens type II and type III. The ma -tu rity in di ca tors (Tmax) in di cate an im ma -ture stage of the or ganic mat ter.
Ac knowl edge ments
The au thors thank the Re search Unit: En vi ron ments Sed i men -tary, Pe tro leum Sys tems and Char ac ter iza tion (UR 11 ES 15) of the Fa culty of Sci ences of Tu nis, Uni ver sity of Tu nis El Manar (Tu ni sia) and the Lab o ra tory Ge ol ogy and Re mote Sens ing Sci en tific In -sti tute, Uni ver sity Mo ham med V-Agdal-Ra bat (Mo rocco) for the preparation of the palynological sam ples. They thank the Joint Co-mmittee Mo rocco-Tu ni sia (Pro ject 88/MT/08) for the fi nan cial sup- port of in tern ships and mis sions in Mo rocco and Tu ni sia. The sec ond au thor ac knowl edges sup port from the Na tional Cen ter of Sci en tific and Tech ni cal Re search (CNRST) (Re search Unit URAC 46) and the Uni ver sity Mo ham med V-Agdal (Pro ject SVT11/09).
The au thors thank the Lab o ra tory of Or ganic Geo chem is try and Or ganic Pe trog ra phy of Tu ni sian Oil Com pany (ETAP) for the geo chem i cal analysis. Two jour nal re view ers, Petr Skupien and an anon y mous one, are kindly thanked for their con struc tive re views and crit i cal com ments that im proved the orig i nal manu script.
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