succession of west central Jordan - stratigraphy and crises
7. Discussion
7.1 Integrated stratigraphical correlation
The combined application of lithological and biostratigraphical data provides a long-range correlation of the Cenomanian and Turonian platform successions. Five units have been defined by lithological characteristics and by biostratigraphical boundaries, mainly based on ammonites and calcareous nannofossils. The five stratigraphical units have been correlated from north to south across the carbonate platform and the paleoecological features of each unit have been described. The correlation is exemplarily illustrated by six sections (Fig. 18).
Unit 1. Unit 1 contains upper Albian to middle Cenomanian deposits. The lower boundary of Unit 1 is defined by the base of the Naur Formation, the upper boundary is marked by its top (member d).
Biostratigraphy: Unit 1 occurs within the CC 9 Zone, evidenced by E. turriseiffelii.
Locally, ammonite occurrences of Mrhiliceras lapparenti mark an lower Cenomanian age (mantelli-dixoni Zone).
Lithology: Unit 1 can be subdivided into four lithological ‘sub-units’, coinciding with the four members of the Naur Formation. The Wadi Juheira Member is generally dominated by marls, while in the north several limestone intercalations are observed (e.g. section RM2, Fig. 13). Towards the south increasing content of terrigenious clastics occur (e.g. section SI1+2, Fig. 17). Similar lithologies and sedimentary patterns are observed for member b, in all parts of the study area. It is characterised by fossiliferous and dolomitic limestones, exhibiting cyclic shallowing-up patterns
CC 9 CC 10 cNaur
c
b d
d Fuheis Shueib WSL Formation
Biozone*
WadiBustaniWB
Naur
Wadi Abu
KusheibaMA 2
Formation
Biozone* CC 9 CC 10 CC 11
HL Shueib
Fuheis
Wadi Abu KusheibaMA 3
Biozone*
Formation
CC 9 CC 10 CC 11
SalhubSH
Formation Biozone*
Wadi As Sir Shueib
Hummar Fuheis
CC 9 CC 10 CC 11
Formation Shueib HL
NL
Fuheis
Wadi Mujib MD 1
Biozone*
CC 9 CC 10 CC 11
Wadi al KarakGM2
Biozone*
Formation
NL Fuheis HL Shueib
H
CC9 CC10 CC11
CENOMANIAN ALB.
LOWER
U MIDDLE UPPER LOWER MIDDLE UPPER
Shueib Wadi As Sir
Hummar Fuheis
Naur
TURONIAN
dixoni
mantelli rhotomagense jukesbrownei guerangeri geslinianum judii coloradoense nodosoides woollgari
T3T1 T2 T4 T5 T6a T6b T7
U4
Calc. nannof. Bioz.
Substage
Unit Formation Stage
Ammonitebiozonation
Southern Europe
Near East
? SillaSI 1+2
CC 9 CC 11
Naur Fuheis Hummar Shueib
WJ b c d Formation
Biozone*
CC 10
m1 m2
BFA1
BFA4
BFA1
BFA1 BFA1 BFA1BFA1 BFA1 BFA3 BFA4 BFA4
BFA2 BFA2 BFA2 BFA4 BFA4 BFA4
BFA2/3 BFA4 BFA3BFA2/3
BFA2/3 BFA2/3 N. vibrayeanus N. vibrayeanus
BFA3
BFA2 BFA1
BFA1 BFA3 BFA3 BFA5 BFA5
BFA1 BFA2 BFA2 BFA3 BFA4
N. vibrayeanus
OA1
OA1 OA1
OA1 OA2
OA2m3
m1
BFA2 U5
U3U2
U1 65km27km25km61km21kmNS
10m
0m
Schulze-fig. 18 I 1 I 2I 3I 2 I 3 I 4I 1 BFA4
BFA4 Northern Study AreaCentral Study AreaSouthern Study Area
m3
m3
Fig. 18: An integrated stratigraphic north to south correlation, based on six sections is illustrated, including five stratigraphic units (U1-U5), defined by lithological and biostratigraphical characteristics. The biostratigraphic framework bases on ammonite and calcareous nannofossil occurrences. Occurrences of benthic foraminifer assemblages (BFA 1-5), ostracode associations (OA1, 2) and ‘high-fertility intervals’ (I 1-I 4; calcareous nannofossils) additionally provide paleoecological reconstructions; the top column of Figure 19 shows a subdivision into a northern, a central and a southern part of the study area (compare Fig. 1).
(sections RM2, MA2, SI1+2; Figs. 13, 14, 17). The overlying member c is in northern and central sections predominated by marls (RM2, MA2, WK1; Figs. 13, 14, 16), but further south intercalations of nodular limestones or shales, increase (e.g. sections SI1+2, WB; Fig. 18). The uppermost part of Unit 1 (member d) mostly shows the same lithologic characteristics than member b (mentioned above). Moreover, the top of that member is often represented by a hardground (surface with vertical borings) or a dolomitic limestone bed with iron crusts. In some central and southern sections (GM2, WB, Fig, 18) nodular limestones prevail the upper member d and a hardground is not clearly observable.
Paleoecological considerations: The distribution of benthic foraminifer assemblages (BFA, Fig. 18) within Unit 1 exhibit a clear subdivision: BFA 1 exclusively occurs within fossiliferous limestones that mostly belong to the members b and d. The assemblage provides determination of open shallow subtidal to intertidal facies intervals with ‘normal’ oxygen content and well-lit water within the Unit 1-succession. Single associations are dominated by larger, agglutinated forms (Orbitolina spp., Chrysalidina gradata, Pseudolituonella reicheli) and indicate a higher water energy, probably induced by local paleorelief differences, like e.g. shoals or bars on the inner shelf. Moreover, the marly and clayey parts of Unit 1, mainly within the Wadi Juheira Member and member c, predominantly contain a diverse BFA 2 that often occurs together with the ostracode association 1 (OA1, Fig. 18). Both assemblages generally reflect open subtidal conditions and a transgressive trend.
Moreover, the homogenous distribution patterns of foraminifer and ostracode assemblages within Unit 1 exhibit similar paleoecological conditions in all parts of the study area.
Unit 2. This Unit exhibits a middle Cenomanian age. The base of Unit 2 coincides with the top of the Naur Formation, while the top of Unit 2 is defined by the boundary between the CC9 and the CC10 Zone (Fig. 18).
Biostratigraphy: Unit 2 is placed within the CC 9 Zone. Local ammonite occurrences reflect a middle Cenomanian age (rhotomagense Zone).
Lithology: The lowermost part of Unit 2 is generally characterised by softer deposits, overlying the mostly cliffbuilding top of Unit 1. Nevertheless, the lithologies within Unit 2 clearly differ between sections of the study area. In northern and some southern sections (SH, WB; Fig. 18) nodular, massive and marly limestones
predominate. Furthermore, central sections exhibit increased clay content and local occurrences of dark, bituminous marls and limestones (MD1, GM2; Fig. 18), in contrast to the light marls which occur northwards and further south.
Paleoecological considerations: Varying distributions of faunal assemblages underline, additionally to the lithological changes, paleoecological differences within Unit 2. In northern sections, BFA 3 reflects a transgressive phase and deposition in deeper water environments, respectively. Moreover, the faunal assemblages exhibit normal oxygen content within the water column and the sediment surface. In contrast, sections of Wadi Abu Kusheiba (MA2+3, Figs. 1; 18) contain an assemblage of highly diverse agglutinated benthic foraminifers (BFA 2), co-occurring with diverse ostracodes (OA1, Fig. 18). Supplemented by ammonite occurrences (N.
vibrayeanus, Fig. 18) an open deeper subtidal environment can be assumed, while clayey marls and faunal content (mentioned above, BFA 2) seem to imply an increased siliciclastic content. Central sections (MD1, GM2; Fig. 18) contain a mixture of lower diversity BFA 2 and BFA 3 in the lower Unit 2. They reflect a stepwise deepening, while occurrences of BFA 4 above indicate dysoxic conditions in a restricted deeper subtidal environment. Moreover, intervals with high productivity indicators (I 1; MD1, GM2; Fig. 18) co-occur and suggest a combination of high productivity and preservation to be responsible for the high amounts of organic material. Information about the microfauna content within Unit 2 of sections from the south (SI 1+2, WB; Fig. 18) is rare but a relatively low abundance and low diversity nannoflora seem to reflect a shallowing trend towards the coast.
Unit 3. Unit 3 comprises middle to upper Cenomanian deposits. The base of Unit 3 coincides with the CC9/CC10 Zone-boundary and the top is defined by the top of the Hummar Formation (Fig. 18).
Biostratigraphy: Unit 3 contains the CC 10 Zone and the top of the unit coincides with last occurrences of larger alveolinid foraminifers (Praealveolina spp.)
Lithology: A combination of marls/clays and limestones mostly characterises the lower Unit 3, while massive limestones mark the top, but in section MA3 (Wadi Abu Kusheiba, Fig. 1) and in the southern sections (SI1+2, WB; Fig. 18), lithologies are generally predominated by massive (dolomitic) limestones.
Paleoecological considerations: Lower diversity BFA 2 and BFA 3 predominate the lower Unit 3 in northern and central sections (SH1, MD1, GM2; Fig. 18). Therefore,
open subtidal environments and a transgressive trend are assumed. In the central study area, intervals with high fertility indicators (I 2; MD1, GM2; Fig. 18) occur above these deposits and underline the exceptional environmental position of that part of the study area. Moreover, the mentioned lithologies and occurrences of BFA 1 (sections MD1, WB; Fig. 18) indicate a relative shallowing towards the top of Unit 3.
Unit 4. Unit 4 straddles the Cenomanian/Turonian-boundary and exhibits an upper Cenomanian to middle Turonian age. The unit is bordered by the top of the Hummar Formation (basis Unit 4) below the unit and by the base of the Wadi As Sir Formation (top Unit 4) above (Fig. 18).
Biostratigraphy: CC 10 and CC11 occur in Unit 4. Moreover, ammonites of the geslinianum-woollgari biozones occur, while three marker beds are separated (m1-m3).
Lithology: Similar to Unit 2, the lowermost Unit 4 is characterised by soft deposits but overlying lithologies distinctively differ. In Wadi Mujib and north of it, limestones prevail in Unit 4 up to the CT-boundary. In sections south of Wadi Mujib, marls and claystones predominate. Above the CT-boundary, limestones and dolostones still prevail in the north and in most proximal areas (Fig. 18), while marls, claystones and nodular limestones abundantly occur in between. Northern sections yield dolostones in the uppermost Unit 4. Equivalents are evaporites in the centre, and siltstones/sandstones in the south (Fig. 18).
Paleoecological considerations: The transgressive trend within lower Unit 4 is in northern and southern sections (SH, WB; Fig. 18) exhibited by occurrences of BFA 3, while high productivity intervals of calcareous nannofossils indicate deepening in the central study area (I 3; MD1, GM2; Fig. 18). Locally, abundant ammonite occurrences additionally reflect the deeper water conditions in the lower Unit 4 (m1;
MA3, SI1+2; Fig. 18). Sections of Wadi Al Karak and those further south, yield BFA 4 in overlying deposits, and reflect a change from a well oxygenated open marine environment to dysoxic conditions within a restricted deeper water environment. A persisting high sea level is still indicated by benthic ‘platform crisis assemblages’
(BFA 3, BFA 4, OA2; Fig. 18) above the CT-boundary. Sections of Wadi Al Karak (GM2, Fig. 18) additionally yield a fourth nannofossil interval (I4, Fig. 18) that may indicate deeper water and high productivity conditions. Moreover, a relative sea-level
highstand is locally marked by ammonite-bearing limestones (m2 and m3; sections MA3, GM2, SI1+2; Fig. 18).
Unit 5. Unit 5 contains deposits of a middle-upper Turonian age, and both, base and top of the unit coincide with base and top of the Wadi As Sir Formation.
Lithology: The lowermost Unit 5 is in distal areas marked by marly limestones (section SH, Fig. 18) and by the first fully marine deposits (mostly marls) above the supratidal to terrestrial evaporites and sandtones of the central and southern study area (Fig. 18). Platform deposits of Unit 5 above these transgressive lithologies are dominated by limestones and dolostones in the entire study area.
Paleoecological considerations: The nondiverse and often Miliolidae-dominated platform association BFA 5 characterises restricted intertidal to shallow subtidal environments. It occurs in the entire study area and within most parts of Unit 5 (sections SH, WB; Fig. 18), whereby faunal data of the uppermost dolomitic part are generally rare.
7.2 Paleoceanographic interpretations
Spatial and temporal correlations of all mentioned stratigraphic and paleoecological data, exhibit on the one hand major paleoceanographic patterns that are comparable with global schemes but on the other hand also regional and local fluctuations of the carbonate platform development. Two major platform crises are reconstructed for upper Albian to Turonian times in west central Jordan, while both are locally underlined by ‘basinal’ deposition on the inner shelf.
Crisis 1. A first distinct break in platform development is observed in the centre of the study area during middle Cenomanian times (Unit 2, Figs. 18, 19a). Reduced carbonate production, increased clay content and bituminous deposits are the lithological markers for this crisis. Moreover, a clear transition from benthic open shallow platform faunas (BFA 1) and transgression reflecting assemblages (BFA 2, BFA 3), to low diversity stress environment indicators (BFA 4), exhibit a sea-level rise that culminate in a platform flooding and unfavourable life conditions for benthic faunas. The latters are indicated by opportunistic benthic assemblages, characteristic of dysoxic conditions (BFA 4). They co-occur with planktic assemblages (calcareous nannofossils, planktic foraminifers, which mirror times of high production rates (I 1,
Fig. 19a: the photograph shows bituminous marls and limestones of the Fuheis Formation in the central section MD1 (Fig. 1), example for platform crisis 1; the light-coloured upper part of the section includes limestones of the Hummar Formation.
b: The photograph shows bituminous marls of the upper Shueib Formation in the central section GM1 (Fig. 1), example for (dysoxic) ‘basinal’ environments during platform crisis 2.
Fig. 18). Similar transgressive deposits of middle Cenomanian age are e.g. described by Lipson-Benitah et al. (1990), for shelf areas in north Israel. The local occurrences
of these platform crisis markers, imply paleorelief differences. Therefore, we assume a minor transgression during middle Cenomanian times, that transported nutrient-rich water masses towards the coast. That resulted in increased productivity rates, and locally increased preservation of organic material, related to small-scale basinal structures, exhibiting deposition under dysoxic conditions.
Crisis 2. Similar lithological and faunal characteristics that are mentioned for crisis one also occur within the Cenomanian/Turonian-boundary interval (Unit 4, Figs.
18, 19b). In contrast to the first platform crisis, the second one is observable within the entire study area but indications for basinal deposition (BFA 4; I 2-I 4; Fig. 18) occur again only locally. In the Wadi Al Karak area (GM2) and further south (SI1+2, WB), dysoxic, deeper water conditions are reflected during upper Cenomanian times.
Furthermore, dark clays containing BFA 4 probably mark a depression in the area of Wadi Abu Kusheiba (MA3) during lower Turonian times. Therefore, a major transgression during upper Cenomanian-lower Turonian times is assumed and correlated with a eustatic sea-level rise (Haq et al., 1987) and with a regional deepening, referred from adjacent shelf areas (Israel, Sinai; compare Schulze et al., 2003). Furthermore, a shifting of the dysoxic, basinal facies towards the continent and back has been observed.