Sedimentary sequences (S1-S8)

Based on the new stratigraphic data mentioned above, eight sedimentary sequences separated by seven sequence boundaries (SBs) are distinguished within the investigated succession. Comparisons between measured sections, enable us to correlate the succession from north to south on the platform and to recognise the major architectural elements.

A comparison between biostratigraphic and lithostratigraphic frames and the sedimentary sequences (S1-S8) is illustrated in figures 3 and 10a, b.

The sedimentary sequences, the positions of the sequence boundaries and the maximum flooding surfaces (mfs) within seven primary sections are illustrated in figures 10a, b and are described in the following.

8.1 Sequence 1 (S1)

The sequence is defined by the base of the Naur Formation and the top of member

‘b’ (Naur Formation) that coincides with SB CeJo1 (sections RM2, MA2, SI1+2; Fig.

10). Sequence 1 contains TST (member a, Naur Formation) and HST deposits (member b, Naur Formation).

In the northern sections (RM2, Fig. 10a), the transgression is marked by marls and marly limestones, with an abundant and diverse fauna derived from open shallow subtidal environments. Decreased thickness and silty/sandy deposits in the southern

Fig. 10a, b: North to south correlation of eight sedimentary sequences (S1-S8, this work).

Also shown are sequence boundaries (dashed lines) and maximum flooding surfaces (dotted lines), based on seven primary sections (locations in figure 1). Datum line coincides with the Cenomanian-Turonian boundary.

See legend in figure 4 for symbols, signatures and abbreviations.

sections (SI1+2, Fig. 10b) exhibit a more proximal position in concordance with siliciclastic input from the continent. The maximum transgression (mfs) is defined at the base of the first massive limestone unit (member b, sections RM2, MA3, SI1+2).

In the entire working area, the overlying HST is characterised by prograding and aggrading limestones and dolostones. Their thickness decreases southwards owing to the proximal/distal shallowing trend. Shallowing-upward cycles (subtidal/intertidal to supratidal) are present within the HST deposits. Their lithologies and facies patterns are very similar in northern, central, and southern sections (sections MA2, SI1+2; Fig.10), and thus exhibit a wide transgression over the shelf and nearly the same environmental conditions (e.g. water depth, relief) within the study area.

8.2 Sequence 2 (S2)

The base of S2 is marked by a sharp contact to overlying marls/shales of member c (Naur Formation), while a (dolomitic) horizon with iron impregnations and vertical burrows on top of member d (Naur Formation) defines the top of S2 and coincides with sequence boundary CeJo2 (e.g. sections RM2, SI1+2; Fig. 10). The sequence contains deposits of a TST and of a HST. The marls/shales of member c include a rich fauna (foraminifers, echinoids, bivalves, and locally ammonites) and represent transgression and deposition in open subtidal environments. This transgressive pulse can be traced over the whole working area (sections RM2, MA2, SI1+2, WB; Fig. 10) and reflects a transgression flooding the continent (compare S1). Several limestone horizons are intercalated in southern sections (SI1+2, WB; Fig. 10), probably owing to their proximal position (shallower water conditions) and an occasionally increased carbonate production. The maximum flooding (mfs) is defined at the transition to the first massive limestones (member d, e.g. sections RM2, MA3, MD1, SI1+2; Fig. 10), aggradation and shallowing-upward cycles are present within these HST deposits in most studied sections. The uppermost part of S2 (‘late’ HST) is locally characterised by sheet-like grown rudist associations, indicating deposition in shallow subtidal to high-energy environments (RM2, Fig. 5; SI1+2, Fig. 8).

8.3 Sequence 3 (S3)

The base of S3 is defined by a sharp transition to ‘post-CeJo2’ deeper water deposits of the lower Fuheis Formation reflecting TST deposits. The top is defined by HST which reflect deposition during a relative sea-level highstand. Similar to S1, shallow-water limestones, and coincides with the sequence boundary CeJo3 (e.g. sections SH, MD1, WB; Fig. 10).

An abrupt sea-level rise is reflected by marls and shales, containing abundant planktic foraminifers and calcareous nannofossils. This transition occurs in the entire working area (sections MA3, MD1, WK2; Fig. 10). The highest amounts of planktic foraminifers within the deeper water succession locally indicate the position of the mfs (section MA3, Fig. 10), but in places (sections MD1, WK2; Fig. 10) the maximum flooding surface coincides with the transition to the overlying shallow subtidal or peritidal limestones (HST). Lithologies and fossil contents of the TST deposits differ in the central study area (MD1, WK2, Fig. 10) compared to those from the north and south. Claystones or bituminous marls and limestones locally contain ammonites in

the central sections, and the total thickness of TST deposits increases in that area.

These differences may reflect a local depression or increased subsidence on the inner shelf. In combination with the middle Cenomanian sea-level rise, a decrease in circulation and oxygen content may have occurred within the ‘basinal’ settings, allowing the increased preservation of organic material at the same time. An increase of the productivity and/or input of clastic material (carbonate ‘dilution’) are different possible explanations for the lithologic differences mentioned above.

Shallow-water limestones (containing abundant oysters, ostracodes) predominate in the upper S3 and exhibit deposition during a HST. In some central and southern sections (WK2, WB, Fig. 10), the HST deposits correspond to the Karak Limestone Member within the lower/middle Fuheis Formation.

8.4 Sequence 4 (S4)

The lithologic transition between S3 and S4 is indicated by marls/claystones. The top is marked by the top of the Hummar Limestone Formation, which also defines the position of sequence boundary CeJo4. In places, the SB coincides with a hardground (iron impregnations, vertical burrows and/or reworked pebbles; e.g. sections SH, WB;

Fig. 10). S4 is composed of TST and HST deposits.

High amounts of planktic foraminifers and calcareous nannofossils within the marls and shales at the base of S4 indicate deeper water conditions and therefore suggest a relative sea-level rise (TST) within all parts of the study area (e.g. sections SH, MA3, MD1; Fig. 10). The maximum flooding can locally be defined at the base of overlying shallow-marine limestones of the Hummar Limestone Formation (e.g.

sections SH, MA3; Fig. 10), while the highest amounts of planktic foraminifers and calcareous nannofossils characterise the mfs primarily in the central sections (e.g.

WK2; Fig. 10). The following HST is again indicated by fossiliferous shallow-water limestones, aggrading from the north towards the south (e.g. sections MA3, MD1, SI1+2; Fig. 10). In some northern sections (SH, Fig. 10), these limestones exhibit cyclic bedding. Distinct thickness changes from north to south can be observed during S3 and S4. A large thickness in the north (section SH, Fig. 10) and in the central working area (section WK2, Fig. 10) contrasts with reduced thickness near Wadi Abu Kusheiba (section MA3; Figs. 1, 10) and in southern sections (SI1+2, WB;

Fig. 10). Synsedimentary movements on the inner shelf may have induced these lateral differences, in addition to the distal/proximal trend towards the continent (see

discussion below). Local elevation in the area north of Wadi Mujib and subsidence in the central parts probably took place during progradation and retrogradation of inner platform deposits in S3 and S4.

8.5 Sequence 5 (S5)

A sharp transition from shallow-water limestones (HST, S4) to marls/shales, defines the base of S5. The top is defined by a hardground (iron crusts), or a dolomite horizon on top of the Wala Limestone Member in the middle/upper Shueib Formation (sections SH, MA3, MD5, WK2, SI1+2, WB; Fig. 10). The top of S5 coincides with SB TuJo1. Sequence 5 comprises transgressive and HST deposits.

A ‘post-CeJo4’ sea-level rise at the base of S5 is exhibited in the entire study area.

Stepwise increasing amounts of planktic foraminifers and calcareous nannofossils indicate a deepening and mark the onset of the platform flooding in most sections (e.g. SH, WK2, WB; Fig. 10). In some places, fully open marine conditions are reflected by limestones, containing ammonites and abundant planktic foraminifers/calcispheres (MA3, SI1+2; Fig. 10). A major transition and complete flooding of the investigated shelf area is evidenced by a nearly simultaneous decrease of carbonate production, deeper water deposits (mentioned above) and a change within the benthic fauna associations in all parts of the study area. Therefore, the maximum flooding surface is in most sections (e.g. sections MA3, SI1+2; Fig. 10) marked by the highest amounts of planktic foraminifers and/or calcareous nannoplankton and a stop in carbonate production. The mfs occurs near the CT-boundary (Fig. 10). A restricted facies occurring in the central sections (WK2, Fig. 10) interfingers with TST deposits (mentioned above) in the north and south. Low oxygen contents and high preservation of organic material are reflected by strongly increased TOC-values and high amounts of ‘opportunistic’ benthic foraminifers.

Slightly decreasing amounts of planktic foraminifers and a local increase of carbonate production (SH, MD5, WB; Fig. 10) characterise the overlying early HST deposits of S5 in all parts of the investigated area. In response to the rapid sea-level rise and the associated destruction of the shallow shelf carbonate factory (mentioned above), no clear aggradation patterns are observed during this lower Turonian HST.

The following late sea-level highstand can also be traced over the whole working area, and is evidenced by bioclastic and/or dolomitic limestones in the north and in some southern sections (e.g. SH, WB; Fig. 10). These limestones interfinger with

ammonite-bearing limestones/claystones (sections e.g. MD5, WK2; Fig. 10).

Phosphate pebbles, fishbones/fishteeth, oyster shells and intraclasts within these HST limestones exhibit local condensation events (section GM, Fig. 1) during late HST sedimentation.

Thicker S5 deposits in sections of Wadi Abu Kusheiba (MA3, Fig. 10) and a reduced thickness in the central area (section WK2, Fig. 10) may reflect (?inverse) movements on the inner shelf (compare to S3, S4). Increased subsidence in the north (MA3) but a slower subsidence (or a stop of it) in the central part might explain the thickness variations.

8.6 Sequence 6 (S6)

Deposits of S6 occur in the north (section SH, Fig. 10) and in the central sections (MA3, WK2) with different lithologic characteristics. The base of S6 in northern sections is marked by massive (dolomitic) limestones and the top is defined by a dolomite horizon that coincides with SB TuJo2 (in places with iron impregnations, section SH, Fig. 10). A clear differentiation between TST and HST deposits is not possible. In the central working area (sections MA3, WK2, Fig. 10), the base of S6 is characterised by the transition from HST limestones of S5 to claystones. The top is marked by a dolomite horizon, locally topped by iron crusts/impregnations (section WK2, Fig. 10) that coincides with SB TuJo2. TST and HST deposits are distinguishable in these central sections.

Thick claystones, shales and marly deposits in the lower S6 of the central working area contain an open marine fauna and exhibit deeper water conditions. These deposits reflect a transgressive phase (TST). The mfs is defined at the base of overlying limestones from shallow subtidal environments (section WK2, Fig. 10).

These limestones are assigned to the HST of S6.

The restriction of S6 deposits to most proximal sections (SH, Fig. 10) and basinal areas (MA3, WK2; Fig. 10) reflects a less intense transgression, which did not reach the southern study area. Furthermore, a persisting/reinforced subsidence of the Wadi Abu Kusheiba and Wadi Al Karak regions may be assumed.

8.7 Sequence 7 (S7)

The base of S7 is marked by shallow subtidal to supratidal deposits of the upper Shueib Formation, while the top of the sequence is defined by limestones/dolomites,

in places topped by a dolomite bed and a hardground/iron crust. This bed coincides with SB TuJo3 (sections SH, MD6, WB; Fig. 10).

In contrast to the other sequences, S7 contains LST, TST, and HST deposits.

Dolomitic shallow-water limestones and dolostones reflect the LST in northern sections (SH, Fig. 10). In central sections (WK2, Fig. 10) and in some southern successions (SI1+2; Fig. 10), the LST is marked by supratidal deposits (claystones, evaporites). Siltstones and sandstones (with intercalated coal layers) replace the evaporites in the southernmost sections (WB, Fig. 10). These differences reflect a general shallowing trend on the platform from north to south. Furthermore, the clastic input mentioned above reaches northward into the area of Wadi Mujib and reflects a wide basinward progradation of coastal environments and deposits and a major sea-level fall.

Rising sea level and recovering of the carbonate platform after drowning (upper Cenomanian – lower Turonian) is evidenced in all parts of the working area by the first marls and marly limestones of the lower Wadi As Sir Limestone Formation (sections SH, MD6, Fig. 10). These deposits contain abundant organisms from open subtidal to intertidal facies realms, while the diversity of some faunal groups is reduced in comparison to associations (e.g. benthic foraminifers) of Cenomanian platform sequences. Nevertheless, carbonate producing biota occur frequently within transgressive sediments of S7. These sediments furthermore exhibit cyclic bedding in many sections (e.g. MD6, Fig. 10). Thick aggrading limestone/dolostone successions of the TST locally contain oolithic shoal deposits or rudist patch reefs (high-energy environments) (e.g. section MD6, Fig. 10). A mfs is only defined in places, either on top of the shoal/patch reef succession mentioned above (sections SH, MD6; Fig. 10) or at the transition of marls to massive limestones (section WB, Fig. 10). The following sea-level highstand is evidenced by deposits from peritidal facies belts (gastropod horizons, microbial lamination) in all parts of the investigated area.

8.8 Sequence 8 (S8)

The base of S8 is defined by marls or marly limestones of the upper Wadi As Sir Limestone Formation, while the top coincides with the top of that formation. TST and HST deposits occur within sequence 8.

Marls and marly limestones mark a ‘post-TuJo3’ relative sea-level rise (TST) during lower S8, while limestones and dolostones from peritidal environments and a decreasing diversity of included benthic micro- and macrofauna reflect a shallowing trend during the following HST. A clear definition of a mfs is not possible, but both systems tracts can be traced over the whole study area (sections SH, MD6, WB; Fig.

10).