succession of west central Jordan - stratigraphy and crises
MFT 15 MFT 11
6.2 Environments of deposition
Based on microfacies investigations eight environments of deposition that belong to three major facies belts are subdivided (Figs. 5, 6).
6.2.1. Peritidal facies belt
Peritidal facies belts are, after e.g. Pratt et al. (1992) and Wright and Burchette (1996), situated above the normal high-tide level or between normal low-tide and high-tide levels. Intertidal and supratidal environments of deposition are included and are influenced by semidiurnal submergence and emersion (intertidal). Moreover, they are often affected by spring tides or storm events (supratidal). Stress conditions, like
Fig. 4 (opposite page): Thin section photographs, exemplarily showing characteristic component distributions and textures of microfacies type 9 to 15, defined in this study. The definition follows the carbonate classification and the models of Dunham (1962), Folk (1962), Wilson (1975), and Flügel (1982). Abbreviations: ms= mudstone, ws= wackestone, ps=
packstone, gs= grainstone;scale bar is in each photograph equivalent to 100µm
MFT 9: packstone (ps) with rudist fragments; diverse biogene components (e.g. algae, foraminifers, bivalves; mostly well-or sub- rounded), peloids, and coated grains are associated, sparitic cements prevail, moderate winnowing; arrows indicate rudist fragments;
Silla, section SI1 (Fig. 1, lower Cenomanian, Naur Formation)
MFT 10: ws/ps with algal debris; undefined bioclasts, filaments, and planktic foraminifers are associated, micritic matrix; Kuthrubba, section KB1 (Fig. 1, lower Cenomanian, Naur Formation)
MFT 11: packstone (ps)/grainstone (gs) with large shell fragments; bivalves prevail, gastropods, ostracodes, and extraclasts may be associated, often poor sorting, low to intensive winnowing, sparitic cements prevail; Wadi Al Karak, section GM1 (Fig. 1, middle Turonian, Shueib Formation)
MFT 12: ps with ooids (mostly superficial); coated grains, peloids, intraclasts, extraclasts, and ostracodes are associated, moderate to intensive winnowing, sparitic cements prevail, (a) quartz grains (subrounded, rounded), arrows indicate ooids; Wadi Abu Kusheiba, section KU2 (Fig. 1, Turonian, Shueib Formation)
MFT 13: gs with ooids; normal ooids may be associated with coated grains, intraclasts, and bioclasts, sparitic cement, micritic matrix is absent, components are mostly well sorted; Wadi Mujib, section MD6 (Fig. 1, Turonian, Wadi As Sir Formation)
MFT 14: ms with organic material; organic material, phosphate and planktic foraminifers are often enriched in thin laminae; Wadi Al Karak, section WK2 (Fig. 1, upper Cenomanian, Shueib Formation)
MFT 15: ms/ws with planktic foraminifers; calcispheres, and ammonite tests may be associated, planktic foraminifers consists of globular forms, only, (a) Hedbergella spp., (b) Heterohelix spp., micritic matrix (clouds of organic or phosphatic material occasionally occur within); Salhub, section SH1 (Fig. 1, upper Cenomanian, Shueib Formation)
8, 9, 10, 11, 12 transitionzone open marine
(2), 1514 restricted/dysoxic Facies beltsdeep subtidalshallowsubtidalperitidal
Environment ofdeposition
Componentsandtextures
skeletal
Bathymetricalprofile + MFT
planktic foraminifers calcispheres
opportunistic benth. f.
DasycladaceaRhodophytaalgal crusts/laminae miliolidslarger alveolinid foram.larger agglutinated for. 13 high-energetic
3,4,121,2,3 intertidalsupratidal
4,5 restricted/protected
rudistsgastropods 6,7,8 openmarine
textures non-skeletal
lamination intraclasts peloids
winnowing coated grainsoncoids
quarz grains
fenestral fabric ooidsphosphatic material
frequent Abundance of components (semiquantitative):Energy regime/oxygen content:
commonfewlow energy/dysoxic
high energy+E -E/-O2 -E/-O2-E+E+E
Fig. 5: Semi-quantitative abundance (absent to frequent) and distribution of skeletal and non-skeletal components, and limestone textures within the eight environments of deposition (I – VIII) are illustrated. The environments are assigned to three facies belts on the inner shelf (peritidal to deep subtidal; top column). The bathymetrical profile below, shows occurrences of the 15 microfacies types (see Figs. 3, 4, 6), topographic differences on the inner shelf and characterising facies conditions (water energy and oxygen contents) for some environments.
Different types of dolomitization occur, while euhedral and zoned rhombi (alternating cloudy and clear) of uniform size predominate (Fig. 3, MFT 2). The rhombi show a random distribution within the micritic matrix, or they are enriched in clouds (bioturbation?) or in single horizons. Rarely, dolomite neomorphisms substitute parts of matrix, cements or components.
deviant salinity, lower oxygen contents, persistent reworking or occasionally high sedimentation rates (storms, input from the continent) are reflected by e.g. algal crusts or laminae, gastropods, ostracodes, peloids, quartz grains, and fenestrate fabrics. These components and textures characterise the first four microfacies types (MFT 1-4; Figs. 5, 6) and point to deposition in e.g. tidal flats or ‘ponds’.
6.2.2 Shallow subtidal facies belt
The shallow subtidal facies belt includes four environments of deposition, and various microfacies types occur (MFT 4-13, Figs. 5, 6).
Restricted or protected shallow subtidalenvironments of deposition are characterised by mudstones/wackestones which contain an ostracode assemblages of low diversity, benthic foraminifers or gastropods. The foraminifer associations are often predominated by miliolid forms (MFTs 4, 5; Figs. 5, 6). Thus, environments with unfavourable life conditions for many benthic organisms are indicated and a fluctuating salinity and/or decreased oxygen content can be assumed. Bioclasts (e.g.
of larger benthic foraminifers, echinoids), of nearby open subtidal environments co-occur. They are often damaged and rounded. Furthermore, bioclasts often occur as coated grains (micritisation).
Open marine shallow subtidal environments are characterised by microfacies types that include abundant and highly diverse faunal associations of calcareous green algae and benthic foraminifers, e.g. associated with rudists, corals, gastropods and planktic foraminifers (MFTs 6-8, Figs. 5, 6). The high faunal diversities and intensive bioturbation reflect well-lit water and normal salinities and oxygen contents within the water column, at the sediment surface and within the upper sediment. A frequently observed peloidic matrix and abundant intraclasts additionally mark moderate water energy.
A transition zone is evidenced by higher-energy indicators, like e.g. abundant larger agglutinated foraminifers, red algae, rudists, few intraclasts or ooids and winnowing textures (MFT 8-12, Figs. 5, 6).
High-energetic shallow subtidal environments, like shoals or ‘patch reefs’, are indicated by wave agitated, ‘winnowed’ deposits that contain e.g. ooids, bioclasts (oysters, rudist fragments, gastropods) or intraclasts (MFT 13, Figs. 5, 6).
6.2.3 Deep subtidal facies belt
Deep subtidal facies belts include restricted and open marine deeper water environments.
A restricted deep subtidal area of deposition with occasionally dysoxic conditions is characterised by thin lamination and enriched phosphatic and organic material. Either abundant calcispheres / planktic foraminifers or assemblages of small opportunistic benthic foraminifers (e.g. buliminids, MFT 14; Figs. 5, 6) may additionally occur.
Open marine deep subtidal environments are indicated by high amounts of well preserved planktic foraminifers, calcispheres or ammonites (MFT 15, Figs. 5, 6).
Phosphate grains or phosphatic fish remains may also occur. Dolostones that exhibit a lack of components and textures may also be assigned to this facies belt (Fig. 5).
6.2.4 Comparison with Sinai / Egypt
A comparison of microfacies types and depositional environments of this study with the facies models of the adjacent shelf area of Sinai (Bauer et al., 2003; Fig. 6), exhibits many analogies, but also some differences. Bauer et al. (2003) divide the upper Cenomanian to Turonian inner shelf of Sinai into a deep water facies belt, a subtidal facies belt and the siliciclastic shoreface, while the subtidal is again splitted into high-energy, open shallow and restricted (lagoonal) environments. This subdivision mainly corresponds with the described environments of this study (Figs.
5, 6). However, the siliciclastic shoreface as the most proximal facies belt is after Bauer et al. (2003) indicated by high-energetic deposits, rich in quartz, ooids, and bioclasts (MFT S1, S2; Fig. 6). The present facies scheme does not contain such a quartz-dominated environment. Instead, the present scheme includes supratidal and intertidal environments, like tidal flats or ‘ponds’ that are indicated by MFTs 1-3, Figs.
5, 6). On the other hand, deeper water environments characterised by a microfacies type of deep subtidal, restricted / dysoxic environments (MFT 14; Figs. 5, 6) are described herein and have no equivalents within the scheme of Bauer et al. (2003).
Resulting differences in platform organisation are discussed later.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
deep
subtidal shallow subtidal peritidal
basin continent MicrofaciesType
ps/gs+bivalves(+gastropods, extraclasts) ws/ps+ algal debris (planktic f.) dolomitems+algae laminae(+ostracods) ms+fenestral fabric
ws/ps+calcareous algae(+planktic foraminifers) ws/ps+benthic foraminifers(high diverse assemblages) ps+rudists (+algal debris,planktic foraminifers) ws/ps+larger alveolinid foraminifers (+calcareous algae)
gs+ooids/intraclasts/bioclasts ws/ps+gastropods(+peloids, fecal pellets/koprolithes)ms/ws+low diverse benthic foram.(+echinoids/ostracods)
ps+ooids/intraclasts/peloids/oncoids
ms/ws+planktic foraminifers, calcipheres laminated ms (phosphate,oppor-tunistic f./planktic foraminifers) Environment ofdeposition Faciesbelt
MFT
-E/-O2-E
-E -E/-O2
open marine high-energetic transition zone restricted /lagoon),protected intertidal supratidal
openmarine
restr. / dysox. siliciclasticshoreface
deepwater high-energy
subtidal shallow
subtidal lagoon
B1 W4 W3 W2 W1 P5 P4 P3 P2 P1 L3 L2 L1 S2 S1 West Central Jordan(this study) Sinai/Egypt(Baueretal.,2003)
Legend
restr. / dysox.S2 microfacies types orfacies belts / environmentswhich occur only in one scheme eight environments ofdeposition (this study) highenergy
lowenergy
lowoxygencontent
-Fig. 6: Microfacies types (MFTs) and facies belts of Jordan (left column) and Sinai / Egypt (right column) are compared, while the MFTs of this study are briefly characterised. The block diagram in between illustrates a reconstruction of all mentioned facies belts on the shelf (compare environments of deposition I - VIII, Fig. 5). Differences between both models are indicated in grey, congruent data are marked in black. For explanation of abbreviations see legend.