The general objective of this study was to document a certain succession of sedimentary rocks with respect to the depositional environment and (trace) fossil content. Most of the previous work on this Member did not provide a detailed picture concerning these parameters. So it was my task to figure out which palaeo-environments (e.g. estuary, delta or tidal flat) are recorded by these sandstones and shales. The sexy thing about the Hanneh Member is that it is highly fossiliferous (extraordinarily preserved trace fossils!). Fossils, and in particular trace fossils (they are "in situ" structures), are well suited for environment characterisation since they evidence biological, physical (and chemical) parameters during and after deposition. Furthermore, they are perfect to assess the ecological relationships. The Hanneh Member and the underlying Numayri Member, respectively, is biostratigraphically well fixed with Trilobite body fossils and dated as lowermost Middle Cambrian (or Cambrian Stage 5 in the updated stratigraphic nomenclature). In fact, this is approximately the age of the well known Burgess Shale and Chengjiang Fossil Lagerstätte (this is slightly older though). So, the Hanneh Member documents ecological conditions right on the edge of the Cambrian Radation as well as the Substrate or "Agronomic Revolution".
This is the whole Burj Formation exposed in the upper course of Wadi Umm Jafna. The distinct cliff represents the middle calcareous Numayri Member which is reconstructed as a open marine carbonate-ramp system succeeding into an intertidal to supratidal sabkha-like environment. The purple shales below are interpreted as restricted to marginal marine system that documents the initial marine transgression upon a fluvial braid plain. The green slope at the upper part is the Hanneh Member which is suggested to has been laid down in lagoonal, tide-dominated environments. The documentation of these strata is very general (e.g. BENDER 1974, AMIREH et al. 1994, SCHNEIDER et al. 2007), and only two ichnotaxa were described by SEILACHER (1990) from this member. The uppermost strata (Umm Ishrin Formation) represent fluvial sediments. So in general we have a terrestrial-marine-terrestrial succession exposed. In terms of sequence stratigraphy: a typical Transgression-Highstand-Regression profile.
The smooth, greenish slope represents the whole Hanneh Member. Probably the best exposure in Wadi Uhaymir/ Tayan if you want to study it bed by bed. In general, you can see and overall fining upward trend with sandy portions in the lower and shales in the upper part.
Just some shots of the sediments, trace fossils, and some suggestions about the facies and structures.
Me and Dr. Gabriela Mángano studying tidal flat sediments (Zerqa Ma'In Outcrop, Northern Dead Sea).
Typical tidal-channel sediments. Trough cross-bedded sandstones with distinct alternating flow direction. Good evidence for waning flow conditions (typical for tides) are tidal bundles or double mud drapes (dark laminae within the cross bed, Zerqa Ma'In Outcrop, Northern Dead Sea)
The lower Hanneh at Wadi Issal. You see cross beddings representing bar-accretion in subtidal sandbars. In general, a high energy environment below the subtidal/ intertidal boundary where sea bottom is subjected to permanent wave action and currents. "Tree" for scale (1,3 m).
The middle Hanneh at Wadi Qunai. Essentially, both pictures display the same facies, intertidal heterolithics. Rhythmic alternations of shales and sandstones. Plane beds, climbing ripple sequences (the bright level above the hammer) as well as mud drapes indicate strong alternations in current strenghts. However, evidence for emergence (desiccation cracks, flat-topped ripples) lack and an alternative interpretation of these strata would be a slightly subtidal prodelta. As I said above, we are still debating.
A nice specimen of Rosselia, a dwelling burrow of worms (most likely Polychaetes) maintained for deposit feeding and ?suspension feeding. These ones were very crucial in the interpretation in discriminating intertidal from subtidal environments. Such deep, robust burrows are not likely to occur in Cambrian tidal flats. In the lower Palaeozoic, you need stable, marine conditions to host a fauna like this. So the surrounding sediment most likely represents a subtidal prodelta. Wadi Uhaymir.
This seems to be the upper delta front to delta top. I think the story is, that absent vegetation (it's Cambrian !) and arid climatic conditions (during time of deposition) led to an impermanent, dynamic fluvial run-off. Accordingly, the resulting delta body is not very distinct. Wadi Umm Jafna.
The Delta plain (Umm Ishrin Formation). Some sort of sheet flood deposits. Probably the most attractive sandstone I'd ever seen. Wadi Uhaymir.
Superbly preserved arthropod scratches (most likely Trilobites). Some people say they are an ichnospecies of Dimorphichnus. I am still not very happy with the interpretation. Such structures are suggested to represent superficial grazing performed by trilobites. I think they are just current-drifted arthropods trying to get their feet on the ground. Accordingly, most likely Monomorphichnus isp. Wadi Uhaymir.
Wonderfull specimens of Archaeonassa fossulata. Superficial grazings of worms, small arthropods or early gastropods. Wadi Qunai.
500-something million years old arthopod traces.
Massive! Contorted beds referred to as "ball and pillow" structures. Either these are load- structures due to high sedimentation rates on water-saturated stacks of sediment or seismites (seismic shock-induced bedding failure). Wadi Tayan.
A last geology goodie. This is textbook-like unconformity. Lower Cambrian sedimentary rocks superposing Precambrian Volcanites. Wadi Qunai.
Gorgeous Wadi landscape in Wadi Al Hisa.
We didn't investigate this stuff. I suppose these are Cretaceous Limestones and Marls. Very widespread on the Arabian Peninsula. The dark range in the background most likely is Ordovician.
On the way to Petra.
Amireh, B. S., Schneider, W., Abed, M. A., 1994: Evolving fluvial-transitional-marine deposition through the Cambrian sequence of Jordan. Sedimentary Geology, 89, pp. 65 – 90.
Bender, F., 1974: Geology of Jordan. Borntraeger, Berlin.
Schneider W., Amireh B. S., Abed A.M., 2007: Sequence analysis of the Early Paleozoic sedimentary systems of Jordan. Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, 158 (2), pp. 225 – 247.
Seilacher, A., 1990: Chapter 32: Paleozoic trace fossils. in SAID, R., (ed.), The Geology of Egypt. A.A. Balkema, Rotterdam, pp. 649 – 722.