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Jurassic Forum » JURASSIC references & paper reviews » Jurassic around the world » Tchoumatchenco et al. (2008) (Did Glaciation Occur during the Toarcian?)
Tchoumatchenco et al. (2008)
mhornДата: Tuesday, 25.11.2008, 22:28 | Сообщение # 1
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Tchoumatchenco P., Philippe M., Yaneva M. (2008) Did Glaciation Occur during the Toarcian (Early Jurassic) in the East Stara Planina Mts. (East Bulgaria)? // Comptes rendus de l’Acade'mie bulgare des Sciences. Vol. 61. No.10. P.1301-1308.

Pdf: http://www.proceedings.bas.bg/PDF/08_10-10.pdf

The Lower Jurassic rocks in Eastern Stara Planina Mts. are of two types: shelf and basin. The shelf sediments are limestones, sedimentary allochtonous, redeposited in the basin as olistolites and/or conglomerates; the basin sediments are relatively deeper marine water (tectonically allochtonous), represented by siliciclastic flsch alternation - Sinivir Formation (Middle Norian - Lower Toarcian (p.p.) and by relatively thick bedded sandstones - Balaban Formation (Toarcian, p.p.); the last ones are of two types: proximal - in the southern exposures - sandstones intercalated by predominantly calcareous conglomerates (Debelets Member of the Balaban Formation), and distal - in the northern exposures - only sandstones (Balaban Formation - senso stricto). In the distal facies wood fragments have been discovered, determined as Xenoxylon phyllocladoides Gothan, marker for a cold and/or humid climate. The conglomerates in the Debelets Member are of two types - clasts supported and matrix supported. The matrix supported conglomerates are non-sorted and are interpreted as connected with the activity of local glaciers, which probably occupied the summits of the relatively high uplifted Zlatarski Exotix Range, formed at 370N - to cc. 200 km to south from the present day exposures. The Xenoxylon phyllocladoides Gothan probably inhabited their piedmonts. The clasts supported conglomerates are relatively well sorted, probably a result of mass debris ows.


Middle Jurassic - Lower Cretaceous ammonites & aptychi
 
mhornДата: Tuesday, 25.11.2008, 22:57 | Сообщение # 2
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Comment:
Hypothesis proposed by Tchoumachenko & his co-authors is interesting but contradicts with other climate indicators or supports dating bias
So, in the Siberia Toarcian indicates by occurrence of warm water species and strict fades of the dropstones and glendonites, which are very characteristics for the uppermost Pliensbachian. If dating of Balaban Fm is at least partially incorrect (it based upon age of the underlying and overlying strata only, but usually known age of formation showed its MAXIMAL range which could change through the different sections), these records could be suggested as possible traces of the Pliensbachian, not Toarcian glaciation. From the other hand, authors have not strong evidences for paleoclimate, conglomerates described by them have not typical moraine features and fossil wood record a) possibly indicate humid climate and/or b) could drifted from the other place


Middle Jurassic - Lower Cretaceous ammonites & aptychi
 
Jurassic Forum » JURASSIC references & paper reviews » Jurassic around the world » Tchoumatchenco et al. (2008) (Did Glaciation Occur during the Toarcian?)
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