Can we conclude that sedimentation rate in a sedimentary basin increases when chemical weathering at the source area intensifies? (Lacustrine black shale)
Dear Mr. Moradi,
the critical parameters to give a general answer to your question is the ratio between weathering intensity (physical+chemical) and vertical displacement (uplift in the provenance area + subsidence in the depocenter). If we ignore the physical part of weathering, the parameter which counts is the ratio between uplift/erosion and chemical weathering which depends upon the climatic conditions and in general increases from the pole to the ecquator.
Erosion and weathering are to different processes which work separately from each other.
Your problem has to be discussed from a more geodynamic point of view.
It is the interplay of geology and geomorphology that is reflected in the rate of uplift and weathering. Geodynamic setting, regional geology and geomorphology are closely linked with each other and necessarily have to play hand in hand to concentrate and preserve a zone of chemical weathering . Modern fold belts still on the rise like the Alpine -Central Asian fold belt or the Andes extending along an active plate margin are less likely to provide good conditions for large regolith deposits in the hinterland, even if these geodynamic settings are located in a morphoclimatic zone most suitable for chemical weathering. In contrast, cratonic crustal sections stable over a long period of time with little vertical displacement and passive margin geodynamic settings are preferred crustal sections for thick regolith deposition and preservation. The interaction of vertical displacement and of chemical weathering are decisive for the accumulation and preservation. During slow uplift, chemical weathering operative in the peneplai¬ned hinterland and on the sedimentary bodies in the foreland are instrumental during decomposition of labile constituents from the parent material and their well-balanced interaction enhance the quality and increase the thickness of the residual clay deposits. With increasing rate of uplift, the trend is reversed. Reducing the slope angle or the paleogradient, or in other words moving from the alluvial-colluvial fan system , through the alluvial-fluvial systems into deltaic and swampy rises the likelihood of delineating clay concentration of economic significance like black shales.
As long as your geodynamic setting is not disclosed to the audience I can give you only this general answer.
Best regards
H.G.Dill
Dear Experts
Thanks for your good explanations and contribution, and also for sharing your knowledge.
The study area is located in Cankara-Corum Basin (Central Turkey). The CCB was formed as a marine foreland depression between the Kırşehir and Sakarya continents in central Anatolia during the closure of Neo-Tethys Ocean in a time interval between the Late Cretaceous and Early Eocene. After the Neo-Tethys closure, the ÇÇB became a large intermontane basin that occupied continental sedimentary environments.
As a result, the alluvial fan and braided and meandering rivers sediments of İncik, Güvendik and Kızılırmak formations were deposited under compressional regime. From the Early Miocene onwards, an intercontinental compression regime was replaced by an extensional tectonic regime, probably due to orogenic collapse, which is supported by fining upward sequences and syn-sedimentary tectonic structures . During Early–Middle Miocene, large lacustrine areas dominated by organic/clastic deposits developed in the study area and Hançili Formation (the studied formation) was deposited as a result of the extensional tectonic regime. With a thickness of 400 m, the Hançili Formation is composed mainly coals and organic-rich shales and claystones reflecting lacustrine and coastal environments.
A younger evaporitic lake formed in Early Pliocene. From Late Pliocene, a tectonic wedge took place along the western rim of the basin under the effect of a NW–SE compression between the North Anatolian Fault (NAF) and the Kırıkkale-Erbaa Fault Zone.
CIA values range from 75 to 85 which are high (moderate to intense chemical weathering). Redox indicators suggest that the depostional environment was OXIC during the deposition of studied black shales which contain more than 10% TOC. The organic matter type is algal and AOM (highly oil-prone). there is NO sign of oxidation of OM under oxic conditions. We deduced that this happened by high sedimentation rate which preserved the OM from oxidation and weathering.
Now, we are looking for sedimentological or geochemical proxies to support our Idea. I wonder if we can relate this to high chemical weatherin rate at the time of the deposition of these black shales.
- Badges
- Science topic
- Similar topics
- Linguistics
- Composition Studies
- Publications