Turbidite sediments

The deep-water turbiditic sediments of the North Helvetic Flysch, which represents the earliest stage of basin development, were deposited during Pria-... 

The first modem publication of Li isotope data from sediments came from Chan et al. (1994a), who reported the isotopic compositions of unaltered turbidites from DSDP Hole 477 and All A, from the Gulf of California. These samples have been reanalyzed (LH Chan, written communication 2003), yielding lighter values. Similarly, Chan and Frey (2003) suggested a range for marine clastic sediments (5 Li = -1 to +5.6) based on new data and re-analysis of samples previously considered to be isotopicaUy heavy. 

Sediments ranging from clay-rich to carbonate-rich from ODP Sites 1039 and 1040, outboard of Costa Rica, had variable isotopic compositions, unrelated to their bulk chemistry (5 Li = +9.5 to +23.3 Chan and Kastner 2000). Turbidites and underlying ash-rich mudstones at ODP Site 808, southwest of Japan, defined a similarly large range in isotopic compositions (5 Li = -1 to +8 You et al. 1995). James et al. (1999) reported 8 Li for variably altered sandy to silty turbidites to hemipelagic muds from ODP Site 1038, off the coast of northern California (-0.5 to +5.6). 

Clastic sediments from oxic environments (loess, turbidites, grey shales) 1 ... 

Since these sediments contain only clay- and silt-sized particles, the graded bedding in these deposits is not as pronounced as in the nearshore turbidites. 

This further emphasizes the importance of sedimentary processes in the development of such fractionated Rb/Sr and Eu/Sr ratios. Second, in the context of the LFB, the Ordovician turbidites have progressively lower Eu/Sr ratios than the feldspathic Cambrian sediments from which they were partly derived. Thus, it also appears that the displacement to higher Eu/Sr is linked to the number of weathering and erosion cycles involved in the formation of particular sedimentary rock suites. In the examples in Figure 20, the reduction in strontium content for the most evolved Ordovician sediments is nearly 10-fold, and this clearly results in an associated increase in Rb/Sr, and hence with time in strontium isotope ratios. 

Profiles of the weight percent organic carbon (%OC) and pollen abundances down two sequences of the f-turbidite from the Madeira Abyssal Plain. Oxidized sediments are those that have been exposed to oxygen after thousands of years of burial. See text for significance of these results. From Cowie et al. (1995). 

As soon as the calcite saturation level is reached, biogeochemical carbonate crystals accumulate, mixed with remains of ostracods sediments prograding towards the lake centre form foresets. Foresets can include turbidite beds a few centimetres thick due to turbid underflow. Calcium carbonate precipitates only when Characeae are present. Along the talus, and with depth, the water cools down increasing calcite dissolution. 

A) Horizontal beds forming a transition from floodplain deposits to a palustro-lacustrine environment and lacustrine limestones. (B) Lacustrine deposits with stromatolitic bioherms (C) Palustrine limestone with abundant root traces. (D) Lacustrine bottom-set sediments enriched in organic matter and showing thin turbiditic layers. (E) Palustrine limestone with a well developed palaeosol at the top. (F) Various types of crushed shell fragments in a lacustrine mud. (G) Lacustrine bioclastic and oolitic sand deposited near a shore. 

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