What would be some geologically-based reasons for boulder samples from the morai

Question

What would be some geologically-based reasons for boulder samples from the moraine giving results which are (a) younger than and (b) older than the true age of the moraine?

Scaling scheme
for spallation: Desilets and others
(2003,2006) Dunai
(2001) Lifton and others
(2005) Time-dependent
Lal (1991)/Stone (2000) Sample name Exposure age
(yr) External
uncertainty (yr) Exposure age
(yr) External
uncertainty (yr) Exposure age
(yr) External
uncertainty (yr) Exposure age
(yr) External
uncertainty (yr) CG-06 59848 7866 60227 7887 57690 6563 57277 5800 CG-02 15273 2128 15439 2144 14977 1846 14375 1611 CG-04 14737 1898 14901 1912 14467 1608 13883 1369 CG-03 53991 7720 54212 7727 51731 6568 51825 6009 CG-05 14123 1960 14282 1976 13871 1701 13292 1481 CG-01 59553 8602 59797 8610 57048 7333 57033 6709

Explanation / Answer

During the last two decades, cosmogenic exposure dating of moraines has vastly improved knowledge for the timing of glaciation all over the world. Because of many geologic complications, like moraine degradation, snow cover, bedrock erosion and isotopic inheritance, samples from multiple large boulders (>1– 2 m) may lead to the accurate moraine age.

The 10Be ages could be found of the moraines and they could reveal that collections of moraine surface pebbles and boulders can yield indistinguishable 10Be ages.

The morphology of the much younger moraine could indicates that it has not significantly degraded since deposition and vice versa. Approximately there was a period of glacier recession during the time between 1400 to 2200 yrs. Therefore the moraines of these ages are young comparatively. Its a similar extent to the advance during the Last Glacial Maximum.

According to the giving information below for exposure age or depositional age of moraines the sequence from youngest to oldest is:

For CG-06, CG-02, CG-04, CG-03, CG-05, CG-01:  

Time-dependent Lal (1991)/Stone (2000) is the youngest then comes Lifton and others (2005) then Desilets and others (2003,2006) and at last Dunai (2001).

We can say that Dunai (2001) is the oldest and Time-dependent Lal (1991)/Stone (2000) is the youngest.

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