Short and nasty comments on some aspects of geoarchaeology.

[Jacques Cinq-Mars]

All,

Anyone interested in the sorry state of Palaeolithic/palaeoenvironmental research in northwestern Canada should have a look at the following URL
 

Just looking at the references listed in the article clearly indicates that the Jackson/Wilson's paper is very good example of what one could characterize as a highly selective and self serving geoarchaeological exercise. Among other things, it completely ignores some of the Siberian/Beringian evidence/dates, as well as that from South America, -- Brazil in particlular –- in order to propose so-called evidence in support of a "wet" equivalent –- "a maritime blitz" -- to the dying, classical "Clovis First/blitz" myth.

Very cynically, I am tempted to say that the absence of a "corridor" is primarily intellectual in nature. Papers like this one may be very scientific, but they are certainly not characterized by true interdisciplinarity.

Jacques Cinq-Mars

PS   Thanks to Mikey Brass' Palaeoanthropology list for bringing this up to my (our) attention.

Jacques Cinq-Mars

[Grant Zazula]

I too was very interested to read the "Ice-free corridor revisted" in Geotimes by Jackson and Wilson.

In particular, the points made regarding the northern ice-free corridor (ie Mackenzie Mountains and Mackenzie Valley). There is a substantial amount of radiocarbon and stratigraphic evidence that the Laurentide ice-sheet reached its maximum extent to the front ranges of the Mackenzie mountains by 35,000 - 30,000 years BP - supporting the original hypothesis of A. Duk Rodkin and O. Hughes. This is best supported by the glaciolacustrine chronology in the Old Crow, Bell, and Bluefish Basins. The maximum advance of the Laurentide ice sheet diverted the Peel and Porcupine Rivers, flooding the basins by ca. 35,000 years ago.  A series of short lived lakes occupied the basins until a readvance of the Laurentide ice sheet (Katherine Creek phase) at ca. 21,000 - when the glacial Lake Old Crow reached its maximum elevation. The lake eventually overtopped the western divide at the Ramparts of the Porcupine river at ca. 15,000 with catastrophic drainage.

The revisited chronology mentioned in the paper cannot account for the glaciolacustrine chronology in the Old Crow basin.

So, any discussion of the northern ice-free corridor must account for glacial lake chronology of the Old Crow basin and the glacial chronology of the Mackenzie mountain front. If people did infact utilize this "corridor" it must have been before 35,000 yr BP - during the height of the mid-Wisconsinan interstadial (Marine isotope stage 3) - or after the glacial lake drainage at 15,000 yr BP.

One thing that is rarely considered in the discussion of the "ice-free corridor" is that a corridor did in fact exist during the mid-wisconsinan interstadial, before 35,000 yr BP. A corridor at that time can account for the large body of archaeological literature that indicates pre-LGM human occupation of South America. Thus, the west-coast migration route is not necessary when one considers the mid-wisconsinan "ice-free corridor" through the interior. The coastal migration is only necessary for very conservative estimates of the first entry of people into the Americas (ca. 15-12 ka BP). Any discussion on the corridor also needs to consider the literature on human occupation of the Old Crow region by ca. 40 ka BP (see R.E. Morlan, 2003 Quaternary Research vol. 60, issue 1, Pages 123-132) and Bluefish Caves by 25,000 BP.

[Jacques Cinq-Mars]

I too was very interested to read the "Ice-free corridor revisted" in Geotimes by Jackson and Wilson.

In particular, the points made regarding the northern ice-free corridor (ie Mackenzie Mountains and Mackenzie Valley). There is a substantial amount of radiocarbon and stratigraphic evidence that the Laurentide ice-sheet reached its maximum extent to the front ranges of the Mackenzie mountains by 35,000 - 30,000 years BP - supporting the original hypothesis of A. Duk Rodkin and O. Hughes. This is best supported by the glaciolacustrine chronology in the Old Crow, Bell, and Bluefish Basins. The maximum advance of the Laurentide ice sheet diverted the Peel and Porcupine Rivers, flooding the basins by ca. 35,000 years ago.  A series of short lived lakes occupied the basins until a readvance of the Laurentide ice sheet (Katherine Creek phase) at ca. 21,000 - when the glacial Lake Old Crow reached its maximum elevation. The lake eventually overtopped the western divide at the Ramparts of the Porcupine river at ca. 15,000 with catastrophic drainage.

The revisited chronology mentioned in the paper cannot account for the glaciolacustrine chronology in the Old Crow basin.

So, any discussion of the northern ice-free corridor must account for glacial lake chronology of the Old Crow basin and the glacial chronology of the Mackenzie mountain front. If people did infact utilize this "corridor" it must have been before 35,000 yr BP - during the height of the mid-Wisconsinan interstadial (Marine isotope stage 3) - or after the glacial lake drainage at 15,000 yr BP.

One thing that is rarely considered in the discussion of the "ice-free corridor" is that a corridor did in fact exist during the mid-wisconsinan interstadial, before 35,000 yr BP. A corridor at that time can account for the large body of archaeological literature that indicates pre-LGM human occupation of South America. Thus, the west-coast migration route is not necessary when one considers the mid-wisconsinan "ice-free corridor" through the interior. The coastal migration is only necessary for very conservative estimates of the first entry of people into the Americas (ca. 15-12 ka BP). Any discussion on the corridor also needs to consider the literature on human occupation of the Old Crow region by ca. 40 ka BP (see R.E. Morlan, 2003 Quaternary Research vol. 60, issue 1, Pages 123-132) and Bluefish Caves by 25,000 BP.

Grant,

Thanks for posting this. While I agree with the "early" part of the chronology, I have problems with the dates you bring up for the latter part, i.e., the end of the glaciolacustrine sequence.

A maximum (lake) elevation of these basins dating to 21,000 years ago is, in my view, impossible, and this, for a number of reasons. First, it does not match up with the sequence that Ager and Dixon have come up with for the Alaskan part of the Porcupine Ramparts. Second, we have evidence that the Old Crow basin lower beach lines and offshore bars date to about 21-22,000 years ago. So, the lake was draining out at that time. And for it to do so means that the Porcupine Ramparts had already been carved up, i.e., a long time before 15,000 years ago. Finally, studies carried out on the Bluefish loess indicate that its sources are likely to be from the Bluefish and Old Crow basins. At this time, the earliest dates I can come up with for the Bluefish loess fall around 25,000 years ago. This indicates to me that the sources of the loess (the Crow and Bluefish basins) were in the process of draining out prior to 25,000 ago. So, there is more work to be done!

Finally, I agree with your statement about the pre-Full Glacial "corridor". As a matter of fact, Morlan and I have been saying (and writing) this all along.

Jacques

[Grant Zazula]

Hi Jacques,

The ages for maximum lake levels in the Old Crow, Bluefish and Bell Basins come from radiocarbon dates on the deltaic sequence found at Bluefish Exposure (the site I worked on with Schweger for my M.A. thesis). The site has a deltaic sequence overlain by glaciolacustrine sediments. We have 9 radiocarbon ages that place the sequence between ca. 18.5 and 16.5 ka BP. THis was the first time that the lake reached the southwest edge of Bluefish Basin. Also, Norm Catto's PhD work on upper Rat River has a glaciolacustrine sequence starting at about 21 ka BP - overlying till found in McDougall pass. Thus, the lake reached its maximum elevetation, flooding McDougall pass at that time.

We think that the early part of the lake chronology (ie 35-25ka BP) was characterized by short-lived lakes that repeatedly filled and then drained eastward along meltwater channels. This is suggested sedimentologically in the silt/sand sediments (lacustrine/alluvial...) found underneath the thick glaciolacustrine sediments at Chi'jee's bluff and several Old Crow basin localities. These sediments also have reworked Mississippian palynomorphs (from the Eagle channel) with many 14C dates between 35-25 ka BP. The ice margin in Bonnet Plume basin must have been fluctuating and did not permit the formation of a prolonged deep water lake. Ages from Cadzow bluff of 25 ka BP indicate the major glaciolacustrine phase took place after 25 ka BP - reaching SW Bluefish basin by 18.5 ka and Upper rat River at ca. 21 ka BP. So, the 25,000 year old Bluefish loess probably came from the sediments in the basins during the early, intermittent lake phase. From what I recall, Bernard's ages on the loess at Jackson Rock falls near the Ramparts are around 16-15 ka BP. THorson and Dixon's chronology for the Ramparts in Alaska is not very clear - only that some major catastrophic drainage occured at some time after 26 ka BP.

I agree - there is still much work to be done on the topic.

It still puzzles me why very few people (except you and Morlan) consider a mid-wisconsinan "corridor" for the entry of people into the america.

Grant

[Jacques Cinq-Mars]

Hi Jacques,

The ages for maximum lake levels in the Old Crow, Bluefish and Bell Basins come from radiocarbon dates on the deltaic sequence found at Bluefish Exposure (the site I worked on with Schweger for my M.A. thesis). The site has a deltaic sequence overlain by glaciolacustrine sediments. We have 9 radiocarbon ages that place the sequence between ca. 18.5 and 16.5 ka BP. THis was the first time that the lake reached the southwest edge of Bluefish Basin. Also, Norm Catto's PhD work on upper Rat River has a glaciolacustrine sequence starting at about 21 ka BP - overlying till found in McDougall pass. Thus, the lake reached its maximum elevetation, flooding McDougall pass at that time.

We think that the early part of the lake chronology (ie 35-25ka BP) was characterized by short-lived lakes that repeatedly filled and then drained eastward along meltwater channels. This is suggested sedimentologically in the silt/sand sediments (lacustrine/alluvial...) found underneath the thick glaciolacustrine sediments at Chi'jee's bluff and several Old Crow basin localities. These sediments also have reworked Mississippian palynomorphs (from the Eagle channel) with many 14C dates between 35-25 ka BP. The ice margin in Bonnet Plume basin must have been fluctuating and did not permit the formation of a prolonged deep water lake. Ages from Cadzow bluff of 25 ka BP indicate the major glaciolacustrine phase took place after 25 ka BP - reaching SW Bluefish basin by 18.5 ka and Upper rat River at ca. 21 ka BP. So, the 25,000 year old Bluefish loess probably came from the sediments in the basins during the early, intermittent lake phase. From what I recall, Bernard's ages on the loess at Jackson Rock falls near the Ramparts are around 16-15 ka BP. THorson and Dixon's chronology for the Ramparts in Alaska is not very clear - only that some major catastrophic drainage occured at some time after 26 ka BP.

I agree - there is still much work to be done on the topic.

It still puzzles me why very few people (except you and Morlan) consider a mid-wisconsinan "corridor" for the entry of people into the america.

Grant

Thanks for this nice summary, but I think that too many things don't jive, here.  Perhaps it is because the entire series of Yukon/Porcupine basins (Bell, Bluefish, and Old Crow Flats) has always been studied as a unit, as a fully integrated fluvio/lacustrine network in which "dates" have to be fitted. I have been thinking about this for a long time, now, and I am increasingly convinced that the Old Crow Flats regime could well have been, for a very long time, separate from that of the Porcupine system itself.

It would take a paper to talk about this, but, for the time being, I'll just briefly mention a few things about the Crow Flats "anomalies.

First, there is our age estimate for the lowermost beaches and associated offshore bars that I mentioned earlier: around 21,000 years ago (give or take). The estimate is based on TL determinations.

Now, if one looks, altitudinally, at the entire beach sequence that serves to delineate the Old Crow Glacial Lake, one can see, along segments of the basin, that the highest ones are nearly completely degraded and eroded and that as you go down the slopes to the present level of the basin they get fresher and fresher looking. In this regard,  there is a very good example, along the northern edge of the Flats, of a small fan that is made up, in part, from eroded material from the higher beaches and that is that is "scarred" at its base, by fresh looking beach lines. All this to say that, from a geomorphological point-of-view, the highest beaches have to be much older than the lower ones, and I don't think that this fits well with the age of the high stand you have reconstructed for the Bluefish Basin.

So, the 25,000 year old Bluefish loess probably came from the sediments in the basins during the early, intermittent lake phase.

At the Bluefish Caves, the loess – which is clearly coming from deflating basins to the north (presumably, Bluefish and Old Crow Flats)  -- suggests that there were three shifts in terms of source areas, and this, over a period of about 18,000 years. There are no clear indications of depositional disconformities that would match your chronological scenario.

From what I recall, Bernard's ages on the loess at Jackson Rock falls near the Ramparts are around 16-15 ka BP.

Yes. But much of the loess, there, is derived from the Ramparts shales which would have had to have been exposed at that time.

THorson and Dixon's chronology for the Ramparts in Alaska is not very clear - only that some major catastrophic drainage occured at some time after 26 ka BP.

I don't have the paper in hand, but if I recall, their dates for "catastrophism" are a bit ealier than that. More in the range of 30,000 or older. (And I apologize for confusing Ager with Thorson!).

I agree - there is still much work to be done on the topic.

Yes, and it is fun.

It still puzzles me why very few people (except you and Morlan) consider a mid-wisconsinan "corridor" for the entry of people into the america.

My comments on this will come later.

Jacques