Ancient time data from the (2.9 Ga - 2.8 Ga) Central Rand Group,
Witwatersrand Supergroup, South Africa


The Central Rand Group belongs to the The Witwatersrand Supergroup,
South Africa and its age (below Livingstone Reef) is estimated to be
about 2902 +-13 Ma - 2780+- 3 Ma (ref.3) and age of the whole Cental
Rand Group is estimated from other source to be about ca. 2886 Ma -
2764 +- 5 Ma (ref. 4).

Some ancient time data could be present in the tidalite from the
Central Rand Group (ref. 1, the tidalite Fig 7.5-1d below Livingstone
Reef and
measurements Fig 7.5-2).

My observations about peaks of Laminae Number which I consider could

significant from Fig 7.5-2 (ref. 1):

I see following peaks which could be significant:

(1-3)
5
7
(9-10)
(13-14)-16
18
26
(30-31)
(33-35)
(37-38-39-40)
(43-44)
48- (50-52)
54
61
(63-64)
(67-68)
-------end of Fig 7.5-2-------------

If Laminae Number corresponds Foreset Number (ref. 2, ref. 1) and if
question is semi-diurnal tides (ref.1) (I have understood (ref.2,
ref.1) that two Laminae Numbers corresponds one day due slack water's
mud laminae are very thin (submillimeter scale in general) and hence
not visible in Fig 7.5-2) and if Laminae set is complete then I would
have (from division by 2)

(1-3) ----- (0.5-1.5)
5 ------ 2.5
7 ----- 3.5
(9-10) ----- (4.5-5)
(13-14)-16 ---- (6.5-7)-8
18 ------- 9
26 -------- 13
(30-31) ----- (15-15.5)
(33-35) ---- (16.5-17.5)
(37-38-39-40) ---- (18.5-19-19.5-20)
(43-44) ----- (21.5-22)
48-(50-52) ---- 24- (25-26)
54 ---------- 27
61 ---------- 30.5
(63-64) ---- (31.5-32)
(67-68) ----- (33.5-34)
-----end of Fig 7.5-2------------

(I consider peaks above the peak Laminae Number 30 significant

check figure if I have missed any) and maybe Laminae Number 1 belogs

other synodic month so 0.5 should be subtracted from my

? All peaks ( two week signs (fortnight) and possible week signs and
even sub-week signs exists?) should be interpreted but I don't tryto
do it here.)

My interpretation of this result (I consider only possible time

if all assumptions are correct, especially integrated sedimentation
rate should be checked with accurate age determinations, present
estimation with too inaccurate age determinations is min. 18 m / Ma
(ref. 3):

There could have been (30.5-34) lunar days per synodic month at

Rand (below Livinstone Reef) time about 2902 +-13 Ma - 2780 +- 3 Ma
ago (ref.3) and possible (if only strongest peaks are taken into
account) there could even have been (31.5 - 32) lunar days per
synodic month.

These figures would mean:
about (31.5-35) mean solar days per synodic month or even (32.5-33)
mean solar days per synodic month.

And they also would mean:
about (29.5-33) mean solar days per sideric month and even (30.5-31)
mean solar
days per sideric month.

If Earth's rotation rate has slowed down constant rate (ref. 6 and
ref. 7)

1 + 1.7361*10^ -8 * T

, where T is uniform centuries and past time is - signed, these
figures would mean at time about 2840 Ma ago (if I take age

from my oscillating month formula (ref. 6)

29.53 - 3.53*10^-7 * T* (1 - sin(( 2*Pi*T / 429.4* 10^4)))

for value 33 mean solar days per synodic month, 2840 Ma / 33 and 2845
Ma / 32.5, I choose 2840 Ma corresponding approximately both values

simplicity and due accuracy is possible order +- 50 Ma ?), that

we would have 30.5 mean solar days per sideric month at about 2840 Ma
ago and this would correspond about 15.46 present mean solar days per
sideric month (41.16 R_Earth) and 31 mean solar days per sideric

at about 2840 Ma ago would correspond about 15.71 present mean solar
days (41.60 R_Earth).
There should exist signs of strong ancient tidal currents in the
Witwatersrand Supergroup area, some signs possible exists in (ref. 5)

At time 2902 Ma we would have Earth's rotation period about 11.91
present hours
(ref. 6, ref. 7) And at time 2780 Ma we would have Earth's rotation
period about 12.42 present hours (ref. 6, ref. 7). At time 2840 Ma

would have Earth's rotation period about 12.17 present hours (ref. 6,
ref. 7). I gave these figures due that it would be possible to

at least three of the five essential Earth's tidal parameters and try
to figure out with aid of computer programs of Earth's tides to
figure out this situation. Age 2840 Ma was only used due age
determination of Central Rand Group below Livingstone Reef is not
accurate enough for this purpose.

Best Regards,

Hannu Poropudas
(amateur geologist)
Vesaisentie 9E,
90900 Kiiminki
Finland



References:

1. Eriksson, K. A. and Simpson, E. L., 2004.
Precambrian tidalites: recognition and significance.
In:
Eriksson, P. G., alterman W., Nelson D. R., Mueller W. U.,
Catuneanu O., (Editors), 2004.
The Precambrian Earth: Tempos and Events.
Developments in Precambrian Geology 12.
Elsevier B. V., Printed in The Netherlands.
Pages 631-642, Fig 7.5-1d on page 635, Fig 7.5-2 on page 637.
Article's references are among book's references on pages 771-922.
2. Eriksson, K A., Simpson, E. L., 2000.
Quantifying the oldest tidal record: The 3.2 Ga Moodies Group,
Barberton Greenstone Belt, South Africa.
Geology; September 2000; v.28; no.9; p.831-834; 5 figures.
3. Frimmel, H. E., (2004 in press, publication 2005 ?).
Archaean atmospheric evolution: evidence from Witwatersrand
gold fields, South Africa.
Earth-Science Reviews. 46 pages.
0012-8252/$ - doi:10.1016/j.earscirev.2004.10.003.
Received 6 July 2004, accepted 12 October 2004, 15 Dec 2004 on line.
(My copy is printed 13 January 2005.)
(age of the Central Rand Group below the Livingstone Reef is between:
2902 +- 13 Ma - 2780 +- 3 Ma)
4. Rasmussen, B., 2005.
Radiometric dating of sedimentary rocks: the application of

xenotime geochronology.
Earth-Science Reviews, vol. 68, 2005, 197-243.
(age of the Cental Rand Group is between ca. 2886 Ma (age of the
youngest detrical zircon) - 2764 +- 5 Ma (unequivocal age for any
authigenic mineral in the Central Rand Group))
5. Hargraves, R. B., 1970.
Sedimentologic Evidence of Strong Tidal Currents in the Early
Proterozoic.
Pages 471-478.
(example worth of check from the Witwatersrand System)
In:
Runcorn, S. K. (Editor), 1970.
Paleogeophysics.
Academic Press Inc. (London) Ltd. Printed in Great Britain by
The Whitefriars Press Ltd., London and Tonbridge.
518 pages.
6. Poropudas, H. K. J., 1996.
Harrastelijan ajatuksia p=E4iv=E4n, kuukauden ja vuoden pituudesta
muinaisina aikoina.
Geologi, 4-5 / 1996, sivut 92 - 96. (Finnish text).
7. Allen, C. W., 1973.
Astrophysical Quantities.
3. ed. University of London. The Athlone Press, pp. 18-22 and