The evolution of fluvial patterns through pre-vegetated Earth is a complex and fascinating topic. Before the evolution of plants, there were no roots to bind the soil together, so rivers were able to erode more easily and create a variety of different fluvial patterns. One of the most common fluvial patterns in pre-vegetated Earth was the braided river. Braided rivers are characterized by a wide, shallow channel with multiple branches that frequently split and rejoin. This type of river pattern is formed when there is a lot of sediment in the water, which makes it difficult for the river to maintain a single, stable channel. Another common fluvial pattern in pre-vegetated Earth was the meandering river. Meandering rivers are characterized by a sinuous channel that twists and turns as it flows across the landscape. This type of river pattern is formed when there is a balance between the amount of sediment in the water and the amount of energy that the river has to erode the landscape. As plants evolved, they began to bind the soil together, which made it more difficult for rivers to erode. This led to a change in fluvial patterns, with braided rivers becoming less common and meandering rivers becoming more common. Today, braided rivers are still found in some areas, such as where there is a lot of sediment in the water or where the climate is very dry. However, meandering rivers are the most common type of fluvial pattern on Earth. Here is a table summarizing the different fluvial patterns that can be found in pre-vegetated Earth: Fluvial Pattern Description Braided river Wide, shallow channel with multiple branches that frequently split and rejoin. Meandering river Sinuous channel that twists and turns as it flows across the landscape. Anabranching river Channel with multiple branches that flow in parallel for a significant distance before rejoining. Anastomosing river Channel with multiple branches that repeatedly split and rejoin, forming a network of interconnected channels. The evolution of fluvial patterns through pre-vegetated Earth is a fascinating example of how the Earth's surface is shaped by the dynamic interplay of water, sediment, and vegetation. The evolution of fluvial patterns through pre-vegetated Earth is a complex and fascinating topic. Before the advent of vegetation, fluvial systems were much more dynamic and unpredictable. There were no roots to anchor the banks of rivers and streams, so they were constantly shifting and changing course. This led to the formation of a variety of fluvial landforms, including braided rivers, meandering rivers, and anastomosing rivers. Braided rivers are characterized by a complex network of channels that are constantly splitting and rejoining. This type of river is typically found in areas with high sediment loads, such as in the arid southwestern United States. Meandering rivers are characterized by a single, sinuous channel that winds its way through the landscape. This type of river

1. Presented by
Soumyadeep Dey
Exam Roll- BGEO226011
UG-III,Geological Sciences
Jadavpur University
EVOLUTION OF FLUVIAL PATTERNS
THROUGH PREVEGETATED EARTH

2.  OUTLINE
Introduction (a quick review)
Fluvial Controlling Factors
Case Study of Fluvial Deposits
Fluvial Depositional Systems Throughout
Precambrian
Precambrian River System : Case Study- I
(Kuujjua Formation)
Precambrian River System : Case Study- II
(Waterberg Group)
 Precambrian River System : Case Study- III
(Sonia Formation)
Conclusion
References
Acknowledgment

3.  INTRODUCTION
Figure 1 :- Classification of Fluvial
Channels(after Galloway & Hobday,1996)
River Channel can be classified according to
hydrogeology, grain size of bed load material, ratio
of bed load to suspension load or channel patterns.
According to channel patterns river are commonly
classified as---

4.  FLUVIAL CONTROLLING FACTORS
• Gradient or slope are steep in braided river.
• Vegetation cover enhances bank stability and helps binding
sediments.
• More supply of mud and rise in suspension load with fall in
bed load tend to meandering pattern from braided one.
• Depth and width of channel control the surface run-off and
also the net discharge.
• More chemical weathering produces smaller particles of
sediments- from boulders to sands to finer silt and clays.

5. Figure 2&3 :-Relationship between channel
styles and valley slope and discharge
FLUVIAL CONTROLLING FACTORS

6. FLUVIAL CONTROLLING FACTORS
Precambrian
The higher gradient & steeper slope-Braided River
Lack of proper vegetation- Braided River
Coarse sediment deposited- Braided River
High bed load & bank stability-Braided River
Smaller width and depth-Braided River
Dominance of weathering-Braided River

7.  Fluvial Depositional Systems
Throughout Precambrian
 The Moodies Group of the Barberton greenstone
belt (ca. 3.0 Ga), Kaapvaal proto-craton in
southern Africa
• Matrix-supported conglomerates deposited by
sediment gravity-flow processes.
• Clast-supported stream flow Conglomerates.
• Trough cross-bedded sandstones displaying
unimodal paleocurrent patterns.
 Witwatersrand Supergroup 3.0– 2.7 Ga,
Kaapvaal proto-craton in southern Africa
• Lower thick epeiric sea deposits (West Rand and
Mozaan Groups).
• Upper Central Rand Group is dominated by
sandy and conglomeratic braid plain deposits.
 Rivieradal sandstones of Neoproterozoic in
eastern North Greenland.
• Fining- and thickening-upward cycles of muddy
fluvial sediments.
• Combination of mixed-load, braided channels and
stable banks and floodplains, which formed under
a humid paleoclimatex subject to limited seasonal
fluctuations.

8.  PRECAMBRIAN RIVER SYSTEM: CASE STUDY I
Figure- 4:- Braidplain depositional model for the Neoproterozoic Kuujjua
Formation, Victoria Island, Northwest Territories, Canada. Components of
the palaeogeographic model include: 1, large channel forms with
macroforms; 2, large, two-dimensional simple dunes; 3, three-dimensional
dunes deposited in chute channels; 4, flood-basin playa lakes.
In the Proterozoic, after the widespread
appearance of large cratons, and with the
possibility of Precambrian supercontinents
continental interiors probably were occupied by
very large, perennial braided systems. An
example from the Canadian shield, the
Neoproterozoic Kuujjua Formation, developed
on a braidplain greater than 150 km wide.
Components of the typical vertical profile
include: a, macroform deposits (compound
cross-bedding); b, simple planar cross-bedding;
c, simple trough cross-bedding; d, fine-grained
lithofacies. Modified after Rainbird (1992).
 Kuujjua Formation

9.  PRECAMBRIAN RIVER SYSTEM: CASE STUDY II
 Waterberg Group
Figure 5:- Waterberg Group (Callaghan et
al. (1991) and Eriksson et al. (2006))
• The Waterberg group of South Africa is a clastic
sedimentary succession in the northern part of
the Kaapvaal craton, is generally thought to
have been deposited during late Proterozoic.
• The Mogalakwena Formation comprises
cyclically interbedded sheets of medium- to
coarse-grained sandstone or granulestone, and
matrix supported, largely massive conglomerate
sheets. These cycles generally fine upwards, and
are equated with architectural element CHS.
• Common trough cross-bedding with a consistent
unimodal palaeocurrent trend characterizes the
predominant sandstone granulestone sheets. A
general braided fluvial model is inferred for
these deposits, and for those of the Blouberg and
Wilgerivier Formations.
Mogalakwena Formation

10.  PRECAMBRIAN RIVER SYSTEM: CASE STUDY III
 Sonia Formation
The Marwar Supergroup(703+-40 Ma) of NW India is one of
the largest Neoproterozoic sedimentary successions of India.
Figure 7:-Stratigraphy of Jodhpur Group From Marwar basin, Rajasthan
(Sarkar, S., Bose, P.K., Samanta, P., Sengupta, P., Eriksson, P.G., 2008)
Figure 6 :-Location of Marwar and
adjoining basins of western India
(redrawn after Chauhan, 1999).

11. Figure 8:-Lateral thickness variation of the three divisions of
the fluvial interval at the base of the Sonia Sandstone(Sarkar,
S., Bose, P.K., Samanta, P., Sengupta, P., Eriksson, P.G., 2008)
• Abundance of aeolian products in them,
being substantial in the middle, restricted in
the lower and subordinate in the upper
division.
• The Sandy Lateral Accretion element
dominates over Downsream Accretion
elements. in the lower and the upper
divisions of the fluvial interval of the
Sonia Formation, while not a single
example of the former was encountered in
the middle division.
• The Laminated Sand Sheet element is
present in all three divisions, but in the
form of levee facies, is developed only
marginally in the lower division and
profusely in the upper division, while
being completely absent in the middle.
• The river system was apparently
ephemeral in the middle, perennial in
the upper and probably semi-perennial
in the lower division.

12.  CONCLUSION
o The Precambrian rivers, in general, possibly had comparatively shorter width and
depth, lacked the binding, baffling and trapping of sediment by vegetation roots,
and as a result, flashy surface runoff, lower bank stability, broad channels with
abundant bedload, and faster rates of channel migration would have been
common, compared to younger vegetated area gives rise to a braided fluvial systems
that most likely for pre-vegetational environments.
o The interpretation of fluvial style in preserved deposits of all ages is
problematic, braided systems appear to have been preponderant in the
Precambrian. Semi-perennial fluvial systems formed under relatively humid
palaeo-climatic conditions may reflect a style unique to pre-vegetational
times.
o On river plains river gradient was, in general, steeper during the
Precambrian period than what it was in post-Cambrian times.

13.  REFERENCES
• Ethridge, F.G., Schumm, S.A., 1978. Reconstructing Palaeochannel morphologic and flow characteristics:
methodology, limitations and assessment. In: Miall, A.D. (Ed.), Fluvial Sedimentology. Can. Soc. Petrol. Geol. Mem.
vol. 5, Calgary, pp. 703–721.
• Holbrook, J.M., 2001. Origin, genetic interrelationships, and stratigraphy over them continuum of fluvial channel-
form bounding surfaces: an illustration from middle Cretaceous strata, southeastern Colorado. Sed. Geol. 124,
202–246
• Leclair, S.F., Bridge, J.S., Wang, F., 1997. Preservation of cross strata due to migration of subaquaous dunes over
aggrading and non-aggrading beds: comparison of experimental data with theory. Sedimentology 46, 189–200.
• Leeder, M.R., 1973. Fluviatile fining upward cycles and the magnitude of the palaeochannels. Geol. Mag. 110,
265–276.
• Leeder, M.R., 1978. A quantitative stratigraphic model for alluvium, with special reference to channel deposit
density and interconnectedness. In: Miall, A.D. (Ed.), Fluvial Sedimentology. Can. Soc. Petrol. Geol., Calgary, Mem.
vol. 5, pp. 587–596.
• Leopold, L.B., Miller, J.P., 1956. Ephemeral streams: hydraulic factors and their relation to drainage. Net. Prof.
Pap. USGS 282-A, p. 38

14.  ACKNOWLEDGEMENT
I express my sincere thanks to my supervisor Dr. Soumik Mukhopadhyay
whose guidance and supervision helped me throughout the course and
enabled me to complete my work successfully. I am grateful to the
department of Geological Sciences Jadavpur University for providing me
his platform. I am also thankful to all those who helped me directly or
indirectly in completion of this research seminar 2022.