STROMATOPOROIDS FROM THE MIDDLE DEVONIAN JIWOZHAI REEF OF SOUTH CHINA AND THEIR PALAEOECOLOGICAL IMPLICATION

1. Jiayuan Huang1,2, Kun Liang1, Stephen Kershaw3,4,
Juwan Jeon1,2, Yue Li1,2 and WenKun Qie1,2
Stromatoporoids from the Middle
Devonian Jiwozhai reef of South China and
their palaeoecological implication
3rd Palaeontological Virtual Congress
1Nanjing Institute of Geology and Palaeontology,
Chinese Academy of Sciences, Nanjing, China;
2University of Chinese Academy of Sciences, Beijing, China
3Brunel University, United Kingdom;
4Natural History Museum, London, United Kingdom
December 1st–15th, 2021

2. Introduction
Geological setting
Material and Methods
Results
Discussion
Conclusions

3. 1. Background: Givetian (Middle
Devonian) is diversity peak of
stromatoporoid (37 genera) and reef-
building acme in the South China;
2. Problems: Traditional studies of
stromatoporoids in South China were
poorly illustrated and written in
Chinese and their palaeoecological
implications in reef ecosystems were
not fully investigated;
3. Aims: provide a systematic
treatment and interpret the
palaeoecological habits of
stromatoporoids in Givetian Jiwozhai
reef in Dushan of Guizhou province.
Introduction
Jin and Ju, 1998
The Jiwozhai reef
382Ma

4. Geological setting
The Givetian Jiwozhai reef, which located in the lower part of
Jiwozhai member of Dushan Formation, is dominated by the
stromatoporoid coverstone. Stromatoporoids mainly present as
laminar forms, and are the most significant organisms.

5. Material and Methods
1. 28 quadrats (0.5 m × 0.5 m for each one),
occupying 7 m2 altogether, were chosen from
the vertical outcrop of the reef unit for
quantitative statistics of abundance, diversity
and ecological parameters of reef fauna;
2. 15 to 45 samples per quadrat were randomly
numbered and collected in situ, with detailed
photographs showing sample locations;
3. A total of 517 samples (some samples
contain more than one stromatoporoid) of
different sizes (10 to 150 mm in diameter) were
collected from the Jiwozhai reef, and prepared
into longitudinal and tangential thin sections,
with 773 skeletons of stromatoporoids being
identified in 1740 thin sections.

6. Results: Stromatoporoid composition
11 species
9 genera
Clathrodictyida Stromatoporida Stromatoporellida Syringostromatida
Diversity Abundance

7. Results: Representative stromatoporoids (1)
Gerronostromaria grossum Dong, 1974 Clathrocoilona spissa (Lecompte, 1951)

8. Results: Representative stromatoporoids (2)
Stictostroma saginatum (Lecompte, 1951) (A, B)
Synthetostroma actinostromoides Lecompte, 1951 (C)
Pseudotrupetostroma porosum (Yang and Dong, 1979) (A)
Salairella bücheliensis (Bargatzky, 1881) (B)

9. Results: Representative stromatoporoids (3)
Stachyodes costulata Lecompte, 1952 Stachyodes fasciculata Dong, 1989

10. Results: Spatial distribution of stromatoporoids
Numbers: 1, Gerronostromaria grossum; 2, Clathrocoilona spissa; 3, ?Habrostroma laminosum; 4, Parallelopora sp.; 5,
Pseudotrupetostroma porosum; 6, Salairella bücheliensis; 7, Stachyodes costulata; 8, Sta. fasciculata; 9, Stachyodes sp.;
10, Stictostroma saginatum; and 11, Synthetostroma actinostromoides.

11. Results: Palaeoecology of the stromatoporoid fauna (1)
Laminar growth forms of stromatoporoids are
the most predominant in the Jiwozhai reef.
Dendroid and bulbous growth forms also occur,
but these morphologies are relatively rare.
1. External morphology
Ger: Gerronostromaria grossum; Cla: Clathrocoilona spissa;
Hab: ?Habrostroma laminosum; Par: Parallelopora sp. Pse:
Pseudotrupetostroma porosum; Sal: Salairella bücheliensis;
Stac: Stachyodes costulata; Staf: Stachyodes fasciculata; Sta:
Stachyodes sp.; Sti: Stictostroma saginatum; Syn:
Synthetostroma actinostromoides.

12. Results: Palaeoecology of the stromatoporoid fauna (2)
2. Size
Small sizes of the skeletons dominate the whole
stromatoporoid fauna, 66 % of which present a thin
thickness below 5 mm, including the most common Cla.
spissa and a small portion of Ger. grossum, Sti. saginatum
and laminar Sta. fasciculata. A few stromatoporoids range
mainly from 5 mm to 10 mm in thicknesses, including Ger.
grossum and laminar Sta. fasciculata. Very few
stromatoporoids show large sizes, with Ger. grossum
exceeding 10 mm in thickness, even more than 20 mm.

13. Results: Palaeoecology of the stromatoporoid fauna (3)
High-relief organisms (e.g., solitary rugose corals,
branching and massive tabulate corals, dendroid
stromatoporoids) are the most common substrates
especially for the small thin laminar Cla. spissa. The
relatively large skeletons of Ger. grossum generally show
preference to cover a large area of sediments including
bioclasts and clay-rich micrites after initial settlement. In
addition to encrusting on high-relief organisms, a number of
stromatoporoids, such as Cla. spissa, overgrew different
laminar organisms (e.g., chaetetids, tabulate corals or
laminar stromatoporoids) buried by sediments.
3. Substrate

14. Results: Palaeoecology of the stromatoporoid fauna (4)
4. Growth interruption
Growth interruptions are common in the stromatoporoids,
represented by latilaminae. More than half of latilaminae
are less than 2 mm, 36% of them ranges from 2 to 4 mm,
and the rest of them are over 4 mm in thinkness. The
thickness and numbers of latilaminae are considered to be
evidence that Ger. grossum and Syn. actinostromoides
were exceedingly resilient and recovered quickly after
interruptions (which were most likely caused by sediment
deposition). However, Cla. spissa, Sti. saginatum and
laminar Sta. fasciculata were presumably relatively
vulnerable to the interruption triggered by sedimentation
and could hardly keep overgrowing.

15. Discussion
Reef-building implications of the stromatoporoids
Laminar stromatoporoid fossils are common in
shallow marine environments and presumably
contributed to stabilize soft, muddy substrates.
The interactions between stromatoporoids and
their substrates can be divided into two patterns:
i) ambitopic, growth pattern that expanded on
unconsolidated substrates after initial settlement,
and ii) encrusting, growth on hard substrates
during their entire life without lateral expansion.
Webby and Kershaw, 2015

16. Discussion
Reef-building implications of the stromatoporoids
In the Jiwozhai reef, Cla. spissa, with thickness between 0.5 to 5.0 mm, is the most abundant laminar
stromatoporoids. The initial growth stages of this species commonly encrusted on hard surfaces of high-relief
organisms forming a spherical skeleton. It seems that Cla. spissa rarely sustained itself to grow large or
expand laterally, and could hardly further stabilize the substrates. In contrast, Ger. grossum generally
presents thick and wide skeletons, possibly corresponding to stronger vertically and laterally growth abilities,
which were conducive to preventing sediment winnowing by episodic water currents, thus further stabilizing
substrates. Pse. porosum, Sal. bücheliensis and Syn. actinostromoides are quantitatively less than the
other stromatoporoids, but their laterally extensive and vertically thick skeletons account for their abilities in
covering sediments. Advantages of these laminar stromatoporoids are manifested by sediment stability that
presumably pioneered development of Middle Devonian carbonate platform in South China.
Clathrocoilona spissa
Gerronostromaria grossum Salairella bücheliensis

17. 1. Stromatoporoids from Jiwozhai reef, Dushan, Guizhou, South China documents 11 species belonging to 9
genera. The stromatoporoid assemblage is characterized by diverse syringostromatids, abundant
stromatoporellids and clathrodictyids, and a small number of stromatoporids.
2. The stromatoporoid fauna was dominated by laminar stromatoporoids (Clathrocoilona spissa,
Gerronostromaria grossum, Stictostroma saginatum, Synthetostroma actinostromoides, Pseudotrupetostroma
porosum, Salairella bücheliensis, ?Habrostroma laminosum, Parallelopora sp., Stachyodes fasciculata and Sta.
sp. ), which pioneered the formation of the reef coverstone by stabilizing large bioclasts and micrite sediment.
Dendroid stromatoporoids (Stachyodes costulata and Sta. fasciculata) are also common, but generally present
fragmented skeletons mixed in the matrix. Bulbous forms (Sta. fasciculata) are rare. The variation of
stromatoporoid growth form indicates different growth strategies of stromatoporoid taxa.
3. Compared with morphology, substrate, size and growth interruption, Gerronostromaria grossum is the main
reef-building stromatoporoid in relation to its absolute predominance of growth advantage in stabilizing
sediments. By contrast, Clathrocoilona spissa contributed less in the formation of the Jiwozhai reef. Advantages
of these laminar stromatoporoids are manifested by sediment stability that presumably pioneered development
of Middle Devonian carbonate platform in South China.
Conclusions