Increased growth disturbances in Early Triassic bivalves

1. Increased growth disturbances in Early
Triassic bivalves
Jia Yan1,*, Haijun Song1
1. State Key Laboratory of Biogeology and Environmental Geology,
School of Earth Sciences, China University of Geosciences, Wuhan,
China
* jiayan.cug@qq.com

2. Increased growth disturbances in Early Triassic bivalves
Introduction
01
02
03
04
Methods
Results&Discussion
Conclusion&Plans

3. Introduction: PTME environmental fluctuations
Figure 1. Long-term environmental variations
from the Late Cambrian through the Pliocene
（Cui et al., 2015）
PTME
Sea level 87Sr/86Sr
Event：
the eruption of the Siberian
large igneous province
Environmental fluctuations:
destabilisation of the carbon cycle
global warming
ocean anoxia
acidification
weathering
(Song et al., 2016; Wang et al., 2020; Joachimski et
al., 2012; Sun et al, 2012; Wu et al., 2021; Payne et
al., 2004; Tong et al., 2007; Clarkson et al., 2015)
δ34S δ13C δ18O Genera

4. Introduction: PTME environmental fluctuations
Event：
the eruption of the Siberian
large igneous province
Environmental fluctuations:
destabilisation of the carbon cycle
global warming
ocean anoxia
acidification
weathering
(Song et al., 2016; Wang et al., 2020; Joachimski et
al., 2012; Sun et al, 2012; Wu et al., 2021; Payne et
al., 2004; Tong et al., 2007; Clarkson et al., 2015)
Scale: Ma--Million years
How does the environment
changes during the
organism life history?

5. Introduction: Periodic lines in shells
Bivalve shell records the environmental changes
during their own life history.
Growth line sequences Mean mechanisms
Daily/Tidal Tidal/Light cycle
Fortnightly Distance between the moon and the Earth
Annual Temperature change
Table 1. Periodic growth patterns of bivalve shells.
(Clark, 1974; Schöne&Surge, 2013; Goodwin et al., 2001; Moss et al, 2021)

6. Introduction: Daily&Fortnightly cycle
For example: the bivalve shell can record daily
environmental change and the fortnightly cycle.
(Goodwin et al., 2001)
The variation of daily increment widths
is associated with fortnightly tidal cycle.
Half fortnightly cycle
Figure 2. Daily growth increments of Chione cortezi
daily increment

7. Methods: Disturbance lines in shells
Growth interuption —— The abnormal environmental
conditions such as storms, temperature changes,
predations would interupt the shell growth.
Disturbance lines —— Environmental disturbance can
cause the shell to stop growing, and when the environment
returns to normal, the shell can resume growing or attempt
to repair the mark left behind.
Bivalve shells also can record the aperiodic disturbance of
the environment.

8. For example: the bivalve disturbance lines casued by El Nino
Figure 3. El Nino break of bivalve Chione
subrugosa shells
( D: shell radial ornamentation are disocated,
E: the covex of shell abnormally changed)
(Rollin, 1987)
Figure 3. Inconsistent Sr/Na&δ18O change
Mainly environmental change caused by
El Nino： elevated sea surface temperatures
Methods: Disturbance lines in shells

9. Identification method ：
1. The disturbance line should be distributed throughout the
shell rather than the highest convex area;
2. Compared with the other shells from the same species, if
the shell growth break occurs in similar position, it is not
disturbance line.
3. When the external growth lines can be observed on the
shell, the growth increment widths would change abruptly
rather than decrease uniformly in advance of the disturbance
lines.
Methods: Recognize the disturbance lines

10. Types of the disturbance lines：
1. the distortion of concentric ornamentation;
2. the dislocation of radial ornamentation;
3. the abnormal convex change of shell surface.
Methods: Recognize the disturbance lines

11. The distortion of concentric ornamentation
Figure 5. Example for Type 1.
(Huang et al, 2014)
Methods: Recognize the disturbance lines

12. The dislocation of radial ornamentation
(Claraia of the Gujiao section, South China)
Figure 6. Example for Type 2.
Methods: Recognize the disturbance lines

13. The abnormal convex change of shell surface
(Hofmann et al, 2014)
Figure 7. Example for Type 3.
Methods: Recognize the disturbance lines

14. Table 2. Permian-Triassic marine bivalve disturbance line dataset
Figures References genus&species geological time collected area
Methods: Dataset
Disturbance lines
We collected the marine bivalve data from the publised Permian-Triassic references.

15. Results
Table 3. Global Marine bivalve growth disturbance analyses
from the Permian to the Triassic
Table 4. Marine bivalve growth disturbance analyses
of South China from the Lower-Middle Triassic

16. Results&Discussion
Proportion
of
disturbed
specimen
0
0.05
0.1
0.15
0.2
0.25
upper Permian middle Permian early Permian Upper Triassic Middle Triassic Lower Triassic
Global data Fossil data of South China
Figure 8. Permian-triassic bivalve disturbance data
from global references VS South China fossils
The propotion of disturbed specimen of global references data are higher
than the South China fossils, however, the trend is almost the same.
The higher propotion of global reference data might be due to the fact
that researchers tend to select larger individuals when making plates.

17. Discussion
Potential reason for increased proportion of disturbed bivalves
in the Early Triassic----- high ocean temperature
In the Early Triassic, the oxygen isotope records indicate that sea water temperature
increased to 35-36℃, on the other side, the living marine bivalve resaerch indicate that
temperature is a better predictor of bivalve shell growth coefficient than food supply.
Figure 10. Linear regression and quantile regression plotted for
minimum and maximum temperature and chlorophyll-a concentration.
(Saulsbury et al., 2019)
Figure 10. The seawater temperature increased to 35-36℃ during
the Early Triassic. (Joachimski et al., 2012)

18. Preliminary conclusion
1. The bivalve shells can record the environmental disruptions during their
own life history as growth disturbance lines .
2. The growth disturbances in bivalve shells include three types: (1) the
distortion of concentric ornamentation, (2) the dislocation of radial
ornamentation, and (3) the abnormal convex change of shell surface.
3. The increased proportion of disturbed bivalves in the Early Triassic,
suggesting that the marine environmental disturbances at interannual level was
relatively frequent during the Early Triassic.

19. Future work
1. We are going to prove the hypothesis about the potential reason for
increased proportion of disturbed bivalves in the Early Triassic by the Marine
environment simulation experiments.
2. Also, we will combine with the machine learning method, it can
automatically judge whether there is disturbance in the bivalve fossil image and
reducing the subjectivity of manual judgment.
3. We will continue to collect the bivalve fossil data of South China from the
Permian to the Triassic.

20. Thanks for watching!