1 The Indication of Mid Miocene Climatic Optimum (MMCO) from Cibulakan Formation,
2 Bogor Basin, Indonesia
3 R. Kapid1), W.D. Santoso1), B. Ikhsan1), M.A. Jambak2), and D.E. Irawan1)*
4 1) Department of Geology, Institut Teknologi Bandung, Indonesia.
5 2) Department of Geology, Trisakti University, Indonesia
6 *Correspondence author: Dasapta Erwin Irawan ([email protected] cc
8 Abstract
9 Nannoplankton analyses have been proven to identify rapid climate shifts in sedimentary records. Here,
10 we took 58 samples from Early Miocene to Late Miocene sediments of Cibulakan Formation (Bogor
11 Basin, Indonesia), to evaluate climatic benchmarks for Middle Miocene Climate Optimum in the tropical
12 region. The Helicosphaera carteri and Umbilicosphaera jafari were counted to identify the salinity signal.
13 We identify seven-biostratigraphy zones of Cibulakan Fm, indicating the change of seawater temperature
14 and salinity. We identify that warmer temperature in Middle Miocene as the effect of MMCO. The
15 temperature increased until Late Miocene triggered by global increasing temperature at Pacific Ocean and
16 widely distributed flow of terrestrial water at North West Java Basin.
17 Keywords: Mid Miocene Climatic Optimum (MMCO), nannoplankton, temperature, salinity, Cibulakan
18 Formation
19
20 Introduction
21 Mid-Miocene Climatic Optimum (MMCO) was a global climatic event during Middle Miocene featuring
22 increasing global temperature (You et al., 2009; Hansen et al., 2003). The CO2 content in the atmosphere
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23 increased with the increasing temperature during MMCO period. The impact of MMCO was widely
24 distributed and associated with 60C of temperature warming in the mid latitude region (Flower and
25 Kennet, 1994). Nannoplankton is very sensitive to temperature change. The number of population
26 increases when the seawater temperature rises from 50C to 80C (Haq, 1973).
27 Information of MMCO in the tropical region (low latitude) is rare, especially in long continuous section
28 of Middle Miocene sediments. This study aims to identify the impact of MMCO in Early - Middle
29 Miocene in Cibulakan Formation using nannoplankton observation.
30 The research area is situated in Cileungsi River, Bogor, as a part of North West Java Basin (Martodjojo,
31 2003) (Figure 1A.). This basin was formed by the collision of the Eurasian Plate with the Indian
32 Australian Plate during Late Cretaceous to Early Eocene (Hamilton 1979; Martodjojo, 2003; Hall,
33 2002; Netherwood, 2000). The trend of regional structures are east - west, parallel to the Java subduction
34 (Martodjojo, 2003).
35 On Early – Late Miocene, Cibulakan Formation was deposited in Bogor Basin in back arc environment
36 (Martodjojo, 2003) (Figure 1B). The formation consists of interbedded of claystone and sandstone, and
37 minor insertion of limestone (Arpandi and Padmosukismo, 1975; Suherman and Syahbuddin, 1986). This
38 formation had a conformity contact with Parigi Formation in the upper part, and unconformity contact
39 with Jatibarang Formation in the lower part (Martodjojo, 2003). Moreover, Cibulakan Formation had a
40 interfingering contact with deep water Jatiluhur Formation (Abdurrokhim, 2016).
41 Transgressive phase took place during Cibulakan Formation deposition. Sea level rose during Early
42 Miocene that drowned the Jatibarang Formation and shifted the environment, from terrestrial and volcanic
43 environment to transitional deposit (Arpandi and Padmosukismo, 1975). At the bottom part,
44 The Cibulakan Formation was deposited in paralic environment and close to active
45 delta progradation (Atkinson et al., 1993). Trangressive phase continued to middle part
46 of Cibulakan Formation and the environment gradually changed from paralic to shallow water with a
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47 significant influx of fresh water into the basin. At the upper part, offshore bar sediments was formed. It
48 contained claystone to bioturbated silty claystone and calcarenite limestone (Abdurrokhim, 2016).
49
50 Figure 1. (A). Structure map of West Java (Modified from Martodjojo, 2003). The research area (red box) is located
51 in the Bogor Through. (B) Schematic cross section of West Java SW – NE (Modified from Netherwood, 2000).
52 Cibulakan Formation infill back-arc basin setting in Bogor Through (red box).
53
54 Materials and Methods
55 Measuring section and samples collecting were performed during fieldwork from the outcrop of
56 Cibulakan Formation exposed in the Cileungsi River, Bogor . We collected 58 samples at a samping
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57 interval of around x m. The sampling was focused on the claystone and limestone layers. The outcrop
58 condition was good to represent the sedimentology dynamic, and to cover the short term of
59 nannoplankton ecological changes. We observed in total of 5 km of outcrop to understand the succession
60 profile (Figure 2).
61 The smear-slides have been prepared from the untreated samples, in order to preserve the original
62 composition (Kapid, 2003). Samples were crushed and the resulted powders were smeared in a glass
63 sample plate. Then, we use Canada Balsam and glass cover for the plate. The analyses have been
64 performed using a polarizing light microscope Nikon Alphashot YS2-H at 1600x magnification. Both
65 qualitative and quantitative studies have been performed. Quantitative methods were completed using
66 Field of View (FOV) Method (Kapid 2003) following taxonomic identification from Perch-Nielsen
67 (1985) and Young (1998). Samples were identified to the species level if possible, then they were grouped
68 according to their stratigraphic range, to create a stratigraphic framework.
69
70 Figure 2. Sampling locations in Cileungsi River (Modified from Effendi et al., 1998). Green color shows Cibulakan
71 Formation area.
72 Results and Discussions
73 Cibulakan Formation in the research area was formed in the offshore environment, as indicated by thick
74 offshore shale deposit and capped by bioclastic limestone. The vertical section shows Cibulakan
75 Formation profile (from bottom to top) that can be divided into three sequences, which is bordered by
76 bioclastic limestone. Sequence I is characterized by 350 meters thickness of claystone, followed by 500
77 interlamination of thin sandstone and claystone, and wackestone to packestone limestone at the top of
78 sequence (Figure 3). Limestone layer contains biota fragments of coral and foraminifera, which indicate a
79 transgressive carbonates at the offshore.
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80
81 Sequence II contains of 1250 m thin layers of claystone and sandstone at the bottom, and closed with
82 3000 m of thick limestone and claystone. The concentration of biota fragments in limestone in Sequence
83 II is more intensive than the one in Sequence I (Figure 4). This change is interpreted as the impact of sea
84 level rise. Sequence III shows layers of claystone and sandstone as the representation of regressive
85 sediment (Figure 5).
86
5
87
88 Figure 3. Sequence I at Cibulakan Formation; (A) Section of Sequence I at Cibulakan Formation in the research
89 area. (B) Claystone at the bottom of Sequence I with Cruziana sp. ichnofossil (location of photograph is bordered
90 by black box at sedimentation profile). (C) Interbedded sandstone and claystone at the middle of Sequence I
91 (location of photograph is bordered by blue box at sedimentation profile). (D). Limestone at the top of Sequence I
92 with coral (CR) and large benthic foraminifera (LBF) fragments (location of photograph is bordered by red box at
93 sedimentation profile).
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94
95 Figure 4. Sequence II at Cibulakan Formation; (A) Section of Sequence II at Cibulakan Formation in the research
96 area. (B) Interbedded sandstone and claystone at the middle of Sequence I (location of photograph is bordered by
97 black box at sedimentation profile). (C). Limestone at the top of Sequence II with intensive encrusting algae (Alg)
98 and large benthic foraminifera (Fr) fragments (location of photograph is bordered by red box at sedimentation
99 profile).
100
101
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102
103 Figure 5. Sequence III at Cibulakan Formation; (A) Section of Sequence III at Cibulakan Formation in the research
104 area. (B) Interbedded sandstone (SS) and claystone (CS) at Sequence III (location of photograph is bordered by red
105 box at sedimentation profile).
106
107 Cibulakan Formation in the research area was deposited during Early – Late Miocene, based on
108 nannoplankton biozones by Martini (1971). We observe many calcareous nannoplankton events. First
109 Appearance Datum (FAD) and Last Appearance Datum (LAD) from nannoplankton fossil can be used to
110 divide biostratigraphy event which correlates with age and stratigraphy succession. Several
111 nannoplankton species which act as index fossils consist of Sphenolithus belemnos, Helicosphaera
112 vederii, Sphenolithus heteromorphus, Discoaster challengeri, Catinaster coalithus, and Discoaster
113 neohamatus (Figure 6).
114 There are seven biostratigraphy zones in Cibulakan Formation (Figure 7):
115 Sphenolithus belemnos zone
116 This zone is bordered by LAD (Last Appearance Datum) of Sphenolithus belemnos, from RBK – 58 to
117 RBK – 45 in claystone layer. Sphenolithus belemnos zone equal with NN-3 (Martini, 1971) and relates
118 with Early Miocene, around 17.95 mya or older (Gradstein et al., 2012).
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119 Sphenolithus belemnos – Helicosphaera vederii zone
120 Partial zone is marked by interval from extinction of Sphenolithus belemnos and FAD (First Appearance
121 Datum) of Helicosphaera vederii. This zone can be observed in RBK – 44 to RBK 42 and equal with NN
122 – 4 (Martini, 1971), border of Early Miocene and Middle Miocene, around 14.91 mya (Gradstein et al.,
123 2012).
124
125
126 Figure 6. Index fossils of biostratigraphy zone; (A) Spenolithus belemnos, (B) Helicosphaera vederii,
127 (C) Spenolithus heteromorphus, (D) Discoaster challengeri, (E) Catinaster coalithus, (F) Discoaster neohamatus.
128
129 Helicosphaera vederii - Sphenolithus heteromorphus zone
130 Concurrent zone is bordered by FAD (First Appearance Datum) of Helicosphaera vederii and extinction
131 of Sphenolithus heteromorphus. This zone is found in RBK – 41 to RBK - 39 which is equal to NN – 5
132 (Martini, 1971), Middle Miocene around 13.53 mya. (Gradstein et al., 2012).
133 Sphenolithus heteromorphus - Discoaster challengeri zone
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134 Partial zone is bordered by extinction of Sphenolithus heteromorphus and FAD (First Appearance Datum)
135 of Discoaster challengeri. This zone can be observed from RBK – 38 to RBK - 23, equal with NN -6
136 (Martini, 1971), Middle Miocene around 13.27 mya. (Gradstein et al., 2012). Moreover LAD (Last
137 Appearance Datum) of Sphenolithus heteromorphus, Discoaster brouweri has the first appearance in this
138 zone.
139 Discoaster challengeri - Catinaster coalithus zone
140 This zone is marked by interval from e FAD (First Appearance Datum) of Discoaster challengeri and
141 FAD (First Appearance Datum) of Catinaster coalithus. This zone is found in RBK – 23 to RBK - 16
142 which is equal with NN – 7 (Martini, 1971), Middle Miocene around 10.89 mya (Gradstein et al., 2012).
143 Catinaster coalithus - Discoaster neohamatus zone
144 This zone is bordered by FAD (First Appearance Datum) of Catinaster coalithus and FAD (First
145 Appearance Datum) of Discoaster neohamatus. This zone can be observed in RBK – 15 to RBK - 13,
146 equal with NN -8 (Martini, 1971), which is the border of Middle Miocene and Late Miocene, around
147 10.55 mya (Gradstein et al., 2012).
148 Discoaster neohamatus zone
149 This zone is marked by FAD (First Appearance Datum) of Discoaster neohamatus and the extinction of
150 Spenolithus moriformis. This zone can be observed from RBK – 12 to RBK – 1, which is equal to NN -9
151 (Martini, 1971), Late Miocene age, younger than 10.55 mya (Gradstein et al., 2012).
152 The total of nannoplankton population rises with the rising of temperature and decreases with the
153 dropping of temperature. Salinity change is observed by comparing the population of Helicosphaera
154 carteri and Umbilicosphaera jafari. Helicosphaera carteri has ellipsoid coccolith, flange end in wings,
155 and two narrow pores in central-area (Figure 8A and 8B). Increasing population of Helicoshapera carteri
156 represents low salinity and brackish environment (Wade and Brown, 2006; Melinte 2004). The similar
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157 result was revealed by Santoso et al. (2014), which analyzed the population of Helicosphaera carteri on
158 Late Miocene – Pliocene Sediments in North East Java Basin, Indonesia. Conversely, the
159 Umblicosphaera jafari represents high salinity environment (>35 ppt) (Wade and Brown, 2006).
160 Umbilicosphaera jafari is marked by small circular species of coccolith, narrow central-area, and wide
161 distal shield with complex suture (Figure 8C and 8D).
162 The total of nannoplankton population rises with the rising temperature and decreases with the dropping
163 temperature. Salinity change is observed by comparing the population of Helicosphaera carteri and
164 Umbilicosphaera jafari. Helicosphaera carteri has ellipsoid coccolith, flange end in wings, and two
165 narrow pores in central-area (Figure 8A and 8B). Increasing population of Helicoshapera carteri
166 represents low salinity and brackish environment (Wade and Brown, 2006; Melinte 2004). The similar
167 result is revealed by Santoso et al. (2014) which analyzed the population of Helicosphaera carteri on Late
168 Miocene – Pliocene Sediments in North East Java Basin, Indonesia. Conversely, the Umblicosphaera
169 jafari represents high salinity environment (>35 ppt) (Wade and Brown, 2006). Umbilicosphaera jafari is
170 marked by small circular species of coccolith, narrow central-area, and wide distal shield with complex
171 suture (Figure 8C and 8D).
172 The fluctuation of sea surface temperature occurred from Early to Late Miocene on Cibulakan Formation.
173 Fluctuation of temperature in cooling phase was observed on Early Miocene, which was also indicated,
174 by the minimum population of nannoplankton. Subsequently, sea surface temperatures became warmer
175 followed by increasing population of nannoplankton. The warm temperature continued until Middle
176 Miocene. Maximum temperature was identified on Late Miocene, which was indicated by the blooming
177 of nannoplankton (Figure 9).
178
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179
180 Figure 7. Biostratigraphy zone of Cibulakan Formation in the Cileungsi River.
181
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182
183 Figure 8. Salinity indicator. A (paralel nicol) and B (cross nicol) Helicosphaera carteri. C (paralel nicol) and D
184 (cross nicol) Umbilicospahera jafari.
185
186 On Early Miocene (NN3 or older zone), the fluctuation of nannoplankton population was observed as the
187 effect of rapid environment change due to temperature fluctuation in Early Miocene. The temperature
188 fluctuation was presumably correlated with active volcanism in North West Java Basin (Clements and
189 Hall, 2007) and global cooling and climatic transition events in Early Miocene (Billups and Scheiderich,
190 2010). Locally at North West Java Basin, new subduction trend was formed at Southern Java, south of
191 North West Java Basin (Hamilton, 1979; Clements and Hall, 2007), which deposited volcanic debris
192 Jatiluhur Formation, and built an interfingering contact with Early Miocene Cibulakan Formation
193 (Abdurrokhim, 2015). Then, the temperature decreased + 20C, which was observed from drilling project
194 site 747, in Indian Ocean. This event was a result of small scale Early Miocene Glaciation, confirmed by
195 the increasing of 18O isotope value in foraminifera by Billup and Schrag (2002). The fluctuation of δ18O
196 value ranged from 1.8 to 2 ‰ (Figure 10).
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197 The population of nannoplankton increased during Middle Miocene period (NN4 – NN7) as the result
198 from MMCO. The global event influenced the population and species diversification of nannoplankton
199 (Haq, 1973). The blooming of nannoplankton in this period also indicates a shallow sea environment and
200 warm seawater (Melinte, 2004). Moreover, the decline of volcanic activity in Middle Miocene (Clements
201 and Hall, 2007) provides a stable environment which triggers more fresh water and carbonate build up.
202 The increasing of nannoplankton abundance fits with δ18O trend by Zachos et al. (2001) (Figure 10). On
203 NN4 – NN7, the peak of nannoplankton abundance is followed by lowest value of global δ18O curve,
204 which ranging from 1.4 to 1.7 ‰. This fact supports the evidence of MMCO to control the rising of
205 temperature.
206 On Late Miocene (NN8 – NN9), the blooming nannoplankton had continued to reach the peak of
207 population. Increasing temperature, around 40C at Pacific Ocean (Lear et al., 2003), triggered the
208 increasing population of nannoplankton. Hence, the impact was warm and shallow marine at North West
209 Java Basin (Clements and Hall, 2007; Pertamina, 1996) that was a suitable environment for
210 nannoplankton growth. This local event can also be observed by the development of Late Miocene
211 Carbonate of Parigi Formation.
212 As the effect of sea surface temperature fluctuation, the change of salinity was detected during deposition
213 of Cibulakan Formation (Figure 11). On the Early Miocene (NN3 or older zone), we found a fluctuation
214 in salinity to indicate unstable environment. Helicosphaera carteri dominated samples, which was taken
215 from the base of Early Miocene layer. The deposition of Cibulakan Formation started in low salinity
216 environment, before the salinity went higher with the increasing of Umbilicosphaera jafari population in
217 the middle part of Early Miocene. Subsequently salinity decreased as sandstone and claystone layers were
218 deposited in the late part of Early Miocene. In that period, we found more Helicosphaera carteri than
219 Umbilicosphaera jafari.
220
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221
222 Figure 9. Variations of paleotemperature changes at Cibulakan Formation using total nannoplankton population.
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223
224 Figure 10. Paleotemperature changes at Cibulakan Formation and δ18O curve. The δ18O curve was cited from
225 Zachos et al. (2001). On NN4 – NN7, paleotemperature was increasing followed by decreasing of δ18O curve.
226
227
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228
229 Figure 11. Variations of salinity changes at Cibulakan Formation using total nannoplankton population.
230 On Middle Miocene (NN4 – NN7), we identified that the MMCO event had formed a stable environment,
231 during deposition of Cibulakan Formation, with the increasing evaporation and high salinity. We found a
232 higher population of Umbilicosphaera jafari than Helicosphaera carteri.
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233 The suitable and stable environment continued to Late Miocene (NN8 – NN9), as the salinity slightly
234 increased with the blooming of Umbilicosphaera jafari. Conversely, the population of Helicosphaera
235 carteri decreased drastically. The same situation was also marked by Wade and Brown (2006).
236
237 Conclusions
238 Nannoplankton population can be used to identify paleoecology changes, where the of blooming
239 nannoplankton in the Cibulakan Formation is related with the global event of MMCO.
240 The biostratigraphy of Cibulakan Formation can be divided into seven zones, namely: Sphenolithus
241 belemnos zone, Sphenolithus belemnos – Helicosphaera vederii zone, Helicosphaera vederii -
242 Sphenolithus heteromorphus zone, Sphenolithus heteromorphus - Discoaster challengeri zone, Discoaster
243 challengeri - Catinaster coalithus zone, Catinaster coalithus - Discoaster neohamatus zone, Discoaster
244 neohamatus zone. The zone indicates the change of water temperature and salinity.
245 Fluctuation of temperatures and environment observed on Early Miocene, which was characterized by
246 fluctuated nannoplankton population. This event was influenced by small-scale Early Miocene glaciation
247 and active tectonic during this period. Population of nannoplankton increased on Middle Miocene as the
248 effect of warm open sea environment during MMCO. Then, the optimum population on Late Miocene
249 drawn the suitable environment triggered by global increasing temperature at Pacific Ocean and widely
250 distribution of fresh water in the North West Java Basin.
251 The change of salinity was also detected in Cibulakan Formation deposition. On the Early Miocene,
252 salinity changed rapidly indicating an unstable environment. On Middle Miocene, stable environment was
253 observed as the effect of increasing temperature, which caused high evaporation. The high salinity
254 continued to Late Miocene to reach maximum value.
255
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256 Acknowledgement
257 The authors thank to Micropaleontology Laboratory, ITB for all the support. We would like to thank you
258 to Pak Paryadi for his hard work to prepare our samples. In addition, thank you to undergraduate student
259 volunteer from Department of Geology ITB and Universitas Trisaksi Jakarta for helping with the
260 fieldwork.
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