Bartonian reticulate Nummulites of Kutch

Figures & data

Table 1. Reticulate species of Nummulites reported from India.

Species	Age	Proloculus diameter in A forms (μm)	Surface features
N. fichteli^a	Oligocene	290–370	Reticulate; surface smooth
N. clypeus^a		250–360	Reticulate; apical mamelon (polar plug)
N. hormoensis^b	Middle Eocene	400	Sinuous septal filaments in A forms but crude reticulate structure reported in B forms; coarse, spirally arranged granules;
N. cf fichteli^c	Oligocene	600–800	Reticulate; surface smooth
N. fabianii forma fabinii^d	Late Eocene	220–500	Reticulate; no pustules
N. fabinii forma primitiva^d	Middle Eocene	400–700	Primitive reticulation; no pustules, sometimes small polar pillars
N. fichteli forma fichteli^d	Oligocene	400–750	Reticulate; no pustules or polar plug
N. fichteli forma clypeus^d		350–800	Reticulate; raised polar plug
N. fichteli forma granulata^d		400–600	Reticulate; small pustules near polar region; no polar plug
N. sp cf. N. ptukhiani^d	Uppermost Middle Eocene	200–500	Primitive reticulations at periphery; small granules, pillars in polar region

^a Nuttall, 1925.

^b Samanta et al., 1990.

^c Sengupta, 2000.

^d Shukla, 2008.

Figure 1. Locations of samples on the geological map of the study area (A), and the lithologs of the borehole (B) and outcrop sections (C).

Figure 2. Schematic section of Nummulites to illustrate biometric measurements carried out in this study: P1, vertical proloculus height; P2, horizontal proloculus height; WD, distance from centre of proloculus to edge of deuteroloculus; W1, W2, W3, successive whorl radii; LL, HL, length and height of the chamber in last whorl; D, Diameter (schematic drawing of Nummulites after Drooger, Marks, & Papp, 1971).

Table 2. Statistical summary of the morphometric parameters of the reticulate Nummulites, Type-1, Type-2 and N. acutus from the Bartonian section of Kutch.

	Sample		P1	P2	WD	W1	W2	W3	W4	D	T	D/T	CW1	CW2	CW3	LI	HI	LL	HL	M	LI/HI	LL/HL
TYPE-1	J/3/1 21.20 (n = 6)	Mean	336	403	371	695	973	1250	1533	2690	1430	1.9	8.3	15	21	168	84	199	185	111	2.1	1.1
		Min	363	359	288	588	919	1179	1454	2211	1150	1.8	8	15	21	127	63	143	135	96	2.9	1.0
		Max	363	434	446	773	1023	1347	1609	3468	1890	1.9	9	15	21	191	105	227	210	133	2.9	1.1
		SD	26	29	57	63	44	52	78	460	264	.0	.5	.5	.6	22	18	30	29	13	.6	.0
	Outcrop (n = 2)	Mean	319	417	312	596	893	1123	–	2195	1200	1.8	8	15	21	177	92	230	181	115	1.9	1.3
TYPE-2	J/3/1- 21.55 (n = 12)	Mean	482	594	450	799	1098	1328	–	2787	1711	1.6	8	13	19	238	92	252	171	111	2.6	1.5
		Min	388	505	318	679	937	1135	–	2114	1365	1.8	9	14	18	147	66	164	111	90	1.7	1.2
		Max	619	752	555	964	1371	1648	–	3812	2353	1.8	9	14	21	357	123	374	236	138	3.8	1.7
		SD	75	64	78	103	142	170	–	416	260	.1	.6	.8	1.1	67	20	66	44	16	.7	.2
	J/3/1- 31.88 (n = 8)	Mean	489	611	415	716	1001	1234	–	2775	1715	1.6	8	13	18	281	129	245	162	99	2.2	1.5
		Min	405	465	331	646	870	1081	–	3616	1381	1.5	7	10	19	154	108	207	103	75	1.3	1.2
		Max	573	699	529	821	1107	1340	–	3616	2310	1.7	9	14	19	405	159	319	204	133	2.8	2.1
		SD	54	83	68	61	90	103	–	514	336	.1	.8	1.2	1.3	78	18	37	31	21	.5	.3
N. acutus	BR-17 (n = 13)	Mean	–	625	–	–	–	–	–	3625	2325	1.6	–	–	–	358	317	458	329	160	1.1	1.4
		Min	–	550	–	–	–	–	–	2880	1720	1.3	–	–	–	300	280	390	300	140	1.0	1.1
		Max	–	690	–	–	–	–	–	4320	3280	2.0	–	–	–	480	350	540	390	180	1.5	1.8
		SD	–	45	–	–	–	–	–	439	453	.2	–	–	–	44	22	41	25	12	.1	.2

Figure 3. Bivariate plots of diameter and thickness of the three species of Nummulites. The tests of Type-1 and Type-2 samples fall in the field of inflate lenticular tests and N. acutus are inflate lenticular to sub-globular.

Figure 4. Bivariate plots of length and height of chambers in last whorl of the three species of Nummulites. All the samples have longer than high chambers.

Figure 5. Cluster analysis of the biometric data of Type-1 and Type-2 Nummulites. Except for one mismatch (B10), the specimen of Type-1 and Type-2 are distinctly clustered at high similarity coefficients.

Figure 6. Cluster analysis of biometric data of Type-1, Type-2 and N. acutus. The phenogram shows that Type-1, Type-2 and N. acutus are closely clustered at high similarity coefficient, some of the specimen of N. acutus are however clustered with Type-1 and some with Type-2.

Figure 7. Spiral diagram of the three species. It shows tighter coiling in Type-1 compared with Type-2. Coiling of N. acutus falls between the two types. The sample from Tanzania (TDP 4; Cotton et al., 2016) falls in the broader field Type-2.

Figure 8. Cluster analysis of Type-2 and Tanzania samples suggesting close similarities of most specimens from the two regions.

Table 3. Comparison of morphometric data of Type-1 reticulate species of Kutch with N. hormoensis. The data of N. hormoensis are after Roveda (1970).

Characters	Type-1	N. hormoensis
Diameter (mm)	1.8–3.5	3.0 – 4.45
Thickness (mm)	.9–1.9	1.0 – 1.60
D/T	1.7–1.9	2.4 – 3.7
Diameter of proloculus (μm)	312–521	132 – 185
Number of whorls	3–4	6
Shape of chambers in last whorl (expressed as length/height ratio of chambers for Type-1)	1.0–1.4	Sub quadrate or slightly longer than higher

Figure 9. A binary tree model of N. acutus, N. ptukhiani and N. aff. hormoensis discriminating the three taxa on the basis of height of chambers in the first whorl (HI) and diameter of the protoconch (P2).

Plate 1. Photomicrographs of N. aff. hormoensis (external view: A, B, C; side view: E; equatorial section: D, F, G; axial section: I) and N. ptukhiani (external view: H). Scale bar: 1000 μm. A, B, D, E, I: borehole 21.20 m;; F,G: borehole 21.55 m; H: borehole 31.88 m depth; C: outcrop sample.

Plate 2. Photomicrographs of N. ptukhiani (external view: A; equatorial section: C, D; axial section: B, D) and N. acutus (external view: E; equatorial section: F, H; axial section: G). Scale bar: 1000 μm. A, B, C: borehole 21.55 m; D, E, F, G, H: outcrop.

Nuttall, W. L. F. (1925). Indian reticulate Nummulites. Annals and Magazine of Natural History, Ser 9, 9, 661–667.

 Google Scholar

Samanta, B. K., Bondhopadhaya, K. P., & Lahiri, A. (1990). The occurrence of Nummulites Lamarck (Foraminiferida) in the Middle Eocene Harudi formation and Fulra Limestone of Kutch. Bulletin of Geological Mineralogical and Metallurgical Society of India, 55, 1–66.

 Google Scholar

Sengupta, S. (2000). Problems of classifying Early Oligocene reticulate Nummulites (Foraminiferida) from southwestern Kutch, Gujarat. Journal of the Geological Society of India, 56, 673–677.

 Web of Science ®Google Scholar

Shukla, S. (2008). Atlas of taxonomic and bio-chronostratigraphic studies on Paleogene larger benthic foraminifera from Indian sedimentary basins. In Paleontographica Indica (Vol. 9, 183 pp). Dehradun: KDMIPE, ONGC.

 Google Scholar

Drooger, C. W., Marks, P., & Papp, A. (1971). Small radiate Nummulites of northwestern Europe. Utrecht Micropalaeontological Bulletin, 5, 1–137.

 Google Scholar

Cotton, L. J., Pearson, P. N., & Renema, W. (2016). A new Eocene lineage of reticulate Nummulites (Foraminifera) from Kilwa district, Tanzania; a place for Nummulites ptukhiani? Journal of Systematic Palaeontology, 14, 569–579. doi:10.1080/14772019.2015.1079562

 Web of Science ®Google Scholar

Roveda, V. (1970). Revision of the Nummulites (Foraminiferida) of the N. fabianii-fichteli group. Revista Italiana di Paleontologia, 76, 235–324.

 Google Scholar