Estuarine foraminifera record Holocene stratigraphic changes and Holocene climate changes in ENSO and the North American monsoon: Baffin Bay, Texas

Palaeogeography, Palaeoclimatology, Palaeoecology 404 (2014) 44–56

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Estuarine foraminifera record Holocene stratigraphic changes and Holocene climate changes in ENSO and the North American monsoon: Baffin Bay, Texas Pamela Buzas-Stephens a,⁎, Daniel N. Livsey b, Alexander R. Simms b, Martin A. Buzas c a b c

Department of Geosciences, Midwestern State University, Wichita Falls, TX 76308, USA Earth Science Department, University of California, Santa Barbara, CA 93106, USA Department of Paleobiology, Smithsonian Institution, Washington, DC 20560, USA

a r t i c l e

i n f o

Article history: Received 28 August 2013 Received in revised form 18 March 2014 Accepted 19 March 2014 Available online 31 March 2014 Keywords: Holocene climate change Foraminifera El Niño-Southern Oscillation North American monsoon Baffin Bay, Texas

a b s t r a c t During the last Quaternary sea level fall (120– ka), Baffin Bay was formed by the down-cutting of the Los Olmos, San Fernando, and Petronila Creeks of south Texas. When sea level rose, this incised valley was then filled with mixed siliciclastic/carbonate sediments that record coastal environmental change over the past 10 ky. Previous sedimentological and seismic analysis shows that Baffin Bay contains atypical depositional environments as a result of its semi-arid climate setting and isolation from the Gulf of Mexico. Three prominent stratigraphic surfaces can be recognized within the bay deposits, and are chronostratigraphically constrained using radiocarbon dates. The purpose of the present study is to use foraminifera to create a separate account of change and to determine if foraminiferal data corroborate sedimentological evidence for sea level and climate fluctuations. Foraminifera were sampled at 20 cm intervals from a 14.4 m dated core and from surface and subsurface sediments of five cores along a dip transect. Multiple discriminate analysis was used to compare sections of the core by species proportions, and clearly delineates three different foraminiferal communities: deltaic, open-bay, and hypersaline. Breaks between these communities coincide with two of the surfaces observed in the core, one at about 8.0 ky and the other around 5.5 ky. Rapid sea level rise at the 8.0 ky flooding surface corresponds with a shift from a deltaic to an open-bay foraminiferal assemblage, while faunal change across the 5.5 ky surface is due to the formation of a large barrier island (Padre Island) and the onset of more arid climate conditions. Prior to the isolation of Baffin Bay at 5.5 ky, foraminiferal assemblages do not correspond to climate change records, perhaps because open circulation with the Gulf of Mexico tempered regional climate effects on bay salinity. After 5.5 ky, changes in foraminiferal assemblages correspond to independently derived records of the El Niño-Southern Oscillation and North American monsoon. Foraminiferal analysis supports sedimentological interpretations in that assemblages and sediments track climate change. © 2014 Elsevier B.V. All rights reserved.

1. Introduction 1.1. Bay setting and geological/geographical history Baffin Bay lies on the Texas coast in the northwestern Gulf of Mexico, approximately 55 km south of Corpus Christi, Texas (Fig. 1). The climate is semi-arid, and the area receives 60–80 cm/yr precipitation, with evaporation exceeding rainfall by approximately 60 cm/yr (Behrens, 1966). Strong winds (15–24 km/h) prevail from the southeast for seven months, from February to August (Rusnak,

⁎ Corresponding author at: Department of Geological Sciences, University of Colorado at Boulder, Boulder, CO, 80309, USA. E-mail addresses: [email protected] (P. Buzas-Stephens), [email protected] (D.N. Livsey), [email protected] (A.R. Simms), [email protected] (M.A. Buzas).

http://dx.doi.org/10.1016/j.palaeo.2014.03.031 0031-0182/© 2014 Elsevier B.V. All rights reserved.

1960), and are important in controlling water-level changes in the bay (Dalrymple, 1964). About 5.0 ka, formation of the Padre Island barrier complex isolated the bay from the Gulf of Mexico (Fisk, 1959). Most Texas bays maintain communication with the Gulf, but this combination of isolation and a semi-arid climate results in a unique setting with an essentially permanent state of hypersalinity (Rusnak, 1960). Average salinities range from 40 to 50‰ but can soar to 85‰ in drought conditions (Behrens, 1966) and drop to 2‰ during rainstorms (Gunter, 1945). Baffin Bay is the incised valley of the Petronila, San Fernando and Los Alamos Creeks (Fig. 1) (Fisk, 1959; Behrens, 1963; Simms et al., 2010). The bay was cut from 120 to 20 ka during the Last Glacial Maximum as sea level fell along the Gulf Coast (Simms et al., 2006, 2007) and subsequently infilled with mixed siliciclastic/carbonate sediments that record ~ 10 ky of environmental change (Simms et al., 2010). Since incised valleys are important potential hydrocarbon reservoirs

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45

Fig. 1. Location of Baffin Bay along the Texas Gulf Coast and sample sites of cores within the bay. Modified from Simms et al. (2010).

(Van Wagoner et al., 1990; Zaitlin et al., 1994), much work has been done to study their sedimentary architecture (e.g., Zaitlin et al., 1994; Boyd et al., 2006; Simms et al., 2006). Zaitlin et al. (1994) incorporated earlier studies (Wright, 1980; Rahmani, 1988; Dalrymple et al., 1992; Allen and Posamentier, 1993) to produce a standard incised-valley fill model showing mostly fluvial deposits proximally, a central segment with fluvial deposits topped by central-basin sediments, and a distal segment with basal fluvial deposits overlain by central-basin and then marine sediments (Fig. 2). Simms et al. (2006) expanded the Zaitlin et al. (1994) standard model by proposing two end members, underfilled and over-filled, with respect to the amount of fluvial sediments. Under-filled incised valleys fit the classic model and contain fluvial,

estuarine, and marine sediments. The Trinity, Matagorda, Nueces, and Baffin Bay incised valley systems along the Texas Gulf Coast are examples of under-filled valleys. Over-filled systems contain only fluvial or fluvial/deltaic deposits, hence not fitting the classic model, and the Brazos, Colorado, and Rio Grande incised valleys are examples of such systems on the Texas Coast (Simms et al., 2006) (Fig. 2). Since most publications on Late Quaternary/modern incised-valley systems deal with deposition in wetter climates, Baffin Bay provides an opportunity to model the sedimentary composition of an incised valley filled during arid to semi-arid conditions (Simms et al., 2010). To characterize the facies architecture of the bay, Simms et al. (2010) analyzed high-resolution seismic data and 18 cores, which allowed for

Fig. 2. Incised-valley fill models for two end members. (A) is the under-filled model after Zaitlin et al. (1994), and (B) is the over-filled model (Simms et al., 2006).

46

A

P. Buzas-Stephens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 404 (2014) 44–56

BB08-01

BB06-02

BB07-04

3275-3900

4.8

4870-5580

?

ka f s

SPIT

WORM-TUBE REEF

UPPER BAY

BARRIER ISLAND

HYPERSALINE BAY

OYSTER REEF

OPEN BAY

FLUVIAL

DELTA

10 5.5 ka change

8.0

?

5750-6630

ka

?

?

7590-7970

fs

15

BB08-01

8600-9260 9260-9910

BB06-02

? 0

Padre Island

?

4090-5320

5730-6290 6280-6790 7960-8405 LOWER BAY / WASHOVER

5

2060-3160

?

4580-5440

5320-5880 6410-6910

MUD FLAT

0

3575-3005

3930-4525 4260-4520 4255-4835

?

A’

BB07-11

5

10

20

Depth below sea level (m)

535-905 1560-2315

BB07-01

BB07-04 BB07-01

?

BB07-11

kilometres

Fig. 3. Sedimentary environments in Baffin Bay along a dip profile. Lowermost surface in core BB07-01 is 8.0 ka flooding surface; surface above that is 5.5 ka change (after Simms et al., 2010). See Fig. 6 for detail of BB07-01.

the recognition of two or three major stratigraphic surfaces (Fig. 3). The ages of these surfaces were chronostratigraphically constrained with 14 C dates taken mainly from mollusk shells and also wood and algal mats. The northern hemisphere terrestrial curve was used to calibrate dates, and ages were corrected for 12C/13C and applicable radiocarbon reservoirs. The oldest surface, at about 8.0 ky, is a flooding surface that appears to be related to worldwide sea level rise (Rodriguez et al., 2010; Simms et al., 2010). This climatic event is recorded locally in other Gulf estuaries (Anderson et al., 2008; Milliken et al., 2008; Rodriguez et al., 2008; Simms et al., 2008; Rodriguez et al., 2010; Troiani et al., 2011) as well as on a global basis (Cronin et al., 2007; Hori and Saito, 2007; Hijma and Cohen, 2010), and can be recognized in Baffin Bay by an extensive pronounced seismic reflection (Simms et al., 2010). At about 5.5 ka, a second distinct change occurs in the bay as evident from a change in sedimentary facies. Below the 5.5 ky surface the fill consists of open bay sediments, silts, and very fine sands containing abundant shell fragments. This open bay facies is similar to the modern sediments found in other Texas bays. But above the 5.5 ky surface, the sediments change to those of the semi-arid hypersaline regime still found in Baffin Bay today. Two occurrences served to alter the nature of the facies in the bay 5.5 ka: one was the formation of Padre Island (Fisk, 1959) and the other was an increasingly arid climate (Bryant and Holloway, 1985; Toomey et al., 1993; Nordt et al., 2008). A possible third event at about 4.8 ka, also a flooding surface, is indicated by a marked seismic reflection and a sharp sedimentary contact shown as the flooding of mudflats or erosion of internal spits in some cores (Simms et al., 2010). Baffin Bay has five depositional environments not seen in other incised valleys along the northern Gulf. These unique fill deposits result from the combination of a semi-arid climate and isolation from the Gulf of Mexico and include well-laminated, interbedded siliciclastic and carbonate muds; ooid beaches; sandy-shell internal spits; serpulid reefs; and prograding mudflats in upper tributaries (Simms et al., 2010). Faunal assemblages in the bay are also indicative of dry, hypersaline conditions. Deposits below the 5.5 ky horizon contain a more diverse bivalve assemblage (including Crassostrea virginica, Tetusacanaliculata, and Chionecancellata) characteristic of wetter conditions (Simms et al., 2010), and above the horizon the assemblage changes to one of lower diversity (mainly Anomalocardia cuneimeris and Mulinia lateralis [Breuer, 1957]) as aridity and isolation ensue. The presence of serpulid-worm tube reefs, which tend to form reefs in hypersaline environments, is another distinctive faunal feature (Simms et al., 2010). The nature of the sedimentary environments and fauna of Baffin Bay allowed Simms et al. (2010) to propose the following criteria to recognize incised-valley fills of semi-arid environments in the rock record:

aeolian beds; carbonate and/or evaporite beds; lack of peat/organicrich shoreline deposits; minimal bay-head deltaic deposits; and, most pertinent to the current study, presence of hypersaline faunas. 1.2. Foraminifera of Baffin Bay Past published research on the foraminifera in Baffin Bay, Texas consists of a morphological study of Ammonia parkinsoniana (Colburn and Baskin, 1998) and the micropaleontological analysis of a core representing approximately 4000 years of deposition (Stewart et al., 1994). The morphological paper recognizes A. parkinsoniana as the most common taxon in the surface sediments (top 1 cm), and correlates statistically significant differences in test morphology with changes in salinity. In particular, living individuals collected during a period of higher salinity (50‰) exhibited a larger proloculus and fewer chambers in the first two whorls as compared to those collected during lower salinity (14‰) (Colburn and Baskin, 1998). The qualitative core analysis by Stewart et al. (1994) identifies three predominant biofacies typical of different salinity regimes. Ammonia parkinsoniana is representative of more brackish conditions, miliolids (especially Quinqueloculina spp. and Triloculina spp.) dominate in hypersaline settings, and Elphidium spp. are characteristic of a range of salinities. The bottom portion of their core (4.2–4.9 m) contained mostly Elphidium spp. with very few miliolids, thus indicative of lower salinities, while the top part (upper 4.2 m) showed fluctuations in the three biofacies and hence salinity conditions. Interestingly, no agglutinated foraminifera were found in the core (Stewart et al., 1994), although living agglutinated Ammotium salsum were noted as common (up to 18% of the population) in the upper part of the bay by Pitakpaivan (1988) in her master's thesis. Correlations between foraminiferal assemblages and salinity have been well documented on the Texas coast (e.g., Parker et al., 1953; Phleger, 1956; Wantland, 1969; Poag, 1981; Pitakpaivan, 1988; Williams, 1995; Buzas-Stephens et al., 2003, 2011) and show prevalence of agglutinated taxa such as Ammotium with more fluvially-dominated, brackish conditions, transitioning to an Ammonia–Elphidium assemblage in the bay proper, and then miliolids with more saline/open water conditions. 1.3. Foraminifera and Holocene sea level change Research on the response of foraminifera to Holocene sea level change has been ongoing, with most studies focusing on coastal environments (e.g., Scott and Medioli, 1980; Horton et al., 1999; Leorri and Cearreta, 2004; Alday et al., 2006; Edwards and Horton, 2006; Leorri et al., 2006). In general, most workers find that changes in foraminiferal

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Table 1 Baffin Bay foraminiferal counts, 10 ml, all cores. Baffin Bay foraminiferal counts, 10 ml, core BB07-01 Core depth (cm)

0–2

8–10

22–24

38–40

54–56

70–72

94–96

118–120

142–144

166–168

182–184

Ammonia parkinsoniana Ammonia tepida Elphidium gunteri Elphidium excavatum Elphidium galvestonense Elphidium poeyanum Nonionella atlantica Palmerinella palmerae Rosalina floridana Bolivina striatula Bolivina lowmani Bolivina pulchella Buliminella elegantissima Haynesina germanica Quinqueloculina agglutinans Quinqueloculina seminula Quinqueloculina impressa Quinqueloculina poeyana Quinqueloculina costata Quinqueloculina wiesneri Triloculinella obliquinodus Triloculina sidebottomi Triloculina fitterrei Triloculina sp. Miliolinella subrotunda Unidentified Number counted Fraction counted Relative density/10 ml

214 0 32 53 0 0 0 0 0 0 0 0 0 21 0 24 0 0 0 0 0 3 0 1 0 0 348 0.26 1340

257 0 6 44 3 0 0 0 0 0 0 0 0 2 0 3 0 0 0 0 0 0 0 0 0 0 315 0.2 1575

228 0 30 97 3 0 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 0 366 0.05 7320

202 0 9 33 3 0 0 0 0 0 0 0 0 1 0 67 2 0 0 0 0 0 0 0 0 0 317 0.09 3520

273 0 2 31 5 2 0 0 0 0 0 0 0 0 0 10 0 0 0 0 0 0 0 0 0 0 323 0.03 11,745

172 0 2 121 3 5 0 0 0 0 0 0 0 0 0 15 0 0 0 0 0 1 0 0 0 1 319 0.17 1876

218 0 3 31 0 0 0 0 0 0 0 0 0 0 0 48 9 0 0 0 1 0 0 0 0 1 311 0.03 11,309

153 0 1 88 4 5 0 0 0 0 0 0 0 0 0 44 0 0 0 0 4 0 0 29 0 0 328 0.1 3280

200 1 0 119 13 1 0 0 0 0 0 0 0 0 0 14 0 0 0 0 0 0 0 2 0 0 350 0.02 23,333

31 0 0 202 10 0 0 0 0 0 0 0 0 1 0 55 2 0 0 0 2 0 0 19 0 0 322 0.04 7156

6 0 1 201 8 1 0 0 0 0 0 0 0 0 0 116 0 0 0 0 0 0 0 30 0 0 363 0.05 7260

Core depth (cm)

230–232

254–256

426–428

448–450

472–474

492–494

590–592

614–616

638–640

654–656

672–673

Ammonia parkinsoniana Ammonia tepida Elphidium gunteri Elphidium excavatum Elphidium galvestonense Elphidium poeyanum Haynesina germanica Nonionella atlantica Palmerinella palmerae Rosalina floridana Bolivina striatula Bolivina lowmani Bolivina pulchella Buliminella elegantissima Quinqueloculina agglutinans Quinqueloculina seminula Quinqueloculina impressa Quinqueloculina poeyana Quinqueloculina costata Quinqueloculina wiesneri Triloculinella obliquinodus Triloculina sidebottomi Triloculina fitterrei Triloculina sp. Miliolinella subrotunda Unidentified Number counted Fraction counted Relative density/10 ml

64 0 0 125 10 2 0 0 0 0 0 0 0 0 0 136 2 0 0 0 3 1 0 10 0 0 353 0.1 3530

38 0 0 158 0 15 0 0 0 0 0 0 0 0 0 89 3 1 0 0 14 0 0 29 0 0 347 0.08 4082

57 4 0 164 2 0 43 0 0 0 0 0 0 0 0 66 1 0 0 0 9 3 1 19 0 3 372 0.05 7440

14 0 4 187 8 3 1 0 0 0 0 0 0 0 0 83 0 0 0 0 6 0 2 26 16 2 352 0.08 4400

22 0 0 102 0 0 0 0 0 0 0 0 0 0 0 132 2 0 0 0 13 0 0 43 2 1 317 0.04 9057

25 0 0 40 1 0 0 0 0 0 0 0 0 0 0 30 1 0 0 0 1 0 0 5 0 0 103 1 103

50 0 4 199 3 25 0 0 0 0 0 0 0 0 0 3 0 0 0 0 1 0 0 13 0 0 298 0.5 596

15 0 1 3 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 23 1 23

11 0 4 8 1 2 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 2 0 0 30 0.25 120

59 0 5 47 27 5 0 0 0 0 0 0 0 0 0 16 0 1 0 0 0 0 0 8 0 0 168 0.5 336

56 1 2 1 1 0 0 0 0 0 0 0 0 0 0 15 0 0 0 0 0 0 0 1 0 0 77 1 77

Core depth (cm)

730–736

752–754

774–776

796–800

822–824

846–848

890–892

914–916

938–940

956–958

976–978

Ammonia parkinsoniana Ammonia tepida Elphidium gunteri Elphidium excavatum Elphidium galvestonense Elphidium poeyanum Haynesina germanica

114 1 3 7 0 1 0

3 0 2 0 0 0 1

112 22 21 128 4 20 0

80 2 19 213 1 21 1

17 0 1 238 39 14 0

34 0 3 259 3 12 0

118 25 12 120 7 16 5

137 19 23 95 3 30 3

127 21 26 108 3 24 7

142 25 27 102 0 17 11

123 12 15 120 2 24 6

(continued on next page)

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Table 1 (continued) Baffin Bay foraminiferal counts, 10 ml, core BB07-01 Nonionella atlantica Core depth (cm)

0 730–736

0 752–754

1 774–776

1 796–800

0 822–824

0 846–848

6 890–892

1 914–916

4 938–940

3 956–958

6 976–978

Palmerinella palmerae Rosalina floridana Bolivina striatula Bolivina lowmani Bolivina pulchella Buliminella elegantissima Quinqueloculina agglutinans Quinqueloculina seminula Quinqueloculina impressa Quinqueloculina poeyana Quinqueloculina costata Quinqueloculina wiesneri Triloculinella obliquinodus Triloculina sidebottomi Triloculina fitterrei Triloculina sp. Miliolinella subrotunda Unidentified Number counted Fraction counted Relative density/10 ml

0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 1 129 0.5 258

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 1 6

0 0 3 0 0 0 0 9 0 2 0 0 0 0 0 0 0 0 322 0.12 2683

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 338 0.4 845

0 0 0 0 0 0 0 14 0 0 0 0 0 0 0 4 0 1 328 0.12 2852

0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 2 314 0.35 898

0 0 1 0 0 6 0 4 0 0 0 0 0 0 0 0 0 1 321 0.04 7133

0 0 4 4 2 16 0 8 0 4 0 0 0 0 0 0 0 1 350 0.07 5000

0 0 3 2 0 4 0 1 0 0 0 0 0 0 0 0 0 0 330 0.09 3666

0 0 2 3 0 6 0 1 0 1 0 0 0 0 0 0 0 4 344 0.06 5733

0 0 3 1 1 2 0 1 0 0 0 0 0 0 0 0 0 0 316 0.08 3950

Core depth (cm)

1050–1052

1066–1068

1090–1092

1106–1108

1122–1124

1228–1230

1246–1248

1270–1272

1286–1288

1372–1374

1394–1396

Ammonia parkinsoniana Ammonia tepida Elphidium gunteri Elphidium excavatum Elphidium galvestonense Elphidium poeyanum Haynesina germanica Nonionella atlantica Palmerinella palmerae Rosalina floridana Bolivina striatula Bolivina lowmani Bolivina pulchella Buliminella elegantissima Quinqueloculina agglutinans Quinqueloculina seminula Quinqueloculina impressa Quinqueloculina poeyana Quinqueloculina costata Quinqueloculina wiesneri Triloculinella obliquinodus Triloculina sidebottomi Triloculina fitterrei Triloculina sp. Miliolinella subrotunda Unidentified Number counted Fraction counted Relative density/10 ml

102 16 6 151 3 21 22 8 0 1 5 3 1 7 0 5 0 2 6 0 1 0 0 0 0 1 361 0.07 5143

114 18 3 122 3 30 6 6 0 0 5 4 0 11 0 3 0 0 0 0 1 0 0 0 0 0 326 0.07 4657

118 27 30 92 1 36 6 12 0 0 4 2 0 5 0 4 0 2 3 0 1 0 0 0 0 3 346 0.06 5767

66 35 32 131 2 27 21 4 0 0 4 0 0 2 0 5 0 0 0 0 2 0 0 0 0 0 331 0.05 6620

123 13 24 103 4 23 0 3 0 1 5 3 0 1 0 5 0 6 2 3 0 0 0 0 0 0 319 0.04 7089

116 3 80 64 2 14 13 0 1 0 1 1 0 3 0 4 3 6 0 12 0 0 0 2 0 0 325 0.04 8125

122 2 48 82 9 21 8 1 0 0 0 1 0 2 0 13 0 1 0 2 0 0 0 0 0 0 312 0.09 3468

139 3 47 96 2 19 4 0 0 0 0 0 0 0 1 24 1 5 0 4 0 0 0 0 0 0 345 0.09 3632

142 5 38 101 4 10 9 0 0 0 0 2 0 0 0 7 0 1 0 0 0 0 0 0 0 0 319 0.13 2408

193 1 26 51 15 9 3 0 0 0 0 0 0 0 0 15 0 2 1 1 0 0 0 3 0 0 320 0.07 4412

154 5 29 45 22 21 7 0 0 0 0 0 0 0 0 16 2 0 0 2 0 0 0 2 0 2 307 0.17 1842

Core depth (cm)

1406–1408

1428–1430

Ammonia parkinsoniana Ammonia tepida Elphidium gunteri Elphidium excavatum Elphidium galvestonense Elphidium poeyanum Haynesina germanica Nonionella atlantica Palmerinella palmerae Rosalina floridana Bolivina striatula Bolivina lowmani Bolivina pulchella Bolivina sp. Buliminella elegantissima Quinqueloculina agglutinans Quinqueloculina seminula

181 4 21 37 5 11 8 0 0 0 0 0 0 0 0 0 33

198 0 38 41 10 11 9 0 1 0 0 0 0 0 0 0 23

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Table 1 (continued) Baffin Bay foraminiferal counts, 10 ml, core BB07-01 Core depth (cm)

1406–1408

1428–1430

Quinqueloculina impressa Quinqueloculina poeyana Quinqueloculina wiesneri Quinqueloculina costata Triloculinella obliquinodus Triloculina sidebottomi Triloculina fitterrei Triloculina sp. Miliolinella subrotunda Unidentified Number counted Fraction counted Relative density/10 ml

0 1 5 4 0 1 0 0 0 1 312 0.33 936

0 2 0 0 0 0 0 0 0 0 333 0.5 666

Baffin Bay foraminiferal counts, 10 ml, additional cores Core and depth

Ammonia parkinsoniana Ammonia tepida Elphidium gunteri Elphidium excavatum Elphidium galvestonense Elphidium poeyanum Haynesina germanica Nonionella atlantica Palmerinella palmerae Rosalina floridana Bolivina striatula Bolivina lowmani Bolivina pulchella Bolivina sp. Buliminella elegantissima Quinqueloculina agglutinans Quinqueloculina seminula Quinqueloculina impressa Quinqueloculina poeyana Quinqueloculina wiesneri Quinqueloculina costata Triloculinella obliquinodus Triloculina sidebottomi Triloculina fitterrei Triloculina sp. Miliolinella subrotunda Ammontium salsum Unidentified Number counted Fraction counted Relative density/10 ml

BB08-01

BB08-01

BB06-02

BB07-04

BB07-11

22–24 (cm)

33–35 (cm)

5–7 (cm)

b10 (cm)

2–4 (cm)

220 11 21 27 6 1 14 0 0 0 0 0 0 0 0 0 3 1 0 0 0 0 0 0 0 0 14 2 320 0.03 10667

208 3 1 42 4 2 0 0 0 0 0 0 0 0 0 0 51 1 0 0 0 4 0 0 0 0 3 0 319 0.16 1994

261 2 15 54 5 0 2 0 1 0 1 0 0 0 0 0 18 0 0 0 0 0 0 0 0 0 0 0 359 0.03 11967

233 1 11 49 2 1 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 1 307 0.17 1805

189 9 7 69 0 0 0 0 0 0 0 0 0 0 0 0 26 0 0 0 0 0 0 1 0 0 3 0 304 0.51 596

assemblages are tied to shifts from fluvial–estuarine–marine settings brought on by sea level fluctuation. Leorri and Cearreta (2004) and Leorri et al. (2006) used dated cores along with foraminiferal and sedimentological analyses to recognize system tracts that correlate with climate-driven sea level change. Recent work by Horton and Murray (2006) considers elevation and salinity as the main factors influencing distributions of living foraminifera in intertidal areas, and looks at the utility of using foraminifera along with litho- and chronostratigraphic data to provide high-resolution data for Holocene sea level change. 1.4. Foraminifera and Holocene climate change In addition to sea level driven environmental changes, climate may play an important role in determining bay environments thereby affecting foraminiferal populations (Leorri and Cearreta, 2004; Leorri et al., 2006). Climate-driven changes in precipitation for example may affect

fluvial sediment supply, nutrient supply for foraminifera, and estuarine salinity. The primary source of interannual and decadal global climate variability is the El Niño-Southern Oscillation (ENSO) (Tudhope et al., 2001). Recent studies suggest that changes in ENSO frequency, modulated by changes in incoming solar radiation, affect not only the North American monsoon (Asmerom et al., 2007) but also changes in southwestern Mexico precipitation patterns (herein referred to as the southwestern Mexico monsoon; Bernal et al., 2011). Thus changes in foraminiferal populations, modulated by estuarine salinity and nutrient supply, may also reflect past changes in ENSO and the regional (North American and southwest Mexico) monsoon systems. The objective of the current work is to use foraminifera to establish an independent record of environmental change in Baffin Bay, Texas, and to examine if these changes are in accord with sedimentological interpretations (Simms et al., 2010), past records of ENSO variability, and

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Table 2 Baffin Bay foraminiferal assemblage data, BB07-01; used in Fig. 4 of manuscript. Core depth (cm) 0–2

8–10

22–24

38–40

54–56

70–72

94–96

118–120

142–144

166–168

182–184

230–232

254–256

Main genera Community 1 Ammonia, 62% Elphidium, 24% Quinqueloc., 7% Ammonia, 82% Elphidium, 17% Quinqueloc., 1% Ammonia, 62% Elphidium, 36% Quinqueloc., 2% Ammonia, 64% Quinqueloc., 22% Elphidium,14% Ammonia, 84% Elphidium, 12% Quinqueloc., 3% Ammonia, 54% Elphidium, 40% Quinqueloc., 5% Ammonia, 70% Quinqueloc., 18% Elphidium, 11% Ammonia, 47% Elphidium, 30% Quinqueloc., 13% Ammonia, 57% Elphidium, 38% Quinqueloc., 4% Elphidium, 66% Quinqueloc., 18% Ammonia, 10% Elphidium, 58% Quinqueloc., 32% Triloculina, 8% Quinqueloc., 39% Elphidium, 39% Ammonia, 18% Elphidium, 50% Quinqueloc., 27% Ammonia, 11%

Rel. density/ total species

448–450

472–474

485 cm 492–494

Missing section 590–592

614–616

638–640

654–656

667 cm 672–673

752–754

1575 5

774–776

7320 5

796–800

3520 7

822–824

11,745 6

846–848

11,309 7 3280 8

Missing section 890–892

23,333 7

914–916

7156 8

938–940

7260 7

946 cm 956–958

3530 10

976–978

4082 8

Missing section 1050–1052

7440 11

1066–1068

4400 11

1090–1092

9057 8

1106–1108 4580–5440

Elphidium, 40% Quinqueloc., 29% Ammonia, 24%

103 7

Elphidium, 78% Ammonia, 17% Triloculina 4% Ammonia, 65% Elphidium, 22% Triloculina 13% Elphidium, 50% Ammonia, 37% Triloculina 7% Elphidium, 50% Ammonia, 35% Quinqueloc, 10%

596 8

1113 cm 1122–1124

Rel. density/ total species

1228–1230

120 8

1246–1248

336 9

1270–1272

1286–1288

C-date/surface

258 7 6 3 2683 10 845 7 2852 7 5730–6290 5.5 ky surface

Community 2 Elphidium, 88% Ammonia, 11% Quinqueloc., 1%

Elphidium, 48% Ammonia, 44% N., 2%; Bulim., 2% Ammonia, 44% Elphidium, 19% Buliminella, 5% Elphidium, 49% Ammonia, 44% Haynesina, 2%

898 8

7133 12 5000 13 3666 11 6280–6790

Ammonia, 49% Elphidium, 16% Haynesina, 3% Elphidium, 51% Ammonia, 43% H., 2%; N., 2%

Elphidium, 50% Ammonia, 33% Haynesina, 6% Elphidium, 48% Ammonia, 41% Buliminella, 3% Elphidium, 46% Ammonia, 42% Nonionella, 4% Elphidium, 58% Ammonia, 30% Haynesina, 6%

5733 12 3950 11

5143 17 4657 13 5767 15 6620 12 7960–8405

Elphidium, 49% Ammonia, 43% Quinqueloc., 5%

7089 15 8.0 ky surface

Missing section

23 4

77 7

Ammonia, 88% Elphidium, 9% Quinqueloc., 2% Ammonia, 50% Elphidium, 33% Haynesina, 17% Elphidium, 54% Ammonia, 42% Quinqueloc, 4% Elphidium, 75% Ammonia, 24% H., .3; Nonion, .3% Elphidium, 89% Ammonia, 5% Quinqueloc., 4%

Approx. 1160 cm

4870–5580 Ammonia, 73% Quinqueloc., 19% Elphidium, 4%

Main genera

837 cm

1876 8

3275–3900

Elphidium, 44% Quinqueloc., 18% Ammonia, 16% Elphidium, 57% Quinqueloc., 24% Triloculina 7% Quinqueloc., 42% Elphidium, 32% Triloculina 14%

Core depth (cm) Missing section 730–736

1340 7

262 cm Missing section 426–428

C-date/surface

Table 2 (continued)

Community 3 Elphidium, 49% Ammonia, 37% Quinqueloc., 8% Elphidium, 51% Ammonia, 40% Quinqueloc., 5% Elphidium, 48% Ammonia, 41% Quinqueloc., 10% Elphidium, 48% Ammonia, 46% Haynesina, 3%

8125 16 3468 13 3632 12 2408 10

P. Buzas-Stephens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 404 (2014) 44–56 Table 2 (continued) Core depth (cm) Missing section 1372–1374

1394–1396

1406–1408

1428–1430

Main genera

Ammonia, 61% Elphidium, 32% Quinqueloc., 6% Ammonia, 52% Elphidium, 38% Quinqueloc., 6% Ammonia, 60% Elphidium, 24% Quinqueloc., 12% Ammonia, 60% Elphidium, 30% Quinqueloc., 8%

Rel. density/ total species

C-date/surface

4412 12 1842 11 936 12 666 9

changes in the North American and southwest Mexico monsoon systems outlined above. 2. Methods Foraminifera were studied from vibracores (7.6 cm diameter; up to 4.2 m length) and push–rotary cores (5.1 cm diameter; up to 17.7 m taken in 1.5 m sections) previously sampled for sediments and macrofauna by Simms et al. (2010) (Fig. 1). From a 14.4 m radiocarbondated core, BB07-01, 10 ml of sediment was sampled at approximately 20 cm intervals for foraminifera (the interval examined was often dependent on the amount of sediment left from earlier analyses). Sediment was washed through a .063 mm sieve in order to retain all sizes of foraminifera, and when possible 300 individuals were counted from each interval (Table 1). After transforming species proportions to arcsine square root, a multiple discriminant analysis was used to compare sections of the core for the most common species present. Results from this core form the main basis for the current study. In order to determine if certain foraminifera were characteristic of some of the unique sedimentary environments found in Baffin Bay, 10 ml of sediment was also sampled at selected intervals from four additional cores: BB08-01 (sandy-shell internal spit), BB06-02 (upper bay mudflat), BB07-04, and BB07-11 (open bay muds) (Fig. 1; Tables 1 and 2). Proportions of Ammonia spp., Quinqueloculina spp., and Elphidium spp., generally indicative of brackish, hypersaline, and a range of salinities respectively, were also compared to past records of the ENSO (Moy et al., 2002), the North American monsoon (Asmerom et al., 2007), and the southwestern Mexico monsoon (Bernal et al., 2011) and a record of Great Plains aridity (northern Texas to North Dakota, United States; Nordt et al., 2008) to determine if foraminiferal assemblages of Baffin Bay reflect regional-scale changes in climate (Fig. 4). Seven radiocarbon ages, six from Simms et al. (2010) and one from Rodriguez et al. (2010), were utilized to compute an age-model for BB07-01 (Fig. 5; Tables 3 and 4). The ages for samples below 13.95 m from the core top were estimated by using seismic stratigraphy of Simms et al. (2010). The initial flooding of several Texas estuaries [e.g., Corpus Christi Bay (Simms et al., 2008) and Galveston Bay (Anderson et al., 2008)] occurred about 9.6 ka; therefore the initial flooding surface of Baffin Bay at 15 m from the core top between the bay-head delta and fluvial deposits was estimated to be 9.6 ka and used in the age model (Fig. 5). 3. Results and discussion 3.1. Foraminiferal assemblages A total of 26 species of foraminifera were found in Baffin Bay, although there was a maximum of 17 for any one interval. The most

51

abundant species present are those typical of other Texas bays and include Ammonia parkinsoniana, Elphidium spp., and Quinqueloculina seminula. However, unlike other Texas bays there were no recognizable agglutinated taxa (Ammotium salsum) found throughout the length of the long core, BB07-01, which records over 8.0 ky of sedimentation (Fig. 6). This lack of an agglutinated fauna is in line with the study by Stewart et al. (1994), who likewise did not find any agglutinated foraminifera in a core dated 4.0 ka. Poag (1981) also noted that Baffin Bay was atypical in that it does not have the “Ammotium predominance facies”. Still, it is possible that in the storing and/or processing of these long cores the agglutinated specimens were destroyed as Pitakpaivan (1988) recorded living A. salsum and some A. salsum were also found in the other cores from this study (BB08-01: 14 specimens at 22–24 cm and 3 at 33–35 cm; BB07-11: 3 specimens at 2–4 cm) (Fig. 1; Table 1). While the BB08-01 core was taken landward in a shelly spit south of the input of San Fernando Creek, the BB07-11 core was in shallow mid-bay muds. Accordingly it appears that A. salsum does maintain populations in the bay. At present, reasons for the absence of agglutinated taxa in long core BB07-01 are unclear and may include 1) a high-energy deltaic environment toward the bottom of the core below the 8.0 ky surface, 2) presence of a hypersaline environment for sediments above the 5.5 ky surface, and 3) low preservation potential/ core desiccation (Table 1). 3.2. Statistical analysis and communities: long core BB07-01 The multiple discriminant analysis, which compares sections of the core by the proportions of the most common species, clearly delineates three different groups, or communities, of foraminifera (Fig. 7). Separations between these three groups correspond to two of the most important surfaces recognized by the sedimentological and geophysical work (Simms et al., 2010): the 8.0 ky flooding surface from glacioeustatic sea level rise and the 5.5 ky surface marking a change in climate and the physical isolation of Baffin Bay. Canonical variates show that communities 2 (between the 5 ky and 8.0 ky surfaces) and 3 (below the 8.0 ky surface) contrast the most. Canonical discriminant functions, representing 60% (CV1) and 40% (CV2) of the variability among groups, show that Ammonia tepida, Nonionella atlantica, Bolivina striatula, and Buliminella elegantissima are the source of most of the contrast among the communities. The foraminiferal assemblage designated as community 3 or deltaic lies below the 8.0 ky flooding surface (1228–1430 cm) (Table 2). Sedimentological analysis indicates a higher-energy deltaic environment present in the bay prior to this time (Simms et al., 2010), and foraminifera are typical of delta mouth bar/delta plain deposits (with the notable absence of agglutinated taxa). Ammonia spp. and Elphidium spp. together comprise nearly the entire population, from 84 to 94% of the fauna at each interval. The third most common genus is generally Quinqueloculina spp., which makes up 5–12% of the fauna. Relative densities are somewhat lower (666–4412 per interval; average 1964) in the delta mouth bar deposits at the base of the core (1372–1430 cm) as compared to the densities (2408–8125 per interval; average 4408) in the delta plain sediments (1228–1288 cm). The number of species in the delta mouth bar sediments, from 9 to 12 per interval, is also somewhat lower than that in the delta plain deposits, from 10 to 16 per interval (Tables 1 and 2). These deltaic sedimentary and foraminiferal facies at the bottom of BB07-01 are similar to those found in other present-day Texas estuaries. Between the 8.0 ky and the 5.5 ky surfaces (846–1124 cm), statistical analysis recognizes foraminiferal fauna community 2 (Table 2). With a change to more open-bay conditions as sea level rises and the shoreline steps back at the 8.0 ky event (Simms et al., 2010), several changes are noted in the assemblage. Though Ammonia spp. and Elphidium spp. are still the most common genera, they are not so exclusive, and usually make up a smaller percentage of the fauna at each interval. The third most common genus then varies among Haynesina, Nonionella, and

52

P. Buzas-Stephens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 404 (2014) 44–56

A

0 Radiocarbon age with 2σ error

Radiocarbon age Stratigraphic flooding surface Line indicating correlation

20

10

0

Wet

-9 -8.5

Dry

-8

-4.5

500

1000

1500 0

2

4

6

8

Thousand years before present Fig. 5. Age-model for core BB07-01 computed from 6 radiocarbon ages published in Simms et al., 2010 and one radiocarbon age published in Rodriguez et al., 2010, with depth of foraminifera samples indicated. Age-model computed using linear interpolation between median calibrated radiocarbon ages. Predicted age at 15 m from the core top was estimated from seismic stratigraphy of Simms et al., 2010. Radiocarbon ages calibrated using northern hemisphere atmospheric curves of Calib 6.0 (Reimer et al., 2009). See Table 3 for uncalibrated and calibrated radiocarbon data.

Wet

-4 Dry

-3.5 -40 -30

Wet

-20 -10 Dry

E

M Modern 0

10

0

D

Δ%C 4 (Great Plains aridity)

δ 18 O ‰ (North american monsoon proxy)

C

δ 18 O ‰ (southwest Mexico)

B -9.5

Predicted age Foraminifera sample

Depth (cm)

El Niño events per 100 yr

30

0.2 Dry

0.4 0.8 0.6

Wet

0.4 0.2

Dry

Proportion Elphidium

G

0.8 0.6 0.4 0.2 0

2

4

6

8

10

Thousand years before present

F Proportion Ammonia

Proportion Quinqueloc

Wet

Buliminella. Relative densities are generally higher in the open-bay environment (898–7133 per interval; average 5060), and richness (8–17 species per interval) is mostly higher as well. Ammonia tepida, Bolivina spp., and Buliminella elegantissima are more numerous than they are in the deltaic facies, Nonionella atlantica appears for the first time, and miliolids are not as common (Tables 1 and 2). While counting specimens it was evident that these open-bay individuals are larger and more robust, as if they were benefiting from ideal environmental conditions. But above the 5.5 ky surface (824 cm) (Table 2), an increasingly arid environment and the formation of Padre Island (Simms et al., 2010) change the hospitable setting to the hypersaline situation still present in the bay today. Statistical analysis identifies community 1, which is at the beginning dominated by Ammonia spp. and Elphidium spp. Miliolids (mostly Quinqueloculina seminula and Triloculina sp.),which are noted as preferring higher salinities (Poag, 1981; Stewart et al., 1994), generally make up a larger percentage of the top three genera. In this hypersaline setting, richness drops to 3–11 species per interval, and at first (492–824 cm) density likewise decreases (6–2852 per interval; average 718) before picking up (1340–23,333 per interval; average 6764) toward the top of the core (0–474 cm). Species seen in the lower deltaic and open-bay facies, such as Ammonia tepida, Bolivina spp., Buliminella elegantissima, and Nonionella atlantica, are nearly absent (Tables 1 and 2). The decrease in foraminiferal richness and density as well as the change in faunal composition readily illustrate the marked change in the depositional environment of Baffin Bay since its isolation by Padre Island. Another possible flooding surface at 4.8 ky noted by Simms et al. (2006) is not statistically recognized by foraminifera, though numbers of miliolids do peak about this time (Tables 1 and 2; 492–494 cm).

Fig. 4. Foraminiferal assemblages Ammonia spp., Quinqueloculina spp., and Elphidium spp., indicative of brackish, hypersaline, and a range of salinities respectively from core BB07-01 (E, F, and G) compared to independently derived records of the El Niño-Southern Oscillation (a; Moy et al., 2002), the southwestern Mexico monsoon, (B; Bernal et al., 2011), the North American monsoon (C; Asmerom et al., 2007), and Great Plains aridity (D; Nordt et al., 2008). Note correspondence among paleoclimate records (A, B, C, and D), foraminiferal assemblages (E, F, and G) and stratigraphic flooding surfaces is identified by Simms et al., 2010.

P. Buzas-Stephens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 404 (2014) 44–56

53

Table 3 Radiocarbon and estimated ages for BB07-01 age model; used in Fig. 5 of manuscript. Material Depth (cm from core top)

Lab

Lab code

NA University of Tokyo University of Tokyo University of Tokyo

NA MTC-08900 MTC-08899 MTC-08904

University of Tokyo University of Tokyo University of Tokyo Not provided in referenced paper NA

MTC-08901 837 MTC-08903 946 MTC-08902 1113 OS-73348 1394 NA

0 262 485 667

1500

NA Unknown Rangia flexuosa (J) a Anomalocardia cuneimeris a Rangia flexuosa (J) a Mulinia lateralis a Mulinia lateralis a Anomalocardia cunemeiris NA a

14

C ageb Error d13C Radiocarbon (years) years (years) reservoirc (years before present)

Calendar age 2σ upper age (years before present)

Calendar age 2σ lower age (years before present)

Median 2σ calendar error age (years)

Reference

NA 3140 4170 4350

NA 75 80 75

NA −0.3 −0.3 −0.3

NA 200 200 200

NA 3900 5440 5580

NA 3275 4580 4870

0 3587.5 5010 5225

NA 312.5 430 355

NA Simms et al. (2010) Simms et al. (2010) Simms et al. (2010)

5050 5515 7175 8440

80 75 80 50

1.07 −0.8 −0.8 −0.3

200 200 200 200

6290 6790 8405 9400

5730 6280 7960 9030

6010 6535 8182.5 9210

280 255 222.5 190

Simms et al. (2010) Simms et al. (2010) Simms et al. (2010) Rodriguez et al. (2010)

NA

NA

NA

NA

NA

NA

9600

NA

Estimated from seismic stratrigraphy of Simms et al. (2010)

Abbreviations: explanation. NA 2σ a b c

not applicable. Two standard deviation. Articulated. Ages from Beta Analytical corrected for actual d13C measured from sample. Radiocarbon reservoir used herein from respective references.

Unlike the rest of the core, from 494 to 184 cm miliolids steadily comprise from 18 to 42% of the assemblage before their numbers decline toward the present. Together with the changes in community structure seen at the 8.0 ky and 5.5 ky surfaces, the foraminifera in Baffin Bay clearly respond to salinity and other environmental changes accompanying fluctuations in sea level and climate through time. 3.3. Foraminiferal assemblages and Holocene climate change Prior to the formation of Padre Island (5.5 ka) changes in foraminiferal assemblages of Baffin Bay, Texas does not show a clear correspondence to changes in ENSO, the North American monsoon, or the southwest Mexico monsoon (Fig. 4). Tidal exchange between the Gulf of Mexico and Baffin Bay may be responsible for the lack of correspondence (Fisk, 1959). Before 5.5 ka circulation between Baffin Bay and the Gulf of Mexico was less restricted; shifts in regional climate therefore could be modulated by readily circulating marine waters from the Gulf of Mexico. With the formation of Padre Island circulation between Baffin Bay and the Gulf of Mexico was more restricted, making Baffin Bay more sensitive to regional climate changes reflected in the foraminiferal assemblages. After about 5.5 ka, changes in foraminiferal assemblages of Baffin Bay, Texas reflects large-scale changes in ENSO, the North American monsoon, and the southwest Mexico monsoon (Fig. 4). Ammonia spp. increases with increased ENSO and with weakening of the North American monsoon and southwest Mexico monsoon. Species of Quinqueloculina decrease during times of increased ENSO and strengthening of the North American monsoon and the southwest Mexico monsoon. The Elphidium spp., which tolerate a broad range of salinities, increase with the strengthening of the North American monsoon and southwest Mexico monsoon but generally decrease after about 2.5 ka when ENSO variability increases (Fig. 4). The increase in Ammonia spp. and decrease in Quinqueloculina spp. after around 2.5 ka correspond to a decrease in the strength of the North American monsoon and southwest Mexico monsoon and an increase in ENSO activity (Fig. 4; Moy et al., 2002; Conroy et al., 2008; Bernal et al., 2011). The increase in Ammonia spp., which prefer more freshwater conditions, and decrease in Quinqueloculina spp., which prefer hypersaline waters, during periods of increased ENSO activity is likely a response to increased precipitation during El Niño years in Texas (Li et al.,

2014). Decreases in Ammonia spp. and increases in Quinqueloculina spp. during periods of enhanced monsoon indicate that precipitation regimes over Baffin Bay, Texas and the North American monsoon region are anti-phased. This anti-phased precipitation regime with the North American monsoon region (i.e. the southwestern United States) is also true for the upper Mississippi River valley (southwestern Wisconsin, United States; Knox, 2000) and U.S. Great Plains (Fig. 4). For example during the Middle Holocene Thermal Maximum (approximately 6 ka–4.5 ka), increases in the North American monsoon and the southwest Mexico monsoon precipitation are coincident with increases in storms in the southwestern United States (Knox, 2000). They are also coincident with drier conditions over the U.S. Great Plains (Nordt et al., 2008), and decreases in storms over the upper Mississippi River valley (Knox, 2000). This anti-phased relationship of precipitation patterns is consistent with modern observations that indicate enhanced North American monsoon precipitation results in reduced precipitation over the U.S. Great Plains region and Texas (Higgins et al., 1997). During an enhanced North American monsoon northward migration of an upper-tropospheric monsoon high-pressure zone leads to midtropospheric subsidence over the Great Plains and Texas regions thereby limiting precipitation (Higgins et al., 1997). The decline in monsoon precipitation and increase in ENSO may be explained by the orbitallydriven southern migration of the Intertropical Convergence Zone (ITCZ) since about 5.5 ka (Bernal et al., 2011; Yuan et al., 2013) and by changes in the seasonal distribution of insolation over the tropical Pacific, respectively (Clement et al., 2000). The sediments and foraminiferal communities in Baffin Bay are part of a transgressive systems tract deposited as sea level rose over the past 10 ky following glaciation. The stratigraphic flooding surfaces coincident with changes in foraminiferal communities at about 8.0 ky and 5.5 ky occur during times of rapid global-scale climate changes during the Holocene (Mayewski et al., 2004). Stratigraphic flooding surfaces occurring around the same time periods (i.e. 8.0 ky and 5.5 ky) are documented in numerous bays throughout the Gulf of Mexico (Rodriguez et al., 2008; Simms et al., 2008; Anderson et al., in press), on the east coast of the United States (Delaware Bay) (Leorri et al., 2006), the Bay of Biscay in northern Spain (Leorri and Cearreta, 2004), and MontSaint-Michel Bay, France (Billeaud et al., 2009). In two of the papers (Leorri and Cearreta, 2004 and Leorri et al., 2006), the authors were

54

P. Buzas-Stephens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 404 (2014) 44–56

Table 4 Calibrated ages of foraminifera samples from core BB07-01 determined from age model. Core depth (cm)

Top of sample (cm from top)

Bottom of sample (cm from top)

Midpoint depth of sample (cm from top)

Thickness of sample (cm)

Approximate younger age (yr BP)

Approximate older age (yr BP)

Approximate midpoint age (yr BP)

Approximate time averaged (years)

0–2 8–10 22–24 38–40 54–56 70–72 94–96 118–120 142–144 166–168 182–184 230–232 254–256 426–428 448–450 472–474 492–494 590–592 614–616 638–640 654–656 672–673 730–736 752–754 774–776 796–800 822–824 846–848 890–892 914–916 938–940 956–958 976–978 1050–1052 1066–1068 1090–1092 1106–1108 1122–1124 1228–1230 1246–1248 1270–1272 1286–1288 1372–1374 1394–1396 1406–1408 1428–1430

0 8 22 38 54 70 94 118 142 166 182 230 254 426 448 472 492 590 614 638 654 672 730 752 774 796 822 846 890 914 938 956 976 1050 1066 1090 1106 1122 1228 1246 1270 1286 1372 1394 1406 1428

2 10 24 40 56 72 96 120 144 168 184 232 256 428 450 474 494 592 616 640 656 673 736 754 776 800 824 848 892 916 940 958 978 1052 1068 1092 1108 1124 1230 1248 1272 1288 1374 1396 1408 1430

1 9 23 39 55 71 95 119 143 167 183 231 255 427 449 473 493 591 615 639 655 672.5 733 753 775 798 823 847 891 915 939 957 977 1051 1067 1091 1107 1123 1229 1247 1271 1287 1373 1395 1407 1429

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 6 2 2 4 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.00 109.54 301.24 520.32 739.41 958.49 1287.12 1615.74 1944.37 2273.00 2492.08 3149.33 3477.96 4633.64 4773.98 4927.07 5018.27 5134.04 5162.39 5190.74 5209.64 5248.09 5515.91 5617.50 5719.09 5820.68 5940.74 6053.35 6265.28 6380.87 6496.47 6633.65 6830.96 7560.99 7718.83 7955.60 8113.44 8219.13 8607.38 8673.31 8761.22 8819.83 9134.83 9215.41 9259.36 9339.94

27.39 136.93 328.63 547.71 766.79 985.88 1314.50 1643.13 1971.76 2300.38 2519.47 3176.72 3505.34 4646.40 4786.74 4939.83 5020.63 5136.40 5164.75 5193.10 5212.01 5252.71 5543.62 5626.74 5728.32 5839.15 5949.97 6062.98 6274.91 6390.50 6506.10 6653.38 6850.69 7580.72 7738.56 7975.33 8133.17 8222.79 8611.05 8676.98 8764.88 8823.49 9138.49 9219.07 9263.02 9343.60

13.69 123.23 314.93 534.02 753.10 972.19 1300.81 1629.44 1958.06 2286.69 2505.77 3163.02 3491.65 4640.02 4780.36 4933.45 5019.45 5135.22 5163.57 5191.92 5210.82 5250.40 5529.76 5622.12 5723.71 5829.91 5945.35 6058.17 6270.09 6385.69 6501.28 6643.52 6840.82 7570.85 7728.70 7965.46 8123.31 8215.47 8603.72 8669.65 8757.56 8816.16 9131.16 9211.74 9255.70 9336.28

13.69 13.69 13.69 13.69 13.69 13.69 13.69 13.69 13.69 13.69 13.69 13.69 13.69 6.38 6.38 6.38 1.18 1.18 1.18 1.18 1.18 2.31 13.85 4.62 4.62 9.24 4.62 4.82 4.82 4.82 4.82 9.87 9.87 9.87 9.87 9.87 9.87 1.83 1.83 1.83 1.83 1.83 1.83 1.83 1.83 1.83

likewise able to see changes in their foraminiferal assemblages that were coincident with sea level and climate changes. In Leorri and Cearreta (2004), a few of the same dominant genera (Ammonia; Elphidium; Quinqueloculina) were used to track sea level change in the Bay of Biscay, showing the usefulness of these taxa to interpret environmental conditions on a worldwide basis. While the 8.0 ky surface in Baffin Bay is likely also the result of global sea level changes, the 5.5 ky surface is mostly due to regional events (Padre Island and an arid climate). 4. Conclusions In a sediment core from Baffin Bay, Texas dating to over 8.0 ka, three foraminiferal communities were recognized using multiple discriminant analysis. Separations between these communities correspond to the two main surfaces identified by sedimentological data: the 8.0 ky glacioeustatic flooding surface and the 5.5 ky flooding surface resulting from the onset of arid conditions and the formation of Padre Island. Community 3, below the 8.0 ky surface, is deltaic with mostly Ammonia and Elphidium. Between the 8.0 ky and 5.5 ky surfaces, community 2 is

open bay, exhibiting higher richness and density than community 3. Individuals are more robust, evidently benefiting from ambient conditions. But at 5.5 ka when the bay is isolated from the Gulf of Mexico by Padre Island, a hypersaline foraminiferal fauna, community 1, becomes established and persists to the present. Community 1 has lower richness and density and a preponderance of miliolids. The correspondence among ENSO, the North America and southwest Mexico monsoon records, Great Plains aridity, and foraminiferal assemblages after 5.5 ka suggest that Baffin Bay estuarine environments are affected not only by sea-level driven changes but also regional climate changes modulated by changes in the strength of the North American monsoon and ENSO. These results further indicate that foraminiferal assemblages of Baffin Bay can be used to reconstruct millennial-scale ENSO changes and monsoonal driven variability along the Texas coast. Foraminiferal assemblages are consistent with sedimentary facies observed in the core and corroborate sedimentological evidence for climate and sea-level driven changes. Together sedimentological and foraminiferal analyses provide a valuable tool for gauging sea-level and climate fluctuations in the Holocene as well as in the geologic past.

P. Buzas-Stephens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 404 (2014) 44–56

55

BB07-01 0

550

1000

50

600

1050

100

650

Sand Sandy Mud

Wet Open Bay

1100

7960-8405

4870-5580 Clay or Silt

Dry Open Bay

700

200

750

1200

800

1250

Laminated Mud Shell Material

1150

150

Bivalves 250

Plant fragments

3275-3900

Burrows

Delta Plain

5730-6290 1300

350

900

1350

400

950

450

1000

Dry Open Bay

6280-6790 Wet Open Bay Fine Sand Silt Clay

4580-5440 500

1400

Mouthbar

Fine Sand Silt Clay

850

300

Radiocarbon date

550 Fine Sand Silt Clay Fig. 6. Sediments and 14C dates (all in calendar years BP) for BB07-01. Modified from Simms et al. (2010).

9.0

Acknowledgments This work was made possible by a supplemental summer grant from the Petroleum Research Fund of the American Chemical Society (grant number 44868-GB8), and was also partially supported by an NSF grant EAR-0921963 and an NSF Graduate Research Fellowship grant DGE-1144085. The authors also wish to thank the editor and reviewers for their constructive comments which have served to strengthen this paper.

5.2

CV2

1.4

-2.4

Communities

-6.2

-10.0 -10.0

1 2 3 -6.2

-2.4

1.4

5.2

9.0

CV1 Fig. 7. Canonical score plot showing three foraminiferal communities in bay. Canonical variates CV1 and CV2 represent 60% and 40% of variability, respectively.

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